JP3087808B2 - Manufacturing method of magnetic particle powder for magnetic recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention has a high particle size uniformity, does not contain dendritic particles, and has a large axial ratio (major axis diameter / short axis diameter-the same applies hereinafter). Provided is a method for producing a magnetic particle powder for magnetic recording having a magnetic force, which can be obtained industrially.

[0002]

2. Description of the Related Art In recent years, as the size of a magnetic recording / reproducing apparatus has been reduced, a recording medium such as a magnetic tape or a magnetic disk has been required to have high recording density, high sensitivity characteristics, high output characteristics, and the like.

The characteristics of the magnetic particle powder required to satisfy the above requirements for the magnetic recording medium are to have high coercive force and excellent dispersibility.

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

To increase the recording density of a magnetic recording medium, the condition for high-density recording on a coating tape is as follows: High output characteristics can be maintained with low noise with respect to the wavelength signal. For this purpose, it is necessary that both the coercive force Hc and the residual magnetization Br are large and the thickness of the coating film is thinner. As described in “‥‥”, it is necessary that the magnetic recording medium has a high coercive force and a large remanent magnetization Br, and for that, the magnetic particle powder has a high coercive force,
It is required that the dispersibility in the vehicle, the orientation in the coating film, and the filling property are excellent.

The residual magnetization Br of a magnetic recording medium depends on the dispersibility of the magnetic particle powder in a vehicle, the orientation in a coating film, and the filling property. It is required that the magnetic particle powder has a large axial ratio, a uniform particle size, and no dendritic particles.

The relationship between the characteristics of the magnetic recording medium and the characteristics of the magnetic particle powder used will be described in detail below. In order to obtain high image quality as a magnetic recording medium for video, Nikkei Electronics (1976) 133 No. 8
As is clear from the description on pages 2 to 105, the video S /
Improvements in N ratio, chroma S / N ratio, and video frequency characteristics are required.

In order to improve the video S / N ratio and the chroma S / N ratio, it is necessary to improve the dispersibility of the magnetic particle powder in a vehicle, the orientation and the filling property in a coating film, and It is important to improve the surface smoothness of a magnetic recording medium. As described above, such a magnetic particle powder is also required to have a uniform particle size, not to include dendritic particles, and to have a large axial ratio.

[0009] For video floppy, for DAT, 8m
The coercive force of metal magnetic particle powder mainly composed of iron used for m-video and Hi-8 is 1300 Oe to 1800
Oe level is required.

[0010] The coercive force of the magnetic particle powder used for these is
As is well known, it depends on any of shape anisotropy, crystal anisotropy, strain anisotropy and exchange anisotropy, or their interaction. Generally, the coercive force tends to increase as the axial ratio of the particles increases, since the coercive force is generated due to the shape anisotropy.

These magnetic particle powders are obtained by heating and reducing goethite particles as starting materials or hematite particles obtained by heat-treating the goethite particles in a reducing gas such as hydrogen to obtain magnetite particles or iron as a main component. The magnetite particles are obtained by heating and oxidizing the magnetite particles in air to form maghemite particles.

[0012] Further, it may be modified by known Co or
The magnetic iron oxide particles powder modified with and Fe ²⁺ uses magnetite particles or maghemite particles as precursor particles, and uses the precursor particles as an alkaline suspension containing cobalt hydroxide or cobalt hydroxide / hydroxide hydroxide. It is obtained by dispersing in an alkaline suspension containing ferrous iron and subjecting the dispersion to heat treatment.

As described above, magnetic particle powders having a large axial ratio, a uniform particle size, and free from dendritic particles are presently the most demanded and have such characteristics. In order to obtain magnetic particle powder, it is necessary that the starting material, goethite particle powder, has a uniform particle size, does not contain dendritic particles, and has a large axial ratio.

Conventionally, as a method for producing goethite particle powder as a starting material, a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent or more of an aqueous alkali hydroxide solution to an aqueous ferrous salt solution is used. A method of producing needle-like goethite particles by passing an oxygen-containing gas at a temperature of not less than 11 and a temperature of not more than 80 ° C. to carry out an oxidation reaction (Japanese Patent Publication No.
No. 9-5610), an oxygen-containing gas is passed through a suspension containing FeCO ₃ obtained by reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution to perform an oxidation reaction, thereby exhibiting a spindle shape. A method for producing goethite particles (JP-A-50-80999) and the like are known.

Further, an oxygen-containing gas is passed through a suspension obtained by adding an equivalent amount or more of an aqueous alkali hydroxide solution to a mixed aqueous solution of an aqueous ferrous salt solution and an aqueous cobalt salt solution to carry out an oxidation reaction, thereby allowing the oxidation reaction to proceed. A method for producing acicular goethite particles containing the same (JP-A-48-82395);
In the method described above, a method of adding an aluminum compound to the suspension for the purpose of improving the acicularity of the acicular goethite particles to be produced (Japanese Patent Publication Nos. Sho 47-30377 and Sho 59-17161). And JP-A-64-3
No. 3019) is also known.

Further, a method for obtaining goethite particles containing cobalt and aluminum (Japanese Patent Laid-Open No. 58-6050)
No. 4, JP-A-3-82103 and JP-A-3-82103.
No. 88306) is also known.

[0017]

The particle size is uniform,
Dendritic particles are not mixed, and magnetic particle powder having a large axial ratio is the most required at present, but in the case of the above-mentioned method for producing goethite particle powder as a starting material, Needle-like goethite particles having a large axial ratio, particularly an axial ratio of 10 or more, are produced, but dendritic particles are mixed, and it is hard to say that the particles have a uniform particle size.

In the case of the above-mentioned method, spindle-shaped particles having a uniform particle size and containing no dendritic particles are produced, while the axial ratio is at most about 7, and the axial ratio is at most about 7. However, this phenomenon tends to become more pronounced as the major axis diameter of the produced particles decreases.

According to the above method, acicular goethite particles having a large axial ratio can be produced, but ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution. Since the viscosity of the alkaline suspension containing the compound becomes high and the reaction time becomes long, the particle size of the acicular goethite particles formed is uneven, and dendritic particles are mixed.

According to the above method, acicular goethite particles having excellent acicularity can be produced.
If the amount of the aluminum compound added to the reaction solution is small, the effect cannot be obtained, and if the amount is large, magnetite is mixed with goethite, which causes a problem.

Further, in the case of combining the above method and the method of the above method, a problem arises that magnetite is more likely to be mixed because the aqueous solution of the cobalt salt and the aluminum compound are used in combination.

Iron magnetic particles, magnetite particles, maghemite particles, and magnetic iron oxide modified with Co or modified with Co and Fe ²⁺ , obtained by using these goethite particles as starting material particles Magnetic particle powders for magnetic recording, such as particle powders, are also uniform in particle size, do not contain dendritic particles, and cannot be said to have a large axial ratio.

Therefore, the present invention relates to a method for producing a powder having a uniform particle size,
It is a technical object of the present invention to obtain each magnetic recording magnetic particle powder having a high coercive force since dendritic particles are not mixed and have a large axis ratio.

[0024]

The above technical object can be achieved by the following method of the present invention.

That is, according to the present invention, an oxygen-containing gas is passed through an alkaline suspension having a pH value of 11 or more containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution. By performing an oxidation reaction to generate needle-like goethite particles, then, the needle-like goethite particles or needle-like hematite particles obtained by heating and dehydrating the needle-like goethite particles are reduced by heating in a reducing gas. In a method for producing magnetic particle powder for magnetic recording comprising needle-shaped metal magnetic particles containing iron as a main component, a water-soluble cobalt salt in the ferrous salt aqueous solution is 0.1 to 0.1% in terms of Co with respect to Fe in advance.
10.0 atomic% is added, and the water-soluble aluminum salt is added to either one of the ferrous salt aqueous solution and the alkali hydroxide aqueous solution in an amount of from 0.5 to 0.5 in terms of Al with respect to Fe.
5.0 atomic% is added, and the aqueous ferrous salt solution is reacted with the aqueous alkali hydroxide solution to obtain an alkaline suspension containing ferrous hydroxide and having a pH value of 11 or more.
In the course of oxidizing by passing an oxygen-containing gas through the suspension, needle-like goethite particles containing Co and Al are generated by further adding a water-soluble aluminum salt aqueous solution. This is a method for producing magnetic particle powder for magnetic recording comprising needle-like metal magnetic particle powder containing iron as a main component.

The present invention also provides a needle-like goethite particle containing the above-mentioned Co and Al, which is obtained by heat-treating the needle-like goethite particle or the needle-like goethite particle at 300 to 700 ° C. Heat-reducing hematite particles in a reducing gas to obtain acicular magnetite particles, or
Further oxidizing to obtain acicular maghemite particles, a method for producing magnetic particle powder for magnetic recording, and the acicular magnetite particles or the acicular maghemite particles are used as precursor particles, and the precursor particles are formed of cobalt hydroxide. Dispersed in an alkaline suspension containing cobalt hydroxide or ferrous hydroxide, and denatured by Co or denatured by Co and Fe ²⁺ by heat-treating the dispersion. A method for producing magnetic particle powder for magnetic recording, comprising obtaining acicular magnetite particles or acicular maghemite particles.

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

The aqueous ferrous salt solution in the present invention includes:
An aqueous solution of ferrous sulfate, ferrous chloride or the like can be used.

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

As the water-soluble cobalt salt in the present invention, cobalt sulfate, cobalt chloride and the like can be used.

The addition amount of the water-soluble cobalt salt is 0.1 to 10.0 atomic% in terms of Co with respect to Fe in the aqueous ferrous salt solution. If the content is less than 0.1 atomic%, the effect of obtaining a large axial ratio is insufficient, and if it is more than 10.0 atomic%, the excess cobalt salt becomes independent other than the acicular goethite particles. It is not preferable because a cobalt compound may be formed or magnetite or the like may be mixed.

The water-soluble cobalt salt in the present invention is involved in the form such as the particle size and the axial ratio of the acicular goethite particles to be formed. It is necessary to add and dissolve in the solution of ferrous salt aqueous solution,
Alternatively, an aqueous solution in which a water-soluble cobalt salt is dissolved in water is added and mixed.

As the water-soluble aluminum salt in the present invention, aluminum sulfate, aluminum chloride, sodium aluminate and the like can be used.

In the present invention, the water-soluble aluminum salt added to one of the aqueous ferrous salt solution and the aqueous alkali hydroxide solution before the production of ferrous hydroxide causes the growth of the particles of the produced ferrous hydroxide. It is involved in the morphology of the needle-like goethite particles generated by the oxidation reaction, such as the particle size and the axial ratio, and is added and dissolved in advance in one of the aqueous ferrous salt solution and the aqueous alkali hydroxide solution. Alternatively, an aqueous solution obtained by dissolving a water-soluble aluminum salt in water is added to and mixed with one of the above.

In this case, the addition amount of the water-soluble aluminum salt is 0.5 to 5.0 atomic% in terms of Al with respect to Fe in the aqueous ferrous salt solution. When the content is less than 0.5 atomic%, the effect of suppressing the growth of the generated ferrous hydroxide particles, which is the object of the present invention, cannot be obtained, and the effect is not more than 5.0 atomic%.
If the ratio exceeds 1, magnetite may be mixed.

In the present invention, the water-soluble aluminum salt added during the oxidation of the suspension reduces the viscosity of the alkaline suspension containing ferrous hydroxide to increase the reaction rate in the oxidation reaction. Because it is involved, it is preferable to dissolve the water-soluble aluminum salt in water and add it to the suspension as an aqueous solution in order to quickly disperse and uniformly act in the liquid.

In this case, the amount of the water-soluble aluminum salt aqueous solution added is such that Al
It is 0.5 to 5.0 atomic% in conversion. When the content is less than 0.5 at%, the effect of lowering the viscosity of the suspension is not sufficient, and when it exceeds 5.0 at%, magnetite may be mixed.

During the oxidation, it can be added in several portions within the range of the addition amount, and the amount of the water-soluble aluminum salt added before the ferrous hydroxide is formed can be added. Is 1.0 to 10.0 atomic% in terms of Al with respect to Fe in the aqueous ferrous salt solution. If the total amount exceeds 10.0 atomic%, there is a high risk of magnetite being mixed in the goethite particles as the final product.

The pH value of the suspension containing ferrous hydroxide in the present invention is 11 or more. When the pH value is less than 11, magnetite may be mixed, and when the pH value exceeds 14, the viscosity becomes high and the reaction time becomes long. It is not economical to use. Therefore, it is preferable that the pH value is in the range of more than 12 and less than 14.

The oxidation reaction temperature in the present invention is 30 to 4
5 ° C. When the temperature is lower than 30 ° C., acicular goethite of fine particles may be formed and the particle size may be uneven.
If the temperature exceeds ℃, magnetite may be mixed, which is not preferable.

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

In the present invention, in order to improve the properties of the magnetic particles and the like, it is possible to add different elements such as Ni, Zn, P, and Si which are usually added during the reaction for producing goethite particles.

The filtration, washing and drying for obtaining the acicular goethite particles may be carried out according to a conventional method.

In the present invention, needle-like goethite particles as a starting material are preliminarily made of Ni, Al, and Si, P, Co, Mg, B
And one or more metal compounds selected from Zn and Zn are preferably applied. Since these metal compounds not only have an effect of preventing sintering, but also have a function of controlling the oxidation and reduction rates, It is preferable to use them in combination as needed.

The starting material coated with the metal compound can be heated and dehydrated as it is to obtain acicular hematite particles according to a conventional method.
~ 500 ° C. Furthermore, if necessary, heat reduction,
The magnetic particles for magnetic recording can be obtained by heat treatment such as heat oxidation.However, in order to control the magnetic properties, powder properties and shape, prior to each heat treatment, It is desirable to perform a heat treatment in a non-reducing gas atmosphere in advance.

The heat treatment in the non-reducing gas atmosphere is performed under the flow of air, oxygen gas, and nitrogen gas at 300 to 800
C., and the heat treatment temperature is more preferably selected as appropriate according to the type of the metal compound used for coating the starting material particles. When the temperature exceeds 800 ° C., deformation of the particles and sintering between the particles and the particles are caused.

In the present invention, acicular magnetite particles can be obtained by heat reduction, or acicular metal magnetic particles containing iron as a main component. In this case, the temperature range is 300 to 550 ° C. Is preferred. When the temperature is lower than 300 ° C., the progress of the reduction reaction is slow and a long time is required. If the temperature exceeds 550 ° C., the reduction reaction proceeds rapidly, causing deformation of the particles and sintering between the particles.

The needle-like magnetic metal particles containing iron as a main component after heat reduction in the present invention can be obtained by a known method, for example, a method of immersing the particles in an organic solvent such as toluene, or a metal containing iron as a main component after reduction. After the atmosphere of the magnetic particle powder is once replaced with an inert gas, the oxygen content in the inert gas is gradually increased while gradually converting the atmosphere into air, and then the air can be taken out into the air by a method such as slow oxidation. .

The oxidation temperature of the acicular magnetite particle powder in the present invention is further oxidized, if necessary, to obtain acicular maghemite particle powder.
Can be done with

Incidentally, acicular beltride compound particles, which are intermediate oxides of acicular magnetite particles and acicular maghemite particles, can also be used. The hematite particles are reduced by heating in a reducing gas. Get
Beltride compound particles obtained by further adjusting oxidized and contained ferrous iron or beltride obtained by adjusting and reducing ferrous iron by heating and reducing the maghemite particles again in a reducing gas. It can be compound particles.

In the present invention, the transformation of magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles into Co or Co and Fe ²⁺ can be carried out by a conventional method.
For example, Japanese Patent Publication No. 52-24237, Japanese Patent Publication No. 52-237
No. 24238, JP-B-52-36651, and JP-B-52-36863, an alkaline suspension containing cobalt hydroxide or cobalt hydroxide / ferrous hydroxide is used. Disperse in the liquid,
This is performed by heating the dispersion.

The magnetic iron oxide particles according to the present invention contain Co
Alternatively, the cobalt hydroxide in the case of the transformation of Co and Fe ²⁺ uses the above-mentioned water-soluble cobalt salt and the above-mentioned aqueous alkali hydroxide solution, and ferrous hydroxide uses the above-mentioned aqueous ferrous salt solution and the above-mentioned alkali hydroxide. It is obtained by using an aqueous solution.

In the transformation of Co or Co and Fe ²⁺ ,
The conditions for the heat treatment are 50 to 1 in a non-oxidizing atmosphere.
It is preferable to carry out in a temperature range of 00 ° C.

The transformation temperature of Co or Co and Fe ²⁺ is
It is related to the processing time, and if the temperature is 50 ° C. or less, it is difficult to generate acicular magnetite particles or acicular maghemite particles modified with Co or modified with Co and Fe ²⁺ , and even if it is formed, Requires long processing times.

The conversion amount of the water-soluble cobalt salt in the present invention is 0.5 to 15.0 atomic% in terms of Co with respect to Fe. If the content is less than 0.5 atomic%, the effect of improving the coercive force of the obtained acicular magnetite particles or acicular maghemite particles cannot be sufficiently achieved.
When it exceeds 15.0 atomic%, the coercive force of the obtained acicular magnetite particles or acicular maghemite particles is improved, but the distribution of crystal magnetic anisotropy due to the composition is generated and the coercive force distribution is deteriorated. .

Almost all of the added water-soluble cobalt salt is used for denaturation on the surface of the magnetic iron oxide particles, and the water-soluble cobalt salt in consideration of the coercive force and the coercive force distribution of acicular magnetite particles or maghemite particles is taken into consideration. The conversion amount of the cobalt salt is preferably 2.0 to 13.0 atomic%.

In the conversion of Co or Co and Fe ²⁺ , the above-mentioned beltlide compound particles can be used as magnetic iron oxide particles.

[0058]

The operation of the present invention having the above-described configuration is as follows.

An oxygen-containing gas is added to an alkaline suspension containing ferrous hydroxide obtained by adding an aqueous ferrous salt solution and a water-soluble cobalt salt to the aqueous solution and reacting with an aqueous alkali hydroxide solution. In order to obtain acicular goethite particles having a large axial ratio by oxidizing by aeration, simply adding a water-soluble cobalt salt increases the reaction time, and the resulting acicular goethite particles have an uneven particle size. And dendritic particles are also mixed.

Accordingly, a water-soluble aluminum salt is added to the alkaline suspension to lower the viscosity of the suspension,
It is conceivable to promptly promote the oxidation reaction to shorten the reaction time. However, if a water-soluble aluminum salt is simply added, magnetite may be mixed in the acicular goethite particles.

Incidentally, a method of adding a water-soluble silicate to the alkaline suspension (Japanese Patent Application Laid-Open No. 54-20998).
However, when a water-soluble silicate is added, the viscosity may decrease but the axial ratio may decrease, and insoluble alkali metal salts may be precipitated. Is not preferred.

As described above, in the present invention, before the ferrous hydroxide is formed, the water-soluble cobalt salt is added to the aqueous solution of the ferrous salt in advance, and A water-soluble aluminum salt in an amount of 0.5 to 5.0 atomic% in terms of Al with respect to Fe in an aqueous iron salt solution is formed when one of the aqueous ferrous salt solution and the aqueous alkali hydroxide solution is added thereto. It has been found that there is an effect of suppressing the growth of ferrous hydroxide fine particles.

The results are shown by electron micrographs (× 30000) of ferrous hydroxide in FIGS. 1 and 2. FIG.
It shows the particle structure of ferrous hydroxide generated by adding a water-soluble aluminum salt to the aqueous solution of ferrous salt, and it can be confirmed that the particle size is uniform with fine particles, No. 2 shows the particle structure of ferrous hydroxide when no water-soluble aluminum salt is added, and it can be confirmed that the particles are large and the particle size is uneven.

From the above results, the present inventor concludes that the aluminum compound formed from the added water-soluble aluminum salt is adsorbed on the surface of the generated ferrous hydroxide fine particles to suppress the growth. thinking. Further, it was confirmed that magnetite did not precipitate within the range of the above addition amount.

The ferrous hydroxide particles are large and non-uniform, so that in the process of forming acicular goethite particles, dendritic particles are formed and the particle size of the goethite particles is also non-uniform. It is considered to be.

However, when the resulting alkaline suspension containing fine ferrous hydroxide is oxidized by passing an oxygen-containing gas to oxidize the needle-like goethite particles, the ferrous hydroxide is preliminarily prepared. It has been found that as the oxidation reaction proceeds with only the water-soluble aluminum salt added before the formation, the effect is lost, the viscosity of the suspension increases, and the reaction time also increases.

In order to shorten the reaction time by maintaining the large axial ratio of the acicular goethite particles produced by utilizing the fine ferrous hydroxide particles, the present inventor has considered that In addition to the addition of the water-soluble aluminum salt to either one before the formation of iron, the viscosity of the suspension is reduced by appropriately adding the water-soluble aluminum salt during the oxidation reaction to reduce the reaction. It has been found that time can be shortened.

Therefore, in the present invention, fine ferrous hydroxide particles can be obtained, and the minor axis diameter of the acicular goethite particles can be reduced in the oxidation reaction to increase the axial ratio. Thus, needle-like goethite particles containing Co and Al having a large axial ratio, a more uniform particle size, and free of dendritic particles are obtained.

Further, in the present invention, since a large amount of Al can be contained in the acicular goethite particles, the acicular hematite particles obtained by heat-treating the acicular goethite particles are converted into a reducing gas such as hydrogen. It is obtained by heating and reducing in the form of acicular magnetite particles or acicular metal magnetic particles containing iron as a main component, and heating and oxidizing the acicular magnetite particles in air to form acicular maghemite particles. Excellent needle-like properties can be maintained when used as magnetic particles for magnetic recording, and when used as a magnetic paint when kneaded with a binder resin for a magnetic recording medium, the binder resin can also be used. It is also excellent in dispersibility when it is used as a magnetic paint because of its good compatibility.

In the above-mentioned Japanese Patent Application Laid-Open No. Sho 64-33019, for example, the method of adding an aluminum compound to a suspension of ferrous hydroxide is described as “(1) while supplying an oxygen-containing gas. It may be performed continuously or intermittently, or various methods such as adding only the first half or only the latter half may be adopted. However, in this case, it is added to the suspension after the production of ferrous hydroxide, and there is no description about the effect of the addition before the production of ferrous hydroxide.

[0071]

Next, the present invention will be described with reference to examples and comparative examples.

The major axis diameter and the axial ratio of the particles in the examples and comparative examples are all shown by the average of the values measured from electron micrographs.

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

The amount of Co and A contained in the goethite particles
The l amount was measured by X-ray fluorescence analysis.

The magnetic properties of the magnetic iron oxide particles were measured using a vibration sample magnetometer VSM-3S-15 (manufactured by Toei Kogyo Co., Ltd.).
, And the metal magnetic particle powder containing iron as a main component was measured under an external magnetic field of 10 KOe. In addition, the magnetite particles and the maghemite particles have an external magnetic field of 5 KO.
e, Co or magnetic iron oxide particles modified with Co and Fe ²⁺ were measured up to an external magnetic field of 10 KOe.

As for the compatibility of the metal magnetic particles containing iron as a main component with the binder resin, n-butylamine (basic substance) was adsorbed on the magnetic powder, and n-butylamine was not adsorbed.
The concentration of butylamine was titrated with a 0.1N HClO ₄ / acetic acid solution, and the amount of solid acid or myristic acid (acidic substance) was adsorbed to the magnetic powder, and the concentration of myristic acid that was not adsorbed was measured as “ion chromatograph HIC”. -6A "(manufactured by Shimadzu Corporation).

<Production of Goethite Particle Powder> Examples 1 to 5, Comparative Examples 1 to 4;

Example 1 168.5 g of cobalt sulfate (3.0 at.% In terms of Co with respect to Fe) was added to 20 l of 1.0 mol / l ferrous sulfate aqueous solution.
Corresponds to. ) And 34 g of aluminum sulfate (corresponding to 1.0 atomic% in terms of Al with respect to Fe), and after adding and dissolving 30 l of 3.33 mol / l NaOH aqueous solution, at pH 13.5 and a temperature of 45 ° C. Fe (OH)
A suspension containing ₂ , Co (OH) ₂ and Al (OH) ₃ was obtained.

At a temperature of 45 ° C., 1 minute
After 60 minutes of passing 50 l of air, 200 ml of a 0.5 mol / l aqueous solution of aluminum sulfate (corresponding to 1.0 atomic% in terms of Al with respect to Fe) was added. further,
This operation was repeated once after 60 minutes. Continued
At a temperature of 45 ° C., 150 liters of air per minute was aerated for 80 minutes to produce acicular goethite particles. The produced particles were washed with water, separated by filtration, dried and pulverized by a conventional method. The acicular goethite particles contained 2.5 atomic% of Co / Fe and 1.77 atomic% of Al / Fe.

The electron micrograph (× 30) shown in FIG.
000), it is clear that the major axis is 0.34 on average.
The average particle size was 15 μm, the axial ratio was 15, and the standard deviation was 0.73. The particles were uniform in particle size and did not contain dendritic particles.

Examples 2 to 5 and Comparative Examples 1 to 4 Type and amount of water-soluble cobalt salt, type, amount and timing of addition of water-soluble aluminum salt, type and amount of aqueous solution of water-soluble aluminum salt during oxidation Example 1 was repeated except that the addition method and the reaction temperature were variously changed.
In the same manner as in the above, acicular goethite particles were produced.

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

[0083]

[Table 1]

[0084]

[Table 2]

The needle-like goethite particles obtained in Comparative Examples 1 and 3 contained dendritic particles as shown in the electron micrographs (× 30000) shown in FIGS. 6 and 8, respectively. The acicular goethite particles obtained in Comparative Example 2 were asymmetric particles, and the electron micrograph (× 3
0000), the axial ratio was small.

<Production of Hematite Particle Powder> Examples 6 to 8, Comparative Examples 5 to 8;

Example 6 A considerable amount of a press cake was suspended in 40 l of water on 1500 g of the acicular goethite particles obtained by filtration and washed with water obtained in Example 1. At this time, the pH of the suspension was 8.9. Next, 1 liter of an aqueous solution in which 180 g of cobalt acetate (corresponding to 12 wt% of cobalt acetate with respect to goethite) was added to the suspension, and the mixture was stirred for 10 minutes.
After dispersing, 180 g of boric acid (corresponding to 12 wt% of boric acid with respect to goethite) was added to the above suspension, followed by stirring for 10 minutes. Next, an aqueous ammonia solution having a concentration of 15% was added so that the pH of the suspension became 7.3, and the resulting mixture was separated by filtration to remove unnecessary salts. The goethite press cake obtained by filtration was dried to obtain acicular goethite particles coated with a Co compound and a B compound. The Co and B contents in the obtained goethite were respectively Co compound Co
The conversion was 3.7 atomic%, and the B compound was 0.71 atomic% in terms of B.

Next, the needle-like goethite particles were heated and dehydrated in air at 400 ° C. for 30 minutes to obtain needle-like hematite particles.

Examples 7 and 8, Comparative Examples 5 to 8 Hematite particles were obtained in the same manner as in Example 6, except that the type of particles to be treated was changed. In Comparative Example 5, C
In addition to the o compound and the B compound, an Al compound (corresponding to 20 wt% of aluminum nitrate with respect to goethite) was coated. Table 3 shows the main production conditions and various characteristics at this time.

[0090]

[Table 3]

<Production of Metallic Magnetic Particle Powder Containing Iron as Main Component> Examples 9 to 11 and Comparative Examples 9 to 12;

Example 9 100 g of the acicular hematite particle powder obtained in Example 6 was charged into a rotary retort reduction vessel having a volume of about 10 l, and H ₂ gas was passed at a rate of 20 l / min while being driven and rotated.
Reduction was performed at a reduction temperature of 400 ° C.

The needle-like metal magnetic particles containing iron as a main component obtained by the reduction were immersed in a toluene solution and taken out so as not to cause rapid oxidation when taken out into the air. A part was taken out and a stable oxide film was formed on the surface while evaporating toluene.

As a result of observation with an electron microscope, the acicular metal magnetic particles containing iron as a main component were found to have an average major axis of 0.23 μm,
The axial ratio was 11, the particle size was uniform, and there were few dendritic particles. The Co compound is 4.63 wt% in terms of Co with respect to Fe, the Al compound is 2.46 wt% in terms of Al with respect to Fe, and the magnetic characteristics are as follows.
21 Oe, the saturation magnetization s was 123 emu / g.
The amount of solid acid was 1.4 / 個, and the amount of solid base was 1.8 / Å.

Examples 10 and 11 and Comparative Examples 9 to 12 Metal magnetic particles containing iron as a main component were obtained in the same manner as in Example 9 except that the kind of particles to be treated and the reduction temperature were variously changed. Table 4 shows the main manufacturing conditions and various characteristics at this time.

[0096]

[Table 4]

<Production of Magnetite Particle Powder> Examples 12 to 14, Comparative Examples 13 to 16;

Example 12 5.3 kg of a paste of filtered and washed needle-like goethite particles obtained in Example 1 (corresponding to about 1.6 kg of goethite particles) was suspended in 28 l of water. The pH at this time was 8.0. Next, 240 ml of an aqueous solution containing 24 g of sodium hexametaphosphate (corresponding to 1.15 wt% of PO _{3 with} respect to goethite particles) containing 24 g of sodium hexametaphosphate was added to the suspension, and the mixture was stirred for 30 minutes. To obtain acicular goethite particle powder coated with.

The acicular goethite particle powder having the particle surface coated with the P compound was heated at 660 ° C. in air to obtain a acicular hematite particle powder coated with the P compound.

1000 g of acicular hematite particle powder whose particle surface is coated with a P compound was put into a retort reduction vessel, and H ₂ gas was passed at a rate of 2 liters per minute while being driven to rotate. To obtain acicular magnetite particle powder coated with the P compound.

The obtained acicular magnetite particle powder coated with the P compound was observed by electron microscopy to have a mean major axis of 0.31 μm, an axial ratio of 10, and a uniform particle size. Dendritic particles were not mixed. As a result of magnetism measurement, the coercive force Hc was 401 Oe and the saturation magnetization s was 82.3 emu / g.

Examples 13 and 14, Comparative Examples 13 to 16 Magnetite particle powders were obtained in the same manner as in Example 12, except that the types of starting materials were variously changed. Table 5 shows the main production conditions and the characteristics of the particle powder at this time.

[0103]

[Table 5]

<Production of Maghemite Particle Powder> Examples 15 to 17, Comparative Examples 17 to 20;

Example 15 300 g of the acicular magnetite particle powder obtained in Example 12 having the particle surface coated with a P compound was placed in air in 300 g.
Oxidation was performed at 60 ° C. for 60 minutes to obtain acicular maghemite particle powder whose particle surface was coated with a P compound.

The obtained acicular maghemite particle powder having the particle surface coated with the P compound has a major axis of 0.30 μm and an axial ratio of 10 as a result of observation with an electron microscope. Dendritic particles were not mixed.
As a result of magnetism measurement, the coercive force Hc was 388 Oe and the saturation magnetization s was 73.6 emu / g.

Examples 16 and 17, Comparative Examples 17 to 20 Except that the type of the magnetite particles was variously changed,
In the same manner as in Example 15, maghemite particle powder was obtained.
Table 6 shows the main production conditions and the characteristics of the particle powder at this time.

[0108]

[Table 6]

<Production of powder of magnetite particles modified with Co or Co and Fe ²⁺ > Examples 18 to 20, Comparative Examples 21 to 24;

Example 18 100 g of the acicular magnetite particle powder obtained in Example 12 whose surface is coated with a P compound was treated with cobalt sulfate and ferrous sulfate while preventing the incorporation of air as much as possible. 0.085 mol of cobalt and 0.179 mol of ferrous iron
Is poured into 1.0 liter of water in which is dissolved, and dispersed until a fine slurry is formed.
An OH aqueous solution (102 ml) was added, and water was further added to adjust the total volume to 1.3 liter, thereby obtaining a dispersion having an OH group concentration of 1.0 mol / l. The temperature of the dispersion was raised to 100 ° C., and after 5 hours with stirring at this temperature, the slurry was taken out, filtered, washed with water, dried at 60 ° C., and converted into a needle-like substance modified with Co and Fe ^2+. A magnetite particle powder was obtained.

The obtained particles were observed by an electron microscope.
The precursor particles had the shape and particle size of the acicular magnetite particles whose surface was coated with the P compound, had a major axis of 0.30 μm, an axial ratio of 9, and were uniform in particle size. As a result of the magnetic measurement, the coercive force Hc was 782 Oe,
The saturation magnetization as was 88.3 emu / g.

Examples 19 and 20 and Comparative Examples 21 to 24 Example 18 was repeated except that the amount of the magnetite particles as the precursor was 100 g and the total volume of the treatment liquid was 1.3 l, and the kind of the precursor was variously changed. Co or Co and Fe
^The magnetite particles modified by ²⁺ were obtained. Table 7 shows the main manufacturing conditions and characteristics at this time.

[0113]

[Table 7]

<Production of Co or Maghemite Particle Powder Modified with Co and Fe ²⁺ > Examples 21 to 23, Comparative Examples 25 to 28;

Example 21 100 g of acicular maghemite particles having the particle surface coated with a P compound obtained in Example 15 were treated with cobalt sulfate and ferrous sulfate while preventing as much as possible air from entering. 0.085 mol of cobalt and 0.179 mol of ferrous iron
Is poured into 1.0 l of water in which is dissolved, and dispersed until a fine slurry is formed.
An aOH solution (102 ml) was added, and water was further added to adjust the total volume to 1.3 l to obtain a dispersion having an OH group concentration of 1.0 mol / l. The temperature of the dispersion was raised to 100 ° C., and after 5 hours with stirring at this temperature, the slurry was taken out, separated by filtration, washed with water, dried at 60 ° C., and needle-shaped modified with Co and Fe ^2+. Maghemite particles were obtained.

The obtained particles were observed by an electron microscope.
The precursor particles had the shape and particle size of the acicular maghemite particles whose surface was coated with a P compound, had a major axis of 0.24 μm, an axial ratio of 9, and were uniform in particle size. As a result of the magnetic measurement, the coercive force Hc was 753 Oe,
The saturation magnetization s was 80.4 emu / g.

Examples 22 and 23, Comparative Examples 25-28 The amount of maghemite particles as the precursor was 100 g and the total volume of the processing solution was 1.3 liters.
Maghemite particles modified with Co or Co and Fe ²⁺ were obtained in the same manner as in Example 21 except that the addition amount of Fe ^{2+, the} addition amount of the NaOH aqueous solution, the temperature, and the time were variously changed.
Table 8 shows the main manufacturing conditions and characteristics at this time.

[0118]

[Table 8]

[0119]

According to the method for producing magnetic particle powder for magnetic recording according to the present invention, the particle size is uniform, dendritic particles are not mixed, and Acicular goethite particles having an axial ratio can be obtained, and the acicular goethite particles thus obtained are used as a starting material, and acicular magnetite particles obtained by heat reduction or needles containing iron as a main component. Metal magnetic particle powder, acicular maghemite particle powder obtained by heating and oxidizing the magnetite particle powder in air, and using the acicular magnetite particles or the acicular maghemite particles as precursor particles, modified with Co or Co modified acicular magnetite particles or acicular magnetic recording magnetic particles made from getting maghemite particles, dendritic particles size is a uniformity is mixed with and Fe ²⁺ It not without and, moreover, because they have a high coercive force because it has a large axial ratio, high recording density currently most requested, sensitive, is suitable as magnetic particles for high output.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (× 30000) showing the particle structure of particles obtained from a suspension containing ferrous hydroxide obtained in Example 1.

FIG. 2 is an electron micrograph (× 30000) showing the particle structure of particles obtained from the suspension containing ferrous hydroxide obtained in Comparative Example 1.

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

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

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

FIG. 6 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particles obtained in Comparative Example 1.

FIG. 7 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particles obtained in Comparative Example 2.

FIG. 8 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particles obtained in Comparative Example 3.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01F 1/06 C01G 49/02 H01F 1/11

Claims (3)

(57) [Claims] A pH value containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkali hydroxide solution is 1
An oxygen-containing gas was passed through one or more alkaline suspensions to perform an oxidation reaction to generate acicular goethite particles, and then the acicular goethite particles or the acicular goethite particles were obtained by heating and dehydration. In a method for producing magnetic particle powder for magnetic recording comprising acicular metal magnetic particles containing iron as a main component by heating and reducing acicular hematite particles in a reducing gas, water-soluble cobalt is previously added to the aqueous ferrous salt solution. A salt is added to Fe in an amount of 0.1 to 10.0 atomic% in terms of Co, and a water-soluble aluminum salt is added to one of the ferrous salt aqueous solution and the alkali hydroxide aqueous solution. The ferrous salt aqueous solution is reacted with the alkali hydroxide aqueous solution in an amount of 0.5 to 5.0 atomic% in terms of conversion, and the pH value of the alkaline suspension containing ferrous hydroxide is 11 or more. A suspension is obtained, and then, while oxidizing by passing an oxygen-containing gas through the suspension, needle-like goethite particles containing Co and Al are further added by adding a water-soluble aluminum salt aqueous solution. A method for producing magnetic particle powder for magnetic recording, comprising acicular metal magnetic particles containing iron as a main component, characterized by being produced. 2. C generated by the method of claim 1.
Using acicular goethite particles containing o and Al, the acicular goethite particles or
Acicular hematite particles obtained by heat treatment at 0 to 700 ° C. are heat-reduced in a reducing gas to obtain acicular magnetite particles, or further oxidized to obtain acicular maghemite particles. Of producing magnetic particles for magnetic recording. 3. An acicular magnetite particle or acicular maghemite particle obtained by the method according to claim 2 is used as a precursor particle, and the precursor particle is an alkaline suspension containing cobalt hydroxide or cobalt hydroxide. Needle-like magnetite particles or needle-like maghemite particles that are dispersed in an alkaline suspension containing ferrous hydroxide and that are denatured with Co or denatured with Co and Fe ²⁺ by heat-treating the dispersion. A method for producing magnetic particle powder for magnetic recording, comprising: