JP2010076962A - MnZnLi-BASED FERRITE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new MnZnLi-based ferrite which has excellent high saturation magnetic flux density characteristics and excellent characteristics of reducing the temperature dependency of magnetic loss (core loss), can improve bending strength and further improve product yield, and are excellent in thermal shock resistance. <P>SOLUTION: The MnZnLi-based ferrite contains 54.0-58.0 mol% iron oxide expressed in terms of Fe<SB>2</SB>O<SB>3</SB>, 3.0-10.0 mol% zinc oxide expressed in terms of ZnO, 0.3-1.5 mol% lithium oxide expressed in terms of LiO<SB>0.5</SB>and the balance manganese oxide (expressed in terms of MnO) as main constituents and 500-2,000 weight ppm Co expressed in terms of CoO is incorporated as an accessary constituent to the main constituents. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an MnZnLi-based ferrite, and more specifically, an MnZnLi-based ferrite used for a magnetic core of a power transformer such as a switching power supply, and particularly has a small magnetic loss (core loss) in a wide temperature range and is sintered. The present invention relates to a MnZnLi-based ferrite that can improve the strength of the body, particularly the bending strength (bending strength).

  In recent years, electronic devices have been rapidly reduced in size and output. Along with this, various components have been highly integrated and high-speed processing has progressed, and there has been a demand for increasing the current of the power supply line for supplying power. Drives with high power are also required for components such as transformers and choke coils. Furthermore, stable driving at around 100 ° C is required due to high temperatures in the usage environment of automobiles and temperature rise due to heat generated during driving. It has been.

  In order to cope with a large current drive, the ferrite core is required to have a high saturation magnetic flux density at a high temperature, for example, in a temperature region of 100 ° C. or higher. Furthermore, in order to ensure excellent magnetic stability and high reliability, the magnetic loss (core loss) value near 100 ° C can be reduced, and the temperature dependence of the magnetic loss (core loss) value near 100 ° C can be reduced. There is a demand for a ferrite that can be made small and excellent in high-temperature storage.

  In addition, a high bending strength is required in order to reduce the size and thickness of ferrite cores. However, MnZn ferrite mainly used for transformers has a problem of low bending strength. Further, when there is a step of soldering by immersing the transformer in a solder bath, the thermal shock resistance of the core is required.

  There are the following documents as prior art which is considered to be related to the present application.

(1) Japanese Patent No. 3487243 A MnZn system in which Li, Ca, and Si are added as essential components for the purpose of facilitating the temperature at which the saturation magnetic flux density is high and the magnetic core loss is minimized to a practical temperature. Ferrite is disclosed.

(2) Japanese Unexamined Patent Publication No. 2007-238429 Disclosure of MnZn ferrite with Li added as an accessory component for the purpose of providing a ferrite material having a higher saturation magnetic flux density at 100 ° C. and a low core loss at 100 ° C. Has been made.

(3) Patent No. 3924272 Disclosure of MnZn-based ferrite to which Co is added as an auxiliary component for the purpose of providing a ferrite material with small core loss in a high temperature range and little deterioration of core loss even under high temperature storage Has been made.

(4) JP 4-3089
A ferrite material containing Co in lithium-zinc-manganese ferrite has been disclosed. However, the lithium content is larger than the respective contents of zinc and manganese, and is completely different from the scope of the present invention. Furthermore, the amount of Fe ₂ O ₃ in this prior art is less than the stoichiometric composition.

Japanese Patent No. 3487243 JP 2007-238429 A Japanese Patent No. 3924272 JP 30-3089

  There is no limit to the requirements for the high saturation magnetic flux density characteristics, the characteristics for reducing the temperature dependence of the magnetic loss (core loss) value, and the like, and proposals for MnZnLi-based ferrites that can further improve the characteristics are demanded.

  Furthermore, each of the above prior arts is a composition blended, paying attention to effects such as a high saturation magnetic flux density, a decrease in core loss near 100 ° C., and a deterioration in core loss under high temperature storage. It is not formulated for the purpose of improving the bending strength. Therefore, the bending strength of conventional MnZnLi ferrite products cannot be said to be sufficient. For example, the production yield of the product is extremely effectively prevented from occurring, such as cracking and chipping in the manufacturing process of the transformer core and the transformer assembly process. There has been a demand for a new MnZnLi-based ferrite that can further improve the thermal resistance of the core and that is excellent in the thermal shock resistance of the core.

  The present invention was devised based on such a situation, and its purpose is excellent in high saturation magnetic flux density characteristics, characteristics that reduce the temperature dependence of magnetic loss (core loss) value, and resistance to bending. An object of the present invention is to provide a new MnZnLi-based ferrite that can improve the strength, improve the product yield, and have excellent thermal shock resistance of the core.

In order to solve such problems, the present invention has, as main components, iron oxide in an amount of 54.0 to 58.0 mol% in terms of Fe ₂ O ₃ and zinc oxide in an amount of 3.0 to 10.0 in terms of ZnO. MnZnLi ferrite containing 0.3% to 1.5% by mole of lithium oxide in terms of LiO _0.5 and the balance of manganese oxide (in terms of MnO), Co being CoO as an accessory component with respect to the main component. It is comprised so that it may contain 500-2000 weight ppm in conversion.

Further, as a preferred embodiment of the MnZnLi ferrite of the present invention, the value of magnetic loss (core loss) Pcv obtained by applying a sinusoidal AC magnetic field of 100 kHz and 200 mT and changing the measurement temperature in various ways is related to the measurement temperature. In the graph shown, the value of magnetic loss (core loss) at the bottom temperature Tb corresponding to the lowest point of the graph is Pcv _b , and the value of magnetic loss (core loss) at a temperature 20 ° C. higher than the bottom temperature Tb (Tb + 20 ° C.) Pcv _{b. +20} , the magnetic loss change rate value δ2 = [(Pcv _{b + 20} −Pcv _b ) / Pcv _b × 100] between 20 ° C. is 15% or less.

  Moreover, as a preferable aspect of the MnZnLi ferrite of the present invention, the saturation magnetic flux density Bs at 100 ° C. is configured to be 430 mT or more.

  Moreover, as a preferable aspect of the MnZnLi ferrite of the present invention, the bottom temperature Tb is configured to be 70 ° C. or higher.

  The transformer magnetic core of the present invention is composed of the MnZnLi ferrite.

  The transformer of the present invention is configured using the transformer magnetic core.

The present invention, as a main component, 54.0 to 58.0 mol% of iron oxide calculated as Fe ₂ O _3, zinc oxide 3.0 to 10.0 mol% in terms of ZnO, the lithium oxide in LiO _0.5 in terms 0.3 to 1.5 mol%, MnZnLi ferrite containing the remainder of manganese oxide (in terms of MnO), wherein Co is contained as an accessory component in an amount of 500 to 2000 ppm by weight in terms of CoO with respect to the main component. Therefore, the high saturation magnetic flux density characteristics and the characteristics that reduce the temperature dependence of the magnetic loss (core loss) value are excellent. Furthermore, the bending strength can be improved and the product yield can be further improved. In addition, the effect of excellent thermal shock resistance of the core is exhibited.

  Hereinafter, the MnZnLi ferrite of the present invention will be described in detail.

[Description of MnZnLi ferrite of the present invention]
(Description of the main component composition)
MnZnLi ferrite of the present invention, as a main component, 54.0 to 58.0 mol% of iron oxide calculated as Fe ₂ O ₃ (preferably, 54.5 to 57.5 mol%, more preferably, 55. 0 to 57.0 mol%) and zinc oxide in terms of ZnO, 3.0 to 10.0 mol% (preferably 3.5 to 9.0 mol%, more preferably 4.0 to 8.0 mol) %), _0.3 to 1.5 mol% (preferably 0.35 to 1.45 mol%, more preferably 0.4 to 1.4 mol%) of lithium oxide in terms of LiO _0.5 , manganese oxide Is contained (in terms of MnO).

In the above-mentioned main component composition, if the amount of Fe ₂ O ₃ exceeds 58.0 mol%, there is a tendency that the inconvenience that the core loss increases. In addition, when the amount of Fe ₂ O ₃ is less than 54.0, there is a tendency that the saturation magnetic flux density is lowered.

  Further, in the above main component composition, when the ZnO amount is less than 3.0 mol%, there is a tendency that the temperature characteristic of the core loss becomes high. On the other hand, if the amount of ZnO exceeds 10.0 mol%, there is a tendency for the disadvantage that the saturation magnetic flux density is lowered.

In the above main component composition, when the amount of LiO _0.5 is less than 0.3 mol%, there is a tendency that the bending strength is lowered. On the other hand, when the amount of LiO _0.5 exceeds 1.5 mol%, there is a tendency that the core loss increases. Further, the amount of LiO _0.5 exhibits a synergistic effect for improving the thermal shock resistance of the core in relation to the amount of CoO described later.

(Explanation about subcomponent composition)
The MnZnLi ferrite of the present invention contains Co as an essential component as a subcomponent. As a raw material for the auxiliary component, an oxide or a powder of a compound that becomes an oxide by heating is used. Specifically, CoO can be used in the form at the time of addition.

  Such subcomponents contain 500 to 2000 ppm by weight of Co in terms of CoO (preferably 600 to 1800 ppm by weight, more preferably 700 to 1500 ppm by weight) with respect to the main component.

When the amount of CoO is less than 500 ppm by weight, there is a tendency that the temperature characteristic of the core loss becomes large. On the other hand, when the amount of CoO exceeds 2000 ppm by weight, there is a tendency that the core loss increases. This amount of CoO exhibits a synergistic effect for improving the thermal shock resistance of the core in relation to the amount of LiO _0.5 .

Further, without departing from the effects of the present invention, in addition to the sub-components of _{the, ZrO 2, SiO 2, CaCO} 3, Nb 2 O 5, V 2 O 5, Ta 2 O 5, NiO, TiO 2, Other subcomponents such as SnO ₂ can be added.

The sintered density of the ferrite sintered body is preferably 4.70 g / cm ³ or more. The upper limit is not particularly limited, but is usually about 5.00 g / cm ³ . When the sintered density is less than 4.70 g / cm ³ , there is a tendency that the saturation magnetic flux density is lowered and the bending strength is lowered.

(Description of physical properties of the ferrite sintered body of the present invention)
The ferrite of the present invention has the following physical properties.

(1) Folding strength
The bending strength in this invention is calculated | required in the following ways.
This is a three-point bending test at room temperature for fine ceramics, and is determined according to JIS R1601. The greater the value, the higher the bending strength.

The target value of bending strength in the present invention is 14.0 Kgf / mm ² or more.

(2) Temperature dependence of magnetic loss (core loss) value
The temperature dependence of the magnetic loss value in the present invention is obtained in the following manner.
The value of magnetic loss (core loss) Pcv obtained by applying a sinusoidal AC magnetic field of 100 kHz and 200 mT and changing the measurement temperature in various ways is graphed in relation to the measurement temperature.

In this graph, the magnetic loss (core loss) value Pcv _{b at} the bottom temperature Tb corresponding to the lowest point of the graph, and the magnetic loss (core loss) value Pcv _{b + at a} temperature 20 ° C. higher than the bottom temperature Tb (Tb + 20 ° C.). _{Find 20} each. The bottom temperature Tb in the present invention is preferably 70 ° C. or higher.

The target value of the magnetic loss (core loss) value Pcv _{b at} the bottom temperature Tb in the present invention is 450 KW / m ³ or less.

Using these values, the value δ2 = [(Pcv _{b + 20} −Pcv _b ) / Pcv _b × 100] of the magnetic loss change rate at 20 ° C. is calculated. In the present invention, the value δ2 of the magnetic loss change rate between 20 ° C. is 15% or less.

(3) Saturation magnetic flux density Bm
The saturation magnetic flux density Bs at 100 ° C. is 430 mT or more.

(4) Thermal shock resistance
Evaluation criteria are as follows

○ ... No cracks in the core when immersed in a solder bath at 400 ° C.
X: The core is cracked when immersed in a solder bath at 400 ° C.

[Method for producing MnZnLi-based ferrite]
Next, an example of a suitable manufacturing process for the MnZnLi ferrite of the present invention will be described.

(1) Step of weighing so that the ratio of metal ions is a predetermined component so that a target ferrite can be obtained. As a raw material of a main component, an oxide or a compound that becomes an oxide by heating, for example, carbonate, hydroxide Powders such as oxalate and nitrate are used. What is necessary is just to select suitably the average particle diameter of each raw material powder in the range of about 0.1-3.0 micrometers. In addition, not only the raw material powder mentioned above but it is good also considering the powder of the complex oxide containing 2 or more types of metals as raw material powder. Each raw material powder is weighed so as to have a predetermined composition.

The Li compound is preferably a compound that is insoluble or hardly soluble in water. In the present invention, “a compound that is insoluble or hardly soluble in water (hereinafter simply referred to as“ water-insoluble compound ”)” refers to the amount of solute (grams) in 100 g of water (temperature 20 ° C.). ) Refers to a compound of 1 g or less. Such a water-insoluble Li compound is an oxide containing at least one component selected from Li and Fe, Mn, and Zn in order to be used for MnZn ferrite. Is desirable. Preferably, (1) an oxide such as LiFeO ₂ , LiFe ₅ O ₈ , Li ₂ Fe ₃ O ₅ , or Li ₅ FeO ₄ containing components of Li and Fe, or (2) Li and Mn It is an oxide such as LiMn ₂ O ₄ or LiMnO ₂ containing a component. By using such a water-insoluble Li compound, it is possible to suppress variation in characteristics between product lots, and to improve manufacturing yield and reliability of product quality.

(2) The calcining process raw material powder after the weighed product is mixed by wet or drying, for example, wet-mixed by a ball mill, dried, pulverized and sieved, and then held within a temperature range of 700 to 1000 ° C. for a predetermined time. Calcination is performed. What is necessary is just to select suitably the holding time of calcination within the range of 1 to 5 hours.

(3) Crushing step of calcined powder After calcining, the calcined body is pulverized to an average particle size of about 0.5 to 5.0 μm, for example.

  Usually, a predetermined amount of CoO as a subcomponent is added in this pulverization step. That is, a predetermined amount of CoO as a subcomponent is added to and mixed with the main component powder obtained after calcining and pulverization. Note that the Li component may be added in this pulverization step instead of the blending step.

(4) Granulation / molding process The pulverized powder is granulated into granules to facilitate the subsequent molding process. At this time, it is desirable to add a small amount of an appropriate binder such as polyvinyl alcohol (PVA) to the pulverized powder. The particle size of the obtained granules is preferably about 80 to 200 μm. For example, a toroidal shaped product obtained by pressure-molding the granulated powder is formed.

(5) Firing step The molded body is fired in the firing step.

  In the firing step, it is necessary to control the firing temperature and firing atmosphere. Firing is performed by holding for a predetermined time in the range of 1150 to 1350 ° C.

Hereinafter, the present invention will be described in more detail with reference to specific examples.
[Experimental Example I]
Sample No. in Table 1 below. As shown in I-3, the final 56.0 mol% of iron oxide in the composition in terms of Fe ₂ O _3, 37.1 mol% manganese oxide in terms of MnO, zinc oxide 6.0 mol% calculated as ZnO The main component material as the main component was weighed so that lithium oxide was 0.9 mol% in terms of LiO _0.5 . Note that LiFeO ₂ was used as the Li raw material, and the Fe component was adjusted in consideration of the amount of Fe in LiFeO ₂ .

  The weighed raw materials were wet-mixed for 16 hours using a wet ball mill and then dried.

  Next, the dried product was calcined in the atmosphere at 900 ° C. for 3 hours and then pulverized.

  To the obtained calcined powder, CoO powder was added as a raw material of an auxiliary component, a binder was added to the mixture powder obtained by mixing and pulverizing, granulated, and then molded to obtain a toroidal shaped body. The subcomponent raw material was added so that CoO was contained at 1000 ppm by weight with respect to the main component raw material. The Li component may be added during pulverization.

  The toroidal shaped product was fired at a temperature of 1350 ° C. while controlling the oxygen partial pressure. A sintered ferrite body of I-3 was prepared.

  This sample No. Various samples shown in the following Table 1 were produced based on the production method of the sintered ferrite body of I-3.

For each sample shown in Table 1,
(1) Bottom temperature Tb,
(2) Magnetic loss (core loss) Pcv _{b at} the bottom temperature Tb,
(3) Magnetic loss (core loss) value Pcv _{b + 20 at} a temperature 20 ° C. higher than the bottom temperature Tb (Tb + 20 ° C.),
(4) Core loss temperature dependency δ2,
(5) Folding strength (3-point bending strength),
(6) saturation magnetic flux density Bm,
(7) Thermal shock resistance,
Was measured respectively.

Each measurement procedure was as described above.
The results are shown in Table 1 below.

The effect of the present invention is clear from the results of Experimental Example I shown in Table 1 above.
That is, the present invention provides, as a main component, 54.0 to 58.0 mol% of iron oxide calculated as Fe ₂ O _3, 3.0 to 10.0 mol% of zinc oxide calculated as ZnO, lithium oxide LiO _0.5 MnZnLi-based ferrite containing 0.3 to 1.5 mol% in terms of conversion and the remainder of manganese oxide (in terms of MnO), and containing 500 to 2000 ppm by weight of Co as a subcomponent with respect to the main component in terms of CoO As a result, the high saturation magnetic flux density characteristics and the characteristics that reduce the temperature dependence of the magnetic loss (core loss) value are excellent. Furthermore, the bending strength can be improved and the product yield can be further improved. Furthermore, the effect of excellent thermal shock resistance of the core is manifested.

  The method for producing MnZnLi ferrite of the present invention can be widely used in various electric parts industries.

Claims (6)

As a main component, 0.3 to iron oxide from 54.0 to 58.0 mol% in terms of Fe ₂ O _3, 3.0 to 10.0 mol% of zinc oxide calculated as ZnO, lithium oxide with LiO _0.5 in terms A MnZnLi-based ferrite containing 1.5 mol% and the remainder of manganese oxide (in terms of MnO),
An MnZn-based ferrite comprising 500 to 2000 ppm by weight of Co as a subcomponent with respect to the main component. In the graph showing the value of magnetic loss (core loss) Pcv obtained by applying a sinusoidal AC magnetic field of 100 kHz and 200 mT and changing the measurement temperature in various ways, it corresponds to the lowest point of the graph. When the value of the magnetic loss (core loss) at the bottom temperature Tb is Pcv _b and the value of the magnetic loss (core loss) at the temperature 20 ° C. higher than the bottom temperature Tb (Tb + 20 ° C.) is Pcv _{b + 20} , the magnetism between 20 ° C. 2. The MnZnLi ferrite according to claim 1, wherein the loss change rate value δ < _b > ₂ = [(Pcv _{b + 20} −Pcv _b ) / Pcv _b × 100] is 15% or less.   The MnZnLi ferrite according to claim 1 or 2, wherein a saturation magnetic flux density Bs at 100 ° C is 430 mT or more.   The MnZnLi-based ferrite according to claim 2 or 3, wherein the bottom temperature Tb is 70 ° C or higher.   A transformer magnetic core comprising the MnZnLi-based ferrite according to any one of claims 1 to 4.   A transformer using the transformer magnetic core according to claim 5.