JPH07245210A - Low loss oxide magnetic material and its preparing method - Google Patents

Abstract

PURPOSE:To prepare Mn-Zn system soft ferrite material having a low power loss by a method wherein, as a very small amount of impurities of a Mn-Zn system soft ferrite sintered body having a specific main compound composition, content of P and Cr is respectively a specific amount or less. CONSTITUTION:This embodiment is a Mn-Zn system soft ferrite sintered body having a main compound composition of FE2O3 51 to 55mol%, MnO 31 to 44mol% and ZnO 5 to 14mol%. The reason why the main compound is limited to this range is that, when excluding this range, a power loss may increase or saturated magnetic flux density may lower. Further, content of P and Cr fairly affects the power loss of the sintered body. The content of P is 20ppm or less and the content of Cr is 50ppm or less, whereby it is possible to prepare a ferrite core of a low power loss like 350kW/m<3> or less, or 270kW/m<3> as conditions demand. Further, a reduction in P is effective in improving DELTAB.

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 magnetic material which can be used for a transformer core for high frequency switching power supplies, a flyback transformer core for televisions and display monitors.

[0002]

2. Description of the Related Art In recent years, power transformers used for switching power supplies and the like have been required to be smaller and lighter. Therefore, the driving frequency is expanding to about 100 kHz to 500 kHz. However, the eddy current loss, which is a particular problem in the high frequency region of the power loss, is proportional to the square of the driving frequency, so that the power loss also increases as the frequency increases, and the amount of heat generated cannot be ignored. Therefore, there is a demand for magnetic materials with lower loss. Further, the saturation magnetic flux density (Bs) is large and the residual magnetic flux density (Br) is small,
That is, it is also important that ΔB = Bs−Br is large.

In order to solve such a problem, Mn-Z
In n-ferrite, reduction of power loss has hitherto been attempted by adding various trace components.
For example, in JP-A-58-15037, Mb ₂ O ₅
Addition of CaO, Nb ₂ O ₅ and V ₂ O ₅ in JP-A-60-16863 and JP-A-62-142303, CaO and SiO ₂ in JP-A-61-252608. , V ₂ O ₅ and SeO ₂ and Ca in JP-A-2-30660.
With the addition of O, SiO and P, the method disclosed in
In 9905, the power loss is improved by adding CaO, SiO, Nb ₂ O ₅ and Cl. Further, in JP-A-60-132301, Fe,
CaO and Nb ₂ O ₅ are added to the main components of Mn and Zn, and SiO ₂ , Al ₂ O ₃ , CoO, CuO, and ZrO _{2 are} further added.
We are trying to reduce the loss by adding one of them. However, in order to achieve higher frequencies, smaller size and lighter weight, materials with lower loss are required.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a Mn-Zn based soft ferrite material having a lower loss than conventional low loss oxide magnetic materials and a method for producing the same.

[0005]

In order to solve the above-mentioned problems, the inventors of the present invention have conducted earnest research on the cause of worsening the power loss of Mn-Zn ferrite. As a result, the trace impurities contained in the sintered body, especially P and Cr, are the cause of worsening the power loss, and the power loss can be suppressed low by reducing the content of these elements. I found out. The present invention has been completed based on these findings from a viewpoint different from the conventional addition of trace elements.

The subject matter of the present invention is as follows. ₍₁₎ Fe ₂ O 3 51~55 mol%, MnO 31
The content of P as a trace impurity is 20 ppm or less, and the content of Cr is 50 ppm or less. A low loss oxide magnetic material characterized by the above. (2) The main component composition obtained by pyrolyzing a solution obtained by mixing Fe, Mn, and Zn, which are the main components, in the form of a chloride solution at a predetermined ratio and spraying the solution into a spray roasting furnace, is Fe ₂ O ₃
51-55 mol%, MnO 31-44 mol% and Z
Regarding the mixed oxide powder having nO of 5 to 14 mol%,
The content of P as a trace impurity is set to 20 ppm or less and the content of Cr is set to 50 ppm or less.
A method for producing an oxide magnetic material, which comprises granulating, molding, and baking the calcined powder heat-treated as a main raw material.

The present invention will be described in detail below. First,
The reasons for limiting the composition of the main components will be described. Fe ₂
O ₃ 51 to 55 mol%, MnO 31 to 44 mol% and ZnO 5 to 14 mol% are limited in the range because when the main component of the ferrite core is out of this range, power loss becomes large or saturation occurs. This is because the magnetic flux density may decrease, and the ferrite core intended by the present invention may not be obtained.

A feature of the present invention is that the amounts of P and Cr in the sintered body are reduced. Conventionally, there are many unclear points about the relationship between trace impurities and the electromagnetic characteristics of ferrite,
Little quantitative knowledge has been obtained. Therefore, as a result of examining the relationship between the power loss and the amount of trace impurities such as P, Cr, Cn, and Al in the sintered body, it was found that the P and Cr contents significantly affect the power loss of the sintered body. I found it. In particular, it has been found that the inclusion of P is one of the causes for causing abnormal grain growth during firing and significantly deteriorates power loss.

From these results, by setting the P content to 20 ppm or less and the Cr content to 50 ppm or less, 1
350 kW / m ^{3 under} the measurement condition of 00 kHz-200 mT
Below, we succeeded in producing a ferrite core with an unprecedented low power loss of 270 kW / m ³ depending on the conditions. It was also found that the reduction of P is also effective in improving ΔB.

Next, a method for producing the raw material calcined powder used in the present invention will be described. Fe, Mn and Zn, which are the main components, are mixed at a predetermined ratio in the form of a chloride solution, and the resulting liquid is sprayed in a spray roasting furnace to be pyrolyzed, and Fe, Mn having a particle size of several hundred angstroms, After forming a mixed oxide powder of Zn, 200 to 1000 ° C. in order to improve moldability
Heat treated at 400 ° C. to 800 ° C. for 1 to 4 hours, and the average primary particle diameter is 0.3 to 1.0.
The grain is grown to about μm to produce a calcined powder.

When such a method is applied, since the starting material is a solution, a highly pure material can be obtained relatively easily by refining the solution. On the other hand, Fe, M
In the usual method for producing a calcined powder, in which each oxide powder of n and Zn is mixed, calcined, and pulverized by a ball mill, an attritor, etc., impurities from the production equipment are easily mixed during pulverization, It is difficult to mass-produce such high-purity calcined powder.

[0012]

EXAMPLES The present invention will be further described below based on examples. Fe ₂ O ₃ 53.5 mol% by spray roasting,
Oxide mixed powders having a main component composition of 36.5 mol% MnO and 10.0 mol% ZnO and various amounts of P and Cr were produced. After heat-treating this at 800 ℃, SiO
150 ppm of Ca ₂ and 600 ppm of CaO were added and mixed.
After adding PVA as a binder and granulating, the outer diameter 29
mm, inner diameter 18 mm, and height 7 mm. This molded body was heated at 1275 ° C. in a nitrogen atmosphere with controlled oxygen concentration.
And baked at 1300 ° C. for 4 hours.

The fired core thus obtained is at 80 ° C.
Power loss value (100kHz-200mT) and P,
The relationship with the amount of Cr is shown in FIGS. 1 and 2. Further, FIG. 3 shows the relationship between the value of ΔB and the amount of P at 25 ° C. 1 to 3, the solid line portion shows the range of the present invention, and the dotted line portion shows a comparative example.

As is clear from FIGS. 1 and 2, the smaller the amount of P and Cr, the smaller the power loss. It can be seen that when P is 20 ppm or less and Cr is 50 ppm or less as in the present invention, a core with particularly small power loss can be obtained.
Further, as is clear from FIG. 3, it can be seen that ΔB becomes large when P is 20 ppm or less.

[0015]

As described above, according to the present invention, a core having a very low power loss and a large ΔB can be manufactured. Therefore, it is possible to miniaturize various cores including a transformer power supply core. It is extremely beneficial.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the power loss value and the amount of P at 80 ° C. of a fired core.

FIG. 2 is a graph showing the relationship between the power loss value of a fired core at 80 ° C. and the amount of Cr.

FIG. 3 is a graph showing the relationship between the value of ΔB and the amount of P.

Claims (2)

[Claims] 1. Fe ₂ O ₃ 51-55 mol%, MnO
A Mn-Zn-based soft ferrite sintered body having a main component composition of 31 to 44 mol% and ZnO 5 to 14 mol%, the content of P as a trace impurity is 20 ppm or less, Cr
A low loss oxide magnetic material, characterized in that its content is 50 ppm or less. Wherein the major component Fe, sprayed with Mn and Zn the solution mixed at a predetermined ratio in the form of a chloride solution in the spray roasting furnace, the main component composition obtained by pyrolysis Fe ₂ O
₃ 51-55 mol%, MnO 31-44 mol% and ZnO 5-14 mol%, the content of P as a trace impurity is 20 ppm or less, Cr
Content of 50ppm or less, 200 ~ 1000
A method for producing an oxide magnetic material, which comprises using a calcined powder heat-treated at ℃ as a main raw material, granulating, molding and firing.