JP2735885B2 - Method for producing metal magnetic powder for magnetic recording - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing fine metal magnetic powder for magnetic recording (hereinafter referred to as metal magnetic powder) suitable for high-density magnetic recording. More specifically, it has an optimal coercive force and high saturation magnetic flux density as a magnetic material for 8 mm video tape, video floppy, and other high-density magnetic recording media,
The present invention relates to a method for producing a metal magnetic powder containing iron as a main component, which is fine and excellent in dispersibility.

[Conventional technology and its problems]

Conventionally, γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , CrO _{2 and the} like have been used as magnetic powders for magnetic recording. As a material, metal magnetic powder mainly composed of iron is used.

The following method has been studied as a method for producing such a metal magnetic powder.

(1) A method in which a metal organic acid salt (mainly oxalate) is thermally decomposed and reduced with a reducing gas.

(2) A method for decomposing a metal carbonyl compound.

(3) A method of depositing a metal magnetic powder by mercury electrolysis.

(4) A method of performing wet reduction of a ferromagnetic metal salt with sodium borohydride or the like in the solution.

(5) A method in which a metal magnetic powder is generated by a discharge explosion through a high impact current.

(6) A method of evaporating a ferromagnetic metal or alloy in an inert gas.

(7) A method in which iron oxyhydroxide or a material obtained by doping the same with another metal (for example, Co or Ni), or an iron oxide or an oxide containing ferrite is reduced with a reducing gas.

Among the various methods for producing metal magnetic powders, the method (7) is the mainstream in terms of cost and performance, and the present invention also belongs to this category.

Conventionally, metal magnetic powders having various physical properties and magnetic properties suitable for high-density magnetic recording media have been developed by this method, and are used for audio metal tapes, 8 mm video metal tapes, video floppies, and the like. However, in recent years, with the digitization of audio, the development of high-band 8mm video, and the development of floppy disks for high-density memory,
There is a demand for the development of a magnetic recording medium with higher performance. That is, high output characteristics of the magnetic recording medium and a reduction in noise level are required. These characteristics of the magnetic recording medium are closely related to the characteristics of the magnetic material used for the magnetic recording medium, and the following items can be mentioned as the main characteristics that the magnetic powder of the high-density magnetic recording medium should have.

a Have an appropriate coercive force (Hc).

b The saturation magnetic flux density (σs) must be large.

c Squareness ratio (σr / σs) is large.

d The particle size is small and uniform.

e It must have a dense structure and be easily dispersed.

f Having excellent weather resistance after tape formation.

In order to obtain high output characteristics as a magnetic recording medium, items a, b, c, and e are particularly required for magnetic materials. It is necessary to control the coercive force of item a to a value suitable for the purpose of use of the magnetic recording medium. As a method for controlling the coercive force, the particle size of iron oxyhydroxide as a starting material is mainly controlled.

The characteristic of the metal magnetic powder is that the saturation magnetic flux density of b is large, but the metal magnetic powder as it is reduced has a large activity, and when it is taken out into the atmosphere, it suddenly reacts with oxygen in the atmosphere. It is changed to α iron oxide without magnetism. Therefore, the metal magnetic powder after reduction is treated to form an oxide film on the surface of the particles before being exposed to the atmosphere, so that it can be handled safely in the atmosphere. The magnetism of the oxide film is weak, and the saturation magnetic flux density decreases as the proportion of the oxide film per unit particle increases. In particular, when the size of the metal magnetic powder is reduced for the purpose of reducing the noise of the magnetic recording medium, the saturation magnetic flux density is remarkably reduced.

In order to increase the squareness ratio of item c, it is important to increase the acicular ratio of the raw material iron oxyhydroxide and make the particle size uniform, but the acicular ratio also has a relationship with the coercive force of item a. It is controlled in consideration. Further improvement of squareness ratio
It is important how to prevent the collapse of the particle shape during the reduction, the cutting and sintering of the particles. Regarding item e, it is desired that the metal magnetic fine particles have no pores and are dense and have good surface smoothness.

In order to reduce the noise of the magnetic recording medium, it is important to reduce the size of the metal magnetic powder to increase the number of particles per unit volume of the magnetic recording medium. Generally S / N of tape
(Output-noise ratio) depends on the particle size, dispersibility, filling property, and smoothness of the tape surface of the applied magnetic powder. When surface properties and dispersibility are constant, S / N
Is known to be proportional to the square root of the average number of particles per unit volume. Therefore, it can be said that a magnetic powder having as small a particle size as possible and having a higher filling property is more advantageous. (Tamagawa, Nakabachi, Journal of the Japan Society of Applied Magnetics Vol.7, No.3, 1983, P20
4) However, as described above, the miniaturization of the metal magnetic powder particles leads to a decrease in the saturation magnetic flux density, and the increase in the specific surface area tends to increase the cohesiveness of the particles, making dispersion difficult.

As described above, there is a demand for a metal magnetic powder that is finer, has a high saturation magnetic flux density, and is excellent in dispersibility and weather resistance of a medium. Not manufactured to date.

[Object of the invention]

An object of the present invention is to solve the above-mentioned problems of the prior art, and has an optimum coercive force according to the type of magnetic recording medium, and has a small but high saturation magnetic flux density, and has a high dispersibility. An object of the present invention is to produce a metal magnetic powder having excellent weather resistance when used as a magnetic recording medium.

[Means for solving the problem]

The present invention performs a treatment for depositing a compound of cobalt and nickel on iron oxyhydroxide doped with nickel and zinc, and then a treatment for depositing a compound of silicon and aluminum, and then heats the treated product. Process,
Next, the present invention provides a method for producing a metal magnetic powder for magnetic recording, which is reduced under a flow of hydrogen.

The metal magnetic powder produced by the method of the present invention is characterized by being in an appropriate coercive force (Hc) range, and having a large saturation magnetic flux density (σs) and a large squareness ratio. The crystallite size calculated from the half-width of the diffraction line peak on the α-Fe (110) plane by an X-ray diffractometer is as fine as 140 to 170 °, and has excellent sintering and vacancy-free dispersibility. Metal magnetic powder.

Nickel and zinc-doped iron oxyhydroxide used in the present invention has an average major axis length of 0.15 to 0.7 μm and an average minor axis length of 0.015 to 0.05 μm, nickel- and zinc-doped α-FeOOH, β -FeOOH and γ-FeOOH,
In view of various requirements for miniaturization and high saturation magnetic flux density of the product, α-FeOOH is particularly preferable among them. However, β-FeOOH and γ-FeOOH may be used.

The compounds of Co, Ni, Si and Al used in the present invention may be any of water-soluble or colloidal compounds. Compounds that are preferably used include CoCl
_2, chlorides such as NiCl _2, AlCl _3, CoSO _4, sulfates such as NiSO _4, and salts such as nitrates or these portions hydroxide, water glass, colloidal silica, sodium aluminate, alumina sol and the like Can be mentioned.

In the present invention, first, a compound of cobalt and nickel is deposited on iron oxyhydroxide doped with nickel and zinc. This deposition is performed by the following method. That is, when a water-soluble salt is used as the compound of Co and Ni, this is dissolved in water and added to the iron oxyhydroxide or iron oxide slurry previously dispersed in water. Next, if the soluble salt is alkaline, an acid such as hydrochloric acid, sulfuric acid or phosphoric acid is added, and if the soluble salt is acidic, an alkali such as caustic soda, caustic potash, or ammonia is appropriately added to obtain a hydroxide of Co and Ni. Alternatively, an oxide is deposited.

The purpose of adding Co and Ni is to increase the saturation magnetic flux density of the metal magnetic powder after reduction, and to improve oxidation resistance and dispersibility.These effects are obtained in the later steps of the present invention, namely, Si and It appears only in combination with the steps of applying an Al compound, heat treating the treated product, and then reducing it.

Next, Si and Al compounds are added to the treatment liquid, and neutralized with an acid or an alkali according to the kind of the compound added in the same manner as described above to further deposit the Si and Al compounds on the treated material. Let it. The purpose of the deposition of Si and Al is to prevent sintering during reduction, and if the addition amount is too small, there is no effect of preventing sintering, and if it is too large, Si and Al do not have magnetism. The saturation magnetic flux density decreases.

After the above deposition process is completed, the processed material is filtered,
Wash thoroughly.

The treated product after the cleaning is dried, and then heat-treated in a non-reducing atmosphere, for example, in air or an inert gas such as nitrogen. The temperature of this heat treatment is preferably 500 to 850 ° C. If the temperature is too low, the effect of the heat treatment is not obtained. If the temperature is too high, the shape of the particles changes during the heat treatment and the characteristics of the product are deteriorated.

Next, the treated product is charged into a reduction reactor and reduced under a flow of hydrogen. If the reduction temperature is too low, the reaction time becomes longer, which is not economical. When the temperature is high, the reaction time is short, but the metal magnetic powder is sintered, the coercive force and the squareness are reduced, and the noise level when used as a medium is high. Therefore, the choice of the reduction temperature is important, but the reduction temperature in the method of the present invention is
A range from 300 to 600 ° C is preferred.

After the reduction, the reduction reactor is cooled, and the metal magnetic powder is stabilized and taken out of the system by an ordinary method such as flowing a mixed gas of nitrogen and air.

The metal magnetic powder produced in this way has an average major axis length.
0.15-0.4 μm, average minor axis length 0.015-0.03 μm, needle ratio 7-15, and crystallite calculated from the half-width of the diffraction line peak of α-Fe (110) plane by X-ray diffractometer Size 140
It is as fine as ~ 170 °, the coercive force is 1350 ~ 16500e, and the saturation magnetic flux density is 125 ~ 145emu / g.

In the present invention, the preferable doping amounts of nickel and zinc with respect to the iron oxyhydroxide are 0.5 to 5.0% by weight of nickel and 0.3 to 5.0% by weight of the iron in the iron oxyhydroxide.
% By weight.

Further, the amount of cobalt and nickel, and the amount of silicon and aluminum compound to be deposited is 2.0 to 3 with respect to iron in the nickel and zinc-doped iron oxyhydroxide.
0 wt%, nickel is 1.0-20 wt%, silicon is 0.3-7
The preferred ranges are 0.5% by weight and 0.5-10% by weight of aluminum.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 Average minor axis length 0.02 μm, average major axis length 0.26 μm, needle ratio 13
2.0% by weight of nickel (to iron) and 1.5% by weight of zinc
150 g of (to iron) -doped α-FeOOH was placed in 30 distilled water and dispersed well. A solution prepared by dissolving 0.08 mol of each of separately prepared cobalt chloride and nickel chloride in 300 ml of distilled water was added thereto, and the mixture was stirred well. Then, a 2N aqueous sodium hydroxide solution was added dropwise over 1 hour to neutralize to pH = 8. Next, an aqueous solution 1 in which 0.105 mol of aluminum chloride was dissolved was added, and the mixture was stirred well for 30 minutes. Next, 500 ml of an aqueous solution in which 0.05 mol of sodium silicate was dissolved was slowly added dropwise over 2 hours, and then 2N caustic soda solution was added dropwise to adjust the pH.
= 8. Thereafter, stirring was continued for 1 hour, and the attached goethite was washed with water and filtered to obtain a Co and Ni compound and a Si and Al compound attached goethite. After drying, the attached goethite was heated in an electric furnace at 650 ° C. for 2 hours. Next, the heat-treated product was reduced in a hydrogen gas stream at a temperature of 460 ° C. for 5 hours. After completion of the reduction, the gas in the reaction system was changed to nitrogen gas and cooled to room temperature, and then air was gradually fed in to stabilize the reduced product to obtain a metal magnetic powder. When the composition analysis of the metal magnetic powder was performed using an X-ray fluorescence spectrometer, Co = 5.1, Ni = 7.1, Si = 1.5, Al =
3.0.

The metal magnetic powder was used as a sample vibration magnetometer (VS.
M) measured the magnetic properties with a maximum magnetic field of 10KOe,
Coercive force (Hc) = 15800e, saturation magnetic flux density (σs) = 137emu
/ g, squareness ratio = 0.517. The crystallite size of the metal magnetic powder was 159 ° (measurement method = X
(Calculated from the half width of the diffraction line peak on the α-Fe (110) plane by a line diffraction apparatus.) Further, the particle morphology of the metal magnetic powder was examined by a transmission electron microscope (TEM). As a result, the metal particles were free from sintering and voids and had good needle-like properties with an average needle-like ratio of 10. From these results, it was confirmed that the magnetic material had good characteristics as a magnetic material for a magnetic recording medium.

Next, the metal magnetic powder was dispersed in a solution in which a vinyl chloride-vinyl acetate copolymer resin was dissolved together with a dispersing agent, a lubricant, and an abrasive, and a urethane elastomer was added thereto and mixed to sufficiently disperse. After adding a cross-linking agent to the dispersion paint and mixing well, 14 μm of gravure coater was used.
Apply on PET film and leave the magnetic paint dry.
A magnetic field orientation treatment was performed with a 500 gauss magnet, and after drying, a super calender treatment was performed, and slits were formed to a width of 8 mm to produce an 8 mm video tape. When the magnetic properties of the tape were measured by a VSM at a maximum magnetic field of 10 KOe, Hc
= 15480 e, Br = 2840 G, Bm = 3381 G, Br / Bm = 0.82.

In addition, the tape slit to 8 mm was placed in a thermo-hygrostat at a temperature of 60 ° C. and a relative temperature of 90% for one week, a deterioration promotion test was performed, and the Bm of the tape measured by VSM was 3.208 G. Was 5.1%.

Table 1 shows the metal doped in the raw material iron oxyhydroxide, its doping amount, the deposited metal, its deposited amount, and the heat treatment temperature.
The magnetic properties, specific surface area (nitrogen adsorption method) and crystallite size of the reduced metallic magnetic powder, the magnetic properties of the tape,
Table 2 shows the deterioration rate of Bm (denoted as ΔBm).

When Si and Al are applied in the following Examples and Comparative Examples,
It was applied by the method of this example.

Examples 2 to 4 Table 1 shows the weight percent of Ni and zinc doped in the raw material α-FeOOH with respect to iron, the weight percent of iron to be deposited with respect to iron, and the heat treatment temperature. The following steps were performed in accordance with Example 1.

Table 2 shows the magnetic properties and specific surface area values of the reduced metallic magnetic powder, crystallites, magnetic properties when formed into a tape, and the Bm deterioration rate of the tape (denoted as ΔBm).

Comparative Example 1 α-Fe not doped with nickel and zinc as a raw material
The same deposition treatment as in Example 1 was performed using OOH. All subsequent processes were performed in the same manner as in Example 1. Since no doped metal exists, the shape of goethite is irregular,
Dispersion was poor.

Comparative Example 2 The same operation as in Example 1 was performed except that silicon and aluminum were not applied. Sintering of the particles occurred, and the coercive force and the squareness ratio were remarkably reduced. Furthermore, the crystallites were large and the dispersion was poor due to the progress of sintering.

Comparative Example 3 The same α-FeOOH as in Example 3 was used as a raw material, and the deposition of cobalt and nickel was omitted, and silicon and aluminum were deposited. However, the saturation magnetic flux density of the metal magnetic powder was low, and Br was also low. Further, ΔBm of the tape was large and the oxidation stability was poor.

Comparative Example 4 Reduction was performed by omitting the heat treatment in Example 2, but the metal magnetic powder was inferior in Hc, crystallite, and squareness ratio of the tape as compared with Example 2.

Table 1 shows the metal doped in the raw material iron oxyhydroxide of Comparative Examples 1 to 4, the amount of the metal doped, the amount of the metal deposited, the amount of the metal deposited, and the heat treatment temperature. Table 1 shows the magnetic properties of the reduced metal magnetic powder. , Specific surface area and crystallite size, magnetic properties of the tape, and Bm degradation rate are shown in Table-2.

[Effects of the Invention] As is clear from the examples and comparative examples, the metal magnetic powder produced by the method of the present invention has a high saturation magnetic flux density and a high squareness ratio, and has a small crystallite and excellent dispersibility. This is an extremely high performance suitable for a high-density magnetic recording medium having excellent tape oxidation stability.

Claims (1)

(57) [Claims] 1. A treatment for depositing a compound of cobalt and nickel on iron oxyhydroxide doped with nickel and zinc, followed by a treatment for depositing a compound of silicon and aluminum, and then the treated product Is subjected to a heat treatment and then reduced under a stream of hydrogen to produce a metal magnetic powder for magnetic recording.