JP2651795B2 - Method for producing ferromagnetic fine powder for magnetic recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferromagnetic fine powder for magnetic recording comprising barium ferrite crystal particles suitable for high-density magnetic recording, in particular, perpendicular magnetic recording using residual magnetization perpendicular to the surface of a medium. It relates to a manufacturing method.

[0002]

[Technical Background of the Invention and its Problems] Magnetic recording generally involves the use of acicular magnetic powders such as γ-Fe ₂ O ₃ , cobalt-coated γ-Fe ₂ O ₃ , iron-based metals, and CrO ₂ as a recording medium. Oriented in the in-plane direction of
The longitudinal recording method using the residual magnetization in this direction is most often used. However, in the case of this method, the demagnetizing field in the medium increases when the recording density is increased,
In particular, the recording / reproducing characteristics in the short wavelength region are easily deteriorated, and it is difficult to achieve sufficient high density recording. In recent years, a so-called perpendicular magnetic recording method, which achieves high-density recording by reducing the demagnetizing field by magnetizing the surface of the recording medium layer in a direction perpendicular to the above-described longitudinal recording method, has recently attracted attention. .

As the perpendicular magnetic recording medium, besides a method using an alloy film method such as a Co-Cr system which has been tried for practical use, a hexagonal ferrite crystal particle powder such as barium ferrite is used as a binder resin. A so-called coating type recording medium in which a dispersion is applied on a base film has been proposed. In the case of the coating type, as in the case of the conventional longitudinal recording type recording medium, it can be produced economically and advantageously with good productivity and the durability of the recording medium is excellent. I'm in a hurry.

On the other hand, the barium ferrite magnetic powder used for the perpendicular magnetic recording medium usually comprises hexagonal plate-like crystal grains and has an easy axis of magnetization in a direction perpendicular to the particle plate surface. It has a large saturation magnetization and a coercive force (usually 200 to 2,000 Oe) suitable for magnetic recording that can match the characteristics of the magnetic head used for recording and reproduction, and fine particles (usually having an average particle diameter of 0. 3μ or less)
It is desired that the dispersibility in the magnetic layer be good. Barium ferrite crystal particles generally have a high coercive force (usually 3,000 Oe or more), making it difficult to magnetically record and erase a recording medium with the magnetic head, and to make high density recording with a perpendicular magnetic recording medium extremely difficult. I have to.

For this reason, various methods have been proposed to control the coercive force to a desired range suitable for magnetic recording.
Many of them include a part of Fe of the barium ferrite crystal particles of BaO.nFe ₂ O ₃ (where n is an integer of 5 to 6) other elements such as Co, Ti, Sn, Zr, Ge, Nb, V is a method of substituting at least one kind of metal element such as V. Particularly, it is preferable to use a Co element and a tetravalent or 5-
It is known that the coercive force can be easily controlled to a desired range without deteriorating the perpendicular magnetization characteristics by combining and substituting the valence elements in such a manner that their average ionic value becomes approximately 3.

The inventors of the present invention have focused on the coercive force control by the cobalt substitution in barium ferrite magnetic powder for perpendicular magnetic recording media and have made various studies, and as a result, have compared the coercive force to a desired range suitable for magnetic recording. On the other hand, the coercive force of barium ferrite changes with temperature, and the coercive force increases with increasing temperature.In particular, barium ferrite, whose coercive force is controlled using cobalt, is The change tends to be larger, the lower the coercivity, the more coercivity 1,000
For barium ferrite below Oe, the degree of change in coercive force increases. Therefore, when such a barium ferrite is used as a magnetic recording medium, the coercive force changes when there is a temperature change due to a change in environment or contact with a magnetic head. To obtain the knowledge that improvement of the temperature characteristics of the coercive force is extremely important to measure,
As a result of further study on a method which can be industrially advantageously produced, the present invention has been completed.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a cobalt-substituted barium ferrite magnetic powder having an improved saturation magnetization suitable for a perpendicular magnetic recording medium and a remarkably improved temperature characteristic of coercive force. .

[0008]

SUMMARY OF THE INVENTION The present invention provides a cobalt this with valence different average ion valence and cationic elements is combined to become 3 Co-M ₁ substituted barium ferrite crystal particles, the specific metal element It was completed based on the finding that magnetic powder suitable for a perpendicular magnetic recording medium having significantly improved temperature characteristics of saturation magnetization and coercive force can be effectively produced by adding it by a specific method. is there.

That is, according to the present invention, the molar ratio of the metal element is 1/4 ≧ Ba / (Fe + Co + M ₁ ) ≧ 1/12 [where M ₁ is Ti,
At least one element selected from the group consisting of Sn, Zr, Ge, Nb and V, wherein the average ionic value of (Co + M ₁ ) is 3 and the molar ratio (x) to Fe is 0.2 ≧ x> 0 a is] was mixed with aqueous solutions of an alkali compound of a metal element comprising a ratio of, to form a precursor material of Co-M ₁ substituted barium ferrite, and then with respect to the precursor material, or The precursor substance was heat-treated in the presence of an alkali, and at least one metal element compound selected from the group consisting of Ni, Cu, Zn, Mg and Mn was added in an amount of 0.2 to 0.2 mol per mol of Co.
A method for producing a ferromagnetic fine powder for magnetic recording, characterized by adding 3 mol and then baking the treated material.

In the method of the present invention, the molar ratio of the metal element is
1/4 ≧ Ba / (Fe + Co + M ₁ ) ≧ 1/12 [where M ₁ is Ti, Sn,
At least one element selected from the group consisting of Zr, Ge, Nb and V, having an average ionic value of (Co + M ₁ ) 3 and Fe
Various methods to prepare a molar ratio (x) is Co-M ₁ substituted barium ferrite crystal particles is in the range of a 0.2 ≧ x> 0] (hereinafter referred to as the base constituent particles) against, for example, Ba
A so-called hydrothermal method in which an alkaline suspension containing Fe and a substitution component as necessary is subjected to a high-temperature, high-pressure reaction treatment, and a barium ferrite constituent metal ion solution was mixed with an alkali solution to obtain a coprecipitate. It can be carried out by applying a coprecipitation-firing method of post-firing or a glass crystallization method of melting and reacting the above-mentioned barium ferrite constituent metal component with a glass-forming substance.

In the production of the ferromagnetic fine powder according to the present invention, the desired particles constituting the substrate are first prepared relatively industrially relatively easily by the hydrothermal synthesis method or the coprecipitation-calcination method. It is preferred to apply That is, (1) a barium compound, an iron compound, and a cobalt compound for coercive force control.
M ₁ is at least one of Ti, Sn, Zr, Ge, Nb and V compounds.
An aqueous solution containing a predetermined amount of each seed is prepared. These compounds may use various water-soluble compounds, but are preferably chlorides, nitrates and the like. The barium component is
In a molar ratio with respect to the other constituent metal components _{(Fe + Co + M 1)} 1 /
It is preferably 4 to 1/12, and in particular, when further miniaturization of, for example, 0.2 .mu.m or less is to be performed, it is preferable that the adjustment be made in the range of 1/4 to 1/10. If the molar ratio is less than the above range, the obtained barium ferrite crystal particles are likely to be coarsened, and it is inevitable that the dispersibility decreases, and the orientation and surface smoothness of the recording medium decrease. On the other hand, if the molar ratio is larger than the above range, it is not preferable because a decrease in the saturation magnetization and a non-uniform shape cannot be avoided. (Co + M ₁ ) has a molar ratio (x) to Fe of 0.2 ≧ x> 0, preferably 0.17 ≧
It is preferable that x is adjusted so as to be in the range of x> 0. If x is larger than the above range, the perpendicular magnetization characteristics are easily damaged, and it becomes difficult to obtain required performance as a recording medium. The M ₁ of the, Ti, Sn, Zr, Ge, but is at least one metallic element selected from Nb and V group, especially a coercive force control without sacrificing much of the perpendicular magnetization characteristic relatively easily preferably used Ti element as M ₁ in terms of performing. Further, the combination ratio of the (Co + M ₁ ) elements is used so that their average ionic value becomes approximately 3.

Next, an aqueous solution of, for example, NaOH, KOH, NH ₄ OH, etc. is brought into contact with and mixed with the aqueous solution of the metal compound for preparing the base constituting particles to form an alkaline suspension having a pH of 10 or more.
The alkali concentration of the suspension is 1.5 mol / l based on free OH
More preferably, it is at least 2 mol / l in order to achieve finer particles and improved dispersibility.

[0013] The alkaline suspension obtained as described above may be subjected to a calcination treatment described below as a ferrite precursor substance obtained by filtering the alkaline suspension and washing it with water.
The suspension is placed in a reaction vessel equipped with a heating device or in a pressure vessel such as an autoclave at 60 to 250 ° C., preferably 10 to 250 ° C.
A heat reaction treatment may be performed at 0 to 200 ° C. to form a precipitate of plate-like particles. If the treatment temperature is lower than the above range, the progress of the reaction is slow, and if the heat treatment temperature is higher than the above range, formation of coarse particles and broadening of the particle size distribution are unavoidable or unfavorable. The precipitate of plate-like particles obtained as described above can be filtered and washed with water, and the obtained cake can be calcined as a ferrite precursor substance to form desired plate-like barium ferrite crystal particles. .

Next, in order to bake the ferrite precursor material obtained as described above to obtain plate-like barium ferrite crystal particles, the temperature is preferably 650 to 1,000 ° C., preferably 7 to 1000 ° C.
Bake at 00-900 ° C. If the firing temperature is lower than the above range, the crystallization of the ferrite particles does not proceed sufficiently and the saturation magnetization is low, and if the firing temperature is higher than the above range, the ferrite particles adhere to each other and sintering occurs, and aggregation occurs. Lumps are formed, and the dispersibility in the preparation of the paint is likely to be greatly impaired. The calcination can be usually performed in about 0.5 to 5 hours using various types of apparatuses such as a rotary furnace and a fluidized bed furnace. Further, in order to further prevent particle sintering, control shape or improve magnetic properties, the precursor substance is subjected to a silicon compound or a phosphorus compound before the baking treatment, or an alkali metal or After adding and mixing a halide or a sulfate of an alkaline earth metal, baking may be performed.

According to the present invention, as described above, Co
-M _per substituted barium ferrite crystal grains, Ni, C
u, Zn, at least one metal element M ₂ of 0.2 to 3 moles with respect Co1 mol selected from Mg and Mn group, preferably 0.
Although the invention is constructed by 4 to 2 mol adduct, if the content of the metal element M ₂ is less than the above range is not brought effect of improving the temperature characteristics of the saturation magnetization and the coercive force is sufficiently and said If it is larger than the range, the particle diameter of the obtained magnetic powder tends to be large, and the saturation magnetization is undesirably reduced. Note Examples of the compound made of the metal element M ₂ various water-soluble compounds such as chlorides, may be used nitrates.

[0016] In the present invention method, allowed to contain the metal element M ₂ to the base constituent particles can be carried out by various methods. For example, a metal element may be added to the precursor substance.
Adding an aqueous solution of M _2, mixed or evaporated to dryness, or the regulation to M ₂ metal hydroxide precipitate or allowed deposited onto the precursor particles pH, the metal element compound powder to the precursor material Alternatively, it can be performed by kneading. Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples.

[0017]

EXAMPLES Example 1 180 ml of 1 mol / l BaCl ₂ aqueous solution, 1248 ml of 1 mol / l aqueous FeCl ₃ solution, 1 mol / l Co
96 ml of a Cl ₂ aqueous solution and 96 ml of a 1 mol / l TiCl ₄ aqueous solution were mixed [Ba / (Fe + Co + Ti) molar ratio: 1/8,
(Co + Ti) /Fe=0.154 (molar ratio) Then, this mixture was added to 2,623 ml of a 10 mol / l NaOH aqueous solution to form an alkaline suspension containing a brown precipitate (free OH group concentration 5 mol / l). Prepared. Subsequently the suspension was placed in the autoclave, was heated 3 hours at 0.99 ° C. to produce a Co-M ₁ substituted barium ferrite precursor material particles. Then, the obtained ferrite precursor material is filtered, washed with water,
It was repulped with water. 48 ml of a 1 mol / liter aqueous solution of NiCl ₂ was added to the slurry, and the slurry was treated with an aqueous NaOH solution to adjust the pH of the slurry to 7.5 (Ni / Co molar ratio: 0.5).
5) Further, an aqueous solution of NaCl was added so that the ratio of NaCl / ferrite precursor substance was 1/1 (weight ratio), and this was evaporated to dryness at 110 ° C. Thereafter, the evaporated and dried product was fired at 800 ° C. for 1 hour, and then the obtained fired product was immersed in an aqueous acetic acid solution, filtered, and washed with water and dried to obtain a ferromagnetic fine powder. This sample is designated as (A).

Example 2 The procedure of Example 1 was repeated except that 48 ml of a 1 mol / l aqueous ZnCl ₂ solution was added instead of the 1 mol / l NiCl ₂ aqueous solution (Zn / Co molar ratio: 0.5). The treatment was performed in the same manner as in Example 1 to obtain a ferromagnetic fine powder. This sample is designated as (B).

Comparative Example 1 A comparative sample was obtained in the same manner as in Example 1 except that a 1 mol / liter aqueous solution of NiCl ₂ was not used (Sample C).

Comparative Example 2 180 ml of 1 mol / l BaCl ₂ aqueous solution, 1248 ml of 1 mol / l FeCl ₃ aqueous solution, 1 mol / l C
96 ml of an oCl ₂ aqueous solution and 96 ml of a 1 mol / l TiCl ₄ aqueous solution and 48 ml of a 1 mol / l NiCl ₂ aqueous solution were mixed [Ba / (Fe + Co + Ti) molar ratio: 1/8, (Co + Ti)
/Fe=0.154 (molar ratio), Ni / Co = 0.5 (molar ratio)], and then mix this mixture with a 10 mol / liter NaOH aqueous solution 2,62.
It was added to 3 ml to prepare an alkaline suspension containing a brown precipitate (free OH group concentration: 5 mol / l). Subsequently, the suspension was placed in an autoclave and heated at 150 ° C. for 3 hours to produce ferrite precursor material particles. Next, the obtained ferrite precursor substance was filtered, washed with water, and repulped with water. To this slurry, add NaCl aqueous solution to Na
Cl / ferrite precursor substance was added so as to be 1/1 (weight ratio), and this was evaporated to dryness at 110 ° C. Thereafter, the precursor substance particles were fired at 800 ° C. for 1 hour to obtain cobalt-substituted barium ferrite crystal particles. Next, the obtained powder was immersed in an acetic acid aqueous solution, filtered, washed with water and dried to obtain a ferromagnetic fine powder. This sample is designated as (D).

Each of the samples obtained in the above Examples and Comparative Examples was found to have a magnetoplumbite crystal phase as a result of X-ray diffraction.

The average particle size (Dp: electron microscopy), room temperature coercive force, Hc (RT),
The saturation magnetization (δs) was measured, and the change (Td) of the coercive force with respect to temperature was determined by measuring the room temperature coercive force Hc (RT) and the coercive force Hc (60) at the time of heating at 60 ° C., and was obtained by the following equation.

[0023]

(Equation 1)

The results are shown in Table 1.

[0025]

[Table 1]

As is evident from the results in Table 1, the cobalt-substituted barium ferrite ferromagnetic powder according to the method of the present invention not only improves the saturation magnetization but also significantly reduces the change in coercive force with temperature. .

[0027]

According to the present invention, not only the saturation magnetization value suitable as a magnetic powder for perpendicular magnetic recording is improved, but also the desired coercive force control and the temperature characteristics of the coercive force are significantly improved. The barium ferrite magnetic powder can be produced efficiently, and the present invention is a very industrially advantageous method.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-149328 (JP, A) JP-A-60-240107 (JP, A) JP-A-61-40823 (JP, A) JP-A 60-240 46932 (JP, A)

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein the molar ratio of the metal element is 1/4 ≧ Ba / (Fe + Co).
+ M ₁ ) ≧ 1/12 [where M ₁ is at least one element selected from the group consisting of Ti, Sn, Zr, Ge, Nb and V; and (Co + M ₁ )
Has an average ionic value of 3 and a molar ratio to Fe (x)
There was mixed with an aqueous solution of 0.2 ≧ x> aqueous solution and the alkali compound of a metal element comprising a proportion of 0 and is], Co-M ₁
A precursor material of the substituted barium ferrite is formed and then Ni, Cu, Z to the precursor material or to the precursor material heat-treated in the presence of alkali.
magnetic recording characterized in that at least one metal element compound selected from the group consisting of n, Mg and Mn is added in an amount of 0.2 to 3 mol based on 1 mol of Co, and then the resultant is calcined. Of manufacturing ferromagnetic fine powder for use.