JPH0371378B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides magnetic iron oxide particles for magnetic recording, particularly magnetic iron oxide particles for rigid disks, floppy disks, and digital recording. are not mixed, and the axis ratio (major axis: short axis) is small at 4:1.
The following relates to a magnetic iron oxide particle powder consisting of spindle-shaped magnetite particles or maghemite particles, which has a ratio of 2:1 or less, and has a high coercive force and excellent temperature stability, and a method for producing the same. . [Prior Art] In recent years, as magnetic recording and reproducing equipment has become longer recording time and has become smaller and lighter, both these magnetic recording and reproducing equipment and magnetic recording media such as magnetic tapes and magnetic disks have become more efficient and sophisticated. Demand for density recording is increasing. This fact can be seen, for example, in "Development of Magnetic Materials and Highly Dispersed Magnetic Powder Technology (1982)" published by the General Technology Center.
On page 134 of ``The technological improvement that has been consistently pursued <sub>since</sub> the advent of magnetic disk devices to this day has been to increase the recording <sub>density</sub> . Despite using iron powder as a magnetic material, recording density has been dramatically improved by more than two orders of magnitude over the past 20 years.The main reason for this is the improvement of γ-Fe <sub>2</sub> O <sub>3</sub> itself. In addition, other improvements include thinner coatings, higher precision on the surface of the thin film, adoption of magnetic field alignment technology, lower head flying height, and improved head characteristics. In order to improve the performance and recording density of magnetic recording media, it is necessary to improve dispersibility, filling properties, residual magnetic flux density Br and coercive force Hc, improve the smoothness of the tape surface, and make the coating film thinner. It is. This fact is based on page 140 of the aforementioned ``Development of magnetic materials and high dispersion technology of magnetic particles'', ``Increasing recording density...
...It is necessary to increase Br to ensure a constant output. In order to increase Br, it is necessary to increase not only the magnetic field orientation but also the filling rate of the magnetic powder. '', page 15 of the same document states, ``An important index expressing performance in magnetic recording is...recording density. Until now, its increase has mainly been achieved by improving magnetic heads and recording media. To summarize the direction of improvement in this field to date,...
...Recording medium; thin and high coercive force (coercive force)
Emphasis has been placed on realizing a magnetic layer of (Hc)...
...'', the statement on page 141 of the same document, ``For high-density recording, thinning of the coating film is an important factor'', and in the case of floating heads such as rigid disks. On page 143 of the same document, ``The flying height of the head is the controlling factor for high-density recording.
By making this smaller, higher density becomes possible. ...When the flying height is lowered, if the surface of the disk is poor, the reproduction output decreases due to chipping of the head, and stable flying is disturbed, resulting in head crash. Therefore, high-precision finishing of the coating film surface is important. It is clear from the statement ``. These properties of magnetic recording media are closely related to the magnetic iron oxide particles used in magnetic recording media, and there is a strong desire to improve the properties of magnetic iron oxide particles. The relationship between the various characteristics of the magnetic recording medium and the characteristics of the magnetic iron oxide particles used will now be detailed as follows. First, the residual magnetic flux density Br of a magnetic recording medium depends on the dispersibility of the magnetic iron oxide particles in the vehicle, the orientation and filling properties in the coating film. In order to improve the dispersibility in the vehicle, the orientation and filling properties in the coating film, the particle size of the magnetic iron oxide particles dispersed in the vehicle must be uniform, and dendritic particles must be mixed. As a result, a high bulk density is required. Next, in order to improve the surface properties of magnetic recording media,
A magnetic iron oxide particle powder with good dispersibility, good orientation, and small particle size is preferable.As such magnetic iron oxide particle powder, the particle size is uniform and dendritic particles are not mixed. , high bulk density is required. Furthermore, in order to thin the coating film of magnetic recording media,
On page 141 of the above document, ``To make the coating film thinner, it is necessary to reduce the size of the magnetic powder and improve its orientation in the coating film thickness direction.In the end, forming a thin coating film requires 2.3 As mentioned above, using magnetic powder with low oil absorption leads to the production of magnetic paint with good coating properties.''As is clear from the description, magnetic iron oxide particle powder has good dispersibility and orientation. As such a magnetic iron oxide particle powder,
As mentioned above, it is required that the particle size is uniform and that dendritic particles are not mixed. As mentioned above, the coercive force Hc of the magnetic recording medium is
For high-density recording, it is necessary that the coercive force Hc of the magnetic particles dispersed in the vehicle be as high as possible. On the other hand, one of the methods for improving recording density in magnetic recording and reproducing equipment is to reduce the width of the magnetic head cap. This fact is based on the statement on page 15 of the above-mentioned document that states, ``An important index expressing performance in magnetic recording is...recording density.'' Until now, its increase has been mainly due to improvements in magnetic heads and recording media. To summarize the directions of improvement so far in this field:
This is clear from the description "...magnetic head; narrow gap width and narrow track width...". The recording principle of the recording medium and the magnetic head in the conventionally adopted longitudinal recording direction (a method of recording signals in the longitudinal direction of the magnetic layer) is as described on page 18 of the aforementioned document, ``In the ring head (Figure 2a), the winding The signal current creates an arc-shaped magnetic field near the gap in the magnetic core.This has a strong longitudinal component at the center of the gap, so the medium is mainly magnetized in the longitudinal (in-plane) direction.'' It is as follows. In recent years, for the purpose of high-density recording, the gap width of magnetic heads has become increasingly narrower. However, when the gap width of magnetic heads is narrowed, the magnetic field near the gap of the magnetic core has a strong vertical component as well as a longitudinal component. will be included. Therefore, in the surface layer of the magnetic recording medium that is in contact with the head, the magnetic flux distribution in the direction perpendicular to the medium increases significantly. Therefore, in order to achieve high-density recording, it is preferable that the magnetic recording medium have an easy magnetization direction perpendicular to the medium. Typical magnetic particles conventionally used are acicular magnetite particles or maghemite particles, and in this case, due to shape anisotropy, the direction of easy magnetization is the longitudinal direction of the acicular shape, so acicular iron oxide particles are used. It is preferable to increase the vertical component by vertically oriented in the coating film or randomly oriented three-dimensionally. This fact is explained in Japanese Unexamined Patent Publication No. 183626/1983, "Also, in recent years, the concept of perpendicular magnetization recording has been introduced.
There is also a proposal to effectively use the residual magnetization component in the direction perpendicular to the surface of the magnetic recording medium. This perpendicular magnetization recording increases the recording density defined above, and...
..." and "A coated magnetic layer that uses diagonal or perpendicular magnetization components that are not parallel to the magnetic surface..."
It is clear from the statement "...". In order to randomly orient the magnetic iron oxide particles three-dimensionally in the coating film and increase the vertical component,
As mentioned above, in addition to having uniform particle size and no dendritic particles mixed in, the particle size of the magnetic iron oxide particles is made small, and the axial ratio is made as small as possible to 4:1 or less, especially 2:1. It is effective to do the following, that is, to be isotropic in shape. This fact is based on the above-mentioned Japanese Unexamined Patent Publication No. 57-183626, which states, ``The present invention... has a major diameter of 0.4 to 2μ or 0.3 to 1μ and an aspect ratio of 5 to 20, which is used in the above-mentioned prior art.
Instead of regular acicular particles, the particle size is 0.30μ
By making it as small as below and having a short shape with an aspect/width ratio of more than 1 and less than 3,... in-plane orientation due to thinning of the coating film in the thickness direction during application and drying, and flow during application. It is characterized by suppressing the tendency of the particles to be oriented in the direction of the casting and lying in the plane, and to actively increase the perpendicular residual magnetization if necessary. . It is clear from the statement ``. Currently, acicular magnetite particles or acicular maghemite particles are mainly used as magnetic particles for magnetic recording. These are generally produced by air oxidizing a colloidal aqueous solution with a pH of 11 or higher containing ferrous hydroxide particles obtained by reacting an aqueous ferrous salt solution with an alkali (usually called a "wet reaction"). The obtained acicular α-FeOOH particles are reduced to acicular magnetite particles in a reducing gas such as hydrogen at 300 to 400°C, or are then oxidized in air at 200 to 300°C to form acicular crystals. It is obtained by making it into maghemite particles. As mentioned above, magnetic particles with uniform particle size, no dendritic particles mixed in, and a small axis ratio (long axis: short axis) are currently most in demand, and these characteristics are In order to obtain magnetic particles with the following properties, it is necessary that the particle size of the goethite particles used as the starting material be uniform, that dendritic particles are not mixed, and that the axial ratio (major axis: short axis) of the particles is small. be. Conventionally, the most typical known method for producing goethite particles in the alkaline range of pH 11 or higher is to add a solution containing ferrous hydroxide particles obtained by adding an equivalent or more alkaline solution to a ferrous salt solution, and then add a solution containing ferrous hydroxide particles to pH 11.
Goethite particles are obtained by carrying out the oxidation reaction at a temperature of 80° C. or lower. By the way, as is well known, the magnitude of the coercive force of magnetic particles depends on shape anisotropy, crystal anisotropy, strain anisotropy, and exchange anisotropy, or on their interaction. . Acicular magnetite particles or acicular maghemite particles, which are currently used as magnetic particles for magnetic recording, have a relatively high coercive force (350 ~450Oe). In this way, known acicular magnetite particles or acicular maghemite particles utilize their shape anisotropy to obtain a relatively high coercive force, but when Co is added to these particles, It is generally known that the coercive force can be further improved by utilizing the crystal anisotropy. In this case, it is known that as the amount of Co added increases, the coercive force increases. [Problems to be solved by the invention] At present, magnetic particle powders with uniform particle size, no dendritic particles mixed in, and a small axial ratio (long axis: short axis) are
The most demanded point is that the particles obtained by the above-mentioned known method for producing acicular goethite particles as a starting material are acicular with an axial ratio (major axis:minor axis) of 10:1 or more. The particles have a certain shape, and dendritic particles are mixed therein, and considering the particle size, it is difficult to say that the particles have a uniform particle size. Therefore, the present inventor developed a method for producing goethite particles by passing an oxygen-containing gas through an aqueous solution containing FeCO ₃ obtained by reacting a ferrous aqueous salt solution with an alkali carbonate to oxidize it (Unexamined Japanese Patent Publication No. Showa 50-
80999). When using this method, the particle size is uniform,
A powder consisting of spindle-shaped goethite particles without dendritic particles mixed therein is obtained. However, the axial ratio (major axis:minor axis) of goethite particles obtained by this method is about 7:1, and it is required to further reduce the axial ratio (major axis:minor axis). On the other hand, when the axial ratio (long axis: short axis) of magnetic iron oxide particles is reduced, the coercive force of these magnetic iron oxide particles is about 300 Oe or less because the anisotropy derived from the shape cannot be utilized. I become confused. Therefore, as described above, it is known that the coercive force can be increased by adding Co to magnetic iron oxide particles having a small axial ratio (long axis: short axis). Furthermore, when magnetic iron oxide particles with a small axial ratio (major axis: short axis) are doped with Co, they are not only isotropic in shape but also magnetically isotropic. This is the most requested magnetic iron oxide particle powder for recording. However, it is known that Co-doped magnetic iron oxide particles have poor magnetic (especially coercive force) stability against temperature (hereinafter simply referred to as temperature stability), and the amount of cobalt doped increases. The higher the temperature, the lower the temperature stability tends to be. The instability of Co-doped magnetic iron oxide particles with respect to temperature is shown, for example, in "Figure 3" of JP-A-48-87397, and the coercive force of Co-doped magnetic iron oxide particles changes with temperature. It tends to decrease as the value increases. That is, according to the same figure, in the case of Co-containing maghemite (γ-Fe ₂ O ₃ ) particles, the value was about 678 Oe at 25°C, but it became about 420 Oe at 120°C,
258Oe is also decreasing. For Co-doped magnetite (Fe ₃ O ₄ ) particles,
What was about 572 Oe at 25℃ is now 120℃
It was around 341Oe, which is also a decrease of 231Oe. [Means for Solving the Problems] The present inventor has developed various methods to obtain magnetic iron oxide particles having a uniform particle size, no dendritic particles, and a small axis ratio (long axis: short axis). As a result of repeated consideration,
In producing spindle-shaped goethite particles by oxidizing an aqueous solution containing FeCO ₃ obtained by reacting an aqueous ferrous salt solution and an alkali carbonate with an oxygen-containing gas, ferrous salt Aqueous solution, water-soluble silicate for Fe is added to either the _FeCO3 -containing aqueous solution before the alkali carbonate and oxygen-containing gas is passed through the FeCO3-containing aqueous solution to carry out the oxidation reaction.
When 0.1 to 20 atomic % is added in terms of Si, the axis ratio (long axis: short axis) of the spindle-shaped goethite particles, which is the starting material, is shortened to 4:1 or less, especially 2:
We have already obtained the knowledge that it is possible to reduce the number to 1 or less (Patent Application No. 58-200621, Patent Application No. 87011-1982).
issue). Furthermore, the present inventor has found that the particle size is uniform, dendritic particles are not mixed, and the axial ratio (long axis: short axis) is small, 4:1 or less, especially 2:1 or less. Moreover, as a result of various studies to obtain magnetic iron oxide particles with high coercive force and excellent temperature stability, we found that when cobalt is added in the method for producing spindle-shaped goethite particles, The spindle-shaped magnetic iron oxide particles doped with Si and Co obtained by reducing or reducing and oxidizing goethite particles doped with Si and Co are geometrically and magnetically isotropic. The present invention was completed based on the completely new knowledge that this material has a high coercive force and excellent temperature stability. That is, the present invention has an axial ratio (long axis: short axis) of 4:1.
0.1 to 20 atomic% of Si to Fe and
Co is doped with 0.5 to 10.0 atom% of Fe,
In addition, magnetic iron oxide particle powder consisting of spindle-shaped magnetite particles or maghemite particles, which is characterized by excellent temperature stability, and a ferrous salt aqueous solution, obtained by reacting with an alkali carbonate.
In producing spindle-shaped goethite particles by passing an oxygen-containing gas through an aqueous solution containing FeCO ₃ for oxidation, the ferrous salt aqueous solution, the alkali carbonate, and the oxygen-containing gas are passed through to carry out the oxidation reaction. Add water-soluble silicate to any of the aqueous solutions containing FeCO ₃ in terms of Fe to Si before carrying out the process.
0.1 to 20 atom% water-soluble cobalt salt to Fe
By adding 0.5 to 10.0 atomic % in terms of Co, spindle-shaped goethite particles doped with Si and Co are generated, and the spindle-shaped goethite particles doped with Si and Co are heated. Spindle-shaped hematite particles doped with Si and Co obtained by dehydration are thermally reduced in a reducing gas to produce spindle-shaped magnetite particles doped with Si and Co, which have excellent temperature stability. or, if necessary, further oxidize to obtain spindle-shaped maghemite particles doped with Si and Co, which have excellent temperature stability. This is a method for producing iron oxide particle powder. [Function] First, the magnetic iron oxide particles according to the present invention have a small axial ratio (major axis: short axis) of 4:1 or less, especially 2:1 or less, and a high coercive force (300~
900Oe) and has excellent temperature stability, and as the amount of Si added increases, the axial ratio (long axis: short axis) tends to decrease, and it becomes geometrically and magnetically isotropic. . Although it is not yet clear why the magnetic iron oxide particles according to the present invention have excellent temperature stability, the inventor has found that as the Si content increases, the temperature stability increases. Since it tends to improve, it is thought that this is due to the synergistic effect between Si and Co. The following is an explanation of some of the many experimental examples conducted by the present inventor. Figure 1 shows the amount of water-soluble silicate added and Si and
FIG. 3 is a diagram showing the relationship between the axial ratio of spindle-shaped goethite particles doped with Co. That is, 3.0% of a ferrous sulfate aqueous solution containing 1.0mol/1 Fe ²⁺ was added to sodium silicate prepared in advance in a reactor in an amount of 0 to 20 atomic % in terms of Si relative to Fe.
Cobalt sulfate was added to an aqueous sodium carbonate solution 2.0 obtained by adding 4.5 atomic % of cobalt sulfate in terms of Co to Fe to obtain a suspension containing FeCO ₃ at a pH of about 10, and the suspension was added at a temperature of 50°C. Axial ratio (long axis: short axis) of spindle-shaped goethite particles doped with Si and Co obtained by performing an oxidation reaction by passing air at a rate of 15 per minute and addition of water-soluble silicate This shows the relationship with quantity. As is clear from FIG. 1, the axial ratio (long axis:short axis) tends to become shorter as the amount of water-soluble silicate added increases. 2 and 3 are graphs showing the relationship between the amount of water-soluble silicate added and the axial ratio of spindle-shaped magnetic iron oxide particles doped with Si and Co,
FIG. 2 shows the case of magnetite particle powder, and FIG. 3 shows the case of maghemite particle powder. That is, Figure 2 was obtained in the same way as Figure 1.
Axial ratio (major axis: short axis) of spindle-shaped magnetite particles doped with Si and Co obtained by heating and reducing 200 g of spindle-shaped goethite particles doped with Si and Co at 400°C for 45 minutes. shaft)
This figure shows the relationship between the amount of water-soluble silicate added and the amount of water-soluble silicate added. As is clear from FIG. 2, as the amount of water-soluble silicate added increases, the axis ratio (long axis:short axis) of spindle-shaped magnetite particles tends to decrease. When water-soluble silicate is added at 0.1 atomic % or more in terms of Si relative to Fe, the axial ratio of the resulting spindle-shaped magnetite particles can be made 4:1 or less, and 0.3 atomic % or more is added. In this case, the axial ratio of the resulting spindle-shaped magnetite particles can be set to 2:1 or less. Figure 3 shows the spindle-shaped maghemite containing Si and Co obtained by oxidizing 150 g of spindle-shaped magnetite particles doped with Si and Co obtained in Figure 2 for 15 minutes in air. This figure shows the relationship between the particle axial ratio (long axis: short axis) and the amount of water-soluble silicate added. As is clear from FIG. 3, as the amount of water-soluble silicate added increases, the axis ratio (long axis: short axis) of the spindle-shaped maghemite particles doped with Si and Co tends to decrease. When water-soluble silicate is added at 0.1 atomic % or more in terms of Si relative to Fe, the axial ratio of the resulting spindle-shaped magnetite particles can be made 4:1 or less, and 0.3 atomic % or more is added. In this case, the axial ratio of the resulting spindle-shaped magnetite particles can be set to 2:1 or less. FIG. 4 shows the change in coercive force Hc with respect to temperature of spindle-shaped magnetite particles doped with Si and Co obtained in the same manner as in FIG. 2. In FIG. 4, straight lines a, b, and c correspond to cases where the Si content is 0 atomic %, 2 atomic %, and 6 atomic %, respectively. As is clear from FIG. 4, the temperature stability tends to improve as the Si content increases. FIG. 5 shows the change in coercive force Hc with respect to temperature of spindle-shaped maghemite particles doped with Si and Co obtained in the same manner as in FIG. 3. In FIG. 5, straight lines a, b, and c correspond to cases where the Si content is 0 atomic %, 2 atomic %, and 6 atomic %, respectively. As is clear from FIG. 5, the temperature stability tends to improve as the Si content increases. Next, various conditions for implementing the present invention will be described. Examples of the ferrous salt aqueous solution used in the present invention include a ferrous sulfate aqueous solution and a ferrous chloride aqueous solution. As the alkali carbonate used in the present invention, sodium carbonate, potassium carbonate, and ammonium carbonate are used alone or in combination with an alkali hydrogen carbonate such as sodium hydrogen carbonate, potassium hydrogen carbonate, and ammonium hydrogen carbonate. be able to. The reaction temperature in the present invention is 40 to 80°C.
If the temperature is lower than 40°C, spindle-shaped goethite particles cannot be obtained. If the temperature exceeds 80°C, particulate Fe ₃ O ₄ will be mixed. The PH in the present invention is 7-11. If it is less than 7 or more than 11, spindle-shaped goethite particles cannot be obtained. The oxidation means in the present invention is carried out by passing an oxygen-containing gas (for example, air) into the liquid. Water-soluble silicates used in the present invention include sodium and potassium silicates. The water-soluble silicate in the present invention is involved in the axis ratio (major axis: short axis) of spindle-shaped goethite particles to be produced, and therefore, the production reaction of spindle-shaped goethite particles is It is necessary to be present before the oxidation reaction is started and added to either the ferrous salt aqueous solution, the aqueous solution containing FeCO ₃ before bubbling the alkali carbonate and oxygen-containing gas to carry out the oxidation reaction. I can do it. The amount of water-soluble silicate added in the present invention is
It is 0.1 to 20 atomic % based on Fe in terms of Si. If it is less than 0.1 atomic %, the effect of shortening the axis ratio (long axis: short axis) of spindle-shaped magnetite particles or maghemite particles cannot be sufficiently achieved. If it exceeds 20 atom %, it is not preferable because the saturation magnetization of the magnetic iron oxide particles obtained by reducing or further oxidizing the resulting powder consisting of spindle-shaped goethite particles decreases. When considering the axial ratio (long axis: short axis) and saturation magnetization of spindle-shaped magnetite particles or maghemite particles, 0.3 to 15 atomic % is preferable. Almost the entire amount of the added water-soluble silicate is contained in the generated goethite particles, and as shown in Table 1 below, the obtained goethite particles have a Si equivalent amount of approximately the same amount of Fe as the added amount. at 0.38~12.98
atomic%, and the particles are reduced by heating or
Furthermore, magnetic iron oxide particles obtained by oxidation also
As shown in Tables 2 and 3 below, it contains 0.37 to 12.99 atomic % in terms of Si with respect to approximately the same amount of Fe as the added amount. Water-soluble cobalt salts used in the present invention include cobalt sulfate and cobalt chloride. The water-soluble cobalt salt in the present invention is involved in improving the coercive force of spindle-shaped magnetic iron oxide particles obtained by reducing, or reducing and oxidizing spindle-shaped goethite particles produced. Therefore, it is necessary that the ferrous salt aqueous solution,
It can be added to any aqueous solution containing FeCO ₃ before an oxidation reaction is performed by passing an alkali carbonate and an oxygen-containing gas through the atmosphere. The amount of water-soluble cobalt salt added in the present invention is 0.5 to 10.0 atomic % based on Fe in terms of Co.
If it is less than 0.5 atomic %, the effect of improving the coercive force of the resulting spindle-shaped magnetite particles or maghemite particles cannot be sufficiently achieved. If it exceeds 10.0 atom%,
The effect of improving the temperature stability of the resulting spindle-shaped magnetite particles or maghemite particles is not sufficient. When considering the coercive force and temperature stability of the spindle-shaped magnetite particles or maghemite particles, the content is preferably 4.0 to 7.0 at %. Almost all of the added water-soluble cobalt salt was contained in the produced goethite particles, as shown in Table 1 below.
As shown in , the obtained goethite particles have a Co equivalent of 1.01 to 7.99 for almost the same amount of Fe as the added amount.
As shown in Tables 2 and 3 below, the magnetic iron oxide particles obtained by thermally reducing or further oxidizing the particles are also doped with approximately the same amount of Fe as the added amount, as shown in Tables 2 and 3 below. 0.97 to 7.98 atomic% in terms of Co
is dope. The heating reduction temperature in the present invention is determined by a conventional method.
It can be carried out at 300-500°C. If the temperature is lower than 300°C, the reduction reaction progresses slowly and takes a long time. Furthermore, if the temperature exceeds 500°C, the reduction reaction rapidly progresses, resulting in deformation of the particle morphology and sintering of the particles and the particles themselves. [Example] Next, the present invention will be explained with reference to Examples and Comparative Examples. In addition, the axial ratio (long axis: short axis) and long axis of the particles in the above experimental examples, the following examples, and comparative examples are as follows:
All values are shown as average values of values measured from electron micrographs. The amount of Si and Co in the particles can be measured using a “fluorescent X-ray analyzer”.
JIS K
The measurement was carried out by performing fluorescence X-ray analysis according to the "General Rules for Fluorescence X-ray Analysis" of 0119. The temperature stability of the magnetic iron oxide particles was expressed as the value (Oe) obtained by subtracting the coercive force value at 120°C from the coercive force value at 25°C. <Production of spindle-shaped goethite particles> Examples 1 to 9 Example 1 A ferrous sulfate aqueous solution 30 containing 1.0 mol of Fe ²⁺ was
Si is added to the Fe prepared in advance in the reactor.
Sodium silicate (3
) (SiO ₂ 28.55wt%) 25.3g and 337.2g of cobalt sulfate to contain 4.0 atomic% in terms of Co compared to Fe.
In addition to the 3.53 mol/Na ₂ CO ₃ aqueous solution 20 obtained by adding
Co-doped FeCO ₃ was produced. Goethite particles doped with Si and Co were produced by passing air at a rate of 130/min for 6.5 hours at a temperature of 50° C. into the aqueous solution containing FeCO ₃ doped with Si and Co. The end point of the oxidation reaction was determined by extracting a portion of the reaction solution and acidifying it with hydrochloric acid, and then using a red blood salt solution to determine the presence or absence of a blue coloring reaction of Fe ²⁺ . The generated particles are separated, washed with water, dried, and
Shattered. As is clear from the electron micrograph (×20000) shown in Figure 6, the goethite particles doped with Si and Co have a spindle with an average long axis of 0.17 μm and an axial ratio (long axis: short axis) of 1.5:1. It consisted of shaped particles, had uniform particle size, and did not contain any dendritic particles. Furthermore, as a result of fluorescent X-ray analysis, this spindle-shaped goethite particle powder was found to be doped with 0.41 atomic % of Si and 3.99 atomic % of Co with respect to Fe. Examples 2 to 9 The type of Fe ²⁺ aqueous solution, the type of alkali carbonate, the type, amount and timing of addition of water-soluble silicate, and the type, amount and timing of addition of water-soluble cobalt salt were varied. Goethite particles exhibiting a spindle shape were produced in the same manner as in Example 1 except for the above. Table 1 shows the main manufacturing conditions and characteristics of the produced goethite particles. FIG. 7 shows an electron micrograph (×20,000) of the spindle-shaped goethite particles obtained in Example 4. <Production of spindle-shaped hematite particles> Example 10 1000 g of spindle-shaped goethite particles doped with Si and Co obtained in Example 2 were placed in air.
By heating and dehydrating at 300°C, spindle-shaped hematite particles containing Si and Co were obtained. As a result of electron microscopy, the particles had an average long axis of 0.15 μm and an axial ratio (long axis:short axis) of 1.3:1, and the particle size was uniform and dendritic particles were not mixed. In addition, as a result of fluorescent X-ray analysis, Si was found to be 6.01% of Fe.
It was doped with 3.99 atomic % of Co to Fe. <Production of spindle-shaped magnetite particle powder> Examples 11 to 20 Example 11 1000 g of spindle-shaped goethite particle powder doped with Si and Co obtained in Example 1 was placed in 10 retort reduction containers. H ₂ gas is aerated at a rate of 2 per minute while driving and rotating, until the reduction temperature is reached.
A spindle-shaped magnetite particle powder doped with Si and Co was obtained by reduction at 400°C. As a result of fluorescent X-ray analysis, the obtained spindle-shaped magnetite particles doped with Si and Co contained 0.40 atomic % of Si relative to Fe and Co relative to Fe.
As is clear from the electron micrograph (×20000) shown in Figure 8, the particle size is 3.98 atomic% doped, with an average long axis of 0.15 μm and an axial ratio (long axis: short axis) of 1.5:1. It was uniform and did not contain any dendritic particles. In addition, as a result of magnetic measurement, the coercive force Hc is 615Oe,
The saturation magnetization σs was 83.2 emu/g, and the temperature stability was 180 Oe. Examples 12 to 20 Spindle-shaped magnetite particles doped with Si and Co were obtained in the same manner as in Example 11, except that the types of starting materials and the reduction temperature were varied.
Table 2 shows the main manufacturing conditions and characteristics of the powder particles at this time.
Shown below. As a result of electron microscopic observation, all of the spindle-shaped magnetite particles doped with Si and Co obtained in Examples 12 to 20 were found to have uniform particle size and no dendritic particles were present. FIG. 9 shows an electron micrograph (×20,000) of spindle-shaped magnetite particles containing Si and Co obtained in Example 14. <Production of spindle-shaped maghemite particle powder> Examples 21 to 30 Example 21 700 g of spindle-shaped magnetite particle powder doped with Si and Co obtained in Example 11 was heated in air at 300°C for 60 minutes. A spindle-shaped maghemite particle powder doped with Si and Co was obtained by oxidation. As a result of fluorescent X-ray analysis, the obtained spindle-shaped maghemite particles doped with Si and Co contained 0.40 at% of Si relative to Fe and Co relative to Fe.
The long axis
0.15μm, axial ratio (long axis: short axis) 1.5:1,
The particle size was uniform and no dendritic particles were present. In addition, as a result of magnetic measurement, the coercive force Hc is
610 Oe, saturation magnetization σs was 573.0 emu/g, and temperature stability was 170 Oe. Examples 22 to 30 Except for varying the type of spindle-shaped magnetite particles doped with Si and Co,
In the same manner as in Example 21, maghemite particles doped with Si and Co and exhibiting a spindle shape were obtained. Table 3 shows the main manufacturing conditions and characteristics of the particles at this time. As a result of electron microscopy, all of the spindle-shaped maghemite particles doped with Si and Co obtained in Examples 22 to 30 were found to have uniform particle size and no dendritic particles were present. FIG. 11 shows an electron micrograph (×20,000) of the spindle-shaped maghemite particles doped with Si and Co obtained in Example 24. <Manufacture of magnetic tape> Examples 31 to 40 Example 31 Using the spindle-shaped magnetite particle powder doped with Si and Co obtained in Example 11, an appropriate amount of a dispersant and a vinyl chloride-vinyl acetate copolymer was added. , thermoplastic polyurethane resin and toluene, methyl ethyl ketone,
A mixed solvent consisting of methyl isobutyl ketone was blended to a certain composition, and then mixed and dispersed in a ball mill for 8 hours to obtain a magnetic paint. 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. This magnetic tape had a coercive force Hc of 621 Oe, a residual magnetic flux density Br of 1450 Gauss, a square shape Br/Bm of 0.75, and an orientation degree of 1.00. Examples 32 to 40 Magnetic tapes were produced in exactly the same manner as in Example 31, except that the type of spindle-shaped magnetic iron oxide particles doped with Si and Co was varied. Table 4 shows the characteristics of this magnetic tape.

【table】

【table】

【table】

【table】

〔effect〕

As shown in the above examples, the magnetic iron oxide particles according to the present invention have uniform particle size, do not contain dendritic particles, and have a small axial ratio (major axis: short axis). 4:1 or less, especially 2:1 or less,
In addition, since they are spindle-shaped magnetite particles or maghemite particles that have high coercive force and excellent temperature stability, they are suitable as magnetic materials for high recording density, which is currently most required. In addition, when the above-mentioned magnetite particle powder or maghemite particle powder is used in the production of magnetic paint, the dispersibility in the vehicle is good, and the orientation and filling properties in the coating film are excellent, making it desirable for magnetic recording. medium can be obtained.

[Brief explanation of drawings]

Figure 1 shows the amount of water-soluble silicate added and Si and
FIG. 2 is a relationship diagram of the axial ratio of spindle-shaped goethite particles containing Co. 2 and 3 are graphs showing the relationship between the amount of water-soluble silicate added and the axial ratio of spindle-shaped magnetic iron oxide particles doped with Si and Co, and FIG. In the case of powder, FIG. 3 shows the case of maghemite particle powder. Figures 4 and 5 show the change in coercive force Hc with respect to temperature of spindle-shaped magnetic iron oxide particle powder doped with Si and Co.
is the case of magnetite particle powder, and FIG. 5 is the case of maghemite particle powder. FIGS. 6 to 11 are
Both are electron micrographs (x20,000) showing the particle structure of the particles. 6 and 7 show spindle-shaped goethite particles doped with Si and Co obtained in Example 1 and Example 4, respectively. 8 and 9 show spindle-shaped magnetite particles doped with Si and Co obtained in Example 11 and Example 14, respectively. FIGS. 10 and 11 show spindle-shaped maghemite particles doped with Si and Co obtained in Example 21 and Example 24, respectively.

Claims (1)

[Claims] 1. The axial ratio (major axis:minor axis) is 4:1 or less,
0.1 to 20 atomic% Si to Fe and Co to Fe
A magnetic iron oxide particle powder consisting of spindle-shaped magnetite particles doped with 0.5 to 10.0 atom % and having excellent temperature stability. 2 The axial ratio (major axis: minor axis) is 2:1 or less,
0.3 to 15 atomic% Si to Fe and Co to Fe
A magnetic iron oxide particle powder comprising spindle-shaped maghemite particles according to claim 1, which is doped with 0.5 to 10.0 atom % and has excellent temperature stability. 3 The axial ratio (major axis: minor axis) is 4:1 or less,
0.3 to 15 atomic% Si to Fe and Co to Fe
A magnetic iron oxide particle powder consisting of spindle-shaped magnetite particles doped with 0.5 to 10.0 atom % and having excellent temperature stability. 4 The axial ratio (major axis: minor axis) is 2:1 or less,
0.3 to 15 atomic% Si to Fe and Co to Fe
A magnetic iron oxide particle powder comprising spindle-shaped maghemite particles according to claim 3, which is doped with 0.5 to 10.0 atomic % and has excellent temperature stability. 5 In producing spindle-shaped goethite particles by passing an oxygen-containing gas through an aqueous solution containing FeCO ₃ obtained by reacting a ferrous salt aqueous solution with an alkali carbonate to oxidize the ferrous salt aqueous solution and an alkali carbonate, A water-soluble silicate of 0.1 to 20 atomic % based on Fe in terms of Si is added to either the aqueous salt solution, the aqueous solution containing FeCO ₃ before the oxidation reaction is carried out by passing the alkali carbonate and oxygen-containing gas through the aqueous solution, By adding water-soluble cobalt salt to Fe in an amount of 0.5 to 10.0 atomic percent in terms of Co, spindle-shaped goethite particles doped with Si and Co are generated, and the Si and
Co-doped spindle-shaped goethite particles or Si and Co obtained by heating and dehydrating them
The spindle-shaped hematite particles doped with Si and Co are heated and reduced in a reducing gas to obtain spindle-shaped magnetite particles doped with Si and Co, which have excellent temperature stability. A method for producing magnetic iron oxide particles powder consisting of magnetite particles. 6 Addition amount of water-soluble silicate is 0.3 to 15 at%
A method for producing magnetic iron oxide particles comprising spindle-shaped magnetite particles according to claim 5. 7 In producing spindle-shaped goethite particles by passing an oxygen-containing gas through an aqueous solution containing FeCO ₃ obtained by reacting a ferrous salt aqueous solution with an alkali carbonate to oxidize it, the ferrous iron A water-soluble silicate of 0.1 to 20 atomic % based on Fe in terms of Si is added to either the aqueous salt solution, the aqueous solution containing FeCO ₃ before the oxidation reaction is carried out by passing the alkali carbonate and oxygen-containing gas through the aqueous solution, By adding water-soluble cobalt salt to Fe in an amount of 0.5 to 10.0 atomic percent in terms of Co, spindle-shaped goethite particles doped with Si and Co are generated, and the Si and
Co-doped spindle-shaped goethite particles or Si and Co obtained by heating and dehydrating them
A spindle-shaped hematite particle doped with Si and Co is further oxidized to obtain maghemite particles doped with Si and Co, which have excellent temperature stability, after being heated and reduced in a reducing gas. A method for producing magnetic iron oxide particles consisting of maghemite particles exhibiting 8 Addition amount of water-soluble silicate is 0.3 to 15 at%
A method for producing magnetic iron oxide particles comprising spindle-shaped maghemite particles according to claim 7.