JP2735910B2 - Method for producing metal magnetic powder for magnetic recording - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a metal magnetic powder having excellent oxidation stability and excellent dispersibility, which is used as a magnetic powder for a high-density magnetic recording medium. is there.

[Conventional technology and its problems]

As magnetic powder suitable for high-density magnetic recording media, the development of metal magnetic powder containing iron as the main component has been promoted and used for 8m / m video tape, audio metal tape, DAT metal tape, video floppy, etc. ing. Several methods have been proposed for the production of metal magnetic powders used in these media, but in general, they are produced by reducing acicular iron oxyhydroxide or iron oxide containing iron as a main component. Have been.

Since the magnetic metal powder is fine and highly active, if reduced, it reacts violently with oxygen in the atmosphere and burns, and cannot be safely handled in the atmosphere. In order to solve this problem, the metal magnetic powder is stabilized by contacting it with an oxygen-containing gas under mild conditions in a liquid or gaseous phase and gradually forming an oxide film on the surface of the metal magnetic powder particles. Have been proposed. For example, the stabilization method in the liquid phase is disclosed in JP-A-52-85054, and the stabilization method in the gas phase is described in JP-A-48-79153,
9-11760, JP-A-51-10669, JP-A-52-8
It is proposed in Japanese Patent No. 5054.

However, the methods proposed so far have the following disadvantages. In other words, in the stabilization method in the liquid phase, the formation of an oxide film is performed gradually, which is a preferable method in terms of magnetic characteristics. However, the coexistence of combustibles and highly active metal magnetic powder that can be an ignition source Due to the presence of fire hazard due to the catalyst and the catalytic effect of the metal magnetic powder, a part of the used organic solvent is oxidized and decomposed to produce various altered products, which adhere to the surface of the metal magnetic powder, and as a result Insufficient density of the oxide film, high temperature and high humidity of metal magnetic powder (60 ℃, RH = 90
%) Is poor oxidation stability.

On the other hand, the gas phase stabilization method converts oxygen into an inert gas (for example,
(Nitrogen, argon, helium), and the reaction is performed by controlling the oxygen concentration in the gas and the reaction temperature, but there is no danger due to the use of a solvent as in the case of stabilization in the liquid phase, and oxidation stability Under high temperature and high humidity (60
(° C, RH = 90%), the oxidation stability is superior to that of the product stabilized in the liquid phase. However, compared to a metal magnetic powder which is oxidized and stabilized in a liquid phase, in a coating process for forming a medium, it is less compatible with a resin and has poor dispersibility. This phenomenon is becoming more remarkable by miniaturizing the magnetic particles in accordance with the recent development of the high-density medium.

[Means for solving the problem]

The present inventors have conducted intensive studies in order to solve the above-described problems.As a result of staging the metal magnetic powder in the gas phase, the metal magnetic powder is brought into contact with an oxidizing gas diluted with an alkylbenzene compound vapor and an inert gas, By attaching the oxidation product of an alkylbenzene compound to the surface of metal magnetic powder particles, it has the same oxidation stability as gas-phase stabilized products and the same dispersibility as liquid-phase stabilized products. The present inventors have found that a metal magnetic powder suitable as a magnetic material for a recording medium can be obtained, and have completed the present invention.

That is, the present invention dry-reduces needle-shaped iron oxyhydroxide or iron oxide containing iron as a main component, oxidizes and stabilizes the metal magnetic powder in a gas phase, and then adds the inert gas to the metal magnetic powder. A method for producing a metal magnetic powder for magnetic recording, wherein an alkylbenzene compound vapor is brought into contact with a diluted oxidizing gas, and an oxidation product of an alkylbenzene compound mainly containing an aliphatic alcohol having a benzene ring is attached. .

The metal magnetic powder produced by the method of the present invention has excellent oxidation stability under high temperature and high humidity (60 ° C., RH = 90%) and excellent dispersibility, and is suitable for high-density magnetic recording media. It is suitable as a magnetic material.

The needle-shaped iron oxyhydroxide or iron oxide containing iron as a main component used in the present invention is a needle-shaped α- obtained by a conventional method.
FeOOH, γ-FeOOH, β- FeOOH _{or,, α-Fe 2 O 3} ,
γ-Fe ₂ O ₃ , β-Fe ₂ O ₃ , Fe ₃ O ₄ etc.
n, Mn, Cr, Ca, Mg, Ba, P, Si, Al, B, Zr or the like, which is doped and / or coated with one or more metal compounds selected from metal such as Zr is used. .

After the raw materials were dry-reduced and cooled by a conventional method, they were oxidized and stabilized in a gas phase by a conventional method, and then the oxidation stabilization of the alkylbenzene compound vapor was completed with an oxidizing gas diluted with an inert gas. It is brought into contact with the metal magnetic powder.

Alkylbenzene compounds suitable for the purpose of the present invention are In the structural formula represented by, R is an alkyl group having 1 to 5 carbon atoms, and the structure may be linear or have a steric structure. However, in the case of an alkyl group having 3 or more carbon atoms, the steric structure is better. preferable. It should be noted that the alkyl group may have an unsaturated bond. The number of substituents represented by X is from 0 to 5, and the structure of the substituents is an alkyl group, other oxygen-containing ones (for example, ether, alcohol, aldehyde, carboxylic acid, etc.), and nitrogen-containing ones (for example, Amines, nitrates, etc.) can also be suitably used.
In order to bring such an alkylbenzene compound into contact with the metal magnetic powder as a vapor, a vapor pressure of a certain level or more is required at the treatment temperature, and the boiling point of the alkylbenzene compound that can be suitably used at atmospheric pressure is 110 to 300 ° C. Yes, more preferably 110-200 ° C.

The temperature of the metal magnetic powder layer to be brought into contact with the vapor of the alkylbenzene compound is preferably from 0 to 100 ° C, more preferably from 10 to 70 ° C. If the temperature is too low, the oxidation reaction of the alkylbenzene compound will be slow, and it will take a long time to deposit a desired amount of oxidation product, which is not economical. On the other hand, if the temperature is too high, the oxide film on the surface of the metal magnetic powder becomes thicker, and the saturation magnetic flux density decreases more than necessary.Also, the oxidation reaction of the alkylbenzene compound also proceeds excessively, and lower carbonic acids are generated. To form a metal salt of acid at high temperature and high humidity (60 ℃, RH = 90
%) Is not preferred because the oxidation stability at

As an apparatus for carrying out the present invention, the apparatus used for the gas-phase oxidation stabilization in the preceding stage can be used as it is. As a reaction system, any of a fixed bed, a fluidized bed and a stirring system can be applied.

The timing of bringing the metal magnetic powder into contact with the alkylbenzene compound vapor is such that the oxidation of the metal magnetic powder, which has been oxidized and stabilized with an oxidizing gas diluted with an inert gas in the preceding stage, does not generate heat when taken out into the atmosphere. It is preferable after the conversion. If the metal magnetic powder is brought into contact with the vapor of the alkylbenzene compound while the activity remains sufficiently, the same reaction as at high temperature occurs, and the oxidation stability under high temperature and high humidity deteriorates, which is not preferable.

The concentration of the oxidizing gas to be brought into contact with the metal magnetic powder together with the alkylbenzene compound vapor ranges from 0.01 to 21 vol of the atmospheric composition when general oxygen is used as the oxidizing gas.
Used in the range of%. The selection of the oxidizing gas concentration is controlled in consideration of the supply amount of the alkylbenzene compound vapor so that the oxidizing gas concentration in the gas does not fall within the explosion range.

As oxidizing gases other than oxygen, nitrous oxide, nitric oxide and nitrogen dioxide can also be used.

Further, as the inert gas for diluting the oxidizing gas, nitrogen, argon, helium, carbon dioxide, or the like can be used.

The reaction time is preferably in the range of 1 to 6 hours. When the reaction time is too short, the progress of the oxidation reaction of the alkylbenzene compound is not sufficient, and when the reaction time is too long, the saturation magnetic flux density of the metal magnetic powder is preferably lower than a desired value. Absent.

The amount of the oxidation product adhered to the metal magnetic powder is preferably 0.05 to 3.0% by weight, more preferably 0.1 to 2.0% by weight of the amount of carbon in the metal magnetic powder measured using a carbon measuring device in steel. % By weight. If the amount of adhesion is too small, the effect of improving the dispersibility is small, while if too large, there is no further effect of improving the dispersibility even if the amount is more than the optimum range, and the adverse effect when the medium is used is preferably considered. Absent.

Further, the unreacted alkylbenze compound remains on the metal magnetic powder, but does not affect the effect of the present invention.

〔Example〕

Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Example-1 The average major axis length was 0.25 μm, the average axis ratio was 14, and the contained metal was Zn =
1.5 wt% / Fe, Ni = 4.5 wt% / Fe, Si = 1.2 wt% / Fe,
Α-FeOOH in which Al = 3.6% by weight / Fe is subjected to a baking treatment at 650 ° C. for 2 hours, and then reduced at 450 ° C. for 4 hours under a hydrogen stream to obtain a metal magnetic powder to be subjected to an oxidation stabilization treatment. . This is designated as raw material A.

The raw material A was transferred and stored in a nitrogen-filled intermediate container, and an oxidation stabilization treatment and an adhesion experiment of an oxidation product of an alkylbenzene compound were performed. In the other examples and comparative examples, the raw material A was used.

The entire apparatus shown in FIG. 1 was replaced with nitrogen gas, 400 g of raw material A was charged into the reactor 1, the circulation floor 2 was operated while supplying nitrogen, and the valve 5 was adjusted to adjust the nitrogen gas to 50 N / min. Was circulated in the system to stop the supply of nitrogen. Thereafter, an oxidation stabilization treatment was performed by a conventional method using oxygen as an oxidizing gas. After the stabilization was completed, a part of the metal magnetic powder was taken out to the atmosphere, but no exothermic phenomenon was observed. The magnetic properties of this metal magnetic powder (measured with a magnetic field of 10 kg using VSM manufactured by Toei Kogyo Co., Ltd.) were as follows: HC = 1583 Oe, δs = 132.4 emu /
g, σr / σs = 0.514.

Thereafter, the gas in the circulation system was entirely nitrogen, and while circulating at 50 N / min, the temperature of the reaction section was maintained at 40 ° C. by adjusting the temperature of the jacket 10 and the heat exchanger 6 to increase the pressure in the system. The minute amount of circulating gas was adjusted by adjusting the valve 8 so that it could be discarded. Then, air with a water content of 500 ppm or less is
Per minute, and then 4 g of isopropylbenzene (boiling point = 152.4 ° C.) was fed into the circulation system using the micro metering pump 9 for 2 hours. Thereafter, while the reactor temperature was lowered to room temperature, air supply and gas circulation were continued for 1 hour. Magnetic properties of metal magnetic powder after treatment (Toei Kogyo
Using a VSM, measured with a measuring magnetic field of 10KG, the following measurements were measured under these conditions): Hc = 1580 Oe, δs = 127.0 emu / g, σr /
σs = 0.515, and the carbon content was 0.6% by weight (measured by EMIA-1200 manufactured by Horiba, Ltd.). This one 60
Δs after exposure for one week in an atmosphere at 90 ° C. and RH = 90% = 112.
It was 1 emu / g, and both magnetic properties and oxidation stability were excellent. The oxidation product adhering to the metal magnetic powder was dissolved in hydrochloric acid under mild conditions under mild conditions, extracted with ether, and qualitatively analyzed. The main component was α, α'-dimethylbenzyl alcohol. Only a small amount of Zen was detected.

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 mixed with the dispersion and sufficiently dispersed. After adding a crosslinking agent to the dispersion paint and mixing well, a 14 μm PE
Apply on a T film and leave the magnetic paint dry.
Perform a magnetic field orientation treatment with a 0 Gaussian magnet, and after drying,
Super calendering was performed, and slit to 8 mm width to produce an 8 mm video tape. When the magnetic properties of the tape were measured by VSM, Hc = 1562Oe, Br = 2875G, Bm
= 3402G, Br / Bm = 0.845. Also, the tape slit to 8 mm was exposed to high temperature and high humidity (60 ° C, RH = 90%) for one week, a deterioration promotion test was performed, and the Bm of the tape was measured by VSM. ｛(Before test Bm−
(Bm after test) / (Bm × 100% before test) was 7.0%.

Example 2 Using the raw material A, stabilization in the former stage was performed in the same manner as in Example 1, and the next reaction was also performed except that toluene (boiling point = 110.6 ° C.) was used as the alkylbenzene compound and the reaction temperature was 30 ° C. The processing was performed in the same manner as in Example-1. The magnetic properties of the treated metal magnetic powder were as follows: Hc = 1585 Oe, δs = 126.3 emu / g, δ
r / δs = 0.515. Carbon content is 0.5% by weight
Δs after one week exposure at 60 ° C and RH = 90%
It was 110.8 emu / g (hereinafter indicated by Δδs). As a result of qualifying the oxidation product of toluene attached to the metal magnetic powder in the same manner as in Example 1, the main components were benzyl alcohol and benzoic acid.

The tape was formed in the same manner as in Example 1, and the deterioration acceleration test was also performed. The measured values are Hc = 1558 Oe, Br = 2792
G, Bm = 3312G, Br / Bm = 0.843, and the deterioration rate (hereinafter referred to as ΔBm) = 8.1%.

Example 3 Mixed xylene (boiling point =
138-144 ° C) under the same conditions as in Example-2.
The magnetic properties of the metal magnetic powder after the treatment are as follows: Hc = 1587 Oe, δs
= 125.9 emu / g and δr / δs = 0.514. Δδs = 11
At 1.2 emu / g, the carbon content was 0.6% by weight. Example of oxidation product of xylene attached to metal magnetic powder
As a result of qualification in the same manner as in Example 1, a mixture of methylbenzyl alcohol and a mixture of methylbenzoic acid were the main components.

The tape was formed in the same manner as in Example 1, and the deterioration acceleration test was also performed. The measured values are Hc = 1555Oe, Br = 2820
G, Bm = 3337G, Br / Bm = 0.845, and ΔBm = 7.5%.

Example-4 Using mesitylene as an alkylbenzene compound,
The treatment was carried out under the same conditions as in Example 1 except that the reaction temperature was 50 ° C. and the amount used was 2 g. The tape was formed in the same manner as in Example 1. Table 1 shows the magnetic properties and Δδs of the metal magnetic powder, and Table 2 shows the magnetic properties and ΔBm of the tape.

Example-5 Example-5 was repeated except that ethylbenzene was used as the alkylbenzene compound, the reaction temperature was 30 ° C, and the amount used was 8 g.
The same conditions as 1 were processed. The tape was formed in the same manner as in Example 1. Table 1 shows the magnetic properties and Δδs of the metal magnetic powder.
Table 2 shows the magnetic properties and ΔBm of the tape.

Comparative Example-1 Example-1 except that 8 g of ethyl ethyl ketone was used instead of the alkylbenzene compound, and the reaction temperature was set to 20 ° C.
Treated under the same conditions as The tape was also formed in the same manner as in Example 1. The organic matter attached to the metal magnetic powder was pretreated and qualitatively analyzed in the same manner as in Example 1. As a result, together with dehydration condensate of methyl ethyl ketone and alcohols by dimerization, Many formic and acetic acids were detected.

Table 1 shows the magnetic properties and Δδs of the metal magnetic powder, and Table 2 shows the magnetic properties and ΔBm of the tape. (The same applies to Comparative Example-2 and the following.) The oxidation stability is inferior to that using an alkylbenzene compound as an organic substance, but it is presumed that this is due to the formation of lower carboxylic acids.

Comparative Example 2 Using 8 g of cyclohexane as an organic substance,
The treatment was performed under the same conditions as in Example 1 except that the temperature was changed to 30 ° C. The tape was formed in the same manner as in Example 1.

The organic substance attached to the metal magnetic powder was mainly composed of lower carboxylic acids such as formic acid, acetic acid, and propionic acid, as in Comparative Example-1.

Comparative Example 3 Raw material A was gas-phase stabilized by a conventional method. Oxidation stability is excellent, but dispersibility is inferior to those treated with organic substances. The tape was formed in the same manner as in Example 1.

Comparative Example-4 The raw material A was oxidized in toluene to stabilize the liquid phase. As a result of qualitative analysis of organic substances adhering to the metal magnetic powder, benzoic acid was the main component, and benzyl alcohol and many lower carboxylic acids such as formic acid and acetic acid were also detected. This product had a good dispersibility, but the oxidation stability was inferior to those of the examples. The tape was formed in the same manner as in Example 1.

[Effects of the Invention] As is clear from the examples and comparative examples, the metal magnetic powder of the present invention has the same oxidation stability as the gas phase stabilized product, and the same dispersibility as the liquid phase stabilized product. It is suitable as a magnetic material for a high-density magnetic recording medium.

[Brief description of the drawings]

 FIG. 1 is a schematic diagram of a reaction apparatus used in the present invention. DESCRIPTION OF SYMBOLS 1 ... Reaction container 2 ... Gas circulation blower 3 ... Buffer tank 4 ... Flow meter 5 ... Flow control valve 6 ... Heat exchanger (heating) 7 ... Heat exchanger (cooling) 8 ... Gas abandonment Valve 9: Micro metering pump 10: Jacket

Claims (1)

(57) [Claims] An iron-based acicular iron oxyhydroxide or iron oxide is dry-reduced, and the metal magnetic powder is oxidized and stabilized in a gas phase. A method for producing a metal magnetic powder for magnetic recording, wherein an alkylbenzene compound vapor is brought into contact with a diluted oxidizing gas to attach an oxidation product of an alkylbenzene compound mainly composed of an aliphatic alcohol having a benzene ring.