JPS5869729A - Preparation of ferromagnetic iron oxide powder - Google Patents

Abstract

PURPOSE:To obtain ferromagnetic iron oxide powder having improved magnetic properties, by applying specific amounts of total cobalt salt and total ferrous salt to be added to the surface of magnetic iron oxide powder, followed by applying the rests to the surface. CONSTITUTION:In the preparation of ferromagnetic iron oxide powder by covering the surface of magnetic iron oxide powder with 1-20atom% based on iron atom of the powder of a cobalt compound and 2-30atom% of ferrous compound, first 5-95wt% based on total cobalt salt to be added of cobalt salt and 1- 20wt% based on total ferrous salt to be added to ferrous salt are applied to the surface of the powder with an alkali in a nonoxidizing atmosphere. The rest of the cobalt salt and that of the ferrous salt are applied to the surface of the cobalt salt and that of the ferrous salt are applied to the surface of the coated surface with the alkali in a nonoxidizing atmosphere. Berthollide compound powder, etc. obtained by reducing partially gamma-Fe<2>O3, Fe3O4 powder, etc. in a reducing gas flow, etc. may be cited as the magnetic iron oxide used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing ferrous iron oxide powders containing cobalt & V ferrous which are useful as recording elements in magnetic recording media.

Magnetic iron oxide powder containing cobalt and tI' ferrous iron has a lower magnetic flux than magnetic iron oxide powder containing no cobalt and ferrous iron, such as γ-1'' e= (,') J powder, which is commonly used in the United States. It has high coercive force,
When used in magnetic recording media, it has many advantages, such as high-density recording and high sensitivity in the high frequency range.

In recent years, various methods for producing such magnetic iron oxides containing cobalt and ferrous iron have been proposed. For example, magnetic iron oxide powder is dispersed in a mixed aqueous solution of cobalt salt and ferrous salt, and an aqueous alkaline solution is added to this and treated at a temperature below the boiling point to form an iron oxide layer containing cobalt on the powder. There is a method of producing magnetic iron oxide powder by
Improvements in the manufacturing method are required.

As a result of various studies in order to obtain a ferromagnetic iron oxide powder with high magnetic properties, the present inventors have noticed that the precipitation rate of ferrous compounds is faster than that of cobalt compounds on the surface of the powder particles. However, by adjusting the addition ratio of cobalt salt and ferrous salt, it was found that the resulting magnetic iron oxide had good magnetic properties, and the present invention was completed.

In other words, the present invention provides a method for producing a ferromagnetic iron oxide powder in which a cobalt compound and a ferrous compound are coated on the surface of a magnetic iron oxide powder. - 555% ferrous cobalt salt and 1 to 20% ferrous iron salt of the total ferrous salts added, with an alkali;
The surface of the powder is coated in a non-oxidizing atmosphere, and then the remaining cobalt salt and the remaining ferrous salt are further coated on the surface of the coated layer with an alkali in a non-oxidizing atmosphere. This is a method for producing ferromagnetic iron oxide powder.

The magnetic iron oxide powder used in the present invention is γ-F"
e2(').

Powder, Fe50. Powder or γ-Fe20. For example, bertolide compound powder obtained by partially reducing γ-
Fe203 powder is preferred. Examples of cobalt salts include inorganic and organic acid salts of cobalt, such as cobalt sulfate, cobalt chloride, and cobalt acetate, with cobalt sulfate being preferred industrially. As a ferrous salt, ferrous sulfate
Examples include ferrous salts of mineral acids such as iron, #S1 iron nitrate, and ferrous chloride, with ferrous sulfate being industrially preferred. As the alkali, hydroxides, oxides, or carbonates of alkali metals or alkaline earth metals are used, and examples thereof include sodium hydroxide, potassium hydroxide, sodium oxide, and calcium carbonate. Industrially, sodium hydroxide and potassium hydroxide are preferred. Examples of the cobalt compound or ferrous compound formed by a salt and a 3-alkali include hydrated hydroxide, hydrated oxide, and hydrated oxyhydroxide. The non-oxidizing atmosphere here refers to an atmosphere in which the reactants are not oxidized as much as possible.1 For example, by replacing the reaction vessel with an inert gas or bubbling an inert gas into the solution in the reaction vessel. You may.

In the method of the present invention, magnetic iron oxide powder is usually dispersed in water, a weak alkaline aqueous solution, an alkaline aqueous solution, or an aqueous solution of a cobalt salt and a ferrous salt in a specific addition ratio; Dispersing the powder in an aqueous solution in which an iron salt and an alkali are mixed in advance, first neutralizing the cobalt salt and the ferrous salt and depositing them on the surface of the powder in a non-oxidizing atmosphere, Next, an aqueous solution of the remaining cobalt salt and the remaining ferrous salt is added to the system to neutralize it, and further deposition is performed on the surface of the deposited layer in a non-oxidizing atmosphere. As a preparation method for forming this adhesion layer,
Specifically, (1) the powder is dispersed in water or a weak alkaline aqueous solution, to which specific amounts of cobalt salts and ferrous salts and the alkali necessary to neutralize these salts are simultaneously added; A method of adding additional alkali until the OH group concentration is -4., and then simultaneously adding the remaining cobalt salt and @1 iron salt and an amount of alkali necessary to neutralize these salts, ■ The powder is dispersed in an aqueous solution containing a specific amount of cobalt salt and ferrous salt, neutralized by adding an alkali, further adding an alkali to a specific 014 group concentration, and then dispersing the remaining cobalt salt. and a method of simultaneously adding ferrous salts and the alkali necessary to neutralize these salts, (2) dispersing the powder in an aqueous alkali solution necessary for the neutralization in the first step, and adding a specific amount of cobalt salt; and ferrous salt, then additional alkali is added until a certain OH group concentration is reached, followed by addition of the remaining cobalt salt and ferrous salt and the amount of alkali necessary to neutralize these salts. Examples include a method of simultaneously adding
In the methods of ~■, the alkali necessary for neutralization in the latter stage may be added before the deposition in the latter stage, and in the methods of Alternatively, the ferromagnetic iron oxide powder obtained by the method of the present invention may be added at the same time to the surface of the magnetic iron oxide powder in an amount of usually 1. to 10 atomic %, preferably 1. to 10 at. 2 to 7 atom%, more preferably 3 to 7 atom%
7 atom % cobalt compound and usually 2 to 30 atom %, 5
- Preferably 4-25 at%, more preferably 5-20
It is coated with atomic percent of ferrous compound, and the ratio of cobalt compound to ferrous compound is usually 0.1 to 2:1.
, preferably 0.2 to 1:1, more preferably 0.3
~0.5:1, but is not limited to this.

In the deposition of the method of the present invention, first, in the first stage, cobalt salt is added in an amount of 5 to 95% by weight, preferably 50 to 80% by weight of the total cobalt salt added, and 1 to 1% of the total #1 iron salt added.
) 9% by weight, preferably from 5 to 15% by weight, of ferrous salt must be neutralized with an alkali and deposited on the surface of the powder. If this addition ratio is outside the above range, each compound may precipitate separately or the coercive force may vary, making it impossible to obtain the desired effect. The addition time of these raw materials depends on the preparation method for forming the adhesion layer, the molar concentration of OH groups,
Generally, 15 minutes or more is required, although it varies somewhat depending on the temperature at the time of deposition, and preferably 1 to 2 hours. Said ■
When the powder is dispersed and reacted in a weakly alkaline aqueous solution as in the method of
9, preferably 7.5 to 8.5. If a more effective effect is expected, the addition ratio of (20/Fe) should be selected depending on the pH in the system, the molar concentration of OH groups, the temperature at the time of deposition, the method of adding raw materials, etc. It is..

For example, if the deposition at room temperature is -1 and the pH is 13 (OH group concentration: 0.1 mol/ If the ratio is 1,1[,5 to 9, the Co/Fe addition ratio should exceed 1, preferably 2.-8,
More preferably, the pH is 3.about.5, and in this case, the pH is more preferably 7.about.8.5.
In the method described above, the Co/Fe addition ratio is strained to exceed 1, the pH is adjusted to 6.5 to 9, and the process is carried out at room temperature.
Among the various methods, it is even more desirable that after the first stage of deposition,
It is preferable to additionally add alkali so that the OH group concentration within the prefecture is (), 5~], 5+ool/θ, preferably (), 7~1.2 0110. Next, the remaining core salt and the remaining ferrous salt are added to the slurry in which the deposited powder is dispersed in the latter step, and the remaining ferrous salt is neutralized with an alkali to form the deposited I.
- It is necessary to adhere to the surface of This alkali may be added to the system for a month, or the co/belt salt and ferrous salt may be added at the time of coating in the amount necessary for mixing or in an excess amount. It's good, and when it's applied, it's on &; the density of the bruise '0, 7-
It is preferable to adjust the amount to 1,2 mol/&, and it is especially preferable to use three types of raw materials in parallel.

7- Also, in the deposition method of the present invention, the suspension or rally concentration of the powder is usually 20 to 200 g/ρ, preferably 50 g/ρ.
~150g/(l), and the deposition reaction temperature is usually below the boiling point, preferably below 50°C.In addition, the deposition in the method of the present invention must be carried out in a non-oxidizing atmosphere; If not, the ferrous compound will be unnecessarily oxidized and the desired effect will not be obtained.In addition, in the method of the present invention, in addition to cobalt salts and ferrous salts, manganous salts, zinc salts, nickel salts, etc. Metal salts may be added as appropriate.

The ferromagnetic iron oxide obtained by the above-mentioned method can be obtained as ferromagnetic iron oxide powder by filtration, washing with water, and drying by a conventional method. This filtration may be preceded by wet treatment in an autoclave at a temperature of 100-200°C, or after filtration or drying in a non-oxidizing atmosphere.
Dry heat treatment at a temperature of 0°C or after this filtration
It is desirable to perform a steam treatment at a temperature of 0 to 200°C, since this yields a ferromagnetic iron oxide powder having even higher magnetic properties.

The steam treatment here refers to the filtered wet cake of ferromagnetic iron oxide, either as it is or after washing with water and drying it at the lowest possible temperature in a non-oxidizing atmosphere, in a closed container for 8 hours. A method of heating in the presence of water vapor in a fluidized bed, a method of contacting the heated water vapor in the presence of a fluidized bed, etc.
be. In addition, after wet treatment in an autoclave,
After the water vapor treatment, a dry heat treatment in a non-oxidizing atmosphere as described above may be further performed. In carrying out the method of the present invention, after the deposition of the method of the present invention, among the treatments mentioned above, autoclaving (wet treatment or steam treatment, or after these treatments, a non-acidic atmosphere) is carried out. It is preferable to perform a dry heat treatment inside the container.

The ferromagnetic iron oxide embankment obtained by the above-mentioned method has advanced magnetic properties, and a magnetic chip 7 was manufactured using this material.
1° High coercive force, simultaneous diagonal ratio, orientation, and saturation magnetic flux density (these are excellent.

The reason for this is not completely clear. C; It is uniform, but in this method, O
Since the H group concentration is controlled by the pH 1, the addition ratio is controlled by the grain formation force of the L compound, and (2) the rapid precipitation force of the ferrous compound is relaxed. Because of this, the cono-root compound and the first
It is presumed that the precipitation of the iron salt compound is well-balanced and uniform.

9- The method of the present invention will be understood in more detail from the following examples and comparative examples.

Example 1 50g of γ-Fe20 powder (Kani 3800e, average particle diameter (fk axis) 0.6μ, axial ratio: 8:1) was dispersed in 10% water to make a slurry, and the reaction vessel was heated with NzN gas. After substituting the IJ, a 0.6 mol/ρ ferrous sulfate aqueous solution 24-〇 and a 5 mol/# ferrous sulfate aqueous solution 14-〇 were added to the IJ-. While maintaining the pH at 8t for 1 hour,
Add in parallel and then (1 in 5 mol/12 sodium hydroxide IJ
290 mff of aluminum was added and stirred for 30 minutes. Subsequently, 1 mol/Q cobalt sulfate aqueous solution 6- and 0
．． 6 mol/a ferrous sulfate aqueous solution 90- and 5 mol/a
# of hydroxide solution) was simultaneously added over 1 hour, and the resulting slurry was added while stirring.
Holds time. Filter this sura IJ,- by a conventional method,
After washing with water and drying, the desired ferromagnetic ferric acid powder A was obtained. When the coercive force of this material was measured using the usual method, it was found to be 570.
It was 0e.

Example 2 Same γ-F e203350 as used in Example 1
After dispersing 110 g of water in 110-ρ to make a ζ slurry and replacing the reaction vessel with N2 gas, 1 dol/ρ cobalt sulfate aqueous solution 24- and 0.6 dol/ρ ferrous sulfate aqueous solution 5 Sodium hydroxide solution 1 with 5 dol/ρ
1- and were added simultaneously over 1 hour, then 5 mol
/# of sodium hydroxide aqueous solution 317- was added and stirred for 30 minutes. Subsequently, a 1+ol/d cobalt sulfate aqueous solution 6- and a 0.6 sool/12 ferrous sulfate aqueous solution 90- were added in parallel over 1 hour, and the resulting slurry was held for 3 hours with stirring. This slurry was filtered, washed with water, and dried in a conventional manner to obtain the desired ferromagnetic iron oxide powder B. When the holding power of this product was measured by a conventional method, it was 56 ('l Oe).

Comparative Example 1 Same as that used in Example 1 γ-Fe2(-)350B
was dispersed in 1 g of water to make a slurry, and after replacing the reaction vessel with N2 gas, this slurry contained 30- and 0.6 mol/l aqueous solutions of cobalt sulfate at Imol/ff. ferrous sulfate aqueous solution 1 (1 (1-), then 5III
An aqueous sodium hydroxide solution of 36 - ol/ρ was added over 1 hour, and then 51 dol/ρ of an aqueous sodium hydroxide solution i292m (2) was added and held for 3 hours with stirring. This slurry was filtered by a conventional method, washed with water, After drying, a magnetic iron oxide powder C was obtained.The coercive force of this product was measured by a conventional method and was found to be 4800e.

A blend of the powders A-C obtained above was prepared according to the blending ratio shown below, and the mixture was kneaded in a ball mill to produce a magnetic paint.

(1) Magnetic iron oxide powder A, B or cioo parts by weight (2) Soybean lecithin 1
(3) Surfactant 4 〃(
4) Vinyl chloride-vinyl acetate copolymer resin 15〃(5
) Noogetil 7 tallate 5 〃(6
) Methyl ethyl ketone 111 〃(
7) Toluene 122 Next, each magnetic coating material was applied to a polyester film using a conventional method, oriented and dried to produce a magnetic tape having a magnetic coating film about 9 μm thick. For each tape, the coercive force (He) and squareness ratio (
Br/Bg+), orientation (OR), saturation magnetic flux density (h)
and switching field distribution (SFD) were measured, and the results shown in Table 1 were obtained.

#1 Table Example 3 The treated slurry obtained in Example 1 (before filtration) was placed in an autoclave, wet-treated at 120°C for 3 hours, cooled, washed with water and dried in a conventional manner to obtain ferromagnetic iron oxide powder. I got it. When the coercive force of this material was measured using a conventional method, it was found to be 6
It was 930e.

Example 4 The treated slurry obtained in Example 2 (before filtration) was wet-treated in an autoclave in the same manner as in Example 3 to obtain the desired ferromagnetic iron oxide powder E. The coercive force of the second sample was measured using a conventional method and was found to be 6600e.

Comparative Example 2 The treated slurry obtained in Comparative Example 1 (before filtration) was placed in an autoclave, wet-treated at 120°C for 3 hours, cooled, washed with water and dried in a conventional manner to obtain magnetic iron oxide powder F. Obtained. When the coercive force of this material was measured using a conventional method, it was found to be 5520.
It was e.

Example 5 The treated slurry (before filtration) obtained in Example 1 was filtered by a conventional method and washed with water. The wet cake was then placed in an autoclave and treated with steam at 100°C for 24 hours (pressure 1
kg/cm2), and after cooling, was washed with water and dried by a conventional method to obtain the desired ferromagnetic iron oxide powder G. The coercive force of this material was measured using a conventional method and was found to be 6400e.

Example 6 Powder A obtained in Example 1 was heated to 150% in an N2 gas atmosphere.
The desired ferromagnetic iron oxide powder H was obtained by dry heat treatment at ℃ for 1 hour. When the coercive force of this material was measured using a conventional method, it was found that
It was 6080e.

Magnetic tapes were prepared using the powders D-H obtained in Examples 3 to 6 and Comparative Example 2 in the same manner as in Example 1, and the coercive force (He), coercive force (He), Squareness ratio (Br/B+e), orientation (OR)
, saturation magnetic flux density (B+m) and switching field distribution (SFD)
were measured and the results shown in Table 2 were obtained.

14-IJ42 Table 115 Completed- Procedural amendment (voluntary) October 30, 1981 1. Case description Patent application filed on October 22, 1988 2. Title of invention Method for producing ferromagnetic iron oxide powder 3
, Relationship to the case of the person making the amendment Patent applicant address 3-22-4 Edobori-chome, Nishi-ku, Osaka 550, Japan Subject of amendment Column 5 for detailed description of the invention in the specification
, Contents of the amendment As shown in the attached document Detailed explanation of the attached invention (1) In the specification, [Usually 1 to 10 atom% 1] is corrected to [Usually 1 to 20 atom%] on page 5, lines 18 to # & 19 do.

(2) Same, same page, line 19 [preferably 2 to 7 atom%]
is corrected to [preferably 2 to 10 atomic %1].

Claims (1)

[Claims] On the surface of magnetic iron oxide powder, 1~
・20 atomic % of fluorocarbon compound and 2. to 3 atomic %
In the method for producing ferromagnetic iron oxide powder coated with Ml iron compound, first, 5=95! of the total cobalt salts added.
Cobalt salt of 2% and ferrous salt of 1 to 20% of the total ferrous salts to be added were deposited with alkali on Table 11 of the powder in a non-acidic atmosphere. and then further depositing the remaining ferrous salt of the cobalt salt powder on the surface of the sample liquid adhesion layer in a non-oxidizing atmosphere using an alkali. Method.