JPH0611651B2 - Method for producing cobalt-containing ferromagnetic iron oxide - Google Patents

Description

The present invention relates to a method for producing a cobalt-containing ferromagnetic iron oxide having excellent magnetic properties, which is useful as a material for a magnetic recording medium.

[Conventional technology]

Cobalt-containing ferromagnetic iron oxide has a high coercive force, and the magnetic tape produced using it can record at high density and has excellent sensitivity in the high frequency region, and has been actively used in fields such as audio and video in recent years. ing. In order to obtain a cobalt-containing ferromagnetic iron oxide with high coercive force, many methods have been proposed, for example, (1) γ-Fe ₂ O ₃ powder in a liquid containing a cobalt salt, a specific OH group concentration, Method of treatment in high temperature non-oxidizing atmosphere (Japanese Patent Publication No. Sho 52-24238), (2) Method of coating magnetic iron oxide with cobalt compound and then heat treatment at temperature of about 400 ° C (Japanese Examined Patent Publication No. Sho 48-10994) , (3) 120 magnetic iron oxide powder in an alkaline solution containing cobalt salt
Method of hydrothermal reaction treatment at a temperature of ~ 200 ° C (Japanese Patent Publication No. 48-4)
4040), (4) A method in which magnetic iron oxide powder is treated in an alkaline solution containing a cobalt salt at a temperature as high as possible below the boiling point, washed with water, filtered, and then dispersed in water without heating and heated. (Japanese Patent Laid-Open No. 55-56016).

[Problems to be solved by the invention]

However, in the method (1), the epitaxial reaction proceeds rapidly, the coercive force distribution is widened, and in the method (2), cobalt ions are diffused inside the magnetic iron oxide,
Satisfactory in terms of thermal properties and stability over time, etc., were not obtained, and in the methods of (3) and (4), the surface of the magnetic iron oxide was partially dissolved by the alkali, and the surface was roughened and further epitaxial There are drawbacks such that the reaction proceeds rapidly and the coercive force distribution becomes wider.

As described above, the conventional technique has a problem that other magnetic properties cannot be satisfied even if a high coercive force is obtained. In recent years, as audio and video tapes have become more sophisticated, it is required to have high coercive force as well as excellent in other magnetic properties. Cobalt that balances both of them and satisfies them at the same time The inclusion of ferromagnetic iron oxide was strongly desired.

[Means for solving problems]

As a method for solving the problems of the prior art, the present inventors have disclosed in Japanese Patent Application No. 61-112271 and Japanese Patent Application No. 62-118686 a magnetic iron oxide powder in an aqueous medium and a cobalt salt and The surface of the powder particles is treated with a metal salt containing a ferrous salt and an alkali to deposit a metal compound containing cobalt and ferrous iron (hereinafter, the slurry obtained by this depositing treatment is
After deposition treatment called slurry), then this powder (hereinafter,
The magnetic iron oxide (cobalt such as cobalt) is filtered off, washed with water, and an acidic substance is added to obtain a dispersion slurry having a pH of 6.5 to 9.5.
We have proposed a method of heat treatment in an aqueous medium. According to this method, a useful cobalt-containing ferromagnetic iron oxide (I) having a high coercive force and an excellent saturation magnetization, coercive force distribution, thermal characteristics, stability over time and other magnetic characteristics can be obtained. When the wet cake obtained by filtering and washing the slurry after the deposition treatment is repulped in an aqueous medium liquid, this slurry is
The pH is usually 9.7 to 11.5 even if it is sufficiently washed with water.
Indicates. Although the reason for this is not clear, the present inventors presume that the OH group on the surface of the magnetic iron oxide particles coated with cobalt or the like has an effect.

The present inventors further filed Japanese Patent Application No. 62-333625 (application for “method for producing cobalt-containing ferromagnetic iron oxide” made by the same applicant as December 28, 1987). We proposed a method that eliminates the steps of filtering and washing.
This method is, for example, a slurry after the deposition treatment (b) a concentrated slurry obtained by removing the mother liquor from the slurry after the deposition treatment by a sedimentation method (c) a cleaning slurry obtained by further removing the mother liquor by a decantation washing method using an aqueous medium liquid, etc. Added
The heat treatment is performed by adjusting the pH to a constant value. According to this method, the above-mentioned effects described in Japanese Patent Application No. 61-112271 and Japanese Patent Application No. 62-118686 can be obtained, the quality is more stable, and there is less variation in magnetic characteristics between manufacturing lots. Cobalt-containing ferromagnetic iron (II) oxide having an excellent saturation magnetization (σs) can be industrially advantageously manufactured.

As a result of continued research, the inventors of the present invention have adjusted the pH of an aqueous medium liquid-dispersed slurry of magnetic iron oxide to be deposited such as cobalt to a specific value and heat-treated it to produce a metal compound containing cobalt and ferrous iron. Cobalt-containing ferromagnetic iron oxide (III) of superior quality by further adhering a certain compound to the magnetic iron oxide powder (hereinafter referred to as heat-treated cobalt or other magnetic iron oxide) deposited by It has been found that the present invention can be produced and the present invention has been provided.

That is, the present invention adjusts the pH of the aqueous magnetic medium / liquid dispersion slurry of the magnetic iron oxide to which cobalt or the like is deposited to be 6.5 to 9.5 and heat-treats it to produce the heat-treated cobalt or other magnetic iron oxide to be produced. On the other hand, the method for producing cobalt-containing ferromagnetic iron (III) oxide is characterized by further depositing at least one compound selected from the group consisting of silicon, aluminum, titanium, vanadium and manganese compounds.

Although a series of treatments of the present invention partially include conventional treatments, magnetic iron oxides deposited on cobalt and the like were produced, and subsequently the pH of the aqueous medium-dispersed slurry was also adjusted. It is a treatment that is unique in that it is entirely heat-treated, and the obtained magnetic iron oxide such as cobalt is further coated with a certain compound (hereinafter referred to as surface treatment).

Since the present invention is configured as described above, pH adjustment and heat treatment are particularly performed, and the effect of the surface treatment is remarkable as compared with the case where the step is not performed. That is, the degree of improvement in stability with time, fatty acid adsorption characteristics, and squareness, orientation, and reversal magnetic field distribution as tape characteristics is large. As will be described later, it can be said that the manifestation of such an effect is based on the synergistic action of the pH adjustment and the heat treatment and the surface treatment.

In the present invention, the magnetic iron oxide used is γ-Fe ₂
There is a needle-shaped magnetic iron oxide powder such as a beltride compound obtained by partially reducing O ₃ , Fe ₃ O ₄ , and γ-Fe ₂ O ₃ . Examples of the cobalt salt used for producing the coated magnetic iron oxide such as cobalt include cobalt chloride, cobalt sulfate, cobalt nitrate and cobalt acetate, and examples of the ferrous salt include ferrous sulfate. Ferrous chloride, ferrous nitrate,
Examples include ferrous carbonate. Further, as the other metal salt used as necessary, manganese salt, zinc salt, chromium salt, nickel salt and the like are appropriately selected. As the alkali, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia or the like is appropriately selected.

Various methods can be used as a method for depositing the cobalt salt and the ferrous salt. For example, there are various methods as described below depending on the order of adding the cobalt salt, the ferrous salt and the alkali to the slurry in which the magnetic iron oxide powder is dispersed.

(1) A method of adding an aqueous alkali solution after adding an aqueous solution containing a cobalt salt and a ferrous salt.

(2) After adding the alkaline aqueous solution, the cobalt salt and the first
A method of adding an aqueous solution containing an iron salt.

(3) A method of adding a cobalt salt aqueous solution to precipitate cobalt hydroxide with an alkali, and then adding a ferrous salt aqueous solution.

(4) A method of adding an aqueous alkaline solution, then an aqueous cobalt salt solution, and further adding an aqueous ferrous salt solution.

(5) A method of adding an aqueous solution of ferrous salt, precipitating ferrous hydroxide with an alkali, and then adding an aqueous solution of cobalt salt.

(6) A method of adding an aqueous solution of ferrous salt and then an aqueous solution of cobalt salt after adding the aqueous alkaline solution.

In addition, an appropriate method such as simultaneously or partially treating all or part of the other metal salt together with the cobalt salt and the ferrous iron salt can be adopted.

This deposition treatment is preferably performed in a non-oxidizing atmosphere, that is, in an atmosphere in which cobalt, ferrous iron, and other metal atoms are not substantially oxidized. For example, bubbling an inert gas in the reaction solution, It is advisable to replace the air in the reaction vessel with an inert gas for the reaction. This treatment is usually performed at room temperature to 100 ° C., preferably at room temperature to 50 ° C. If this temperature is too low, the treatment time becomes long, while if it is too high, ferrous iron diffuses inside the magnetic powder or the coercive force is increased. It is not desirable because the distribution etc. becomes wider,
The OH group concentration in the system is usually 0.01 to 3 mol / day, preferably 0.05 to 1 mol / day, and if the concentration is too low, the desired coercive force cannot be obtained, while if it is too high, the OH group concentration is once The cobalt compound is partially dissolved, which is not desirable. Further, the deposition treatment time is usually 0.1 to 10 hours. The amount of cobalt deposited is 0.5 to 3 based on the weight of magnetic iron oxide.
0%, preferably 1-10%, 1 for ferrous iron
-30%, preferably 2-20%, otherwise 0-
It is about 10%.

Next, the pH of the slurry after the adhesion treatment is adjusted.
One aspect of the pH adjustment in the present invention is to filter the slurry after the deposition treatment by a usual method, wash with water, and disperse the wet cake in an acidic substance-containing aqueous medium, or the wet cake in an aqueous medium. An acidic substance is added to the slurry dispersed in A to adjust the pH value of the slurry to a desired value, and then heat treatment is performed.

Another aspect of pH adjustment in the present invention is as follows. That is, in some cases, an acidic substance is directly added to the slurry after the adhesion treatment to adjust the pH to a constant value. After the deposition treatment, the free alkali concentration of the slurry is, for example, 1 to 3 mol /
When the solid content is as low as 100 g / or less, it is not preferable because the amount of acidic substance required for pH adjustment becomes too large or the amount of acidic substance liquid becomes too large. Therefore, it is recommended to adjust the pH after separating the mother liquor by the sedimentation method. Further, the slurry after separation of the mother liquor may be washed with an aqueous medium by decantation to further remove the mother liquor, and then the pH may be adjusted. As the aqueous medium, industrial water, pure water (treated with an ion exchange resin), or those obtained by dissolving buffer salts such as sodium sulfate, potassium sulfate, ammonium sulfate, ammonium chloride, etc. are usually used. It should be noted that it is desirable to use industrial water, pure water or the like which has been previously bubbled with an inert gas to suppress its oxidizing action. Further, in the above case, the separation method is used as the mother liquor separation means, and a separation method using a pressure filter such as a filter press, a suction filter such as an Oliver filter or a Muer filter, or a centrifugal separator is adopted. Good. When such a sorting method is adopted,
The pH is adjusted after dispersing the wet cake in the aqueous medium. In this case, it is preferable to select a model in which the wet cake is not exposed to the air as much as possible, and it is also preferable to take measures to suppress the oxidation of the wet cake as much as possible during repulping.

Desirable of these operations is that the deposition treatment is performed under an appropriate free alkali concentration and solid content,
The same as when the acidic substance was added to the slurry after the deposition treatment to adjust the pH, or the slurry in which the mother liquor was separated from the slurry after the deposition treatment by the sedimentation method or the slurry which was washed with the aqueous medium by the gradient method. It was when the pH was adjusted. In these cases, since the adhered magnetic iron oxide such as cobalt does not come into contact with the atmosphere, the adherend, in particular, the oxidation of the ferrous iron is suppressed, and the cleaning unevenness observed when washing with a normal filter can be avoided. In addition, it is possible to avoid adverse effects on the magnetic properties of the product due to excessive washing. Therefore, the product obtained through such a process produces a cobalt-containing ferromagnetic iron oxide (II) with stable quality, less variation in magnetic characteristics between production lots, and more excellent saturation magnetization. be able to. Further, according to such a process, the manufacturing process can be simplified and the facility capacity can be improved, so that an industrially advantageous operation can be performed.

Still another aspect of pH adjustment in the present invention is as follows. For example, a) after the deposition treatment, the mother liquor is removed from the slurry as described above to form a slurry of a dispersion of magnetic iron oxide, such as cobalt, deposited in an aqueous medium, and cation exchange resin coarse particles are added to this slurry to perform decationization treatment. To adjust the pH to the desired value, then fractionate the cation exchange resin coarse particles,
(2) Similarly, from the slurry after the deposition treatment, the above aqueous medium liquid dispersion slurry is prepared, and the pH of the slurry is adjusted to a desired value by using a cation exchange resin membrane. To remove the mother liquor, and wash the resulting wet cake or concentrated slurry with an acidic substance-containing aqueous medium, or an aqueous medium and an acidic substance-containing aqueous medium.
The pH can be adjusted to a desired value. Incidentally, the pH adjusting means is not limited to the above-mentioned one, and a wide range of suitable means can be adopted within the range meeting the object of the present invention.

The above pH adjustment is carried out so that the value thereof is usually 6.5 to 9.5, preferably 7.0 to 9.5, and more preferably 7.0 to 8.5. When the pH is less than 6.5, the deposited cobalt compound is eluted, which is not preferable, and the pH is 9.5.
If it exceeds, the desired effect cannot be obtained. The acidic substance used for pH adjustment is not particularly limited, but for example, inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid, boric acid, formic acid, acetic acid, oxalic acid, tartaric acid, benzoic acid, etc. Examples thereof include carboxylic acids, sulfonic acids such as methanesulfonic acid and benzenesulfonic acid, sulfinic acids, and various acidic salts. Also, other commonly used neutralizing agents may be used. As the cation exchange resin used for pH adjustment, those generally used in industry can be widely adopted.

Even if only pH adjustment in the present invention, the saturation magnetization and aging stability of the product are improved as compared with the case where pH adjustment is not performed, but in particular to sufficiently improve the change with time of the coercive force. Requires a heat treatment to be performed subsequently. That is, by performing the heat treatment, the saturation magnetization amount becomes higher as the temperature of the heat treatment increases so that the degree of improvement effect by the pH adjustment slides. Similarly, the change with time of the coercive force becomes noticeable when the heat treatment temperature is 80 ° C. or higher because the improvement effect by the pH adjustment is further amplified. However, when the treatment temperature exceeds 160 ° C., changes in the saturation magnetization and coercive force with time tend to worsen, and the effect of pH adjustment diminishes. In this way, the processing temperature is 80 ℃ -160 ℃
Within the range, the improvement of the coercive force over time becomes remarkable, and the coercive force distribution is improved because the presence of cobalt is more maintained in the surface layer and the ferrous iron near this surface is contained inside the magnetic powder. It is presumed that it is fixed near the surface without diffusion. Whereas the technology so far focuses only on improving the coercive force by heat treatment, the present invention is not intended to improve the coercive force more than necessary, and the pH adjustment-heat treatment is performed. By applying it, the holding power tends to be rather lower than that of the comparison. If the coercive force is not increased more than necessary, it is considered that the improvement of the saturation magnetization amount leads to various characteristics such as the improvement of the coercive force over time and the improvement of the coercive force distribution. Considering this, it can be seen that the pH adjustment-heat treatment of the present invention is a proprietary treatment. In the present invention, the saturation magnetization tends to be slightly decreased by the subsequent surface treatment, so it is effective to increase the saturation magnetization in pH adjustment and heat treatment.

As described above, the heat treatment temperature is usually 160 ° C. or lower, preferably 80 ° C. to 160 ° C., more preferably 100 ° C.
155 ° C., more preferably above boiling point to 150 ° C., most preferably 110 ° C. to 145 ° C., treatment time is usually 1
~ 10 hours. In addition, since it becomes a pressurized system at a boiling point or higher and the pressure is usually about 1.1 to 10 atm, it is necessary to perform heat treatment in a closed container, for example, an autoclave. Further, it is desirable that this heat treatment be performed in a non-oxidizing atmosphere.

If the heat-treated cobalt-based magnetic iron oxide slurry produced by the above heat treatment is normally filtered, washed with water and dried, the above-mentioned Japanese Patent Application No. 61-112271, Japanese Patent Application No. 62-118686 and Japanese Patent Application No.
Cobalt-containing ferromagnetic iron oxides (I), (II) or other cobalt-containing ferromagnetic iron oxides, which is the object of No. 62-333625, can be obtained. These are generally
It is excellent in coercive force distribution, stability over time, thermal characteristics, fatty acid adsorption characteristics, and the like, and when used in a tape, the squareness ratio and reversal magnetic field distribution are also improved.

In addition, according to the present invention, the above cobalt-containing ferromagnetic iron oxide is obtained by subjecting the heat-treated cobalt-containing magnetic iron oxide to a surface treatment with at least one compound selected from the group consisting of silicon, aluminum, titanium, vanadium and manganese compounds. In addition to the excellent magnetic properties of iron (I) oxide, (II), etc., it is possible to produce a product having further excellent stability over time, fatty acid adsorption properties, and various magnetic properties as tape properties.

These surface treatment compounds include hydroxides, hydrated oxides, hydrated oxyhydroxides, oxides, silicates, phosphates and others. Further, as a surface treatment agent used for precipitating these compounds, for example, for sodium, sodium or potassium salt of orthosilicic acid or metasilicic acid, and for aluminum, sodium or potassium aluminate salt, aluminum sulfate, aluminum chloride, etc. For titanium, titanium sulfate, titanium chloride, etc.,
Examples of vanadium include vanadyl sulfate and sodium vanadate, and examples of manganese include sulfate, nitrate and chloride.

As the acidic or alkaline substance that neutralizes the surface treatment agent and precipitates the surface treatment 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.

Inorganic compounds are given as examples of the surface treatment agent and the neutralizing agent, but of course, suitable organic compounds can be used. Examples of the neutralizing agent include tartaric acid, benzoic acid, metal sulfonic acid, sulfinic acid and the like.

It is advantageous that the surface treatment of the above-described compound on the heat-treated cobalt-based magnetic iron oxide is directly performed on the heat-treated cobalt-based magnetic iron oxide-dispersed slurry obtained through the heat treatment step of the present invention. However, it is of course possible to separate the cake containing magnetic iron oxide to be deposited such as heat-treated cobalt from this dispersion slurry, wash it if necessary, and then repulp it in an aqueous medium liquid to perform this.
A surface treating agent or a surface treating agent and a neutralizing agent are added to these slurries to precipitate and deposit the above surface treating compound. The surface-treating agent (in the case of two or more kinds) or the surface-treating agent and the neutralizing agent can be added in any order, all at once, or in parallel over a certain period of time. Appropriate addition means can be employed at any time in order to produce a coating compound having desired properties.

The surface-treating agent and the neutralizing agent can be added after being dissolved or dispersed in water and / or other solvent or added as they are, but industrially it is preferable to add them in liquid form. If an alkaline or acidic surface treatment agent is selected, the addition of a neutralizing agent is unnecessary or the amount thereof is reduced. According to the above-mentioned adding means, the surface-treating compound is precipitated in the aqueous medium in all cases, but the surface-treating compound may be preliminarily precipitated outside the system and the dispersion may be added to the slurry.

In this way, the treatment temperature for precipitating the surface treatment compound and applying it to the magnetic iron oxide to be adhered such as heat-treated cobalt is
Usually, it is room temperature to boiling point, preferably room temperature to 90 ° C. If necessary, it is aged for several tens of minutes to a few hours, but it is generally preferable that this aging is carried out under stirring for 15 minutes to 5 hours at the treatment temperature at the time of deposition and deposition.

The slurry in which the surface treatment compound has been applied and matured is usually 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 magnetic iron oxide coated with heat-treated cobalt or the like, which has been surface-treated as described above, is less likely to be affected by the atmosphere as compared with those which are not surface-treated, so that it is easy to handle and suitable for industrial operation.

The treatment amount of the surface-treated compound for heat-deposited magnetic iron oxide such as cobalt can not be said unequivocally due to the type of the compound, difference in surface treatment means, etc. As an atom contained in the treatment compound, 0.01 to 3%, usually 0.02 to 2
%. If the amount of the surface treatment compound is too small, the desired stability over time, the improvement of the fatty acid adsorption property, etc. is not sufficiently brought, or if it is too large, the coercive force decreases, the saturation magnetization decreases, etc. The magnetic properties may be impaired. The fatty acid adsorption property is represented by the C ₁₄ adsorption amount shown in the table, and generally, the smaller this value, the better the property.

Desirable as the surface treatment compound in the present invention are, for example, aluminum, water-soluble acidic salts such as manganese neutralized with alkali, alkali silicates neutralized with water-soluble acidic salts such as aluminum and manganese. is there. Further, industrially desirable, a certain surface treatment method is such that the pH value of the slurry to be used is basically around neutral, so that the surface treatment agent aqueous solution and the acidic or alkaline substance aqueous solution necessary for neutralization are kept constant. This is a method of performing parallel addition over a period of time, or when the slurry is alkaline or acidic, adding an acidic or alkaline aqueous surface treatment agent solution over a certain period of time, and then appropriately aging.

Here, as the surface treatment method, a neutralization method which is usually used has been described as an example, but of course, a heating hydrolysis method, an immersion evaporation method and the like can be adopted. The heating hydrolysis method is, for example, a method of heating a deposited magnetic iron oxide dispersion slurry such as heat-treated cobalt in which a surface treatment agent is dissolved, as necessary, and precipitating a surface treatment compound by hydrolysis. Further, the immersion evaporation method, for example, the magnetic iron oxide adhered such as heat-treated cobalt is fractionated from the slurry, and this is dispersed and immersed in water and / or an organic solvent in which the surface treatment agent or the surface treatment compound is dissolved or dispersed, respectively. Then, the immersion liquid is evaporated.

Although the method of subjecting the magnetic iron oxide to be deposited such as heat-treated cobalt to the surface treatment has been described above, it is needless to say that the magnetic iron oxide to be deposited such as heat-treated cobalt can be dried.
However, in the latter case, the number of industrial processes is generally increased and the effect of improving the magnetic properties is inferior to the former, so the former method is usually recommended.

〔Example〕

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

Example 1 100 g of γ-Fe ₂ O ₃ powder (coercive force Hc405 Oe, average major axis particle size of about 0.4 μ, axial ratio of about 8) was dispersed in water 1 to form a slurry. While blowing nitrogen gas into this slurry, 70 ml of 0.85 mol / cobalt sulfate aqueous solution at room temperature and 168 ml of 0.90 mol / ferrous sulfate aqueous solution at room temperature.
And 184 ml of a 10 mol / aqueous sodium hydroxide solution were added, and the mixture was stirred for 5 hours to subject γ-Fe ₂ O ₃ to metamorphic deposition. The resulting slurry is filtered and washed with water, the obtained wet cake is dispersed in water, diluted sulfuric acid is added with stirring to make a slurry having a pH of 8.5, and the slurry is put into an autoclave and the inside is filled with nitrogen gas. After the replacement, it was sealed and heat-treated at 90 ° C. for 3 hours. After the heat treatment, the pH of the slurry was adjusted to 10 by adding a dilute aqueous solution of sodium hydroxide while stirring the slurry at 30 ° C. under a nitrogen gas atmosphere. About the obtained slurry, first, an aqueous sodium orthosilicate solution (20 g / as Si) was added, and then sulfuric acid was added so that 0.25% of Si and 0.024% of Al were deposited on the weight basis with respect to iron oxide. Aluminum aqueous solution (1.6g as Al
/) Was added. After the addition is complete, stir for 1 hour, filter,
After washing with water, it was dried at 120 ° C. in a nitrogen atmosphere to obtain the desired cobalt-containing ferromagnetic iron oxide (A).

Example 2 In Example 1, the target cobalt-containing ferromagnetic iron oxide (B) was obtained in the same manner as in Example 1 except that the heat treatment temperature was 110 ° C.

Example 3 The target cobalt-containing ferromagnetic iron oxide (C) was obtained in the same manner as in Example 1 except that the heat treatment temperature was 130 ° C.

Comparative Example 1 The slurry subjected to the metamorphic deposition treatment was filtered and washed in the same manner as in Example 1, and the obtained wet cake was dispersed in water and then filtered, washed with water and nitrogen without any treatment. Cobalt-containing ferromagnetic iron oxide (D) was obtained by drying at 120 ° C. in a gas atmosphere.

Comparative Example 2 Cobalt-containing ferromagnetic iron oxide (E) was obtained in the same manner as in Example 1, except that pH adjustment with dilute sulfuric acid and heat treatment were not performed.

Comparative Example 3 In the same manner as in Example 1 except that the heat treatment temperature was set to 110 ° C. and the treatment with the sodium orthosilicate aqueous solution and the aluminum sulfate aqueous solution was not performed, the cobalt-containing ferromagnetic oxidation was performed. Iron (F) was obtained.

Example 4 Except that in Example 1, the deposition amounts of the sodium orthosilicate aqueous solution and the aluminum sulfate aqueous solution were changed to 0.125% for Si and 0.012% for Al, respectively, based on the weight of iron oxide. In the same manner as in Example 1, the desired cobalt-containing ferromagnetic iron oxide (G) was obtained.

Example 5 In Example 1, the heat treatment temperature was set to 110 ° C., and the deposition amounts of the sodium orthosilicate aqueous solution and the aluminum sulfate aqueous solution were 0.125% as Si and 0 as Al, respectively, based on the weight of iron oxide. The same as in Example 1 except that the content was changed to 0.012%,
The target cobalt-containing ferromagnetic iron oxide (H) was obtained.

Example 6 In Example 1, the heat treatment temperature was set to 130 ° C., and the deposition amounts of the sodium orthosilicate aqueous solution and the aluminum sulfate aqueous solution were 0.125% as Si and 0 as Al, respectively, based on the weight of iron oxide. The same as in the case of Example 1 except that it was changed to 0.012%,
The target cobalt-containing ferromagnetic iron oxide (I) was obtained.

Comparative Example 4 In Example 1, the pH adjustment with dilute sulfuric acid and the heat treatment were not performed. The treatment amounts of the sodium orthosilicate aqueous solution and the aluminum sulfate aqueous solution were 0.125% as Si and 0.1% as Al, respectively, based on the weight of iron oxide. 0.0
Cobalt-containing ferromagnetic iron oxide (J) was obtained in the same manner as in Example 1 except that the content was changed to 12%.

Example 7 In the same manner as in Example 1, the slurry obtained by the metamorphic deposition treatment was filtered and washed with water, the separated wet cake was dispersed in water, and diluted sulfuric acid was added with stirring to pH = 8. 5 slurries. This was placed in an autoclave, the inside of which was replaced with nitrogen gas, which was then sealed and heat-treated at 110 ° C. for 3 hours. After the heat treatment, the pH of the slurry was adjusted to 10 by adding a dilute aqueous solution of sodium hydroxide while stirring the slurry at 30 ° C. under a nitrogen gas atmosphere. The obtained slurry was treated with an aluminum sulfate aqueous solution (Al.
6 g /) was added, and a dilute aqueous sodium hydroxide solution was added in parallel from the middle of the addition so that the pH was maintained at 8.5. After the addition was completed, the mixture was stirred for 1 hour, filtered, washed with water, and dried at 120 ° C. in a nitrogen gas atmosphere to obtain the target cobalt-containing ferromagnetic iron oxide (K).

Comparative Example 5 Cobalt-containing ferromagnetic iron oxide (L) was obtained in the same manner as in Example 7, except that pH adjustment with dilute sulfuric acid and heat treatment were not performed.

Example 8 In Example 7, instead of the aluminum sulfate aqueous solution,
The target cobalt-containing ferromagnetism was obtained in the same manner as in Example 7 except that an aqueous solution of manganese sulfate (3.6 g / Mn as Mn) was added and 0.125% as Mn was deposited on the basis of iron oxide. Iron oxide (M) was obtained.

Comparative Example 6 The desired cobalt-containing ferromagnetic iron oxide (N) was obtained in the same manner as in Example 8 except that pH adjustment with dilute sulfuric acid and heat treatment were not performed.

Example 9 In Example 7, a sodium orthosilicate aqueous solution (20 g / as Si) and dilute sulfuric acid were used instead of the aluminum sulfate aqueous solution and the dilute sodium hydroxide aqueous solution, respectively, and 0.125% of Si was added based on the weight of iron oxide. The target cobalt-containing ferromagnetic iron oxide (O) was obtained in the same manner as in Example 7 except that the deposition treatment was performed.

Example 10 In Example 7, a vanadyl sulfate aqueous solution (1.25 g / V as V) was used instead of the aluminum sulfate aqueous solution.
The target cobalt-containing ferromagnetic iron oxide (P) was obtained in the same manner as in Example 7, except that 0.125% of V based on the weight of iron oxide was applied.

Example 11 In Example 7, an aqueous solution of titanium tetrachloride (1.25 g / as Ti) was used instead of the aqueous solution of aluminum sulfate.
The target cobalt-containing ferromagnetic iron oxide (Q) was obtained in the same manner as in Example 7 except that 0.125% of Ti was coated on the weight basis of iron oxide.

Example 12 For a slurry adjusted to pH 10 in the same manner as in Example 7, 0.125 as Si based on the weight of iron oxide.
% Orthosilicate aqueous solution (20 g / Si as Si) was added so that the adhesion treatment would be 8%, and then the pH was 8.
Manganese sulphate solution (Mn 3.6g /
) Was added (0.124% as Mn based on the weight of iron oxide). After the addition was completed, the mixture was stirred for 1 hour, filtered, washed with water, and dried at 120 ° C. in a nitrogen gas atmosphere to obtain the desired cobalt-containing ferromagnetic iron oxide (R).

With respect to the samples (A) to (R), the coercive force (Hc) and the saturation magnetization (σs) were measured by a usual method, and
The change with time (ΔHc) of the holding force was calculated by the following calculation formula, and these results are shown in the table.

Change with time of coercive force (ΔHc) = [Coercive force after standing for 14 days at a temperature of 60 ° C. and 80% (Hc)]-[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 the table.

Magnetic powder 10g and solvent (MEK: toluene = 1: 1) 3
Mix with 0 ml and myristic acid 4% (based on the weight of magnetic powder) and mix with a Red Devil Shaker for 15
After shaking for a minute, the supernatant was separated by centrifugation and quantitatively analyzed. From the added amount of myristic acid and the quantitative analysis amount, the C ₁₄ adsorption amount is calculated by the following formula.

In addition, for each sample, a compound was prepared according to the following compounding ratio and dispersed by a ball mill to produce a magnetic coating material.

(1) Cobalt-containing ferromagnetic iron oxide 100.0 parts by weight (2) Surfactant 3.8 〃 (3) Vinyl chloride vinyl acetate copolymer resin 8.0 〃 (4) Polyurethane resin 35.5 〃 (5 ) Methyl ethyl ketone 108.1 〃 (6) Toluene 108.1 〃 (7) Cyclohexanone 36.0 〃 Then, apply each magnetic paint by the usual method of polyester film, orient and then dry it to a magnetic film of about 9 μm thick. A magnetic tape having a coating film was prepared. The coercive force (Hc) and squareness ratio (Br
/ Bm), orientation (OR) and switching field distribution (SFD) were measured. The results are shown in the table.

As shown in Tables 1 to 3, each of the examples is significantly improved in stability over time (ΔHc) and fatty acid adsorption property (C ₁₄ adsorption amount) as compared with each of the comparative examples.
In addition, the tape characteristics such as squareness ratio (Br / Bm) and orientation (O
R) and the switching field distribution (SFD) are also excellent. Further, according to the present invention, the coercive force (Hc) and the saturation magnetization amount (σs)
Also has a desirable value.

According to the present invention, the amount of surface treatment compound can be significantly reduced. For example, when samples A and D are compared now, the effect of the present invention is clearly exerted on A, and this effect is manifested even if the amount of the compound is reduced to half as in the case of G. However, the effect of the comparative example E was inferior to that of the comparative examples A, B, and C, and, as can be seen by comparing E and J, the amount of the compound was halved. When it is done, the effect is further inferior, and the magnetic characteristic of J approaches that of D in the case of no treatment.

The reducing effect of this surface treatment compound is particularly industrially desirable. For example, when the compound itself is colloidal as seen in the case of some Si-type compounds, if this required amount is large, it may be difficult to filter and wash and it may not be practically applicable. It will be possible. Further, the use of a large amount of the surface treatment compound generally has various undesired effects on the production and use of the magnetic recording medium, but it can be avoided from its adverse effects due to the mitigating effect.

(Effect of the Invention) According to the present invention, cobalt-containing ferromagnetic iron (I) oxide,
Compared with (II) etc., the cobalt-containing ferromagnetic iron oxide (excellent in stability over time and fatty acid adsorption properties, and even better in tape characteristics such as squareness ratio, orientation, switching field distribution, etc.) III) can be manufactured.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuo Ishikawa 1 Ishihara-cho, Yokkaichi-shi, Mie Ishihara Industrial Co., Ltd. Yokkaichi Plant (72) Inventor Masaji Ota 1-site Ishihara-cho, Yokkaichi-shi, Mie Ishihara Industrial Co., Ltd. Yokkaichi Factory

Claims (1)

[Claims] 1. A magnetic iron oxide powder is treated with a metal salt containing a cobalt salt and a ferrous salt and an alkali in an aqueous medium to deposit a metal compound containing cobalt and ferrous iron on the surface of the powder particles. Then, regarding the produced magnetic iron oxide to be deposited, the pH of the aqueous medium-dispersed slurry was 6.5 to 9.5.
The magnetic iron oxide powder coated with a metal compound containing cobalt and ferrous iron produced is heat-treated, and is further selected from the group of silicon, aluminum, titanium, vanadium and manganese compounds. A method for producing a cobalt-containing ferromagnetic iron oxide, which comprises depositing at least one compound.