JPH0142894B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing an oxide magnetic material, and more particularly to a method for producing a magnetoplumbite-type ferrite powder suitable as a high-density magnetic recording material. Ferrite powder as a representative example of the oxide magnetic material targeted by the present invention has the general formula: MO.
It is a magnetoplumbite-type ferrite powder that can be expressed as nFe ₂ O ₃ . Here, M in the above general formula represents at least one metal element selected from the group consisting of Ba, Sr and Pb, and n represents a numerical value within the range of 3.0 to 6.0. Normal magnetic recording uses a method in which the recording medium is magnetized in the in-plane longitudinal direction, but with this method, the demagnetizing field within the recording medium increases as the recording density increases, and the magnetization of the medium becomes stronger. Since it will be subject to demagnetization, it will be difficult to further increase the density. In contrast to such longitudinal recording methods, a perpendicular magnetic recording method, which is characterized by magnetization in a direction perpendicular to the surface of the recording medium layer, has been proposed as a high-density recording method, and is being put into practical use. According to this method, for adjacent magnetizations in the medium,
Since the N and S different polarities are lined up, the demagnetizing field is reduced and a strong residual magnetization can be maintained.For this reason, the shorter the recording wavelength, the less the demagnetizing field and the stronger the magnetization of the adjacent different polarities. It will be done. In this way, the perpendicular magnetic recording method can be said to be a recording method essentially suitable for high-density recording. Incidentally, the recording medium used in this perpendicular magnetic recording system must have an axis of easy magnetization in the direction perpendicular to the surface of the medium, and a Co--Cr film formed by sputtering has been developed as this recording medium.
However, this Co--Cr sputter film has a complicated manufacturing method, and is disadvantageous in terms of cost because it requires high raw materials. On the other hand, in contrast to such a Co--Cr sputter film, a coated recording medium in which magnetoplumbite-type ferrite powder is coated on a base film has also attracted attention and is being developed. Since this coating method is the most commonly used method, it is easy to apply storage technology to the production of perpendicular magnetic recording media using this method.
Furthermore, since existing equipment can be used in combination, there is no need for large-scale new equipment investment, and productivity is good, which is economically advantageous. By the way, the magnetoplumbite-type ferrite powder used in the coating type recording medium, for example, Ba-ferrite particles, has a hexagonal thin plate shape and has an axis of easy magnetization perpendicular to the particle plate surface. When coated on a base film, since it has a thin plate shape, it can be easily oriented in the direction parallel to the base film surface and can provide uniaxial anisotropy in the direction perpendicular to the coating surface. . Thus, Ba-ferrite powder is suitable as a magnetic powder for perpendicular magnetic recording. Furthermore, Ba
- In addition to ferrite powder, magnetoplumbite-type Sr-ferrite powder, Pb-ferrite powder, and composite ferrite powder consisting of two or more of these are also suitable for perpendicular magnetic recording media. The present invention provides a magnetoplumbite type ferrite powder most suitable for this coated perpendicular magnetic recording medium. By the way, as for the characteristics of the magnetoplumbite type ferrite powder used as the magnetic powder for perpendicular magnetic recording, first of all, it is desirable that the saturation magnetization is high and that it has a coercive force of 200 to 2000 (Oe). Furthermore, it is required that the ferrite powder is thin in shape, has a particle size of 0.01 to 0.5 μm, and is fine and has good dispersibility. As a typical manufacturing method of the magnetoplumbite type ferrite powder for perpendicular magnetic recording,
No. 56-125219, JP-A-56-149328 and JP-A-56
A method described in JP-A-160328 is known. The method described in JP-A No. 56-125219 involves mixing the basic components of magnetoplumbite-type ferrite powder, low coercive force components, and glass-forming substances in a predetermined ratio, melting, and then rapidly melting the molten material. The amorphous body obtained by cooling is heat-treated to precipitate fine particles of ferrite, and then the glass-forming substance is removed, resulting in a particle size of 0.01-0.3 μm and a coercive force of 200-200 μm.
2000 (Oe) of ferrite powder, but with this method, it is difficult to completely remove the glass-forming substance, and as a result, the residual glass substance exists as a binder between individual particles, resulting in particle agglomeration. It is difficult to obtain ferrite powder that is easy to disperse and has good dispersibility. Furthermore, the manufacturing method is complicated, which is disadvantageous from an industrial perspective. On the other hand, JP-A-56-
The methods described in No. 149328 and JP-A-56-160328 are both hydrothermal synthesis of Ba-ferrite powder using an autoclave. The former has a molar ratio of 1/12 to Fe to Fe.
molar ratio of 1.0/12 to Ba and Fe of 3/12
The average ion valence of ~1.8/12 equivalent is trivalent and
To a solution containing metal salts of metal elements other than Ba and Fe, add an alkaline solution equivalent to 1 to 5 times the total amount of the metal salts, and react at high temperature and pressure of 400°C or higher in an autoclave to form the desired ferrite. This is a method to obtain particles, but at high temperatures and pressures of over 400℃,
Ba-ferrite particles tend to sinter, making it difficult to prepare ferrite powder with good dispersibility. In addition, it is difficult to prepare ferrite powder with the desired high saturation magnetization using an autoclave. For example, as described in the above publication, the saturation magnetization of Ba-ferrite powder obtained by reacting at a temperature of 550°C for 2 hours in a container is It is 47emu/g. In this way, even Ba-ferrite powder synthesized under extremely high temperature and high pressure conditions cannot be used as a general-purpose Ba-ferrite powder used in magnets, etc.
It is difficult to prepare magnetoplumbite-type ferrite powder with high saturation magnetization by this method, which is lower than the saturation magnetization of ferrite powder (50 emu/g or more). Furthermore, since the temperature and pressure are extremely high, it is industrially disadvantageous. On the other hand, in the latter publication, in order to suppress grain growth and sintering agglomeration in the manufacturing method described in the former publication, the reaction temperature in the autoclave was selected to be as low as 150 to 250°C. In this method, a precursor of Ba-ferrite with very low saturation magnetization is first produced by reacting at According to this method, individual Ba-ferrite particles are sintered and aggregated during heat treatment at 800° C. or higher, making it difficult to obtain Ba-ferrite powder with good dispersibility. In view of these circumstances, the present invention provides a method for easily producing magnetoplumbite-type ferrite powder that has a large saturation magnetization, is fine, and has good dispersibility without complicated operations. That is, the present invention provides a slurry with a pH of 11 or more containing Fe and one or more metal elements selected from Ba, Sr, or Pb in a molar ratio of 1/12 to 2/12 to Fe. and at least one additive base selected from alkyl sulfonates, lauramine acetate, beef tallow diamine, metal soaps of higher fatty acids, and higher fatty acid esters (hereinafter, these additive groups are referred to as agent A). and at least one additive and adjuvant selected from phosphates, phosphate esters, oxycarboxylate salts, silicates, and colloidal silica (hereinafter, these additive groups are referred to as additives), and The amount of these additions is
Based on the weight of the precipitate contained in the above alkaline solution, agent A should be at least 1wt%, agent B should be at most 20wt%,
After surface treatment of the precipitate, 200%
This is a method for producing magnetoplumbite-type ferrite powder, which is characterized by carrying out the reaction at ~400°C. It is generally said that the biggest drawback of the hydroxyl synthesis method is that the obtained magnetoplumbite-type ferrite powder has a low saturation magnetization. For example, as described in JP-A-56-149328, the autoclave reaction temperature is extremely high at 550°C and 120°C.
Even after reacting for minutes, the saturation magnetization of the Ba-ferrite powder obtained is about 47 emu/g. To address this situation, the present invention provides magnetoplumbite-type ferrite powder that has an autoclave reaction temperature of 200 to 400°C and a reaction time of 60 minutes or less, has a saturation magnetization of 50 emu/g or more, and has good dispersibility. easily obtained. That is, the present inventors brought a solution containing a predetermined amount of alkali into contact with a solution containing a predetermined amount of Fe and one or more metal elements selected from Ba, Sr, or Pb. To the obtained slurry containing metal hydroxide or metal hydroxide and iron oxyhydroxide, alkyl sulfonate, laurylamine acetate, tallow diamine,
Agent A selected from metal soaps of higher fatty acids and higher fatty acid esters and Agent B selected from phosphates, phosphoric acid esters and oxycarboxylic acid salts, silicates and colloidal silica, either alone or together with Agent A. After being added in combination with a chemical agent, the reaction is carried out in a high-pressure container at a lower reaction temperature of 200 to 400°C, resulting in good dispersibility and a saturation magnetization of 50 emu/g or higher, which has never been reported in a hydrothermal synthesis method. It has been found that magnetoplumbite-type ferrite powder with high saturation magnetization can be obtained. Furthermore, the magnetoplumbite-type ferrite powder obtained in this way has a major axis diameter of 0.5 μm or less, exhibits an extremely thin plate shape with an average thickness of crystal grains of 0.02 μm, and has a coercive force of 200 μm. ~2000 (Oe), which indicates that the magnetic powder is suitable as a magnetoplumbite-type ferrite powder used in perpendicular magnetic recording media. The present invention will be explained in detail below. The present invention has the general formula: MO・nFe ₂ O ₃ (M is Ba, Sr,
Represents any one of Pb or two or more metals selected from Pb. n is called a molar ratio and is a numerical value of 3 to 6. ) A solution containing each metal element mixed in a ratio based on the composition formula of magnetoplumbite-type ferrite (here, the solution refers to a solution containing not only metal ions but also metal hydrides, iron oxyhydroxide, etc.) ) is brought into contact with an alkaline solution containing a predetermined amount of alkali so that the pH becomes 11 or higher to form a precipitate. The reason why the molar ratio n is selected in the range of n=3 to 6 is that when n<3, compounds other than the magnetoplumbite phase are generated;
On the other hand, in the range of n>6, non-magnetic a-Fe ₂ O ₃ is present, and both of these act as impurities and cause a decrease in saturation magnetization. Furthermore, if the pH of the solution is less than 11, the amount of magnetoplumbite phase produced will be extremely small. To the alkaline slurry containing the precipitate obtained in this manner, a solution containing an additive selected from the following Agent A or Agent B is added at a predetermined ratio to the weight of solids contained in the slurry. In this case, the additive may be added during the ferritization reaction process. Specifically, the additives used in the present invention include agent A, alkyl sulfonates such as sodium alkylbenzenesulfonate and sodium lauryl sulfonate, laurylamine acetate, tallow diamine, sodium oleate, potassium oleate, and sodium stearate. , higher fatty acid soaps such as potassium stearate, and sorbitan fatty acid esters are effective, and an effective amount of addition is 1 wt % or more based on the weight of the precipitate. In addition, as a second agent, phosphates such as sodium trimetaphosphate and sodium hexametaphosphate, phosphates such as monoalkyl phosphates and dialkyl phosphates, oxycarboxylate salts such as sodium citrate and tartaric acid, sodium silicate, and Additives such as colloidal silica are chosen, in which case good results are obtained when used in combination with agent A. At this time, it is effective to add the additive in an amount of 20wt% or less based on the solid weight contained in the alkaline slurry, and if it is more than 20wt%, the magnetoplumbite type ferrite crystal particles obtained by hydrothermal synthesis will be It becomes coarser and the saturation magnetization decreases. In the present invention, the alkaline slurry thus obtained is reacted in a high pressure vessel at a high temperature of 200 to 400°C. Here, the reaction temperature is set to 200°C or higher because magnetoplumbite-type ferrite powder with the desired saturation magnetization cannot be obtained at temperatures below the same temperature, whereas ferrite crystal particles become coarse at high temperatures of 400°C or higher. This is because it becomes difficult to obtain fine particles of 0.5 μm or less. Since the solution containing magnetoplumbite-type ferrite particles obtained in this manner exhibits high alkalinity, it is repeatedly filtered and washed to sufficiently remove impurities. Next, it is dried and granulated to obtain the desired magnetoplumbite-type ferrite powder. The magnetoplumbite-type ferrite powder obtained by the method described above has the following properties during the ferritization reaction:
Since the additive according to the present invention is interposed between the produced ferrite particles, each particle becomes independent and exhibits excellent dispersibility. Further, when it is necessary to desorb additives adsorbed on the ferrite powder, it can be easily desorbed by heat treating the ferrite powder at 250 to 400°C. The heating temperature selected here is the temperature necessary to desorb the additive, and as mentioned above, a low temperature is sufficient. Therefore, without sintering and agglomeration between ferrite particles,
Good dispersibility before additive desorption can be maintained. As described above, the magnetoplumbite type ferrite powder obtained in the present invention has a saturation magnetization.
50 emu/g or more, and the autoclave reaction temperature described in the aforementioned Japanese Patent Publication No. 56-149328
It has a high saturation magnetization at a much lower autoclave reaction temperature than the saturation magnetization of 47 emu/g of the 550°C product, and has a coercive force of 200 to 2000 (Oe).
Furthermore, the size of the ferrite crystal particles is 0.5μ in major axis diameter.
They are extremely thin plate-like particles with an average thickness of 0.02 μm or less, and each particle is independent.
It exhibits good dispersibility and is suitable for perpendicular magnetic recording media. The present invention will be explained in more detail below with reference to Examples. Example 1 210 ml of 3.0M FeCl ₃ aqueous solution, 0.5M BaCl ₂ aqueous solution
Add 127 ml of the mixed solution to 8.3 M NaOH aqueous solution 732
ml to obtain an alkaline slurry containing a brown precipitate. Next, 216 g of an aqueous solution containing 16 g of sodium oleate was added as an additive to the alkaline slurry containing the precipitate, and after forced stirring for 10 minutes, the mixed slurry was heated in an autoclave at 280 °C.
The reaction was carried out at ℃ for 60 minutes. After washing and drying the reaction product thus obtained, the temperature was raised to 300°C to desorb the oleic acid coating the reaction product.
A Ba-ferrite powder was obtained by heat treatment for 30 minutes. The magnetoplumbite type Ba-ferrite powder thus obtained has a specific surface area of 21
m ² /g, particle size of 0.5 μm or less, platelet ratio of 10 or more, individual particles are isolated, and the particles are extremely thin plate-like fine particles with good dispersibility. In addition, the magnetic properties of this Ba-ferrite powder are saturation magnetization of 56.8emu/
g, and the coercive force was 825 (Oe). Examples 2 to 8 Type and amount of starting material BaCl ₂ or SrCl ₂ , amount of 3.0 mol FeCl ₃ solution, amount of alkali added,
Except for changing the type of additive, amount and order of addition, autoclave reaction temperature and reaction time,
By the same operation as in Example 1, Ba-ferrite powder,
Sr-ferrite powder or Ba, Sr-composite ferrite powder was obtained. The magnetoplumbite-type ferrite powder thus obtained has a particle size of 0.5 μm or less, a platelet ratio of 10 or more, and individual particles are isolated to form extremely thin plate-like fine particles with good dispersibility. It is a particle. Table 1 shows the manufacturing conditions that were changed in Examples 2 to 8 and the characteristics of the obtained ferrite powder.

[Table] Comparative example 1 210ml of 3.0M FeCl ₃ aqueous solution, 0.5M BaCl ₂ aqueous solution
Add 127 ml of the mixed solution to 8.3 M NaOH aqueous solution 732
ml to obtain a brown precipitate. The alkaline slurry containing this precipitate is then placed in an autoclave.
The reaction was carried out at 280°C for 60 minutes. The reaction product thus obtained was washed with water and dried to obtain Ba-ferrite powder. The Ba-ferrite powder thus obtained has a specific surface area of 27.2 m ² /g,
The particle size was 0.5 μm or less, and the platelet ratio was 10 or more.
In addition, the magnetic properties are saturation magnetization 28.6emu/g coercive force
It was 1220 (Oe). Furthermore, when the Ba-ferrite powder was heat-treated at 300°C for 30 minutes in the same manner as in Example 1, the specific surface area was 26.9 m ² /g, and the saturation magnetization was
The coercive force was 29.13 emu/g and 1210 (Oe), showing almost no change. Comparative example 2 210ml of 3.0M FeCl ₃ aqueous solution, 0.5M BaCl ₂ aqueous solution
Add 127 ml of the mixed solution to 8.3 M NaOH aqueous solution 732
ml to obtain an alkaline slurry containing a brown precipitate. Next, an aqueous solution containing 21.6 g of gelatin was added to the alkaline slurry containing the precipitate as an additive.
After 10 minutes of forced stirring, the slurry was reacted in an autoclave at 280° C. for 60 minutes. The reaction product thus obtained was thoroughly washed with water, and then dried and granulated. The specific surface area of the magnetoplumbite-type Ba-ferrite powder thus obtained is 5.3 m ² /g.
The grain size becomes coarser than 1μm, and the saturation magnetization becomes
It was 33.8 emu/g. Furthermore, when the Ba-ferrite powder was heat-treated at 300° C. for 30 minutes in an electric furnace in the air in the same manner as in Example 1, the saturation magnetization was 34.1 emu/g, showing almost no change. Comparative example 3 210ml of 3.0M FeCl ₃ aqueous solution, 0.5M BaCl ₂ aqueous solution
Add 127 ml of the mixed solution to 8.3 M NaOH aqueous solution 732
ml to obtain an alkaline slurry containing a brown precipitate. Next, a silane coupling agent (chemical name: gamma-aminopropyl trimezoxy silane) is added to the alkaline slurry containing the precipitate as an additive.
After adding 216 g of an aqueous solution containing 16.2 g and forced stirring for 10 minutes, the slurry was reacted in an autoclave at 280° C. for 60 minutes. In the reaction product thus obtained, Ba-ferrite was not detected by material identification by X-ray diffraction, and the saturation magnetization was extremely low at 1.6 emu/g. Comparative example 4 210ml of 3.0M FeCl ₃ aqueous solution, 0.5M BaCl ₂ aqueous solution
Add 127 ml of the mixed solution to 8.3 M NaOH aqueous solution 732
ml to obtain an alkaline slurry containing a brown precipitate. Next, 216 g of an aqueous solution containing 21.6 g of Na citrate was added as an additive to the alkaline slurry containing this precipitate, and after forced stirring for 10 minutes,
The slurry was heated in an autoclave at 280℃ for 60 minutes.
Allowed to react for minutes. The reaction product thus obtained was identified as α-Fe ₂ O ₃ by X-ray diffraction.
found.

Claims (1)

[Claims] 1 General formula: MO・nFe ₂ O ₃ (However, in the above formula, M represents at least one element selected from the group consisting of Ba, Sr, and Pb, and n is a numerical value of 3.0 to 6.0. PH11 containing the necessary metal elements to produce magnetoplumbite-type ferrite represented by
At least one compound selected from the following group A (hereinafter referred to as "agent A") is added to the slurry containing the above solids. Group A: alkyl sulfonate, laurylamine acetate, tallow diamine, metals of higher fatty acids. Soap and higher fatty acid ester; or the above-selected agent A and at least one compound selected from the group O below (hereinafter referred to as “agent O”)
That's what it means. ) and both groups: phosphates, phosphoric acid esters, oxycarboxylate salts, silicates, and colloidal silica; are added as additives, and the alkaline slurry thus obtained is heated at a temperature of 200 to 400°C in a high-pressure container. 1. A method for producing an oxide magnetic material, which comprises reacting with. 2. The method according to claim 1, wherein only Agent A is added as an additive in an amount of 1% by weight or more based on the weight of the precipitate contained in the alkaline slurry. 3. As additives, in addition to Agent A in an amount of 1% by weight or more based on the weight of the precipitate contained in the alkaline slurry, Agent B in an amount of not more than 20% by weight based on the weight of the precipitate contained in the alkaline slurry. The method according to claim 1, characterized in that: 4. The method according to any one of claims 1 to 3, which includes a step of firing the produced ferrite powder at a temperature of 250 to 400°C and desorbing additives adsorbed to the ferrite powder. Method.