JPS6018609B2 - Ferromagnetic powder and its manufacturing method - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a ferromagnetic powder and a method for producing the same, and an object thereof is to produce a cobalt-containing iron oxide ferromagnetic powder that has a good coercive force distribution and excellent thermal stability. It is in.

Since cobalt-containing iron oxide ferromagnetic powder has excellent magnetic properties such as high coercive force, it is widely used as a recording element of high-performance magnetic recording media, and is also used as a magnet material.

Various methods have been proposed to date for producing such cobalt-containing iron oxide ferromagnetic powder, and one of the most useful methods is to use y-Fe203 powder as a nucleus crystal, and then add a cobalt salt to the ferromagnetic powder. A method has been proposed in which iron oxide is dispersed in a solution containing cobalt and ferrous salt, and then an alkaline solution is added thereto to form an iron oxide layer containing mainly cobalt on the nuclear crystals.

However, the y-Fe203 powder used in this method is usually mixed with a ferrous salt and an alkaline aqueous solution at a concentration of 30 to 600
The raw material is Q-iron oxyhydroxide powder, which is obtained by mixing and reacting at a temperature of zero and oxidizing the powder, which is then heated and reduced and further oxidized.

However, since such y-Fe203 powder has a large magnetic field ratio and an uneven particle size distribution, it also has a wide coercive force distribution, and when trying to obtain a fine powder, it requires transfer, heating demagnetization, etc. It lacked thermal stability and could not satisfy the characteristics of cobalt-containing iron oxide using it as a nucleus crystal. The inventors conducted various studies to improve these drawbacks, and as a result, when producing y-Fe203 ferromagnetic powder before forming a surface layer that mainly contains cobalt, it was found that it contained trivalent iron ions. The aqueous solution is added to an alkaline aqueous solution in an amount equivalent to or more than the iron ion at a temperature of 3°C or lower, and reacted to produce ferric hydroxide, which is aged and then subjected to a hydrothermal reaction in an autoclave. to produce Q-iron oxyhydroxide powder, filtered and dried, and then heat-reduced and further oxidized to produce a y-Fe203 ferromagnetic powder.
Fe208 ferromagnetic powder is obtained, and this y-Fe203 ferromagnetic powder is dispersed in a solution containing a cobalt salt, and an alkaline aqueous solution is added to this to form a surface layer containing mainly cobalt on the surface of the y-Fe203 powder. When formed, the maximum axis diameter is 30 mm or less, the axial ratio is 5 or less, the specific surface area by BET method is 40〆/ta or less, and the coercive force is 23. Song A/
It was discovered that a cobalt-containing iron oxide ferromagnetic powder having a uniform particle size distribution of m or more, a narrow coercive force distribution, good thermal stability, and little transfer and heat demagnetization can be obtained, and this invention was achieved.

In this invention, when the aqueous solution containing trivalent iron ions is added to the alkaline aqueous solution to produce ferric hydroxide, the reaction temperature is 3000° C. or higher to appropriately control the growth of ferric hydroxide. Since it is difficult to obtain fine Q-ferric oxyhydroxide with a uniform particle size distribution, it is preferable to carry out the process at a temperature of 3000°C or below. More preferably, it is carried out at temperature.

In addition, the aging is preferably carried out for 10 minutes or more at 100 oo or less, usually for 3 minutes or more at room temperature, preferably 3 to 7. If the aging time is too short, the growth of ferric hydroxide will be insufficient. If it is too long, growth will proceed excessively, making it difficult to obtain a uniform particle size distribution. The aqueous solution containing trivalent iron ions can be prepared by dissolving one or more of various soluble ferric salts such as ferric chloride, ferric sulfate, and ferric nitrate in water; or ferrous chloride, ferrous sulfate,
It is prepared by adding one or more of various soluble ferrous salts such as ferrous nitrate to water and then oxidizing it with an oxidizing agent, etc., and containing trivalent iron ions. used.

These iron salts are preferably used in aqueous solutions with a concentration of 0.5 mol/less. The alkaline aqueous solution to which the aqueous solution containing trivalent iron ions is added is preferably a caustic alkaline aqueous solution such as sodium hydroxide or potassium hydroxide, and the amount used is such that ferric hydroxide is produced well. , and in order to make the particle size of ferric hydroxide appropriate, it is sufficient that the amount is equivalent to or more than the trivalent iron ion; Since it becomes heterogeneous and widens the particle size distribution, it is preferable to use it within a range where the free alkali concentration is 1 mol/or less.

In this way, an aqueous solution containing trivalent iron ions is added to an equivalent or more alkaline aqueous solution at a temperature of 30q0 or less and reacted to produce ferric hydroxide, which is further aged at room temperature to produce ferric hydroxide. A suspension with appropriately controlled iron growth is obtained, and when this suspension is placed in an autoclave and subjected to a hydrothermal reaction, fine Q particles with a uniform particle size distribution and a small
- Iron oxyhydroxide powder is obtained.

Then, this Q-iron oxyhydroxide powder is washed with water, filtered, and dried, and then heated for 250 min in a reducing gas such as hydrogen stream.
By thermal reduction at a temperature of ~400 oo and further oxidation at a temperature of 20,000 or higher in air, for example, fine needle-shaped y-Fe203 ferromagnetic powder with a small axial ratio and a uniform particle size distribution can be obtained. In the hydrothermal reaction in an autoclave when producing Q-iron oxyhydroxide powder, if it is carried out at a temperature of 12,000 or less, it will take a long time to crystallize, and if it is carried out at a temperature of 25,000 or more, Q-Fe203 powder will be Therefore, it is preferable to carry out the process at a temperature in the range of 120 to 25,000 degrees Celsius, and more preferably in the range of 150 to 220 degrees Celsius.

In addition, when heating and reducing the temperature at 250°C or higher, a product with effective magnetic properties can be obtained, and reduction is promoted as the heating temperature increases, but heating at 40,000°C or higher causes crystallization and decreases the coercive force. 250-400q○ for
It is preferable to carry out the test within the range of . Further, the temperature at which the oxidation is carried out after heating reduction is preferably 20 mm or higher, since at low temperatures the oxidation becomes insufficient or takes a long time. The thus obtained y-Fe203 ferromagnetic powder is then dispersed in a solution containing a cobalt salt and a ferrous salt, and an aqueous alkaline solution is further added thereto for reaction, resulting in a major axis diameter of 30 m. Below, the bag ratio is 5 or less, the specific surface area by BET method is 40/ta or less, and the coercive force is 23. Mackerel A
A cobalt-containing iron oxide ferromagnetic powder with a uniform particle size distribution of /m or more can be obtained. Suitable cobalt salts include cobaltous sulfate, cobaltous chloride, cobaltous nitrate, etc., and ferrous salts include ferrous sulfate, ferrous chloride, ferrous nitrate, etc. As the alkaline aqueous solution, a caustic alkali aqueous solution such as sodium hydroxide or potassium hydroxide is preferably used.

The concentration of the alkaline aqueous solution must be such that at least cobalt and ferrous hydroxides precipitate, and the reaction temperature is preferably 50 qo or less in order to allow the reaction to proceed uniformly. The cobalt-containing iron oxide ferromagnetic powder obtained as described above has a major axis diameter of 30 m or less, a ball ratio of 5 or less, a specific surface area of 40 m/m or less by the BET method, and a coercive force of 23. The diameter is A/m or more, the particle size distribution is uniform, the coercive force distribution is narrow, the thermal stability is good, the transfer characteristics are excellent, and there is little heating demagnetization. Next, embodiments of the invention will be described.

Example 1 A ferric chloride aqueous solution was prepared by dissolving 10 moles of ferric chloride (FeC131 fine 20) in 30 ml of water, and a sodium hydroxide aqueous solution was prepared by dissolving 60 mol of sodium hydroxide in 60 ml of water. At ○, an aqueous ferric chloride solution was added to an aqueous sodium hydroxide solution to obtain a brown precipitate. Next, after aging this at room temperature for one hour, this suspension was placed in an autoclave and a hydrothermal reaction was carried out at 180q0 for 1 hour. After the reaction is complete, wash the yellow precipitate with water, filter it,
After drying, iron oxyhydroxide powder was obtained. Next, the obtained Q-iron oxyhydroxide powder was heated in air at 60,000 ℃ for 1 hour to produce Q-Fe203 powder, and this Q-Fe
80 pieces of 203 powder were spread on a quartz board, softened in a tubular air furnace, and hydrogen gas was bubbled through at a rate of 300 pieces per minute.
00 to obtain Fe304 powder, which was further oxidized in air at a temperature of 250 oo to obtain a powder with a major axis diameter of 20 m and an axial ratio of 4.
, specific surface area 25th/evening by BET method, coercive force 23 view A
/m, saturation magnetization amount (〇s) 9.11×10-3Kb・m
/k9 y-Fe203 powder was obtained.

Next, 80 pieces of this y-Fe20 powder were treated with 0 cobalt sulfate.
．． 4 moles of ferrous sulfate and 1.2 moles of ferrous sulfate were dispersed in an aqueous solution 3, and an aqueous sodium hydroxide solution 3 containing 16 moles of sodium hydroxide dissolved therein was added.

The temperature of this dispersion liquid was raised to 45° C., and the dispersion was continued for 6 hours while maintaining this temperature. Next, the magnetic powder was taken out, thoroughly washed with water to remove the reaction solution, and then dried to obtain a cobalt-containing iron oxide ferromagnetic powder. The thus obtained cobalt-containing iron oxide ferromagnetic powder had a maximum axis diameter of 20 m, a short axis diameter of 5 m, an axial ratio of 4, and a specific surface area of 22.1 by the BET method. The magnetic force was 51.7 KA/m, and the content of cobalt atoms was 2.5% by weight.

Using the thus obtained cobalt-containing y-Fe203 powder, 8 parts by weight of Co-containing y-Fe203 powder VAGH (manufactured by U.C.C., USA, 11" vinyl chloride-vinyl acetate-vinyl alcohol copolymer) ) Pandex T-5250 (manufactured by Dainippon 7″ Ink Co., Ltd., urethane elastomer) Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd., trifunctional low molecular weight isocyanate compound) Composed of cyclohexanone 60″ toluene 60″ A magnetic paint was prepared by mixing and dispersing the composition in a ball mill.

This magnetic paint was applied onto a polyester base film with a thickness of 12 mm to a dry thickness of 4 mm, dried, surface treated, and then cut into predetermined shapes to produce a magnetic tape. Example 2 In Example 1, the temperature when adding the ferric chloride aqueous solution to the sodium hydroxide aqueous solution was set to 0°C to obtain a brown precipitate, and this suspension was placed in an autoclave and heated at 180°C for 1 hour. A hydrothermal reaction was carried out to obtain Q-iron oxyhydroxide. At 28.7/
In the evening, the cobalt atom content was 5 with a coercive force of 50.1 KA/m.
．． Obtain 90% by weight cobalt-containing y-Fe203 powder,
Furthermore, a magnetic tape was produced in the same manner as in Example 1 using this cobalt-containing y-Fe203 powder.

Example 3 In the process of obtaining cobalt-containing iron oxide powder in Example 2, the procedure was the same as in Example 2 except that the amount of cobalt sulfate used was 0.8 mol and the amount of ferrous sulfate was 2.4 mol. , long axis diameter 12 meters, short axis diameter 3 meters, mouse ratio 4, BET
Specific surface area by method: 28.1/unit, coercive force: 75. Ship A/
A cobalt-containing y-Fe2Q powder having a cobalt source content of 4.50% by weight was obtained using m, and a magnetic tape was produced in the same manner as in Example 2 using this cobalt-containing y-Fe203 powder.

Comparative Example A ferrous sulfate aqueous solution in which 10 moles of ferrous sulfate (FeS04.740) was dissolved in 40 mL of water, and a sodium hydroxide aqueous solution in which 70 moles of thorium hydroxide were dissolved in 40 mL of water were prepared. A sodium hydroxide aqueous solution was added to the ferrous aqueous solution to obtain a pale green precipitate.

Next, this suspension was placed in a constant temperature water bath, and the air was blown into the suspension at 4 picoC per minute, and an oxidation reaction was carried out for 6 hours to obtain a yellow precipitate, which was washed with water, filtered, and dried. TeQ
- Iron oxyhydroxide powder was obtained. Next, this Q-iron oxyhydroxide was heated and reduced in the same manner as in Example 1, further oxidized to obtain y-Fe203 powder, and then treated with cobalt to give a long magnetic diameter of 20 m and a short koji diameter. 3.m, Koji ratio 6.7,
Specific surface area by BET method: 39.5/unit, coercive force: 39.
A cobalt-containing y-Fe203 powder having a cobalt atom content of 2.55% by weight at peach A/m was obtained. Furthermore, a magnetic tape was produced in the same manner as in Example 1 using this cobalt-containing y-Fe203 powder. In order to investigate the coercive force distribution of the cobalt-containing iron oxide ferromagnetic powders obtained in Example 1 and Comparative Example, the anisotropic magnetic field distribution was measured using a sample vibrating magnetometer.

Figure 1 shows this result graphically, and graph A
Graph B shows the anisotropic magnetic field distribution of the magnetic powder obtained in Example 1, and graph B shows the anisotropic magnetic field distribution of the magnetic powder obtained in Comparative Example. As is clear from this graph, the cobalt-containing iron oxide ferromagnetic powder obtained according to the present invention has a narrower anisotropic magnetic field distribution than that obtained in the comparative example, which indicates that the cobalt-containing iron oxide ferromagnetic powder obtained according to the present invention has a narrower anisotropic magnetic field distribution than that obtained in the comparative example. It can be seen that the ferromagnetic powder has a good coercive force distribution. Furthermore, in order to examine the thermal stability of the cobalt-containing iron oxide ferromagnetic powders obtained in each of the Examples and Comparative Examples, thermal demagnetization was measured and transfer characteristics were tested.

For heating demagnetization, a container with a diameter of 6 yen and a height of 3 was filled with the obtained magnetic powder, which was then saturated magnetized at room temperature in a magnetic field of 79 A/m, and the saturated residual magnetization amount lrs was measured. This saturated magnetized sample was held at 60 pm for 2 hours, taken out at room temperature, and the residual magnetization lr was measured. Set the rod; xlo. The percentage of fly loss was measured.

In addition, for the transfer property test, a container with a diameter of 6 mm and a height of 3 mm was filled with the obtained magnetic powder, and the magnetic powder was poured into a container with a diameter of 6 mm and a height of 3 mm. After holding the sample in a magnetic field of Anom for 1 hour, the residual magnetization lr was measured, and then it was saturated in a magnetic field of 79 A/m, and the saturation residual magnetization, rS, was -2. 10 and the foot of the mountain) and decimals.

Table 1 below shows the results.

As is clear from the above table of Table 1, the cobalt-containing iron oxide ferromagnetic powders obtained in the present invention (Examples 1 to 3) are superior to the subordinate cobalt-containing iron oxide ferromagnetic powders (comparative examples). In all cases, thermal demagnetization and transfer were small, which indicates that the cobalt-containing iron oxide ferromagnetic powder obtained by the present invention has excellent thermal stability.

Furthermore, regarding the magnetic tapes obtained in each example and comparative example, coercive force (Hc), residual magnetic flux density (Br), square shape (
Br/&), DCS/N and ACS/N were measured to test the erasure characteristics.

In the erasing characteristic test, the IKEz signal was recorded on a magnetic tape with a tenth B input, and the erasing characteristic of the reference tape (BASFC401R) was 0. &Measure the difference in the playback output signal before and after erasing when erasing with an erase current 20% higher than the old erase current,
Expressed in dB. Table 2 below shows the results.

As is clear from the upper table of Table 2, the magnetic tape obtained using the cobalt-containing iron oxide ferromagnetic powder of the present invention (Example 1
-3) have higher coercive force, higher residual magnetic flux density, higher squareness, lower DCS/N and ACS/N, and better erasing characteristics than conventional magnetic tapes (comparative example). It can be seen that the magnetic recording medium obtained using the cobalt-containing iron oxide ferromagnetic powder of the present invention has excellent magnetic properties, has less noise, and has improved erasing properties.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the anisotropic magnetic field of the cobalt-containing iron oxide ferromagnetic powder obtained by the present invention and the volume percent of the powder particles. Figure 1

Claims (1)

[Claims] 1 Iron oxide ferromagnetic powder is used as a core crystal, and the major axis diameter is 300n, which has a surface layer mainly containing cobalt on the core crystal.
m or less, an axial ratio of 5 or less, a specific surface area of 40 m^2/g or less by the BET method, and a coercive force of 23.9 KA/m or more. is added to an alkaline aqueous solution at a temperature below 30°C and reacted to produce ferric hydroxide. After further aging, this ferric hydroxide was hydrothermally reacted in an autoclave to form α
- After producing iron oxyhydroxide powder, filtering and drying, this produced powder is heated and reduced, and further oxidized to obtain γ-Fe_2O_3 powder, and then this γ-Fe_2O_3 powder is placed in a solution containing cobalt salt and ferrous salt. 1. A method for producing a ferromagnetic powder cape, which comprises dispersing the γ-Fe_2O_3 powder into a powder and adding an alkaline aqueous solution thereto to form a surface layer containing mainly cobalt on the surface of the γ-Fe_2O_3 powder.