JPH03263303A - Manufacture of magnetic powder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain magnetic recording medium having high recording density and large reproducing output, by containing a specified amount of pottasium oxide in noncrystalline solid wherein composition for forming specified hexagonal system ferrite and glass forming constituent are mixed. CONSTITUTION:After composition for forming hexagonal system ferrite powder shown by a formula AO.n{(Fe1-xMx)2O3} and glass forming constituent are mixed, heated, and melted, these are rapidly cooled and noncrystallized. Pottasium oxide of 1-5mol% is contained. In the formula, A is one kind of element selected out of Ba, Sr, Ca and pb, M is one kind of element selected out of Co, Ti, In, Ni, Cu, Zn, Nb, Zr, V, Ta, Al, Cr, Sb, Hf, Mo, W, Ir, Sn and Mg, 5.0<=n<=6.5 and 0.02<=x<=0.24. When the substitution amount (x) of a substituting element is smaller than 0.02, the coercive force becomes too large. When (x) exceeds 0.24, the coercive force becomes too small. When the ratio of pottasium oxide exceeds 5mol%, noncrystalline solid becomes apt to absorb water content and carbon dioxide gas, and stable manufacturing is made difficult.

Description

Detailed Description of the Invention [Purpose of the Invention (Field of Industrial Application) The present invention relates to a method for producing magnetic powder mainly used in the construction of high-density perpendicular recording media, and in particular has a narrow particle size distribution and
The present invention relates to a method for producing magnetic powder for magnetic recording media with excellent dispersibility.

(Prior art) Hexagonal ferrite, such as Ba ferrite, whose axis of easy magnetization is easily oriented in the perpendicular direction, has been used as a high-density perpendicular recording medium suitable for a perpendicular recording method that uses magnetization perpendicular to the substrate. The one used is known. That is, Ba
It is known that a magnetic paint is prepared by mixing fine ferrite powder with a resin binder, a solvent, and various additives, and this magnetic paint is coated on a non-magnetic substrate.

By the way, in general, in Ba ferrite, the coercive force is reduced to a value suitable for magnetic recording by replacing some of the constituent atoms of the ferrite with a specific metal element. Furthermore, compared to other magnetic powders, Ba ferrite has a drawback of low saturation magnetization that affects the medium output, so the above characteristics are improved by adding ZnO or Nb2o5.

As a method for manufacturing hexagonal ferrite magnetic powder for use in magnetic recording media, for example, a basic component of hexagonal ferrite, a substitute component for reducing coercive force, and a component for improving characteristics such as improving saturation magnetization are used. The additive components and glass-forming components are mixed and heated to melt, the melt is rapidly cooled to become amorphous (vitrified), and the resulting amorphous body is heat treated to form hexagonal ferrite. After precipitating crystal particles, they are crushed, and the resulting fine powder is washed with dilute acid such as phosphoric acid or acetic acid to dissolve and remove the glass-forming components, thereby producing the desired hexagonal ferrite magnetism. The glass crystallization method is used to separate and extract the powder.

(Problems to be Solved by the Invention) However, in such a conventional manufacturing method, the obtained magnetic powder has a coarse outer particle diameter and a wide particle size distribution. For this reason, in the process of turning the magnetic powder into a paint, it is difficult to disperse it in a resin binder, and the S/N ratio (ratio of output signal to noise level) of the constructed magnetic recording medium is low. In other words, although it is expected to be used for high-density magnetic recording media, it has the disadvantage that it cannot fully perform the required functions.

The present invention was made in order to solve these problems, and it uses a hexagonal crystal system with a narrow particle size distribution and good dispersibility, which makes it possible to obtain a magnetic recording medium with high recording density and large reproduction output. The purpose of the present invention is to provide a method for producing ferrite magnetic powder.

[Structure of the Invention] (Means for Solving the Problems) The magnetic powder for magnetic recording media of the present invention has the general formula: AO-n f (Fe M )20B+x x (where A is Ba, Sr, Ca, and Pb). At least one element selected from among these, M is Co.

Tis In, Ni, C11% ZnSNb, Zrs
V%Ta5At, Cr5Sb, Hf, MO, W% I
At least one element selected from rsSn and Mg, 5,0≦n≦6.5.0.02≦x≦0.24)
A step of mixing a composition that forms a hexagonal ferrite powder represented by and other glass-forming components and heating and melting the mixture, followed by rapid cooling to make it amorphous; A step of precipitating hexagonal ferrite by subjecting the amorphous body to a heat treatment at a required temperature, and a step of pulverizing the precipitated crystals and then performing a treatment to dissolve and remove glass-forming components to extract hexagonal ferrite powder. A method for producing a magnetic powder for a magnetic recording medium, comprising: potassium oxide being contained in the amorphous body at a ratio of 1 to 5 mo1%.

Here, element M is a substitution component for controlling the coercive force of the hexagonal ferrite to be formed. However, if the substitution mx of this substitution element is less than 0.02, the coercive force will become too large, whereas if X exceeds 0.24, the coercive force will become too small, which is not preferable.

In addition, the 20 components of potassium oxide contained in the amorphous body together with the hexagonal ferrite-forming components play a role in narrowing the particle size distribution of the obtained magnetic powder, and the ratio of these components to the total other components is If it exceeds 5111o1%, the amorphous body will easily absorb moisture and carbon dioxide, making it difficult to stably produce hexagonal ferrite. Furthermore, even if the amorphous body is prevented from absorbing moisture or carbon dioxide gas, the melting point of the amorphous body decreases, making it difficult to sufficiently substitute the required elements and crystallize without causing sintering. It is.

Therefore, the content ratio of potassium oxide is 5m.

It is necessary that it be 1% or less.

On the other hand, if the ratio of potassium oxide is less than 1 mo1%, the particle size ratio/1i cannot be effectively narrowed, which is not preferable.

(Function) In the method for producing magnetic powder for magnetic recording media of the present invention, a composition mainly consisting of a component that forms hexagonal ferrite is melted by heating and then rapidly cooled to become amorphous. 20 in potassium oxide and 1-5I in the amorphous body
Although the reason is not clear, the type and composition ratio of the raw material components were selected so that the IIO content was 1%, but it was possible to easily and reproduce magnetic powder with a narrow particle size distribution and excellent magnetic properties and dispersibility. You can get it easily.

In other words, the method of the present invention makes it possible to provide a magnetic powder suitable for constructing a magnetic recording medium having high recording density and large reproduction output.

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

Examples 1 to 3 First, the basic component of ferrite Fe2O3, the substituted component CoO for reducing coercive force, the additive components ZnO and Nb2O5 for improving saturation magnetization, and the glass forming component Bad
The raw materials of Bengara, cobalt oxide, barium carbonate, oxalic acid, and potassium oxide were weighed out so that the composition ratio (mo1%) of SB203 and potassium oxide was as shown in Table 1.

Table 1 Next, after thoroughly mixing the weighed raw materials, they were placed in a platinum crucible and heated to 1350°C using a high-frequency heater.
It was heated and melted at a temperature of ℃. Thereafter, the melt was poured onto water-cooled twin rolls with a rotational speed of 500 rpm and a pressure of 5 ton/cIIY to be rapidly cooled to obtain a flaky amorphous material with a thickness of 50 μm.

Each of the amorphous bodies obtained above was heated at a temperature of 800°C for 5
After heat treatment for a period of time to precipitate Ba ferrite crystals, the obtained crystallized product was pulverized, and then this crystal powder was put into an acetic acid solution (10%), and the agglomerates were decomposed by ultrasonic waves for 12 hours. At the same time, the glass components were melted and removed.

Thereafter, washing was repeated using hot water of 80° C. or higher to completely remove glass-forming components, and then dehydration and drying were performed to obtain three types of hexagonal ferrite powders.

Further, as a comparative example, each raw material component was weighed out so as to have the composition ratio shown in Table 1, and hexagonal ferrite powder was manufactured in the same manner as in the example.

Regarding the magnetic powders obtained as above, average particle diameter D (nm), coercive force Hc (Oe), saturation magnetization a g
(emu/g) and specific surface area 5s (nf/g) were measured, and the results were as shown in Table 2. (The following is a blank space) Table 2 Further, the particle size distribution of the magnetic powders obtained in Example 1, Example 3, and Comparative Example is shown in FIG. In FIG. 1, curve a shows the case of Example 1, curve S shows the case of Example 3, and curve C shows the case of Comparative Example.

Note that for the coercive force He and saturation magnetization σg, vS
The specific surface area Ss was measured using a BET measuring device. Further, the average particle size was measured using a transmission electron microscope photograph.

Next, 100 g of each of the hexagonal ferrite magnetic powders obtained in the above Examples and Comparative Examples was weighed and mixed in a mixed solvent of methyl ethyl ketone and toluene (1:1).
After suspending the suspension in 200 g, 3 g of lecithin was added as a dispersant, and the mixture was dispersed using a sand grinder (ball mill) for 4 hours.

Next, polyurethane resin N- is added to this as a binder.
After adding 50 g of a 35% solution of 3022 in methyl acetate and further dispersing for 2 hours, the glass beads were filtered off to obtain a magnetic paint.

After that, the magnetic paint obtained above was coated with a thickness of 25 μm.
The tape was coated onto a polyester film using a roll coater, dried at 100°C in a tunnel type drying oven, and then calendered and slit using conventional methods to obtain a tape having a magnetic layer with a film thickness of 10 μm. A magnetic recording medium of the shape was obtained.

Next, the results of measuring the medium squareness ratio, coating gloss, and S/N ratio (dB) of the obtained magnetic recording medium are shown below.

In Table 3 and FIG. 2, the medium squareness ratio is a value measured by VSM, and the coating film glossiness is a value measured by JIS Z8741 r Glossiness Measuring Method. In addition, the S/N ratio (dB) of the medium is the S/N ratio of a magnetic recording medium obtained from a magnetic powder (comparative example) manufactured without adding 20 to potassium oxide, based on the standard (O
dB).

As is clear from the above examples, potassium oxide
The magnetic powder of the example prepared by the glass crystallization method so as to be contained in an appropriate proportion in the amorphous body has a small average particle size and a narrow and sharp particle size distribution.

2. Therefore, when the magnetic powder according to the present invention is made into a paint, it exhibits good dispersibility in a resin binder, and the constructed magnetic recording medium also has a good media squareness ratio, coating gloss,
It maintains and exhibits excellent characteristics such as the S/N ratio of the medium.

[Effects of the Invention] As is clear from the above description, according to the production method of the present invention, magnetic powder with a narrow particle size distribution and good dispersibility when made into a paint can be obtained with good reproducibility. By using the obtained magnetic powder, a magnetic recording medium with high recording density and reproduction output can be manufactured.

[Brief explanation of drawings]

Figure 1 is a curve diagram comparing the particle size distribution of magnetic powders produced by the method of the present invention and the conventional method, and Figure 2 is a curve diagram showing a comparison of the particle size distribution of magnetic powders produced by the method of the present invention and the conventional method. FIG. 2 is a characteristic diagram showing a comparison of S/N ratios of magnetic recording media. 3 JP-A-3-263303 (5)

Claims (1)

[Claims] General formula, AO・n{(Fe_1_−_xM_x)_2O_3}(
However, A is at least one element selected from Ba, Sr, Ca, and Pb, and M is Co, Ti, In, and Ni.
, Cu, Zn, Nb, Zr, V, Ta, Al, Cr, S
b, at least one element selected from Hf, Mo, W, Ir, Sn and Mg, 5.0≦n≦6.5, 0
．． 02≦x≦0.24) A step in which a composition that forms hexagonal ferrite expressed by the formula 0.2≦x≦0.24 is mixed with a glass-forming component, heated and melted, and then rapidly cooled to become amorphous. a step of precipitating hexagonal ferrite by subjecting the formed amorphous body to a heat treatment at a predetermined temperature; and a step of pulverizing the precipitated crystals and then dissolving and removing glass-forming components to obtain hexagonal ferrite powder. A method for producing a magnetic powder for a magnetic recording medium, comprising a step of extracting potassium oxide in the amorphous body in a proportion of 1 to 5 mol%. Production method.