JPS62260724A - Production of ferromagnetic fine powder for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain the titled ferromagnetic fine powder consisting of highly dispersible hexagonal ferrite crystal particles having improved perpendicular orientation property, by adding a phosphorus compound to a ferrite precursor prepared by heat-treating a basic aqueous suspension containing a metal compound, e.g. Ba, etc., and an iron compound, treating and firing the resultant blend. CONSTITUTION:An aqueous solution containing one or more metal compounds (Ma) of Ba, Sr and Pb, an iron compound and, as desired, one or more of Co, Ti, Mn compounds, etc., as a substitution element (Mb) for controlling coercive force in respective specific amounts is prepared. The molar ratio of the above-mentioned Ma component is 1/4-1/12 based on the Fe+Mb components. An solution of NaOH, KOH, etc., is brought into contact and blended with the above-mentioned aqueous solution of the metal compound to afford a basic aqueous suspension, which is then put in, e.g. a reaction vessel equipped with a heating device, and treated by reaction while heating at 60-250 deg.C, preferably 100-200 deg.C to give a plate particulate hexagonal ferrite precursor. A phosphorus compound, e.g. orthogphosphoric acid, is added to the resultant hexagonal ferrite precursor and fired at 650-950 deg.C to afford the above- mentioned ferromagnetic fine powder for magnetic recording.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a method for producing a fine ferromagnetic powder for magnetic recording comprising hexagonal ferrite crystal grains suitable for high-density magnetic recording, particularly perpendicular magnetic recording media.

(Technical background of the invention and its problems) Magnetic recording generally employs a method of magnetizing the recording medium in the in-plane longitudinal direction. However, in this method, when attempting to increase the recording density, the demagnetizing field within the recording medium increases, making it difficult to achieve sufficiently high density recording. In contrast to such longitudinal recording methods, the so-called perpendicular magnetic recording method, which aims at high-density recording by magnetizing the surface of the recording medium perpendicularly to the surface of the recording medium to reduce the strength of the demagnetizing field within the recording medium, has recently attracted attention. It has been done.

By the way, as the perpendicular magnetic recording medium, in addition to those using an alloy film method such as a Co-Cr system, which has been attempted to be put into practical use, there is also a method using a hexagonal ferrite crystal particle powder such as barium ferrite dispersed in a binder. A so-called coated recording medium has been proposed in which a base film is coated with a base film. In the case of the coating type,
As with the conventional method of manufacturing recording media, it can be manufactured with high productivity and economically advantageous, and the durability of the recording medium is excellent, so its practical application is urgently needed. There is.

On the other hand, for the above-mentioned perpendicular magnetic recording 'Jj, as a magnetic powder made of hexagonal ferrite crystal grains used for wood, it has a coercive force (He: 400 to 20,000e) in an appropriate range that does not cause magnetic hend saturation during recording. It has a large saturation magnetization and an axis of easy magnetization perpendicular to the plane of the particle plate, and is less than 0.3μ, especially 0.2μ.
It is said that it is important that the particles have a fine particle size of μ or less and have good dispersibility in the magnetic layer.

However, in recent years, the characteristics required of the above-mentioned magnetic powders, combined with the trend towards higher recording densities, are those that can satisfy the requirements for reducing the noise level and increasing output in the short wavelength region in perpendicular magnetic recording media. It is becoming more and more desirable that

For this reason, it has a finer particle size and a sharper particle size distribution, and also has good dispersibility and excellent coating surface smoothness, with high orientation and high filling properties. There is an increasing need to develop hexagonal heptagonal 7-elite particles that exhibit the following properties.

Conventionally, various methods have been known for manufacturing hexagonal ferrite particles, and many proposals have been made for making the particles finer, but in general, as the particles become finer, dispersibility and The orientation is easily impaired to a large extent, and for this reason, the above-mentioned requirements have not yet been fully satisfied, and a solution to this problem is strongly desired. For example, as a method for producing fine powder of hexagonal ferrite particles, it is well known that a precursor suspension obtained by mixing a metal salt aqueous solution containing constituent components of hexagonal ferrite and an alkaline aqueous solution is heated and then fired. It is being This method is relatively easy to manufacture, and it is easy to obtain fine particles with high saturation magnetization, but as the ferrite precursor particles become finer, interparticle sintering and particle shape changes occur during the firing process. It is easy to collapse, and as a result, deterioration in orientation, filling properties, dispersibility, etc. is unavoidable.

Additionally, hexagonal ferrite particles generally have a high coercive force;
For this reason, it is necessary to control the coercive force within an appropriate range as a recording medium, and usually Co, Ti, Ni, Mn,
A method of substituting a portion of Fe' in the ferrite constituent atoms by adding an appropriate amount of an element such as Zr is carried out, but unless the substitution is uniformly and efficiently and sintering is not suppressed, the coercive force is low. In the end, in order to obtain the desired low coercive force powder, it is necessary to increase the amount of substitution of these elements, which tends to reduce the saturation magnetization and damage the perpendicular anisotropy of the axis of easy magnetization. There was a problem.

(Objective of the Invention) The present invention is a method that can substantially avoid interparticle sintering and easily control coercive force, and has a sufficiently high saturation magnetization.
To provide a method for producing a hexagonal ferrite crystal powder having a fine particle size, a well-shaped hexagonal plate shape, excellent perpendicular alignment, and high dispersion, suitable for magnetic recording, especially perpendicular magnetic recording. The purpose is to

(Importance of the Invention) The present inventors have been conducting various studies to solve the above-mentioned problems in the production of hexagonal plate-shaped hexagonal ferrite crystal particles, and as a result, the present inventors have fired a fine heptagonal ferrite precursor material. By using a specific firing treatment agent,
Obtaining the knowledge that interparticle sintering can be substantially avoided without impairing saturation magnetization, that the composition can be partially replaced by Co, Ti, etc., and that coercive force can be easily controlled; This completes the present invention.

That is, the present invention provides a method for selecting from the group of barium, strontium, and lead; An aqueous solution containing at least one or more metal compounds and an iron compound is mixed with an alkaline aqueous solution to form an alkaline suspension, and then the suspension is
A ferrite precursor material is obtained by heat treatment at a temperature of 0.degree. That's what you do! This is a method for producing ferromagnetic fine powder for magnetic recording.

In the method of the present invention, first, one or more metal compounds Ma selected from the group of barium, strontium, and lead, an iron compound, and optionally Co, Ti5Ni, Mn, Zr, Zn, Ge5Nb
, (2) Prepare an aqueous solution containing a predetermined amount of at least one of the compounds.

Various water-soluble compounds can be used as these compounds, but
Preferred are chlorides and nitrates. The Ma component has a molar ratio of 1/4 to 1/12 with respect to the Fe+Mb component,
Preferably it is 176 to 1/10. When the molar ratio is smaller than the above range, the resulting 7-layer crystal grain powder tends to become coarse, resulting in a decrease in dispersibility and a decrease in properties such as orientation and surface smoothness in the recording medium. Moreover, if the molar ratio is larger than the above range, a crystal phase different from the magnetobrambite crystal may coexist, resulting in a decrease in saturation magnetization and non-uniform shape, which is not preferable. Note that the substituted component Mb is Co, Ti5Ni, Mn
, Zr, Zn, Ge, Nb, and V with Fe
It can be used in an amount of 0.2 mol or less, preferably 0.17 mol or less per 1 mol, but especially the Fe component is at least C
It is preferable to substitute with O and Ti elements.

Next, for example, N a OH, K
Aqueous solutions such as OH, NH, and OH are brought into contact and mixed to form an alkaline suspension. The amount of the alkali added should be at least equivalent to the metal salt contained in the metal compound aqueous solution, and especially when trying to obtain fine ferrite ferromagnetic powder, the alkali concentration of the suspension should be 1 or more based on free OH. .5 mol/Q or more, preferably 2 mol/ρ or more, and if it is too low than the above range, the reaction will not proceed sufficiently and many non-plate-shaped particles will be formed, and these particles will be sintered during the sintering process. It is easy to form particles, and deterioration of orientation, dispersibility, etc. is unavoidable.

Next, the alkaline suspension is heated and reacted at 60 to 250°C, preferably 100 to 200°C, using a reaction vessel equipped with a heating device or in a pressure vessel such as an autoclave, to form a ferrite precursor of plate-like particles. Form body substances.

If the temperature during the hydrothermal treatment is lower than the above range, amorphous bodies are likely to form and agglomerates are likely to form, making it difficult to obtain ferrite particles with a uniform shape and decreasing orientation. Sometimes I can't avoid it. On the other hand, if it is higher than the above range, the formation of coarse particles and broadening of the particle size distribution are undesirable.

Next, in the present invention, when adding a phosphorus compound to the orthogonal ferrite precursor material obtained as described above, various phosphorus compounds can be used, such as orthophosphoric acid or metaphosphoric acid. or their salts, Kuroiso phosphorus compounds such as pyrophosphoric acid or hexaphosphoric acid or their condensed phosphates, phosphorous acid or hypophosphorous acid or their salts, and sleeping phosphorus compounds such as various phosphoric acid esters. You can, but
Usually, it is desirable to use an aqueous solution of orthophosphoric acid, sodium hexametaphosphate, etc. To add a treatment agent made of the phosphorus compound to the ferrite precursor material,
This can be carried out by various methods, but for example, it can be carried out by adding an aqueous phosphoric acid solution to an aqueous suspension containing the ferrite precursor particles and adsorbing a phosphorus compound onto the particle surface. can.

The amount of the phosphorus compound added is 0.05 to 1.0%, preferably 0.1 to 0.5%, based on P based on the weight of the ferrite precursor material. If the amount added is too small than the above range, the effect of preventing sintering etc. will not be sufficiently reduced, and if it is too large, the saturation magnetization will be greatly reduced, which is not preferable.

Further, a more desirable effect may be obtained by adding a silicon compound, an aluminum compound, a boron compound, an alkali metal compound, an alkaline earth metal compound, etc. to the phosphorus compound as a firing treatment agent.

In the method of the present invention, after adding the sintering agent to the ferrite precursor material obtained by the heat reaction treatment as described above, the ferrite precursor material is then sintered.
If the firing temperature is lower than 950℃ (preferably 700-900'C''c), the crystallization of the ferrite particles will not proceed sufficiently, and the saturation magnetization may be low. When the temperature increases, the heptadolite particles tend to stick to each other and sinter, forming agglomerates, which greatly impairs the dispersibility of paints, resulting in unavoidable deterioration of the magnetic properties and surface smoothness of the recording medium. The above-mentioned calcination can be carried out using various types of equipment such as a rotary furnace and a fluidized bed furnace, and usually takes about 0.5 to 5 hours. By carrying out the treatment, interparticle sintering can be suppressed, and particles with high saturation magnetization and fine particle size can be obtained.

The ferrite crystal particle powder obtained as described above is
In an aqueous medium or, if necessary, in an arsenic aqueous medium (two immersion treatments are performed to remove excess barium and other impurities.In addition, in the above case, use a strong acidic medium for the aqueous WC Treatment may further enhance dispersibility.

As detailed above, the ferromagnetic fine powder obtained by the manufacturing method of the present invention has a saturation magnetization of approximately 45 to 60 emu7.
'g, a magnetobrambite type ferrite crystal grain powder with a coercive force of about 400 to 2,0000 e, which has a hexagonal plate shape and an average particle size of iro, 05 to 0.
．． It has a particle diameter of 15 μm, has a small particle size distribution, and has excellent dispersibility in the magnetic layer of a magnetic recording medium, making it extremely suitable as a material for high-density perpendicular magnetic recording.

(Examples of the Invention) The present invention will be further explained below with reference to Examples and Comparative Examples.

Example 1 mol/ρ BaCρ2 aqueous solution 360 mR 11 mol/Q
of FeCρ, aqueous solution 2496 mQ, 1 mol/ρ of Co
TiCJ with CQ 2 aqueous solution 192 mρ and fJ 1 mol/θ
! 4 aqueous solution 19 aqueous solution 1 temperature 1.5/10.4), then this mixture was mixed with 10 mol/Q NaOH aqueous solution KL3
480 mO to prepare an alkaline suspension containing a brown precipitate. Subsequently, the suspension was placed in an autoclave and heated at 150° C. for 5 hours to produce ferrite precursor particles (which, according to X-ray diffraction, were not crystalline or magnetite). It had a brambite crystal structure).

The resulting precipitate was then filtered, washed with water, and repulped with water to form a slurry (solid concentration SOg/ff).

Orthophosphoric acid aqueous solution n (P concentration 10g
15 mρ) was added and thoroughly stirred.Then, this mixture was filtered, dried (110'C), and then coarsely crushed.

After that, the ferrite precipitate particle powder subjected to the above-mentioned addition treatment was fired at different firing temperatures for 1 hour each to obtain barium ferrite crystal particle powder.Then, the obtained powder was immersed in an aqueous hydrochloric acid solution, and then filtered. Sample (A) 80
Sample (B) was prepared at 0°C.

Comparative Example A ferromagnetic powder was obtained in the same manner as in the above Example, except that no phosphorus compound was added. At this time, the firing temperature was set to 750°C as sample (C), and the firing temperature was set as 800°C as sample (D).

As a result of X-ray diffraction, the samples obtained in the Examples and Comparative Examples were found to have a magnetobrambite crystal phase.

The average particle diameter (Dp
:electron microscopy), coercive force (He), saturation magnetization (σS)
A magnetic paint was prepared with the following composition, and this was applied onto a polyester film and subjected to orientation treatment to produce a recording medium.

These results are shown in the table below.

Magnetic powder 100 parts by weight Vinyl acetate vinyl chloride copolymer resin 16.2 //Surfactant
4 〃Methyl nityl ketone
186 For the recording medium, the coercive force (Hc: perpendicular to the medium surface), orientation ratio (OR), squareness ratio (SQ: perpendicular to the medium surface, after demagnetizing field correction) ) These results are shown in Table 1.

Table 1 As is clear from the results in Table 1, by firing a ferrite precursor material in which a phosphorus compound has been added in advance as in the present invention, particle sintering during firing can be suppressed without impairing saturation magnetization. It can be seen that a fine powder of hexagonal ferrite crystal particles with excellent squareness ratio, excellent orientation, especially vertical orientation, very good dispersibility, and sufficiently high saturation magnetization can be obtained.

(Results of the invention) Between particles J9. A ferromagnetic powder consisting of highly dispersed hexagonal ferrite crystal grains with suppressed crystallization, large saturation magnetization, and excellent perpendicular orientation can be easily produced by a relatively simple means, and can be used as a perpendicular magnetic recording medium. This is extremely useful in reducing the nozzle level and increasing output.

Claims (1)

[Claims] An alkaline suspension is obtained by mixing an aqueous solution containing at least one or more metal compounds selected from the group of barium, strontium, and lead and an iron compound with an alkaline aqueous solution;
Next, a ferrite precursor material is obtained by heat-treating the suspension at 60 to 250°C, and a phosphorus compound is added to the obtained precursor material, and then a ferrite precursor material of 650 to 950
A method for producing ferromagnetic fine powder for magnetic recording, characterized by firing it at a temperature range of ℃ to form hexagonal ferrite crystal particles.