JPH0518441B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for producing iron-based metal magnetic powder suitable as a recording element of a magnetic recording medium. [Technical background of the invention and its problems] In recent years, magnetic recording media such as magnetic tapes, magnetic disks, and magnetic sheets for audio, video, and computers have become smaller and have improved performance due to increased recording capacity. In conjunction with this, iron or iron-based materials, which are expected to have higher coercive force and higher saturation magnetization than conventional iron oxide-based magnetic powders, have recently become more popular as magnetic materials for magnetic recording media. Iron-based metal magnetic powders such as alloys are attracting particular attention. By the way, the above-mentioned iron-based metal magnetic powder is usually produced by heating hydrated iron oxide particles such as goethite needle crystal particles or iron oxide particles obtained by heating and dehydrating them in a reducing gas atmosphere such as hydrogen. It is obtained by reducing iron to metallic iron.
However, since the rate of the reduction reaction is largely determined by the heating temperature, in high-temperature heat treatment, although the reduction is completed quickly, the shape of the resulting metal iron particles may collapse or sintering between particles may occur. Magnetic properties are easily impaired. Furthermore, while low-temperature heat treatment can avoid the above-mentioned problems, the reduction rate is greatly reduced, which is extremely disadvantageous industrially. For this reason, various proposals have been made to complete the reduction reaction in a relatively short time without causing the aforementioned particle shape collapse or interparticle sintering. For example, the surface of hydrated iron oxide or iron oxide particles is often coated with a silicate-based treatment agent such as sodium silicate or an organic treatment agent consisting of an alkoxide-based silane compound, and then subjected to heat reduction treatment. Are known. However, in the above-mentioned coating treatment method, when a silicate is used as the coating treatment agent, the coating treatment agent may cause silicic acid generated on the particle surface of iron hydroxide or iron oxide or other than the particle surface during precipitation formation of the coating layer. The gel tends to gel rapidly, which makes it difficult to form a uniform continuous coating layer, and the formation of sintered particles and deformation of the particle shape are unavoidable. In addition, in the treatment with the silicate, neutralizing agents such as acids used for precipitate formation and their neutralization products tend to remain in the metal iron magnetic powder, and organic coating agents such as Even when using materials such as alkoxychlorosilane, it is difficult to form a uniform and strong coating layer, and furthermore, hydrogen chloride gas is generated during heating and reduction, resulting in deformation of the particle shape and the formation of a metallic iron magnetic powder. Unavoidable residual chlorine content in the paint can cause gelation, dropouts, and corrosion of the head when it is made into a paint. In any case, even with the various methods described above, the effect of suppressing the collapse of particle shape and interparticle sintering during reduction is not sufficiently brought about, and as a result, the magnetic properties of the obtained iron-based metal magnetic powder are impaired. There are many problems that need to be resolved. [Object of the Invention] An object of the present invention is to solve the above-mentioned problems and to produce magnetic recording for high recording density without impairing the particle shape of hydrated iron oxide or iron oxide and without causing interparticle sintering. It is an object of the present invention to provide a method for efficiently producing iron-based metal magnetic powder with excellent characteristics suitable for media. [Structure of the Invention] While conducting various studies to solve the above-mentioned problems, the present inventors focused on the strong reactivity between active hydrogen compounds and isocyanate groups on the surface of hydrated iron oxide or iron oxide particles. However, as a result of further investigation, we found that when hydrated iron oxide or metal compound powder mainly containing iron oxide is coated with a silylating agent having an isocyanate group, some or all of the silylating agent reacts with the particle surface. An extremely uniform coating layer of siloxane compound is formed,
In addition to suppressing mutual sintering of particles in heat reduction treatment after heat treatment at a temperature of 150 to 850°C, it is possible to extremely efficiently produce iron-based metal magnetic powder with excellent magnetic properties without deformation of particle shape. The present invention has been completed based on the knowledge that silyl isocyanate compound is coated on the particle surface of hydrous iron oxide or a metal compound mainly containing iron oxide, and the compound is coated with a siloxane compound. After that, heat reduction treatment or
This is a method for producing iron-based metal magnetic powder, characterized by heat treatment at a temperature of 150 to 850°C, followed by heat reduction treatment. In the method of the present invention, various starting materials can be used as hydrous iron oxide or iron oxide, but a typical example of hydrous iron oxide is iron oxyhydroxide, such as α −FeO
(OH), β-FeO(OH), γ-FeO(OH), etc. In addition, examples of iron oxides include α-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ , γ-Fe ₂ O ₃
For example, in order to improve performance such as magnetic properties to the above-mentioned hydrated iron oxide or iron oxide, for example, Co, Ni, Ti, Cr, Mn can be added. It is also possible to use materials to which metal components other than iron are added, such as. The above-mentioned metal components may be co-precipitated during the production of hydrated iron oxide, adsorbed onto the surface of hydrated iron oxide particles, coated with their hydroxides, etc. Doping can be achieved by subjecting the contained hydrated oxide to treatments such as dehydration, reduction, and oxidation. Note that the particle shape of these hydrous iron oxides or iron oxides is typically needle-shaped, but various other shapes can be used, such as spindle-shaped, rice grain-shaped, rod-shaped, Examples include flat plate and dice shapes. In the method of the present invention, the silyl isocyanate compound used for coating treatment has the general formula
AnSi(NCO) _4-o (A: an alkyl group, alkoxy group, alkenyl group, or aryl group having 1 to 22 carbon atoms, or hydrogen, n: O or an integer of 3 or less, where n is 2 or 3) (In some cases, the alkyl group, alkoxy group, alkenyl group or aryl group may be the same or different.) Specific examples thereof include, for example. , Si(NCO) ₄ , CH ₃ Si
(NCO) ₃ , (CH ₃ ) ₂ Si(NCO) ₂ , (CH ₃ ) ₃ SiNCO,
C ₄ H ₉ OSi (NCO) ₃ , C ₁₃ H ₁₇ OSi (NCO), C ₁₃ H ₁₇ Si
(NCO) ₃ , CH=CHSi(NCO) ₃ , CH ₂ =CHSi
(NCO) ₂ CH ₃ ,

Examples include [Formula] (NCO) ₃ . In the method of the present invention, coating the surface of particles of hydrated iron oxide or iron oxide with the silyl isocyanate compound can be carried out by various methods, such as (1) coating of hydrated iron oxide or iron oxide particles. to form an aqueous suspension in water or an organic aqueous medium, to which a solution of the silyl isocyanate compound is added, or (2) hydrated iron oxide or iron oxide is dissolved in the silyl isocyanate compound. (3) by spraying a solution of the silyl isocyanate compound onto hydrated iron oxide or iron oxide powder;
Part or all of the silyl isocyanate compound reacts very easily due to the presence of active hydrogen such as hydroxyl groups on the surface of hydrated iron oxide or iron oxide particles, resulting in a uniform and strong siloxane compound coating layer with silyl groups added to the surface of the particles. is formed. In addition,
The coating treatment may be performed at room temperature,
This may be carried out under heating if necessary. Also mentioned above
When the silyl isocyanate compound is brought into direct contact with hydrated iron oxide or iron oxide powder as in (3), the amount of hydroxyl groups is increased on the surface of hydrated iron oxide or iron oxide particles using water or steam prior to coating treatment. Preliminary processing may be performed to In the method of the present invention, the amount of the silyl isocyanate compound to be treated varies depending on the particle size of the hydrated iron oxide or iron oxide, and cannot be definitively stated, but it is based on the weight of Fe of the hydrated iron oxide or iron oxide.
Silyl isocyanate compound 0.1 based on Si weight
~20%, preferably 0.5-10%. If the processing amount is too small than the above range, the desired effect will not be obtained, while if it is too large, it will not be advantageous in terms of cost, and the characteristics of the obtained iron-based metal magnetic powder, such as saturation magnetization, will be affected. This may have undesirable effects such as a decrease in The hydrated iron oxide or iron oxide particles coated as described above are recovered from the treatment system through filtration and washing as necessary, and then subjected to a heat reduction treatment. In the above, for example, when hydrated iron oxide is used as the starting material and is subjected to the coating treatment, it is heated and dehydrated at 150 to 850°C to form α-Fe ₂ O ₃ etc. after the coating treatment, and then heated and reduced. It is desirable to do so.
Even when iron oxide is used as a starting material, it may be heat-treated at 150 to 850° C. after coating, and then heat-reduced. The thermal reduction treatment can be carried out by various well-known methods, but it is usually carried out in a reducing gas such as hydrogen gas at a heating temperature of 300 to 550°C for 1 to 20 hours. substantially all of the oxide metal can be reduced to metal. Note that the temperature is 150 to 850°C prior to the heat reduction treatment.
When the heat treatment is carried out, the coating layer tends to become a strong silicon compound layer, which is more preferable in terms of suppressing particle sintering and particle shape deformation during the heat reduction treatment. The present invention will be further explained below with reference to Examples. Example 1 Acicular particles of α-FeOOH (long axis 0.3μ, axial ratio 10)
A slurry prepared by dispersing 25 g of 1 in water was maintained at 40°C while stirring. Si in the slurry
262 ml of ethyl acetate solution (10 g/) of (NCO) ₄
was gradually added dropwise over 1 hour, and after the addition, the mixture was further stirred at the same temperature for 1 hour to ripen. Then, it was filtered, washed with water, and then dried. Then, the hydrated iron oxide particles subjected to the coating treatment were heated at 750° C. for 2 hours under atmospheric pressure in a Matsufuru furnace to form α-Fe ₂ O ₃ . After that, the α-
7 g of Fe ₂ O ₃ was placed in a stainless steel board and heated and reduced in a tube furnace at 450° C. for 4 hours under a hydrogen flow of 2 times per minute. The obtained reduced product was cooled in a nitrogen stream, immersed in toluene, and then dried to obtain a sample (A) according to the method of the present invention. Example 2 The same as in Example 1 except that 226 ml of an ethyl acetate solution of CH ₃ Si(NCO) ₃ (10 g/) was used instead of the ethyl acetate solution of Si(NCO) ₄ in Example 1. A sample (B) according to the method of the present invention was obtained by processing in the same manner as above. Example 3 25g of α-FeOOH powder used in Example 1 was
A wet cake was prepared by moistening with a small amount of water. Then
Si(NCO) ₄ in ethyl acetate solution (52.4g/), 50ml
A sample (C) according to the method of the present invention was obtained in the same manner as in Example 1, except that the mixture was added to the wet cake, thoroughly kneaded, and then dried. Example 4 The same as in Example 1 except that in Example ₃ , 50 ml of an ethyl acetate solution of CH ₃ Si(NCO) ₃ (45.2 g/) was used instead of the ethyl acetate solution of Si(NCO) 4 A sample obtained by the method of the present invention was processed in the same manner as
I got (D). Comparative Example 1 In Example _{1, an ethanol solution of CH 3 Si} (OCH ₃ ) ₃ (10
The process was carried out in the same manner as in Example 1, except that 182 ml of the sample was used. Sample (E) Comparative Example 2 In Example _{1, an aqueous solution of CH 2 =} CHSi(OCH ₃ ) ₃ (10
The process was carried out in the same manner as in Example 1, except that 197 ml of the solution (197 ml) was used. Sample (F) Comparative Example 3 Example 3 except that 50 ml of n-C ₁₀ H ₂₁ Si(OCH ₃ ) ₃ ethanol solution (68 g/) was used instead of the Si(NCO) ₄ ethyl acetate solution. was treated in the same manner as in Example 1. Sample (G) Comparative Example 4 The α-FeOOH slurry used in Example 1 was
After adjusting the pH to 13 by adding NaOH aqueous solution, add 16 ml of water glass aqueous solution (30 g/Si) under stirring at 40℃.
Added. Then, CO ₂ gas was blown into the solution to neutralize it to pH 7 over about an hour. After further aging with stirring for 1 hour, the mixture was filtered, washed with water, and dried. Thereafter, in the same manner as in Example 1, a heating dehydration treatment followed by a heating reduction treatment was performed. Sample (H) Comparative Example 5 The same treatment as in Example 1 was carried out, except that the surface of the α-FeOOH acicular particles was not coated with Si(NCO) ₄ . Sample (I) Using a vibrating magnetometer (VSM) in a conventional manner for each sample powder obtained in the above examples and comparative examples, coercive force (Hc) and saturation magnetization (σs, value in a magnetic field of 10 KOe) were measured. , the squareness ratio (Rs) was measured. The results are shown in the table below.

〔Effect of the invention〕

The method of the present invention can uniformly and firmly form a protective film consisting of a coating layer of a silyl isocyanate compound on the surface of particles of hydrated iron oxide or iron oxide, so that problems that occur when using conventional coating treatment agents can be avoided. It is possible to extremely easily produce an iron-based metal magnetic powder with excellent magnetic properties in which mutual sintering of particles is suppressed and the particle shape does not collapse without causing any sintering.

Claims (1)

[Claims] 1. After coating the particle surface of hydrated iron oxide or a metal compound mainly containing iron oxide with a silyl isocyanate compound to convert the compound into a siloxane compound, heat reduction treatment or heating at 150 to 850°C
A method for producing iron-based metal magnetic powder, which comprises heat treatment at a temperature of , followed by heat reduction treatment.