JPS6158215A - Manufacture of magnetic iron oxide powder - Google Patents

Abstract

PURPOSE:To obtain fine acicular shape of the titled item by a method wherein alkaline aqueous solution containing carbonic acid ion is reacted with aqueous solution containing bivalent iron ion and makes deposit created thereby oxidized and then subjected to water thermal reaction. CONSTITUTION:Alkaline aqueous solution, which contains carbonic acid ion of equivalent or more is reacted with aqueous solution with bivalent iron ion and said iron ion. By this reaction, deposit is created and spindle shape particu late is obtained by oxidation thereof. The spindle shape particle obtained by such a way is subjected to water thermal reaction in autoclave under the condi tion of neutral or weak alkalinity. After alpha-iron oxyhydroxide powder, which consists of acicular particle obtained by such a way, is reducted in vapor-phase, the magnetic iron oxide powder which consists of gamma-iron oxide oxidating as necessary or magnetite is obtained. As acicular particle of the alpha-iron oxyhydroxide is of low axial ratio, even in the case of particulates, said powder is hard to sinter at the time of oxidation and reduction, thus acicular shape is kept favorably.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing magnetic iron oxide powder used in magnetic tapes and other magnetic recording media.

[Prior Art] Magnetic iron oxide powder made of T-iron oxide or magnetite, which is generally used in various magnetic recording media, is produced by reducing α-iron oxyhydroxide in a gas phase and then oxidizing it as necessary. However, in recent years, magnetic iron oxide powder consisting of ultrafine particles with a specific surface area of around 40rrl/9' has been required for audio and video magnetic tapes in order to reduce noise and improve the SIN ratio. .

However, the above-mentioned α-iron oxyhydroxide is usually obtained by oxidizing Fe(OH)2 precipitated by a reaction between a divalent iron salt and a strong alkali such as NaOH or KOH by blowing air. (Reference unknown), axial ratio (major axis/minor axis)
Since it is a very elongated particle with 15 or more,
When fine particles are made to meet the above requirements, the short axis becomes smaller and the particles easily sinter with each other during reduction in the gas phase in the subsequent process. There is a problem that the shape is lost.

In addition, as a means to solve this problem, the above-mentioned axial ratio 1
A method has been proposed in which α-iron oxyhydroxide having a molecular weight of 5 or more is subjected to a hydrothermal reaction in an autoclave to convert it into α-iron oxyhydroxide with a low axial ratio, and then reducing and oxidizing this (Japanese Patent Publication No. 59/1989). -562, JP-A No. 55-21143, etc.). However, the above metamorphosis in this proposed method is PH13
Since the dissolution precipitation reaction is carried out in a strong alkaline solution of about 14 to 14%, it is difficult to control the particle shape (size and axial ratio), and granular α-Fe20. , is unavoidable, and the use of a highly concentrated strong alkali poses a high operational risk.

[Problems to be Solved by the Invention] This invention solves the problem that, in the conventional general manufacturing method of magnetic iron oxide powder, α-iron oxyhydroxide is acicular particles with a high axial ratio, so it becomes fine particles. During reduction in the phase, the acicular shape is lost due to sintering, and in order to avoid this, it is difficult to control the particle shape when reducing the axial ratio of α-iron oxyhydroxide through hydrothermal treatment. -Fe20. To solve the problem that the spindle-shaped particles obtained by a specific method are mixed with α-Fe203, are not dangerous to work, and have almost no change in particle size. α consisting of acicular particles with low axial ratio due to unaccompanied hydrothermal treatment
The object of the present invention is to provide a method for producing magnetic iron oxide powder, which makes it possible to maintain a good acicular shape during reduction in a gas phase by using iron oxyhydroxide.

[Means for Solving the Problems] The present inventors have developed an ultrafine magnetic particle that has a high specific surface area that can meet the demands for reducing noise and improving the S/N ratio in magnetic tapes for audio and video. As a result of extensive research into the production method of iron oxide powder, spindle-shaped particles were obtained by oxidizing the reaction product of divalent iron ions and carbonate ions, and the spindle-shaped particles were heated to neutral or weak in an autoclave. When hydrothermally treated in an alkaline region, α-iron oxyhydroxide consisting of acicular particles with a low axial ratio that almost inherits the size of the spindle-shaped particles is obtained, and therefore this α-iron oxyhydroxide is ultrafine particles. As a result, it is difficult to sinter and maintains a good acicular shape during reduction in the gas phase, and as a result, it is possible to finally obtain ultrafine magnetic iron oxide powder with excellent magnetic properties. Moreover, P)I during the above hydrothermal reaction
It was discovered that the axial ratio can also be controlled through adjustment, leading to this invention.

That is, the present invention oxidizes a precipitate precipitated by a reaction between an aqueous solution containing divalent iron ions and an alkaline aqueous solution containing carbonate ions in an amount equivalent to or more than the iron ions to generate spindle-shaped particles. The particles are subjected to a hydrothermal reaction in a neutral to weakly alkaline region in an autoclave, and the obtained α-iron oxyhydroxide powder is reduced in the gas phase, and then oxidized as necessary to form T-iron oxide or T-iron oxide. The present invention relates to a method for producing magnetic iron oxide powder, characterized in that it is a magnetic iron oxide powder such as magnetite.

[Structure and operation of the invention]

In this invention, first, an aqueous solution containing divalent iron ions is reacted with an aqueous alkaline solution containing carbonate ions instead of a strong alkali such as NaOH or KOH in the conventional general-purpose method. This reaction produces iron carbonate (FeCO
A precipitate estimated to be 3.nH2O) is formed, which is then oxidized to obtain spindle-shaped particles.

Examples of aqueous solutions containing divalent iron ions include ferrous sulfate (FeS04.7H20) and ferrous chloride (FeC1).
The concentration of ferrous salts such as 2.2H20) is 0.5 to 3 mol/
1 of the aqueous solution is used. On the other hand, as an alkaline aqueous solution containing alkali carbonate, sodium carbonate (Na
2 CO3), ammonium carbonate [:(NH3)2
CO3:l, concentrated 1 such as potassium carbonate (K2CO3)
j11m 0.5-2 mol//! An aqueous solution of about 100% is preferably used, but the amount of carbonate ion needs to be at least equivalent to the divalent iron ion, preferably 1.0 to 8 equivalents. That is, if the amount of carbonate ions is less than the equivalent amount, the remaining iron ions will generate magnetite in the later oxidation process, which will cause granular particles to be mixed in, which is not preferable. Note that the temperature of the above reaction is preferably about 30 to 60°C.

Further, in this invention, an aqueous solution containing cobalt ions together with divalent iron ions may be used, and the iron component and cobalt 02 may be co-precipitated by reaction with an aqueous solution containing carbonate ions.
This finally yields cobalt-containing magnetic iron oxide powder. Such cobalt ions can be provided as an aqueous solution of cobalt nitrate h [Co (N03)2.H20], cobalt chloride (CoCff2), cobalt sulfate (CO5O4), etc., and are usually applied in an amount per mole of divalent iron ions. It is preferable to use it in a range of 0.005 to 0.1 mol.

As a means for oxidizing the precipitate produced as described above, generally 30 to 6
A method of blowing an oxidizing gas, ie, air or oxygen gas, at a temperature of 0°C is adopted. The spindle-shaped particles obtained by this oxidation reaction usually have an axial ratio of 2 to 2.
It is about 5 and α-iron oxyhydroxide (α-FeOO
It is estimated to have the structure H).

The size of these spindle-shaped particles depends on the concentration of divalent iron ions and carbonate ions in the first reaction, the reaction temperature,
It can also be controlled by adjusting the rate of introduction of oxidizing gas and reaction temperature during the subsequent oxidation reaction. That is, the higher the reaction temperature in the front and rear stages, the lower the ion concentration, and the slower the introduction rate of the oxidizing gas, the larger the size of the spindle-shaped particles obtained (in general, the longer the long axis is 0.07~0.
It can be arbitrarily adjusted within a range of about 5μ.

In this invention, the spindle-shaped particles obtained as described above are placed in an autoclave under a neutral to weakly alkaline region,
Preferably, the hydrothermal reaction is carried out at pH 7 to 11. This hydrothermal reaction does not transform α-iron oxyhydroxide from a high axial ratio to a low axial ratio through solution deposition, as in the conventional proposed method, but rather changes its particle size from spindle-shaped particles to approximately It metamorphoses into inherited acicular particles, and as a result of being carried out in a neutral to weakly alkaline region, granular α-F
Contamination with E.e. 203 is avoided and there are no operational hazards such as those associated with the use of strong alkalis.

During such a hydrothermal reaction, the suspension containing the spindle-shaped particles after the oxidation reaction becomes neutral or weakly alkaline due to the use of an alkali carbonate component in an amount equal to or more than the ferrous salt component in the preceding stage. Therefore, there is no problem in putting this suspension in an autoclave as it is.
There is no need to make any special pH adjustments. However, when removing or reducing the remaining alkali carbonate components to control the axial ratio as described below, spindle-shaped particles are separated from the suspension after the oxidation reaction, washed with water as necessary, and then placed in water. What is necessary is to use the one that has been redispersed. The hydrothermal reaction is usually carried out at 100 to 200° C. for about 5 to 2 hours.

As mentioned above, the α-iron oxyhydroxide obtained through the above hydrothermal reaction almost inherits the size of the spindle-shaped particles of the raw material and is long-sleeved.
．． The result is acicular particles with a diameter of about 0.07 to 0.5 oak and an axial ratio of about 2 to 5, but it is possible to control the axial ratio to some extent by adjusting the pH during this hydrothermal reaction, which is an advantage of the present invention. one of. In other words, it has been confirmed that the axial ratio increases as the above-mentioned pH approaches neutrality, which affects the temperature conditions of the reduction and oxidation steps in the gas phase and the necessary properties of the T-iron oxide or magnetite finally obtained. The axial ratio can be changed within the above range accordingly.

In this invention, the thus obtained a-iron oxyhydroxide consisting of acicular particles is filtered and dried, and the resulting powder is reduced in the gas phase in the same manner as in the past, and then oxidized as necessary to produce T-iron oxide. The acicular particles of α-iron oxyhydroxide have a low axial ratio that almost inherits the size of the spindle-shaped particles of the raw material.
Even fine particles are difficult to sinter during reduction and oxidation,
A good needle-like shape is maintained. The reduction and oxidation steps in the gas phase may be carried out in the same manner as conventional methods; generally, reduction is carried out in a hydrogen stream at 250 to 400°C for about 1 to 4 hours, and oxidation is carried out at 200 to 300°C. It is said that the time required is about 0.5 to 2 hours, but as is known, depending on the presence or absence of oxidation in the latter stage and its degree, the final magnetic iron oxide powder may be mixed with T-iron oxide, magnetite, or an intermediate oxide between the two. Can be set to

[Effects of the Invention] The method for producing magnetic iron oxide powder according to the present invention involves the reaction between an aqueous solution containing divalent iron ions and an aqueous solution containing carbonate ions of at least 70% of the iron ions. Since the spindle-shaped particles obtained by oxidizing the vi spindle-shaped particles are subjected to a hydrothermal reaction in a neutral to weakly alkaline region, the α-iron oxyhydroxide obtained in the hydrothermal reaction becomes the spindle-shaped particles. It becomes acicular particles with a low axial ratio that almost inherits the same size, and even if these are fine particles, they are difficult to sinter in the reduction and oxidation process in the gas phase later, making it possible to obtain magnetic iron oxide powder with a good acicular shape. can. In addition, granular α-Fe20. .

Contamination with other substances is avoided, and since no strong alkali is used, operational hazards are also prevented. Furthermore, by adjusting the pH during the hydrothermal reaction, the axial ratio of the acicular particles of the α-iron oxyhydroxide obtained is controlled, and the temperature conditions during reduction and oxidation in the gas phase and the magnetic iron oxide powder finally obtained are controlled. It is also possible to address the required characteristics of

Therefore, in view of these points, the method of the present invention provides magnetic iron oxide powder suitable for various magnetic recording media, especially for noise reduction and S for recent audio and video magnetic tapes.
/Specific surface area 40rrl/ that can meet the demand for improvement of N ratio
f? A high-performance magnetic iron oxide powder made of the above ultrafine particles can be provided.

〔Example〕 Hereinafter, this invention will be specifically explained based on examples.

Example 1 An aqueous solution of 10 mol of ferrous sulfate dissolved in 101 mol of water and carbonic acid) 40 mol of IJum was added to 30 7 mol of ferrous sulfate. When the mixture was mixed and stirred at 40°C with an aqueous solution dissolved in water, a white precipitate presumed to be iron carbonate was formed. Next, air was blown into the water containing this white precipitate at a rate of 101/min for 3 hours at 40°C under stirring to oxidize it.
Spindle-shaped particles of 3 μm were precipitated, and the pH of the liquid was 10.5.

Subsequently, the suspension containing the spindle-shaped particles was charged into an autoclave and subjected to a hydrothermal reaction at 200°C for 1 hour.
Washing with water, filtration, and drying were performed to obtain α-iron oxyhydroxide powder consisting of acicular particles with an average long axis of 0.07 pn and a short axis of 0.03/=1. This powder was dehydrated at 300°C, then reduced to magnetite (Fe304) at 280°C in a hydrogen stream for 2 hours, and then heated at 250°C.
Oxidized for 1 hour, average major axis 0.07, minor axis 0.0
A T-iron oxide powder consisting of 3/'' acicular particles was produced.

This powder has coercive force (Hc) -3200e, saturation magnetization (σs) = 74.5 emu/y1 squareness ratio (σr/
σs ) = 0.47, specific surface area (
SBET) = 83 trf/y.

Example 2 The temperature during oxidation by air blowing in Example 1 was set to 6
In the same manner as in Example 1 except that the average major axis Q
, 3,117111 spindle-shaped particles with a minor axis of 0.05 tones were obtained. The spindle-shaped particles were filtered from the mother liquor and washed with pure water, then redispersed in water to obtain a suspended β5 solution with a pH of 7.0, which was charged into an autoclave, subjected to a hydrothermal reaction in the same manner as in Example 1, and washed with water. , filtration.

Dry 14 yen long length Q, 3) tyr, same short axis 0.0
An α-iron oxyhydroxide powder consisting of sword-shaped particles with five tones was obtained. Next, this powder was subjected to dehydration, reduction, and oxidation treatment in the same manner as in Example 1 to produce T-iron oxide powder having an average major axis of 0.3P and a minor axis of 0.05μ. This powder has Hc=3400e, σs
=76. Oemu/f/, σr/σs=0.47, Sn
It showed xT=43m/7.

Example 3 0.0 was added in advance to the ferrous sulfate aqueous solution in Example 1.
A spindle-shaped material with an average major axis of 0.27-1 and a minor axis of 0.03μ was prepared in the same manner as in Example 1, except that 6 mol of cobalt nitrate was dissolved and the temperature during oxidation by air blowing was 50°C Particles were obtained. Next, a hydrothermal reaction was carried out in the same manner as in Example 1, followed by washing with water, filtration, and drying to obtain cobalt-containing α- particles consisting of acicular particles with an average major axis of 0.2 μ and average minor axis of 0.04/=”l.
Iron oxyhydroxide powder was obtained. Next, this powder was dehydrated, reduced, and oxidized in the same manner as in Example 1 to reduce the average long axis to 0.2/-
”, a cobalt-containing T-iron oxide powder with a minor axis of 0.03μ was produced. This powder had Hc = 7200e and σs = 7.
3. Oemu/9, σr/crs=-0.62, Sn
showed rr = 56 nl/9.

Comparative Example 1 An aqueous solution of 10 moles of ferrous sulfate dissolved in 401! water and 40 moles of sodium hydroxide were mixed in 201! An aqueous solution dissolved in water was mixed and stirred under cooling at 20°C to react, and a precipitate of ferrous hydroxide [Fe(OHz)) was generated. Next, air was blown into the water containing this precipitate at a rate of 101/min for 72 hours at 20°C under stirring to oxidize it. α-Iron oxyhydroxide was precipitated. This α-Iron oxyhydroxide was washed with water, filtered, and dried, and the powder obtained was dehydrated, reduced, and oxidized in the same manner as in Example 1 to obtain T- An iron oxide powder was produced. This powder consists of acicular particles irregularly combined by sintering, with an average long axis of 02 mm and a short axis of 0.05 μm, Hc = 2800 e1.
σs=68 emu/! , σr/σs=0.40, S
It showed BgT=36 m'/9.

Comparative Example 2 The suspension containing α-iron oxyhydroxide (PH 13,8) after the oxidation reaction in Comparative Example 1 was charged into an autoclave, subjected to a hydrothermal reaction at 200°C for 2 hours, and then washed with water and filtered. , when dried, average length @ 0.3p1 short axis 0.0
An α-iron oxyhydroxide powder consisting of acicular particles of 81t1n was obtained, but it was observed that a considerable amount of granular α-Fe203 particles were mixed in this powder. Next, this powder was subjected to dehydration, reduction, and oxidation treatment in the same manner as in Example 1 to obtain T-iron oxide powder consisting of acicular particles with an average major axis of 0.3/='' and average minor axis of 0.08μ. This powder was produced as Hc
=2600e, σs=72emu/ys σr/σs=
0.40, showing S BET = 25 m'/y.

Comparative Example 3 Cobalt-containing T-
Iron oxide powder was produced. In this method, the cobalt-containing α-oxyiron oxide powder consists of acicular particles with an average major axis of 0.2)tm and the average minor axis of 0.0211M, and the cobalt-containing T-iron oxide powder has acicular particles that are sintered. Average long axes (32, gm) irregularly coalesced by knots.

Consists of particles with the same short axis of 0.057", Hc = 6040e
, σ5==72. Oemu/ysσr/σs=0.64
, SBaT=30m'/7.

For each 80 parts by weight of magnetic iron oxide powder consisting of T-iron oxide or cobalt-containing T-iron oxide obtained in the above examples and comparative examples, 11 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer was added. A magnetic paint was prepared by blending 7 parts by weight of polyurethane resin, 2 parts by weight of a low molecular weight incyanate compound, 7760 parts by weight of cyclohexane, and 60 parts by weight of toluene.
It was coated on a μ polyester film to a dry thickness of 4 pn, dried, calendered, and then cut to a predetermined width to produce magnetic tapes T-1 to T-6.

The coercive force (Hc), residual magnetic flux density (Br), and squareness ratio (Br/Bs) were measured for these magnetic tapes, and for magnetic tapes T-1 to T-4, the S/N ratio (DC and AC) was measured. DC-5/N, AC-S/N
), and for magnetic tapes T-5 and T-6, the video output and C/N at 4 MHz were measured.

The results are shown in Tables 1 and 2 below. Furthermore, jl
! Both S/N in Table 1 are Od for magnetic tape T-3, and video output and C/N in Table 2 are Od for magnetic tape T-6.
It is shown as a relative value when it is set as B.

Table 10 Table 2 As is clear from the results in the above diagram, the magnetic iron oxide powder obtained by the method of this invention is composed of good acicular particles, has excellent magnetic properties, and has a large specific surface area. magnetic tape T-1, T-2, T-5 using this
It can be seen that it exhibits very excellent magnetic properties. On the other hand, magnetic iron oxide powder obtained by conventional general-purpose methods loses its acicular shape due to sintering, resulting in poor magnetic properties and a small specific surface area. T
-6's magnetic properties are also insufficient, and while the magnetic iron oxide powder obtained by the conventional proposed method that undergoes hydrothermal treatment has improved magnetic properties due to reduced sintering, it is difficult to control the particle shape during hydrothermal reaction. Because the specific surface area is rather small due to certain reasons, magnetic tape T-4 using this material has improved magnetic properties to some extent compared to magnetic tape T-3, but S
It can be seen that the /N ratio decreases◇

Claims (1)

[Claims] (1) The precipitate precipitated by the reaction between an aqueous solution containing divalent iron ions and an alkaline aqueous solution containing carbonate ions in an amount equivalent to or more than the iron ions is oxidized to produce spindle-shaped particles. is subjected to a hydrothermal reaction in a neutral to weakly alkaline region in an autoclave, and the obtained α-iron oxyhydroxide powder is reduced in a gas phase and then oxidized as necessary to obtain magnetic iron oxide powder. A method for producing characteristic magnetic iron oxide powder.