KR20140139983A - Ferrite and transformer - Google Patents

Abstract

[TASK] The present invention provides MnZn-based ferrite having a high saturation magnetic flux density Bs, a low magnetic low Pcv, and a high loss strength. [SOLUTION] MnZn-based ferrite according to the present invention contains a main component which is composed of 66 mol% to 70 mol% of iron oxide in terms of Fe2O3, 10 mol% to 20 mol% of zinc oxide in terms of ZnO, and 0.4 mol% to 2 mol% of nickel oxide in terms of NiO, and the remainder which is substantially composed of MnO, and contains 0.005 wt% to 0.3 wt% of Si in terms of SiO2, 0.02 wt% to 0.15 wt% of Ca in terms of CaO, 0.01 wt% to 0.1 wt% of Nb in terms of Nb2O5, 0.005 wt% to 0.04 wt% of Zr in terms of ZrO2, and 0.05 wt% to 0.35 wt% of Sn in terms of SnO, with respect to the total weight of the oxide which is the main component.

Description

FERRITE AND TRANSFORMER < RTI ID = 0.0 >

The present invention relates to a ferrite including Fe, Mn, Zn and Ni and a transformer using the ferrite.

2. Description of the Related Art In recent years, miniaturization and multifunctionalization of electronic devices have progressed rapidly, and the integration and high frequency of various components have progressed, and the current supplied is also being increased. As the current increases, the heat from various components increases. In consideration of the temperature rise due to heat generation when the electronic device is driven, a magnetic core material used for circuit components such as a transformer and a choke coil, It is required to secure a high saturation magnetic flux density Bs up to a high temperature of about 120 DEG C, and stable and reliable driving of various components at high temperatures is required.

MnZn ferrites are generally used as materials for transformers and choke coils. To meet this demand, MnZn ferrites used in transformers, choke coils, and the like are required to have a high saturation magnetic flux density Bs at operating temperature and a low magnetic loss Pcv.

On the other hand, ferrite is required to have high mechanical strength in order to improve the handling properties during ferrite production and transportation, and to improve the bobbin attachability to the ferrite core and the workability of the winding to the mounted bobbin. Among them, it is important that the defect of the ferrite due to impact is hard to occur, that is, the defect strength is high.

Several methods have been proposed for a MnZn-based ferrite material with a high saturation magnetic flux density Bs and a low magnetic loss Pcv and a method for producing the same.

Japanese Patent Application Laid-Open No. 2007-31210 Japanese Laid-Open Patent Publication No. 2011-195415 Japanese Patent Application Laid-Open No. 2005-272229

However, although Patent Literature 1 improves the characteristics of low magnetic loss at 100 ° C and high saturation magnetic flux density, since the amount of Fe ₂ O ₃ is small, the saturation magnetic flux density Bs is low and the Curie point Lower. Further, the improvement of the characteristics of the saturation magnetic flux density at a high temperature of 120 占 폚 has not been studied. In addition, the ferrite obtained by the technique of Patent Document 2 does not necessarily have sufficient defect strength. In Patent Document 3, the saturation magnetic flux density Bs at 120 占 폚 is not sufficiently obtained because NiO is contained in a large amount.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to provide a Mn-Zn ferrite having a high saturation magnetic flux density Bs and a low magnetic loss Pcv at a high temperature (120 ° C)

It has been found that it is important to control the main component and the minor component of the granulated powder as the ferrite raw material to an appropriate range in order to solve the above problems and achieve the target.

That is, the Mn-Zn ferrite according to the first means is composed of 66 mol% or more and 70 mol% or less of iron oxide in terms of Fe ₂ O ₃ , 10 mol% or more and 20 mol% or less of zinc oxide in terms of ZnO, 0.4 mol% By mass or more and 0.03% by mass or less in terms of CaO, based on the total mass of said oxide as a main component, in terms of SiO ₂ , less than 0.15% by mass or less, Nb to Nb ₂ O 0.01% by mass to ₅ in terms of 0.1% by mass or less, 0.005% or more by weight of Zr to ZrO ₂ in terms of 0.04% by mass or less, less than 0.05% by mass of Sn as SnO in terms of 0.35% by weight Or less.

The Mn-Zn ferrite according to the second means is characterized in that in the ferrite according to the first means, the defect ratio in the defect test is less than 2%.

The Mn-Zn ferrite according to the third means is characterized in that V, Ta, and Hf are V ₂ O ₅ and Ta, respectively, with respect to the total mass of the oxide as the main component in the ferrite according to the first or second means, ₂ O ₅ and 0.001 to 0.01 mass% of at least one of V, Ta and Hf in terms of HfO ₂ .

The fourth means is a transformer composed of ferrite according to any one of the first to third means.

INDUSTRIAL APPLICABILITY According to the present invention, by using ferrite according to the present invention as a transforming magnetic core used in a power transformer or the like such as a switching power supply, or a transformer (a coil is wound around a magnetic core), high saturation flux It is possible to obtain a ferrite core having a density Bs and having a low magnetic loss and hardly causing defects in the manufacturing process.

1 is a graph showing an example of temperature setting in the main firing process.

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

[Description of MnZn ferrite according to the present invention]

(Explanation of main component composition)

The Mn-Zn ferrite of the present invention contains 66 to 70 mol% (preferably 66.0 to 69.0 mol%, more preferably 66.0 to 68.0 mol%) of iron oxide as the main component in terms of Fe ₂ O ₃ , 10 to 20 mol% (preferably 14.5 to 16.0 mol%, more preferably 15.0 to 16.0 mol%) in terms of ZnO, 0.4 to 2.0 mol% in terms of NiO as nickel oxide and manganese oxide MnO in the balance , 0.001 to 0.03 mass% of Si in terms of SiO ₂ , 0.02 to 0.15 mass% of Ca in terms of CaO, 0.01 to 0.1 mass% of Nb in terms of Nb ₂ O ₅ , 0.005 to ₁ mole of Zr in terms of ZrO ₂ , 0.04 mass%, and Sn is 0.05 to 0.35 mass% in terms of SnO.

In the above-mentioned main component composition, increasing the amount of Fe ₂ O ₃ has the effect of increasing the saturation magnetic flux density Bs. However, when the amount of Fe ₂ O ₃ exceeds 70.0 mol%, the magnetic loss Pcv tends to increase. If the amount of Fe ₂ O ₃ is less than 66.0 mol%, the saturation magnetic flux density Bs tends to deteriorate.

When the amount of ZnO exceeds 20.0 mol% in the above-mentioned main component composition, the saturation magnetic flux density Bs tends to be lowered and the magnetic loss Pcv tends to become high. When the amount of ZnO is less than 10.0 mol%, a defect that the magnetic loss Pcv increases tends to occur.

Ni has an effect of lowering the magnetic anisotropy of ferrite, and at the same time, enhances the defect strength. By containing an appropriate amount of Ni, it is possible to achieve low magnetic loss and improve the defect strength. Ni has a tendency that a saturation magnetic flux density Bs is lowered when NiO content exceeds 2.0 mol% in the main component composition. Also, when the amount of NiO is less than 0.4 mol%, defective strength tends to be deteriorated.

(Explanation of subcomponent composition)

Ca has an effect of increasing the sinterability of ferrite and contributes to a higher resistance of the grain boundaries. Therefore, by containing Ca in an appropriate amount, the magnetic loss can be reduced. If the Ca content (in terms of CaO) of the ferrite is less than 0.02% by mass based on the total mass of the main component oxide, the grain boundary is not formed well and the resistivity is lowered and the eddy current loss tends to become large. , Crystal grain growth is promoted and abnormal grains are generated, so that the eddy current loss tends to increase. The Ca content (in terms of CaO) is preferably 0.028 to 0.084 mass%.

Si has an effect of enhancing the sintering property of ferrite and contributes to a higher resistance of grain boundaries. Therefore, by containing a proper amount of Si, it is possible to reduce the magnetic loss Pcv. If the Si content (in terms of SiO ₂ ) of the ferrite is less than 0.005% by mass with respect to the total mass of the oxide as the main component, the formation of the high resistance layer at the grain boundaries becomes insufficient and the reduction of the magnetic loss Pcv becomes insufficient. On the other hand, when the content of Si (in terms of SiO ₂ ) exceeds 0.03 mass%, the abnormal grain growth is promoted and the reduction of the magnetic loss Pcv becomes insufficient. The content of Si (in terms of SiO ₂ ) is preferably 0.005 to 0.01% by mass.

Since Nb contributes to increase the resistance of the grain boundaries of ferrite, by containing a proper amount of Nb, it is possible to reduce the magnetic loss Pcv. If the content of Nb (in terms of Nb ₂ O ₅ ) in the ferrite sintered body is less than 0.01% by mass based on the total mass of the oxide as the main component, the increase in the resistance of the grain boundaries tends to become insufficient and the reduction in the magnetic loss Pcv tends to be insufficient have. On the other hand, when the content of Nb (in terms of Nb ₂ O ₅ ) exceeds 0.1% by mass, the nonuniformity of crystal structure tends to be promoted. The content of Nb (in terms of Nb ₂ O ₅ ) is preferably 0.025 to 0.050 mass%.

Since Zr contributes to high resistance of the grain boundaries of ferrite, by containing a proper amount of Zr, it is possible to reduce the magnetic loss Pcv. When the content of Zr (in terms of ZrO ₂ ) of the ferrite is less than 0.005% by mass with respect to the total mass of the oxide as the main component, the increase in the resistance of the grain boundary tends to be insufficient and the reduction of the magnetic loss Pcv tends to become insufficient. On the other hand, when the content of Zr (in terms of ZrO ₂ ) exceeds 0.04 mass%, the nonuniformity of the crystal structure tends to be promoted. The content of Zr (in terms of ZrO ₂ ) is preferably 0.005 to 0.02 mass%.

Since Sn has an effect of increasing the specific resistance of the crystal grains of ferrite, by containing an appropriate amount of Sn, the eddy current loss can be lowered and the magnetic loss Pcv can be reduced. When the content of Sn (in terms of SnO) of the ferrite is less than 0.05% by mass with respect to the total mass of the oxide as the main component, the effect of increasing the resistance is not exhibited and the reduction of the magnetic loss Pcv tends to become insufficient. On the other hand, when the content of Sn (in terms of SnO) exceeds 0.35% by mass, the nonuniformity of the crystal structure tends to be promoted. The content of Sn is preferably 0.1 to 0.3 mass%.

The ferrite according to the present embodiment may further contain components other than those described above. For example, Ta (Ta ₂ O ₅ ), Hf (HfO ₂ ), and V (V ₂ O ₅ ) contribute to the high resistance of the grain boundaries of the ferrite core, like Nb and Zr described above. By containing an appropriate amount, it is possible to reduce the magnetic loss Pcv. If the content of Ta, Hf and V (in terms of Ta ₂ O ₅ , HfO ₂ and V ₂ O ₅ ) of the ferrite is less than 0.005 mass% with respect to the total mass of the oxide as the main component, the increase in the resistance of the grain boundary is likely to become insufficient , The reduction of the magnetic loss Pcv tends to be insufficient. On the other hand, when the content of Ta, Hf and V (in terms of Ta ₂ O ₅ , HfO ₂ and V ₂ O ₅ ) exceeds 0.040 mass%, the nonuniformity of the crystal structure tends to be promoted. The content of Ta, Hf and V (in terms of Ta ₂ O ₅ , HfO ₂ and V ₂ O ₅ ) is preferably 0.005 to 0.030 mass%.

Next, a method for producing ferrite will be described.

Initially, iron oxide? -Fe ₂ O ₃ , manganese oxide Mn ₃ O ₄ , zinc oxide ZnO and nickel oxide NiO, which constitute the main component, are prepared and mixed to obtain a mixture. At this time, another oxide may be mixed together with the oxide so that the composition ratio of each oxide component in the finally obtained mixture is within a predetermined range.

Subsequently, the mixture of the main components is calcined to obtain a calcined product (calcination step). The plasticity is usually carried out in air. The firing temperature depends on the components constituting the mixture, but it is preferably 800 to 1100 캜. Further, the calcination time depends on the components constituting the mixture, but it is preferably 1 to 3 hours. Thereafter, the obtained fired product is pulverized by a ball mill or the like to obtain a pulverized powder.

When pulverizing the calcined product of the main component material, a predetermined amount of Ca is added as calcium carbonate (CaCO ₃ ) or calcium oxide (CaO), and the two are mixed to obtain a raw material mixture for main constitution (mixing step).

On the other hand, a predetermined amount of silicon oxide (SiO ₂ ) constituting the subcomponent is prepared and added when the calcination product of the main component material is pulverized, and the two are mixed. As a result, a raw material mixture is obtained. Here, subcomponents (Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , HfO ₂ , V ₂ O ₅ and the like) other than the above components may be appropriately added. Further, other compounds may be used in place of the above-mentioned compounds so that the content of each subcomponent in the finally obtained mixture is within the above range.

Then, the raw material mixture obtained as described above is mixed with a suitable binder such as polyvinyl alcohol to obtain a molded product of a ferrite core.

Next, the formed body is fired in a heating furnace (main firing step). 1 is a graph showing an example of temperature setting in the main firing step. As shown in Fig. 1, the main firing step includes a temperature raising step S1 for gradually heating the molded body in the heating furnace, a temperature holding step S2 for maintaining the temperature at 1200 to 1300 deg. C, a slow cooling Cooling) step S3, and a quenching step S4 for quenching after completion of the slow cooling step S3.

The temperature raising step S1 is a step of raising the temperature in the heating furnace to a holding temperature to be described later. The temperature raising rate is preferably 10 to 300 占 폚 / hour.

When the temperature reaches a predetermined temperature (1200 to 1300 占 폚) by the temperature raising step S1, a temperature holding step S2 for holding the temperature at this temperature is performed. If the holding temperature in the temperature holding step S2 is less than 1200 占 폚, the grain growth of the ferrite core becomes insufficient and the hysteresis loss increases, so that the reduction of the magnetic loss Pcv becomes insufficient. On the other hand, if the holding temperature exceeds 1300 占 폚, the grain growth of the ferrite core becomes excessive and the eddy current loss increases, so that the reduction of the magnetic loss Pcv becomes insufficient. By setting the holding temperature at 1200 to 1300 占 폚, a balance between the hysteresis loss and the eddy current loss is achieved, and the magnetic loss Pcv in the high temperature region can be sufficiently reduced.

It is preferable that the firing time (holding time) is 2 hours or more. If the holding time is less than 2 hours, even when firing is performed at a temperature of 1200 to 1300 占 폚, the grain growth becomes insufficient and the reduction of the magnetic loss Pcv tends to become insufficient. The holding time depends on the raw material constituting the pulverized powder, but it is more preferably 3 to 10 hours.

After completion of the temperature holding step S2, the slow cooling step S3 is performed. The slow cooling rate in the slow cooling step S3 is preferably 200 DEG C / hour or less. If the slow cooling rate exceeds 200 ° C / hour, the residual stress in the particles of the ferrite core tends to be large, and the reduction of the magnetic loss tends to become insufficient. Further, the slow cooling rate means an average value in the slow cooling zone, and there may be a portion where the temperature decreases at a rate exceeding this.

In the slow cooling step S3, when the temperature is lowered from the holding temperature, the oxygen concentration in the heating furnace is controlled and an operation of continuously or stepwise lowering is performed (oxygen concentration adjusting step). By carrying out such an operation, it is preferable to set the oxygen concentration at 1200 占 폚 to 0.2 to 1.0% by volume and the oxygen concentration at 1100 占 폚 to 0.02 to 0.10% by volume.

It is preferable that the temperature at which the slow cooling step S3 is completed and the quenching step S4 is started (slow cooling end temperature) is 900 to 1150 deg. If the slow cooling termination temperature is higher than 1150 占 폚, the formation of grain boundaries of the ferrite core tends to be insufficient, and the reduction of the magnetic loss Pcv tends to become insufficient. On the other hand, if the slow cooling termination temperature is lower than 900 占 폚, the grain boundary of the ferrite core tends to be anomalous, and the reduction of the magnetic loss Pcv tends to be insufficient.

After completion of the slow cooling step S3, quenching step S4 is carried out. It is preferable to set the cooling rate at 150 ° C / hour or more for at least the temperature range from the slow cooling end temperature to 700 ° C.

[Example]

Hereinafter, the present invention will be described based on more detailed examples, but the present invention is not limited to these examples.

Examples 1 to 21 and Comparative Examples 1 to 17

Each component material was finally weighed so as to have the composition shown in Table 1, and wet-mixed using a ball mill. The raw material mixture was dried and then calcined at a temperature of about 900 ° C in the air. The obtained calcined powder was put into a ball mill, and wet pulverization was carried out for 3 hours until a desired particle diameter was obtained.

The pulverized powder thus obtained was dried, and 0.8 parts by mass of polyvinyl alcohol was added to 100 parts by mass of the pulverized powder. The resulting mixture was granulated, and the obtained mixture was pressure-molded under a pressure of about 150 MPa to obtain a toroidal powder. Shaped molded body and a molded body for defect test were obtained. The molded body was subjected to firing in the range of firing conditions shown below to obtain a plurality of toroidal ferrite cores and a ferrite core for defect test. In this main firing step, the holding temperature was set to 1200 to 1300 占 폚, and the slow cooling termination temperature was set to 900 to 1150 占 폚.

 The magnetic loss Pcv of the ferrite core was measured as follows. That is, the magnetic loss in the temperature range of 25 to 150 ° C was measured under the conditions of a magnetic flux density of 200 mT and a frequency of 100 kHz with a BH analyzer (type SY-8217) manufactured by Iwatsu Keisei Co., Respectively.

The saturation magnetic flux density of the ferrite core was measured as follows. That is, a toroidal shape having an outer diameter of 20 mm was measured at a saturation magnetic flux density Bs at 1194 A / m using a DC BH tracer to obtain a value of 120 ° C.

The defect strength of the ferrite core was measured as follows. That is, five cylindrical specimens having a diameter of 10 mm and a height of 10 mm (preliminarily measured in weight) were placed in a cylindrical stainless-steel pot having an inside diameter of 100 mm and an inside height of 118 mm provided with shielding plates on the inner circumferential side, The stainless steel pot was rotated at a revolution of 100 rpm for 20 minutes. Thereafter, the cylindrical sample was taken out, and the weight after the test was measured to determine the defect rate.

The defect rate is given by the following calculation formula.

(%) - [(weight before test) - (weight after test) / (weight before test) x 100

In the above equation, the defect ratio is more resistant to impact as the numerical value is smaller.

In the present invention, it is judged that the degree of deficiency is less than 2% as the acceptable level.

Table 1 shows the measurement results. It can be seen from the results shown in Table 1 that in the samples (Examples 1 to 21) in which the composition of the main component of the ferrite and the addition of the trace components were suitably controlled, the magnetic loss Pcv at 120 ° C and the saturation magnetic flux density Bs were satisfactory, %. ≪ / RTI >

As described above, the MnZn ferrite according to the present invention has high saturation magnetic flux density Bs, low magnetic loss Pcv, and high defect strength, so that it can be suitably used for components such as transformers and choke coils.

Claims (4)

The main component is composed of 66 to 70 mol% of iron oxide in terms of Fe ₂ O ₃ , 10 to 20 mol% of zinc oxide in terms of ZnO, 0.4 to 2 mol% of nickel oxide in terms of NiO, and the balance of substantially MnO , 0.001 to 0.03 mass% of Si in terms of SiO ₂ , 0.02 to 0.15 mass% of Ca in terms of CaO, 0.01 to 0.1 mass% of Nb in terms of Nb ₂ O ₅ , and Zr in terms of Nb ₂ O _{5 based} on the total mass of the oxide as a main component 0.005 to 0.04 mass% in terms of ZrO ₂ and 0.05 to 0.35 mass% in terms of SnO. The ferrite according to claim 1, characterized in that the defect ratio in the defect test is less than 2%. The method according to claim 1 or 2, wherein V, Ta and Hf are converted into V ₂ O ₅ , Ta ₂ O ₅ and HfO ₂ , respectively, with respect to the total mass of the oxide as the main component, and 0.001 to 0.01 mass% of V , Ta, and Hf. A transformer comprising ferrite according to any one of claims 1 to 3.

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