JPH07153611A - Manufacture of magnetic particle powder for magnetic recording - Google Patents

Abstract

PURPOSE:To make large the axial ratio of the particles of magnetic particle powder and to equipoise the particle size of the particles by a method wherein water-soluble aluminium salt is kept added to either of a ferrous salt aqueous solution and an alkali hydroxide aqueous solution before an iron hydroxide is formed and at the same time, the water-soluble aluminium salt is properly added in the middle of an oxidation reaction. CONSTITUTION:Water-soluble cobalt salt is kept added to a ferrous salt aqueous solution in a ratio of 0.1 to 10.0 atomic % expressed in terms of Co to Fe, water-soluble aluminium salt is kept added to either of the ferrous salt aqueous solution and an alkali hydroxide aqueous solution in a ratio of 0.5 to 5.0 atomic % expressed in terms of Al to the Fe and the ferrous salt aqueous solution is reacted with this alkali hydroxide aqueous solution to obtain an alkaline suspension having an iron hydroxide-including pH value of 11 or more. Then, while oxygen-containing gas is passed in this suspension, a water-soluble aluminium salt aqueous solution is further added, thereby magnetic particle powder containing iron, which makes needle-like goethite particles containing Co and Al form, as its main component is manufactured.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention has a high particle size that is uniform, does not contain dendritic particles, and has a large axial ratio (major axis diameter / minor axis diameter-the same applies hereinafter). Provided is a manufacturing method by which magnetic particle powder for magnetic recording having a magnetic force can be industrially obtained.

[0002]

2. Description of the Related Art In recent years, with the progress of downsizing and weight reduction of magnetic recording / reproducing equipment, high recording density, high sensitivity characteristics, high output characteristics, etc. for recording media such as magnetic tapes and magnetic disks are required.

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

That is, in order to increase the sensitivity and output of the magnetic recording medium, it is necessary that the magnetic particle powder have a coercive force as high as possible. "Development of magnetic materials and high-dispersion technology of magnetic particles" (1982), page 310, "... The aim of improving magnetic tape performance was to increase sensitivity, increase output and reduce noise. The focus was on high coercive force and fine particle formation of the Fe ₂ O ₃ particle powder.

In order to increase the recording density of the magnetic recording medium, the condition for high density recording in the coating tape on page 312 of "Development of Magnetic Material and High Dispersion Technology of Magnetic Powder" is short. It is possible to maintain high output characteristics with low noise with respect to a wavelength signal. For that purpose, it is necessary that both the coercive force Hc and the residual magnetization Br are large and the coating film is thinner. As described above, it is necessary for the magnetic recording medium to have a high coercive force and a large remanent magnetization Br. Therefore, 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 remanent magnetization Br of the magnetic recording medium depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property. To improve these properties, the remanent magnetization Br is dispersed in the vehicle. It is required that the magnetic particle powder to be produced has a large axial ratio, the particle size is uniform, and that dendritic particles are not mixed.

The relationship between various characteristics of the magnetic recording medium and the characteristics of the magnetic particle powder used will be described in detail below. Nikkei Electronics (1976), No. 133, No. 8 for obtaining high image quality as a magnetic recording medium for video
As is clear from the description on pages 2-105, 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, the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film and the filling property are improved, and It is important to improve the surface smoothness of magnetic recording media. As described above, such a magnetic particle powder is also required to have a uniform particle size, no dendritic particles mixed therein, and a large axial ratio.

For video floppy, DAT, 8 m
The coercive force of the iron-based metal magnetic particle powder used for m-video and Hi-8 has a coercive force of 1300 Oe to 1800.
About Oe is required.

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, because the coercive force is generated due to the shape anisotropy.

These magnetic particle powders contain magnetite particles or iron as a main component by heating and reducing goethite particles as a starting material or hematite particles obtained by heating the goethite particles in a reducing gas such as hydrogen. It is obtained by using the magnetic metal particles as described above, or by heating and oxidizing the magnetite particles in air to obtain maghemite particles.

In addition, a known Co-modified or Co
A magnetic iron oxide particle powder modified with Fe ²⁺ and magnetite particles or maghemite particles is used as a precursor particle, and the precursor particle is an alkaline suspension containing cobalt hydroxide or a cobalt hydroxide / hydroxide no. It is obtained by dispersing in an alkaline suspension containing ferrous iron and subjecting the dispersion to heat treatment.

As described above, a magnetic particle powder having a large axial ratio, a uniform particle size and no mixed dendritic particles is currently most demanded, and has such characteristics. In order to obtain the magnetic particle powder, it is necessary that the particle size of the goethite particle powder as the starting material is uniform, that the dendritic particles are not mixed, and that the powder has a large axial ratio.

Conventionally, as a method for producing goethite particle powder as a starting material, a suspension containing ferrous hydroxide colloid obtained by adding an equivalent amount or more of an aqueous solution of alkali hydroxide to a ferrous salt aqueous solution is used. A method of forming needle-shaped goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas at a temperature of 11 or more at a temperature of 80 ° C. or less (Japanese Patent Publication No.
No. 9-5610), a suspension containing FeCO ₃ obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali carbonate was passed through an oxygen-containing gas to carry out an oxidation reaction to give a spindle shape. A method for producing goethite particles (Japanese Patent Laid-Open No. 50-80999) is known.

Further, an oxygen-containing gas is passed through a suspension obtained by adding an equivalent amount or more of an alkali hydroxide aqueous solution to a mixed aqueous solution of a ferrous salt aqueous solution and a cobalt salt aqueous solution to carry out an oxidation reaction. A method of forming needle-shaped goethite particles containing the particles (Japanese Patent Laid-Open No. 48-82395),
In the above-mentioned method, a method of adding an aluminum compound to the suspension for the purpose of improving the acicularity of the acicular goethite particles produced (Japanese Patent Publication No. 47-30477 and Japanese Patent Publication No. 59-17161). And JP-A-64-3
No. 3019) is also known.

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]

[Problems to be Solved by the Invention] The particle size is uniform,
A magnetic particle powder having no dendritic particles mixed therein and having a large axial ratio is currently most demanded, but in the case of the above-mentioned method for producing the goethite particle powder as a starting material, Needle-shaped goethite particles having a large axial ratio, in particular, 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, the particles have a uniform particle size, and spindle-shaped particles in which dendritic particles are not mixed are produced. On the other hand, the axial ratio is about 7 at most, and the axial ratio is at most 7. Has a drawback that it is difficult to generate large particles, and in particular, this phenomenon tends to become more remarkable as the major axis diameter of the generated particles becomes smaller.

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

According to the method described above, 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 it is large, there is a problem that magnetite is mixed with goethite.

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

Metallic magnetic particles containing iron as a main component, obtained by using these goethite particle powders as starting material particles, magnetite particles, maghemite particles, and magnetic iron oxide modified with Co or modified with Co and Fe ^2+. It is hard to say that magnetic particle powders for magnetic recording such as particle powders also have a uniform particle size, do not contain dendritic particles, and have a large axial ratio.

Therefore, in the present invention, the particle size is uniform,
It is a technical object to obtain the magnetic particle powder for magnetic recording having high coercive force because dendritic particles are not mixed and have a large axial ratio.

[0024]

The above technical problems 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 solution of ferrous salt with an aqueous solution of alkali hydroxide. To produce acicular goethite particles by performing an oxidation reaction, and then acicular hematite particles obtained by heating and dehydrating the acicular goethite particles or the acicular goethite particles are heated and reduced in a reducing gas. In the method for producing magnetic particle powder for magnetic recording comprising acicular metal magnetic particles containing iron as a main component, a water-soluble cobalt salt is previously added to the ferrous salt aqueous solution in an amount of 0.1 to 0.1 in terms of Co in terms of Co.
10.0 atomic% has been added, and a water-soluble aluminum salt is added to Fe in an amount of 0.5 to 0.5 in terms of Al in one of the ferrous salt aqueous solution and the alkali hydroxide aqueous solution.
5.0 atomic% was added and the aqueous solution of ferrous salt was reacted with the aqueous solution of alkali hydroxide to obtain an alkaline suspension containing ferrous hydroxide having a pH value of 11 or more.
A feature is that acicular goethite particles containing Co and Al are generated by further adding a water-soluble aluminum salt aqueous solution during the oxidation of the suspension by aerating an oxygen-containing gas. A method for producing magnetic particle powder for magnetic recording, comprising acicular metal magnetic particle powder containing iron as a main component.

In the present invention, the acicular goethite particles containing Co and Al are used, and the acicular goethite particles or acicular goethite particles obtained by heating the acicular goethite particles at 300 to 700 ° C. The hematite particles are heated and reduced in a reducing gas to obtain acicular magnetite particles, or
Further, the method for producing a magnetic particle powder for magnetic recording, which comprises oxidizing to obtain acicular maghemite particles, and the acicular magnetite particles or acicular maghemite particles as precursor particles, wherein the precursor particles are cobalt hydroxide. Dispersed in an alkaline suspension containing it or an alkaline suspension containing cobalt hydroxide / ferrous hydroxide, and heat-treating the dispersion to transform it with Co or with Fe and ^2+. A method for producing magnetic particle powder for magnetic recording, which comprises obtaining needle-shaped magnetite particles or needle-shaped maghemite particles.

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

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

As the alkali hydroxide aqueous 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 or the like can be used.

The amount of the water-soluble cobalt salt added is 0.1 to 10.0 atom% in terms of Co with respect to Fe in the aqueous ferrous salt solution. If it is less than 0.1 atom%, the effect for obtaining a large axial ratio is insufficient, and if it exceeds 10.0 atom%, excess cobalt salt becomes independent other than acicular goethite particles. Cobalt compounds may be generated, and magnetite and the like may be mixed, which is not preferable.

Since the water-soluble cobalt salt in the present invention is involved in the shape of the acicular goethite particles to be formed, such as the particle size and axial ratio, the oxygen-containing gas is aerated to carry out the oxidation reaction when the water-soluble cobalt salt is added. It is necessary to add or dissolve it in the solution of the ferrous iron salt aqueous solution before
Alternatively, an aqueous solution in which a water-soluble cobalt salt is dissolved is added and mixed separately.

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

The water-soluble aluminum salt added to either the aqueous ferrous salt solution or the aqueous alkali hydroxide solution before the production of ferrous hydroxide in the present invention is the growth of ferrous hydroxide particles produced. It is related to the shape of the needle-shaped goethite particles produced by the oxidation reaction, such as the particle size and the axial ratio, and therefore is added and dissolved in advance in either the ferrous salt aqueous solution or the alkali hydroxide aqueous solution. Or an aqueous solution in which a water-soluble aluminum salt is dissolved in water is added and mixed to either one of the above.

In this case, the amount of the water-soluble aluminum salt added is 0.5 to 5.0 atom% in terms of Al with respect to Fe in the ferrous salt aqueous solution. If it is less than 0.5 atom%, the effect of suppressing the growth of particles of the produced ferrous hydroxide, which is the object of the present invention, cannot be obtained, and 5.0 atom%
If it exceeds, magnetite may be mixed.

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

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

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

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 is more than 14, the viscosity is high and the reaction time is long, and unnecessarily excessive alkali hydroxide aqueous solution is added. 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
It is 5 ° C. If the temperature is lower than 30 ° C., fine needle-shaped goethite may be formed and the particle size may become asymmetric.
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.

Further, in the present invention, in order to improve the characteristics of the magnetic particle powder and the like, a different element such as Ni, Zn, P or Si, which is usually added, can be added during the formation reaction of goethite particles.

The filtration, washing with water and drying to obtain the acicular goethite particle powder may be carried out according to a conventional method.

In the present invention, in order to prevent the particle shape from being deformed and the particles to be sintered due to various heat treatments such as heat dehydration and heat reduction, needle-like goethite particles which are starting materials are preliminarily used as Ni, Al, Si, P, Co, Mg, B
It is desirable to perform a coating treatment with one or more metal compounds selected from Zn and Zn. Since these metal compounds have not only a sintering prevention effect but also a function of controlling the oxidation / reduction rate, It is preferable to use them in combination as necessary.

The starting material coated with the above metal compound can be heated and dehydrated as it is by a conventional method to obtain acicular hematite particle powder, and the temperature in that case is 250.
Is in the range of up to 500 ° C. Furthermore, if necessary, heat reduction,
The target magnetic particle powder for magnetic recording can be obtained by each heat treatment such as heating and oxidation, but in order to control the magnetic properties, powder properties and shape, by a conventional method, prior to each heat treatment, It is desirable to perform heat treatment in a non-reducing gas atmosphere in advance.

The heat treatment in the non-reducing gas atmosphere is carried out under the flow of air, oxygen gas and nitrogen gas at 300 to 800.
It can be carried out in a temperature range of 0 ° C., and the heat treatment temperature is more preferably selected appropriately according to the kind of the metal compound used for the coating treatment of the starting material particles. If it exceeds 800 ° C., deformation of particles and sintering between particles and each other are caused.

In the present invention, needle-like magnetite particle powder can be obtained by heat reduction or needle-like metal magnetic particle powder containing iron as a main component, and the temperature range in that case is 300 to 550 ° C. Is preferred. When the temperature is lower than 300 ° C, the reduction reaction proceeds slowly and requires a long time. On the other hand, when the temperature exceeds 550 ° C., the reduction reaction rapidly progresses, causing deformation of the particles and sintering between the particles.

The acicular metal magnetic particle powder containing iron as a main component after heat reduction in the present invention is a known method, for example, a method of immersing in an organic solvent such as toluene or a metal containing iron after reduction as a main component. After the atmosphere of the magnetic particle powder is once replaced with an inert gas, it can be taken out into the air by a method such as gradual oxidation by gradually changing the oxygen content in the inert gas to finally turn it into air. .

The needle-shaped magnetite particle powder in the present invention is further oxidized, if necessary, to obtain needle-shaped maghemite particle powder at an oxidation temperature of 200 to 500 ° C. according to a conventional method.
Can be done at.

Needle-shaped magnetite particle powder and needle-shaped maghemite particle powder, which are intermediate oxides of acicular beltride compound particles, can be used as the magnetite particles by heating and reducing the hematite particles in a reducing gas. Got
Bertride compound particles obtained by further adjusting the ferrous iron contained by oxidation or by heating and reducing the maghemite particles in a reducing gas again and adjusting the ferrous iron contained. It can be a compound particle.

The magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles in the present invention can be transformed by Co or Co and Fe ²⁺ by a conventional method.
For example, Japanese Patent Publication No. 52-24237 and Japanese Patent Publication No. 52-
As described in JP-B No. 24238, JP-B No. 52-36571 and JP-B No. 52-36863, precursor particles are alkaline suspension containing cobalt hydroxide or cobalt hydroxide / ferrous hydroxide. Disperse in liquid,
It is carried out by heating the dispersion.

Co was added to the magnetic iron oxide particle powder in the present invention.
Alternatively, the cobalt hydroxide in the case of the transformation of Co with Fe ²⁺ uses the above-mentioned water-soluble cobalt salt and the above-mentioned alkali hydroxide aqueous solution, and the ferrous hydroxide is the above-mentioned ferrous iron salt aqueous solution and the above-mentioned alkali hydroxide hydroxide. Obtained by using an aqueous solution.

Upon 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 the temperature range of 00 ° C.

The temperature for the transformation of Co or Co and Fe ²⁺ is
It is related to the treatment time, and if the temperature is 50 ° C. or lower, it is difficult to generate needle-shaped magnetite particles or needle-shaped maghemite particles modified with Co or modified with Co and Fe ²⁺ , and even if they are generated, It requires a long processing time.

The amount of the water-soluble cobalt salt modified in the present invention is 0.5 to 15.0 atomic% in terms of Co with respect to Fe. If it is less than 0.5 atom%, 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 the transformation of the magnetic iron oxide particles on the particle surface, and the water-soluble cobalt salt in consideration of the coercive force and coercive force distribution of the acicular magnetite particles or maghemite particles. The amount of modification of the cobalt salt is preferably 2.0 to 13.0 atomic%.

Incidentally, in the conversion of Co or Co and Fe ²⁺ , the above-mentioned bertride compound particles can be used as the magnetic iron oxide particle powder.

[0058]

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

An oxygen-containing gas was added to an alkaline suspension containing ferrous hydroxide obtained by reacting an aqueous solution of ferrous salt with a water-soluble cobalt salt in the solution and reacting with an aqueous solution of alkali hydroxide. To obtain acicular goethite particles with a large axial ratio by aeration and oxidation, simply adding a water-soluble cobalt salt will increase the reaction time, and the acicular goethite particles obtained will have an asymmetric particle size. And dendritic particles are also mixed.

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

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

From the above, in the present invention, before the production of ferrous hydroxide, the water-soluble cobalt salt is added to the solution of the ferrous salt aqueous solution in advance, and A water-soluble aluminum salt of 0.5 to 5.0 atom% in terms of Al with respect to Fe in the iron salt aqueous solution is formed by adding it to one of the ferrous salt aqueous solution and the alkali hydroxide aqueous solution. It was 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. Figure 1
It shows the particle structure of ferrous hydroxide produced by adding a water-soluble aluminum salt to the solution of an aqueous solution of ferrous salt, and it can be confirmed that the particle size is fine and the particle size is uniform. No. 2 shows the particle structure of ferrous hydroxide when the water-soluble aluminum salt is not added, and it can be confirmed that the particles are large and the particle size is also asymmetric.

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

Since the ferrous hydroxide particles are large and asymmetric, dendritic particles are generated in the process of forming acicular goethite particles, and the size of the goethite particles is also asymmetric. It is supposed to be.

However, when acicular goethite particles are formed by an oxidation reaction in which an oxygen-containing gas is passed through the obtained alkaline suspension containing fine ferrous hydroxide to oxidize it, the ferrous hydroxide is not It was found that the water-soluble aluminum salt added before the formation of the reaction alone loses its effect, increases the viscosity of the suspension, and prolongs the reaction time as the oxidation reaction progresses.

In order to maintain a large axial ratio of the acicular goethite particles produced by utilizing the fine particles of ferrous hydroxide, the present inventor has made In addition to adding the water-soluble aluminum salt to either one of the above before iron is formed, the viscosity of the suspension is lowered by adding the water-soluble aluminum salt during the oxidation reaction. We have found that the time can be shortened.

Therefore, in the present invention, fine particles of ferrous hydroxide 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-shaped goethite particles containing Co and Al having a large axial ratio, a more uniform particle size, and no mixed dendritic particles can be obtained.

Further, in the present invention, since a large amount of Al can be contained in the needle-shaped goethite particles, the needle-shaped hematite particles obtained by heat-treating the needle-shaped goethite particles are treated with a reducing gas such as hydrogen. It is obtained by heating and reducing in the form of needle-shaped magnetite particles or acicular metal magnetic particles containing iron as a main component, and the acicular magnetite particles are heated and oxidized in air to form acicular maghemite particles. When it is made into a magnetic particle powder for magnetic recording, it is possible to maintain excellent acicularity, and also when it is kneaded with a binder resin for a magnetic recording medium to form a magnetic paint, It has good compatibility and is excellent in dispersibility when used as a magnetic paint.

In the above-mentioned Japanese Patent Laid-Open No. 64-33019, for example, a method of adding an aluminum compound to a suspension of ferrous hydroxide is described in "... While supplying an oxygen-containing gas. , May be carried out continuously or intermittently, or various methods such as adding only in the first half or only in the second half, etc. may be employed. However, in this case, it is added to the suspension after the ferrous hydroxide is produced, and there is no description about the effect of addition before the production of ferrous hydroxide.

[0071]

The present invention will be described below 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 shown by the average of the numerical values measured from electron micrographs.

The particle size distribution of the particles is shown by the geometric standard deviation value (σg) obtained by the following method. That is, the major axis diameter of 350 particles shown in an electron micrograph at 120,000 times is measured, and the logarithmic normal is calculated from the actual major axis diameter and the number of particles calculated from the measured values according to a statistical method. On the probability paper, the major axis diameter of the particles is plotted on the horizontal axis, and the cumulative number of particles belonging to each major axis diameter section equally spaced on the vertical axis is plotted as a percentage. Then, the values of the major axis diameters corresponding to the numbers of particles of 50% and 84.13% are read from this graph, and the geometric standard deviation value (σg) = the major axis diameter when the number of particles is 50% (μm) / Long axis diameter (μm) when the number is 84.13%
The value calculated according to

Co content and A contained in goethite particles
The amount of 1 was measured by fluorescent X-ray analysis.

The magnetic characteristics of the magnetic iron oxide particle powder are shown in "Vibration sample magnetometer VSM-3S-15" (manufactured by Toei Industry Co., Ltd.).
The metal magnetic particle powder containing iron as a main component was measured by applying an external magnetic field up to 10 KOe. In addition, magnetite particle powder and maghemite particle powder have an external magnetic field of 5 KO.
The magnetic iron oxide particle powder modified with e, Co or Co and Fe ²⁺ was measured under an external magnetic field of 10 KOe.

Regarding the familiarity of the metallic magnetic particle powder 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.
Myristic acid (acidic substance) was adsorbed to the amount of solid acid or magnetic powder measured by titrating the concentration of butylamine with 0.1N HClO ₄ / acetic acid solution, and the concentration of non-adsorbed myristic acid was measured by “ion chromatograph HIC”. -6A "(manufactured by Shimadzu Corp.).

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

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

1 minute per minute was added to the above suspension at a temperature of 45.degree.
After 60 minutes of bubbling 50 l of air, 200 ml of a 0.5 mol / l aluminum sulfate aqueous solution (corresponding to 1.0 atom% in terms of Al with respect to Fe) was added. further,
After 60 minutes, this operation was repeated once. Continuing,
At a temperature of 45 ° C., 150 l / min of air was aerated for 80 minutes to generate acicular goethite particles. The produced particles were washed with water, separated by filtration, dried and pulverized by a conventional method. The needle-shaped goethite particles contained 2.5 atomic% of Co / Fe and 1.77 atomic% of Al / Fe.

Further, the electron micrograph (× 30
000), it is clear that the long axis is 0.34 on average.
The particles had an average particle size of .mu.m, an axial ratio of 15, and a standard deviation value of 0.73 and 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 of water-soluble aluminum salt, amount and timing of addition, type and amount of water-soluble aluminum salt aqueous solution during oxidation And Example 1 except that the addition method and the reaction temperature were variously changed.
Needle-shaped goethite particles were produced in the same manner as in.

The main manufacturing conditions and various characteristics at this time are shown in Tables 1 and 2.

[0083]

[Table 1]

[0084]

[Table 2]

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

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

Example 6 1500 g of needle-shaped goethite particles obtained by filtering and washing with water obtained in Example 1 was suspended in 40 l of water to give a corresponding amount of presscake. The pH of the suspension at this time was 8.9. Next, 1 l of an aqueous solution in which 180 g of cobalt acetate (corresponding to 12 wt% as cobalt acetate with respect to goethite) was dissolved was added to the above suspension and stirred for 10 minutes.
After being dispersed, 180 g of boric acid (corresponding to 12 wt% as boric acid with respect to goethite) was added to the above suspension and stirred for 10 minutes. Then, a 15% aqueous ammonia solution was added so that the pH of the suspension became 7.3, and then filtered to remove unnecessary salts. The filtered goethite press cake was dried to obtain needle-shaped goethite particles coated with the Co compound and the B compound. The Co and B contents in the obtained goethite are Co compounds and Co, respectively.
It was 3.7 atomic% in terms of conversion, and the B compound was 0.71 atomic% in terms of B.

Next, the acicular goethite particles were heated and dehydrated in air at 400 ° C. for 30 minutes to obtain acicular 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% as aluminum nitrate with respect to goethite) was coated. Table 3 shows the main manufacturing 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 placed in a rotary retort reduction container having a volume of about 10 l, and H ₂ gas was aerated at a rate of 20 l / min while being driven and rotated,
Reduction was carried out at a reduction temperature of 400 ° C.

The acicular metal magnetic particle powder containing iron as a main component, which was obtained by reduction, was taken out by dipping in a toluene solution so as not to cause rapid oxidation when taken out in air. A part was taken out and a stable oxide film was formed on the surface while evaporating toluene.

As a result of electron microscope observation, the acicular metal magnetic particle powder containing iron as a main component was found to have an average major axis of 0.23 μm,
The axial ratio was 11, the particle size was uniform, and the number of dendritic particles was small. Further, the Co compound is 4.63 wt% in terms of Co with respect to Fe, and the Al compound is 2.46 wt% in terms of Al with respect to Fe. The magnetic characteristics are that the coercive force Hc is 18%.
21 Oe, saturation magnetization σs was 123 emu / g.
The amount of solid acid was 1.4 / Å and the amount of solid base was 1.8 / Å.

Examples 10 and 11, Comparative Examples 9 to 12 Metal magnetic particle powders containing iron as a main component were obtained in the same manner as in Example 9 except that the type 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 and Comparative Examples 13 to 16;

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

The acicular goethite particle powder whose surface was coated with the P compound was heat-treated in air at 660 ° C. to obtain a needle compound hematite particle powder coated with the P compound.

1000 g of acicular hematite particle powder whose surface is coated with a P compound was placed in a retort reduction vessel, and H ₂ gas was aerated at a rate of 2 l / min while being driven and rotated at a reduction temperature of 360 ° C. To obtain acicular magnetite particles powder coated with P compound.

As a result of electron microscopic observation, the obtained acicular magnetite particle powder coated with the P compound had an average value of 0.31 μm in the major axis and an axial ratio of 10 and was a particle having a uniform particle size. The dendritic particles were not mixed. As a result of magnetic measurement, the coercive force Hc was 401 Oe, and the saturation magnetization σs 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 kinds 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 and Comparative Examples 17 to 20;

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

The obtained acicular maghemite particle powder having the particle surface coated with the P compound was observed by an electron microscope and found to have a major axis of 0.30 μm and an axial ratio of 10 and had a uniform particle size. The dendritic particles were not mixed.
As a result of magnetic measurement, the coercive force Hc was 388 Oe, and the saturation magnetization σs was 73.6 emu / g.

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

[0108]

[Table 6]

<Production of Magnetite Particle Powder Modified with Co or Co and Fe ²⁺ > Examples 18 to 20 and Comparative Examples 21 to 24;

Example 18 100 g of acicular magnetite particle powder having the particle surface coated with a P compound obtained in Example 12 was mixed with cobalt sulfate and ferrous sulfate while preventing air from entering as much as possible. Cobalt 0.085 mol and ferrous iron 0.179 mol
Is dissolved in 1.0 l of water and dispersed until a fine slurry is formed, and then 18-N Na is added to the dispersion.
102 ml of an OH aqueous solution was added, and water was further added to make the total volume 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., the slurry was taken out after stirring for 5 hours at this temperature, filtered, washed with water, dried at 60 ° C., and needle-shaped denatured with Co and Fe ^2+. Magnetite particle powder was obtained.

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

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

[0113]

[Table 7]

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

Example 21 100 g of acicular maghemite particle powder obtained in Example 15 whose surface is coated with a P compound was mixed with cobalt sulfate and ferrous sulfate while preventing air from entering as much as possible. Cobalt 0.085 mol and ferrous iron 0.179 mol
Was dissolved in 1.0 l of water and dispersed until a fine slurry was formed.
102 ml of an aOH solution was added, and water was further added to make the total volume 1.3 l to obtain a dispersion having an OH group concentration of 1.0 mol / l. The temperature of the dispersion liquid was raised to 100 ° C., and after stirring for 5 hours, the slurry was taken out, filtered, washed with water, dried at 60 ° C., and acicularly modified with Co and Fe ^2+. Maghemite particles were obtained.

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

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

[0118]

[Table 8]

[0119]

EFFECTS OF THE INVENTION According to the method for producing magnetic particle powder for magnetic recording according to the present invention, as shown in the above-mentioned Examples, the particle sizes are uniform, dendritic particles are not mixed, and large particles are obtained. It is possible to obtain needle-shaped goethite particles having an axial ratio, needle-shaped magnetite particles obtained by heating and reducing the needle-shaped goethite particles thus obtained as a starting material, or needles containing iron as a main component. -Like metal magnetic particle powder, and needle magnetized maghemite particle powder obtained by heating and oxidizing the magnetite particle powder in air and the needle-shaped magnetite particles or the needle-shaped 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 drawings]

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

FIG. 2 is an electron micrograph (× 30000) showing a 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 needle-shaped goethite particles obtained in Example 1.

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

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

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

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

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

Claims (3)

[Claims] 1. A pH value containing ferrous hydroxide obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of alkali hydroxide is 1
A needle-like goethite particle was generated by performing an oxidation reaction by passing an oxygen-containing gas through one or more alkaline suspensions, and then obtained by heating and dehydrating the needle-like goethite particle or the needle-like goethite particle. In the 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 ferrous salt aqueous 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 Fe in either one of the ferrous iron salt aqueous solution and the alkali hydroxide aqueous solution. 0.5 to 5.0 atomic% is added as conversion, and the aqueous solution of ferrous salt is reacted with the aqueous solution of alkali hydroxide to produce an alkaline suspension having a pH value of 11 or more containing ferrous hydroxide. A turbid liquid is obtained, and then acicular goethite particles containing Co and Al are added by adding a water-soluble aluminum salt aqueous solution during the course of oxygenation by passing an oxygen-containing gas into the suspension. A method for producing magnetic particle powder for magnetic recording, comprising acicular metal magnetic particles containing iron as a main component, which is characterized by being generated. 2. A C produced by the method of claim 1.
Using acicular goethite particles containing o and Al, the acicular goethite particles or the acicular goethite particles are
The needle-like hematite particles obtained by heat treatment at 0 to 700 ° C. are heated and reduced in a reducing gas to obtain needle-like magnetite particles, or further oxidized to obtain needle-like maghemite particles. Method for producing magnetic particle powder for magnetic recording. 3. The acicular magnetite particles or acicular maghemite particles obtained by the method according to claim 2 are used as precursor particles, and the precursor particles are an alkaline suspension containing cobalt hydroxide or cobalt hydroxide. Needle-like magnetite particles or needle-like maghemite particles modified with Co or modified with Co and Fe ²⁺ by dispersing in an alkaline suspension containing ferrous hydroxide and heating the dispersion. A method for producing a magnetic particle powder for magnetic recording, comprising: