JPS5853045B2 - Manufacturing method of magnetic powder - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for producing ferromagnetic powder, and in particular, a method for producing ferromagnetic metal 1 alloy powder for magnetic recording media with high coercive force and high saturation magnetic flux density suitable for high-density recording. It is related to.

The ferromagnetic powder conventionally used in magnetic recording materials is r Fe2O3* Co-containing 7 Fe 203 e
Fe30. , Co-containing Fe3O4, Fe3O47”
There were Fe2es e CrO2, etc.

However, these ferromagnetic powders cannot be said to be suitable for the future trend toward higher densification in which the recording signal per unit volume of the magnetic layer is increased.

In other words, for use in high-density recording, the coercive force (Hc)
It has insufficient magnetic properties such as magnetic flux density (σ) and magnetic flux density (σ), and is not very suitable for magnetic recording of signals with short recording wavelengths.

Therefore, recently, efforts have been made to develop ferromagnetic media suitable for high-density recording.

One of the target materials is powder of ferromagnetic metal 1 alloy.

That is, γ-Fe2O3 has a saturation magnetic flux density of about 5000 Gauss per unit volume.
o alloy, etc., it is about 2000, which is about 4 times that of γ-Fe2O3.
It is said to have a high saturation magnetic flux density ranging from 0 to 25,000 Gauss, and in very simple terms, it is expected that the reproduction output will be about four times as high, making higher density recording possible.

Conventionally, the following methods have been studied as methods for producing such ferromagnetic metal 1 alloy powder.

(1) A method of thermally decomposing an organic acid salt (mainly oxalate) of a ferromagnetic metal 1 alloy and reducing it with a reducing gas.

For example, Tokuko Sho 36-11412. Tokuko Sho 36-2223
0,4? , Kosho 40-8027. Tokuko Sho 41-1481
8. Special Publication Showa 42-24032゜Special Publication No. 43-22394
．． Special Publication No. 47-38417° No. 47-38523.
Special Publication No. 48-29280° No. 48-22346. %
1972-22994゜US Patent No. 3186829. U.S. Patent No. 3190748, Japanese Patent Publication No. 47-4286゜ (2) Iron oxyhydroxide or those doped with other metals (e.g. Co), iron oxide, or ferrite as those using phthalates. A method of reducing composition oxides with a reducing gas.

For example, Tokuko Sho 35-3862. Tokuko Show 3711520,
Special Publication No. 39-20939. Special Publication Showa 47-29706. Special Publication No. 47-30477° Special Publication No. 47-39477, % Publication No. 46-5057° No. 46-7153. Special Public Service 1977
-24952° Japanese Patent Publication No. 48-79153. Japanese Unexamined Patent Publication 1973-
82393゜Special Publication Showa 49-7313. Unexamined Patent Publication 1973-13
5867゜Special Publication Showa 51-5608. U.S. Patent No. 3598
568° U.S. Patent No. 3,607,220. US Patent No. 370,227Q, British Patent No. 640,438° (3) Method of vaporizing ferromagnetic metal 9 alloy in an inert gas.

For example, Tokuko Sho 47-27718. Special Public Service 1977-964
．． Special Publication Showa 48-42783゜ Japanese Patent Publication No. 48-25662～
25665. Japanese Patent Publication No. 48-31166, Japanese Patent Publication No. 48-5
5400° Japanese Patent Publication No. 48-81092. Japanese Unexamined Patent Publication 1972-1985
134゜(4) Method for decomposing metal carbonyl compounds.

For example, Tokuko Sho 45-16868. US Pat. No. 2,983,997, US Pat. No. 3,172,776, US Pat. No. 3,200,007. US Pat. No. 3,228,882 (5) A method of electrodepositing ferromagnetic metal powder by mercury electrolysis and then decomposing and removing mercury.

For example, Tokuko Sho 39-15525. Special Public Service 1977-812
5. Tokuko Showa 47-6007. U.S. Patent No. 3156650
．． US Pat. No. 3,262,812 (6) A method of wet reduction of a ferromagnetic metal salt with sodium hypophosphite, sodium borohydride, etc. in its solution.

For example, Tokuko Sho 38-20520. Tokuko Sho 38-265
55. Special Publication No. 43-20116゜ Special Publication No. 45-9869
．． Special Publication No. 47-7820° Special Publication No. 47-16052. Special Publication No. 47-41718, Special Publication No. 47-41719. JP-A-47-1
353. Japanese Patent Publication No. 47-42252. Japanese Patent Publication No. 47-422
53. Japanese Patent Publication No. 48-7585. Japanese Patent Publication No. 48-25896
．． JP-A-48-44194° JP-A-48-79754.
JP-A-48-82396° JP-A-48-28999,4
! f 1977-1998゜U.S. Patent No. 3607218
, U.S. Patent No. 3,494,760゜U.S. Patent No. 3,535,104
, U.S. Patent No. 3661556゜U.S. Patent No. 366331
8, U.S. Patent No. 3669643゜U.S. Patent No. 36728
67゜(7) Other methods include, for example, producing ferromagnetic metal powder by discharge explosion through a large impact current.

In the case of PI, various methods have been studied as described in Japanese Patent Application Laid-Open No. 47-3385775:
, each method has its advantages and disadvantages, and still
None of these methods can be a definitive method in an industrial or practical sense.

For example, the method (1) using decomposition of oxalate is a method that has been studied for a long time.
If left as is, when used as a magnetic tape, the surface of the tape will be rough, the noise level will be poor, and the magnetic head will wear out, and the adhesion between the head and tape surface will deteriorate.
5; Obstructed and targeted densification layer recording actual TF
There is a drawback that it is difficult to use.

Furthermore, the evaporation method (3) requires complicated equipment and operations, and its large-scale implementation has disadvantages in terms of industrial efficiency and economy.

In addition, in the mercury electrolysis method (5), the electrodeposited product is dendritic particles containing 4 to 6% mercury, which is removed from the dendritic particles by heat treatment. It is difficult to completely remove it, and there are also problems such as mercury pollution that make it difficult to put it into practical use.

In addition, regarding the wet reduction reaction method (6), the ferromagnetic metal 9 alloy powder obtained by this method has strong surface activity and has strong natural properties (it is weak against oxygen and moisture in the air,
Even at room temperature and humidity, it is gradually oxidized and tends to deteriorate its magnetic properties.

In addition, the individual particles obtained by this method are filamentous, but in the process of mixing and dispersing with a binder, the particle shape is destroyed and the magnetic field orientation deteriorates. It has the disadvantage of poor characteristics, especially the squareness ratio.

Now, the present invention belongs to the method (2) of dry reducing iron oxyhydroxide or iron oxide with a reducing gas.
Several drawbacks have been pointed out regarding conventional methods related to this.

First, the reduction process is usually carried out in a high-temperature hydrogen stream, resulting in a reduction in volume.

Porousness, shape changes, and sintering occur, and even if we start from iron oxide with the desired shape, we cannot expect any magnetic properties.
) Two are difficult to obtain.

This is because even in the normal manufacturing process of γ-Fe 203, changes in shape and sintering are most likely to occur in the process of α-Fe203→Fe3O4, that is, the process of removing oxygen from α-Fe 203 using hydrogen gas. This is said to be the case, and considerable efforts have been made to prevent this.

In comparison, in the case of metal 9 alloy, all the oxygen is taken up, so it can be said that the change in shape and sintering are even more severe, and the coercive force (Hc).

Square ratio-! Two evils: Dispersion is incomplete when tape is made, and although it has promising properties as a recording material, it has not been practical.

Furthermore, the metal 9 alloy powder obtained by this method also has the drawback of being flammable, which hinders its practical use.

That is, β-Fe00H or γFeO of the present invention
By using OH as a raw material and treating it in an alkaline solution, filtering it, washing it with water, drying it, and then reducing it in a reducing gas, the above drawbacks of shape collapse and sintering crabs are prevented, and the holding power (He ), squareness ratio (σr/σs) 9 A metal powder is obtained which has excellent dispersibility, is stable with suppressed ignitability, and is sufficiently usable as a ferromagnetic material for magnetic recording.

β-FeOOH or γ-FeOOH used in the present invention
For these, CO+ Nte T'l* BteM
Even those doped with metals such as o e a g are included, and the alkalis include caustic soda and caustic potash.

Ammonia etc. can be listed as crab.

Furthermore, a mixture of each of these raw materials and alkali may be used.

To explain the present invention in more detail below, β-FeOOH used in the present invention can be obtained by precipitating β-FeOOH by passing oxygen or an oxygen-containing gas into a ferrous chloride aqueous solution, for example.
γ-FeOOH is obtained by distributing this from door to door.
For example, it can be obtained by adding an alkali to an aqueous ferrous oxide solution to neutralize about 80% of the total ferrous chloride, then passing oxygen or an oxygen-containing gas to precipitate γ-FeOOH, and distributing it from house to house.

Also, using the usual method, Coo Ni, T L
B it Mo+ Ag etc. to β-Fe00H or γ
-FeOOH can also be doped and used as a raw material.

In the alkali treatment, for example, when caustic soda is used, the concentration of the aqueous solution is preferably 1N to 20 Hz, and if it is less than IN, no effect will be observed.

Further, if the pressure is 2ON or more, it is not industrially or economically viable due to the cleaning operation and the amount of NaOH consumed.

The processing temperature is 30-100'C. There is no particular restriction on the treatment time, but in order to make the effect noticeable, it is preferably 0.5 hours or more.

As mentioned above, caustic potash, ammonia, etc.-I)N can be used as the alkali, and the preferable conditions for use thereof are also the same as above.

Furthermore, the present inventors have already filed a patent application filed in 1973 before or at the same time as this alkali treatment.
Example of treatment for adsorbing or precipitating aluminum compounds and/or silicon compounds as described in No. 51795, patent application No. 5179
Treatment for adhering, adsorbing or precipitating one or more compounds of Zn, Cr, and Cu as described in No. 3-30150, and CoeNi9Mnes as described in Japanese Patent Application No. 30151-1983.
Even greater effects can be expected by performing treatments such as attaching, adsorbing, or precipitating one or more of the compounds described in (b).

After treatment in an alkaline solution, it is filtered, washed with water, and dried.

Subsequently, these treatments-75: β-Fe00
H or γ-Fe00H is reduced in a hydrogen atmosphere at a temperature not exceeding 600°C, preferably at a humidity not exceeding 500°C.

Although there is practically no lower limit for temperature, the reaction proceeds very slowly at low temperatures, so from a practical standpoint it is recommended to use temperatures of at least 250'C to avoid long reaction times that are impractical. Should.

However, temperatures as low as 200° C. are also possible.

After reduction, the reducer is cooled down to 1% air and 99% nitrogen.
is introduced into the reductor, and the air content of this gas is doubled at intervals of approximately 30 minutes.

After 4 to 5 hours, it is possible to switch to air only and take out the magnetic iron powder from the reducer.

It can also be used as magnetic tape or other magnetic recording media.

Next, embodiments of the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 A vinyl chloride container with a diameter of 15CTL and a height of 3m was used as a reaction column, and the reaction tower was approximately 70? /1! Take 301 ml of ferrous chloride FeCl2 solution, neutralize about 80% of the total FeCl2 by blowing NH3 gas, and while keeping the temperature at 10 to 15 °C,
Oxygen gas was blown in at a rate of about 201/min, and the reaction time was about 9
Uniform acicular particles of γ-FeOOH (lepidocrocite) with an average long axis of about 1 μm were obtained over time.

The wet cake of γ-Fe00H obtained in this way after furnace separation is 1802 in terms of Fe2O3, which is about 61 5-N-
A NaOH solution was added and the mixture was dispersed at about 80° C. for about 3 hours without stirring.

Thereafter, it was filtered, washed with water until the pH of the p-liquid f'=about 7.5, and dried.

Then this dried cake about 20'? The boat (width approx. 5c)
Take rrL length 10 tax) and radial line 10c11L
, put in a reducer with a length of about 100 CrrL and add about 3 H2 gas.
The mixture was poured at a rate of 1/min and heated at approximately 400° C. for approximately 5 hours to obtain metal powder.

The reductor is then cooled down to room temperature and a gas mixture consisting of 1% air and 99% nitrogen is introduced, doubling the air content in the gas mixture at approximately 30 minute intervals.

After about 5 hours, only air is allowed to flow through the reducer, and then the iron powder is taken out.

The magnetic properties measured at Hm=10KOe were as follows.

Hc=900 Q6 σr=73.2 emu/gσB = 151 0m11/7 σr/σs=0.485 Comparative Example 1 Magnetic powder was obtained in the same manner as in Example 1 without the treatment of the present invention. The magnetic properties were measured.

The results are as follows.

Hc = 650 0e σr = 43.2 emu/g σ5 = 175 emu/g σr/σs = 0.247 Example 2 Magnetic powder was prepared in the same manner as in Example 1 except that a 10-N -N a OH solution was used. The magnetic properties were measured.

The results are as follows. Hc = 920 0e σy = 72.6 emu/P σs = 150.3 emu/g σr/σs = 0.485 Example 3 In Example 1, an acid-resistant vessel with a diameter of 30 vessels and a height of 5 m was used as the reaction tower. A gas chamber with the same diameter and a height of 30 cm was installed with an oxygen gas dispersion material sandwiched in the bottom part by flange connection.

2001 of water at 70°C was injected into the reaction tower, 185 ferrous chloride Fec12.6H6H2O was dissolved therein, and water at 70°C was added to make the total amount 2501.

Ferrous chloride is 400 as F e C4? It is #.

Next, while keeping the reaction solution at 70'C by introducing live steam from time to time, oxygen gas finely divided by a dispersion material was injected at a rate of 250 mm per minute for oxidation.

The reaction rate reached 85% in about 5 hours, and uniform β-Fe00H (akaganite) acicular particles with an average long axis of about 1μ were produced.
I got 5yo.

Magnetic powder was obtained in the same manner as in Example 1 except that β-Fe00H thus obtained was used, and the magnetic properties of this powder were measured.

The results are as follows.

c. σr σS σr/σS Comparative example 2 Processing in alkaline solution and therefore filtration, washing with water.

Magnetic powder was obtained in the same manner as in Example 3 except that it was not dried.
The magnetic properties of this material were measured.

The results are as follows.

c. σr σS σr/σS e emu/L? emu/? e emu/'? e m u /g 50 32.1 178.5 0.180 50 75.2 165.3 0.455

Claims (1)

[Claims] 1. A method for producing magnetic powder, which comprises treating β-Felon or γ-FeOOH in an alkaline solution, followed by filtering, washing with water, drying, and then reducing. 2. The manufacturing method according to claim 1, wherein the alkaline solution concentration is 1 to 2 ON. 3. The manufacturing method according to claim 1, wherein the treatment temperature in the alkaline solution is 30 to 100°C. 4. The production method according to claim 1, wherein the reduction is carried out at 200 to 600°C under a flow of reducing gas. 5. The production method according to claim 1, wherein the alkaline solution is a mixture of one or more selected from the group consisting of an aqueous caustic soda solution, an aqueous caustic potash solution, and aqueous ammonia. 6. The production method according to claim 1, wherein the reducing gas is hydrogen.