JPH0552645B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to ferromagnetic metal powder particles as a magnetic material in a magnetic recording medium suitable for high-density recording, and a method for producing the same. <Prior art> In order to achieve high output and low noise in a wide recording wavelength range, magnetic materials for magnetic recording are made of highly uniform finely shaped particles and have a high coercive force (Hc).
Basically, magnetic properties are required, including large saturation magnetization (σs) and residual magnetization (σr), and as large a squareness ratio (Rs = σr/σs) as possible, as well as affinity with paint resins and dispersibility. In addition, it is desired that the coating film has excellent properties in terms of orientation and filling properties, and that the media has a sufficient lifespan to ensure reliability. In recent years, there has been a social demand for high-density recording, and in addition to magnetic powder as a material powder, binder resins, various additives,
In addition, research has been carried out to improve a wide range of media processing methods (for example, Goro Akashi, "Advances in magnetic tape", Journal of the Japan Society of Applied Magnetics, 7(3), 185).
(1983). ). Of these, regarding magnetic powder as a magnetic material, ferromagnetic metal powder was first put to practical use as a material for audio magnetic tape due to its excellent magnetic properties, and in the near future it is expected that it will be used as a material for video. There is. In the case of acicular metal powder particles containing iron as the main component, excellent magnetic potential based on sufficiently high Hc-value and σs-value is utilized, but usually Since it is a fine particle of 1μ or less, it has extremely strong oxidizing activity against air, and stability is considered an important physical property to ensure applicability as a magnetic recording medium and to provide reliability. Conventionally, methods for ensuring this kind of stability include (1) a method of providing an oxidized layer on the surface of the fine particles, (2) a method of forming a special layer on the surface of the fine particles, and a combination of these methods. Are known.
Methods belonging to (1) are classified into methods in which the oxidation layer is formed by a gas phase contact reaction and methods in which the oxide layer is formed by a liquid phase reaction. −127701,
57-9211, etc., and examples of the latter include JP-A-52-85054, 55-164001, 57-85901, 57
-93504, 58-110433, 58-159311, etc. Furthermore, methods belonging to (2) can be divided into methods that deposit organic materials and methods that deposit inorganic materials. JP-A-46-5057, 50-104164, 51-122655, 51
−140860, 52−155398, 53−5798, 53−76958,
54−24000, 55−69660, 55−69661, 55−39662,
56-29841, 56-54013, 56-148726 Furthermore, as a method for coating resins, JP-A-53-13906, 53-78099, 54-139508, 56
-130831 etc. In addition, the latter is a method for depositing aluminum silicate, aluminum oxide, etc., as described in Japanese Patent Application Laid-Open Nos. 53-8798, 56-98401, 57-9802, 57-
63601, 58−159306, 58−159307, 58−159308,
Examples include 58-161708, 58-161709, 58-161725, etc. <Problems to be Solved by the Present Invention> The method of depositing or forming a film of an organic or inorganic substance on the surface of fine ferromagnetic metal powder particles containing iron as a main component is practical and effective. Although many cases have been reported,
In many cases, taking into consideration the subsequent application of paint, the product must be fully compatible with the media binder resin, and if it is a low molecular weight material with strong liquid characteristics, the media Therefore, there has been a desire for a system and method that can form a strong film and maintain affinity with the binder resin. Moreover, in the case of acicular metal powder particles considered for video use, the major axis diameter is approximately 0.1μ and the minor axis diameter is 0.01μ.
They belong to the so-called ultrafine particle system, which is extremely small in size, and it has been impossible to provide a sufficient effect of suppressing changes over time by simply depositing organic matter on them. <Means for Solving the Problems> In order to solve the above problems, the present inventors have conducted various studies, and as a result, have developed a method using a catalytic reduction reaction using a reducing gas such as H ₂ gas. The inventors have discovered that the fine particles and method in which a toluene polycondensate is formed on the surface of fine ferromagnetic metal powder particles containing iron as a main component are extremely effective, and have arrived at the present invention. It should be noted that the method of coating or forming a film on metal powder particles with an organic polymer is well known.
Examples include polyurethane resin (Japanese Unexamined Patent Publication No. 53-78099), polyvinyl butyral resin (Japanese Unexamined Patent Publication No. 56-130831), and others. However, when coating or adhering a polymer resin with a high molecular weight,
Generally, it is extremely difficult to uniformly adsorb fine metal powder particles onto the individual surface layers, and usually the metal powder particles tend to form agglomerated pairs. The present inventors have researched and considered methods to solve these basic problems, and have
When ferromagnetic metal fine particles containing Fe as the main component are immersed in a toluene solvent containing a small amount of aldehyde and heat-treated in the range of 80 to 150°C, toluene is polycondensed on the surface of the metal powder fine particles. The present invention was achieved by discovering that it is possible to form a resin film without agglomeration of fine particles. The magnetic metal powder particles containing iron as a main component used in the present invention are produced by the method disclosed by the present inventors (:
Unexamined Japanese Patent Publication No. 56-114833, 57-96504, 57-106527, 57
-106526, 57-113202, 58-48612, etc.), that is, a shape-retaining component is applied to the surface layer of acicular iron oxyhydroxide fine particles, and after a washing, drying, and pulverizing process, calcining and gas phase catalytic reduction It can be produced by subjecting it to a reaction. The reduced iron powder fine particles contain P as a shape-retaining component,
Atomic weight ratio of Si and/or B to Fe: P/Fe=0.1/100 to 5/100, Si/Fe=0.1/100 to 5/100, B/Fe=0.1/100 to 5/100, It is preferable that the content be within the range of . When P, Si and/or B are less than this range, the ability to form polycondensation of toluene is low, and the effect of improving the aged deterioration characteristics of the target magnetic metal powder particles is small. In addition, if P, Si, and/or B exceed this range, the polycondensation reaction of toluene will proceed too strongly, and as a result, although the affinity with the binder resin will improve, the dispersibility in the coating process will decrease. I ended up doing it and I don't like it. As the aldehydes to be added, formaldehyde and its polymers, ie, paraform, etc. are most preferred because they are easy to use, but the use of aromatic aldehydes such as acetaldehyde and benzoic aldehyde is not limited. The amount added is from 0.01 to 5%, preferably from 0.5 to 3%, based on the weight ratio of the metal powder to the fine particles.
When less than 0.01% is added, the amount of toluene polycondensate formed is small, and the intended effect of improving the aging properties of fine metal powder particles is not significant. Moreover, if it is added in excess of 5%, the amount of toluene polycondensate formed becomes too large, causing problems in dispersibility in the coating process as described above. To form the toluene polycondensate, a general stirred reactor that can be pressurized can be used.
There are no other special conditions. That is, toluene to which a small amount of the aforementioned aldehydes had been added was charged into this reactor, and then the aforementioned reduced iron powder produced by gas phase catalytic reduction reaction was immersed therein, and stirring was continued for about 5 hours. A step is provided to completely wet the material with the solvent. Next, while stirring the reduced iron powder fine particles, 80~
The mixture was heated to 150°C and continued for 10 to 1 hour to complete the polycondensation reaction of toluene, and then the temperature was lowered to room temperature. If the reaction temperature is less than 80°C, the polycondensation reaction of toluene will hardly proceed, and if it exceeds 150°C, the reaction will proceed rapidly, making it difficult to achieve a uniform resin coating. Further, when the content of P, Si and/or B that has been expanded earlier is small, the reaction at a high temperature is efficient within this range, and when the content is large, the reaction at a low temperature is preferable. [Operation] In the method of the present invention, magnetic metal powder particles containing iron as a main component and containing a predetermined amount of P, Si, and/or B are placed and immersed in a toluene solvent containing a trace amount of aldehydes, and then subjected to a heating reaction. It is characterized by carrying out a polycondensation reaction of toluene. It was not previously known that toluene undergoes a polycondensation reaction on the surface of metal powder particles containing iron as a main component, and was discovered for the first time by the present inventors. This reaction was particularly noticeable in magnetic metal powder fine particle systems whose main component was iron and which contained a certain amount of P, Si, and/or B. It is generally known that toluene reacts with aldehydes using perchloric acid as a catalyst to form an oily oxygen-containing resin (Naokawa and Kakiuchi, "Formation of toluene-formaldehyde resin and its composition",
Journal of Industrial Chemistry, 65(10), 1679 (1962)). In the case of the already mentioned reduced iron powders, it is not known that strong acid sites such as perchloric acid occur, but they contain a certain amount of P, Si, and/or B by a mechanism similar to the so-called Tabe rule. In the case of a magnetic metal powder particle system containing iron as a main component, it is assumed that active sites as solid acids were formed and these acted as catalytic sites for the initiation of polycondensation. In this way, the polycondensation reaction with aldehydes will proceed after the ferromagnetic metal powder particles are sufficiently wetted with toluene, which is also a solvent, so that even in the case of fine metal powder particles, agglomeration due to adhesion and coating will occur. does not occur. In addition, since the resin formed can be substantially controlled by the amount of aldehydes added,
This is extremely convenient. The ferromagnetic metal powder particles coated with toluene polycondensate by the method of the present invention can be completely dried and powdered by removing the solvent by evaporation or other methods. Since the oxidation reaction is already completed, the oxidation reaction by air is efficiently controlled, and a preferable gradual oxidation is performed. Therefore, the magnetic properties after slow oxidation, especially the σs value, are stabilized at a high level, which is extremely preferable. In addition, it has good wettability with vinyl chloride/vinyl acetate copolymers that are often used as binder resins, improves dispersibility in the coating process, and improves the magnetic properties of the coating medium, especially the squareness ratio. Effects such as these are observed. Furthermore, when the processed media is subjected to an accelerated aging test in a high temperature and high humidity environment, the deterioration of magnetic properties, especially residual magnetic flux density (Br), is greatly improved. [Example] Hereinafter, the method and effects of the present invention will be described in detail with reference to Examples and Comparative Examples. Example 1 This example is an example showing an overview of the method of the present invention and its effects on ferromagnetic metal powder containing iron as a main component for audio use. <Manufacture of reduced iron powder> By the method described in JP-A No. 57-106527 and No. 57-96504, P and Si components were adjusted to a weight ratio of P/Fe=0.3/
Iron oxyhydroxide fine particles with acicular characteristics containing only 100 and Si/Fe=1.5/100 were synthesized. The shape of the Goe. particles has a specific surface area (SA) of 40.2 m ² /gr. calculated from the adsorption characteristics of N ₂ -gas, and a major axis diameter ( The ratio of the short axis diameter (:D) to the short axis diameter (:D), that is, the axial ratio (:L/D), was 15. Next, adhesion modification treatment with zinc borate was applied by the method described in JP-A-58-48612 (:B/Fe=
0.6/100 weight ratio), after drying and grinding process, _H2
- Gas phase catalytic reduction reaction with gas (temperature = 375℃,
It was made into reduced iron powder by gas space velocity= ^20Nm3 - ^H2 /Kgr-Fe.Hr.). A portion of the iron powder is extracted under an N ₂ − gas atmosphere, and
Specific surface area measured by N ₂ - gas method and vibration type magnetic property measurement made by Toei Kogyo Co., Ltd. Differences: When evaluation of magnetism was performed using VSM- type, SA = 35.2 m ² /gr., Hc
= 1205 Oe., σs = 182 emu/gr., Rs = 0.490. <Coating treatment with toluene polycondensate> A pressurizable reactor with an internal volume of 1 and equipped with a stirrer is prepared, and 400 g of toluene to which 1.12 g of commercially available paraform with a purity of 89.0% is added is charged. Next, 100g of the reduced iron powder was immersed, the reactor was sealed, and the atmosphere was replaced with N ₂ gas.
Continue stirring for about an hour. Next, the entire system is heated to 105°C, held there for 5 hours, then cooled to room temperature, and the reactor is unsealed. First, a portion of the solvent was recovered and subjected to infrared absorption spectroscopy, gas chromatography-mass coupled analysis, and nuclear magnetic resonance analysis, and the formaldehyde content was found to be 100 ppm or less. Next, take out a part of the reaction-treated iron powder and put it in _N2
- An attempt was made to recover the resin-like components in the waste solvent by adding washing with methyl ethyl ketone in a gas atmosphere, but it was not successful. Next, a portion of the iron powder that had been subjected to the same reaction treatment was taken out and put into the solution to dissolve the iron content, and when an attempt was made to recover the resin-like component in the solution, an oily substance was obtained. When this product was subjected to the same spectroscopic analysis as described above, a structure in which several toluene molecules were bonded with methylene was identified. From the above, formaldehyde polycondenses the toluene molecules used as a solvent on the surface of the reduced iron powder particles to form a structure of several nuclei, and furthermore, this polycondensate forms a strong coating on the surface of the iron powder particles. It turned out that it was morphed. <Air Drying of Treated Iron Powder> Next, 50g of the treated iron powder was transferred onto an enamel vat to a thickness of about 1 cm, and subjected to a solvent scattering treatment in the atmosphere. When the solvent odor was completely gone, the iron powder was collected and made into air-dried iron powder. When the physical properties of the air-dried iron powder were evaluated, SA=
33.3m ² /gr., Hc=1295Oe., σs=152emu/gr.,
It was Rs=0.496. <Evaluation of air-dried iron powder for paint/coating and tape properties> Collect 10g of the air-dried iron powder and put it into a pot with an internal volume of 550ml along with the following materials, and add paint made by Red Devil Co., Ltd., USA. Continue mixing and dispersing for 5 hours using a sheaker (as a dispersion media, 2
m/m diameter α-alumina beads). ●Salt vinyl acetate polymer manufactured by UCC, USA VAGH: 1.0
gr. ●Polyurethane NL-2448 manufactured by Mitsui Toatsu Chemical Co., Ltd.:
1.0gr. ●Phosphate ester AP-13 manufactured by Daihachi Chemical: 0.2gr. ●α-Alumina AKP-30 manufactured by Sumitomo Chemical: 0.2g
r. ●Solvent Toluene: 14gr., MEK: 14gr. After that, the dispersion media is separated and used as a magnetic paint.
Coat on a 12μ thick Toray polyester film: Lumirror (:12B-L100) using a precision coater using magnetic tape and an applicator. Thereafter, the coated film surface is smoothed by calender roll treatment, and then heat treated at 50°C for 2 days to complete the polyurethane curing reaction.
Cut it to 3.81m/m to make magnetic tape of the current compact cassette specification size. When the magnetic properties of the magnetic tape were measured and evaluated using the above-mentioned measuring device, Hc=1190 Oe, Br=3450 G, and Br/Bm=0.845, showing sufficient characteristic values. <Test for accelerating deterioration of magnetic tape> The magnetic tape was subjected to an aging acceleration treatment experiment for one week in an environment of 60° C. and 90% relative humidity to evaluate the magnetic properties, particularly the rate of deterioration of the residual magnetic flux density. The Br- value was 3345G, which was only 3.0% lower than the initial value. This value is sufficiently small for the deterioration characteristics exhibited by this type of magnetic medium, and can be said to exhibit excellent aging properties. Example 2 This example is an example showing an overview of the method of the present invention and its effects regarding a ferromagnetic metal powder containing iron as a main component for video use. <Manufacture of reduced iron powder> JP-A-57-106527 and 57-96504, further application filed in 1982
-209748, P, Si, and Mn
and Co components in a weight ratio of P/Fe=0.5/100, Si/Fe=2.0/100, and Mn/Fe=2.0/100.
We synthesized acicular iron oxyhydroxide fine particles containing only Co/Fe=2.0/100. The shape of the Goe. particles has a specific surface area (SA) of 10.5 m ² /gr. calculated from the adsorption characteristics of N ₂ -gas, and a major axis diameter ( :L) and the short axis diameter (:D), that is, the axial ratio (:L/D) was 20. Next, adhesion modification treatment with zinc borate was applied by the method described in JP-A-58-48612 (:B/Fe=
0.9/100 weight ratio), after drying and grinding process, _H2
- Gas phase catalytic reduction reaction with gas (temperature = 355℃,
It was made into reduced iron powder by gas space velocity= ^20Nm3 - ^H2 /Kgr-Fe.Hr.). A portion of the iron powder is extracted under an N ₂ − gas atmosphere, and
When we evaluated the specific surface area using the N ₂ -gas method and the magnetism using the magnetic property measuring device described above, we found that SA=
71.5m ² /gr., Hc=1425Oe., σs=170emu/gr.,
It was Rs=0.501. <Coating treatment with toluene polycondensate> A pressurizable reactor equipped with a stirrer having an internal volume of 1 is prepared, and 400 g of toluene to which 2.24 g of commercially available Polaform with a purity of 89.0% is added is charged. Then,
100g of the reduced iron powder is immersed in the reactor, the reactor is sealed, the atmosphere is replaced with _N2 gas, and stirring is continued for about 5 hours. Next, the entire system is heated to 105°C, held there for 5 hours, then cooled to room temperature, and the reactor is unsealed. First, a portion of the solvent was recovered and subjected to infrared series spectroscopy, gas chromatography-mass coupled analysis, and nuclear magnetic resonance analysis, and the formaldehyde content was found to be less than 100 ppm. Next, take out a part of the reaction-treated iron powder and put it in _N2
- An attempt was made to recover the resin-like components in the waste solvent by adding washing with methyl ethyl ketone in a gas atmosphere, but it was not successful. Next, a part of the iron powder that had been subjected to the same reaction treatment was taken out and put into a hydrochloric acid solution to dissolve the iron content. When an attempt was made to recover the resin-like component in the solution, an oily substance was obtained. When this product was subjected to the same spectroscopic analysis as described above, a structure in which several toluene molecules were linked with methylene and ether was identified. From the above, formaldehyde polycondenses the toluene molecules used as a solvent on the surface of the reduced iron powder particles to form a structure of several nuclei, and furthermore, this polycondensate forms a strong coating on the surface of the iron powder particles. It turned out that it was morphed. <Air Drying of Treated Iron Powder> Next, 50g of the treated iron powder was transferred onto an enamel vat to a thickness of about 1 cm, and subjected to a solvent scattering treatment in the atmosphere. When the solvent odor was completely gone, the iron powder was collected and made into air-dried iron powder. When the physical properties of the air-dried iron powder were evaluated, SA=
62.1m ² /gr., Hc=1505Oe., σs=135emu/gr.,
It was Rs=0.502. <Evaluation of air-dried iron powder for paint/coating and tape properties> Collect 10g of the air-dried iron powder and put it into a pot with an internal volume of 550ml along with the following materials, and add paint made by Red Devil Co., Ltd., USA. Continue mixing and dispersing for 5 hours using a sheaker (as a dispersion media, 2
m/m diameter α-alumina beads). ●Salt vinyl acetate polymer made by UCC, USA VAGH: 0.8
gr. ●Polyurethane NL-2448 manufactured by Mitsui Toatsu Chemical Co., Ltd.:
1.2gr. ●Phosphate ester AP-13 manufactured by Daihachi Chemical: 0.5gr. ●α-Alumina AKP-30 manufactured by Sumitomo Chemical: 0.2g
r. ●Solvent Toluene: 15gr., MEK: 15gr. After that, the dispersion media is separated and used as a magnetic paint.
Coat on a 13μ thick Toray polyester film: Lumirror (:13W-Q06S) using a precision coater using magnetic tape and an applicator. Thereafter, the coated film surface is smoothed by calender roll treatment, and then heat treated at 50°C for 2 days to complete the polyurethane curing reaction. It is cut into 1/2-inch pieces to make magnetic tape of current home video specification size. When the magnetic properties of the magnetic tape were measured and evaluated using the above-mentioned measuring device, Hc=1420 Oe, Br=2150 G, and Br/B=0.810, showing sufficient characteristic values. <Test for accelerating deterioration of magnetic tape> The magnetic tape was subjected to an aging acceleration treatment experiment for one week in an environment of 60° C. and 90% relative humidity to evaluate the magnetic properties, particularly the rate of deterioration of the residual magnetic flux density. The Br- value was 2060G, which was only 4.2% lower than the initial value. This value is sufficiently small for the deterioration characteristics exhibited by this type of magnetic medium, and can be said to exhibit excellent aging properties. Comparative Example 1 This comparative example shows the evaluation of the characteristics of a ferromagnetic metal powder containing iron as a main component for audio use without being subjected to toluene polycondensation treatment. <Manufacture of reduced iron powder> The reduced iron powder described in Example 1 was used. <Air Drying of Treated Iron Powder> Next, 50g of the treated iron powder was transferred onto an enamel vat to a thickness of about 1 cm, and subjected to a solvent scattering treatment in the atmosphere. When the solvent odor was completely gone, the iron powder was collected and made into air-dried iron powder. When the physical properties of the air-dried iron powder were evaluated, SA=
31.0m ² /gr., Hc=1280Oe., σs=145emu/gr.,
It was Rs=0.488. <Evaluation of air-dried iron powder into paint/coating and tape properties> 10g of the air-dried iron powder was collected and prepared as a paint in the same manner as described in Example 1, and thereafter coated, smoothed, and coated.
After post-annealing and cutting, it is made into a magnetic tape of the current compact cassette specification size. The magnetic properties of the magnetic tape were measured and evaluated using the measuring device described above, and found to be Hc = 1190 Oe, Br = 3000 G, and Br/Bm = 0.800. <Test for accelerating deterioration of magnetic tape> The magnetic tape was subjected to an aging acceleration treatment experiment for one week in an environment of 60° C. and 90% relative humidity to evaluate the magnetic properties, particularly the rate of deterioration of the residual magnetic flux density. The Br− value was 2850G, which was 5.0% lower than the initial value. (3.0% reduction in corresponding Example 1). Comparative Example 2 This Comparative Example is an example showing the evaluation of the characteristics of a ferromagnetic metal powder containing iron as a main component for video use when no toluene polycondensation treatment was applied. <Manufacture of reduced iron powder> The reduced iron powder described in Example 2 was used. <Air Drying of Treated Iron Powder> Next, 50g of the reduced iron powder was transferred onto an enamel vat to a thickness of about 1 cm, and subjected to a solvent scattering treatment in the atmosphere. Once the solvent odor was completely gone, the iron powder was collected and made into air-dried iron powder. When the physical properties of the air-dried iron powder were evaluated, SA=
60.5m ² /gr., Hc=1490Oe., σs=130emu/gr.,
It was Rs=0.501. <Evaluation of air-dried iron powder as paint/coating and tape properties> 10g of the air-dried iron powder was collected and prepared as a paint in the same manner as described in Example 2, and then coated, smoothed, and coated.
Add post annealing and cutting to the current home
It shall be a magnetic tape of video specification size. The magnetic properties of the magnetic tape were measured and evaluated using the above-mentioned measuring device, and were found to be Hc = 1410 Oe, Br = 2010 G, and Br/Bm = 0.780. <Test for accelerating deterioration of magnetic tape> The magnetic tape was subjected to an aging acceleration treatment experiment for one week in an environment of 60° C. and 90% relative humidity to evaluate the magnetic properties, particularly the rate of deterioration of the residual magnetic flux density. The Br− value was 1890G, which was 6.0% lower than the initial value. (4.2% reduction in corresponding Example 2). Comparative Example 3 This comparative example is an example showing the evaluation of the characteristics of a ferromagnetic metal powder containing iron as a main component for audio use, which is not based on the method of the present invention. <Manufacture of reduced iron powder> The well-known wet method, i.e., the neutralization reaction of ferrous sulfate and excess caustic soda, followed by the oxidation reaction with air, results in the production of reduced iron powder, which contains no trace impurities that are inevitably mixed in. We synthesized fine acicular iron oxyhydroxide particles. The shape of the Goe. particles has a specific surface area (SA) of 39.5 m ² /gr. calculated from the adsorption characteristics of N ₂ -gas, and a major axis diameter ( :L) and the minor axis diameter (:D), that is, the axial ratio (:L/D) was 12. Next, adhesion modification treatment with zinc borate was applied by the method described in JP-A-58-48612 (:B/Fe=
0.05/100 weight ratio), after drying and crushing process,
Gas phase catalytic reduction reaction with H ₂ − gas (temperature = 365
°C, gas space velocity = 20Nm ³ −H ² /Kgr−Fe.Hr)
It was made into reduced iron powder. A portion of the iron powder is extracted under an N ₂ − gas atmosphere, and
When evaluating the specific surface area using the N ₂ -gas method and the characteristics using a magnetic property measuring device, SA = 34.2
^m2 /gr., Hc=1200Oe., σs=180emu/gr., Rs
= 0.492. <Coating treatment with toluene polycondensate> A pressurizable reactor with an internal volume of 1 and equipped with a stirrer is prepared, and 400 g of toluene to which 1.12 g of commercially available paraform with a purity of 89.0% is added is charged. Then,
100g of the reduced iron powder is immersed in the reactor, the reactor is sealed, the atmosphere is replaced with _N2 gas, and stirring is continued for about 5 hours. Next, the entire system is heated to 105°C, held there for 5 hours, then cooled to room temperature, and the reactor is unsealed. First, a portion of the solvent was recovered and subjected to infrared series spectroscopy, gas chromatography-mass coupled analysis, and nuclear magnetic resonance analysis, and the formaldehyde content was found to be approximately 2000 ppm. Next, take out a part of the reaction-treated iron powder and put it in _N2
- An attempt was made to recover the resin-like components in the waste solvent by adding washing with methyl ethyl ketone in a gas atmosphere, but it was not successful. Next, a portion of the iron powder that had been subjected to the same reaction treatment was taken out and put into the solution to dissolve the iron content, and when an attempt was made to recover the resin-like components in the solution, a very small amount of oil-like material was obtained. When this product was subjected to the same spectroscopic analysis as described above, a structure in which several toluene molecules were bonded with methylene was identified. From the above, it can be seen that although the surface layer of ferromagnetic metal powder fine particles containing iron as a main component that is not produced by the method of the present invention is bound to form a strong film, toluene molecules, which were used as a solvent by formaldehyde, It was found that polycondensation proceeded only slightly. <Air Drying of Treated Iron Powder> Next, 50g of the treated iron powder was transferred onto an enamel vat to a thickness of about 1 cm, and subjected to a solvent scattering treatment in the atmosphere. Once the solvent odor was completely gone, the iron powder was collected and made into air-dried iron powder. When the physical properties of the air-dried iron powder were evaluated, SA=
30.0m2 ^/ gr., Hc=1280Oe., σs=140emu/gr.,
It was Rs=0.485. <Evaluation of making air-dried iron powder into paint, coating, and tape properties> 10g of the air-dried iron powder was collected and made into paint, coating, smoothing, post-annealing, and cutting in the same manner as described in Example 1. In addition, it becomes a magnetic tape of the current compact cassette specification size. The magnetic properties of the magnetic tape were measured and evaluated using the above-mentioned measuring device, and found to be Hc = 1180 Oe, Br = 3020 G, and Br/Bm = 0.810. <Test for accelerating deterioration of magnetic tape> The magnetic tape was subjected to an aging acceleration treatment experiment for one week in an environment of 60° C. and 90% relative humidity to evaluate the magnetic properties, particularly the rate of deterioration of the residual magnetic flux density. The Br− value was 2865G, which was 5.1% lower than the initial value. The above results are summarized in Table-1.

【table】

【table】

[Table] *Note: For units, see main text.
[Effects] The effects and effects of the present invention can be summarized as follows based on the results of Examples and Comparative Examples shown in comparison thereto. That is, in ferromagnetic metal powder fine particles as a magnetic material in a magnetic recording medium suitable for high-density magnetic recording, the metal powder fine particles mainly contain iron containing a predetermined amount of P, Si, and/or B. It is a fine particle system with
After production by gas-phase catalytic reduction reaction, the surface layer of the metal fine particles is coated with a polycondensate of toluene by pouring into a toluene solvent to which a predetermined amount of aldehydes has been added, and heating and maintaining the metal at a predetermined temperature. (1) Regarding the metal powder particles themselves, gradual oxidation by solvent evaporation is carried out extremely mildly, and the magnetic properties after gradual oxidation, sometimes the saturation magnetization, are maintained at a sufficiently high level; (2) ) The affinity for paint resins improves, and as a result, the magnetic properties at the stage of media processing, especially the squareness ratio, are greatly improved. It can be said that it has been found that this has a significant improvement effect on aging deterioration as a reliability index. As described above, the method of the present invention provides a ferromagnetic metal powder containing iron as a main component and having significantly improved properties for audio and video applications, and a method thereof.

Claims (1)

[Claims] 1. P coated with toluene polycondensate and
Ferromagnetic metal powder whose main component is Fe containing Si and/or B. 2 The content of P, Si, and/or B is the polymerization ratio with Fe: P/Fe=0.1/100 to 5/100, Si/Fe=0.1/100 to 5/100, B/Fe=0.1/ A ferromagnetic metal powder containing Fe as a main component according to claim 1, which is in the range of 100 to 5/100. 3. Acicular iron oxyhydroxide particles modified with a shape-retaining component are made into reduced iron powder by a gas phase catalytic reduction reaction using a reducing gas, and then immersed in a toluene solvent containing a small amount of aldehyde. , 80
Stabilized iron-based ferromagnetic metal powder with improved affinity for coating resins, which is heated to ~150°C to coat the surface layer of each reduced iron powder fine particle with toluene polycondensate. manufacturing method. 4. The method for producing ferromagnetic metal powder according to claim 3, wherein the shape-retaining component contains P, Si, and/or B.