JPH0676218B2 - Method for producing cobalt-containing ferromagnetic iron oxide - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION 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 and its problems] Research and development of recording materials used for magnetic recording media such as audio, video, computers and word processors have been actively conducted. An example is the improvement of cobalt-containing ferromagnetic iron oxide.

The applicants of the present patent application are the Japanese Patent Application Nos. 61-112271 and 62-11.
Japanese Patent Application No. 8686 and Japanese Patent Application No. 62-333624 have proposed the following method for producing ferromagnetic iron oxide containing cobalt. In this method, a magnetic iron oxide powder is treated in an aqueous medium with a metal salt containing a cobalt salt and a ferrous salt and an alkali to deposit a metal compound containing cobalt and ferrous iron on the surface of the powder particles. Then, the obtained adherend dispersion slurry, that is, the slurry after the adhesion treatment, is filtered, washed with water, or obtained without any one or both of the operations, cobalt in the aqueous medium. , To a slurry in which magnetic iron oxide powder coated with a metal compound such as ferrous iron (hereinafter referred to as magnetic iron oxide coated with cobalt) is dispersed, an acidic substance is added to adjust the pH to 6.5 to 11.5 and heat treatment is performed. To do.

Compared to the one obtained by heat treatment without adjusting the pH as described above, the one obtained by this method improves the various magnetic properties including the switching field distribution (SFD). , The coercive force (Hc) tended to decrease, which was a problem.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned problems and to maintain a good switching field distribution and to improve the coercive force as compared with the case where the above-mentioned adherend dispersion slurry is simply pH-adjusted and heat-treated. Another object of the present invention is to provide a method for producing a cobalt-containing ferromagnetic iron oxide having excellent magnetic properties.

[Outline of Invention]

The present invention includes the above-mentioned Japanese Patent Application Nos. 61-112271 and 62-118686.
No. 62-333624 and Japanese Patent Application No. 62-333624, the magnetic iron oxide coated on cobalt in the adherend dispersion slurry is further coated with an aluminum compound and then heat-treated in an aqueous medium to obtain the present invention. It is based on the investigation of the fact that the above-mentioned purpose can be achieved.

The investigation of this fact is the discovery of a phenomenon that the present inventors could not expect, and the present inventors have not yet clarified the reason why this phenomenon occurs. Surprisingly, however, even if it is similarly treated with a compound used as a surface treatment agent for a pigment in the same row as an aluminum compound, such as zinc, titanium, or silicon, the effect of the present invention is substantially brought about. It was found that it was not performed or the effect was poorly expressed. It should be noted that the desired effect of the present invention cannot be obtained by simply depositing an aluminum compound on the magnetic iron oxide deposited on cobalt or the like, and the effect is that following deposition of these compounds, an aqueous medium is formed under a constant pH condition. It is obtained only after heat treatment in liquid.

That is, according to the present invention, 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. And, further, an aluminum compound is further adhered to the adhered magnetic iron oxide powder obtained, and the pH of the adhered dispersion slurry is adjusted to 7.0 to 0.7, and heat treatment is performed in an aqueous medium. It is a method for producing a cobalt-containing ferromagnetic iron oxide.

In the present invention, it is important to use the ferrous salt together with the cobalt salt, and as the magnetic iron oxide to be used, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , and γ-Fe ₂ O ₃ are partially used. There are acicular magnetic iron oxide powders such as beltride compounds obtained by reduction. Examples of the cobalt salt include cobalt chloride, cobalt sulfate, cobalt nitrate, and cobalt acetate.
Examples of the ferrous salt include ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous carbonate and the like. Further, as the other metal salt used as necessary, manganese salt, zinc salt, chromium salt, nickel salt, aluminum 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 for depositing the cobalt and ferrous compound. For example, in a slurry in which magnetic iron oxide powder is dispersed in an aqueous medium liquid, cobalt salt and first
There are various methods as follows depending on the order of adding the iron salt and the alkali.

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

(2) A method of adding an alkaline aqueous solution and then adding an aqueous solution containing a cobalt salt and a ferrous 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 a ferrous iron salt aqueous solution, precipitating ferrous hydroxide with an alkali, and then adding a cobalt salt aqueous solution.

(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.

Further, 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 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 carried out at room temperature to 100 ° C, preferably at room temperature to 50 ° C. If this temperature is too low, the treatment time will be long, while if it is too high, ferrous iron will diffuse into the magnetic powder, or it will be stored. The magnetic force distribution becomes wider, which is not desirable. The OH group concentration in the system is usually 0.01 to 3 mol / l, preferably 0.05.
If the concentration is too low, the desired coercive force cannot be obtained. On the other hand, if the concentration is too high, the cobalt compound once deposited is partially dissolved, which is not desirable. Incidentally, this deposition treatment time is usually 0.1 to 10 hours. The amount of cobalt deposited is
0.5 to 30%, preferably 1 to 10% by weight based on the magnetic iron oxide, 1 to 30% in the case of ferrous iron, preferably 2 to 20%, and 0 to 10% in other cases. .

Next, the pH of the obtained adherend-dispersed slurry is adjusted. One embodiment of the pH adjustment in the present invention, the slurry is filtered by a normal method, washed with water, and the wet cake is dispersed in an acidic substance-containing aqueous medium, or a slurry obtained by dispersing the wet cake in an aqueous medium. An acidic substance is added to the mixture to adjust the pH value of the slurry to a constant value. Several other aspects of pH adjustment in the present invention are as follows.

That is, in some cases, the acidic substance is directly added to the adherend dispersion slurry obtained by the above-mentioned adhesion treatment.
Adjust pH to constant value. When the free alkali concentration of the adherend treatment slurry is high, for example, 1 to 3 mol / l, when the solid content is low, for example, 100 g / l or less, the pH is
Since the amount of the acidic substance necessary for the adjustment becomes excessively large or the amount of the acidic substance liquid becomes too large, it is not preferable. Therefore, it is recommended to separate the mother liquor by the sedimentation method and then adjust the pH. Further, the slurry after separation of the mother liquor may be washed with an aqueous medium by a decantation method 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. Industrial water,
As pure water, it is desirable to use bubbling with an inert gas in advance to suppress its oxidizing action. Further, in the above-mentioned case, the mother liquor separating means is changed to a sedimentation method, and a pressure filter such as a filter press, Oliver
A separation method using a filter, a suction filter such as a Muir filter, or various centrifugal separators may be adopted. When such a separation method is adopted, the wet cake is dispersed in an aqueous medium and then the pH is adjusted. In this case, it is preferable to select a model in which the wet cake is not exposed to the atmosphere 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.

The acidic substance used for adjusting the pH is not particularly limited, and examples thereof include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid, boric acid, formic acid, acetic acid, oxalic acid, tartaric acid, and benzoic acid. And sulfonic acids such as methanesulfonic acid and benzenesulfonic acid, sulfinic acid, and various acidic salts. In addition, other commonly used neutralizing agents may be used.

This pH adjustment is usually carried out in the vicinity of neutrality, and then an aluminum compound is further deposited on the magnetic iron oxide coated with cobalt or the like in the obtained slurry for depositing the deposited material. Examples of the adherent used for precipitating the aluminum compound include sodium aluminate, potassium salt, aluminum sulfate, aluminum chloride and the like.

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. The addition of the coating agent and the neutralizing agent to the coating material dispersion slurry can be performed in any order, at the same time, or in parallel over a certain period of time, and the coating with the desired properties can be performed. In order to form the compound, any appropriate addition means can be adopted.

The treatment temperature for precipitating the coating compound in this manner and coating the magnetic iron oxide coated with cobalt or the like is usually room temperature to boiling point, preferably room temperature to 90 ° C, more preferably 25 to 65 ° C. Is. If necessary, it is ripened for several tens of minutes to several hours, and it is generally preferable that this ripening is carried out under stirring for about 15 minutes to 5 hours within the treatment temperature range for deposition and deposition.

The amount of the aluminum compound deposited on the magnetic iron oxide deposited on cobalt, etc. is usually Al based on the weight of the magnetic iron oxide.
Is 0.01 to 3%, preferably about 0.02 to 2%.
If the amount of deposition is too large or too small, it becomes difficult to obtain the desired effect of the present invention.

The recommended method for depositing the aluminum compound in the present invention is to use an aluminum acid salt such as a sulfate or hydrochloride thereof as the acidic substance used for the pH adjustment. By operating in this way, it is possible to perform both pH adjustment and deposition of aluminum compound, simplifying the process with saving of acidic substances and neutralizing agents,
It will be industrially advantageous.

The pH of the adherend-dispersed slurry after the deposition of the aluminum compound is usually 7.0 to 0.7, and preferably 7.5 to 9.5. The temperature for the subsequent heat treatment is usually 150 ° C or lower, preferably 70 to 150 ° C, more preferably 80 ° C.
The treatment time is usually 1 to 10 hours. It should be noted that since it becomes a pressurized system at a boiling point or higher and the pressure is usually about 1.1 to about 7 atm, it is necessary to perform heat treatment in a closed container such as an autoclave. Further, it is desirable that this heat treatment is performed in a non-oxidizing atmosphere. The above-mentioned pH value and heat treatment temperature are more neutral in the former and milder in the latter than in the case where the aluminum compound is not deposited. This is based on the deposition of the compound,
It is difficult to obtain the desired effect outside the range of these conditions.

Further, based on the method described in Japanese Patent Application No. 63-10375, cobalt-containing ferromagnetic iron oxide obtained by subjecting to the above heat treatment, silicon, aluminum, calcium, titanium, vanadium, manganese, nickel, zinc In addition to the excellent magnetic properties of the ferromagnetic iron oxide powder, the dispersibility, durability, stability over time, and fatty acid adsorption properties can be partially or entirely covered by further depositing a compound such as phosphorus, phosphorus, etc. Can be improved.

Ferromagnetic iron oxide that has been subjected to the above heat treatment is usually filtered, washed with water, and dried to become a cobalt-containing ferromagnetic iron oxide having desired properties, but in an inert atmosphere, 100 ° C to 2 ° C.
By performing the dry heat treatment at 00 ° C, a magnetic powder having improved coercive force and other magnetic properties may be obtained.

〔Example〕

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

Example-1 γ-Fe ₂ O ₃ powder (coercive force 390 Oe, average major axis particle size 0.35 μ,
Axial ratio of about 10) 200 g was dispersed in water to make a 2 l slurry.
While blowing nitrogen gas into this slurry, at room temperature
140 ml of an 85 mol / l aqueous solution of cobalt sulfate and 308 ml of a 0.90 mol / l aqueous solution of ferrous sulfate were added, and further 360 ml of a 10 mol / l aqueous solution of sodium hydroxide was added to modify γ-Fe ₂ O ₃ . Then, this product is filtered and washed with water, and the separated cake is repulped in water, and while blowing nitrogen gas into this, an aluminum sulfate aqueous solution (1.6 g as Al is added at room temperature).
/ l) is gradually added, and a dilute aqueous sodium hydroxide solution is added in parallel from the middle of the addition so as to maintain pH 8.5, and after stirring for 1 hour, the content of Al is 0.06% by weight based on the weight of iron oxide. Transforming aluminum compound γ-Fe ₂ O ₃
Deposited on. The obtained slurry was divided into two and placed in an autoclave, the inside was made into a nitrogen gas atmosphere, then sealed, and heat-treated at 90 and 130 ° C. for 3 hours each. After the heat treatment, each produced slurry is filtered, washed with water, and the separated cake is dried at 120 ° C. in a nitrogen gas atmosphere to obtain the desired cobalt-containing ferromagnetic iron oxide powders (A) and (B).
Got

Comparative Example-1 A cobalt-containing ferromagnetic material was prepared in the same manner as in Example 1 except that the aqueous solution of sulfuric acid was used instead of the aqueous solution of aluminum sulfate and the diluted aqueous solution of sodium hydroxide, and the pH was adjusted to 8.5. Iron oxide powders (C) and (D) were obtained.

Example-2 γ-Fe ₂ O ₃ powder (coercive force 375 Oe, average major axis particle size about 0.30
μ, axial ratio of about 9) 200 g was dispersed in water to make a 2 l slurry. While blowing nitrogen gas into this slurry, 146 ml of 0.85 mol / l cobalt sulfate aqueous solution and 0.90 mol / l at room temperature were blown.
280 ml of a ferrous sulfate aqueous solution of 10 mol / l are further added, and 352 ml of a 10 mol / l sodium hydroxide aqueous solution is further added, and the mixture is stirred for 3 hours to
-Fe ₂ O ₃ was modified. The product is then filtered,
After washing with water and repulping the separated cake into water, while blowing nitrogen gas into this, add aluminum sulfate aqueous solution (1.6 g / l as Al) at room temperature until the pH becomes 8.3,
Stir for 1 hour after the addition is completed
0.04% of aluminum compound as γ-Fe ₂ O ₃
Deposited on. The obtained slurry was divided into two and placed in an autoclave, the inside was made into a nitrogen gas atmosphere, then sealed, and heat-treated at 90 and 130 ° C. for 2.5 hours each. After the heat treatment, the cake was separated by filtration, washed with water, and dried at 120 ° C. in a nitrogen gas atmosphere to obtain the target cobalt-containing ferromagnetic iron oxide powders (E) and (F).

Comparative Example-2 Cobalt-containing ferromagnetic iron oxide powders (G) and (H) were prepared in the same manner as in Example 3 except that the aqueous solution of sulfuric acid was used instead of the aqueous solution of aluminum sulfate.
Got

With respect to the samples (A) to (H), the coercive force (Hc) was measured by an ordinary method, and the Fe ⁺⁺ content (% by weight) in the total Fe amount was measured by the potassium dichromate titration method. The results are shown in Table 1.

In addition, for each sample, a blend was prepared according to the following blending 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) PVC-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, 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 9 μm thick. The coercive force (Hc) and the switching field distribution (SFD) of each tape were measured by the usual methods. The results are shown in Table 1.

In addition, in Examples 1 and 2, γ-Fe is represented as a magnetic iron oxide powder.
_Although the case of ₂ O ₃ has been mentioned, Fe ₃ O ₄ and beltride compounds can be handled in the same manner.

EFFECTS OF THE INVENTION According to the present invention, as can be seen by comparing Example 1 and Comparative Example 1 and Example 2 and Comparative Example 2 shown in Table 1, a good switching field distribution (SFD) is obtained. With coercive force (Hc)
It is possible to produce a cobalt-containing ferromagnetic iron oxide with improved performance and excellent industrial performance.

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, the obtained adhered magnetic iron oxide powder is further adhered with an aluminum compound, and the pH of the adherend dispersion slurry is adjusted to 7.0 to 0.7 and heat treated in an aqueous medium. Method for producing cobalt-containing ferromagnetic iron oxide.