JPS58110433A - Stabilizing method for needlelike magnetic metallic powder - Google Patents

Abstract

PURPOSE:To enhance the corrosion resistance and stability of needlelike magnetic metallic powder by blowing air into a mixture prepared by dipping the powder in a specified org. solvent to form a passive oxide film on the surface of the powder. CONSTITUTION:A gas dispersing plate 3 having many pores is placed in a stainless steel vessel 1, and a mixture 2 prepared by dipping needlelike magnetic metallic powder for a magnetic recording medium in an org. solvent such as pentane, hexane, heptane or toluene is put on the plate 3. A gas (a), (b) having <=30% oxygen content such as air is forced to be uniformly blown into the mixture 2 through the plate 3, and the mixture 2 is treated at room temp. below 50 deg.C for 5-24hr. By the treatment the metallic powder coated with the org. solvent is dried to form an oxide film on the surface. Thus, the surface of the metallic powder is stabilized by oxidation. The resulting metallic powder for a high density recording medium is not made chemically unstable in the air, and the deterioration of the magnetic characteristics due to aging is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stabilizing acicular magnetic metal powder used in magnetic recording media such as magnetic tape.

Magnetic materials for magnetic recording media for high output and high recording speed are also required to have high saturation magnetization and high coercive force.

Acicular magnetic metal powder is generally known as such a magnetic material. This acicular magnetic metal powder is made of hydrated iron oxide (
Pe00H), iron oxide, or spult-containing iron oxide, etc., are heated, dehydrated, and subjected to an aqueous treatment. The magnetic metal powder obtained in this way has a Kml film on its surface, that is, a passive oxidation film, in order to provide chemical stability against oxidation and combustion in the atmosphere and corrosion resistance with rust prevention properties. A surface stabilization treatment is performed to form a film.

A typical method for stabilizing such nail-shaped magnetic metal powder is to immerse the magnetic powder in an organic solvent such as toluene and then gradually evaporate the organic solvent. There is a method of forming an oxide film. However,
When such a method is used, the chemical stability of the magnetic metal powder is almost satisfied, and the dispersibility and orientation of the magnetic metal powder in the magnetic coating film in the magnetic medium are satisfactory. , its stabilization treatment, that is, oxide film formation Kl
! The drawback is that it takes a long time to complete and is not suitable for mass production.

Another method is a so-called liquid phase oxidation treatment method in which magnetic metal powder is suspended in an organic solvent and a gas containing KwR elements, such as air, is blown into the suspension to form an oxide film on the surface of the magnetic metal powder. This method has an industrial advantage in that safe oxidation treatment can be performed in a short time. However, when using this method, the chemical stability and corrosion resistance of the magnetic metal powder are not fully satisfactory, and furthermore, the dispersibility and orientation of the magnetic powder in the magnetic coating film in the magnetic medium are poor. , this is a serious drawback in magnetic media.

The present invention corrects such drawbacks, satisfies the chemical stability of magnetic metal powder, and furthermore satisfies the chemical stability of magnetic metal powder, and further improves the Ksi
- Excellent dispersibility and orientation, and its stabilization properties
A stabilization treatment method for acicular magnetic metal powder that does not generate heat and ignite during the drying process of magnetic metal powder in LLK, and allows stabilization treatment by surface oxidation treatment of a large amount of magnetic metal powder in a short time. It provides:

That is, in the present invention, in the liquid phase oxidation round ring method, organic ** evaporates during the drying process of KS-turbid metal powder in an organic solvent, and when the metal surface is oxidized by an oxygen-containing gas, oxidation heat is generated. The metal powder accumulates heat and ignites and burns, and this ignition phenomenon becomes more pronounced as the amount of metal powder increases. By forcibly blowing a large amount of the contained gas, the accumulated oxidation heat is forcibly radiated, and at the same time, the evaporation rate of the organic solvent is increased, making it possible to stabilize a large amount of acicular magnetic metal powder by surface oxidation in a short time. In other words, in method V& of the present invention, in the drying process of metal powder, there is first an endothermic process accompanying the evaporation of the organic #l! medium, and then there is a forced heat dissipation process of oxidation heat by forced feed jLK. In both cases, heat accumulation and ignition phenomena of the metal powder were avoided.It was also confirmed that the dispersibility and orientation of the stabilized acicular magnetic metal powder obtained by K in this way were satisfactory. In other words, the dispersibility and orientation are influenced by the surface structure of the oxide layer of the metal powder, but in the case of the method of the present invention, this point is satisfied and can be tolerated. It became clear.

FIG. 1 shows an example of an apparatus for carrying out the stabilization treatment method according to the present invention. A mixture (2) of magnetic metal powder immersed in an organic solvent is placed. (3) is a gas dispersion plate that distributes oxygen-containing gas from below the mixture (2) of metal powder and organic solvent in the container (1) as shown by arrows l and bK.
) and forcefully blow the air through the mixture (2). On the other hand, a metal filter (4) is placed above the container (1), and exhaust air is provided from above the container (1) as shown by the arrow cK.The container (1)K prevents the filter (4) from clogging. A supply port (5) for backflow gas such as nitrogen gas or air is provided. (6) indicates the regulating valve, for example, an electric valve, so that the oxygen-containing gas is uniformly blown onto the metal 11 to be treated by such a device. In this way, the metal powder to be treated is dried uniformly in the container (1), and heat generated by oxidation is prevented from being locally accumulated. The state of the mixed metal powder in the organic solvent is fine powder state, pellet shape W
A'jtG can take on any form of not-so-large clumps.

In addition, if the organic solvent in which the metal powder is immersed is one that is highly compatible with water or has a polar group, moisture in the air will slowly penetrate into the metal powder and accelerate oxidation of the metal powder, making it difficult to control. Therefore, the organic solvent should be selected from solvents that have low compatibility with water and do not have any functional groups. Examples of such organic solvents include pentane, hexane, heptane, and methane of the Otatan group. It is selected from 1 g of verticalized water or aromatic hydrocarbons such as benzene, tricone, and xylene.

Further, as the oxygen-containing gas, it is desirable to use a mixed gas of an inert gas containing oxygen with an oxygen concentration of 30% by weight or less, and air can be used as such a gas, In this case, it is economical and the oxygen concentration has an optimum value. Furthermore, when the oxygen St reaches a high level of 11& exceeding 30% by weight, the oxidation reaction of the metal powder becomes rapid, and there is a risk of ignition due to the heat generated by the oxidation. K and K significantly deteriorate the magnetic properties of the metal. On the other hand, if the oxidation concentration is extremely low, the time required for the surface oxidation stabilization treatment of gold metal becomes long, resulting in industrially undesirable lIK. It is the optimal gas.

Further, the flow rate of this gas needs to be varied depending on the amount of metal powder to be treated, but this flow rate is selected to be a flow rate necessary for heat dissipation so that the heat generated by oxidation of the metal powder does not accumulate.

In addition, it is highly desirable that the treatment temperature for the surface oxidation treatment be around room temperature below so''C.In other words, if this treatment temperature is extremely low, the metal powder is immersed in the organic 5iIII.
/), ii) The firing rate becomes too slow, and the surface oxidation treatment of the metal powder takes a long time, making it impractical. On the other hand, if the processing temperature is too high, the evaporation rate of the organic solvent becomes too fast, and a rapid oxidation reaction occurs in the metal powder, causing ignition due to the oxidation heat, or rapid oxidation even without ignition KM. Therefore, the air quality of the metal powder is significantly deteriorated. In addition to these considerations, it is also important to consider the process from the viewpoint of efficiency and economy! It is desirable that the vertical position be selected at room temperature.

The treatment time of the surface oxidation treatment is greatly affected by the treatment temperature and oxygen concentration, but from the viewpoint of practicality, it is preferably selected to be 5 to 24 hours.

Additionally, K is added to the nail-shaped magnetic metal powder used in the present invention in order to further enhance oxidation stabilization.

Before the reduction treatment, chromium, aluminum, titanium, etc. can be added. Furthermore, in order to prevent sintering, it can be treated with silicone oil or a V9 coupling agent in advance.

Next, examples of the present invention will be given.

Example 1 Acicular α-F containing 10 atoms of N& and 5 atoms of another
BOsf, 21/min water 1 [0 which was reduced at 3110''C for 3 hours, then the atmosphere was reduced to 10011N8
The atmosphere was changed to kW and left to cool in this condition in a Tomion trench. After cooling, the reduced metal powder was injected into toluene and immersed, and the mixture obtained by immersion in toluene was placed in the reaction vessel 0) for surface oxidation treatment described in FIG. In this case, the metal powder to be treated in the mixture is approximately sog.

The total weight was 120 g with 70 g of toluene.

The bed height of the mixture (2) in the reaction vessel (1) was approximately sas.

Next, in this state, air was blown into the reaction vessel (1) from below to perform a surface oxidation stabilization treatment on the metal powder.

This treatment was carried out at room temperature for 24 hours at an air flow rate of 7 min/min. In the case of Mukai and Jin, no heat generation occurred during this treatment.

Example 2 The PIllt metal powder used in Example 1 was prepared, and about 180 g of it was injected and immersed in about 230 iK of toluene, and a mixture of about 3 sO was added to the reaction vessel (1 ), and air was blown into the reaction vessel (1) from below to perform surface oxidation stabilization treatment on the metal powder. In this case reaction volume II (mixture in 11 (
The layer height of 2) was about 20 aa. The stabilization treatment was carried out at room temperature for 27 hours by blowing air at a flow rate of 71/min. In this case as well, there was no heat generation at all during this treatment process.

Example 3 Prepare metal powder similar to that used in Example 1, and add about 1.0 kg of it to toluene for $1! The JIJkgK injected and immersed mixture, that is, the mixture of approximately 2.6% and 2%, was placed in the reaction vessel (ri) explained in Fig. 1, and air was blown into the reaction vessel (1) from below to remove the metal powder. surface oxidation stabilization treatment. The mixture (2) in the reaction vessel (1) in this case
The layer height was approximately 4,051 cm. The stabilization treatment was carried out at room temperature for 24 hours using an air flow rate of 751/min. Even in the case of keratin, there was no heat generation at all during this treatment process.

Example 4 Co is 15Ji, Ni is 2m and 18i.
The nail-shaped α-F@g0g containing fertilized particles was reduced for 3 hours at 480° C. with a water bulk flow rate of 2 min/min. Next, the atmosphere was replaced with a 1001N11 atmosphere, and in this state, it was allowed to cool in a temperature trench. After cooling, the reduced metal powder was injected into toluene and immersed, and the mixture obtained by immersion in toluene was placed in the reaction vessel (1) for surface oxidation treatment described in FIG. 1.

In this case, the treated metal powder in the mixture is about 7051. ) Luene is 1101 and the total weight is 180
The bed height in the reaction vessel (1) and in the mixture (2) was about 8 clI. Next, in this state, enter the reaction container (1)! 2! Air was blown from below to perform surface oxidation stabilization treatment on the metal powder. This treatment was carried out at an air flow rate of 71/min and at 1wi temperature for 24 hours. Of these, in this case, there was no heat generation at all in this treatment Haruka 1.

Furthermore, a comparative example of a power number comparison with the present invention will be given.

Comparative Example 1 The same metal powder as used in Example 1 was prepared, and 50
A surface stabilization treatment was carried out by blowing air into the mixture at a flow rate of 417 min at room temperature for 9 hours while stirring the mixture in which the toluene was immersed in toluene.

Comparative Example 2 The same metal powder as used in Example 1 was prepared, and about 5
Mixture B where 0g is immersed in about 701g of toluene! Og
The toluene was evaporated in the air at room temperature, and the surface was oxidized and stabilized by air drying for about S days.

Comparative Example 3 A mixed food in which about sOg of the metal powder used in Example 4 was immersed in about II toluene vm While stirring, air was blown into this mixture at a flow rate of about 41/min to stabilize the surface by oxidation at room temperature for 9 hours. processed.

These Examples 1 to 4 according to the present invention, and further Comparative Examples 1 to 3
Characteristics of the metal powder that have been stabilized by: magnetization amount σ6, square ratio, coercive force Hc, specific surface area of the metal powder, and orientation sheet of the magnetic layer composed of this metal powder)! Figure 2 shows the -j constant results for coercive force Hc, squareness ratio H@, and residual magnetic flux degree Br. It can be seen that similar characteristics can be obtained.

In addition, it was confirmed that the magnetic umbrella j4 powder treated according to the present invention has excellent stability with little change over time.

That is, 1 g of magnetic metal powder treated in Example 1 and Comparative Example 2 was immersed in 100111 distilled water under pressure, then separated, taken out, dried in air at room temperature, and visually inspected for the presence of rust. It has no rust,
The magnetization amount σS was 147 emu/If, whereas in Comparative Example 2, rust was detected, and the magnetization amount σI was 147 emu/If.
It decreased to 130 emu/g.

[Brief explanation of the drawing]

FIG. 1 shows the stabilization treatment method according to the present invention! A schematic diagram of an example of the equipment used for this purpose, Part 1! The figure is a IIj diagram of the characteristic measurement results of each magnetic metal powder subjected to stabilization treatment. (1) is a reaction vessel, and (2) is an organic*m mixture of magnetic metal powder.

Claims (1)

[Claims] A gas containing oxygen is blown through a mixture of dry-reduced acicular magnetic metal powder mixed in an organic solvent to forcibly evaporate the organic solvent to form an oxide film on the surface of the magnetic metal powder. Characteristic stabilization treatment method for acicular magnetic metal powder.