JP3363017B2 - Ni-based ferrite sintered body - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ferrite sintered body used for a transformer such as a switching power supply and a liquid crystal backlight.

[0002]

2. Description of the Related Art Switching power supplies and liquid crystal backlights have been widely used in consumer equipment, office automation equipment, and industrial equipment, and are currently being made smaller, thinner, and lighter. Conventionally, a Mn-based ferrite core has been used for the transformer used for the switching power supply, the liquid crystal backlight, and the like.

[0003]

The Mn-based ferrite core has a large saturation magnetic flux density and permeability, and a loss (core loss) of about 10 kW / m ³ (50 kHz, 50 mT).
It has been used for transformers such as switching power supplies and liquid crystal backlights. However, the specific resistance is relatively low, about 10 Ω · m, and leakage current occurs when the coil is wound directly on the core. For this reason,
When a Mn-based ferrite core is used for a transformer such as a switching power supply or a liquid crystal backlight, the core is covered with a bobbin or treated with an insulating coating or the like before winding, which increases the manufacturing cost. There was a problem that miniaturization was difficult. On the other hand, the Ni-based ferrite core generally has a very high specific resistance of about 10 ⁶ Ω · m and can be wound directly on the core, but the loss (core loss) is 60 kW / m ³ ( 50kHz, 50m
Since it is as large as T), the core easily heats up and is not suitable for a transformer such as a switching power supply. In view of the above, it is an object of the present invention to provide a ferrite material having a high specific resistance, a small loss (core loss), and a ferrite material that can be used for a transformer such as a switching power supply or a liquid crystal backlight. And

[0004]

The present invention is a Ni-based ferrite sintered body containing Fe ₂ O ₃ of 48.0 to 50.0 m.
Ni system characterized in that the content of Ca in the sintered body is 350 ppm or less and the minimum value of the loss (core loss) at 20 to 140 ° C. is 30 kW / m ³ or less (50 kHz, 50 mT) in ol%. It is a ferrite sintered body. Further, the present invention is a Ni-based ferrite sintered body having an average crystal grain size of 3 to 30 μm, and the number of crystal grains exceeding twice the average crystal grain size is 10% or less of the entire crystal grains. The present _{invention, Fe 2 O 3 48.0~50.0mol%,} Ni
O 14.0 to 24.0 mol%, ZnO 28.0
A Ni-Zn ferrite sintered body having a composition of 36.0 mol% or a Ni-Cu-Zn ferrite sintered body having a composition in which 12.0 mol% or less of NiO is replaced with CuO.

In the present invention, a research was conducted on a Ni-based ferrite material which can be used for a transformer such as a switching power supply and a liquid crystal backlight. Fe ₂ O ₃ 48.0-5
The content of Ca in the sintered body is 350 p at 0.0 mol%
Loss at 20 to 140 ° C (core loss) below pm
Was less than 30 kW / m ³ (50 kHz, 50 mT). Further, it was found that the loss is further reduced when the content of Ca in the sintered body is more preferably 6 to 250 ppm. Further, the content of ZnO is 28.0 to 36.0.
When it is mol%, the temperature at which the minimum value of core loss is obtained is 20 to
It can be controlled in the range of 140 ° C. According to the invention, Fe ₂
O ₃ 48.0~50.0mol%, NiO 14.0
˜24.0 mol%, ZnO 28.0 to 36.0 mo
a material having a main composition of 1%, or Ni
It is desirable that the material has a main composition in which 12.0 mol% or less of O is replaced with CuO. Further Fe ₂ O ₃ 4
9.0-50.0 mol%, NiO 15.0-24.
It is desirable that the material has a main composition composed of 0 mol% and ZnO 28.0 to 36.0 mol%, or that the material has a main composition in which 3.0 to 12.0 mol% of NiO is replaced with CuO. . The Ni-based ferrite according to the present invention has an average crystal grain size of 3 to 30 μm.
It is desirable that the number of crystal grains is m, the number of crystal grains that exceeds twice the average crystal grain size is 10% or less of the entire crystal grains, and the crystal grain size is a predetermined size and uniform. A more preferable average crystal grain size is 4 to 20 μm. In addition, the number of crystal grains that exceeds twice the average crystal grain size is 5% of the total crystal grains.
The following is more preferable. The crystal grain size is observed at a predetermined magnification by SEM after mirror-polishing the cross section of the sintered body, acid etching or heat treatment. Then, a square region in which the number of crystal grains is 50 or more is defined, the area of each crystal in the region is measured, the diameter is calculated in circle from the area, and this is taken as the crystal grain size of each crystal. . The average in that region is defined as the average crystal grain size. Therefore, the number of crystal grains having a crystal grain size exceeding twice the average crystal grain size in the region is 10% or less of the number of crystal grains in the region.
It should be noted that those in which crystals overlap the area line of the above area are not included.

The reasons for limiting the scope of the claims are as follows. When the loss (core loss) exceeds 30 kW / m ³ , the practicality becomes low. Preferably 25 kW / m
^{It is 3} or less, and more preferably 20 kW / m ³ or less. The effect of the present invention is exhibited when the content of Ca in the sintered body is 350 ppm or less. The effect of Ca is to prevent crystal swelling, which improves crystal uniformity,
It is thought that core loss will decrease. When the content of Ca exceeds 350 ppm, the sinterability decreases and the core loss increases. When Fe ₂ O ₃ is less than 48.0 mol%, core loss becomes large, and 50.0 mol
If it exceeds%, the specific resistance tends to be low, and the insulating property, which is a characteristic of Ni, is impaired, which is unsuitable. ZnO is 28.0m
If it is less than ol%, the core loss becomes large, and also 3
If it exceeds 6.0 mol%, the temperature at which the minimum value of core loss is obtained becomes room temperature or lower, and the loss does not become low in the temperature range actually used. The temperature at which the minimum value of core loss is obtained is 20 to 20.
140 ° C is suitable. When CuO exceeds 12 mol%, core loss increases. If the crystal grain size is less than 3 μm, the core loss becomes large, and if it exceeds 30 μm, the crystal grows abnormally and the core loss becomes large. Further, when the number of crystal grains that exceeds twice the average crystal grain size exceeds 10% of the total crystal grains, the core loss increases.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the ferrite material according to the present invention will be described in detail below. Example 1 A predetermined amount of raw material powders of Fe ₂ O ₃ , NiO, ZnO, and CuO were weighed so that the Ca content was variously changed, and a predetermined amount of ion-exchanged water was added to the raw material powder, which was then mixed with a ball mill. Mix for hours and use an electric furnace at maximum temperature of 850 ° C.
After calcination for 5 hours, this is furnace cooled and crushed with a 40 mesh sieve. After that, a material to which a predetermined amount of ion-exchanged water has been added is pulverized by a ball mill for 6 hours, and the pulverized slurry raw material is dried and pulverized. Add binder (polyvinyl alcohol) to this and granulate.
Using a dry compression molding machine and a mold, the granules sized with a mesh sieve are molded into a ring-shaped core with an outer diameter of 16.8 mm, an inner diameter of 8.5 mm and a height of 5.4 mm at a molding pressure of 147 MPa. Was fired in the air at 1100 ° C. for 1.5 hours.
After measuring the component composition and the firing density of each obtained sample,
The loss (core loss) was measured in the temperature range of 20 to 140 ° C. under the measurement conditions of a frequency of 50 kHz and a magnetic flux density of 50 mT. Also, the crystal structure of the sintered body (crystal grain size, composition distribution)
Was observed. Also, the composition of ingredients changes during the process,
Since it is slightly different from the weighed composition, it is listed in Table 1 as the final composition. The relationship between the Ca content, the core loss, and the average crystal grain size is shown in FIG.

[0008]

[Table 1]

As shown in Table 1 and FIG. 1, C in the sintered body
It was possible to obtain a Ni-based ferrite sintered body in which the content of a was 350 ppm or less and the minimum core loss at 20 to 140 ° C. was 30 kW / m ³ or less. Further, FIG. 2 shows frequency characteristics of core loss of sample 2 in Table 1 and the conventional material. From FIG. 2, the core loss of the product of the present invention has a frequency of 25 kHz to 1 MH.
In a wide frequency range of z, about 1 / compared to conventional products
It has been reduced to 3. Further, it can be seen that the core loss of the product of the present invention is excellent under each condition.

[0010]

According to the present invention, in Ni-Zn ferrite and Ni-Cu-Zn ferrite, a very low loss ferrite sintered body having a core loss of 30 kW / m ³ or less can be obtained, and moreover, a Ni-based ferrite sintered body can be obtained. A ferrite sintered body having a high specific resistance of ferrite is obtained, which is useful for a transformer such as a switching power supply and a liquid crystal backlight, and it is very useful for downsizing the transformer and reducing the manufacturing cost.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of Ca, core loss, and crystal grain size in an example according to the present invention.

FIG. 2 is a diagram showing a comparison of frequency characteristics of core loss between an example according to the present invention and a conventional example.

Claims (4)

(57) [Claims] 1. A Ni-based ferrite sintered body comprising Fe
₂ O ₃ is 48.0 to 50.0 mol% and Ca in the sintered body is
Content of 350 ppm or less, the minimum value of core loss at 20 to 140 ° C. is 30 kW / m ³ or less (5
0 kHz, 50 mT). 2. The average crystal grain size according to claim 1,
A Ni-based ferrite sintered body having a size of 30 μm, and the number of crystal grains exceeding twice the average crystal grain size is 10% or less of the entire crystal grains. 3. The Fe ₂ O ₃ 48.0 according to claim 1.
~ 50.0 mol%, NiO 14.0-24.0 mo
A Ni-based ferrite sintered body having a composition of 1% and 28.0 to 36.0 mol% ZnO. 4. The method according to claim 3, wherein 12 mo of NiO is used.
A Ni-based ferrite sintered body having a composition in which 1% or less is replaced by CuO.