JPH01212231A - Production of magnetic iron oxide for magnetic recording - Google Patents

Abstract

PURPOSE:To improve the shape retentiveness, dispersibility, heat resistance, and magnetic characteristics of acicular particles by adding water soluble silicate to the aq. suspension of the iron oxyhydroxide obtd. by a specific method and depositing a silicon compd. on the surface of the iron oxyhydroxide, then separating and drying said iron and oxidizing the iron to the magnetic iron oxide. CONSTITUTION:An aq. soln. prepd. by dissolving a ferrous salt (e.g.: FeSO4) in water to 30-100g/l Fe concn. is partially neutralized and oxidized to form the nuclear crystal of the iron oxyhydroxide. While this liquid is neutralized with an alkali (e.g. NaOH) in the presence of a water soluble phosphorus compd. (e.g.: orthophosphoric acid), the liquid is subjected to, for example, air oxidation to incorporate the phosphorus into the above-mentioned nuclear crystal and to grow said crystal. After the resulted iron oxyhydroxide is separated from the reaction mother liquid, the iron oxyhydroxide is suspended in water. A water soluble silicate (e.g.: sodium silicate) is added to this suspension to deposit the silicate compd. on the surface of the iron oxyhydroxide. The deposited iron oxyhydroxide is separated and dried and is then dehydrated at 650-750 deg.C in the air atmosphere in a heat treatment furnace; thereafter, the iron oxyhydroxide is reduced at about 400 deg.C in gaseous H2 flow to magnetite which is further oxidized in the air at about 300 deg.C. The titled magnetic oxide is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing magnetic iron oxide useful as a recording element of a magnetic recording medium. The present invention relates to a method for producing magnetic iron oxide for magnetic recording, which has excellent magnetic properties such as orientation and reversal magnetic field distribution, and has improved dispersibility in various organic binders.

[Conventional technology]

Magnetite (r-FezOi) and magnetite (FezO4) are commonly used as recording elements in magnetic recording media.
, bertolide compound (Fed, 1', 33<
X <1.5), magnetic iron oxides modified with metal compounds such as cobalt, or acicular metals (α-Fe s
Magnetic powders such as iron alloy (ferroalloy) are usually mixed with iron oxyhydroxide powder (iron oxyhydroxide powder).
α.

β, r-FeOOH) is heat treated to dehydrate, reduce, or reduce and then oxidize.

Magnetic powder produced by this method often has uneven particle size distribution, which makes it difficult for the magnetic powder to be uniformly dispersed when kneaded with a resin binder to prepare magnetic paint. It is said that it is difficult to obtain a magnetic recording medium that is filled and has good magnetic properties.

However, in conjunction with the recent increase in the density of magnetic recording media, a magnetic powder with uniform particle size distribution and greater filling properties is desired.

Conventionally, as a countermeasure against this problem, for example, (1) a method of adding phosphate ions, Zn ions, Sn ions, etc. during the generation of iron oxyhydroxide nuclei (Japanese Patent Publications No. 39-25546, No. 55-23217, No. 56-155024) and (
2) Method for producing iron oxyhydroxide under highly alkaline conditions (
JP-A-53-127400).

On the other hand, in the production of magnetic powder, techniques using phosphorus and silicon include, for example, (3) iron oxyhydroxide is separated from the mother liquor after the reaction is completed, washed with water, and then suspended in water to form a phosphorus compound on the particle surface. and a method of depositing a silicon compound (JP-A-53-129198) and (4) γ-Fe
,0. During production, phosphorus, silicon, etc. are deposited on the surface of acicular iron oxide or its hydrate, a cobalt compound is deposited on the magnetite obtained by reducing this, and then heat treatment is performed to dope cobalt ions. How to do it (Unexamined Japanese Patent Publication No.
[Problems to be Solved by the Invention] However, the iron oxyhydroxide obtained by the methods (1) to (4) above is not necessarily sufficient in terms of particle size distribution, particle shape, etc. In addition, when it is subjected to heat treatments such as dehydration, reduction, and oxidation, particle sintering tends to occur, so the magnetic properties of magnetic recording media derived from the magnetic iron oxide obtained have not been satisfactory.

The present invention solves the problems of the conventional technology, has a uniform particle size distribution, has excellent magnetic properties such as coercive force, squareness ratio, orientation, and reversal magnetic field distribution, and has improved dispersibility in various organic binders. An object of the present invention is to provide a method for producing magnetic iron oxide for magnetic recording.

(Means for Solving the Problems) The present inventors have attempted to solve these problems (after various studies). As a result, the ferrous salt aqueous solution is partially neutralized and oxidized to produce oxyhydroxy Iron core crystals are generated, and then the liquid is neutralized and oxidized in the presence of a water-soluble phosphorus compound to grow the core crystals to obtain iron oxyhydroxide containing phosphorus in the solid phase. If magnetic iron oxide is produced after forming a heat-resistant layer mainly composed of a silicon compound on the surface of iron hydroxide particles, magnetic powder with uniform particle size distribution and clear crystal shape can be obtained. We obtained the knowledge that various magnetic properties are significantly improved compared to those obtained with conventional technology,
The invention has been completed.

That is, the present invention partially neutralizes and oxidizes an aqueous ferrous salt solution to generate nuclear crystals of iron oxyhydroxide, and then oxidizes the liquid while neutralizing it with an alkali in the presence of a water-soluble phosphorus compound. The iron oxyhydroxide obtained is separated from the reaction mother liquor, suspended in water, and a water-soluble silicate is added to the suspension to form a silicon compound on the surface of the iron oxyhydroxide. This is a method for producing magnetic iron oxide for magnetic recording, which is characterized in that magnetic iron oxide is produced from the deposited, separated and dried material.

The ferrous salts used include ferrous sulfate, ferrous chloride,
There are ferrous salts of mineral acids such as ferrous nitrate and ferrous carbonate, and ferrous sulfate is preferred industrially.As alkalis, sodium hydroxide, sodium carbonate, potassium hydroxide, and calcium carbonate are available. , ammonia, ammonium carbonate, etc., and industrially, sodium hydroxide and ammonia are preferred. Phosphorus compounds added during iron oxyhydroxide core crystal growth include water-soluble ones such as orthophosphoric acid, pyrophosphoric acid, Examples include tripolyphosphoric acid, metaphosphoric acid, condensed phosphoric acids other than those mentioned above, hypophosphoric acid, phosphorous acids, hypophosphorous acid, and salts thereof.

As the oxidizing agent, air, oxygen, hydrogen peroxide, chlorate, and other oxidizing agents can be used, but air is preferred.

In the method of the present invention, a ferrous salt solution is first partially neutralized with an alkali and oxidized to convert a portion of the Fe content in the solution into nuclear crystals of iron oxyhydroxide. At this time, the Fe concentration of the ferrous salt solution is usually 30 to 100 g/I! The amount of alkali added is usually the amount necessary to precipitate 5 to 50% of Fe ions in the mother liquor.

The reaction temperature for nucleation crystal formation is usually 30 to 60°C.

In addition, a water-soluble phosphorus compound or the like may be present as a crystal modifier in the system during this nucleation crystal formation reaction.

The liquid after the above-mentioned nucleation crystal formation reaction is a ferrous salt solution in which iron oxyhydroxide nucleus crystals are suspended, and is then oxidized while adding an alkali in the presence of the above-mentioned water-soluble phosphorus compound. Nucleic crystals are grown to obtain iron oxyhydroxide containing phosphorus as a solid solution.

At this stage of nuclei crystal growth, a phosphorus compound may be mixed with the alkali in advance or added separately. ~2% by weight, preferably 0.1
~1.0% by weight. If the amount of phosphorus is too small than the above range, it may be difficult to obtain the desired effect, while if it is too large, non-magnetic substances in the magnetic iron oxide derived from it will increase. The zero reaction temperature for lowering the saturation magnetization (σS) is usually 35 to 80°C, preferably 50 to 70°C.pl
l is usually kept between 3 and 6.0 In order to obtain a grain size distribution with a small width and less branching, the growth rate of the nuclei should be adjusted to 1.
The method of growing the nuclei, which is preferably adjusted to approximately 20 g/l/hour, is to adjust the depth of the mother liquor and the amount of nuclei crystals produced in advance, and after the completion of the nucleation reaction, add an alkali. Nucleic crystals can be grown to an appropriate particle size by starting addition and performing neutralization and oxidation, or by replenishing ferrous salt after nucleation and then performing neutralization and oxidation. The growth rate of iron oxyhydroxide nuclear crystals based on the weight of the nuclear crystals is 1.2 to 4.
．． 0, preferably 1.5 to 3.

Next, the liquid after the nucleus crystal growth reaction is filtered, the obtained iron oxyhydroxide is suspended in water, and the pII of the liquid is set to 6 or more.
Desirably, after adjusting the number to 8 or more, a water-soluble silicate is added to coat the surface of the iron oxyhydroxide particles with a silicon compound. The pII during deposition is preferably adjusted to 7 or less by adding an acidic substance to the liquid in order to uniformly deposit the silicon compound on the particle surface.The water-soluble silicate used is orthosilicate. , disilicate, tetrasilicate, metasilicate, etc. The amount of this silicon compound added is 0 in terms of Si based on the total amount of iron oxyhydroxide normally produced.
．． 05 to 2% by weight, preferably 0.1 to 1.0% by weight. If the amount of silicon is too small than the above range, the heat resistance of the powder particles will decrease when iron oxyhydroxide is heat-treated, and the resulting magnetic iron oxide will have poor acicular properties (on the other hand, if it is too large, the magnetic This is undesirable because the content of nonmagnetic substances in iron oxide increases, resulting in a decrease in saturation magnetization (σS).

Iron oxyhydroxide coated with a silicon compound is obtained as iron oxyhydroxide powder through conventional filtration, water washing, drying and pulverization. Magnetic iron oxide for magnetic recording can be obtained from this iron oxyhydroxide powder by a conventional method. That is, first, it is dehydrated in air at a temperature of 300 to 800°C, and then this dehydrated product is reduced with hydrogen or hydrogen containing water vapor at a temperature of 300 to 500°C to obtain Fe, 0.
or further this Fe, O, 200~4
T-FelO can be obtained by oxidizing with oxygen or air at a temperature of 00°C.

[For production]

The present invention uses a phosphorus compound and a silicon compound in the production process of iron oxyhydroxide, but instead of depositing them on the surface of the iron oxyhydroxide or iron oxide produced as in the prior art described above. , is characterized in that phosphorus is contained in the solid phase during the growth process of iron oxyhydroxide core crystals, and then a layer of silicon compound is formed on the surface of the obtained iron oxyhydroxide. As a result, it is possible to improve particle size distribution and heat resistance during heat treatment, and the synergistic effects of these also result in good acicularity, good particle size distribution, fewer pores, and excellent magnetic properties. It is possible to produce magnetic iron oxide that has a magnetic iron oxide and has good paint dispersibility.The reason why such an excellent effect is obtained in the present invention is not clear, but it is thought as follows. .

When a phosphorus compound is present in the system during the growth reaction of iron oxyhydroxide, the generation of branched crystals is suppressed, resulting in oxyhydroxide with good acicularity and well-defined phosphorus particle shape. Iron is obtained. Furthermore, since generation of fine nuclides during the reaction can be prevented, particles with uniform particle size distribution can be obtained.

It is known that phosphorus compounds are applied to iron oxyhydroxide and iron oxide as sintering inhibitors, but when a silicon compound is applied to the surface of iron oxyhydroxide as in the present invention, It is preferable that the phosphorus compound is dissolved in solid solution in the particles in advance rather than being deposited on the surface of the particles, from the viewpoint of improving the heat resistance of the particles and also from the viewpoint of various magnetic properties of magnetic iron oxide.

〔Example〕

Next, the present invention will be explained using specific examples.

Example-1 (1) Production of iron oxyhydroxide core crystals A 1.50 mol/Il ferrous sulfate aqueous solution 201 was placed in a reaction vessel equipped with an air blowing tube and a stirrer, and the temperature was raised to 60°C. Then, while maintaining this temperature, 1.07 ffi of a 10 mol/1 aqueous sodium hydroxide solution was added with stirring (precipitated Fe15 g/i
), air is blown into this at a speed of 101/min.
The reaction was performed for ~200 minutes to obtain iron oxyhydroxide core crystals.

(2) Nucleic crystal growth reaction In order to grow to the desired particle size, while maintaining the above nuclide slurry i at 60 to 65°C, ION sodium hydroxide aqueous solution 1.6111 was added at a rate of 8 to 7 minutes. , air 5
Neutralization and oxidation reactions were carried out by feeding at a rate of 1/min.

The growth rate is 2.5 times the weight ratio to the core crystal.

In this growth reaction, a 1 mol/i orthophosphoric acid aqueous solution was continuously added in parallel with the sodium hydroxide aqueous solution. The amount of orthophosphoric acid added was 0.3% in terms of P based on the weight of iron oxyhydroxide to be produced.

The specific surface area of iron oxyhydroxide obtained in this way is 4
It was 5 to 50 rrr/g.

(3) Adhesion of silicon compounds The above-mentioned iron oxyhydroxide reaction solution is separated by filtration in a filtration step.
Washed with water. The washed iron oxyhydroxide was dispersed in water so that the slurry concentration was 100 g/l, and the pII of this slurry was adjusted to 8 with a 400 g/l aqueous sodium hydroxide solution, and then the pII was adjusted to 50 in terms of Si. A sodium silicate aqueous solution having a concentration of g/II was added to form a silicon compound film on the surface of the iron oxyhydroxide. The amount of sodium silicate added is 0.0% in terms of Si based on the weight of iron oxyhydroxide.
It was set at 3%. Thereafter, the pn of the slurry was gradually lowered to 6 with dilute sulfuric acid.

(4) Formation of magnetic iron oxide The iron oxyhydroxide subjected to the above treatment was filtered, washed with water, and further dried at 100 to 150°C. This iron oxyhydroxide is heated to a temperature of 650 to 750 in a heat treatment furnace in an air atmosphere.
dehydrated at a temperature of
It is reduced to magnetite at 00℃, and further reduced to 30℃ in air.
Magnetic iron oxide (A), which is T-iron oxide, was obtained by oxidation at 0°C.

(5) Formation into paint and measurement of magnetic properties For each of r-Fe and O, a mixture was prepared according to the proportions shown below and kneaded in a ball mill to produce a magnetic paint.

■ r-Pe, O, powder 100 parts by weight ■
Soy lecithin 1.6〃■ Surfactant
4 〃■ Vinegar vinyl PVC copolymer resin
10.5 〃■ Dioctyl phthalate 4
〃■ Methyl ethyl ketone 84〃■ Toluene 93〃Next, each magnetic coating material was coated on a polyester film by a conventional method, oriented and dried to prepare a magnetic recording medium having a magnetic coating film about 7μ thick. For these magnetic recording bodies, coercive force (Ilc), magnetic flux density (Br), squareness ratio (fir/B), orientation (OR), and switching field distribution (SPD) were measured and displayed using conventional methods.

(6) Measurement of particle size distribution Method for measuring particle size distribution (σL/, The average axial length T:, (μ) and standard deviation σL (μ) are determined, and the particle size distribution (L distribution) is determined according to the following formula.

L distribution = σL/L The smaller the value of this distribution, the sharper the particle size distribution, and this value was used as an index of particle size distribution improvement.

Examples 2 and 3 The pII of the iron oxyhydroxide slurry when adding the sodium silicate aqueous solution in Example 1 was 10 (Example 2)
Magnetic iron oxide (B) (Example-2) and magnetic iron oxide (C) (Example-3) were obtained in the same manner as in Example-1 except that 12 (Example-3) was changed. Ta.

Example-4 Magnetic iron oxide ( D) was obtained.

Comparative Example-1 A magnetic iron oxide (I
F,) was obtained.

Comparative Example-2 A magnetic iron oxide ( F) was obtained.

Comparative Example-3 The procedure was the same as in Comparative Example-1 except that the orthophosphoric acid aqueous solution in Comparative Example-1 was added to the slurry after the growth reaction of iron oxyhydroxide was completed, and magnetic iron oxide (G ) was obtained.

Comparative Example-4 The case of Comparative Example-2 except that the orthophosphoric acid aqueous solution in Comparative Example-2 was added to the slurry after the growth reaction of iron oxyhydroxide was completed, and then the sodium silicate aqueous solution was added. In the same way as magnetic iron oxide (H)
I got it.

Comparative Example 5 A magnetic iron oxide was prepared in the same manner as in Comparative Example 4 except that the addition of the sodium silicate aqueous solution in Comparative Example 4 was changed to the slurry after filtration of iron oxyhydroxide and washing with water. (1) was obtained.

Comparative Examples 6, 7, 8 The orthophosphoric acid aqueous solution in Comparative Examples 3, 4, and 5 was added to the slurry after iron oxyhydroxide was filtered and washed with water, and then the sodium silicate aqueous solution was added. The same procedures as Comparative Examples 3 and 4゜5 were made except for the changes, and magnetic iron oxide (J) (Comparative Example-6) and magnetic iron oxide (K) (Comparative Example-7) were prepared.
) and magnetic iron oxide (L) (Comparative Example-8) were obtained.

〔Effect of the invention〕

The present invention, configured as described above, achieves various excellent effects such as those mentioned above.

(2) The magnetic iron oxide obtained by the present invention has a uniform particle size distribution, a clear particle shape, and good acicularity. This is due to improved particle size distribution and particle shape of iron oxyhydroxide, improved heat resistance during heat treatment, and improved shape retention of acicular particles.

■ Improved heat resistance allows sufficient heat treatment to bring out magnetic properties, improving coercive force (Hc), reversal magnetic field distribution (SF port), squareness ratio (SQ), and orientation (OR).
), magnetic properties such as magnetic flux density (Br) are improved.

(2) In addition, when a magnetic paint is prepared using this magnetic iron oxide, the dispersibility is good, the mixing and dispersion time with the paint resin liquid is shortened, and the ability to fill the magnetic coating film with the magnetic substance is improved.

Claims (6)

[Claims] 1. A ferrous salt aqueous solution is partially neutralized and oxidized to generate iron oxyhydroxide core crystals, and then the solution is neutralized and oxidized with an alkali in the presence of a water-soluble phosphorus compound to grow the core crystals. The obtained iron oxyhydroxide is separated from the reaction mother liquor, suspended in water, and a water-soluble silicate is added to the suspension to deposit a silicon compound on the surface of the iron oxyhydroxide, followed by separation. A method for producing magnetic iron oxide for magnetic recording, characterized by drying the product and producing magnetic iron oxide from this product. 2. Claim 1 wherein the iron oxyhydroxide core crystal contains phosphorus.
A method for producing magnetic iron oxide for magnetic recording as described in . 3. 3. The method for producing magnetic iron oxide for magnetic recording according to claim 1, wherein the water-soluble phosphorus compound is orthophosphoric acid or a salt thereof. 4. Claim 1 wherein the water-soluble silicate is sodium silicate.
, 2 or 3. The method for producing magnetic iron oxide for magnetic recording according to . 5. 5. The method for producing magnetic iron oxide for magnetic recording according to claim 1, wherein the suspension has a pII value of 6 or more when the water-soluble silicate is added. 6. 5. The method for producing magnetic iron oxide for magnetic recording according to claim 1, 2, 3, or 4, wherein the suspension has a pII value of 8 or more when the water-soluble silicate is added.