JPS61111508A - Manufacturing method for magnetic powder used in magnetic recording - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for magnetic iron oxide powder having its superior coercive force, conductivity, saturated magnetic characteristics and transfer characteristics and its narrow distribution of the coercive force by performing cobalt modification of gamma-iron oxide particles dispersed in alkali solution under the presence of alkali earth metal salt and next, introducing bivalent iron salt thereto, thereby to perform modification by use of bivalent iron. CONSTITUTION:gamma-iron oxide particles are dispersed in alkali solution and added with calcium salt, strontium salt or barium salt and cobalt salt to perform cobalt modification of the gamma-iron oxide particles. Next, they are added with bivalent iron salt to perform modification of bivalent iron and then they are filtered and dried. In this time, and amount of cobalt modification and an amount of bivalent iron modification are respectively 0.1-10% by weight as metal to the gamma-iron oxide and loadings of one kind among calcium salt, strontium salt or barium salt is 0.01-3% by weight as metal to the gamma-iron oxide. The OH density in alkali solution during reaction is 1.0-8.0mol/lcm<2> and the reaction is carried out in the range of temperature 50-104 deg.C.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing γ-iron oxide magnetic powder used for the purpose of magnetic recording, and more specifically relates to a method for producing γ-iron oxide magnetic powder that has been surface-treated with cobalt and divalent iron. -Relates to a method for producing iron oxide powder.

[Prior art] Conventionally, as high-density magnetic recording media, acicular chromium dioxide,
Cobalt-containing acicular magnetic iron oxides are widely used. However, tapes using acicular chromium dioxide have the disadvantage that the head 6 is more worn than conventional tapes using iron oxide, resulting in deterioration of characteristics with repeated use. There are also problems with manufacturing costs and pollution. On the other hand, cobalt-containing acicular magnetic iron oxides can be roughly divided into the following two types. That is, there is a so-called cobalt-doped magnetic iron oxide in which cobalt is uniformly dispersed within the particles, and a type in which cobalt is deposited only on the surface of the magnetic iron oxide particles. In general, the cobalt-doped type and the cobalt-doped type have a higher particle coercivity when the cobalt content is the same, and the cobalt-doped type has a higher particle coercive force than the cobalt-doped type. However, the cobalt-doped type has problems with demagnetization characteristics and changes over time when made into a tape.
It also has the disadvantage of poor transfer characteristics. In the type in which cobalt is precipitated only on the particle surface, these defects are improved and excellent magnetic particles can be obtained. γ cobalt
- For particles deposited only on the surface of iron oxide particles, the coercive force of the particles increases almost linearly as the area of deposited cobalt increases. The addition of cobalt also improves the transfer characteristics when made into a tape by 2 to 8 dB compared to the original γ-iron oxide. However, if the cobalt content is too large, the magnetic properties change over time and the stability against pressure and temperature deteriorates. Also, from the viewpoint of manufacturing costs, it is desirable to reduce the number of cobalt detectives.

Furthermore, as a powder magnetic material, there is a demand for a material that has not only high coercive force but also high saturation magnetization and lower electrical resistance. Also VH8￥! For VTR tapes, it is necessary to make the tape black, and a magnetic material with a high degree of blackening when used in an arc is required, and it is necessary to make the magnetic material as black as possible. Magnetic tapes, especially tapes for VTRs, run at high speeds and therefore become charged due to friction, making them run unsmoothly and causing problems such as dropouts due to the accumulation of dust. Furthermore, the S/N ratio also decreases due to the generation of discharge noise. These problems caused by the generation of static electricity can be solved by making the magnetic tape conductive.

Adding divalent iron to the particle surface is effective in giving powdered magnetic materials high saturation magnetization and low electrical resistance. However, the addition of divalent iron has the disadvantage that the transfer effect of the tape deteriorates.

A method for improving the coercive force and saturation magnetic properties of magnetic powder is to deposit cobalt onto iron oxide powder in the presence of an aqueous salt solution of barium or strontium (Japanese Patent Application Laid-Open No.
7-198607), and a method of adding an aqueous ferrous salt solution (Japanese Unexamined Patent Publication No. 57-181) has been proposed.
102) has also been proposed.

In both of these methods, an aqueous solution of cobalt salt, barium salt, etc. is added to a dispersion of iron oxide particles, and in the latter case, an aqueous ferrous salt solution is added, and finally an alkali is added and a heating reaction is carried out. It undergoes metamorphosis using cobalt, etc.

However, in these methods, the reaction rate is fast, for example, the reaction is completed in 3 to 4 hours at a reaction temperature of 100°C, but the coercive force of the final product is lower than that of the present invention, and moreover, the coercive force of the magnetic powder is lower than that of the present invention. The drawback is that the magnetic force distribution is wide. The reason for this is that it is difficult for cobalt to uniformly deposit on the surface of the γ-iron oxide particles, and therefore a larger amount of cobalt is required than in the present invention to obtain the required coercive force, and the cobalt distribution is not uniform. has wide drawbacks.

[Object of the Invention] An object of the present invention is to provide a method for producing magnetic iron oxide powder that has excellent coercive force, conductivity, saturation magnetic properties, and transfer properties, and has a narrow coercive force distribution.

[Structure of the invention] The present invention comprises dispersing γ-iron oxide particles in an alkaline aqueous solution,
At least one of calcium salt, strontium salt, and barium salt and cobalt salt are added to perform cobalt modification of γ-iron oxide, and then divalent iron salt (ferrous salt) is added to further transform divalent iron. It is characterized by applying makeup and then oven-drying.

The present invention will be explained in detail below.

In the present invention, γ-iron oxide particles dispersed in an alkaline solution are first subjected to cobalt metamorphosis in the presence of an alkaline earth metal salt, and then 21111i iron j8 is added to carry out metamorphosis with divalent iron. . This series of steps is the key point of the present invention, and it has been discovered that by doing so, the γ-iron oxide magnetic powder not only improves conductivity and saturation magnetic properties, but also surprisingly increases coercive force. If cobalt metamorphosis and then divalent iron metamorphosis are performed without adding an alkaline earth metal salt, the coercive force will decrease, resulting in an effect completely opposite to that of the present invention. These conditions are shown in Figure 1.

Furthermore, in the metamorphism reaction process, adding an alkaline aqueous solution at the end to simultaneously deposit (transform) cobalt and divalent iron has drawbacks such as a wide distribution of coercive force, as previously mentioned.

Figure 1 shows γ-iron oxide particles (10
Disperse 0gz and add each alkaline earth metal chloride shown in Figure 1 to 0.5% by weight in the solution after adding m of the metal, and add cobalt chloride to 3.0% by weight between cobalt. Deposition of cobalt (transformation) by processing at 100℃
and investigate the relationship between reaction time and coercive force.
Further, ferrous chloride was added to the reacted product for 5 hours to make the iron content 5%, and heated at 100°C for 1 hour to perform divalent iron transformation (deposition), and the resulting powder was preserved. This shows the results of measuring magnetic force.

In the figure, white circles indicate the case where an alkaline earth metal salt is added, and black circles indicate the case where no addition is made, for comparison. In these cases, the reaction time for cobalt transformation is 5 hours (
After the time (arrow in the figure) had elapsed, ferrous chloride was added, and a heating reaction was carried out to perform metamorphosis with divalent iron. For this last one, the cobalt deposition (m) is approximately 3% relative to iron oxide, and the amount of divalent iron deposited is approximately 5% relative to iron oxide.
It represents the content of ferrous iron relative to Zj of iron oxide and divalent iron, and the ratio is expressed on a weight basis unless otherwise specified. The same applies to the following.

As can be seen from the figure, the coercive force increases slightly with the addition of alkaline earth metal salts, but when ferrous chloride is added afterwards,
The effect is completely opposite depending on the presence or absence of alkaline earth gold B salt. That is, it can be seen that in the absence of an alkaline earth metal salt, the coercive force decreases, whereas in the presence of an alkaline earth metal salt, the coercive force increases rapidly.

Cobalt nl to obtain the desired coercive force.
It is possible to reduce it even further.

Another major feature of the method of the present invention is that magnetic powder with a very narrow coercive force distribution can be obtained as shown in the Examples.

In the present invention, the effects of addition of alkaline earth metal salts and divalent iron salts as described above have not yet been fully elucidated, but the alkaline earth metal acts as a catalyst, and cobalt is uniformly distributed on the surface of the γ-iron oxide particles. It is thought that the coercive force increases because a magnetite or cobalt ferrite layer is uniformly formed on the surface by divalent iron, or a crystal alignment layer similar to the magnetoblanbite structure known from ferrite magnets is formed. It can also be estimated that

It is also thought that cobalt and divalent iron are deposited uniformly in each particle, resulting in a narrow coercive force distribution.

Regarding the transfer effect, the addition of monovalent iron generally worsens the transfer characteristics, but in the present invention, the transfer improvement due to the cobalt deposition effect due to the addition of alkaline earth metal is superior, so the final transfer characteristics are improved. The value is obtained.

In the present invention, the γ-iron oxide particles dispersed in the alkaline aqueous solution have a particle size of the commonly used particle size of about 0.2 to 00 g/μm, and the appropriate amount of dispersion is 80 to 150 g/l.

The appropriate alkali concentration is 1 to 8 mol/1 in terms of OH group concentration. The higher the alkali concentration, the faster the reaction rate, but this has the disadvantage of increasing the cost of the alkali and requiring a large amount of water and time to wash the reaction product. For these reasons, preferably 2 to 8 mol/OHIIEI degree
It is 1.

As the alkali, caustic potash, caustic soda, lithium hydroxide, etc. can be used, but industrially, caustic soda is advantageous in terms of cost for SJ production.

Calcium salts, strontium salts used in the present invention,
As for the barium salt, any water-soluble salt can be used. i.e. chloride, bromide, iodide, acetate, GI
:A, nitrates and the like can be used, but chlorides are preferred industrially due to manufacturing costs. The appropriate amount of the alkaline earth metal to be added is 0.01 to 3% based on γ-iron oxide.

If it is less than 0.01%, the effect will not be sufficient, and if it exceeds 3%, the amount of components that do not contribute to magnetization will increase, which is not preferable.

Next, as for the cobalt salt, the same salts as those normally used for cobalt modification of iron oxide particles, such as cobalt chloride, cobalt nitrate, and MM cobalt, can be used. In addition, in the present invention, the amount of cobalt metamorphosis (deposition amount) can be considerably reduced, for example, 0 for γ-iron oxide.
．． Even 1% is effective. The upper limit is preferably about 10%. The amount of cobalt chloride, etc. added is determined so that the amount of cobalt transformation falls within these ranges. The amount added remains almost the same as metamorphic Φ.

The alkaline earth metal salt and cobalt salt are added as solids or their aqueous solutions. There is no particular restriction on the order of addition of these.

The above mixed solution is heated and stirred to react. Its temperature is 5
A temperature of 0° to the boiling point is suitable. The higher the temperature, the faster the reaction rate, but it is necessary to pressurize the reaction system to raise the temperature above the boiling point, which is industrially disadvantageous. Although the boiling point varies depending on the concentration of salt dissolved in the solution, the upper limit of the boiling point is approximately 104° C. within the above concentration range. Therefore, it is appropriate to select the heating temperature within the range of 50 to 104°C.

The reaction by heating is preferably carried out with stirring; therefore, if the atmosphere in the reaction system is oxidizing, divalent iron and cobalt will be oxidized, so it is preferably non-oxidizing. The reaction time is suitably 4 hours or more, preferably 4 to 8 hours.

Through the above treatment, the cobalt salt turns into cobalt hydroxide, which is deposited on the surface of the γ-iron oxide particles.

In this way, cobalt transformation of the γ-iron oxide particles is carried out. At this time, most of the alkaline earth metal salts are deposited on the particle surfaces.

Once the cobalt transformation has been completed, divalent iron salt is then added to the solution. As the divalent iron salt, ferrous sulfate, ferrous chloride, etc. are used. This ferrous salt-added solution is treated at the same temperature, time, and atmosphere as the above-mentioned cobalt modification to perform modification with divalent iron. The metamorphic n1 of divalent iron is suitably 01 to 10% as metallic iron relative to γ-iron oxide. Therefore, the amount of divalent iron salt added is determined so that the amount of metamorphosis falls within this range.

The normal addition amount becomes the metamorphic amount.

γ- metamorphosed by cobalt and divalent iron in this way
The precipitated iron oxide particles are separated from the solution in a furnace, washed repeatedly with water, and finally dried to form a product. Even if alkaline earth metals remain in the product, there is no harm to the magnetic properties within the scope of the present invention.

Effects of the present invention] According to the present invention, iron oxide magnetic powder having excellent conductivity, saturation magnetic properties, transfer properties, and high coercive force can be obtained. Moreover,
Normally, the coercive force does not increase due to metamorphosis of divalent iron, but
According to the method of the present invention, it has become possible to significantly increase this. Therefore, cobalt metamorphosis can be reduced, and drawbacks such as stability problems caused by cobalt addition can therefore be eliminated.

The present invention will be specifically explained below using Examples.

(Average of major axis 0.4 μ, major f * / minor axis = 8/1, coercive force HC = 390 Oe, saturation magnetization (σ, = 73
．． 4emu/g) was dispersed and heated and stirred in a nitrogen stream while dispersing CaCJlz ・61-hollg(
An aqueous solution of 0.5% Ca (based on γ-iron oxide) dissolved in 100 d of distilled water was added, and heating and stirring were continued. When the reaction solution reached 80℃, 00SO4・7H2057
, 7g (3% as CO to γ-iron oxide) at 300m
Add the aqueous solution dissolved in distilled water and adjust the reaction temperature to 100℃.
Continue stirring for 5 hours. 5 hours later Zarani Fe SO
4.7 Add an aqueous solution of H2097.5g (5% as Fc to γ-iron oxide) dissolved in 500-g distilled water,
The reaction was further carried out at 100°C for 1 hour. After the reaction was completed, the mixture was separated from the furnace, thoroughly washed with water, and dried at 100°C. Table 1 shows the properties of the obtained magnetic powder.

A magnetic paint is made using the magnetic paint, which is then applied onto a 20μ polyethylene terephthalate film to a dry thickness of 10μ, oriented in a 2500 Gauss magnetic field, dried, and the film is slit into 1/4 inch pieces to meet JIS standards. C-5
It was measured using the measurement method of No. 542.

Binder composition ta Bamboo powder 100 parts Vinyl chloride vinyl acetate copolymer (VAGH) 25 parts Rosin
3 parts silicone oil 1 part lecithin 0° 2 parts toluene
150g5MIBK
It is the difference between the value of the magnetic flux density on the 150 part curve and the value of the magnetic flux density on the magnetization decline curve, and 3m is the saturation magnetic flux density.

The higher the value of ΔB/Bi, the better the transfer characteristics, and the smaller the value of ΔB/Bi, the narrower the distribution.

Example 2 3rCJ12-6 instead of calcium chloride in Example 1
H206,1g (0.5 as Sr for γ-iron oxide
%) in 100 d of distilled water was added, but the reaction was carried out in the same manner as in Example 1. The obtained γ−
Table 1 shows the magnetic properties of iron oxide powder.

Example 3 Instead of calcium chloride in Example 1, (3aC1z・2
H203,513'J (0.5% as 3a for 7-R electric railway) was used. The rest is exactly the same as in Example 1. The magnetic properties of the obtained γ-iron oxide powder are shown in Table 1.

Comparative Example 1 The reaction was carried out in the same manner as in Example 1 except that calcium chloride was not used. Table 1 shows the characteristics of the results.

Comparative Example 2 Cobalt sulfate (Co 304 ・7 H20) 57
．． 2g and ferrous sulfate (Fe 804 ・7H20) 97
．． 5 g (for γ-iron oxide, 3 as COI[:e, respectively)
%, 5%) in distilled water 341, 400 g of the same γ-acid electric iron as used in Example 1 was added to the solution, and heating and stirring were continued. When the temperature of the reaction solution reaches 80° C., an aqueous solution of 960 g of caustic soda dissolved in 11 distilled water is added.

The temperature of the reaction solution rose to 100°C due to the heat of dilution. 100% reaction solution
Stirring was continued for 4 hours while maintaining the temperature at °C. After the reaction is finished, it is different.
It was thoroughly washed with water and dried at 100°C. Table 1 shows the properties of the obtained γ-iron oxide magnetic powder.

Comparative Example 3 A γ-iron oxide magnetic powder was obtained in the same manner as in Comparative Example 2, except that 6.1 g of strontium chloride (1.5% based on γ-iron oxide) was added together with caustic soda. Its characteristics are shown in Table 1.

(Margin below)

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the effects of addition of alkaline earth metal salts and ferrous salts. The vertical axis of the figure shows the coercive force Hc of the product, and the horizontal axis shows the reaction time. Agent Patent Attorney Sei Kikuchi −
Figure 1 1/2 hours (h)

Claims (5)

[Claims] (1) γ-iron oxide particles are dispersed in an alkaline aqueous solution, at least one of calcium salt, strontium salt, or barium salt and cobalt salt are added to convert the γ-iron oxide particles into cobalt, and then divalent iron is added. A method for producing magnetic powder for magnetic recording, which comprises adding salt to perform bivalent iron transformation, followed by filtering and drying. (2) Claim 1 in which the amount of cobalt modification is 0.1 to 10% by weight as metallic cobalt based on γ-iron oxide.
A method for producing magnetic powder for magnetic recording as described in Section 1. (3) The amount of at least one of calcium salt, strontium salt, or barium salt added is 0.01 as calcium, strontium, or barium metal relative to γ-iron oxide.
3% by weight of the magnetic powder for magnetic recording according to claim 1. (4) The method for producing magnetic powder for magnetic recording according to claim 1, wherein the amount of metamorphosed divalent iron is 0.1 to 10% by weight as metallic iron relative to γ-iron oxide. (5) A method for producing magnetic powder for magnetic recording in which the OH concentration in the alkaline aqueous solution is 1.0 to 8.0 mol/l and the reaction temperature is 50 to 104°C in the reaction according to claim 1.