JPH0388307A - Manufacture of magnetic powder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain hexagonal ferrite by which a high filling rate can be achieved in a medium readily by mixing and fusing a compound for every element forming the hexagonal ferrite and each specified compound, quickly cooling the mixture so as to form amorphous material, performing heat treatment of the amorphous material, depositing the hexagonal ferrite, cleaning the ferrite, and extracting the ferrite. CONSTITUTION:In the formulas I-III, A expresses one or more kinds of elements which are selected among Ba, Sr, Ca, and Pb, and M expresses one or more kinds of elements selected among Co, Ti, In, Ni, Cu, Zn, Nb, Zr, V, Ta, Al, Cr, Sb, Hf, Mo, W, Ir, Sn and Mg. Hexagonal ferrite is formed of said elements. The compound of every element is mixed and fused with each compound of R, A and B. The mol ratio of R2O (R expresses at least one kind of elements selected among Li, Na, k, Rb and Cs), AO and B2O3 as other components is made to be 1.0<(AO+R2O)/B2O3<2.0, and 0.0<R2O/AO<1.0. The material is quickly cooled so as to obtained an amorphous material. Heat treatment and cleaning are performed for said amorphous material, and the hexagonal ferrite is extracted. In this way, the hexagonal ferrite by which high filling rate can be achieved in a medium can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for producing magnetic powder mainly used in high-density perpendicular magnetic recording media.

(Prior Art) A coated magnetic recording medium is composed of a base made of polyethylene terephthalate or the like, and a magnetic layer formed on the surface of the base, the main components of which are ferrite and binder resin. Conventionally, ferrite used in magnetic recording media is 7-re 2O 3. C
o Deposition r-Fe 2O 3. Co-doped r-Fe
2O3. Cr02. Acicular ferrites such as metal Fe are known, and magnetic recording is performed by a method using magnetization in the longitudinal direction in the plane.

However, in magnetic recording media that use magnetization in the in-plane longitudinal direction, when attempting to improve recording and reproduction in the high frequency range, the demagnetizing field within the recording medium increases, making it impossible to improve the recording density that much. There's a problem.

In recent years, in order to significantly improve magnetic recording density, a perpendicular magnetic recording system has been proposed that uses magnetization in a direction perpendicular to the base of a magnetic recording medium. A magnetic recording medium using this method is suitable for high-density recording because it does not suffer from demagnetization field problems even in high frequency ranges.

As a magnetic recording medium suitable for such a perpendicular magnetic recording system, one in which a Co--Cr alloy or the like is deposited on a substrate surface by a vacuum evaporation method or a sputtering method has been proposed. However, this type of magnetic recording medium has problems in terms of environmental stability, running durability, productivity, etc. On the other hand, magnetic recording media that have solved these problems include hexagonal ferrites whose axis of easy magnetization is easily oriented perpendicular to the substrate surface, such as M-type BaPe2OlI and W-type BaM.
ez Fe, 027 (Me is a substitutional metal element), etc., and hexagonal ferrites in which some of their atoms are substituted with other elements have been developed.

One method for manufacturing hexagonal ferrite for coating-type magnetic recording media is to mix and melt an element that forms hexagonal ferrite and an element that forms glass as other components. A glass crystallization method is known in which a hexagonal ferrite is precipitated by performing rapid cooling and heat treatment on an amorphous body, followed by washing treatment to extract the hexagonal ferrite. In this glass crystallization method,
It is known to use B2O3 and AO (A is at least one element selected from Ba, Sr, Ca, and pb) as elements that form glass. Furthermore, it is also known to use sodium borate as a raw material for forming glass.

(Issue 8 to be solved by the invention) However, in the conventional glass crystallization method described above, the elements forming glass are B2O3 and AO (A is Ba,
At least one selected from Sr, Ca, and pb
When using a magnetic seed element), there is a problem that the degree of filling of the obtained ferrite in the medium is low, and the output of the magnetic recording medium is low, resulting in low S/N characteristics. Furthermore, when boric acid is used, non-uniform melting tends to occur and the atomic distribution in the amorphous body tends to be biased. difficult,
Another problem is that the S/N characteristics of the magnetic recording medium are low.

The present invention has been made in order to solve the above-mentioned problems when obtaining a magnetic recording medium having high recording density and high S/N characteristics, and is directed to hexagonal ferrite that can be highly filled in the medium. The purpose of this invention is to provide a method for manufacturing.

C Structure of the Invention] (Means for Solving the Problems) Hexagonal ferrite used in magnetic recording media is sufficient in the recording wavelength region of 1 μm or less, where perpendicular magnetization recording is more significant than in-plane recording. In order to perform accurate recording and reproduction, particles with a particle size of 0.01-0.3 μm and high S
/N, it is preferable to use particles with uniform particle size. Further, if the coercive force of the hexagonal ferrite is too high, the head magnetic field will be saturated during recording, and if it is too low, it will be impossible to hold the recording signal, so it is preferable to have a coercive force of 200 to 2000 Oersted. Therefore, the hexagonal ferrite according to the present invention may be one in which some of the constituent atoms of barium ferrite or strontium ferrite are replaced with specific other atoms to control the coercive force. and,
The present invention has been accomplished as a method for producing such particles, and has the general formula (%), where A: at least one element selected from Ba, Sr, Ca, and pb, M : Co, T1. I
n, N1. Cu, Zn, Nb, Zr, V, Ta, A1.
A compound of each element forming a hexagonal ferrite such as at least one element selected from Cr, Sb, IIf', Mo, W, lr, Sn, and Mg, and other components R2O(R: Ll, Na, R
h, at least one type selected from CS), AO and B2O3 have a -of ratio of 1.0 < (AO + R2O)/B 2O3 < 2
．． The compounds R, A, and B are mixed and melted so that 00.0 < R2O/AO < 1.0, rapidly cooled to become amorphous, and then heat treated to this amorphous body. This is a method for producing magnetic powder for magnetic recording media, in which hexagonal ferrite is precipitated using a washing process, and the hexagonal ferrite is extracted by washing.

Here, M is used to control the coercive force of the hexagonal ferrite, but if the substitution ff1X is smaller than 0.02, the coercive force becomes too large, and if it exceeds 0.24, the coercive force becomes small. It's too much and I don't like it.

Also ^0 as other ingredients. R2O and B2O3
is the sol ratio, (AO+R2O)/B2O3≦1, O
When the composition is set such that the following, the degree of filling of the obtained ferrite in the medium does not become very large. Furthermore, when (AO+R2O)/B2O3≧2.0, multi-domain particles appear. Furthermore, in the case of AO≦R2O, the amorphous body intensely absorbs water and carbon dioxide, making it difficult to stably produce hexagonal ferrite. Moreover, even if the amorphous body is well-preserved and does not absorb moisture or carbon dioxide, the melting point of the amorphous body decreases, making sintering of the ferrite particles more likely.

(Function) According to the method for producing magnetic powder for magnetic recording media according to the present invention, the molar ratio of the compound for each element forming hexagonal ferrite and other components is 1.0 < (AO+
R2O)/B2O3<2.0 and 0.0<R2
The compounds R, A, and B are mixed and melted so that O/AO<1.0, and the mixture is rapidly cooled to become amorphous and then crystallized, so it has a hexagonal shape that can be highly filled in the medium. Crystalline ferrite can be easily obtained. Further, a medium manufactured using the obtained magnetic powder can realize a large output, a high recording density, and a high S/N characteristic. Moreover, R
Since we do not use already synthesized complex compounds such as 2B and 07 as raw materials, we use simple compounds of each essential component as raw materials, so it can be melted with good uniformity and is amorphous with no bias in atomic distribution. Amorphous materials with good properties can be obtained.

(Example) The present invention will be explained in detail below using examples.

Ba ferrite was selected as the target magnetic powder, and the substitution element for coercive force control was a combination of Co and Ti ions, so that the substitution was X-0,14, and a composition with ns 8.0 was attempted. Other ingredients include B,
Ba and Na compounds were used. The ferrite component was 40so1%.

Examples 1 to 6, Comparative Examples 1a to 5a The raw material components of Ba ferrite and other components were the first
Carbonates of each element were heated to 1400°C in the proportions shown in the table.
After melting, the material was rapidly cooled and rolled using twin rolls to obtain an amorphous body. This amorphous body was heat-treated at 800° C. for 5 hours to precipitate hexagonal ferrite, and then washed with acetic acid and pure water, extracted, and dried to obtain magnetic powder.

Table 1 The magnetic properties of each of the hexagonal ferrites obtained above were measured using a sample vibrating magnetometer, and the shape was measured from photographs taken using a transmission electron microscope. Table 2 shows the results.

(Margins below) In Comparative Example 4a in Table 2, the squareness ratio was small, probably due to the production of multi-domain particles, and the coercive force was 185 (Oe), which was too small to be used as a magnetic recording medium. .

Using the hexagonal ferrite obtained above, a magnetic paint was prepared with the composition shown in Table 3.

Table 3 Ingredients Compounding amount Hexagonal ferrite lOO parts by weight Sulfonated hydrochloride acid waste resin lO // Dispersant (lecithin)
3 No.I abrasive (A12O3)
2 /I lubricant (StAIStBu
)2 Hardening agent (Coronate) 4 Methyl ethyl ketone 40/l toluene
40〃Cyclohexanone 4
0 These were sufficiently kneaded with a sand grinder to form a paint, and then applied onto the surface of a 9 μm thick polyethylene terephthalate film, dried, calendered and cured to obtain a magnetic recording medium.

The characteristics of the obtained magnetic powder and the characteristics of the magnetic recording medium were
Shown in the table. The degree of filling was expressed as 1 (the ratio of the saturation magnetization of the obtained medium to the theoretical value of the saturation magnetization assuming that the medium had no voids) in the case of Comparative Example 1.

Table 4 Filling degree S (λ-0,5μ) dB Example 1 1.08 +0.72
1.13 +t,.

3 1.17 +1.
54 1.28 +2
．． 05 1.22 +
1.76 1.10
+0.8 Comparative Example 1a 1.00 0.
02a 1.00
0.03a 0.93 -
0.84a 0.71
-3.05a 0.68
-3.3 When using the magnetic powder obtained in Examples 1 to 6,
A medium with a high degree of filling and high output was obtained.

Although the reason why the degree of filling of ferrite in a medium is improved is not clear, the composition according to the present invention changes the surface properties of ferrite, improves compatibility with binder resin, etc., and improves dispersibility. It is thought that it is the same as above. That is, the molar ratio of other components is 1.0<(80+R2O)/B2O3<2.0 and O19<R2
A medium with high output was obtained using hexagonal ferrite manufactured with a composition of O/^O<1.0.

Furthermore, regardless of the ratio of ferrite and other components, other ferrites such as Sr ferrite instead of Ba ferrite, substitution elements other than Co-Tl ions, and compounds other than Na as R among other components. A similar effect was obtained.

[Effect of the invention]

Claims (1)

[Claims] General formula AO・_n(Fe_1_-_xM_x)_2O_35.
0≦n≦6.5 0.02≦x≦0.24 However, A: At least one element selected from Ba, Sr, Ca, and Pb, M: Co, Ti, In, Ni
, Cu, Zn, Nb, Zr, V, Ta, Al, Cr, S
A compound of each element forming a hexagonal ferrite represented by at least one element selected from b, Hf, Mo, W, Ir, Sn, and Mg, and as other components, R_2O (R: Li, Na, K,
at least one selected from Rb, Cs), AO and B_2O_3 have a molar ratio of 1.0<(AO+R_2O)/B_2O_3<2.00
．． The compounds R, A, and B are mixed and melted so that 0<R_2O/AO<1.0, and then rapidly cooled to become amorphous. This amorphous body is then heat-treated to form a hexagonal shape. A method for producing magnetic powder for magnetic recording media, in which crystalline ferrite is precipitated, followed by washing treatment to extract hexagonal ferrite.