JPH04284604A - Manufacture of hexagonal-system ferrite for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain a hexagonal-system ferrite whose particle-size distribution is narrow and whose crystallinity is good by a method wherein a compound by individual elements forming the hexagonal-system ferrite expressed by a specific structural formula, SiO2 and a compound which can become a specific compound are mixed and their mixture is heated and melted. CONSTITUTION:A compound by individual elements forming a hexagonal-system ferrite expressed by the formula, a glass formation component, a compound which can become SiO2 as a glass modification component and a compound which can become AO (where A represents one out of Ba, Sr, Ca and Pb) are mixed; their mixture is heated and melted; after that, it is quenched and made amorphous. (In the formula, 0.8<=n<=2.0, 0.55<=x<=2.7, 0.0<=y<2.0, 0.0<=a<=1.0, A represents at least one out of Ba, Sr, Ca and Pb, M1 represents at least one kind out of Co, Ni, Cu, Zr, Mn and Mg, and M2 represents at least one out of Ti, Nb, Sn, Zr, V, Al, Cr, Mo, Ge and W.) Then, this amorphous substance is heat-treated and the ferrite is precipitated and extracted.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hexagonal ferrite mainly used in the construction of high-density magnetic recording media.

0003

[Prior Art] For example, a coated magnetic recording medium has a base made of polyethylene terephthalate film, etc.
It is composed of magnetic powder formed on the base surface and a magnetic layer mainly composed of binder resin. Conventional magnetic powders used in the construction of such magnetic recording media include γ-Fe2O3, Co-coated γ-Fe2O
3. A magnetic recording method was adopted that utilized acicular magnetic powder such as CrO2 or metal Fe and utilized magnetization in the longitudinal direction in the plane.

However, in a magnetic recording medium that utilizes magnetization in the in-plane longitudinal direction, when attempting to improve recording and reproduction in a high frequency range, the demagnetizing field within the recording medium increases, making it difficult to improve the recording density that much. The problem is that I can't.

On the other hand, in order to significantly improve the magnetic recording density, a perpendicular magnetic recording system has been proposed that utilizes magnetization in a direction perpendicular to the base of a magnetic recording medium. In other words, this perpendicular magnetic recording method is suitable for high-density recording because it does not cause the problem of demagnetizing fields within the recording medium even in a high frequency range.

As a recording medium suitable for the above-mentioned perpendicular magnetic recording system, one in which a Co--Cr alloy or the like is deposited and formed on a substrate surface by a vacuum evaporation method or a sputtering method is known. However, this type of magnetic recording medium has problems in terms of environmental stability, running durability, productivity, etc.

[0007] Furthermore, as a magnetic recording medium free from such problems, a high-density perpendicular recording medium suitable for a perpendicular recording method that uses magnetization in a direction perpendicular to the surface of the substrate is used, in which the axis of easy magnetization is easily oriented in the perpendicular direction. Hexagonal ferrite, for example M
type BaFe12O19, W type BaMe2 Fe16
It is known to contain O27 (Me is a substitution metal element), M-type ferrite and spinel ferrite at the same time, or to use hexagonal ferrite in which some of these atoms are replaced with other elements. That is, it is known that a magnetic paint is prepared by mixing the hexagonal ferrite powder with a binder resin, a solvent, and various additives, and this magnetic paint is applied onto a nonmagnetic substrate.

By the way, as a method for manufacturing such hexagonal ferrite for magnetic recording media, for example,
The basic components of hexagonal ferrite, substituent components for reducing coercive force, additive components for improving properties such as improving saturation magnetization, and glass forming components/glass modifying components are mixed and melted by heating, and this melt is rapidly melted. Cool to become amorphous (vitrified)
Then, the obtained amorphous body is heat-treated to precipitate hexagonal ferrite crystal particles, which are then crushed and the resulting fine powder is washed with dilute acid such as phosphoric acid or acetic acid. A glass crystallization method is used in which hexagonal ferrite is separated and extracted by dissolving and removing glass-forming components.

[0009]

[Problems to be Solved by the Invention] However, in the conventional glass crystallization method, AO (A is at least one element selected from Ba, Sr, Ca, and Pb) can be used as a glass forming component/glass modifying component. Compound and B
A compound that can become 2 O3 is used. However,
In the amorphous body obtained from the melt of these raw material mixture components, hexagonal ferrite crystals begin to precipitate at a temperature of about 630°C, but in order to obtain hexagonal ferrite with good crystallinity, it is necessary to It is desirable to make the heat treatment temperature of the crystalloids as high as possible; for example, if the temperature is set at about 850°C or higher, the particles will not be suitable for high-density magnetic recording, but instead will have large particle sizes. This causes problems such as the generation of multi-domain particles.

The present invention has been made to solve these problems, and its object is to provide a method that can consistently produce hexagonal ferrite having a narrow particle size distribution and good crystallinity. [Structure of the invention]

[0011]

[Means for Solving the Problems] A method for manufacturing a hexagonal ferrite for magnetic recording according to the present invention has a general formula: AO・n(
Fe12-x-yM1 x M2 y O18-a)(
However, 0.8≦n≦2.0, 0.55≦x≦2.7
,0.0≦y<2.0 ,0.0≦a≦1.0
, A is at least one element selected from Ba, Sr, Ca and Pb, M1 is Co, Ni, Cu, Z
At least one element selected from n, Mn and Mg, M2 is Ti, Nb, Sn, Zr, V, Al, C
At least one selected from r, Mo, Ge and W
Compounds of each element forming hexagonal ferrite shown as seed elements), compounds that can become SiO2 as a glass forming component/glass modifying component, and AO (A is Ba, S
at least one selected from r, Ca, and Pb)
After mixing and heating and melting a compound that can become It is characterized by extracting crystalline ferrite.

[0012] Furthermore, in the above method, the composition ratio of the glass-forming component and the glass-modifying component is selected and set to 0.8 <AO/SiO2 <2.5.

[0013] If n, x, y, and a are out of the above range, the coercive force of the hexagonal ferrite formed will be 200
-2000 Oe, and it becomes impossible to hold the recording signal or recording becomes difficult. Further, the ratio of the glass forming component/glass modifying component is not necessarily limited, but as mentioned above, 0.8 <AO/Si
When O2 is selected and set outside the range of <2.5, it tends to be difficult to extract hexagonal ferrite from the heat-treated material, and phases other than hexagonal ferrite tend to be generated. Furthermore, the sum of the amounts of the basic component of the hexagonal ferrite and the substituted component for coercive force control is preferably in the range of 30 to 50 mol%. In other words, if it is less than 30 mol%, the particle size tends to become too large, and if it exceeds 50 mol%, not only does the melting temperature become high, but it also tends to be difficult to extract hexagonal ferrite after heat treatment. It is from.

In the present invention, the basic components of the hexagonal ferrite are at least one selected from BaO, SrO, CaO and PbO and Fe2O3, and
Substitution components for coercive force control include CoO, NiO, and Cu.
O, ZnO, MgO, TiO2, Nb2O5, S
nO2, ZrO2, V2O5, CrO2, M
It is at least one selected from oO2, MoO, Al2O3, GeO2 and WO2. moreover,
Glass forming components and glass modification components include BaO, SrO,
at least one selected from CaO and PbO, and S
iO2 is used. For each of these components, other forms of compounds such as carbonate compounds may be used.

The manufacturing method according to the present invention is generally carried out as follows. That is, after the raw materials selected as described above are sufficiently mixed and melted by heating at a temperature of, for example, about 1,350 to 1,600° C., the melt is dropped between, for example, twin rolls and rapidly cooled to form an amorphous material. Next, this amorphous body is heated to about 800 to 1050°C, preferably 900°C.
After precipitating hexagonal ferrite by heat treatment at a temperature of ℃ or higher, the glass component is removed with acid and water after pulverization, and the precipitated hexagonal ferrite is extracted and dried to form the desired material. Hexagonal ferrite with good crystallinity is obtained.

[0016]

[Function] In the method for producing hexagonal ferrite for magnetic recording according to the present invention, by using a compound that can become SiO2 and a compound that can become AO as glass-forming components and glass-modifying components, a melt with good uniformity can be obtained. Hexagonal ferrite is not only easily obtained, but also has fine grain size, narrow particle size distribution, and large plate-like ratio, and has good crystallinity suitable for magnetic recording, and can be obtained with good reproducibility.

[0017]

[Examples] Examples of the present invention will be described below.

Each raw material composition was weighed so that the sum of the basic component of the hexagonal ferrite and the substituted component for coercive force control was 37.5 mol %. In addition, Co and T
Let i be a replacement component and its replacement amount x = y = 0.77,
n=1.0, a=0.0, and AO=BaO
And so.

In addition, the shape of the precipitated hexagonal ferrite was calculated by measuring 400 particles on a transmission electron micrograph, and the amount of CoO in the acid washing waste liquid was measured by ICP emission spectrometry to compare the crystallinity. Examined. Furthermore, the magnetic properties were measured by applying a maximum magnetic field of 10 KOe using a vibrating sample magnetometer.

Example 1 In the preparation of the above raw material composition, BaO/SiO2 =
1.0 and the raw material compositions selected and prepared were respectively placed in a platinum crucible and melted at 1500°C. Each of the melts was dropped onto rapidly rotating twin rollers and rapidly cooled by rolling to obtain an amorphous body. The amorphous body thus obtained was heated to 900°C.
Hexagonal Ba ferrite was precipitated by heat treatment under conditions of holding for 5 hours, and then crushed, followed by acid washing with a 20% acetic acid solution and water washing to extract hexagonal Ba ferrite, which was then dried. After treatment, hexagonal Ba ferrite powder was obtained.

When the magnetic properties of the hexagonal Ba ferrite obtained above were measured, the coercive force was 910 Oe, the saturation magnetization was 56 emu/g, the squareness ratio was 0.50, the average grain size was 48 nm, and the specific surface area was 40 m2. /g. Further, the amount of CoO in the acid washing waste liquid was 8 ppm.

Example 2 In the preparation of the above raw material composition, BaO/SiO2 =
2.0 and the selected raw material compositions were placed in a platinum crucible and melted at 1500°C. Each of the melts was dropped onto rapidly rotating twin rollers and rapidly cooled by rolling to obtain an amorphous body. The amorphous body thus obtained was heated to 900°C.
Hexagonal Ba ferrite was precipitated by heat treatment under conditions of holding for 5 hours, and then crushed, followed by acid washing with a 20% acetic acid solution and water washing to extract hexagonal Ba ferrite, which was then dried. After treatment, hexagonal Ba ferrite powder was obtained.

When the magnetic properties of the hexagonal Ba ferrite obtained above were measured, the coercive force was 1100 Oe,
Saturation magnetization 55 emu/g, squareness ratio 0.50,
The specific surface area was 46 m2/g. Further, the amount of CoO in the acid washing waste liquid was 10 ppm.

Comparative Example 1 In the preparation of the above raw material composition, BaO/B2 O3
= 1.14 and the raw material compositions selected and prepared were each placed in a platinum crucible and melted at 1500°C. Each of the melts was dropped onto rapidly rotating twin rollers and rapidly cooled by rolling to obtain an amorphous body. The amorphous body thus obtained was 760
Hexagonal Ba ferrite was precipitated by heat treatment at ℃ for 5 hours, then crushed and washed with 20% acetic acid solution and water to extract hexagonal Ba ferrite. A hexagonal Ba ferrite powder was obtained by drying.

When the magnetic properties of the hexagonal Ba ferrite obtained above were measured, the coercive force was 1070 Oe,
Saturation magnetization 53.5 emu/g, squareness ratio 0.47
The average particle size was 48 nm, and the specific surface area was 40 m2/g. In addition, the amount of CoO in the acid washing waste liquid was 38 pp.
It was m.

Comparative Example 2 In the preparation of the above raw material composition, BaO/SiO2 =
0.5 and the selected raw material compositions were placed in a platinum crucible and melted at 1500°C. Each of the melts was dropped onto rapidly rotating twin rollers and rapidly cooled by rolling to obtain an amorphous body. The amorphous body thus obtained was heated to 900°C.
Hexagonal Ba ferrite was precipitated by heat treatment under conditions of holding for 5 hours, which was then crushed and further acid washed with a 20% acetic acid solution and water washed sequentially to extract the hexagonal Ba ferrite. Diffraction revealed that crystallized glass remained.

Comparative Example 3 In the preparation of the above raw material composition, BaO/SiO2 =
3.0 and the selected raw material compositions were placed in a platinum crucible and melted at 1500°C. Each of the melts was dropped onto rapidly rotating twin rollers and rapidly cooled by rolling to obtain an amorphous body. The amorphous material thus obtained was heat treated at 1050° C. for 5 hours to precipitate hexagonal ferrite, and then ground, followed by acid washing with a 20% acetic acid solution.
The hexagonal Ba ferrite was extracted by successive water washings, but X-ray diffraction revealed that Fe3O4 was produced. As can be seen from the above Examples and Comparative Examples, when the amorphous material is heat-treated at a low temperature, Co
The amount of O is also large. This suggests that CoO as a substituted component is not sufficiently incorporated into the hexagonal Ba ferrite, resulting in poor crystallinity. This can be easily inferred from the fact that the saturation magnetization and squareness ratio are smaller in Comparative Example 1 than in Example 1.

Note that the method for manufacturing hexagonal ferrite for magnetic recording according to the present invention is not limited to the above-mentioned example; for example, when the sum of the amounts of the basic component and substituted component of the hexagonal ferrite is 37.5 In cases other than mol%, Ba
Similar trends and results were observed when other ferrites such as Sr ferrite were used instead of ferrite, or when the substitution element was other than Co or Ti.

[0029]

[Effects of the Invention] As is clear from the above explanation, in producing hexagonal ferrite by the glass crystallization method,
According to the production method of the present invention, in which a compound capable of forming SiO2 and a compound capable of forming AO are used as glass-forming components and glass-modifying components, it is possible to increase the heat treatment temperature of the amorphous material, resulting in good crystallinity. It precipitates hexagonal ferrite, which has a narrow particle size distribution and a large plate-like ratio, and exhibits good dispersibility when made into a paint. That is, according to the manufacturing method of the present invention, hexagonal ferrite suitable for high-density magnetic recording can be obtained with good reproducibility.

Claims (2)

[Claims] [Claim 1] General formula, AO・n(Fe12-x-yM1 x M2 y O1
8-a) (However, 0.8≦n≦2.0, 0.55≦
x≦2.7, 0.0≦y<2.0, 0.0≦a
≦1.0, A is at least one element selected from Ba, Sr, Ca and Pb, M1 is Co, Ni
, Cu, Zn, Mn and Mg; M2 is Ti, Nb, Sn, Zr, V
, Al, Cr, Mo, Ge, and W) and SiO2 as a glass-forming component and a glass-modifying component. The obtained compound and AO(
A is a compound that can be at least one selected from Ba, Sr, Ca, and Pb), a step of mixing and melting by heating, and then rapid cooling to make it amorphous; A hexagonal ferrite for magnetic recording, comprising the steps of: precipitating hexagonal ferrite by subjecting the amorphous body to heat treatment at a predetermined temperature; and extracting the precipitated hexagonal ferrite. manufacturing method. 2. According to claim 1, the glass-forming component/
A method for producing hexagonal ferrite for magnetic recording, in which a molar ratio of a compound as a glass modification component in terms of oxide is selected and set to 0.8 <AO/SiO2 <2.5.