JP2660714B2 - Method for producing cobalt-containing ferromagnetic iron oxide powder - Google Patents

Description

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

[Conventional technology]

With the development of technologies such as audio, video, computers, and word processors, higher quality recording materials are required for these magnetic recording media. Cobalt-containing ferromagnetic iron oxide powder is no exception. As a part of this, those with excellent coercive force, switching magnetic field distribution, erasing characteristics, transfer characteristics, etc. are being actively researched and developed.

For example, Japanese Patent Application Laid-Open No. 50-85612 (a) discloses a technique of γ-Fe ₂
The present invention relates to a metamorphic treatment method in which a cobalt compound is deposited on O ₃ particles and then a ferrous compound is deposited.
A cobalt salt, an alkali, and a ferrous salt are added in this order to an aqueous slurry in which γ-Fe ₂ O ₃ particles are dispersed. This technique aims at improving the temperature dependence of coercive force and squareness ratio, orientation, transfer characteristics, and the like. Next, the technique of JP-A-59-151402 (b) relates to a modification treatment method in which a cobalt compound and a ferrous compound are simultaneously applied to a magnetic iron oxide powder, and more specifically, a magnetic iron oxide powder is dispersed. An aqueous solution of a cobalt salt and a ferrous salt is added to the alkali-dissolved aqueous slurry. This technique aims at improving coercive force distribution, erasing characteristics, output, and the like. JP-A-59-107924 (c) relates to a metamorphic treatment method in which a ferrous compound is applied to a magnetic iron oxide powder and then a cobalt compound is applied. The ferrous salt and the cobalt salt are added in this order to the alkali-dissolved aqueous slurry in which is dispersed. This technique aims to improve the stability over time of the coercive force, the squareness ratio, the orientation, the switching magnetic field distribution, and the like. Also, JP-A-61-17
Technology 426 No. (d) is allowed to deposited ferrous compound γ-Fe ₂ O ₃ particles, then it relates to a modified processing method of depositing cobalt compound, specifically, a γ-Fe ₂ O ₃ particles The ferrous salt is added to the dispersed alkali-dissolved slurry, and the mixture is stirred for a predetermined time under a constant temperature condition, and then the cobalt salt is added. This technique aims at improving coercive force, electromagnetic conversion characteristics, and the like. JP-A-51-23697 (e) discloses a method of depositing a magnetite layer on a ferromagnetic iron oxide powder and then depositing a ferromagnetic iron oxide layer containing cobalt atoms on the magnetite layer. Has been described,
In the example, the needle-like γ-Fe ₂ O ₃ powder was added to the solution in which the hydroxide of iron was precipitated, and then an oxidation reaction was performed to precipitate magnetite on the powder. Is added to a solution in which a hydroxide of iron and cobalt is precipitated, and then an oxidation reaction is carried out.

[Problems to be solved by the invention]

The relationship of the prior art is considered to be that the methods (c) and (d) attempt to improve the switching field distribution and the erasing characteristics with respect to the methods (a) and (b). However, even in the methods (c) and (d), the degree is still insufficient, especially when the magnetic iron oxide powder is fine particles having a specific surface area of, for example, 50 m ² / g, or when the coercive force is 700O.
Further improvement is desired for high coercivity powders of e or higher. Further, the method (e) has a defect that it is difficult to obtain a material having a high coercive force.

[Means for solving the problem]

The present inventors added an aqueous solution of a ferrous salt and a cobalt salt to an alkali-dissolved aqueous slurry in which a magnetic iron oxide powder is dispersed, which is described in (b) above among the conventional modified deposition techniques. As a result of various studies on how to
No. 1 in magnetic iron oxide powder in alkali-dissolved aqueous slurry
The applicant has filed a patent application by finding out that the addition of an aqueous solution of an iron salt and a cobalt salt at a distance, that is, so-called parallel addition, results in excellent switching field distribution, erasing characteristics, and transfer characteristics. (Japanese Patent Application No. 63-25199) After further investigation, it was found that (a) a part of the ferrous salt was preliminarily coated before the parallel addition, and (b) this coating was magnetically oxidized. It has been found that by employing a method in which an alkali is added to a ferrous salt-dissolved aqueous slurry of iron powder to cause a reaction, surprisingly, the switching field distribution, the erasing characteristics and the transfer characteristics are remarkably improved. Is completed.

That is, the present invention relates to a method of modifying and applying a magnetic iron oxide powder with a ferrous compound and a cobalt compound. In the first step, alkali is added to a ferrous iron salt-dissolved aqueous slurry of the magnetic iron oxide powder as a first step. A ferrous compound is applied, and, as a latter stage, an alkali is present in the slurry obtained in the former stage, and the alkali and the ferrous salt and the cobalt salt are simultaneously and separately reacted to form a ferrous compound and a cobalt compound. And a method for producing a cobalt-containing ferromagnetic iron oxide powder.

In the present invention, in which a ferrous compound and a cobalt compound are applied to a magnetic iron oxide powder for denaturation treatment, first, as a first step, a first iron salt aqueous solution obtained by adding a ferrous salt aqueous solution to an aqueous medium of the magnetic iron oxide powder is used. An alkali is added to the iron-salt-dissolved aqueous slurry to neutralize the ferrous salt in the slurry and deposit a ferrous compound. Thereafter, as a subsequent stage, an alkali is present in the neutralized aqueous slurry obtained in the preceding stage, and the alkali and the ferrous salt and the cobalt salt are simultaneously and separately reacted to deposit the ferrous compound and the cobalt compound. .

As the magnetic iron oxide powder used in the present invention, γ-Fe
₂ O _3, obtained by partial reduction of the γ-Fe ₂ O ₃ berthollides,
Needle-like magnetic iron oxide powder such as Fe ₃ O ₄
-Fe ₂ O ₃ is preferable. As the aqueous medium, industrial water, pure water (ion exchange resin treatment) or the like is generally used. Note that it is preferable to use those in which the oxidizing action is suppressed by bubbling with an inert gas (for example, nitrogen gas) in advance. Also, suitable dispersants, buffer salts and the like can be added. Examples of the ferrous salt include ferrous salts of mineral acids such as ferrous sulfate, ferrous nitrate, and ferrous chloride. Ferrous sulfate is industrially preferable, and generally 0.1 to 1.5.
Add as an aqueous solution with a concentration of about mol / l.

In the first deposition step, the concentration (content) of the magnetic iron oxide powder in the aqueous medium of the magnetic iron oxide powder is usually 20 to
It is 200 g / l, desirably 50 to 150 g / l, and when a fine powder having a large specific surface area is used, it is preferable to set the concentration to a low concentration. The dispersion of the magnetic iron oxide powder in the aqueous medium is usually performed by mechanical stirring, but other means such as ultrasonic waves can be used. The amount of the ferrous salt to be dissolved is such that the amount of the deposited iron is 0.5
-25% by weight, preferably 1-15% by weight. If the ratio is too large or too small, the switching field distribution, the erasing characteristics and the transfer characteristics are not improved, and the coercive force is not sufficiently improved.

As the alkali used as the neutralizing agent used in the present invention, hydroxides, oxides or carbonates of alkali metals or alkaline earth metals are used, for example, sodium hydroxide, potassium hydroxide, sodium oxide, calcium carbonate and the like. Industrially, sodium hydroxide and potassium hydroxide are preferred. In the present invention, it is desirable to add at least the total amount of the neutralization equivalent of the ferrous salt in the former stage and the neutralization equivalent of the ferrous salt and the cobalt salt in the latter stage in the former stage. After completion of the neutralization reaction, a necessary alkali may be added at a later stage.

The pre-deposition treatment is usually performed in a non-oxidizing atmosphere such that the ferrous compound is not substantially oxidized at 50 ° C. or lower, preferably 10 to 30 ° C. If the temperature is too high, the coercive force will not rise sufficiently, and industrially,
In order to lower the temperature to below ℃, it is necessary to install a refrigerator or the like, which is not preferable.

In the subsequent deposition treatment, an alkali is present in the neutralized aqueous slurry obtained in the preceding stage, and the alkali and the ferrous salt and the cobalt salt are simultaneously and separately reacted to deposit the ferrous compound and the cobalt compound. Let it. “Separately simultaneously” means that the ferrous salt and the cobalt salt do not directly react with the alkali in a mixed state before each of the ferrous salt and the cobalt salt react with the alkali, and A reaction means that there is at least some overlapping time. This condition is, for example, the first to the alkaline slurry.
This is achieved by adding iron salts and cobalt salts separately and in parallel. Usually, a ferrous salt aqueous solution and a cobalt salt aqueous solution are added to the slurry from separate supply pipes over a certain period of time. In this case, the addition may be started and finished at substantially the same time (parallel addition deposition process), or may be superimposed so as to be partially simultaneous (partial superposition deposition process). Good. In a method in which a ferrous salt solution and a cobalt salt solution are mixed and added, or a cobalt salt is added after completion of the addition of the ferrous salt solution, it is difficult to obtain the desired effects of the present invention.

The time required for adding the ferrous salt and the cobalt salt in the subsequent deposition process cannot be generally specified, but generally ranges from 10 minutes to 5 minutes.
Time, preferably 20 minutes to 3 hours, more preferably 30 minutes to 2 hours. This addition is usually carried out with stirring at a temperature in the system below 50 ° C., preferably below 30 ° C., for example below 35 ° C., particularly preferably below 30 ° C.
After completion of the addition, the temperature is maintained at a constant temperature range under stirring for generally 3 hours or more, preferably 5 to 20 hours, and the coating is completed by aging. Aging is usually performed at a temperature not much higher than 50 ° C., for example, at 60 ° C. or less, preferably at 50 ° C. or less.

The atmosphere during the subsequent deposition process is non-oxidizing as in the previous stage. In order to obtain desired magnetic properties, the atmosphere may be adjusted so that the ferrous compound is oxidized to some extent.

The ferrous salt used in the latter stage is preferably the same as that in the former stage, and the cobalt salt is, for example, cobalt sulfate, cobalt chloride or cobalt acetate, and industrially, cobalt sulfate is preferred. These ferrous salts and cobalt salts are usually used as respective aqueous solutions, and their concentrations are industrially the first ferrous salts and cobalt salts.
About 0.1 to 1.5 mol / l of iron salt and about 0.2 to 2.0 mol / l of cobalt salt are recommended.

The OH group concentration (free OH group concentration equal to or higher than the neutralization equivalent) in the slurry after the application treatment in the latter stage is usually 0.01 to 3 mol / l, preferably 0.5 to 2 mol / l. Therefore,
The amount of alkali added in the latter stage is set based on the types and amounts of ferrous salt and cobalt salt based on these conditions.

The amount of ferrous salt and cobalt salt deposited in the latter stage is
For the total Fe content of the magnetic iron oxide powder, the former is 1 as Fe.
-30% by weight, preferably 2-20% by weight, the latter being Co
0.1 to 20% by weight, desirably 0.5 to 15% by weight. If the amount of ferrous iron is too small, the coercive force and the saturation magnetization cannot be increased, which is not preferable because it causes problems such as an increase in electric resistance of the obtained magnetic powder. Conversely, if the content is too large, it is not preferable because problems such as a decrease in specific surface area and deterioration of the coercive force and erasing characteristics over time are easily caused. If the addition amount of the cobalt salt is too small, an increase in the coercive force cannot be expected, and if it is too large, the coercive force distribution and the dispersibility tend to be deteriorated, which is not preferable.

After the modified deposition treatment, the product is usually dehydrated and washed with water to remove alkalis, and then dried.

Drying may be performed in an inert atmosphere such as nitrogen, or in an atmosphere of air or a mixed gas of air and an inert gas. Those obtained by drying in a non-oxidizing atmosphere seem to be generally superior in coercive force development as compared with those in an oxidizing atmosphere. The drying temperature may be a normal temperature used industrially, and generally about 60 to 150 ° C. is often used.

In this way, a cobalt-containing ferromagnetic iron oxide powder having the desired properties is obtained, which is further reduced by 100 to 2
By performing the dry heat treatment at a temperature of 00 ° C., the coercive force and other magnetic properties may be improved in some cases.

The cobalt-containing ferromagnetic iron oxide powder obtained by performing the above-mentioned metamorphic deposition treatment was subjected to silicon, aluminum, calcium, titanium, vanadium, nickel and nickel based on the method described in JP-A-63-10375. zinc, by coating the compound on a surface, such as phosphorus, wherein the outside of excellent magnetic properties having a ferromagnetic iron oxide powder, both the desired stability over time (△ Hc) and fatty acid adsorption properties (C ₁₄ adsorption) Can be manufactured.

〔Example〕

Example 1 γ-Fe ₂ O ₃ powder (coercive force 310 Oe, average major axis particle size 0.12 μm
m, axial ratio about 6) A slurry of 100 g dispersed in water 1
0.90 mol under a nitrogen gas atmosphere while maintaining the temperature
105 ml of a 1 / l aqueous solution of ferrous sulfate was added to obtain a ferrous salt-dissolved slurry. Next, 201 ml of a 10 mol / l aqueous solution of sodium hydroxide was added to the slurry to deposit a ferrous compound on the surface of the γ-Fe ₂ O ₃ powder. Subsequently, 0.90
The ferrous compound and the cobalt compound were deposited by adding 105 ml of an aqueous solution of ferrous sulfate (mol / l) and 84 ml of an aqueous solution of 0.85 mol / l cobalt sulfate in parallel. This parallel addition is performed by a small pump with a controlled supply rate so that both aqueous solutions are supplied in about 60 minutes, a supply pipe (inner diameter: about 2.5 mm, a distance between both supply pipes of about 1
5 cm) so as to simultaneously start and end the addition. After completion of the addition, the mixture was stirred and aged for 1 hour, heated to 35 ° C., and further stirred and aged for 4 hours. Thereafter, the resultant was filtered, washed with water, and dried at 120 ° C. in a nitrogen gas atmosphere to obtain the desired cobalt-containing ferromagnetic iron oxide powder (A).

Example 2 The same procedure as in Example 1 was carried out except that the amount of the aqueous ferrous sulfate solution added in the former stage was changed to 42 ml and the amount of the aqueous ferrous sulfate solution added in the latter stage was changed to 168 ml. A cobalt-containing ferromagnetic iron oxide powder (B) was obtained.

Example 3 The same procedure as in Example 1 was carried out except that the amount of the aqueous ferrous sulfate solution added in the former stage was 168 ml and the amount of the aqueous ferrous sulfate solution added in the latter stage was 42 ml, and the desired A cobalt-containing ferromagnetic iron oxide powder (C) was obtained.

Comparative Example 1 100 g of the same γ-Fe ₂ O ₃ powder as used in Example 1 was dispersed in a mixed solution of water 1 and 201 ml of a 10 mol / l sodium hydroxide aqueous solution to form a slurry. While maintaining the temperature, 294 ml of a mixed aqueous solution of 210 ml of a 0.90 mol / l ferrous sulfate aqueous solution and 84 ml of a 0.85 mol / l aqueous cobalt sulfate solution was added in about 60 minutes under a nitrogen gas atmosphere, and the first solution was added.
An iron compound and a cobalt compound were deposited. Thereafter, aging, filtration, washing with water and drying were performed in the same manner as in Example 1 to obtain a cobalt-containing ferromagnetic iron oxide powder (D).

Comparative Example 2 A cobalt-containing ferromagnetic substance was treated in the same manner as in Comparative Example 1 except that the addition of the mixed aqueous solution of the ferrous sulfate aqueous solution and the cobalt sulfate aqueous solution in Comparative Example 1 was replaced with the parallel addition employed in Example 1. An iron oxide powder (E) was obtained.

Comparative Example 3 Example 1 was repeated except that, instead of the parallel addition deposition treatment in the subsequent stage, a mixed addition deposition treatment was performed in which a mixed aqueous solution of ferrous sulfate and cobalt sulfate was added as in Comparative Example 1. In the same manner as in the above, a cobalt-containing ferromagnetic iron oxide powder (F) was obtained.

Example 4 In Example 1, the subsequent deposition treatment was performed such that the addition of the aqueous ferrous sulfate solution was completed in about 45 minutes.
15 minutes after the start of the addition, the same treatment was carried out except that the addition of the aqueous solution of cobalt sulfate was completed in about 60 minutes to obtain the desired cobalt-containing ferromagnetic iron oxide powder (G). Was.

Comparative Example 4 0.90 mol / l of sulfuric acid sulfuric acid was added under a nitrogen gas atmosphere while maintaining a slurry in which 100 g of the same γ-Fe ₂ O ₃ powder as used in Example 1 was dispersed in water 1 at a temperature of 20 ° C. 1 iron aqueous solution
210 ml was added to obtain a ferrous salt dissolved slurry. Next, 201 ml of a 10 mol / l aqueous solution of sodium hydroxide was added to the slurry to deposit a ferrous compound on the surface of the γ-Fe ₂ O ₃ powder. Subsequently, 84 ml of a 0.85 mol / l aqueous solution of cobalt sulfate was added to the slurry to deposit a cobalt compound. Thereafter, aging, filtration, washing with water and drying were performed in the same manner as in Example 1 to obtain a cobalt-containing ferromagnetic iron oxide powder (H).

Comparative Example 5 A slurry obtained by dispersing 100 g of the same γ-Fe ₂ O ₃ powder as that used in Example 1 in a mixed solution of water 1 and 201 ml of a 10 mol / l aqueous sodium hydroxide solution while maintaining the temperature at 20 ° C. with nitrogen In a gas atmosphere, the addition of 210 ml of a 0.90 mol / l ferrous sulfate aqueous solution was performed in about 45 minutes to complete the addition.
After 15 minutes, 0.85 mol / l cobalt sulfate aqueous solution 84
The addition of the ml was made to complete in about 60 minutes to deposit the ferrous and cobalt compounds. After that, Example 1
In the same manner as in the above, aging, filtration, washing with water and drying were performed to obtain a cobalt-containing ferromagnetic iron oxide (I).

For the samples A to I, the coercive force (Hc) was measured by an ordinary method, and the results are shown in Table 1.

Further, for Samples A to I, a blend was prepared according to the following blend ratio, and kneaded with a ball mill to produce a magnetic paint.

(1) Cobalt-containing ferromagnetic iron oxide powder 100.0% by weight (2) Additive 3.8 〃 (3) PVC-vinyl acetate copolymer 8.0 〃 (4) Polyurethane resin 35.5 〃 (5) Mixed solvent (toluene / MEK = 1 / 1) 216.2 {(6) 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 of about 9 μm. For each tape, measure coercive force (Hc), squareness ratio (Br / Bm), orientation (OR), switching field distribution (SFD), erasing characteristics (dB) and transfer characteristics (dB) by the usual method The result of the first
It is shown in the table.

[Effects of the invention] As is clear from Table 1, the cobalt-containing ferromagnetic iron oxide obtained by the method of the present invention has excellent magnetic properties, and is compared with the magnetic iron oxide obtained by the conventional method. In particular, they are much more excellent in the switching magnetic field distribution, the erasing characteristics, and the transfer characteristics.

Claims (2)

(57) [Claims] In a method for modifying a magnetic iron oxide powder with a ferrous compound and a cobalt compound, an alkali is added to a ferrous salt-dissolved aqueous slurry of the magnetic iron oxide powder as a first step. A ferrous compound is deposited, and, as a subsequent step, an alkali is present in the slurry obtained in the preceding step, and a ferrous salt and a cobalt salt are separately added in parallel to the slurry to cause a reaction. A method for producing a cobalt-containing ferromagnetic iron oxide powder, comprising applying a compound and a cobalt compound. 2. The method according to claim 1, wherein the first and second deposition processes are performed in a non-oxidizing atmosphere.