JPS63248104A - Manufacture of ferromagnetic fine powder for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain magnetic powder having a designated coersive force, high degree of saturated magnetization and excellent vertically magnetized orientational property of high dispersibility by a method wherein the specific quantity of a bivalent metal element is allowed to be present when a sintering operation and a barium ferrite precursor growing process are performed. CONSTITUTION:A barium ferrite precursor is obtained by conducting a heat treatment at 60-250 deg.C on the alkaline suspension having pH of 11 or more and containing the metal element of the molar ratio of 1/6>=Ba/Fe+M1+ M2>=1/12 (M1 indicates a kind selected from a group of Co, Ni, Zn, Cu, Mg and Mn, and M2 indicates a kind selected from a group of Ti, Sn, Zr, Ge, Nb and V), the molar ratio of M2 is 0.01-0.2 against Fe of 1, and M2 is 0-0.5 against M1. The metal element compound M2 or M1 and M2 is added to said precursor in such a manner that the total amount of M1 and M2 becomes 0.3 mol or less against 1 mol of M2 or M1, M2 and Fe, then they are sintered at 650-1000 deg.C, and barium ferrite crystal grains are obtained.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a magnetic recording material made of barium ferrite crystal particles suitable for high-density recording, particularly perpendicular magnetic recording that uses residual magnetization perpendicular to the plane of the medium. This invention relates to a method for producing ferromagnetic fine powder.

[Technical background of the invention and its problems]

Magnetic recording is generally performed using γ-Fe20. , cobalt deposited γ-
The most commonly used method is a longitudinal recording method in which acicular magnetic powder such as Fe, 03, iron-based metal, CrO□, etc. is oriented in the in-plane direction of the recording medium and residual magnetization in this direction is utilized. However, with this method, when attempting to achieve high recording density, the demagnetizing field within the medium increases, and the recording and reproducing characteristics, particularly in the short wavelength region, tend to deteriorate, making it difficult to achieve sufficiently high density recording. In contrast to the above-mentioned longitudinal recording method, the so-called perpendicular magnetic recording method, which aims at high-density recording by reducing the demagnetizing field by magnetizing the surface of the recording medium layer in a direction perpendicular to the surface, has recently been attracting attention. .

By the way, the perpendicular energy recording medium is not only based on an alloy film method such as a Co-Cr system, which has been attempted to be put to practical use, but also a method using a hexagonal ferrite crystal particle powder such as barium ferrite dispersed in a binder resin. 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 in the case of conventional longitudinal recording type recording media, this recording medium can be manufactured economically and with good productivity, and has excellent durability, so its practical application is urgently needed.

However, the barium ferrite magnetic powder used in the perpendicular magnetic recording medium usually consists of hexagonal plate-shaped crystal grains, has an axis of easy magnetization perpendicular to the particle plate surface, and has a large saturation magnetization. It is desired to have a coercive force suitable for magnetic recording (usually 200 to 2,0000e) that can match the characteristics of the magnetic head used for recording and reproduction, and the particle size should also be determined according to the recording medium. The finer the particle size, the more advantageous it is in reducing the noise level and increasing the surface smoothness of the recording medium to achieve a high S/N ratio. It is desired that the material itself has high orientation in the recording medium.
It is desired to have good dispersibility in order to maintain high filling properties.

Various methods have been proposed for producing barium ferrite magnetic powder for magnetic recording media, but the so-called wet method uses metal ion compounds of Ba and Fe, and Go and Ni+ for coercive force control. Zn,
A method in which an alkali is added to a raw material mixture containing metal ion compounds such as Ti+ Sn, Zr, V, and In, reacted to obtain a coprecipitate, and the precipitate is fired at 900°C or higher (coprecipitation-calcination method) , a method of hydrothermally synthesizing the suspension containing the coprecipitate in an autoclave at a high temperature of 250°C or higher and under high pressure (hydrothermal method), and a comparison of the suspension of the coprecipitate at 250°C or lower. A fine barium ferrite crystal precursor material (hereinafter referred to as barium ferrite precursor) is obtained by hydrothermal synthesis at a relatively low temperature.
A method of firing at 50°C (hydrothermal firing method) is well known. However, compared to the coprecipitation-calcination method and the hydrothermal method, the hydrothermal-calcination method described above has less interparticle sintering and a decrease in saturation magnetization, and has relatively good dispersibility and filling properties. As mentioned above, there are few problems in equipment and operation under high temperature and high pressure, so there is an urgent need to put it into practical use.

On the other hand, in recent years, there has been an increasing trend toward higher recording densities, higher signal-to-noise ratios, and higher outputs for magnetic recording media. There has been a strong demand for even finer barium ferrite magnetic powder having the so-called ultrafine particle size below.
Even by applying the calcination method, there are still many problems that need to be solved in order to produce fine barium ferrite powder having the desired particle size with good reproducibility and industrial advantage. In particular, when attempting to reduce the desired coercive force by adjusting the amount of so-called substitutional elements added to control coercive force in the process of producing barium ferrite precursors, it is difficult to make the resulting barium ferrite particles fine. A solution to these problems is desired in order to achieve the above-mentioned fine particle size.

[Purpose of the invention]

The present invention is suitable for magnetic recording media made of barium ferrite fine particles having a predetermined coercive force and sufficiently high saturation magnetization, having a so-called ultrafine particle size, and having high dispersibility and excellent perpendicular magnetization orientation. The object of the present invention is to provide a method for easily obtaining magnetic fine powder with good stability using relatively simple means.

[Summary of the invention]

The inventors of the present invention have long discovered the above-mentioned method for industrially easily manufacturing so-called ultrafine particle-based barium ferrite magnetic powder, which is a coercive force control element substitution type suitable for increasing the recording density of magnetic recording media. Focusing on the application of the hydrothermal sintering method and conducting various studies to solve the above problems, we found that in the process of producing a barium ferrite precursor, a specific amount of a coercive force control component of a divalent metal element is present. On the other hand, the coercive force control component of the high valence element is not present or is kept below a specific amount, and when the precursor is fired, the high valence element and, if necessary, a divalent element are present in a specific amount. As a result, the present invention has been completed based on the knowledge that desired coercive force control and fine particle formation in barium ferrite magnetic powder can be achieved together. That is, the molar ratio of the metal element is 1/6≧B
a/Fe+M, +Mz≧1/12 (However, M is Co
, Nil, Zn, Cu, at least one element selected from the group of Mg and Mn, Ml is Ti, Sn,
at least one element selected from the group consisting of Zr, Ge, Nb and (2)], and MI is 0.01 to 0.2 mol per mol of Pe and Ml is 0 to 0. 5
Contains each metal element selected to have a molar ratio of pt
+ is 11 or more, the alkaline suspension is 60 to 250
A barium ferrite precursor is obtained by heat treatment at ℃, and then Ml or Ml and M is added to the obtained precursor, and Fe
Ml or a metal element compound of Ml and Ml is added so that the sum of M and Ml is 0.3 mol or less per 1 mol, and then this product is heated to 650~
This is a method for producing ferromagnetic fine powder for magnetic recording, which is characterized by firing at 100° C. to obtain barium ferrite crystal particles.

In the method of the present invention, first, M, a metal element (CO'
l Nil Zn+ Cu+ Mg or Mn), M
An aqueous solution containing a predetermined amount of each compound containing a Z metal element (Tt, Sn+Zr, Ge, Nb or ■) is prepared. Various water-soluble compounds can be used as these compounds, but chlorides, nitrates, etc. are preferable. In the Ba compound, Ba has a molar ratio of Pe+M++Mt
176 to 1/12, preferably 177 to 1/1
It is 0. When the molar ratio is smaller than the above range, the obtained barium ferrite crystal particles tend to become coarse, and a decrease in dispersibility and properties such as orientation and surface smoothness in the recording medium are unavoidable. Moreover, if the molar ratio is larger than the above range, crystal phases different from the magnetoblanbite type crystals may coexist, making it undesirable to avoid a decrease in saturation magnetization and non-uniformity of the shape. Therefore, the element M1 added as a replacement component is 0.01 to 0.2 mol, preferably 0.03 to 0.1 mol, per 1 mol of Fe.
5 moles, and if the number of moles is smaller than the above range,
The barium ferrite precursor cannot be refined sufficiently,
Moreover, broadening of the particle size distribution is unavoidable. Furthermore, if the molar ratio is larger than the above range, the perpendicular magnetization characteristics are likely to be impaired, making it difficult to obtain the desired performance as a perpendicular magnetic recording medium. Further, when the additive element M2 is used in combination with M, Ml is 0.5 mol or less, preferably 0.3 mol or less per 1 mol of M. If the number of moles of Mt is larger than the above range, the desired refinement of the barium ferrite precursor will not be sufficiently achieved. As M and Ml, Go and Tt are particularly preferred.

In the method of the present invention, to prepare the alkaline suspension of the metal compound, for example, NaO
Contact and mix aqueous solutions such as H, KOH, NHaO)1. The alkaline concentration of the alkaline suspension is 'f1 separation O
It is more preferable that the amount is 1.5 mol/It or more, preferably 2 mol/e or more, based on H, in order to make the produced particles finer and improve their dispersibility. Next, in order to heat-treat the alkaline suspension thus obtained, the suspension is heated in a reaction vessel equipped with a heating device or in a pressure vessel such as an autoclave for 6 hours.
A heating reaction treatment is performed at 0 to 250°C, preferably 100 to 200°C to produce a barium ferrite precursor. In the heat treatment, if the treatment temperature is too low than the above range, the reaction progresses slowly, and if the temperature is too high than the above range,
This is undesirable because formation of coarse particles and broadening of particle size distribution are unavoidable.

In the method of the present invention, when the barium ferrite precursor obtained as described above is fired, the coercive force may not be sufficiently controlled or the perpendicular magnetization property may be easily damaged. Ml and M,
Addition treatment is carried out using a combination of metal compounds. The addition treatment can be carried out by various methods, but for example, after filtering the barium ferrite precursor-containing slurry obtained by the above-mentioned heat treatment and repulping the obtained filter cake to form an aqueous slurry. The water-soluble metal compound of M2°Ml is added to the slurry, and then this slurry is dried once to treat the surface of the precursor particles with the metal compound, or the aqueous precursor to which the water-soluble metal compound is added is This can be carried out by, for example, adding an alkali to the slurry to adjust the pH and depositing a hydroxide precipitate of the metal on the surface of the precursor particles. Various water-soluble compounds of the metals can be used, and examples include chlorides and nitrates. When using the M2 metal compound or a combination of M2 and M, the amount added to the barium ferrite precursor is such that the sum of M and M2 is 0.3 per mole of Fe.
If the amount of the metal compound added is too much above the above range, it is not preferable because the saturation magnetization is likely to decrease or the perpendicular magnetization characteristics are likely to be impaired.

In the method of the present invention, the precursor is M2 or M2
In order to obtain plate-shaped barium ferrite crystal particles by firing the precursor treated product which has been subjected to the addition treatment of metal compounds of and Ml, the temperature is 650 to 1000°C, preferably 700 to
Fire at 900°C. If the firing temperature is too low than the above range, the crystallization of the ferrite particles will not proceed sufficiently and the saturation magnetization may be low, and if the firing temperature is too high than the above range, the ferrite particles will stick to each other and the particles will sinter, resulting in agglomerates. The dispersibility of paints is likely to be significantly impaired.

For the calcination, various types of equipment such as a rotary furnace and a fluidized bed furnace can be used. In addition, in order to further prevent particle sintering, control shape, and improve magnetic properties,
Prior to the firing process, the precursor may be coated with, for example, a silicon compound or a phosphorus compound, or an alkali metal halide or sulfate may be added and mixed therein, followed by firing.

The present invention will be further explained by giving examples and comparative examples below.

〔Example〕

Example 1 1 mol/l BaCl, aqueous solution 150 mj 2.1 mol/l
1030 ml of a FeC13 aqueous solution of 2 and 85n+6 of a 1 mol/2 CoClt aqueous solution were mixed, and then this mixture was added to 197 TmJ of a 10 mol/1 NaOH aqueous solution to prepare an alkaline suspension containing a brown precipitate (B
a/ (pe+M++Mg) molar ratio: 1/7.43,
M+/Fe molar ratio: 0.083, ? h/M+molar ratio: 0
]Subsequently, put the suspension into an autoclave 15
The precursor was generated by heating at 0° C. for 3 hours.

Next, the obtained barium ferrite precursor was filtered, washed with water, and repulped with water. This slurry contains 1 mol/l of T.
85 mg of iC+l'a aqueous solution and 1 mol/l NaOH
Aqueous solution 340ae1 was added to treat the barium ferrite precursor with a Ti compound ((L+Mt)/Fe molar ratio: 0.165).

Next, the Ti-treated barium ferrite precursor was filtered, washed with water, and repulped with water, and the BaCAz aqueous solution was converted into BaC1
g/barium ferrite precursor was added at a weight ratio of 171 and then evaporated to dryness at 110°C.

Thereafter, the precursor particles were fired at 900° C. for 1 hour to obtain 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 of the present invention. This sample is referred to as (A).

Example 2 150 m of 1 mol/1 BaClz aqueous solution 4.1 mol/l
PeCl! x aqueous solution 1030 IIl, 1 mol/
1 of CoCll z aqueous solution 60ml! This mixture was then mixed with a 10 mol/l Na0)l aqueous solution 1942
mj! (Ba/(Fe+Mt+Mz) molar ratio: 1/
7.27, M+/Fe molar ratio: 0.058, ? b/M
+ Molar ratio: 0] Subsequently, the suspension was placed in an autoclave and heated at 150° C. for 3 hours to produce a barium ferrite precursor.

Next, the obtained barium ferrite precursor was filtered, washed with water, and repulped with water. To this slurry, 1 mol/l TiC1, aqueous solution 851I+1 and 1 mol/l CoC
1, 25 nl of aqueous solution and 390 investigations of 1 mol/l NaOH aqueous solution! Then, C was added to the barium ferrite precursor.
DM1+M2)/Fe molar ratio treated with O and Ti compounds: 0.165).

Thereafter, it was treated in the same manner as in Example 1 to obtain a ferromagnetic fine powder of the present invention. This sample is referred to as (B).

Example 3 In the same manner as in Example 1, an alkaline suspension was placed in an autoclave and heated to obtain a barium ferrite precursor, and then TiCj! , 1 instead of an aqueous solution
A ferromagnetic fine powder of the present invention was obtained by processing in the same manner as in Example 1, except that 85 m of SnCβ4 aqueous solution of mol/Il was added ((Ml+Mz)/Fe molar ratio: 0.165). This sample is designated as (C).

Example 4 In the same manner as in Example 1, a barium ferrite precursor was obtained by heating an alkaline suspension in an autoclave, and then adding 1 mol/1 Zr0C1! instead of TiCl4 to the precursor. , 85 mJ of aqueous solution was added ((M1+
The ferromagnetic fine powder of the present invention was obtained by the same method as in Example 1 except that M2)/Fe molar ratio: 0.165). This sample is designated as (D).

Example 5 1 mol/l BaCA, aqueous solution 150 mj! , 1 mol/
l of FeCl3 aqueous solution 10103O! , 1 mol/1 M
nCl was mixed with 130 mA of an aqueous solution, and then this mixture was added to 1900 mff of a 10 mol/l NaOH aqueous solution to form an alkaline solution containing a brown precipitate! ! ! A suspension was prepared (Ba/(Fe+M1+M2) molar ratio: 1/7.07
, M1/Fe molar ratio: 0.029, M2/M1 molar ratio 20] Subsequently, the suspension was placed in an autoclave and 1
A barium ferrite precursor was produced by heating at 50° C. for 3 hours.

Then add 1 mole/7! to the precursor. TiCA'a aqueous solution 85I111 and 1 mol/1 CoCI! z aqueous solution 85
m1 and 1 mol/1 NaOH aqueous solution 510n+1! (M1+M2)/Fe molar ratio: 0.194')
,! , and then treated in the same manner as in Example 1 to obtain a ferromagnetic fine powder of the present invention. This sample is designated as (E).

Example 6 150 ml of 1 mol/1 BaCl 2 aqueous solution! , 1 mol/l Fe (J, aqueous solution 1030 m/, 1 mol/l (
:uCI! z aqueous solution 60a+47, and then this mixture was mixed with 10 mol/l NaOH aqueous solution 194
An alkaline suspension containing a brown precipitate was prepared. (Ba/(Fe+Mt+Mz) molar ratio: 1/7.
27, M1/Fe molar ratio: 0.058, Mt/M1 molar ratio 20] Subsequently, the suspension was placed in an autoclave and heated at 150°C for 3 hours to produce a barium ferrite precursor.

The precursor was then treated with 1 mol/2 TiCl, an aqueous solution of 85
ml, 1 mol/l of CoC&, 85 rnl of aqueous solution and 510 rnl of 1 mol/l of NaOH aqueous solution! Shikaku(
M1+Mz)/Fe molar ratio: 0.223), and then treated in the same manner as in Example 1 to obtain a ferromagnetic fine powder of the present invention. This sample is designated as (P).

Example 7 1 mol/l BaCl, 150+ll aqueous solution, 1 mol/l
l of FeCl 3 aqueous solution 10103O, 1 mol/l! of CoCl , aqueous solution 85 ml 1.1 mol/l of TiCj!
a Mix 20II11 of aqueous solution, then add 1
An alkaline suspension containing a brown precipitate was prepared by adding 0 mol/1 Na0)1 aqueous solution 2013III1 (
Ba/(Fe+M1+M2) molar ratio: 1/7.57,
Mt/Fe・Mo/Lz ratio: 0.083, Mz/? L molar ratio: 0.24). Subsequently, the suspension was placed in an autoclave and heated at 150° C. for 3 hours to produce a barium ferrite precursor.

Next, the obtained barium ferrite precursor was filtered, washed with water, and repulped with water. In this slurry, 1 mol/
It's Tick<Aqueous solution 65n/! and 1 mol/1 N
The barium ferrite precursor was treated with a Ti compound by adding a011 aqueous solution 2601111 ((M I +
M2) /Fe molar ratio: 0.165).

Thereafter, it was treated in the same manner as in Example 1 to obtain the ferromagnetic fine powder of the present invention. This sample (G)
shall be.

Comparative Example 1 1 mol/It BaCl, 150 nL aqueous solution 7.1 mol/l FeCl, 1030 ml aqueous solution, 1 mol/l
85 ml of CoCl z aqueous solution, 1 mol/l of TiC
jl! 4 aqueous solution 8511/l, and then this mixture was mixed with a 10 mol/l Na 011 aqueous solution 2130nj!
(Ba/(Fe+M1+M2) molar ratio = l/8,
M, /Fe molar ratio: 0.083, M2/M, molar ratio: 1
．． 0) Subsequently, the suspension was placed in an autoclave and heated at 150° C. for 3 hours to produce a barium ferrite precursor.

Next, a comparative sample ((MI+M2)/Fe molar ratio: 0.165) was obtained by processing in the same manner as in Example 1, except that the barium ferrite precursor was not treated with a Ti compound in Example 1. H) was obtained.

Comparative Example 2 In Comparative Example 1, 1 mol/7! 85 ml of 1 mol/1 Zr0Cj2z instead of TiCl4 (Ba/(
Fe+M1+Mz) molar ratio = l/8, M+/Fe molar ratio: 0.083, M27MI molar ratio: 1. O) A comparative sample (J) was obtained in the same manner as in Comparative Example 1 except for the above. ((M++M□)/Pe molar ratio: 0.165) Comparative Example 3 In Comparative Example 1, 1 mol/l BaC#z aqueous solution, F
eCj! 3 aqueous solution, CoC1, aqueous solution and Tic 1
.

In addition to adding a predetermined amount of aqueous solution, an additional 1 mol/l! Mn of
Cj! , 30 ml of aqueous solution, and then this mixture was mixed with 10 mol/i NaOH aqueous solution 2172++4! An alkaline suspension containing a brown precipitate was prepared by adding
Ba/(Fe+M1+M2) molar ratio: 1/8.2, M
, /Fe molar ratio: 0.11SMz/L molar ratio: 0
．． 74, (M1+M2)/Fe molar ratio: 0.194)
Other than that, the same treatment as in Comparative Example 1 was carried out to obtain a comparative sample (K).

Comparative Example 4 In Comparative Example 1, 1 mol/l of BaClz water? S liquid, FeC13 aqueous solution, CoCl2 aqueous solution and TiCl
In addition to adding a predetermined amount of 4 aqueous solution, 1 mol/1 Cu
Mix 60 mj+ of aqueous Cl2 solution and then add this mixture to 2214 mj+ of 10 mol/l aqueous NaOH solution.
An alkaline suspension containing a brown precipitate was prepared (B
a/(10M Fe+10Mg) molar ratio: 1/8.4, M+/
Fe molar ratio: 0.140, M2/Ml molar ratio: 0
．． 586, (M1+M2)/Fe molar ratio: 0.223
) Except for this, a comparative sample (L) was obtained by processing in the same manner as in Comparative Example 1.

The average particle diameter (Dp: electron microscopy), coercive force (
! lc) and saturation magnetization (σS) were measured, and the results are shown in Table 1.

In addition, the electron w of the sample (8) of the present invention and the comparative sample (1 ())
Microscopic photographs of A are shown in FIGS. 1 and 2, respectively.

As a result of X-ray diffraction, the samples obtained in the Examples and Comparative Examples were all magnetobrambite barium ferrite. Further, when each of the samples was observed using an electron microscope, the particle shape was plate-like.

As is clear from the results in Table 1 and the electron micrographs in Figures 1 and 2, the M5 element is present during heating or hydrothermal treatment of the alkaline suspension containing the constituent elements of barium ferrite crystal particles, and the M2 element is not present. It can be seen that by not allowing or controlling the barium ferrite crystal grains within a specific range, it is possible to obtain fine ferromagnetic powder with a good particle size distribution, a coercive force suitable for magnetic recording, and a high saturation magnetization.

A magnetic coating material was prepared by dispersing each sample of the above-mentioned Examples and Comparative Examples in a binder mainly composed of vinyl chloride-vinyl acetate copolymer resin, and the magnetic coating material was coated and oriented on a polyester film by a conventional method to form a magnetic recording medium. I created it and looked at its characteristics,
The product of the present invention was excellent in orientation and surface smoothness.

〔Effect of the invention〕

According to the present invention, the barium ferrite fine particles have a predetermined coercive force, have a sufficiently high saturation magnetization, have a so-called ultra-fine particle size, and are highly dispersible and have excellent vertical orientation. This makes it possible to obtain magnetic powder suitable for magnetic recording media.

In addition, the method of the present invention replaces a part of Fe among the basic components of the barium ferrite (653) powder with a specific element to achieve stable coercive force control and fine particle formation using a relatively clean means. It is something that can be achieved together harmoniously,
This is a very advantageous method for industrial implementation.

[Brief explanation of drawings]

FIG. 1 is an electron w4ait mirror photograph (60,000x) showing the crystal structure of sample (A) in the present invention, and FIG. 2 is an electron microscope showing the crystal structure of comparative sample (11) in the comparative example. Photo (60,000x)

Claims (1)

[Claims] The molar ratio of the metal elements is 1/6≧Ba/Fe+M_1+M_
2≧1/12 [However, M_1 is Co, Ni, Zn, C
At least one element selected from the group of u, Mg and Mn
species, M_2 is at least one element selected from the group of Ti, Sn, Zr, Ge, Nb and V] and M_
1 is 0.01 to 0.2 mol per mol of Fe, and M_
An alkaline suspension having a pH of 11 or higher and containing metal elements selected such that 2 is 0 to 0.5 mole relative to M_1 is heated at 60 to 250°C to form a barium ferrite precursor. M_2 to the obtained precursor
, or M_2 and M_1 are M for 1 mole of Fe.
M_2 or the metal element compound of M_2 and M_1 is added so that the sum of _1 and M_2 is 0.3 mol or less, and then this product is
A method for producing ferromagnetic fine powder for magnetic recording, which comprises firing at 0°C to obtain barium ferrite crystal particles.