KR0139130B1 - Method of preparing cubic ferrite powder for magnetic tape - Google Patents

Abstract

By using the unique properties of k-sn among substituted ions to control the magnetic properties of hexagonal ferrites, the coefficient of coercivity is zero as well as the specific surface area of 0.05 µm or less without decreasing the saturation magnetization value compared to conventional hexagonal ferrites. Hexagonal ferrite fine powder manufacturing method having more than 50㎡ / g and having excellent coercive force distribution.

Description

Manufacturing method of hexagonal ferrite fine powder for magnetic recording

The present invention relates to a method for producing a hexagonal ferrite fine powder for magnetic recording, and more particularly, to a method for producing a hexagonal ferrite fine powder for magnetic recording by glass crystallization using the unique characteristics of k-sn.

High density magnetic recording tapes are required to have extremely smooth surfaces, high coercive force and excellent short wavelength characteristics. At this time, the magnetic powder used should have high coercivity and specific surface area of particles, and small magnetic field phenomenon at short wavelength. Hexagonal ferrite, which is adopted as a high density magnetic recording material, has ultra-fine particle size of less than 0.1㎛, has excellent magnetization inversion distribution, excellent short wavelength output, and wide range of coercivity by controlling magnetic anisotropy. In addition, it is easy to mass-produce and handle as a chemically stable oxide, and has the advantage that the existing tape coating technology and apparatus can be used as it is.

However, it has a disadvantage of low saturation magnetization value and high coercive temperature coefficient of 3 to 5 Oe (Oersted) / ℃.

The composition of the hexagonal ferrite properties control depends on the type of the substitution ion, the substitution amount and the production method. Pure barium ferrite has high coercive force due to large crystallite anisotropy, and its particle size is also larger than several micrometers, which is not suitable for magnetic recording magnetic powder.

Barium ferrite has a high coercivity because the fifth coordination site in the plane containing Ba ions having a large ionic radius in crystal structure exhibits crystal asymmetry and shows large crystal magnetic anisotropy. In order to reduce such high coercivity, Fe + 3 ions of the 5th coordination site are divalent ions of Co, Ni, and Zn, and tetravalent ions such as Ti, Sn, and Nb.

When only divalent ions are substituted, spinel ferrites with irregular insertion or release of spinel blocks are formed inside the structure of hexagonal ferrites and hexagonal ferrites with inconsistent substitutions are generated to lower coercivity and increase saturation magnetization. And the effect of improving the temperature coefficient of the coercive force, but the particle size and the distribution of the coercive force become very nonuniform.

On the other hand, in the case of replacing only tetravalent and tetravalent ions such as Ti, Sn, and Nb, the particle size is reduced and does not appear to be non-uniform, and there are disadvantages of reducing the saturated magnetization pack and maintaining a high coercivity pack. Therefore, since the substitution of +2 and +4 or +5 ions plays different roles in the structure, the substitution amount must be adjusted while achieving valence compensation.

Techniques for manufacturing a hexagonal waste light for high density magnetic recording include hydrothermal synthesis-heat crystallization method (Japanese Patent Publication No. 63-164203, Japanese Patent Publication No. 3-3361, Korean Patent Publication 89-1120, 89-5137, etc.), Coprecipitation-firing method (Japanese Patent Publication No. 63-12107, Hei 1-278425, etc.), Glass-Recrystallization Method (Japanese Patent Publication No. 56-169128, No. 61-36685, Hei 1-22205, Republic of Korea Patent Publication No. 89-5660 And the like) have been known.

The glass-recrystallization method of the above-mentioned known technology has the advantages of small particle size, large saturation magnetization, and easy elemental substitution, so that the coercive force can be precisely controlled and good dispersibility, compared to hexagonal waste lye produced by other methods. Have. Therefore, it is known that it is most advantageous to prepare a magnetic fine powder having excellent recording characteristics based on the glass-recrystallization method.

The most effective substitution ion known is Co-Ti-based, which significantly reduces the coercive force, but has the disadvantage of increasing the temperature coefficient of the coercive force to 3 to 50e / ° C.

The reason why the coercive temperature coefficient increases is due to the substitution elements Co and Ti, and the crystallinity of the crystal is closely related.

The crystallinity of the crystal depends on the heat treatment temperature in addition to the composition. The higher the heat treatment temperature, the better the crystallinity and the better the distribution of the coercive force, but the temperature coefficient of the coercivity increases. In addition, if the temperature coefficient of the coercivity is large, the magnetic recording and reproducing characteristics are changed according to the surrounding environment, which makes it difficult to preserve stable data.

Therefore, it is required to develop hexagonal ferrite magnetic powders having a specific surface area of more than 50 m2 / g and excellent coercive force distribution, as well as zero coercive temperature coefficients, without decreasing the saturation magnetization, compared to conventional hexagonal pate.

As a well-known technique for improving the coercive temperature coefficient of hexagonal ferrites, an excess of +2 valent ions are used. 9 Japanese Patent Publication No. Hei 3-108303) or substitution of Co-Sn, Zn-Sn, Co-W or Co-Mo. System (Japanese Patent Publication Nos. 63-193505, 62-91425, Hei 2-23601) and a method of coating spinel ferrite on a hexagonal ferrite surface (Japanese Patent Publication Nos. 61-197426 and 63-250103). .

In the case of the technique using an excess of +2 ions in the known technology, the spinel ferrite in which the spinel block is irregularly inserted or released in the structure of the sharp hexagonal ferrite, and the hexagonal ferrite having an irregular substitution amount is generated. The effect of lowering the coercive force, increasing the saturation magnetization value and improving the temperature coefficient of the coercive force is that the particle size and the distribution of the coercive force are very uneven.

In addition, among the known techniques such as a method using a substitution system of Co-Sn, Zn-Sn, Co-W or Co-Mo, uniform physical properties are first assumed that substitution ions are uniformly substituted into a hexagonal ferrite structure. Should be assessed. Therefore, Sn has a lower substitution capacity than Ti, and Co is a substitution ion which makes the coercive force distribution uneven compared to Zn. In addition, the use of Sn in Ti and Nb, which helps uniform substitution of substituted ions, can improve the coercive force coefficient coefficient, but leads to a decrease in saturation magnetization value.

In the case of W or Mo, the atomic radius is relatively smaller than that of Fe, and ions which are not easily substituted are mixed with non-uniform magnetic phases, and particle sizes tend to be very nonuniform.

In addition, the method of coating the spinel ferrite on the surface of the hexagonal ferrite in the known technique is the most ideal method, but it is very difficult to uniformly coat the individual ultrafine particles of about 0.05㎛.

Accordingly, the present invention improves the problems of the above-described high technology by using a complex action of two substituted ions, and the first object of the present invention is hexagonal having a coercivity of zero thermal coefficient without decreasing saturation magnetization value compared to conventional hexagonal ferrites. It is to provide a method for producing a magnetic ferrite powder.

A second object of the present invention is to provide a method for producing an excellent hexagonal ferrite powder having a specific surface area of 0.05 µm or less and a coercive force distribution of 50 m ² / g or more.

Hereinafter, the present invention will be described in detail.

AO and Fe₂O₃, which form hexagonal ferrite, and substituted components for controlling physical properties were mixed, heat treated at 800 to 1300 ° C, and then ground to prepare a precursor containing excess AO. Thus, Na₂CO₃ and B₂O₃, which are glass components, were prepared. Mix uniformly. Thereafter, the mixtures were put in a platinum crucible and then melted at 1100-1350 ° C. to melt the molten material in water and quenched to obtain an amorphous body.

The amorphous body thus obtained is heat-treated at 640-760 ° C. in an electric furnace, and then pulverized to dissolve the glass component and the surplus element in an acid solution, washed with water and dried to prepare a hexagonal ferrite fine powder having the composition shown in the following general formula. will be.

A ₁ - _W K _W F e _{12- (x + y + z)} M ⁱ x {M ^j } _y S n _Z O 2 ₁₉

here

0.04 ≤ w ≤ 0.15, 0 ≤ x ≤ 1, 0.2 ≤ y ≤ 0.6, 0.25 ≤ z ≤ 0.7, A is at least one element selected from Ba, Sr, Pb, Ca, and M ⁱ is Co, Ni, Zn At least one element selected from among, M ^j is at least one element selected from among Ti, Nb, Ta, Si.

According to the present invention, the preparation of the precursor containing the AO of the superphosphate is that the amorphous body obtained by melting and quenching by mixing with the glassy component after preparing the precursor rather than mixing the respective raw materials to obtain an amorphous body by melting and quenching This is because the distance between the ions is short and the crystallization reactivity is increased, so that the uniform substitution of the substituted ions within the crystal of the hexagonal ferrite is easy, and the particle distribution and the coercive force distribution of the powder obtained are excellent.

In addition, K and Sn of the substituted ions cause a very unique phenomenon as described below when using two substituted ions at the same time rather than the effect as individual components. The high coercivity of barium ferrite is due to the distortion of the 5th coordination site in the plane containing Ba ions having a large ionic radius in crystal structure, resulting in crystal asymmetry and high crystal anisotropy. K has almost the same atomic radius as Ba, but when only K is substituted, it is not easy to substitute into the structure, resulting in a very nonuniform distribution of coercive force. Sn has a lower substitution capacity than Ti, but when K and Sn are used simultaneously, the substitution into the structure is very easy.

Since the five ion sites in the hexagonal ferrite have selectivity for substitution ions, not all the added ions are substituted into the structure.

When using K-Sn at the same time, the coercive force value decreases while the saturation magnetization is constant, and the particle height becomes 0.05 μm or less, so that the specific surface area is 50 m ² / g or more, and the coercive temperature coefficient is almost zero. do.

Preferably, the substitution amount of K is 0.04 to 0.5, and the substitution amount of Sn is 0.25 to 0.7. When the substitution amount of K is 0.04 or less, the effect obtained by substituting is insufficient. When the substitution amount is 0.15 or more, the effect obtained by substitution is as it is, but it is difficult to mix due to the hygroscopic phenomenon of the raw materials. Is unaffected and removed together with the glassy component in subsequent processes.

In the case of Sn, when the substitution amount is 0.25 or less, the particle size becomes uneven and the coercive force temperature coefficient is maintained as it is. When the substitution amount is 0.7 or more, the decrease in pore magnetization value and the coercivity temperature coefficient are -1 Oe / ℃ or less. It leads to the fall of magnetic property.

In the method of measuring the coercive force distribution used in the present invention, the shape and the half width of the dM / dH curve according to the change of the external magnetic field were measured by using a magnetometer (VSM) for measuring magnetic properties. As the dM / dH curve is not separated and the half width (ΔH) decreases, the distribution of coercive force becomes narrower, which means that the magnetic properties of the magnetic powder become more uniform.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Examples 1-3

In the present embodiments, the substitution amount of Sn is changed to the state where K is added. BaCO₃ and Fe₂O₃, which form hexagonal ferrite, and Co₃O₄, TiO₂, Nb₂O ₅ , SnO₂, SiO₂, and K₂CO₃, which are substituted components for controlling physical properties, were weighed according to Table 1, mixed uniformly, heat treated at 1000 ° C, and then pulverized. A precursor having an average particle diameter of 1 to 2 µm was made.

Here, Na₂CO₃ and B₂O3, which are glass components, were weighed and uniformly mixed into a platinum crucible, melted at 1200 ° C., and the amorphous material obtained by water-cooling the melt was dried.

This was heat-treated and pulverized at 700 ° C. for 2 hours in an electric furnace to dissolve the glassy component and the surplus element in 20% acetic acid solution, which was washed with water and dried to obtain a hexagonal ferrite fine powder. The magnetic fine powder thus obtained is shown in Table 2 below.

Comparative Examples 1-2

Comparative Example 1 is a case where only K is substituted, and Comparative Example 2 is a case where only Sn is substituted. The preparation method was the same as in Example, and the characteristics of the magnetic fine powder thus obtained are shown in Table 2 below.

TABLE 1

TABLE 2

* Coercive force (Hc), saturation magnetism (σ _s ) and residual magnetization (σ _r ), square ratio (SR), coercive force temperature coefficient (ΔHc / ΔT, 20 ℃ -60 ℃) and distribution of coercive force (dM / dH vs. H The half width of the curve, ΔH), was measured at 10 KOe magnetic field with a highly sensitive vibration sample magnetic force (VSM, VSM-P7 from TOEI), and the specific surface area (SSA) was measured by the BET method (SORPTY 1750 series). In the case of the comparative example, fertilizer example 1 shows the ease of uniform magnetization reversal as the coercive force distribution (ΔH) is lower when using only K. Therefore, the coercive force of magnetic powder is very uneven because the coercive force distribution (ΔH) is high as 2800 Oe. In this case, it is understood that the particle size at this time is not more than 0.1 µm, which is not suitable for a high density magnetic recording medium. In Comparative Example 2, the coercive force coefficient was slightly improved when only Sn was used, but the saturation magnetization value was lowered to 52.5 emu / g, resulting in a decrease in reproduction power in the magnetic medium. As described above, the physical properties of the hexagonal ferrite fine powder of the present invention have a coercive force coefficient (ΔHc / ΔT) of zero and a ratio of 0.05 μm or less, without decreasing the saturation magnetization value (σ _s ), compared to the conventional hexagonal ferrite powder. It has a surface area (SSA) of 50m ² / g or more and excellent coercive force distribution (ΔH), which is a magnetic component for magnetic recording media for various purposes such as computer magnetic tape, high density floppy disk, audio magnetic tape and 8mm magnetic tape for video. Suitable.

Claims (3)

AO and Fe₂O₃ forming hexagonal ferrite and a substitution element for controlling physical properties are mixed, heat treated at 800 to 1300 ° C., and then ground to prepare a precursor containing excess AO, which includes glassy components NaCO₃ and After uniformly mixing B ₂ O ₃ , the mixtures were put in a platinum crucible, and then a melt melted at 1100 to 1350 ° C. was added to water and quenched to obtain an amorphous body. A heat treatment at 760 ° C., a glass component and a surplus element are dissolved in an acid solution, washed with water, and dried to prepare a powder having a composition represented by the following general formula. A ₁ - _W K _W F e _{12- (x + y + z)} M ⁱ x M ^j _y S n _Z O ₁₉ here 0.04≤w≤0.15, 0≤x≤1, 0.2≤y≤0.6, 0.25≤z≤0.7, A is at least one element selected from Ba, Sr, Pb, and Ca, M ⁱ is at least one element selected from Co, Ni, and Zn, M ^j is at least one element selected from Ti, Nb, Ta, and Si. The method for preparing hexagonal ferrite fine powder according to claim 1, wherein K and Sn are used together as the substitution element. The method for producing a hexagonal ferrite fine powder according to claim 1 or 2, wherein the substitution amount of K is 0.04 to 0.15 and the substitution amount of Sn is 0.25 to 0.7.