JPH0717386B2 - Cobalt-containing ferromagnetic iron oxide powder and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cobalt-containing ferromagnetic iron oxide powder having excellent magnetic properties, which is useful as a recording material for a magnetic recording medium, and a method for producing the same.

[Conventional technology and its problems]

Cobalt-containing ferromagnetic iron oxide has a high coercive force, and when it is used as a recording element of a magnetic recording medium, high density recording is possible and it has excellent sensitivity in the high frequency region. Is widely used in the field of magnetic recording. As a recent tendency, in the video home system (VTR), there is a tendency to make the recording wavelength shorter in order to further improve the recording density. Therefore, cobalt content as a recording element used in the magnetic recording medium for VTR is included. As the ferromagnetic iron oxide powder, high coercive force ultrafine particles having a higher coercive force and a higher specific surface area are required.

That is, in the field where higher density recording is required, in general, when the specific surface area is smaller than 35 m ² / g, noise cannot be sufficiently reduced, and when the coercive force is lower than 700 Oe, short wavelength recording is performed. It is said that the self-demagnetization loss in becomes large and it becomes difficult to obtain a sufficient output, and in the case of a cobalt-containing ferromagnetic iron oxide powder having a specific surface area of 35 m ² / g or more and a coercive force of 700 Oe or more, the target in the field is set. It is said that the noise reduction is achieved, the self-demagnetization of the recording signal is suppressed, and the target short wavelength output characteristic is achieved.

The coercive force of the cobalt-containing ferromagnetic iron oxide powder can be made higher by increasing the cobalt content, but the coercive force distribution becomes larger as the coercive force becomes higher by simply increasing the cobalt content. However, only inferior erase characteristics can be obtained. In addition, it causes problems such as deterioration of coercive force over time and increase of heat demagnetization.
Cannot be used as a magnetic recording medium for use. Further, as the particles become finer, the coercive force distribution of the magnetic iron oxide powder itself used as the core for cobalt deposition tends to increase, and when the cobalt deposition is further performed, this coercive force distribution further expands. In this way, the major obstacles to achieving higher coercive force and finer particles are
There are coercive force distribution, deterioration of erasing characteristics, change of coercive force with time, increase of heat demagnetization, etc., and it is strongly desired to improve them.

Various methods for attempting this improvement have been proposed. For example, (1) after coating the surfaces of γ-Fe ₂ O ₃ particles with cobalt hydroxide, an aqueous solution of a ferrous salt is added, and then, Method of heating and boiling (Japanese Examined Patent Publication No. 56-48444), (2) Ferromagnetic needle-shaped iron oxide and cobalt salt are mixed at room temperature and then in an alkaline aqueous solution.
Method of heat treatment at a temperature of 80 to 100 ° C (Japanese Patent Publication No. 53-2111)
8), (3) Ferromagnetic iron oxide, cobalt ion and first
The temperature at which iron ions are neutralized with an alkali and deposited is 50 ° C.
The following method is followed by reacting in the presence of alkali at a temperature of 60 ° C to the boiling point (JP-A-59-126605), (4) γ-Fe ₂ O
_There is a method (Japanese Patent Publication No. 52-36751) in which the concentration of alkali OH group is 0.05 to 3.0 mol / l and the temperature is 50 to 100 ° C. when the _three- particle powder is modified with ferrous iron and cobalt.

However, all of these are in the presence of an alkali during or after deposition in the metamorphic deposition method of magnetic iron oxide.
Since it takes a means to accelerate the reaction by heating at a temperature between ℃ and boiling point, it is a useful method for increasing the coercive force, but it is a useful method for increasing the coercive force. Further improvement has been desired as it does not satisfy the improvement of magnetism and the like.

On the other hand, if it becomes ultrafine magnetic powder of 35 m ² / g or more by finely pulverizing, it becomes difficult to uniformly disperse in the binder when preparing a magnetic coating material by kneading with various organic binders. In terms of characteristics, there arises a problem that the effect of atomization cannot be obtained. As a countermeasure against this, for example, a method of adding a ferrous salt to an alkaline suspension containing γ-Fe ₂ O ₃ particles, stirring the mixture for 30 minutes or more, and then adding a cobalt salt (JP-A-61-17426). There is a suggestion such as. However, in the case of these methods, even if it can be a measure to improve the above problems, the coercive force cannot be sufficiently increased, and if the coercive force is raised by heating to a temperature near the boiling point, However, not only the requirement of 700 Oe or more cannot be satisfied, but also the drawbacks such as the possibility of losing the improvement effect become conspicuous. Therefore, further improvement is desired.

Furthermore, various additives (such as fatty acids) are used in the preparation of magnetic paints in order to improve physical properties such as running property and durability of the tape, but as described above, the magnetic powder becomes fine particles and the specific surface area increases. The adsorbability of the magnetic powder increases, and the degree of adsorption of the additive also tends to increase. There is also a problem that it affects the improvement of durability.

As described above, when the conventional technique is used, the coercive force can be increased, but various characteristics such as loss of the effect of atomization are brought about, and even if the deterioration of various characteristics can be prevented, the coercive force is reduced. As it cannot be increased, it is difficult to obtain a magnetic powder having a high coercive force of 700 Oe or more, and an excellent coercive force distribution in the ultrafine magnetic iron oxide having a particle size of 35 m ² / g or more, and having excellent other various properties. The development of a new manufacturing method that can solve these problems and the emergence of ultrafine-particle high-coercivity cobalt-containing ferromagnetic iron oxide powder with excellent coercive force distribution are strongly awaited.

[Object of the Invention]

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a cobalt-containing ferromagnetic iron oxide powder having excellent magnetic properties and a method for producing the same. Another object of the present invention is to provide a cobalt-containing ferromagnetic iron oxide powder having a particularly high coercive force and a high specific surface area and excellent in dispersibility and coercive force distribution, and a method for producing the same. Further, it is another object of the present invention to provide a cobalt-containing ferromagnetic iron oxide powder having not only these excellent magnetic properties but also desirable stability over time and fatty acid adsorption properties, and a method for producing the same.

[Outline of Invention]

The present inventors, as a result of repeated various studies to achieve the above objects, in order to solve the problem that dispersion becomes difficult due to atomization, for example, as a deposition method of γ-Fe ₂ O ₃ ,
The first method is to deposit the ferrous compound first, and then the cobalt compound. Also, during the deposition / aging reaction, which has been often used as a means for increasing the coercive force, especially during the deposition reaction. It was found that the operation of heating to a temperature of 50 ° C. or higher causes the spread of the coercive force distribution, and the method of treating at a high temperature is not always desirable. Based on this knowledge, it is possible to increase the coercive force to 700 Oe or more in the method of depositing ferrous compound → cobalt compound in this order without increasing the amount of cobalt and without heating during the deposition / aging reaction. If you can make improvements such as
Further research was conducted, paying attention to the fact that ultrafine magnetic powder having excellent dispersibility and coercive force distribution and high coercive force of 700 Oe or more can be provided.

First, in order to know the range of heating temperature conditions that do not deteriorate the coercive force distribution, in the method of depositing ferrous compound → cobalt compound in this order, the deposition condition of ferrous iron to be deposited first is the heating temperature condition. I investigated how it was related.
That is, taking the case where the starting material is γ-Fe ₂ O ₃ powder as an example, γ-Fe ₂ O ₃ particles are suspended in an alkaline aqueous solution, and the total amount of ferrous salt is added all at once to this slurry. ,
It was determined how the reaction rate of the precipitated ferrous hydroxide adsorbed on the γ-Fe ₂ O ₃ surface and transformed into magnetite changes with temperature.

As a result, it was found that the rate of conversion reaction to magnetite conversion gradually increased as the temperature increased, and the gradient was obviously different at the boundary of 30 ° C, and the degree of the increase gradually increased.

This is considered to indicate that the formation of magnetite proceeds not only to the surface of the magnetic iron oxide but also to the inside, and in this state the cobalt salt to be deposited next was added. In this case, it is considered that cobalt is more likely to be diffused inward, and a direct reaction product of magnetite and cobalt is also likely to be partially produced, and such a phenomenon is caused by the generation of an ultra-high coercive force component that causes deterioration of erasing characteristics. It is presumed that this may cause deterioration of the coercive force distribution and deterioration of other magnetic properties.

However, there is a drawback that the coercive force cannot be sufficiently increased at a temperature of 30 ° C or lower. However, as already proposed to compensate for this, if a method of raising the coercive force by raising the coercive force by heating to 50 ° C. or more during the deposition / aging reaction, the coercive force distribution is deteriorated. I will end up. Therefore, the temperature condition is preferably 30 ° C. or lower through the deposition / aging reaction, and it is not preferable to treat at 50 ° C. or higher.

Next, when the relationship between the amount of magnetite conversion and the coercive force expression when starting the addition of the cobalt salt was examined, the smaller the amount of magnetite conversion was, that is, the adsorption that did not yet contribute to the magnetization reaction. There was a tendency that the larger the amount of ferrous hydroxide in the above state, the higher the coercive force.

Then, in the method of depositing the ferrous compound and the cobalt compound in this order, the depositing conditions including the addition timing of the ferrous salt and the cobalt salt were variously changed to deposit, for example, Example 1 and Table 1 below. Surprisingly, as shown in
The coercive force is the highest when the partially superposed deposition method (hereinafter referred to as the partially superposed deposition process) such as iron salt addition → ferrous iron salt / cobalt salt parallel addition → cobalt salt addition・ Those with a high coercive force of 700 Oe or more can be easily obtained through aging without increasing the amount of cobalt even at a temperature of 30 ° C. or less, and those having excellent dispersibility even in the partial superposition adhesion treatment It was found that it was obtained, and that it was important to continuously perform the addition.

A coating layer composed of a layer composed of a compound of iron and cobalt, a layer composed of an iron compound and / or a layer composed of a cobalt compound on the nuclei of the magnetic iron oxide powder by the partial superposition deposition treatment. Is formed. In this case, at the boundary between the layer made of a compound of iron and cobalt and the layer made of an iron compound and / or the layer made of a cobalt compound in the coating layer, a concentration gradient (iron and cobalt (The composition ratio of and changes with a gradient) is formed, which is referred to as a partially overlapped adhered portion.

The partial superposition deposition treatment is, for example, a method in which a cobalt salt is added in parallel from the middle of the addition of the ferrous salt to an alkaline suspension containing an i-magnetic iron oxide powder as a nucleus crystal. A method of starting the addition of the cobalt salt in accordance with the gradual decrease of the addition amount of the ferrous salt to the alkaline suspension containing as a nucleation crystal, and gradually increasing the addition amount of the cobalt salt in accordance with the gradual decrease amount, etc. By. In these cases, the cobalt hydroxide contained in the ferrous hydroxide layer gradually increases, and eventually the method of (i) forms a layer in which the ratio of ferrous hydroxide and cobalt hydroxide is constant, and the method of (b) hydroxylates. It is a layer of cobalt only.

Up to now, there have been proposed examples such as a method of depositing a ferrous compound and a cobalt compound by co-precipitation and a method of depositing the ferrous compound and the cobalt compound in a distinct order. In the method of depositing the compound and the cobalt compound in order, there is no proposed example of the partial superposition deposition treatment for partially producing the mixed co-precipitation deposition portion.

Next, the present invention will be described by taking the case of the first embodiment as a typical example. When partially overlaid as in Example 1, a layer of cobalt compound and ferrous compound (inner layer) on top of the thin magnetite product on the magnetic iron oxide surface and the layer of ferrous compound (inner layer). The intermediate layer) is formed, and the cobalt compound layer (outer layer) is further formed on the intermediate layer), and there are partially overlapped adhered portions between the inner layer and the intermediate layer and between the intermediate layer and the outer layer. In this way, it is possible to easily obtain a ferromagnetic iron oxide powder having a high coercive force of 700 Oe or more, which has an excellent coercive force distribution and is excellent in dispersibility, and the effect of atomizing even in an ultrafine particle powder of 35 m ² / g or more. It has been found that it becomes possible to provide an ultrafine particle high coercive force cobalt-containing ferromagnetic iron oxide powder having excellent properties without losing the properties. This partial superposition deposition treatment is applied not only to the ultrafine particle magnetic iron oxide powder as described above, but also to a magnetic iron oxide powder having a normal particle size, for example, a specific surface area of 25 to 35 m ² / g. The effect is brought.

What was obtained by the method of Example 1 was the ultrafine particle high coercive force cobalt-containing ferromagnetic iron oxide powder as described above,
The coercive force distribution and dispersibility are excellent, and the demand for higher performance of the magnetic recording medium can be sufficiently satisfied. Such an improving effect is obtained by forming an inner layer which is a magnetite and a ferrous compound formed on a nuclear crystal of magnetic iron oxide powder, an intermediate layer which is a cobalt compound and a ferrous compound, an outer layer which is a cobalt compound, and an inner layer. It is provided by an intermediate layer and a partially overlapped deposit formed between the intermediate layer and the outer layer.

The amount of cobalt mainly forming the intermediate layer is 0.05 to 15% by weight, preferably 0.05 to 12% by weight, based on the total amount of Fe,
The amount of cobalt that mainly forms the outer layer is based on the total amount of Fe.
The amount is 0.05 to 15% by weight, preferably 0.05 to 11% by weight. Note that mainly when the amount of cobalt for forming the outer layer increases, the effect of increasing the coercive force decreases at 30 ° C or less,
On the other hand, when the amount of cobalt for forming the intermediate layer is too large, the effect of improving the coercive force distribution and dispersibility becomes small. Therefore, it is preferable to prepare the deposited cobalt in a ratio of mainly outer layer: mainly intermediate layer = 1: 1 to 1: 2.

In addition, the amount of divalent iron in the particles of the obtained cobalt-containing ferromagnetic iron oxide powder increases the coercive force as the amount increases, but it tends to cause deterioration of the coercive force distribution, especially the erasing property deteriorates. It is not preferable that the amount is too large, because it tends to occur and further deteriorates the stability over time. Therefore, when the starting material is γ-Fe ₂ O ₃ , the ratio of divalent iron to the total iron content is preferably 0.08 or less, more preferably 0.07 or less.

The magnetic iron oxide used in the present invention includes γ-Fe ₂ O ₃ and F
Examples thereof include acicular magnetic iron oxide powders such as e ₃ O ₄ or beltride compounds (for example, those obtained by partially reducing γ-Fe ₂ O ₃ ), of which γ-Fe ₂ O ₃ fine powder is preferable.

In order to produce the cobalt-containing ferromagnetic iron oxide powder as described above, the ferrous iron oxide is first added to an alkaline suspension of the magnetic iron oxide powder while keeping the temperature in the system below 50 ° C, preferably below 30 ° C. The salt is added at a constant rate to form a precipitate of ferrous hydroxide, which is adsorbed on the surface of the magnetic iron oxide. It is not preferable that the addition of the ferrous salt be slower than the adsorption rate of ferrous hydroxide, and the adsorption rate changes depending on the temperature condition, but it cannot be said unconditionally, but the addition time is 2 hours or less. It is preferably 1 hour or less. In this case, the condition when adding the ferrous salt is essential, keep cooling so that the temperature does not rise during the addition, less than 50 ° C, preferably 30 ° C.
It is more preferable to select a temperature in the range of 15 to 25 ° C. so as to maintain the following, and to keep the set temperature so that it does not move.

The timing of adding the cobalt salt in parallel with the ferrous salt depends on the conditions such as the specific surface area of the magnetic iron oxide powder used, the amount of the ferrous salt or cobalt salt added, and the set temperature during the addition.
In addition, in order to obtain the desired magnetic characteristics, it can be changed appropriately. In addition, the parallel addition of the cobalt salt and the ferrous salt includes the case where a required amount of the ferrous salt aqueous solution and the cobalt salt aqueous solution are mixed in advance and then added.

When the parallel addition of the cobalt salt and the ferrous salt is completed, only the cobalt salt is continuously added, but the total addition time of both is 30 minutes or more, preferably 1 to 2 hours. .

After the addition of only the cobalt salt is completed, the aging reaction period is agitated for 3 hours or more, preferably 5 to 20 hours. Since this aging reaction period, especially in the subsequent stage, is less affected by temperature conditions than in the case of the deposition reaction period, for example, in order to industrially improve equipment capacity and reduce costs, the aging reaction time If you want to shorten
It is possible to heat to a temperature not much above 0 ° C.
However, as mentioned above, it has never been treated at a temperature lower than 50 ° C.

The dispersion concentration of the magnetic iron oxide powder is usually 20 to 20.
It is 0 g / l, preferably 50 to 150 g / l, and when using fine powder having a high specific surface area, it is preferable to set it to a low concentration.
The atmosphere during the deposition operation is usually non-oxidizing so that the ferrous compound is not substantially oxidized. However, it goes without saying that the atmosphere may be adjusted so as to oxidize the ferrous compound to some extent in order to obtain the desired magnetic characteristics.

Examples of the ferrous salt used in the present invention include ferrous sulfate,
Examples thereof include ferrous salts of mineral acids such as ferrous nitrate and ferric chloride, and ferrous sulfate is industrially preferable. Examples of the cobalt salt include inorganic or organic acid salts of cobalt, such as sulfuric acid. Examples thereof include cobalt, cobalt chloride, and cobalt acetate, and industrially cobalt sulfate is preferable. As the alkali, a hydroxide of an alkali metal or an alkaline earth metal,
Oxides or carbonates are used, for example, sodium hydroxide, potassium hydroxide, sodium oxide, calcium carbonate and the like, industrially, sodium hydroxide,
Potassium hydroxide is preferred.

The amount of the first iron salt and the amount of cobalt salt deposited is 1 to 30% by weight as Fe, preferably 2 to 20% by weight, and 0.1% as Co for the latter with respect to the total Fe amount of the magnetic iron oxide powder. ~ 20
%, Preferably 0.5 to 15% by weight. If the addition amount of ferrous iron is too small, improvement of coercive force distribution cannot be achieved,
This is not preferable because it causes problems such as high electric resistance of the obtained magnetic powder. On the other hand, if the amount is too large, the specific surface area tends to decrease, and problems such as deterioration in magnetic characteristics and aging such as erasing tend to occur, which are not preferable. If the addition amount of the cobalt salt is too small, the coercive force cannot be expected to increase, and conversely, if it is too large, the dispersibility tends to deteriorate, which is not preferable. Note that in the amount of ferrous and cobalt salts deposited, C
The molar ratio of o: Fe is preferably 1: 1.5 or more, and according to the present invention, a cobalt-containing magnetic iron oxide having a saturation magnetization (σs) of 74 emu / g or more can be easily produced.

In Example 1, a ferrous salt and a cobalt salt were added to an alkaline suspension containing magnetic iron oxide powder as nuclei to precipitate ferrous hydroxide and cobalt hydroxide. Regarding the method, various methods can be appropriately adopted as seen in the prior art. For example, a method of adding a slurry containing fine particles of ferrous hydroxide or cobalt hydroxide precipitation, a method of adding an aqueous solution of ferrous salt or an aqueous solution of cobalt salt in parallel with an aqueous alkaline solution, either of ferrous iron and cobalt. Examples thereof include a method of adding the above as a hydroxide-precipitated particle dispersion slurry and the other as an aqueous salt solution.

The concentration of OH groups (concentration of free OH groups equal to or more than the neutralization equivalent) in the suspension after the deposition of the first iron salt and cobalt salt is usually 0 to 3 mol.
/ l, preferably 0.5 to 2 mol / l.

After completion of the deposition / aging reaction, dehydration and water washing are performed to remove alkali, and then drying is performed. The alkali-removed cake or slurry after dehydration / washing does not need to be maintained in a non-oxidizing atmosphere and may be operated in the atmosphere. Further, after removing the alkali, the coercive force distribution is not deteriorated even if heating is performed at 50 ° C. or higher.

At the time of drying, an inert gas such as N ₂ gas may be used, or air or a mixed gas of air and an inert gas may be used. The drying temperature may be a normal temperature used industrially, and generally about 60 to 150 ° C. is often used.

The magnetic iron oxide after drying becomes a cobalt-containing ferromagnetic iron oxide powder having desired properties, but it was improved in coercive force and other magnetic properties by further performing dry heat treatment at a temperature of 100 to 200 ° C. Magnetic powder may be obtained in some cases.

The present invention has been described above mainly based on the first embodiment.
The essential point of the present invention is that a magnetic iron oxide powder is used as a nuclear crystal, the nuclear crystal is coated with at least an iron compound and a cobalt compound, and the coating layer has a partially superposed adhered portion. A ferromagnetic iron oxide powder containing cobalt, and a modified deposition method in which a magnetic iron oxide powder is used as a nucleation crystal, which includes at least a ferrous hydroxide deposition step and a cobalt hydroxide deposition step. The method for producing a cobalt-containing ferromagnetic iron oxide powder is characterized in that a partial superposition deposition treatment is performed between the two. Furthermore, the outermost layer of these cobalt-containing ferromagnetic iron oxide powders is silicon,
A coating layer of at least one compound selected from the group of aluminum, calcium, titanium, vanadium, manganese, nickel, zinc and phosphorus compounds, and a method for producing the same.

The partially overlapped adhered portion in the present invention is as defined above, and the adhered portion can be formed by, for example, the above methods (a), (b) and the like. As in the case of Example 8 (corresponding to (b)), the state of the adhered portion is such that the amount of the ferrous salt added to the alkaline suspension containing the magnetic iron oxide powder as nuclei gradually decreases. It can be easily understood by considering the method of starting the addition of the cobalt salt in combination and gradually increasing the addition amount of the cobalt salt in accordance with the gradually decreasing amount.

In addition, in Examples 3 and 9 (corresponding to a), the ferrous salt was added to the alkaline suspension containing the magnetic iron oxide powder as the nuclei, and then the cobalt salt was added, as in Example 1. A method of adding the ferrous salt in parallel with the addition of the ferrous salt, and then stopping the addition of the ferrous salt and adding only the cobalt salt to deposit ferrous hydroxide and cobalt hydroxide on the nuclei. That is, the partially overlapped adhered portions are formed when the addition of the cobalt salt is started and when the addition of the ferrous salt is stopped. That is, in the former period, the concentration of cobalt in the ferrous hydroxide layer gradually increases and a concentration gradient is formed during the transition to the ferrous hydroxide and cobalt hydroxide layers. 1 A concentration gradient is formed while the amount of iron gradually decreases and shifts to the cobalt layer.

The sample symbols C (Example 8), C (Example 3) and Si (Example 9) having the partially overlapped adherends thus obtained were compared with those of the conventional method. Magnetic force Hc
Excellent in (Oe), squareness ratio (Br / Bm) and orientation (OR). The reversal magnetic field distribution (SFD) usually deteriorates as the coercive force increases, but it does not deteriorate in the case of the sample symbols C, C and C, and shows excellent values.

In the present invention, as described above, it is desirable to deposit the ferrous compound in the first step of the magnetic iron oxide metamorphic deposition method, but by utilizing the effect of the partial superposition deposition treatment,
Other aspects are possible. For example, it is a method in which the parallel addition of the ferrous salt and the cobalt salt is simultaneously started to the alkaline suspension of the magnetic iron oxide powder, the addition of the ferrous salt is stopped on the way, and only the cobalt salt is continuously added. . In this method, the partially overlapped adhered portion is formed when the addition of the ferrous salt is stopped, and Examples 6 and 10 are examples.

Further, the present invention can take various aspects other than these. For example, when the deposition process of the ferrous compound or the cobalt compound is provided before or after the process relating to the partial superposition deposition treatment (Examples 4 and 5), three or more partial superposition deposition parts are provided. This is the case (Example 7). In the present specification, the deposition layer further formed on the deposition layer for the partial superposition deposition process is referred to as an additional deposition layer.

Further, in the present invention, in addition to the ferrous salt and the cobalt salt as the metamorphic deposition agent for magnetic iron oxide, compounds such as manganese, nickel and zinc which are usually used in the metamorphic deposition method of this kind are also used. be able to. For example, at least one of these is mixed with a ferrous salt or cobalt salt and added to an alkaline suspension of magnetic iron oxide powder, or in parallel with the addition of the ferrous salt and / or cobalt salt. It can be added to the suspension. Further, for example, a deposition layer of at least one of the above is provided below the deposition layer for partial overlay deposition processing, or a deposition layer for partial overlay deposition processing and an additional deposition layer An adhering layer of at least one of the above may be provided between or between the layers constituting the additional adhering layer.

Examples of the magnetic iron oxide as a starting material used in the present invention include γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and beltride as described above, and as shown in Examples 1 to 11, γ-Fe ₂ O _{Although 3} is desirable, as shown in Example 12, the effect of the present invention that is preferable is also provided for the belt ride, and there is nothing that prevents the application of the present invention for Fe ₃ O ₄ .

Furthermore, according to the present invention, with respect to the cobalt-containing ferromagnetic iron oxide powder obtained through the partial superposition deposition treatment, silicon, aluminum, calcium, titanium, vanadium,
By coating at least one compound selected from the group of manganese, nickel, zinc and phosphorus compounds, the ferromagnetic iron oxide powder has not only excellent magnetic properties but also desirable stability over time and fatty acid adsorption properties. Can be manufactured.

These deposition compounds include hydroxides, hydrated oxides, hydrated oxyhydroxides, oxides, silicates, phosphates and others. Further, as an adherent used for precipitating these compounds, for example, for silicon, sodium or potassium salt of orthosilicic acid or metasilicic acid,
For aluminum, sodium aluminate, potassium salt, aluminum sulfate, aluminum chloride, etc., for titanium, titanium sulfate, titanium chloride, etc., for vanadium, vanadyl sulfate, sodium vanadate, etc., for calcium, chloride, nitrate, etc., manganese, Sulfates, nitrates and chlorides of nickel and zinc, and orthophosphoric acid and pyrophosphoric acid of phosphorus.

As the acidic or alkaline substance for neutralizing the above-mentioned adherent and precipitating the adherent compound, sulfuric acid, hydrochloric acid, nitric acid and the like are used for the former, and sodium hydroxide, potassium hydroxide, sodium oxide, calcium carbonate and the like are used for the latter. It is illustrated.

Although inorganic compounds have been given as examples of the adherent and the neutralizing agent, it is of course possible to use a suitable organic compound. For example, zinc acetate, calcium formate, etc. may be used as the adherent, and tartaric acid, benzoic acid, methanesulfonic acid, sulfinic acid, etc. may be used as the neutralizing agent.

The cobalt-containing ferromagnetic iron oxide powder-containing cake is separated from the modified reaction product suspension obtained through the partial superposition deposition treatment of the present invention, and after washing if necessary, it is dispersed in an aqueous medium liquid. Use a ferromagnetic iron oxide dispersion slurry. This dispersion is usually carried out by mechanical stirring, but ultrasonic waves may be used or a suitable dispersant may be added. An adhering agent and a neutralizing agent are added to this slurry to precipitate and deposit the above-mentioned adhering compound. The adhering agent and the neutralizing agent can be added in an arbitrary order, all at once, or in parallel over a certain period of time to form an adhering compound having desired properties. Therefore, an appropriate addition means can be adopted at any time.

The adherent and the neutralizing agent can be added after being dissolved or dispersed in water and / or another solvent or added as they are, but it is industrially preferable to add them in liquid form. If an alkaline or acidic adhesive is selected, the addition of a neutralizing agent is unnecessary or the amount thereof is reduced. For example, Example 16 is a method in which sodium orthosilicate and manganese sulfate are selected and no neutralizing agent is used.Examples 13 and 15 select similar adherends and use them as neutralizing agents. This is a method in which the amount of sulfuric acid and the amount of sodium hydroxide are reduced. According to the above-mentioned adding means, the depositing compound is precipitated in the aqueous medium in both cases, but even if the depositing compound is precipitated outside the system in advance and this dispersion is added to the ferromagnetic iron oxide dispersion slurry. Good.

The treatment temperature for precipitating the depositing compound and adsorbing it onto the cobalt-containing ferromagnetic iron oxide particles is usually room temperature to boiling point, preferably room temperature to 90 ° C, more preferably 25 to 65 ° C. If necessary, it is aged for several tens of minutes to a few hours, and this aging is generally carried out under stirring by the above precipitation,
It is advisable to perform the treatment at the treatment temperature during adsorption for about 15 to 5 hours.

The slurry on which the coating compound has been deposited and matured is usually
This is filtered, washed and dried to obtain a product. The drying atmosphere and temperature are, for example, 60 to 150 ° C. in air or in a non-oxidizing atmosphere (such as N ₂ gas stream). The one in which the coating compound is applied to the outermost layer is less susceptible to the influence of the atmosphere as compared with the one in which the coating compound is not coated, so that it is easy to handle and suitable for industrial operation.

The amount of the adhered compound deposited on the cobalt-containing ferromagnetic iron oxide powder cannot be unequivocally determined depending on the type of the compound, the difference in the depositing means, etc. 0.01 to 3% as contained atoms,
Usually, it is about 0.02 to 2%. If the amount of the adhered compound is too small, the desired aging properties and fatty acid adsorption properties are not sufficiently improved, and if it is too large, the coercive force decreases, the saturation magnetization decreases, and the like. The characteristics may be impaired. The fatty acid adsorption property is represented by the C ₁₄ adsorption amount shown in Table 3, and generally, the smaller the value, the better the property. However, since this kind of magnetic powder needs a proper amount of resin adsorption, if the resin adsorption degree is too small, the running property and durability of the tape are deteriorated.

Desirable as the deposition compound in the present invention are, for example, water-soluble acidic salts of aluminum, manganese, nickel, zinc, etc. neutralized with an alkali, alkali silicates of aluminum, calcium, water-soluble acidic salts of manganese, etc. Alternatively, it is neutralized with various phosphoric acids.

In addition, although the neutralization method which is usually used has been described as an example of the deposition method, a heating hydrolysis method, an immersion evaporation method, or the like can also be adopted.
The thermal hydrolysis method is, for example, a method in which the ferromagnetic iron oxide dispersion slurry in which the adherend is dissolved is heated as necessary to precipitate the adherend compound by hydrolysis. Further, the immersion evaporation method, for example, the cobalt-containing ferromagnetic iron oxide is fractionated from the ferromagnetic iron oxide dispersion slurry, and this is placed in water and / or an organic solvent in which the coating agent or coating compound is dissolved or dispersed, respectively. It is a method of dispersing and dipping, and then evaporating the dipping liquid.

By properly selecting the type, the amount of addition and the means of deposition of the above-mentioned coating compound according to the present invention, as shown in Table 3, not only the change with time and the drastic improvement of the fatty acid adsorption property but also the coercive force is improved. And the squareness and orientation can be significantly improved without substantially affecting the switching field distribution.

〔Example〕

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

Example 1 γ-Fe ₂ O ₃ powder (coercive force is Hc350Oe, average major axis particle size is about 0.
15μ, axial ratio about 8) 100g is dispersed in water 1 and 195ml of 10mol / l sodium hydroxide aqueous solution to make slurry, and the temperature is 2
Cooling was controlled so as to maintain 0 ° C., and under a non-oxidizing atmosphere, 180 ml of 0.90 mol / l ferrous sulfate aqueous solution was added at a rate of 3 ml / min to complete the addition in 60 minutes, and 45 minutes At the end of time, 90 ml of 0.85 mol / l cobalt sulfate aqueous solution was added to 60 ml.
The addition was started at a rate of 1.5 ml / min so that the addition was completed in minutes, and after the addition of the cobalt sulfate aqueous solution was completed, the mixture was stirred at a temperature of 20 ° C. for 10 hours. This slurry was filtered, washed with water, and dried at 120 ° C. to obtain the target cobalt-containing ferromagnetic iron oxide powder (A).

Example 2 γ-Fe ₂ O ₃ powder (coercive force is Hc380Oe, average major axis particle size is about 0.
The target cobalt-containing ferromagnetic iron oxide powder (ii) was obtained in the same manner as in Example 1 except that 18 μ and an axial ratio of about 8) were used.
Got

Example 3 γ-Fe ₂ O ₃ powder (coercive force is Hc400Oe, average major axis particle size is about 0.
28μ, axial ratio about 10) 100g is dispersed in water 1 and 10mol / l sodium hydroxide aqueous solution 185ml to make a slurry, and the temperature is 2
Cooling was controlled so as to maintain 5 ° C., and under a non-oxidizing atmosphere, addition of 160 ml of 0.90 mol / l ferrous sulfate aqueous solution was started at a rate of 3.6 ml / min so as to complete addition in about 45 minutes, After 15 minutes, 0.8 ml of 0.85 mol / l cobalt sulfate aqueous solution
Was started at a rate of 1.3 ml / min so that the addition was completed in 60 minutes. After completion of the addition of the cobalt sulfate aqueous solution, the mixture was aged with stirring for 5 hours. After 1 hour of aging, the temperature was raised to 35 ° C, and after aging was completed, the product was filtered, washed with water, and dried at 120 ° C to obtain the desired cobalt-containing ferromagnetic iron oxide powder (c).

Example 4 100 g of the same γ-Fe ₂ O ₃ powder as used in Example 3 was added to 1 part of water.
And 185 ml of a 10 mol / l sodium hydroxide aqueous solution to form a slurry, which is cooled and controlled to maintain a temperature of 25 ° C., and 53.3 ml of a 0.90 mol / l ferrous sulfate aqueous solution in a non-oxidizing atmosphere. Was added for about 15 minutes (3.6 ml / min), and after the addition was completed, the mixture was aged with stirring for 2 hours. Then, 106.7 ml of 0.90 mol / l ferrous sulfate aqueous solution and 80 ml of 0.85 mol / l cobalt sulfate aqueous solution are added in about 30 minutes (3.6 ml / min) and about 60 minutes (1.3 ml / min), respectively, so that the addition is completed. At the same time, the addition was started in parallel. After the addition was completed, the mixture was aged with stirring for 5 hours. After 1 hour of aging, the temperature was raised to 35 ° C, and after aging was completed, the product was filtered, washed with water, and dried at 120 ° C to obtain the desired cobalt-containing ferromagnetic iron oxide powder (d).

Example 5 100 g of the same γ-Fe ₂ O ₃ powder used in Example 3 was added to water 1
And 185 ml of a 10 mol / l sodium hydroxide aqueous solution to form a slurry, which was cooled and controlled so that the temperature was maintained at 25 ° C., and 160 ml of a 0.90 mol / l ferrous sulfate aqueous solution was added in a non-oxidizing atmosphere. The addition was started at a rate of 3.6 ml / min so that the addition was completed in about 45 minutes, and after 15 minutes, 40 ml of 0.85 mol / l cobalt sulfate aqueous solution was added in about 30 minutes ( The addition was started at a rate of 1.3 ml / min so that the addition was completed simultaneously. After the addition was completed, the mixture was aged with stirring for 2 hours. Then, 40 ml of 0.85 mol / l cobalt sulfate aqueous solution was added for about 30 minutes (1.3 ml / min), and the mixture was aged with stirring for 5 hours. After 1 hour of aging, the temperature was raised to 35 ° C., after completion of aging, filtration, washing with water, and drying at 110 ° C. to obtain the desired cobalt-containing ferromagnetic iron oxide powder (e).

Example 6 100 g of the same γ-Fe ₂ O ₃ powder used in Example 3 was added to 1 part of water.
And 185 ml of a 10 mol / l sodium hydroxide aqueous solution to form a slurry, which was cooled and controlled so that the temperature was maintained at 25 ° C., and 160 ml of a 0.90 mol / l ferrous sulfate aqueous solution under a non-oxidizing atmosphere, and 80 ml of 0.85 mol / l cobalt sulfate aqueous solution for about 45 minutes (3.6 ml / min) and about 60 minutes (1.3 ml / l, respectively)
Min) was added at the same time in parallel so that the addition was completed. After the addition was completed, the mixture was aged with stirring for 5 hours. After 1 hour of aging, the temperature was raised to 35 ° C. After aging, filter, wash with water, 120
After drying at ℃, the target cobalt-containing ferromagnetic iron oxide powder (f) was obtained.

Example 7 100 g of the same γ-Fe ₂ O ₃ powder used in Example 3 was added to 1 part of water.
And 185 ml of 10 mol / l sodium hydroxide aqueous solution were dispersed into a slurry, and ferrous sulfate and cobalt sulfate were added as follows in a non-oxidizing atmosphere while maintaining the temperature at 25 ° C. First, 100 ml of 0.90 mol / l ferrous sulfate aqueous solution
Was started at a rate of 4 ml / min. After 20 minutes from the start of this addition, 0.85 mol / l cobalt sulfate aqueous solution 45
ml was added at a rate of 1.5 ml / min. After 25 minutes from the starting point, the addition of the ferrous sulfate aqueous solution is completed, and only the cobalt sulfate aqueous solution is added. After 45 minutes from the starting point, 60 ml (0.90 mol / l) of ferrous sulfate aqueous solution was added again at a rate of 4 ml / min. After 50 minutes have passed from the starting point, the addition of the cobalt sulfate aqueous solution is completed, and only the ferrous sulfate aqueous solution is added. After 55 minutes from the starting point, an aqueous solution of cobalt sulfate is again used.
35 ml (0.85 mol / l) was added at a rate of 1.5 ml / min. After 60 minutes from the starting point, the addition of the ferrous sulfate aqueous solution was completed, and only the cobalt sulfate aqueous solution was added. After about 78 minutes from the starting point, all the additions were completed. By this addition method, the ferrous sulfate aqueous solution and the cobalt sulfate aqueous solution were added in parallel over 3 times for 5 minutes. After the addition was completed, the mixture was aged with stirring for 5 hours. After 1 hour of aging, the temperature was raised to 35 ° C. After completion of aging, the product was filtered, washed with water, and dried at 120 ° C. to obtain the desired cobalt-containing ferromagnetic iron oxide powder (g).

Example 8 100 g of the same γ-Fe ₂ O ₃ powder used in Example 3 was added to 1 part of water.
And 185 ml of a 10 mol / l sodium hydroxide aqueous solution were dispersed to form a slurry, and ferrous sulfate and cobalt sulfate were added as follows in a non-oxidizing atmosphere while maintaining the temperature at 25 ° C. First, add 160 ml of 0.90 mol / l ferrous sulfate aqueous solution.
The mixture was added at a rate of 3.6 ml / min, and after 15 minutes, the addition rate of the ferrous sulfate aqueous solution was gradually decreased, and at the same time, the addition of 0.85 mol / l cobalt sulfate aqueous solution (80 ml) was started. The amount of the cobalt sulfate aqueous solution was gradually increased in accordance with the gradually decreasing amount. It took 60 minutes from the start of gradually reducing the amount of the ferrous sulfate aqueous solution added to the end of the addition. Then, the addition rate of cobalt sulfate at the end of addition of the ferrous sulfate aqueous solution was 1.3 ml /
The minutes were held for 30 minutes. The addition amounts of ferrous sulfate and cobalt sulfate are the same as in Example 3. After addition is complete, 5
The mixture was aged with stirring for an hour. After 1 hour of aging, the temperature was raised to 35 ° C. After completion of aging, the product was filtered, washed with water, and dried at 120 ° C. to obtain the desired cobalt-containing ferromagnetic iron oxide powder (h).

Comparative Example 1 100 g of the same γ-Fe ₂ O ₃ powder used in Example 3 was added to 1 part of water.
And 185 ml of 10 mol / l sodium hydroxide aqueous solution to make a slurry, and 160 ml of 0.90 mol / l ferrous sulfate aqueous solution in a non-oxidizing atmosphere while maintaining the temperature at 25 ° C. for about 45 minutes (3.6 ml / Min), and after completion of addition, the mixture was aged with stirring for 1 hour. Next, about 80 ml of 0.85 mol / l cobalt sulfate aqueous solution
Added over 60 minutes (1.3 ml / min). After the addition was completed, the mixture was aged with stirring for 5 hours. After 1 hour of aging, the temperature was raised to 35 ° C. After completion of aging, the product was filtered, washed with water, and dried at 120 ° C. to obtain a cobalt-containing ferromagnetic iron oxide powder (ke).

Comparative Example 2 In Comparative Example 1, except that the aqueous sodium hydroxide solution was 197 ml, and the addition amounts of the ferrous sulfate aqueous solution and the cobalt sulfate aqueous solution were 189 ml and 92 ml, respectively.
In the same manner as in Comparative Example 1, a cobalt-containing ferromagnetic iron oxide powder (K) was obtained.

Comparative Example 3 100 g of the same γ-Fe ₂ O ₃ powder used in Example 3 was added to 1 part of water.
And 185 ml of 10 mol / l sodium hydroxide aqueous solution to make a slurry, and about 100 ml of 0.90 mol / l ferrous sulfate aqueous solution of about 30 ml under non-oxidizing atmosphere while keeping the temperature at 25 ° C.
After the addition was completed, the mixture was aged for 1 hour with stirring. Then, 80 ml of 0.85 mol / l cobalt sulfate aqueous solution was added in about 60 minutes (1.3 ml / min), and after completion of addition, the mixture was aged with stirring for 1 hour. Furthermore, 60 ml of 0.90 mol / l ferrous sulfate aqueous solution
After adding for 15 minutes (4 ml / min), the mixture was stirred and aged for 5 hours, and the temperature was raised to 35 ° C. after 1 hour of aging. After completion of aging, filtration,
It was washed with water and dried at 120 ° C. to obtain a cobalt-containing ferromagnetic iron oxide powder (SA).

Example 9 γ-Fe ₂ O ₃ powder (coercive force Hc395Oe, average major axis particle size of about 0.40
μ, axial ratio about 12) 100 g was dispersed in 1 ml of water and 180 ml of 10 mol / l sodium hydroxide aqueous solution to make a slurry, and the temperature was 28
While maintaining the temperature at ℃ under a non-oxidizing atmosphere, add 161 ml of 0.90 mol / l ferrous sulfate aqueous solution to complete the addition in about 45 minutes.
Start the addition at the rate of ml / min, and after 15 minutes, add 0.8
63 ml of a 5 mol / l cobalt sulfate aqueous solution was added at a rate of 1.1 ml / min so that the addition was completed in about 60 minutes. After the addition of the cobalt sulfate aqueous solution was completed, the temperature was raised to 40 ° C. and the mixture was aged with stirring for 3 hours. After completion of aging, the product was filtered, washed with water, and dried at 120 ° C. to obtain the desired cobalt-containing ferromagnetic iron oxide powder (shi).

Example 10 100 g of the same γ-Fe ₂ O ₃ powder used in Example 9 was added to water 1
And 180 ml of a 10 mol / l sodium hydroxide aqueous solution to form a slurry, and in a non-oxidizing atmosphere while maintaining the temperature at 28 ° C., 0.91 mol / l ferrous sulfate aqueous solution 161 ml and 0.8
63 ml of 5 mol / l cobalt sulfate aqueous solution was simultaneously started in parallel so that the addition was completed in about 45 minutes (3.6 ml / min) and about 60 minutes (1.1 ml / min), respectively. 40 after addition is complete
The temperature was raised to ° C and the mixture was aged with stirring for 3 hours. After completion of aging, filtration,
It was washed with water and dried at 120 ° C. to obtain the desired cobalt-containing ferromagnetic iron oxide powder (s).

Comparative Example 4 100 g of the same γ-Fe ₂ O ₃ powder used in Example 9 was added to 1 part of water.
And 180 ml of a 10 mol / l sodium hydroxide aqueous solution to form a slurry, and under a non-oxidizing atmosphere while maintaining the temperature at 28 ° C., 161 ml of 0.90 mol / l ferrous sulfate aqueous solution for about 45 minutes (3.6 ml / Min), and after completion of addition, the mixture was aged with stirring for 1 hour. Then about 63 ml of 0.85 mol / l cobalt sulfate aqueous solution
Added over 60 minutes (1.1 ml / min). After the addition was completed, the temperature was raised to 40 ° C. and the mixture was aged with stirring for 3 hours. After aging, filter, wash with water,
It was dried at 120 ° C to obtain the desired cobalt-containing ferromagnetic iron oxide powder (CE).

Example 11 100 g of the same γ-Fe ₂ O ₃ powder as used in Example 3 was added to 1 part of water.
And 185 ml of a 10 mol / l sodium hydroxide aqueous solution to form a slurry, and 54 ml of a 0.90 mol / l ferrous sulfate aqueous solution (3.6 ml) was first prepared in a non-oxidizing atmosphere while maintaining the temperature at 25 ° C.
At a rate of 4.8 ml / min, 106 ml of the ferrous sulfate aqueous solution and 40 ml of a 0.85 mol / l cobalt sulfate aqueous solution were added at a rate of 4.8 ml / min. After the completion of the addition, the desired cobalt-containing ferromagnetic iron oxide powder (SO) was obtained in the same manner as in Example 3 except that 40 ml of the cobalt sulfate aqueous solution was added at a rate of 1.3 ml / min.

Example 12 γ-Fe ₂ O ₃ powder (coercive force Hc410Oe, average major axis particle size about 0.35
μ ⁺ axial ratio about 12) is reduced in a hydrogen stream to obtain Fe ⁺⁺ / total Fe 9.
100 g of Bertride powder made up to 3% by weight in a non-oxidizing atmosphere, water 1 and 10 mol / l sodium hydroxide aqueous solution 154 m
While maintaining the temperature at 19 ° C, add 0.90 mol / l ferrous sulfate 70 ml aqueous solution at a rate of 1.5 ml / min, and after 15 minutes, 0.85 mol / l cobalt sulfate aqueous solution 70 ml. Was started at a rate of 1.2 ml / min. After the addition is complete
The temperature was raised to 30 ° C. and the mixture was aged with stirring for 5 hours. After completion of aging, the product was filtered, washed with water, and dried at 100 ° C. to obtain the desired cobalt-containing ferromagnetic iron oxide powder (ta).

Comparative Example 5 The method of adding the ferrous sulfate aqueous solution and the cobalt sulfate aqueous solution in Example 12 was changed so that the cobalt sulfate aqueous solution was added after the stirring and aging time of 2 hours after the completion of the addition of the ferrous sulfate aqueous solution. Cobalt-containing ferromagnetic iron oxide powder (H) was obtained in the same manner as in Example 12 except for the above.

Example 13 The slurry obtained by the metamorphic deposition treatment in the same manner as in Example 1 was filtered and washed with water, and the separated cake was dispersed in water to obtain a slurry of 100 g / l. Aqueous sodium orthosilicate solution (SiO ₂ /
Na ₂ O molar ratio of 0.5, Si of 20 g / l) was added in 25 ml, and subsequently manganese sulfate aqueous solution (Mn of 6.5 g / l) was added in an amount of 15.4 ml (0.5% as Si based on the weight of iron oxide, 0.1 as Mn). %). Then, dilute sulfuric acid was added to the slurry to neutralize it to pH 8.0, followed by stirring for 30 minutes for aging. The slurry obtained by applying the silica-manganese coprecipitate was filtered and washed with water, and the obtained cake was treated with N ₂ gas at 120 ° C.
It was dried at ℃ and the target cobalt-containing ferromagnetic iron oxide powder (A-1) was obtained.

Example 14 In Example 13, the addition amount of the sodium orthosilicate aqueous solution and the manganese sulfate aqueous solution was 0.5% as Si and 0 as Mn.
The target cobalt-containing ferromagnetic iron oxide powder (A-2) was obtained in the same manner as in Example 13 except that the content was changed to 025%.

Example 15 In Example 13, the addition amount of the sodium orthosilicate aqueous solution and the manganese sulfate aqueous solution was 0.5% as Si and 0 as Mn.
It was changed to 5%, and dilute sodium hydroxide was added in parallel while the manganese sulfate aqueous solution was being added.
Except that the pH was maintained at 8.0, the target cobalt-containing ferromagnetic iron oxide powder (a-
3) was obtained.

Example 16 In Example 13, the addition amount of the sodium orthosilicate aqueous solution was changed to 0.25% as Si, and the addition of the manganese sulfate aqueous solution was stopped when the pH reached 8.0 (the addition amount was about 0.2 as Mn.
%), And the target cobalt-containing ferromagnetic iron oxide powder (A-4) was obtained in the same manner as in Example 13 except that dilute sulfuric acid for neutralization was not used.

Example 17 In Example 13, an aluminum sulfate aqueous solution (about 3 g / l as Al) was used in place of the manganese sulfate aqueous solution, and this addition was stopped when the pH reached 8.0 (the amount added was Si).
0.5%, Al as 0.084%), and the target cobalt-containing ferromagnetic iron oxide powder (A-5) was obtained in the same manner as in Example 13 except that dilute sulfuric acid for neutralization was not used.

Example 18 Example 13 was carried out except that 16 ml of a mixed aqueous solution of manganese sulfate and aluminum sulfate (0.5% as Si, about 0.05% as Mn, about 0.024% as Al) was used instead of the manganese sulfate aqueous solution. In the same manner as in Example 13, the desired cobalt-containing ferromagnetic iron oxide powder (A-6) was obtained.

Example 19 In Example 13, instead of the sodium orthosilicate aqueous solution and manganese sulfate aqueous solution, only the sodium orthosilicate aqueous solution was used, and the addition amount was 50 ml (Si
1.0%) except that the target cobalt-containing ferromagnetic iron oxide powder (A-7) was obtained in the same manner as in Example 13.

Example 20 In the same manner as in Example 13, except that the slurry after the metamorphic deposition treatment used in Example 13 was changed to the slurry after the metamorphic deposition treatment in Example 2, Cobalt-containing ferromagnetic iron oxide powder (A-1) was obtained.

Example 21 The slurry obtained by the metamorphic deposition treatment in the same manner as in Example 3 was filtered, washed with water, and the separated cake was dispersed in water to give a slurry of 100 g / l. Aqueous titanium tetrachloride solution (5 g / Ti as Ti)
l) was added until the pH was 8.0 (about 0.06% as Ti based on the weight of iron oxide). After completion of the addition, the mixture was stirred and aged for 1 hour, filtered, washed with water, and dried at 120 ° C. to obtain the desired cobalt-containing ferromagnetic iron oxide powder (C-1).

Example 22 Slurry 1 used in Example 21 was heated to 60 * ° C. and stirred, and an aqueous vanadyl sulfate solution (30.1 g / v as v) was obtained.
l) 26.6 ml was added (0.8% as v by weight based on iron oxide). In addition, a 60 g / l sodium hydroxide aqueous solution was added in parallel midway so that the pH did not fall below 7.5 during this addition. After stirring for 30 minutes after the addition was completed, 13.2 ml of a manganese sulfate aqueous solution (30.2 g / l as Mn) and a 60 g / l sodium hydroxide aqueous solution were added in parallel so that the pH was maintained at 7.5 (weight relative to iron oxide). 0.4% as the standard Mn). After the addition was completed, the temperature was raised to 80 ° C., the mixture was stirred and aged for 3 hours, filtered,
It was washed with water and dried at 120 ° C. to obtain the target cobalt-containing ferromagnetic iron oxide powder (C-2).

The coercive force Hc of each of the samples A to C-2 was measured by the usual method, and the specific surface area of each of the samples A to C was measured by the BET method. In addition, the Fe ⁺⁺ content (% by weight) in the total Fe was measured by the potassium dichromate titration method.

Further, with respect to the samples A to C-2, the formulations were adjusted according to the following blending ratios, and kneaded with a ball mill to produce magnetic paints.

(1) Cobalt-containing ferromagnetic iron oxide powder 100.0 parts by weight (2) Additive 3.8 〃 (3) Vinyl chloride-vinyl acetate copolymer 8.0 〃 (4) Polyurethane resin 35.5 〃 (5) Mixed solvent (toluene / MEK = 1 / 1) 216.2 〃 (6) Cyclohexanone 36.0 〃 Next, each magnetic paint was applied to a polyester film by a usual method, oriented, and dried to prepare a magnetic tape having a magnetic coating film of about 9µ. Tables 1 to 3 show the results of measuring the coercive force (Hc), the squareness ratio (Br / Bm), the orientation (OR), and the reversal magnetic field distribution (SFD) of each tape by a usual method.

The change with time (ΔHc) of the coercive force was calculated by the following formula, and these results are shown in Table 3.

Coercive force change with time (ΔHc) = [Coercive force (Hc) after left at 60 ° C and 80% humidity for 14 days]-[Initial coercive force (Hc)] In order to investigate the reactivity between the fatty acid and the magnetic powder, the fatty acid (myristic acid: C ₁₄ ) adsorption amount: fatty acid adsorption property was measured by the following method, and the results are shown in Table 3.

10g of magnetic powder, 30ml of solvent (MEK: toluene = 1: 1) and 4% of myristic acid (based on the weight of magnetic powder) were mixed together to obtain a red devil disperser (Red and the fatty acid and magnetic powder used in the preparation of the magnetic paint). In order to investigate the reactivity of the above, the adsorption amount of fatty acid (myristic acid: C ₁₄ ): fatty acid adsorption property was measured by the following method, and the results are shown in Table 3.

Magnetic powder 10g, solvent (MEK: toluene = 1: 1) 30ml and myristic acid 4% (magnetic powder weight basis) were mixed, shaken with Red Devil Disperser (Red Devil Shaker) for 15 minutes, and then centrifuged. The supernatant was collected by a machine and quantitatively analyzed. From the added myristic acid amount and the quantitative analysis amount, the adsorption amount is calculated by the following formula.

[Effects of the Invention] As can be seen from Tables 1 to 3, it is understood that the cobalt-containing ferromagnetic iron oxide powder obtained by the present invention has excellent magnetic properties. Further, according to the present invention, it is possible to manufacture a product having a specific surface area of 35 m ² / g or more, a coercive force of 700 Oe or more, and excellent dispersibility and coercive force distribution. Further, according to the present invention, in addition to these excellent magnetic properties, desirable stability over time and fatty acid adsorption properties (Table 3
It is possible to provide a cobalt-containing ferromagnetic iron oxide powder that also has a better fatty acid adsorption property as the C ₁₄ adsorption amount decreases.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuro Suzuki 1 Ishihara-cho, Yokkaichi-shi, Mie Ishihara Sangyo Co., Ltd. Yokkaichi factory (72) Inventor Masahide Miyashita 1-site, Ishihara-cho, Yokkaichi-shi, Mie Ishihara Sangyo Co., Ltd. Yokkaichi Plant (72) Inventor Tsunetaka Hatanaka 1 Ishihara-cho, Yokkaichi-shi, Mie Ishihara Industrial Co., Ltd. Yokkaichi Plant Inspector Kenshi Yoneda (56) Reference JP-A-59-107924 (JP, A)

Claims (15)

[Claims] 1. A magnetic iron oxide powder is used as a nuclear crystal, and a coating layer composed of a layer made of a compound of iron and cobalt, a layer made of an iron compound and / or a layer made of a cobalt compound is formed on the nuclear crystal. A cobalt-containing ferromagnet, characterized in that it has a partially overlapped adhered portion at a boundary between a layer made of a compound of iron and cobalt and a layer made of an iron compound and / or a layer made of a cobalt compound. Iron oxide powder. 2. The cobalt-containing ferromagnetic iron oxide powder according to claim 1, wherein the inner layer and the outer layer of the coating layer are a layer made of an iron compound and a layer made of a compound of iron and cobalt, respectively. 3. The cobalt-containing ferromagnetic iron oxide powder according to claim 1, wherein the inner layer and the outer layer of the coating layer are a layer made of a compound of iron and cobalt and a layer made of a cobalt compound, respectively. 4. An inner layer, an intermediate layer and an outer layer of the coating layer are a layer composed of an iron compound, a layer composed of a compound of iron and cobalt and a layer composed of a cobalt compound, respectively, and a boundary between the inner layer and the intermediate layer and 2. The cobalt-containing ferromagnetic iron oxide powder according to claim 1, wherein one or both of the boundary between the intermediate layer and the outer layer is a partially overlapped adhered portion. 5. The method according to claim 1, further comprising at least one additional coating layer of an iron compound layer, a cobalt compound layer and an iron / cobalt compound layer on the outer layer of the coating layer. Cobalt-containing ferromagnetic iron oxide powder. 6. Silicon, aluminum on the outer layer of the coating layer,
Claim 1 having a layer consisting of at least one compound selected from the group of calcium, titanium, vanadium, manganese, nickel, zinc and phosphorus compounds.
The cobalt-containing ferromagnetic iron oxide powder according to the item. 7. The specific surface area according to the BET method is 35 m ² / g or more, and the coercive force is 700 O _e or more.
The cobalt-containing ferromagnetic iron oxide powder according to the item. 8. A modified deposition method comprising the step of depositing at least ferrous hydroxide and cobalt hydroxide using a magnetic iron oxide powder as a nuclei crystal, wherein the first hydroxide hydroxide is used as a part of the deposition step. A method for producing a cobalt-containing ferromagnetic iron oxide powder, characterized in that a partial superposition deposition treatment is carried out by simultaneously depositing iron and cobalt hydroxide. 9. The method according to claim 8, wherein the depositing treatment is carried out by adding a cobalt salt in parallel with the addition of the ferrous iron salt to an alkaline suspension containing magnetic iron oxide powder as nuclei. A method for producing a cobalt-containing ferromagnetic iron oxide powder, which is a process of adding as an additive. 10. The method according to claim 8, wherein the deposition treatment gradually reduces the amount of ferrous salt added to an alkaline suspension containing magnetic iron oxide powder as nuclei. A method for producing a cobalt-containing ferromagnetic iron oxide powder, which is a process of starting the addition of the cobalt salt and gradually increasing the addition amount of the cobalt salt in accordance with the gradually decreasing amount. 11. A cobalt-containing material according to claim 8, wherein magnetic iron oxide powder is used as a nuclei crystal, and ferrous hydroxide and cobalt hydroxide are simultaneously deposited, and then cobalt hydroxide is deposited. Method for producing ferromagnetic iron oxide powder. 12. The method according to claim 8, wherein the magnetic iron oxide powder is used as a nuclide, first ferrous hydroxide is deposited, and then ferrous hydroxide and cobalt hydroxide are simultaneously deposited. Method for producing cobalt-containing ferromagnetic iron oxide powder. 13. The method according to claim 8, wherein the ferrous salt is added to the alkaline suspension containing the magnetic iron oxide powder as nuclei, and then the cobalt salt is added. A method for producing a cobalt-containing ferromagnetic iron oxide powder, which is a process of adding in parallel and thereafter stopping the addition of the ferrous salt and adding only the cobalt salt. 14. The method for producing a cobalt-containing ferromagnetic iron oxide powder according to claim 8, wherein the deposition temperature is 30 ° C. or lower. 15. The method according to claim 8, wherein the ferrous salt is added to an alkaline suspension containing magnetic iron oxide powder as nuclei while maintaining the deposition and aging temperature of 30 ° C. or lower. A method for producing a cobalt-containing ferromagnetic iron oxide powder, which is a process of adding a cobalt salt and a ferrous salt in parallel, and further adding a cobalt salt to the alkaline suspension.