JPH0688794B2 - Method for producing ferromagnetic fine powder for magnetic recording - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a ferromagnetic fine powder for magnetic recording, which comprises barium ferrite crystal particles, which is suitable for a medium for high density magnetic recording, particularly for perpendicular magnetic recording.

[Technical background of the invention and its problems]

Magnetic recording generally employs a method of magnetizing in the longitudinal direction of the recording medium. However, in the case of this method, if the recording density is increased, the demagnetizing field in the recording medium increases and it is difficult to achieve sufficient high-density recording. In contrast to such a longitudinal recording method, a so-called perpendicular magnetic recording method, which aims at high density recording by reducing the demagnetizing field in the recording medium by magnetizing in the direction perpendicular to the surface of the recording medium layer, has been noticed in recent years. ing.

By the way, as the perpendicular magnetic recording medium, in addition to those by an alloy film method such as Co-Cr system, which has been attempted to be practically used in the past, 60,000 crystal ferrite crystal particle powder such as barium ferrite is dispersed in a binder. A so-called coating-type recording medium has been proposed in which a base film is coated with the same. In the case of the coating type, as in the case of the production of the conventional longitudinal type recording medium, since it can be produced with good productivity and economical advantage, and the durability of the recording medium is excellent, Practical application is urgent.

On the other hand, as the magnetic powder composed of 60,000 barium ferrite crystal particles used for the perpendicular magnetic recording medium, a coercive force (He: 400 to 2000 Oe) and a large saturation value in a suitable range that does not saturate the magnetic head during recording. It has magnetization and has an easy axis of magnetization in the direction perpendicular to the surface of the grain plate, and has a fine grain size of 0.3 μ or less, especially 0.2 μ or less, and dispersibility in the magnetic layer. Good things are said to be important. Recently, however, the characteristics required of the above magnetic powder, together with the orientation of the high recording density, can satisfy the reduction of the noise level in the perpendicular magnetic recording medium and the high output in the short wavelength region. It is becoming more and more desirable. Therefore, the particle size is finer and the particle size distribution is sharper, and the dispersibility is good and the coating surface is excellent in smoothness, high orientation, and high filling property. There is an urgent need to develop barium ferrite particle powders that exhibit On the other hand, various methods have been conventionally known for producing barium ferrite particles, and many proposals have been made for making particles finer, but in general, dispersibility and orientation are accompanied by making particles finer. However, the above demand has not yet been fully satisfied, and there is a strong demand for a solution thereof.

[Object of the Invention]

The present invention provides a ferromagnetic fine powder suitable for perpendicular magnetic recording, which comprises plate-like barium ferrite fine particle powder having a sufficiently high saturation magnetization, a fine particle size, and excellent high-dispersion perpendicular magnetization orientation. Is to provide a stable and easily obtainable method by a relatively simple means.

[Outline of Invention]

A method of hydrothermally treating an alkaline suspension containing Ba and Fe at a high temperature of, for example, 250 ° C. or higher under high pressure is known as one of the methods for producing barium ferrite particle powder. Compared to the so-called dry method and coprecipitation-calcination method, the method is generally relatively small in the formation of coarse fixed particles, but it is difficult to obtain a large saturation magnetization, and the reaction easily proceeds locally, For this reason, it is difficult to obtain a product having a uniform particle size, and it is unavoidable that the hydrothermal treatment is carried out at high temperature and high pressure, resulting in problems in the apparatus and complexity in operation. Further, if the barium ferrite precipitated particles are further miniaturized, the particles may be easily sintered or the shape of the particles may be broken during the firing process, and the orientation, the filling property, the dispersibility, etc. may not always be sufficient. The present inventors have conducted various studies to solve the above problems in the hydrothermal method in order to achieve the above object, and as a result, Ba and Fe
A barium ferrite precursor substance is produced by a temporary heat treatment in the presence of an alkali having a + Me ratio within a specific molar ratio range and at a certain concentration or higher, and then the precursor. By calcining the body substance under a specific temperature range, it is of fine particle size and dispersibility while substantially avoiding coarsening of the particles,
Fine barium ferrite precipitates that can be obtained as barium ferrite crystal particles having excellent magnetic properties with excellent orientation, and further, when firing the barium ferrite precursor substance, by adding a specific compound to the precursor substance in advance. Based on the finding that it is possible to effectively suppress the inter-particle sintering of particles and the collapse of particle shape, and obtain a ferromagnetic fine powder of barium ferrite crystal particles having further excellent dispersibility and orientation. It has been completed.

That is, in the present invention, Ba is a molar ratio of Fe + Me (where Me is
At least one element selected from the group consisting of Co, Ti, Ni, Mn, Zr, Zn, Ge, Nb and V, and a ratio of 1/6 to 1/10 with respect to 0.2 mol or less per 1 mol of Fe) The alkaline suspension containing each element selected to have a free OH group concentration of 1.5 mol / 1 or more is heat-treated at a temperature range of 60 ° C or higher and lower than 120 ° C to obtain a barium ferrite precursor substance. Then, the precursor material is then calcined in a temperature range of 650 to 950 ° C., or at the time of the calcining, the precursor material contains at least a silicon compound or a sodium compound, a potassium compound, a lithium compound, a barium compound or a strontium compound. This is a method for producing a ferromagnetic fine powder for magnetic recording, characterized in that barium ferrite crystal particles are obtained by adding and burning one type in advance. In the method of the present invention, first, as a substitution element Me for controlling the coercive force with a barium compound and an iron compound, Co, Ti, Ni, Mn, Zr, Zn,
An aqueous solution containing a predetermined amount of at least one of Ge, Nb, and V compounds is prepared. As these compounds, various water-soluble compounds can be used, but chlorides, nitrates and the like are preferable. The barium component has a molar ratio of 1/6 to 1/10, preferably 1/7 to 1/9, with respect to the Fe + Me component. When the molar ratio is smaller than the above range, the obtained ferrite crystal particle powder is liable to be coarsened, and the dispersibility is deteriorated, and the characteristics such as orientation in the recording medium and surface smoothness are unavoidable. On the other hand, if the molar ratio is larger than the above range, a crystal phase different from the magnetoplumbite type crystal may be mixed, and a decrease in saturation magnetization or a non-uniform shape may be unavoidable, which is not preferable. The substitution component Me is Co, Ti, N.
At least one of i, Mn, Zr, Zn, Ge, Nb, and V can be used in an amount of 0.2 mol or less, preferably 0.17 mol or less, based on 1 mol of Fe, and in particular, the Fe component can be replaced with at least Co and Ti elements. preferable.

Next, in the above metal compound aqueous solution, for example, NaOH, KOH, NH ₄ OH
An aqueous solution such as the above is contacted and mixed to form an alkaline suspension.
The alkaline concentration of the alkaline suspension is 1.
If the amount is 5 mol / l or more, preferably 2 mol / l or more, and is lower than the above range, the reaction does not proceed sufficiently and non-plate-like particles are often generated. Are easily formed, and a decrease in orientation and dispersibility is unavoidable.

Then, the alkaline suspension is used as a reaction vessel of a heating device or placed in a pressure vessel such as an autoclave and subjected to a heat reaction treatment at 60 ° C. or higher and lower than −120 ° C., preferably 80 to 110 ° C. to obtain plate-like particles. Forming a barium ferrite precursor material. When the temperature during the heat treatment is lower than the above range, this tends to form sintered particles, so that it is difficult to obtain barium ferrite particle powder having a uniform shape, and deterioration of orientation is unavoidable. Or On the other hand, if it is higher than the above range, it is not preferable for producing a fine particle size.

In the method of the present invention, the barium ferrite precursor substance of the plate-like particles obtained by the heat reaction treatment as described above is washed with water, dried, and then fired usually at 650 to 950 ° C, preferably 700 to 900. Perform at ℃. When the firing temperature is lower than the above range, the crystallization of barium ferrite particles does not proceed sufficiently and the saturation magnetization is low, and when the firing temperature is higher than the above range, the barium ferrite particles stick to each other or sinter easily to form aggregates. In some cases, the dispersibility in coating material is significantly impaired and the magnetic characteristics and surface smoothness of the recording medium are unavoidably deteriorated. The calcination can be carried out usually for about 0.5 to 5 hours using various types of devices such as a rotary furnace and a fluidized bed furnace.

In the present invention, when firing the fine particle barium ferrite precursor material obtained as described above, a silicon compound, a sodium compound, a potassium compound, a lithium compound, a barium compound or a strontium compound is added to the precursor material in advance. In the case of firing after treatment, barium which is extremely effective in suppressing inter-particle sintering and collapse of particle shape during firing of fine barium ferrite precipitated particles, and which is more excellent in dispersibility and orientation. Ferrite crystal particles can be obtained.

Examples of the silicon compound used as the treatment agent include sodium orthosilicate, sodium metasilicate, potassium metasilicate, calcium metasilicate, silicates such as magnesium silicate, silicone oil, silicone range, chlorosilane, and silane such as alkoxyten. Examples thereof include siloxane and siloxane, but it is usually preferable to use an aqueous silicate solution of water glass having various compositions. The treatment agent comprising the silicon compound may be added to the barium ferrite precursor substance by various methods. For example, silicic acid may be added to an aqueous suspension containing the barium ferrite precursor substance. By adding a salt solution and neutralizing it with an acidic substance, the surface of the particles is coated as a hydrated silicic acid (SiO ₂ · nH ₂ O), or in a solution in which an organosilicon compound is dissolved in an organic solvent. In, to suspend the barium ferrite precursor substance to adsorb the silicon compound on the surface of the particles,
Further, it can be carried out by spray-adsorbing the above-mentioned silicate aqueous solution or the solution of organosilicon on the surface of the particles. The addition amount of the silicon compound is 0.1 to 10 as Si on a weight basis with respect to the barium ferrite precursor substance.
It is 1.5%, preferably 0.2 to 1%. If the amount of addition treatment is too small, the desired effects such as sintering prevention may not be sufficiently obtained if it is too small, while if it is too large than the above range,
It is not preferable because the magnetic properties are impaired such as the saturation magnetization being lowered.

Further, as the metal compound used as the treatment agent, a sodium compound, a potassium compound, a lithium compound, a barium compound or a strontium compound,
Various kinds of chlorides, sulfates, carbonates, nitrates and the like of these metals can be used, but chlorides and sulfates are particularly preferable. The addition treatment of the metal compound can be performed by various methods, for example, a wash cake of a barium ferrite precursor substance obtained by heating, filtering and washing after heating treatment is added to an aqueous solution of the metal compound and suspended. After that, it can be performed by drying, or by adding an aqueous solution of the metal compound to a wash cake of the barium ferrite precursor substance, kneading, and drying if necessary. The processing amount of the metal compound added is
5 to 120% by weight based on barium ferrite precursor material
Is. If the addition treatment amount is less than the above range, the effect of suppressing interparticle sintering and adjusting the particle shape to a hexagonal plate shape is not sufficient, and if the treatment amount is too much than the above range, it is economically advantageous. Not. When the addition treatment of the metal compound is performed, the coercive force can be more effectively reduced by the substituting element in controlling the coercive force of the barium ferrite crystal particles in the desired range described above. It should be noted that a more desirable effect may be brought about by adding the silicon compound and a metal compound such as a sodium compound, a potassium compound, a lithium compound, a barium compound or a strontium compound as a baking treatment agent together.

The barium ferrite particle powder obtained as described above is immersed in an aqueous medium or, if necessary, an acidic aqueous medium to remove excess barium and impurities by pickling.
In the above case, the dispersibility may be further enhanced by treating the aqueous medium with a strongly acidic medium.

As described in detail above, the ferromagnetic fine powder obtained by the manufacturing method of the present invention is a magnetoplumbite-type barium ferrite crystal particle powder having a saturation magnetization of about 45 to 60 emu / g and a coercive force of about 400 to 2,000 e. , Which has a plate-like shape and has an average particle size of approximately 0.05 to 0.15μ and a small particle size distribution and has excellent dispersibility in the magnetic layer of a magnetic recording medium, and is very suitable as a material for high density perpendicular magnetic recording. It is something.

Example of Invention

The present invention will be further described below with reference to Examples and Comparative Examples.

Example 1. 360 ml of 1 mol / l BaCl ₂ aqueous solution, 1 mol / l FeCl ₃ aqueous solution 2
496 ml, 1 mol / l CoCl ₂ aqueous solution 192 ml and 1 mol / l TiC
192 ml of ₄ aqueous solution was mixed (Ba / Fe + Me molar ratio: 1/8, Ba / Fe
Molar ratio 1.5 / 10.4), then mix this mixture with 10 mol / l NaOH
An alkaline suspension containing a brown precipitate was prepared by adding it to 3480 ml of an aqueous solution. The suspension was subsequently placed in an autoclave and heated at 100 ° C. for 3 hours to form a barium ferrite precursor material. Then, the obtained barium ferrite precursor substance was filtered, washed with water, dried at 110 ° C., and then crushed.

Then, this powder was fired in a box-type electric furnace at 800 ° C. for 1 hour to obtain barium ferrite crystal particle powder. Then, the obtained powder is immersed in a weakly acidic aqueous solution and then filtered,
What was washed with water was dried to obtain the ferromagnetic powder of the present invention.
(Sample A) Example 2. The same procedure as in Example 1 was performed except that the alkaline suspension containing Ba, Fe, Co, and Ti in Example 1 was heat-treated at 80 ° C. for 3 hours. To obtain a ferromagnetic powder according to the present invention. (Sample B) Example 3. The barium ferrite precursor material obtained by heating the alkaline suspension at 100 ° C. in Example 1 was filtered, washed with water,
This washed cake was repulped with water, and a water glass solution (Si concentration 10 g / l) was added to the slurry (solid concentration 50 g / l), and the pH was adjusted to pH 7.3 with hydrochloric acid (0.1 N) while stirring. Then, the surface of the barium ferrite starting material particles was coated with a silicon compound in an amount of 0.5% by weight in terms of Si. The treated product was filtered, washed with water, dried at 110 ° C., and then roughly crushed. Then, the dried powder was fired in the same manner as in Example 1 to obtain the ferromagnetic powder of the present invention. (Sample C) Example 4. To the washed cake obtained by filtering and washing the barium ferrite starting material obtained by the heat treatment in Example 3, 350 ml of an aqueous solution in which 50 g of NaCl was dissolved was added, well stirred and dried at 110 ° C. Water was evaporated (additional treatment amount of NaCl was 100% by weight based on the barium ferrite precursor material).

The dried material obtained as described above was fired at a firing temperature of 800 ° C. in the same manner as in Example 3 to obtain a ferromagnetic powder according to the present invention. (Sample D) Comparative example. A comparative sample was prepared in the same manner as in Example 1, except that the alkaline suspension containing Ba, Fe, Co and Ti elements was heat treated at 40 ° C. for 3 hours. .
(Sample E) In addition, each sample obtained in the above-mentioned Examples and Comparative Examples is X
As a result of line diffraction, all were magnetoplumbite type barium ferrite. Further, when each sample of the above-mentioned Examples was observed with an electron microscope, the particle shape was plate-like.

The average particle diameter (Dp: electron microscopy), coercive force (Hc), and saturation magnetization (σs) of each sample were measured by a conventional method,
Further, a magnetic coating material was prepared with the following composition, which was coated on a polyester film and subjected to orientation treatment perpendicular to the coated surface to prepare a magnetic recording medium.

Magnetic powder ・ 100 parts by weight Vinyl acetate-vinyl chloride copolymer resin 16.2 〃 Surfactant 4 〃 Methylethylkent 186 〃 Holding power (Hc⊥: perpendicular to the media surface) and orientation of the recording medium Ratio (OR), Squareness ratio (SQ⊥:
These values are in the direction perpendicular to the medium surface and after demagnetizing field correction.) These results are shown in Table 1.

As is clear from the results in Table 1, the molar ratio of Ba / Fe + Me,
When the concentration of free OH groups, the heat treatment temperature and the calcination temperature are within the range of the present invention, a precursor precipitate of barium ferrite is formed.
A target plate-like magneplanbite type fine barium ferrite powder having a small grain size and a good crystal state can be obtained. Thus, this one has a sufficiently high saturation magnetization, and also has excellent perpendicular dispersibility in terms of squareness ratio and orientation characteristics and good dispersibility. In addition, the one to which the baking treatment agent is added can be made to have more excellent orientation and dispersibility by suppressing inter-particle sintering. In addition, when a metal compound such as sodium, potassium, barium, or strontium was added as a baking treatment agent, coarsening due to particle growth was hardly observed by observation with an electron microscope, and the particle shape was particularly well adjusted. In addition, the formation of agglomerated particles due to interparticle sintering is suppressed, and the coercive force control by the substitution element can be more effectively performed.

〔The invention's effect〕

Ferromagnetic fine powder composed of highly dispersible barium ferrite crystal particles having a large saturation magnetization and excellent perpendicular orientation can be easily produced by the optimum condition treatment by a relatively simple means. This is extremely useful for reducing the noise level and increasing the output.

Claims (3)

[Claims] 1. Ba is a molar ratio of Fe + Me (where Me is Co, Ti,
At least one element selected from the group consisting of Ni, Mn, Zr, Zn, Ge, Nb, and V, with a ratio of 1/6 to 1/10 to 0.2 mol or less per 1 mol of Fe) The alkaline suspension containing each element selected in and the free OH group concentration is 1.5 mol / 1 or more is heat-treated at a temperature range of 60 ° C or higher and lower than 120 ° C to obtain a barium ferrite precursor substance, and then A method for producing a ferromagnetic fine powder for magnetic recording, characterized in that the precursor substance is fired in a temperature range of 650 to 950 ° C to form barium ferrite crystal particles. 2. Ba in a molar ratio of Fe + Me (where Me is Co, Ti,
At least one element selected from the group consisting of Ni, Mn, Zr, Zn, Ge, Nb, and V, with a ratio of 1/6 to 1/10 to 0.2 mol or less per 1 mol of Fe) The alkaline suspension containing each element selected in and the free OH group concentration is 1.5 mol / 1 or more is heat-treated at a temperature range of 60 ° C or higher and lower than 120 ° C to obtain a barium ferrite precursor substance, and then In the method of firing the precursor substance in the temperature range of 650 to 950 ° C. to form barium ferrite crystal particles, the precursor substance is added with a silicon compound and then fired, followed by firing. Powder manufacturing method. 3. Ba in a molar ratio of Fe + Me (where Me is Co, Ti,
At least one element selected from the group consisting of Ni, Mn, Zr, Zn, Ge, Nb, and V, with a ratio of 1/6 to 1/10 to 0.2 mol or less per 1 mol of Fe) The alkaline suspension containing each element selected in and the free OH group concentration is 1.5 mol / 1 or more is heat-treated at a temperature range of 60 ° C or higher and lower than 120 ° C to obtain a barium ferrite precursor substance, and then In the method of firing the precursor substance in the temperature range of 650 to 950 ° C. to form barium ferrite crystal particles, at least one kind of sodium compound, potassium compound, lithium compound, barium compound or strontium compound is added to the precursor substance. A method for producing a ferromagnetic fine powder for magnetic recording, which comprises firing after treatment.