JP3366707B2 - Mn-Zn ferrite - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-resistance and low-power-loss Mn-Zn ferrite suitable for use in a transformer for a switching power supply or the like. is there. [0002] Mn-Zn ferrite is widely used in various communication devices,
It is widely used as a material for coils and transformers in power supplies, etc., and has greatly contributed to the miniaturization of electronic devices, especially as a switching power supply transformer material that operates in the high frequency range of about 100 kHz or higher. Mn-Zn ferrite used as a transformer material of such a switching power supply is required to have characteristics such as high saturation magnetic flux density, high magnetic permeability, and low loss. You. [0003] For this reason, the inventors have disclosed in Japanese Patent Laid-Open No.
No. 54103 proposes to add one of TiO ₂ and Sb ₂ O ₃ in addition to SiO ₂ , CaO and Nb ₂ O ₅ as subcomponents, and to obtain a power loss of 240% for the obtained ferrite. and ~300 mW / cm ^3, has achieved the highest level in the current. [0004] However, Mn-Zn
In order to further reduce the size of the power supply,
It is expected that the power loss will be further reduced. The present invention relates to a Mn-Zn ferrite capable of further reducing the maximum power loss of 240 to 300 mW / cm ³ at 100 kHz and 0.2 T achieved in JP-A-3-254103. The purpose is to propose. SUMMARY OF THE INVENTION The present invention for solving the above-mentioned problems comprises Fe ₂ O ₃ : 51.5 to 54.5 mol%, MnO: 30 to 40 mol% and ZnO: 6 to 18 mol% as basic components. and then, silicon oxide as a subcomponent: SiO ₂ converted at 0.005 ~0.04wt%, calcium oxide: CaO converted at 0.02 to 0.2 wt%, niobium oxide: 0.01~0.08wt% calculated as Nb ₂ O _5, titanium oxide: TiO ₂ converted at 0.05 to 0.4 wt% and antimony oxide: a Mn-Zn ferrite containing 0.005 ~0.08wt% by Sb ₂ O ₃ conversion. First, in the present invention, the composition ratio of the basic component is
_{Fe 2 O 3: 51.5~54.5 mol%} , MnO: 30~40 mol% , and Zn
O: The reason for limiting the range to 6 to 18 mol% will be described. [0008] The operating temperature of a switching power supply transformer is usually 60 to 70 ° C. Therefore, power loss is small in this temperature range,
It is desirable that the power loss has a negative temperature dependence over a temperature range up to about 120 ° C. From this point of view, Fe ₂ O ₃ ,
As a result of studying the suitable composition ratio of MnO and ZnO, each of the above ranges was obtained. Next, in the present invention, silicon oxide, calcium oxide, niobium oxide,
A composite of titanium oxide and antimony oxide is contained. The reasons for limiting the content ranges of these subcomponents are as follows. Silicon oxide: 0.005 to 0.04% by weight in terms of SiO ₂ Silicon oxide increases the specific resistance of grain boundaries by coexistence with calcium oxide, and effectively contributes to reduction of eddy current loss. If less than 0.005 wt%, the effect of addition is poor,
On the other hand, if the content exceeds 0.04% by weight, abnormal grain growth tends to occur during firing, and the characteristics become unstable. Therefore, the range is limited to the range of 0.005 to 0.04% by weight. Calcium oxide: 0.02-0.2 wt% in terms of CaO
% Calcium oxide is a useful component that effectively enhances grain boundary resistance in the presence of silicon oxide and thus reduces loss. However, if the content is less than 0.02 wt%, the effect of improving grain boundary resistance is improved. However, if the content exceeds 0.2 wt%, the loss will increase. Therefore, the content is added in the range of 0.02 to 0.2 wt%. Niobium oxide: 0.01 to 0.08 wt% in terms of Nb ₂ O ₅ Niobium oxide (mainly Nb ₂ O ₅ ) contributes to reduction of loss in a high frequency region. The reason why the loss is improved by the addition of niobium oxide has not yet been fully elucidated, but niobium oxide alters the high-resistance grain boundary phase formed by the complex content of silicon oxide and calcium oxide. This is considered to be due to the effect of increasing the electric resistance and alleviating the adverse magnetic effect caused by the presence of the foreign phase at the grain boundary. However, its content is 0.01wt
%, The effect is poor. On the other hand, if it exceeds 0.08 wt%, abnormal grain growth tends to occur during sintering.
It was limited to the range of 0.01 to 0.08 wt%. Titanium oxide: 0.05 to 0.4 wt% in terms of TiO ₂ Titanium oxide (mainly TiO ₂ ) promotes reoxidation of grain boundaries during the cooling process during sintering of the ferrite core, thereby increasing the electrical resistance of the core. This has the effect of increasing the eddy current loss in the high frequency range, and this effect is further enhanced by the complex content with antimony oxide. However, if the content is less than 0.005 wt%, the effect of the addition is poor. On the other hand, if the content exceeds 0.4 wt%, the loss increases, and in the worst case, abnormal grain growth occurs during sintering. Limited to the wt% range. Antimony oxide: 0.005 to 0.1 in terms of Sb ₂ O ₃
08 wt% antimony oxide (mainly Sb ₂ O ₃ ) significantly improves sinterability and increases sintering density without causing abnormal grain growth in the presence of calcium oxide. This allows
This is considered to have had a favorable effect on the saturation magnetic flux density, the magnetic permeability, and the like. In addition, the electric resistance is increased particularly by the composite content with titanium oxide, which effectively contributes to further reduction of the loss in a high frequency region. However, the content is 0.
If it is less than 005 wt%, the effect of improving sinterability is poor, while
If the content exceeds 0.08% by weight, the loss will be increased instead. Therefore, the content is limited to the range of 0.005 to 0.08% by weight. [0015] As described above, the present invention achieves the above object by mixing and uniformly dispersing silicon oxide, calcium oxide, niobium oxide, titanium oxide and antimony oxide as accessory components at grain boundaries. It was done. The ferrite of the present invention may be processed according to a conventional method. That is, the final composition of the ferrite, for example, iron oxide in terms of Fe ₂ O ₃ 51.5～
54.5 mol%, manganese oxide is 30-40 mol% in terms of MnO,
Zinc oxide is mixed so as to contain 6 to 18 mol% in terms of ZnO, and then, as an auxiliary component, 0.005 to 0.04 wt% of silicon oxide (in terms of SiO ₂ ) and calcium oxide (in terms of CaO).
The 0.02 to 0.2 wt%, 0.01 to niobium oxide (Na ₂ O ₅ equivalent)
0.08 wt%, a material obtained by adding titanium oxide (TiO ₂ basis) of 0.05～0.4Wt% and antimony oxide (Sb ₂ O ₃ conversion) to contain 0.005 ~0.08wt% as a raw material. However, the addition time of the auxiliary component may be after calcination described later. This raw material is calcined at a temperature of 800 ° C. or more, then finely pulverized, and then calcined at a high temperature of 1150 ° C. or more in a nitrogen gas having a controlled oxygen concentration. The raw material of iron oxide is not only Fe ₂ O _3, but also FeO, Fe ₃ O ₄ , and compounds that can be converted to Fe ₂ O ₃ by firing, such as iron hydroxide and iron oxalate. Etc. can be used. As the manganese oxide raw material, not only MnO but also MnO ₂ , Mn ₃ O ₄ , and a compound that can be converted to MnO ₂ by firing, such as manganese carbonate and manganese oxalate, can be used.
Further, as the zinc oxide raw material, not only ZnO but also a compound that can be converted to ZnO 2 by firing, such as zinc carbonate and zinc oxalate, can be used. Similarly, the addition of each of the oxides of Si, Ca, Nb, Ti and Sb may be in the form of an oxide, and may be changed to an oxide by heating during the manufacturing process. And the like. EXAMPLE The final composition was Fe ₂ O ₃ : 53.0 mol%, MnO
: 35.0 mol% and ZnO: 12.0 mol% after mixing, and then calcined in the air at 900 ° C for 3 hours. With respect to the calcined powder, SiO ₂ , CaO (using CaCO ₃ ), Nb ₂ O ₅ ,
TiO ₂ and Sb ₂ O ₃ were added and blended, and simultaneously pulverized by a wet ball mill. Next, after adding PVA as a binder to the pulverized powder and granulating, it was formed into a ring-shaped sample having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm. The molded body was fired at 1320 ° C. for 3 hours in a nitrogen atmosphere having a controlled oxygen concentration. The density of the sintered core thus obtained was measured by the Archimedes method. Further, the DC specific resistance was measured by a four-terminal method. Further, the electron loss at a frequency of 100 kHz, a maximum magnetic flux density of 0.2 T, and a temperature of 80 ° C.
It was measured with an H loop tracer. The measurement results are also shown in Tables 1 and 2. The sintering density was 5.1 g / cm.
It is shown as a percentage of ³ . [Table 1] [Table 2] Tables 1 and 2 show Examples and Comparative Examples, respectively. As apparent from these results,
In accordance with the present invention, any of the compounds containing silicon oxide, calcium oxide, niobium oxide, titanium oxide and antimony oxide as auxiliary components in accordance with the present invention has a higher DC specific resistance than one lacking either titanium oxide or antimony oxide. Have increased, and a reduction in power loss has been achieved. Thus, according to the present invention, as a transformer material for a switching power supply having a driving frequency of about 100 kHz, the power loss in a high magnetic field is remarkably smaller than that of a conventional material, and it has a high resistance and a high resistance. A low loss Mn-Zn ferrite can be obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-267040 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01F 1/12-1/375

Claims (1)

(57) [Claims 1] _{Fe 2 O 3: 51.5~54.5 mol%} , MnO: 30~40 mol% and ZnO: a having 6 to 18 mol% as basic components, silicon oxide as a secondary component containing: SiO ₂ converted at 0.005 ~0.04wt%, calcium oxide: CaO converted at 0.02 to 0.2 wt%, niobium oxide: Nb ₂ O ₅ 0.01~0.08wt% in terms of titanium oxide: 0.05 to 0.4 wt in terms of TiO ₂ % and antimony oxide: Sb ₂ O ₃ in terms of in 0.005 Mn-Zn ferrite, characterized in that it contains ～0.08Wt%.