JPS6411575B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved method for producing cobalt- and ferrous-containing ferromagnetic iron oxide powders useful as recording elements in magnetic recording media. Magnetic iron oxide powder containing cobalt and ferrous iron has a higher coercive force than magnetic iron oxide powder that does not contain cobalt and ferrous iron, such as the conventionally used γ-Fe ₂ O ₃ powder. When used in magnetic recording media, there are 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
A product with even higher magnetic properties is required,
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. death,
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. That is, the present invention provides a method for producing a ferromagnetic iron oxide powder, in which a cobalt compound and a ferrous compound are deposited on the surface of a magnetic iron oxide powder in a dispersion of the powder. The deposition of cobalt compounds and ferrous compounds with alkali is carried out in the first stage and second stage, and the cobalt salt and ferrous salt used for deposition in the first stage are the total cobalt salt and total ferrous salt added in the second stage. 50 to 95% by weight of the salt and 5 to 20% by weight of the ferrous salt, respectively, and the cobalt salt and ferrous salt used for deposition in the previous step.
The Co/Fe ratio exceeds 1, and the pH of the dispersion is adjusted to 6.5 by adding cobalt salt and ferrous salt to an alkali in the first stage.
In steps 9 to 9, the powder is coated on the surface of the powder in a non-oxidizing atmosphere, and in a subsequent step, the remaining cobalt salt and the remaining ferrous salt are applied to the surface of the coated layer with an alkali in a non-oxidizing atmosphere. This is a method for producing ferromagnetic iron oxide powder, characterized by further performing deposition. The magnetic iron oxide powder used in the present invention is γ
Examples include -Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, or bertolide compound powder obtained by partially reducing γ-Fe ₂ O ₃ in a reducing gas such as hydrogen, among others. γ-Fe ₂ O ₃ powder is preferred. Examples of cobalt salts include inorganic and organic acid salts of cobalt, such as cobalt sulfate, cobalt chloride, and cobalt oxide, with cobalt sulfate being preferred industrially. Ferrous salts include ferrous sulfate,
Examples include ferrous salts of mineral acids such as ferrous 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. Cobalt compounds or ferrous compounds formed by salts and alkalis include:
Examples 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, such as replacing the reaction vessel with an inert gas or bubbling an inert gas into the solution in the reaction vessel. It's okay. In the method of the present invention, magnetic iron oxide powder is usually dispersed in water, a weak alkaline aqueous solution, or an alkaline aqueous solution, and a cobalt salt, a ferrous salt, and an alkali are added to the powder, or a cobalt salt and an alkali are added to the powder in a specific addition ratio. The cobalt compound and ferrous compound produced by neutralizing a certain amount of cobalt salt and ferrous salt with alkali in the previous stage are dispersed in an aqueous solution of ferrous salt and an alkali is added to the powder. The surface is coated in a non-oxidizing atmosphere, and then the remaining cobalt salt and ferrous salt are added to the system in a later stage to neutralize it, and the surface of the deposited layer is further coated in a non-oxidizing atmosphere. Cobalt and ferrous compounds are deposited. Specifically, the method for forming this deposit is to disperse the powder in water or a weak alkaline aqueous solution, and add specific amounts of cobalt salts and ferrous salts and the alkali necessary to neutralize these salts. and then additional alkali is added until a specific OH group concentration is reached, followed by simultaneous addition of the remaining cobalt salts and ferrous salts and the amount of alkali necessary to neutralize these salts. A method of dispersing the powder in an aqueous solution containing a specific amount of cobalt salt and ferrous salt, adding an alkali to the solution to neutralize it, and further adding an alkali to achieve a specific OH group concentration,
Next, the remaining cobalt salts and ferrous salts and an amount of alkali necessary to neutralize these salts are simultaneously added. and the necessary alkali to neutralize these salts,
Examples include a method in which an alkali is further added until a specific OH group concentration is reached, and then the remaining cobalt salt and ferrous salt are simultaneously added with an amount of alkali necessary to neutralize these salts. , said~
In the method described above, the alkali necessary for the subsequent neutralization may be added before the subsequent deposition. The ferromagnetic iron oxide powder obtained by the method of the present invention is usually 1 to 20 atomic %, preferably 2 to 10 atomic %, more preferably 3 atomic %, based on the iron atoms of the powder, on the surface of the magnetic iron oxide powder. ~7 atom % cobalt compound and usually 2 to 30 atom %, preferably 4 to 25 atom %
It is coated with a ferrous compound of atomic %, more preferably 5 to 20 atomic %, 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~
The ratio is 0.5:1, but is not limited to this. In the deposition of the method of the present invention, in the first step, 50 to 95% by weight of the total cobalt salt added, preferably
Cobalt salt in an amount of 50-80% by weight and 5-20% by weight of the total ferrous salts added, preferably 5-15% by weight
amount 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, for example when using a conventional method such as Comparative Example 1 described below, 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 is
Although it varies somewhat depending on the method of forming the deposited layer, the molar concentration of OH groups, the temperature at the time of deposition, etc., it generally requires 15 minutes or more, and preferably 1 to 2 hours.
When the powder is dispersed in water or a weak alkaline aqueous solution and reacted as in the above method, the pH of the dispersion is usually 7 to 9, preferably 7.5 to 8.5.
It is better to If a better effect is expected, the ratio of Co/Fe to be added should be appropriately selected depending on the molar concentration of PH or OH groups in the system, the temperature during deposition, the method of adding raw materials, etc. In the case of PH6.5 to 9 in the first stage, the Co/Fe addition ratio is set to exceed 1, preferably 2 to 8, more preferably 3 to 8.
5, and in this case, it is more preferable to set the pH to 7 to 8.5. It is further preferred that the method is carried out at room temperature. After the first stage deposition, the OH group concentration in the system is 0.5 to 1.5 mol/, preferably
It is preferable to additionally add alkali so that the amount becomes 0.7 to 1.2 mol/. Then, in the latter stage, it is necessary to add the remaining cobalt salt and the remaining ferrous salt to the slurry in which the adhering powder is dispersed, neutralize it with an alkali, and apply it to the surface of the adhering layer. This alkali may be added to the system in advance, or the cobalt salt and the first
The amount necessary to neutralize iron salts or a slight excess amount may be added at the time of deposition, and the OH group concentration at the time of deposition is 0.7.
It is preferable to adjust the amount to ~1.2 mol/part, and it is especially preferable to add three types of raw materials in parallel. In addition, in the deposition method of the present invention, the suspension slurry concentration of the powder is usually 20 to 200 g/, preferably 50 to 150 g/, and the deposition reaction temperature is:
It 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, and if the atmosphere is not non-oxidizing, the first
The iron compound is unnecessarily oxidized and the desired effect cannot be obtained. In addition, in the method of the present invention, cobalt salt,
In addition to ferrous salts, transition metal salts such as manganese salts, zinc salts, and nickel salts may be added as appropriate. The ferromagnetic iron oxide obtained by the above method can be obtained as ferromagnetic iron oxide powder by filtration, washing with water, and drying by a conventional method. before this filtration
Wet treatment in an autoclave at a temperature of 100-200℃, or after this filtration or drying, dry heat treatment in a non-oxidizing atmosphere at a temperature of 120-250℃, or after this filtration at a temperature of 60-200℃. It is desirable to perform a steam treatment at a temperature of 100 to 100 ml, since this yields a ferromagnetic iron oxide powder with even higher magnetic properties. The steam treatment here refers to the wet cake of ferromagnetic iron oxide that has been filtered, either as it is, or after being washed with water and then dried at the lowest possible temperature in a non-oxidizing atmosphere. There are methods such as heating in the presence of heated water vapor and contacting it in the presence of heated steam in a fluidized bed. Further, after the wet treatment using an autoclave or after the steam 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, it is preferable to perform a wet treatment in an autoclave or a steam treatment, or a dry heat treatment in a non-acetic acid atmosphere after the above-mentioned treatments after the deposition of the method of the present invention. preferable. The ferromagnetic iron oxide obtained by the above method has advanced magnetic properties, and magnetic tapes manufactured using this material have high coercive force, squareness ratio, orientation,
Excellent saturation magnetic flux density. The reasons for this are not fully clear, but (1) the precipitation rates of cobalt compounds and ferrous compounds are different, and the reaction rates of cobalt compounds and ferrous compounds are usually uneven on the surface of powder particles, but this method Then, the OH group concentration or PH,
(2) Since the addition ratio is controlled, the grain growth of the cobalt compound is regulated, and (2) the rapid precipitation of the ferrous compound is alleviated, so the cobalt compound and the ferrous salt compound are deposited on the surface of the powder particles. It is presumed that the precipitation is carried out in a well-balanced and uniform manner. The method of the present invention will be understood in more detail from the following Examples and Comparative Examples. Example 1 50 g of γ-Fe ₂ O ₃ powder (coercive force: 380 Oe, average particle diameter (major axis) 0.6 μ, axial ratio: 8:1) was dispersed in 1 part water to make a slurry, and reacted with N ₂ gas. After replacing the container, 24 ml of 1 mol/cobalt sulfate aqueous solution and 0.6 mol/1 sulfuric acid were added to this slurry.
10 ml of an aqueous iron solution and 14 ml of a 5 mol/aqueous sodium hydroxide solution were added simultaneously over 1 hour while keeping the pH at 8, then 290 ml of 5 mol/aqueous sodium hydroxide was added, and the mixture was stirred for 30 minutes. Subsequently, 6 ml of a 1 mol/cobalt sulfate aqueous solution and
90ml of 0.6mol/ferrous sulfate aqueous solution and 5mol/
24 ml of an aqueous sodium hydroxide solution was simultaneously added over 1 hour, and the resulting slurry was held for 3 hours with stirring. This slurry is filtered, washed with water, and dried in a conventional manner to obtain the desired ferromagnetic iron oxide powder A.
I got it. The coercive force of this material was measured using a conventional method and was found to be 570 Oe. Example 2 350 g of γ-Fe ₂ O ₃ same as that used in Example 1
was dispersed in 1 part of water to make a slurry, and after replacing the reaction vessel with _N2 gas, in this slurry
24ml of 1mol/cobalt sulfate aqueous solution and
5 ml of 0.6 mol/ferrous sulfate aqueous solution and 5 mol/
11 ml of an aqueous sodium hydroxide solution was added over 1 hour, and then 317 ml of a 5 mol/aqueous sodium hydroxide solution was added, followed by stirring for 30 minutes. Next, 6 ml of 1 mol/cobalt sulfate aqueous solution
and 90 ml of a 0.6 mol/ferrous sulfate aqueous solution were simultaneously added 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. The coercive force of this material was measured using a conventional method and was found to be 560 Oe. Comparative Example 1 50 g of γ-Fe ₂ O _3, the same as that used in Example 1, was dispersed in 1 part of water to make a slurry, and after replacing the reaction vessel with N ₂ gas, 1 mol/g of γ-Fe 2 O 3 was dispersed in this slurry.
30 ml of cobalt sulfate aqueous solution and 100 ml of 0.6 mol/ferrous sulfate aqueous solution, then 5 mol/
36 ml of an aqueous sodium hydroxide solution was added over 1 hour, and further 292 ml of a 5 mol/aqueous sodium hydroxide solution was added, and the mixture was maintained for 3 hours with stirring. This slurry is filtered, washed with water, and
After drying, magnetic iron oxide powder C was obtained. The coercive force of this material was measured using a conventional method and was found to be 480 Oe. A blend of the powders A to 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 C 100 parts by weight (2) Soybean lecithin 1 〃 (3) Surfactant 4 〃 (4) PVC-vinyl acetate copolymer resin 15 〃 (5) Dioctyl phthalate 5 〃 ( 6) Methyl ethyl ketone 111 〃 (7) Toluene 122 〃 Next, each magnetic coating was applied to a polyester film by a conventional method, oriented and dried to produce a magnetic tape having a magnetic coating film about 9μ thick. For each tape, the coercive force (Hc), squareness ratio (Br/Bm), orientation (OR), saturation magnetic flux density (Bm), and switching field distribution (SFD) were measured using the usual methods, and the results shown in Table 1 were measured. Got the results.

[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 the desired ferromagnetic oxidation. Iron powder D was obtained. The coercive force of this material was measured using a conventional method and was found to be 693 Oe. Example 4 The treated slurry obtained in Example 2 (before filtration) was subjected to wet treatment in an autoclave in the same manner as in Example 3, and after cooling, it was washed with water and dried in a conventional manner to obtain the desired ferromagnetic oxidation. Iron powder E was obtained. When the coercive force of this material was measured using a conventional method, it was found to be 660Oe.
It was hot. 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. . The coercive force of this material was measured using a conventional method and was found to be 552 Oe. Example 5 After filtering the treated slurry (before filtration) obtained in Example 1 and washing with water, the wet cake was placed in an autoclave and treated with steam at 100°C for 24 hours (pressure: 1 kg/kg). cm ² ), 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 640 Oe. Example 6 Powder A obtained in Example 1 was dry heat treated at 150° C. for 1 hour in an N ₂ gas atmosphere to obtain the desired ferromagnetic iron oxide powder H. The coercive force of this material was measured using a conventional method and was found to be 608 Oe. Magnetic tapes were prepared using the powders D to H obtained in Examples 3 to 6 and Comparative Example 2 in the same manner as in Example 1, and the coercive force (Hc), Squareness ratio (Br/
Bm), orientation (OR), saturation magnetic flux density (Bm), and switching field distribution (SFD), and the results shown in Table 2 were obtained.

[Table] Example 7 75 g of γ-Fe ₂ O ₃ powder (coercive force: 390 Oe, average major axis particle diameter of about 0.5 μ, axial ratio: about 11) was dispersed in 1.5 g of water to prepare a slurry. The pH of this slurry is
After adjusting the temperature to 8.0 with a 5 mol/aqueous sodium hydroxide solution, 36 ml of an aqueous solution of 1 mol/cobalt sulfate (equivalent to 80% of the total amount of cobalt sulfate added) and
15ml of 0.6mol/ferrous sulfate aqueous solution (ferrous sulfate
(equivalent to 10% of the total amount of iron added) and 5 mol/aqueous sodium hydroxide solution to bring the pH to 8.0 for 1 hour.
Then, 194 ml of a 10 mol/aqueous sodium hydroxide solution was added and stirred for 30 minutes. Next, 9 ml of a 1 mol/cobalt sulfate aqueous solution (equivalent to 20% of the total amount of cobalt sulfate added) and 135 ml of a 0.6 mol/ferrous sulfate aqueous solution.
(equivalent to 90% of the total amount of ferrous sulfate added) and 5 mol/aqueous sodium hydroxide solution equivalent to neutralization.
Additions were made in parallel over time. After the addition was completed, the slurry was stirred and aged for 3 hours, then filtered, washed with water, and dried to obtain the desired ferromagnetic iron oxide powder (). When the coercive force of this material was measured using a conventional method, it was found that
It was 576 Oe. Example 8 In Example 7, the ratio of the amount of cobalt sulfate added in the first and second stages to the total amount of added cobalt sulfate was changed to 95% and 5%, respectively, and
The desired ferromagnetic iron oxide powder (J) was obtained in the same manner as in Example 7 except that the pH was changed to 6.5. When the coercive force of this material was measured using a conventional method, it was found that
It was 584 Oe. Example 9 In Example 7, the ratio of the amount of cobalt sulfate added in the first and second stages to the total amount of added cobalt sulfate was both changed to 50%, and the pH of the first stage was changed to 9.0. The desired ferromagnetic iron oxide powder (K) was obtained in the same manner. The coercive force of this material was measured using a conventional method and was found to be 569 Oe. Example 10 In Example 7, the ratio of the amount of ferrous sulfate added in the first and second stages to the total amount of ferrous sulfate added was changed to 5% and 95%, respectively, and the pH of the first stage was changed.
The desired ferromagnetic iron oxide powder (L) was obtained in the same manner as in Example 7 except that the amount was changed to 6.5. When the coercive force of this material was measured using a conventional method, it was found to be 597Oe.
It was hot. Example 11 In Example 7, the ratio of the amount of ferrous sulfate added in the first and second stages to the total amount of ferrous sulfate added was changed to 20% and 80%, respectively, and the pH of the first stage was changed.
The desired ferromagnetic iron oxide powder (M) was obtained in the same manner as in Example 7 except that the value was changed to 9.0. When the coercive force of this material was measured using a conventional method, it was found that
It was 560 Oe. Comparative Example 3 A ferromagnetic iron oxide powder (N) was obtained in the same manner as in Example 7 except that the PH in the first stage was set to 13.5. The coercive force of this material was measured using a conventional method and was found to be 586 Oe. Comparative Example 4 75g of the same γ-Fe ₂ O ₃ powder used in Example 7
was dispersed in 1.5 ml of water to form a slurry, and while maintaining the temperature of this slurry at 25°C, 45 ml of a 1 mol/cobalt sulfate aqueous solution and
150 ml of 0.6 mol/ferrous sulfate aqueous solution was added.
Next, 54 ml of a 5 mol/aqueous sodium hydroxide solution was added to the slurry over 60 minutes, and an additional 10 mol/aqueous solution was added to the slurry.
194 ml of an aqueous sodium hydroxide solution was added over 30 minutes. After the addition was completed, the slurry was stirred and aged for 3 hours, filtered, washed with water, and dried to obtain ferromagnetic iron oxide powder (O). The coercive force of this material was measured using a conventional method and was found to be 505 Oe. Regarding the powders I to O obtained in Examples 7 to 11 and Comparative Examples 3 to 4, magnetic tapes were prepared in substantially the same manner as in the above case, and various magnetic properties were measured.
Obtained the results in the table. In addition, the case of Examples 1 to 6 and Comparative Examples 1 to 2, and the case of Examples 7 to 11 and Comparative Examples 3 to 4
The methods for measuring the coercive force as a powder property and the coercive force as a tape property are both conventional methods, but depending on the measurement model and other factors, the coercive force as a powder property in the former case is generally different from the coercive force in the latter case. The coercive force of the former tape is relatively high, and the coercive force of the former tape is lower than that of the latter.

【table】

Claims (1)

[Claims] 1. On the surface of magnetic iron oxide powder, a cobalt compound of 1 to 20 atomic % and 2 to 30 atomic % of the iron atoms of the powder is added.
A method for producing a ferromagnetic iron oxide powder in which atomic percent of a ferrous compound is deposited in a dispersion of the powder, in which the deposition of the cobalt compound and the ferrous compound by a cobalt salt, a ferrous salt, and an alkali is performed as a preliminary step. The cobalt salt and ferrous salt used for deposition in the first stage are 50 to 95% by weight and 5 to 20% by weight of the total cobalt salt and total ferrous salt added in the first and second stages, respectively.
% by weight, and the Co/Fe ratio of the cobalt salt and ferrous salt used for deposition in the first step exceeds 1, and the pH of the dispersion is adjusted to 6.5 to 6.5 with an alkali in the first step. In step 9, the powder is coated on the surface of the powder in a non-oxidizing atmosphere, and in the latter stage, the remaining cobalt salt and ferrous salt are further coated on the surface of the coated layer with an alkali in a non-oxidizing atmosphere. 1. A method for producing ferromagnetic iron oxide powder.