JPH08268748A - Manufacture of ni-zn base ferrite - Google Patents

Abstract

PURPOSE: To manufacture a ferrite magnetic core having high sintered density and initial magnetic permeability even when the sintering time is short by using four stages consisting of a binder removal stage, a temp. rising stage, a constant temp. stage and a temp. lowering stage, for sintering the ferrite and specifying the total time of these four stages in the manufacture. CONSTITUTION: In this manufacture, the following four stages for sintering an Ni--Zn base ferrite are used: a binder removal stage in which the time required for raising the temp. from room temp. to 600 deg.C is adjusted to 3min to 5hr in order to prevent cracks from being generated; a temp. rising stage in which the time required for raising the temp. from 600 deg.C to the sintering temp. is adjusted to 18min to 5hr while preventing insufficiency of the magnetic properties and strength due to the densification and insufficient crystal growth of the ferrite from occurring; a constant temp. stage in which the time from the point that the temp. reaches the sintering temp. up to the point that lowering of the temp. is begun at is adjusted to 5min to 5hr; and a temp. lowering stage in which the time from the beginning point of the temp. lowering up to the point that the temp. is lowered to 150 deg.C at is adjusted to 24min to 3hr. At this time, the total time of these four stages is adjusted to 50min to 8hr. In this manufacture, a ferrite raw material powder which has a 4,500 to 15,000m<2> Kg BET specific surface arca and a 0.9 to 0.6μm average particle size is used, and the sintered compact contains at least two metal oxides such as oxides of Li and Mg.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ferrite used in high frequency soft magnetic parts such as consumer appliances and communication devices.

[0002]

2. Description of the Related Art Conventionally, a batch type firing furnace and a pusher type tunnel furnace have been used for firing ferrite. The batch-type firing furnace is a system in which a compact is filled into the furnace for each cycle of firing, the furnace is closed, a predetermined program is set and firing is performed, and after completion, the furnace is opened and a fired product is taken out. Therefore, it is not efficient when baking a large amount of products. On the other hand, in the pusher type tunnel furnace, the compacts are loaded on a base plate made of refractory, and one plate is intermittently inserted from the entrance side of the furnace to enter the furnace. This is a method in which a plate is sent toward the exit side, and after firing, the fired body that has come out is taken out at the exit of the furnace, and most of the industrially produced ferrite is fired in a pusher tunnel furnace.

[0003]

In recent years, demands for low cost and high quality in high frequency soft magnetic parts have been increasing, and it is desired that the ferrite cores used therefor be low cost and high quality. There is. In the production of ferrite, the firing process is a process that requires a considerable amount of time,
It is clear that shortening the firing process time leads to improved production efficiency. However, if the firing time is shortened, various characteristics of the ferrite core may be deteriorated, and the reliability of the parts may be impaired. In view of the above, the present invention provides a method for producing a Ni-Zn-based ferrite, which can obtain a ferrite core having a high sintering density and an initial permeability even with a short firing time of 50 minutes to 8 hours. The purpose is to provide.

[0004]

The present invention relates to a method for producing a Ni—Zn-based ferrite, which includes a binder removal step of increasing the temperature from room temperature to 600 ° C. for 3 minutes to 5 hours, and firing from 600 ° C. The temperature rise time to reach the temperature is 1
A temperature raising step of 8 minutes or more and 5 hours or less, a constant temperature step of 5 minutes or more and 5 hours or less after reaching the firing temperature, and a time of 150 ° C. or more after starting the temperature reduction are 24 hours. It consists of a temperature lowering process for more than 3 minutes and less than 3 hours,
In addition, the total time of the four steps is set to 50 minutes to 8 hours. Further, the BET specific surface area of the ferrite raw material powder used in the method for producing the above Ni—Zn ferrite is set to 4500 to 15000 m ² / kg.

[0005]

In the present invention, the reason for limiting the firing time of ferrite is as follows. In the binder removal step, when the temperature rise time from room temperature to 600 ° C. is less than 3 minutes, the reaction of binder removal rapidly progresses and cracks occur. 600 in the temperature raising step and the constant temperature step
If the temperature rising time from ℃ to reach the firing temperature is less than 18 minutes, or if the time from reaching the firing temperature to starting the temperature reduction is less than 5 minutes, densification and crystal growth become insufficient, Sufficient magnetic properties and strength cannot be obtained. In the temperature lowering step, if the time from the start of temperature lowering to 150 ° C. is less than 24 minutes, residual stress occurs in the product or deformation due to uneven temperature distribution occurs, and the characteristics deteriorate as in the above. The total time of the 4 steps is 8
If the time is exceeded, the improvement in production efficiency will be insufficient. Therefore, the firing time shown in the claims is limited. More preferably, the binder removal step is performed to increase the temperature from room temperature to 600 ° C. for 37 minutes or more and 1.5 hours or less, and the heating time for reaching the firing temperature from 600 ° C. is 30 minutes or more and 1 hour or less. A temperature raising step, a constant temperature step in which the time from the reaching of the firing temperature to the start of the temperature decrease is 13 minutes or more and within 1 hour, and a time from the start of the temperature decrease to 150 ° C. is 40 minutes or more and within 1.5 hours. And the total time of the four steps is 120 minutes to 5 hours. Further, the BET specific surface area of the ferrite raw material powder used in the above-mentioned ferrite manufacturing method is 4500 m ² / kg.
If it is less than the above range, sufficient magnetic properties and strength cannot be obtained with the above firing time because the reaction rate is slow. Therefore, the BET specific surface area of the ferrite raw material shown in the claims is limited. More preferably, B of the ferrite raw material powder
The ET specific surface area is set to 5000 to 7000 m ² / kg. This BET specific surface area is 5000-7000 m
The average particle size of the ferrite raw material powder of ² / kg is 0.9 to 0.6 μm as measured by the air permeation method. The ferrite raw material powder mentioned here means the ferrite raw material powder after pulverization or before firing. The ferrite to which the technique according to the present invention is applied is mainly composed of Li, Mg, and
It means a ferrite containing at least two kinds of components which become oxides of Mn, Fe, Co, Ni, Cu and Zn. In addition to the above components, B as a sub-component after firing,
Al, Si, Ca, Ti, V, Cr, Zr, Nb, M
A component which becomes an oxide of o, In, Sn, Ta, W and Bi may be included. The furnace used for firing is not particularly limited as long as firing that satisfies the conditions of the present invention is possible, but it is preferable to use, for example, a roller hearth type continuous firing furnace. In this roller hearth type continuous firing furnace, a base plate on which a molded body is loaded is placed on a plurality of refractory rollers mounted in the furnace, and the products are conveyed from an inlet to an outlet by rotating the rollers. Therefore, it does not require a solid base plate such as a pusher type tunnel furnace, and a lightweight and thin base plate is sufficient.Therefore, the temperature difference of the product during firing is small, and the product size and characteristics are remarkably high. Is stable. Also, the heating method is not particularly limited as long as firing that satisfies the conditions of the present invention is possible, and an electric heating method,
A gas combustion method or both methods may be used.

[0006]

EXAMPLES Examples of the method for firing ferrite according to the present invention will be described in detail below. First, Fe ₂ O ₃ 49mo
1%, NiO 27 mol%, CuO 6 mol% and ZnO 18 mol% equivalent oxide raw material powders were weighed, mixed for 1 hour in a vibration mill, and calcined at a maximum temperature of 800 ° C. for 2 hours using an electric furnace. After that, cool it in the furnace,
Crush with a 40-mesh sieve. After that, crushed with a medium stirring mill what added a predetermined amount of water and dispersant,
Add 2 wt% of binder (polyvinyl alcohol) to the raw material, granulate with a spray dryer, and
Using a dry compression molding machine and a die, the granules sized by a 0 mesh sieve were used, with an outer diameter of 16.8 mm, an inner diameter of 8.5 mm,
Molding pressure 1.5ton / on a ring-shaped core with a height of 5.4mm
It was molded in cm ² . This was fired using a roller hearth continuous firing furnace under the following six firing conditions. Firing condition 1 In the air, room temperature to 600 ° C for 1 minute, 600 ° C to 1
The temperature was raised to 136 ° C. in 7 minutes, held at 1136 ° C. for 2 minutes, and then lowered to 150 ° C. in 8 minutes (calcination time 18
Minutes). This is referred to as Comparative Example 1. Firing condition 2 In the air, from room temperature to 600 ° C for 3 minutes, from 600 ° C to 1
The temperature was raised to 136 ° C. in 7 minutes, held at 1136 ° C. for 2 minutes, and then lowered to 150 ° C. in 8 minutes (calcination time 20
Minutes). This is Comparative Example 2. Firing condition 3 In the air, the temperature was raised from room temperature to 600 ° C in 4.5 minutes, from 600 ° C to 1130 ° C in 10.5 minutes, held at 1130 ° C for 3 minutes, and then lowered to 150 ° C in 12 minutes. (Baking time 30 minutes). This is Comparative Example 3. Firing condition 4 In the air, room temperature to 600 ° C for 3 minutes, 600 ° C to 1
The temperature was raised to 130 ° C. in 18 minutes, held at 1130 ° C. for 5 minutes, and then lowered to 150 ° C. in 24 minutes (calcination time 5
0 minutes). This is Example 1. Firing condition 5 In the air, the temperature was raised from room temperature to 600 ° C. in 37 minutes, from 600 ° C. to 1120 ° C. in 30 minutes, held at 1120 ° C. for 13 minutes, and then lowered to 150 ° C. in 40 minutes (firing time 120 Minutes). This is Example 2. Firing condition 6 In the air, the temperature was raised from room temperature to 600 ° C. in 90 minutes, from 600 ° C. to 1120 ° C. in 60 minutes, held at 1120 ° C. for 60 minutes, and then lowered to 150 ° C. in 90 minutes (firing time 300 Minutes). This is Example 3. As a comparative example, ferrite raw materials having different BET specific surface areas were prepared,
The ring-shaped core granulated and molded in the same procedure as described above was fired under the same conditions as firing condition 5 using a roller hearth type continuous firing furnace. This is Comparative Example 4. The sintered density and the initial magnetic permeability of the fired body thus obtained were measured. The results are shown in Table 1 as Comparative Examples 1 to 4 and Examples 1 to 3, respectively. Further, FIG. 1 shows the relationship between the initial magnetic permeability and the firing time in Examples 1 to 3 and Comparative Examples 2 to 3.

[0007]

[Table 1]

Next, Fe ₂ O ₃ 49 mol% and NiO
17 mol%, CuO 6 mol% and ZnO 28
An oxide raw material powder in an amount corresponding to mol% was weighed, and a ring-shaped core was formed by the same procedure as in the above-mentioned example. This was fired under the same conditions as in the above example, and the sintered density and initial magnetic permeability of the obtained fired body were measured. The results are shown in Table 2 as Comparative Examples 5 to 8 and Examples 4 to 6, respectively. Example 4
6 and Comparative Examples 6 to 7 show the relationship between the initial magnetic permeability and the firing time.

[0009]

[Table 2]

Further, Fe ₂ O ₃ 49 mol%, NiO
15 mol%, CuO 6 mol% and ZnO 3
An oxide raw material powder in an amount equivalent to 0 mol% was weighed, and a ring-shaped core was formed by the same procedure as in the above-mentioned example. This was fired under the same conditions as in the above example, and the sintered density and initial magnetic permeability of the obtained fired body were measured. Comparative Examples 9 to 12
And Examples 7 to 9 and the results are shown in Table 3. Further, the relationship between the initial magnetic permeability and the firing time in Examples 7 to 9 and Comparative Examples 10 to 11 is shown in FIG.

[0011]

[Table 3]

From Tables 1 to 3, when the temperature rising time from room temperature to 600 ° C. is less than 3 minutes, cracks occur in the fired body,
It can be seen that the reliability of the parts is low. If the time from 600 ° C to the firing temperature is less than 18 minutes, if the time from reaching the firing temperature to starting the cooling is less than 5 minutes, or from the start of cooling to 150 ° C is less than 24 minutes In the case of, the sintered density and the initial magnetic permeability become low, and it becomes impossible to obtain high quality parts. Also, the BET specific surface area is 4
It is clear that when a ferrite raw material powder of less than 500 m ² / kg is used, the sintered density and the initial magnetic permeability become low, and high quality parts cannot be obtained. From the above results,
It is apparent that the method for producing a ferrite of the present invention can obtain a ferrite having a high initial magnetic permeability and a high sintering density in a short firing time of 50 minutes to 8 hours, improving the production efficiency and reducing the cost.

[0013]

EFFECTS OF THE INVENTION According to the present invention, a ferrite core having a high sintered density and a high initial permeability can be obtained in a short firing time of 50 minutes to 8 hours. Very advantageous for improvement.

[Brief description of drawings]

FIG. 1 is a schematic diagram of Examples 1 to 3 and Comparative Examples 2 to 3 of the present invention.
It is a figure showing the relationship of the initial magnetic permeability and baking time.

FIG. 2 shows Examples 4 to 6 and Comparative Examples 6 to 7 in the present invention.
It is a figure showing the relationship of the initial magnetic permeability and baking time.

FIG. 3 is a schematic diagram of Embodiments 7 to 9 and Comparative Examples 10 of the present invention.
It is a figure showing the relationship of the initial magnetic permeability of No. 11, and baking time.

Claims (2)

[Claims] 1. In the firing of a Ni—Zn-based ferrite, a binder removal step in which a temperature rising time from room temperature to 600 ° C. is 3 minutes or more and 5 hours or less, and a temperature rising time from 600 ° C. to the firing temperature are included. A temperature raising step of 18 minutes or more and 5 hours or less, a constant temperature step of 5 minutes or more and 5 hours or less after reaching the firing temperature, and a temperature of 150 ° C. or more after starting the temperature reduction are 24 hours. A method for producing a Ni-Zn-based ferrite, comprising a temperature lowering step of not less than 3 minutes and less than 3 hours, and a total time of the 4 steps being 50 minutes to 8 hours. 2. The method for producing a Ni—Zn ferrite according to claim 1, wherein the BET specific surface area is 4500 to 1
A method for producing a Ni-Zn-based ferrite, which comprises using a ferrite raw material powder of 5000 m ² / kg.