JPH07272917A - Low-loss oxide soft magnetic material - Google Patents

Abstract

PURPOSE:To propose an Ni-Zn ferrite which shows high-resistance and low-loss property in a frequency band of 1MHz or over and a high magnetic filed of 0.1Oe. CONSTITUTION:This is a low-loss oxide soft magnetic material which has fundamental ingredient composition being constituted by adding Mo oxides of 100-10000ppm in terms of MoO3 further to a substance which includes Fe2O3 by 48-51mol%, ZnO by over 25-34mol%, and NiO by 15-27mol% and the rest of which consists of inevitable impurities, or a substance which includes Fezes by 48-51mol%, ZnO by over 25-34mol%, CuO by under 3mol%, and NiO by 15-27mol% and the rest of which consists of inevitable impurities, and the sintered density is 83-97% of the theoretical.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low loss oxide soft magnetic material, particularly a switching power supply main transformer, a backlight transformer, a power supply choke coil, a TV flyback transformer, etc., which are used under high frequency and high magnetic field. The present invention relates to high-resistance, low-loss Ni-Zn ferrites that are suitable for use in the field of.

[0002]

2. Description of the Related Art In general, switching power supplies are 100 k to 20
It is usually used at conversion frequencies in the 0kHz band. Conventionally, low-loss Mn-Zn ferrite has been used as the transformer material used in such switching power supplies.However, as electronic devices have become smaller and lighter in recent years, in recent years, oxides that exhibit low-loss characteristics even at higher frequency bands have been used. The demand for soft magnetic materials is increasing.

The conventional Mn-Z used for the above applications
n Even if it is ferrite, the basic composition and trace additives,
1MHz by devising the crushing method and firing method
A material having a low loss and a desired temperature characteristic was obtained up to a frequency band of a certain degree. However, with the conventional Mn-Zn ferrite, it was difficult to stably obtain a material exhibiting high resistance and low loss characteristics even in a high frequency band of 1 MHz or higher.

On the other hand, recently, Ni-Zn type ferrite has been attracting attention as an alternative to the above Mn-Zn ferrite. This is because this Ni-Zn ferrite has excellent magnetic characteristics and high resistance even in a high frequency band exceeding 1 MHz. However, this Ni-Zn
The system ferrite has a drawback that it is difficult to use a low-loss material because of large hysteresis loss.

Moreover, this Ni-Zn ferrite is not a low-loss Ni-Zn ferrite developed to be used under a high magnetic field such as a power transformer or a backlight transformer. For example, JP-A-5-3112 and JP-A-5-21
The Mo-containing Ni-Zn ferrites proposed in JP 222 do not include the temperature characteristics of the permeability μ _{i and} the permeability μ _i under a low magnetic field.
It focuses on the control of _i . That is, these conventional techniques were not proposals for a low-loss Ni-Zn system ferrite that is preferably used under a high magnetic field in a high frequency band.

[0006]

As described above,
Conventional Mn-Zn ferrite does not show high resistance and low loss characteristics in the high frequency band, while conventional Ni-Zn ferrite has excellent magnetic characteristics and high resistance in the high frequency band. In addition to being difficult to use as a low loss material,
There was a problem that high magnetic loss was caused when high frequency and high magnetic field were applied.

A main object of the present invention is to solve the above problems of the prior art, that is, to obtain a low loss oxide soft magnetic material exhibiting excellent magnetic characteristics under high frequency and high magnetic field. A specific object of the present invention is to propose a Ni-Zn system ferrite that exhibits high resistance and low loss characteristics even in a high frequency band of 1 MHz or higher and a high magnetic field of 0.1 Oe or higher. Still another specific object of the present invention is to have a specific resistance ≧ 10 ⁶ Ωcm, a core loss value ≦ 120 mW / cm ³ (1
The purpose is to propose a Ni-Zn series ferrite that can simultaneously achieve MHz, 20 mT, 100 ° C).

[0008]

As a result of intensive studies to achieve the above object, the inventors have developed the present invention having the following contents. That is, the present invention _{is, (1) Fe 2 O 3} : 48~51 mol%, ZnO: 25 ultra ~34 mol%, NiO:
It has a basic component composition consisting of 15 to 27 mol% and the balance unavoidable impurities, and further contains 100 to 10,000 ppm of Mo oxide in terms of MoO ₃ , and its sintered density is the theoretical density. It is a low loss oxide soft magnetic material characterized by being 83 to 97% of.

(2) The composition of each component of the low loss oxide soft magnetic material described in (1) above is more preferably in the following range. That is, for Fe ₂ O ₃ , 48.5 to 50.0 mol%, Zn
27-31 mol% for O, 19-24.5 m for NiO
ol%, Mo oxide addition amount is 1000-60 in terms of MoO ₃
00 ppm, and more preferably 2000 to 5000 ppm in terms of MoO ₃ .

(3) Fe ₂ O ₃ : 48-51 mol%, ZnO: over 25-34
mol%, CuO: less than 3 mol%, NiO: those consisting of 15 to 27 mol%, and the balance inevitable impurities, further, calculated as MoO ₃
A low loss oxide soft magnetic material characterized by having a basic composition of 100 to 10,000 ppm of Mo oxide and having a sintered density of 83 to 97% of the theoretical density. .

(4) The composition of each component of the low loss oxide soft magnetic material described in (3) above is more preferably in the following range. That is, for Fe ₂ O ₃ , 48.5 to 50.0 mol%, Zn
27 to 31 mol% for O, 2 mol% or less for CuO, 19 to 24.5 mol% for NiO, and the addition amount of Mo oxide is 1000 to 6000 ppm in terms of MoO ₃ , more preferably 2000 in terms of MoO _3. It is recommended to set it to ~ 5000ppm.

(5) Each of the oxide soft magnetic materials described in (1) to (4) above has a specific resistance of 10 ⁶ Ωcm or more, 1 MHz, 20 mT, 1
It is a low-loss oxide soft magnetic material having a core loss value of 120 mW / cm ³ or less at 00 ° C.

(6) Each of the oxide soft magnetic materials described in (1) to (5) above has a use in a high frequency band of 1 MHz or more,
It is a low-loss magnetic material compatible with high frequencies, such as main transformers for switching power supplies, backlight transformers, choke coils for power supplies, and flyback transformers for TVs used in high magnetic fields of 1 Oe or more.

[0014]

Here, Fe ₂ O ₃ constituting the basic component of the soft oxide magnetic material according to the present invention has a crystal magnetic anisotropy constant k ₁ that controls the hysteresis loss and an electrical resistance that controls the eddy current loss. It plays a role of adjusting, the content is 48-51 mol
%, And more preferably 48.5 to 50.0 mol%. The reason for being limited to this value is that if the Fe ₂ O ₃ content is less than 48 mol%, the hysteresis loss at 100 ° C cannot be reduced, while if it exceeds 51 mol%, the electrical resistance becomes sharp. This is because the eddy current loss increases due to the decrease, and the core cannot be wound directly.

ZnO, which is a basic component of the soft oxide magnetic material according to the present invention, plays a role of adjusting the above-mentioned k ₁ and Curie temperature T _c , and the content thereof is more than 25 to 34 mol.
%, More preferably 27 to 31 mol%. The reason for being limited to this value is that when the ZnO content is 25 mol% or less, the residual loss and the hysteresis loss cannot be reduced, while when it exceeds 34 mol%, the Curie point is lowered, and therefore, it is 100%. This is because the residual loss at ° C significantly increases.

NiO, which is a basic component of the soft oxide magnetic material according to the present invention, plays a role of adjusting k ₁ and T _c , and its content is 15 to 27 mol%, more preferably 19 mol%.
~ 24.5 mol%. The reason for being limited to this value is Ni
This is because if the O 2 content is less than 15 mol%, the Curie point is lowered and the residual loss at 100 ° C. is significantly increased. On the other hand, if it exceeds 27 mol%, the minimum core loss temperature is 100 ° C.
This is because it becomes higher and it becomes impossible to obtain low loss at 100 ° C.

In the present invention, in order to reduce the firing temperature (accelerate the sintering) and reduce the raw material cost, a part of the NiO component may be replaced with the CuO component. The replacement amount is k
_{In order} to keep the fluctuation range of ₁ and T _c within the allowable range and to bring out the effect of adding MoO ₃ sufficiently, it is set to less than 3 mol%, more preferably 2 mol% or less. The reason why the substitution amount of NiO component by CuO component is less than 3 mol% is because
This is because the substitution of CuO greatly changes the magnetocrystalline anisotropy constant and magnetostriction constant in the crystal grains. Further, as described later, the grain boundary stress relaxation effect due to the addition of MoO ₃ cannot be obtained, and the high frequency magnetic loss is significantly deteriorated.

In the present invention, in order to obtain a low loss oxide soft magnetic material, in addition to the basic component of the above Ni-Zn ferrite, Mo oxide is added as a subcomponent. As for this Mo oxide, 100 to 10,000 ppm in terms of MoO ₃ is added, more preferably 1000 to 6000 ppm in terms of MoO ₃ , and more preferably 2000 to 5000 ppm in terms of MoO ₃ . The reason for this is that if the Mo oxide content exceeds 10,000 ppm, abnormal grain growth of crystal grains is likely to occur, and the loss reduction effect cannot be obtained. On the other hand, if it is less than 100 ppm, a remarkable addition effect cannot be obtained.

Next, the inventors further conducted experiments on the significance of adding the above Mo oxide in order to obtain a low loss material. That is, the relationship between the core loss of Ni-Zn ferrite and the sintering density ρ _S , the grain size of the polycrystalline grains, and the grain boundary stress was also examined depending on whether MoO _{3 was} added or not. The basic composition of the Ni-Zn ferrite used in this experiment is Fe ₂ O ₃ :
NiO: ZnO = 49.5: 20.5: 30 mol%. According to this experimental result, the relationship between the core loss and the sintered density ρ _S is shown in FIG.
As shown in Fig. ₅ , in Ni-Zn ferrite without addition of MoO3, the core loss is improved up to about 97% by increasing the effective magnetic material occupancy rate as ρ _S increases. But 35
For Ni-Zn ferrites with 00ppm MoO ₃ , ρ _S
It has been found that the core loss is not necessarily improved even when the value becomes higher. Also, regarding the dependency of the polycrystalline grain size, the same tendency as the relationship between the core loss and the sintered density ρ _S was observed. Furthermore, when the residual stress of the above Ni-Zn system ferrite was evaluated by measuring the three-point bending strength, the compressive residual stress at the same ρ _S was further reduced by the NiO-Zn system ferrite containing MoO _3. The results suggesting Also, SEM observation of the fracture surface shows that intra-grain fracture occurs with the additive-free material,
It is found that grain boundary destruction occurs when O ₃ is added.

From the above experimental facts, the inventors have made the following judgment on the process of reducing the loss by adding MoO ₃ . For example, as a mechanism for improving core loss, by adding MoO ₃ having a boiling point in the firing temperature range of the oxide soft magnetic material, a part of MoO ₃ is evaporated from the grain boundaries during firing,
The compressive stress remaining at the grain boundaries is relaxed, and as a result, hysteresis loss and residual loss are reduced. Because Mo
O ₃ is a low-boiling oxide (boiling point as a simple substance; 1260 ° C.),
This is because sublimation from some grain boundaries in the firing temperature range of the soft oxide magnetic material alleviates the grain boundary stress and suppresses magnetic loss deterioration due to compressive stress remaining at the grain boundaries. This means that after firing at 1200 ℃ for about 3 hours,
It is also clear from the result of elemental analysis that the residual rate of MoO _{3 in} the core is 60 to 90%. In this way, the core loss is improved and the loss is reduced. In addition,
If a large amount of MoO ₃ and a component that lowers the sintering temperature of Ni-Zn ferrites such as CuO, Bi ₂ O ₃ and V ₂ O ₅ exist together with MoO ₃ , the core of MoO ₃ after firing The residual rate is
It became 90 to 100%, and it was found that the grain boundary stress relaxation effect was not obtained and conversely the core loss improvement effect was limited.

Next, in the present invention, in order to more effectively bring out the above-described loss improving effect by adding MoO ₃ ,
The sintered density ρ _S of the magnetic material is 83 to 97% of the theoretical density, more preferably 85 to 95%, and further preferably 88 to 93. The reason for being limited to this value is that when the sintering density ρ _S is less than 83%, the core loss cannot be reduced because the effective occupation ratio of the magnetic material is low, while the density is more than 97%. Then, since the residual compressive stress at the grain boundary becomes high, the core loss cannot be reduced.

According to the oxide soft magnetic material of the present invention having the above-described structure, it is possible to obtain a Ni-Zn ferrite exhibiting high resistance and low loss characteristics even under application of high frequency and high magnetic field. More specifically, the specific resistance ≧ 10 ⁶ Ωcm,
It is possible to obtain a Ni-Zn ferrite that can simultaneously achieve a core loss value ≤ 120 mW / cm ³ (1 MHz, 20 mT, 100 ° C).
Here, the reason for setting the core loss value measurement conditions to 1 MHz, 20 mT, and 100 ° C. is that the main transformer for the switching power supply, which is the application of the present invention, is a typical use condition at high frequencies.
Therefore, the oxide soft magnetic material of the present invention exhibits high resistance and low loss characteristics even under the application of high frequency and high magnetic field.
It is suitable for applications such as main transformers for switching power supplies, backlight transformers, choke coils for power supplies, and flyback transformers for TVs that are used in high frequency bands above Hz and high magnetic fields above 0.1 Oe.

[0023]

【Example】

(Example 1) Fe ₂ O ₃ , ZnO, NiO, and CuO, which are main oxide raw materials, were weighed out so as to have the compositional ratios shown in Table 1, wet-mixed, and calcined at 850 ° C. for 3 hours. Ni-Zn ferrite ferrite calcined powder was obtained. Next, after adding 3000 ppm of MoO ₃ to the above calcined powder, wet pulverizing, drying, and adding PVA as a binder to granulate, and then molding at a molding pressure of 1 ton / cm ² , and an outer diameter of 36 mm, A toroidal shaped body having an inner diameter of 24 mm and a height of 8 mm was obtained. Then, the obtained molded body is placed in the atmosphere for 100
Ni-Z containing Mo after firing at 0,1050,1100,1150,1200 ℃ for 3 hours
An n-type ferrite core was obtained.

Of the cores thus obtained, a Mo-containing Ni-Zn ferrite core having a sintered density ρ _{S of} 85 to 90% has a specific resistance of 1 MHz, 20 mT, and 100 ° C. The measurement was performed at room temperature under the condition of 10 V applied. As a comparative example,
A core was produced by a similar method using a composition outside the range of the present invention, and the core loss and the specific resistance were measured. The results are shown in Table 1.
Shown in. As is clear from the results shown in this table, it can be seen that the loss is low within the component composition range of the present invention.

[0025]

[Table 1]

Example 2 Fe ₂ O ₃ = 49.5 mol%, ZnO = 28.0
mol%, NiO = 21.5 mol%, CuO = 1.0 mol%
The main oxide raw materials were weighed, wet-mixed, and calcined at 850 ° C. for 3 hours to obtain a calcined powder of Ni-Zn ferrite. Next, in the above calcined powder, the amount shown in Table 2; 0 to 15000 ppm (outer frame amount) of MoO ₃
Was added, followed by wet pulverization, and then drying, and then PVA was added as a binder for granulation, and then the molding pressure was 1 to
Molding was performed at n / cm ² to obtain a toroidal shaped body having an outer diameter of 36 mm, an inner diameter of 24 mm and a height of 8 mm. Then, the obtained molded body was fired in the air at a temperature of 950 to 1150 ° C. for 3 hours to obtain a Mo-containing Ni—Zn ferrite core.

With respect to the Mo-containing Ni-Zn ferrite core thus obtained, the core loss was measured under the conditions of 1 MHz, 20 mT and 100 ° C., and the specific resistance was measured under the conditions of room temperature and 10 V application. The results are shown in Table 2. As is clear from the results shown in this table, the effect of reducing core loss depends on the amount of MoO ₃ added.
It can be seen that it is obtained in the range of 100 to 10,000 ppm, and is particularly remarkable in the range of 1000 to 6000 ppm. All the cores shown in Table 2 were in the range of ρ _S = 90 to 95% and specific resistance ≧ 10 ⁸ Ωcm.

[0028]

[Table 2]

(Example 3) Fe ₂ O ₃ = 49.0 mol%, ZnO = 30.0
mol%, NiO = 20.5 mol%, CuO = 0.5 mol%
The main oxide raw materials were weighed, wet-mixed, and calcined at 875 ° C for 3 hours to obtain a calcined powder of Ni-Zn ferrite. Next, the calcined powder was added with 3500 ppm of MoO ₃ and then wet-milled,
Then, after drying, PVA is added as a binder to granulate, and thereafter, molded at a molding pressure of 1 ton / cm ² to form an outer diameter of 36 mm,
A toroidal shaped body having an inner diameter of 24 mm and a height of 8 mm was obtained.
Then, the obtained molded body was fired in the atmosphere at a temperature of 1050 ° C. for 1 to 20 hours to obtain a Ni-Zn ferrite core containing Mo of ρ _S 80 to 98%.

With respect to the Mo-containing Ni-Zn ferrite core thus obtained, the core loss was measured under the conditions of 1 MHz, 20 mT and 100 ° C., and the specific resistance was measured under the conditions of room temperature and 10 V application. The result is shown in FIG. As is clear from the results shown in this figure, it was found that the low loss characteristic was obtained only in the range of ρ _S = 83 to 97%. All cores shown in the figure were in the range of specific resistance ≧ 10 ⁶ Ωcm.

In each of the above-described examples, MoO ₃ was added before pulverization, but if the calcination temperature is in the temperature range of 1000 ° C. or less, it may be added with other components before calcination. The effect is obtained.

[0032]

As described above, according to the oxide soft magnetic material of the present invention, the specific resistance ≧ 10 ⁶ Ωcm and the low loss characteristics are exhibited even in the high frequency band of 1 MHz or more and the high magnetic field of 0.1 Oe or more. The Ni-Zn ferrite shown can be obtained. Therefore, the oxide soft magnetic material of the present invention is
It exhibits excellent characteristics for applications such as switching power supply transformers used in high frequency bands of z or higher and high magnetic fields of 0.1 Oe or higher.

[Brief description of drawings]

[1] relates to the relative sintered density dependence of the core loss is a graph comparing the MoO ₃ added and MoO ₃ without addition.

Claims (3)

[Claims] 1. Fe ₂ O ₃ : 48-51 mol%, ZnO: over 25-34 mol
%, NiO: 15-27 mol% and the balance of unavoidable impurities, and has the basic composition of 100 to 10,000 ppm of Mo oxide in terms of MoO ₃ and the sintered density. Of 83 to 97% of the theoretical density is a low loss oxide soft magnetic material. 2. Fe ₂ O ₃ : 48-51 mol%, ZnO: 25-34 mol
%, CuO: less than 3 mol%, NiO: 15-27 mol% and the balance unavoidable impurities, and further 100 in terms of MoO _3.
A low-loss soft oxide magnetic material having a basic component composition obtained by adding ˜10000 ppm of Mo oxide and having a sintered density of 83 to 97% of the theoretical density. 3. The soft oxide magnetic material according to claim 1 or 2, wherein the specific resistance of the material is 10 ⁶ Ωcm or more, and the core loss value at 1 MHz, 20 mT, 100 ° C. is 120 mW / cm ³ or less. A low-loss oxide soft magnetic material characterized by: