JPS6122604A - Magnetic metal powder and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the orientational characteristics of magnetic metal powder as a magnetic recording medium by a method wherein a magnetic metal is used as the core of the magnetic metal powder, and the SiO2 wherein ZnO is present is used for the shell of the external surface. CONSTITUTION:Iron oxyhydroxide is obtained by oxidizing the aqueous solution of iron salt or the iron salt wherein salts of metls other than iron such as Ni, Co, Cr, Zn, Sn, Al and the like are added. Inorganic silicate is coated on the surface of said iron oxyhydroxide. Then, the mixture of zinc compound or inorganic silicate and zinc compound is coated thereon. Susequently, powder is filtered and separated, dehydrated by heating, and the SiO2 shell wherein ZnO is present is formed by reducing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic metal powder, and more particularly to magnetic iron powder for use in magnetic recording materials with excellent orientation properties and a method for producing the same.

[Conventional technology]

Magnetic iron powder is attracting attention as a magnetic material for high recording density.This magnetic iron powder usually uses iron oxyhydroxide as a starting material, and this is supplemented with iron oxyhydroxide crystals that retain their acicular properties. It is manufactured by depositing a compound, separating it in a furnace, dehydrating it, and reducing it.

The composition, amount, and uniformity of deposition of the compound deposited to maintain the acicular nature of iron oxyhydroxide crystals affect the sinterability between iron particles that occurs during reduction treatment, and the dispersion of the final product. properties, orientation, and magnetic properties are greatly affected.

Silicates are commonly used as compounds that form heat-resistant metal oxides that adhere to iron oxyhydroxide, but they also improve the sinterability during reduction, the dispersibility, and orientation of magnetic iron powder. For this purpose, M compound (Unexamined Japanese Patent Publication No.
8-77505, Japanese Patent Publication No. 57-29523), calcium salts (Japanese Patent Publication No. 58-42704, etc.)
, a method of adding alkaline earth metal salts, etc. has been proposed. Furthermore, a method using an aluminum salt in place of a silicate (Japanese Patent Application Laid-open No. 134858/1983) has also been proposed.

Japanese Patent Publication No. 47-29706 and Japanese Patent Publication No. 56-73
No. 408 proposes that a zinc compound or the like is directly deposited on iron oxyhydroxide or the like to prevent reduction and form an oxidation-resistant iron-zinc alloy layer on the surface of magnetic iron powder.

[Problem that the invention seeks to solve]

Although the methods of directly depositing silicate-based compounds on iron oxyhydroxide have excellent shape retention properties of iron oxyhydroxide crystals, the magnetic iron powder produced by these methods Iron powder has poor orientation properties after being made into a tape.

An object of the present invention is to provide a magnetic metal powder with improved dispersibility and orientation, that is, orientation characteristics as a magnetic recording medium, and a method for producing the same.

[Means for solving problems]

The present invention is a magnetic metal powder consisting of a magnetic metal core and a 5i02 shell with ZnO on the outer surface.

In the present invention, the molar ratio of 5in2:ZnO in the shell is 1:0.1 to 1:0.7, preferably 1:0.25.
~1:0.55. More preferably, the molar ratio of 5i02:ZnO on the outer surface of the shell is 1:1.

In the present invention, magnetic metals include metallic iron and Fe-Co
, Fe-Ni, Fe-Zn, or any other magnetic alloy iron may be used.

The magnetic metal powder of the present invention is produced by depositing an inorganic silicate on the surface of iron oxyhydroxide, then depositing a zinc compound or a mixture of an inorganic silicate and a zinc compound, and then separating the powder in a furnace, heating and dehydrating it, and reducing it. Manufacture in particular.

In the present invention, iron oxyhydroxide is a hydrous oxidized iron salt obtained by oxidizing an aqueous solution of round iron salt by adding iron salt alone or salts of metals other than iron such as Ni, Co, Cr, Zn, and 5n1At. If it is iron and has excellent acicularity, a Fe00Hs β-FeOOH and r -Fe
Either OOH is acceptable. Usually, α-FeOOH is preferably used because it has excellent acicular properties.

The inorganic silicate may be any water-soluble one, and water glass, which is inexpensive and easily available, is used. Further, the zinc compound may also be water-soluble, and inorganic zinc compounds such as zinc sulfate and zinc nitrate are preferably used.

There are no particular restrictions on the method for depositing the inorganic silicate and then the zinc compound or the mixture of the inorganic silicate and zinc compound on the iron oxyhydroxide, but the following method can be used.

By adding iron oxyhydroxide to an aqueous solution of a dispersing agent such as sodium hexametaphosphate and dispersing it to form a slurry, and adding an inorganic silicate to the slurry, a part of the inorganic silicate becomes iron oxyhydroxide. Adheres to the surface. Next, an aqueous solution of a zinc compound is added to the slurry, and acid is added to neutralize the slurry, so that the mixture of the zinc compound and the inorganic silicate is coated on the iron oxyhydroxide. wear it.

By adjusting the timing of addition of the zinc compound aqueous solution, it is possible to change the mixing ratio of the zinc compound and inorganic silicate deposited in the second step, and it is also possible to substantially change the mixing ratio of the zinc compound and inorganic silicate to be deposited on the inorganic silicate plate. can be coated.

After the iron oxyhydroxide coated with an inorganic silicate and a zinc compound or a mixture of an inorganic silicate and a zinc compound is removed from house to house, it is dehydrated by heating in air at a temperature of 500 to 7 to 00°C, for example. By doing so, the acicular iron oxide core produced by dehydration of iron oxyhydroxide and ZnO or Z
5tO2 with a mixed oxide film of nO and SiO□
shell is formed. By reducing this powder using a conventional method, for example, using hydrogen gas at a temperature of 400°C or higher, ZnO or ZnO and 5
It is possible to produce a magnetic metal powder having a shell of S i 02 having a coating of a mixed oxide with i 02 .

[For production]

The magnetic metal powder of the present invention has ZnO on the outer surface of its shell.
Due to the presence of powder, the residual saturation magnetic flux density (
Br) and squareness ratio (Rs). That is, it is presumed that ZnO present on the surface affects the dispersibility and orientation of the magnetic metal powder in some way. Therefore, in the shell as a whole, the molar ratio of 5i02:ZnO is 1:0.1 to 1:0.7, preferably 1:0.
．． It is necessary to contain ZnO of 25 to 1:0.55,
The ZnO is concentrated on the outer surface of the shell, and the ZnO is on the outer surface.
O must exist.

〔Example〕

The present invention will be explained in more detail below with reference to Examples. However, the scope of the present invention is not limited in any way by the following examples.

Example 1 Ni 1.5 atm% synthesized in a high alkaline region in a sodium hexametaphosphate aqueous solution with a concentration of 0.3 f/
/Fe-containing α-iron oxyhydroxide crystals are added, and 1
2 t suspensions were prepared with a concentration of 5 f/. To the suspension was added 259 g of a 2.6 wt % aqueous solution of Mizu Glass No. 2 and stirred. As a result of the analysis, converted to sio□, 4. Owt%/F
The silicon compound of e was deposited on the α-iron oxyhydroxide crystal.

To the obtained suspension, an aqueous solution of zinc sulfate 10-10% having a concentration of 0.84 mol/mole was gradually added, then an aqueous IN sulfuric acid solution was added to neutralize the suspension, and the suspension was aged for 10 hours.

α-Iron oxyhydroxide crystals are collected from this aqueous suspension by filtration, washed with water, dried, heated to a temperature of 675°C to dehydrate, and then reduced in a hydrogen stream at a temperature of 400°C. SiO coated with mixed oxide of ZnO and SiO2
A magnetic metal powder having 2 shells was obtained.

Table 1 shows the analysis results of ZnO and SlO□ of the obtained magnetic metal powder, the specific surface area measured by the BET method, and the powder magnetic properties.

Example 2 Synthesizing in a weakly alkaline region in a sodium hexametaphosphate aqueous solution with a concentration of 0.3f/6Nf 1.5 atm%
/Fe-containing α-iron oxyhydroxide crystals are added,
2 t of suspension with a concentration of / was prepared. Add 2 ml of water glass to the suspension.
No. s, 7vtrts aqueous solution 569- was added and stirred.

As a result of the analysis, a silicon compound of 7.2 wt %/Fe in terms of 5102 was adhered to the α-iron oxyhydroxide crystal.

To this suspension, 101d of an aqueous zinc sulfate solution having a concentration of 0.84 mol/m was gradually added, and then neutralized using an IN aqueous sulfuric acid solution, and then aged for 10 hours.

The α-iron oxyhydroxide crystals coated with the silicon compound and the zinc compound were separated from the resulting suspension, washed with water and dried, and then heated to a temperature of 625° C. in the atmosphere for dehydration. Then, it was reduced in hydrogen gas and liquid at a temperature of 380° C. to obtain magnetic iron powder having a SiO□ shell coated with a mixed oxide of ZnO and 5in2.

Various powder properties of the obtained magnetic iron powder are shown in Table 1.

Example 3 A magnetic iron powder was obtained by processing under the same conditions as in Example 2.

Various powder properties of the obtained magnetic iron powder are shown in Table 1.

Comparative Examples 1.2 and 3 Examples 1.2 and 3 were treated under the same conditions except that no zinc compound was added, and magnetic powders having only Sho□ shells were obtained.

Various powder characteristics of the obtained magnetic powder are shown in Table 1.

Test Examples A tape orientation test was conducted on the magnetic iron powder obtained in Examples and Test Examples.

100ml of magnetic iron powder, dispersant (Diomine, commercially available), binder (vinyl chloride-vinyl acetate copolymer), and solvent (mixed solvent of toluene and cyclohexanone)
The mixture was mixed and kneaded in a stainless steel ball mill to form a paint.

The obtained magnetic paint was applied to a plastic tape to a thickness of 5 μm while applying a magnetic field of 4800 Gauss to prepare a magnetic tape.

The orientation characteristics of the obtained magnetic tape are shown in Table 1. [Effects of the Invention] As shown in Table 1, the magnetic metal powder of the present invention has a residual saturation magnetic flux density of 2Br and 2Br, which are the orientation characteristics of the tape. Squareness ratio: R8 has a higher value than that of the conventional method (see comparative example). That is, the magnetic metal powder has excellent dispersibility and orientation, and by using this magnetic metal powder, it is possible to manufacture a magnetic recording medium with high recording density.

The present invention provides a magnetic metal powder with improved dispersibility and orientation, and a method for producing the same, and has extremely great industrial significance.

Claims (6)

[Claims] (1) S with magnetic metal core and ZnO on the outer surface
Magnetic metal powder consisting of iO_2 shell (2) Magnetic metal powder according to claim (1), wherein the magnetic metal is iron or a magnetic alloy mainly composed of iron. (3) ZnO/SiO_2 molar ratio in the shell is 0.1~
0.7 magnetic metal powder according to claim (1) (4) depositing an inorganic silicate on the surface of iron oxyhydroxide, then depositing a zinc compound or a mixture of a zinc compound and an inorganic silicate on the inorganic silicate, followed by heating and dehydration;
A method for producing magnetic metal powder characterized by further heating and reducing the powder in a reducing gas. (5) The method for producing magnetic metal powder according to claim (4), wherein the inorganic silicate is a water-soluble salt of silicic acid. (6) The method for producing magnetic metal powder according to claim (4), wherein the zinc compound is a water-soluble salt of zinc.