Powder cores and electronic components

Abstract

A pressed powder magnetic core has an epoxy resin binder and magnetic particles dispersed in the binder. The epoxy resin in the pressed powder magnetic core has at least two mesocrystalline frameworks between two closely spaced epoxy bonds along the molecular chain.

Description

Technical Field

[0001] This invention relates to pressed powder magnetic cores and electronic components having the pressed powder magnetic cores. Background Technology

[0002] As a magnetic core for magnetic electronic components such as inductors or reactors, the pressed powder core shown in Patent Document 1 is known. This pressed powder core can be manufactured, for example, by mixing magnetic particles together with a binder (adhesive material) and then compressing them into shape.

[0003] Here, the adhesive, by melting and flowing during the molding process and filling the spaces between the magnetic particles, serves to bond the magnetic particles together while simultaneously insulating them electrically. Therefore, the properties of the adhesive affect the density or strength, relative permeability, and other characteristics of the pressed powder core, making it one of the important design considerations for pressed powder cores.

[0004] Representative adhesives used in powder-pressed magnetic cores include, for example, silicone resin, epoxy resin, phenolic resin, polyamide resin, polyimide resin, polysilazane resin, polyester resin, polycarbonate resin, water glass, and low-melting-point glass. Among these adhesives, epoxy resin is widely used due to its excellent adhesive strength, electrical insulation, dimensional stability, solvent resistance, curing ability at low temperatures below 200°C, and ease of industrial-scale availability at low cost. In particular, Patent Document 1 discloses that by using an epoxy resin with a defined mesocrystalline framework, powder-pressed magnetic cores with high relative permeability, high strength, and high thermal conductivity can be obtained.

[0005] However, when using conventional epoxy resins, depending on the molding conditions, molding defects such as adhesion of the molded part to the mold can sometimes occur. In particular, these adhesion defects are prone to occur when thermoforming is performed to further increase the core density. Therefore, there is a need to develop a technology that can also be used with thermoforming and can more effectively achieve high relative permeability, high strength, and high heat resistance.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2016-12671 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] The present invention was developed in view of the above-mentioned actual situation, and its purpose is to provide a pressed powder magnetic core with excellent relative permeability, strength and heat resistance, and an electronic component using the pressed powder magnetic core.

[0011] Technical solutions for solving the problem

[0012] To achieve the above objectives, the present invention provides a pressed powder magnetic core.

[0013] It contains an epoxy resin-based adhesive and magnetic particles dispersed in the adhesive.

[0014] The aforementioned epoxy resin has at least two mesocrystalline frameworks between two epoxy bonds that are close to each other along the molecular chain.

[0015] The inventors conducted intensive research and discovered that the number of mesocrystalline skeletons in epoxy resin affects poor adhesion during thermoforming. Specifically, according to their experiments, when using epoxy resins without mesocrystalline skeletons or epoxy resins with only one mesocrystalline skeleton between epoxy bonds, the molded part tends to adhere to the mold during thermoforming, easily leading to poor molding. Therefore, in these conventional epoxy resins, it is necessary to use lubricants that do not easily cause a decrease in strength, or to manufacture by cold forming instead of thermoforming. On the other hand, when using epoxy resins with at least two or more mesocrystalline skeletons between epoxy bonds, poor adhesion during thermoforming can be prevented. As a result, the pressed powder magnetic core of the present invention exhibits higher strength, relative permeability, and heat resistance than when using conventional epoxy resins.

[0016] Preferably, the magnetic particles are metallic magnetic particles, and the content of the adhesive relative to 100 parts by mass of the metallic magnetic particles is 1.0 part by mass or more and 4.0 parts by mass or less.

[0017] In addition, preferably, the mesocrystalline framework described above has a structure represented by the following formula (I).

[0018]

[0019] In formula (I), Y is selected from -H, alkyl (aliphatic hydrocarbons with 4 or fewer carbon atoms), acetyl, and halogen. The Y atoms in the mesocrystalline framework can be all the same or different. * indicates the bonding site with adjacent atoms.

[0020] The pressed powder magnetic core of the present invention can be applied to various electronic components such as inductors, reactors, transformers, non-contact power supply coils, and magnetic shielding parts, and is particularly preferred for use as a magnetic core for inductors.

[0021] In inductors with the aforementioned pressed powder core,

[0022] Let the volume resistivity after storing at 175°C for 100 hours be R. A The volume resistivity before storage is set as R. B Preferably, R A / R B >0.001.

[0023] In the aforementioned inductor, epoxy resin with two or more mesocrystalline frameworks between epoxy bonds is contained within the powder core, thereby enabling the aforementioned R... A / R B >0.001. As a result, in the above inductors, energy loss can be reduced, and the miniaturization or high current of the inductors can be well realized. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of an inductor element according to one embodiment of the present invention.

[0025] Figure 2 It is Figure 1 The image shows an enlarged cross-sectional view of a portion of the pressed powder magnetic core.

[0026] Explanation of reference numerals in the attached figures

[0027] 100 Inductor components, 110 Pressed powder cores, 2 Adhesives, 4 Magnetic particles, 4a Large particles, 4b Small particles, 120 Coils Detailed Implementation

[0028] The present invention will now be described in detail based on the embodiments shown in the accompanying drawings.

[0029] like Figure 1 As shown, an inductor element 100 according to one embodiment of the present invention has a pressed powder core 110 and a coil 120 embedded inside the pressed powder core 110.

[0030] The shape of the pressed powder core 110 is not particularly limited; for example, it can be cylindrical, elliptical cylindrical, or prismatic. Furthermore, as... Figure 2 As shown, the pressed powder magnetic core 110 includes an adhesive 2 as a bonding material and magnetic particles 4 dispersed in the adhesive 2. It may also include non-magnetic inorganic particles, etc. That is, the pressed powder magnetic core 110 is formed into a predetermined shape by bonding multiple magnetic particles 4 together via the adhesive 2. The adhesive 2 and magnetic particles 4 constituting the pressed powder magnetic core 110 will be described in detail below.

[0031] Adhesive 2 is mainly composed of cured epoxy resin and phenolic resin, and may also contain trace amounts of organic components. Here, "trace amounts of organic components" refers to components such as lubricants, curing accelerators, softeners, plasticizers, dispersants, colorants, and anti-settling agents, which may contain less than 1.0 part by weight relative to 100 parts by weight of the main component of adhesive 2, namely epoxy resin.

[0032] In this embodiment, the epoxy resin of the adhesive 2 is characterized by having a defined molecular structure. Specifically, the epoxy resin of the adhesive 2 has a plurality of mesocrystalline frameworks between two epoxy bonds close to each other along the molecular chain.

[0033] In this embodiment, "epoxy bond" refers to the molecular arrangement formed by the ring-opening of epoxy groups present in the prepolymer through a polymerization reaction (curing reaction). Additionally, "mesocrystalline framework" is a general term for atomic groups containing polycyclic aromatic hydrocarbons or two or more aromatic rings, possessing rigidity and orientation.

[0034] More specifically, the mesocrystalline framework is preferably a partial structure as shown in the following formula (J).

[0035]

[0036] In the above formula (J), X is a single bond or at least one linking group selected from group (A) below.

[0037]

[0038] Furthermore, in formula (J) above, Y is selected from -H (hydrogen), alkyl (aliphatic hydrocarbons with 4 or fewer carbon atoms), acetyl, and halogen. The Y atoms in the mesocrystalline framework can be all the same or different. Moreover, * in formula (J) indicates the bonding site with adjacent atoms.

[0039] In particular, in this embodiment, the mesocrystalline framework is more preferably a partial structure as shown in the following formula (I).

[0040]

[0041] The Y and * in equation (I) above are the same as in equation (J). That is, in the mesocrystalline framework shown in equation (I), X in equation (J) is set as a single bond, and compared with equation (J), the number of Y that can be configured with functional groups (side chains of alkyl, acetyl, halogen, etc.) is limited.

[0042] It is believed that the aforementioned mesocrystalline framework enhances the lubricity between magnetic particles 4 during the molding process and efficiently promotes the rearrangement of magnetic particles 4. Furthermore, it is also believed that stacking (molecular overlap) easily forms between the cured mesocrystalline framework, which contributes to the improvement of the mechanical strength of the binder 2 and the pressed magnetic core 110. Moreover, it is also believed that the mesocrystalline framework reduces the thermal resistance between magnetic particles 4. Therefore, by forming the pressed magnetic core 110 from epoxy resin containing a mesocrystalline framework, improvements in density, strength, relative permeability, and thermal conductivity can be expected. In addition, the "rearrangement of magnetic particles 4" mentioned above refers to the particles moving under pressure, approaching a state of maximum density filling.

[0043] In the epoxy resin of the adhesive 2 of this embodiment, there are at least two (preferably 10 or less, more preferably 3 or less) mesocrystalline skeletons between two adjacent epoxy bonds along the molecular chain. There is no particular upper limit to the number of mesocrystalline skeletons present between epoxy bonds; for example, it can be 100 or less. Furthermore, the multiple mesocrystalline skeletons present between adjacent epoxy bonds can be different from each other, or they can all be the same structure. Additionally, between two adjacent epoxy bonds, multiple mesocrystalline skeletons can exist continuously linked by single bonds, or they can be linked via one or more linking groups.

[0044] Here, the term "two adjacent epoxy bonds" is explained in more detail. A molecular structure having the aforementioned multiple mesocrystalline frameworks can be achieved, for example, by curing an epoxy resin having a prepolymer as shown in the following formula (K).

[0045]

[0046] In the prepolymer shown in formula (K), E1 and E2 at the ends are both epoxy groups. Additionally, M1 and M3 in formula (K) form a mesocrystalline framework. If an epoxy resin having the prepolymer of formula (K) is cured, the epoxy groups of E1 and E2 undergo ring-opening to form a polymer chain. In this case, the ring-opening E1 and E2 corresponds to "two epoxy bonds close together along the molecular chain," and between these epoxy bonds exists a mesocrystalline framework of "1 (M1) + n (M3)".

[0047] When only a single mesocrystalline framework exists between two closely spaced epoxy bonds, poor molding can easily occur during thermoforming, causing the molded part to adhere to the mold. On the other hand, as mentioned above, when multiple mesocrystalline frameworks exist between closely spaced epoxy bonds, poor adhesion can be suppressed. This allows the powder core 110 to be manufactured not only through cold forming but also through thermoforming. In other words, in the powder core 110 of this embodiment, by containing epoxy resin with two or more mesocrystalline frameworks between epoxy bonds, higher strength, relative permeability, and heat resistance can be obtained compared to using epoxy resin with only a single mesocrystalline framework.

[0048] Furthermore, the amount of mesocrystalline framework present between epoxy bonds can be specified by analyzing the molecular structure of binder 2. For example, the molecular structure of binder 2 can be analyzed appropriately using nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR), gas chromatography-mass spectrometry (GC / MS), liquid chromatography-mass spectrometry (LC / MS), etc. Additionally, the sample for measurement can be obtained from... Figure 1 The powder-pressed magnetic core 110 shown can be prepared by collecting adhesive 2.

[0049] In this embodiment, the magnetic particle 4 can also be a soft ferrite or other oxide magnetic particle, but it is preferably a soft magnetic metal particle. Examples of soft magnetic metal particles include pure iron, Fe-Si alloys (iron-silicon), Fe-Al alloys (iron-aluminum), permalloys (Fe-Ni), iron-silicon-aluminum alloys (Fe-Si-Al), Fe-Si-Cr alloys (iron-silicon-chromium), Fe-Si-Al-Ni alloys, Fe-Ni-Si-Co alloys, Fe amorphous alloys, and Fe nanocrystalline alloys.

[0050] Preferably, an insulating coating is formed on the surface of the aforementioned soft magnetic metal particles. Examples of insulating coatings include, for instance, oxide films formed by oxidation of the particle surface, phosphate films, silicate films, glass coatings, inorganic films containing BN, SiO2, MgO, Al2O3, etc., or organic films. These insulating coatings can be formed through surface treatments such as heat treatment, phosphate treatment, mechanical alloying, silane coupling treatment, and hydrothermal synthesis. By forming an insulating coating on the soft magnetic metal particles, high-frequency losses in the powder core 110 can be suppressed.

[0051] The average particle size (D50) of the magnetic particles 4 is not particularly limited, for example, it can be less than 50 μm, preferably in the range of 20 μm to 40 μm. Furthermore, the average particle size of the magnetic particles 4 can be determined by... Figure 2 The cross-section of the powder-pressed magnetic core 110 shown can be measured by image analysis. Specifically, by measuring... Figure 2 The particle size distribution of magnetic particle 4 can be obtained by calculating the equivalent circle diameter of each particle based on the area of ​​each particle in the cross-section shown. In this measurement, the size of the measurement field of view can be appropriately adjusted according to the observed particle size of magnetic particle 4, and it is preferable to perform the analysis with at least 5 fields of view to obtain the particle size distribution.

[0052] Furthermore, the magnetic particles 4 contained in the pressed powder core 110 can be all made of the same material, or they can be composed of multiple particle groups made of different materials. Additionally, as... Figure 2 As shown, magnetic particles 4 can also be composed of multiple groups of particles with different particle sizes. For example, magnetic particles 4 can be formed by mixing large particles 4a made of Fe-Si alloy and small particles 4b made of pure iron with an average particle size smaller than that of the large particles 4a.

[0053] Furthermore, while the average sphericity of the magnetic particles 4 on the cross-section of the pressed powder core 110 is not particularly limited, considering the DC superposition characteristics, the average sphericity of the magnetic particles 4 is preferably 0.9 or higher, more preferably 0.95 or higher. The average sphericity of the magnetic particles 4 can be determined by... Figure 2The cross-section of the powder-pressed magnetic core 110 shown is measured by image analysis. Specifically, the area S and the length L of the outline of each magnetic particle 4 contained in the cross-sectional image are measured, and the roundness is calculated based on the following formula. The roundness distribution is obtained by performing this measurement on at least 50 magnetic particles 4, and the average roundness is calculated using the roundness of the cumulative frequency of 50%.

[0054] Circularity = 4πS / L 2

[0055] Here, we will supplement the discussion on the correlation between the average sphericity of the magnetic particles 4 and the strength of the pressed powder core 110. As mentioned above, in the case of spherical magnetic particles with high average sphericity, entanglement between adjacent particles, known as the anchoring effect, is less likely to occur, and generally, the strength of the pressed powder core decreases. In the pressed powder core 110 of this embodiment, even when using magnetic particles 4 with high sphericity, high strength can be obtained by containing epoxy resin with multiple mesocrystalline frameworks between the epoxy bonds.

[0056] Furthermore, when the magnetic particles 4 are metallic magnetic particles, the content of the binder 2 in the pressed powder core 110 is preferably 4.0 parts by mass or less, more preferably 1.0 to 4.0 parts by mass, relative to 100 parts by mass of the magnetic particles. In the pressed powder core 110 of this embodiment, by using an epoxy resin having multiple mesocrystalline frameworks between epoxy bonds, shape retention can be ensured even when the proportion of binder 2 relative to the magnetic particles 4 is reduced, and high strength can be obtained. In addition, by keeping the content of binder 2 within the above range, both high strength and high magnetic properties can be balanced and improved.

[0057] Furthermore, the binder content can be estimated by analyzing the pressed magnetic core using inductively coupled plasma atomic emission spectrometry (ICP-AES). At this time, the pressed magnetic core is dissolved using, for example, hydrochloric acid, to prepare an analytical sample, and the binder content is calculated by estimating the intensity of the elements detected by ICP-AES.

[0058] The inductor element 100 having a pressed powder core 110 containing the aforementioned binder 2 and magnetic particles 4 exhibits excellent heat resistance. Specifically, the volume resistivity of the pressed powder core 110 after storing the inductor element 100 at 175°C for 100 hours is set as R. A The volume resistivity of the pressure powder core 110 before storage is set to R. B Preferred to satisfy R A / R B >0.001, more preferably satisfying R A / R B ≥0.01. This R A / R BR represents the rate of change of volume resistivity after storage. A / R B The larger the value and the closer it is to 1.0, the less the volume resistivity changes and the better the heat resistance of the inductor element.

[0059] In addition, the volume resistivity R before storage B Preferably 1×10 12 The volume resistivity R after storage is above Ω·cm. A Preferably 1×10 9 Above Ω·cm. Alternatively, volume resistivity can be measured using a high resistance meter (such as HP's 4339B).

[0060] In the inductor element 100 of this embodiment, epoxy resin having two or more mesocrystalline frameworks between epoxy bonds is contained in the powder core, thereby achieving the aforementioned heat resistance. As a result, energy loss can be reduced in the inductor element 100, and miniaturization or high current capacity of the inductor can be well achieved.

[0061] Next, for Figure 1 An example of the manufacturing method of the inductor element 100 shown will be described.

[0062] First, prepare the raw materials for the adhesive 2, namely the resin material and the raw material powder for the magnetic particles 4. The raw material powder for the magnetic particles 4 can be produced by known powder manufacturing methods. Examples of powder manufacturing methods include gas atomization, water atomization, rotary disc method, and carbonyl method. Alternatively, the raw material powder can be produced by mechanically pulverizing a thin strip obtained by a single-roller method. Furthermore, after obtaining the raw material powder for the magnetic particles 4 by the above methods, the particle size of the magnetic particles 4 can be controlled by performing sieving or air classification. In addition, if an insulating coating is formed on the surface of the magnetic particles 4, the raw material powder obtained above can be subjected to surface treatments such as heat treatment, phosphate treatment, mechanical alloying treatment, silane coupling treatment, or hydrothermal synthesis.

[0063] As the resin raw material for adhesive 2, an epoxy resin composed of a prepolymer before curing is prepared. The epoxy resin has at least two mesocrystalline skeletons between two epoxy groups located at the ends of the prepolymer.

[0064] Furthermore, a coating is prepared by dissolving the aforementioned epoxy resin and curing agent in a solvent. In this case, a phenolic resin with a molecular weight of approximately 500 to 10,000 is preferably used; for example, a biphenyl aryl type curing agent or a p-xylene type curing agent is preferred. There are no particular limitations on the solvent; acetone, isopropanol (IPA), methyl ethyl ketone (MEK), butyl diethylene glycol acetate (BCA), methanol, etc., can be used. Moreover, curing accelerators (curing catalysts), lubricants, softeners, plasticizers, dispersants, colorants, anti-settling agents, etc., can be appropriately added to the above-mentioned coating. Furthermore, the amount of curing agent added can be appropriately determined based on the amount of epoxy resin added.

[0065] Next, the raw material powder of magnetic particles 4 and the coating containing epoxy resin are fed into various mixing machines such as a kneader or a twin-screw extruder and mixed to produce a precursor for pressed magnetic cores. At this time, it is preferable to combine the raw material powder and coating with a binder 2 in a ratio of 1 to 4 parts by weight per 100 parts by weight of magnetic particles. Furthermore, in this mixing process, non-magnetic ceramic particles may be added appropriately depending on the application of the inductor element.

[0066] Next, the aforementioned precursor is used to manufacture the powder-pressed magnetic core. Figure 1 In the case of the inductor element 100 shown, the precursor and the hollow coil, which serves as an insert component, are filled into a mold and compressed. This yields a molded body having the shape of the powder-coated magnetic core to be manufactured. The epoxy resin in the molded body is then cured by appropriately subjecting it to heat treatment. There are no particular restrictions on the heat treatment conditions, as long as the epoxy resin is sufficiently cured. For example, the heat treatment temperature can be set to 150°C to 200°C, and the treatment time to 1 hour to 5 hours. There are no particular restrictions on the atmosphere during heat treatment; an atmospheric atmosphere can also be used.

[0067] Through the above process, an inductor element 100 with a coil 120 embedded inside the pressed powder magnetic core 110 can be obtained.

[0068] (Summary of this implementation method)

[0069] The pressed powder magnetic core 110 of this embodiment has a binder 2 containing epoxy resin and phenolic resin and magnetic particles 4 dispersed in the binder 2. Moreover, the epoxy resin contained in the binder 2 has at least two or more mesocrystalline frameworks between two epoxy bonds close to each other along the molecular chain.

[0070] The inventors conducted in-depth research and found that the number of mesocrystalline skeletons between epoxy bonds affects poor adhesion during thermoforming. Specifically, according to their experiments, when using epoxy resins without mesocrystalline skeletons or epoxy resins with only one mesocrystalline skeleton between epoxy bonds, the molded part tends to adhere to the mold during thermoforming, easily leading to poor molding. Therefore, in these conventional epoxy resins, it is necessary to use lubricants that may reduce strength, or to manufacture by cold forming instead of thermoforming. On the other hand, when using epoxy resins with at least two or more mesocrystalline skeletons between epoxy bonds, poor adhesion during thermoforming can be prevented. As a result, the pressed powder magnetic core 110 of this embodiment exhibits higher strength, relative permeability, and heat resistance than when using conventional epoxy resins.

[0071] The reason for the above effect may not be clear, but it can be thought to be related to the three-dimensional barrier formed by multiple mesocrystalline frameworks.

[0072] In the inductor element 100 with the pressed powder core 110, the volume resistivity after being stored at 175°C for 100 hours is set as R. A The volume resistivity before storage is set as R. B When R is satisfied A / R B >0.001. As a result, in the inductor element 100 of this embodiment, energy loss can be reduced, and the miniaturization or high current of the inductor can be well realized.

[0073] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention.

[0074] For example, electronic components such as inductors can also be constructed by combining multiple pressed powder cores. Furthermore, the shape of the pressed powder core is not particularly limited, and it can be, for example, toroidal, FT, ET, EI, UU, EE, EER, UI, drum-shaped, pot-shaped, or cup-shaped. Moreover, in the above embodiments, a coil is embedded in the pressed powder core, but the arrangement of the coil is not limited to... Figure 1 The structure shown can also be used to form a coil by winding a wire around the outside of the powder core.

[0075] The manufacturing method of pressed powder magnetic cores is not limited to the above-described embodiments. Pressed powder magnetic cores can be manufactured by sheet molding or injection molding, or by two-stage compression. In the manufacturing method based on two-stage compression, for example, after pre-compressing the precursor to produce multiple pre-formed bodies, these pre-formed bodies are combined with the air-core coil for formal compression.

[0076] Furthermore, while the inductor element 100 has been described in the above embodiments, the pressed powder magnetic core of the present invention can also be applied to various electronic components such as reactors, transformers, contactless power supply devices, and magnetic shielding parts.

[0077] [Example]

[0078] The present invention will now be described in further detail based on specific embodiments. However, the present invention is not limited to the following embodiments.

[0079] Examples 1-16

[0080] In this embodiment, the inductor samples of Examples 1 to 16 are manufactured by the steps shown below.

[0081] First, Fe-4.5Si alloy powder, which serves as the raw material powder for magnetic particles 4, is prepared by gas atomization. A SiO2 film with an average thickness of approximately 100 nm is then formed on the surface of this raw material powder through heat treatment.

[0082] Next, a biphenyl-type epoxy resin composed of a prepolymer is prepared. This epoxy resin has a plurality of mesocrystalline skeletons as shown in Formula (I) between the epoxy groups located at the ends of the prepolymer. Specifically, the number of mesocrystalline skeletons present between the epoxy groups is 2 in Examples 1-3, 3 in Examples 4-7 and 14, 10 in Examples 8-10 and 15, and 20 in Examples 11-13 and 16.

[0083] The coating was obtained by dissolving the epoxy resin and curing agent in acetone solvent. In Examples 1-13, a biphenyl aryl type curing agent A was used, and in Examples 14-16, a p-xylene type curing agent B was used. Furthermore, in all examples, the amount of curing agent added was 50 parts by weight relative to 100 parts by weight of the epoxy resin, and 1 part by weight of a curing accelerator was added relative to 100 parts by weight of the epoxy resin.

[0084] Next, the above-mentioned coating and Fe-4.5Si alloy powder are kneaded using a kneader to obtain the precursors for pressed magnetic cores of Examples 1 to 16. At this time, the mixing ratio of the coating and alloy powder is adjusted such that the content of binder 2 relative to 100 parts by weight of magnetic particles is in the range of 1 to 5 parts by weight.

[0085] Next, the aforementioned precursor was placed into a mold for compression molding, thereby obtaining a molded body in the shape of a magnet. Compression molding was performed using both cold forming and thermoforming, resulting in samples manufactured by cold forming and samples manufactured by thermoforming for each embodiment. Cold forming was performed at a molding pressure of 8.0 MPa, and thermoforming was performed at a molding pressure of 4.0 MPa and a mold temperature of 110°C. After compression molding, the molded body was heated at 180°C for 3 hours to cure the epoxy resin, obtaining the pressed powder magnetic core samples of Examples 1-16. Furthermore, the fabricated magnetic mold had an outer diameter of 17.5 mm and an inner diameter of 10.0 mm, and the pressed powder magnetic core sample was made by weighing 5.0 g. The thickness (height) of the fabricated pressed powder magnetic core sample was approximately 5 mm.

[0086] The following evaluation was performed on the powder-pressed magnetic core samples of each embodiment.

[0087] (Measurement of the number of mesocrystalline frameworks)

[0088] Analytical samples for molecular structure analysis were collected from the fabricated pressed powder magnetic core samples. Then, the molecular structure of binder 2 was analyzed by performing NMR, FT-IR, GC / MS, and LC / MS to determine the number of mesocrystalline frameworks existing between two adjacent epoxy bonds.

[0089] (Analysis of pressed powder magnetic cores)

[0090] Furthermore, the pressed powder magnetic core samples were analyzed by ICP-AES to determine the amount of binder contained in the pressed powder magnetic core. Moreover, based on the strength of the measured elements, the content of binder 2 relative to 100 parts by mass of magnetic particles was calculated. As a result, in all embodiments, it was confirmed that the content of binder 2 was the target value during manufacturing, consistent with the formulation ratio of epoxy resin in the precursor.

[0091] Furthermore, the average particle size (D50) and average sphericity of the magnetic particles 4 were measured when the cross-section was observed using SEM. The results showed that in all embodiments, the average particle size was in the range of 20–40 μm, and the average sphericity was above 0.95.

[0092] (Ring strength test)

[0093] The strength of the pressed powder core was evaluated by performing a ring strength test based on JIS.Z2507 and calculating the ring strength. A ring strength of 120 MPa or higher was considered to indicate good strength characteristics in the sample.

[0094] (Determination of relative permeability)

[0095] In addition, 30 turns of wire are wound around the manufactured toroidal molded powder magnetic core sample to fabricate an inductor element, and its relative magnetic permeability is measured. The relative magnetic permeability is measured as follows. Using an LCR meter and a DC bias power supply, the inductance at a measurement frequency of 100 kHz and a DC superposed magnetic field of 50 mT is measured, and the relative magnetic permeability at room temperature is calculated from this inductance. Regarding the relative magnetic permeability, a value of 25 or more is judged as qualified, 26 or more as good, and 28 or more as particularly good.

[0096] (Heat resistance evaluation)

[0097] In the heat resistance test, the inductor element is maintained at 175 °C for 100 hours, and the change rate of the volume resistance before and after the test is measured. Specifically, the volume resistance after storage at 175 °C for 100 hours is designated as R A , and the volume resistance before storage is designated as R B , and R A / R B is calculated for each embodiment. A / R B The higher the value of R A / R B , the better the heat resistance. In this embodiment, a value of R A / R B > 0.001 is judged as qualified, and a value of R A / R B ≥ 0.01 is judged as particularly good. In addition, the volume resistance is measured using a high resistance tester (4339B of HP Inc.) with a Φ1.0 mm probe aligned parallel to the thickness direction.

[0098] Comparative Examples 1-3

[0099] In Comparative Example 1, a cresol novolac type epoxy resin without a mesogenic skeleton is used to fabricate a molded powder magnetic core sample. In addition, in Comparative Example 2 and Comparative Example 3, a biphenyl type epoxy resin having only one mesogenic skeleton between adjacent epoxy bonds is used to fabricate a molded powder magnetic core sample. Further, in Comparative Example 2, a biphenyl aralkyl type curing agent A is used, and in Comparative Example 3, a p-xylene type curing agent B is used. Thus, the type of epoxy resin used is changed in Comparative Examples 1 to 3, but the experimental conditions other than the type of epoxy resin are the same as those in the above embodiments, and the same evaluations as those in each embodiment are performed.

[0100] The evaluation results of each embodiment and each comparative example are shown in Table 1.

[0101] [Table 1]

[0102]

[0103] As shown in Table 1, in Comparative Example 1 (which lacks a mesocrystalline framework) and Comparative Examples 2 and 3 (which have only one mesocrystalline framework), the ring strength is less than 120 MPa, failing to meet the strength qualification standard. Furthermore, in Comparative Examples 1-3, R... A / R B If the value is below 0.001, it cannot meet the criteria for heat resistance. Furthermore, in Comparative Examples 1 to 3, defects occurred during thermoforming, such as adhesion to the mold, making it difficult to ensure the quality of qualified products. In other words, in Comparative Examples 1 to 3, the characteristics of thermoformed samples could not be evaluated, and only cold-forming-based methods could be applied.

[0104] On the other hand, in Examples 1 to 16, where the number of mesocrystalline frameworks existing between epoxy bonds is two or more, higher strength than Comparative Examples 1 to 3 can be obtained when manufactured by cold forming, and the criteria for heat resistance can be met. Based on this result, it can be seen that by setting the number of mesocrystalline frameworks existing between epoxy bonds to multiple rather than a single one, high strength, high relative permeability, and high heat resistance can be achieved simultaneously.

[0105] Furthermore, in Examples 1-16, adhesion defects during thermoforming can be suppressed, and powder cores with higher strength and relative permeability than those obtained by cold forming can be obtained through thermoforming. Based on these results, it is evident that by setting the number of mesocrystalline frameworks existing between epoxy bonds to multiple rather than a single one, forming defects can be significantly suppressed, and improvements in various properties (strength, relative permeability, heat resistance) can be achieved more efficiently.

[0106] Furthermore, comparing the evaluation results of each embodiment, it can be confirmed that a lower binder content in the pressed magnetic core leads to a higher relative permeability, and a higher binder content leads to higher strength. It is also found that when the binder content is 1 to 4 parts by mass, both strength and magnetic properties can be improved in a balanced manner. Moreover, the results of Example 7 confirm that if the binder content is more than 4 parts by mass, there is a trend of decreasing permeability. Based on the above results, it is determined that the binder content relative to 100 parts by mass of the metallic magnetic particles is preferably in the range of 1 to 4 parts by mass.

Claims

1. A pressed powder magnetic core, characterized in that, It contains an epoxy resin binder and magnetic particles dispersed in the binder. The epoxy resin has at least three mesocrystalline frameworks between two epoxy bonds that are close to each other along the molecular chain.

2. The pressed powder magnetic core as described in claim 1, characterized in that, The magnetic particles are metallic magnetic particles. The adhesive contains more than 1.0 parts by mass and less than 4.0 parts by mass relative to 100 parts by mass of the metallic magnetic particles.

3. The pressed powder magnetic core as described in claim 1 or 2, characterized in that, The mesocrystalline framework has a structure represented by the following formula (I). （I） In formula (I), Y is selected from -H, alkyl, acetyl and halogen, wherein the alkyl group is an aliphatic hydrocarbon with 4 or fewer carbon atoms, and the Y in the mesocrystalline framework is different or all the same, and * indicates the bonding site with the adjacent atom.

4. An inductor, characterized in that, It has the powder-pressed magnetic core as described in any one of claims 1 to 3.

5. The inductor as described in claim 4, characterized in that, The volume resistivity of the inductor after being stored at 175°C for 100 hours is set as R. A The volume resistivity before storage is set as R. B hour, Satisfy R A / R B >0.001.

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