CN110600239A

CN110600239A - Core, reactor, method for manufacturing core, and method for manufacturing reactor

Info

Publication number: CN110600239A
Application number: CN201910489575.7A
Authority: CN
Inventors: 大岛泰雄; 有间洋
Original assignee: Tamura Corp
Current assignee: Tamura Corp
Priority date: 2018-06-13
Filing date: 2019-06-06
Publication date: 2019-12-20
Also published as: JP6858158B2; JP2019216199A

Abstract

The invention provides a core, a reactor, a method for manufacturing the core and a method for manufacturing the reactor, which are easy to form and can obtain excellent magnetic characteristics. The core is a core containing a magnetic powder and a resin, the magnetic powder contains a first magnetic powder and a second magnetic powder having an average particle diameter smaller than that of the first magnetic powder, the amount of the first magnetic powder added to the magnetic powder is 60 to 80 wt%, the proportion of the apparent density of the core to the true density of the magnetic powder is 76.6 to 82%, the initial permeability is 30 or more, and the permeability of 12kA/m is 24 or more.

Description

Core, reactor, method for manufacturing core, and method for manufacturing reactor

Technical Field

The present invention relates to a core including a metal composite core (metal composite core) including magnetic powder and resin, a reactor (reactor), a method of manufacturing the core, and a method of manufacturing the reactor.

Background

Reactors are used in various applications such as Office Automation (OA) equipment, solar power systems (solar power systems), automobiles, and uninterruptible power supplies (uninterruptible power supplies). The reactor is used in, for example, a filter (filter) for preventing harmonic current from flowing into a power output system, a converter (converter) for voltage increase and decrease for increasing and decreasing voltage, and the like.

Magnetic characteristics such as magnetic permeability (magnetic permeability), inductance value (inductance value), and iron loss (iron loss) are required for a reactor according to the application. For example, since a reactor used in a converter for voltage increase and decrease is required to improve energy conversion efficiency, iron loss, which is an energy loss, is required to be small.

In order to meet various applications, it is also strongly required to mold the core used in the reactor into an arbitrary shape. A reactor that copes with such an urgent demand is a reactor including a core of a type called a metal composite core. The metal composite core (hereinafter also referred to as MC core) is a core obtained by molding a material in which metal magnetic powder and resin are mixed into a predetermined shape and curing the molded material.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent laid-open No. 2012-33727

Disclosure of Invention

[ problems to be solved by the invention ]

The conventional MC core is formed by pouring a slurry-like material into a container, and therefore can be easily formed into a desired shape, and is advantageous in formability with less restriction on the shape. However, in the conventional MC core material, the content of resin is increased in order to improve the fluidity in the container. Therefore, the proportion of the magnetic powder in the material decreases, resulting in a decrease in the core density, with a resultant decrease in the magnetic characteristics.

On the other hand, there is also a so-called powder magnetic core (powder magnetic co)re) (hereinafter also referred to as a dust core) which obtains high magnetic permeability even when used in a high magnetic field, thereby obtaining excellent magnetic characteristics. However, the magnetic powder core was prepared by adding soft magnetic powder coated with insulating resin to a mold at 10t/cm²～20t/cm²Is press-molded at a high pressure. Therefore, the manufacturing equipment including the mold is large in size and high in cost. In addition, in order to mold the magnetic powder core, a mold capable of withstanding high pressure is required. Therefore, the shape of the mold is limited, and the shape that can be molded is also limited. Further, since the magnetic powder core needs to be removed from the mold for molding, a surface perpendicular to the removal direction may not be formed, and the degree of freedom of the shape is low.

In order to cope with this, it is conceivable to form a magnetic powder core of a desired shape by combining partial cores of a shape that can be easily molded by a mold. However, in the case of such a division structure, since a plurality of types of molds are prepared, each core is molded by each mold, and a process of combining them is further required, there is a problem in cost and productivity.

The invention aims to provide a core, a reactor, a core manufacturing method and a reactor manufacturing method, wherein the core and the reactor can have excellent formability and magnetic characteristics.

[ means for solving problems ]

In order to achieve the above object, the present invention is a core including a magnetic powder and a resin, the magnetic powder including a first magnetic powder and a second magnetic powder having a smaller average particle diameter than the first magnetic powder, wherein an amount of the first magnetic powder added to the magnetic powder is 60 wt% to 80 wt%, a ratio of an apparent density of the core to a true density of the magnetic powder is 76.6% or more and less than 82%, an initial magnetic permeability is 30 or more, and a magnetic permeability of 12kA/m is 24 or more.

The resin may be 3 wt% to 5 wt% with respect to the magnetic powder. The proportion of the apparent density of the core with respect to the true density of the magnetic powder may be 77% or more.

The circularity of the first magnetic powder may be 0.93 or more. The entire surface of the core may be a non-slip surface. A reactor including the core and the coil is also an embodiment of the present invention.

A method for producing a core according to the present invention is a method for producing a core including a magnetic powder and a resin, the magnetic powder including a first magnetic powder and a second magnetic powder having an average particle diameter smaller than that of the first magnetic powder, the amount of the first magnetic powder added to the magnetic powder being 60 to 80 wt%, the method for producing the core including: a mixing step of mixing a resin with the magnetic powder; a molding step of adding the mixture obtained in the mixing step to a predetermined container to mold the mixture; a pressing step of pressing the mixture so that the ratio of the apparent density of the core to the true density of the magnetic powder becomes 76.6% or more and less than 82% in the molding step; and a curing step of curing the resin in the molded body obtained in the molding step.

The pressure of the pressurizing process for extruding the mixture may be 1.6kg/cm²The above. Further, a method of manufacturing a reactor including a core manufactured by the method of manufacturing a core and a coil mounted on the core is also an embodiment of the present invention.

[ Effect of the invention ]

According to the present invention, it is possible to provide a core, a reactor, a method for manufacturing the core, and a method for manufacturing the reactor, which are easy to mold and can obtain excellent magnetic characteristics.

Drawings

Fig. 1 is a flowchart for explaining a method of manufacturing a reactor according to an embodiment.

Fig. 2 is a diagram for explaining the molding step and the pressing step.

Fig. 3 is a graph of theoretical densities with respect to surface pressure for examples 1 to 4 and comparative example 1.

FIG. 4 is a Scanning Electron Microscope (SEM) photograph (magnification 100) of a core cross-section of example 3.

FIG. 5 is an SEM photograph (magnification 100) of a core cross-section of comparative example 1.

Fig. 6 is a graph of magnetic permeability with respect to surface pressure for examples 1 to 4 and comparative example 1.

Fig. 7 is a graph of the iron loss with respect to the surface pressure in examples 1 to 4 and comparative example 1.

Fig. 8 is a graph of magnetic permeability with respect to the amount of resin for examples 5 to 9 and comparative examples 2 to 4.

Fig. 9 is a graph showing the iron loss with respect to the amount of resin in examples 5 to 9 and comparative examples 2 to 4.

Fig. 10 is a graph of magnetic permeability with respect to surface pressure for examples 10 to 13.

Fig. 11 is a graph of the iron loss with respect to the surface pressure in examples 10 to 13.

Fig. 12 is a graph of the magnetic permeability with respect to the amount of the second magnetic powder added in example 2, example 14, example 15, and comparative examples 5 to 7.

Fig. 13 is a graph of the density with respect to the amount of addition of the second magnetic powder in example 2, example 14, example 15, and comparative examples 5 to 7.

Fig. 14 is an SEM photograph (100 × magnification) of a core cross section corresponding to the present embodiment.

FIG. 15 is an SEM photograph (1000 times) of a cross section of the magnetic powder core.

Fig. 16 is a graph of inductance with respect to a dc excitation current of the reactor in example 16, example 17, and comparative example 8.

Description of the symbols

1: first magnetic powder

2: second magnetic powder

3: resin composition

4: voids

10: container with a lid

20: composite magnetic material

30. 32: extruded member

40: coil

Detailed Description

[1. embodiment ]

[1-1. Structure ]

The reactor of the present embodiment includes a core and a coil. The core is a metal composite core (hereinafter also referred to as an MC core) including magnetic powder and resin. The core can be formed into a predetermined shape by filling a predetermined container with a clay-like mixture in which magnetic powder and resin are mixed and pressurizing the mixture. The shape of the core may be set, for example: various shapes such as a ring core, an I core, a U core, a theta core, an E core, an EER core, etc.

As the magnetic powder, soft magnetic powder can be used, and in particular: fe powder, Fe — Si alloy powder, Fe — Al alloy powder, Fe — Si — Al alloy powder (sendust), or mixed powder of two or more of these powders. As the Fe-Si alloy powder, for example, Fe-6.5% Si alloy powder and Fe-3.5% Si alloy powder can be used. The average particle diameter (D50) of the soft magnetic powder is preferably 20 to 150. mu.m. In the present specification, the "average particle diameter" refers to D50, i.e., a median particle diameter, unless otherwise specified.

The magnetic powder includes magnetic powders having different average particle diameters. That is, the magnetic powder includes a first magnetic powder and a second magnetic powder having a smaller average particle diameter than the first magnetic powder. The amount of the first magnetic powder added to the magnetic powder is preferably 60 to 80 wt%. That is, when the magnetic powder is constituted by the first magnetic powder and the second magnetic powder, the weight ratio of the first magnetic powder: second magnetic powder 80: 20-60: 40. by setting the range, the density is increased, the magnetic permeability is also increased, and the iron loss can be reduced.

The average particle diameter of the first magnetic powder is preferably 100 to 200 μm. The second magnetic powder is preferably 3 to 10 μm. This is because the second magnetic powder having a small average particle diameter enters the gap between the first magnetic powders, and the density and permeability can be improved and the iron loss can be reduced. The initial permeability of the core of the present embodiment is 30 or more, and the permeability of 12kA/m is 24 or more.

The first magnetic powder and the second magnetic powder are preferably spherical. The circularity of the first magnetic powder is preferably 0.93 or more, and the circularity of the second magnetic powder is preferably 0.95 or more. This is because the gap between the first magnetic powder is reduced, and more second magnetic powder easily enters the gap, thereby improving the density and the magnetic permeability. In the case of the MC core, the pressure applied in the pressing step is several kg/cm²About several tens kg/cm²And the required number t/cm²About several tens of t/cm²The powder magnetic core (hereinafter also referred to as a magnetic powder core) is very small, as compared with about 1/1000, and therefore can maintain the circularity of the magnetic powder. That is, in the case of a magnetic powder core that needs to be pressurized with a high pressure, such circularity of the magnetic powder cannot be obtained.

Further, since the second magnetic powder having a smaller average particle diameter is contained in the first magnetic powder having the largest average particle diameter, the second magnetic powder may contain magnetic powders having different average particle diameters. That is, the second magnetic powder may be a magnetic powder whose average particle diameter can be defined as one, or may be a magnetic powder whose average particle diameter is defined as two or more. The first magnetic powder and the second magnetic powder may be made of the same material, i.e., different kinds. The number of the species may be 3 or more in the case where the species is different. When the magnetic powder is constituted by 3 or more kinds of powder, the average particle diameters of the respective kinds can be made different.

The first magnetic powder is preferably a pulverized component. The second magnetic powder may be produced by a water atomization method, a gas atomization method, or a water/gas atomization method, and particularly preferably a powder formed by a water atomization method. The reason is that the water atomization method rapidly cools at the time of atomization, and thus the powder is difficult to crystallize.

The resin is mixed with the magnetic powder to hold the magnetic powder. When the magnetic powder contains powders having different average particle diameters, the respective powders are held in a uniformly mixed state. The resin may be a thermosetting resin, an ultraviolet-curable resin, or a thermoplastic resin. The thermosetting resin may be used: phenol resins, epoxy resins, unsaturated polyester resins, polyurethanes, diallyl phthalate resins, silicone resins, and the like. As the ultraviolet-curable resin, acrylic urethane-based, acrylic epoxy-based, acrylic ester-based, or epoxy-based resins can be used. The thermoplastic resin is preferably a resin having excellent heat resistance such as polyimide or fluororesin. The epoxy resin cured by adding the curing agent can be adjusted in viscosity by the amount of the curing agent added, and is therefore suitable for the present invention. Thermoplastic acrylic or silicone resins may also be used.

The resin is preferably contained in an amount of 3 to 5 wt% based on the magnetic powder. If the content of the resin is less than 3 wt%, the bonding force of the magnetic powder is insufficient and the mechanical strength of the core is lowered. If the resin content is more than 5 wt%, the resin formed between the first magnetic powders enters, and the second magnetic powder cannot fill the gap, and the core density decreases, and the magnetic permeability decreases.

The viscosity of the resin is preferably 50 to 5000 mPas when mixed with the magnetic powder. When the viscosity is less than 50mPa · s, the resin is not entangled in the magnetic powder during mixing, the magnetic powder and the resin are easily separated in the container, and unevenness occurs in the density or strength of the core. If the viscosity exceeds 5000mPa · s, the viscosity excessively increases, and for example, the resin formed between the first magnetic powder enters, and the second magnetic powder cannot fill the gap, and the density of the core decreases, and the magnetic permeability decreases.

Among the resins, SiO can be used₂、Al₂O₃、Fe₂O₃、BN、AlN、ZnO、TiO₂And the like as the viscosity adjusting material. The average particle diameter of the filler as the viscosity adjusting material is preferably equal to or smaller than the average particle diameter of the second magnetic powder, and is preferably equal to or smaller than 1/3 of the average particle diameter of the second magnetic powder. This is because, if the average particle diameter of the filler is large, the density of the obtained core decreases. In addition, Al may be added to the resin₂O₃High thermal conductivity materials such as BN and AlN.

The proportion of the apparent density of the core to the true density of the magnetic powder is preferably 76.6% or more and less than 82%. More preferably 77% or more. If the ratio is 76.6% or more, the magnetic permeability can be maintained high even in a high magnetic field. Conversely, if the ratio is less than 76.6%, the permeability tends to decrease easily in a high magnetic field due to the low density. In addition, when the magnetic powder core is used to have the same permeability, the ratio of the apparent density of the core to the true density of the magnetic powder is about 82% to 88%. This is because the magnetic powder core is formed by coating the resin with the powder alone and compacting the powder with a very high pressure as described above. In the MC core, the magnetic powder is dispersed and mixed in the resin, and the resin is cured without being compressed because the inside air is removed by the low pressure as described above. Therefore, the ratio of the apparent density of the MC core of the present embodiment to the true density of the magnetic powder is less than 82%.

The MC core surface of the present embodiment differs from the magnetic powder core surface in the following manner. First, the magnetic powder core is produced by subjecting a molded body, which is formed by adding soft magnetic powder coated with an insulating resin to a mold and press-molding at a very high pressure as described above, to heat treatment such as annealing. Therefore, the surface of the magnetic powder core is relatively smooth. On the other hand, the MC core is molded into a predetermined shape by charging the composite magnetic powder mixed with the insulating resin into a container of a predetermined shape and applying a relatively low pressure as described above. Therefore, the surface of the MC core is rough compared to the magnetic powder core. For example, there are the following differences: the MC core has micro holes or concave-convex parts which are not possessed by the magnetic powder core, and the surface roughness is coarser than that of the magnetic powder core.

The magnetic powder core is molded by pouring soft magnetic powder coated with insulating resin into a region formed by the inner peripheral surface of the molding hole of the outer die and the upper surface of the lower die, compressing the powder with the upper die, and then removing the upper die. At this time, the soft magnetic powder coated with the insulating resin is pressurized at high pressure in the mold, and thus a pressing force is applied to the mold when the formed magnetic powder core is taken out. Therefore, a sliding mark is formed on the surface of the magnetic powder core at a portion that slides against the inner peripheral surface of the mold at the time of removal. The slide mark is a plurality of linear marks formed by moving while rubbing the surface of the mold. The MC core of the present embodiment is a core formed by curing a resin in a mold, and therefore the core is not pressed against the mold and has no slip mark on the surface. The surface having no sliding mark is a non-sliding surface. All surfaces of the MC core of the present embodiment are non-sliding surfaces.

The coil is a wire that has been subjected to insulation coating, and a copper wire or an aluminum wire may be used as the wire. The coil is formed or attached by winding a wire around at least a part of the core, and is disposed around at least a part of the core. The winding form of the coil and the shape of the wire are not particularly limited.

[1-2. method for manufacturing reactor ]

A method for manufacturing a reactor according to the present embodiment will be described with reference to the drawings. As shown in fig. 1, the method for manufacturing the reactor includes (1) a mixing step, (2) a molding step, (3) a pressing step, and (4) a curing step.

(1) Mixing procedure

The mixing step is a step of mixing the magnetic powder with the resin. When the magnetic powder includes two types of magnetic powder having different average particle diameters, the mixing step includes: a magnetic powder mixing step of mixing a first magnetic powder with a second magnetic powder having a smaller average particle diameter than the first magnetic powder to form a magnetic powder; and a resin mixing step of adding 3 to 5 wt% of a resin to the magnetic powder to mix the magnetic powder with the resin.

The mixing in each mixing step can be performed automatically or manually using a predetermined mixer. The mixing time in each mixing step is not particularly limited, and may be, for example, 2 minutes.

By the mixing step described above, a mixture of the magnetic powder and the resin (hereinafter also referred to as a composite magnetic material) can be obtained. In the mixing step, the magnetic powder and the resin may be filled into a container for molding the composite magnetic material in the molding step and mixed. This eliminates the need to transfer the composite magnetic material to a container, and can reduce the number of manufacturing steps.

(2) Shaping step

The molding step is a step of adding the composite magnetic powder to a container having a predetermined shape and molding the composite magnetic powder into the container having the predetermined shape. In the molding step, the coil may be molded by adding the composite magnetic powder together.

As the container, containers of various shapes are used according to the shape of the core to be manufactured. In the case of incorporating a coil, a box-shaped or dish-shaped container having an open top surface is used to allow insertion of the coil from above. The container used in the molding process may be used as it is as a packaging case for a reactor that houses the core and the coil. If the container is used as a packaging box, there is an advantage that the container does not need to be taken out after the composite magnetic powder is cured. In the case where the container is not used as a packing case, a plurality of reactors can be manufactured by using one container. That is, a plurality of recesses may be formed in advance in the bottom of the container, and the composite magnetic material and the coil may be added to the recesses to manufacture a plurality of reactors. As described above, since a plurality of reactors are completed in one molding step, the manufacturing efficiency can be improved.

The container used in the molding step may be formed entirely or partially by a resin molded article. By making the container of resin, the manufacturing cost can be reduced, and the advantage of any shape that can be formed into the MC core can be effectively utilized. That is, since the resin is a relatively inexpensive material, the manufacturing cost of the container can be suppressed, and the core having an arbitrary shape can be formed by injection molding or the like. Examples of the material for the resin molded article include: unsaturated polyester resin, urethane resin, epoxy resin, Bulk Molding Compound (BMC), polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), and the like.

The container may be entirely or partially made of a metal having high thermal conductivity, such as aluminum or magnesium. This is because, as described later, the composite magnetic material is easily heated in the pressurizing step.

(3) Pressurizing step

The pressing step is a step of pressing the composite magnetic material with a pressing member in the molding step. The clay-like composite magnetic material charged into the container is extruded by the extrusion member to expand the composite magnetic material into the shape of the container, and voids contained in the composite magnetic material are reduced to improve the apparent density and magnetic permeability.

In the case where no coil is added to the container, the composite magnetic material is formed into the shape of the inside of the container by the above-described steps. That is, a molded article having a predetermined shape including the composite magnetic material can be obtained.

In the case of adding a coil to a container, as shown in fig. 2, a composite magnetic material 20 is added to a container 10, and the composite magnetic material 20 is expanded into the shape of the container by a pressing member 30. Then, the coil 40 is inserted into the space formed by pressing the composite magnetic material 20, the composite magnetic material 20 is filled, and the composite magnetic material 20 is pressed together with the coil 40 from above by the pressing member 32. Alternatively, the composite magnetic material 20 may be put into the container 10, and then the coil 40 may be embedded in the composite magnetic material 20 including the inner and outer peripheries thereof, and the composite magnetic material 20 may be pressed from above together with the coil 40. As described above, by pressing the composite magnetic material 20 together with the coil 40, the voids contained in the composite magnetic material 20 can be reduced, and the apparent density and the magnetic permeability can be improved. Further, it is also possible to avoid the portion where the coil 40 exists and to press only the composite magnetic material 20. As described above, the composite magnetic material molded body having a predetermined shape including the coil can be obtained by the above-described steps.

As described above, in the pressurizing step, the composite magnetic material can be extruded by the extruding member to form the material into the shape of the container, and in this case, the pressurizing step can be understood as a pressurizing step and a molding step.

The pressure for extruding the composite magnetic material is preferably 1.6kg/cm²The above. By the pressure, the initial permeability can be set to 30 or more, and the permeability of 12kA/m can be set to 24 or more. However, if it is 6.3kg/cm²The above is more preferable. The reason for this is that if it is less than 6.3kg/cm²Then squeeze outThe pressure is small, and the effect of improving the apparent density is small. In addition, even if the value is above, preferably 15.7kg/cm²The following. This is because, even if the extrusion is performed beyond the above value, the effect of increasing the apparent density is small. When the pressing force exceeds the above value, only the resin is pressed, and the insulation between the magnetic powders is deteriorated.

The time for extruding the composite magnetic material can be appropriately changed depending on the content or viscosity of the resin. For example, 10 seconds may be set.

The pressurizing step may be performed by setting the container or the pressing member for pressing the composite magnetic material to a temperature higher than normal temperature (e.g., 25 ℃). By raising the temperature of the container or the pressing member, the resin is heated and becomes soft. Therefore, the composite magnetic material easily flows into the gap in the container, the moldability can be improved, and the material easily flows into the void in the composite magnetic material, the density can be improved. The temperature of the container or the pressing member for pressing the composite magnetic material is preferably higher than the softening point of the resin contained in the composite magnetic material. This is because the resin can be effectively softened. The pressurizing step may be performed while maintaining the temperature of the container or the pressing member for pressing the composite magnetic material.

In addition, in the pressurizing step, the composite magnetic material itself may be heated in advance to extrude the composite magnetic material, in addition to the temperature of the container or the extruding member being increased in advance. It is also possible to maintain the temperature of the container or the pressing member that presses the composite magnetic material, and previously warm the composite magnetic material itself for pressing.

(4) Curing step

The curing step is a step of curing the resin in the molded body obtained in the molding step. In the case where the resin in the molded body is cured by drying, the drying environment may be an atmospheric environment. The drying time may be appropriately changed depending on the kind, content, drying temperature, and the like of the resin, and may be, for example, 1 to 4 hours, but is not limited thereto. The drying temperature may be appropriately changed depending on the kind, content, drying time, and the like of the resin, and may be, for example, 85 to 150 ℃. Further, the drying temperature is the temperature of the drying environment.

The curing of the resin is not limited to drying, and the curing method differs depending on the type of the resin. For example, if the resin is a thermosetting resin, the resin is cured by heating, and if the resin is an ultraviolet-curable resin, the resin is cured by irradiating the molded body with ultraviolet rays.

The curing step may be repeated a plurality of times to cure the molded article at a predetermined temperature for a predetermined time. For example, in the case where the resin is cured by drying, the drying temperature and the drying time may be changed every time the resin is repeatedly dried.

[1-3. Effect ]

(1) The core of the present embodiment is a core including magnetic powder and resin, the magnetic powder including first magnetic powder and second magnetic powder having a smaller average particle diameter than the first magnetic powder, the amount of the first magnetic powder added to the magnetic powder being 60 to 80 wt%, the proportion of the apparent density of the core to the true density of the magnetic powder being 76.6 to 82%, the initial permeability being 30 or more, and the permeability of 12kA/m being 24 or more.

Therefore, excellent moldability and magnetic properties can be achieved at the same time. That is, since the core of the present embodiment is an MC core, the degree of freedom of shape is higher than that of the magnetic powder core, and a core having a desired shape can be easily produced without adopting a division structure. Since the gap can be eliminated by not having the split structure, when the core of the present embodiment is configured as a reactor, leakage flux into the coil can be reduced, copper loss is reduced, and heat generation of the coil can be suppressed. Further, even when compared with the magnetic powder core, the magnetic powder core can obtain a magnetic permeability which is not inferior in a high magnetic field. That is, since the existence of the gap contributes to maintaining the magnetic permeability in a high magnetic field, the magnetic powder core may have a split structure and the gap may be generated. The gap between the magnetic powders also functions as a gap, but the magnetic powder core has a split structure to generate a gap because the magnetic powders are closely spaced and function as a gap is weak. On the other hand, the MC core has a smaller interval between the magnetic powders than the magnetic powder core, and therefore the interval functions as a gap, and thus high magnetic permeability can be obtained even in a high magnetic field without adopting a split structure. Further, since the core of the present embodiment can be molded at a low pressure, the manufacturing equipment can be reduced in size and cost.

(2) In the core of the present embodiment, the resin is 3 to 5 wt% with respect to the magnetic powder. Thus, a core having not only the advantage of moldability but also improved productivity and density can be obtained. That is, since the amount of the resin is set to 3 to 5 wt%, the composite magnetic material is in a clay state and easy to handle, and productivity can be improved.

(3) In the core of the present embodiment, the proportion of the apparent density of the core with respect to the true density of the magnetic powder is 77% or more. Therefore, more excellent magnetic permeability can be obtained.

(4) The entire surface of the core of the present embodiment is a non-sliding surface. Therefore, the excellent magnetic characteristics as described above can be obtained even if the magnetic powder core is not used. That is, the magnetic powder core is peeled off by the insulating film covering the magnetic powder due to the sliding mark, and thus the eddy current loss is deteriorated. On the other hand, the core of the present embodiment does not generate a slip mark, and therefore has a lower loss than the magnetic powder core.

(5) In the core of the present embodiment, the circularity of the first magnetic powder is 0.93 or more. Therefore, the excellent magnetic characteristics as described above can be obtained even without the magnetic powder core. That is, the magnetic powder core is deformed by the pressure, and therefore the hysteresis loss increases. On the other hand, the core of the present embodiment does not deform the magnetic powder due to pressurization, and therefore hysteresis loss can be suppressed. Further, the magnetic powder core needs to be annealed after press molding in order to reduce the deterioration of hysteresis loss. On the other hand, the core of the present embodiment does not require annealing because there is no deterioration of hysteresis loss.

(6) The method for manufacturing a core according to the present embodiment is a method for manufacturing a core including a magnetic powder and a resin, the magnetic powder including a first magnetic powder and a second magnetic powder having an average particle diameter smaller than that of the first magnetic powder, the amount of the first magnetic powder added to the magnetic powder being 60 wt% to 80 wt%, the method for manufacturing a core including: a mixing step of mixing a resin with the magnetic powder; a molding step of adding the mixture obtained in the mixing step to a predetermined container to mold the mixture; a pressing step of pressing the mixture so that the ratio of the apparent density of the core to the true density of the magnetic powder becomes 76.6% or more and less than 82% in the molding step; and a curing step of curing the resin in the molded body obtained in the molding step.

Thus, a core having not only the advantage of moldability but also improved productivity and density can be obtained. By including the pressing step, the advantage of the MC core that can mold the shape of the composite magnetic material into a predetermined shape, that is, the advantage of moldability can be ensured, and by pressing the composite magnetic material, the material easily enters the voids included in the composite magnetic material, and the apparent density and magnetic characteristics of the core can be improved.

(7) The pressurizing step was carried out under a pressure of 1.6kg/cm for extruding the mixture²The above. This improves the magnetic properties of the core, even though the core is an MC core.

[1-4. examples ]

Examples of the present invention will be described below with reference to tables 1 to 3 and fig. 3 to 9.

(1) Measurement items

The measurement items were density, magnetic permeability, and iron loss. For each core sample produced, use was made ofThe reactor was fabricated by winding 40 turns of the copper wire (2). The shape of each sample of the core was a ring shape having an outer diameter of 35mm, an inner diameter of 20mm, and a height of 11 mm. The magnetic permeability and the iron loss of the reactor thus produced were calculated under the following conditions.

< Density >

The density of the core is the apparent density. That is, the outer diameter, inner diameter, and height of each core sample were measured, and based on pi × (outer diameter) from these values²Inner diameter²) X heightTo calculate the volume (cm) of the sample³). Then, the mass of the sample was measured, and the measured mass was divided by the calculated volume to calculate the density of the core.

< magnetic permeability and iron loss >

The permeability and the iron loss were measured under the conditions of a frequency of 20kHz and a maximum magnetic flux density Bm of 30 mT. The permeability is an amplitude permeability when the maximum magnetic flux density Bm is set at the time of measuring the iron loss Pcv. The iron loss was calculated by using a BH analyzer (SY-8232, manufactured by Citon instruments Co., Ltd.) as a magnetic measuring instrument. The calculation is performed by calculating a hysteresis loss coefficient and an eddy current loss coefficient by a least squares method from the frequency curve of the iron loss by the following expressions (1) to (3).

Pcv＝Kh×f+Ke×f²……(1)

Phv＝Kh×f……(2)

Pev＝Ke×f²……(3)

Pcv (Pcv): iron loss

Kh: coefficient of hysteresis loss

And Ke: coefficient of eddy current loss

f: frequency of

Phv: hysteresis loss

Pev: loss of eddy current

In this example, the average particle diameter and circularity of each powder were calculated by using the following apparatus and taking an average value of 3000 powders, the powders were dispersed on a glass substrate, a photograph of the powders was taken with a microscope, and each powder was automatically measured from the image.

Company name: malvern (Malvern)

Device name: particle size particle analyzer (morphologi) G3S

The specific surface area is measured by the Brunauer-EMMETT-Teller (BET) method.

(2) Method for preparing sample

The core sample was prepared from the viewpoints of (a) the pressing surface pressure in the pressing step, (b) the amount of resin, and (c) the difference in temperature of the container, as described below. These production methods and the results thereof are shown in the following order.

(a) Pressing surface pressure in the pressing step

First, as a mixing step, an Fe-6.5% Si alloy powder (circularity of 0.943) having an average particle size of 123 μm and an Fe-6.5% Si alloy powder (circularity of 0.908) having an average particle size of 5.1 μm were mixed in a weight ratio of 70: 30 in a V-blender for 30 minutes to form a magnetic powder. Then, the magnetic powder was added to an aluminum cup, 3.5 wt% of epoxy resin was added with respect to the magnetic powder, and mixed manually for 2 minutes using a spatula. Thereby, a composite magnetic material as a mixture of the magnetic powder and the resin is obtained.

Then, the composite magnetic material obtained in the mixing step was filled in a resin container having an annular space, and the composite magnetic material in the container was pressed for 10 seconds by a press of table 1 using a hydraulic press to prepare an annular molded body. During the extrusion, the temperature of the container was maintained at 25 ℃.

The molded body obtained by the pressing step and the molding step as described above was dried at 85 ℃ for 2 hours, then at 120 ℃ for 1 hour, and further at 150 ℃ for 4 hours in the air, to prepare a toroidal core as a sample.

[ Table 1]

Pcv[20kHz 30mT]

Table 1 and fig. 3 to 7 show the results of the density, permeability, and iron loss of the core in examples 1 to 4 and comparative example 1 obtained by the respective pressing pressures. Examples 1 to 4 were made to have pressing pressures of 100N, 400N, 600N, and 1000N, and comparative example 1 was made to have no pressing. The pressed surfaces were all the same.

The "theoretical density" in table 1 is a ratio calculated from the apparent density of the core/the true density of the magnetic powder. Here, Fe-6.5% Si alloy powder was used as the first magnetic powder and the second magnetic powder, and the true density was set to 7.63g/cm³And the theoretical density was calculated.

FIG. 3 shows examples 1 to 4 and ratiosGraph of theoretical density versus surface pressure for comparative example 1. As shown in table 1 and fig. 3, the theoretical densities with respect to the surface pressure of examples 1 to 4 tended to be as follows: in comparison with comparative example 1 in which the pressurizing step was not performed, examples 1 to 4 in which the pressurizing step was performed had a high theoretical density and increased as the surface pressure increased. The surface pressure was 1.6kg/cm²The theoretical density of example 1 (2) is 76.62%, and the difference from the theoretical density of 76.47% of comparative example 1 without pressurization is small. However, in example 1, as described later, the magnetic permeability can be improved. The surface pressure was 6.3kg/cm²In examples 2 to 4, the theoretical density was 77.5% or more, which is higher than that in comparative example 1 and example 1. That is, the surface pressure was set to 6.3kg/cm²In the above, the material is spread over the gaps included in the composite magnetic material or the corners of the container, whereby the density is increased. It is also found that when the surface pressure reached 6.3kg/cm²The theoretical density is substantially constant as described above.

FIG. 4 is an SEM photograph (100X) of a cross-section of the core of example 3. FIG. 5 is an SEM photograph (magnification 100) of a core cross-section of comparative example 1. In fig. 4 and 5, reference numeral 1 denotes a first magnetic powder, and reference numeral 2 denotes a second magnetic powder. The symbol 3 represents a resin, and the symbol 4 represents a void. The voids 4 are indicated by dark black in the SEM photograph, whereas the portions indicated by relatively light black are the resin 3. As is clear from fig. 4 and 5, in example 3 shown in fig. 4, the number of voids 4 in the composite magnetic material is reduced and the size of the voids 4 itself can be reduced as compared with comparative example 1 shown in fig. 5.

The magnetic permeability is amplitude magnetic permeability, and is calculated from the inductance of the intensity of each magnetic field of 20kHz and 1.0V using the impedance analyzer. "μ 0" in table 1 indicates the initial permeability in a state where no direct current is superimposed, that is, when the intensity of the magnetic field is 0H (a/m). "μ 12000" in Table 1 represents the magnetic permeability at a magnetic field strength of 12kH (kA/m).

Fig. 6 is a graph of magnetic permeability with respect to surface pressure for examples 1 to 4 and comparative example 1. As shown in table 1 and fig. 6, it is understood that the magnetic permeability of the examples 1 to 4 under pressure is higher than that of the comparative example 1 under pressure. For example, it is found that the initial permeability μ 0 of example 2 is increased by about 8.7% as compared with comparative example 1. In addition, in example 1 in which pressure was applied, the magnetic permeability was also increased as compared with comparative example 1 in which pressure was not applied. However, the contribution to the density rise of the core is small. That is, as described above, the theoretical density of example 1 was 76.62%, and the difference from the theoretical density of 76.47% in comparative example 1 without pressurization was small. Therefore, it is assumed that the permeability cannot be dramatically improved in the difference between the theoretical densities of comparative example 1 and example 1, based on the common technical knowledge that the density and the permeability are related to each other. However, the inventors have found that in example 1, initial permeability μ 0 is 33.0 and μ 12000 is 24.4, and thus the permeability can be dramatically improved as compared with initial permeability μ 0 of comparative example 1 being 31.1 and μ 12000 being 23.5. That is, when attention is paid to magnetic permeability, the theoretical density is 76.6% or more, which has a critical meaning.

Fig. 7 is a graph of the iron loss with respect to the surface pressure in examples 1 to 4 and comparative example 1. As shown in table 1 and fig. 7, it is understood that the iron loss is reduced in the examples 1 to 4 in which the pressure was applied, compared with the comparative example 1 in which the pressure was not applied. In particular, it is found that the hysteresis loss (Phv) tends to decrease by increasing the surface pressure. It is understood that in example 1 in which the pressure was applied, the iron loss was reduced as compared with comparative example 1 in which the pressure was not applied, but the iron loss was further reduced in examples 2 to 4.

It can be seen that if the surface pressure reaches 6.3kg/cm²As described above, both the magnetic permeability and the iron loss are substantially constant, and the effect on the magnetic properties due to pressurization tends to be saturated. In other words, it was found that the surface pressure was 1.6kg/cm²～15.7kg/cm²In the range of (1), the effect of improving the magnetic permeability and reducing the iron loss can be obtained by including the pressing step. It is also found that the concentration of the carbon black is 6.3kg/cm²This greatly contributes to the increase in density and has a high effect of reducing iron loss.

(b) Amount of resin

Samples of cores (examples 5 to 9 and comparative examples 2 to 4) were produced in the same procedure as in example 3, with the resin amounts in example 3 set to the conditions shown in table 2. Table 2, fig. 8, and fig. 9 show the results of density, permeability, and iron loss of examples 5 to 9 and comparative examples 2 to 4. In table 2, μ 0 and μ 12000 are the same as those in table 1.

[ Table 2]

Pcv[20kHz 30mT]

Fig. 8 is a graph of magnetic permeability with respect to the amount of resin for examples 5 to 9 and comparative examples 2 to 4. Fig. 9 is a graph showing the iron loss with respect to the amount of resin in examples 5 to 9 and comparative examples 2 to 4. As shown in table 2, fig. 8, and fig. 9, when the amount of the resin is less than 3 wt% with respect to the composite magnetic material, voids included in the core increase, and the density decreases. As a result, the permeability is decreased and the hysteresis loss is increased. If the amount of the resin is less than 3 wt%, the magnetic powders are likely to be in point contact with each other, which causes an increase in eddy current loss. On the other hand, if the amount of the resin exceeds 5 wt% with respect to the composite magnetic material, the decrease in density becomes remarkable. As a result, hysteresis loss increases.

(c) Temperature of the container

The temperature of the vessel was varied to make samples of the core. As described in (a), the temperature of the vessel was set to 25 ℃ in examples 1 to 4 and comparative example 1. The temperature of the vessel was set to 70 ℃ and the same procedure as in the above (a) was carried out except for the temperature of the vessel, and the obtained samples were set as examples 10 to 13. Table 3, fig. 10, and fig. 11 show the results of density, permeability, and iron loss of examples 1 to 4, examples 10 to 13, and comparative example 1. The theoretical densities μ 0 and μ 12000 in table 3 are the same as those in table 1.

[ Table 3]

Pcv[20kHz 30mT]

Fig. 10 is a graph of magnetic permeability with respect to surface pressure for examples 10 to 13. Fig. 11 is a graph of the iron loss with respect to the surface pressure in examples 10 to 13. As shown in table 3 and fig. 6, 7, 10, and 11, it is clear that examples 10 to 13 in which the temperature of the vessel was set to 70 ℃ tended to increase the density and theoretical density and also tended to decrease the iron loss, as compared with examples 1 to 4 in which the temperature of the vessel was set to 25 ℃. The magnetic permeability is increased or decreased according to the surface pressure.

It is also understood that the theoretical density of examples 11 to 13 is 77.9% or more while the temperature of the vessel is set to 70 ℃ and the surface pressure is increased to be higher than that of example 10. As described above, by heating the container to above room temperature (25 ℃), the resin in the composite magnetic material becomes soft, and the material easily flows into the voids in the material, whereby it is considered that the apparent density increases and the theoretical density increases. As a result, it is understood that the effect of reducing the iron loss is obtained.

(d) Measurement of viscosity of resin

The viscosity of the resin used in this example will be described. The viscosity of the resin used in this example was determined as the resin viscosity by measuring the depth of the weight placed on the composite magnetic material.

That is, first, a composite magnetic material was produced in the same manner as in the mixing step (a) with the amount of resin added set to the conditions shown in table 4. Then, the obtained composite magnetic material was put into an aluminum container having a diameter of 5mm so that the thickness thereof became 3mm, and a 10g weight of Japanese Industrial Standard (JIS) was placed on the center of the composite magnetic material. After 10 seconds passed after the weight was placed, the weight was removed, and the depth of the pits in the composite magnetic material formed by the weight of the weight was measured. The results are shown in table 4.

[ Table 4]

The amount of resin [ wt.%]	Depth [ mm ]]
		3	0.264
4	0.489
		5	0.558

As shown in table 4, it was found that the greater the amount of resin added, the deeper the depth of the pits, the lower the viscosity of the composite magnetic material, and the weight easily sunk.

(e) Blending ratio of resin

Samples of cores (example 14, example 15, and comparative examples 5 to 7) were produced in the same procedure as in example 2, with the blending ratio of the first magnetic powder and the second magnetic powder of example 2 set to the conditions shown in table 5. Table 5, fig. 12, and fig. 13 show the results of density, permeability, and iron loss of examples 14 and 15, and comparative examples 5 to 7. The density in table 5 is the same as the theoretical density in table 1, and μ 0 and μ 12000 are the same as in table 1.

[ Table 5]

Fig. 12 is a graph of the magnetic permeability with respect to the amount of the second magnetic powder added in example 2, example 14, example 15, and comparative examples 5 to 7. Fig. 13 is a graph of theoretical densities with respect to the amount of the second magnetic powder added in example 2, example 14, example 15, and comparative examples 5 to 7. As shown in table 5, fig. 12, and fig. 13, when the amount of the second magnetic powder added is less than 20 wt%, voids contained in the core increase, and the density decreases. As a result, the magnetic permeability is reduced and the iron loss is increased. On the other hand, if the amount of the second magnetic powder added exceeds 40 wt%, the decrease in density becomes remarkable. As a result, the iron loss increases.

[ difference between MC core and magnetic powder core ]

(section)

Fig. 14 is an SEM photograph (100 × magnification) of a cross section of the core of the present embodiment. The material of the formed core is as follows.

The first magnetic powder … … had an average particle size of 80 μm

The second magnetic powder … … had an average particle size of 10 μm

First magnetic powder: second magnetic powder 70: 30 (weight ratio)

… … 5 wt% resin

Fig. 15 is an SEM photograph (1000 times) of a cross section of the magnetic powder core. In fig. 14 and 15, reference numeral 1 denotes a first magnetic powder, and reference numeral 2 denotes a second magnetic powder. Symbol 3 represents a resin. As is clear from fig. 14 and 15, the circularity of the first magnetic powder 1 of the MC core shown in fig. 14 is higher than that of the magnetic powder core shown in fig. 15. That is, the magnetic powder core is several t/cm²About several tens of t/cm²The high pressure of (3) causes the powders to contact each other and the particle diameter of the magnetic powder is deformed. On the other hand, MC cores are only in the order of several kg/cm²About several tens kg/cm²The pressure of (2) is so low that air inside the resin containing the magnetic powder is removed, and the core is molded by thermosetting of the resin, so that the magnetic powder is not deformed. This difference is also visually recognizable from the SEM photographs of fig. 14 and 15.

(comparison of characteristics in reactor)

Characteristics of examples 16 and 17, which are reactors to which MC cores corresponding to the present embodiment are applied, are compared with those of comparative example 8, which is a reactor to which magnetic powder cores are applied.

The specifications of example 16, example 17, and comparative example 8 are shown in table 6 below.

[ Table 6]

The magnetic powder of the cores of examples 16 and 17 was the same as example 2, and the magnetic powder of the core of comparative example 8 was sendust. The cores of example 16, example 17, and comparative example 8 have the following structures: the magnetic circuit is formed by connecting a pair of rim portions (leg portions) by a pair of yoke portions. The cross-sectional area of the core was 6.15mm². The cores of example 16 and example 17 were formed entirely without seams, and therefore, no gap was present. The core of comparative example 8 has a split structure in which the yoke portion and the rim portion are molded separately, and gaps of 0.25mm intervals are present in the 4-point connecting portions. In the core of comparative example 8, the initial permeability of the yoke portion was 147, and the initial permeability of the rim portion was 75.

Regarding the number of windings of the coil, in comparative example 8 and example 16, 41[ T (Turns) ] is wound around each of the pair of rim portions, and in example 17, 39[ T ] is wound around each of the pair of rim portions. The length and volume of the orthogonal 3-side L, W, H were the same in comparative example 8 and example 16, but the volume was reduced in example 17, regarding the size of the reactor.

That is, in example 16, the magnetic powder core of comparative example 1 was replaced with the MC core, and in example 17, the number of windings of the coil was decreased so as to obtain an inductance value (L value) equal to that of comparative example 1 at 30A. Therefore, when the core and the coil having the same size are used, the MC core can increase the L value of the reactor at 30A compared to the magnetic powder core, and therefore, when the L values are made equal by reducing the number of turns of the coil, the reactor can be made smaller compared to the magnetic powder core.

Further, the magnetic powder core is inferior in moldability, and therefore, it is necessary to be a divided core, and a gap is formed. However, the MC core can be formed entirely without a seam, and therefore has no gap. Therefore, leakage flux to the coil can be reduced, so that copper loss is reduced and heat generation of the coil can be suppressed.

Table 7 and fig. 16 show in detail the L values corresponding to the respective values (a) of the dc excitation current (Idc) in the reactors of comparative example 8, example 16, and example 17.

[ Table 7]

Idc(A)	Comparative example 8	Example 16	Example 17
				0	850	706.0	644
5	810	700.3	632
				10	763	684.5	609
15	719	661.8	597
				20	672	635.1	579
25	616	607.1	555
				30	550	580.0	545
35	485	551.0	520
				40	422	523.0	504

In the reactor of example 16 using the MC core, a high L value of 30A or more can be obtained as compared with comparative example 8 using the magnetic powder core, and therefore, the dc superimposition characteristic becomes good. Therefore, the number of turns of the coil is reduced as in example 17 to obtain an L value equal to or higher than that of comparative example 1, and the size can be reduced.

[ 3] other embodiments ]

The present invention is not limited to the above-described embodiments, and constituent elements may be modified and embodied in the implementation stage without departing from the gist thereof. In addition, various inventions can be formed by appropriate combinations of a plurality of constituent elements disclosed in the above embodiments. For example, some of the components shown in the embodiments may be deleted. Further, the constituent elements in the different embodiments may be appropriately combined.

Claims

1. A core comprising magnetic powder and a resin, characterized in that,

the magnetic powder includes a first magnetic powder and a second magnetic powder having an average particle diameter smaller than that of the first magnetic powder,

the amount of the first magnetic powder added to the magnetic powder is 60 to 80 wt%,

the proportion of the apparent density of the core with respect to the true density of the magnetic powder is 76.6% or more and less than 82%, and

an initial magnetic permeability of 30 or more and a magnetic permeability of 12kA/m of 24 or more.

2. The core of claim 1,

the resin is 3 to 5 wt% with respect to the magnetic powder.

3. The core according to claim 1 or 2,

the proportion of the apparent density of the core with respect to the true density of the magnetic powder is 77% or more.

4. The core according to any of claims 1 to 3,

the circularity of the first magnetic powder is 0.93 or more.

5. The core according to any one of claims 1 to 4,

the entire surface of the core is a non-slip surface.

6. A reactor, characterized by comprising:

the core of any one of claims 1 to 5, and a coil.

7. A method for manufacturing a core containing magnetic powder and resin, comprising:

the first magnetic powder is added in an amount of 60 to 80 wt% with respect to the magnetic powder, and

the method of manufacturing the core includes: a mixing step of mixing a resin with the magnetic powder;

a molding step of adding the mixture obtained in the mixing step to a predetermined container to mold the mixture;

a pressing step of pressing the mixture so that the ratio of the apparent density of the core to the true density of the magnetic powder becomes 76.6% or more and less than 82% in the molding step; and

and a curing step of curing the resin in the molded body obtained in the molding step.

8. The method of manufacturing a core according to claim 7,

the pressure for extruding the mixture in the pressurizing step is 1.6kg/cm²The above.

9. A method for manufacturing a reactor including a core containing magnetic powder and resin, and a coil mounted on the core,

the manufacturing method of the reactor includes: a mixing step of mixing a resin with the magnetic powder;

10. The reactor manufacturing method according to claim 9, characterized in that,