JPH0261124B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has acicular crystals that are optimal as magnetic materials for magnetic recording such as audio and video, especially magnetic materials for videos, has uniform particle size, does not contain dendritic particles, and has entangled particles. As a result, it has a large bulk density, and has fine particles with a large specific surface area and a high degree of crystallinity on the particle surface and inside the particles, resulting in a substantially high density. The present invention relates to an acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and P that has a magnetic force Hc and a large saturation magnetization σs, and a method for producing the same. When the acicular iron alloy magnetic particle powder containing Si, Cr, Ni and P obtained according to the present invention is used in the production of a magnetic recording medium, it has acicular crystals and has a 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 and have a large specific surface area, and the degree of crystallinity on the particle surface and inside the particles is increased, making it virtually Due to the high coercive force Hc and large saturation magnetization σs, the dispersibility of the magnetic particles in the vehicle, orientation and filling properties in the coating film are low. It is possible to obtain an excellent magnetic recording medium which has a low level of noise generated during recording and reproduction of magnetic tape and can obtain 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 lowered raise levels. filling property,
It is necessary to improve the smoothness of the tape surface, and there is a growing demand for further 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 Video and Audio Magnetic Tapes,'' published on pages 82 to 105 of the Japanese issue, ``The image quality of video tape recorders varies depending on the tape,'' published on pages 83 to 84. The main characteristics that are measured are the S/N ratio, chroma noise, and video frequency characteristics. ...These quantities that represent image quality are determined by the electromagnetic conversion characteristics of the tape and head system, and the electromagnetic conversion characteristics of the tape It is clear from the statement, "The physical properties of the tape are largely determined by the magnetic material." 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 It has smoothness.The surface properties and dispersibility are constant, and the SN ratio improves 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 the magnetic powder is. It is clear from the description. That is, as one method for improving the video S/N ratio, it is important to reduce the noise level caused by magnetic recording media, and for that purpose,
As is clear from the above description, it is known that a method of reducing the particle size of the acicular magnetic particle powder, which is the magnetic material used, 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 27-9 of MR81-11. "Fig. 3" is a diagram showing the relationship between the specific surface area of particles and the noise level in Cr-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, uniform viscosity, and , 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 statements such as "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 depends on the saturation magnetization σs of the magnetic particles as large as possible, 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. …. In order to increase the Br of the tape, the basic principle is to increase the saturation magnetization Is (σs) that the magnetic material has in a perfect state (for example, in a single crystal state). …. Even if the material is the same, depending on the filling degree, which indicates the proportion of magnetic powder, etc.
Br changes. 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 the 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 coercive force Hc of 400 to 800 Oe, but on the other hand, the saturation magnetization σs
It is low at 60-80 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 particles with such characteristics, the starting material, acicular α-FeOOH particles, must 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 growth of FeOOH nuclei. 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 foregoing, the present inventor has discovered a material that has acicular crystals, uniform particle size, no dendritic particles, no intertwining of particles, etc., and a large specific surface area and a particle surface. and substantially high density with an increased degree of crystallinity inside the particles,
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 inventor then discovered that the ferrous salt aqueous solution and the alkaline aqueous solution were
Acicular _crystals α-
In producing FeOOH particles, in any of the suspensions before an oxidation reaction is carried out by passing the alkaline aqueous solution and oxygen-containing gas,
A water-soluble silicate is added in an amount of 0.1 to 0.7 atomic % in terms of Si to Fe, and the ferrous salt aqueous solution,
Water-soluble chromium is present in any one of the alkaline aqueous solution, the suspension before an oxidation reaction is carried out by passing an oxygen-containing gas through it, and the reaction solution in which an oxidation reaction is carried out by passing an oxygen-containing gas through the aqueous solution. By adding 0.1 to 5.0 at% of salt to Fe in terms of Cr and 0.1 to 7.0 at% of water-soluble nickel salt to Fe in terms of Ni, acicular crystals α- containing Si, Cr and Ni can be formed. FeOOH particles are generated and the Si, Cr and Ni
The acicular α-FeOOH particles containing Si, Cr, and Ni are separated from the mother liquor and then suspended in water.
0.1-2wt% (converted to PO ₃ ) based on FeOOH particles
of phosphate and then 0.1-7.0wt% ( ^SiO2
Acicular crystals α containing Si, Cr and Ni coated with P and Si compounds are prepared by adding water-soluble silicate (converted to - Obtain FeOOH particles, separate the particles,
Si, Cr and Ni coated with P and Si compounds by drying and then heat treatment in a non-reducing atmosphere
After forming acicular crystal α-Fe ₂ O ₃ particles containing α-Fe 2 O 3 , the particles are heated and reduced in a reducing gas to obtain acicular crystals, uniform particle size, and a mixture of dendritic particles. There is no entanglement of particles, and
It is substantially dense with a large specific surface area and a high degree of crystallinity on the particle surface and inside the particle, and also has a high coercive force Hc and a large saturation magnetization σs.
The present invention was completed by discovering that an acicular alloy magnetic particle powder having the following properties can be obtained. That is, the present invention provides an acicular iron alloy magnetic particle powder for magnetic recording consisting of acicular iron alloy magnetic particles containing Si, Cr, Ni, and P, and a ferrous salt aqueous solution and an alkaline aqueous solution that are reacted. In order to generate acicular α-FeOOH particles by passing an oxygen-containing gas through the resulting suspension containing Fe(OH) ₂ and having a pH of 11 or higher, the aqueous alkali solution and the oxygen-containing gas are passed through the resulting suspension to produce acicular α-FeOOH particles. A water-soluble silicate is added to any of the suspensions before 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.
5.0 at% Ni and water soluble nickel salt for Fe
By adding 0.1 to 7.0 atomic% in terms of
Acicular α-FeOOH particles containing Si, Cr and Ni are generated, and the acicular α-FeOOH particles containing Si, Cr and Ni are separated from the mother liquor and then suspended in water. Si, Cr when the pH value of the liquid is 8 or higher
and Ni-containing acicular α-FeOOH particles, 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 silicic acid. After adding salt, adjust the pH value of the suspension from 3 to 7.
Acicular crystal α- containing Si, Cr and Ni coated with P compound and Si compound by preparing
FeOOH particles are obtained, the particles are separated, dried, and then heat treated in a non-reducing atmosphere to combine the P compound and Si.
After forming acicular α-Fe ₂ O ₃ particles containing Si, Cr, and Ni coated with a compound, the particles are heated and reduced in a reducing gas to form needles containing Si, Cr, Ni, and P. This is a method for producing acicular iron alloy magnetic particles for magnetic recording by obtaining acicular 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 needle-shaped α-FeOOH core particles from an aqueous solution containing Fe(OH) ₂ and the generation of needle-shaped α−FeOOH core 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 the aqueous alkali solution and oxygen-containing gas in 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
(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 when generating 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, it is possible to obtain acicular α-FeOOH particles with uniform particle size and no dendritic particles. 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. In terms of Si for the same amount of Fe,
Contains 0.203 to 1.03 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 percent, 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, a ferrous iron aqueous solution containing 1.2 mol/Fe ²⁺
A NaOH aqueous solution obtained by adding sodium silicate prepared in advance in a reactor to Fe in an amount of 0 to 1.0 atomic % in terms of Si, and chromium sulfate in an amount of 0 to 5.0 atomic % in terms of Cr to Fe. 400 plus PH13.8
A suspension containing Fe(OH) ₂ was obtained, and 1000 air per minute was passed through the suspension at a temperature of 45°C to carry out an oxidation reaction, thereby forming acicular crystals α-containing Si and Cr. Generate FeOOH particles, then
Specific surface area of acicular crystal iron alloy magnetic particles containing Si and Cr and acicular crystal alloy magnetic particles containing Cr obtained by heating and reducing the particles at 430°C for 4.0 hours and addition of chromium sulfate This shows the relationship between quantities. 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 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 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 nitsul salt added and Si, Cr.
FIG. 2 is a relationship diagram of the coercive force of the acicular iron alloy magnetic particles containing Ni 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 nickel sulfate to an aqueous NaOH solution 400 obtained by adding nickel sulfate to Fe in an amount of 0 to 7.0 atom% in terms of Ni. ,
Si, Cr was produced by aerating 1000 ml of 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 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 synergistic effect of Si, Cr, and Ni. 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 generated after the start of aeration of oxygen-containing gas. Furthermore, even if a water-soluble chromium salt is added at a stage when the formation 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 2.98 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 approximately the same amount of Fe as the added amount.
Contains 2.05 to 7.00 at%. The amount of water-soluble nickel salt added is Fe compared to Ni.
If the amount is 0.1 atomic % or less, 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. Next, regarding the thermal reduction process, Si and Cr have uniform particle sizes and do not contain dendritic particles.
When obtaining acicular iron alloy magnetic particles by thermally reducing acicular α-FeOOH particles containing and Ni,
The higher the reduction temperature, the greater the saturation magnetization of acicular iron alloy magnetic particles can be obtained. The sintering between the particles becomes significant, and the coercive force of the obtained acicular iron alloy magnetic particles is 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 by dehydration on the particle surface and inside the particles, and the growth of single particles is insufficient, resulting in crystal formation. The degree of sexuality 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 during the thermal reduction process, Si, Cr, and
It has a substantially high density with an increased degree of crystallinity by achieving sufficient and uniform particle growth of single acicular α-Fe ₂ O ₃ particles containing Ni, and Si, Cr It is necessary to use acicular α-Fe ₂ O ₃ particles containing Si, Cr, and Ni that maintain and inherit the crystallinity of the acicular α-FeOOH particles containing Si, Cr, and Ni. 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, Cr coated with P compound and Si compound
The acicular α-FeOOH particles containing Si, Cr and Ni were produced by a wet reaction between a ferrous salt aqueous solution and an alkaline aqueous solution, and the acicular α-FeOOH particles containing Si, Cr and Ni were separated from the mother liquor. After that, it is suspended in water, and in a state where the pH value of the suspension is 8 or more, Si,
Adding 0.1 to 2 wt% (calculated as PO ₃ ) of phosphoric acid to acicular α-FeOOH particles containing Cr and Ni,
It can then be obtained by adding 0.1 to 0.7 wt% (in terms of _SiO2 ) of water-soluble silicate, and then adjusting the pH value of the suspension to 3 to 7. The above method will be explained as follows. Generally, acicular crystals α- containing Si, Cr and Ni
During the process of crystal growth in the reaction mother liquor during the wet reaction, FeOOH particles are quite tightly entangled and form a bonded particle group, and the intertwined and bonded Si, Cr, and Ni If the particles of acicular α-FeOOH particles contained therein are coated with an anti-sintering agent, further sintering will only be prevented, and the entanglement that occurred during the crystal growth process in the reaction mother liquor will be prevented. Since the bonds remain as they are, the intertwined and bonded Si and Cr
The acicular crystal alloy magnetic particle powder obtained by heating and reducing the acicular α-FeOOH particles containing Ni in a non-reducing atmosphere also has particles entangled and bonded together. Become. It cannot be said that such particles have sufficient dispersibility in a vehicle, orientation in a coating film, and filling properties. Therefore, the acicular crystal α- containing Si, Cr and Ni
Prior to coating FeOOH particles with Si compound,
It is necessary to disentangle the entanglements and bonds generated during the crystal growth process in the reaction mother liquor in advance. After separating the acicular α-FeOOH particles containing Si, Cr and Ni from the mother liquor, suspend them in water, and in a state where the pH value of the suspension is 8 or more, the needles containing Si, Cr and Ni 0.1 to 2wt% to crystalline α-FeOOH particles
By adding phosphate (calculated as _PO3 ),
It is possible to disentangle the entanglements and bonds of acicular α-FeOOH particles containing Si, Cr, and Ni. Acicular α-FeOOH particles containing Si, Cr and Ni are acicular α-FeOOH particles containing Si, Cr and Ni.
After FeOOH particles are produced, they may be separated 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 the amount of Si, Cr and
PO ₃ for Ni-containing acicular α-FeOOH particles
If the amount is 0.1 to 2 wt%, the entanglement of the particles can be disentangled and the particles can be uniformly dispersed. 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 0.158 to 1.737 atoms of Fe in terms of P. Contains %. If the amount added is less than 0.1wt%, 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 will cause damage in separate separation. This is not desirable because it causes Next, acicular crystal α- containing Si, Cr and Ni
Regarding the Si compound film formed on the particle surface of FeOOH particles, the formation of the Si compound film requires disentangling the acicular α-FeOOH particles containing Si, Cr, and Ni using phosphate. must be done after 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 alone 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 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 determined by _{the amount} of acicular α-
It is 0.1 to 7.0 wt% based on FeOOH particles. 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. 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 7.05 at%. Note that examples of the water-soluble silicate to be added include sodium silicate and potassium silicate. Next, acicular crystal α- containing Si, Cr and Ni
The conditions for separately separating FeOOH particles from a suspension after forming a film 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, for example, leakage of the cloth, clogging of the cloth, and other various overefficiency may be aggravated. In order to increase the overefficiency, it is necessary that the particles dispersed by the addition of the phosphate described above should be appropriately aggregated. When the amount of phosphate added is within the range of 0.1 to 2 wt%, if the pH value of the suspension is set to 7 or less, the viscosity of the suspension will increase and particles will aggregate, making it easier to separate. be able to. Also, when the PH value of the suspension is 3 or less,
Aggregation of acicular α-FeOOH particles containing Si, Cr, and Ni and adsorption of phosphate, as well as the aforementioned SiO ₂
Although it is possible to form a film, it is not preferable because it causes equipment problems and quality problems (during melting). In addition, in order to adjust the pH to 3-7, use acetic acid, sulfuric acid,
Phosphoric acid etc. can be used. Si obtained by heat-treating acicular α-FeOOH particles containing Si, Cr and Ni coated with a P compound and a Si compound obtained as explained above in a non-reducing atmosphere; The acicular α-Fe ₂ O ₃ particles containing Cr and Ni have a substantially high density with an increased degree of crystallinity, and have an excellent acicular shape without particle entanglement or bonding. This is what has been preserved and passed down from generation to generation. 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 crystallinity of the acicular α- _Fe2O3 particles containing Si, Cr and Ni coated with P and Si compounds is reduced. It is difficult to say that the particles have a substantially high density due to the high temperature, and if the temperature is 900° C. or higher, deformation of the acicular crystal particles and sintering of the particles and the particles among themselves will occur. Furthermore, it requires highly accurate equipment and advanced technology, and is not industrially economical. It is a substantially high-density material with an increased degree of crystallinity as described above, and is coated with a P compound and a Si compound that retains excellent acicular crystals without particle entanglement or bonding. Acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and P obtained by heating and reducing acicular α-Fe ₂ O ₃ particles containing Si, Cr, and Ni in a reducing gas It also has a substantially high density with an increased degree of crystallinity on the particle surface and inside the particle, and retains excellent acicular crystals without particle entanglement or bonding. The obtained acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and P contains 0.65 to 7.04 at% of Si and Cr in terms of Si, as shown in Table 5 below.
0.269 to 2.99 atomic% in terms of Cr to Fe, Fe to Ni
It contains 2.02 to 7.00 atomic % of Ni in terms of Ni and 0.157 to 1.737 atomic % of P in terms of P relative to Fe, which is almost the entire amount added. 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. Furthermore, 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 , substantially high density with a large specific surface area and increased degree of crystallinity on the particle surface and inside the particle, and also has a high coercive force.
It is possible to obtain acicular iron alloy magnetic particles containing Si, Cr, Ni, and P that have Hc and large saturation magnetization σs, thereby achieving high image quality, high output, high sensitivity, and It can be used as magnetic particle powder for high recording density. Furthermore, when producing magnetic paint, the above Si,
When using acicular iron alloy magnetic particles containing Cr, Ni and P, the noise level is low and the dispersibility in the vehicle, orientation and filling properties in the coating film are extremely excellent. , a preferable magnetic recording medium can be obtained. Moreover, since the acicular iron alloy magnetic particles containing Si, Cr, Ni and P obtained by the present invention are not ultrafine particles, they are relatively easy to handle when forming into a paint. Next, the present invention will be explained with reference to Examples and Comparative Examples. In addition, the specific surface area of the additives in the above 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 amounts of Si, Cr, Ni, and P in the particles were measured using a Fluorescent X-ray analyzer model 3063M (manufactured by Rigaku Denki Kogyo) and in accordance with the "General Rules for Fluorescent X-ray Analysis" of JIS K0119-1979. Therefore, it was measured by performing fluorescence X-ray analysis. 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 14, Comparative Example 1 Example 1 Ferrous sulfate aqueous solution containing 1.2 mol/Fe ²⁺ 300
Sodium silicate (No. 3) (SiO ₂ 28.55wt%) 152g was added in advance to contain 0.20 atomic% in terms of Si with respect to Fe prepared in the reactor, and 0.50 atomic% in terms of Cr with respect to Fe. Contains 644g of chromium sulfate,
5.45-N obtained by adding 2884g of nickel sulfate to contain 3.0 at% of Ni in terms of Fe.
In addition to NaOH aqueous solution 400, a reaction was performed to produce a Fe(OH) ₂ suspension containing Si, Cr, and Ni at pH 14.0 and temperature 45°C. Into the Fe(OH) ₂ suspension containing Si, Cr and Ni,
Acicular crystal α- containing Si, Cr and Ni was produced by passing 1000 air per minute at a temperature of 50℃ for 6.3 hours
FeOOH particles 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, and Ni that had been washed with water was dried and ground to obtain a sample for evaluating the properties. The obtained acicular crystal α- containing Si, Cr and Ni
As a result of X-ray diffraction, FeOOH particles were found to be α-FeOOH
A diffraction pattern identical to the crystal structure of the particles was obtained. In addition, as a result of fluorescent X-ray analysis, Si was compared to Fe.
0.204 atomic%, Cr to Fe 0.496 atomic%, Ni
The content was 3.02 atomic % based on Fe. Therefore, it is considered that Si, Cr and Ni are dissolved in solid solution in the acicular α-FeOOH particles. This acicular crystal α- containing Si, Cr and Ni
The FeOOH particles are shown in the electron micrograph shown in Figure 3 (×
20000), the average value of the long axis is 0.50μm,
The axial ratio (long axis: short axis) was 28:1. Examples 2 to 14 The type and concentration of the ferrous salt aqueous solution, the concentration of the NaOH aqueous solution, and the type, amount, and timing of addition of the water-soluble silicate, water-soluble chromium salt, and water-soluble nickel salt were varied. is the same as in Example 1.
Acicular α-FeOOH particles containing Si, Cr and Ni were produced. The main manufacturing conditions at this time are shown in Table 1, and the characteristics are shown in Table 2. In Example 5, the reaction for producing Fe(OH) ₂ suspension was carried out at 40°C, and the reaction for producing needle-shaped α-FeOOH was carried out at 45°C. Comparative Example 1 Acicular α-FeOOH particles were produced under the same conditions as in Example 1 except that sodium silicate, chromium sulfate, and nickel 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 4.
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 FeOOH particle powder> Examples 15 to 28 Comparative Example 2 Example 15 3000 g of paste of acicular α-FeOOH particles containing Si, Cr and Ni obtained in Example 1 and washed with water (Si, Cr and Ni-containing acicular crystals α-
This corresponds to approximately 1000g of FeOOH particles. ) was suspended in 60% water. The pH value of the suspension at this time was 9.7. Next, 300 ml of an aqueous solution containing 8 g of sodium hexametaphosphate (as PO ₃ for acicular α-FeOOH particles containing Si, Cr and Ni) was added to the above suspension.
This corresponds to 0.56wt%. ) and stirred for 30 minutes. Next, 148 g of sodium silicate (No. 3 water glass) (corresponding to 4.2 wt% as SiO ₂ based on the acicular α-FeOOH particles containing Si, Cr, and Ni) was added to the above suspension, and the mixture was stirred for 60 minutes. After stirring, the suspension
After adding 10% acetic acid so that the pH value is 5.8,
Acicular α-FeOOH particles containing Si, Cr and Ni are separated by a press fifter and dried to produce acicular α-FeOOH particles containing Si, Cr and Ni coated with a P compound and a Si compound. I got it. The obtained acicular crystal α- containing Si, Cr and Ni
Table 3 shows the properties of the FeOOH particles. Examples 16 to 28, Comparative Example 2 Type of particles to be treated, suspension when phosphate is added
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 15
Acicular α-FeOOH particles or acicular α-FeOOH particles containing Si, Cr and Ni were obtained. Table 3 shows the main manufacturing conditions and characteristics at this time. <Si, Cr and Si coated with P and Si compounds
Production of acicular α-Fe ₂ O ₃ particle powder containing Ni> Examples 29 to 42 Comparative Example 3 Example 29 Si, Cr and Ni coated with the P compound and Si compound obtained in Example 15 Acicular crystals α- containing
Si, Cr coated with P compound and Si compound was prepared by heating 1000g of FeOOH particle powder in air at 750℃.
Acicular crystal α-Fe ₂ O ₃ particle powder containing Ni and Ni was obtained. As a result of electron microscopic observation, this particle has an average value of 0.48 μm on the long axis and an axial ratio (long axis: short axis) of 26:1,
It had excellent needle-like crystals. Examples 30 to 42, Comparative Example 3 Si, Cr and Si coated with P compound and Si compound
P compound and Si
Acicular α-Fe ₂ O ₃ particle powder containing Si, Cr and Ni coated with a compound 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. It was hot. <Manufacture of acicular iron or iron alloy magnetic particles> Examples 43 to 56 Comparative Example 4 Example 43 Needles containing Si, Cr, and Ni coated with the P compound and Si compound obtained in Example 29 120 g of crystalline α-Fe ₂ O ₃ particle powder was put into the retort reduction container of No. 3, and while driving and rotating, H ₂ gas was passed through the container at a rate of 40 per minute, and reduction was carried out at a reduction temperature of 440°C. The acicular iron alloy magnetic particles containing Si, Cr, Ni, and P obtained by reduction were first immersed in toluene solution to prevent rapid oxidation when taken out into the air. By evaporating this, a stable oxide film was formed on the particle surface. As a result of X-ray diffraction, the thus obtained acicular iron alloy magnetic particles containing Si, Cr, Ni, and P had 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 4.70 compared to Fe.
The content of Cr was 0.495 atomic % based on Fe, Ni was 3.01 atomic % based on Fe, and P was 0.631 atomic % based on Fe. Therefore, it is considered that iron, Si, Cr, Ni, and P are in solid solution. This acicular iron alloy magnetic particle powder containing Si, Cr, Ni, and P has an average long axis of 0.30 μm, an axial ratio (long axis: short axis) of 12:1, and a specific surface area of 47.1 m ² /g. The bulk density was 0.47 g/ml, the coercive force was 1420 Oe, and the saturation was 165.2 emu/g. Further, as is clear from the electron micrograph (×20,000) shown in FIG. 5, this particle powder had uniform particle size and did not contain any dendritic particles. Examples 44 to 56, Comparative Example 4 Acicular iron alloy magnetic particles or iron containing Si, Cr, Ni, and P were prepared in the same manner as in Example 43, except that the type of starting materials and the reduction temperature were varied. Magnetic particle powder was obtained. Table 5 shows various properties of the obtained powder particles. As a result of electron microscopic observation, the acicular iron alloy magnetic particles containing Si, Cr, Ni, and P obtained in Examples 44 to 56 had uniform viscosity and did not contain dendritic particles. Ta. 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. 6, this particle powder had asymmetric particle size and a poor axial ratio. <Manufacture of magnetic tape> Examples 57 to 70, Comparative Example 5 Example 57 Using the acicular iron alloy magnetic particles containing Si, Cr, Ni, and P obtained in Example 43, disperse an appropriate amount. After mixing and dispersing in a ball mill for 8 hours, a magnetic coating material was prepared by mixing and dispersing the mixture in a ball mill for 8 hours. 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 1345Oe, the residual magnetic flux density Br is 3910Gauss, and the square type Br/Bm is
0.790, and the degree of orientation was 2.02. Examples 58 to 70, Comparative Example 5 Magnetic tapes were produced in exactly the same manner as in Example 57, except that the type of acicular magnetic particles was varied. Table 6 shows the characteristics of this magnetic tape.

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】 [Brief explanation of drawings]

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 electron micrographs (×20000), and FIG. 3 shows the Si, Cr, and Ni obtained in Example 1.
4 shows the acicular α-FeOOH particles obtained in Comparative Example 1, and FIG. 5 shows the acicular α-FeOOH particles obtained in Example 43 containing Si, Cr, Ni and P. FIG. 6 shows the iron magnetic particles 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, 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. 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. A water-soluble chromium salt is added in an amount of 0.1 to 5.0 atomic % based on Fe in terms of Cr, and a water-soluble nickel salt is added in an amount of 0.1 to 7.0 atomic % based on Fe in terms of Ni. By keeping it in place, acicular α-FeOOH particles containing Si, Cr and Ni are generated, and the Si, Cr
The acicular α-FeOOH particles containing Si, Cr and Ni are separated from the mother liquor and suspended in water, and the acicular α-FeOOH particles containing Si, Cr and Ni are suspended in water with a pH value of 8 or more. Add 0.1 to 2 wt% (calculated as _PO3 ) of phosphate to the particles, then 0.1 to 7.0 wt%
After adding water-soluble silicate (in terms of _SiO2 ), Si, Cr and Ni coated with P and Si compounds were prepared by adjusting the pH value of the suspension to 3-7.
Acicular α-FeOOH particles containing acicular α-FeOOH particles were obtained, the particles were separated, dried, and then heat-treated in a non-reducing atmosphere to obtain Si coated with P and Si compounds.
After forming acicular α-Fe ₂ O ₃ particles containing Cr and Ni, 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, 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.