JPS59110701A - Stabilization of reduced iron powder for magnetic recording - Google Patents

Abstract

PURPOSE:To uniformly stabilize a large amount of reduced iron powder without irregularity, by performing stabilization treatment wherein the reduced iron powder is brought into contact with gas containing oxygen under a specific condition while fluidizing the same. CONSTITUTION:Gas containing oxygen is passed through a reduced iron powder for magnetic powder at 90 deg.C or less under gauge pressure of 0.05-50kg/cm<2> at space linear volocity of 1-10cm/sec and contacted with said iron powder while fluidizing the same to perform stabilization treatment. Oxygen-containing gas is adjusted to about 10ppm-20% (a vol. ratio) in the oxygen content thereof and a contact time is set to about 30min-10hr. By this method, the change with the elapse of time in the magnetic characteristics of the reduced iron powder is suppressed, the re-oxidation thereof is hardly generated, the film thereon is strong and hardly peeled off and the stable pile-up storage is enabled.

Description

[Detailed description of the invention] It is something to do.

Ferromagnetic metal powder has better magnetic properties than conventional oxide-based magnetic powder, and in recent years, it has been developed as a material that meets the demand for even higher magnetic recording densities. Usually about 0.0 mm is required for magnetic recording. 1μ
Particles with a particle size of 1 μm to 1 μm are highly susceptible to oxidation in the air, which poses problems in terms of safe handling of the powder and deterioration of magnetic performance over time after forming into a magnetic tape.

As a method for dealing with such problems, a method is known in which an oxide film is formed on metal powder produced by reduction. For example, JP-A-48-79153 describes a method of carefully passing air through reduced metal powder;
- 112465 describes a method of forming an oxide film by immersing metal powder in an aqueous solution of permanganate, and JP-A-53-114769 discloses a method of forming an oxide film by immersing metal powder in an aqueous solution of sodium hydroxide. , discloses a method for venting oxygen-containing gas.

In addition, a method was proposed in which a protective film was formed on the surface of a metal powder produced by reduction by precipitating a metal having a smaller ionization tendency than the metal from a liquid medium.
47.

However, the conventional method has the following drawbacks. First, changes over time in the magnetic properties of the strong metal powder are sufficiently suppressed. For example, the above-mentioned Japanese Patent Application Laid-Open No. 53-11
For metal powder according to j7 6 9, the metal powder is heated to a temperature of 4
If left in an atmosphere of 5° C. and 90% relative humidity, the saturation magnetization will drop to 120 emu/f or less after 80 days. In addition, in this case, a magnetic tape made using metal powder is held in contact with a magnetic head for 100 minutes.
After running for an hour, if left in an atmosphere with a temperature of 45°C and a relative turbidity of 90°C, the amount of residual magnetization will decrease after 100 days.
Second, ferromagnetic metal powder is susceptible to re-oxidation at high temperatures. For example, the metal powder disclosed in JP-A-51-112465 causes spontaneous combustion due to reoxidation when the temperature in the storage warehouse exceeds 40°C during storage in the summer.
Furthermore, if the magnetic tape is heated to 80° C. to dry the solvent during the temporary coating process, it may catch fire.

Thirdly, the process of forming a coating on ferromagnetic metal powder is complicated. For example, in the method of Japanese Patent Publication No. 54-15547, a method is adopted in which, after reducing the metal powder, the metal powder is added to a liquid medium containing metal ions having a smaller ionization tendency than the metal. The manufacturing process becomes complicated because filtration and drying processes are unavoidable.

Fourth, the coating formed on the ferromagnetic metal powder is easily peeled off. For example, when the metal powder disclosed in JP-A-48-79153 is placed in a ball mill and shaken for about 4 hours, it is observed that some brown powder is mixed in, but it can be inferred from this that the coating is is peeled off by shaking and oxidation progresses.

Furthermore, the practically important characteristics are that in addition to the small average deterioration of the magnetic properties, the dispersion (variation) of the degree of deterioration of these magnetic properties must be within an acceptable range, and It is also required that the variation be within an acceptable range.

However, even if an attempt is made to stabilize reduced iron powder with a gas containing oxygen using a known oxide film forming technique, the degree of deterioration of magnetic properties will vary widely when a large amount of reduced iron powder is processed industrially.

In other words, metallic iron powder with a certain degree of deterioration can only be obtained by careful stabilization treatment on a small scale of a few hundred grams or less in the laboratory, and it is still possible to obtain metallic iron powder with a certain degree of deterioration. The technology for mass production on an industrial scale beyond units has not been perfected.

The present inventors investigated the drawbacks of the various conventional methods mentioned above and conducted numerous experiments. As a result, the inventors found that in order to industrially stabilize a large amount of reduced iron powder, oxygen-containing gas must be We have discovered that a technology is needed to sufficiently penetrate the surface of particles and stabilize a large amount of reduced iron powder unevenly and uniformly, and we have completed the present invention.

That is, the present invention provides a method for stabilizing ferromagnetic metal powder for magnetic recording using a gas containing oxygen, in which oxygen is stabilized at a temperature of 90° C. or less under a gauge pressure of 0.05 to 50 m/-. gas containing a superficial linear velocity of 1 to 20 am/s
This is an invention of a method for stabilizing reduced iron powder for magnetic recording, which is characterized in that the reduced iron powder is stabilized while being aerated with EC and fluidized.

In the method of the present invention, reduced iron powder, which is a raw material, is brought into contact with a gas containing oxygen under conditions of a pressure of 0.05 to 50 Kg/a II (gauge) and a temperature of 90° C. or lower to carry out stabilization treatment. At this time, the oxygen-containing gas is transported at a superficial linear velocity of 1 to 20 cm/
It is necessary to ventilate at sec.

The oxygen-containing gas is dispersed in the powder, and a mixture of the oxygen-containing gas and the homogeneous powder, whose viscosity is significantly lower than that of the powder alone, is formed throughout the processing period. . However, if the aeration rate of the oxygen-containing gas is set to 20 cm/sec or more, the gas passing through the powder will not form solid bubbles, and the bubbles will coalesce and the scattering of fine particles will become noticeable. That's it. In addition, when the aeration rate is set to 1 cm/sec or less, the dispersion of oxygen-containing gas in the powder increases.
decreases and a homogeneous mixture of powder and gas is not formed.

In the method of the present invention, the method for supplying the oxygen-containing gas is as follows:
This is a method in which the powder is blown into the raw material powder through a dispersion plate made of a sintered plate, perforated plate, wire mesh, etc. Or, it has a large number of holes installed near the stirring blade for stirring the powder, which may be blown from a jar.The shaft and arm to which the stirring blade is attached are made into a hollow structure, and the gas flows through the inside thereof. It is also possible to adopt a method in which gas is ejected from a large number of holes provided in the air. In the latter case, where gas is not blown through a distribution plate, a non-porous bottom plate may be used instead of a distribution plate.

What is important in the present invention is that the powder is treated in a fluidized state.

The lower limit of the amount of pressure applied during stabilization treatment in the method of the present invention is 0.
05 Kglctl (gauge) is the minimum pressure required to release oxygen-containing gas to the atmosphere after passing through a dust collector such as a cyclone or bag filter.

When most of the used gas is processed and recycled for reuse, the time required for one round from the circulation blower↓ outlet to the circulation blower through the -1 equipment such as the stabilization treatment device and dust collector is required. This is the minimum pressure required to compensate for pressure loss.

50Kq/cr! (Gauge) pressure or higher is not good because the reaction rate between the reduced iron powder and oxygen becomes too fast, making it difficult to control the stabilization process.

The oxygen-containing gas used in the present invention is composed of oxygen and other gases. Other gases refer to gases that are inert to the metal powder, such as nitrogen and 91, and may also include hydrocarbon gases such as methane and ethane, and nitrogen oxides.

The oxygen content varies depending on the temperature, time, and type of other gas during contact, but the preferred range is 10 ppm-20 (capacity ratio) because the effects of the present invention are significant. range.

The temperature at the time of contact must be 90°C or less.

If the temperature exceeds 90° C., the oxide film formed on the surface of the reduced iron powder becomes rough and the stability is not sufficient, and the magnetic properties of the iron powder obtained by the treatment are low, which is not good.

The contact time varies depending on the oxygen content in the contact gas, but is approximately 30 minutes to 10 hours.

The reduced iron powder in the present invention is a metal powder used for magnetic recording, and the manufacturing method thereof is not particularly limited. for example,
(1) A method of thermally decomposing an organic acid salt of a ferromagnetic metal and reducing it with a reducing gas; (2) A method of acicular hydrated metal oxides or acicular metal oxides containing other metals; A method for reducing acicular iron oxide obtained from a hydrous metal oxide, (3) A method for purifying ferromagnetic metals in a low-pressure inert gas, (4) A method for thermally decomposing metal carbonyl compounds, (5) A method is known in which a reducing agent is added to a solution containing a salt of a ferromagnetic metal for reduction, but any of these methods may be used.

The first effect of the present invention is that there is very little variation in the temporal stability of magnetic properties within and between lots. By using the method of the present invention, stabilization treatment of reduced iron powder, which was conventionally possible only on a laboratory scale, becomes possible on an industrial scale, and the resulting reduced iron powder has excellent stability. And there is little variation in quality.

Therefore, the method of the present invention has high industrial value as a method for stabilizing reduced iron powder.

The second effect of the present invention is that changes in magnetic properties over time are significantly suppressed. This can be evaluated by measuring the saturation magnetic susceptibility σ5, and the stabilized reduced iron powder according to the present invention greatly suppresses the aging deterioration of σ5.

Further, the stabilized reduced iron powder according to the present invention was mixed with a binder, a solvent, etc., and applied to a sheet, and after magnetic field orientation was performed, the sheet was cut to make a magnetic tape, which was pieced together into a circle and brought into contact with a magnetic head. The stabilized reduced iron powder according to the present invention can also be evaluated by running the same for 100 hours and then leaving it at a constant temperature and constant temperature to measure the residual magnetic susceptibility (hereinafter referred to as Br). The magnetic tape produced using this method has significantly suppressed changes in B' over time.

The present invention achieves prevention of deterioration of magnetic performance under more severe conditions than conventional standards.

The third effect of the present invention is that reoxidation is difficult to occur.

This can be evaluated by comparing the height of the oxidation point, if the stabilized reduced iron powder is heated at a constant rate under air circulation, and the temperature at which the oxidation reaction starts to generate heat is defined as the oxidation point. can. The stabilized reduced iron powder according to the present invention has a greatly increased oxidation point, so when handled in air,
This significantly reduces the risk of ignition during storage and transportation during the summer, and during the drying process after the coating process during magnetic tape manufacturing. This imparts new performance that could not be achieved by oxidation stabilization treatment using conventional techniques. Also,
The fact that the oxidation point is greatly increased suggests that the formed protective film is sufficiently dense.

The fourth effect of the present invention is that it has excellent oxidation stability when deposited and stored. This can be determined by whether or not when a certain amount of stabilized reduced iron powder is piled up and stored in the air, there is no heat generation due to re-oxidation of the metal powder, which eventually causes spontaneous combustion. . This gives magnetic recording metal powder new practical performance that has not been achieved with conventional techniques.

The fifth effect of the present invention is that the coating is strong and does not peel off easily. This is determined by placing stabilized reduced iron powder in a ball mill and shaking it for a certain period of time, and then checking whether oxidation has progressed due to peeling of the coating by analyzing the oxide content and measuring the magnetization characteristics. can. This point is
This was considered to be one of the problems in the prior art, but the present invention has improved it to a practically satisfactory degree, and it is also possible to omit the over-drying step, which is unavoidable in liquid phase processing methods.

The present invention will be specifically explained below using Examples and Comparative Examples.

Example I A. Production of reduced iron powder Oro, 7%, Zn 0.6%, Ni 6.5%,
Contains Silchi, long axis 0.4μ, axial ratio 10:1~1
Acicular goethite (a-Fe OOH) with a ratio of 5:1 was calcined at 400°C in air, and then heated and reduced for 6 hours at 350°C using pure hydrogen gas.
It was cooled to room temperature under nitrogen gas flow. The obtained metal powder is designated as P-1.

B. Stabilization Treatment This metal powder was charged into a reactor having an inner diameter of 250[i] and using a sintered metal plate as a gas dispersion plate. To this, the temperature is 50℃, the pressure is 2
Under the condition of Kf/i (gauge), nitrogen gas containing 1.6 volumes of oxygen gas was passed through, and the metal powder was stabilized for 7.5 hours while being fluidized.

From the powder lot after this stabilization treatment, samples were randomly taken from three locations, 8-1, S-2, and S-2, respectively.
The score shall be 8-3.

0, Preparation of magnetic tape 8-1 100 Of, thermoplastic polyurethane resin 25
% methyl ethyl ketone solution 600 f.

Methyl ethyl ketone 1500t as a solvent, silicone additive 2f as a smoothing aid, and stearic acid amide 209 as a lubricity improving aid were placed in a ball mill, and kneaded by rotating for 24 hours using alumina balls as a dispersion medium. After obtaining a mill base, the above thermoplastic polyurethane/resin 25%' methyl ethyl ketone solution 6001 was added and further diluted with methyl ethyl ketone to adjust the viscosity to obtain a magnetic paint.

This magnetic paint was applied to a 12P thick reinforced polyethylene terephthalate film so that the dry film thickness was approximately 4μ, the magnetic particles were oriented through a magnetic field, and then dried with hot air and smoothed using a calendar roll. After that, cut the magnetic tape to a predetermined width and use it as a T-
1) was obtained.

Magnetic tapes S-2 and S-3 are also produced by the same method, and named T-2 and T-3, respectively.

D. Measurement of changes in magnetic properties over time and oxidation stability Clothes 1 were made by connecting T-1 pieces together in a circle, running for 100 hours in contact with a magnetic head, and then placing them in an atmosphere of 45°C and 90% relative humidity. Coercive force Hc after being left for ioo days,
The values of the residual magnetic susceptibility Br 1 and the ratio Br/Bm between Br and the sum magnetic susceptibility Bm are shown.

Table 2 shows s-i at 45℃, 90% relative turbidity by DTA, air 50ml/m1n1 temperature increase rate 10℃/mi
The liquefaction point measured under the conditions of n and the presence or absence of oxidation of the metal powder after S-1 was placed in a ball mill and shaken for 4 hours were determined by composition analysis of the metal powder (this is called a peel test). , and S-1 are piled up in 3K9 piles and stored in the air (this is referred to as a deposition test).

For T-2, T-3, S-2, and S-3, the changes in magnetic properties over time and oxidation stability were measured using the same method as above, and the results are shown in Tables 1, 2, and 3, respectively. Shown below.

From this, it can be seen that S-1, S-2, and S-3 all have high oxidation stability, and that T-1, T-2, and T-3 all show a slight change in magnetic properties over time. Furthermore, it can be seen that there is very little variation in characteristics among the three samples.

Example 2 The metal powder P-1 used in Example 1 was placed in a reactor having a diameter of 1,000 mm, a total height of 4,000 mm, a structure in which a perforated plate and a wire mesh were stacked as a gas distribution plate, and a stirring blade with a blade diameter of soosm.
30kg of gas was charged, gas flow rate was 10cm/see
, temperature 70℃, pressure I Kg/1vl (gauge), 0
2 is 0.05 capacity, CH4 is 2 capacity, CO2 is 0.
．． Stabilization was carried out using 1 volume of nitrogen under flowing conditions for 10 hours. This is designated as S-4.

A magnetic tape obtained using S-4 in the same manner as in Example 1.0 is designated as T-4. T-4 and S-4 in Example 1. The results of measuring changes in magnetic properties over time and oxidation stability using the same method as in D are also shown in Tables 1, 2, and 3, respectively.

From this, it can be seen that 8-4 has high oxidation stability, and T-4 has a slight change in magnetic properties over time. 0 Comparative Example 1 In the same reactor as Example 1, the same metal powder P-
1 was charged in the same amount, and the superficial linear velocity of the nitrogen-containing gas was set to 0.
Stabilization treatment was carried out under the same conditions as in Example 1, except that the reduced iron powder was aerated for 57 seconds to prevent it from flowing. The metal powder after stabilization treatment is designated as 8-5.

After obtaining a magnetic tape (referred to as T-5) using the same method as in Example 1.0 using S-5, Example 1.
The results of measuring changes in magnetic properties over time and acid stability using the same method as in D are also shown in Tables 1, 2, and 3, respectively.
Shown below. This is it! 1) S-5 has low oxidation stability and T
It can be seen that in all cases of -5, the magnetic properties change significantly over time.

Comparative Example 2 5.2 mm of the same metal powder P-1 as in Example 1 was placed in a fixed bed reactor having a diameter of 250 mm and using a sintered metal plate as a gas distribution plate.
Stabilization treatment was carried out in the same manner as in Example 1, except that the cell was filled with 1.5 kg (layer thickness: 150 sTR), the flow rate of oxygen-containing nitrogen gas was 5 cm/sec, and no flow of metal powder was observed. At this flow rate, the temperature of the metal powder layer increased in the gas flow direction, and there were places where the temperature reached 100°C or higher. on top of the layer, inside the layer,
Samples sampled at each lower position (divided into three in the direction of layer thickness) are designated as S-6, S-7, and SS, respectively. In 08-6, the temperature of the metal powder layer was 108°C, 91°C, and 72°C at each sampling location.
Magnetic tapes obtained by the same method as Example 1.0 using S-7 and S-8 were respectively T-6, T-7 and T-
8. T-6 to T-8 and S-6 to S-8 were prepared in Example 1. The results of measuring changes in magnetic properties over time and oxidation stability using the same method as in D are also shown in Tables 1 and 2, respectively.
, shown in Table 3.

From each table, it can be seen that S-6, 8-7, and S-8 all have low oxidation stability, and that T-6, T-7, and T-8 all have large changes in magnetic properties over time. Furthermore, it can be seen that there are extremely large variations in characteristics among the three types of samples.

Example 3 Oro, 7%, Zn0.6%, Ni6.5%, S+1%
Example 1
．． The metal powder obtained by firing and reducing in the same manner as A is designated as P-2.

P-2 in Example 1. Stabilization treatment was performed in the same manner as B to obtain stabilized reduced iron powder S-9.

A magnetic tape obtained by the same method as in Example 1.0 using T-8-9 is referred to as T-9. T-9 and 8-9 in Example 1. The results of measuring changes in magnetic properties over time and oxidation stability using the same method as in D are also shown in Tables 1 and 2, respectively.
It is shown in Table 3.

It can be seen from this that 8-9 has high oxidation stability, and T-9 shows little change in magnetic properties over time.

Example 4゜B1.5%, Oro, 6%, Zn2.0%, Si 4
Example 1. The metal powder obtained by firing and reducing under the same conditions as A is designated as P-3.

P-3 in Example 1. Stabilization treatment is performed in the same manner as B to obtain a stabilized reduced iron powder of 8-10.

5-10, and a magnetic tape obtained by the same method as in Example 1.0 is designated as T-10. T-10 and 5-10 were measured for changes in magnetic properties over time and oxidation stability using the same method as in Example LD. The results are shown in Table 1, respectively.
It is shown in Table 2 and Table 3.

It can be seen from this that 8-10 has high oxidation stability, and both T-10 have little change in magnetic properties over time.

9 Table-1 Example 5 30 parts of ferrous chloride and 5 parts of cobalt chloride were dissolved in water, placed in a non-magnetic container, placed in a DC magnetic field of up to 15,000 e, and stirred gently. Add a 1.3 mol/no aqueous solution of sodium borohydride little by little,
After 5 minutes, black ferromagnetic metal powder was obtained. This powder was separated from the reaction mother liquor, washed with acetone, and dried in a hot air dryer to obtain metal powder. This is designated as P-4.

P-4 in Example 1. Stabilization treatment is performed in the same manner as B to obtain stabilized reduced iron powder 5-11.

5-11, and a magnetic tape obtained by the same method as in Example 1.0 is designated as T-11. T-11 and 8-11 in Example 1. The results of measuring changes in magnetic properties over time and oxidation stability using the same method as in D are also shown in Tables 1 and 2, respectively.
, shown in Table 3.

From this, it can be seen that 5-11 has high oxidation stability, and T-11 has little change in magnetic properties over time.

0

Claims (1)

[Claims] In a method of stabilizing reduced iron powder for magnetic recording using a gas containing oxygen, the gauge pressure is 0.05 to 50119.
The method is characterized in that a gas containing oxygen is aerated at a superficial linear velocity of 1 to 20 cm/sec under a pressure of /cr7H at a temperature of 90°C or less, and stabilization treatment is carried out while flowing the reduced iron powder. , Method for stabilizing reduced iron powder for magnetic recording.