JPS6036603A - Fine magnetic metallic powder having small specific surface area and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture magnetic metallic powder having a small specific surface area by reducing spindle-shaped goethite having a specified major axis size, a specified minor axis size and a specified axial ratio with a reducing gas. CONSTITUTION:Spindle-shaped goethite having 0.05-0.3mum major axis size, 0.015-0.04mum minor axis size and 3-15 axial ratio is optionally dehydrated by heat treatment to prepare iron oxide, and the goethite or the iron oxide is reduced with a reducing gas at about 300-500 deg.C. The starting material is coated with a sintering inhibitor such as potassium silicate before the reduction. The amount of the inhibitor is about 5-10wt% of the amount of the goethite. Magnetic metallic powder having 0.05-0.2mum major axis size, 4-10 axial ratio and 30-55m<2>/g specific surface area is obtd. The specific surface area is measured by adsorbing gaseous N2 by the BET method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal magnetic powder for high-density magnetic recording and a method for producing the same. .

In 2011, with the digitization of audio and the development of 8n video, there was an increasing demand for high-density recording on magnetic recording media.

Therefore, metal magnetic powders with high coercive force (more than 10,000 e) are being used as the magnetic powders used in these magnetic recording media, but with the aim of reducing tape noise levels and increasing output in the short wavelength region. , magnetic powders with increasingly smaller particle size, narrower precision distribution, and greater dispersion were required (Japanese Patent Application Laid-Open No.
7-154618).

8 In the case of baking soda video, the coercive force Hc of metal magnetic powder is 140
It is selected from 0 to 15000e. If Hc is smaller than this, the output during retemplation will be insufficient, and if it is too large, saturation will occur in the recording head and erasing will become difficult. As metal magnetic powder, P is preferred due to the low cost of the material.
E, and Fe-Ni-Co alloys are used, but each of these metals has a high coercive force due to its cubic crystal structure.
For I-row, the particle shape must be sword-shaped to provide −axis anisotropy. The ratio of the major axis to the minor axis of the acicular particles, that is, the axial ratio, may be in the range of 2 to 15. The coercive force increases as the axial ratio increases, but on the other hand, the coercive force is influenced by the grain size, and the coercive force is influenced by the grain size.
The size of C: 1' becomes larger as the particle size becomes smaller. Therefore, the desired coercive force can be obtained by appropriately selecting the grain size and its axial ratio.

On the other hand, the smaller the particle size of metal magnetic powder, the greater its surface energy and the more chemically active it becomes.

Therefore, in order to stabilize this so that it does not burn in the atmosphere, 30 to 50 people of oxidation-resistant protective conversion are required.

Therefore, in order to maintain the properties as a metal magnetic powder, the short axis of the particles (\) must be 0.01 μm or more.
The size of the major axis diameter is determined automatically because the axial ratio is determined by the degree of retention force. Therefore, for example, coercivity)
To make the monthly TC>14000e, the axial ratio is required to be 3 or more, preferably 4 or more, so the major axis diameter is 0.05μ.
m 1it (iR is limited to one.

However, when the particle size of metal magnetic powder is reduced, the specific surface area increases, cohesiveness increases, and oil absorption increases. Therefore, when made into a paint, the viscosity increases, making it difficult to disperse. Therefore, in order to create a highly dispersed magnetic paint with low viscosity even when the particles are miniaturized, it is necessary to obtain metal magnetic powder with a small specific surface area, good surface smoothness, and uniform particle size. .

Therefore, the present inventors (3) [As a result of various studies, by improving the acicularity of goethite, which has conventionally been called spindle-shaped goethite, and reducing the microparticles, the above-mentioned The present invention was created based on the realization that metal magnetic powder could be obtained that did not meet the requirements.

In other words, the conventional spindle type game site is
As stated in Publication No. 0999, it is characterized by having no branches and uniform precision, so the powders of iron oxide, metals, and 4:1 alloys produced using it as a raw material also have a uniform particle size. be.

Therefore, since the packing density in the magnetic coating film can be made crystallized, high-density magnetic recording is possible. However, spindle-shaped goethite has a larger short axis diameter than its long diameter, and according to high-resolution electron microscopy observation, one particle is made up of dozens of hexagonal plate-shaped fine particles. Therefore, when it is reduced, pores are likely to be formed inside the particles, resulting in porous particles. Therefore, the coercive force in the magnetic properties is not constant, and at the same time, due to the leakage magnetic field emanating from the pores, the phase U effect between the particles is large, which tends to cause agglomeration, and the paint dispersibility is poor. was. For example, as for the coercive force, the coercive force of metal magnetic powder produced using spindle-shaped goethite is only 12,000 e, as shown in Japanese Patent Laid-Open No. 55-85605.

Therefore, the inventors used a bubble column to synthesize spindle-shaped goethite with good sword-like properties, and as a result of reducing it and examining its properties as a metal magnetic powder, we found that Set the short axis diameter of the site to 0. (When the volume is lowered by 14/7 ml, preferably 0.02 t!m or lower, the pores disappear and the
It has been found that the internal uniformity of the I-element is improved.

In addition, the major axis diameter can be freely controlled by adjusting the air I and temperature during goethite synthesis, with a minimum of 0.0
It has become possible to shorten the length to 2 μm. Therefore, we investigated the conditions for the coercive force of metal magnetic powder of 14,000e or more, and found that in the case of goethite with an average minor axis diameter of 0.02 μm,
It has been found that an axial ratio of 31u-h, that is, a major axis diameter of 0.06 μm or more is sufficient. Also, games like this
The iron powder, which has been reduced to 1# after being treated with anti-sintering IL coating with potassium silicate, etc., has a short axis of 1 yen 0.015 and 0.00 yen.
5 μm, axial ratio 3 or more, that is, long axis i leather 0.05. cr
It was found that it was more than m.

From the above points, when manufacturing the metal magnetic powder in the present invention, the major axis diameter is 0.05 to 0.3. c+m, minor axis diameter is 0
．． Spindle-shaped goethite with an OI of 5-0, 04 p rn and an axial ratio of 3-15 is required.

On the other hand, the specific surface area of such metal magnetic powder obtained by adsorbing N2 gas by the BET method is 0.1 μm in major axis diameter and 0.1 μm in minor axis diameter.
．． 02 μm, axial ratio 5, and saturation magnetization i1120 emt
Approximately 50 rrr with metal magnetic powder reduced to +/g or more
/g. This value is quite significant compared to the specific surface area of metal magnetic powder with the same volume and axial ratio of 10, which is approximately 64 M/g, obtained by reducing goethite synthesized using caustic soda as an alkali. You can say that you should take the lead.

Therefore, when this metal magnetic powder is made into 'ffII, it is easy to make it into a paint, and the viscosity of the paint is 11 (I). A magnetic tape with high recording density can be produced.

The metals constituting the metal magnetic powder in the present invention are various ferromagnetic metals and ferromagnetic alloys such as iron, cobalt, and iron-:1Hart-nickel alloys.

The goethite used to produce the present metal & f4It powder is obtained by reacting an acid-alkali aqueous solution with a ferrous salt aqueous solution using a bubble column reaction tank, and then introducing air (aeration linear velocity 0.1~ It is a spindle-shaped goethite that is minute and has a large axial ratio, obtained by stirring the slurry in a bubble column, allowing the oxidation reaction to occur at a reaction temperature of room temperature or higher, and aging it if desired. Regarding the method of manufacturing such gamesite, please refer to the previous patent application filed in 1982-'10.
It is disclosed in detail in the specification bottle of No. 5911.

In addition, when reducing Goethite I. mentioned above, potassium silicate is usually used as an anti-sintering agent that coats the particle surface to prevent loss of the sword-like properties of Goethite. , a gay acid ffJ such as a gay acid-〇-sorta', or an aluminum salt,
- Gnesium salt, calcium salt, etc. are used. The amount of each treatment is preferably 5 to 10% by market weight based on goethite.

The reduction temperature is preferably in the range of 300'C to 50'C (1C); if it is lower than this, the reduction time will be too long or the reduction will be insufficient. If it is too high, sintering between particles will become significant and the dispersibility will be impaired. become.

Next, the present invention will be specifically explained with reference to Examples.

Example 1 Soda carbonate (Na2CO3) 5 kg to 61.2 k
After dissolving in 1 g of water, the mixture was introduced into a bubble column reaction tank while flowing N2 gas. Next, ferrous sulfate (F8SC14/7
1tz O) After dissolving 5 kg in 28 kg of water,
Ferrous ions were added to the reactor to precipitate.

After setting the slurry temperature to 40℃, N? The gas was switched to air, and the reaction was carried out for 2 hours with an air flow rate of 100β/min. Next, the slurry was filtered and thoroughly washed with water until the washing liquid became neutral to obtain spindle-shaped goethite with a major axis diameter of 0.25 μm, an axial ratio of 7, and a specific surface area of 110 nm (7 g).

Next, take 100g of this goethite as a solid content,
Distilled water 1728mj! and concentration 4650 ppln
, potassium silicate aqueous solution 272m6 (Si/Pe=4
After stirring thoroughly, the mixture was filtered and dried. 50 g of the obtained λSiO3 to be treated was taken, placed in a fixed-bed tubular reduction furnace, and the temperature was raised to 380 g in hydrogen gas at a flow rate of 30 β/min after replacing the air with nitrogen gas. Reduction was performed at ℃ for 5 hours to obtain metallic iron powder. This was cooled to room temperature, and the hydrogen gas was replaced with nitrogen gas again. This metal powder was immersed in toluene, left to stand for 20 hours to slowly oxidize the surface, then air-dried and taken out into the air.

The size of the gold 1-hole iron powder obtained in this way is 0.5 mm in major axis diameter.
It had a diameter of 2 μm, an axial ratio of 7.5, and a specific surface area of 39 nf/g measured by adsorbing N2 gas using the BET method. In addition, the magnetic properties measured using a vibrating sample type magnetic needle manufactured by Toei Kogyo at a maximum measurement magnetic field of 10 KOe are as follows: coercive force 1c = 15
000e, saturation magnetization amount σm=131 emu/g, and squareness ratio 0.50.

Take 15g of this metal magnetic powder, and
^NDEX-B Dainippon Ink Chemical 1 brand name) 5g1
A magnetic paint was prepared by mixing a 1:1 mixture of methyl isobutyl ketone and toluene with 65 g of lecithin and 0.45 g of lecithin, and stirring the mixture in a paint shaker for 4 hours. The viscosity of this paint was measured using an E-type viscosity needle at a rotation speed of 100 rpm, and the result was 4.5 poise (see Table 1).

Examples 2 to 6 Goethite obtained in the same manner as in Example 1 except that the amount of air and temperature were changed was used to produce a metal magnetic material. Il! I built 7.

The size, specific surface area and magnetic properties of these metal magnetic powders are shown in Table 1 along with the coating viscosity.

Example 7 Metal magnetic powder was produced in the same manner as in Example 6 except that the reduction temperature was increased to 400°C. Table 1 shows the size, specific surface area, and magnetic properties of the metal magnetic powder in this case. Although there is not much difference in particle size compared to Example 6, the specific surface area is slightly decreased. Further, a magnetic paint was prepared in the same manner as in Example 1, and the viscosity was measured. The results are shown in Table 1, but the viscosity was slightly higher than in Example 6.

-10 Comparative Example 1 After dissolving 3.24 kg of hydroxide sulfur in 47 kg of water, it was poured into a bubble column reaction tank while flowing N2 gas, and then potassium oxalate (Kyu5i03) was dissolved in 47 kg of water. ) No. 1
．． 237 mβ of a 38% by weight aqueous solution was added. Next, 7.51 kg of ferrous sulfate (FeSO5+ .7820) was dissolved in 13 kg of water, and then ferrous ions were precipitated.

After setting the slurry temperature to 40℃, 100j! The reaction was carried out for 2 hours by flowing air at /min. Filter the slurry;
After washing, acicular goethite with an average major axis diameter of 0.2511 m, an axial ratio of 8, and a specific surface area of 85%/g was obtained. This game I
When . / g of metallic iron powder was obtained. In addition, the powder magnetic properties of this metal magnetic cup powder are Hc = ] 7000e, σaa = 132
emu/g, σr/σm-0.52. On the other hand, the viscosity of the magnetic paint prepared in the same manner as in Example 1 was approximately 30 poise at a rotational speed of 00 rpn+.

Comparative Example 2 Goethite obtained in the same manner as Comparative Example 1 except that 551 mIV of potassium silicate aqueous solution (equivalent to Si/Fe = 1 at%) was added in the goethite synthesis of Comparative Example 1.
A metal magnetic powder was obtained by reduction in the same manner as in Example 1. The size, surface area, and size of this metal magnetic powder are shown in Table 1, and it was found that there were many branches overall, and the particle size was nonuniform compared to that of Example 11-. In addition, the viscosity of the magnetic paint prepared in the same manner as in Example 1 was 100 po.
ISE became -1- and could not be measured.

Comparative Example 3 Goethite was synthesized by reacting in the same manner as in Example 1, except that in Example I, a stirring tank was used instead of the bubble column, stirring was carried out at a stirring speed of 165 rpm, and an air amount of 30 Il/min was flowed. , the spindle shape is prominent, and the major axis diameter is 0.2 μm.
, short axis diameter 0°08μm, axial ratio 2.5, specific surface area 63J/
It was g. The metal magnetic powder obtained by reducing this goethite in the same manner as in Example 1 had a major axis diameter of 0.018 μm and an axial ratio of 3.
5. The specific surface area is 25rrf/g, and the powder magnetic properties are Hc=11700e, σm=130emu/g, σe
/σm=0.47, and the coercive force I (c is 14000e
I couldn't do more than that. On the other hand, the viscosity of the magnetic paint prepared in the same manner as in Example 1 was as small as 3 poise.

(The results of each comparative example are also listed in Table 1.) Agent Patent Attorney Katsutoshi Takahashi 12-

Claims (1)

[Claims] 1. The major axis diameter is 0.05 to 0.2 μm, and the axial ratio is 4 to 10.
With metal magnetic powder, N? with BET method? A metal magnetic powder characterized by having a specific surface area of 30 to 55 n(/g) when measured by adsorbing a gas.2, Magnetic properties having a coercive force of 1 (c 13000e or more), and a saturation magnetization of 120 emu/g or more. The metal magnetic powder according to claim 1, characterized in that: 3. The major axis diameter is 0.05 to 0.3 μm, and the minor axis diameter is 0.01 μm.
A spindle-shaped goethite with a diameter of 5 to 0.04 μm and an axial ratio of 3 to 15, or a material obtained by dehydrating it to iron oxide by heat treatment, is reduced with a reducing gas, and the major axis diameter is 0.
．． 05~(), 2μm uniaxial ratio is 4~10, N by BET method
The specific surface area measured by adsorbing two gases is 30 to 55 n.
A method for producing metal magnetic powder with i/g.