JPH0618131B2 - Method for producing magnetic powder for magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing magnetic powder for a magnetic recording medium,
In particular, the present invention relates to a method for producing a magnetic powder having improved oxidation resistance when an oxidizing magnetic powder such as a magnetic metal powder is used in a magnetic recording medium.

2. Description of the Related Art Magnetic powders are widely used in magnetic recording media such as video tapes, audio tapes, computer information recording tapes, and floppy disks. This magnetic powder contains
There are metal powders, metal nitride powders, and metal oxide powders, and the former two have higher saturation magnetic flux density and coercive force than the latter, and are superior in terms of their magnetic properties. However, these metal powders and metal nitride powders are easily oxidized, for example, when they are used as magnetic tapes, they are exposed to air and are oxidized.
It has the drawback of degrading its magnetic properties.

For this reason, in order to improve the oxidation resistance of the metal powder and the metal nitride powder, an oxidation treatment for forming a relatively stable oxide film on the surface of these powders is performed in advance, and even when used in air, rapid oxidation does not occur. Some ideas have been proposed that will not happen.

For example, 1/2 to 1/5 of its weight in an organic solvent such as toluene.
The magnetic powder is dipped and stirred at a rotation speed of 1 to 100 times per minute, and in this state while blowing an oxidizing gas such as dry air, it is heated to 80 to 100 ° C to evaporate the solvent, It is known to carry out the method until the solvent is completely evaporated.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, for example, iron nitride powder surface-oxidized by such a method has a smaller saturation magnetization (σ _s ) when the oxidation temperature is increased as shown in FIG. There is also a risk of ignition of magnetic powder. However, as shown in FIG. 5, it is preferable to increase the oxidation treatment temperature because the deterioration rate of the saturation magnetization (σ _s ) becomes small even in relatively high humidity.

In reality, for example, the rate of decrease in saturation magnetization when kept at 60 ° C and 90% relative humidity for 75 hours is taken as the deterioration rate, which is used as a measure of corrosion resistance.

Therefore, the magnetic tape obtained by using the magnetic coating material prepared by using the magnetic powder oxidized at a high temperature is not preferable because it deteriorates the electromagnetic conversion characteristics.

As described above, the relationship between the oxidization temperature of the oxidizable magnetic powder and the magnitude of the saturation magnetization and its deterioration rate has an inverse correlation, and therefore, a method for producing an oxidizable magnetic powder that satisfies both of these has been desired.

An object of the present invention is to provide a method for producing a magnetic powder which has a large saturation magnetization and a small deterioration rate of the oxidizing magnetic powder.

Means for Solving the Problems In order to solve the above problems, the present invention includes a step of adding at least one metal compound of nickel or cobalt to the surface of an oxidizable magnetic powder, and an oxidation step in which the metal compound is added. To obtain stepwise-oxidized magnetic powder by using a step of firing a magnetically-oxidized magnetic powder and a stepwise oxidation step in which the oxidizing magnetic powder obtained by this firing is used and the temperature is raised stepwise in air to perform an oxidation treatment The present invention provides a method for producing a magnetic powder for a magnetic recording medium, which comprises steps.

Next, the present invention will be described in detail.

In the present invention, there is a step of adding at least one metal compound of nickel and cobalt to the oxidizable magnetic powder. Examples of the metal compound include nitrates, chlorides,
Examples thereof include inorganic salts such as sulfates and phosphates, and organic salts such as acetates.

For example, Ni (NO ₃ ) ₂ 6H ₂ O, CoSO ₄ 7H ₂ O, CoCl ₂ 6H ₂ O and the like can be mentioned.

These metal compounds are, for example, along with α-FeOOH, for example Na
The pH is adjusted with an alkaline agent such as OH and mixed in water. Then, the mixture is filtered, and the water adhering to the filtered material is dried, and then those having crystal water are dehydrated and baked. After this, hydrogen reduction treatment is performed. Further, a nitriding treatment is performed to convert the magnetic powder into iron nitride. Then, it is immersed in a non-polar solvent such as toluene and then left to stand for natural oxidation while volatilizing this solvent at room temperature.

The magnetic powder thus treated is taken out into the air and subjected to an oxidation treatment in which the temperature is raised stepwise in the air. This oxidation treatment is, for example, 40 ° C to 140 ° C, preferably 60 ° C.
Several temperature levels are determined stepwise in the temperature rising process up to 120 ° C above, and the heat oxidation treatment is mainly performed at each temperature level, and the treatment time at each temperature level is, for example, 0.5
It can be set arbitrarily such as ~ 3 hours. In this case, if the time is extended at the low temperature level, the same effect as the short-time treatment at the high temperature level may be obtained. The magnetic powder sequentially oxidized to the highest temperature level is naturally or forcibly cooled to complete the oxidation resistance treatment. It should be noted that the stepwise oxidation treatment process may include only the thermal oxidation treatment at each temperature level, but can also include a temperature change process associated therewith.

In the present invention, the oxidizable magnetic powder is a metallic magnetic powder,
Examples thereof include iron nitride powder, and these are not limited to their shape and composition.

Examples of the magnetic metal powder include ferromagnetic alloy powders, in which the metal content is 75% by weight or more, and 80% by weight or more of the metal content is at least Fe, Co, Ni, Fe-Co, Fe-Ni, Co- Ni or Co-Ni
-A ferromagnetic metal of Fe, 20% by weight or less of metal content, preferably 0.5-5% by weight of Al, Si, S, Sc, Ti, V, Cr, M
n, Cu, Zn, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta,
It has a composition of W, Re, Au, Hy, Pb, Bi, La, Ce, Pr, Nd, B, P and the like, and may contain a small amount of water, hydroxide or oxide. These ferromagnetic alloy powders are preferably particles having a major axis of 0.5 μm or less.

Further, in the present invention, as the iron nitride magnetic powder, Ni, C
o, Zn, Al, Si, Zr, Mn, Cr, Mo, Ba, Ca, Mg, Ti, N
Mainly contains iron containing at least one of a, Cu, Sr, etc., and includes those whose surface is oxidized to improve oxidation stability. The particle size is preferably such that the average long axis is 0.05 to 1.0 μm and the average short axis is 0.005 to 0.3 μm.

Since the temperature is raised stepwise and the oxidation treatment is performed for each temperature level, it is possible to perform the oxidation treatment in both the low temperature region and the high temperature region, and to suppress the decrease in saturation magnetization due to the oxidation treatment in the low temperature region. Both features of suppressing the deterioration of the saturation magnetization due to the oxidation treatment in the high temperature region can be harmonized. At this time, when a metal compound of nickel or cobalt is added to the surface of the oxidizable magnetic powder and baked, volatile components such as water of crystallization of the metal compound are removed, and the metal component is closely covered on the surface of the oxidizable magnetic powder. In the process of being deposited and fired, the metal component diffuses and is made uniform, so that the oxidizing magnetic powder is less likely to be oxidized. By oxidizing the surface-treated oxidizing magnetic powder, the effect of suppressing the decrease in saturation magnetization and suppressing the deterioration of the deterioration rate due to this oxidizing treatment can be further enhanced.

Further, due to the effect of the stepwise oxidation treatment and the metal such as nickel, the risk of ignition of the oxidizing magnetic powder in the oxidation treatment can be reduced, and the high temperature oxidation treatment can be performed.

Example Next, an example of the present invention will be described.

Example 1 (in the case of iron nitride) Goethite [needle-shaped α-FeOOH (average major axis 0.24 μm, axial ratio 6.
0)] After the dispersed in 1 of water _{100g, Ni (NO 3) 2} · 6
After adding 94 g of H ₂ O and stirring for 120 minutes with a mixer, the pH is adjusted to 8 with ammonia.

After this, filtration is performed and the filtered product is dried at 100 ° C. in a heating furnace, then heated to 650 ° C. and dehydrated and baked. After that, the atmosphere is changed to a hydrogen atmosphere and then heated at 450 ° C. for 60 minutes to perform a hydrogen reduction treatment. Furthermore, the volume ratio of ammonia gas and hydrogen gas at 400 ° C
Nitriding was performed by passing a mixed gas of 4: 1 for 60 minutes. The iron nitride powder thus obtained was immersed in toluene in an inert gas (N ₂ ) to make it so that a sudden oxidation did not occur even when it was exposed to air, and then taken out into the atmosphere. At this time, the Ni content was 30 wt% with respect to Fe as a result of X-ray analysis.

Next, the iron nitride powder is left to stand in the air at room temperature until the content of toluene is 10% by weight or less and oxidized, and then the powder is stored in a stainless steel pad so that the layer thickness of the powder is 1 cm or less. The pad is then placed in a box drier and heated.
As shown in FIG. 1, when the temperature reaches 40 ° C., the temperature is maintained for 1 hour, and then the temperature is raised to 60 ° C., and the temperature is maintained for 1 hour. After that, the temperature is further raised to 80 ° C., and the temperature is maintained as it is for 2 hours. After completion of this heating, it is naturally cooled and taken out.

For the oxidation-resistant iron nitride magnetic powder obtained in this way, determine the residual toluene content with a thermobalance, and then measure the saturation magnetization (σ _s ) (initial saturation magnetization in the table) using a vibrating magnetometer. In the air at 60 ° C and 90% relative humidity
The saturation magnetization (σ _s ) after standing for 75 hours (saturation magnetization after deterioration test in the table) was measured, and the deterioration rate was calculated. The results are shown in Table 1 together with the weight% of metal to Fe obtained by X-ray analysis. Show.

In Example 2 (in the case of metal powder) Example 1, Co instead of using _{Ni (NO 3) 2 · 6H} 2 O
As 26 g of Cl ₂ · 6H ₂ O was used, no nitriding treatment was performed, and the oxidization treatment was performed while raising the temperature as shown in Fig. 2.
Oxidation-resistant metal magnetic powder is obtained in the same manner except that the treatment is performed at 3 ° C. for 3 hours, at 75 ° C. for 2 hours, and at 100 ° C. for 1 hour. Table 1 shows the saturation magnetization (σ _s ) and the deterioration rate obtained in the same manner as in Example 1.

In Example 3 (when used in combination of two metal compounds of iron nitride) Example 1, instead of using 94g of _{Ni (NO 3) 2 · 6H} 2 O, NiCl 2 · 6H 2 O51g and CoSO ₄ · 7H ₂ O30g Was used and the oxidation treatment was performed at 45 ° C while raising the temperature as shown in Fig. 3.
1.5 hours, 55 ° C for 1 hour, 65 ° C for 1 hour, 75 ° C for 1 hour, 85 ° C for 1 hour, 95 ° C for 1 hour, 105 ° C for 1 hour, 115
Oxidation-resistant metal magnetic powder is obtained in the same manner except that the treatment is performed at 1 ° C. for 1 hour. Table 1 shows the saturation magnetization (σ _s ) and the deterioration rate obtained in the same manner as in Example 1.

Comparative Example 1 In Example 1, the nickel compound was not used, and Example 1 was used.
Similarly to hydrogen reduction treatment, nitriding treatment, immersion treatment in toluene, and natural oxidation treatment while volatilizing this toluene in the air, the temperature at 40 ° C (low temperature region) and 60 ° C (high temperature region) respectively. Table 2 shows the results obtained in the same manner as in Example 1 for each of the magnetic powders obtained by the heat oxidization treatment at.

Comparative Example 2 In Example 2, the cobalt compound was not used, and Example 2 was used.
In the same way as hydrogen reduction treatment, immersion treatment in toluene, and natural oxidation treatment while volatilizing this toluene in the atmosphere, heat oxidation at each temperature of 50 ° C (low temperature region) and 80 ° C (high temperature region) Table 2 shows the results obtained in the same manner as in Example 1 for each magnetic powder obtained by the treatment.

Comparative Example 3 In Example 3, hydrogen reduction treatment, nitriding treatment, dipping treatment in toluene, and natural oxidation treatment while volatilizing this toluene in the air were conducted at 45 ° C. (low temperature region) as in Example 3. Table 2 shows the results obtained in the same manner as in Example 1 for the respective magnetic powders obtained by the heat oxidation treatment at the respective temperatures of 100 and 100 ° C. (high temperature region).

It should be noted that in Comparative Examples 1 to 3, the heat oxidation treatment was performed at 80%, respectively.
The powder ignited after 10 to 30 minutes when carried out at ℃, 100 ℃ and 115 ℃.

In addition, Table 3 shows the results of the same measurement as described above for each of the above examples in which the metal compound was not used, in which the oxidation treatment was not performed, and in which the both were not performed.

From the above results, all of Examples 1 to 3 have a large initial saturation magnetization and a low deterioration rate, but Comparative Examples 1 to 3 have a large deterioration rate at low temperature oxidation and a small saturation magnetization at high temperature oxidation. Recognize.

Comparative Example 4 After performing the hydrogen reduction treatment, the nitriding treatment, and the immersion treatment in toluene in the same manner as in Example 1 except that the dehydration firing was not performed, the natural oxidation treatment was performed while the toluene was volatilized in the air. , 45 ° C. (low temperature region) and 100 ° C. (high temperature region), the respective magnetic powders obtained by the heat oxidation treatment were obtained in the same manner as in Example 1, and the results were as follows.

EFFECTS OF THE INVENTION According to the present invention, since at least one metal compound of nickel and cobalt is added to the surface of the oxidizable magnetic powder and then baked, these metals are finely and uniformly coated on the surface of the oxidizable magnetic powder. If there is too much or too little deposition of the above metal, there is no danger of ignition, etc. even if oxidation is performed in air. It is possible to solve the problem that the magnetic characteristics of No. 1 deteriorate and the deterioration rate of the saturation magnetization decreases, resulting in large variations in the characteristics of both.

Further, since the oxidation treatment is carried out stepwise in the air, the temperature can be controlled mainly without adjusting the concentration of the oxidation, the need for an inert gas, etc., so that the process can be simplified and the cost can be reduced. .

Further, by such stepwise oxidation treatment, the magnitude of saturation magnetization can be obtained by the oxidation treatment at a low temperature level, and the reduction rate of the saturation magnetization can be obtained by the oxidation treatment at a high temperature level, and the oxidation temperature can be increased or decreased. When they are biased to either side, it is possible to satisfy both contradictory characteristics, in which only one of the characteristics can be realized.

As a result, it is possible to provide a magnetic recording medium which is excellent in electromagnetic conversion characteristics and is less deteriorated even after long-term use.

[Brief description of drawings]

FIG. 1 is a view showing a profile of a heat oxidation treatment in one embodiment of the method of the present invention, FIG. 2 is a view showing a profile of a heat oxidation treatment of another embodiment, and FIG. 3 is a view of still another embodiment. FIG. 4 is a graph showing the profile of heat oxidation treatment, FIG. 4 is a graph showing the relationship between the oxidation treatment temperature and the saturation magnetization of conventional iron nitride magnetic powder, and FIG. 5 is a graph showing the deterioration rate of the oxidation treatment temperature and the saturation magnetization. is there.

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-60-221325 (JP, A) JP-A-60-128202 (JP, A) JP-A-56-98401 (JP, A) JP-A-58- 159306 (JP, A)

Claims (1)

[Claims] 1. A step of adding at least one metal compound of nickel or cobalt to the surface of the oxidizable magnetic powder, a step of firing the oxidizable magnetic powder to which the metal compound is added, and an oxidation obtained by the calcination. Of a magnetic powder for a magnetic recording medium, characterized in that it has a step of obtaining a magnetic powder having a stepwise oxidation treatment by using a stepwise oxidation step in which a heat-resistant magnetic powder is used and the temperature is gradually raised in the air to perform an oxidation treatment Method.