JP2691782B2 - Manufacturing method of acicular magnetic iron oxide particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing needle-shaped magnetic iron oxide particles having high coercive force and excellent dispersibility.

[Prior Art] In recent years, with the progress of miniaturization and weight reduction of magnetic recording / reproducing devices, there is an increasing need for higher performance of magnetic recording media such as magnetic tapes and magnetic disks. That is, there has been a demand for high density recording, high output characteristics, especially improvement of frequency characteristics. In order to satisfy various requirements for a magnetic recording medium, the powder of magnetic iron oxide particles, which is a raw material of the magnetic recording medium, must have high coercive force and excellent dispersibility.

Currently used magnetic iron oxide particles for magnetic recording include acicular magnetite particles ((FeO) x.Fe ₂
O ₃ 0 <x ≦ 1), acicular crystal maghemite particle powder, and so-called cobalt-adhered acicular magnetic iron oxide in which these particles are used as precursor particles and the particle surfaces of the precursor particles are coated with a cobalt compound. Particle powder and the like are known.

Conventionally, acicular magnetite particle powder and acicular maghemite particle powder are generally acicular particles obtained by oxidizing a neutralized precipitate of a ferrous salt and an alkaline aqueous solution such as alkali hydroxide or alkali carbonate. Needle-shaped hematite particles obtained by heating and calcining crystallized ferric hydroxide-containing particles or needle-shaped ferric hydroxide-containing particles as starting material particles, and the starting material particles in a reducing gas such as hydrogen 300 It is obtained by reducing at ~ 400 ° C to acicular crystalline magnetite particles, or subsequently oxidizing it at 200-400 ° C in air to acicular crystalline maghemite particles.

The acicular crystal magnetite particle powder and the acicular crystal maghemite particle powder have a relatively high retention by utilizing the anisotropy derived from the shape, that is, by increasing the axial ratio (major axis diameter / minor axis diameter). Although it is possible to have a magnetic force, the conventional method has a problem in that the shape of the particles is deformed and the coercive force is reduced because sintering is likely to occur between particles during the heating and reduction step. In addition, since sintering occurs between particles and each other, the dispersibility is naturally poor.

The above-mentioned cobalt-adhered acicular magnetic iron oxide particle powder is a needle-shaped magnetite particle or a needle-shaped maghemite particle by utilizing the crystal magnetic anisotropy of cobalt in addition to the anisotropy derived from the shape. Although it was possible to have a higher coercive force, the conventional method also causes sintering between particles and each other during the heating and reduction process, which naturally lowers the coercive force and also improves the dispersibility. Was also bad.

Therefore, for a long time, particles and sintering between particles which occur during the heating and reduction process are sufficiently prevented, the particle shape of the starting material particles is maintained, and the particles do not stick to each other.
There has been a strong demand for the production of magnetic iron oxide particle powders which are kept in an individual state.

As a method for preventing the particles and the sintering between the particles that occur during such a heat reduction step, there is a method of coating the particle surfaces of the starting material particles with various organic compounds or inorganic compounds having a sintering preventing action in advance. Is generally known.

A method of using a silicon compound as a compound having a sintering-preventing action is disclosed in, for example, JP-A-48-83100 and JP-A-4949.
-41299, JP-A-50-44498, JP-A-50-98
700, JP 59-207843, JP 59-21362
6, JP-A-63-69714 and JP-A-63-69715
No., etc.

However, even by this method, the coating of the particle surface of the starting material particles is still insufficient, so that the sintering in the heating / reduction step cannot be sufficiently prevented.

[Problems to be Solved by the Invention] The present invention has been made to solve the above problems, and an object of the present invention is to obtain needle-like magnetic iron oxide particles having high coercive force and excellent dispersibility. To provide.

[Means for Solving the Problems] The present invention has been made to solve the above problems, and the above object of the present invention is to provide a needle-shaped hydrous hydroxide having an average major axis diameter of 0.1 to 0.3 μm. Iron particles or acicular hematite particles obtained by heating and firing the acicular ferric hydroxide particles are acicular magnetite particles obtained by heating and reducing in a reducing gas, or further oxidized if necessary. In the method for producing a needle-shaped magnetic iron oxide particle powder obtained from needle-shaped maghemite particles obtained as described above, the needle-shaped ferric hydroxide-containing particles or the needle-shaped hematite particles, and the following general formula (I) At least one of the silicone compounds represented, 120 ℃
This can be achieved by a method for producing acicular crystalline iron oxide particle powder, which comprises contacting in a gas phase at the following temperature to substantially coat the particle surface with a polymer of a silicone compound in advance.

Further, the acicular crystal magnetite particles or the acicular crystal maghemite particles as a precursor particle, at least the precursor particles, a pH including a cobalt salt aqueous solution and an alkaline aqueous solution
It is preferable that the particle surface of the precursor particles is coated with the cobalt compound by heating the dispersion liquid of 11 or more in the temperature range of 50 to 100 ° C.

(In the formula, R ¹ , R ² , R ³ , R ⁴ , R ^{5 and} R ⁶ are each a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms which may be substituted with at least one halogen atom. However, R ¹ , R ² and R ³ cannot be hydrogen atoms at the same time.

Further, a or b is 0 or an integer of 1 or more, and c is 0 or 2. However, when c is 0, a and b
Is an integer of 3 or more. ) [Function] Conventional silicone or silane coupling agents react with each other at a place other than the powder surface, and it is difficult to uniformly coat the particle surface. As a result, uncoated areas, areas where silica lumps were present, etc., were uneven after heating and firing. In addition, the silicone or silane coupling agent acts as a linking agent to connect the particles to each other, and the particles may remain connected to each other even after firing. In the present invention,
Since the silicone compound represented by the general formula (I) is used, the silicone compounds are polymerized on the surface of the particle, and a uniform film made of a polymer of the silicone compound is formed on the surface of the particle. Therefore, even after heating and firing
Particles coated with Si oxide can be obtained.

 Hereinafter, the present invention will be described in more detail.

The starting material particles in the present invention include, for example, the major axis diameter.
0.1 to 0.3 μm and the axial ratio (major axis diameter / minor axis diameter) 3
As described above, preferably 5 or more needle-shaped ferric hydroxide particles can be used. Here, acicular crystals mean particles having an axial ratio (major axis ratio / minor axis diameter) of 3 or more.
It also includes particles in the shape of spindles, rice grains, and inertia circles.

When acicular crystalline ferric hydroxide particles are used as the starting material particles, if necessary, they may be heated and calcined in advance prior to the heat reduction.

In addition, as the starting material particles in the present invention, needle-shaped hematite particles obtained by heating and firing needle-shaped ferric hydroxide-containing particles can be used, if necessary. The heating and firing temperature is 250 to 850 ° C, preferably 300 to 500 ° C. In order to maintain the shape of the starting material particles during the heat reduction, it is preferable that the acicular hematite particles are densified by heating and baking.

The starting material particles in the present invention are usually used to improve various properties of acicular magnetic iron oxide particles powder, Al, Ni,
Different metals other than Fe, such as Co, Si, Zn, and P, may be present inside the particles or on the surface of the particles.

The reduction temperature in the present invention is preferably 300 to 500 ° C.
When the temperature is 300 ° C or lower, the reduction reaction proceeds slowly and requires a long time. Further, when the temperature is 500 ° C. or higher, the reduction reaction rapidly progresses, so that deformation of the particle morphology and sintering between the particles are likely to occur.

In the present invention, acicular crystalline ferric hydroxide particles, any of acicular hematite particles obtained by heating and firing the acicular ferric hydroxide particles, and a silicone compound, 120 It is necessary that the surfaces of the particles are substantially coated with a polymer of a silicone compound in advance by bringing them into contact with each other in a gas phase at a temperature of not higher than 0 ° C.

The silicone compound used in the present invention is represented by the following general formula (I).

(In the formula, R ¹ , R ² , R ³ , R ⁴ , R ^{5 and} R ⁶ are each a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms which may be substituted with at least one halogen atom. However, R ¹ , R ² and R ³ cannot be hydrogen atoms at the same time.

Further, a or b is 0 or an integer of 1 or more, and c is 0 or 2. However, when c is 0, a and b
Is an integer of 3 or more. ) Two typical groups of silicone compounds represented by the above general formula (I) are represented by the following general formula (II) or (III). The first group corresponds to the case where c = 0 in the general formula (I), and is represented by the following general formula (II) (R ¹ HSiO) _a (R ² R ³ SiO) _b (II) (wherein R is ¹ , R ² , R ³ , a and b are the same as above,
Preferably, R ¹ , R ² or R ³ is each a hydrocarbon group having 1 to 10 carbon atoms which may be substituted with at least one halogen atom, and the sum of a and b is an integer of 3 or more. is there. ) Is a cyclic silicone compound. Representative examples of this compound are as follows.

(In the formula, n represents an integer of 3 or more.) (In the formula, a + b = an integer of 3 or more) The compounds (A) and (B) can be used alone or in the form of a mixture thereof.

In each of the formulas of the compounds (A) and (B), n (or a + b) is preferably an integer of 3 to 7, respectively. Since the boiling point decreases as the value of n (or a + b) decreases, the amount of evaporation and adsorption on the powder increases. In particular, when n (or a + b) is an integer of 3 or 4, it is particularly suitable because it is easy to polymerize due to its steric properties.

Specific examples of the cyclic silicone compound represented by the general formula (II) include dihydrogen hexamethylcyclotetrasiloxane, trihydrogenpentamethylcyclotetrasiloxane, tetrahydrogentetramethylcyclotetrasiloxane, dihydrogenoctamethylcyclopentasiloxane. Examples include siloxane, trihydrogenheptamethylcyclopentasiloxane, tetrahydrogenhexamethylcyclopentasiloxane, and pentahydrogenpentamethylcyclopentasiloxane.

Second silicone compound represented by the general formula (I)
The group of corresponds to the case of c = 2 in the general formula (I), and is represented by the following general formula (III) [Wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , a and b are the same as described above, but preferably R ^{1 to} R ⁶ are each at least 1
1 to 10 carbon atoms which may be substituted with halogen atoms
Is a hydrocarbon group. ] It is a linear silicone compound represented by these. As a typical example of this compound, the following general formula (D) (Wherein, n represents an integer of 2 to 5).

Specific examples of the linear silicone compound represented by the general formula (III) include 1,1,1,3,5,7,7,7-octamethyltetrasiloxane and 1,1,1,3,5,7. Examples include 9,9,9,9'-nonamethylpentasiloxane and 1,1,1,3,5,7,9,11,11,11-decamethylhexasiloxane.

The contact between the particles, the specific composition and the silicone compound in the gas phase in the present invention is, for example, 120 ° C. using a closed container.
Below preferably below 100 ℃, preferably 200mm
Under a pressure of Hg or less, more preferably 100 mmHg or less, a method of bringing the vapor of a silicone compound of a specific composition into contact with the particle surface in a molecular state, 120 ° C. or less, preferably 100 ° C.
It can be performed by a method of supplying a mixed gas of a silicone compound having a specific composition and a carrier gas to the particles at the following temperature.

In the present invention, the surface of the acicular crystalline ferric hydroxide particles or acicular hematite particles must be substantially coated with a polymer of a silicone compound, but the term “substantially coated” as used herein. Need only cover the entire surface of the particles, and the thickness, uniformity, shape, etc. of the polymer film do not matter.

The amount of the silicone compound of the specific composition in the present invention is
The content of Fe in the particles to be treated is preferably 0.1 to 15% by weight in terms of Si, and more preferably 0.2 to 12% by weight. If it is less than 0.1% by weight, it is not possible to sufficiently prevent sintering between particles and particles. If it exceeds 15% by weight, it is possible to prevent the particles and the sintering between the particles, but the saturation magnetization of the obtained acicular crystalline iron oxide particles is likely to decrease.

In the present invention, the polymerization reaction of the silicone compounds is caused on the particle surface by bringing the particles and the silicone compound having a specific composition into contact in the gas phase.
On the other hand, when thermal polymerization is caused, it is impossible to form a uniform and dense film. Further, when polymerized in the presence of a catalyst, the polymerization mainly occurs around the catalyst,
It is impossible to uniformly coat only the surface of the powder.

There are two types of polymer structures of the silicone compound in the present invention. That is, a polymer of a silicone compound in which polymerization occurs by cleavage and recombination of a siloxane bond (-Si-O-Si-) has only a chain structure of -Si-O-Si- units, while the polymerization is H ₂ O. or if caused by a crosslinking reaction was what hydrosilyl bond (Si-H) in the presence of O _2: Derived from The polymer of the silicone compound will contain a network of units.

In this case, the polymer of the silicone compound having a network structure (hereinafter referred to as “network structure polymer”) accounts for 20% or more of all Si atoms. It is preferably converted to a unit. The content of this unit can be determined from the IR absorption of the methyl group in the polymer coating.

Further, when the content of this unit increases and the network structure develops, the silicone compound is released by heating and releases only methane without depolymerization to form a Si oxide. This state can be confirmed by pyrolysis gas chromatography.

Since the polymer of the silicone compound with the developed network structure changes into a uniform Si oxide film by heating and baking, if the surface of the particle is coated with the polymer of this network structure, the result superior to the conventional treatment method can be obtained. Can be expected.

The coating of the acicular crystalline iron oxide particles of the present invention with the cobalt compound can be carried out by a conventional method, for example, JP-B-52-24237, JP-B-52-24238,
As described in JP-B-52-36751 and JP-B-52-36863, precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide, and the dispersion is placed in a non-oxidizing atmosphere. The heat treatment is performed in the temperature range of 50 to 100 ° C. However, the alkaline suspension containing cobalt hydroxide may optionally contain ferrous hydroxide. In this case, the coated cobalt compound contains the Fe ² compound.

The cobalt hydroxide is 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 that can be used in combination in the coating step of the cobalt compound is a water-soluble ferrous salt such as ferrous sulfate or ferrous chloride and an alkali hydroxide such as sodium hydroxide or potassium hydroxide. Obtained by using an aqueous solution.

The temperature in the coating process of the cobalt compound is related to the coating treatment time, and if the temperature is less than 50 ° C,
Magnetite particles or maghemite particles coated with the cobalt compound or the cobalt compound and the Fe ² compound are hard to be generated, and even if they are generated, treatment for an extremely long time is required.

The reason why the coating with the cobalt compound is carried out in a non-oxidizing atmosphere is that the transformation of cobalt and ferrous iron occurs only when hydroxide is present, and the oxidation of the cobalt hydroxide and ferrous hydroxide in the dispersion liquid occurs. This is to prevent

Cobalt compound coverage is calculated as cobalt for Fe
It is preferably 0.5 to 15.0 atomic%. If the content is less than 0.5 atom%, the effect of improving the coercive force of needle-like magnetite particles or needle-like maghemite particles whose surface is obtained by coating with a cobalt compound cannot be sufficiently achieved. . If it exceeds 15.0 at%, the coercive force of needle-like magnetite particles or needle-like maghemite particles whose particle surface is coated with a cobalt compound can be improved, but the coercive force distribution is increased by increasing the coating amount. It has the drawback of spreading.

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

Considering the coercive force and saturation magnetization of acicular magnetite particles or acicular maghemite particles, the cobalt compound coverage is 2.0 to 13.0 atomic% in terms of cobalt with respect to Fe.
Is particularly preferred.

When ferric hydroxide is used together, if necessary, the coverage of the Fe ²⁺ compound is preferably 0.5 to 30.0 atomic% in terms of Fe ²⁺ with respect to Fe. If it is less than 0.5 atomic%, the coercive force enhancing effect cannot be sufficiently achieved, and the saturation magnetization is not sufficiently improved. If it exceeds 30.0 atomic%, there is a drawback that the coercive force distribution is widened due to the increase in the coating amount. Considering the coercive force and saturation magnetization of acicular magnetite particles or acicular maghemite particles,
4.0 to 25.0 atom% is particularly preferable.

[Examples] Next, the present invention will be described with reference to Examples and Comparative Examples. The major axis and axial ratio (major axis diameter / minor axis diameter) of the particles in the following Examples and Comparative Examples are average values of the values measured from electron micrographs, and the specific surface area was measured by the BET method. Shown by value.

The magnetic properties of the acicular crystalline iron oxide particles and magnetic tape are described in "VSM-3S-15 vibrating sample magnetometer" (Toei Industry Co., Ltd.).
And the value measured under an external magnetic field of 10 KOe.

The evaluation of dispersibility is carried out by showing the values of the residual magnetic flux density Br in the case of forming a square shape and a tape of acicular magnetic iron oxide particles powder, the square shape and the degree of orientation, and any of the above values is a numerical value. The larger the value, the more improved the dispersibility.

<Acicular Hematite Particles> -Examples 1 to 3, Comparative Examples 1 to 4 Example 1 Needle crystal goethite particles having a major axis of 0.3 µm and an axial ratio (major axis diameter / minor axis diameter) of 15. The long axis was 0.27 μm obtained by heating 1200 g of powder in air at 500 ° C.,
Needle-like hematite particles with an axial ratio (major axis diameter / minor axis diameter) of 10
1 Kg and 50 g of tetramethylcyclotetrasiloxane (n = 4 in general formula (A)) placed in another container were placed in a closed thermostat, and then treated at a pressure of 200 mmHg and 70 ° C. for 5 hours. Then, it was dried at 100 ° C. for 2 hours. As a result of analyzing the dry powder by infrared spectrum, 1260 cm ^-1
The absorption of Si-CH ₃ group is shifted to 1270 cm ^-1 , and Si-H
It was found that the cross-linking of the groups is progressing. Also, 59
As a result of pyrolysis gas chromatography at 0 ° C., only methane was produced, and thus a polymer having a network structure in which tetramethylcyclotetrasiloxane was polymerized was produced. Against
It was 2.3% in terms of Si. From this, it was confirmed that the particle surfaces of the acicular hematite particles were coated with the polymer having a network structure.

Example 2 6 kg of needle-shaped goethite particle powder having a major axis of 0.2 μm and an axial ratio (major axis diameter / minor axis diameter) of 8 was a rotary double-cone type reaction tank having a volume of 100 (stainless steel, heat insulation jacket). ), 500 g of tetramethylcyclotetrasiloxane was placed in a stock solution supply tank directly connected to the reaction tank with a stainless steel tube, and nitrogen was bubbled from the lower side of the stock solution supply tank and supplied to the reaction tank. The temperature of the system was maintained at 70 ° C by supplying the heated heat medium from the heat medium heating tank to the heat insulation jackets of the reaction tank and the stock solution supply tank with a circulation pump.
The reaction tank was rotated by a timer for 3 minutes after standing still for 10 minutes, and this rotation was repeated for 7 hours. Then, the silicone compound in the stock solution supply tank was removed, the temperature of the entire system was raised to 100 ° C. while continuing the nitrogen stream, and rotation was continued for another 2 hours to remove the silicone monomer in the reaction vessel from the system. Thereafter, the temperature was returned to room temperature to obtain a treated goethite. The result of this absorption of Si-CH ₃ groups as the result measured by the infrared absorption spectrum of goethite 1260 cm ^-1 has shifted to 1270 cm ^-1, also measured by pyrolysis gas chromatography 590 ° C., methane only Is generated,
It was found that a polysiloxane having a network structure was formed on the surface of goethite. As a result of elemental analysis, the amount of this polymer was 3.5 wt% in terms of Si with respect to Fe. By heating and calcining 1 kg of this treated goethite at 450 ° C. in air, needle-like hematite particles having a major axis of 0.18 μm and an axial ratio (major axis diameter / minor axis diameter) of 7 were obtained.

Example 3, Comparative Example 1 Type of ferric oxide hydroxide particles, heating and firing temperature, and type and amount of silicon compound in treatment step with silicon compound,
Needle-like hematite particles were obtained in the same manner as in Example 1 except that the treatment time and treatment conditions were changed as shown in Table 1. Table 1 shows the main manufacturing conditions and various characteristics at this time.

Comparative Example 2 Hematite particles were obtained in the same manner as in Example 2 except that the treatment with tetramethylcyclotetrasiloxane was not performed. Table 1 shows the main manufacturing conditions and various characteristics at this time.

<Production of Needle Crystal Magnetite Particle Powder> -Examples 4 to 6 and Comparative Examples 3 to 4 Example 4 Needle crystal hematite in which the surface of the particles obtained in Example 1 is coated with the polymer of the silicone compound. Particle 100g
Was put in a retort reduction container of 1.0, and H ₂ gas was ventilated at a rate of 0.2 per minute while being driven and rotated to reduce the reduction temperature to 400
Reduction was carried out at ℃ to obtain acicular magnetite particles powder. As a result of electron microscope observation, the obtained acicular crystal magnetite particles had a major axis of 0.2 μm and an axial ratio (major axis diameter / minor axis diameter) of 8, and each particle was scattered, The shape of the particles was maintained. The BET specific surface area is 3
7.0m ² / g, magnetic properties are coercive force 403Oe, saturation magnetization σs8
It was 6.0 emu / g and square type 0.460.

Examples 5 to 6 and Comparative Examples 3 to 4 Needle crystal magnetite particles were obtained in the same manner as in Example 4 except that the type of magnetite particles and the reduction temperature were variously changed. Table 2 shows the main manufacturing conditions and various characteristics at this time.

<Production of Needle Crystal Maghemite Particle Powder> -Examples 7 to 9 and Comparative Examples 5 to 6-Example 7 Needle crystal magnetite particle powder 100 g obtained in Example 4
The powder was oxidized in air at 300 ° C for 30 minutes to obtain acicular crystal maghemite particle powder.

As a result of electron microscope observation, the obtained acicular maghemite particle powder had a major axis of 0.2 μm and an axial ratio (major axis diameter / minor axis diameter) of 8
However, the particles were scattered one by one, and the particle shape of the starting material particles was maintained. The BET specific surface area was 37.5 m ² / g, and the magnetic properties were a coercive force of 398 Oe, a saturation magnetization of s73.0 emu / g, and a square type of 0.465.

Examples 8 to 9 and Comparative Examples 5 to 6 Needle crystal maghemite particles were obtained in the same manner as in Example 7 except that the type of hematite particles and the reduction temperature were variously changed. Table 3 shows the main manufacturing conditions and various characteristics at this time.

As is clear from Tables 2 and 3, the acicular crystal magnetite particle powder and acicular crystal maghemite particle powder obtained by the production method of the present invention have a specific surface area, a coercive force, a saturation magnetization and a square shape. And a satisfactory figure was obtained.

<Production of Needle Crystalline Magnetic Iron Oxide Particle Powder Coated with Cobalt Compound> -Examples 10 to 15 and Comparative Examples 7 to 10-Example 10 Needle crystal magnetite particle powder 100 g obtained in Example 4
While preventing the inclusion of air as much as possible, throw it into 1.0 water in which 0.068 mol of cobalt sulfate and 0.143 mol of ferrous iron using cobalt sulfate and ferrous sulfate are dissolved, and dispersed until it becomes a fine slurry. And then add the 18-N NaOH solution to the dispersion.
96 ml was added, and water was further added to adjust the total volume to 1.3 to give a dispersion having an OH group concentration of 1.0 mol /. The temperature of the dispersion is 100 ° C.
After 5 hours while stirring at this temperature, the slurry was taken out, washed with water, filtered off, and dried at 60 ° C. to obtain acicular magnetite particles powder coated with cobalt and Fe ²⁺ compounds.

The obtained acicular crystal magnetite particle powder coated with the cobalt compound and Fe ²⁺ compound was, as a result of electron microscope observation, a major axis of 0.20 μm and an axial ratio (major axis diameter / minor axis diameter) of 7.8. The particles were scattered one by one, and the shape of the needle-shaped magnetite particles was maintained. Also, BET
The specific surface area is 35.5 m ² / g, the magnetic characteristics are coercive force 720 Oe,
The saturation magnetization was s86.3emu / g and the square type was 0.480.

Examples 11 to 15 and Comparative Examples 7 to 10 Types of acicular magnetite particle powder and cobalt addition amount, Fe ²⁺ addition amount, caustic soda addition amount and temperature in a coating process with a cobalt compound or a cobalt compound and Fe ²⁺ compound Except that the values are changed as shown in Tables 4 and 5,
In the same manner as in Example 10, a needle-shaped magnetic iron oxide particle powder coated with the cobalt compound or the cobalt compound and the Fe ²⁺ compound was obtained.

Main manufacturing conditions and various characteristics at this time are shown in Tables 4 and 5.

As is clear from Tables 4 and 5, the acicular crystal magnetite particle powder and the acicular crystal maghemite particle powder obtained by coating the particle surface with the cobalt compound obtained by the production method of the present invention have a specific surface area, a coercive force, Satisfactory figures were obtained for all of the saturation magnetization and squareness.

<Production of Magnetic Tape> -Examples 16 to 27, Comparative Examples 11 to 18-Example 16 Using the acicular magnetite particle powder obtained in Example 4, an appropriate amount of a dispersant and a vinyl chloride-vinyl chloride copolymer were used. A thermoplastic polyurethane resin and a mixed solvent of toluene, methyl ethyl ketone, and methyl isobutyl ketone were mixed in a constant composition, and then mixed and dispersed in a ball mill for 8 hours to obtain a magnetic paint.

The mixed solvent was added to the obtained magnetic paint to adjust the paint viscosity to an appropriate value, and then applied, oriented and dried on a polyester resin film in a usual manner to produce a magnetic tape.

The residual magnetic flux density Br of this magnetic tape was 1950 Gauss, the square type (Br / Bm) was 0.823, and the orientation degree was 2.49.

Examples 17 to 27, Comparative Examples 11 to 18 Magnetic tapes were manufactured in the same manner as in Example 16 except that the types of acicular crystalline magnetic iron oxide particles were changed as shown in Tables 6 to 9.

 Tables 6 to 9 show various characteristics of the magnetic tape.

As is clear from Tables 6 to 9, the magnetic tape obtained by using the acicular crystalline iron oxide particles obtained by the production method of the present invention is satisfactory in all of magnetic flux density, squareness and degree of orientation. It was found that a high value was obtained, and that it had high coercive force and excellent dispersibility.

[Effects of the Invention] As described in detail above, the needle-like magnetic iron oxide particle powder having high coercive force and excellent dispersibility was obtained by the method for producing the needle-like magnetic iron oxide particle powder of the present invention. . This acicular magnetic iron oxide particle powder is useful as a magnetic particle powder for high density recording and high output, which is currently most demanded.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Takedoi 4-1-2, Funariminami, Naka-ku, Hiroshima City, Hiroshima Prefecture Toda Kogyo Co., Ltd. Creative Center Examiner Yoshizo Hiratsuka (56) References 107300 (JP, A) JP 63-113082 (JP, A) JP 63-151621 (JP, A) JP 63-69714 (JP, A)

Claims (2)

(57) [Claims] 1. A needle-shaped ferric hydroxide-containing particle having an average major axis diameter of 0.1 to 0.3 μm, or a needle-shaped hematite particle obtained by subjecting the needle-shaped ferric hydroxide-containing particle to calcination. A needle-like magnetic iron oxide particle powder obtained from needle-like magnetite particles obtained by heating and reducing in a reducing gas or needle-like maghemite particles obtained by further oxidizing, if necessary, Crystallized ferric hydroxide particles or the acicular hematite particles and at least one silicone compound represented by the following general formula (I) at a temperature of 120 ° C. or lower,
A method for producing acicular magnetic iron oxide particle powder, which comprises contacting in a gas phase to substantially coat the particle surface with a polymer of a silicone compound in advance. (R ¹ HSiO) _a (R ² R ³ SiO) _b (R ⁴ R ⁵ R ⁶ SiO _1/2 ) _c (I) (wherein R ¹ , R ² , R ³ , R ⁴ , R ⁵ or R ⁶ is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms which may be substituted with at least one halogen atom, provided that R ¹ and R ^{2 are}
And R ³ are not hydrogen atoms at the same time. Further, a or b is 0 or an integer of 1 or more, and c is 0 or 2. However, when c is 0, a and b
The sum of and is an integer of 3 or more. ) 2. The acicular crystal magnetite particles or acicular crystal maghemite particles obtained in claim 1, as precursor particles,
At least the precursor particles, a dispersion of pH 11 or more containing a cobalt salt aqueous solution and an alkaline aqueous solution is heat-treated in a temperature range of 50 to 100 ° C. to coat the particle surface of the precursor particles with a cobalt compound. And a method for producing acicular magnetic iron oxide particles.