JP2010206087A - Dust core and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core attaining strength and insulation and the density of the dust core, and a method of manufacturing the same. <P>SOLUTION: The dust core includes soft magnetic powder having an insulating film surrounding metal magnetic particles on the surface of the powder and a low-melting glass layer on the surface of the insulating film, at least a part of the insulating film liquefied by annealing and then solidified. The method of manufacturing the dust core includes steps for: forming an insulating film surrounding metal magnetic particles on the surface of the soft magnetic powder and forming a layer containing a low-melting glass component on the surface of the insulating film; compression-shaping the soft magnetic powder where the insulating film and the layer containing the low-melting glass component are formed; annealing the shaped body of the soft magnetic powder which is thus obtained; forming a low-melting glass layer from the layer containing the low-melting glass component; and liquefying at least a part of the insulating film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a dust core in which strength, insulation and density are compatible at a high level. Furthermore, this invention relates to the manufacturing method of this powder magnetic core.

  In powder magnetic cores used for motors and the like, strength, insulation, and density have been very important for improving product efficiency and output. In a dust core, it is a well-known method to bond iron powders using a low melting point glass layer in order to obtain strength and insulation.

  For example, in Patent Document 1, for the purpose of providing a high-frequency powder magnetic core using a magnetic core material having excellent magnetic flux density, iron loss value, and frequency characteristics, and a manufacturing method thereof, P, Mg, B, There has been proposed a high-frequency powder magnetic core obtained by compacting, bonding, and solidifying soft magnetic powder coated with a glassy insulating layer containing Fe as an essential element. In this document, a soft magnetic powder coated with an insulating layer is coated with a resin layer made of an epoxy resin, an imide resin, or a fluorine-based resin.

  Further, in Patent Document 2, for the purpose of providing a dust core with low iron loss and high strength, a powder used therefor, and a method for producing the dust core, the surface of the magnetic powder is an organoalkoxysilane moiety. Powder compact characterized by being coated with at least one layer of a first film comprising a hydrolyzate or / and a precursor thereof, and the first film being further coated with a second film comprising an alkali-silicate glass. A step of mixing magnetic powder and magnetic powder with organoalkoxysilane partial hydrolyzate or / and precursor thereof to form at least one first film covering the surface of the magnetic powder; A step of mixing the formed magnetic powder and alkali-silicate glass to form a second film made of alkali-silicate glass on the first film; the second film is formed And a step of subjecting the obtained molded body to a heat treatment at a temperature of 500 to 900 ° C. to advance polycondensation of the first film and dehydration / polycondensation of the second film. A method of manufacturing a dust core characterized by the above has been proposed.

  Further, in Patent Document 3, an iron base for a dust core having an insulating coating excellent in heat resistance that does not cause dielectric breakdown even when annealing for reducing hysteresis loss is performed, and has a high strength of the molded body. For the purpose of providing a powder, it is a coated iron-based powder formed by coating the surface of an iron-based powder with a coating material, and the amount of the coating material with respect to the coated iron-based powder is 0.02 to 10% by mass The coating material is characterized by comprising, by mass%, glass: 20 to 90%, binder: 10 to 70%, or insulating and heat-resistant substances other than glass and binder: 70% or less. Coated iron-based powders have been proposed.

  Patent Document 4 discloses an oxide solution containing a silicon oxide solution or the like for the purpose of providing a method for producing a composite soft magnetic sintered material having high density, high strength, high specific resistance, and high saturation magnetic flux density. And mixed oxide formed by blending oxide solution or oxide powder containing sol solution or powder such as boron oxide into a specific composition, mixing, drying and coating soft magnetic metal powder with the mixed oxide A method for producing a composite soft magnetic sintered material has been proposed in which an object-coated soft magnetic metal powder is compacted and molded and then sintered at 500 to 1000 ° C.

  Furthermore, in Patent Documents 5 to 8, Mg-Fe-O ternary oxide deposited film is an iron powder for the purpose of providing a composite soft magnetic sintered material having high strength, high magnetic flux density and high resistance. There has been proposed a composite soft magnetic material obtained by bonding an iron powder coated with Mg-containing iron oxide film coated on the surface of this material with a low melting point glass, and a method for producing the same.

  Patent Document 9 discloses a composite using vanadium oxide-based low melting point glass precursor coated iron powder for the purpose of providing a method for producing a composite soft magnetic sintered material having high strength, high magnetic flux density and high resistance. A method for producing a soft magnetic sintered material has been proposed.

  Furthermore, in Patent Document 10, for the purpose of providing a method for producing a composite soft magnetic sintered material having high strength, high magnetic flux density and high resistance used in the production of a motor or the like, on the surface of the iron powder, A low melting point glass precursor coated iron powder is prepared by applying a solution in which an elemental complex or alkoxide constituting the low melting point glass is dissolved in an organic solvent and then drying, and the low melting point glass in the low melting point glass precursor coated iron powder. The low melting point glass-coated iron powder is prepared by thermally decomposing the organic components of the precursor to coat the low melting point glass on the surface of the iron powder. The low melting point glass coated iron powder is compression-molded and then heat-treated. A method for producing a composite soft magnetic sintered material having high strength, high magnetic flux density and high resistance has been proposed.

JP-A-6-260319 JP-A-2005-294428 JP 2004-143554 A JP 2005-332930 A JP 2006-332524 A JP 2006-332525 A JP 2008-91413 A JP 2008-91414 A JP 2008-88459 A JP 2006-278833 A

  However, even when experiments were performed using the methods described in these patent documents, it was difficult to achieve both high strength and insulation and density of the dust core. As a result of intensive studies, the inventors of the present application have found that there are roughly two problems. That is, the first problem is that peeling occurs at the interface between the low melting point glass layer and the insulating film, resulting in insufficient strength, and the second problem is that the outermost layer is covered with glass. Since iron powder has poor moldability, the density is greatly reduced. The present invention is intended to solve such problems and to provide a powder magnetic core in which the strength, insulation and density of the powder magnetic core are compatible at a high level and a method for manufacturing the same.

  That is, the object of the present invention is to improve the interfacial strength between the low melting point glass and the insulating film and the compactability by optimizing the material and the manufacturing method of both the insulating film and the low melting point glass layer. As a result, the object is to make it possible to achieve a high level of strength, insulation and density of the dust core.

The invention according to claim 1 of the present application (hereinafter referred to as “the first invention of the present application”) is a powder magnetic core formed by compression-molding, joining and solidifying a soft magnetic powder.
The soft magnetic powder has an insulating film surrounding metal magnetic particles on its surface, and further has a low melting point glass layer on the surface of the insulating film,
At least a part of the insulating film is solidified after being liquidified by annealing,
A powder magnetic core is provided.

  In the first invention of the present application, it is possible to provide a dust core in which strength, insulation, and density are compatible at a high level.

  In one preferred embodiment of the first invention, the low melting glass layer is formed by mineralizing a mixture of a low melting glass component and an organic binder and / or an inorganic binder by annealing. A manufacturing method is mentioned (refer Claim 2). According to this aspect, it is possible to provide a dust core in which strength, insulation, and density are compatible at a higher level.

As another preferred embodiment of the first invention, there is a dust core in which the insulating film contains Si resin, and the low melting point glass layer contains B ₂ O ₃ and Si resin (see claim 3). . According to this aspect, it is possible to provide a dust core in which strength, insulation, and density are compatible at a higher level.

Invention of Claim 4 of this application (henceforth "the 2nd invention of this application") is a manufacturing method of a powder magnetic core formed by compression-molding, joining and solidifying metal magnetic particles,
Forming an insulating film surrounding the metal magnetic particles on the surface of the metal magnetic particles, forming a layer containing a low melting point glass component on the surface of the insulating film;
Compression molding metal magnetic particles formed with a layer containing the insulating film and a low-melting-point glass component;
Annealing the obtained molded body of metal magnetic particles to form a low-melting glass layer from the layer containing the low-melting glass component, and at least a part of the insulating film is also in a liquid phase, A method for producing a dust core is provided.

  In the second invention of the present application, it is possible to reliably manufacture a dust core in which strength, insulation, and density are compatible at a high level.

  As one preferred embodiment of the second invention, the layer containing a low melting glass component is composed of a mixture of a low melting glass component and an organic binder and / or an inorganic binder, and the low melting glass is obtained by mineralizing the mixture by annealing. A method for producing a dust core is characterized in that a layer is formed and at least a part of the insulating film is also in a liquid phase (see claim 5). According to this aspect, it is possible to more reliably manufacture a dust core in which strength, insulation, and density are compatible at a high level.

Another preferred embodiment of the second invention is a method for producing a powder magnetic core, wherein the insulating film contains Si resin, and the low melting point glass layer contains B ₂ O ₃ and Si resin. 6). According to this aspect, it is possible to more reliably manufacture a dust core in which strength, insulation, and density are compatible at a high level.

In one embodiment of the method for producing a powder magnetic core of the present invention, a metal magnetic particle formed with a layer containing an insulating film and a low-melting glass component is molded and annealed to form a low melting point from the layer containing the low-melting glass component. It is explanatory drawing which shows typically what formed the glass layer and at least one part of the insulating film was also made into the liquid phase. In one mode of the present invention, it is an explanatory view showing an example of an equilibrium diagram of a SiO ₂ -B ₂ O ₃ system. It is explanatory drawing which shows typically one aspect of the manufacturing method of the powder magnetic core of this invention. It is explanatory drawing which shows the relationship between the bending strength and specific resistance in one aspect of the dust core of this invention, and a control example.

  The present invention provides a powder magnetic core excellent in both strength and insulation. Specifically, the metal magnetic particles have an insulating film surrounding the metal magnetic particles on the surface thereof, and further the insulation. The present invention provides a powder magnetic core having a low melting point glass layer on the surface of the coating, and at least a part of the insulating coating is solidified after being liquidified by annealing.

  The metal magnetic particles in the dust core are usually soft magnetic powders, and can be arbitrarily changed according to the composition of the dust core. Generally, the metal magnetic particles can be made of an iron-based material, that is, pure iron or an alloy thereof. Suitable metal magnetic particles are not limited to those described below. For example, iron (Fe), iron (Fe) -silicon (Si) alloy, iron (Fe) -aluminum (Al) alloy, iron ( Fe) -nickel (Ni) alloy, iron (Fe) -cobalt (Co) alloy, iron (Fe) -nitrogen (N) alloy, iron (Fe) -carbon (C) alloy, iron (Fe) Boron (B) alloy, iron (Fe) -phosphorus (P) alloy, iron (Fe) -nickel (Ni) -cobalt (Co) alloy, iron (Fe) -aluminum (Al) -silicon (Si ) Series alloys. These metal magnetic particles may be used alone or in combination of two or more. Among others, suitable metal magnetic particles are Fe, Fe—Si, Fe—Al, Fe—Ni, Fe—Co and mixtures thereof.

  Conventionally, as its name suggests, low-melting glass used in a powder magnetic core melts during annealing to join soft magnetic powders together to maintain strength. However, since there is no intermediate layer or the like at the interface between the insulating coating on the surface of the soft magnetic powder and the low melting point glass layer, the bonding strength is weak. As a result of intensive studies, the inventors of the present application have found that at least a part of the low-melting glass layer and the insulating coating is liquid-phased, that is, melted and solidified, so that the low-melting glass layer and the insulating coating are bonded to the adhesive interface. It has been found that the bonding strength between both layers can be improved by forming such an intermediate layer.

In order to melt at least a part of the insulating film and the layer containing the low melting point glass component during annealing, the material composition and the annealing temperature can be set using a general equilibrium diagram. Further, eutectic and peritectic materials can be applied to the material containing the low melting point glass component and the insulating coating. For example, when the annealing temperature is set to 700 ° C., the material systems that can be used for the low-melting glass layer include SiO ₂ —B ₂ O ₃ system, SiO ₂ —V ₂ O ₅ system, SiO ₂ —PbO system, SiO ₂ -B ₂ O ₃ -Bi ₂ O ₃ system and the like can be mentioned, and the SiO ₂ --B ₂ O ₃ system is particularly preferable as a material system that can be used for the low melting point glass layer.

When the metal magnetic particles are coated with an insulating film and further coated with a layer containing a low melting point glass component, various configurations are possible. In the case the low-melting-point glass layer is SiO ₂ -B ₂ O ₃ -based As an example, (1) SiO ₂ component as a layer to form a film containing SiO _2, comprising a low melting glass component thereon as an insulating film and B ₂ O ₃ or to coat the mixture of the components, or (2) forming a film containing SiO ₂ as an insulating film, or coating the B ₂ O ₃ component as a layer containing a low melting glass component thereon, Or (3) coating a metal magnetic particle with a mixture of a SiO ₂ component and a B ₂ O ₃ component to form a base, and forming a coating containing SiO ₂ as an insulating coating thereon, followed by a low melting glass component Various configurations are possible, such as coating a mixture of SiO ₂ and B ₂ O ₃ components as a layer. In any structure, the outermost layer melts during annealing to form a low-melting glass layer, and at least one of the other layer structures, preferably as a lower layer of the low-melting glass layer, is annealed. It is important to provide an insulating coating that can melt the part.

In order to further increase the strength of the dust core, the ratio of the low melting point compound to the high melting point compound may be increased. For example, if the low melting point glass layer and the insulating film are SiO ₂ —B ₂ O ₃ , the ratio of B ₂ O ₃ (melting point: 450 ° C.) to SiO ₂ (melting point: about 1,700 ° C.) may be increased. Specifically, the ratio of B ₂ O _{3 in} the low melting point glass layer may be increased, or the ratio of the low melting point glass layer to the insulating film may be increased. On the other hand, when the insulation is required, the amount of the high melting point compound may be increased.

An important threshold value for ensuring insulation is whether or not the insulating coating is completely melted. This can be determined using an equilibrium diagram. As an example, when SiO ₂ is in a SiO ₂ —B ₂ O ₃ system at 600 ° C. and SiO ₂ has a molar ratio of 60% or less, it completely becomes a liquid phase, and the insulating film is completely melted. FIG. 2 shows an example of such an equilibrium diagram. As a result, the strength is improved with this value as a boundary, but the insulation may be lowered. Therefore, as a part which melts at the time of annealing in the insulating film, it is preferable that a part of 25 to 95% by volume in the insulating film is melted in order to obtain both strength and insulation, and a part of 50 to 95% by volume is particularly preferable. It is preferable to melt.

In order to achieve both strength and insulation, for example, the weight ratio of SiO ₂ / B ₂ O _{3 in} the SiO ₂ -B ₂ O ₃ system is preferably 0.5 or more, for example, when the low melting point glass layer and the insulating film are combined. And 5.0 or less. Further, the weight ratio is preferably 1.5 or more and 3.0 or less.

  As a preferred embodiment of the powder magnetic core of the present invention, a low melting glass layer is formed by mineralizing a mixture of a low melting glass component and an organic binder and / or an inorganic binder by annealing. Can be mentioned.

  As the layer containing the low melting point glass component, only the low melting point inorganic glass component or a mixture of an organic binder and / or an inorganic binder can be used together with the low melting point inorganic glass component. In particular, it is preferable to use a mixture of an organic binder and / or an inorganic binder together with a low melting point inorganic glass component in the outermost layer containing the low melting point glass component. Since the organic binder and / or inorganic binder plays the role of a lubricant during compaction molding, the friction coefficient between the soft magnetic powders is lowered, the moldability is greatly improved, and the mold wear is also reduced.

Examples of such organic binders are not limited to those listed below, but include Si resin, thermoplastic polyimide, thermoplastic polyamide, thermoplastic polyamideimide, polyphenylene sulfide, polyamideimide, polyethersulfone, polyetherimide, polyether. Thermoplastic resins such as ether ketone, non-thermoplastic resins such as high molecular weight polyethylene, wholly aromatic polyester, wholly aromatic polyimide, zinc stearate, lithium stearate, calcium stearate, lithium palmitate, calcium palmitate, lithium oleate Higher fatty acid compounds such as calcium oleate and the like, and Si resin is particularly preferable. Examples of the inorganic binder include metal alkoxide, amorphous silica, and ρ-alumina (Al ₂ O ₃ · nH ₂ O), and metal alkoxide is more preferable. These organic binders and inorganic binders can be used alone or in combination, but preferably the organic binder is used alone.

For example, when a SiO ₂ —B ₂ O ₃ -based low-melting glass layer is produced, a mixture of Si resin and B ₂ O ₃ as an organic binder may be used. The mixing ratio of the low-melting-point inorganic glass component and the organic binder and / or inorganic binder is such that the ratio (weight ratio) of the low-melting-point inorganic glass component to the organic binder and / or inorganic binder is 0.1 or more in view of the balance between moldability and strength. And 20 or less is desirable.

  The shape of the low-melting glass component used may be powdery, or the low-melting glass component and an organic binder and / or an inorganic binder may be mixed at the molecular level.

As a preferred embodiment of the powder magnetic core of the present invention, the insulating film contains Si resin, that is, a silicone resin, and the low melting point glass layer contains B ₂ O ₃ and Si resin as an organic binder. Is mentioned. As the Si resin, for example, KR220L manufactured by Shin-Etsu Silicone Co., Ltd. can be used.

  The total film thickness of the insulating film and the low melting point glass layer is preferably 0.005 to 20 μm on average, and more preferably 0.05 to 0.3 μm. By setting the total film thickness of the insulating film and the low-melting glass layer to 0.005 μm or more, energization due to the tunnel effect can be suppressed. Further, by setting the thickness to 0.05 μm or more, energization due to the tunnel effect can be more effectively suppressed. On the other hand, when the total film thickness of the insulating film and the low-melting glass layer is 20 μm or less, the insulating film can be prevented from being sheared and destroyed during compression molding. Moreover, since the ratio of the insulating film and the low melting point glass layer in the soft magnetic powder does not become too large, it is possible to prevent the magnetic flux density of the dust core obtained by compression molding the soft magnetic powder from being significantly reduced. Moreover, the fall of magnetic flux density can further be prevented by making the film thickness of an insulating film into 0.3 micrometer or less.

  The present invention provides a method for producing a dust core excellent in both strength and insulation. Specifically, an insulating film surrounding the metal magnetic particles is formed on the surface of the metal magnetic particles to provide insulation. A layer containing a low-melting glass component is formed on the surface of the film, compression-molding the soft magnetic powder on which the insulating film and the layer containing the low-melting glass component are formed, and annealing the obtained soft magnetic powder compact. The present invention provides a method for producing a powder magnetic core, in which a low-melting glass layer is formed from a layer containing a low-melting glass component, and at least a part of the insulating film is also in a liquid phase.

  As one preferable aspect of the method for producing the dust core, the layer containing the low melting glass component is composed of a mixture of the low melting glass component and an organic binder and / or an inorganic binder, and the mixture is mineralized by annealing. And a method for producing a dust core, wherein a low-melting glass layer is formed and at least a part of the insulating film is also in a liquid phase.

Another preferred embodiment of the method for producing a dust core includes a production method in which the insulating film contains Si resin and the low melting point glass layer contains B ₂ O ₃ and Si resin.

  In the preferable aspect regarding the manufacturing method of these powder magnetic cores, the preferable aspect regarding a powder magnetic core as mentioned above may be applied similarly.

  In FIG. 1, in one embodiment of the method for producing a dust core of the present invention, a soft magnetic powder 3 on which an insulating film 1 and a layer 2 containing a low-melting glass component are formed is molded and annealed to obtain a low melting point. An insulating film 5 is schematically shown in which a low melting point glass layer 4 is formed from a layer containing a glass component and at least a part thereof is liquid phase and solidified.

  For the formation of the layer containing the low melting point glass component and the insulating coating, any of wet and dry thin film forming methods including the sol-gel method can be used. Further, after the formation of the insulating coating and the layer containing the low melting glass component, the surface of the layer containing the low melting glass component may be coated with an internal lubricant as necessary.

  The soft magnetic powder thus produced is molded by compacting. Various molding methods such as general biaxial mold molding, HIP, and CIP can be used. However, in order to sufficiently exhibit the effects of the present invention, it is desirable to adjust the relative density of the soft magnetic powder to 90% or more (so that a dust core having a high magnetic flux density can be obtained as a result).

  The ultimate temperature during annealing is preferably 400 ° C to 910 ° C. This is because distortion at the time of compacting cannot be sufficiently removed at 400 ° C. or lower, and conversely at 910 ° C. or higher, the insulating film deteriorates and the metal magnetic particles are sintered. Further, the temperature rising rate is preferably 20 to 7000 ° C./hr, and the holding time at the ultimate temperature is preferably 1 to 200 minutes.

  In particular, when strength is required, it is preferable to coat the surface of the dust core with an epoxy or other resin after the annealing step. As a result, fine cracks on the surface of the green compact can be filled and the strength can be greatly improved.

  FIG. 3 schematically shows one embodiment of the method for producing a dust core according to the present invention. That is, the insulating film 11 is formed on the surface of the metal magnetic particles 13, and the layer 12 containing a low melting point glass component is formed thereon. The obtained coated soft magnetic powder group 17 is compression-molded under a pressure of 1,300 MPa or the like with a compression molding machine. Annealing is performed under conditions such as 60 minutes. By annealing, a powder magnetic core having a metal magnetic particle 13 and a low-melting glass formed from a layer containing a low-melting glass component and a layer 14 made of an insulating film at least partially liquidized and solidified is obtained, Next, if necessary, the surface is further coated with a resin 15 such as an epoxy resin, and at that time, a part 16 of the resin is allowed to enter a gap existing in the vicinity of the surface of the dust core so that the strength of the coating is increased. To further improve.

The “density [g / cm ³ ]” in the present invention is obtained by the weight measured by an electronic balance and the volume calculated based on the dimensions measured by a micrometer. “Strength” means four-point bending strength [MPa], which is obtained based on the maximum load when a rod-shaped specimen is broken by a four-point bending test. “Insulation” means specific resistance. It means [Ω · cm] and is obtained by measuring the sample surface by the four-probe method.

  The thickness of the insulating film and the low melting point glass layer is obtained by processing the surface of the soft magnetic powder into a cross-sectional observation sample and then observing with a transmission electron microscope (TEM). The “solidified part” is confirmed by breaking the annealed sample and observing the fractured surface with a scanning electron microscope (SEM).

  Further, “bending strength [MPa]” in Examples described later means four-point bending strength [MPa], which is obtained based on the maximum load when a rod-shaped specimen is broken by a four-point bending test. .

  Further, “specific resistance [Ω · cm]” in Examples described later is obtained by measuring the surface of a sample by a four-probe method.

  Examples of the present invention will be described below more specifically with reference to examples of the present invention. However, the present invention is not limited to these examples. In addition, unless otherwise indicated, the quantity of each component showing the composition in the following Examples and Comparative Examples is expressed by “parts by weight”.

Examples 1 to 5, Reference Examples 1 and 2
As shown in FIG. 3, the metal magnetic particles (iron-based powder) 13 were coated with Si resin, and subsequently coated with a mixture of B ₂ O ₃ and Si resin. The ratio of each layer was changed as shown in Table 1, and each sample was produced. These coating treatments were performed by dissolving the coating components in IPA (isopropyl alcohol) to prepare a coating solution, and heating to 60 ° C. in a fluidized bed dryer while spraying the coating solution onto metal magnetic particles. . The coated powder was heated at 225 ° C. for 1 hour with a constant temperature bath to completely remove the solvent of each layer, thereby forming the insulating film 11 and the layer 12 containing a low melting point glass component. The strength of each layer was improved for each sample thus obtained.

As the metal magnetic particles (iron-based powder), the water atomized iron powder “Somalloy 700” of Höganäs is used, and as the Si resin, the product name “silicone resin KR220L” manufactured by Shin-Etsu Chemical Co., Ltd. is used. did. In Table 1, “SiO ₂ (inorganic content) / B ₂ O ₃ ” means the weight of residual SiO ₂ (inorganic content) when the Si resin added to the metal magnetic particles is heated to 600 ° C. The ratio divided by the weight of B ₂ O ₃ added to the metal magnetic particles means “no resin coating” means that the surface of the powder magnetic core after annealing is not coated with an epoxy resin (Example) “Corresponding to 1, 2, 4”) “with resin coating” means that the surface of the powder magnetic core after annealing is coated with an epoxy resin (corresponding to Examples 3 and 5).

  In each of the obtained samples, the thickness of the insulating film was about 100 nm, and the thickness of the low melting point glass layer was about 75 to 300 nm.

  The obtained mixed powder was put into a mold and compression molded. As a molding method, a mold lubricant (zinc stearate) was brushed every shot at a mold temperature of 130 ° C. and a molding surface pressure of 1,300 MPa in the atmosphere.

  Next, the strain introduced during the molding was removed by annealing, and the strength was improved by melting a part of the low melting glass and the insulating coating. As annealing conditions, the heating rate was 100 ° C./hr, the ultimate temperature was 600 ° C., and the holding time was 60 minutes.

  Moreover, as a result of rupturing the sample after annealing and observing the fractured surface by SEM, the liquefied and solidified portion of the insulating film was about 50 to 90%.

  Next, the surface of the obtained powder magnetic core was coated with an epoxy resin to further improve the strength. As the epoxy resin, “E530-5” manufactured by Somar was used, and after the softened resin was applied, it was cured at 140 ° C. for 1 hour.

Next, the density, bending strength, and specific resistance of the obtained sample were measured. The density was determined based on the dimensions measured with a micrometer. The bending strength was measured by a four-point bending test, and the specific resistance was measured by a four-probe method on the sample surface. Table 1 shows a sample list obtained as described above. As can be seen from Table 1, the bending strength is improved when the low melting point glass mixed with B ₂ O ₃ is used (Examples 1 to 5) as compared with the case of only the insulating film of Si resin in the reference example. is doing. It can also be seen that both the specific resistance and the bending strength change depending on the SiO ₂ / B ₂ O ₃ ratio.

  As shown in FIG. 4, in the relationship between the specific resistance and the bending strength, the case of “with resin coating” with the same specific resistance (Examples 3 and 5) is more “with no resin coating” (Examples). Bending strength higher than 1, 2, 4) is obtained.

Claims (6)

In a powder magnetic core formed by compression molding, joining and solidifying metal magnetic particles,
The metal magnetic particles have an insulating film surrounding the metal magnetic particles on the surface, and further have a low melting point glass layer on the surface of the insulating film,
At least a part of the insulating film is solidified after being liquidified by annealing,
A dust core characterized by that.   The dust core according to claim 1, wherein the low-melting glass layer is formed by mineralizing a mixture of a low-melting glass component and an organic binder and / or an inorganic binder by annealing. The dust core according to claim 1 or 2, wherein the insulating film includes Si resin, and the low-melting glass layer includes B ₂ O ₃ and Si resin. In a method of manufacturing a powder magnetic core, which is formed by compression-molding soft magnetic powder, joining and solidifying,
Forming an insulating film surrounding the metal magnetic particles on the surface of the soft magnetic powder, forming a layer containing a low-melting glass component on the surface of the insulating film;
Compression-molding a soft magnetic powder having a layer containing the insulating film and a low-melting glass component;
The obtained soft magnetic powder molded body is annealed to form a low-melting glass layer from the layer containing the low-melting glass component, and at least a part of the insulating film is also in a liquid phase, Manufacturing method of a dust core.   The layer containing the low-melting glass component is composed of a mixture of the low-melting glass component and an organic binder and / or an inorganic binder, and forming the low-melting glass layer by mineralizing the mixture by the annealing. The method for manufacturing a dust core according to claim 4, wherein at least a part of the insulating film is also in a liquid phase. The method for producing a powder magnetic core according to claim 4 or 5, wherein the insulating film contains Si resin, and the low-melting glass layer contains B ₂ O ₃ and Si resin.

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