JPH033361B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnetic powder used in high-density magnetic recording media, particularly perpendicular magnetization recording media.

Conventionally, γ-Fe ₂ O ₃ , CrO ₂ ,
A common method is to orient magnetic powder made of acicular crystals such as Co-coated γ-Fe ₂ O ₃ in the in-plane longitudinal direction of the recording medium and utilize residual magnetization in the in-plane longitudinal direction. However, this recording medium has the disadvantage that the demagnetizing field within the magnetic recording medium increases as the recording density increases, and recording and reproducing characteristics are particularly poor in the short wavelength region. In order to overcome this demagnetizing field and perform high-density recording, it is necessary to increase the coercive force of the recording medium and thin the magnetic recording layer, but currently it is difficult to increase the coercive force of the magnetic recording layer, and it is also necessary to thin the magnetic recording layer. Making it thinner has problems such as degrading the characteristics of the reproduced signal. After all, it is difficult to achieve high density magnetic recording using the conventional method of orienting acicular magnetic powder in the in-plane longitudinal direction and utilizing residual magnetization in this direction. Therefore, a method has been proposed that uses residual magnetization in the direction perpendicular to the surface of the magnetic recording medium.
In this perpendicular magnetic recording method, as the recording density increases, the demagnetizing field in the recording medium decreases, so it can be said that it is essentially a recording method suitable for high-density recording. Here, the residual magnetization in the direction perpendicular to the surface of the recording medium may be caused by orienting the magnetic powder over the entire recording medium so that the residual magnetization is perpendicular, or it may be non-oriented without orienting the magnetic powder. A portion of residual magnetization may remain in the perpendicular direction after coating.

As such recording media, there have been proposed media in which a Co--Cr alloy film is formed by sputtering, and media in which the recording film is formed by a coated layer of magnetic fine particles. By the way, in the case where the recording film is formed of a coating layer containing magnetic powder, the following manufacturing method can be considered. That is, as a magnetic powder, for example
A hexagonal ferrite such as BaFe ₁₂ O ₁₉ is used. Uses hexagonal ferrite. The reason is that this ferrite has a flat plate shape and the axis of easy magnetization is perpendicular to the plate surface, so the plate surface of hexagonal ferrite tends to become parallel to the tape surface after coating, and it is difficult to apply magnetic field orientation treatment or mechanical treatment. This is because vertical alignment can be easily achieved by alignment treatment. However, when manufacturing a perpendicular magnetic recording medium by a so-called coating method using the above-mentioned hexagonal ferrite fine powder, the following points need to be taken into consideration. In other words, the above-mentioned hexagonal ferrite has a high coercive force Hc that saturates the head during recording, so by replacing some of the constituent atoms with specific other atoms, the coercive force can be adjusted to be suitable for perpendicular magnetic recording. It is necessary to reduce the amount to a certain value. Further, it is necessary to select the crystal grain size of the hexagonal ferrite in the range of 0.01 to 0.3 μm. The reason for this is that if the thickness is less than 0.01 μm, it will not exhibit the strong magnetism required for magnetic recording, and if it exceeds 0.3 μm, it will be difficult to perform high-density recording advantageously. Various methods for producing the above-mentioned hexagonal ferrite have been proposed. Among these, in the coprecipitation method in which a metal ion solution constituting hexagonal ferrite and an alkaline solution are mixed to obtain a coprecipitate and then fired to obtain hexagonal ferrite, the coprecipitate has a particle size of 100 〓These are the following ultrafine particles, and it requires a large amount of water and time to wash such ultrafine particles with water to remove non-purpose components such as alkali. Furthermore, if this water washing is insufficient and alkali or the like remains in the coprecipitate, sintered powder will be present during firing, making it impossible to disperse the powder during recording medium production, making it difficult to obtain a recording medium with desired characteristics. Another production method, hydrothermal synthesis, uses an autoclave, which makes the production process difficult and difficult. Furthermore, since the hexagonal ferrite is produced under high temperature and high pressure, the reaction proceeds rapidly and the particle size of the obtained hexagonal ferrite becomes coarse. Magnetic powder with such a coarse particle size is unsuitable for high-density magnetic recording, and for this reason, when producing magnetic powder, it is necessary to ensure that the obtained magnetic powder does not contain coarse particles and has a good particle size distribution. To make it sharper,
The reaction must be controlled.

In view of these circumstances, the present invention provides a method for producing powder of a microcrystalline hexagonal ferrite substituted product having a narrow particle size distribution and a uniform shape without requiring complicated equipment and using simple operations. The purpose is to provide the following.

The present invention includes a ferric salt, at least one of barium salt, strontium salt, and calcium salt, and at least one of cobalt, titanium, nickel, copper, zinc, indium, niobium, germanium, and zirconium for controlling coercive force. An aqueous solution containing one or more salts is contacted with an aqueous solution containing an alkali with a pH of 10 or higher, preferably PH12 to 13, and the mixed aqueous solution is kept at a temperature of 50°C or higher and 150°C or lower to obtain a coprecipitate. This is an easy-to-manufacture method for producing hexagonal ferrite, which has a well-organized particle size distribution, excellent dispersibility, and consists of washing and drying the material, and then subjecting it to heat treatment and reaction.

The present invention will be explained in detail.

First, an aqueous solution containing at least one of Ba, Sr, and Ca salts, a ferric salt, and, if necessary, a salt of a substitution element for coercive force control is prepared. These salts are preferably supplied in the form of chloride nitrates and organic acid salts. On the other hand, for example NaOH, KOH,
Create an alkaline aqueous solution whose pH is adjusted with NH ₄ , OH, and Na ₂ CO ₃ (NH ₄ ) ₂ CO ₃ . At this time, if the pH is 10 or higher, a precipitate of each element can be obtained, but in order to make this precipitate stable, the pH is preferably in the range of 12 to 13. Next, the aqueous metal solution and aqueous alkaline solution are brought into contact. At this time, both aqueous solutions can be stirred and mixed in order to uniformly contact them. Also,
Either or both of the solutions can be heated during mixing. In this case, there is no need for particular heating in the next temperature holding step.

The mixture is then maintained at a temperature above 50°C and below 150°C to promote the formation of a precipitate. If this holding temperature is less than 50°C, the saturation magnetization of the obtained precipitate is zero, and no ferromagnetic component is generated. On the other hand, if the holding temperature exceeds 150℃, pressurization is required, resulting in poor workability during manufacturing.
In addition, a large number of ferromagnetic components are rapidly generated, and the resulting magnetic powder becomes coarse and has a wide particle size distribution, making it impossible to obtain desirable properties for use in magnetic recording media. Furthermore, when washing this precipitate with water, the holding temperature is
In the case of precipitates formed at temperatures below 50°C, the settling speed of the precipitates is slow, making washing with water practically difficult. As a result, alkaline components remain in the precipitate, causing sintering between fine particles during heating and baking, making it difficult to form into a paint.

In the above heating and holding process, the heating temperature is 100℃.
In the above case, a pressure vessel such as an autoclave is used. This container has a heating temperature of 150
℃, the internal pressure only increases to about 2.5 atm, so a container simpler than the commonly used pressurized container, an autoclave, can be used. It is necessary to maintain the temperature within the above temperature range for at least 10 minutes or longer. If this time is shorter than 10 minutes, sufficient precipitate will not be obtained and the loss of raw materials will be large. Further, although there is no particular upper limit to the holding time, the upper limit is determined from the viewpoint of work efficiency. After maintaining the temperature, the mixture is allowed to stand, the supernatant liquid is removed, and the precipitate is washed with water. After repeated washing with water until no components such as alkali are extracted into the washing water,
Dry and then bake. Firing temperature is 850℃ or higher
A temperature of 975°C or lower is appropriate, but a temperature of 900°C or higher and 950°C or lower is particularly desirable. If the firing temperature is 850° C. or lower, the saturation magnetization of the obtained hexagonal ferrite will be low, which is not preferable as a magnetic recording medium. On the other hand, at temperatures above 975°C, the fine particles of hexagonal ferrite are sintered, making it difficult to disperse them when made into a paint.

According to the manufacturing method of the present invention as detailed above, it is possible to obtain a hexagonal ferrite powder having a small maximum particle size, a narrow particle size distribution, and no agglomerates due to sintering, and which can be used with, for example, a resin binder, etc. A magnetic recording medium suitable for high-density recording with excellent surface properties can be manufactured by mixing the magnetic material with the magnetic material to form a magnetic coating material and coating it on a non-magnetic support.

This will be explained in detail in Examples below.

Example 1 1.5 l of FeCl ₃ 6H ₂ O aqueous solution contained 126.5 g as Fe ions and 33.6 g as Ba ions.
Contains 0.5 l of BaCl ₂ 2H ₂ O aqueous solution and 12.0 g of Co ions as a substitution element for coercive force control.
As CoCl ₂ 6H ₂ O aqueous solution 0.25l and Ti ion
Mix 0.25 liters of Ticl ₄ aqueous solution containing 9.8 g, and add the mixture to 3 liters of a previously prepared aqueous solution containing 1.2 kg of NaOH with stirring. Immediately the first
Place in a constant temperature bath maintained at the predetermined temperature shown in the figure and hold for one hour while stirring. After taking it out from the constant temperature bath, it was washed repeatedly with pure water, thoroughly washed with water, and then dried and calcined to obtain a precipitate powder. The saturation magnetization values of these precipitate powders are shown in FIG. As is clear from the figure, when the holding temperature is 50°C or lower, the saturation magnetization value is zero, and no residual magnetic component is contained in the precipitate, and at a temperature of 150°C or higher, the saturation magnetization value is zero. The value was extremely large, confirming the presence of many ferromagnetic components in the precipitate.

Among the above samples, the magnetization property of the powder when the holding temperature was set at 850°C was a saturation magnetization of 55 emu/g. The substituted Ba ferrite fine powder had a saturation magnetization of 59.1 emu/g and a coercive force of 810 Oe.
The average particle size of this fine powder is 0.080μm, and the maximum particle size is
At 0.18μm, the particle size distribution is very sharp.
In particular, the maximum particle size that causes noise in magnetic media is
As small as 0.18μm.

Example 2 A mixed solution was prepared with the same composition as in Example 1, and an alkaline solution was prepared in the same manner as in Example 1, and these were mixed and brought into contact. Put this solution in an autoclave
It was held at 130°C for 1 hour. Then take this out and
Washing with pure water is repeated, and after thorough washing, drying is performed to obtain a precipitate powder. The magnetic properties of this powder were a saturation magnetization of 6.3 emu/g. This precipitated powder was subjected to a heating reaction at 900℃ for 45 minutes to replace Co-Ti.
Ba ferrite fine powder was obtained. This fine powder had a saturation magnetization of 59.3 emu/g and a coercive force of 790 Oe.
This particle size distribution is shown in FIG. This figure also shows the autoclave temperature of 200°C for comparison. It can be seen that the hexagonal Ba ferrite obtained by the present invention has a sharper particle size distribution. The S/N of the recording medium made using this hexagonal Ba ferrite is as follows:
S/N of recording medium made using powder in case of
This resulted in a high-performance recording medium that was more than 4 dB higher than the previous one.

Although not shown in the above examples, similar results were obtained with hexagonal ferrite using Sr salt, Ca salt, etc. Similar results were also obtained when Ni, Mn, Cu, Zn, In, Ge, Nb, Zr, etc. were used as substitution elements for coercive force control.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the holding temperature of the metal salt solution and alkaline solution according to the present invention and the saturation magnetization value of the precipitate powder obtained at this time, and Figure 2 is the particle distribution of the hexagonal Ba ferrite according to the present invention. FIG.

Claims (1)

[Claims] 1 General formula AO.n(Fe _11-x −Mx) ₂ O ₃ (wherein A=at least one M of Ba, Sr, and Ca)
=Co, Ti, Ni, Mn, Cu, Zn, In, Ge, Nb,
At least one type of Zr, n=5-6, x=0.08
~0.2) A solution containing ions of each element selected in a proportion constituting a hexagonal ferrite with a pH of 10
A method for high-density magnetic recording characterized by mixing the above alkaline solution and subsequently holding at a temperature of 50°C or more and less than 150°C to obtain a precipitate, washing with water, drying, and then firing the precipitate. Method for producing magnetic powder. 2. The method for producing magnetic powder for high-density magnetic recording according to claim 1, wherein the firing temperature is 850°C or higher and 975°C or lower.