JP2743007B2 - Spindle-shaped magnetic iron oxide particles and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides fine particles, particularly 0.3 μm or less, high coercive force, and excellent transfer characteristics. The present invention relates to a spindle-shaped magnetic iron oxide particle powder whose surface is modified with Co and a method for producing the same.

[Conventional technology]

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, low noise characteristics, and the like are required.

The characteristics of the magnetic iron oxide particles required to satisfy the above requirements for the magnetic recording medium are that the particles are fine and have a high coercive force.

This fact can be seen, for example, in the article “Development of Magnetic Materials and Highly Dispersing Technology of Magnetic Powder” (1982) published by Sogo Gijutsu Center.
On page 310, `` The orientation of magnetic tape performance was to increase sensitivity, increase output, and reduce noise, so emphasis was placed on increasing the coercive force and reducing the particle size of acicular γ-Fe ₂ O ₃ particles. And "Acicular Crystal γ-F" on page 312 of the same document.
It is known that there is a relationship between the particle size of e ₂ O ₃ and the noise of the magnetic tape, and the noise decreases as the particle size becomes finer. It is clear from the description.

At present, so-called Co-doped magnetic iron oxide particles and so-called Co-coated magnetic iron oxide particles are known as magnetic iron oxide particles having a high coercive force. The coercive force tends to increase as the amount of Co increases. In the former reaction, the Co-containing goethite particles are generated by adding a Co salt in advance in the reaction of forming goethite particles as a starting material, and then reduced to Co-containing magnetite particles or, if necessary, further oxidized. By making the Co-containing maghemite particles, the latter reduces the starting material goethite particles or, if necessary, further oxidizes the obtained magnetite particles or maghemite particles as a precursor to form a Co compound on the particle surface of the precursor particles. Obtained by coating.

The former Co-doped magnetic iron oxide particle powder has a high coercive force, but on the other hand, the distribution of the coercive force becomes large due to diffusion of Co into the crystal, and as a result, heat Has the disadvantage that it is unstable over time.
On the other hand, the latter Co-coated magnetic iron oxide particles have a characteristic that they are thermally and temporally stable.

Recently, the demand for improving the properties of the magnetic iron oxide particles has never stopped, and the above-mentioned particles are fine,
In addition to having a high coercive force and being stable thermally and over time, a phenomenon in which a recording signal is transferred to an adjacent magnetic layer, that is, an improvement in so-called transfer characteristics is strongly desired. ing.

The transfer characteristics are described in "Electronic Technology" (1968
Year) No. 10, p. 51, "It is known that there is an unfavorable tendency that the transfer effect deteriorates as the noise level decreases due to the miniaturization of the particle size."
As described, it is known that the magnetic iron oxide particle powder tends to deteriorate as the particle size becomes finer, and that the tendency is particularly remarkable when the particle size is 0.3 μm or less. Therefore, with the demand for high recording density, high sensitivity characteristics and high output characteristics, the magnetic iron oxide particles used tend to be further miniaturized, which is a major problem today.

A method for improving the transfer characteristics of Co-coated magnetic iron oxide particles is to make the particle size distribution of the precursor particles as uniform as possible and to have the axial ratio (major axis diameter / short axis short) as large as possible. For that purpose, it is required that the particle size distribution of the goethite particles as the starting material is as uniform as possible and that the axial ratio (major axis diameter / minor axis diameter) is as large as possible.

Conventionally, as a method for producing goethite particle powder as a starting material, a solution containing ferrous hydroxide particles obtained by adding an equivalent or more of an alkali solution to a ferrous salt solution is adjusted to a pH of 11 or more and a temperature of 80 ° C. or less. A method of producing acicular goethite particles by conducting an oxidation reaction by passing an oxygen-containing gas at a temperature (Japanese Patent Publication No. 39-5610), or by reacting an aqueous ferrous salt solution with an alkali carbonate. A method of producing spindle-shaped goethite particles by passing an oxygen-containing gas through an aqueous solution containing FeCO ₃ to cause an oxidation reaction (Japanese Patent Application Laid-Open No. 50-80999) is known.

[Problems to be solved by the invention]

The particles are fine, have a high coercive force, and are thermally and stable over time, and the magnetic iron oxide particles having excellent transfer characteristics are currently in the most demanded place. However, according to the former known method of producing goethite particle powder as a starting material, needle-like goethite particles having a large axial ratio (major axis diameter / minor axis diameter), particularly 10 or more, are produced. However, dendritic particles are mixed, and from the particle size, it is difficult to say that the particles have a uniform particle size.In addition, Co-coated magnetic iron oxide particles obtained using the goethite particles are: Although it has a high coercive force, the transfer characteristics have not been sufficiently satisfactory.

In the latter method, spindle-shaped particles having a uniform particle size and containing no dendritic particles are produced, while the axial ratio (major axis diameter / minor axis diameter) is at most 7%. And it is difficult to produce particles having a large axial ratio (major axis diameter / minor axis diameter). In particular, this phenomenon tends to become more pronounced as the major axis diameter of the produced particles decreases. . Further, the Co-coated magnetic iron oxide particles obtained using the goethite particles have high coercive force, but their transfer characteristics have not been sufficiently satisfactory.

Therefore, technology for obtaining Co-coated magnetic iron oxide particles having fine particles, having high coercive force, being stable over time and thermally, and having excellent transfer characteristics. The establishment of means is strongly required.

[Means for solving the problem]

The present inventors have obtained Co-coated magnetic iron oxide particles having fine particles, having high coercive force, and being stable over time and thermally, and having excellent transfer characteristics. As a result of various studies, the present invention has been reached.

That is, in the present invention, the major axis diameter is 0.1 to 0.3 μm, the axial ratio (major axis diameter / minor axis diameter) is 7 or more, and the coercive force is 480 to 100.
0 Oe, magnetite particles surface consists in the transfer characteristic is equal to or more than 52dB is exhibited spindle that is modified with Fe and Co to 0.5 to 15.0 atomic% of _{Co (FeOx · Fe 2 O 3} , 0 <x
≦ 1) Particle or coercive force 480-1000 Oe, transfer characteristic 57.0
The particle surface consisting of at least dB is not more than 0.1 for Fe and Co.
Magnetic iron oxide particles composed of spindle-shaped maghemite particles modified with 5 to 15.0 atomic% of Co, having a major axis diameter of 0.1 to 0.3 μm and an axial ratio (major axis diameter / minor axis diameter) of 8
And the coercive force is 480 to 1000 Oe, and the transfer characteristics are
The particle surface consisting of more than 52 dB
Magnetite exhibited fusiform containing zinc that is modified with 0.5 to 15.0 atomic% of _{Co (FeOx · Fe 2 O 3} , 0 <x ≦
1) Particle or coercive force is 480-1000 Oe, transfer characteristic is 57.0dB
The particle surface consisting of
Non-oxidizing aqueous solution containing FeCO ₃ obtained by reacting magnetic iron oxide particle powder consisting of maghemite particles containing zinc denatured with ~ 15.0 atomic% Co and aqueous solution of alkali carbonate and ferrous salt After aging under a neutral atmosphere, an oxygen-containing gas is passed through the suspension containing FeCO ₃ to oxidize the suspension, thereby producing spindle-shaped goethite particles. 1.5 to 3.5 times the equivalent of Fe in the aqueous iron salt solution, and the aging temperature in the aging is 40 to 60.
° C., by setting the aging time to 50 to 100 minutes, or
If necessary, the alkali carbonate aqueous solution, the ferrous salt aqueous solution, the suspension containing FeCO ₃ and the oxygen-containing gas are passed through to ripen the FeCO ₃ before being oxidized.
In any of the suspensions containing, by pre-existing a zinc compound, to produce spindle-shaped goethite particles containing or not containing zinc, obtained by firing and heating the goethite particles or this. Spindle-shaped magnetite (FeOx) containing or not containing zinc obtained by heating and reducing spindle-shaped hematite particles containing or not containing zinc in a reducing gas.
Fe ₂ O ₃ , 0 <x ≦ 1) Particles or, if necessary, spindle-shaped maghemite particles containing or not containing zinc obtained by oxidation are used as precursor particles. By subjecting the aqueous dispersion of the body particles to a mixed solution having a pH of 11 or more obtained by mixing at least a Co salt aqueous solution and an alkaline aqueous solution in a temperature range of 50 to 100 ° C., the particle surface has a 0.5 This is a method for producing spindle-shaped magnetic iron oxide particles comprising spindle-shaped magnetic iron oxide particles denatured by 115.0 atomic% of Co.

[Action]

First, the most important point in the present invention is that, in the method for producing Co-coated magnetic iron oxide particles, an aqueous solution containing FeCO ₃ obtained by reacting an aqueous alkali carbonate solution with an aqueous ferrous salt solution is subjected to non-oxidation. After aging in a neutral atmosphere, the FeCO
_In producing spindle-shaped goethite particles by aerating and oxidizing an oxygen-containing gas into the suspension containing ₃ , the amount of the alkali carbonate aqueous solution is 1.5 to 1.5 with respect to Fe in the ferrous salt aqueous solution. 3.5 times equivalent, the ripening temperature in the ripening 40 ~ 60 ℃, ripening time 50 ~ 100
Minutes to produce spindle-shaped goethite particles having a major axis diameter of 0.15 to 0.45 μm and an axial ratio (major axis diameter / minor axis diameter) of 11 or more, and heating and firing the goethite particles or the goethite particles. The major axis diameter obtained by heating and reducing the obtained spindle-shaped hematite particles in a reducing gas is 0.1 to
Spindle-shaped magnetite with 0.3 μm and axial ratio (major axis diameter / minor axis diameter) of 7 or more (FeOx · Fe ₂ O ₃ , 0 <x ≦ 1)
Particles or, if necessary, a long axis diameter of 0.1 to 0.3 μm obtained by oxidation, and an axial ratio (long axis diameter / short axis diameter) of 7
When the spindle-shaped maghemite particles having the spindle shape described above are used as the precursor particles, the particle size is fine, and has a high coercive force, and the surface of the particles having excellent transfer characteristics is Co. This is the fact that magnetic iron oxide particles that have been denatured can be obtained.

In the above-described reaction for producing spindle-shaped goethite particles according to the present invention, aging before oxidizing by aerating the alkali carbonate aqueous solution, the ferrous salt aqueous solution, the suspension containing FeCO ₃ and the oxygen-containing gas, is performed. FeCO being done
_{When a} zinc compound is previously present in any of the suspensions containing ₃ , the axial ratio (major axis diameter / minor axis diameter) can be further improved, so that the major axis diameter is 0.1 to 0.45 μm. Spindle-shaped goethite particles containing zinc having an axis ratio (major axis diameter / minor axis diameter) of 15 or more can be obtained, and the spindle-shaped goethite particles or zinc obtained by heating and calcining the goethite particles can be obtained. Spindle-shaped magnetite (FeOx.Fe ₂ O ₃ , 0 <x) obtained by heating and reducing spindle-shaped hematite particles in a reducing gas.
≤1) The spindle-shaped maghemite particles containing, if necessary, further oxidized zinc-containing spindles have a major axis diameter of 0.1 to 0.3 μm and an axial ratio (major axis diameter / minor axis diameter). ) Is 8
The above particles are obtained.

Similarly, when these particles are used as precursor particles and denatured with Co, the particles are fine, have high coercive force, and the particle surface with excellent transfer characteristics is denatured with Co. Magnetic iron oxide particles can be obtained.

In the present invention, the axial ratio (major axis diameter / short axis diameter) is 7 or more,
Spindle-shaped magnetic iron oxide particle powder having preferably 8 or more, more preferably 9 or more, and the surface of which is modified with Co, and an axial ratio (major axis / minor axis diameter) of 8 or more, preferably 9 or more, More preferably, it is possible to obtain a magnetic iron oxide particle powder having a spindle-shaped particle containing zinc having 10 or more and modified with Co.

In the present invention, the coercive force is 480 to 1000 Oe, and the transfer characteristic is
Magnetite _{(FeOx · Fe 2 O 3,} 0 <x ≦ 1) the particle surface which exhibited a spindle is modified with Co having more than 52dB particles and the coercive force 480-1,000 Oe, the transfer characteristics than 57.0DB, Koto In addition, it is possible to obtain a maghemite particle powder having a spindle-shaped particle surface having 58.0 dB or more and modified with Co.

The following is a description of a part extracted from a number of examples performed by the inventor of the present invention.

FIG. 1 shows the relationship between the major axis diameter of the maghemite particle powder and the measured transfer value. In FIG. 1, straight lines A, B and C are spindle-shaped maghemite particle powders according to the present invention, acicular maghemite particle powders obtained by the conventional method described in the above-mentioned JP-B-39-5610, respectively. This is the case of the spindle-shaped maghemite particle powder obtained by the conventional method described in the above-mentioned JP-A-50-80999. As shown in FIG. 1, the spindle-shaped maghemite particles according to the present invention have excellent transfer characteristics.

The spindle-shaped magnetite (FeOx.
Fe ₂ O ₃ , 0 <x ≦ 1) The particles also show the same tendency as the straight line A in FIG. 1 and have excellent transfer characteristics.

By the way, it is known that the transfer characteristics are strongly affected by the magnitude of the coercive force when the coercive force is higher than 480 to 500 Oe. That is, FIGS. 2 and 3 show the relationship between the measured coercive force value and the measured transfer value of the magnetite particle powder and the maghemite particle powder obtained by the present inventors from many examples, respectively. It can be seen from the figure that there is a certain relationship between the coercive force and the transfer characteristics.

FIGS. 4 and 5 show the relationship between the transfer correction value and the major axis diameter at 700 Oe of the coercive force of the magnetite particle powder modified with Co and the maghemite particle powder modified with Co, respectively. . In FIGS. 4 and 5, straight lines A, B and C represent the spindle-shaped magnetic iron oxide particles according to the present invention, and the acicular magnetic particles obtained by the conventional method described in JP-B-39-5610. Using iron oxide particle powder and spindle-shaped magnetic iron oxide particle powder obtained by the conventional method described in JP-A-50-80999 as precursor particles, Co-modification is performed in the same manner as in Example 1 described later. This is a magnetic iron oxide particle powder obtained by modifying the particle surface with Co. As shown in FIGS. 4 and 5, the coercive force 700
It can be seen that there is a certain relationship between the transfer correction value in Oe and the major axis diameter. The magnetic iron oxide particle powder according to the present invention, in which the particle surface is modified with Co, has excellent transfer characteristics.

6 and 7 show the relationship between the amount of zinc sulfate present and the major axis and axial ratio (major axis / minor axis diameter) of spindle-shaped goethite particles, respectively.

That is, under the reaction conditions of Example 5 described later, the major axis and the axial ratio of the spindle-shaped goethite particles obtained when the amount of zinc sulfate was 0 to 10.0% by weight (major axis /
The short axis diameter is shown on the vertical axis, and the amount of zinc sulfate present is shown on the horizontal axis.

As shown in FIGS. 6 and 7, the major axis of the formed spindle-shaped goethite particles is less affected by the presence of zinc sulfate, and the axial ratio (major axis diameter / minor axis diameter) is determined by the presence of zinc sulfate. It tends to increase as the amount increases.

From this, it is considered that the zinc compound has an action of suppressing growth of the generated spindle-shaped goethite particles in the short axis direction.

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

As the ferrous salt aqueous solution used in the present invention,
There are aqueous ferrous sulfate and aqueous ferrous chloride.

As the aqueous alkali carbonate solution used in the present invention, an aqueous solution of sodium carbonate, potassium carbonate, ammonium carbonate or the like can be used.

The amount of the aqueous alkali carbonate solution used in the present invention is
It is 1.5 to 3.5 times equivalent to Fe in the aqueous ferrous salt solution. 1.
If the amount is less than 5 equivalents, the obtained spindle-shaped goethite particles have an uneven particle size, and the particles are entangled with each other to form aggregated particles, resulting in poor dispersibility. If it exceeds 3.5 equivalents, the axial ratio (major axis diameter / minor axis diameter) tends to decrease as the amount of addition increases,
Spindle-shaped goethite particles having a large axis ratio (major axis diameter / short axis diameter) are difficult to obtain, and the amount of expensive alkali carbonate aqueous solution increases, which is not economical.

The ripening in the present invention is performed under an inert atmosphere by passing an inert gas such as N ₂ gas through the liquid, and is performed while stirring by the passed gas or mechanical operation.

The aging temperature of the suspension containing FeCO ₃ in the present invention is 40 to 6
0 ° C. When the temperature is lower than 40 ° C., the axial ratio (major axis diameter / minor axis diameter) becomes small, and a spindle-shaped goethite particle powder having a large axial ratio (major axis diameter / minor axis diameter) cannot be obtained. Even when the temperature exceeds 60 ° C., a spindle-shaped goethite particle powder having a large axis ratio (major axis diameter / short axis diameter) can be obtained.
There is no point in raising the aging temperature more than necessary.

The aging time of the suspension containing FeCO ₃ in the present invention is 50
~ 100 minutes. If the time is less than 50 minutes, a spindle-shaped goethite particle powder having a large axis ratio (major axis diameter / short axis diameter) cannot be obtained. Even when it exceeds 100 minutes, a spindle-shaped goethite particle powder having a large axial ratio (long diameter / short axis diameter) can be obtained, but there is no point in setting the time longer than necessary.

As the zinc compound in the present invention, zinc sulfate, zinc chloride and the like can be used.

The amount of the zinc compound is based on Fe in the aqueous ferrous salt solution.
It is 0.3 to 10.0 atomic% in terms of Zn. When it is less than 0.3 atomic%, spindle-shaped goethite particles having a large axial ratio (major axis diameter / minor axis diameter) cannot be obtained. 10.0 atomic%
When the ratio exceeds the above, goethite particles having a spindle shape with a large axial ratio (major axis diameter / short axis diameter) can be obtained. However, these goethite particles can be obtained by heat reduction or, if necessary, further oxidized. The magnetization value of the obtained magnetic iron oxide particles decreases. In consideration of the axis ratio (major axis diameter / minor axis diameter) of the goethite particles having a spindle shape, 0.5 to 8.0 atomic% is preferable.

The added zinc compound is contained in spindle-shaped goethite particles having almost the entire length as shown in Examples described later. Since the zinc compound relates to the axial ratio (major axis diameter / minor axis diameter) of the resulting spindle-shaped goethite particles, the zinc compound is oxidized by passing an oxygen-containing gas through the suspension containing FeCO ₃ before oxidation. It is necessary to keep it present, and therefore, the time of addition is such that an aqueous solution of alkali carbonate, an aqueous solution of ferrous salt, a suspension containing FeCO ₃ and aging before aeration with an oxygen-containing gas are performed. ₃ is most effective when added to a suspension containing FeCO ₃ that has been aged.

The reaction temperature during the oxidation of the present invention is 40 to 70 ° C. When the temperature is lower than 40 ° C., a spindle-shaped goethite particle powder cannot be obtained. When the temperature exceeds 70 ° C., granular hematite particles are mixed in spindle-shaped goethite particles.

The pH in the present invention is 7-11. If it is less than 7 or more than 11, goethite particles having a spindle shape cannot be obtained.

The oxidizing means in the present invention is performed by aerating an oxygen-containing gas (for example, air) into the liquid, and is performed while stirring by the aerated gas or a mechanical operation.

In the present invention, in order to improve the various properties of the magnetic iron oxide particles, conventionally, when producing goethite particles, a different metal other than Fe, such as Co, Ni, Cr, Zn, Al, and Mn, which is usually added, is used. In this case also, a goethite particle powder having a spindle shape having a large axial ratio (major axis diameter / short axis diameter) can be obtained.

Examples of the starting material particles in the present invention include spindle-shaped hematite particles obtained by heating and dehydrating the goethite particles by a conventional method, and the goethite particles obtained by subjecting the goethite particles to non-reducing by a conventional method. Any of densified spindle-shaped hematite particles obtained by heat treatment in a temperature range of 250 to 700 ° C. in an atmosphere can be used.

The heat reduction treatment and the oxidation treatment in the reducing gas in the present invention can be performed by a conventional method.

In addition, the starting material particles are coated with a material having an effect of preventing sintering, such as Si, Al, or a P compound, by a surrounding method prior to the heat reduction treatment to prevent sintering between the particles and the particles. This makes it easy to maintain and inherit the particle shape and the axial ratio (major axis diameter / minor axis diameter) of the starting material particles.

The Co modification of the precursor particle powder in the present invention can be performed by a conventional method, for example, Japanese Patent Publication No. 52-24237,
As described in JP-B-52-24238, JP-B-52-36751, and JP-B-52-36863, an aqueous dispersion of precursor particles is mixed with at least a Co salt aqueous solution and an alkaline aqueous solution. The resulting mixture is heated at a temperature of 50 to 100 ° C. in a temperature range of 50 to 100 ° C.

The Co salt aqueous solution may contain an Fe (II) salt aqueous solution as needed.

As the aqueous solution of the Co salt in the Co modification of the present invention, there is an aqueous solution of cobalt sulfate, cobalt chloride, cobalt nitrate or the like.

Examples of the aqueous solution of Fe (II) salt include ferrous sulfate, ferrous chloride, and ferrous nitrate.

As the alkaline aqueous solution in the Co modification of the present invention,
There are sodium hydroxide, potassium hydroxide and the like.

The temperature of Co transformation in the present invention is related to the processing time, and if the temperature is 50 ° C. or less, Co or Co and Fe
Magnetite particles or maghemite particles denatured in (II) are unlikely to be produced, and even if they are produced, an extremely long treatment is required.

The conversion amount of Co in the present invention is 0.5 to 15.0 atomic% in terms of Co with respect to Fe and Co. When the content is less than 0.5 atomic%, the effect of improving the coercive force of the obtained spindle-shaped magnetite particles or maghemite particles cannot be sufficiently achieved. Even if it exceeds 15.0 atomic%,
Although the effect of improving the coercive force of the obtained spindle-shaped magnetite particles or maghemite particles is obtained, there is no point in modifying the magnetite particles more than necessary.

Almost all of the added Co is used for denaturation on the surface of the magnetic iron oxide particles.

In consideration of the coercive force of the spindle-shaped magnetite particles or maghemite particles, 2.0 to 13.0 atomic% is preferable.

The magnetic iron oxide particle powder obtained by modifying the particle surface with Co obtained by the present invention is, if necessary, a hydroxide such as Al, Si, Zn or the like usually used for improving dispersibility in a binder. Alternatively, the particle surface may be coated with an oxide.

[Examples] 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 zinc content was indicated by a value measured by fluorescent X-ray analysis.

The transfer characteristics of the spindle-shaped magnetite particle powder and the spindle-shaped maghemite particle powder according to the present invention are shown in FIG. 1 which shows the relationship between the measured transfer value and the major axis diameter and the relationship between the measured transfer value and the major axis diameter. The transfer correction value Q ₁ at the major axis diameter of 0.2 μm is inserted into the following equation (1) obtained from the straight line A of
Indicated by

Q ₁ = 40 × (0.2−A) + B (1) The transfer characteristics of the spindle-shaped magnetite particle powder and the spindle-shaped maghemite particle powder according to the present invention in which the particle surface is modified with Co are as follows: The actual measured value of the transfer and the actual measured value of the coercive force are inserted into the following equation (2), and the coercive force is 700 Oe
Obtains a transfer correction value Q ₂ in, release of drawing after showing the relationship between the transfer correction value Q ₂ a major axis diameter, the transcription correction value Q ₂ and a long axis diameter 2
And the transfer correction value Q at a coercive force of 700 Oe and a major axis diameter of 0.2 μm inserted into the following equation (3) obtained from the straight line A in FIG.
Indicated by ₃ .

Q ₂ = (700−C) × 0.02 + B (2) Q ₃ = 40 × (0.2−A) + Q ₂ (3) where Q ₁ = length in the above formulas (1) to (3). Transfer correction value at a shaft diameter of 0.2 μm (dB) Q ₂ = Transfer correction value at a coercive force of 700 Oe (dB) Q ₃ = Transfer correction value at a coercive force of 700 Oe and a long axis diameter of 0.2 μm (dB) A = Long axis diameter (Μm) B = transfer measured value (dB) C = coercive force measured value (dB)

The measured values are based on “Powder and Powder Metallurgy” (1979), Vol. 26, No. 4, page 149, published by the Japan Society of Powder and Powder Metallurgy, and “Technical Report of the IEICE”
This was carried out according to the method described on page 2 of page 77-27. That is, the diameter
6 mm, magnetic iron oxide particles packed in a cylindrical container of height 5 mm, in a magnetic field of 50 Oe, after holding and magnetized at 60 ° C for 80 minutes,
After cooling to room temperature, the remanent magnetization Irp was measured, and then a DC magnetic field was applied to the sample to obtain the saturation remanence Irs, which was calculated by the following equation.

Actual measured value of transfer PT (dB) = − 20 log Irp / Irs <Production of spindle-shaped goethite particle powder> Examples 1 to 8 Comparative Examples 1 to 6; Example 1 N ₂ gas was flowed at a rate of 3.4 cm per second. 1.16 mol / Na ₂ C in a reaction vessel kept in a non-oxidizing atmosphere by
After adding the O ₃ aqueous solution 704, an aqueous ferrous sulfate solution 296 containing 1.35 mol / Fe ²⁺ is added and mixed (the amount of Na ₂ CO ₃ corresponds to 2.0 equivalents to Fe), and the temperature is 47. FeC at ℃
O ₃ was produced.

In the suspension containing FeCO ₃ above, N ₂ gas is continuously supplied every second.
After maintaining at a temperature of 47 ° C. for 70 minutes while blowing at a rate of 3.4 cm, 2.8 cm of air per second at a temperature of 47 ° C. was passed through the suspension containing the FeCO ₃ for 5.0 hours to produce yellow-brown precipitate particles. I let it. The pH during air ventilation was 8.5 to 9.5.

A part of the suspension containing the yellow-brown precipitate particles was prepared by a conventional method.
Separately, washed with water, dried and pulverized.

The obtained tan particle powder was goethite as a result of X-ray diffraction. As is clear from the electron micrograph (× 30000) shown in FIG. 8, the average value of the major axis diameter was 0.30 μm and the axial ratio (major axis diameter). (Small axis diameter): 12.6 spindle-shaped particles, uniform in particle size, and free of dendritic particles.

Separately from the suspension containing the spindle-shaped goethite particles, 3000 g of water-washed paste (corresponding to about 1000 g of spindle-shaped goethite particles) was suspended in 60 pieces of water. At this time, the pH of the suspension was 9.7.

Next, sodium hexametaphosphate 20 was added to the suspension.
g of an aqueous solution containing 300 g (equivalent to 2.0 wt% based on spindle-shaped goethite particles) was added and stirred for 30 minutes, and then 10% acetic acid was added so that the pH of the suspension became 5.8. Thereafter, the spindle-shaped goethite particles were separated by a press filter and dried to obtain spindle-shaped goethite particles powder coated with the P compound.

Example 2 to 4, N ₂ gas flow rate in the production reaction of Comparative Example 1 to 5 FeCO _3, the type of aqueous alkali carbonate solution, the concentration, amount and mixing ratio, the type of Fe ²⁺ solution, the concentration and amount, temperature, P compound or Si compound in the same manner as in Example 1 except that the N ₂ gas flow rate, temperature and time in the aging step, the temperature in the oxidation step, the air flow rate and the reaction time, and the type and amount in the coating step were variously changed. Alternatively, a spindle-shaped goethite particle powder coated with both compounds was obtained.

Tables 1 and 2 show the main production conditions and various characteristics at this time.

The spindle-shaped goethite particle powders obtained in Examples 2 to 4 were all uniform in particle size and free of dendritic particles.

The spindle-shaped goethite particle powder obtained in Comparative Example 5 had a short axial ratio (major axis diameter / minor axis diameter) as shown in the electron micrograph (× 30,000) of FIG.

In Example 3, in the production reaction of FeCO ₃ , the Ni-containing goethite particles powder having a spindle shape by adding 0.5 atomic% of NiSO ₄ in terms of Ni / Fe (Ni content:
(0.49 atomic% in terms of Ni / Fe).

In addition, the spindle-shaped goethite particles obtained in Comparative Example 1 had an uneven particle size as shown in an electron micrograph (× 30000) of FIG. 10, and the particles were entangled to form aggregated particles. Was.

Example 5 In a reaction vessel kept in a non-oxidizing atmosphere by flowing N ₂ gas at a rate of 3.4 cm per second, 1.35 mol / Na ₂ C was introduced.
After adding an O ₃ aqueous solution 600, an aqueous ferrous sulfate solution 300 containing 1.35 mol / Fe ²⁺ is added and mixed (the amount of Na ₂ CO ₃ corresponds to 2.0 equivalents to Fe), and the temperature is 47. FeC at ℃
O ₃ was produced.

In the suspension containing FeCO ₃ above, N ₂ gas is continuously supplied every second.
While blowing at a rate of 3.4 cm, the temperature was maintained at 47 ° C. for 60 minutes, and then an aqueous solution of zinc sulfate 5.0 was added so as to contain 3.0 atomic% of Zn with respect to Fe, and then the temperature was further maintained for 10 minutes. In the suspension containing the aged FeCO ₃ at a temperature of 47 ° C per second
2.8 cm of air was bubbled in for 6.0 hours to produce tan precipitated particles. The pH during air ventilation was 8.5 to 9.5.

A part of the suspension containing the yellow-brown precipitate particles was prepared by a conventional method.
Separately, washed with water, dried and pulverized.

The obtained yellow-brown particle powder was goethite as a result of X-ray diffraction, and as apparent from the electron micrograph (× 30000) shown in FIG. 9, the average value of the major axis diameter was 0.29 μm and the axial ratio (major axis diameter). (Small axis diameter): 17.0, spindle-shaped particles having a uniform particle size without dendritic particles. Also,
The zinc content was 3.0 atomic% of Zn with respect to Fe.

Separately from the suspension containing the spindle-shaped goethite particles, 3000 g of water-washed paste (corresponding to about 1000 g of spindle-shaped goethite particles) was suspended in 60 pieces of water. At this time, the pH was 9.8.

20 g of sodium silicate (No. 3 water glass) in this suspension
(Equivalent to 2.0 wt% with respect to the spindle-shaped goethite particles), and the mixture was stirred for 60 minutes.
After addition of 10% acetic acid, the spindle-shaped goethite particles were separated by a press filter and dried to obtain spindle-shaped particle powder coated with a Si compound.

Tables 1 and 2 show various properties of the obtained spindle-shaped goethite particle powder.

Examples 6 to 8, Comparative Example 6, Kind, concentration and amount of aqueous alkali carbonate in the reaction of producing FeCO ₃ , type, concentration and amount of Fe ²⁺ aqueous solution, temperature, temperature and time in aging step, Zn compound Except that the type, amount and timing of addition, the temperature in the oxidation step, the air flow rate and the reaction time, and the type and amount in the coating treatment step were variously changed, the goethite particle powder having a spindle shape in the same manner as in Example 5. Obtained.

Tables 1 and 2 show the main production conditions and various characteristics at this time.

As a result of observation with an electron microscope, the spindle-shaped goethite particles obtained in Examples 6 to 8 were all uniform in particle size and free of dendritic particles.

The spindle-shaped goethite particle powder obtained in Comparative Example 6 had a small axial ratio (major axis diameter / minor axis diameter) as shown in the electron micrograph (× 30,000) of FIG.

<Production of Spindle-Shaped Hematite Particle Powder> Examples 9 to 16 Comparative Examples 7 to 12; Example 9 800 g of spindle-shaped goethite particle powder coated with the P compound obtained in Example 1 was treated with 600 g of air. Heat treatment was performed at ℃ to obtain a spindle-shaped hematite particle powder coated with the P compound.

As a result of observation with an electron microscope, this particle had a major axis of 0.
The axis ratio (major axis diameter / short axis diameter) was 24 μm.

Examples 10 to 16 and Comparative Examples 7 to 12 The same as Example 9 except that the type of spindle-shaped goethite particle powder coated with the P compound or the Si compound or both compounds and the heat treatment temperature were variously changed. Thus, spindle-shaped hematite particle powder was obtained.

 Table 3 shows the main manufacturing conditions and characteristics at this time.

<Production of Spindle-Shaped Magnetite Particle Powder> Examples 17 to 24 Comparative Examples 13 to 18; Example 17 1000 g of the spindle-shaped hematite particle powder obtained in Example 9 was put into a 13-retort reduction vessel. While driving and rotating, H ₂ gas was passed at a rate of 1.0 per minute, and reduced at a reduction temperature of 300 ° C. for 3 hours to obtain spindle-shaped magnetite particles.

The obtained spindle-shaped magnetite particle powder is
As shown in the electron micrograph (× 30000) shown in Fig. 13, spindle-shaped particles with an average value of 0.23 μm in major axis and an axial ratio (major axis / minor axis) of 10.2 were obtained. Particles were not mixed. As a result of magnetic measurements, the coercive force is a 350 Oe, saturation magnetization 81.5emu / g, transfer the correction value Q ₁ is was 46.8DB.

An electron micrograph (× 30000) of the spindle-shaped magnetite particle powder obtained in Example 17 is shown in FIG.

Examples 18 to 24, Comparative Examples 13 to 18 Spindle-shaped magnetite particle powders were obtained in the same manner as in Example 17, except that the type of hematite particle powder and the reduction temperature were 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 spindle-shaped magnetite particle powders obtained in Examples 18 to 24 were all uniform in particle size and free of dendritic particles.

An electron micrograph (× 30000) of the spindle-shaped magnetite particle powder obtained in Example 21 is shown in FIG.

<Production of Spindle-Shaped Maghemite Particle Powder> Examples 25 to 32 Comparative Examples 19 to 24; Example 25 600 g of the spindle-shaped magnetite particle powder obtained in Example 17 was oxidized in air at 270 ° C. for 30 minutes. As a result, a spindle-shaped maghemite particle powder was obtained.

The obtained spindle-shaped maghemite particle powder is composed of spindle-shaped particles having a major axis of 0.23 μm and an axial ratio (major axis diameter / minor axis diameter) of 10.2 as a result of electron microscopic observation. And no dendritic particles were mixed. As a result of magnetic measurement, the coercive force was 390 Oe, and the saturation magnetization was 72.0 Oe.
A emu / g, transfer the correction value Q ₁ is was 55.8DB.

FIG. 15 shows an electron micrograph (× 30000) of the spindle-shaped maghemite particle powder obtained in Example 25.

Examples 26 to 32 and Comparative Examples 19 to 24 Spindle-shaped maghemite particle powders were obtained in the same manner as in Example 25, except that the type of spindle-shaped magnetite particle powder was variously changed.

Table 5 shows the main production conditions and the characteristics of the particle powder at this time.

As a result of observation by an electron microscope, the spindle-shaped maghemite particle powders obtained in Examples 26 to 32 were all uniform in particle size and free of dendritic particles.

Electron micrographs (× 30000) of the spindle-shaped maghemite particles obtained in Example 29 and Comparative Example 23 are shown in FIGS. 16 and 17, respectively.

<Production of Spindle-Shaped Magnetite Particle Powder Modified with Co> Examples 33 to 40 Comparative Examples 25 to 30; Example 33 100 g of the spindle-shaped magnetite particle powder obtained in Example 17 was used as much as possible. 0.056mol of cobalt using ferrous sulfate and cobalt sulfate using cobalt sulfate and ferrous sulfate while preventing air contamination.
Pour into 1.0 water in which 113 mol is dissolved, disperse until a fine slurry is obtained, and then add 18-N
163 ml of an aqueous NaOH solution, and further add water to make up the entire volume.
A dispersion having an OH group concentration of 2.0 mol / was set as 1.3. The temperature of the dispersion was raised to 100 ° C., and stirring was performed at this temperature for 10 minutes.
After the time, the slurry was taken out, washed with water, separated, and dried at 60 ° C. to obtain spindle-shaped magnetite particles modified with Co.

As a result of electron microscopic observation, the obtained particles have inherited the shape and particle size of magnetite particles having a spindle shape as a precursor, and have a major axis diameter of 0.23 μm and an axial ratio (major axis diameter / minor axis diameter). .
The particles had a spindle shape of 2. As a result of magnetic measurements, the coercive force Hc is 729 Oe, the saturation magnetization σs is a 82.5emu / g, transfer the correction value Q ₃ are was 55.2DB. The particles contained 3.82 at% of cobalt in Co / (Fe + Co).

Examples 34 to 40, Comparative Examples 25 to 30 The amount of magnetite particles having a spindle shape as a precursor was determined.
100 g, the total volume of the processing solution was 1.3, and the procedure was the same as in Example 33, except that the kind of the precursor, the added amount of cobalt, the added amount of Fe (II), the added amount of NaOH, the OH group concentration and the temperature were variously changed. Thus, spindle-shaped magnetite particles modified with Co or Co and Fe (II) were obtained.

 Table 6 shows the main manufacturing conditions and characteristics.

Electron micrograph (× 30) of the spindle-shaped magnetite particle powder modified with Co and Fe (II) obtained in Example 37
000) is shown in FIG.

<Production of Spindle-Shaped Maghemite Particle Powder Modified with Co> Examples 41 to 48 Comparative Examples 31 to 36; Example 41 100 g of the spindle-shaped maghemite particle powder obtained in Example 25 was used as much as possible. 0.048 mol of cobalt using ferrous sulfate and cobalt sulfate using cobalt sulfate and ferrous sulfate while preventing air contamination.
It is poured into 1.0 mol of water in which 107 mol is dissolved, and dispersed until a fine slurry is formed.
53 ml of an aqueous NaOH solution, and further add water to make up the entire volume.
A dispersion having an OH group concentration of 0.5 mol / was set as 1.3. The temperature of the dispersion was raised to 100 ° C., and stirring was performed at this temperature for 10 minutes.
After a lapse of time, the slurry was taken out, washed with water, filtered, and dried at 60 ° C. to obtain spindle-shaped maghemite particles modified with Co.

The obtained particles are shown in an electron micrograph (× 3000) shown in FIG.
As shown in 0), it inherits the shape and particle size of spindle-shaped maghemite particles, which are precursors, and has a major axis diameter of 0.23μ.
m, and spindle-shaped particles having an axial ratio (major axis diameter / short axis diameter) of 9.1. As a result of the magnetic measurement, the coercive force Hc was 508 Oe,
Saturation magnetization σs is a 76.3emu / g, transfer the correction value Q ₃ are 60.
It was 4dB. The particles are made of Co / (Fe + Co) 3.41
Atomic% was contained.

Examples 42-48, Comparative Examples 31-36 The amount of spindle-shaped maghemite particles as precursors was determined.
100 g, the total volume of the processing solution was 1.3, and the procedure was the same as in Example 41, except that the kind of the precursor, the added amount of cobalt, the added amount of Fe (II), the added amount of NaOH, the OH group concentration and the temperature were variously changed. Thus, spindle-shaped maghemite particles modified with Co or Co and Fe (II) were obtained.

 Table 7 shows the main production conditions and characteristics.

[Effect of the Invention] Spindle-shaped magnetic iron oxide particles according to the present invention,
As shown in the previous example, the particles are fine, in particular, 0.3 μm
The following is a particle powder having a high coercive force and excellent transfer characteristics.
It is suitable as the most required magnetic material particle powder for high recording density, high sensitivity and high output.

[Brief description of the drawings]

FIG. 1 shows the relationship between the major axis diameter of the maghemite particle powder and the measured transfer value. 2 and 3 show the relationship between the measured coercive force and the measured transfer of the magnetite particle powder and the maghemite particle powder, respectively. 4 and 5 show the relationship between the transfer correction value at 700 Oe and the major axis diameter of the magnetite particle powder modified with Co and the maghemite particle powder modified with Co, respectively. 6 and 7 show the relationship between the abundance of zinc sulfate and the major axis diameter and the axial ratio (major axis diameter / minor axis diameter) of spindle-shaped goethite particles, respectively. 8 to 12 are electron micrographs (×) showing the particle structure of the spindle-shaped goethite particles obtained in Example 1, Example 5, Comparative Example 1, Comparative Example 5, and Comparative Example 6, respectively.
30000). FIGS. 13 and 14 are electron micrographs (× 30000) showing the particle structure of the spindle-shaped magnetite particles obtained in Examples 17 and 21, respectively. FIGS. 15 to 17 are electron micrographs (× 30000) showing the particle structure of the spindle-shaped maghemite particles obtained in Example 25, Example 29, and Comparative Example 23, respectively. FIGS. 18 and 19 are respectively a spindle-shaped magnetite particle powder modified with Co obtained in Example 37 and a spindle-shaped maghemite particle powder modified with Co obtained in Example 41. It is an electron micrograph (x30000) which shows a particle structure.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaru Isoai 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Examiner, Toda Kogyo Co., Ltd. Creative Center Masahiro Hiratsuka (56) References JP-A 1-115827 (JP, A) JP-A-57-156333 (JP, A) JP-A-62-158801 (JP, A)

Claims (8)

(57) [Claims] 1. A long axis diameter of 0.1 to 0.3 μm, an axis ratio (long axis diameter / short axis diameter) of 7 or more, a coercive force of 480 to 1000 Oe,
The particle surface characterized by a transfer characteristic of 52 dB or more
Based on Fe and Co, magnetite exhibited spindle that is modified with 0.5 to 15.0 atomic% of _{Co (FeOx · Fe 2 O 3} , 0 <x
≦ 1) Spindle-shaped magnetic iron oxide particles composed of particles. 2. A long axis diameter of 0.1 to 0.3 μm, an axis ratio (long axis diameter / short axis diameter) of 8 or more, a coercive force of 480 to 1000 Oe,
The particle surface characterized by a transfer characteristic of 52 dB or more
Spindle-shaped magnetite (FeOx.Fe) containing zinc which is metamorphized with 0.5-15.0 atomic% Co with respect to Fe and Co
₂ O ₃ , 0 <x ≦ 1) Spindle-shaped magnetic iron oxide particles composed of particles. 3. A long axis diameter of 0.1 to 0.3 μm, an axis ratio (long axis diameter / short axis diameter) of 7 or more, a coercive force of 480 to 1000 Oe,
Spindle-shaped magnetic iron oxide particles composed of spindle-shaped maghemite particles wherein the particle surface is modified by 0.5 to 15.0 atomic% of Co with respect to Fe and Co, characterized in that the transfer characteristic is 57.0 dB or more. Powder. 4. A long axis diameter of 0.1 to 0.3 μm, an axis ratio (long axis diameter / short axis diameter) of 8 or more, a coercive force of 480 to 1000 Oe,
Spindle-shaped magnetism composed of spindle-shaped maghemite particles containing zinc whose surface is modified by 0.5 to 15.0 atomic% of Co with respect to Fe and Co, characterized by a transfer characteristic of 57.0 dB or more Iron oxide particle powder. 5. An aqueous solution containing FeCO ₃ obtained by reacting an aqueous solution of alkali carbonate and an aqueous solution of ferrous salt is aged in a non-oxidizing atmosphere, and then an oxygen-containing solution is added to the suspension containing FeCO ₃ . In generating goethite particles having a spindle shape by oxidizing by passing gas therethrough, the amount of the alkali carbonate aqueous solution is 1.5 times the amount of Fe in the ferrous salt aqueous solution.
~ 3.5 equivalents, the ripening temperature in the ripening 40 ~ 60 ° C, and by setting the ripening time 50 ~ 100 minutes, to produce spindle-shaped goethite particles,
Spindle-shaped magnetite (FeOx.Fe) obtained by heating and reducing the goethite particles or spindle-shaped hematite particles obtained by heating and firing the particles in a reducing gas.
₂ O ₃ , 0 <x ≦ 1) Using a particle as a precursor particle, a mixed solution having a pH of 11 or more obtained by mixing an aqueous dispersion of the precursor particle with at least a Co salt aqueous solution and an alkaline aqueous solution is used. 2. The method for producing spindle-shaped magnetic iron oxide particles according to claim 1, wherein the heat treatment is performed in a temperature range of from about 100 [deg.] C. to about 100 [deg.] C. 6. After a suspension containing FeCO _3, obtained by reacting an aqueous alkali carbonate solution and an aqueous solution of a ferrous salt and aged in a non-oxidizing atmosphere, into a suspension containing the FeCO ₃ In generating goethite particles having a spindle shape by oxidizing by passing an oxygen-containing gas, the amount of the alkali carbonate aqueous solution is 1.5 times the amount of Fe in the ferrous salt aqueous solution.
The ripening temperature in the ripening is 40 to 60 ° C., the ripening time is 50 to 100 minutes, and the alkali carbonate aqueous solution, the ferrous salt aqueous solution, the FeCO
_By pre-existing a zinc compound in any of the suspension containing FeCO ₃ and the suspension containing FeCO ₃ that has been aged before oxidizing by aeration with an oxygen-containing gas, zinc is added. Spindle-shaped goethite particles containing the zinc-containing goethite particles or the zinc-containing spindle-shaped hematite particles obtained by heating and calcining the zinc-containing goethite particles are obtained by heating and reducing in a reducing gas. Spindle-shaped magnetite (FeOx ・ Fe
₂ O ₃ , 0 <x ≦ 1) Using a particle as a precursor particle, a mixed solution having a pH of 11 or more obtained by mixing an aqueous dispersion of the precursor particle with at least a Co salt aqueous solution and an alkaline aqueous solution is used. 3. The method for producing spindle-shaped magnetic iron oxide particles according to claim 2, wherein the heat treatment is carried out in a temperature range of from about 100 DEG C. to about 100 DEG C. 7. The spindle-shaped magnetite particles according to claim 5, further obtained by using spindle-shaped maghemite particles obtained by oxidation as precursor particles, wherein an aqueous dispersion of the precursor particles and at least Co A mixed solution having a pH of 11 or more obtained by mixing the salt aqueous solution and the alkaline aqueous solution with 50
4. The method for producing spindle-shaped magnetic iron oxide particles according to claim 3, wherein the heat treatment is performed in a temperature range of from about 100 DEG C. to about 100 DEG C. 8. A spindle-shaped maghemite particle containing zinc obtained by oxidizing the zinc-containing spindle-shaped magnetite particle according to claim 6 and using the zinc-containing spindle-shaped magnetite particle as a precursor particle. Aqueous dispersion of particles and at least Co
5. The spindle-shaped magnetic iron oxide particles according to claim 4, wherein a mixed solution having a pH of 11 or more obtained by mixing the salt aqueous solution and the alkaline aqueous solution is subjected to heat treatment in a temperature range of 50 to 100 [deg.] C. Manufacturing method.