JPS6314484B2 - - 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 no intertwining of particles. There is no match, etc.
As a result, the bulk density is large, and
Si, Cr, Ni, and Mg are fine particles with a large specific surface area, a high degree of crystallinity on the particle surface and inside the particle, and are substantially dense, and also have a high coercive force Hc and a large saturation magnetization σs. The present invention relates to an acicular iron alloy magnetic particle powder containing P and a method for producing the same. When the acicular iron alloy magnetic particle powder containing Si, Cr, Ni, Mg and P obtained by the present invention is used in the production of magnetic recording media, it has acicular crystals and uniform particle size. There are no intermingling of dendritic particles and no intertwining of particles, and as a result, the bulk density is large, and the particles are fine with a large specific surface area and a high degree of crystallinity on the particle surface and inside the particle. The magnetic particles have a substantially high density, and also have a high coercive force Hc and a large saturation magnetization σs. It is possible to obtain an excellent magnetic recording medium that has extremely excellent properties, has a low noise level generated during recording and reproduction of magnetic tape, and has high output characteristics. In recent years, magnetic recording and reproducing equipment for video and audio has become increasingly compact and lightweight.
The popularity of VTRs (recorders) has been remarkable, and VTRs are being actively developed with the aim of recording for longer periods of time and being smaller and lighter.On the other hand, efforts are being made to improve the performance and density of magnetic tape, which is a magnetic recording medium. Demand is 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 are correlated 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 necessary to improve the video S/N ratio, chroma, noise, and video frequency characteristics, as is clear from the above-mentioned Nikkei Electronics description. In order to improve the video S/N ratio, it is necessary to make the magnetic particles finer, improve their dispersibility in the vehicle, improve their 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 MR81-11, page 27, 23-9, "Fig. 3", etc. "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 holds true for the acicular iron magnetic particles and the acicular 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, there is no entanglement of particles, etc., 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 preferred. Such magnetic particle powder has acicular crystals and uniform particle size. , there is no intermingling of dendritic particles, no entanglement of particles, etc., and as a result, it is required that the bulk density is high. This fact is based on the above-mentioned Nikkei Electronics, page 85, which states, ``Chroma noise is caused by relatively long-period roughness of 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 velocity density Br is as large as possible the saturation magnetization σs of the magnetic particle powder, and depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property. 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. ……. of tape
To increase Br, the saturation magnetization Is that the magnetic material has in a perfect state (for example, in a single crystal state)
First of all, it is basic that (σs) is large. ……. Even if the material is the same, Br changes depending on the degree of filling, which indicates the proportion of magnetic powder. Furthermore, since it is proportional to the squareness ratio (amount of residual magnetization/amount of saturation magnetization), this is required to be large. ……. In order to increase the squareness ratio, it is advantageous to use magnetic powder that has uniform particle sizes, a high acicularity ratio, and excellent magnetic field orientation. It is clear from statements such as "...". As detailed above, in order to meet the demands for high performance such as high image quality and high output characteristics of magnetic recording media, especially improved frequency characteristics, and lower noise levels, the magnetic The characteristics of the powder particles include acicular crystals, uniform particle size, no intermingling of dendritic particles, no intertwining of particles, and a large specific surface area with crystals on the particle surface and inside the particles. It is necessary that the magnet has a high degree of magnetic properties and a substantially high density, as well as 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 a saturation magnetization σs70~85emu/g and a coercive force Hc250.
~500Oe. In particular, the σs of the above oxide magnetic particles is the maximum
It is about 85emu/g, and generally σs70~80emu/
g is the main reason for limiting the reproduction output and recording density. Furthermore, Co-magnetite and Co containing Co
-Maghemite magnetic particles are also used, but these magnetic particles have a high coercive force Hc of 400 to 800 Oe, but on the other hand, they have a low saturation magnetization σs of 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 crystal alloy magnetic particle powder. These acicular iron magnetic particles or acicular alloy magnetic particles have a significantly larger saturation magnetization σs than conventionally used magnetic iron oxide particles and Co-containing magnetic iron oxide particles, and have a coercive force Hc.
When coated as a magnetic recording medium, it has a large residual magnetic flux density Br and a high coercive force Hc, resulting in high density recording and high output characteristics, so it has attracted attention and has been put into practical use in recent years. is being done. As mentioned above, acicular iron magnetic particles or acicular alloy magnetic particles having a high coercive force Hc and a large saturation magnetization σs have acicular crystals, uniform particle size, and a mixture of dendritic particles. In order to obtain magnetic particle powder with such characteristics, the starting material, acicular α-FeOOH particles, must first be uniform in particle size. Therefore, it is necessary that there are no dendritic particles mixed in, and then how to maintain and inherit this excellent property while heating and reducing it to make acicular crystal ferromagnetic particles powder or acicular crystal alloy magnetic particle powder. The big question is whether to do so. Conventionally, needle-like α-
The most typical known method for producing FeOOH particles is to add an equivalent or more alkaline solution to a ferrous salt aqueous 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 for the formation of acicular α-FeOOH particles having asymmetric particle sizes and containing dendritic particles will be discussed below. Generally, the formation 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 Fe(OH) ₂ obtained by reacting a ferrous salt aqueous solution with an alkali and dissolved oxygen, but the contact reaction with dissolved oxygen is partially , 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 before the α-FeOOH production reaction is completed, so that the resulting acicular α- It is thought that FeOOH particles have asymmetric particle sizes and contain dendritic particles. In addition, 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 dilute reaction iron concentration of about 0.2 mol/min, the particle size is asymmetric and acicular crystals α-
FeOOH particles were easily generated. In view of the above, the present inventor has found that the present invention has acicular crystals and uniform particle size. It is substantially high-density with no dendritic particles mixed therein, no intertwining of particles, etc., a large specific surface area, and an increased degree of crystallinity on the particle surface and inside the particle,
In addition, various studies have been conducted in order to obtain acicular alloy magnetic particles having a high coercive force Hc and a large saturation magnetization σs. The present inventor then discovered that the ferrous salt aqueous solution and the alkaline aqueous solution were
Acicular _crystals α-
In producing FeOOH particles, water-soluble silicate is added to FeOOH at 0.1% Si equivalent to Fe in any of the above suspensions before the aqueous alkali 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 in an amount of 0.1 to 7.0 atom % in terms of Ni, and Water-soluble magnesium salt is 0.1 to 15.0 as Mg equivalent to Fe.
By adding atomic %, acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are generated, and acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are generated.
- After separating the FeOOH particles from the mother liquor, suspend them in water, and when the pH value of the suspension is 8 or higher, Si, Cr,
To the acicular α-FeOOH particles containing Ni and Mg, 0.1-2 wt% (calculated as PO ₃ ) of phosphate was added, followed by 0.1-7.0 wt % (calculated as SiO ₂ ) of water-soluble silica. After adding the acid salt, the PH value of the suspension is adjusted to 3~
Acicular crystal α containing Si, Cr, Ni and Mg coated with P compound and Si compound by preparing in step 7
-FeOOH particles are obtained, the particles are separated, dried, and then heat treated in a non-reducing atmosphere to form a P compound.
After forming acicular α-Fe ₂ O ₃ particles containing Si, Cr, Ni, and Mg coated with a Si compound, the particles are heated and reduced in a reducing gas to form acicular crystals. However, the particle size is uniform, there are no intermingling of dendritic particles, there is no entanglement of particles, etc., and the specific surface area is large and the degree of crystallinity on the particle surface and inside the particle is increased, making it substantially high density. The present invention was completed by discovering that it is possible to obtain acicular alloy magnetic particles having a high coercive force Hc and a large saturation magnetization σs. That is, the present invention involves reacting an acicular iron alloy magnetic particle powder for magnetic recording comprising acicular iron alloy magnetic particles containing Si, Cr, Ni, Mg, and P with an aqueous ferrous salt solution and an aqueous alkaline solution. Fe obtained by
Acicular _crystals α-
In producing FeOOH particles, water-soluble silicate is added to FeOOH at 0.1% Si equivalent to Fe in any of the above suspensions before the aqueous alkali 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 in an amount of 0.1 to 7.0 atom % in terms of Ni, and Water-soluble magnesium salt is 0.1 to 15.0 as Mg equivalent to Fe.
By adding atomic %, acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are generated, and acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are generated.
- After separating the FeOOH particles from the mother liquor, suspend them in water, and when the pH value of the suspension is 8 or higher, Si, Cr,
To the acicular α-FeOOH particles containing Ni and Mg, 0.1-2 wt% (calculated as PO ₃ ) of phosphate was added, followed by 0.1-7.0 wt % (calculated as SiO ₂ ) of water-soluble silica. After adding the acid salt, the PH value of the suspension is adjusted to 3~
Acicular crystal α containing Si, Cr, Ni and Mg coated with P compound and Si compound by preparing in step 7
- FeOOH particles are obtained, the particles are separated, dried, and then heat treated in a non-reducing atmosphere to form acicular crystals α- containing Si, Cr, Ni and Mg coated with P and Si compounds. Acicular iron alloy magnetic particles containing Si, Cr, Ni, Mg and P are obtained by heating and reducing the particles in a reducing gas after forming Fe ₂ O ₃ particles. This is a method for producing crystalline iron alloy magnetic particles. 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. , the generation of acicular α-FeOOH particles from an aqueous solution containing Fe(OH) ₂ and the formation of acicular α-FeOOH particles.
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 generating the
Water-soluble silicate is added to any of the suspensions before the alkali aqueous solution and oxygen-containing gas are passed through to perform the oxidation reaction.
When added to ~1.7 at%, Fe
(OH) ₂ flocs can be made into sufficiently fine and uniform flocs, and the Fe(OH) ₂ particles themselves that make up the Fe(OH) ₂ flocs can be made into sufficiently fine and uniform particles. , water-soluble silicate
Due to the effect of suppressing the oxidation reaction during the production of acicular α-FeOOH particles from an aqueous solution containing Fe(OH) ₂ , it is possible to suppress the generation of acicular α-FeOOH core particles and the acicular crystals. Since α-FeOOH core particles can be grown in stages, the particle size is uniform.
In addition, acicular crystal α− without dendritic particles
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, and as shown in Table 2 below, the obtained acicular α-FeOOH particles are approximately equal to the added amount. 0.201 in terms of Si for the same amount of Fe
Contains ~1.06 at%. 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 acicular crystal alloy magnetic particle powder obtained by heating and reducing the starting material using the above-mentioned acicular α-FeOOH particles with uniform particle size and no dendritic particles as a starting material also has a uniform particle size. is uniform and does not contain dendritic particles,
As a result, it has the characteristics of high bulk density, good dispersibility when forming into paint, high filling property in the paint film, and high residual magnetic flux density Br, but when it comes to specific surface area, At most 20m ² /
It is about 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 experimental examples conducted 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 mixed with sodium silicate prepared in advance in a reactor at a concentration of 0 to 1.0 atomic % based on Fe in terms of Si.
Add chromium sulfate to a NaOH aqueous solution 400 obtained by adding 0 to 5.0 atomic % of Cr in terms of Fe, and
In step 13.8, a suspension containing Fe(OH) ₂ was obtained, and an oxidation reaction was carried out by passing 1000 air per minute into the suspension at a temperature of 45°C to form acicular crystals α containing Si and Cr. - Acicular crystal iron alloy magnetic particles containing Si and Cr and acicular crystal alloy magnetic particles containing Cr obtained by generating FeOOH particles and then heating and reducing the particles at 430°C for 4.0 hours This figure shows the relationship between the specific surface area of powder and the amount of chromium sulfate added. In the figure, curve a is for the case without Si addition, curves b and c
are the cases where the amount of Si added is 0.35 atomic % and 1.0 atomic %, respectively. 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 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 Cr, the inventors found that Si and Cr
In the production of acicular α-FeOOH particles containing ferrous salt, an aqueous alkali solution, and an oxygen-containing gas are passed through the Fe prior to the oxidation reaction.
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 oxygen-containing gas through the resulting Si, Cr
When acicular α-FeOOH particles containing Si and Ni are thermally reduced, the coercive force of the acicular iron alloy magnetic particles containing Si and Cr can be improved while maintaining a large specific surface area. I learned that it can be done. 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. 3 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 nickel sulfate to Fe to contain 0 to 7.0 at% in terms of Ni. ,
Si, Cr was produced by aerating 1,000 air per minute through the suspension at a temperature of 45°C to carry out an oxidation reaction.
Acicular crystal iron alloy magnetic particles containing Si, Cr, and Ni obtained by producing acicular crystal α-FeOOH particles containing Si, 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 mutual 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. The following is an explanation of some of the many experimental examples conducted by the present inventor regarding this phenomenon. 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 was obtained at pH 14.0, and an oxidation reaction was carried out by passing air through the suspension at a rate of 1000 °C per minute at a temperature of 50 °C.
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 coercive force and specific surface area cannot be obtained even when Si, Cr, Ni, and Mg are removed, the present inventors
We believe that this is due to the synergistic effect of Si, Cr, Ni, and Mg. 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 a water-soluble chromium salt is added at a stage when the generation of acicular α-FeOOH particles has been completely completed, the effect of chromium addition in the present invention cannot be obtained because chromium does not enter the particles. . 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 was contained in the produced acicular α-FeOOH particles, as shown in Table 2 below.
As shown in Fig. 2, the obtained acicular α-FeOOH particles have a Cr-equivalent value for almost the same amount of Fe as the added amount.
Contains 0.296 to 2.97 at%. 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 nitrate, 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 was contained in the produced acicular α-FeOOH particles, and as shown in Table 2 below, the obtained acicular α-FeOOH particles
Particles are equivalent to Ni for almost the same amount of Fe as the added amount.
Contains 2.01 to 5.00 at%. 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. If the content is 7.0 atomic % or more, the object of the present invention can be achieved, but 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. , 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 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 Mg.
Almost all of the added water-soluble magnesium salt was contained in the produced acicular α-FeOOH particles, and as shown in Table 2, the obtained acicular α-FeOOH particles
FeOOH particles contain almost the same amount of Fe and Mg as added.
Contains 1.01 to 14.94 at% in terms of conversion. 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 less, it is not preferable because the saturation magnetization decreases. Next, regarding the thermal reduction process, Si, Cr, which has uniform particle size and no dendritic particles,
When obtaining acicular iron alloy magnetic particles by thermally reducing acicular α-FeOOH particles containing Ni and Mg, the higher the reduction temperature, the greater the saturation magnetization of the acicular iron alloy magnetic particles. However, as the reduction temperature increases, the deformation of the acicular grains of the acicular iron alloy magnetic particles and the sintering of the particles and their mutual particles become significant, resulting in the acicular iron alloy magnetic particles obtained. The coercive force of the particles will be extremely reduced. In particular, the shape of particles is easily affected by the heating temperature, and especially when the atmosphere is reducing, particle growth is significant, and a single particle grows to exceed the size of a skeleton particle. gradually disappears, causing deformation of the particle shape and sintering of the particles and each other. As a result, the coercive force decreases. The causes of the deformation of the acicular crystal particles and the sintering of the particles and their mutual particles 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 acicular 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 low. 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, in 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 during the thermal reduction process, Si, Cr, and Ni must be added in advance to the thermal reduction process.
It has a substantially high density with an increased degree of crystallinity by achieving sufficient and uniform particle growth of a single particle of acicular α-Fe ₂ O ₃ particles containing Si and Mg, and Si, Acicular α containing Cr, Ni and Mg
−Si, which retains and inherits the acicular crystals of FeOOH particles,
It is necessary to use acicular α-Fe ₂ O ₃ particles containing Cr, Ni and Mg. 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, Si coated with P compound and Si compound,
Acicular α-FeOOH particles containing Cr, Ni and Mg are acicular α-FeOOH particles containing Si, Cr, Ni and Mg produced by a wet reaction between a ferrous salt aqueous solution and an alkaline aqueous solution. After separating it from the mother liquor, it is suspended in water and the acicular crystal α-
After adding 0.1-2 wt% (calculated as _PO3 ) of phosphate to FeOOH particles and then 0.1-7.0 wt% (calculated as _SiO2 ) of water-soluble silicate, the PH value was adjusted to 3-3. It can be obtained by adjusting to 7. The above method will be explained as follows. Generally, acicular α-FeOOH particles containing Si, Cr, Ni, and Mg become entangled with each other considerably during the crystal growth process in the reaction mother liquor during a wet reaction, forming a group of bonded particles. However, if the intertwined and bonded acicular α-FeOOH particles containing Si, Cr, Ni and Mg are coated with an anti-sintering agent, further sintering will be prevented. Simply by preventing the entanglements and bonds that occur during the crystal growth process in the reaction mother liquor, the entanglements and bonds that occur during the crystal growth process in the reaction mother liquor remain as they are, so the above-mentioned entanglements and bonds occur.
Acicular crystal α- containing Si, Cr, Ni and Mg
The acicular crystal 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. It cannot be said that such particles have sufficient dispersibility in a vehicle, orientation in a coating film, and filling properties. Therefore, before coating acicular α-FeOOH particles containing Si, Cr, Ni, and Mg with a Si compound, the entanglements and bonds generated during the crystal growth process in the reaction mother liquor are disentangled. It is necessary to keep it. Acicular crystal α- containing Si, Cr, Ni and Mg
After separating the FeOOH particles from the mother liquor, they are suspended in water, and when the pH value of the suspension is 8 or higher, Si, Cr,
By adding 0.1 to 2 wt% (calculated as _PO3 ) of phosphate to the acicular α-FeOOH particles containing Ni and Mg, the acicular α-FeOOH particles containing Si, Cr, Ni and Mg can be It is possible to disentangle the entanglements and bonds of FeOOH particles. Acicular crystal α- containing Si, Cr, Ni and Mg
The FeOOH particles may be those which are separated from the reaction mother liquor and washed with water by a conventional method after the generation of acicular α-FeOOH particles containing Si, Cr, Ni and Mg. 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 the amount of Si, Cr, and Ni in the suspension.
If the amount is 0.1 to 2 wt% in terms of PO ₃ to the acicular α-FeOOH particles containing Mg and Mg, it is possible to disentangle the particles and uniformly disperse the particles. The added phosphate is adsorbed on the surface of the acicular α-FeOOH particles, and as shown in Table 3 below, the obtained acicular α-FeOOH particles contain 0.157 to 1.80 atoms of Fe in terms of P. Contains %. If the amount added is less than 0.1 wt%, the effect of addition is not sufficient. On the other hand, if 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 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 may cause problems in separate separation. This is not desirable because it occurs. Next, acicular crystal α containing Si, Cr, Ni and Mg
- Regarding the Si compound film formed on the particle surface of FeOOH particles, the formation of the Si compound film is always due to the entanglement of acicular α-FeOOH particles containing Si, Cr, Ni, and Mg by phosphate. etc. must be disentangled. When adding the water-soluble silicate, the pH value of the suspension is preferably 8 or higher. If a water-soluble silicate is added when the pH value is 8 or less, it will precipitate independently as solid SiO ₂ upon addition, and it will not be possible to efficiently form a thin film on the particle surface. 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 When adjusted to 3 to 7, SiO ₂ precipitates on the surface of the particles to form a film. The amount of water-soluble silicate added is acicular α-crystalline containing Si, Cr, Ni and Mg in terms of _SiO2
It is 0.1 to 7.0 wt% based on FeOOH particles. The added water-soluble silicate is acicular crystal α-
The obtained acicular α-FeOOH particles are precipitated and adsorbed on the FeOOH particle surface, and as shown in Table 3 below, the obtained acicular α-FeOOH particles are Contains 0.65 to 7.91 at%. If it 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 needle crystal alloy magnetic particles with excellent needle crystals, but the purity may be lowered. This decrease leads to a decrease in saturation magnetic flux density, 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
-The conditions for separately separating the particles from the suspension after forming a film on the FeOOH particles with a P compound and a Si compound will be described. When other ordinary means are used, if the particles are uniformly and strongly dispersed in the liquid, it may cause leakage of the cloth, clogging of the cloth, and various other problems such as excessive efficiency. In order to increase the overefficiency, 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 2wt%, if the pH value of the suspension is set to 7 or less, the particle size of the suspension will increase, causing particle aggregation and making it easier to separate. be able to. Also, when the PH value of the suspension is 3 or less,
Acicular crystal α- containing Si, Cr, Ni and Mg
Although agglomeration of FeOOH particles and adsorption of phosphate, as well as the formation of the SiO ₂ film described above, are possible, this is not preferable because it causes equipment 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 particles containing Si, Cr, Ni and Mg coated with a P compound and a Si compound obtained as described above were heat-treated in a non-reducing atmosphere. Si, Cr, Ni and Mg
The acicular α-Fe ₂ O ₃ particles containing α-Fe 2 O 3 are substantially dense with an increased degree of crystallinity, and retain excellent acicular crystals without particle entanglement or bonding. It was inherited. The temperature range of the heat treatment in a non-reducing atmosphere is preferably 500 to 900°C. If the heat treatment temperature in a non-reducing atmosphere is below 500℃, the
Acicular α-Fe ₂ O ₃ containing Si, Cr, Ni and Mg
It is difficult to say that the particles are substantially high-density particles with an increased degree of crystallinity, and if the temperature is 900°C or higher,
This causes deformation of the acicular grains and sintering of the grains and the grains themselves. Furthermore, it requires highly accurate equipment and advanced technology, and is not industrially economical. It is coated with a P compound and a Si compound, which has a substantially high density with an increased degree of crystallinity as described above, and retains excellent acicular crystals without particle entanglement or bonding. Acicular crystal iron alloy containing Si, Cr, Ni, Mg and P obtained by heating and reducing acicular crystal α-Fe ₂ O ₃ particles containing Si, Cr, Ni and Mg in a reducing gas Magnetic particle powder also has a substantially high density due to the increased degree of crystallinity on the particle surface and inside the particle, and retains excellent acicular crystals without particle entanglement or bonding. . As shown in Table 5 below, the obtained acicular iron alloy magnetic particles containing Si, Cr, Ni, Mg, and P contain 0.64 to 7.91 atomic % of Si and Cr in terms of Si, as shown in Table 5 below. 0.294 to 2.97 atomic% in terms of Cr to Fe,
Ni is 1.98 to 5.00 atomic% in terms of Ni, Mg is
1.01 to 14.94 atomic% of Fe as Mg and P as Fe
Contains 0.125 to 1.55 at% in terms of P,
Almost all of the added amount is contained. The temperature range of thermal reduction in reducing gas is
350°C to 600°C is preferred. If the temperature is below 350°C, the reduction reaction progresses slowly and requires a long time. Further, if the temperature is 600° C. or higher, the reduction reaction rapidly progresses, causing deformation of the acicular crystal particles and sintering of the particles and the particles themselves. The present invention configured as described above has the following effects. That is, according to the present invention, the material has acicular crystals, has a uniform particle size, has no dendritic particles mixed therein, has no entanglement of particles, etc., and has a large bulk density as a result, and It has a large specific surface area, a high degree of crystallinity on the particle surface and inside the particle, and is substantially dense, and has a high coercive force.
Si, Cr, Ni, which have Hc and large saturation magnetization σs,
Since it is possible to obtain acicular iron alloy magnetic particles containing Mg and P, it can be used as magnetic particles for high image quality, high output, high sensitivity, and high recording density, which are currently most required. . Furthermore, when producing magnetic paint, the above-mentioned Si,
When using acicular iron alloy magnetic particles containing Cr, Ni, Mg, and P, the noise level is low, and the dispersibility in the vehicle, orientation and filling properties in the coating film are low. An extremely excellent and preferred magnetic recording medium can be obtained. 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 K5101-1978 "Pigment test method". The Si content, Cr content, Ni content, Mg content, and P content in the particles were measured using the "Fluorescent X-ray analyzer model 3063M" (manufactured by Rigaku Denki Kogyo) and the "Fluorescent X-ray analysis according to JIS K0119-1979. The measurement was carried out by fluorescent X-ray analysis according to the General Rules. The characteristics of the magnetic tape are the results of measurements under an external magnetic field of 10 KOe. <Production of needle-like α-FeOOH particle powder> Examples 1 to 15, 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 were separately washed with water using a conventional method. A part of the acicular α-FeOOH particles containing Si, Cr, Ni, and Mg that had been washed with water was dried and ground to obtain a sample for evaluating the properties. 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
The FeOOH particles are shown in the electron micrograph shown in Figure 5 (×
20000), the average value of the long axis is 0.55μm,
The axial ratio (long axis: short axis) was 33:1. Examples 2 to 15 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 particles were produced under the same conditions as in Example 1, except that sodium silicate, chromium sulfate, nickel sulfate, and magnesium sulfate were not added. The main manufacturing conditions at this time are shown in Table 1, and the characteristics are shown in Table 2. The obtained acicular α-FeOOH particle powder is shown in Figure 6.
As is clear from the electron micrograph (×20000) shown in , the average value of the long axis is 0.45 μm, and the axial ratio (long axis: short axis)
The ratio was 9:1, the particle size was asymmetric, and dendritic particles were mixed. <Acicular crystal α- coated with P compound and Si compound
Production of FeOO particle powder> Examples 16 to 30 Comparative example 2; Example 16 Si, Cr, obtained in Example 1 and washed with water,
3300g paste of acicular α-FeOOH particles containing Ni and Mg (equivalent to approximately 1000g of acicular α-FeOOH particles containing Si, Cr, Ni and Mg)
was suspended in 50 ml of water. The pH value of the suspension at this time was 10.0. Next, 300 ml of an aqueous solution containing 8 g of sodium hexametaphosphate (Si, Cr, Ni and Mg
This corresponds to 0.56 wt% as PO ₃ to the acicular α-FeOOH particles containing . ) and stirred for 30 minutes. Next, 130 g of sodium silicate (No. 3 water glass) (3.7 wt as SiO ₂ for acicular α-FeOOH particles containing Si, Cr, Ni, and Mg) was added to the above suspension.
%. ) was added and stirred for 60 minutes, 10% acetic acid was added so that the pH value of the suspension was 6.0, and acicular crystals α-FeOOH containing Si, Cr, Ni and Mg were collected using a press filter. Separate particles,
Si dried and coated with P compound and Si compound,
Acicular α-FeOOH particles containing Cr, Ni and Mg were obtained. Table 3 shows various properties of the obtained acicular α-FeOOH particle powder containing Si, Cr, Ni, and Mg. Examples 17 to 30, Comparative Example 2 Types of particles to be treated, suspension when adding phosphate
Example except that the PH, the amount of phosphate added, the amount of water-soluble silicate added, and the adjusted PH were varied.
Coated with P compound and Si compound in the same manner as 16
Acicular crystal α- containing Si, Cr, Ni and Mg
FeOOH particles or acicular α-FeOOH particles were obtained. Table 3 shows the main manufacturing conditions and characteristics at this time. <Acicular crystal α- coated with P compound and Si compound
Production of Fe ₂ O ₃ particle powder> Examples 31 to 45 Comparative Example 3; Example 31 Acicular crystals containing Si, Cr, Ni, and Mg coated with the P compound and Si compound obtained in Example 16 α−
700g of FeOOH particles were heat-treated in air at 780°C to form Si, Cr, coated with P and Si compounds.
Acicular α-Fe ₂ O ₃ particle powder containing Ni and Mg was obtained. As a result of electron microscopic observation, this particle has an average value of 0.54 μm on the long axis and an axial ratio (long axis: short axis) of 31:1,
It had excellent needle-like crystals. Examples 32 to 45, Comparative Example 3 Si, Cr, Ni coated with P compound and Si compound
Si and Cr coated with a P compound and a Si compound were prepared in the same manner as in Example 31, except that the type of acicular α-FeOOH particles containing Mg and the heat treatment temperature and non-reducing atmosphere were varied. Acicular α-Fe ₂ O ₃ particle powder containing , Ni and Mg was obtained. Table 4 shows the main manufacturing conditions and characteristics at this time. The acicular α-Fe ₂ O ₃ particle powder coated with P compound and Si compound obtained in Comparative Example 3 had an average long axis of 0.44 μm and an axial ratio (long axis: short axis) of 9:1. This caused deformation of the particle shape and sintering of the particles and their mutual particles. <Manufacture of acicular iron or iron alloy magnetic particles> Examples 46 to 60 Comparative Example 4; Example 46 Si, Cr, Ni and Mg coated with the P compound and Si compound obtained in Example 31 Acicular crystals α-
120g of Fe ₂ O ₃ particle powder was put into the retort reduction container in step 3, and H ₂ gas was supplied every minute while driving and rotating.
It was aerated at a rate of 35% and reduced at a reduction temperature of 480°C. The acicular iron alloy magnetic particles containing Si, Cr, Ni, Mg, and P obtained by reduction were placed in a toluene solution for a while to prevent rapid oxidation when taken out into the air. A stable arrangement film was formed on the particle surface by immersing the particle in water and evaporating it. Si, Cr, Ni, Mg and P thus obtained
As a result of X-ray diffraction, the acicular iron alloy magnetic particle powder containing the following showed a single-phase diffraction pattern with the same body-centered cubic structure as iron. In addition, as a result of fluorescent X-ray analysis, Si is 4.33 compared to Fe.
atomic%, Cr 0.499 atomic% relative to Fe, Ni 3.03 atomic% relative to Fe, Mg 4.96 atomic% relative to Fe, P
The content was 0.630 atomic % based on Fe. Therefore, it is considered that iron, Si, Cr, Ni, Mg, and P are in solid solution. This acicular iron alloy magnetic particle powder containing Si, Cr, Ni, Mg and P has an average long axis of 0.25 μm,
Axial ratio (long axis: short axis) 11:1, specific surface area 52.4 m ² /
g, bulk density 0.45 g/ml, coercive force 1551 Oe,
The saturation magnetization was 157.3 emu/g. Further, as is clear from the electron micrograph (×20,000) shown in FIG. 7, this particle powder had uniform particle size and did not contain dendritic particles. Examples 47 to 60, Comparative Example 4 Acicular iron alloy magnetic particle powder containing Si, Cr, Ni, Mg and P in the same manner as in Example 46 except that the type of starting material and the reduction temperature were varied. Alternatively, iron magnetic particle powder was obtained. Table 5 shows various properties of the obtained powder particles. As a result of electron microscopy observation, the ferruginous iron alloy magnetic particles containing Si, Cr, Ni, Mg, and P obtained in Examples 47 to 60 had uniform particle size and did not contain dendritic particles. It was hot. The ferromagnetic particles obtained in Comparative Example 4 had an average long axis of 0.4 μm, an axial ratio (long axis: short axis) of 5:1, a specific surface area of 19.3 m ² /g, and a bulk density of 0.19 g/ml. , coercive force of 1013 Oe, and saturation magnetization of 166.4 emu/g.
Further, as is clear from the electron micrograph (×20,000) shown in FIG. 8, this particle powder had asymmetric particle size and a poor axial ratio. <Manufacture of magnetic tape> Examples 61 to 75, Comparative Example 5; Example 61 Using the acicular iron alloy magnetic particle powder containing Si, Cr, Ni, Mg, and P obtained in Example 46, After blending an appropriate amount of a dispersant, vinyl chloride copolymer, thermoplastic polyurethane resin, and a mixed solvent consisting of toluene, methyl ethyl ketone, and methyl isobutyl ketone to a certain composition, the mixture was mixed and dispersed in a ball mill for 8 hours to form a magnetic paint. did. The above-mentioned mixed solvent was added to the obtained magnetic paint to adjust the paint viscosity to an appropriate level, and the mixture was coated on a polyester resin film and dried in a conventional manner to produce a magnetic tape. The coercive force Hc of this magnetic tape is 1454Oe, the residual magnetic flux density Br is 3980Gauss, and the square type Br/Bm is
0.793, and the degree of orientation was 2.06. Examples 62 to 75, Comparative Example 5: Magnetic tapes were produced in exactly the same manner as in Example 61, except that the type of acicular magnetic particles was varied. Table 6 shows various properties of this magnetic tape.

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【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. 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. Figures 5 to 8 are all electron micrographs (x20000), and Figure 5 is the one obtained in Example 1.
Acicular crystal α- containing Si, Cr, Ni and Mg
FeOOH particles, Figure 6 shows the acicular α-FeOOH particles obtained in Comparative Example 1, and Figure 7 shows the acicular iron alloy containing Si, Cr, Ni, Mg, and P obtained in Example 46. Magnetic Particle Powder FIG. 8 shows the iron magnetic particle powder obtained in Comparative Example 2.

Claims (1)

[Claims] 1. Acicular iron alloy magnetic particle powder for magnetic recording comprising acicular iron alloy magnetic particles containing Si, Cr, Ni, Mg and P. 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. In producing the product, water-soluble silicate is added to any of the above suspensions before the aqueous alkaline solution and oxygen-containing gas are passed through to perform the oxidation reaction.
0.1 to 1.7 atomic % is added, and the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are aerated to perform the oxidation reaction. In any of the reaction solutions in which the reaction is being carried out, a water-soluble chromium salt is added to Fe in an amount of 0.1 to 5.0 at% in terms of Cr, a water-soluble nickel salt is added to Fe in an amount of 0.1 to 7.0 atom% in terms of Ni, and water-soluble magnesium salts for Fe versus Mg
By adding 0.1 to 15.0 atomic% in terms of
Acicular crystal α- containing Si, Cr, Ni and Mg
FeOOH particles are generated and the Si, Cr, Ni and Mg
The acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are separated from the mother liquor, suspended in water, and the acicular α-FeOOH particles containing Si, Cr, Ni, and Mg are suspended in water with a pH value of 8 or more.
−0.1 to 2wt% (converted to PO ₃ ) based on FeOOH particles
of phosphate and then 0.1-7.0wt% ( _SiO2
Acicular needles containing Si, Cr, Ni and Mg coated with P and Si compounds are prepared by adding a water-soluble silicate (converted to Crystalline α-FeOOH particles are obtained, the particles are separated, dried, and then heat treated in a non-reducing atmosphere to obtain Si, Cr,
After forming acicular α-Fe ₂ O ₃ particles containing Ni and Mg, the particles are heated and reduced in a reducing gas to form Si,
A method for producing acicular iron alloy magnetic particles for magnetic recording, the method comprising obtaining acicular iron alloy magnetic particles containing Cr, Ni, Mg, and P. 3. The method for producing acicular iron alloy magnetic particles for magnetic recording according to claim 2, wherein the temperature range of the heat treatment in a non-reducing atmosphere is 500°C to 900°C. 4 The temperature range of thermal reduction in reducing gas is
The method for producing acicular iron alloy magnetic particles for magnetic recording according to claim 2, wherein the temperature is 350°C to 600°C.