JPH04332102A - Manufacture of magnetic powder for magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing hexagonal system ferrite magnetic powder with less temperature dependency of a magnet-keeping force and an improved environmental stability. CONSTITUTION:A magnetic power (A) where a temperature dependency of a magnet-keeping force is reduced is manufactured from a starting raw material containing BaO, B2O3, Fe2O3, and at least Sn at a substitution constituent by the glass crystallization method. The starting raw material containing substitution constituents excluding BaO, B2O3, Fe2O3, and Sn are blended so that a ratio of BaO to B2O3 is at an excessive BaO side than that for depositing barium ferrite stoichiometrically and then a magnetic powder (B), where an environmental stability of a magnet-keeping force is increased by the glass crystallization method, is manufactured. By mixing these magnetic powders (A) (25-75wt.%) and (B) (75-25wt.%) and then performing wet microgrinding of them, a hexagonal system ferrite magnetic powder with less temperature dependency of magnet- keeping force and a superb environmental stability can be manufactured.

Description

[Detailed description of the invention]

0001

[Purpose of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing magnetic powder suitable for magnetic recording media, and more particularly to a method for producing magnetic powder with excellent coercive force stability by a glass crystallization method.

0003

[Prior Art] Magnetic recording media are used for audio, video,
It is used as a recording medium for recording a large amount of information in a wide range of fields such as computers. In recent years, with the widespread use of floppy disks used in word processors and personal computers, the stability of coercive force, the main characteristic of magnetic materials, has become increasingly important under the various environmental conditions in which these magnetic recording media are used. .

Conventionally, hexagonal ferrite magnetic powder such as barium ferrite has been widely used as magnetic powder for such magnetic recording media. One of the manufacturing methods is a glass crystallization method. This glass crystallization method heats and melts a raw material mixture containing a hexagonal ferrite basic component, a substitution component for reducing coercive force, and a glass forming component, and rapidly cools the resulting molten material to form a non-forming material. The process consists of producing a crystalline body, then subjecting the amorphous body to heat treatment to precipitate hexagonal ferrite, and then extracting this.

[0005] In this glass crystallization method, a combination of BaO and B2 O3, for example, is used as a glass-forming component. Determined based on the composition diagram. The figure shows the three components (Fe2 O3, BaO, B2 O3) during barium ferrite precipitation.
A line representing the stoichiometric ratio (mol %) of is shown.

The hexagonal ferrite magnetic powder produced by the glass crystallization method described above has an average particle size of 50 to 70 nm.
They are plate-shaped particles with a plate-like ratio (particle diameter/particle thickness) of about 3 to 5 and which are very likely to aggregate. Hexagonal ferrites such as barium ferrite and strontium ferrite are made by replacing a part of Fe atoms, which are the constituent elements of uniaxial hexagonal ferrite crystals, with Nb, a pentavalent metal, and carbon, for example.
o, those substituted with divalent metals such as Zn, Ni, Cu, Mg, etc., and further 0.05 to 0.5 per chemical formula.
It is preferable that the Sn atoms of a tetravalent metal be substituted, and the total substitution amount of these elements will increase the coercive force by 500 to 500.
A quantity in the range of 3000 Oe is desirable. The composition of such a hexagonal ferrite substitute is represented by the following general formula, for example.

[0007] Ma O・n (Fe1-x Mb x )
2 O3 (wherein, Ma is Ba, Sr, Ca, P
Mb represents any one element of Co, Zn,
Represents at least two elements selected from the group such as Ni, Cu, Mg, Mn, In, Ti, Sn, and Nb. n
represents a number from 5.4 to 6.0. ) In the case of barium ferrite, it is known that its coercive force (Hc) has a positive variation of about 6 Oe/°C with respect to temperature change. In the following text, a large amount of change in coercive force (Hc) due to a change in environmental temperature will be expressed as a large temperature dependence of coercive force (Hc). On the other hand, it is also known that when stored for a long period of time in a hot and humid environment, the coercive force (Hc) shows a positive change over time even if there is no change in the environmental temperature. Hereinafter, a large amount of change over time in coercive force (Hc) due to long-term storage will be expressed as low environmental stability.

[0008] In such hexagonal ferrite magnetic powder, the temperature dependence of coercive force (Hc) can be reduced by introducing Sn as one of the substituting elements to partially replace Fe in the ferrite component. The coercive force (H
It has been previously found that the amount of change in c) is approximately halved to 3 Oe/°C by this substitution.

On the other hand, with regard to environmental stability, by increasing both the particle size and the plate ratio of the ferrite magnetic powder,
It has been found that the amount of change in coercive force over time can be reduced. Furthermore, in order to increase the plate-like ratio of the ferrite magnetic powder obtained when producing hexagonal ferrite magnetic powder by the glass crystallization method, it is necessary to combine the glass components BaO and B.
It is known that the composition ratio with 2 O3 can be changed to a relatively excess BaO side with respect to the stoichiometric line, as shown by the arrow in FIG.

0010

[Problems to be Solved by the Invention] By the way, when some of the Fe in the ferrite component is replaced with Sn in order to reduce the temperature dependence of the coercive force (Hc) of hexagonal ferrite magnetic powder, the particles The shape tended to become fine particles. It is known that in order to prevent such atomization, the composition of BaO and B2 O3, which are glass components, should be relatively substituted to the side where B2 O3 is in excess of the stoichiometric line shown in Fig. 4. ing. Therefore, in the past, coercive force (H
In order to improve the temperature dependence of c), part of the Fe in the ferrite component is replaced with Sn, and the composition ratio of BaO and B2 O3, which are glass components, is changed to B2 O3.
The aim was to increase the particle size by relatively replacing it on the excess side to prevent micronization.

However, in this way, BaO and B2
Relative substitution of the composition with O3 to the B2 O3 excess side is a means for improving the environmental stability of the coercive force (Hc) of the hexagonal ferrite powder.
This conflicts with relative substitution to the aO excess side. That is, when introducing Sn and relative substitution to the excess B2 O3 side for the purpose of improving the temperature dependence of coercive force (Hc), the environmental stability of coercive force (Hc) is impaired. From these facts, it will be understood that it is difficult to obtain magnetic powder with improved temperature dependence of coercive force and environmental stability by simply modifying the raw material composition.

Therefore, the present invention has been made to solve the problems of the conventional glass crystallization method, and it is possible to reduce the temperature dependence of coercive force (Hc) without simply changing the raw material composition. The object of the present invention is to provide a method for producing hexagonal ferrite magnetic powder having high stability and excellent dispersibility.

[0013]

[Structure of the invention]

[0014]

[Means for Solving the Problems] The present invention provides a method for producing hexagonal ferrite magnetic powder, comprising (A) BaO,
A magnetic powder produced by a glass crystallization method from a starting material containing B2O3, Fe2O3, and at least Sn as a substituent component and whose temperature dependence of coercive force is reduced;
(B) A starting material containing BaO, B2O3, Fe2O3, and substituted components other than Sn is combined with BaO and B2
Blending so that the ratio with O3 is on the excess BaO side than the ratio for stoichiometrically precipitating barium ferrite,
A magnetic powder produced by a glass crystallization method and having increased environmental stability of coercive force is mixed in a ratio of 25 to 75% by weight of the magnetic powder (A) and 75 to 25% by weight of the magnetic powder (B). , characterized by wet pulverization.

In the present invention, when both magnetic powders (A) and (B) are mixed, if the mixing ratio of magnetic powder (A) exceeds 75% by weight, the effect of improving the temperature dependence of coercive force becomes large. However, this is not preferable because the effect of improving environmental stability becomes insufficient. On the other hand, when the mixing ratio of the magnetic powder (B) exceeds 75% by weight, although the environmental stability of coercive force is improved, the effect of improving temperature dependence becomes insufficient, which is not preferable. Therefore, when the mixing ratio of the two types of magnetic powders is within the range of the ratio of the present invention as described above, the effect of improving both the temperature dependence of the coercive force and the environmental stability is sufficiently increased.

[0016]

[Operation] In the method for producing magnetic powder for magnetic recording media of the present invention configured as described above, Fe in the ferrite component is
Magnetic powder (A) in which the temperature dependence of coercive force (Hc) is reduced is produced by a glass crystallization method from a raw material mixture in which part of is replaced with Sn. On the other hand, a magnetic powder (B) with an increased plate-like ratio was produced by a glass crystallization method using a raw material mixture in which the composition ratio of glass components BaO and B2 O3 was relatively changed to the BaO-excess side. do. By increasing the plate ratio, the environmental stability of the coercive force (Hc) of the magnetic powder (B) is improved.

In this way, magnetic powder (A) and magnetic powder (B)
After separately manufacturing the magnetic powders (A) and (A), the magnetic powders (A) and (
A magnetic powder can be obtained that exhibits each of the characteristics of B) at the same time. Therefore, an excellent hexagonal ferrite magnetic powder with low temperature dependence of coercive force (Hc) and high environmental stability can be obtained.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to a specific example in which it is applied to a hexagonal ferrite, such as a magnetoplumbite barium ferrite.

Examples 1 to 3 First, for the production of magnetic powder (A), BaCO3, Fe
2 O3 , TiO2 , Co3 O4 , H3 BO
3 and SnO2 were weighed and mixed in predetermined amounts so as to have the formulation shown in Table 1 below. Similarly, for the production of magnetic powder (B), BaCO3, F
e2O3, TiO2, Co3O4, and H
Similarly, a predetermined amount of 3BO3 was weighed and mixed so as to have the composition shown in the following table.

[0020]

[Table 1]

The component composition of the magnetic powder (B) is as shown by the arrow in FIG. 4, as shown by the arrow in FIG.
It is relatively substituted on the O-excess side (or on the B2 O3-deficient side).

Using the mixtures prepared as described above as raw materials, glass crystallization was performed using the methods shown below to produce magnetic powders (A) and magnetic powders (B). First, each mixture was placed in a platinum crucible and heated to about 1350° C. by high-frequency dielectric heating to homogeneously melt the raw materials. Thereafter, the obtained melt was rapidly cooled by rolling using water-cooled high-speed rotating twin rolls to form amorphous flakes with a thickness of 40 to 50 μm. Then, the obtained amorphous flakes were uniformly sieved (10 mesh passes), and then heat treated to solidify the flakes. Heat treatment conditions: 800℃
The method involves heating at a constant temperature increase of 50°C/hr up to 800°C for 6 hours. Then, the amorphous flakes solidified by heat treatment are crushed into 100 to 300 μm using a dry crusher such as a Braun crusher.
Magnetic powder (A) and magnetic powder (
B) was obtained. Note that the steps up to this point were carried out separately for each of the two mixed compositions.

Next, Mixtures 1 to 3, in which the two types of magnetic powders (A) and (B) obtained as described above were uniformly mixed at various mixing ratios, were mixed by wet pulverization using a ball mill. Pulverized products 1 to 3 were obtained. The grinding conditions were 15 rpm, 1
It was 0 hours. Each of the obtained mixed pulverized products was subjected to acid treatment using a 10% acetic acid solution, and then washed with water repeatedly until the pH reached 5.5 or higher. Then, this was dried to obtain magnetic powder Examples 1 to 3 obtained by the method of the present invention.

Comparative Examples 1 and 2 In addition, for comparison with the conventional method, magnetic powders were prepared by using magnetic powder (B) and magnetic powder (A) alone.
The magnetic powder thus obtained was designated as Comparative Examples 1 and 2 of magnetic powder obtained by the conventional method.

Table 2 below shows the mixing ratio of magnetic powders (A) and (B) in each example and comparative example.

[0026]

[Table 2]

In order to evaluate the barium ferrite magnetic powders of these Examples and Comparative Examples, magnetic recording medium samples were prepared using these magnetic powders (AB) in the following manner, and the coercive force (Hc) of each medium was evaluated. ) temperature changes and changes over time were measured. Note that the sample number of the magnetic powder corresponds to the sample number of the magnetic recording medium prototyped using the magnetic powder.

To prototype a magnetic recording medium, first, 100 g of magnetic powder was suspended in 200 g of a mixed solvent of methyl ethyl ketone and toluene (1:1), and 3 g of lecithin was added to this and dispersed for 4 hours using a sand grinder. Ta. Next, 50 g of a 35% solution of polyurethane resin in methyl acetate was added, and after further dispersion for 2 hours, the glass beads were filtered off to obtain a magnetic paint dispersion solution. Next, this dispersion solution was applied onto a 25 μm thick polyester film using a roll coater method, and then dried in a drying tunnel oven at 100° C. to obtain a magnetic recording medium sample having a magnetic recording layer of 10 μm thick. , Examples 1 to 3, and Comparative Examples 1 and 2 were manufactured. Note that the coercive force (Hc) of each medium sample thus obtained was 700 Oe.

Next, the following measurements were performed to evaluate the temperature dependence and environmental changes of these media. First, in order to evaluate the temperature dependence of coercive force (Hc), the coercive force (Hc) of each medium at each temperature was measured using a sample vibrating magnetometer equipped with a precision warm air supply device. Then, the amount of change in coercive force (ΔHc) per 1° C. was calculated from the measurement results, and the values were compared.

As is clear from the measurement results shown in FIG.
) was used alone, the effect of improving temperature dependence was sufficiently observed.

On the other hand, in order to evaluate the environmental stability of coercive force (Hc), each medium sample was placed and stored in a high temperature and humid tank at 60°C and 90%, and the coercive force (Hc) was measured after 18 days of storage.
) was measured. As is clear from the measurement results shown in Figure 2 below, the amount of change in coercive force (Hc) of the magnetic recording media of Examples 1, 2, and 3 of the present invention after 18 days was
20 Oe or less, and a sufficient effect of improving environmental stability was observed compared to Comparative Example 2 in which magnetic powder (A) was used alone.

Furthermore, Example 2 (magnetic powder (A) 50% by weight
, magnetic powder (B) 50% by weight), and the medium of Example 3 (magnetic powder (A) 75% by weight, magnetic powder (B) 25% by weight) were stored under the same environmental conditions as in the above measurements. , coercive force at the start of storage, after 6 days, and after 30 days (
We investigated changes in Hc) over time. The following FIG. 3 shows the change over time in the coercive force (Hc) of the two media obtained through this measurement. As is clear from FIG. 3, Examples 2 and 3
The media exhibited stable coercive force (Hc) during storage.

[0033]

[Effects of the Invention] As explained above, according to the present invention, magnetic powder with improved temperature dependence of coercive force (Hc) and magnetic powder with improved environmental stability are separately manufactured by glass crystallization method. After that, the two are mixed in a predetermined ratio and pulverized, making it possible to produce hexagonal ferrite magnetic powder with low temperature dependence of coercive force (Hc), excellent environmental stability, and excellent dispersibility. .

[Brief explanation of drawings]

[Fig. 1] A diagram showing the relationship between the mixing ratio of magnetic powders (A) and (B) and the coercive force temperature change amount ΔHc of a magnetic recording medium.

[
Figure 2 is a diagram showing the relationship between the mixing ratio of magnetic powders (A) and (B) and the amount of change in coercive force of a magnetic recording medium in a high temperature and humidity environment.

FIG. 3 is a diagram showing the change in coercive force of the magnetic recording media of Examples 2 and 3 over time in a high temperature and humid environment.

[Figure 4]
Composition diagram of barium ferrite precipitation by glass crystallization method

Claims (1)

[Claims] Claim 1: (A) BaO, B2 O3, Fe2
O3, and a magnetic powder produced by a glass crystallization method from a starting material containing at least Sn as a substituent component and having reduced temperature dependence of coercive force, and (B) BaO, B2O.
3, Fe2O3, and a starting material containing substituted components excluding Sn were prepared so that the ratio of BaO and B2O3 was lower than the ratio at which barium ferrite was stoichiometrically precipitated.
The above magnetic powder (A) is blended in an amount of 25 to 75% by weight, and the above magnetic powder (B) is 75 to 75% by weight.
A method for producing magnetic powder for magnetic recording media, which comprises mixing at a ratio of 25% by weight and wet pulverizing.