Compression powder core and electronic component

Abstract

To provide a dust core having both high initial permeability and high rust resistance and an electronic component using the same.SOLUTION: The dust core includes soft magnetic particles, an epoxy resin, and an additive material. The epoxy resin has one mesogen backbone between two epoxy bonds close to each other along a molecular chain, and the additive material includes Zn.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a compressed powder magnetic core and an electronic component including the compressed powder magnetic core.

Background Art

[0002] Compressed powder magnetic cores used in magnetic application electronic components such as inductors and reactors are generally manufactured by kneading magnetic particles together with a binder (binding material) and compression molding. In this compressed powder magnetic core, it is known to use additives such as lubricants, antiseptics, and dispersants in order to improve characteristics such as moldability and corrosion resistance. For example, Patent Documents 1 and 2 disclose compressed powder magnetic cores to which metal soap powder is added as a lubricant.

[0003] However, additives such as those described above are non-magnetic materials. Therefore, although adding additives such as those described above to a compressed powder magnetic core can be expected to improve moldability and corrosion resistance, conversely, magnetic properties such as magnetic permeability may deteriorate. That is, the effect of improving moldability and corrosion resistance by the additive and the magnetic properties of the compressed powder magnetic core are in an inverse relationship, and in particular, it has been difficult to achieve both high magnetic permeability and high rust resistance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a compressed powder magnetic core having both high magnetic permeability and high rust resistance, and an electronic component using the compressed powder magnetic core.

Means for Solving the Problems

[0006] In order to achieve the above object, the compacted magnetic core according to the present invention comprises soft magnetic particles, an epoxy resin, and an additive, wherein the epoxy resin has one mesogenic skeleton between two epoxy bonds adjacent along the molecular chain, and the additive contains Zn.

[0007] As a result of intensive studies, the inventors have found a specific relationship between the number of mesogenic skeletons in the epoxy resin and the properties of the additive, and have thus completed the present invention.

[0008] Specifically, according to the experiments of the inventors, when a resin having 0 or 2 or more mesogenic skeletons between epoxy bonds is used as the binder, even if an additive containing Zn is added to the compacted magnetic core, effective improvement in rust resistance cannot be achieved. Also, in this case, even if the content rate of the additive is increased to improve the rust resistance, the magnetic permeability decreases, and it is impossible to achieve both high rust resistance and high magnetic permeability. On the other hand, when an epoxy resin having one mesogenic skeleton between epoxy bonds is used as the binder, high magnetic permeability and high rust resistance can be achieved simultaneously by adding an additive containing Zn to the compacted magnetic core.

[0009] Preferably, the weight ratio of Zn to the total weight of the soft magnetic particles, the epoxy resin, and the additive is 100 ppm or more and 600 ppm or less. By controlling the content rate of Zn in the compacted magnetic core within a predetermined range, it is possible to satisfy both higher magnetic permeability and higher rust resistance.

[0010] Preferably, the soft magnetic particles are metal particles mainly composed of Fe.

[0011] The compacted 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 shield parts, and in particular, it is preferably used as the magnetic core of an inductor.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.

[0014] As shown in FIG. 1, an inductor element 100 according to an embodiment of the present invention includes a compacted powder core 110 and a coil 120 embedded inside the compacted powder core 110.

[0015] The shape of the compacted powder core 110 is not particularly limited and can be, for example, a cylindrical shape, an elliptical columnar shape, a prismatic shape, or the like. And as shown in FIG. 2, the compacted powder core 110 includes a binder 2 as a binder material, magnetic particles 4 dispersed in the binder 2, and a predetermined additive 6 (not shown), and may also include non-magnetic inorganic particles and the like. That is, the compacted powder core 110 is formed into a predetermined shape by bonding a plurality of magnetic particles 4 via the binder 2. Hereinafter, the binder 2, the magnetic particles 4, and the additive 6 constituting the compacted powder core 110 will be described in detail.

[0016] The binder 2 mainly consists of a cured epoxy resin and a phenolic resin, and may also contain a small amount of organic components. Here, the "small amount of organic components" are components resulting from lubricants, curing accelerators, flexibilizers, plasticizers, dispersants, colorants, anti-settling agents, etc., and may be contained in an amount of about 1.0 part by mass or less with respect to 100 parts by mass of the epoxy resin which is the main component of the binder 2.

[0017] In this embodiment, the epoxy resin of the binder 2 is characterized by having a predetermined molecular structure. Specifically, the epoxy resin of the binder 2 has one mesogenic skeleton, rather than a plurality, between two adjacent epoxy bonds along the molecular chain.

[0018] Here, the "epoxy bond" in this embodiment means a molecular arrangement formed by the ring-opening of an epoxy group existing in a prepolymer through a polymerization reaction (curing reaction). Further, the "mesogenic skeleton" is a general term for an atomic group that includes polycyclic aromatic hydrocarbons or two or more aromatic rings and has rigidity and orientation.

[0019] More specifically, the mesogenic skeleton is preferably a partial structure represented by the following formula (J).

Chemical formula

Chemical formula

[0020] In particular, in this embodiment, it is more preferable that the mesogenic skeleton is a partial structure represented by the following formula (I).

Chemical formula

[0021] The mesogenic skeleton as described above is considered to enhance the lubricity between the magnetic particles 4 during the molding process and promote the rearrangement of the magnetic particles 4 efficiently. In addition, stacking (molecular overlap) is likely to be formed between the mesogenic skeletons after curing, and this stacking is considered to contribute to the improvement of the mechanical strength of the binder 2 and the powder core 110. Furthermore, the mesogenic skeleton is also considered to reduce the thermal resistance between the magnetic particles 4. Therefore, by forming the powder core 110 with an epoxy resin containing a mesogenic skeleton, improvements in density, strength, relative permeability, thermal conductivity, etc. can be expected. Note that in the above, "rearrangement of the magnetic particles 4" means that the particles move due to pressure and approach the closest packing state.

[0022] In the epoxy resin of the binder 2 in the present embodiment, the mesogenic skeleton as described above exists not in plural but in one between two epoxy bonds that are adjacent along the molecular chain.

[0023] Here, the "two adjacent epoxy bonds" will be described in more detail. A molecular structure having one mesogenic skeleton as described above can be realized, for example, by curing an epoxy resin having a prepolymer as shown in the following formula (K).

Chemical formula

[0024] Note that the number of mesogenic skeletons present between epoxy bonds can be determined by analyzing the molecular structure of Binder 2. For example, the molecular structure of Binder 2 may be analyzed by appropriately combining nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR), gas chromatography-mass spectrometry (GC / MS), liquid chromatography-mass spectrometry (LC / MS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), etc. Also, the sample for measurement may be prepared by collecting Binder 2 from the compacted magnetic core 110 shown in FIG. 1.

[0025] In this embodiment, the magnetic particles 4 may be oxide magnetic particles such as soft ferrite, but are preferably soft magnetic metal particles containing Fe as a main component. Here, "containing Fe as a main component" means that the content rate of Fe contained in the soft magnetic metal particles per unit mass is 60 wt% or more. Examples of such soft magnetic metal particles include pure iron, Fe-Si alloys (iron-silicon), Fe-Al alloys (iron-aluminum), permalloy alloys (Fe-Ni), sendust alloys (Fe-Si-Al), Fe-Si-Cr alloys (iron-silicon-chromium), Fe-Si-Al-Ni alloys, Fe-Ni-Si-Co alloys, Fe-based amorphous alloys, Fe-based nanocrystalline alloys, etc.

[0026] Note that it is preferable that the magnetic particles 4, which are soft magnetic metal particles, do not substantially contain Zn contained in the additive 6. "Do not substantially contain" means that the content rate of Zn contained per unit mass of the soft magnetic metal particles is less than 100 ppm.

[0027] Also, it is preferable to form an insulating coating on the surface of the soft magnetic metal particles as the magnetic particles 4. Examples of the insulating coating include a film formed by oxidation of the particle surface layer (oxide film), phosphate film, silicate film, glass coating, BN, SiO 2 , MgO, Al 2 O 3Examples include inorganic coatings containing such substances, or organic coatings. These insulating coatings can be formed by surface treatments such as heat treatment, phosphate treatment, mechanical alloying treatment, silane coupling treatment, and hydrothermal synthesis. By forming an insulating coating on the metal magnetic particles, the high-frequency loss of the compacted magnetic core 110 can be suppressed.

[0028] The average particle diameter (D50) of the magnetic particles 4 is not particularly limited, and for example, it can be 50 μm or less, and preferably in the range of 20 μm to 40 μm. The average particle diameter of the magnetic particles 4 may be measured by image analysis of the cross-section of the compacted magnetic core 110 as shown in FIG. 2. Specifically, the area of each particle included in the cross-section as shown in FIG. 2 is measured, and the equivalent circle diameter of each particle is calculated from the area value, whereby the particle size distribution of the magnetic particles 4 can be obtained. In this measurement, the dimensions of the measurement field of view may be appropriately adjusted according to the particle size of the observed magnetic particles 4, and it is preferable to perform the analysis in at least 5 fields of view or more to obtain the particle size distribution.

[0029] All of the magnetic particles 4 included in the compacted magnetic core 110 may be composed of the same material, or may be composed of a plurality of particle groups having different materials. Also, as shown in FIG. 2, the magnetic particles 4 may be composed of a plurality of particle groups having different particle sizes. For example, large particles 4a made of an Fe-Si alloy and small particles 4b made of pure iron having an average particle diameter smaller than that of the large particles 4a can be mixed to form the magnetic particles 4.

[0030] When the magnetic particles 4 are soft magnetic metal particles, the content of the binder 2 in the compacted magnetic core 110 is preferably 4.0 parts by mass or less, and more preferably 1.0 part by mass to 4.0 parts by mass with respect to 100 parts by mass of the magnetic particles.

[0031] The content of the binder can be estimated by analyzing the compacted magnetic core with an inductively coupled plasma atomic emission spectrometer (ICP-AES). At this time, the compacted magnetic core is melted with, for example, hydrochloric acid or the like to prepare an analysis sample, and the content of the binder is calculated by estimating the intensity of the elements detected by ICP-AES.

[0032] The additive 6 is an organometallic compound containing Zn. Here, examples of the organometallic compound include metal alkoxides, metal complexes, fatty acid salts, etc., and fatty acid salts are preferred. When the additive 6 is a fatty acid salt, examples of the fatty acid constituting the additive 6 include stearic acid, montanic acid, lauric acid, myristic acid, ricinoleic acid, behenic acid, palmitic acid, 12-hydroxystearic acid, etc., and more preferably stearic acid, montanic acid, and lauric acid.

[0033] The state of existence of the additive 6 in the compacted powder core 110 is not particularly limited, and the additive 6 may be dispersed in the binder 2 or may adhere to the surface of the magnetic particles. This additive 6 functions as a lubricant in the manufacturing process of the compacted powder core 110 and suppresses molding defects. Further, by including the additive 6 containing Zn in the compacted powder core 110, it is possible to improve the rust resistance while suppressing a decrease in magnetic permeability.

[0034] Also, by controlling the Zn content rate in the compacted powder core 110 within a predetermined range, higher magnetic permeability and higher corrosion resistance can be obtained. Specifically, the weight ratio R of Zn with respect to the total weight (100 wt%) of the binder 2 (epoxy resin), magnetic particles 4, and additive 6 Zn can be in the range of 10 ppm to 2500 ppm, and preferably 100 ppm or more and 600 ppm or less.

[0035] When the main components of the compacted powder core 110 are the above-described binder 2, magnetic particles 4, and additive 6 and no other elements such as non-magnetic ceramic particles are included, the above Zn weight ratio R Zn corresponds to the Zn content rate contained per unit mass of the compacted powder core 110. And this Zn weight ratio R Zn may be measured by inductively coupled plasma optical emission spectrometry (ICP) after dissolving the compacted powder core 110 with hydrochloric acid or the like to obtain a measurement sample.

[0036] Also, the above Zn weight ratio R Znis based on the mass of Zn contained in the dust core 110 due to the additive 6. In the present embodiment, components other than the additive 6 such as the magnetic particles 4 do not substantially contain Zn, and based on the amount of Zn detected from the measurement sample collected from the dust core 110, the weight ratio R Zn may be calculated. If the magnetic particles 4 contain Zn, the composition of the magnetic particles 4 collected from the dust core 110 is analyzed by ICP, fluorescence X-ray analysis (XRF), etc., and the mass of Zn detected due to the magnetic particles 4 is subtracted to calculate the weight ratio R Zn .

[0037] Further, the dust core 110 preferably does not substantially contain other organometallic compounds that do not contain Zn, and in particular, preferably does not substantially contain organometallic compounds having Li and Mg. More specifically, the content rate of Li contained per unit mass of the dust core 110 is preferably 10 ppm or less. Also, the content rate of Mg contained per unit mass of the dust core 110 is preferably 100 ppm or less. Furthermore, the total content rate of Li and Mg is preferably 100 ppm or less. By setting the content rates of these organometallic compounds within the above ranges, a decrease in magnetic permeability can be suppressed.

[0038] Next, an example of a method for manufacturing the inductor element 100 shown in FIG. 1 will be described.

[0039] First, prepare a resin material which is a raw material of the binder 2, a raw material powder of the magnetic particles 4, and an additive 6. The raw material powder of the magnetic particles 4 can be produced by a known powder manufacturing method. Examples of the powder manufacturing method include a gas atomization method, a water atomization method, a rotating disk method, a carbonyl method, etc. Alternatively, a raw material powder may be produced by mechanically pulverizing a ribbon obtained by a single roll method. After obtaining the raw material powder of the magnetic particles 4 by the above manufacturing method, the particle size of the magnetic particles 4 can be controlled by performing sieving classification, air classification, etc. When forming an insulating coating on the surface of the magnetic particles 4, the raw material powder obtained above may be subjected to surface treatment such as heat treatment, phosphate treatment, mechanical alloying treatment, silane coupling treatment, hydrothermal synthesis, etc.

[0040] As the resin raw material of the binder 2, an epoxy resin composed of a prepolymer before curing is prepared. This epoxy resin has one mesogenic skeleton between two epoxy groups located at the ends of the prepolymer.

[0041] Then, a paint is prepared by dissolving the above epoxy resin and a phenolic resin as a curing agent in a solvent. At this time, it is preferable to use a curing agent having a molecular weight of about 500 to 10,000. Also, the solvent is not particularly limited, and acetone, isopropyl alcohol (IPA), methyl ethyl ketone (MEK), butyl diglycol acetate (BCA), methanol, etc. can be used. Furthermore, a curing accelerator (curing catalyst), a flexibilizer, a plasticizer, a dispersant, a colorant, an anti-settling agent, etc. may be appropriately added to the above paint. The addition amount of the curing agent may be appropriately determined according to the blending amount of the epoxy resin.

[0042] As the additive 6, a powder of an organometallic compound containing Zn (for example, zinc stearate powder) is prepared. The average particle size (D50) of this organometallic compound powder is preferably about 2 μm to 15 μm, and preferably smaller than the average particle size of the raw material powder of the magnetic particles 4.

[0043] Next, the raw material powder of the magnetic particles 4, the paint containing the epoxy resin, and the additive 6 are put into various kneaders such as a kneader or a twin-screw extruder and kneaded to produce a precursor for the powder compact magnetic core. At this time, it is preferable to mix the raw material powder and the paint so that the binder 2 is 1 to 4 parts by mass with respect to 100 parts by mass of the magnetic particles. Further, the blending ratio of the additive 6 is controlled so that the weight ratio R of Zn in the powder compact magnetic core 110 Zn is within the above-described predetermined range. Note that the additive 6 may be added to and mixed with the raw material powder of the magnetic particles 4 before the kneading step. Also, in the kneading step, non-magnetic ceramic particles or the like may be appropriately added according to the use of the inductor element.

[0044] Next, a powder compact magnetic core is manufactured using the above precursor. In the case of the inductor element 100 shown in FIG. 1, the precursor is filled into a mold together with an air-core coil as an insert member and compression-molded. Thereby, a molded body having the shape of the powder compact magnetic core to be produced is obtained, and the epoxy resin in the molded body is cured by appropriately performing heat treatment on this molded body. The heat treatment conditions at this time are not particularly limited, and may be conditions under which the epoxy resin is sufficiently cured. For example, the heat treatment temperature is set to 150°C to 200°C, and the treatment time is set to 1 hour to 5 hours. The atmosphere during the heat treatment is not particularly limited, and an air atmosphere may be used.

[0045] Through the above steps, an inductor element 100 in which the coil 120 is embedded inside the powder compact magnetic core 110 is obtained.

[0046] (Summary of this embodiment) The powder compact magnetic core 110 of this embodiment has a binder 2 containing an epoxy resin and a phenol resin, magnetic particles 4 dispersed in the binder 2, and an additive 6. In the epoxy resin contained in the binder 2, the number of mesogenic skeletons present between two epoxy bonds adjacent along the molecular chain is one. Further, the additive 6 contains Zn (zinc).

[0047] As a result of intensive studies, the present inventors have found that there is a specific relationship between the number of mesogenic skeletons in an epoxy resin and the properties of an additive. Specifically, according to the experiments of the present inventors, when a resin having 0 or 2 or more mesogenic skeletons between epoxy bonds is used as a binder, even if an additive 6 containing Zn is added to the compacted powder magnetic core, effective improvement in rust resistance cannot be achieved. Also, in this case, even if the content rate of the additive 6 is increased to improve rust resistance, the magnetic permeability decreases, and it is impossible to achieve both high rust resistance and high magnetic permeability. On the other hand, when an epoxy resin having 1 mesogenic skeleton between epoxy bonds is used as the binder 2, by adding the additive 6 containing Zn to the compacted powder magnetic core 110, it is possible to achieve both high magnetic permeability and high rust resistance.

[0048] Further, in the compacted powder magnetic core 110 of the present embodiment, the weight ratio R of Zn to the total weight of the epoxy resin (binder 2), magnetic particles 4, and additive 6 Zn is controlled to be 100 ppm or more and 600 ppm or less, whereby higher magnetic permeability and higher rust resistance can be obtained.

[0049] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0050] For example, electronic components such as inductor elements may be configured by combining a plurality of compacted powder magnetic cores. Also, the shape of the compacted powder magnetic core is not particularly limited, and for example, it may have a toroidal shape, FT shape, ET shape, EI shape, UU shape, EE shape, EER shape, UI shape, drum shape, pot shape, or cup shape. Further, in the above embodiment, a coil is embedded in the compacted powder magnetic core, but the arrangement of the coil is not limited to the configuration shown in FIG. 1, and a coil may be formed by winding a conducting wire around the outside of the compacted powder magnetic core.

[0051] The method for manufacturing the compressed powder core is not limited to the above-described embodiments, and the compressed powder core may be manufactured by a sheet method or injection molding, or may be manufactured by two-stage compression. In the manufacturing method by two-stage compression, for example, after preliminarily compressing a precursor to produce a plurality of preformed bodies, these preformed bodies and an air-core coil are combined and subjected to main compression.

[0052] Also, in the above embodiment, the inductor element 100 has been described. However, the compressed powder core of the present invention is also applicable to electronic components such as reactors, transformers, non-contact power feeding devices, and magnetic shield parts.

Example

[0053] Hereinafter, the present invention will be described in more detail based on specific examples. However, the present invention is not limited to the following examples.

[0054] (Experiment 1) In Experiment 1, in order to evaluate the relationship between the binder and the metal elements in the additive, compressed powder core samples according to Examples 1 to 3 and Comparative Examples 1 to 15 were produced.

[0055] Example 1 First, as the raw material powder of the magnetic particles 4, an Fe-Si alloy powder with an average particle diameter of 25 μm was produced by a gas atomization method. On the surface of this raw material powder, an SiO film with an average thickness of about 100 nm was formed by heat treatment. 2 film was formed.

[0056] Next, a biphenyl-type epoxy resin made of a prepolymer was prepared. The epoxy resin had one mesogenic skeleton shown in formula (I) between the epoxy groups located at the ends of the prepolymer. Then, a paint was obtained by dissolving the epoxy resin and the curing agent in an acetone solvent. At this time, the addition amount of the curing agent was 50 parts by mass with respect to 100 parts by mass of the epoxy resin, and in addition, 1 part by mass of a curing accelerator was added with respect to 100 parts by mass of the epoxy resin.

[0057] Next, the above paint and Fe—Si alloy powder were kneaded with a kneader to obtain a precursor for a compressed powder core according to Example 1. At this time, zinc stearate containing Zn was added as Additive 6. Further, the mixing ratio of the paint and the alloy powder was adjusted so that the content of Binder 2 with respect to 100 parts by mass of the magnetic particles became 3 parts by mass.

[0058] Next, the above precursor was put into a mold and pressed at a molding pressure of 8 MPa to obtain a toroidal shaped molded body. Further, after compression molding, the molded body was heated at 180° C. for 3 hours to cure the epoxy resin in the molded body, thereby obtaining a compressed powder core sample according to Example 1. Incidentally, all of the produced toroidal shaped compressed powder core samples had an outer diameter of 17.5 mm, an inner diameter of 10 mm, and a thickness (height) of around 5 mm.

[0059] Example 2 In Example 2, zinc laurate was used as Additive 6. A compressed powder core sample according to Example 2 was produced with the experimental conditions other than the type of the additive being the same as those in Example 1.

[0060] Example 3 In Example 3, zinc montanate was used as Additive 6. A compressed powder core sample according to Example 3 was produced with the experimental conditions other than the type of the additive being the same as those in Example 1.

[0061] Comparative Examples 1 and 2 In Comparative Examples 1 and 2, a polyimide resin having no mesogenic skeleton was used as the binder. Moreover, in Comparative Example 1, a compressed powder core sample was produced without adding an additive, and in Comparative Example 2, a compressed powder core sample was produced by adding zinc stearate. The experimental conditions other than the above in Comparative Examples 1 and 2 were the same as those in Example 1.

[0062] Comparative Examples 3 and 4 In Comparative Examples 3 and 4, a cresol novolak type epoxy resin with 0 mesogenic skeletons between epoxy bonds was used as the binder. Moreover, in Comparative Example 3, a dust core sample was manufactured without adding additives, and in Comparative Example 4, zinc stearate was added to manufacture a dust core sample. The experimental conditions other than the above in Comparative Example 4 were the same as those in Example 1.

[0063] Comparative Examples 5 to 10 In Comparative Examples 5 to 10, a biphenyl type epoxy resin with 2 or more mesogenic skeletons between epoxy bonds was used as the binder. Moreover, in Comparative Example 5, a dust core sample was manufactured without adding additives, and in Comparative Examples 6 to 10, zinc stearate was added to manufacture a dust core sample, respectively. The experimental conditions other than the above in Comparative Examples 5 to 10 were the same as those in Example 1.

[0064] Comparative Examples 11 to 15 In Comparative Examples 11 to 15, a biphenyl type epoxy resin with 1 mesogenic skeleton between epoxy bonds was used in the same manner as in Example 1. However, in Comparative Example 11, a dust core sample was manufactured without using Additive 6. Also, in Comparative Examples 12 to 15, dust core samples were manufactured using additives containing metal elements other than Zn. Specifically, Comparative Example 12: lithium stearate, Comparative Example 13; barium stearate, Comparative Example 14: magnesium stearate, Comparative Example 15: calcium stearate. The experimental conditions other than the above in Comparative Examples 11 to 15 were the same as those in Example 1.

[0065] For each example and each comparative example in Experiment 1, the following evaluations were carried out.

[0066] (Measurement of the number of mesogenic skeletons) An analysis sample for molecular structure analysis was collected from the manufactured dust core sample. Then, by performing NMR, FT-IR, GC / MS, and LC / MS, the molecular structure of the binder was analyzed, and the number of mesogenic skeletons existing between two adjacent epoxy bonds was specified.

[0067] (Measurement of the weight ratio R of the metal element M M ) Regarding the metal element contained in the additive used in each example and each comparative example as M, the content rate of the metal element M contained per unit mass of the powder compact core was measured by ICP. The content rate of the metal element M measured here is the weight ratio R of the metal element M contained in 100% of the total weight of the magnetic particles, the binder, and the additive M .

[0068] (Measurement of permeability Regarding the powder compact core samples of each example and each comparative example, the initial permeability μi was measured. The initial permeability μi was measured by an LCR meter (LCR428A manufactured by HP) after winding 30 turns of wire around a toroidal powder compact core

[0069] (Evaluation of rust resistance To evaluate the rust resistance of the powder compact core samples, a salt spray test was conducted. The salt spray test was carried out in a salt spray tester with dimensions of W900mm, D600mm, and H350mm. The salt spray amount was 1.5 ± 0.5 mL / h at 80 cm 2 . Under these conditions, a salt spray test was conducted at 35°C for 24 hours. After the salt spray, 10 measurement sites of 3 mm × 3 mm were randomly set. Each measurement site was photographed by a camera attached to an optical microscope (magnification 50 times), and the rust area ratio of each measurement site was calculated. Then, the average rust area ratio of the 10 measurement sites was calculated. It is judged that the lower the rust area ratio, the better the rust resistance of the powder compact core sample

[0070] In this example, when the initial permeability μi is less than 27 and the rust area ratio is 20% or more, it was judged as "Failed: F". Also, when the initial permeability μi is 27 or more and the rust area ratio is less than 20%, it was judged as "Good: G", and when the initial permeability μi is 28.5 or more and the rust area ratio is less than 12.5%, it was judged as "Very Good: VG". The evaluation results of each example and each comparative example are shown in Table 1

[0071]

Table 1

[0072] As shown in Table 1, in Comparative Examples 1 to 10 using a binder having 0 or 2 or more mesogenic skeletons, even when an additive containing Zn was added, the rust resistance was not sufficiently improved. Also, in some comparative examples such as Comparative Example 6 and Comparative Example 10, although an effect of improving the rust resistance was observed, the initial magnetic permeability μi decreased with the improvement of the rust resistance, and it was not possible to achieve both high rust resistance and high magnetic permeability.

[0073] In Comparative Examples 11 to 15 using a binder having 1 mesogenic skeleton, additives containing Li, Ba, Mg, or Ca were used, but in these comparative examples as well, it was not possible to achieve both high rust resistance and high magnetic permeability. On the other hand, in Examples 1 to 3 using a binder having 1 mesogenic skeleton and an additive containing Zn, it was possible to reduce the rust area ratio without decreasing the initial magnetic permeability μi. From these results, it was demonstrated that when an epoxy resin having 1 mesogenic skeleton between epoxy bonds is used as a binder, by adding an additive containing Zn to the powder core, it is possible to achieve both high rust resistance and high magnetic permeability.

[0074] Also, from the results of Examples 2 and 3, it was confirmed that even when the type of fatty acid was changed, it was possible to achieve both high rust resistance and high magnetic permeability.

[0075] (Experiment 2) In Experiment 2, the influence of the metal element content rate derived from the additive in the powder core was evaluated.

[0076] Examples 1-1 to 1-8 Weight ratio R of Zn Zn To evaluate the influence of, the addition amount of zinc stearate was changed to prepare 8 powder core samples (Examples 1-1 to 1-8) related to Example 1. The experimental conditions other than the above were the same as those of Example 1 in Experiment 1. The evaluation results are shown in Table 2.

[0077] Comparative Examples 2-1 to Comparative Example 2-5 Regarding Comparative Example 2 using a polyimide resin, the amount of zinc stearate added was also changed to prepare five kinds of compacted powder core samples (Comparative Examples 2-1 to 2-5) related to Comparative Example 2. The experimental conditions other than the above were the same as those of Comparative Example 2 in Experiment 1. The evaluation results are shown in Table 3.

[0078] Comparative Examples 4-1 to Comparative Example 4-5 Regarding Comparative Example 4 using a cresol novolak type epoxy resin with a mesogen skeleton number of 0, the amount of zinc stearate added was also changed to prepare five kinds of compacted powder core samples (Comparative Examples 4-1 to 4-5) related to Comparative Example 4. The experimental conditions other than the above were the same as those of Comparative Example 4 in Experiment 1. The evaluation results are shown in Table 4.

[0079] Comparative Examples 6-1 to Comparative Example 6-5 Regarding Comparative Example 6 using a biphenyl type epoxy resin with a mesogen skeleton number of 3, the amount of zinc stearate added was also changed to prepare five kinds of compacted powder core samples (Comparative Examples 6-1 to 6-5) related to Comparative Example 6. The experimental conditions other than the above were the same as those of Comparative Example 6 in Experiment 1. The evaluation results are shown in Table 5.

[0080] Comparative Examples 14-1 to Comparative Example 14-5 Regarding Comparative Example 14 using a biphenyl type epoxy resin with a mesogen skeleton number of 1, the amount of magnesium stearate added was also changed to prepare five kinds of compacted powder core samples (Comparative Examples 14-1 to 14-5) related to Comparative Example 14. The experimental conditions other than the above were the same as those of Comparative Example 14 in Experiment 1. The evaluation results are shown in Table 6.

[0081]

Table 2

[0082]

Table 3

[0083]

Table 4

[0084]

Table 5

[0085]

Table 6

[0086] The evaluation results shown in Tables 2 to 6 were summarized in the graph of FIG. 3. In the graph of FIG. 3, the measurement results of Tables 2 to 6 were plotted with the initial permeability μi on the horizontal axis and the rust area ratio on the vertical axis. In the graph of FIG. 3, the closer the plot is to the lower right side of the graph, the higher the permeability and the better the rust resistance. The range surrounded by the broken line is good, and the range surrounded by the alternate long and short dash line is particularly good.

[0087] As shown in Tables 2 to 6 and FIG. 3, in Comparative Examples 2 and 4 using a binder with 0 mesogen skeletons, even when the addition amount of zinc stearate was increased, sufficient improvement in rust resistance could not be achieved, and the permeability also decreased. In Comparative Example 6 using a binder having a plurality of mesogen skeletons, although the rust resistance was improved to some extent by increasing the addition amount of zinc stearate, the permeability decreased. From this result, it was found that when using a binder with 0 or 2 or more mesogen skeletons, it is difficult to achieve both high rust resistance and high permeability even when adding an organometallic compound containing Zn such as zinc stearate.

[0088] Further, in Comparative Example 14 using a binder with 1 mesogen skeleton, even when the addition amount of magnesium stearate was increased, not much improvement in rust resistance could be achieved, and the permeability decreased as the amount of magnesium stearate increased. From this result, it was found that when using an epoxy resin with 1 mesogen skeleton, the Mg content per unit mass of the compacted magnetic core is preferably 100 ppm or less.

[0089] On the other hand, in Example 1 where an epoxy resin having one mesogen skeleton was used, as shown in Table 2 and FIG. 3, by adjusting the weight ratio R Zn of Zn contained in the compacted magnetic core, higher rust resistance and higher magnetic permeability were obtained. More specifically, it was found that the weight ratio R Zn of Zn contained in the compacted magnetic core is preferably 100 ppm to 600 ppm (more preferably 510 ppm or less).

Description of Reference Numerals

[0090] 100... Inductor element 110... Compacted magnetic core 2... Binder 4... Magnetic particles 4a... Large particles 4b... Small particles 120... Coil

Claims

1. A dust core comprising soft magnetic particles, an epoxy resin, and an additive, wherein the epoxy resin has one mesogenic skeleton between two epoxy bonds adjacent to each other along the molecular chain, the additive contains Zn, and the weight ratio of Zn to the total weight of the soft magnetic particles, the epoxy resin, and the additive is 102 ppm or more and 510 ppm or less.

2. The dust core according to claim 1, wherein the soft magnetic particles are metal particles mainly composed of Fe.

3. An electronic component comprising the dust core according to claim 1 or 2.

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