JPS62216921A - Production of hexagonal ferrite powder - Google Patents

Abstract

PURPOSE:To develop hexagonal ferrite for a magnetic recording medium which is extremely fine and excellent in dispersibility and crystallinity and suitable for high-density recording by adding a specified flux to hexagonal powder which is obtained by subjecting a compd. contg. both trivalent Fe compd. and a specified compd. to hydrothermal treatment and heat-treating the mixture. CONSTITUTION:Both trivalent Fe compd. such as ferric chloride, ferric nitrate and ferric sulfate and a compd. contg. at least one kind of chloride, nitrate, hydroxide and carbonate of Ba, Sr and Pb are subjected to hydrothermal treatment for 1-5hr at 200-300 deg.C together with alkali such as KOH and NaOH and hexagonal ferrite powder having <=0.1mum particle diameter is produced. BaCl2 is individually mixed to this powder or after mixing BaCl2 with alkali halide such as NaCl and KCl, the mixture is mixed thereto in proportion of (1:3)-(1:20) for the hexagonal ferrite and heat-treated in air at 700-900 deg.C for 1-10hr.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a treatment method for improving the dispersibility of hexagonal ferrite for magnetic recording media suitable for high-density recording.

(Prior art) F'e' is a method for producing hexagonal ferrite fine particles.
A well-known dry method is a method in which an iron compound containing ions and a compound containing one or more elements of Ba, Sr, and Pb are mixed and fired at high temperatures.On the other hand, a wet method involves mixing the above-mentioned raw materials in an alkaline suspension. There have been several methods in which the material is hydrothermally treated as a liquid and then treated at a high temperature (600 to 900°C).

Sintering between hexagonal ferrite particles obtained by these methods, agglomeration of particles, deformation of crystal shape due to melting, etc. are unavoidable, and when used as a perpendicular magnetic recording medium, dispersibility is poor and packing density is improved. There are often cases where the properties when made into tape are inferior, such as poor orientation and poor orientation, and a solution is desired.
It was

As a means to solve these drawbacks, many studies have been carried out on a method of mixing hexagonal ferrite with a flux and heating it above the melting point of the flux, as described in Japanese Patent Application Publication No. 2003-141000, 55-145.
J (J3, No. 56-56200, Japanese Unexamined Patent Publication No. N56-125299, etc.).

However, in these conventionally proposed methods, the hexagonal ferrite pine powder used in the dry method is a powder with a relatively large particle size of 0, 1 to 6 capes, and it is finely pulverized by pulverization. Because of this, it has an amorphous shape and is treated at high temperatures (900-1200℃) to adjust its shape.

In this way, since the amorphous powder with a large particle size obtained by the dry method is heat-treated at a high temperature, the particle size after flux treatment is extremely large, ranging from several pzn to 1 μm. Grain growth was unavoidable.Thus, although there are references to its use as a magnetic recording material, it is clear that it is usually intended for magnet materials and the like.

Therefore, this method aims to develop a shape accompanied by grain growth by dissolving ferrite in Busix A and re-precipitating it.
It is impossible to apply this method to ferrites with particle sizes below.

On the other hand, regarding the use of a flux as a treatment method for hexagonal fephite for direct magnetic recording bodies, for example, Japanese Patent Laid-Open No. 60-9
Publication No. 0829 includes KNO3 series, cac1! system, LCi
A low melting point two-component flux such as the system is proposed! However, the temperature is low (
250-450° C.), so there is no fear of agglomeration or sintering, but the magnetostatic properties such as saturated magnetization and squareness ratio are not improved, so this method is essentially a less effective method.

In addition, JP-A No. 60-161343 proposes a method using an alkali metal compound as a fluxing agent, but for example, when common salt is used as a fluxing agent, a low area ratio of 6 is significantly lower than the plate-like ratio. In addition to causing a decrease in grain size, grain growth has progressed and the increase in grain size has not been suppressed, and other problems still remain unsolved.

(Problems to be Solved by the Invention) As a solution to these problems, the present invention provides hexagonal ferrite mixed with a novel flux (an improved treatment method for hexagonal ferrite that is heat-treated at a temperature of 700 to 900°C). x') The purpose is to improve dispersibility and orientation without causing growth in crystal grain size and without advancing sintering.

The present invention is characterized in that barium chloride alone or a mixture of barium chloride and an alkali halide is added to a hexagonal crystal ferrite and heat-treated at a temperature of 70Q - 900°C. III) Compound and Ba
, Sr, and Pb are hydrothermally treated in an alkaline aqueous solution to produce fine-particle hexagonal ferrite powder, and then the above-mentioned flux is added to the hexagonal ferrite particles to obtain a powder of 700 to 900 By heating at ℃, sintering or grain growth between particles does not occur, the particle shape is stable, crystallinity is improved, and saturation magnetization is large.
Hexagonal ferrite particles having excellent dispersibility and orientation and suitable for use in high-density recording media can be obtained.

The hexagonal ferrite powder used in the present invention is obtained by hydrothermally treating a Fe(Ill) compound and a compound containing elements of -m or more of Ba, Sr, and Pb in an aqueous alkaline solution as described above. Fine-grained hexagonal ferrite with a particle size of 1 or more is good, and of course, part of the macrogonal ferrite may be other than 4
-! yl with reduced coercive force by substitution with II parallel
For example, Co%Ti, Sn, Sb, In.

Naturally, it is also applicable to materials in which a portion of the θ is replaced with W, Ni, Zn, Mn, etc. Examples of Fe(ill) compounds include ferric chloride, iron nitrate, iron sulfate, etc., while Ba,
Generally, Etr and Pb compounds that exhibit a certain degree of solubility in reaction mixtures are acceptable, and chlorides, nitrates, hydroxides, carbonates, etc. are used.

As the foreign metal compound, chlorides, nitrates, carbonates, sulfates, etc. of the above elements are used.

In addition, the molar ratio (Fe, O,
, /MO) (M = Ba, Sr, Pb) is in the range of 4 to 6, preferably 5 to 6.

The alkali used in the reaction is usually N+tOH,
Note: When a caustic alkali such as KOH is used and the MU is highly concentrated, it is more useful for miniaturization, but adding more than 5ONt may result in indissolution, so it is usually preferable to use a concentration of about 3 M/l to 8 Mμ. A hydrothermal reaction temperature of -300°C is preferable, and a reaction time of 1 UL is preferable because lower temperatures are more effective for micronization, but at lower temperatures the crystal shape is lost and there are many occurrences of loose microcrystals. You can finish it in ~5 hours. The ultra-fine 1JU7” light particles generated by Shishita P-ZU in this way...Invention 4
! ! .

Grain growth is caused by using a specific flux according to; 1.4 It is improved to have extremely improved magnetic properties without C.

The alkali halide used with barium chloride, which is the fluxing agent used in the present invention, is Na(,1, KOI
, NaF , KFlNaBr, KBr 1NaI
, KI, etc., but NaCl, KCl, etc. are preferable in consideration of ease of labor and economy.

The amount of the flux added is preferably about 1=3 to I:20 in molar ratio to the hexagonal ferrite powder to be treated. If it is less than 1:3, sintering tends to occur (low iT surface area is noticeable, or if it is less than 1:3,
Even if it exceeds 20, the effect will not increase that much, so it is uneconomical.

Dilation in a two-component system -8- (molar ratio is BaC1!+M
X (alkali halide) = I + 1-3 is suitable. In the case of a two-component flux, the gap may be added by simply mixing the two compounds, or by preparing a eutectic mixture in advance and adding it.

The fluxing agent can be mixed into the hexagonal ferrite by either dry mixing or wet mixing, but wet addition is more effective.

The processing temperature for hexagonal ferrite mixed with a flux is 70
A temperature in the range of 0 to 900°C is preferable; below 700'C, sufficient crystal perfection is not achieved and no improvement in saturation magnetization can be expected. -Temperatures exceeding 900°C should be avoided since sintering and grain growth will become correspondingly significant. In addition, in the case of barium chloride alone, it is below its melting point at 700 to 900 °C, but even if the flux is not melted in the bath, sintering and grain growth do not occur.
Clarification of the crystal shape and improvement of magnetic properties have been sufficiently achieved, and this is worthy of special mention. Further, the heat treatment time is preferably 1 to 10 hours, and the treatment is preferably performed in an air atmosphere.

Since the fluxing agent of heat-treated mixtures is easily dissolved in water, it can be treated with water, warm water, mineral acid aqueous solution, etc., and removed.
It does not remain as an impurity in the bamancrystalline ferrite.

(Effects of the Invention) The hexagonal ferrite fine powder of the present invention has extremely low dispersibility since there is no sintering between particles, each particle is disjointed, the particle size is extremely small, the crystallinity is good, and the saturation magnetization is low. A hexagonal ferrite powder is obtained which is extremely suitable as a high directivity magnetic recording medium.

The present invention will be explained in detail below with reference to Examples.

Example 1 (Generation of Ba ferrite particles) 100 ml of ferric chloride aqueous solution (3M), 7.3 F of barium chloride dihydrate, 5.4 p of cobalt chloride hexahydrate,
Iron hydroxide and barium hydroxide are co-precipitated by adding 2.1 g of titanium tetrachloride, 3 y of tin powder and 3 y of sodium chloride, and 50 y of caustic soda and 50 y of water. Stir the reaction mixture with a stirrer 1 = r.
At the same time, add 95y of caustic soda to 300ml.
Add ice to reach rttl.

Then, the autoclave was reacted at 270'C for 2 hours to obtain Ba-ferrite particle gold.

(Fluxing agent treatment) The above Ba-ferrite was washed with water until the pH reached 13 or higher, and the Ba-ferrite was
30 g of flux of C11-Na1l (molar ratio 50:50) was added to dissolve and evaporated to dryness. This material was placed in a crucible and treated at 850C for 2 hours, and then the flux was removed with hot water and dried to obtain only Ba-ferrite powder. The si of the obtained Ba-ferrite is 0.
It was 06-. Flux ratio (Ba-ferrite:fluxing agent molar ratio): 1=10 Example 2 The same procedure as in Example 2 was carried out except that BaCl2 alone was used as a fluxing agent of 26 mm (flux ratio). The particle size of the obtained Ba-ferrite powder was 0.07 lin.

Example 3 13ac12-KCI (molar ratio 50:
50) The procedure was the same as in Example 1 except that 70 mm (flux ratio 20) was used. The particle size of the obtained Ba-ferrite powder was 0.06βn.

Comparative Example 1 The same procedure as in Example 1 was carried out except that NaC115 (fusix ratio 10) was used as the fused J-cho. Samurai L, 1 Luta Ba
- The particle size of the flight powder was 0.15 pn.

The magnetic flux properties of Examples 1 to 3 and Comparative Example 1 are shown in the first column.

In the comparative example in Table 1, the values of C8, iHc, and σr/- are good, but the BET decreases significantly, indicating that sintering has occurred, and it is predicted that the filling properties will be poor when forming into a tape. I know.

Claims (1)

[Claims] A Fe(III) compound and a compound containing at least one element among Ba, Sr, and Pb are hydrothermally treated with an alkaline aqueous solution to produce hexagonal ferrite powder, and then barium chloride alone or barium chloride is used as a flux. and an alkali halide, and heated to 700-900°C.
A method for producing hexagonal ferrite powder, the method comprising heating at a temperature of .