JP2012138399A - Ferrite core and electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferrite core capable of achieving both reduction in power loss and a high saturation magnetic flux density in a high-frequency region and of improving a quality factor, and to provide an electronic component to which the ferrite core is applied.SOLUTION: A ferrite core has a core part composed of a ferrite composition, and a coating layer formed on at least a part of a surface of the core part. The ferrite composition contains a main component containing iron oxide, zinc oxide, and manganese oxide, and, as an accessory component, 50-300 ppm of silicon oxide in terms of SiOand 110-1120 ppm of calcium oxide in terms of CaO for the main component 100 wt.%. The Tsp of the ferrite composition, at which a magnetic loss is minimized, is in a range of 5-50°C, and satisfies the following formula (1): Tsp=21.6(X+0.52Z)-1520, and the following formula (2): X≥58.0. A thermal expansion coefficient of the coating layer is equal to or less than that of the core part.

Description

  The present invention relates to a ferrite core and an electronic component. More specifically, the present invention relates to a ferrite core and an electronic component. More specifically, in a high-frequency region (for example, 1 MHz or more), the operating temperature is near room temperature or near outside air temperature. (Bs) and, as a result, the ferrite core which can improve a quality factor (Pvc / Bs), and an electronic component to which the ferrite core is applied.

  In recent years, various electronic devices such as portable devices have rapidly become smaller and lighter, and in order to respond to this demand, there are demands for miniaturization, higher efficiency and higher frequency of electronic components used in electric circuits of various electronic devices. Is growing rapidly.

  For example, Ni-Zn ferrite has been conventionally used as a coil magnetic core for a DC-DC converter of a portable device or the like. However, since Ni—Zn ferrite has a relatively large power loss, it has been difficult to cope with downsizing, high efficiency, and high frequency of components such as a coil magnetic core.

  For such a problem, it is conceivable to use Mn—Zn ferrite instead of Ni—Zn ferrite. Conventionally, Mn—Zn ferrite has been used in power transformers and the like, and has been used in a low frequency and high magnetic field environment.

  In general, a ferrite used as a magnetic core of a transformer or the like has been required to have temperature characteristics that minimize magnetic loss in a temperature range higher than the actual operating temperature range. This is because there is a risk of causing a so-called thermal runaway in which the transformer heats up due to magnetic loss and the temperature of the transformer itself rises, and as a result, the magnetic loss further increases and the heat generation of the transformer increases. is there. In the case of a power transformer, the operating temperature range is usually a temperature near the operating temperature (for example, 80 ° C.).

  However, in recent years, for example, when the transformer is cooled using a fluorine-based inert liquid or the like, it is possible to set the ambient temperature or use temperature to room temperature or lower, and further to an arbitrary temperature. In this case, the temperature at which the magnetic loss is minimized is not particularly limited, and it is only required that the absolute value of the magnetic loss is small.

  On the other hand, when used as a coil magnetic core for a DC-DC converter of a portable device or the like, the environmental temperature or the operating temperature is near room temperature or near the outside temperature, and the voltage is lower than that of a transformer, and there is less risk of thermal runaway. . Further, in such a portable device, it is required that the drive frequency is increased (for example, 1 MHz or more) and the loss in the high frequency region is small.

  Also, in transformers and parts used in portable devices such as DC-DC converters, the response to large currents is progressing. For this reason, a magnetic core used for such a component is required to have excellent direct current superposition characteristics that do not lower the inductance even with a large current. A high saturation magnetic flux density is indispensable for realizing an excellent DC superposition characteristic, and it is necessary to have a high saturation magnetic flux density particularly at the ambient temperature or the use temperature.

  Therefore, there is a demand for a ferrite composition having an ambient temperature or operating temperature near room temperature or near ambient temperature, reducing magnetic loss in a high frequency region, and having a high saturation magnetic flux density.

As an example of a Mn—Zn ferrite having a low loss and a high saturation magnetic flux density, for example, in Patent Document 1, Fe ₂ O ₃ is 52.4 to 53.7 mol% and ZnO is 7.0 to 11 as main components. .5 mol%, and the remainder MnO, as an auxiliary component, and _CaO, and V 2 _{O 5,} and _{Nb 2 O 5, Al 2 O} 3 or _Bi 2 _{O 3} and a have been proposed Mn-Zn ferrite containing specified amounts Yes.

  However, as described in Patent Document 1, the Mn—Zn ferrite described above is a temperature (Pcv min) at which the magnetic loss in the low frequency region is minimized at 60 ° C. or more which is the actual driving temperature of the transformer. There is a problem that it cannot be used near room temperature and in a high frequency region.

  In addition, regarding a ferrite core for various uses, it has been studied to form a glass film on the surface of the core portion. However, conventionally, it has been considered unfavorable due to the influence of the deterioration of the original properties of ferrite due to the stress of the glass coating.

  Patent Document 2 proposes forming a glass coating film on the surface of the core by a barrel coating method. However, in Patent Document 2, such deterioration of the properties of the ferrite core has not been studied, and in particular, no consideration has been given to improvement in power loss (Pcv), increase in magnetic flux density (Bs), or the like. .

JP 2003-128458 A JP 2001-237135 A

  The present invention has been made in view of such a situation, and in a high frequency region (for example, 1 MHz or more) where the use temperature or the environmental temperature is near room temperature or near the outside air temperature, the power loss (Pcv) is reduced and the high saturation magnetic flux density. An object of the present invention is to provide a ferrite core that can achieve both (Bs) and, as a result, improve the quality factor (Pvc / Bs), and an electronic component having the ferrite core.

  As a result of intensive studies, the inventors of the present application have formed a coating layer having a thermal expansion coefficient equal to or less than that of the ferrite core portion on at least a part of the surface of the core portion with the MnZn ferrite composition having a specific composition as the core portion. By doing so, it is possible to achieve both reduction of power loss (Pcv) and high saturation magnetic flux density (Bs) in a high frequency region (for example, 1 MHz or more), and as a result, quality factor (Pvc / Bs) can be improved. The headline and the present invention were completed.

That is, the ferrite core according to the present invention is
A ferrite core having a core part composed of a ferrite composition and a coating layer formed on at least a part of the surface of the core part,
The ferrite composition includes a main component including iron oxide, zinc oxide, and manganese oxide,
With respect to 100% by weight of the main component, as subcomponents, silicon oxide contains 50 to 300 ppm in terms of SiO ₂ , and calcium oxide contains 110 to 1120 ppm in terms of CaO,
The minimum temperature Tsp of magnetic loss of the ferrite composition is in the range of 5 to 50 ° C.
When the content of the iron oxide in the main component is X mol% in terms of Fe ₂ O ₃ , the content of the zinc oxide is Z mol% in terms of ZnO, and the balance is the manganese oxide, the Tsp and the X And Z satisfies the following formulas (1) and (2),
The thermal expansion coefficient of the coating layer is less than or equal to the thermal expansion coefficient of the core portion.
Tsp = 21.6 (X + 0.52Z) -1520 Formula (1)
X ≧ 58.0 Formula (2)

  In the present invention, when the temperature (Tsp) at which the magnetic loss is minimized is in the range of 5 to 50 ° C. in consideration of use near room temperature or near the outside temperature, the above formulas (1) and (2) are It is used to determine the composition of the main component, and the content of the subcomponent is within the specific range. By using such a ferrite composition, it is possible to reduce power loss (Pcv) even in a high frequency region (for example, 1 MHz or more) while maintaining a high saturation magnetic flux density (Bs), resulting in a quality factor (Pcv / Bs). Can be improved.

  In the present invention, the power loss Pcv can be improved by setting the thermal expansion coefficients of the core portion and the coating layer to the above relationship. In addition, the coating layer also has a role as a protective layer that suppresses chipping of the core portion and the like, and can improve production efficiency.

  Preferably, the said coating layer is comprised from the glass composition. By doing in this way, a coating layer can be easily formed in the surface of a core part. Moreover, when the glass composition which has insulation is formed in the core part surface, the insulation with a wire etc. which are wound around a core part can be improved.

  An electronic component according to the present invention is composed of the ferrite composition described above, has a ferrite core in which the thermal expansion coefficient of the core portion and the coating layer is controlled as described above, and is used in a frequency region of 1 MHz or more. The

  Since the Tsp of the ferrite composition is in the temperature range of 5 to 50 ° C., the electronic component according to the present invention is suitable as a component whose use temperature or environmental temperature is near room temperature or near outside temperature. In addition, since the reduction of electrode loss and the high saturation magnetic flux density are compatible, power saving can be realized.

  Such electronic components are not particularly limited, and include DC-DC converter coil components used for portable devices and the like. Examples of the coil component include an inductor and a choke coil. Moreover, the electronic component according to the present invention can be suitably used for the transformer by cooling the transformer to a temperature near Tsp. Examples of transformer parts include power transformers for switching and inverters.

  According to the present invention, while maintaining a high saturation magnetic flux density (Bs), power loss (Pcv) can be reduced even in a high frequency region (for example, 1 MHz or more), and as a result, a quality factor (Pcv / Bs) can be improved. it can.

  Moreover, especially a coating layer can be easily formed in the surface of a core part by comprising a coating layer with a glass composition. Further, when the glass composition is insulative, it is possible to ensure insulation with a wound wire or the like even if the core part is electrically conductive.

FIG. 1 is a schematic cross-sectional view of a ferrite core according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a barrel device used for manufacturing a ferrite core according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of the drum core after winding the coil.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings.

Ferrite core The ferrite core according to the present invention is not limited to the drum type shown in FIG. 1, but FT type, ET type, EI type, UU type, EE type, EER type, UI type, toroidal type, pot type, cup Examples include molds. In the present embodiment, as shown in FIG. 1, the ferrite core 1 has a drum core shape, and has a configuration in which a coating layer 10 is formed on the entire surface of the core portion 2.

The core part core part 2 has a cylindrical or prismatic core part 4 and a pair of flange parts 5 integrally formed on both sides along the axial direction of the core part 4. The outer diameter of the flange portion 5 is larger than the outer diameter of the core portion 4, and a recess 6 surrounded by the flange portion 5 is formed on the outer periphery of the core portion 4. The coil 30 is formed by winding the wire 30 around the recess 6.

  Although the dimension of the core part 2 is not particularly limited, in the present embodiment, the outer diameter of the core part 4 is 0.6 to 1.2 mm, and the axial width of the core part 4 is 0.3 to 1. 0 mm, the outer diameter of the flange part 5 is 2.0 to 3.0 mm, the thickness of the flange part 5 is 0.2 to 0.3 mm, and the depth from the outer peripheral surface of the flange part 5 to the outer peripheral surface of the core part 4 The thickness is 0.5 to 1.0 mm. In addition, the shape of the collar part 5 may be a square, an octagon, etc. other than a circle.

  The core part 2 is comprised with the ferrite composition which concerns on this embodiment.

  The ferrite composition according to this embodiment is a Mn—Zn ferrite and contains iron oxide, manganese oxide, and zinc oxide as main components. The temperature (Tsp) at which the magnetic loss of the ferrite composition according to this embodiment is minimized is in the range of 5 to 50 ° C.

  Conventionally, in Mn—Zn ferrite, the temperature showing Tsp has been explained by the magnetocrystalline anisotropy. That is, it is said that the magnetic loss has a minimum value at a temperature of K1 = 0 where the sign of the magnetocrystalline anisotropy constant K1 changes from a negative value to a positive value as the temperature rises.

Further, it is known that this temperature coincides with a so-called secondary peak of magnetic permeability where the magnetic permeability is maximized. The above K1 increases monotonously with increasing temperature, but Fe ²⁺ has a positive K1, so when the amount of Fe ²⁺ increases (ie, the amount of Fe ₂ O ₃ increases), the temperature of the secondary peak Moves to the low temperature side.

On page 79 of “Electronic Materials Series Ferrite” (published by Maruzen Co., Ltd., 1988), the following formula is used to calculate Tsp when the amount of Fe ₂ O ₃ is X mol% and the amount of ZnO is Z mol%. Is described.
Tsp = -45.5 (X + 0.2Z) +2620

Further, it is known that a high saturation magnetic flux density can be easily obtained by increasing the amount of Fe ₂ O ₃ . However, when the amount of Fe ₂ O ₃ increases, the saturation magnetic flux density is considered to be influenced not only by the amount of Fe ₂ O ₃ but also by the ratio of the amount of Fe ₂ O _{3 and the} amount of ZnO.

Tsp of the ferrite composition according to the present embodiment is in the range of 5 to 50 ° C. In such a ferrite composition, it is conceivable to increase T ₂ within the above range and increase power loss by increasing the amount of Fe ₂ O ₃ . Therefore, if it is attempted to determine the Fe ₂ O ₃ content and the ZnO content using the above formula, for example, Tsp becomes −200 ° C. or less, which is not realistic.

Therefore, it is considered that the above formula for obtaining Tsp does not hold when the amount of Fe ₂ O ₃ is large (for example, 58 mol% or more). However, since there is nothing which is an index for determining the Tsp if the amount of _Fe 2 _{O 3} is large, if the amount of _Fe 2 _{O 3} is large, in 1MHz or more high-frequency region, the ferrite composition having a high saturation magnetic flux density Had no knowledge.

Therefore, the present inventors have conducted intensive experiments and found that when the content of iron oxide in the ferrite composition is relatively large, Tsp and iron oxide and zinc oxide have a relationship different from the above formula. I found it. That is, when the content of iron oxide in the ferrite composition is X mol% in terms of Fe ₂ O ₃ and the content of zinc oxide is Z mol% in terms of ZnO, Tsp, X and Z are as follows: The following expressions (1) and (2) are satisfied.
Tsp = 21.6 (X + 0.52Z) -1520 Formula (1)
X ≧ 58.0 Formula (2)

Therefore, in this embodiment, in 100 mol% of the main component, the content (X) of iron oxide and the content (Z) of zinc oxide satisfy the above formula (1) in terms of Fe ₂ O ₃ and ZnO. To be decided. X is preferably 58.0 to 66.0 mol%.

  When the content of iron oxide is large, the temperature (Tsp) at which the magnetic loss is minimized and the content of iron oxide and zinc oxide satisfy the above relational expression, so that Tsp is 5 to 50 ° C. The optimum iron oxide and zinc oxide content that falls within the range is determined. The remainder of the main component is composed of manganese oxide.

  The ferrite composition according to the present embodiment contains silicon oxide and calcium oxide as subcomponents in addition to the main component calculated by the above formula. By including such a subcomponent, the absolute value of power loss can be reduced and a high saturation magnetic flux density can be obtained.

The content of silicon oxide is 50 to 300 ppm in terms of SiO _{2 with} respect to 100% by weight of the main component. Even if the content of silicon oxide is large or too small, power loss in the high frequency region tends to deteriorate.

  The content of calcium oxide is 110 to 1120 ppm in terms of CaO with respect to 100% by weight of the main component. Even if the content of calcium oxide is large or too small, power loss in the high frequency region tends to deteriorate.

  Note that the ferrite composition according to the present embodiment may include oxides of inevitable impurity elements.

  Specifically, B, C, P, S, Cl, As, Se, Br, Te, I, Li, Na, Mg, Al, K, Ga, Ge, Sr, Cd, In, Sn, Sb, Typical metal elements such as Ba, Pb, and Bi, and transition metal elements such as Sc, Ti, V, Cr, Co, Ni, Cu, Y, Zr, Nb, Mo, Pd, Ag, Hf, and Ta can be given.

Moreover, although the thermal expansion coefficient of the core part 2 changes with compositions of a ferrite composition, it is about 9 * 10 < ^-6 > / degreeC-10 * 10 < ^-6 > / degreeC in general.

The material of the coating layer coating layer 10 is not particularly limited as long as it has a thermal expansion coefficient that is equal to or lower than the thermal expansion coefficient of the core portion 2. For example, glass composition, SiO ₂ , B ₂ O ₃ , ZrO ₂ etc. are illustrated. The covering layer 10 may be composed of a plurality of materials, or may have a laminated structure composed of a plurality of layers.

  In this embodiment, it is preferable that the coating layer 10 is comprised from a glass composition. The glass composition is not particularly limited as long as it is formed in an amorphous state on the surface of the core portion 2 or formed as crystallized glass. For example, Si-B glass (borosilicate) Glass), alkali-free glass, lead-based glass and the like.

  The thermal expansion coefficient of the glass composition varies depending on the composition of components contained in the glass composition, the content of each component, and the like. Therefore, it is necessary to appropriately set the composition and content of the components so that the thermal expansion coefficient of the glass composition is equal to or less than the thermal expansion coefficient of the core portion 2.

  The coating layer 10 is not particularly limited as long as the coating layer 10 is coated to such an extent that an effect of improving power loss is obtained, but may be formed on at least a part of the surface of the core portion 2, with respect to the surface area of the core portion 2. The ratio (coverage) at which the coating layer is formed is preferably 50 to 100%, more preferably 90 to 100%. The higher the coverage, the greater the role as a protective layer for preventing the core portion 2 from being chipped.

  FIG. 1 shows a case where the coverage is 100%. Moreover, if the coating layer 10 is formed in the core portion 2 in the vicinity of a portion where the wire or the like is wound (in the present embodiment, the recess 6), a higher effect is easily obtained.

  The thickness of the coating layer 10 is not particularly limited as long as the effect of improving the power loss is obtained, but is preferably more than 0 μm and 50 μm or less, more preferably 5 μm or more and 25 μm or less. If the coating layer 10 is formed, the power loss is improved. However, if the coating layer is too thick, the contribution to the improvement effect of the power loss is small and the manufacturing cost increases, which is not preferable. Moreover, when the coating layer has a certain thickness, it can also serve as a protective layer for the core portion. Therefore, the thickness of the coating layer 10 is preferably within the above range.

  Furthermore, if the coating layer 10 has an insulating property, it is possible to ensure insulation from the wound wire even if the core portion 2 is conductive.

  Next, an example of the manufacturing method of the ferrite core in which the coating layer 10 is comprised with the glass composition as a ferrite core which concerns on this embodiment is demonstrated.

  First, in order to prepare the raw material of the ferrite composition constituting the core part 2, the starting raw materials (main component raw material and subcomponent raw material) are weighed and mixed so as to have a predetermined composition ratio. obtain. Examples of the mixing method include wet mixing using a ball mill and dry mixing using a dry mixer. It is preferable to use a starting material having an average particle size of 0.1 to 3 μm.

As a raw material for the main component, iron oxide (α-Fe ₂ O ₃ ), zinc oxide (ZnO), manganese oxide (Mn ₃ O ₄ ), or a composite oxide can be used. In addition, various compounds that become oxides or composite oxides by firing can be used. Examples of the oxide that becomes the above-mentioned oxide upon firing include simple metals, carbonates, oxalates, nitrates, hydroxides, halides, organometallic compounds, and the like. In addition, although the content of manganese oxide in the main component is calculated in terms of MnO, Mn ₃ O ₄ is preferably used as the main component material.

As the raw material of the subcomponent, as in the case of the raw material of the main component, not only the oxide but also a composite oxide or a compound that becomes an oxide after firing may be used. In the case of silicon oxide (SiO ₂ ), it is preferable to use SiO ₂ . In the case of calcium oxide (CaO), it is preferable to use calcium carbonate (CaCO ₃ ).

  Next, the raw material mixture is calcined to obtain a calcined material. Calcining causes thermal decomposition of raw materials, homogenization of ingredients, formation of ferrite, disappearance of ultrafine powder due to sintering and grain growth to an appropriate particle size, and converts the raw material mixture into a form suitable for the subsequent process. Done for. Such calcination is preferably performed at a temperature of 800 to 1100 ° C. for about 1 to 3 hours. The calcination may be performed in the air (air), or may be performed in an atmosphere having a higher oxygen partial pressure or in a pure oxygen atmosphere than in the air. The mixing of the main component raw material and the subcomponent raw material may be performed before calcining or after calcining.

  Next, the calcined material is pulverized to obtain a pulverized material. The pulverization is performed in order to break down the coagulation of the calcined material to obtain a powder having appropriate sinterability. When the calcined material forms a large lump, wet pulverization is performed using a ball mill or an attritor after coarse pulverization. The wet pulverization is performed until the average particle diameter of the calcined material is preferably about 1 to 2 μm.

  Next, the pulverized material is granulated (granular) to obtain a granulated product. The granulation is performed in order to convert the pulverized material into aggregated particles having an appropriate size and convert it into a form suitable for molding. Examples of such a granulation method include a pressure granulation method and a spray drying method. The spray drying method is a method in which a commonly used binder such as polyvinyl alcohol is added to the pulverized material, and then atomized in a spray dryer and dried at a low temperature.

  Next, the granulated product is molded into a predetermined shape to obtain a molded body. Examples of the molding of the granulated product include dry molding, wet molding, and extrusion molding. The dry molding method is a molding method in which a granulated product is filled in a mold and compressed and pressed (pressed). The shape of the molded body is not particularly limited, and may be appropriately determined according to the application. In the present embodiment, the shape is a drum core shape.

  Next, the sintered body (core portion 2) is obtained by subjecting the formed body to main firing. This firing is performed in order to obtain a dense sintered body by causing sintering in which the powder adheres at a temperature below the melting point between the powder particles of the molded body containing many voids. Such firing is preferably performed at a temperature of 900 to 1300 ° C. for usually 2 to 5 hours. The main calcination may be performed in the atmosphere (air) or in an atmosphere having a higher oxygen partial pressure than in the atmosphere.

  Next, with respect to the obtained core part 2, the coating layer 10a before heat processing comprised from a glass composition, binder resin, etc. is formed in the surface of the core part 2 using the barrel apparatus shown in FIG.

  The barrel apparatus 20 shown in FIG. 2 has a cylindrical or prismatic cylinder casing 20a, and a barrel container 22 is rotatable in the direction of arrow A (or the opposite direction) around its axis in the hollow interior. Is housed.

  An inlet pipe 23 and an outlet pipe 24 are formed in the casing 20a. The drying gas can enter the casing 20 a from the inlet pipe 23, and the air inside the casing can be discharged from the outlet pipe 24.

  A spray nozzle 25 is arranged along the axial direction at the axial center position in the barrel container 22, and the slurry 26 is directed from the nozzle 25 toward a number of core portions 2 stored in the barrel container 22. Can be sprayed. Since the barrel container 22 rotates in the direction of arrow A, the core portion 2 exists in the state shown in FIG. 2 and is agitated by the rotation of the barrel container 22.

  The nozzle 25 can spray the slurry 26 toward the assembly of the core portions 2. Note that the direction in which the slurry is sprayed from the nozzle 25 may be freely changed. Further, a discharge pipe (not shown) is connected to the casing 20a so that excess slurry 26 can be discharged.

  The wall of the barrel container 22 is formed with a large number of holes communicating with the outside and the inside, and the slurry 26 stored below the casing 20 a also enters the inside of the barrel container 22, and the slurry 26 The core part 2 can be immersed in Further, when the drying gas flows from the inlet pipe 23 through the casing 20 a to the outlet pipe 24, the drying gas also flows inside the barrel container 22.

  In order to form the coating layer 10a before the heat treatment, first, a large number of core portions 2 are accommodated in the barrel container 22 shown in FIG. Then, the barrel container 22 is rotated, and the slurry 26 is sprayed from the nozzle 25 while stirring the assembly of the core portions 2 to form the coating layer 10a before the heat treatment.

  The slurry 26 includes glass powder obtained by pulverizing the glass composition described above, a binder resin, and a solvent. Furthermore, other additives may be included. The glass composition may be made amorphous by mixing, melting, and rapidly cooling raw materials such as non-oxides such as oxides and halides constituting the composition. Moreover, you may use crystallized glass as a glass composition. In this embodiment, Si-B glass is used as the glass powder. The average particle diameter (median diameter) of the glass powder is not particularly limited, but is preferably in the range of 0.1 μm to 10 μm.

  The binder resin contained in the slurry 26 is preferably polyvinyl alcohol (PVA), a modified polyvinyl alcohol resin, or a mixture thereof. By doing in this way, the coating layer 10a before heat processing formed is excellent in adhesiveness with the core part 2. FIG.

  The solvent preferably contains water. The solvent may be water only, but when the contact angle between the surface of the glass powder and water is large, water-soluble alcohol such as ethanol, isopropyl alcohol (IPA), isobutyl alcohol (IBA), etc. is mixed at a certain ratio. It is preferable to suppress aggregation and sedimentation of the glass powder.

  The slurry 26 sprayed on the core part 2 covers the surface of each core part 2, and forms the coating layer 10a before baking. At this time, excess slurry 26 is discharged through a discharge pipe (not shown). Although the processing time which sprays the slurry 26 from the nozzle 25 is not specifically limited, For example, it is about 30 to 180 minutes. The temperature of the slurry 26 at the time of spraying is preferably 40 ° C. or more and 100 ° C. or less although it depends on the composition of the solvent. When using a solvent having a low boiling point, it is preferable to lower the temperature within the above temperature range.

  Next, while the slurry 26 is sprayed, the coating layer 10a before the heat treatment is simultaneously dried. In the drying process, a drying gas is poured into the casing 20 a from the inlet pipe 23 and discharged from the outlet pipe 24. The drying gas used for this drying treatment is, for example, air having a temperature of 50 to 100 ° C. After the spray treatment, a drying treatment may be further performed, for example, for 5 to 30 minutes.

  After the drying process, the core part 2 on which the coating layer 10a before the heat treatment is formed is taken out of the barrel container 22 and subjected to a heat softening process. The heat treatment conditions are determined according to the softening point of the glass powder contained in the coating layer 10a before the heat treatment. Specifically, the heat treatment temperature is preferably 600 to 800 ° C., and the heat treatment time is 5 to 120 minutes.

  In the case of Mn—Zn ferrite, the heat treatment is preferably performed in a nitrogen gas atmosphere with an oxygen partial pressure of 0.1% or less. This is because the oxidation of the core part 2 causes deterioration of characteristics, so that the oxidation can be prevented by lowering the oxygen partial pressure.

  After the heat treatment, a vitrified coating layer 10 is formed on the surface of the core portion 2, and the ferrite core 1 shown in FIG. 1 is obtained. In the present embodiment, vitrification is defined as a continuous amorphous solid film having a rigidity comparable to that of crystals.

  Thereafter, as shown in FIG. 3, a pair of terminal electrodes 32 made of silver, titanium, nickel, chromium, copper, or the like is printed, transferred, or immersed on the end face of one flange 5 in each core 2. It is formed by sputtering, plating or the like. The terminal electrode 32 is insulated because the covering layer 10 exists even if the core 2 is conductive.

  Thereafter, the wire 30 is wound around the core 4 and both ends of the wire are respectively connected to the terminal electrode 32 by thermocompression bonding, welding by ultrasonic waves or lasers, a soldering method, and the like. The coil component according to the form is completed.

  In the ferrite core according to the present embodiment, the power loss (Pcv) can be reduced even in a high frequency region (for example, 1 MHz or more) while maintaining the saturation magnetic flux density (Bs) high, and as a result, the quality factor (Pcv / Bs) is reduced. Can be improved. Moreover, especially a coating layer can be easily formed in the surface of a core part by comprising a coating layer with a glass composition. Further, when the glass composition is insulative, it is possible to ensure insulation with a wound wire or the like even if the core part is electrically conductive.

  The reason why the quality factor (Pcv / Bs) can be improved in the ferrite core according to the present embodiment is not necessarily clear, but can be considered as follows, for example.

  In some cases, an internal compressive stress is already applied to the ferrite core as a residual stress. Such residual stress is caused by stress caused by shrinkage during firing and cooling of the ferrite composition, stress caused by evaporation of components in the ferrite composition during firing and cooling, particularly ZnO component, and the like. It is thought that there is.

  Therefore, by forming a coating layer 10 having a thermal expansion coefficient equal to or lower than the thermal expansion coefficient of the core portion 2 on at least a part of the surface of the core portion 2, Since the thermal expansion of 10 is less than or equal to the thermal expansion of the core part 2, tensile stress resulting from the thermal expansion of the core part 2 is generated in the coating layer 10. And it is thought that this tensile stress may cancel the residual stress (compressive stress) of the core part 2, and it is thought that the power loss Pcv of a ferrite core can be improved for that purpose.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  For example, in the above-described embodiment, the coating layer before the heat treatment is formed on the fired core portion, and the coating layer is formed by heat treatment. However, the firing of the core portion and the heat treatment of the coating layer are performed. You may do it at the same time. By doing so, the process can be simplified.

  In the binder removal step, the particle size of the glass powder may be set to a specific range so that the organic component of the binder resin contained in the slurry is easily volatilized. By doing in this way, the intensity | strength of the coating layer itself before heat processing can be raised, and the crack of the core part at the time of coating layer formation before heat processing can be prevented.

  Further, in the step of forming the coating layer before the heat treatment, for example, by changing the amount of the binder resin contained in the slurry, the strength near the surface of the coating layer before the heat treatment is increased in the vicinity of the boundary with the core portion of the coating layer. You may make it become weaker than the intensity | strength of. By doing in this way, the surface vicinity of this coating layer plays the role of a sacrificial film, and it can prevent the chip | tip of a core part etc. effectively.

  Furthermore, the coating layer before heat treatment is made into a plurality of layers, and the softening point of the glass composition contained in the layer on the surface side of the coating layer is set higher than the softening point of the glass composition contained in the layer close to the core part. Also good. In the heat treatment step, the heat treatment temperature is set higher than the softening point of the glass composition included in the layer close to the core part and lower than the softening point of the glass composition included in the surface layer of the coating layer. By doing in this way, the layer of the surface side of a coating layer can be made into a sacrificial film, and the chip | tip etc. of a core part can be prevented effectively.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

Example 1
First, Fe ₂ O ₃ , ZnO, and Mn ₃ O ₄ were prepared as main components. SiO ₂ and CaCO ₃ were prepared as auxiliary component materials.

  Next, the prepared raw material powder is weighed so as to have the content calculated by the above formula (1), and the subcomponent raw material powder has the amount shown in Table 1. After weighing, wet mixing was performed for 5 hours with a ball mill to obtain a raw material mixture.

  Next, the obtained raw material mixture was calcined in air at 950 ° C. for 2 hours, and then wet pulverized with a ball mill for 20 hours to obtain a pulverized material having an average particle diameter of 1.5 μm.

Next, this pulverized material was dried, and then granulated by adding 1.0% by weight of polyvinyl alcohol as a binder to 100% by weight of the pulverized material, and sized with a 20 mesh sieve to obtain granules. This granule was pressure-molded at a pressure of 196 MPa ( ² ton / cm ² ) to obtain a molded body having a toroidal shape (size = outer diameter 22 mm × inner diameter 12 mm × height 6 mm).

  The obtained molded body was subjected to fluorescent X-ray analysis, the composition of the ferrite core was measured, and it was confirmed that it was consistent with the amount shown in Table 1.

  Next, these molded bodies were fired at 1270 ° C. for 2.5 hours while appropriately controlling the oxygen partial pressure to obtain a core portion as a sintered body.

  Next, the powder of the glass composition for forming a coating layer was prepared. Si-B glass was used as the glass composition. The Si-B glass was prepared by mixing and melting raw materials such as oxides constituting the glass component and then rapidly cooling.

In this example, glass compositions A to D in which the thermal expansion coefficient was changed by changing the composition and content of the components in the Si-B glass were used. The thermal expansion coefficient of the glass composition A is 6 × 10 ⁻⁶ / ° C., the thermal expansion coefficient of the glass composition B is 11 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the glass composition C is 8 × 10 ⁻⁶ / ° C. The thermal expansion coefficient of the glass composition G was 10 × 10 ⁻⁶ / ° C.

  In addition, the thermal expansion coefficient of the core part and the glass composition was measured by TMA.

  Next, a slurry used to form a coating layer before heat treatment was prepared. First, the obtained glass composition powder and PVA were mixed at a predetermined weight ratio. Furthermore, the obtained solid component (a mixture of glass powder and PVA) and a solvent were mixed at a predetermined weight ratio, and mixed by a ball mill to prepare a slurry. As the solvent, a mixture of water and ethanol at 8: 2 was used. The content of the binder resin with respect to the glass powder in the slurry was 10% by weight.

  Next, the core part was thrown into the barrel container of the barrel device, and a coating layer was formed on the entire surface of the core part by spraying using the slurry described above. At the same time as the spraying, drying was performed at a hot air temperature of 70 ° C.

  After that, the core part on which the coating layer before heat treatment was formed was taken out from the barrel container, and this core part was heat treated at 750 ° C. for 1 hour, and the vitrified coating layer was formed on the entire surface of the core part. A core (toroidal shape) was obtained.

  The thickness of the coating layer was about 3 to 25 μm. The thickness of the coating layer was calculated from the dimensions before and after the coating layer was formed.

  Moreover, the coverage was about 98 to 100%. The covering rate was calculated by observing 20 samples visually and measuring the covering area of the sample in which the formation of the coating layer was incomplete.

<Power loss (Pcv)>
The primary winding and the secondary winding are wound three times each on the obtained core part sample and the ferrite core after the coating layer is formed, and the power loss at 0 to 55 ° C. is measured under the condition of 1 MHz-50 mT, The temperature (Tsp) at which the loss was minimized was determined, and the power loss Pcv at Tsp was calculated (unit: kW / m ³ ). The measurement was performed using a BH analyzer (SY-8217 manufactured by Iwasaki Tsushinki Co., Ltd.). The results are shown in Tables 1 and 2.

<Saturation magnetic flux density (Bs)>
After winding the winding 60 times on the obtained core part sample and the ferrite core after forming the coating layer, a magnetic field of 2 kA / m was applied using a BH curve tracer (Model BHS40 manufactured by Riken Denshi Co., Ltd.). The saturation magnetic flux density Bs was measured at Tsp (unit: mT). The results are shown in Tables 1 and 2.

  Tables 1 and 2 show Pcv / Bs indicating the quality factor of the core portion and the ferrite core after forming the coating layer in the high frequency region (1 MHz). The smaller Pcv or the larger Bs, the smaller this Pcv / Bs. Therefore, it is preferable that the value of Pcv / Bs is smaller because a reduction in power loss and a higher saturation magnetic flux density can be achieved at the same time. Further, in Table 2, the Pcv / Bs of the ferrite core after the coating layer is formed is preferably 1.0 or less.

  Table 2 also shows the power before and after the formation of the coating layer, calculated from the power loss (Pcv) value of the core sample before the coating layer was formed and the power loss (Pcv) value of the ferrite core after the coating layer was formed. The improvement rate (change rate) of loss (Pcv) was shown. In this example, an improvement rate (change rate) of 17% or more was considered good, more preferably 20% or more.

  From Table 1, it was confirmed that the Tsp obtained by the calculation and the Tsp obtained by the measurement of Pcv almost coincided. In Samples 2 to 5, it was confirmed that Tsp was in the range of 5 to 50 ° C. Furthermore, in samples 2 to 5, it was confirmed that the power loss (Pcv) in the high frequency region (1 MHz) was lower than those of samples 1 and 6 where Tsp was not in the range of 5 to 50 ° C.

Samples 2a to 5a in Table 2 have Samples 2 to 5 whose Tsp is within the scope of the invention of the present application (Tsp is within the range of 5 to 50 ° C.) as a core portion, and the thermal expansion coefficient (10 × 10 10) of the core portion. the glass a having a ^-6 / ° C.) low thermal expansion coefficient than ^{(6 × 10 -6 / ℃)} , and covers the surface of the core portion.

  In such samples 2a to 5a, it was confirmed that the power loss (Pcv) in the high frequency region (1 MHz) was reduced as compared with the samples 2 to 5 before the coating layer was formed. That is, compared to the core part samples (samples 2 to 5), the ferrite core (samples 2a to 5a) in which the coating layer made of glass A is formed has a power loss (Pcv) in the high frequency region (1 MHz) of 20 to 35. % Improvement was confirmed.

  Furthermore, before and after forming the coating layer made of glass A on the surface of the core portion, a high saturation magnetic flux density (Bs) is maintained. As a result, the ferrite core (sample 2a) in which the coating layer made of glass A is formed In ~ 5a), it was confirmed that the quality factor represented by Pcv / Bs was improved.

  However, when Samples 1 and 6 whose Tsp is not within the scope of the invention of the present application are used as the core portion, even if the coating layer made of glass A is formed on the surface of the core portion, before and after the formation of the coating layer It was confirmed that the effect of improving the power loss (Pcv) in the high frequency region (1 MHz) could not be sufficiently obtained (Samples 1a and 6a).

  From these results, when the Tsp of the ferrite composition forming the core portion is within the scope of the present invention (Tsp is within the range of 5 to 50 ° C.), the coating layer having a thermal expansion coefficient equal to or lower than that of the core portion. Is formed on the surface of the core portion, while maintaining a high saturation magnetic flux density (Bs), power loss (Pcv) can be reduced even in a high frequency region (for example, 1 MHz or more), resulting in a quality factor (Pcv / Bs). ) Could be improved.

  In particular, such an effect of improving the power loss is an effect that appears remarkably when the Tsp of the ferrite composition forming the core portion is within the range of the present invention (Tsp is within the range of 5 to 50 ° C.). .

Samples 1b to 6b in Table 2 were samples except that instead of the glass A used in the samples 1a to 6a, a glass B having a thermal expansion coefficient (11 × 10 ⁻⁶ / ° C.) larger than that of the core portion was used. Ferrite cores were prepared in the same manner as 1a to 6a, and the same evaluation was performed.

  In the samples 1b to 6b, the power in the high frequency region (1 MHz) before and after the formation of the coating layer of the glass B regardless of whether or not the Tsp of the ferrite composition forming the core portion is within the scope of the present invention. It was confirmed that the loss (Pcv) improvement effect could not be obtained but rather deteriorated.

  That is, when the core part is covered with a coating layer having a thermal expansion coefficient larger than that of the core part, the effect of improving the power loss (Pcv) cannot be obtained before and after the formation of the coating layer regardless of the Tsp range. Was confirmed.

Moreover, in the samples 4c and 4d in Table 2, instead of the glass A used in the sample 4a, the glass C having a smaller thermal expansion coefficient (11 × 10 ⁻⁶ / ° C.) than the core portion, or the same thermal expansion as the core portion. Except for using glass D having a coefficient (10 × 10 ⁻⁶ / ° C.), a ferrite core was prepared in the same manner as Sample 4a, and the same evaluation was performed.

  In samples 4c and 4d, the core part sample of sample 4 in which the Tsp of the ferrite composition forming the core part is within the scope of the present invention is used, and the coating layer having a thermal expansion coefficient equal to or lower than the thermal expansion coefficient of the core part is used. Since the core portion is covered, it was confirmed that the effect of improving the power loss (Pcv) in the high frequency region (1 MHz) was obtained before and after the formation of the covering layer, as in 4a.

Example 2
A sample to be the core portion was prepared in the same manner as the sample 4 of Example 1 (Tsp is 16 ° C.) except that the content of the subcomponent in the ferrite composition forming the core portion was changed as shown in Table 3. The same evaluation was performed (Samples 7 to 15). The results are shown in Table 3.

  Next, the ferrite composition shown in Table 3 was used as a core part, and a ferrite core (toroidal shape) in which a coating layer was formed on the surface of the core part with glass A or glass B was obtained. Evaluation similar to Example 2 was performed with respect to the obtained ferrite core sample (samples 7a to 15a and samples 7b to 15b). The results are shown in Table 4.

  From Table 3, in Samples 4, 8, 9 and 12 to 14 in which the content of the subcomponent in the ferrite composition is within the scope of the present invention, the sample in which the content of the subcomponent is not within the scope of the present invention Compared to 7, 10, 11, and 15, it was confirmed that the power loss (Pcv) in the high frequency region (1 MHz) was low.

  Samples 4a, 8a, 9a, and 12a to 14a in Table 4 are samples 2 to 5 in which the content of subcomponents in the ferrite composition is within the scope of the invention of the present application, and the thermal expansion is smaller than the core portion. The surface of the core part was covered with glass A having a coefficient.

  In such samples 4a, 8a, 9a and 12a to 14a, the power loss (Pcv) in the high frequency region (1 MHz) is reduced compared to the samples 4, 8, 9 and 12 to 14 before forming the coating layer. It was confirmed that That is, in the ferrite core (samples 4a, 8a, 9a, and 12a to 14a) in which the coating layer made of glass A is formed as compared with the core part samples (samples 4, 8, 9, and 12 to 14), the high frequency region ( It was confirmed that the power loss (Pcv) at 1 MHz was improved by about 25 to 30%.

  Furthermore, before and after forming the coating layer made of glass A on the surface of the core portion, a high saturation magnetic flux density (Bs) is maintained, and as a result, a ferrite core (sample 4a) in which the coating layer made of glass A is formed. 8a, 9a and 12a-14a), it was confirmed that the quality factor expressed by Pcv / Bs was improved.

  However, when Samples 7, 10, 11, and 15 in which the content of subcomponents in the ferrite composition is not within the scope of the present invention are used as the core portion, a coating layer made of glass A is formed. It was also confirmed that the effect of improving the power loss (Pcv) in the high frequency region (1 MHz) was not sufficiently obtained before and after the formation of the coating layer (Samples 7a, 10a, 11a, and 15a).

  From these results, when the content of subcomponents in the ferrite composition of the ferrite composition forming the core part is within the scope of the present invention, a coating layer having a thermal expansion coefficient equal to or lower than the core part is determined as the core. By forming on the surface of the part, the power loss (Pcv) can be reduced even in a high frequency region (for example, 1 MHz or more) while maintaining a high saturation magnetic flux density (Bs), resulting in a quality factor (Pcv / Bs). It was confirmed that it could be improved.

  In the samples 7b to 15b, before and after the formation of the coating layer of the glass B, regardless of whether or not the content of subcomponents in the ferrite composition of the ferrite composition forming the core portion is within the scope of the present invention. It was confirmed that the improvement effect of power loss (Pcv) in the high frequency region (1 MHz) was not obtained, but rather deteriorated.

  That is, when the core part is coated with a coating layer having a thermal expansion coefficient larger than that of the core part, the power loss (Pcv) before and after the formation of the coating layer, regardless of the content of subcomponents in the ferrite composition. It was confirmed that no improvement effect was obtained.

DESCRIPTION OF SYMBOLS 1 ... Ferrite core 2 ... Core part 10 ... Coating layer 10a ... Coating layer 20 before heat processing ... Barrel apparatus

Claims (3)

A ferrite core having a core part composed of a ferrite composition and a coating layer formed on at least a part of the surface of the core part,
The ferrite composition includes a main component including iron oxide, zinc oxide, and manganese oxide,
With respect to 100% by weight of the main component, as subcomponents, silicon oxide contains 50 to 300 ppm in terms of SiO ₂ , and calcium oxide contains 110 to 1120 ppm in terms of CaO,
The minimum temperature Tsp of magnetic loss of the ferrite composition is in the range of 5 to 50 ° C.
When the content of the iron oxide in the main component is X mol% in terms of Fe ₂ O ₃ , the content of the zinc oxide is Z mol% in terms of ZnO, and the balance is the manganese oxide, the Tsp and the X And Z satisfies the following formulas (1) and (2),
The ferrite core, wherein a thermal expansion coefficient of the coating layer is equal to or less than a thermal expansion coefficient of the core portion.
Tsp = 21.6 (X + 0.52Z) -1520 Formula (1)
X ≧ 58.0 Formula (2)   The ferrite core according to claim 1, wherein the coating layer is made of a glass composition.   An electronic component having the ferrite core according to claim 1.

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