JPH044253B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for producing hexagonal ferrite magnetic powder that is effective for use in perpendicularly magnetized recording media, and more specifically to a method for producing hexagonal ferrite magnetic powder that is extremely fine and has a sharp particle size distribution. Regarding the manufacturing method. [Technical background of the invention and its problems] Conventionally, γ-Fe ₂ O ₃ , CrO ₂ ,
A commonly used method is to orient magnetic powder made of acicular crystals such as γ-Fe ₂ O ₃ coated with Co 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 property that the demagnetizing field within the magnetic recording medium increases as the recording density increases, and there is a drawback that the 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 to make the magnetic recording layer thinner. However, at present, it is difficult to increase the coercive force of the magnetic recording layer, and making the magnetic recording layer thinner is not preferable because it causes problems such as deterioration of characteristics of reproduced signals. For this reason, it has been difficult to achieve high density magnetic recording using a method in which acicular magnetic powder is oriented in the in-plane longitudinal direction and residual magnetization in this direction is utilized. To solve this problem, 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 such that the magnetic powder is oriented over the entire recording medium and the residual magnetization is perpendicular, or the magnetic powder is not oriented and is not oriented. A part of the residual magnetization may remain in the perpendicular direction. Such recording media include, for example, a recording layer formed by sputtering a Co-Cr alloy, or a coated layer of magnetic powder that is flat in shape and has an axis of easy magnetization perpendicular to the plate surface. has been proposed. In the latter case, the magnetic powder to be applied is, for example,
Hexagonal ferrites such as BaFe ₁₂ O ₁₉ are used. This is because hexagonal ferrite has a flat plate shape and an axis of easy magnetization in the direction perpendicular to the plate surface, so after coating, the plate surface is easily aligned parallel to the tape circle and can be easily aligned by magnetic field orientation treatment or mechanical orientation treatment. This is based on the reason that vertical alignment can be easily achieved. When a coating layer is made of such hexagonal ferrite, the ferrite itself has a high coercive force Hc and saturates the head during recording, so some of its constituent atoms must be replaced with specific other atoms to maintain the head. It is necessary to reduce the magnetic force, and it is also necessary to select the crystal grain size in the range of 0.01 to 0.3 μm. Control of particle size is especially important, and particle size of 0.01μ
This is because if the thickness is less than 0.3 μm, strong magnetism necessary for magnetic recording cannot be obtained, and if it exceeds 0.3 μm, it becomes difficult to advantageously perform high-density recording. For this reason, various hexagonal ferrite magnetic powders have been developed. Among them, the following formula:
AO・n(Fe _1-n Mm) ₂ O ₃ (where A is barium (Ba), strontium (Sr), calcium (Ca)
M represents at least one element selected from the group of; M is cobalt (Co), titanium (Ti), nickel (Ni), manganese (Mn), copper (Cu), zinc (Zn),
Represents at least one element selected from the group of indium (In), germanium (Ge), niobium (Nb), and zirconium (Zr); m and n each represent
The substituted hexagonal ferrite fine powder represented by the number satisfying the relationships of 0.08≦m≦0.2 and 5≦n≦6 is useful for the above-mentioned purposes (Japanese Patent Application Laid-open No.
56-61101). This hexagonal ferrite magnetic powder is generally produced as follows. That is, it is a method in which a solution of metal salts blended so that each metal has the above-mentioned composition and an alkaline solution are mixed, a coprecipitate is obtained by a hydrothermal synthesis reaction, and this is calcined at a predetermined temperature ( (See Japanese Patent Application Laid-open No. 16032/1983). It can also be produced by the glass crystallization method disclosed in JP-A-56-67904. The former method is particularly useful because it can produce hexagonal ferrite magnetic powder of the required particle size at a relatively high yield. However, the magnetic powder produced by this coprecipitation-sintering method does not necessarily have a sharp particle size distribution and cannot fully satisfy the demands for higher densities in today's magnetic recording. Therefore, it is desired to develop a method for stably mass-producing hexagonal ferrite magnetic powder having a particle size of 0.01 to 0.3 μm with a sharp particle size distribution at a low cost. [Object of the invention] The present invention provides coprecipitation of hexagonal ferrite magnetic powder.
The purpose of the present invention is to provide a method for stably producing magnetic powder with a sharp particle size distribution when produced by a firing method. [Summary of the Invention] In order to achieve the above object, the present inventors investigated in detail the relationship between the equivalent ratio of the two types of reaction solutions described above and the hydrothermal synthesis temperature, and found that both satisfy a certain relationship. The present invention was completed based on the discovery that magnetic powder of 0.01 to 0.3 μm can be stably produced with a sharp particle size distribution. That is, in the method of the present invention, the following formula: AO・n(Fe _1-n
Mm) ₂ O ₃ (wherein A represents at least one element selected from the group of Ba, Sr, and Ca; M is Co,
Represents at least one element selected from the group of Ti, Ni, Mn, Gu, Zn, In, Ge, Nb, and Zr;
m and n represent numbers satisfying the relationships of 0.08≦m≦0.2 and 5≦n≦6, respectively. , alkaline solution ()
heating the mixed solution to form a precipitate; then washing the precipitate with water, drying, and firing to produce a hexagonal ferrite magnetic powder, in which the alkali equivalent of the solution () and solution()
The ratio of the sum of the equivalents of each metal ion contained in x,
When the heating temperature is y (℃), x is 1≦x≦8
, and x and y are: When 1≦x<1.9, 5x+30≦y≦180; When 1.9≦x<2.2, 5x+30≦y≦−200x+
560; When 2.2≦x<4, 5x+30≦y≦100x−100; When 4≦x≦8, it satisfies the following relationships: 5x+30≦y≦300. The hexagonal ferrite magnetic powder produced by the method of the present invention has the general formula: AO・n(Fe _1-n Mm) ₂ O ₃ (A,
M, n, m each have the same meaning as above). The starting materials for this magnetic powder are a solution () containing ions of each metal constituting the ferrite in a predetermined ratio and an alkaline solution (). Here, the solution () may be anything as long as it is alkaline, and examples thereof include aqueous solutions of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonium hydroxide, and ammonium carbonate. Usually, an aqueous sodium hydroxide solution is used because it is inexpensive and easily available. Further, the solution (2) is prepared by dissolving in water a predetermined amount of a metal salt necessary to form a magnetic powder having a desired composition. In the method of the present invention, first, solution () and solution () are mixed at the equivalence ratio described below. Next, the mixed solution is heated at a temperature described later to cause coprecipitation of each metal ion. At this time, the applied temperature is 100℃
In the above cases, the entire reaction is carried out in a pressure-tight closed container such as an autoclave. Preferably, the reaction is carried out under stirring. Thereafter, the obtained precipitate is sufficiently washed with water to remove the alkali, and then dried and calcined. If water washing is insufficient and alkali remains, agglomerated particle agglomerates, which are thought to be caused by the alkali, are formed, and the particle size distribution of the magnetic powder obtained after firing becomes broad, making it impossible to achieve the purpose.
Firing may be performed in air using a common heating furnace such as an electric furnace. Firing temperature is 700-950
It is ℃. Preferably it is 700-850°C. In the above steps, the greatest feature of the method of the present invention is that the ratio of the alkali equivalent of the solution () to the sum of the equivalents of each metal ion in the solution () is x, and the temperature during the hydrothermal synthesis reaction of the mixed solution is y. (℃), x,
The purpose is to manage y as follows. That is, first, x satisfies the relationship 1≦x≦8. And the relationship between x and y is when 1≦x<1.9, 5x+30≦y≦180; when 1.9≦x<2.2,
5x+30≦y≦−200x+560; When 2.2≦x<4,
5x+30≦y≦100x−100; When 4≦x≦8, 5x
This is a relationship that satisfies +30≦y≦300. The relationship between x and y is shown in the figure. In the diagram, x, y
are the coordinates a(1, 35), b(1, 180), c(1.9,
180), d (2.2, 120), e (4, 300), f (8, 300
)
and g(8, 70) are shown as coordinate points within the diagonally shaded range drawn by connecting them with straight lines in this order. Area outside this shape (not including the border)
Both are unsuitable areas for the method of the present invention. That is, the magnetic powder produced under the conditions of region A has extremely low saturation magnetization and coercive force, and cannot be used as a magnetic powder for magnetic recording media. Under the conditions of region B, the obtained magnetic powder has a particle size larger than 0.3 μm, and the particle size distribution is uneven and broad. Since region C is a high temperature region and therefore a high pressure region, the equipment used becomes large and the manufacturing cost increases, and mass productivity is poor, making it industrially impractical. Further D
Since a large amount of alkali is used in this area, a large amount of water and time are required to wash the precipitate. Moreover, if the water washing is insufficient, there is a possibility that the residual alkali during firing may have an adverse effect as described above. Finally, under the conditions of region E, the particle size of the obtained precipitate becomes ultrafine, about 100 mm or less. Therefore, the sedimentation rate is extremely low, and washing the precipitate with water to remove alkali and other unnecessary components requires an extremely large amount of water and time, which is not preferable. When x and y are within the shaded range in the figure, the obtained magnetic powder has a saturation magnetization of 58 emu/g or more, a large coercive force of 750 to 810 Oe, and above all, a continuity distribution of 0.01 to 0.3. It is in the μm range and is suitable as magnetic powder for high-density recording. [Embodiment of the invention] 1000 ml of a 2.0 mol FeCl ₃ .6H ₂ O aqueous solution, 206 ml of a 1.0 mol BaCl ₂ .2H ₂ O aqueous solution, 1.0 mol
Mix 167 ml of CoCl ₂ H ₂ O aqueous solution and 167 ml of 1.0 mol TiCl ₄ aqueous solution, and make a solution ()
And so. The sum of the equivalents of each metal ion in the solution () is 6 + 0.412 + 0.334 + 0.668, or 7.414
It is. An aqueous sodium hydroxide solution was used as the solution (). An equivalent amount of sodium hydroxide was weighed out so that the equivalent ratio between solution () and solution () was as shown in the table, and this was dissolved in 1500 ml of pure water.
Depending on the amount of sodium hydroxide, solution () may become a suspension in which sodium hydroxide is not completely dissolved, but it can be completely dissolved by stirring and mixing with solution (). First, the solution () was cooled to about 20°C, and the solution () was added dropwise thereto and mixed with stirring. Stirring was continued for 30 minutes to obtain an aqueous solution containing a precipitate. The whole was heat-treated for 1 hour at the temperature shown in the table to carry out a hydrothermal synthesis reaction. An autoclave was used for heat treatment at 100°C or higher. The obtained precipitate was thoroughly washed with water, dried, and finally calcined in the atmosphere at 800° C. for 3 hours using an electric furnace. Thus, the composition is BaO・5.67 [(Fe _0.860 Co _0.0715
A powder of _Co --Ti _{substituted Ba} ferrite was obtained. For each powder obtained, the saturation magnetization and coercive force were measured using a sample vibrating magnetometer with a maximum magnetic field strength of 10 KOe, and the particle size and its distribution were observed using a transmission electron microscope and a scanning electron microscope. The above results are summarized in the table.

【table】

〔Effect of the invention〕

As is clear from the above explanation, according to the method of the present invention, the obtained hexagonal ferrite magnetic powder is
It has a uniform particle size distribution within the range of 0.01 to 0.3 μm, and has high saturation magnetization and coercive force, making it extremely useful as a magnetic powder for high-density recording.

[Brief explanation of drawings]

The figure shows the relationship between the sum of alkali equivalent/metal ion equivalent and hydrothermal synthesis temperature applied in the method of the present invention.

Claims (1)

[Claims] Primary formula: AO・n(Fe _1-n Mm) ₂ O ₃ (wherein A represents at least one element selected from the group of barium, strontium, and calcium; M is cobalt , represents at least one element selected from the group of titanium, nickel, manganese, copper, zinc, indium, germanium, niobium, and zirconium; m and n are 0.08≦m≦0.2 and 5≦, respectively.
A solution () containing each of the above-mentioned metal ions selected in a proportion constituting a hexagonal ferrite represented by a number satisfying the relationship n≦6) and an alkaline solution () are mixed; the mixed solution is heated to form a precipitate; then, the precipitate is washed with water, dried, and fired to produce a hexagonal ferrite magnetic powder. When the ratio to the sum of equivalents of metal ions is x and the heating temperature is y (℃), x is a number satisfying 1≦x≦8, and
and y are: When 1≦x<1.9, 5x+30≦y≦180; When 1.9≦x≦2.2, 5x+30≦y≦−200x+
560; When 2.2≦x<4, 5x+30≦y≦100x−100; When 4≦x≦8, 5x+30≦y≦300 A hexagonal ferrite magnetic powder characterized by a number satisfying the following relationships. manufacturing method. 2. The method for producing hexagonal ferrite magnetic powder according to claim 1, wherein the firing temperature is 700 to 950°C. 3. The method for producing hexagonal ferrite magnetic powder according to claim 1 or 2, wherein the firing temperature is 700 to 850°C.