JP3486918B2 - Manufacturing method of ferrite core - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ferrite core used as a rotary transformer or a shield ring.

[0002]

2. Description of the Related Art Conventionally, choke coils, micro inductors, rotary transformers, shield rings, etc.
For example, it is prepared by injection molding a ferrite resin slurry composed of a polymer material and ferrite powder, degreasing and firing.

For example, in the magnetic head device for a floppy disk, the shield ring 3 magnetically shields the magnetic head element 1 and the ceramic slider material 2 sandwiching the magnetic head element 1 as shown in FIG. It is used for.

Conventionally, a metal material such as a permalloy material was used for roll punching, but with the miniaturization of the magnetic head, Mn-Zn excellent in high frequency shielding was formed.
Ferrite materials have come to be used. Along with this, it has been proposed to obtain a ferrite core by injection molding and form a shield ring.

Further, for example, the rotary transformer transmits a recording signal from the VTR main body to the rotary head,
On the contrary, in order to transmit the reproduced signal picked up by the head to the main body, the primary coil that rotates with the head and the secondary coil that is connected to the main body and does not rotate are opposed to each other with a minute gap, and are tightly coupled in a magnetic circuit. It is a thing. Then, in this rotary transformer, Ni—Zn based ferrite is used and is composed of a ferrite core obtained by injection molding.

Since the above-mentioned devices are required to have higher performance and smaller size, various studies have been made as a method for manufacturing a ferrite core used as the above-mentioned devices. ing.

[0007]

For example, the content of ferrite powder in the ferrite resin may be increased in order to increase the magnetic permeability of the above device, but the ferrite powder and the thermoplastic resin have a low affinity. Therefore, it is difficult to obtain a ferrite resin slurry in which ferrite powder is sufficiently dispersed. In addition, a ferrite resin slurry having a high ferrite powder content has poor fluidity and poor injection moldability. For example, the shield ring described above
Since the wall thickness is about 0.5 mm, the ferrite resin slurry is required to have high fluidity.

Further, when the fluidity of the ferrite resin slurry is low, defects are likely to occur in the produced product and the yield is also reduced. However, even if the amount of the binder added is simply increased in order to improve the fluidity, not only the magnetic permeability cannot be increased, but also degreasing takes time, and defects such as cracks occur during degreasing. Problems also occur.

Therefore, the present invention has been proposed in view of the above conventional circumstances, and an object thereof is to provide a method for producing a ferrite core in which defects are less likely to occur by a ferrite resin slurry having high fluidity.

[0010]

The present invention has been proposed in order to achieve the above-mentioned object, and a ferrite resin slurry is obtained by heating and kneading a ferrite powder and a binder,
In the method for producing a ferrite core, which comprises degreasing and firing the ferrite resin slurry after injection molding, the ferrite powder is Mn-Zn ferrite, the median diameter is 0.5 to 2.5 μm, and the specific surface area is 1. 2-2.
8 m ² / g and a bulk density of 0.55 to 0.70 g / c
m ³ and a ferrite resin slurry having a fluidity of 0.08 ml / sec to 0.4 ml / sec, which is composed of the Mn—Zn ferrite and a binder, is prepared, injection-molded,
By degreasing and firing, the initial permeability μ is 5500-6000.
To produce a ferrite core having

In addition, in a method for producing a ferrite core, in which ferrite powder and a binder are heated and kneaded to obtain a ferrite resin slurry, the ferrite resin slurry is injection molded, and then degreased and fired, the ferrite powder is N
It is an i-Zn ferrite and has a median diameter of 1.2 to
4.0 μm, and a specific surface area of 1.2 to 2.3 m ² / g,
And has a bulk density of 0.65 to 0.95 g / cm ³ ,
0.08 consisting of the above Ni-Zn ferrite and a binder
A ferrite resin slurry having a fluidity of ml / sec to 0.4 ml / sec is produced, injection-molded, degreased and fired to produce a ferrite core having an initial magnetic permeability μ of 2300 to 2400. .

When the ferrite powder is a Mn-Zn type ferrite and the median diameter is less than 0.5 μm, the fluidity of the ferrite resin slurry is poor,
On the other hand, when the median diameter exceeds 2.5 μm, the initial permeability of the produced ferrite core becomes low.

Similarly, the ferrite powder is Ni--Zn.
When the ferrite is ferrite, the median diameter is 1.2 μm
If it is less than the above range, the fluidity of the ferrite resin slurry is poor. On the other hand, if the median diameter exceeds 4.0 μm, the ferrite core produced has a low initial magnetic permeability.

When the ferrite powder is Mn-Zn type ferrite, the specific surface area is 1.2 m ² / g.
If it is less than this, the density of the ferrite core after firing will be small and the strength will be insufficient, and the initial permeability of the prepared ferrite core will also be low. On the other hand, if the specific surface area exceeds 2.8 m ² / g, the fluidity of the ferrite resin slurry will be poor.

The specific surface area is measured by the BET method.

Similarly, the ferrite powder is Ni--Zn.
The specific surface area of the ferrite is 1.2 m ² /
If it is less than g, the density of the ferrite core after firing will be small and the strength will be insufficient, and the initial permeability of the prepared ferrite core will also be low. On the other hand, if the specific surface area exceeds 2.3 m ² / g, the fluidity of the ferrite resin slurry will be poor.

Further, the ferrite powder is Mn-Zn.
When it is ferrite, the bulk density is 0.55g /
If it is less than cm ³ , it lacks in fluidity and conversely the bulk density is 0.7.
If it exceeds 0 g / cm ³ , the density of the ferrite core after firing will be small and the strength will be insufficient, and the initial permeability of the prepared ferrite core will also be low. In addition,
The above-mentioned bulk density is obtained by depositing powder that has been sieved with a predetermined sieve in a container having a predetermined volume without tapping and examining the weight.

Similarly, the ferrite powder is Ni--Zn.
When it is ferrite, the bulk density is 0.65g /
If it is less than cm ³ , fluidity is lacking, and conversely, the bulk density is 0.9.
If it exceeds 5 g / cm ³ , the density of the ferrite core after firing will be small and the strength will be insufficient, and the initial permeability of the prepared ferrite core will also be low.

Here, the Mn-Zn type ferrite is
For example, a material used for a shield ring, Fe
₂ O ₃ : 50 to 65 mol%, ZnO: 5 to 30 mol%,
MnO: preferably has 10 to 40 mol% having a composition, TiO ₂ further material of the composition, SnO _2, C
It is desirable to add at least one of aO and ZrO ₂ . This improves workability and magnetic characteristics. The addition amount of these may be appropriately determined in the conventional manner.

On the other hand, the Ni-Zn ferrite is a material used in, for example, a rotary transformer, and is F
It is made of e ₂ O ₃ , ZnO, NiO, CuO, etc., and the addition amount of these may be appropriately determined in the conventional manner.

The addition amount of the binder to the ferrite resin slurry is preferably 16 to 33% by volume. If the amount of the binder added is less than the above range, sufficient fluidity cannot be obtained, resulting in poor molding. On the other hand, if the amount exceeds the above range, cracks and the like tend to occur during degreasing firing.

[0022]

[Function] By properly controlling the median diameter, specific surface area and bulk density of the ferrite powder, the fluidity of the ferrite resin slurry can be improved,
Defects are unlikely to occur in the created ferrite core. Also,
It is possible to manufacture a ferrite core in which deterioration of the initial magnetic permeability μ is suppressed.

[0023]

EXAMPLES Preferred examples of the present invention will be described based on experimental results, but it goes without saying that the present invention is not limited to these examples.

Experiment 1 First, the following Mn-Zn ferrite powder and a binder were mixed and heated and kneaded to prepare a ferrite resin slurry.

Mn-Zn ferrite powder Fe ₂ O ₃ 52 mol% ZnO 20 mol% MnO 28 mol%

Binder Ethylene vinyl acetate copolymer 50% by weight PMAE (methacrylic resin) 30% by weight Stearic acid 17% by weight Paraffin wax small amount

The amount of the binder added was 27% by volume with respect to the ferrite resin slurry.

Next, the above-mentioned ferrite resin slurry was injected into the mold of the injection molding machine to form a core. Further, the injection molded body was put in a degreasing furnace to remove the binder. In addition, this degreasing treatment was performed at a temperature in the degreasing furnace of 150
~ 300 ° C for 2-10 ° C / hour, 300-600 ° C for 6
The heating was performed at 0 ° C./hour.

The degreased injection molded body was fired at 1300 ° C. for 3 hours to obtain a ferrite core.

Here, in producing the above ferrite core, the median diameter, the specific surface area, the bulk density, etc. of the Mn-Zn type ferrite powder used were changed, and the fluidity of the obtained ferrite resin slurry and the composition thereof were produced. We will investigate the change in the initial permeability of the ferrite core.

FIG. 2 shows the relationship between the median diameter of the ferrite powder and the fluidity of the ferrite resin slurry. From this, it is found that the ferrite resin slurry using a ferrite powder having a large median diameter is more excellent in fluidity. In order to obtain fluidity of 0.08 ml / sec or more, the median diameter of the ferrite powder is 0.5 μm. It turns out that it is necessary to do above.

Further, FIG. 3 shows the relationship between the median diameter of the ferrite powder and the initial magnetic permeability μ of the prepared ferrite core. From this, it is understood that the median diameter of the ferrite powder needs to be 2.5 μm or less in order to obtain a sufficient initial magnetic permeability. Therefore, it was found that the ferrite powder preferably has a median diameter of 0.5 to 2.5 μm.

Next, FIG. 4 shows the relationship between the specific surface area of the ferrite powder and the fluidity of the ferrite resin slurry. From this, it is found that the ferrite resin slurry using a ferrite powder having a large specific surface area is inferior in fluidity. ^It can be seen that the amount needs to be ² / g or less.

FIG. 5 shows the relationship between the specific surface area of the ferrite powder and the initial magnetic permeability μ of the ferrite core. From this, it is understood that when the specific surface area of the ferrite powder is smaller than 1.2 m ² / g, sufficient initial magnetic permeability cannot be obtained. Therefore, the specific surface area of the ferrite powder is 1.2 to
It was found that it is preferable to set it to 2.8 m ² / g.

Further, FIG. 6 shows the relationship between the bulk density of the ferrite powder and the fluidity of the ferrite resin slurry. From this, it is found that the ferrite resin slurry using the ferrite powder having a large bulk density has a better fluidity, and in order to obtain a fluidity of 0.08 ml / sec or more,
It is understood that the bulk density of the ferrite powder needs to be 0.55 g / cm ³ or more.

FIG. 7 shows the relationship between the bulk density of the ferrite powder and the initial magnetic permeability μ of the ferrite core. From this, it is understood that if the bulk density of the ferrite powder is larger than 0.70 g / cm ³ , the density of the ferrite core after sintering becomes low, so that sufficient initial permeability cannot be obtained. Therefore, the bulk density of the ferrite powder is 0.55 to
It has been found that it is preferable to set 0.70 g / cm ³ .

From the above results, the ferrite powder is Mn-
If it is a Zn-based ferrite, the median diameter is 0.5 to
2.5 μm and specific surface area of 1.2 to 2.8 m ² /
It was found that a ferrite core having excellent characteristics can be prepared by setting the g and the bulk density to 0.55 to 0.70 g / cm ³ .

Experiment 2 Further , the following Ni-Zn ferrite powder and a binder were mixed and kneaded by heating to prepare a ferrite resin slurry.

Ni-Zn ferrite powder Fe ₂ O ₃ 49.7 mol% ZnO 31.9 mol% NiO 9.0 mol% CuO 9.4 mol%

Binder Ethylene vinyl acetate copolymer 50% by weight PMAE (methacrylic resin) 30% by weight Stearic acid 17% by weight Paraffin wax small amount

The amount of the binder added was 27% by volume based on the ferrite resin slurry.

Next, the above-mentioned ferrite resin slurry was injected into the mold of the injection molding machine to form a core. Further, the injection molded body was put in a degreasing furnace to remove the binder. In addition, the temperature in the degreasing furnace is 150 to 300 ° C.
The temperature was raised at 10 ° C./hour and 300 to 600 ° C. at 60 ° C./hour.

The degreased injection molded article was fired at 1000 ° C. for 3 hours to obtain a ferrite core.

Here, in producing the above ferrite core, the fluidity of the ferrite resin slurry and the fluidity of the ferrite resin slurry when the median diameter, the specific surface area, the bulk density, etc. of the Ni-Zn ferrite powder used were changed. We will investigate the change in the initial permeability of the ferrite core.

FIG. 8 shows the relationship between the median diameter of the ferrite powder and the fluidity of the ferrite resin slurry. From this, it is found that the ferrite resin slurry using a ferrite powder having a large median diameter has better fluidity, and in order to obtain fluidity of 0.08 ml / sec or more, the median diameter of the ferrite powder is 1.2 μm. It turns out that it is necessary to do above.

Further, FIG. 9 shows the relationship between the median diameter of the ferrite powder and the initial magnetic permeability μ of the prepared ferrite core. From this, it is understood that the median diameter of the ferrite powder needs to be 4.0 μm or less in order to obtain a sufficient initial magnetic permeability. Therefore, it was found that the median diameter of the ferrite powder is preferably 1.2 to 4.0 μm.

Next, FIG. 10 shows the relationship between the specific surface area of the ferrite powder and the fluidity of the ferrite resin slurry. From this, it is found that the ferrite resin slurry using a ferrite powder having a large specific surface area is inferior in fluidity, and in order to obtain fluidity of 0.08 ml / sec or more,
It is understood that the specific surface area of the ferrite powder needs to be 2.3 m ² / g or less.

FIG. 11 shows the relationship between the specific surface area of the ferrite powder and the initial magnetic permeability μ of the ferrite core. From this, it is understood that when the specific surface area of the ferrite powder is smaller than 1.2 m ² / g, sufficient initial magnetic permeability cannot be obtained. Therefore, the specific surface area of the ferrite powder is 1.2 to
It has been found that it is preferable to set it to 2.3 m ² / g.

Further, FIG. 12 shows the relationship between the bulk density of the ferrite powder and the fluidity of the ferrite resin slurry.
From this, it is found that the ferrite resin slurry using a ferrite powder having a large bulk density has a better fluidity, and in order to obtain a fluidity of 0.08 ml / sec or more, the bulk density of the ferrite powder is 0.65 g. It turns out that it is necessary to make it / cm ³ or more.

FIG. 13 shows the relationship between the bulk density of the ferrite powder and the initial magnetic permeability μ of the ferrite core. From this, it is understood that if the bulk density of the ferrite powder is larger than 0.95 g / cm ³ , the density of the ferrite core after sintering will be low, and thus sufficient initial permeability cannot be obtained. Therefore, the bulk density of the ferrite powder is 0.65 to 0.
It has been found that it is preferable to use 95 g / cm ³ .

From the above results, the ferrite powder is N
If it is an i-Zn-based ferrite, the median diameter is 1.
2 to 4.0 μm and specific surface area of 1.2 to 2.3 m ²
It was found that a ferrite core having excellent characteristics can be produced by adjusting the bulk density to be 0.65 to 0.95 g / cm ³ / g.

[0052]

As is clear from the above description, when the median diameter, the specific surface area and the bulk density of the ferrite powder are properly regulated, the fluidity of the ferrite resin slurry can be improved, so that the injection It is possible to manufacture a ferrite core having excellent formability and few defects. Further, it is possible to manufacture a ferrite core in which deterioration of the initial magnetic permeability μ is suppressed.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of use of a shield ring.

FIG. 2 is a characteristic diagram showing a relationship between median diameter of Mn—Zn based ferrite powder and fluidity of ferrite resin slurry.

FIG. 3 is a characteristic diagram showing the relationship between the median diameter of Mn—Zn based ferrite powder and the initial magnetic permeability of the ferrite core.

FIG. 4 is a characteristic diagram showing the relationship between the specific surface area of Mn—Zn ferrite powder and the fluidity of the ferrite resin slurry.

FIG. 5 is a characteristic diagram showing the relationship between the specific surface area of Mn—Zn based ferrite powder and the initial magnetic permeability of the ferrite core.

FIG. 6 is a characteristic diagram showing the relationship between the bulk density of Mn—Zn ferrite powder and the fluidity of the ferrite resin slurry.

FIG. 7 is a characteristic diagram showing the relationship between the bulk density of Mn—Zn based ferrite powder and the initial magnetic permeability of the ferrite core.

FIG. 8 is a characteristic diagram showing a relationship between median diameter of Ni—Zn ferrite powder and fluidity of ferrite resin slurry.

FIG. 9 is a characteristic diagram showing the relationship between the median diameter of Ni—Zn based ferrite powder and the initial magnetic permeability of the ferrite core.

FIG. 10 is a characteristic diagram showing the relationship between the specific surface area of Ni—Zn ferrite powder and the fluidity of the ferrite resin slurry.

FIG. 11 is a characteristic diagram showing the relationship between the specific surface area of Ni—Zn based ferrite powder and the initial magnetic permeability of the ferrite core.

FIG. 12 is a characteristic diagram showing the relationship between the bulk density of Ni—Zn ferrite powder and the fluidity of the ferrite resin slurry.

FIG. 13 is a characteristic diagram showing the relationship between the bulk density of Ni—Zn ferrite powder and the initial magnetic permeability of the ferrite core.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-208257 (JP, A) JP-A-5-55065 (JP, A) JP-A-4-270166 (JP, A) JP-B 2- 3288 (JP, B2) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C04B 35/26-35/40 C04B 35/00 H01F 1/12-1/375 H01F 41/02 B28B 1/24

Claims (2)

(57) [Claims] 1. A method for producing a ferrite core, comprising heating and kneading a ferrite powder and a binder to obtain a ferrite resin slurry, injection molding the ferrite resin slurry, and then degreasing and firing the ferrite powder. Series ferrite,
The median diameter is 0.5 to 2.5 μm, and the specific surface area is 1.
2 to 2.8 m2 / g and a bulk density of 0.55 to 0.7
0 g / cm3, 0.08 comprising the Mn-Zn ferrite and a binder
Ferrite having fluidity of ml / sec to 0.4 ml / sec
After making resin slurry, injection molding, degreasing and baking
Therefore, the initial magnetic permeability μ should be 5500 to 6000.
A method for manufacturing a ferrite core, comprising: 2. A ferrite powder and a binder are kneaded by heating.
Obtain the ferrite resin slurry and
Ferrite core that is degreased and fired after injection molding of Lee
In the manufacturing method of, the ferrite powder is Ni-Zn ferrite,
The median diameter is 1.2 to 4.0 μm, and the specific surface area is 1.
2-2.3 m2 / g, and bulk density is 0.65-0.9
5 g / cm3, 0.08 comprising the above Ni-Zn ferrite and a binder
Ferrite having fluidity of ml / sec to 0.4 ml / sec
After making resin slurry, injection molding, degreasing and baking
That the initial permeability μ is 2300 to 2400.
A method for manufacturing a ferrite core, comprising: