JPS6239203B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a magnetic material for magnetic recording such as audio and video, and in particular, has acicular crystals that are optimal as a magnetic material for video, has uniform particle size, does not contain dendritic particles, and has As a result, the particles coated with Ni and/or Al, or coated with P compound and Si compound and Ni and/or Al, have a large bulk density, are fine particles, have a large specific surface area, and have a high coercive force Hc and a large saturation magnetization σs. The present invention also relates to a method for producing acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with an Al compound. When producing a magnetic recording medium, containing Si, Cr, Ni and Mg coated with Ni and/or Al obtained according to the present invention, or coated with a P compound and a Si compound and a Ni and/or Al compound. When acicular iron alloy magnetic particles are used, they have acicular crystals, uniform particle size, and no dendritic particles, resulting in a large bulk density and fine particles. Large specific surface area and high coercive force Hc
Due to the large saturation magnetization σs, the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film are extremely excellent, and the noise level generated during recording and reproduction of magnetic tape is extremely low. low,
Moreover, an excellent magnetic recording medium with high output characteristics can be obtained. In recent years, magnetic recording and reproducing devices for video and audio have become increasingly compact and lightweight. VTRs are being actively developed with the aim of reducing their weight, and on the other hand, demands for higher performance and higher density recording of magnetic tape, which is a magnetic recording medium, are increasing. In other words, magnetic recording media are required to have high image quality, high output characteristics, especially improved frequency characteristics, and lower noise levels. filling property,
It is necessary to improve the smoothness of the tape surface, and there is an increasing demand for an improvement in the S/N ratio. These characteristics of magnetic recording media are closely related to the magnetic materials used in magnetic recording media.
For example, Nikkei Electronics (1976) May 3
In the document "Recent Advances in Magnetic Tapes for Video and Audio" published on pages 82 to 105 of the Japanese issue, "Video Tape" described on pages 83 to 84.
The main characteristics of recorder image quality that change depending on the tape are the S/N ratio, chroma noise, and video frequency characteristics. ...These quantities representing image quality are determined by the electromagnetic conversion characteristics of the tape and head system, and the electromagnetic conversion characteristics have a correlation with the physical characteristics of the tape. Furthermore, the physical properties of the tape are largely determined by the magnetic material. It is clear from the statement, etc. As described above, the various characteristics of magnetic recording media, such as high image quality, are closely related to the magnetic materials used, and there is a strong desire to improve the characteristics of magnetic materials. The relationship between the various characteristics of the magnetic recording medium and the characteristics of the magnetic material used will now be detailed as follows. In order to obtain high image quality as a magnetic recording medium for video, it is clear from the above description of Mekyo Electronics that the video S/N ratio, chroma,
Improvements in noise and video frequency characteristics are required. In order to improve the video S/N ratio, it is necessary to make the magnetic particles finer, improve their dispersibility in peaks, improve orientation and filling properties in the coating film, and improve the surface of the magnetic recording medium. It is important to improve the smoothness of the surface. This fact is based on the aforementioned Nikkei Electronics, p. 85, ``The physical quantities of the tape that are related to the SN ratio (CN ratio) of the luminance signal are the average number of particles per unit volume, their dispersion state (dispersibility), and the surface If the surface properties and dispersibility are constant, the SN ratio will improve in proportion to the square root of the average number of particles, so the smaller the particle volume and the higher the degree of filling, the more advantageous is the magnetic powder. It is clear from the description. That is, as one method for improving the video S/N, it is important to reduce the noise level caused by the magnetic recording medium, and for this purpose, as is clear from the above description, it is necessary to reduce the noise level caused by the magnetic recording medium. It is known that a method of reducing the particle size of acicular magnetic particles is effective. The value of the specific surface area of the magnetic particles is often used as a general method of expressing the particle size of the magnetic particles, but the noise level caused by the magnetic recording medium tends to decrease as the specific surface area of the magnetic particles increases. This is also generally known. This phenomenon can be seen, for example, in the Technical Research Report of the Institute of Electronics and Communication Engineers.
This is shown in "Fig 3" on page 27, 23-9 of MR81-11. "Fig. 3" is a diagram showing the relationship between the specific surface area of particles and the noise level in Co-coated acicular maghemite particle powder, and the noise level decreases linearly as the specific surface area of the particles increases. This relationship also applies to the acicular iron magnetic particles and the acicular iron alloy magnetic particles. In order to improve the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film, it is necessary that the magnetic particles dispersed in the vehicle have acicular crystals and have a uniform particle size. It is required that dendritic particles are not mixed therein, and as a result, the bulk density is high. Next, in order to improve chroma noise, it is important to improve the surface properties of magnetic recording media, and for this purpose, magnetic particle powder with good dispersibility and orientation is recommended. It is required to have acicular crystals, uniform particle size, no dendritic particles, and, as a result, a high bulk density. This fact is based on the above-mentioned Nikkei Electronics, page 85, which states, ``Chroma noise is caused by relatively long-period roughness on the tape surface and is closely related to coating technology. It is clear from the statement, "It is easier to improve the surface properties." Furthermore, in order to improve the video frequency characteristics, it is necessary that the magnetic recording medium has a high coercive force Hc and a high saturation residual magnetic flux density Br. In order to increase the coercive force Hc of the magnetic recording medium, it is required that the coercive force Hc of the magnetic particles be as high as possible. The saturated residual magnetic flux density Br is determined by the saturation magnetization σs of the magnetic particles as large as possible, and depends on the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film. This fact is based on Nikkei Electronics No. 84~
On page 85, "The maximum output is the saturation residual magnetic flux density of the tape.
Determined by Br and Hc and effective spacing. If Br is large, more magnetic flux will enter the reproducing head and the output will increase. …. Increasing Hc reduces self-demagnetization and increases output. ……. To increase the Br of the tape, the saturation magnetization Is (σs) that the magnetic material has in a perfect state (for example, in a single crystal state)
First of all, it is basic that it is large. ……. Even if the material is the same, Br changes depending on the degree of filling, which indicates the proportion of magnetic powder. In addition, the squareness ratio (residual magnetization amount/
Since it is proportional to the saturation magnetization (amount of saturation magnetization), it is required that this is large. ……. In order to increase the squareness ratio, it is advantageous to use magnetic powder that has uniform particle sizes, a large acicular ratio, and excellent magnetic field orientation. ...”
It is clear from the descriptions such as. As detailed above, improvements in high image quality and high output characteristics, especially frequency characteristics, of magnetic recording media, and
In order to meet the demands for higher performance such as lower noise levels, the magnetic particles used must have acicular crystals, uniform particle size, and no dendritic particles. In addition, it is necessary to have a large specific surface area, a high coercive force Hc, and a large saturation magnetization σs. By the way, magnetic materials conventionally used in magnetic recording media include magnetite, maghemite,
Magnetic powder such as chromium dioxide, these magnetic powders have saturation magnetization σs70~85emu/g and coercive force.
It has an Hc of 250 to 500 Oe. In particular, the σs of the above oxide magnetic particles is the maximum
It is about 85emu/g, and generally σs70~
80 emu/g is the main reason for limiting the reproduction output and recording density. Furthermore, Co-magnetite and Co containing Co
-Maghemite magnetic powder is also used, but these magnetic particles have a high coercive force Hc of 400 to 800 Oe, but on the other hand, the saturation magnetization σs is low at 60 to 80 emu/g. . Recently, there has been active development of magnetic particles with characteristics suitable for high output and high density recording, that is, magnetic particles with large saturation magnetization σs and high coercive force. The powder is generally acicular crystals obtained by heating and reducing acicular crystal hydrated iron oxide particles, acicular iron oxide particles, or particles containing a different metal other than iron in a reducing gas at about 350°C. It is iron magnetic particle powder or acicular iron alloy magnetic particle powder. These acicular iron magnetic particles or acicular iron alloy magnetic particles have significantly larger saturation magnetization σs than conventionally used magnetic iron oxide particles and Co-containing magnetic iron oxide particles, and have a coercive force.
It is characterized by high Hc, and when coated as a magnetic recording medium, it has a large residual magnetic flux density Br.
Because it has a high coercive force Hc, it can achieve high density recording and high output characteristics, so it has attracted attention and has been put into practical use in recent years. In the method for producing the acicular ferromagnetic particles or acicular ferroalloy magnetic particles, the higher the temperature of heating and reduction in the reducing gas, the higher the saturation magnetization of the acicular ferromagnetic particles or the acicular ferromagnetic particles. It is known that acicular iron alloy magnetic particle powders can be obtained. On the other hand, the higher the heating reduction temperature in a reducing gas, the higher the saturation magnetization of acicular iron magnetic particles or acicular iron alloy magnetic particles can be obtained. ,
The deformation of the acicular crystal grains of the acicular ferromagnetic particles or the acicular ferromagnetic particles and the sintering between the particles and the particles become significant, and the resulting acicular ferromagnetic particles or acicular ferromagnetic particles become The coercive force of the crystalline iron alloy magnetic particles will be extremely reduced. That is, the coercive force of the acicular iron magnetic particles or the acicular iron alloy magnetic particles largely depends on the shape anisotropy. Acicularity is one of the important properties. As mentioned above, acicular iron magnetic particles or acicular iron alloy magnetic particles having high coercive force Hc and large saturation magnetization σs have acicular crystals, uniform particle size, and dendritic particles. In order to obtain magnetic particle powder with such characteristics, it is necessary that the starting material acicular crystal α-
It is necessary that the FeOOH particles have a uniform particle size and do not contain dendritic particles.Next, how can we maintain and inherit this particle morphology, especially needle-like crystals, by heating and reducing them to produce needle-like crystals? The major issue is whether to use iron magnetic particles or acicular iron alloy magnetic particles. First, the production of acicular α-FeOOH particle powder, which is a starting material, will be described. Conventionally, acicular crystals α-
The most typical known method for producing FeOOH particles is to add an equivalent or more alkaline solution to an aqueous ferrous salt solution to obtain an aqueous solution containing Fe(OH) ₂ at a pH of 11 or higher and a temperature of 80°C or lower. Acicular α-FeOOH particles are obtained by performing an oxidation reaction. Acicular crystals α- obtained by this method
FeOOH particles have a needle-like shape with a length of about 0.5 to 1.5μ, but they also contain dendritic particles, and in terms of particle size, they cannot be said to have a uniform particle size. hard. The reason why acicular α-FeOOH particles having asymmetric particle sizes and dendritic particles are generated will be discussed below. Generally, the generation of acicular α-FeOOH particles involves the generation of acicular α-FeOOH nuclei and the acicular α-FeOOH particles.
It consists of two stages of FeOOH nucleus growth. Acicular α-FeOOH nuclei are generated by the reaction between dissolved oxygen and Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkali, but the contact reaction with dissolved oxygen is partially induced. , and because it is non-uniform, the needle-like crystal α-
The generation of FeOOH nuclei and the growth of the acicular α-FeOOH nuclei occur simultaneously, and many new nuclei are generated until the α-FeOOH production reaction is completed, so that the resulting acicular α-FeOOH The particles are asymmetric in particle size and contain a mixture of dendritic particles. Further, the reaction iron (Fe ²⁺ ) concentration in the reaction aqueous solution in the above method is usually about 0.2 mol/,
Moreover, it takes a long time to generate acicular α-FeOOH particles. That is, according to the above method, even at a low reaction iron concentration of about 0.2 mol/min, the particle size is asymmetric and needle-shaped α-
FeOOH particles were easily generated. Next, how to reduce the particle shape of the acicular α-FeOOH particles by heating and reducing them while retaining and inheriting the acicular crystals to form acicular ferromagnetic particles or acicular iron alloy magnetic particles. The question is whether to do so. The causes of deformation of the acicular grains and sintering of the grains and of each other during the thermal reduction process will be explained below. Generally, acicular α-Fe ₂ O ₃ is obtained by heating and dehydrating acicular α-FeOOH particles at a temperature around 300°C.
The particles retain and inherit needle-like crystals, but on the other hand, there are many pores generated on the particle surface and inside the particles due to dehydration, and the growth of single particles is not sufficient. , the degree of crystallinity is very small. When thermal reduction is performed using such acicular α-Fe ₂ O ₃ particles, uniform particle growth of a single particle is difficult to occur because the physical change is rapid. Therefore, it is considered that sintering of the particles and the particles among themselves occurs in the portion where the particle growth of a single particle occurs rapidly, and the particle shape becomes easily distorted. Furthermore, during the thermal reduction process, rapid volumetric contraction from the oxide to the metal occurs, making the particle shape more likely to collapse. Therefore, in order to prevent particle shape deformation and sintering between particles and particles during the thermal reduction process, relatively mild reduction conditions that do not cause rapid particle growth of single particles, such as 300~ Reduction may be carried out within a temperature range of 500°C. In addition, in order to carry out the reduction efficiently, prior to the thermal reduction process, the crystallinity can be improved by growing a single particle of acicular α-Fe ₂ O ₃ particles sufficiently and uniformly. The acicular α-Fe ₂ O ₃ particles may have an increased degree of substantially high density and retain and inherit the acicular structure of the acicular α-FeOOH particles. A method for obtaining substantially high-density acicular α-Fe ₂ O ₃ particles with an increased degree of crystallinity is to heat-treat acicular α-FeOOH particles in a non-reducing atmosphere. Are known. Generally, the higher the heat treatment temperature in a non-reducing atmosphere, the more effectively the acicular α-Fe ₂ O ₃ particles obtained by heating and dehydrating acicular α-FeOOH particles become single particles. It is possible to measure the particle growth of
Therefore, the degree of crystallinity can also be increased, but
On the other hand, it is known that when the heat treatment temperature exceeds 650°C, sintering progresses and the acicular crystal grains break down. Therefore, acicular α-Fe ₂ O ₃ particles are obtained which have a substantially high density with an increased degree of crystallinity and retain and inherit the acicular structure of the acicular α-FeOOH particles. A known method for this purpose is to coat the surface of acicular α-FeOOH particles with an organic or inorganic compound that has an anti-sintering effect prior to heat treatment in a non-reducing atmosphere. . The present inventor has been involved in the production and development of acicular crystal magnetic particles for many years, and in the course of his research, he discovered acicular crystals coated with a Si compound that has a sintering prevention effect. We have already developed a method to produce α-FeOOH particles. For example, as described below. That is, the acicular α-FeOOH particles coated with the P compound and the Si compound are obtained by separating the acicular α-FeOOH particles produced by a wet reaction between a ferrous salt aqueous solution and an alkaline aqueous solution from the mother liquor. Suspend in water, add 0.1 to 2 wt% (in terms of PO ₃ ) of phosphate to the acicular α-FeOOH particles while the pH value of the suspension is 8 or higher, and then add 0.1 to 7.0 wt % of phosphate to the acicular α-FeOOH particles. %
It can be obtained by adding a water-soluble silicate (in terms of SiO ₂ ) and then adjusting the PH value to 3-7. The above method will be explained as follows. In general, acicular α-FeOOH particles form a group of highly entangled and bonded particles during the crystal growth process in the reaction mother liquor during a wet reaction. If a group of acicular α-FeOOH particles is coated with an anti-sintering agent, it will only prevent further sintering and eliminate the entanglement and bonds that occur during the crystal growth process in the reaction mother liquor. is in the same state, so the intertwined and bonded needle crystals α−
The acicular iron alloy magnetic particles obtained by heat-treating FeOOH particles in a non-reducing atmosphere and then thermally reducing the particles also become entangled and bonded together. Such particles are characterized by their dispersibility in the vehicle,
It cannot be said that the orientation and filling properties in the coating film are sufficient. Therefore, before coating the acicular α-FeOOH particles with a Si compound, it is necessary to disentangle the entanglements and bonds generated during the crystal growth process in the reaction mother liquor. After separating the acicular α-FeOOH particles from the mother liquor, suspend them in water, and add 0.1 to 2 wt% to the acicular α-FeOOH particles when the pH value of the suspension is 8 or higher.
By adding phosphate (in terms of PO ₃ ), it is possible to loosen the entanglements and bonds of the acicular α-FeOOH particles. Acicular α-FeOOH particles are acicular α-
After FeOOH particles are produced, they may be filtered from the reaction mother liquor and washed with water using a conventional method. The concentration of the suspension is preferably 20 wt% or less based on water. If it is 20 wt% or more, the viscosity of the suspension will be too high, and the effect of disentangling entanglements caused by the addition of phosphate will be insufficient. The amount of phosphate added is determined by adjusting the amount of acicular crystals α-
If it is 0.1 to 2 wt% in terms of PO ₃ based on the FeOOH particles, it is possible to disentangle the particles and uniformly disperse the particles. The added phosphate is adsorbed on the surface of the needle-like α-FeOOH particles, and almost all of it is absorbed into the formed needle-like α-FeOOH particles.
Contained in FeOOH particles. If the amount added is less than 0.1wt%, the effect of addition is not sufficient. On the other hand, when the amount added is 2 wt% or more, the particles can be dispersed, but since the particles are uniformly and strongly dispersed in the liquid, it is difficult to separate them by filtration from the liquid, which is not appropriate. Examples of the phosphate to be added include sodium metaphosphate and sodium pyrophosphate. The pH value of the suspension to which phosphate is added must be 8 or higher. If the PH value is 8 or less, 2wt% or more of phosphate must be added to disperse the particles, and as mentioned above, adding 2wt% or more of phosphate will cause problems in filtration separation. This is not desirable because it causes harmful effects. Next, regarding the Si compound film formed on the particle surface of the acicular α-FeOOH particles, the formation of the Si compound film must be done by disentangling the acicular α-FeOOH particles using a phosphate. must be done after When adding the water-soluble silicate, the pH value of the suspension is preferably 8 or higher. If water-soluble silicate is added when the pH value of the suspension is below 8, it will precipitate as solid SiO ₂ at the same time it is added, and it will form on the particle surface. It cannot be efficiently formed as a thin film. Therefore, water-soluble silicate is added when the pH value of the suspension is 8 or more, and after being mixed uniformly into the suspension, the pH value is adjusted to the range where SiO ₂ precipitates, that is, the pH value is If adjusted to 3 to 7, SiO ₂ will precipitate on the surface of the particles to form a film. The amount of water-soluble silicate to be added is 0.1 to 7.0wt in terms of SiO ₂ to the acicular α-FeOOH particles.
%. The added water-soluble silicate is acicular crystal α-
It is precipitated and adsorbed on the FeOOH particle surface, and almost the entire amount is contained in the produced acicular α-FeOOH particles. If the amount is less than 0.1wt%, the effect of addition will not be noticeable, and if it is more than 7.0wt%, it is possible to obtain acicular iron alloy magnetic particles with excellent acicular crystals, but the purity is low. As a result, the saturation magnetic flux density decreases, which is undesirable. Note that examples of the water-soluble silicate to be added include sodium silicate and potassium silicate. Next, acicular crystal α containing Si, Cr, Ni and Mg
- Conditions for forming a film on FeOOH particles with a P compound and a Si compound and then separating the particles by filtration from a suspension will be described. When using ordinary filtration means, if the particles are uniformly and strongly dispersed in the liquid, this may cause leakage of the filter cloth, clogging of the filter cloth, and other factors that may deteriorate the filtration efficiency. In order to increase the filtration efficiency, it is necessary that the particles dispersed by the addition of the phosphate described above are appropriately aggregated. When the amount of phosphate added is within the range of 0.1 to 2 wt%, adjusting the pH of the suspension to 3 to 7 will increase the viscosity of the suspension, causing particle aggregation and making it easier to filter. It can be carried out. Furthermore, even if the pH value of the suspension is set to 3 or less, it is possible to aggregate the acicular α-FeOOH particles, adsorb phosphate, and form the SiO ₂ film described above, but this This is not desirable as it may cause problems and quality problems (dissolution, etc.). In addition, in order to adjust the pH to 3-7, use acetic acid, sulfuric acid,
Phosphoric acid etc. can be used. Acicular α-FeOOH coated with P compound and Si compound obtained as explained above
The acicular α-Fe ₂ O ₃ particles obtained by heat-treating the particles in a non-reducing atmosphere have a substantially high density with an increased degree of crystallinity, and are free from particle entanglement. It retains and inherited excellent needle-like crystals with no interlocking or bonding. The temperature range of the heat treatment in a non-reducing atmosphere is preferably 500 to 900°C. When the heat treatment temperature in a non-reducing atmosphere is 500℃ or less, the degree of crystallinity of the acicular α- _Fe2O3 particles coated with P and _Si compounds is increased. It is hard to say that it is a dense particle, and the temperature is 900℃.
If this is the case, deformation of the acicular crystal grains and sintering of the grains and the grains may occur. Also,
Industrial, requiring highly accurate equipment and advanced technology,
It's not economical. In view of the above, the present inventor has developed a material that has acicular crystals, uniform particle size, no dendritic particles, large specific surface area, high coercive force Hc, and large saturation. Various studies have been conducted to obtain acicular iron alloy magnetic particles having magnetization σs. The present inventor then oxidized the suspension containing Fe(OH) ₂ with a pH of 11 or higher, which was obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution, by passing an oxygen-containing gas through the suspension to form a acicular shape. In producing crystalline α-FeOOH particles, a water-soluble silicate is added to any of the suspensions before the alkali aqueous solution oxygen and gas contained therein are passed through to perform the oxidation reaction.
Add 0.1 to 1.7 atomic% in terms of Si to Fe,
and the ferrous salt aqueous solution, the alkaline aqueous solution, the suspension before an oxidation reaction is carried out by passing an oxygen-containing gas through the solution, and the reaction solution in which an oxidation reaction is carried out by passing an oxygen-containing gas through the suspension. Water-soluble chromium salt in either solution is 0.1 to Cr equivalent to Fe.
Si, Cr, Ni and Mg-containing acicular α-FeOOH particles, and the Si, Cr,
Acicular α-FeOOH particles containing Ni and Mg, or acicular α-Fe ₂ O ₃ particles containing Si, Cr, Ni and Mg obtained by heating and dehydrating the same, or
Acicular crystal α- containing Si, Cr, Ni and Mg
Ni and/or Ni _and / _or
Or, if it is coated with an Al compound and then heated and reduced in a reducing gas while retaining and inheriting needle-like crystals, it has needle-like crystals, uniform particle size, and no dendritic particles. , there is no particle entanglement, etc., and the specific surface area is large, and the degree of crystallinity on the particle surface and inside the particle is increased, and the density is substantially high.Moreover, it has a high coercive force Hc and a large saturation magnetization σs. The present invention was completed by discovering that an acicular iron alloy magnetic particle powder for magnetic recording having the following properties can be obtained. That is, the present invention provides a PH containing Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution.
In producing acicular α-FeOOH particles by passing an oxygen-containing gas through the suspension of 11 or more to oxidize, A water-soluble silicate is added in an amount of 0.1 to 1.7 atomic % based on Fe in terms of Si, and the ferrous salt aqueous solution, the alkaline aqueous solution,
Adding a water-soluble chromium salt to Fe in either the suspension before an oxidation reaction is carried out by passing an oxygen-containing gas through it, or the reaction solution before an oxidation reaction is carried out by passing an oxygen-containing gas through the solution. 0.1 to 5.0 in Cr conversion
Si, Cr, Ni and Acicular α-FeOOH particles containing Mg are generated, and the Si, Cr, Ni
and Mg-containing acicular α-FeOOH particles or Si, Cr, Ni and
A suspension containing Mg-containing acicular α-Fe ₂ O ₃ particles is prepared, and 0.5 to 10.0 atomic % of Ni and/or Al is added to Fe in the suspension. By adding and mixing compounds, acicular α-FeOOH particles containing Si, Cr, Ni and Mg coated with Ni and/or Al compounds or acicular crystals containing Si, Cr, Ni and Mg can be produced. After forming α-Fe ₂ O ₃ particles, heat reduction is performed in a reducing gas to produce Ni and/or
Obtain acicular iron alloy magnetic particles containing Si, Cr, Ni and Mg coated with an Al compound, or if necessary, acicular α-FeOOH particles containing the above Si, Cr, Ni and Mg. Or acicular crystals α containing Si, Cr, Ni and Mg obtained by heating and dehydrating this
- Fe ₂ O ₃ particles are suspended in water, and when the pH value of the suspension is 8 or higher, 0.1 to 2 wt% (PO ₃ ) of phosphate is added to form a dispersion, and then 0.1 to 7.0 wt% (SiO ₂
By adding and mixing 0.5 to 10.0 at. Acicular crystal α containing Si, Cr, Ni and Mg coated with Al compound
- FeOOH particles or acicular α-Fe ₂ O ₃ particles containing Si, Cr, Ni and Mg are formed, and then heated and reduced in a reducing gas to form P and Si compounds and Ni and/or
or Si, Cr, Ni and Mg coated with Al compounds
or, if necessary, add Si, Cr, Ni and
0.1 for acicular α-FeOOH particles containing Mg
Acicular crystals α containing Si, Cr, Ni and Mg coated with P and Si compounds by adding ~7.0 wt% (calculated as _SiO2 ) of water-soluble silicate
- Obtain FeOOH particles and place the particles in a non-reducing atmosphere.
Acicular α- crystals containing Si, Cr, Ni and Mg coated with P and Si compounds densified by heat treatment in the temperature range of 500-900℃
Acicular iron alloy containing Si, Cr, Ni, and Mg, which is formed into Fe ₂ O ₃ particles and then heated and reduced in a reducing gas and coated with a P compound, a Si compound, and a Ni and/or Al compound. To form magnetic particles, either 0.5 to 10.0 atomic % of Ni and/or Al compounds are added to the dispersion liquid in terms of Ni and/or Al based on Fe, or densified P after the above heat treatment is added. Acicular α-Fe ₂ O ₃ particles containing Si, Cr, Ni and Mg coated with compounds and Si compounds are suspended in water,
0.5 in terms of Ni and/or Al relative to Fe in the suspension
By adding and mixing ~10.0 at% Ni and/or Al compound and coating with Ni and/or Al compound, Si coated with P compound and Si compound and Ni and/or Al compound This is a method for producing acicular iron alloy magnetic particles for magnetic recording, which comprises obtaining acicular iron alloy magnetic particles containing Cr, Ni, and Mg. Next, the technical background that led to the completion of the present invention and the structure of the present invention will be described. As described above, the acicular α-FeOOH particles produced by the conventional method in the alkaline region of pH 11 or higher have asymmetric particle sizes and contain dendritic particles. For many years, the inventor has developed needle-shaped α-FeOOH.
We are involved in the production and development of particle powders, and in the process, we are developing acicular α- crystals with uniform particle size and no dendritic particles.
We have already established a technology that allows us to obtain FeOOH particles. That is, acicular α-FeOOH particles with uniform particle size and no dendritic particles were obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution.
In a method of generating acicular α-FeOOH particles by passing an oxygen-containing gas through a suspension containing Fe(OH) ₂ for oxidation, the oxidation reaction is carried out by passing the alkaline aqueous solution and the oxygen-containing gas through the suspension. It can be obtained by adding water-soluble silicate in an amount of 0.1 to 1.7 at.
8461, Special Publication No. 55-32652). Acicular α-FeOOH particles conventionally obtained in an alkaline region with a pH of 11 or higher generally have asymmetric particle sizes and contain dendritic particles;
The Fe(OH) ₂ floc, which is the precursor of FeOOH particles, is asymmetric, and at the same time, the Fe(OH) ₂ particles themselves that make up the Fe(OH) ₂ floc are asymmetric. Generation of acicular α-FeOOH core particles from an aqueous solution containing Fe(OH) ₂ and the acicular α
This is due to the fact that -FeOOH core particles grow simultaneously, and new nuclei are generated many times until the α-FeOOH production reaction is completed. As mentioned above, acicular α-FeOOH particles are produced by passing an oxygen-containing gas through a suspension containing Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution to oxidize it. In producing the aqueous alkaline solution and oxygen-containing gas, water-soluble silicate is added to any of the suspensions before the oxidation reaction is carried out by passing the aqueous alkali solution and oxygen-containing gas through the aqueous alkali solution and the oxygen-containing gas.
When added to 1.7 at%, Fe
The (OH) ₂ flocs are made into sufficiently fine and uniform flocs, and the Fe(OH) ₂ flocs are also formed.
The Fe(OH) ₂ particles themselves can be made into sufficiently fine and uniform particles, and furthermore, water-soluble silicate
Acicular crystals α−FeOOH from an aqueous solution containing Fe(OH) ₂
Due to the effect of suppressing the oxidation reaction during particle generation, generation of acicular α-FeOOH core particles and growth of the acicular α-FeOOH core particles can be performed in stages. Therefore, the particle size is uniform, and the acicular crystal α-
FeOOH particles can be obtained. The water-soluble silicates used in the above method include sodium and potassium silicates. The amount of water-soluble silicate added to the alkaline aqueous solution is 0.1 to 1.7 atomic % based on Fe in terms of Si. Almost all of the added water-soluble silicate is contained in the produced acicular α-FeOOH particles. If the amount of water-soluble silicate added is less than 0.1 atomic % based on Fe in terms of Si, the effect of obtaining acicular grains with uniform grain size and no dendritic grains will not be sufficient; If it is more than atomic %, granular magnetite particles will be mixed in. The above-mentioned acicular α-FeOOH particles having a uniform particle size and no dendritic particles, or acicular α-Fe ₂ O ₃ particles obtained by heating and dehydrating the acicular α-FeOOH particles. or the above needle-like α-FeOOH
Highly densified acicular α-Fe ₂ O ₃ particles obtained by heat-treating particles in a non-reducing atmosphere are used as a starting material, and acicular particles obtained by heating and reducing the starting material are used as starting materials. The crystalline iron alloy magnetic particles also have a uniform particle size and do not contain dendritic particles, but as a result, they have a large bulk density, have good dispersibility when made into paints, and are easily dispersed in paint films. Although it has the characteristics of high filling properties and a large residual magnetic flux density Br, its specific surface area is at most about 20 m ² /g. Therefore, as a result of various studies on methods for improving the specific surface area of Si-containing acicular iron alloy magnetic particles with uniform particle size and no dendritic particles, the inventors have found that the particle size is uniform. It is symmetrical,
In the production of acicular α-FeOOH particles containing Si without dendritic particles, Fe(OH) is prepared before the oxidation reaction by passing through a ferrous salt aqueous solution, an alkaline aqueous solution, and an oxygen-containing gas. ₂ A water-soluble chromium salt is added to either the suspension or the reaction solution in which an oxidation reaction is carried out by passing oxygen-containing gas through the suspension, and the resulting acicular crystals containing Si and Cr α-
We have found that when FeOOH particles are thermally reduced, the specific surface area of Si-containing acicular iron alloy magnetic particles can be improved. This phenomenon will be explained as follows by extracting some of the many examples carried out by the present inventor. Figure 1 shows the amount of water-soluble chromium salt added and Si and
Acicular iron alloy magnetic particles containing Cr and Cr
FIG. 2 is a relationship diagram of the specific surface area of acicular iron alloy magnetic particles containing . That is, 300% of an aqueous ferrous sulfate solution containing 1.2 mol of Fe ²⁺ was added, sodium silicate prepared in advance in a reactor was mixed with 0 to 1.0 atomic % of Si in terms of Fe, and chromium sulfate was mixed with Cr in terms of Fe. In addition to the NaOH aqueous solution 400 obtained by adding 0 to 5.0 atom% in terms of Fe(OH)2, a suspension containing Fe(OH) ₂ at pH 13.8 was obtained, and the suspension was heated at a rate of 1000 NaOH per minute at a temperature of 45°C. Acicular α-FeOOH particles containing Si and Cr are generated by aeration of air to perform an oxidation reaction, and then the particles are heated and reduced at 430°C for 4.0 hours to obtain Si and Cr. This figure shows the relationship between the specific surface area and the amount of chromium sulfate added for acicular iron alloy magnetic particles containing Cr and Cr-containing acicular iron alloy magnetic particles. In the figure, curve a is for the case without Si addition, curves b and c
The Si addition amount is 0.35 at% and 1.0 at%, respectively.
This is the case. As shown in curves b and c, when Si and Cr are added together, the specific surface area of the resulting acicular iron alloy magnetic particles containing Si and Cr can be significantly improved; , the specific surface area tends to increase as the amount of chromium sulfate added increases. Since this phenomenon appears more markedly than when Cr is added alone, as shown by curve a in FIG. 1, the present inventor believes that it is due to the synergistic effect of Si and Cr. As mentioned above, the acicular iron alloy magnetic particles containing Si and Cr have uniform particle size, do not contain dendritic particles, and have a large specific surface area. There was a tendency for the coercive force to decrease as the amount added increased. Therefore, as a result of various studies on methods for improving the coercive force of acicular iron alloy magnetic particles containing Si and Co, the inventors found that Si and Cr
In the production of needle-shaped α-FeOOH particles containing Fe
A water-soluble nickel salt is added to either the (OH) ₂ suspension or the reaction solution in which an oxidation reaction is carried out by passing an oxygen-containing gas through the solution, and the resulting mixture contains Si, Cr, and Ni. We obtained the knowledge that when acicular α-FeOOH particles are thermally reduced, the coercive force of acicular iron alloy magnetic particles containing Si and Cr can be improved while maintaining a large specific surface area. Ta. This phenomenon will be explained as follows by extracting some of the many experimental examples conducted by the present inventor. Figure 2 shows the amount of water-soluble nickel salt added and Si,
FIG. 2 is a relationship diagram of coercive force of acicular iron alloy magnetic particles containing Cr and Ni. That is, 300% of an aqueous ferrous sulfate solution containing 1.2 mol of Fe ²⁺ was mixed with sodium silicate, prepared in advance, in a reactor at 0.35 atomic % relative to Fe in terms of Si, and chromium sulfate in an amount equivalent to Cr relative to Fe. A suspension containing Fe(OH) ₂ was obtained at pH 14.0 by adding 0.5 at% nickel sulfate to an aqueous NaOH solution 400 obtained by adding 0 to 7.0 at% nickel based on Fe. , Si,
Acicular crystal iron alloy magnetic particles containing Si, Cr, and Ni obtained by generating acicular crystal α-FeOOH particles containing Cr and Ni, and then heating and reducing the particles at 420°C for 4.0 hours. This figure shows the relationship between the coercive force of the powder and the amount of nickel sulfate added. As shown in FIG. 2, as the amount of nickel sulfate added increases, the coercive force of the acicular iron alloy magnetic particles containing Si, Cr, and Ni tends to increase. This phenomenon of increasing coercive force while maintaining a large specific surface area cannot be achieved by removing Si, Cr, or Ni;
The present inventor believes that this is due to the synergistic effect of Si, Cr, and Ni. Furthermore, as a result of repeated studies on methods for improving the specific surface area and coercive force of acicular iron alloy magnetic particles containing Si, Cr, and Ni, the present inventors found that
In the production of acicular α-FeOOH particles containing Si, Cr, and Ni, Fe(OH) ₂ suspension is mixed with a ferrous salt aqueous solution, an alkaline aqueous solution, and an oxygen-containing gas before being subjected to an oxidation reaction. A water-soluble magnesium salt is added to either of the reaction solutions in which an oxidation reaction is carried out by passing oxygen-containing gas through the resulting acicular crystal α- containing Si, Cr, Ni, and Mg.
It has been found that when FeOOH particles are thermally reduced, the specific surface area and coercive force of acicular iron alloy magnetic particles containing Si, Cr, and Ni can be further improved. This phenomenon will be explained as follows by extracting some of the many experimental examples conducted by the present inventor. FIGS. 3 and 4 are graphs showing the relationship between the amount of water-soluble magnesium salt added and the coercive force and specific surface area of acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg, respectively. That is, 300% of an aqueous ferrous sulfate solution containing 1.2 mol of Fe ²⁺ was mixed with sodium silicate, prepared in advance, in a reactor at 0.35 atomic % relative to Fe in terms of Si, and chromium sulfate in an amount equivalent to Cr relative to Fe. 0.50 atomic%, nickel sulfate 3.0 atomic% based on Ni in terms of Ni, magnesium sulfate 0 to 15.0 atomic% based on Fe in terms of Mg.
NaOH aqueous solution obtained by adding 400
In addition, a suspension containing Fe(OH) ₂ at pH 14.0 was obtained, and the suspension was heated at a rate of 1000 min/min at a temperature of 50°C.
By ventilating the air and causing an oxidation reaction
Acicular crystal α- containing Si, Cr, Ni and Mg
Generate FeOOH particles and then store the particles at 420°C.
Si obtained by heating reduction for 4.5 hours at
This figure shows the relationship between the coercive force and specific surface area of acicular iron alloy magnetic particles containing Cr, Ni, and Mg and the amount of magnesium sulfate added. As shown in Figures 3 and 4, as the amount of magnesium sulfate added increases, both the coercive force and specific surface area of the acicular iron alloy magnetic particles containing Si, Cr, and Ni further improve. be able to. Since the phenomenon of further improving the coercive force and specific surface area cannot be obtained by removing any of Si, Cr, Ni, and Mg, the present inventors
We believe that this is due to the synergistic effect of Si, Cr, Ni, and Mg. Furthermore, as a result of repeated studies on a method for further improving the specific surface area of acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg, the inventors found that Si,
Acicular α-FeOOH particles containing Cr, Ni and Mg, or acicular α obtained by heating and dehydrating them
- Fe ₂ O ₃ particles or a suspension containing densified acicular α-Fe ₂ O ₃ particles obtained by heat-treating the above acicular α-FeOOH particles in a non-reducing atmosphere; By preparing a liquid and adding and mixing 0.5 to 10.0 atomic % of Ni and/or Al compounds in terms of Ni and Al to Fe into the suspension, it is possible to coat with Ni and/or Al compounds. Si, Cr, Ni and
Acicular α-FeOOH particles containing Mg or
Acicular α-Fe ₂ O ₃ containing Si, Cr, Ni and Mg
When particles or acicular α-Fe ₂ O ₃ particles containing densified Si, Cr, Ni and Mg are heated and reduced in a reducing gas, Si, Cr, Ni and We have found that the specific surface area of acicular iron alloy magnetic particles containing Mg can be further improved. This phenomenon will be explained as follows by extracting some of the many experimental examples conducted by the present inventor. Figure 5: Coated with Ni and/or Al compounds
FIG. 2 is a diagram showing the relationship between Mg content and specific surface area of acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and Mg. That is, 2000 g of acicular α-FeOOH particles containing Si, Cr, Ni, and Mg obtained in FIGS. 3 and 4 were
60 in water, then added nickel sulfate and/or aluminum sulfate to the suspension, mixed, filtered, and dried to obtain Al and/or Ni.
Si coated with Ni and/or Al compounds obtained by reducing acicular α-FeOOH particles containing Si, Cr, Ni, and Mg coated with compounds under the same conditions as in FIGS. 3 and 4. , which shows the relationship between Mg content and specific surface area of acicular iron alloy magnetic particles containing Cr, Ni, and Mg. In the figure, curve a shows 2.0 atomic% of Ni equivalent to Fe.
For acicular iron alloy magnetic particle powder containing Si, Cr, Ni and Mg coated with Ni compound, curve b is
In the case of acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and Mg coated with an Al compound of 4.0 atomic % in terms of Al relative to Fe, curve c is 2.0 atomic % in terms of Ni and 2.0 atomic% Al in terms of Al compared to Fe
In the case of acicular iron alloy magnetic particle powder containing Si, Cr, Ni and Mg coated with compounds and Ni compounds, curve d is
This is the case of acicular iron alloy magnetic particle powder containing Si, Cr, Ni and Mg. As shown in Figure 5, when coated with Ni and/or Al compounds, Si, Cr, Ni and Mg
It is possible to further improve the specific surface area of the acicular iron alloy magnetic particles containing the following. This phenomenon is caused by acicular crystals α-
When Ni and/or Al compounds are added during the FeOOH particle production reaction, or when Mg-free acicular α-FeOOH particles are coated with Ni and/or Al compounds, acicular iron Since the effect of increasing the specific surface area of the alloy magnetic particles is not so great, the present inventor believes that this is due to the synergistic effect of Mg and the Ni and/or Al compounds. Next, various conditions for implementing the present invention will be described. As the water-soluble chromium salt used in the present invention, chromium sulfate and chromium chloride can be used. Regarding the timing of addition of the water-soluble chromium salt, in the present invention, it is necessary to make chromium present during the formation reaction of acicular α-FeOOH particles, and for this purpose, it is necessary to add chromium in the ferrous salt aqueous solution or in the alkaline aqueous solution. ,
It may be added either to a suspension containing Fe(OH) ₂ or to a reaction solution in which acicular α-FeOOH particles are being formed after the start of aeration of oxygen-containing gas. Furthermore, even if water-soluble chromium salt is added at a stage when the formation of acicular α-FeOOH particles has been completely completed, chromium will not enter the particles, so the effect of chromium addition in the present invention cannot be obtained. . The amount of water-soluble chromium salt added in the present invention is
It is 0.1 to 5.0 atomic % in terms of Cr relative to Fe. Almost all of the added water-soluble chromium salt is formed into needle-shaped α crystals.
-Contained in FeOOH particles. If the amount of the water-soluble chromium salt added is 0.1 atomic % or less in terms of Cr based on Fe, the effect of increasing the specific surface area of the obtained acicular iron alloy magnetic particles cannot be obtained. If the content is 5.0 atomic % or more, the effect of increasing the specific surface area of the obtained acicular iron alloy magnetic particles can be obtained, but the coercive force and saturation magnetization decrease, which is not preferable. As the water-soluble nickel salt used in the present invention, nickel sulfate, nickel chloride, nickel sulfate, etc. can be used. Regarding the timing of adding the water-soluble nickel salt, in the present invention, it is necessary to have nickel present during the formation reaction of acicular α-FeOOH particles, and for this purpose, it is necessary to add the water-soluble nickel salt to the ferrous salt aqueous solution or the alkaline aqueous solution. , into a suspension containing Fe(OH) ₂ , or into a reaction solution in which acicular α-FeOOH particles are being formed after the start of aeration of oxygen-containing gas. Furthermore, even if water-soluble nickel salt is added at a stage when the formation of acicular α-FeOOH particles has been completely completed, the effect of nickel addition in the present invention cannot be obtained because nickel does not enter the particles. . The amount of water-soluble nickel salt added in the present invention is
It is 0.1 to 7.0 atomic % based on Ni in terms of Ni. Almost all of the added water-soluble nickel salt is formed into needle-shaped crystals α.
-Contained in FeOOH particles. If the amount of water-soluble nickel salt added is less than 0.1 atomic % based on Fe in terms of Ni, the effect of increasing the coercive force of the obtained acicular iron alloy magnetic particles cannot be obtained. Although it is possible to achieve the object of the present invention when the content is 7.0 atomic % or more, it is not preferable because foreign substances other than needle crystals are mixed during the production of α-FeOOH particles. As the water-soluble magnesium salt used in the present invention, magnesium sulfate and magnesium chloride can be used. Regarding the timing of addition of the water-soluble magnesium salt, in the present invention, it is necessary to make magnesium present during the formation reaction of acicular α-FeOOH particles, and for this purpose, it is necessary to add the water-soluble magnesium salt to the ferrous salt aqueous solution or the alkaline aqueous solution. , in a suspension containing Fe(OH) ₂ , or
After the start of aeration of the oxygen-containing gas, acicular α-FeOOH particles may be added to any part of the reaction solution that is being produced. Furthermore, even if water-soluble magnesium salt is added at a stage when the formation of acicular α-FeOOH particles has been completely completed, magnesium will not enter the particles, so the effect of magnesium addition in the present invention cannot be obtained. . The amount of water-soluble magnesium salt added in the present invention is 0.1 to 15.0 atomic % based on Fe in terms of Ni.
Almost all of the added water-soluble magnesium salt is contained in the produced acicular α-FeOOH particles. Addition amount of water-soluble magnesium salt relative to Fe
If it is 0.1 atomic % or less in terms of Mg, the effect of further increasing the specific surface area and coercive force of the obtained acicular iron alloy magnetic particles cannot be obtained. Although the object of the present invention can be achieved when the content is 15.0 at % or more, it is not preferable because the saturation magnetization decreases. As the nickel compound used in the present invention, nickel sulfate, nickel chloride, nickel nitrate, etc. can be used, and as the aluminum compound, aluminum sulfate, aluminum chloride, sodium aluminate, etc. can be used. The coating particles used in the coating treatment with Ni and/or Al compounds include Si, Cr, Ni and Mg-containing acicular crystals α generated in the reaction mother liquor.
- FeOOH particles, Si, Cr, Ni and Mg-containing acicular crystals α after being filtered from the reaction mother liquor, washed with water and dried -
FeOOH particles, Si, Cr, Ni and Mg containing acicular α
- Fe ₂ O ₃ particles and acicular α-FeOOH particles containing Si, Cr, Ni, and Mg that are densified by heat-treating acicular α- _FeOOH particles at _high temperatures. can also be used, and the same effect can be obtained in either case. It is necessary that the Ni and/or Al compound be uniformly coated on the particle surface.
Preferably, the compound is deposited as a hydroxide of Ni and/or Al using an alkali. The amount of Ni and/or Al compound added is
It is 0.5 to 10.0 atomic % in terms of Ni and/or Al. If it is less than 0.5 atomic %, the object of the present invention cannot be fully achieved. If the content is 10.0 atomic % or more, Si, Cr, Ni and
Acicular iron alloy magnetic particles containing Mg are undesirable because their saturation magnetization is significantly reduced due to a decrease in purity. Examples of alkalis used in coating with Ni and/or Al compounds include sodium hydroxide and potassium hydroxide. The Ni and/or Al compound and the alkali may be added in any order, or may be added at the same time. The present invention configured as described above has the following effects. That is, according to the present invention, it has acicular crystals, uniform particle size, no dendritic particles, large bulk density, large specific surface area, high coercive force Hc, and large saturation magnetization. Magnetic acicular iron alloy containing Si, Cr, Ni and Mg coated with Ni and/or Al compound having σs or coated with P compound and Si compound and Ni and/or Al compound Since it is possible to obtain particle powder, it is possible to obtain high image quality, high output, high sensitivity, which are currently most required.
It can be used as magnetic particle powder for high recording density. Furthermore, in the production of magnetic paint, it contains Si, Cr, Ni, and Mg coated with the above-mentioned Ni and/or Al compounds, or coated with P compounds and Si compounds and Ni and/or Al compounds. When acicular iron alloy magnetic particles are used, the noise level is low, and the dispersibility in the vehicle, the orientation and filling properties in the coating film are excellent, and a desirable magnetic recording medium can be obtained. I can do it. Next, the present invention will be explained with reference to Examples and Comparative Examples. In addition, the specific surface area of the particles in the previous experimental examples, the following examples, and comparative examples was measured by the BET method, and the particle axis ratio (long axis: short axis) and long axis were measured using an electron microscope. It is shown as the average value of the numerical values measured from the photographs. Moreover, the bulk density was measured according to JIS K 5101-1978 "Pigment test method". P content in particles Si content, Cr content, Ni content, Mg content and Al
The amount was determined by performing fluorescence X-ray analysis using a "fluorescence X-ray analyzer model 3063M" (manufactured by Rigaku Denki Kogyo) in accordance with the "General Rules for Fluorescence X-ray Analysis" of JIS K 0119-1979. It was measured. The magnetic property values are the results measured under an external magnetic field of 10 KOe using a sample vibrating magnetometer. <(Manufacture of needle-shaped α-FeOOH particles) Examples 1 to 4, Comparative Example 1 Example 1 Ferrous sulfate aqueous solution containing 1.2 mol/Fe ²⁺ 300
Sodium silicate (No. 3) (SiO ₂ 28.55wt%) 379g was prepared in advance in a reactor to contain 0.50 at% in terms of Si, and 0.50 at% in terms of Cr was added to Fe. Contains 644g of chromium sulfate,
In addition to 400 g of a 5.46-N NaOH aqueous solution obtained by adding 2,884 g of nickel sulfate to contain 3.0 atomic % of Fe in terms of Ni, and 4473 g of magnesium sulfate to contain 5.0 atomic % of Fe in terms of Mg, PH
13.8, a reaction was carried out to produce a Fe(OH) ₂ suspension containing Si, Cr, Ni and Mg at a temperature of 45°C. The above Fe(OH) ₂ suspension containing Si, Cr, Ni and Mg was fed with 1000 air per minute at a temperature of 50°C at 5.1
After aeration for a period of time, acicular α-FeOOH particles containing Si, Cr, Ni, and Mg were produced. The end point of the oxidation reaction was determined by extracting a portion of the reaction solution and acidifying it with hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a blue coloring reaction of Fe ²⁺ . The generated particles are separated by filtration, washed with water, dried, and
Shattered. The obtained acicular α-FeOOH particles containing Si, Cr, Ni and Mg were found to be α-FeOOH particles as a result of X-ray diffraction.
A diffraction pattern similar to the crystal structure of FeOOH particles was obtained. In addition, as a result of fluorescent X-ray analysis, Si was compared to Fe.
0.504 atomic%, Cr to Fe 0.498 atomic%, Ni
3.03 at% to Fe, 4.98 at% Mg to Fe
It contained. Therefore, Si, Cr, Ni and Mg have acicular crystals α-
It is thought that it is dissolved in FeOOH particles. This acicular crystal α- containing Si, Cr, Ni and Mg
As a result of electron microscopic observation, the FeOOH particles had an average long axis of 0.55 μm and an axial ratio (long axis: short axis) of 33:1. Examples 2 to 4 The type and concentration of ferrous salt aqueous solution, the concentration of NaOH aqueous solution, and the type, amount, and timing of addition of water-soluble silicate, water-soluble chromium salt, water-soluble nickel salt, and water-soluble magnesium salt. Acicular α-FeOOH particles containing Si, Cr, Ni, and Mg were produced in the same manner as in Example 1, except for making various changes. The main manufacturing conditions at this time are shown in Table 1, and the characteristics are shown in Table 2. Comparative Example 1 Acicular α-FeOOH particle powder was produced in the same manner as in Example 1, except that sodium silicate, chromium sulfate, nickel sulfate, and magnesium sulfate were not added and the concentration of the NaOH aqueous solution was varied. The main manufacturing conditions at this time are shown in Table 1, and the characteristics are shown in Table 2. As a result of electron microscopic observation, the obtained acicular α-FeOOH particles had an average long axis of 0.45 μm and an axial ratio (long axis: short axis) of 9:1, and the particle size was asymmetric.
It contained a mixture of dendritic particles. <Acicular crystal α- containing Si, Cr, Ni and Mg
Production of Fe ₂ O ₃ particle powder> Example 5 2000 g of the acicular α-FeOOH particle powder containing Si, Cr, Ni and Mg obtained in Example 3 was dissolved in air at 300 g.
The mixture was heated and dehydrated at ℃ to obtain acicular α-Fe ₂ O ₃ particle powder containing Si, Cr, Ni, and Mg. This particle is
As a result of electron microscopy observation, the average value of the long axis is 0.44μm,
The axial ratio (long axis: short axis) was 30:1, the particle size was uniform, and dendritic particles were not mixed. <Coating treatment with Ni and/or Al compound or P
Compound and coating treatment with Si compound and Ni and/or Al compound> Examples 6 to 16, Comparative Examples 2 and 3 Example 6 Si, Cr, after filtration and water washing obtained in Example 1,
Acicular α-FeOOH particle powder containing Ni and Mg
2000g was suspended in 60ml of water. The pH value of the suspension at this time was 10.0. Next, 296 g of nickel sulfate (NiSO ₄ 6H ₂ O) (Ni for Fe) was added to the above suspension.
This corresponds to 5.0 atomic% in terms of conversion. ) was added and, with stirring, 1.13 of a 2-N aqueous NaOH solution was added. This suspension was stirred for 20 minutes, and the pH of the suspension was
After adding 10% acetic acid to give a concentration of 8.0, the acicular α-FeOOH particles containing Si, Cr, Ni and Mg were filtered out using a press filter and dried.
Acicular α-FeOOH particle powder containing Si, Cr, Ni and Mg coated with a Ni compound was obtained. Table 3 shows the main manufacturing conditions at this time. Examples 7 to 9 Type of particles to be treated, pH of suspension, Ni and/or
Alternatively, Ni
Acicular α-FeOOH particle powder containing Si, Cr, Ni and Mg coated with and/or Al was obtained. Table 3 shows the main manufacturing conditions at this time. Example 10 9500 g of paste of acicular α-FeOOH particles containing Si, Cr, Ni and Mg obtained in Example 4
(Acicular crystal α- containing Si, Cr, Ni and Mg
This corresponds to approximately 3000g of FeOOH particles. ) was suspended in 100% water. The pH value of the suspension at this time was 9.8. Next, 500 ml of an aqueous solution containing 18 g of sodium hexametaphosphate (Si, Cr, Ni and
PO ₃ for Mg-containing acicular α-FeOOH particles
This corresponds to 0.42wt%. ) was added and stirred for 30 minutes, and then 133 g of nickel sulfate (NiSO ₄ 6H ₂ O) (corresponding to 1.5 atomic % of Ni in terms of Fe) and sodium aluminate (NaAlO ₂ ) were added to the suspension. 55.4g (2.0 atomic% in terms of Al compared to Fe)
Applies to. ) and add 2-N while stirring.
0.5 of NaOH aqueous solution was added. Subsequently, sodium silicate (3
240g (as SiO ₂ for acicular α-FeOOH particles containing Si, Cr, Ni and Mg)
This corresponds to 2.3wt%. ) and stirred for 30 minutes, 10% acetic acid was added so that the pH value of the suspension was 6.0, and then Si,
Acicular α-FeOOH particles containing Cr, Ni and Mg are separated by filtration and dried to produce acicular α-FeOOH particles containing Si, Cr, Ni and Mg coated with a P compound, a Si compound, a Ni compound and an Al compound. Crystalline α-FeOOH particle powder was obtained. Examples 11 to 13 Except for various changes in the type of particles to be treated, the pH of the suspension, the amount of P compound added, the type and amount of Ni and/or Al compound added, the amount of Si compound added, and the adjustment of PH. is the P compound and Si in the same manner as in Example 10.
coated with compound and Ni and/or Al compound
Acicular crystal α- containing Si, Cr, Ni and Mg
FeOOH particle powder was obtained. The acicular α-FeOOH particle powder containing Si, Cr, Ni, and Mg coated with the above P compound and Si compound and Ni and/or Al compound was heat-treated at the heat treatment temperature and atmosphere shown in Table 3. P compound and Si compound densified by
or Si, Cr, Ni and Mg coated with Al compounds
Acicular α-Fe ₂ O ₃ particle powder containing acicular crystals was obtained. Table 3 shows the main manufacturing conditions and characteristics at this time. Example 14 6.3 kg of paste of acicular α-FeOOH particles containing Si, Cr, Ni and Mg obtained in Example 2
(Acicular crystal α- containing Si, Cr, Ni and Mg
This corresponds to approximately 2000g of FeOOH particles. ) was suspended in 60% water. The pH value of the suspension at this time was 9.6. Next, 500 ml of an aqueous solution containing 16 g of sodium hexametaphosphate (Si, Cr, Ni and
PO ₃ for Mg-containing acicular α-FeOOH particles
This corresponds to 0.56wt%. ) was added and stirred for 30 minutes, and then 200 g of sodium silicate (No. 3 water glass) (as SiO ₂ for acicular α-FeOOH particles containing Si, Cr, Ni, and Mg) was added to the suspension.
This corresponds to 2.9wt%. ) and stirred for 30 minutes, 10% acetic acid was added so that the pH value of the suspension was 7.0, and then Si,
Acicular α-FeOOH particles containing Cr, Ni and Mg are filtered and dried to produce acicular α- FeOOH particles containing Si, Cr, Ni and Mg coated with P and Si compounds.
FeOOH particle powder was obtained. Si coated with the above P compound and Si compound,
1500g of acicular α-FeOOH particles containing Cr, Ni and Mg were coated with densified P and Si compounds by heat treatment at 600℃ in air.
Acicular α-Fe ₂ O ₃ containing Si, Cr, Ni and Mg
A particulate powder was obtained. 1000 g of acicular α-Fe ₂ O ₃ particle powder containing Si, Cr, Ni and Mg coated with the densified P and Si compounds was suspended in 30 g of water. Next, nickel sulfate ( _NiSO4 .
65.8 g of 6H ₂ O) (corresponding to 4.0 atom% of Ni in terms of Fe) was added, and then 2-N NaOH was added.
After adding 0.25% aqueous solution and stirring for 30 minutes, 10% acetic acid was added so that the pH value of the suspension was 8.0, and Si, Cr, Ni and
Acicular α- Fe ₂ O ₃ particles containing Mg are filtered and dried to produce acicular α- Fe 2 O 3 particles containing Si, Cr, Ni and Mg coated with P compound, Si compound and Ni compound.
Fe ₂ O ₃ particle powder was obtained. Table 3 shows the main manufacturing conditions and characteristics at this time. Examples 15, 16 Type of particles to be treated, PH of suspension, amount of P compound added, type and amount of Ni and/or Al compound added, amount of Si compound added, PH adjustment, heat treatment temperature and atmosphere The densified P compound and Si compound were prepared in the same manner as in Example 14 except that various changes were made.
Si coated with Ni compound and/or Al compound,
Acicular α-Fe ₂ O ₃ particle powder containing Cr, Ni and Mg was obtained. Table 3 shows the main manufacturing conditions and characteristics at this time. Comparative Example 2 Without coating with Ni and Al compounds,
Acicular α-FeOOH particle powder coated with a P compound and a Si compound was prepared in the same manner as in Example 10 by varying the type of particles to be treated, the pH of the suspension, the amount of Si compound added, and the adjustment of the pH. I got it. Table 3 shows the main manufacturing conditions and characteristics at this time. Comparative Example 3 Without coating with Ni compound, the type of particles to be treated, the pH of suspension, the amount of Si compound added, and
Examples by varying pH adjustment and heat treatment temperature
Acicular α-Fe ₂ O ₃ particle powder coated with a highly densified P compound and a Si compound was obtained in the same manner as in Example 11. Table 3 shows the main manufacturing conditions and characteristics at this time. <Production of acicular iron or iron alloy magnetic particles> Examples 17 to 27, Comparative Examples 4 to 6 Example 17 Si coated with the Ni compound obtained in Example 6,
120 g of acicular α-FeOOH particle powder containing Cr, Ni, and Mg was put into the rotary retort container in step 3, and H ₂ gas was passed through at a rate of 50 per minute while driving the retort container, and the reduction temperature was 380°C. I returned it with Si coated with Ni compound obtained by reduction,
The acicular iron alloy magnetic particles containing Cr, Ni and Mg are first immersed in toluene solution and evaporated to prevent rapid oxidation when taken out into the air. A stable oxide film is applied to the particle surface. Si, Cr, Ni and Mg coated with this Ni compound
Table 4 shows the properties of the acicular iron alloy magnetic particles containing . The bulk density of the acicular iron alloy magnetic particles was 0.44 g/ml. Examples 18 to 27, Comparative Examples 4 to 6 Acicular iron alloy magnetic particles were obtained in the same manner as in Example 17, except that the types of starting materials and the reduction temperature were varied. Table 4 shows the main manufacturing conditions at this time and various properties of the obtained particles.

【table】

【table】

【table】

【table】

【table】 [Brief explanation of the drawing]

Figure 1 shows the amount of water-soluble chromium salt added and Si and
Acicular iron alloy magnetic particles containing Cr and Cr
FIG. 2 is a relationship diagram of the specific surface area of acicular iron alloy magnetic particles containing . FIG. 2 is a diagram showing the relationship between the amount of water-soluble nickel salt added and the coercive force of acicular iron alloy magnetic particles containing Si, Cr, and Ni. Figure 3
and FIG. 4 are graphs showing the relationship between the amount of water-soluble magnesium salt added and the coercive force and specific surface area of acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg. FIG. 5 is a diagram showing the relationship between Mg content and specific surface area of acicular iron alloy magnetic particles containing Si, Cr, Ni, and Mg coated with Al and/or Ni compounds.

Claims (1)

[Scope of Claims] 1. A suspension containing Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution and having a pH of 11 or above is oxidized by passing an oxygen-containing gas through it to form a acicular shape. In producing crystalline α-FeOOH particles, water-soluble silicate is added to Fe in any of the suspensions before the alkali aqueous solution and oxygen-containing gas are passed through to perform the oxidation reaction. 0.1 in conversion
~1.7 atomic % is added, and the suspension and oxygen-containing gas before the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are aerated to perform the oxidation reaction, and the oxidation reaction is carried out by aerating the suspension and the oxygen-containing gas. A water-soluble chromium salt is added to any of the above reaction solutions in which the reaction is carried out.
0.1 to 5.0 atomic% of Fe in terms of Cr, water-soluble nickel salts of 0.1 to 7.0 atomic% of Ni in terms of Fe, and water-soluble magnesium salts of Fe to 0.1 to 7.0 atomic% in terms of Ni.
By adding 0.1 to 15.0 atomic%, Si,
Si, Cr obtained by generating acicular α-FeOOH particles containing Cr, Ni and Mg, and heating and dehydrating the acicular α-FeOOH particles containing Si, Cr, Ni and Mg , prepare a suspension containing acicular α-Fe ₂ O ₃ particles containing Ni and Mg, and prepare a suspension containing acicular α-Fe 2 O 3 particles containing Ni and Mg.
Acicular crystal α- containing Si, Cr, Ni and Mg coated with Ni and/or Al compound by adding and mixing atomic % of Ni and/or Al compound.
After forming FeOOH particles or acicular α-Fe ₂ O ₃ particles containing Si, Cr, Ni and Mg, Si, Cr, Si, Cr, coated with Ni and/or Al compounds are heated and reduced in a reducing gas. A method for producing acicular iron alloy magnetic particles for magnetic recording, the method comprising obtaining acicular iron alloy magnetic particles containing Ni and Mg. 2 Acicular α-FeOOH particles are produced by passing an oxygen-containing gas through a suspension containing Fe(OH) ₂ and having a pH of 11 or higher obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution to oxidize it. To generate the water-soluble silicate, add 0.1 of the water-soluble silicate to Fe in terms of Si in any of the suspensions before the aqueous alkaline solution and oxygen-containing gas are passed through to perform the oxidation reaction.
~1.7 atomic % is added, and the suspension and oxygen-containing gas before the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are aerated to perform the oxidation reaction, and the oxidation reaction is carried out by aerating the suspension and the oxygen-containing gas. In any of the reaction solutions in which the reaction is carried out, a water-soluble chromium salt is added to Fe in an amount of 0.1 to 5.0 atom% in terms of Cr, a water-soluble nickel salt is added as Fe to 0.1 to 7.0 atom% in terms of Ni,
By adding 0.1 to 15.0 atomic % of water-soluble magnesium salt to Fe in terms of Mg,
Acicular crystal α- containing Si, Cr, Ni and Mg
FeOOH particles are generated and the Si, Cr, Ni and Mg
Acicular α-FeOOH particles containing Si, Cr, Ni and Mg obtained by heating and dehydrating the acicular α- _FeOOH particles containing Si, Cr, Ni and _Mg are suspended in water,
Si, Cr, Ni and
0.1 for acicular α-FeOOH particles containing Mg
~2wt% (calculated as _PO3 ) of phosphate is added to form a dispersion, and then Si, Cr, Ni and Mg are added to the dispersion.
0.1 to acicular α-FeOOH particles containing
7.0wt% (calculated as _SiO2 ) of water-soluble silicates and
0.5 to 10.0 atomic% in terms of Ni and/or Al relative to Fe
Acicular α-FeOOH particles containing Si, Cr, Ni and Mg coated with P compound and Si compound and Ni and/or Al compound or Si , Cr, Ni and
After forming acicular α-Fe ₂ O ₃ particles containing Mg,
Si coated with a P compound, a Si compound, and a Ni and/or Al compound by heating reduction in a reducing gas;
A method for producing acicular iron alloy magnetic particles for magnetic recording, the method comprising obtaining acicular iron alloy magnetic particles containing Cr, Ni, and Mg. 3 Acicular α-FeOOH particles are produced by passing an oxygen-containing gas through a suspension containing Fe(OH) ₂ and having a pH of 11 or higher obtained by reacting a ferrous salt aqueous solution with an alkaline aqueous solution to oxidize it. To generate the water-soluble silicate, add 0.1 of the water-soluble silicate to Fe in terms of Si in any of the suspensions before the aqueous alkaline solution and oxygen-containing gas are passed through to perform the oxidation reaction.
~1.7 atomic % is added, and the suspension and oxygen-containing gas before the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are aerated to perform the oxidation reaction, and the oxidation reaction is carried out by aerating the suspension and the oxygen-containing gas. In any of the reaction solutions in which the reaction is carried out, a water-soluble chromium salt is added to Fe in an amount of 0.1 to 5.0 atom% in terms of Cr, a water-soluble nickel salt is added as Fe to 0.1 to 7.0 atom% in terms of Ni,
By adding 0.1 to 15.0 atomic % of water-soluble magnesium salt to Fe in terms of Mg,
Acicular crystal α- containing Si, Cr, Ni and Mg
FeOOH particles are generated and the Si, Cr, Ni and Mg
Acicular α-FeOOH particles containing Si, Cr,
0.1 to 2 wt% (calculated as PO ₃ ) of phosphate is added to the acicular α-FeOOH particles containing Ni and Mg to form a dispersion, and then Si, Cr, Ni, and Mg are added to the dispersion. Containing acicular α-FeOOH particles
Acicular α-FeOOH particles containing Si, Cr, Ni and Mg coated with P and Si compounds are produced by adding 0.1 to 7.0 wt% (calculated as _SiO2 ) of water-soluble silicate. Acicular crystals containing Si, Cr, Ni, and Mg coated with a P compound and a Si compound are densified by heating the particles at a temperature range of 500 to 900°C in a non-reducing atmosphere. α−
Acicular iron alloy containing Si, Cr, Ni, and Mg, which is formed into Fe ₂ O ₃ particles and then heated and reduced in a reducing gas and coated with a P compound, a Si compound, and a Ni and/or Al compound. In preparing the magnetic particles, 0.5 to 10.0 atomic % of Ni and/or Al compounds are added to Fe in the dispersion liquid, or Ni and/or Al compounds are added to the dispersion liquid in an amount of 0.5 to 10.0 atomic % in terms of Ni and Al, or the particles are densified after the heat treatment. Acicular α-Fe ₂ O ₃ particles containing Si, Cr, Ni and Mg coated with a P compound and a Si compound are suspended in water,
0.5 in terms of Ni and/or Al relative to Fe in the suspension
By adding and mixing ~10.0 atom% of Ni and/or Al compound and coating with Ni and/or Al compound, Si coated with P compound and Si compound and Ni and/or Al compound, A method for producing acicular iron alloy magnetic particles for magnetic recording, the method comprising obtaining acicular iron alloy magnetic particles containing Cr, Ni, and Mg.