JP2894495B2 - Manufacturing method of metal magnetic powder for magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a magnetic powder suitable for a magnetic recording material such as a magnetic tape and a magnetic disk.

[Background of the Invention]

When a ferromagnetic metal fine particle having a large saturation magnetization (hereinafter, referred to as σ _s ) is used in a magnetic recording medium, the maximum magnetic flux density (hereinafter, referred to as Bm) when taped is increased. , Br) is increased and the output is increased. Also,
It is also known that the larger the specific surface area (hereinafter referred to as BET) of the ferromagnetic metal fine particles is, the lower the particle noise and the surface noise of the tape are, and the total noise (N) is reduced.

Therefore, if both σ _s and BET of the ferromagnetic metal particles are increased, the C / N (Carrier t
o Noise: The ratio of carrier signal to noise can be expected to increase.

[Problems to be solved by the invention]

However, the BET of ferromagnetic metal fine particles, particularly metal powder obtained by gas-reducing needle-like iron oxide or iron oxyhydroxide, generally decreases when σ _s is increased. Therefore, the effect of improving the C / N ratio of the magnetic recording medium is unlikely to be exhibited.

For example, a conventional metal magnetic powder containing Fe as a main component is produced by reducing acicular iron oxide or iron oxyhydroxide in a reducing gas (usually, H ₂ gas) stream. It has been the usual practice to maintain the reduction temperature constant (eg, at 450 ° C.). At that time, σ _s can be improved by increasing the reduction temperature in the early stage of reduction. However, it is difficult to increase BET. Therefore, although this metal magnetic powder has a high σ _{s, the} effect of improving the C / N ratio of a magnetic recording medium using the same cannot be sufficiently exhibited.

An object of the present invention is to provide a method for producing a metal magnetic powder that increases σ _s without reducing BET.

[Means for solving the problem]

The gist of the present invention, which has been achieved to achieve the above object, is to produce a metal magnetic powder for a magnetic recording medium by heating and reducing acicular iron oxide or iron oxyhydroxide with hydrogen gas. Of the total reduction time from the start to the end of the reduction, the processing temperature in the initial stage of the reduction over a predetermined time from the start of the reduction is lower than the processing temperature in the subsequent time zone, and the processing temperature in the initial stage of the reduction is 370 to 700 ° C.

That is, when the present inventors treat gaseous reduction of acicular iron oxide or iron oxyhydroxide with a relatively low initial temperature and a high temperature thereafter, the resulting reduced powder has a reduced BET. Instead, it was found that σ _s increased. It is not clear that such effects were obtained, but when the initial stage of reduction is performed at a low temperature, the phenomenon that BET decreases can be suppressed, sintering of particles can be suppressed, and at the stage when reduction is almost completed. It is presumed that if the temperature is further raised to a high temperature, the pores can be pulled out while maintaining the shape by the shrinkage effect. Here, the stage where the reduction is almost completed means that the iron oxide or iron oxyhydroxide
90% or more, preferably 95% or more, is reduced to iron. Therefore, according to the method of the present invention, a metal magnetic powder having needle-like property and BET is obtained.

In carrying out the present invention, needle-like iron oxide or iron oxyhydroxide powder is heated and reduced using H ₂ gas as a reducing gas, and the temperature difference between the initial temperature and the subsequent temperature is 5 ° C. Otherwise, the effects of the present invention cannot be obtained. It is preferable that a sufficient amount of H ₂ gas necessary for the reduction be present over the entire reduction time, and that the initial temperature of the reduction be 370 to 700 ° C., and that the temperature in the subsequent time zone be further increased. If the initial temperature is lower than 370 ℃, the reduction becomes unstable and 700 ℃
If it exceeds, BET will be small. When the reduction temperature is generally increased, the total reduction time is shorter than when the reduction temperature is low, but 5% to 95% of the total reduction time is effective as the initial time for reduction to a relatively low temperature. In the time period after the initial stage of the reduction, the temperature is higher than the processing temperature in the initial stage of the reduction. In practice, it is effective to raise the temperature to 500 ° C. or more as shown in the examples described later.

 Hereinafter, the effects of the present invention will be clarified by examples.

EXAMPLE 1 using the acicular iron oxide as a starting material, was charged with this rotary furnace, was subjected to heat reduction treatment by introducing H ₂ gas stream. Total time from the start to the end of the reduction process is 24
It was 0 minutes, during which only the reduction temperature was changed.
That is, the processing temperature is maintained at 370 ° C. for 120 minutes from the start of reduction, and then raised to 500 ° C. over 60 minutes.
The reduction was completed by holding at 60 ° C for 60 minutes. The reduction was terminated by replacing the atmosphere in the furnace from H ₂ gas to N ₂ gas and cooling.

After the obtained reduced powder was immersed in toluene, it was spread on a metal vat and exposed to air set at 50 ° C. for 2 hours. Needle-like reduced powder having no ignitability was obtained by this toluene air drying. Table 1 shows the BET value and bulk properties of the obtained reduced powder.

Next, a magnetic tape was produced using the reduced powder according to a usual method. That is, the reduced powder was made into a paint by a usual method, applied to a polyester film, oriented by passing a magnetic field, dried, calendered, and cut into a predetermined size to prepare a tape.

 Table 1 shows the properties of the obtained magnetic tape.

[Example 2] The same acicular iron oxide as in Example 1 was used as a starting material,
This was placed in a stainless steel board, inserted into a quartz tube, heated in an electric furnace, and heated and reduced by sending H ₂ gas into the furnace. The total time from the start to the end of the reduction process was 150 minutes, during which only the reduction temperature was changed. First, the inside of the furnace was replaced with N ₂ , and when the temperature reached a predetermined temperature, the supply of N ₂ was stopped, and the reduction was started by supplying H ₂ gas. The reduction starting temperature is 520 ° C and this temperature is
Hold for minutes. Next, the temperature was raised to 600 ° C. 60 minutes after the start of the temperature rise, and the temperature was kept at 600 ° C. for 60 minutes to complete the reduction.

Thereafter, a non-ignitable acicular reduced powder was obtained in the same manner as in Example 1, and taped as in Example 1. Table 1 shows the BET and bulk properties of the reduced powder and the properties of the tape.

[Example 3] The processing temperature was maintained at 650 ° C for 10 minutes from the start of reduction, then raised to 750 ° C over 60 minutes, and maintained at 750 ° C for 30 minutes to complete the reduction. Needle-like reduced powder was obtained by the same operation as in 1, and taped. Of the obtained reduced powder
Table 1 shows the BET, bulk characteristics and tape characteristics.

Comparative Example 1 Example 1 except that the reduction was performed at a constant temperature of 500 ° C. for 240 minutes.
Needle-like reduced powder was obtained by the same operation as described above, and taped.

Comparative Example 2 Example 1 except that the reduction was performed at a constant temperature of 600 ° C. for 150 minutes.
Needle-like reduced powder was obtained by the same operation as described above, and taped.

Comparative Example 3 Example 1 except that the reduction was performed at a constant temperature of 700 ° C. for 100 minutes.
Needle-like reduced powder was obtained by the same operation as described above, and taped.

Table 1 also shows the BET, bulk properties, and tape properties of the reduced powders obtained in Comparative Examples 1 to 3. FIG. 1 shows the relationship between σ _s of the reduced powder of each example and BET.

Table 1 and Figure 1 results, the magnetic powder prepared according to the present invention is seen to have a larger BET while maintaining the equivalent comparative example or more sigma _s. In particular, as is clear from FIG. 1, σ _s at the same level as compared with the comparative example.
Then, the method of the present invention has a large BET and a high σ _s at the same BET level. In the present invention, Br / Bm of the tape characteristics is higher than that of the comparative example, and the tape exhibits excellent performance as a high-density magnetic recording material.

The X-ray particle size (α) of the metal powder of each of the examples and comparative examples was
When the -Fe the (110) calculated from X-ray diffraction peaks of the surface) was measured, it was found that small X-ray particle diameter in spite of sigma _s towards the Examples. This also contributes to reducing the output and the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows BET and σ _{s of} metal magnetic powder produced according to the present invention.
FIG. 6 is a diagram showing the relationship between the present invention and the comparative example.

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Claims (2)

(57) [Claims] In producing metal magnetic powder for a magnetic recording medium by heat-reducing needle-like iron oxide or iron oxyhydroxide with hydrogen gas, the reduction of the total reduction time from the start to the end of the reduction is reduced. Making the initial processing temperature of the reduction over a predetermined time from the start lower than the processing temperature in the subsequent time period;
A process for producing a metal magnetic powder for a magnetic recording medium, wherein the processing temperature in the initial stage of the reduction is 370 to 700 ° C., and the processing temperature in the time zone after the initial stage of the reduction is 500 ° C. or higher. 2. The method according to claim 1, wherein the initial stage of the reduction over a predetermined time from the start of the reduction is a process in which the reduction to the metal powder is substantially completed.