Dust core and method for producing same

Abstract

This dust core comprises: a compression-molded body containing soft magnetic powder; and a resin part which has impregnated the compression-molded body. The resin part is a cured product of an impregnation liquid which is a curable resin composition. The ratio of the open porosity of the dust core to the total porosity of the dust core is 53% or less. The contact angle of the compression-molded body to the impregnation liquid may be 70° or less.

Description

Powder magnetic core and manufacturing method thereof

[0001] The present disclosure relates to a powder magnetic core and a method for manufacturing the same.

[0002] As the magnetic core of an electromagnetic component, a powder magnetic core formed by compression molding of soft magnetic powder is sometimes used (for example, Patent Documents 1 to 3).

[0003] Japanese Patent Application Publication No. 2021-36600 Japanese Patent Application Publication No. 4044591 Japanese Patent Application Publication No. 2022-94461

[0004] One aspect of the present disclosure relates to further improving the mechanical strength of a powder magnetic core.

[0005] The present disclosure includes the following. [1] A powder magnetic core comprising: a compression-molded body containing soft magnetic powder; and a resin portion impregnated in the compression-molded body, wherein the resin portion is a cured product of an impregnation liquid that is a curable resin composition, and wherein a ratio of open porosity of the powder magnetic core to the total porosity of the powder magnetic core is 53% or less. [2] The powder magnetic core according to [1], wherein a contact angle of the compression-molded body with the impregnation liquid is 70° or less. [3] A powder magnetic core according to [1], wherein a ratio of open porosity of the powder magnetic core to the total porosity of the powder magnetic core is X １ [%], and the ratio of the open porosity of the compression molded body to the total porosity of the compression molded body is X ０ When [%], X １ / X ０[4] The powder magnetic core according to any one of [1] to [3], wherein the soft magnetic powder is a powder containing soft magnetic particles having base particles containing a metal and an insulating coating covering the surfaces of the base particles. [5] The powder magnetic core according to any one of [1] to [4], wherein the curable resin composition contains an epoxy resin. [6] The powder magnetic core according to any one of [1] to [4], wherein the curable resin composition contains a compound having a (meth)acryloyl group. [7] A method for producing a powder magnetic core, comprising: filling a molding die with a molding material containing soft magnetic powder, forming a compression-molded body by compression molding in the molding die, impregnating the compression-molded body with an impregnating liquid that is a curable resin composition, and curing the impregnating liquid to form a powder magnetic core including the compression-molded body and a resin portion that is the cured product of the impregnating liquid, wherein a ratio of the open porosity of the powder magnetic core to the total porosity of the powder magnetic core is 53% or less. [8] The method according to [7], wherein a contact angle of the compression-molded body with the impregnating liquid is 70° or less. [9] The method according to [7] or [8], wherein impregnating the compression-molded body with the impregnating liquid comprises immersing the compression-molded body in the impregnating liquid.

[10] The method according to [7] or [8], wherein impregnating the compression-molded body with the impregnation liquid comprises immersing the compression-molded body in the impregnation liquid under a reduced pressure atmosphere, and then placing the compression-molded body, while still immersed in the impregnation liquid, under atmospheric pressure or a pressurized atmosphere for 1 minute or more.

[11] The method according to any one of [7] to

[10] , wherein the molding material further comprises a lubricant, and the method further comprises heating the compression-molded body to thereby remove the lubricant before impregnating the compression-molded body with the impregnation liquid.

[12] The method according to any one of [7] to

[11] , further comprising forming a film of lubricant on the inner surface of the molding die before filling the molding material into the molding die, and heating the compression-molded body removed from the molding die to thereby remove the lubricant adhering to the compression-molded body.

[0006] The mechanical strength of the powder magnetic core can be further improved. The powder magnetic core according to the present disclosure also has good magnetic properties.

[0007] 1 is an example of a scanning electron microscope photograph of a cross section of a powder magnetic core.

[0008] The present invention is not limited to the following examples.

[0009] An example of a powder magnetic core is primarily composed of a compression-molded body containing soft magnetic powder and a resin portion impregnated into the compression-molded body. The compression-molded body is an aggregate of particles formed by compression molding of a molding material containing soft magnetic powder, and includes openings or voids formed between the particles. The resin portion is filled into these openings or voids.

[0010] The soft magnetic powder is composed of soft magnetic particles containing a metal. The soft magnetic particles may contain metal particles, and the metal particles may be amorphous. The metal constituting the soft magnetic particles may be, for example, pure iron or an alloy containing iron. Examples of alloys containing iron include an Fe—Cr alloy (stainless steel), an Fe—Ni—Cr alloy (stainless steel), an Fe—Si alloy, an Fe—Si—Al alloy (sendust), an Fe—Ni alloy (permalloy), an Fe—Cu—Ni alloy (permalloy), an Fe—Co alloy, an Fe—Co—V alloy (permendur), an Fe—Cr—Si alloy (electromagnetic stainless steel), and an Fe—Ni—Mn—C alloy (invar). The metal particles constituting the soft magnetic particles may be particles containing an Fe amorphous alloy or an alloy with a nanocrystalline structure.

[0011] The average particle size of the soft magnetic particles or metal particles may be, for example, 30 μm or more and 350 μm or less. The median diameter (D50) of the soft magnetic powder or metal particles may be, for example, 60 μm or more and 150 μm or less. The average particle size or median diameter (D50) here may be a value determined by sieving or laser diffraction particle size distribution measurement. The median diameter may be a value determined from a volume-based or number-based particle size distribution.

[0012] The shapes of the soft magnetic particles and metal particles are not particularly limited, and may be, for example, amorphous, spherical, flat, or acicular.

[0013] The soft magnetic particles may have, for example, a base particle containing a metal and an insulating coating covering the surface of the base particle. The base particle may be the above-mentioned metal particle.

[0014] The insulating coating constituting the soft magnetic particles can be a film containing an insulating inorganic material, an insulating organic material, or a combination thereof. The insulating coating may be composed of multiple layers. For example, the insulating coating may contain one or more insulating materials selected from phosphoric acid, silicone, and silicate glass. The insulating coating may include multiple layers each containing an insulating material selected from these. For example, the insulating coating may include a layer containing phosphoric acid (e.g., a phosphoric acid-based conversion coating) and a layer containing silicone.

[0015] The thickness of the insulating coating may be, for example, 1 nm or more and 300 nm or less. When the thickness of the insulating coating is greater than 1 nm, sufficient insulation tends to be easily obtained. When the thickness of the insulating coating is 300 nm or less, the compression-molded body tends to have an appropriate density and a good magnetic flux density tends to be easily maintained. The thickness of a single-layer insulating coating may be 1 nm or more and 300 nm or less. The total thickness of an insulating coating composed of multiple layers may be 1 nm or more and 300 nm or less.

[0016] The resin portion constituting the powder magnetic core can be a cured product of an impregnation liquid that is a curable resin composition. According to the findings of the present inventors, the resin portion not only covers the surface of the compression-molded body but also sufficiently fills the open pores or gaps inside the compression-molded body, thereby further improving the mechanical strength of the powder magnetic core. Specifically, the ratio X of the open porosity of the powder magnetic core to the total porosity of the powder magnetic core is １ may be 53% or less, or may be 0% or more and 53% or less. １ is calculated by the following formula: １ = (open porosity of powder core / total porosity of powder core) × 100

[0017] The total porosity of a powder magnetic core can be a value calculated by the following formula from the theoretical density of the metal (e.g., pure iron) constituting the soft magnetic powder and the bulk density of the powder magnetic core measured by the Archimedes method in accordance with JIS R 1634: Total porosity (%) = {(theoretical density of metal - bulk density) / theoretical density of metal} × 100 The theoretical density of a metal is the density at room temperature (20°C), and when the metal is pure iron, its theoretical density is 7.9 g / cm ３ When the metals constituting the soft magnetic powder are an alloy, the theoretical density of the alloy is used. Examples of the theoretical densities of some alloys are as follows. In the following examples, the percentage of each metal is a value based on the total mass of the alloy, with the remainder being Fe. Fe-Cr alloy (Cr: 10 mass%): 7.79 g / cm ３ Fe-Ni-Cr alloy (Cr: 25% by mass, Ni: 20% by mass): 7.86g / cm ３ Fe-Si alloy (Si: 3% by mass): 7.8g / cm ３ Fe-Si alloy (Si: 6.5% by mass): 7.7g / cm ３ Fe-Ni alloy (Ni: 47% by mass): 8.25g / cm ３ Fe-Cu-Ni alloy (Cu: 4% by mass, Ni: 32% by mass): 8.24g / cm ３ Fe-Co-V alloy (Co: 49% by mass, V: 2% by mass): 8.1g / cm ３

[0018] The open porosity of the powder magnetic core can also be measured by the Archimedes method in accordance with JIS R 1634. The open porosity can be calculated using the following formula: Open porosity (%) = {(apparent density of powder magnetic core - bulk density) / apparent density of powder magnetic core} x 100

[0019] Fig. 1 is an example of a scanning electron microscope photograph of a cross section of a powder core. The powder core 10 shown in Fig. 1 is composed of a compression-molded body 2, which is an aggregate of a plurality of soft magnetic particles 1, and a resin portion 5 filled in the open pores or gaps in the compression-molded body 2. The ratio X of the open porosity of the powder core to the total porosity of the powder core is １ A small ratio X corresponds to the fact that the pores or gaps in the compression molded body 2 are sufficiently filled with the resin portion. １If the thickness is large, a large gap may remain between the soft magnetic particles 1 and the resin portion 5 .

[0020] From the viewpoint of further improving the mechanical strength of the powder magnetic core, the ratio X of the open porosity of the powder magnetic core to the total porosity of the powder magnetic core is １ may be 50% or less, 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, or 20% or less. １ may be 1.0% or more, 2.0% or more, or 3.0% or more.

[0021] The ratio of the open porosity of the compression molded body not including the resin portion to the total porosity of the compression molded body not including the resin portion is X ０ When [%], X １ / X ０ may be 0.72 or less, or may be 0.0 or more and 0.72 or less. １ / X ０ When X is 0.72 or less, the mechanical strength of the powder magnetic core can be further improved. １ / X ０ may be 0.70 or less, 0.65 or less, 0.60 or less, 0.55 or less, 0.50 or less, 0.45 or less, or 0.40 or less. １ / X ０ The ratio X may be 0.05 or more. ０ The ratio X may be, for example, 20% or more and 80% or less. ０ However, it may be 25% or more, 30% or more, or 35% or more, and may be 75% or less, or 70% or less.

[0022] The compression molded body not including the resin portion may have an open porosity of, for example, 0.5% or more and 6.0% or less. The compression molded body not including the resin portion may have a total porosity of, for example, 2.0% or more and 10% or less.

[0023] The open porosity of the powder magnetic core including the resin portion may be, for example, 0.01% or more and 5.0% or less, and the total porosity of the powder magnetic core including the resin portion may be, for example, 1.0% or more and 8.0% or less.

[0024] The density of the compression molded body not including the resin portion is, for example, 5.0 g / cm ３ 10g / cm or more ３The density of the compression molded body may be 6.0 g / cm or less. ３ or more, or 7.0 g / cm ３ or more, and 9.0 g / cm ３ or less, or 8.0 g / cm ３ It may be the following:

[0025] The impregnating liquid can be a curable resin composition that is liquid at room temperature (25°C) and atmospheric pressure. If the impregnating liquid has high wettability with respect to the compression-molded body, the mechanical strength of the powder magnetic core can be further improved. An impregnating liquid with high wettability can easily penetrate sufficiently deep into the compression-molded body, which is thought to contribute to improving the mechanical strength. By using an impregnating liquid with high wettability, the above-mentioned ratio X １ may be reduced. From the above viewpoints, the contact angle of the compression-molded body with the impregnating liquid may be 70° or less, or may be 5° or more and 70° or less. The contact angle of the compression-molded body with the impregnating liquid may be 65° or less, 60° or less, 55° or less, 50° or less, 45° or less, or 40° or less. The contact angle of the compression-molded body with the impregnating liquid may be 1° or more, 5° or more, or 10° or more. The contact angle here may be a static contact angle measured by a method including dropping 2 μL of impregnating liquid onto the surface of the compression-molded body, obtaining images of the impregnating liquid and the compression-molded body 1 second after the droplet of impregnating liquid contacts the compression-molded body, and determining the contact angle from the images.

[0026] The contact angle of the compression-molded body with the impregnating liquid can be reduced by selecting a combination of the compression-molded body and the impregnating liquid so that the wettability is increased, taking into consideration the degree of hydrophilicity of both materials, etc. For example, a sufficiently small contact angle can be easily obtained by combining a compression-molded body formed from a soft magnetic powder having an insulating coating containing one or more insulating materials selected from phosphoric acid, silicone, and silicate glass with the impregnating liquid (curable resin composition) exemplified below.

[0027] The curable resin composition used as the impregnation liquid may be a thermosetting or photocurable resin composition. The curable resin composition may contain one or more curable components selected from an epoxy resin, a compound having a (meth)acryloyl group, and an unsaturated polyester resin. A curable resin composition or impregnation liquid containing an epoxy resin can contribute to achieving particularly high mechanical strength of the powder magnetic core. "(Meth)acryloyl" means acryloyl, methacryloyl, or both.

[0028] The epoxy resin is an epoxy compound having an epoxy group. The curable resin composition (impregnation liquid) may contain one or more polyepoxy compounds having two or more epoxy groups, examples of which include bisphenol F type epoxy resin.

[0029] The curable resin composition (impregnation liquid) containing an epoxy resin may further contain a curing agent that reacts with the epoxy resin to promote curing. Examples of the curing agent include aromatic amine compounds.

[0030] The curable resin composition (impregnation liquid) may contain a compound having two or more (meth)acryloyl groups. The curable resin composition (impregnation liquid) may contain a compound having two or more (meth)acryloyl groups and a compound having one (meth)acryloyl group. Examples of the compound having two or more (meth)acryloyl groups include polyalkylene glycol di(meth)acrylate (e.g., polyethylene glycol di(meth)acrylate) and ethylene oxide-modified bisphenol A di(meth)acrylate. The compound having one (meth)acryloyl group may be an alkyl (meth)acrylate, examples of which include methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-dodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-hexadecyl (meth)acrylate, and dicyclopentenyloxy (meth)acrylate.

[0031] The curable resin composition may contain a compound having a polar functional group and a (meth)acryloyl group. The polar functional group may be, for example, a phosphate group, a hydroxy group, a carboxy group, or a combination thereof. The phosphate group here may be a phosphate H３ P.O. ４ It means a group obtained by removing 1 to 3 hydrogen atoms from the above. An example of a compound having a phosphate group and a (meth)acryloyl group includes bis(2-(meth)acryloyloxyethyl)phosphate. Examples of a compound having a hydroxy group and a (meth)acryloyl group include 3-hydroxypropyl(meth)acrylate and 2-hydroxyethyl(meth)acrylate. An example of a compound having a carboxy group and a (meth)acryloyl group includes (meth)acrylic acid.

[0032] The curable resin composition (impregnation liquid) may contain one or more compounds having a (meth)acryloyl group selected from the compounds exemplified above.

[0033] The curable resin composition containing the compound having a (meth)acryloyl group may further contain a thermal radical polymerization initiator or a photoradical polymerization initiator. The thermal radical polymerization initiator may be, for example, a peroxide, an azo compound, or a combination thereof.

[0034] The curable resin composition (impregnation liquid) may be substantially free of a solvent. For example, the solvent content may be 0% by mass or more and 2% by mass or less, 0% by mass or more and 1% by mass or less, or 0% by mass or more and 0.5% by mass or less, based on the mass of the curable resin composition (impregnation liquid).

[0035] The viscosity of the curable resin composition (impregnation liquid) may be, for example, 10 Pa s or less, or may be 0.5 Pa s or more and 10 Pa s or less. The viscosity of the curable resin composition (impregnation liquid) may be 9.0 Pa s or less, 8.0 Pa s or less, 7.0 Pa s or less, 6.0 Pa s or less, 5.0 Pa s or less, 4.0 Pa s or less, or 3.0 Pa s or less. The viscosity of the impregnation liquid at the time of impregnation into the compression molded body may be within these ranges. The viscosity here can be a value measured at 25 ° C. using a rotational viscometer.

[0036] If the cured product formed by curing the impregnation liquid has high mechanical strength, the mechanical strength of the powder magnetic core can be further improved. From this perspective, the tensile shear strength of the cured product of the impregnation liquid at 25°C may be, for example, 1.0 MPa or more, 2.0 MPa or more, 4.0 MPa or more, 5.0 MPa or more, 8.0 MPa or more, 10.0 MPa or more, 12.0 MPa or more, 13.0 MPa or more, 14.0 MPa or more, 15.0 MPa or more, 16.0 MPa or more, 17.0 MPa or more, 18.0 MPa or more, 19.0 MPa or more, 20.0 MPa or more, 21.0 MPa or more, 22.0 MPa or more, 23.0 MPa or more, or 24.0 MPa or more. The tensile shear strength of the cured product of the impregnation liquid at 25°C may be 70 MPa or less.

[0037] The powder magnetic core according to the present disclosure can be produced, for example, by a method including filling a molding die with a molding material containing soft magnetic powder, forming a compression-molded body containing open pores by compression molding in the molding die, impregnating the compression-molded body with an impregnation liquid that is a curable resin composition, and curing the impregnation liquid to thereby form a powder magnetic core that includes a compression-molded body and a resin portion that is a cured product of the impregnation liquid.

[0038] The molding material to be subjected to compression molding may further contain a lubricant. In this case, the compression molded body (green compact) may be heated before being impregnated with the impregnation liquid, thereby removing the lubricant. In this case, a small amount of lubricant may remain in the compression molded body after heating. The lubricant may be selected from those commonly used in compression molding. For example, the lubricant may include ethylene bisstearic acid amide.

[0039] Before filling the molding material into the mold, a film of lubricant may be formed on the inner surface of the mold. In this case, the compression molded body removed from the mold may be heated to remove the lubricant adhering to the compression molded body. In this case, a small amount of lubricant may remain on the compression molded body after heating.

[0040] The molding die typically has a cavity having a shape corresponding to the desired shape of the powder magnetic core. The molding conditions, such as the pressure for compression molding, may be adjusted so as to form a compression-molded body, and may be, for example, 300 MPa to 2500 MPa. The temperature of the molding die during compression molding may be, for example, 15°C to 200°C.

[0041] The compression-molded body removed from the mold is impregnated with the impregnation liquid. To this end, for example, the compression-molded body is immersed in the impregnation liquid. The compression-molded body may be immersed in the impregnation liquid under a reduced pressure atmosphere. In this case, the pressure of the reduced pressure atmosphere may be, for example, 0.2 MPa or less or 0.1 MPa or less, or 0.0005 MPa or more or 0.001 MPa or more. The time for immersing the compression-molded body in the impregnation liquid under the reduced pressure atmosphere may be, for example, 1 minute or more, or 1 minute to 120 minutes or less. The temperature of the reduced pressure atmosphere is adjusted to a range in which the hardening of the impregnation liquid does not proceed excessively. The temperature of the reduced pressure atmosphere may be, for example, 15°C to 50°C.

[0042] After immersing the compression-molded body in the impregnation liquid under a reduced pressure atmosphere, the compression-molded body immersed in the impregnation liquid may be left in an atmospheric pressure atmosphere or a pressurized atmosphere exceeding atmospheric pressure for a predetermined time. During this time, impregnation of the impregnation liquid into the compression-molded body can further progress. The pressure of the pressurized atmosphere may be, for example, 0.1 MPa or more or 0.2 MPa or more, and may be 10 MPa or less. The predetermined time for leaving the compression-molded body immersed in the impregnation liquid under an atmospheric pressure atmosphere or a pressurized atmosphere may be, for example, 1 minute or more and 120 minutes or less. The predetermined time may be 3 minutes or more, 5 minutes or more, 7 minutes or more, or 10 minutes or more, and may be 60 minutes or less, or 30 minutes or less. In the case of a pressurized atmosphere, impregnation of the impregnation liquid into the compression-molded body tends to proceed sufficiently even in a relatively short time. Therefore, in the case of a pressurized atmosphere, the predetermined time may be 1 minute or more and 60 minutes or less, such as 3 minutes or more, 5 minutes or more, 7 minutes or more, or 10 minutes or more, or may be 30 minutes or less.

[0043] The impregnation liquid impregnated into the compression-molded body is cured. By curing the impregnation liquid, a cured product of the impregnation liquid is formed as a resin portion. To cure the impregnation liquid, the compression-molded body and the impregnation liquid may be heated, or the compression-molded body and the impregnation liquid may be irradiated with actinic rays (e.g., ultraviolet rays). The conditions for heating and irradiation with actinic rays are adjusted so that the curing of the impregnation liquid proceeds. For example, in the case of thermal curing, the heating temperature may be 60°C or higher and 250°C or lower.

[0044] The powder magnetic core, which is mainly composed of a compression-molded body and a resin portion, can have any shape suitable for its application, etc. The powder magnetic core can be used as a component of various devices selected from, for example, inductors, transformers, reactors, thyristor valves, noise filters (EMI filters), choke coils, iron cores for motors, rotors or yokes, solenoid cores (fixed iron cores) for electromagnetic valves incorporated into electronically controlled fuel injection devices, position sensors, and magnetostrictive sensors.

[0045] The present invention is not limited to the following examples.

[0046] 1. Compression-Molded Body Production Example 1-1 A commercially available iron-based soft magnetic powder (Somaloy110i (5P), manufactured by Höganäs AB, main particle size distribution: 106 to 150 μm) was prepared. This iron-based soft magnetic powder was a powder consisting of iron-based soft magnetic particles including iron particles (mother particles) and an insulating coating covering the surfaces of the iron particles. The insulating coating contained a phosphate-based conversion coating containing phosphoric acid and a lubricant (ethylene bisstearamide) that covered the phosphate-based conversion coating. The insulating coating was formed non-uniformly on the surfaces of the iron particles, and the minimum thickness of the insulating coating was approximately 20 nm. This iron-based soft magnetic powder was filled as a molding material into a mold having a ring-shaped cavity, and compression-molded at a molding pressure of 1200 MPa to form a ring-shaped green compact (density: 7.40 g / cm) with an outer diameter of 30 mm, an inner diameter of 20 mm, and a height of 5 mm. ３ The resulting green compact was heated to 600°C to obtain a ring-shaped compression molded body from which the lubricant had been removed. A green compact having a rectangular parallelepiped shape with a bottom surface measuring 34 mm in length and 12 mm in width and a height of 5 mm was formed in the same manner as above, except that a molding die having a rectangular parallelepiped cavity was used, and the compression molded body was obtained by heating the green compact.

[0047] Production Example 1-2: A density of 7.50 g / cm was obtained in the same manner as in Production Example 1, except that the molding pressure for compression molding was changed to 1500 MPa. ３ The resulting green compact was heated to 600° C. to obtain a ring-shaped or rectangular parallelepiped compression molded body from which the lubricant had been removed.

[0048] Production Example 2-1: A commercially available iron-based soft magnetic powder (ML28D, manufactured by Kobe Steel, Ltd., with a particle size distribution of 106 to 150 μm) was prepared. This iron-based soft magnetic powder consisted of iron-based soft magnetic particles, including iron particles (parent particles) and an insulating coating covering the surfaces of the iron particles. The insulating coating included a phosphoric acid-containing phosphate-based conversion coating and a silicone resin coating, which were applied in this order from the inside to the outside. The phosphate-based conversion coating contained one or more elements selected from the group consisting of Co, Na, S, Si, and W. The insulating coating was formed non-uniformly on the surfaces of the iron particles, and the minimum thickness of the insulating coating was approximately 50 nm. This iron-based soft magnetic powder corresponds to the iron-based soft magnetic powder described in Japanese Patent No. 4044591. This iron-based soft magnetic powder was filled as a molding material into a mold having a ring-shaped cavity, and compression molding was performed at a molding pressure of 700 MPa to produce a ring-shaped green compact (density: 7.40 g / cm) with an outer diameter of 30 mm, an inner diameter of 20 mm, and a height of 5 mm. ３ ) was formed. An insulating lubricant composition (see, for example, JP 2022-94461 A) was applied to the inner surface of the pressing mold in advance to form a lubricant film. The formed powder compact was heated to 600°C to obtain a ring-shaped compression molded body. In the same manner as above, except that a pressing mold having a rectangular parallelepiped cavity was used, a rectangular parallelepiped powder compact with a bottom surface measuring 34 mm in length and 12 mm in width and a height of 5 mm was formed, and a compression molded body from which the lubricant had been removed by heating was obtained.

[0049] Production Example 2-2: A density of 7.50 g / cm was obtained in the same manner as in Production Example 1, except that the molding pressure for compression molding was changed to 850 MPa. ３ The resulting green compact was heated to 600° C. to obtain a ring-shaped or rectangular parallelepiped compression molded body from which the lubricant had been removed.

[0050] Production Example 3: Commercially available pure iron powder (300NH, manufactured by Kobe Steel, Ltd.) was prepared as base particles. A treatment solution containing 200 g of water glass (Toso Sangyo Co., Ltd., No. 1 C2) per liter of water was prepared. Next, 100 g of pure iron powder, which had been pre-screened using a sieve of 60 mesh or less (opening: 250 μm), was mixed with 15 mL of the treatment solution to obtain a mixed powder. This mixed powder was dried by heating at 200°C for 30 minutes. The dried mixed powder was deagglomerated to obtain an iron-based soft magnetic powder (main particle size distribution: 106-150 μm) consisting of iron-based soft magnetic particles having pure iron particles and a silicate glass coating as an insulating coating covering the pure iron particles. The silicate glass coating (insulating coating) was formed non-uniformly on the surface of the pure iron particles, and the thickness of the silicate glass coating (insulating coating) was approximately 30 nm at a minimum. Lithium stearate was added as a lubricant to the iron-based soft magnetic powder in a ratio of 0.3 mass % relative to the mass of the iron-based soft magnetic powder. The resulting mixture was filled into a mold having a ring-shaped cavity as a molding material. A ring-shaped green compact (density: 7.50 g / cm) with an outer diameter of 30 mm, an inner diameter of 20 mm, and a height of 5 mm was obtained by compression molding at a molding pressure of 1500 MPa. ３ The resulting green compact was heated to 600°C to remove the lubricant and obtain a compression molded body. A green compact having a rectangular parallelepiped shape with a bottom surface measuring 34 mm in length and 12 mm in width and a height of 5 mm was formed in the same manner as above, except that a mold having a rectangular parallelepiped cavity was used, and a compression molded body from which the lubricant was removed was obtained by heating.

[0051] Table 1 shows the main components of the base particles and insulating coatings and the densities of the compression molded bodies 1-1, 1-2, 2-1, 2-2 and 3 obtained in Production Examples 1-1, 1-2, 2-1, 2-2 and 3.

[0052]

[0053] 2. Impregnation Solution The following impregnation solutions were prepared. Impregnation liquid 1: Commercially available unsaturated polyester resin. Impregnation liquids 2 to 6: Commercially available thermosetting acrylic resins containing a compound having a (meth)acryloyl group. Impregnation liquid 7: Thermosetting acrylic resin containing polyethylene glycol dimethacrylate, alkyl methacrylate, 3-hydroxypropyl methacrylate, methacrylic acid, and a thermal radical polymerization initiator. Impregnation liquid 8: Thermosetting acrylic resin containing polyethylene glycol dimethacrylate, acrylic methacrylate, 2-hydroxyethyl methacrylate, and a thermal radical polymerization initiator. Impregnation liquid 9: Thermosetting acrylic resin containing polyethylene glycol dimethacrylate, a dimethacrylate having a phosphate group, and a thermal radical polymerization initiator. Impregnation liquid 10: Thermosetting acrylic resin containing polyethylene glycol dimethacrylate, alkyl methacrylate, and a thermal radical polymerization initiator. Impregnation liquid 11: Thermosetting acrylic resin containing polyethylene glycol dimethacrylate, ethylene oxide-modified bisphenol A dimethacrylate, and a thermal radical polymerization initiator. Impregnation liquid 12: Thermosetting epoxy resin composition containing bisphenol F type epoxy resin and aromatic amine.

[0054] 3. Mechanical Properties of Impregnation Solutions Test specimens were prepared by bonding the edges of two steel plates via the cured products of Impregnation Solutions 1 to 12. Tensile tests were conducted using the prepared test specimens to determine the tensile shear strength at 25°C of the cured products of each impregnation solution. The results are shown in Table 2.

[0055]

[0056] 4. Contact Angle The contact angle of the compression molded body with the impregnating liquid before curing was measured using a fully automatic contact angle meter DropMaster 700 (Kyowa Interface Science Co., Ltd.) in an environment of about 25 ° C. using the following method. A rectangular compression molded body with a long side of 34 mm and a short side of 12 mm was placed so that the bottom was horizontal. 2 μL of the impregnating liquid before curing was dropped onto the surface of the compression molded body using a microsyringe. A still image of the droplet of impregnating liquid on the compression molded body was taken with a video microscope 1 second after the droplet contacted the compression molded body. The static contact angle was determined from the obtained still image using the θ / 2 method. The average value of four measurements was recorded as the contact angle.

[0057] 5. Powder magnetic core The impregnation liquid was poured into a container in a vacuum impregnation apparatus. A ring-shaped or rectangular parallelepiped compression molded body was completely immersed in the impregnation liquid in the container. Next, the pressure inside the vacuum impregnation apparatus was reduced to approximately 0.08 MPa at a temperature of approximately 20°C, and the body was degassed under vacuum for a predetermined time (vacuum impregnation time). The pressure inside the vacuum impregnation apparatus was then released to atmospheric pressure, and the impregnation liquid and the compression molded body were left for a predetermined time (atmospheric pressure release time). In the cases of Examples 53 and 54, after the ring-shaped or rectangular parallelepiped compression molded body was completely immersed, the pressure inside the vacuum impregnation apparatus was reduced to approximately 0.001 MPa at a temperature of approximately 20°C, and the body was degassed under vacuum for a predetermined time (vacuum impregnation time). In Examples 53 and 54, the pressure inside the vacuum impregnation apparatus was then adjusted to approximately 0.5 MPa at a temperature of approximately 20°C, and the impregnation liquid and the compression-molded body were left at that pressure for the predetermined time (pressurization time) shown in Table 7. The excess impregnation liquid present on the surface of the compression-molded body removed from the vacuum impregnation apparatus was removed using a centrifuge, and the compression-molded body impregnated with the impregnation liquid was then heated at 200°C to harden the impregnation liquid. Through these operations, powder magnetic cores of Examples and Comparative Examples were obtained, each composed of a compression-molded body and a resin portion, which was the cured product of the impregnation liquid. The combinations of the compression-molded body and the impregnation liquid for each Example and Comparative Example are shown in Tables 3, 4, 5, 6, and 7. The powder magnetic cores of Comparative Examples 1, 5, 8, 10, and 12 are compression-molded bodies before being impregnated with the impregnation liquid.

[0058] 6. Evaluation of Powder Cores (1) Total Porosity and Open Porosity The bulk density and open porosity of powder cores were measured by the Archimedes method in accordance with JIS R 1634. The dry mass of a powder core sample was measured. The dried sample was immersed in water and degassed until no more bubbles were generated, and then the sample's mass in water and saturated with water were measured. The bulk density and open porosity of the powder core were calculated from the dry mass, the mass in water, and the mass saturated with water. The total porosity of the powder core was calculated using the following formula: Total Porosity (%) = {(Theoretical Density of Pure Iron - Bulk Density) / Theoretical Density of Pure Iron} × 100 The theoretical density of pure iron is 7.9 g / cm ３ From the obtained values ​​of total porosity and open porosity, the ratio X of the open porosity of the powder core to the total porosity of the powder core was calculated using the following formula: １ X１ = (open porosity of powder core / total porosity of powder core) × 100 The total porosity and open porosity of the compression-molded body before impregnation with the impregnation liquid were measured in the same manner, and the ratio X of the open porosity of the compression-molded body to the total porosity of the compression-molded body was calculated from these values ​​using the following formula: ０ X ０ = (open porosity of compression molded body / total porosity of compression molded body) × 100

[0059] (2) Flexural Strength The flexural strength of the rectangular parallelepiped powder magnetic cores was measured in accordance with JIS Z 2511. A precision universal testing machine (Autograph AG-10TB, manufactured by Shimadzu Corporation) was used as the measuring device. In a three-point bending test of a test piece of each powder magnetic core, the flexural strength was calculated from the load at the time the test piece broke.

[0060] (3) AC Magnetic Properties An insulating polyethylene terephthalate film was wrapped around a ring-shaped powder core. A polyester copper wire with a wire diameter of 0.5 mm was wound 100 times around the powder core on top of the polyethylene terephthalate film using an automatic winding machine. Furthermore, a polyester copper wire with a wire diameter of 0.26 mm was wound 20 times around the powder core as a secondary winding using an automatic winding machine. Using an AC magnetic property evaluation device (SY-947, manufactured by Iwasaki Electric Co., Ltd.), iron loss was measured at frequencies of 500 Hz, 1000 Hz, or 2000 Hz at a magnetic flux density of 1 T. The iron loss of the compression-molded body before impregnation with the impregnation liquid was also measured using the same method.

[0061] (4) Results Tables 3 to 7 show the evaluation results for each type of compression molded body. In the tables, the impregnation conditions for forming the powder magnetic core, the viscosity of the impregnation liquid, and the ratio X １ / X ０ The viscosity of the impregnation liquid here is the viscosity at 25°C measured using a rotational viscometer. In the powder cores of each example, the ratio of the open porosity of the powder core to the total porosity of the powder core was 53% or less, and it was confirmed that the bending strength was improved compared to the compression molded body before impregnation with the impregnation liquid (Comparative Examples 1, 5, 8, 10, or 12). The powder cores of each example also exhibited good AC magnetic properties.

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[0065]

[0066]

[0067] 1...soft magnetic particles, 2...compression molded body, 5...resin part, 10...dust core

Claims

1. A powder magnetic core comprising: a compression-molded body containing soft magnetic powder; and a resin portion impregnated in the compression-molded body, wherein the resin portion is a cured product of an impregnation liquid that is a curable resin composition, and the ratio of the open porosity of the powder magnetic core to the total porosity of the powder magnetic core is 53% or less.

2. The powder magnetic core according to claim 1, wherein the contact angle of the compression-molded body with the impregnation liquid is 70° or less.

3. The ratio of the open porosity of the powder magnetic core to the total porosity of the powder magnetic core is X １ [%], and the ratio of the open porosity of the compression molded body to the total porosity of the compression molded body is X ０ When [%], X １ / X ０ The powder magnetic core according to claim 1 , wherein the value of ρ is 0.72 or less.

4. The dust core according to claim 1, wherein the soft magnetic powder is a powder containing soft magnetic particles having base particles containing a metal and an insulating coating covering the surfaces of the base particles.

5. The powder magnetic core according to claim 1, wherein the curable resin composition comprises an epoxy resin.

6. The powder magnetic core according to claim 1, wherein the curable resin composition contains a compound having a (meth)acryloyl group.

7. A method for producing a powder magnetic core, comprising: filling a molding die with a molding material containing soft magnetic powder; forming a compression-molded body by compression molding in the molding die; impregnating the compression-molded body with an impregnation liquid that is a curable resin composition; and hardening the impregnation liquid to thereby form a powder magnetic core that includes the compression-molded body and a resin portion that is a hardened product of the impregnation liquid; wherein a ratio of the open porosity of the powder magnetic core to the total porosity of the powder magnetic core is 53% or less.

8. The method according to claim 7, wherein the contact angle of the compression-molded body with the impregnating liquid is 70° or less.

9. The method of claim 7, wherein impregnating the compact with the impregnating liquid comprises immersing the compact in the impregnating liquid.

10. The method according to claim 7, wherein impregnating the compression-molded body with the impregnation liquid comprises immersing the compression-molded body in the impregnation liquid under a reduced pressure atmosphere, and then placing the compression-molded body, while still immersed in the impregnation liquid, under atmospheric pressure or a pressurized atmosphere for one minute or more.

11. The method according to claim 7, wherein the molding material further comprises a lubricant, and the method further comprises heating the compact, thereby removing the lubricant, before impregnating the compact with the impregnating liquid.

12. The method according to claim 7, further comprising: forming a film of lubricant on the inner surface of the molding die before filling the molding material into the molding die; and heating the compact removed from the molding die, thereby removing the lubricant adhering to the compact.

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