JPH08702B2 - 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 co-magnetic fine powder for magnetic recording, which comprises barium ferrite crystal particles, which is suitable for a medium for high-density magnetic recording, particularly perpendicular magnetic recording.

[Technical background of the invention and its problems]

Magnetic recording is generally performed by magnetizing the inner surface of the recording medium in the longitudinal direction. 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, hexagonal 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 material is coated on a base film. In the case of the coating type, since the durability of the recording medium is excellent as well as the productivity can be economically advantageously produced in the same manner as in the case of the production of the conventional longitudinal recording type recording medium, Its practical application is urgent.

On the other hand, as the magnetic powder composed of hexagonal barium ferrite crystal particles used in the perpendicular magnetic recording medium,
It has a coercive force (Hc: 400 to 2000 Oe) in an appropriate range that does not saturate the magnetic head during recording, has a large saturation magnetization, and has an easy axis of magnetization in the direction perpendicular to the surface of the grain plate. It is considered important that the particles have a fine particle size of μ or less, especially 0.2 μ or less, and have good dispersibility in the magnetic layer. Recently, however, the characteristics required of the above magnetic powder, together with the trend toward higher recording density, can satisfy the reduction of noise level in perpendicular magnetic recording media and the higher 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. Is greatly damaged,
For this reason, the above-mentioned demand has not yet been fully satisfied, and a solution thereof is strongly desired.

[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 method that is stable and easily obtained by a relatively simple means.

[Outline of Invention]

Conventional method 1 for producing barium ferrite particle powder
As one, a method of hydrothermally treating an alkaline suspension containing Ba and Fe, for example, at a high temperature of 250 ° C. or higher under high pressure is known, and this method is a so-called dry method or coprecipitation-calcination method. In general, the formation of coarse fixed particles is relatively small, but it is difficult to obtain a large saturated magnetization,
Further, the reaction is likely to proceed locally, so that it is difficult to obtain a product having a uniform particle size, and the hydrothermal treatment is performed at a high temperature,
In some cases, problems with the device and complexity of operation due to high pressure are inevitable. 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 +
By hydrothermal treatment in the presence of an alkali with a certain molar ratio of Me in a specific molar ratio range and above a certain concentration, it has a magnetoplumbite structure of low crystallinity and grain size. A barium ferrite precipitate of fine plate-like particles having a uniform particle size, and then firing the precipitate in a specific temperature range to obtain a particle having a fine particle size while substantially avoiding coarsening of the particle. Which is a barium ferrite crystal particles having desired magnetic properties excellent in dispersibility and orientation, further, when firing the barium ferrite precipitate, a specific compound is added to the precipitate in advance. It is possible to effectively suppress the inter-particle sintering of fine barium ferrite precipitate particles and the collapse of the particle shape, and further improve the dispersibility and orientation of barium ferrite. Based on knowledge of the ferromagnetic powder of the crystal grains can be obtained and completed the present invention.

That is, in the present invention, Ba has a molar ratio of Fe + Me (however, Me
Is at least one element selected from the group consisting of Co, Ti, Ni, Mn, Zr, Zn, Ge, Nb and V, and is 1/6 to 1/10 with respect to 0.2 mol or less per 1 mol of Fe). Alkaline suspension containing each element selected so that the free OH group concentration is 1.5 mol / or more is heat-treated at a temperature range of 120 to 200 ° C. to obtain a barium ferrite precipitate. The precipitate
Calcination in a temperature range of 650 to 950 ° C., or, during the calcination, the precipitate contains a silicon compound or sodium,
Chloride of potassium, lithium or strontium,
A method for producing a ferromagnetic fine powder for magnetic recording, characterized in that barium ferrite crystal particles are obtained by previously adding and burning at least one of sulfate, carbonate and nitrate. In the method of the present invention, first, at least one of Co, Ti, Ni, Mn, Zr, Zn, Ge, Nb and V compounds as a substitution element Me for controlling coercive force is used in a predetermined amount. Make an aqueous solution containing. As these compounds, various aqueous solution 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. Further, the molar ratio is
If it is larger than the above range, a crystal phase different from the magnetoplumbite type crystal may be mixed and the decrease of the saturation magnetization and the nonuniformity of the shape may be unavoidable, which is not preferable. The substitution component Me is Co, Ti, Ni, Mn, Zr, Zn, Ge, Nb, V
It is possible to use at least one of 0.2 mol or less, preferably 0.17 mol or less, relative to 1 mol of Fe, and it is particularly preferable to replace the Fe component with at least Co and Ti elements.

Next, in the above metal compound aqueous solution, for example, NaOH, KOH, NH ₄
An aqueous solution such as OH is contacted and mixed to make an alkaline suspension. The alkaline concentration of the alkaline suspension is 1.5 mol / mol or more, preferably 2 mol / mol or more on the basis of free OH. If it is lower than the above range, the reaction does not proceed sufficiently and non-plate-like particles are often produced. However, this product easily forms sintered particles during the firing process, and deterioration of orientation, dispersibility, etc. is unavoidable.

Then put the alkaline suspension in a pressure vessel such as an autoclave, 120 ~ 250 ℃, preferably 150 ~ 200 ℃
And hydrothermal reaction is performed to form a barium ferrite precipitate of plate-like particles. When the temperature during the hydrothermal treatment is lower than the above range, the ferritization reaction does not proceed sufficiently and non-plate-like particles are often generated, which easily forms sintered particles and therefore has a uniform shape. It is difficult to obtain the barium ferrite particle powder, and the decrease in orientation is unavoidable. On the other hand, if it is higher than the above range, the reaction is likely to proceed rapidly, and formation of coarse particles and spread of the particle size distribution are unavoidable, which is not preferable.

In the method of the present invention, the barium ferrite precipitate of the plate-like particles obtained by the hydrothermal reaction treatment as described above is washed with water, dried, and then calcined usually at 650 to 950 ° C, preferably 700 to 900. Perform at ℃. If the firing temperature is lower than the above range, the crystallization of the barium ferrite particles does not proceed sufficiently and the saturation magnetization is low, and if the firing temperature is higher than the above range, the barium ferrite particles stick to each other or sinter to form agglomerates. It is easy to do so, and the dispersibility in the form of coating material is greatly impaired, and the magnetic characteristics and surface smoothness of the recording medium are unavoidable. 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 the fine particle barium ferrite precipitate obtained as described above is fired, the precipitate contains a silicon compound, or a chloride, sulfate, carbonate or nitrate of sodium, potassium, lithium or strontium. In the case of firing after the addition treatment in advance, it is extremely effective in suppressing the inter-particle sintering and the collapse of the particle shape during firing of the fine barium ferrite precipitated particles, and is more effective in dispersibility and orientation. It is possible to obtain excellent barium ferrite crystal particles.

Examples of the silicon compound used as the treatment agent include sodium orthosilicate, sodium metasilicate,
Examples thereof include silicates such as potassium metasilicate, calcium metasilicate, and magnesium silicate, silanes such as silicone oil, silicone resin, chlorosilane, and alkoxyten, siloxanes, etc. It is desirable to use an aqueous salt solution. The treatment agent containing the silicon compound may be added to the barium ferrite precipitate by various methods. For example, an aqueous silicate solution may be added to an aqueous suspension containing the barium ferrite precipitate particles. Is added, and the particles are neutralized with an acidic substance to coat the surface of the particles as hydrated silicic acid (SiO ₂ · nH ₂ O),
Alternatively, in a solution of an organic silicon compound dissolved in an organic solvent, the barium ferrite precipitated particles are suspended to adsorb the silicon compound on the particle surface, and further, a solution of the silicate aqueous solution or the organic silicon solution. Can be carried out by spray adsorption on the surface of the ferrite precipitated particles. The amount of the silicon compound added is 0.1 to 10 as Si on a weight basis with respect to the barium ferrite precipitated particles.
It is 1.5%, preferably 0.2 to 1%. If the addition treatment amount is less than the above range, the desired effects such as sintering prevention cannot be sufficiently exerted, while if it is more than the above range, the magnetic properties may be impaired such as a decrease in saturation magnetization. Is not preferable.

Regarding chlorides, sulfates, carbonates and nitrates of sodium, potassium, lithium or strontium used as the treating agent, those chlorides and sulfates are particularly preferable. The addition treatment of the metal compound is
It can be carried out by various methods, for example, after hydrothermal treatment, filtration, washing cake of barium ferrite precipitated particles obtained by washing is added to an aqueous solution of the metal compound and suspended, or dried, or barium. It can be carried out by adding an aqueous solution of the above-mentioned metal compound to a washing cake of the ferrite precipitate, kneading, and drying if necessary. The addition amount of the metal compound is 5 to 120% by weight, preferably 5 to 20% by weight based on the barium ferrite precipitated particles. If the addition treatment amount is less than the above range, the effect of suppressing interparticle sintering or adjusting the particle shape into a hexagonal plate shape is not sufficient, and if the treatment amount is more than the above range, it is economical. Not advantageous. 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 Oe. , 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 mol of 1 mol / BaCl ₂ aqueous solution, 1 mol / FeCl ₃
Aqueous solution 2520 ml, 1 mol / CoCl ₂ aqueous solution 180 ml and 1 mol / TiCl ₄ aqueous solution 180 ml were mixed (Ba / Fe + Me molar ratio; 1/8, Ba / Fe molar ratio; 1.5 / 10.5), and then this mixed solution To
An alkaline coprecipitate suspension containing a coprecipitate was prepared by adding it to 2730 ml of a 10 mol / aqueous NaOH solution. Subsequently, the suspension was placed in an autoclave and heated at 150 ° C. for 3 hours to form a barium ferrite precipitate. (The precipitate had a magnetoplumbite crystal structure according to X-ray diffraction, and was plate-like particles having an average particle size of approximately 0.13 μ). The precipitate thus obtained was filtered and washed with water. After drying at 110 ° C, it was crushed. Then, this powder was placed in a small rotary furnace for 80
It was baked at 0 ° C. for 1 hour to obtain barium ferrite crystal particle powder. Then, the obtained powder was immersed in an aqueous hydrochloric acid solution, filtered, washed with water and dried to obtain a ferromagnetic fine powder of the present invention. (Sample A) The thus obtained ferromagnetic fine powder of the present invention is a magnetoplumbite type barium ferrite plate crystal grain powder and is desirable as a magnetic material for a perpendicular magnetic recording medium as shown in Table 1. It was

Example 2. Treated in the same manner as in Example 1 except that the Ba content in the alkaline suspension was set to 1/6 in terms of the molar ratio Ba / Fe + Me in Example 1. Then, a ferromagnetic fine powder according to the present invention was obtained. (Sample B) Example 3. In Example 1, the Ba content of the alkaline suspension was
A ferromagnetic fine powder according to the present invention was obtained by treating in the same manner as in the case of the same example except that the molar ratio of Ba / Fe + Me was set to 1/10. (Sample C) Example 4. In Example 1, the Ba / Fe ratio was changed to 1.5 / 10.4, the concentration of free OH groups in the alkaline suspension was changed to 4 mol / hour, and the hydrothermal treatment was performed at 150 ° C. for 5 hours. Other than the above, the ferromagnetic fine powder according to the present invention was obtained by the same method as in the case of the same example. (Samples D and 8 with a firing temperature of 800 ° C
A sample obtained at 50 ° C. is referred to as Sample E. Example 5. The hydrothermal reaction treatment precipitate obtained in Example 4 was filtered and washed with water, and the washed cake was repulped with a slurry (solid content concentration 50 g / ) Water glass solution (Si concentration 10
g /) and add it with hydrochloric acid (0.1N) with stirring.
The pH was adjusted to 7.3 and the surface of the barium ferrite precipitated particles was coated with a silicon compound in an amount of 0.5% by weight in terms of Si. The processed product is filtered,
It was washed with water, dried at 110 ° C., and then roughly crushed.

Thereafter, the ferrite-precipitated particle powder subjected to the above coating treatment was fired in the same manner as in Example 4 to obtain a ferromagnetic fine powder according to the present invention. At this time, the firing temperature was 800 ° C for sample F, and the firing temperature for 850 ° C was sample G
And

Example 6. In Example 5, 350 ml of an aqueous solution in which 50 g of Na ₂ SO ₄ was dissolved was added to the washed cake obtained by filtering and washing the hydrothermally treated precipitate, and after stirring well, the mixture was dried at 110 ° C. to evaporate the water content. (The addition amount of Na ₂ SO ₄ was 10 per barium ferrite precipitate particles.
0% by weight) The dried product obtained as described above is baked at a temperature of 800 ° C.
Then, firing treatment was carried out in the same manner as in Example 5 to obtain a ferromagnetic fine powder according to the present invention. (Sample H) Example 7. Similar to Example 6 except that KCl was used instead of Na ₂ SO ₄ and the addition amount was 10% by weight based on the barium ferrite precipitated particles. To obtain a ferromagnetic fine powder according to the present invention. (Sample I) Example 8. By the same method as in Example 6 except that NaCl was used instead of Na ₂ SO ₄ in Example 6 (100% by weight based on the barium ferrite precipitated particles). After processing, a ferromagnetic fine powder according to the present invention was obtained. (Sample J) Example 9. The same method as in the case of Example 6 except that BaCl ₂ was used instead of Na ₂ SO ₄ in Example 6 (100% by weight based on the barium ferrite precipitated particles). To obtain a ferromagnetic fine powder according to the present invention. (Sample K) Example 10. The same method as in the case of Example 6 except that SrCl ₂ was used instead of Na ₂ SO ₄ in Example 6 (100% by weight based on the barium ferrite precipitated particles). To obtain a ferromagnetic fine powder according to the present invention. (Sample L) Example 11. Compared with the same example as in Example 6, except that NaCl and BaCl ₂ were used instead of Na ₂ SO ₄ (each 50 wt% relative to barium ferrite precipitated particles). The ferromagnetic fine powder according to the present invention was obtained by the same treatment. (Sample M) Comparative Example 1. Compared with the same example as in Example 1, except that the Ba content in the alkaline suspension was set to 1/11 in terms of the molar ratio of Ba / Fe + Me. A comparative sample was obtained by processing in the same manner. (Sample N) Comparative Example 2. In Example 1, the Ba content in the alkaline suspension was
A comparative sample was obtained by treating in the same manner as in the case of the example except that the molar ratio of Ba / Fe + Me was set to 1/4. (Sample P) Comparative Example 3. A comparative sample was obtained in the same manner as in Example 1 except that the temperature during the hydrothermal treatment was 100 ° C. in Example 1. (Sample Q) Comparative Example 4. A comparative sample was obtained by treating in the same manner as in the case of Example 1, except that the temperature during the hydrothermal treatment was 300 ° C. in Example 1. (Sample R) Comparative Example 5. A comparative sample was obtained in the same manner as in the case of Example 1, except that the baking temperature was set to 600 ° C. (Sample S) Comparative Example 6. A comparative sample was obtained in the same manner as in Example 1 except that the baking temperature was set to 1000 ° C. in Example 1. (Sample T) Comparative Example 7. A comparative sample was obtained by the same method as in the case of Example 1, except that the concentration of free OH groups in the alkaline suspension was changed to 1 mol / l in Example 1. It was (Sample U) Each sample obtained in the above-mentioned Examples and Comparative Examples
As a result of X-ray diffraction, all were magnetoplumbite type barium ferrite. When each of the samples 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, and a magnetic coating material was prepared with the following composition, and this was used as a polyester. A magnetic recording medium was prepared by coating on a film and orienting perpendicularly to the coated surface.

Magnetic powder 100 parts by weight Vinyl acetate / vinyl chloride copolymer resin 16.2 〃 Surfactant 4 〃 Methyl ethyl ketone 186 〃 Coercive force (Hc⊥: perpendicular to the medium surface), orientation ratio (OR ), Squareness ratio (SQ
⊥: It is the direction perpendicular to the medium surface and is the value after demagnetizing field correction.) These results are shown in Table 1.

As is clear from the results shown in Table 1, when the molar ratio of Ba / Fe + Me, the concentration of free OH groups, the hydrothermal treatment temperature and the calcination treatment temperature are within the ranges of the present invention, barium having a uniform size by hydrothermal treatment is obtained. Since a precursor precipitate of ferrite crystal particles is formed, the product obtained by firing this product is a plate-shaped magneplanbite-type uniform barium ferrite fine powder with a small particle size and a desired crystal state. To be Thus, this product has a sufficiently high saturation magnetization and is excellent in dispersibility because it is excellent in the squareness ratio and the orientation, particularly the vertical orientation. 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. 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. The thing
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.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-175707 (JP, A) JP-A-56-160328 (JP, A) JP-A-60-81804 (JP, A) JP-A-60- 122725 (JP, A) JP 61-168532 (JP, A) JP 62-138330 (JP, A) JP 62-216921 (JP, A)

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) An alkaline suspension containing each element selected in 1. and having a free OH group concentration of 1.5 mol / or more is heat-treated in the temperature range of 120 to 200 ° C. to obtain a barium ferrite precipitate, and then the precipitate is 650-950
A method for producing a ferromagnetic fine powder for magnetic recording, comprising firing at a temperature range of ° C to obtain 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) An alkaline suspension containing each element selected in 1. and having a free OH group concentration of 1.5 mol / or more is heat-treated in the temperature range of 120 to 200 ° C. to obtain a barium ferrite precipitate, and then the precipitate is 650-950
A method for producing a ferromagnetic fine powder for magnetic recording, comprising a step of firing in the temperature range of ° C to obtain barium ferrite crystal particles, which comprises adding a silicon compound to the precipitate and then firing. 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) An alkaline coprecipitate suspension containing each element selected in step 1 and having a free OH group concentration of 1.5 mol / or more, in a temperature range of 120 to 200 ° C., without filtering the coprecipitate and washing with water. A method of heat-treating to obtain a barium ferrite precipitate, and then calcining the precipitate in the temperature range of 650 to 950 ° C. to form barium ferrite crystal particles, which comprises adding sodium, potassium, lithium or strontium to the precipitate. , Chloride, sulfate, carbonate,
A method for producing a ferromagnetic fine powder for magnetic recording, comprising adding and treating at least one nitrate.