dust core

Abstract

The powder magnetic core contains: magnetic nano-particles having an average particle diameter of 1 to 300 nm, and an aromatic compound having 2 or more functional groups selected from at least one of carboxyl and hydroxyl groups.

Description

Technical Field

[0001] This invention relates to pressed powder magnetic cores, and more specifically, to pressed powder magnetic cores using magnetic nanoparticles. Background Technology

[0002] Powder cores are obtained by compressing magnetic particles whose surface is covered by an insulating film. Powder cores are used in various products utilizing electromagnetism, such as transformers, electric motors, generators, loudspeakers, induction heaters, and various actuators. Such powder cores are disclosed, for example, in the following documents. Patent Document 1 discloses a core obtained by coating the surface of a powder with a particle size of 5-200 μm, made of a soft magnetic material, with silicone resin; further coating with a high-grade fatty acid lubricant made of stearic acid or its metal salt; pressing the soft magnetic powder; and heat-treating it. Patent Document 2 discloses a powder core comprising composite magnetic particles, which include: metallic magnetic particles; an insulating film surrounding the surface of the metallic magnetic particles containing at least one of a metal phosphate salt and a metal oxide; and a lubricant film surrounding the surface of the insulating film containing a metal soap made of a metal salt such as stearic acid. Patent Document 3 discloses a pressed powder magnetic core obtained by pressing and heat-treating an iron-based powder having an average particle size of 30-500 μm with an insulating film composed of phosphate on its surface and a lubricant containing an ester of fatty acid having OH groups. Patent Document 4 discloses a pressed powder magnetic core comprising: coated iron powder having an average particle size of 200-450 μm with an insulating film; and a lubricant composed of fatty acid amides.

[0003] Magnetic nanoparticles exhibit properties different from bulk magnetic materials due to their extremely small size. For example, in the range of particle sizes exceeding approximately 100 nm, coercivity increases with decreasing particle size, reaching its maximum near approximately 100 nm. However, if the particle size becomes less than approximately 20 nm, superparamagnetism is observed, and the coercivity becomes extremely small. Therefore, it is believed that hysteresis losses can be minimized in powder-pressed magnetic cores using magnetic nanoparticles with particle sizes of approximately 20 nm or less. Furthermore, it is believed that in powder-pressed magnetic cores using insulating magnetic nanoparticles and conductive magnetic nanoparticles with an insulating coating on their surface, eddy current losses can be reduced by using magnetic nanoparticles with particle sizes of approximately 300 nm or less, as the path of eddy currents at high frequencies is confined. In particular, it is believed that eddy current losses can be minimized by using magnetic nanoparticles with particle sizes of approximately 20 nm or less. Thus, pressed powder cores using magnetic nanoparticles with a particle size of about 20nm or less are highly anticipated as transformer core materials for power supply applications due to their extremely low hysteresis loss and eddy current loss.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2000-223308

[0007] Patent Document 2: Japanese Patent Application Publication No. 2005-129716

[0008] Patent Document 3: Japanese Patent Application Publication No. 2007-211341

[0009] Patent Document 4: Japanese Patent Application Publication No. 2016-12688 Summary of the Invention

[0010] However, the density of pressed magnetic cores obtained by mixing existing lubricants such as stearic acid or their metal salts, fatty acid esters, or fatty acid amides with magnetic nanoparticles and compressing them under existing molding conditions (e.g., molding temperature: 150°C, molding pressure: 1.4 GPa) is not necessarily high enough. This is believed to be because if the magnetic particles are as small as nanoparticles, their plastic deformation strength becomes high, and under existing molding conditions, the magnetic nanoparticles do not undergo sufficient plastic deformation. Therefore, increasing the molding temperature is considered to allow for sufficient plastic deformation of the magnetic nanoparticles. However, increasing the molding temperature reduces the strength of the mold.

[0011] The inventors focused on the fact that the melting point of metal nanoparticles is lower than that of bulk metals, and believed that the temperature at which the plastic deformation strength of metal nanoparticles decreases is also lower than that of bulk metals. Furthermore, they believed that even at temperatures higher than existing molding temperatures, there exists a temperature range where the plastic deformation strength of magnetic nanoparticles decreases without reducing the strength of the mold. They argued that by heating magnetic nanoparticles at temperatures within this range, sufficient plastic deformation of the magnetic nanoparticles can be achieved, resulting in high-density pressed powder magnetic cores.

[0012] However, if existing lubricants are mixed with magnetic nanoparticles and compressed at a temperature higher than the existing molding temperature, the lubricant will evaporate, decompose, or deteriorate. Therefore, its effectiveness as a binder is reduced. Furthermore, the increased thermal strain associated with high-temperature molding leads to larger cracks in the resulting pressed powder core, or even core breakage.

[0013] The purpose of this invention is to provide a pressed powder magnetic core that is formed at temperatures above 300°C, has high density, and suppresses the formation of cracks.

[0014] In order to achieve the above-mentioned objective, the inventors have conducted repeated and in-depth research and found that by adding an aromatic compound having at least one functional group selected from carboxyl and hydroxyl groups to magnetic nanoparticles and then compressing them, a high-density powder magnetic core with suppressed crack formation can be obtained even when the molding is carried out at a temperature above 300°C, thus completing the present invention.

[0015] That is, the pressed powder magnetic core of the present invention contains: magnetic nanoparticles with an average particle size of 1 to 300 nm; and an aromatic compound having at least one functional group selected from carboxyl and hydroxyl groups.

[0016] In the pressed powder magnetic core of the present invention, the aromatic compound is preferably selected from at least one of the following aromatic compounds:

[0017] (i) Aromatic compounds in which two or more functional groups bonded to the same aromatic ring are one or more carboxyl groups and one or more hydroxyl groups, and the positional relationship between the carboxyl groups and hydroxyl groups is meta and / or para.

[0018] (ii) Aromatic compounds in which two or more functional groups bonded to the same aromatic ring are all carboxyl groups, and the positional relationship of the two carboxyl groups is either meta or para.

[0019] (iii) Aromatic compounds in which two or more functional groups bonded to the same aromatic ring are all hydroxyl groups and the positional relationship of the two hydroxyl groups is meta or para.

[0020] Furthermore, more preferably, the aromatic compound is selected from at least one of 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, 5-hydroxyisophthalic acid, 4-hydroxyphthalic acid, 1,4-phthalic acid, 1,3-phthalic acid, 1,3,5-benzenetricarboxylic acid, 1,4-benzenediol, 1,3-benzenediol, and 1,3,5-benzenediol.

[0021] Furthermore, in the pressed powder magnetic core of the present invention, the aromatic compound is preferably a monocyclic aromatic compound. Additionally, the content of the aromatic compound is preferably 0.01% to 5% by mass relative to the total mass of the magnetic nanoparticles and the aromatic compound.

[0022] The rationale for obtaining a pressed powder magnetic core containing the aforementioned magnetic nanoparticles, exhibiting high density and suppressed crack formation by adding the aforementioned aromatic compounds to the aforementioned magnetic nanoparticles is not necessarily clear, but the inventors speculate as follows: Aromatic compounds having at least one functional group selected from carboxyl and hydroxyl groups have high melting points and are therefore less prone to volatilization, decomposition, or deterioration at high temperatures. Furthermore, since the aforementioned aromatic compounds have two or more functional groups (carboxyl and / or hydroxyl groups) that can form strong bonds with the magnetic nanoparticles, the bonding force between the magnetic nanoparticles can be improved. Moreover, since the aforementioned aromatic compounds possess strong bonding forces between aromatic compounds originating from the planarity of aromatic rings, it is speculated that even when molding at temperatures above 300°C, a pressed powder magnetic core with high density and suppressed crack formation can be obtained.

[0023] According to the present invention, even when molding at a temperature of 300°C or higher, it is possible to obtain a pressed powder magnetic core with high density and minimal crack formation. Attached Figure Description

[0024] Figure 1 It is a coordinate graph showing the relationship between the content of 3,4,5-trihydroxybenzoic acid (gallic acid) and the density of the pressed magnetic core. Detailed Implementation

[0025] The present invention will now be described in detail according to its preferred embodiments.

[0026] The pressed powder magnetic core of the present invention contains: magnetic nanoparticles with an average particle size of 1 to 300 nm; and an aromatic compound having at least one functional group selected from carboxyl and hydroxyl groups.

[0027] The magnetic nanoparticles used in this invention are not particularly limited to any magnetic nanoparticles used in powder-pressed magnetic cores; examples include Fe nanoparticles, Fe-containing alloy nanoparticles, and Fe-containing metal oxide nanoparticles. Furthermore, Fe nanoparticles and Fe-containing alloy nanoparticles may have an insulating layer on their surface. These magnetic nanoparticles can be used individually or in combination of two or more types. From the viewpoint of reducing hysteresis and eddy current losses, achieving higher saturation magnetic flux density, and minimizing performance degradation at high temperatures, Fe nanoparticles and Fe-containing alloy nanoparticles with an insulating layer on their surface are preferred.

[0028] There are no particular restrictions on the types of Fe-containing alloy nanoparticles used in powder-pressed magnetic cores. Examples include FeNi alloy nanoparticles (permalloy B nanoparticles, etc.), FeSi alloy nanoparticles (silicon steel nanoparticles, etc.), FeCo alloy nanoparticles (permalloy nanoparticles, etc.), and NiFe alloy nanoparticles (permalloy C nanoparticles, etc.). Similarly, there are no particular restrictions on the types of Fe-containing metal oxide nanoparticles used in powder-pressed magnetic cores. Examples include NiZn ferrite nanoparticles, MnZn ferrite nanoparticles, and other ferrite-based nanoparticles.

[0029] Examples of insulating layers include those composed of metal oxides such as SiO2, Al2O3, Fe2O3, Fe3O4, NiZn ferrite, and MnZn ferrite; those composed of organic compounds such as fatty acids (e.g., decanoic acid, lauric acid, stearic acid, oleic acid, and linolenic acid) and organosilicon-based organic compounds (e.g., methyl silicone resin, methylphenyl silicone resin, dimethyl polysiloxane, and silicone hydrogel); and those composed of inorganic compounds such as phosphorus-based compounds (e.g., calcium phosphate, iron phosphate, zinc phosphate, and manganese phosphate).

[0030] Furthermore, the average particle size of the magnetic nanoparticles used in this invention is 1 to 300 nm. If the average particle size of the magnetic nanoparticles is less than the lower limit, the influence of the particle surface is large, and the magnetic properties of the magnetic nanoparticles themselves decrease. On the other hand, if the average particle size of the magnetic nanoparticles exceeds the upper limit, eddy current losses increase, and core losses become larger. From the viewpoint that superparamagnetism can be exhibited, coercivity becomes extremely small, hysteresis losses are extremely small, and the eddy current path is restricted at high frequencies, thus minimizing eddy current losses, the average particle size of the magnetic nanoparticles is preferably 1 to 100 nm, more preferably 1 to 20 nm. The average particle size of the magnetic nanoparticles can be obtained by measuring the particle size of 100 particles under TEM observation and averaging them.

[0031] The aromatic compounds used in this invention have at least one functional group selected from carboxyl and hydroxyl groups. By adding such aromatic compounds to magnetic nanoparticles, even when molding at temperatures above 300°C, it is possible to obtain powder-pressed magnetic cores with high density and suppressed crack formation.

[0032] There are no particular limitations on such aromatic compounds, but the following aromatic compounds are preferred:

[0033] (i) Aromatic compounds in which two or more functional groups bonded to the same aromatic ring are one or more carboxyl groups and one or more hydroxyl groups, and the positional relationship between the carboxyl groups and hydroxyl groups is meta and / or para.

[0034] (ii) Aromatic compounds in which two or more functional groups bonded to the same aromatic ring are all carboxyl groups, and the positional relationship of the two carboxyl groups is either meta or para.

[0035] (iii) Aromatic compounds in which two or more functional groups bonded to the same aromatic ring are all hydroxyl groups and the positional relationship of the two hydroxyl groups is meta or para.

[0036] Aromatic compounds with meta- and / or para-positional functional groups are less prone to anhydride formation due to dehydration and de-alcoholization reactions even at high temperatures, and remain stable even at higher temperatures. Therefore, even when molding at temperatures above 300°C, powder-pressed magnetic cores with high density and suppressed crack formation can be obtained. On the other hand, aromatic compounds with ortho-positional functional groups undergo anhydride formation through dehydration and de-alcoholization reactions at high temperatures, thus failing to form strong bonds with magnetic nanoparticles and making it difficult to form a stable coating layer. Therefore, there is a tendency to obtain powder-pressed magnetic cores with high density and suppressed crack formation.

[0037] Examples of such aromatic compounds include the following aromatic compounds. Examples of aromatic compounds (i) include 4-hydroxybenzoic acid (formula (i-1) below), 3-hydroxybenzoic acid (formula (i-2) below), 3,5-dihydroxybenzoic acid (formula (i-3) below), 3,4-dihydroxybenzoic acid (formula (i-4) below), 3,4,5-trihydroxybenzoic acid (formula (i-5) below), 5-hydroxyisophthalic acid (formula (i-6) below), 4-hydroxyphthalic acid (formula (i-7) below), 4,5-dihydroxyphthalic acid (formula (i-8) below), and 5-hydroxyphenyl-1,2,3-tricarboxylic acid (formula (i-9) below).

[0038]

[0039] Examples of aromatic compounds (ii) include 1,4-phthalic acid (formula (ii-1) below), 1,3-phthalic acid (formula (ii-2) below), and 1,3,5-benzenetricarboxylic acid (formula (ii-3) below).

[0040]

[0041] Examples of aromatic compounds (iii) include 1,4-benzenediol (formula (iii-1) below), 1,3-benzenediol (formula (iii-2) below), and 1,3,5-benzenediol (formula (iii-3) below).

[0042]

[0043] These aromatic compounds can be used alone or in combination of two or more. Furthermore, from the viewpoint that a pressed powder core with even higher density and further suppressed crack formation can be obtained even when molding at temperatures above 300°C, aromatic compounds (i) are preferred (more preferably 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, 5-hydroxyisophthalic acid, 4-hydroxyphthalic acid; further preferably 4-hydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid) and aromatic compounds (ii) (more preferably 1,4-phthalic acid, 1,3-phthalic acid, 1,3,5-benzenetricarboxylic acid; further preferably 1,3,5-benzenetricarboxylic acid), especially aromatic compound (i) (further preferably 4-hydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, particularly preferably 4-hydroxybenzoic acid).

[0044] Furthermore, the aromatic compound used in this invention can be a monocyclic aromatic compound or a polycyclic aromatic compound such as a fused ring. However, polycyclic aromatic compounds have low coordination with particles due to steric hindrance, while monocyclic aromatic compounds have high coordination with particles. From this point of view, monocyclic aromatic compounds are preferred.

[0045] Furthermore, the melting point of the aromatic compound is preferably 200°C or higher, more preferably 250°C or higher. If the melting point of the aromatic compound is lower than the lower limit, the aromatic compound will melt when molding is performed at a temperature of 300°C or higher. Therefore, strong bonding forces cannot be obtained between the aromatic compound and the magnetic nanoparticles, making it difficult to form a stable coating layer. Consequently, there is a tendency to fail to obtain a powder-pressed magnetic core with high density and suppressed crack formation. It should be noted that the upper limit of the melting point of the aromatic compound is not particularly limited, but from the viewpoint that it can be easily removed during the annealing process after molding, it is preferably 500°C or lower.

[0046] There is no particular limitation on the content of aromatic compounds, but it is preferably 0.01% to 5% by mass relative to the total mass of magnetic nanoparticles and aromatic compounds, more preferably 0.1% to 2% by mass, and particularly preferably 0.1% to 1% by mass. If the content of aromatic compounds is less than the lower limit, the aromatic compounds are not sufficiently distributed between the magnetic nanoparticles, thus reducing the fluidity of the magnetic nanoparticles in this portion and making it difficult to increase the density of the pressed magnetic core. On the other hand, if the content of aromatic compounds exceeds the upper limit, the proportion of non-magnetic components increases, and the magnetic properties of the pressed magnetic core tend to decrease.

[0047] The density of the pressed powder magnetic core of this invention is 7.0 g / cm³. 3The above-mentioned materials exhibit high relative permeability. Furthermore, from the viewpoint of achieving even higher relative permeability, the density of the powder core is preferably 7.1 g / cm³. 3 The above, more preferably 7.3 g / cm³ 3 above.

[0048] The pressed powder magnetic core of the present invention can be manufactured, for example, by the following method. First, magnetic nanoparticles and aromatic compounds are mixed in a predetermined amount. The mixture of magnetic nanoparticles and aromatic compounds exhibits high homogeneity. Therefore, the flowability of the magnetic nanoparticles can be ensured during the pressure molding process described later, resulting in a high-density pressed powder magnetic core.

[0049] There are no particular limitations on the method for mixing magnetic nanoparticles and aromatic compounds. Examples include mixing using a ball mill or mortar and pestle; or mixing by dispersing and dissolving the magnetic nanoparticles and aromatic compounds in a solvent, followed by removing the solvent through drying. Furthermore, because magnetic nanoparticles have poor rearrangement properties, a particulate mixture can be prepared by dispersing and dissolving the magnetic nanoparticles and aromatic compounds in a solvent, followed by spray drying. During compression molding, the particulate mixture collapses while the magnetic nanoparticles easily rearrange, thus increasing the density of the pressed magnetic core.

[0050] Next, the mixture of magnetic nanoparticles obtained in this manner and aromatic compounds is filled into a mold coated with a lubricant. There are no particular limitations on the lubricant; examples include metal salts of saturated fatty acids such as lithium stearate and zinc stearate, and greases (e.g., "M-HGSSC-H500" manufactured by Misumi Co., Ltd.).

[0051] Next, the pressed powder magnetic core of the present invention can be obtained by press molding the mixture of magnetic nanoparticles and aromatic compounds filled in the mold. The molding temperature is preferably 300–600°C, more preferably 300–400°C. If the molding temperature is below the lower limit, the plastic deformation strength of the magnetic nanoparticles will not be sufficiently reduced, and there is a tendency for the density of the obtained pressed powder magnetism to be difficult to increase. On the other hand, if the molding temperature exceeds the upper limit, the strength of the mold will decrease, and there is a tendency for the mold life to be shortened. It should be noted that the mold can be heated to the set temperature (molding temperature) before filling the mixture of magnetic nanoparticles and aromatic compounds, or it can be heated to the set temperature after filling.

[0052] The molding pressure is preferably 500 MPa to 3 GPa, more preferably 800 MPa to 2 GPa. If the molding pressure is less than the lower limit, the mixture is not sufficiently compressed, and therefore, there is a tendency for the density of the pressed powder core to decrease. On the other hand, if the molding pressure exceeds the upper limit, the effect of springback is significant, and there is a tendency for cracks to form, resulting in a decrease in the density of the pressed powder core.

[0053] In addition, the powder-pressed magnetic core manufactured in this manner can be heat-treated as needed. This mitigates the strain generated in the powder-pressed magnetic core due to pressure application, thereby improving its magnetic properties. The temperature for such heat treatment is typically 500–800°C.

[0054] Example

[0055] The present invention will now be described in more detail based on embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0056] (Example 1)

[0057] 4.975 g (99.5% by mass) of FeNi alloy nanoparticles (manufactured by Aldrich) with an average particle size of 100 nm as magnetic nanoparticles and 0.025 g (0.5% by mass) of gallic acid (3,4,5-trihydroxybenzoic acid, manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.) as an aromatic compound were mixed and further crushed in a mortar for 30 minutes. The resulting crushed mixture was filled into a particle test mold coated with grease (M-HGSSC-H500 manufactured by Misumi Co., Ltd.), and heated at 350°C for 1 minute while pressurizing to 1.4 GPa using a manual hydraulic vacuum heating press (IMC-1946 type modified manufactured by Imoto Co., Ltd.). After stopping the pressurization, the mixture was cooled to room temperature, and the resulting magnetic nanoparticle molded body (pressed magnetic core particles (outer diameter)) was removed from the mold. The density is determined from the mass and volume of the resulting molded body. The results are shown below. Figure 1 See Table 1.

[0058] (Example 2)

[0059] The amount of FeNi alloy nanoparticles was changed to 4.995 g (99.9% by mass), and the amount of gallic acid was changed to 0.005 g (0.1% by mass). Otherwise, the magnetic nanoparticle molded body (pressed magnetic core particles (outer diameter)) was prepared in the same manner as in Example 1. )) , calculate its density. The results are shown in Figure 1 .

[0060] (Example 3)

[0061] The amount of FeNi alloy nanoparticles was changed to 4.990 g (99.8% by mass), and the amount of gallic acid was changed to 0.010 g (0.2% by mass). Otherwise, the magnetic nanoparticle molded body (pressed magnetic core particles (outer diameter)) was prepared in the same manner as in Example 1. )) , calculate its density. The results are shown in Figure 1 .

[0062] (Example 4)

[0063] The amount of FeNi alloy nanoparticles was changed to 4.950 g (99.0% by mass), and the amount of gallic acid was changed to 0.050 g (1.0% by mass). Otherwise, the magnetic nanoparticle molded body (pressed magnetic core particles (outer diameter)) was prepared in the same manner as in Example 1. )) , calculate its density. The results are shown in Figure 1 .

[0064] (Example 5)

[0065] Using 0.025 g (0.5% by mass) of pyromellitic acid (1,3,5-phenyltricarboxylic acid, manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.) as an aromatic compound, magnetic nanoparticle molded bodies (pressed magnetic core particles (outer diameter)) were prepared in the same manner as in Example 1. )) , calculate its density.

[0066] The results are shown in Table 1.

[0067] (Example 6)

[0068] Using 0.025 g (0.5% by mass) of p-hydroxybenzoic acid (4-hydroxybenzoic acid, manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.) as an aromatic compound, magnetic nanoparticle molded bodies (pressed magnetic core particles (outer diameter)) were prepared in the same manner as in Example 1. )) , calculate its density.

[0069] The results are shown in Table 1.

[0070] (Example 7)

[0071] Hydroquinone (1,4-benzene, manufactured by Fujifilm and Kojun Chemical Co., Ltd.) 0.025 g (0.5% by mass) was used as an aromatic compound. Otherwise, magnetic nanoparticle molded bodies (pressed magnetic core particles (outer diameter)) were prepared in the same manner as in Example 1. The density was calculated. The results are shown in Table 1.

[0072] (Comparative Example 1)

[0073] No aromatic compounds were mixed in; otherwise, the magnetic nanoparticle molded bodies (pressed magnetic core particles (outer diameter)) were prepared in the same manner as in Example 1. The density was calculated. The results are shown in Table 1 and... Figure 1 .

[0074] (Comparative Example 2)

[0075] Gallic acid was replaced with 0.025 g (0.5% by mass) of ceramide acid (manufactured by Tokyo Chemical Industry Co., Ltd.), a saturated aliphatic carboxylic acid. Otherwise, magnetic nanoparticle molded bodies (pressed magnetic core particles (outer diameter)) were prepared in the same manner as in Example 1. The density was calculated. The results are shown in Table 1.

[0076] (Comparative Example 3)

[0077] Using 0.025 g (0.5% by mass) of phenol (manufactured by Fujifilm and Koko Pure Chemical Industries, Ltd.) instead of gallic acid, magnetic nanoparticle molded bodies (pressed magnetic core particles (outer diameter)) were prepared in the same manner as in Example 1. The density was calculated. The results are shown in Table 1.

[0078] (Comparative Example 4)

[0079] Benzoic acid (manufactured by Fujifilm and Koko Pure Chemical Industries, Ltd.) 0.025 g (0.5% by mass) was used instead of gallic acid. Otherwise, magnetic nanoparticle molded bodies (pressed magnetic core particles (outer diameter)) were prepared in the same manner as in Example 1. The density was calculated. The results are shown in Table 1.

[0080] <Crack Rate>

[0081] The pressed powder magnetic core particles obtained in Examples 1, 5-7, and Comparative Examples 1-4 were cut and ground on a plane parallel to the long side of the particles. Then, the cross-section of the pressed powder magnetic core particles was observed using a scanning electron microscope. The length of the cracks was measured in the image obtained at 50x magnification, and the crack ratio (unit: mm / mm) was calculated by dividing the crack length by the area of ​​the observed cross-section of the pressed powder magnetic core particle. 2 The determination was performed on each particle at four locations, and the average value was calculated. The results are shown in Table 1.

[0082] [Table 1]

[0083]

[0084] like Figure 1As shown, the pressed magnetic cores (Examples 1-4) formed by mixing magnetic nanoparticles with aromatic compounds having at least one functional group selected from carboxyl and hydroxyl groups, even when molded at a temperature of 300°C or higher, exhibit a higher density (7.0 g / cm³) compared to pressed magnetic cores without aromatic compounds (Comparative Example 1). 3 (Above). Furthermore, as shown in Table 1, it can be seen that even when molded at temperatures above 300°C, the powder cores containing aromatic compounds (Examples 1-4) exhibit a smaller crack rate (0.50 mm / mm) compared to the powder cores without aromatic compounds (Comparative Example 1). 2 the following).

[0085] On the other hand, as shown in Table 1, the pressed magnetic cores formed by mixing magnetic nanoparticles with saturated aliphatic carboxylic acids (Comparative Example 2) or aromatic monohydric alcohols (Comparative Example 3), even when molded at a temperature of 300°C or higher, exhibited higher density and lower crack rate compared to pressed magnetic cores without aromatic compounds (Comparative Example 1). Conversely, the pressed magnetic cores of Comparative Examples 2 or 3 had lower density (less than 7.0 g / cm³) compared to pressed magnetic cores mixed with aromatic compounds (Examples 1, 5-6). 3 The crack rate increased (exceeding 0.50 mm / mm). 2 Furthermore, the pressed magnetic core, formed by mixing magnetic nanoparticles with an aromatic monocarboxylic acid (Comparative Example 4), achieved a density (7.0 g / cm³) similar to that of pressed magnetic cores mixed with aromatic compounds (Examples 1, 5-6), even when molded at temperatures above 300°C. 3 (Above). On the other hand, the powder core of Comparative Example 4 also showed a higher crack rate (exceeding 0.50 mm / mm) compared to the powder core mixed with aromatic compounds (Examples 1, 5-6). 2 ).

[0086] Based on the above results, it was confirmed that by combining magnetic nanoparticles with aromatic compounds having at least one functional group selected from carboxyl and hydroxyl groups, even when molding at temperatures above 300°C, it is possible to obtain pressed magnetic cores with higher density and further suppression of crack formation.

[0087] Industrial availability

[0088] As explained above, according to the present invention, even when molding at a temperature of 300°C or higher, it is possible to obtain a pressed powder magnetic core with high density and suppressed crack formation. Therefore, the pressed powder magnetic core of the present invention has high relative permeability and low hysteresis loss and eddy current loss, making it useful as a core material for products utilizing electromagnetic fields such as transformers, electric motors, generators, loudspeakers, induction heaters, and various actuators.

Claims

1. A pressed powder magnetic core, comprising: Magnetic nanoparticles with an average particle size of 1–300 nm, and 3,4,5-Trihydroxybenzoic acid, The pressed magnetic core is obtained by pressing the magnetic nanoparticles with 3,4,5-trihydroxybenzoic acid under pressure at a molding temperature of 300-600℃ and a molding pressure of 500MPa-3Gpa.

2. The pressed powder magnetic core according to claim 1, wherein, The content of the 3,4,5-trihydroxybenzoic acid is 0.01% to 5% by mass relative to the total amount of the magnetic nanoparticles and the 3,4,5-trihydroxybenzoic acid.

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