JP2762530B2 - Manufacturing method of ferrite magnetic material - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultra-low shrinkage ferrite magnetic material obtained by binding and solidifying a highly crystalline ferrite magnetic powder with a glass material. Is used as a useful electronic component.

2. Description of the Related Art Most of the conventional methods for producing a ferrite magnetic material are mainly a powder metallurgy method, that is, a sintering method that requires steps of powder molding and high-temperature firing.

When a ferrite magnetic material is produced, the starting materials are mixed in a predetermined ratio, calcined under appropriate conditions, degassing and a certain amount of solid-phase reaction are advanced (this is called calcined powder), and then pulverized and formed. After the steps of graining and compacting, the compact is fully baked in an appropriate atmosphere at a temperature higher than the pre-baking temperature to obtain a polycrystalline ferrite sintered body having desired magnetic properties and mechanical strength. It has gained.

FIG. 3 shows a schematic diagram of the fine structure of this polycrystalline ferrite sintered body. In FIG. 3, 4 is a crystal grain, 5 is a grain boundary, 6 is a grain boundary pore, and 7 is a pore of the crystal grain 4.

The calcining temperature in the above process is set between 700 and 1000 ° C., at which the starting material of a predetermined blending ratio starts the solid-phase reaction, and the main calcining temperature for sufficient sintering is the material and composition of the calcined powder and the granules. Although it depends on the diameter and shape, it is usually a high temperature of 1000 to 1400 ° C. The firing atmosphere at this time depends on the required material,
An oxidizing atmosphere or a non-oxidizing atmosphere is selected depending on the composition.

A disadvantage of the ferrite sintering method is that sintering of the calcined powder compact in the main firing step necessarily causes a dimensional change. In other words, usually 10 to 20 after final firing
%, When it is large, it shrinks more, and deteriorates the dimensional accuracy and yield of the sintered product. Therefore, post-processing, which is mechanical processing such as cutting and polishing, is required.

The above-mentioned shrinkage in the sintering process occurs for the following reasons.
That is, a compact obtained by simply pressing the calcined powder usually has a particle size of 2
The molding density is low due to the use of powder of about 5 μm or less, that is, there are still many voids although the powders are in contact with each other, and when heated at a temperature of 700 to 1000 ° C. or more, the contact portion between the calcined powders Interdiffusion of the atoms constituting the particles occurs, and the sintering phenomenon starts. As a result, the gap between the calcined powders decreases with the progress of sintering, and when it is large,
It shrinks by over 20%.

Therefore, it is important to make the temperature rise and fall during the main firing relatively slow in order to ensure that the sintering is exactly uniform and that the molded body is not subjected to thermal shock. As a result, the main calcination step may be as long as at least half a day or more in two days.

There have been many studies to improve the disadvantages of the ferrite sintering method. Among them, regarding the problem of shrinkage of the sintered body, various methods have been studied to reduce the shrinkage as much as possible and to control the shrinkage at a constant level. However, in order to ensure the performance and characteristics of ferrite, some shrinkage is avoided. The reality is that it cannot be done. For example, JP-A-58-135133
As described in JP-A-58-135606, after mixing ferrite calcined powder and glass powder,
When firing at a temperature at which ferrite densification (sintering) progresses, the glass powder added at this time covers the periphery of the ferrite particles, thereby partially suppressing ferrite densification and reducing the shrinkage of the sintered body. Can be obtained.
However, even in this case, since the calcined powder production temperature is lower than the final firing temperature of the compact afterwards, mutual diffusion occurs between the calcined powders that are still in direct contact during the final firing, so that the compaction shrinkage phenomenon Was unavoidable and in fact shrank by a few percent.

Problems to be Solved by the Invention As described above, in the conventional ferrite sintered body, the more the sintering is performed in order to obtain the desired performance, the larger the shrinkage is, and conversely, if the shrinkage is suppressed, the performance is reduced. It is difficult to achieve both because they cannot be secured However, sintered ferrites are
It is widely used as a device material, and its performance and high dimensional accuracy are increasingly regarded as important.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art, and to provide a glass-bound ultra-low-shrinkage ferrite magnetic material having almost no shrinkage and excellent magnetic properties, and a method for manufacturing the same at a low cost. Things.

Means for Solving the Problems In order to solve the above-mentioned problems, the method for producing a ferrite magnetic material of the present invention comprises a highly crystalline ferrite magnetic powder which has been sufficiently ferritized at high temperature firing and a softening point lower than the firing temperature. The glass powder interposed between the magnetic particles is softened and melted by heat treatment at a temperature not higher than the firing temperature of the high crystalline ferrite magnetic powder while pressing and molding the formed mixture with the glass powder having the high crystalline ferrite magnetic properties. After binding the powder with a glass material, the powder is fired at a temperature not higher than the firing temperature of the ferrite magnetic powder.

Action Since the ferrite magnetic powder to be used has already been crystallized to near perfection by high-temperature sintering, sintering between the highly crystalline ferrite magnetic powders hardly occurs in the subsequent heat treatment at a lower temperature. Instead, the glass powder mixed between the high crystalline ferrite magnetic powders is simply melted to bind the high crystalline ferrite magnetic powder.

In other words, the pressure sintering method conventionally used for making a sintered body is generally expected to have the effect of promoting sintering in order to reduce the porosity (to increase the density) and lower the sintering temperature. First of all, after obtaining a high-density molded body in which the pressure between the magnetic particles is greatly reduced by applying pressure under a temperature state in which the glass powder interposed in the magnetic powder is molten, In order to heat treatment below the production temperature of the high crystalline ferrite, as a result, since the porosity in the molded body does not change much before and after the heat treatment, high dimensional accuracy close to the mold molding dimensions and magnetic properties An excellent new ferrite magnetic material can be obtained.

In addition, in the conventional hot press machine, since the sintering is performed at a high temperature of 700 ° C. or more, a metal cannot be generally used as a mold material, and a mold material such as carbon, alumina, or SiC must be used. Since the working temperature at this time is 700 ° C. or less, a metal mold material of the conventional type can be used, and the device is a simple device that is not different from an ordinary press machine.

Furthermore, the heat treatment of the molded body does not expect sinterability, and it is basically sufficient if the glass powder is melted as described above and a flow binding effect can be obtained between the high crystalline ferrite magnetic powders. It is much shorter than the firing time.
For this reason, equipment costs and electricity costs are low, and the manufacturing method is simple, so that it can be manufactured at low cost.

Further, in the case of soft ferrite, it is desired to increase the resistance because it is necessary to minimize the eddy current loss of the ferrite itself. Since the high crystalline ferrite magnetic powder is electrically insulated, there is also obtained an advantage that the resistance value increases and the high frequency characteristics are improved.

Examples Hereinafter, examples of the present invention will be described.

That is, as shown in FIG. 1, the present invention comprises a structure in which a highly crystalline ferrite magnetic powder 1 is bonded with a glass material 2 which is softened and melted at a temperature lower than the firing temperature of the highly crystalline ferrite magnetic powder 1 under pressure. It is assumed that.

Specifically, the highly crystalline ferrite magnetic powder 1 in this compact is mixed while the highly crystalline ferrite magnetic powder 1 and the glass powder are mixed well, and the granulated mixed granule is molded under pressure.
By softening and melting the glass powder mixed in between, a high-density magnetic material in which the high-crystalline ferrite magnetic powder 1 is simply bound with the glass material 2 and solidified is first prepared before firing, and then this is prepared. It refers to a ferrite magnetic material that has been heat-treated at a temperature equal to or lower than the production temperature of the high crystalline ferrite magnetic powder. In the figure, reference numeral 3 denotes pores in the highly crystalline ferrite magnetic powder 1.

The highly crystalline ferrite magnetic powder 1 used here is one which has been sufficiently ferrite-reacted by firing at a high temperature, and is usually preferably fired at 1000 ° C. or higher.

When it is desired to obtain a soft ferrite magnetic material, the smaller the coercive force H of the highly crystalline ferrite magnetic powder 1 is, the better the size of the magnetic particles is. Therefore, the packing density of the highly crystalline ferrite magnetic powder 1 is preferably small. Actually go down 10
A diameter of 0 to 200 μm is suitable. When a hard ferrite magnetic material is obtained, it is preferable to use magnetic fine particles that can be single magnetic domain particles in order to increase the coercive force H 力 of the highly crystalline ferrite magnetic powder 1 to increase the energy product.

Next, the softening temperature of the glass powder that binds the high-crystalline ferrite magnetic powder 1 may be lower than the firing temperature of the high-crystalline ferrite magnetic powder 1;
The temperature at which the magnetic powder 1 quickly penetrates into the voids is optimal. In other words, since the glass powder is pressurized in the molten state, the ferrite magnetic powder 1 is further compacted to realize a high filling state. Further, considering the application of the ferrite magnetic material according to the present invention, the lower limit is desirably 300 ° C. or higher from the viewpoint of heat resistance.

Normally, the firing start temperature of the sintered mold magnetic material produced by the powder metallurgy method is from about 700 ° C., and the practical temperature of the metal mold is limited to about 700 ° C. The glass bonding work temperature at the time of preparation must be below this temperature, the glass powder used here is 650
Those which soften at a temperature of not more than ℃ and become a liquid phase are preferred.

The amount of the glass powder added to the high crystalline ferrite magnetic powder 1 is preferably 0.3 to 30% by weight, and if it is less than 0.3%, the binding effect of the high crystalline ferrite magnetic powder 1 is so small that mechanical strength cannot be secured. On the other hand, when the amount of glass is more than 30%, the binding force becomes sufficiently strong, but the amount of non-magnetic material increases, so that the magnetic properties of the ferrite magnetic material are not significantly deteriorated.

The main purpose of the heat treatment of the mixed molded body of the highly crystalline ferrite magnetic powder 1 and the glass material 2 is to further melt and infiltrate the glass material 2, and thus the holding time of the heat treatment and the time required for raising and lowering the temperature Or less than 3 hours.

The heat treatment temperature may be basically higher than the softening temperature of the glass. However, as the temperature approaches the sintering temperature of the highly crystalline ferrite magnetic powder 1, especially when the temperature becomes 800 ° C. or more, the glass material 2
Has been obtained, and the favorable effect that the magnetic properties are excellent despite the low shrinkage property was obtained.

When the magnetic powder 1 is a magnetic oxide such as ferrite, the atmosphere for producing the ferrite magnetic material of the present invention can be either an oxidizing or non-oxidizing atmosphere.

 Hereinafter, specific examples will be described.

(Examples 1 to 7) A starting mixed granulated powder composed of 50 mol of Fe ₂ O ₃ , NiO 18 and ZnO of 32 mol% was baked at 1320 ° C. for 6 hours, and pulverized to a particle size of 50 to 100.
A μm Ni-Zn soft ferrite main firing powder was prepared. As a result of X-ray analysis of this powder, a sharp spinel structure diffraction line unique to soft ferrite was obtained, and it was confirmed that the powder was a magnetic powder having extremely high crystallinity.

The softening point (T
d) Alkali-free lead borosilicate glass powder having an average particle size of 1 μm at 370 ° C is added in 0.5, 1, 3, 5, 10, 30, 40 wt% each, mixed and granulated. Into a stellite mold at a prescribed temperature, pressurized at 3 ° C / cm ^{2 at} 420 ° C, and hot-pressed in air for 2 minutes to obtain an inner diameter of 7 mmφ and an outer diameter of 12 mmφ.
Glass-bound ring-shaped molded articles having different glass contents of mm were produced. Next, each of the molded products was placed in an electric furnace and heated at 1200 ° C. for 60 minutes in air to obtain a glass-bound ring-shaped ferrite core.

Table 1 shows the material properties of the samples of Examples 1 to 7 described above.

(Comparative Example 1) The Ni-Zn ferrite powder used in Example 1 was granulated and molded without glass powder, and a ring-shaped molded product having an inner diameter of 7 mmφ, an outer diameter of 12 mmφ, and a thickness of 3 mm was prepared in the same manner as in Example 1. did. This molded product was placed in an electric furnace for high temperature, fired in air at 1200 ° C. for one hour, and then cooled in a furnace to obtain a ZNi-Zn ferrite sintered ring core. At this time, the initial permeability of the magnetic material was a low value.

(Comparative Example 2) 5 wt% of the same alkali-free lead-based glass powder was added to the same Ni-Zn-based ferrite powder used in Example 1 and mixed and granulated, and then the inner diameter was increased at a pressure of 3 t / cm ^2. 7mmφ, outer diameter 12mm
A ring-shaped molded product with a diameter of 3 mm was created. After placing this molded product in an electric furnace and holding it at 1200 ° C in air for 1 hour,
The furnace was cooled to obtain a glass-bound ring-shaped core. FIG. 2 is a schematic diagram of the magnetic material obtained by this method.

 Table 1 shows the material properties of Comparative Examples 1 and 2.

(Example 8) 5 wt% of a non-alkali lead-based glass powder having a softening temperature of 650 ° C and an average particle diameter of 1 µm was added to the same magnetic powder used in Example 1, mixed well and granulated. A predetermined amount of mixed granulated powder is filled in a stellite mold, and the temperature is 700 ° C and the pressure is 3
t / cm ² , hot press in air for 2 minutes, inner diameter 7mm
A glass-bound ring-shaped core having a diameter of φ, an outer diameter of 12 mm and a thickness of 3 mm was prepared, and baked at 1200 ° C. for 1 hour in the same manner as in Example 1 to obtain Example 8. The properties of this sample are shown in Table 1.

When the hot press temperature was 800 ° C., the stellite mold was deformed and the sample could not be taken out.

(Examples 9 to 13) 5 wt% of the same glass powder was added to the same ferrite main firing powder used in Example 1 and mixed and granulated, and the mixed granulated powder was placed in a stellite mold. A predetermined amount was filled and hot-pressed in the air at a temperature of 420 ° C. under a pressure of 3 t / cm ² for 2 minutes to produce five glass-bound ring-shaped molded products having an inner diameter of 7 mmφ, an outer diameter of 12 mmφ, and a thickness of 3 mm. .

Place each of these molded products in an electric furnace one at a time
The glass-bound ring-shaped ferrite core was obtained by treating and heating in air at 000 ° C, 800 ° C, 600 ° C, and 450 ° C for 60 minutes.

Table 2 shows the material properties of the samples of Examples 9 to 13 described above.

(Examples 14 to 22) A starting mixed granulated powder comprising Fe ₂ O ₃ 48, NiO 13, ZnO 34, and CuO 5 mol% was baked at 1320 ° C. for 6 hours and pulverized. A Ni-Zn-Cu soft ferrite main firing powder having a diameter of 70 µm was prepared. As a result of X-ray analysis of this powder, a sharp spinel structure diffraction line unique to soft ferrite was obtained, and it was confirmed that the powder was a magnetic powder having extremely high crystallinity.

The softening point (T
d) Add 0.1,0.3,0.5,1,3,5,10,30,40wt% each of alkali-free lead borosilicate glass powder with average particle size of 1μm at 370 ℃, mix and granulate. A predetermined amount of the granulated powder is filled in a stellite mold, and the temperature is 420 ° C., the pressure is 3 ton / cm ² ,
Perform hot press in air for 2 minutes, inner diameter 7mmφ, outer diameter 1
Ring-shaped molded articles having a glass content of 2 mmφ and a thickness of 3 mm, each having a different glass content, were produced.

Each of these molded products is individually set in an electric furnace,
Heat treatment was performed in the air for 1 minute to obtain a glass-bound ring-shaped ferrite core.

Table 3 shows the material properties of the samples of Examples 14 to 22.

The Ni-Zn-Cu ferrite powder used in Example 14 was granulated and molded without a glass powder, and the inner diameter was 7 mmφ in the same manner as in Example 14.
A ring-shaped molded product with an outer diameter of 12mmφ and a thickness of 3mm was created. Each of the molded products was placed in a high-temperature electric furnace,
After firing in air for a period of time, the furnace was cooled to obtain a Ni-Zn-Cu ferrite sintered ring core.

Comparative Example 4 The same alkali-free lead-based glass powder was added to the same Ni-Zn-Cu-based ferrite powder used in Example 14 at 5 wt%, mixed and granulated, and then subjected to a pressure of 3 ton / cm ² . 7mmφ inside diameter, 12m outside diameter
A ring-shaped molded product of mφ and thickness of 3 mm was produced. The molded articles were individually placed in a high-temperature electric furnace, fired in air at 1200 ° C. for 1 hour, and then cooled in a furnace to obtain a glass-bound ring-shaped core.

 Table 3 shows the material properties of Comparative Examples 3 and 4.

In the above Examples and Comparative Examples, the initial magnetic permeability was measured according to the JIS standard (C2561). First, an insulating tape was wound around the above-mentioned ring-shaped ferrite core, and then the wire diameter was measured.
A sample was prepared by further winding an insulated copper wire of 0.26 mmφ all around. Next, this self-inductance was measured with a Maxwell bridge when the strength of the measured magnetic field was 0.8 (A / m) or less, and the initial magnetic permeability at a frequency of 1 (MHz) was calculated from this.

In addition, the saturation magnetic flux density is determined by JIS standard (C25
According to 61), the magnetic flux density at a magnetic field of 10 (Oe) was measured by the self-recording magnetometer method.

Furthermore, the shrinkage was measured by measuring the outer diameters of the ring-shaped molded product before the heat treatment and the ring-shaped ferrite core after the heat treatment, and calculating the dimensional shrinkage before and after the heat treatment. According to JIS standard (C2564), two thin wires were passed through the ring core once, and one of them was fixed. Then, the remaining one was pulled vertically at a speed of 5 mm / mm or less. The tensile load at the moment when the core was broken was measured and determined.

Example 23 A mixed granulated powder composed of 1 mol% of BaO and 6 mol% of Fe ₂ O _{3 was} mixed with 1300%
A barium ferrite hard magnetic material having an average particle diameter of 1 μm and having good crystallinity was prepared by pulverizing the material fired at 2 ° C. for 2 hours.

An alkali-free lead borosilicate glass powder having a softening point of 370 ° C. and an average particle size of 1 μm was added to the barium ferrite powder.
After mixing and granulating by adding 5 wt%, a predetermined amount of the mixed granulated powder is filled into a stellite mold, and the temperature is 420 ° C. and the pressure is 3 t / cm.
^{2. A 10} mmφ × 7 mm thick columnar compact was prepared by hot pressing in air for 2 minutes.

Next, this was placed in an electric furnace and heat-treated in air at 1200 ° C. for 30 minutes to obtain a glass-bound barium ferrite magnet. The magnet did not change much from the original molding dimensions. Table 4 shows the characteristics of the sample of Example 23.

Effect of the Invention As described above, according to the present invention, a glass-bound high-density low-shrinkage ferrite magnetic material has good dimensional accuracy, is a magnetic material having excellent magnetic properties, and can be manufactured at low cost. It can provide excellent effects as useful electronic components and materials used in various magnetic products.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of the fine structure of a ferrite magnetic material according to the present invention, FIG. 2 is a schematic diagram of the fine structure of a ferrite magnetic material formed under normal pressure by a comparative example, and FIG. It is a schematic diagram of the fine structure of a shaped ferrite magnetic material. 1 ... High crystalline ferrite magnetic powder, 2 ... Glass material,
3 ... Pore.

Claims (6)

(57) [Claims] 1. A high-crystalline ferrite magnetic powder which has been sufficiently ferritized by high-temperature sintering and a glass powder having a softening point lower than the sintering temperature are mixed and granulated. A ferrite magnetic material which is softened and melted by heat treatment at a temperature not higher than the firing temperature of the ferrite magnetic powder, binds the highly crystalline ferrite magnetic powder with a glass material, and is fired at a temperature not higher than the firing temperature of the ferrite powder. Manufacturing method. 2. The method for producing a ferrite magnetic material according to claim 1, wherein the heat treatment temperature of the mixture of the highly crystalline ferrite magnetic powder and the glass powder is 800 ° C. or higher and the firing temperature of the highly crystalline ferrite magnetic powder or lower. . 3. The method for producing a ferrite magnetic material according to claim 1, wherein a soft magnetic powder is used as the highly crystalline ferrite magnetic powder. 4. The method for producing a ferrite magnetic material according to claim 1, wherein a soft magnetic powder is used as the highly crystalline ferrite magnetic powder. 5. The method for producing a ferrite magnetic material according to claim 1, wherein the glass powder has a softening temperature of 650 ° C. or lower. 6. The method for producing a ferrite magnetic material according to claim 1, wherein the material ratio of the glass to the highly crystalline ferrite magnetic powder is 0.3 to 30 wt%.