JP7804931B2 - Magnetic resin composition and processed products - Google Patents

Description

This disclosure relates generally to magnetic resin compositions and processed articles, and more specifically to magnetic resin compositions containing ferrite particles and processed articles made using the same.

Magnetic materials are used in applications such as inductors, motors, and antenna modules. Known magnetic materials include magnetic resin compositions that are paste-like and easily processed into desired shapes and properties depending on the purpose and application.

For example, Patent Document 1 proposes an invention related to a magnetic paste containing magnetic powder with a predetermined particle size distribution and a binder resin, and describes that this magnetic paste suppresses uneven distribution of the magnetic powder that occurs over time or with degassing operations such as centrifugation.

International Publication No. 2020/075745

Magnetic resin compositions used in applications such as inductors are required to have high magnetic permeability and a low loss factor. Furthermore, with the recent trend toward miniaturization of electronic components and finer patterning of wiring boards, there is also a demand for improved filling capabilities of the composition during processing. For example, when filling small through-holes with a diameter of approximately 500 μm or less with a magnetic resin composition, it is desirable for the composition to have low viscosity and low thixotropy. Furthermore, since processed products made using magnetic resin compositions are expected to be able to be used without problems in high-temperature environments, they are also desirable for the composition to have a high glass transition temperature, which indicates excellent heat resistance.

The present disclosure has been made to solve the above problems, and aims to provide a magnetic resin composition and processed product that exhibits low viscosity and low thixotropy while maintaining favorable magnetic permeability and loss factor, and that has a glass transition temperature in the cured product that is high enough to exhibit excellent heat resistance.

A magnetic resin composition according to one embodiment of the present disclosure contains ferrite particles (A) having a particle size (D50) at 50% cumulative total in the particle size distribution of 0.05 μm or more and 0.50 μm or less, magnetic particles (B) having a D50 of 3.0 μm or more and a particle size (D90) at 90% cumulative total in the particle size distribution of 5.0 μm or more, a liquid epoxy compound (C) that is liquid at 25°C, and a curing agent (D). The liquid epoxy compound (C) includes a liquid epoxy compound (C-1) having two or less epoxy groups per molecule and a multifunctional liquid epoxy compound (C-2) having three or more epoxy groups per molecule.

A processed product according to one embodiment of the present disclosure includes a cured product of the magnetic resin composition.

According to the present disclosure, the magnetic resin composition exhibits low viscosity and low thixotropy while maintaining suitable magnetic permeability and loss factor, and the cured product has a glass transition temperature high enough to exhibit excellent heat resistance. The processed product exhibits excellent heat resistance while maintaining suitable magnetic permeability and loss factor.

(1) Magnetic Resin Composition The magnetic resin composition according to this embodiment contains a magnetic filler and a resin material. The magnetic filler includes ferrite particles (A) and magnetic particles (B). The resin material includes a liquid epoxy compound (C) and a curing agent (D).

Here, the liquid epoxy compound (C) is liquid at 25°C. The liquid epoxy compound (C) includes a liquid epoxy compound (C-1) having two or less epoxy groups per molecule and a multifunctional liquid epoxy compound (C-2) having three or more epoxy groups per molecule.

When measured at 25°C and 5 rpm, the E-type viscosity of the magnetic resin composition is preferably 20 Pa·s or more and 50 Pa·s or less, and the thixotropy index is preferably 1.5 or more and 5.0 or less. By keeping the values within this range, even when filling through holes with an inner diameter of 500 μm or less with the magnetic resin composition, voids and filling defects are less likely to occur, and filling can be carried out without any problems.

The glass transition temperature (Tg) of the cured magnetic resin composition is preferably 100°C or higher. Cured magnetic resin compositions that satisfy this requirement have excellent heat resistance.

(1.1) Magnetic Filler As described above, the magnetic filler includes ferrite particles (A) and magnetic particles (B). The magnetic filler is a particulate material that can be magnetized. In this way, when the magnetic resin composition includes ferrite particles (A) and magnetic particles (B), a processed product having magnetic properties can be obtained. The processed product includes a cured product of the magnetic resin composition. The magnetic properties are magnetic properties exhibited when magnetized. Specific examples of magnetic properties include magnetic permeability and magnetic flux density.

As described above, the processed product has magnetic properties, and the processed product according to this embodiment in particular can have high magnetic permeability at high frequencies. The high-frequency frequency band is, for example, from several MHz to several GHz, including 70 MHz. The real part (μr') of the complex relative magnetic permeability (μr) of the processed product at 70 MHz is preferably 6.0 or greater. This can further increase the magnetic permeability at high frequencies. In addition, the loss factor (tan δ) of the processed product at 70 MHz is preferably 0.10 or less, and more preferably 0.08 or less. This can further reduce loss.

Complex relative magnetic permeability (μr) is expressed by the formula μr = μ/μ0 (μ: complex magnetic permeability, μ0: magnetic permeability of a vacuum). Complex relative magnetic permeability (μ) is expressed by the formula μ = μ' - iμ" (μ': real part, μ": imaginary part, i: imaginary unit). In this embodiment, "permeability" mainly refers to the real part (μr') of complex relative magnetic permeability (μr). The real part (μr') of complex relative magnetic permeability (μr) is expressed by the formula μr' = μ'/μ0. The imaginary part (μr") of complex relative magnetic permeability (μr) is expressed by the formula μr" = μ"/μ0. The loss factor (tan δ) is expressed by the formula tan δ = μr"/μr' = μ"/μ'. The relationship between complex relative magnetic permeability (μr) can be summarized as follows: Formula (1).

"50% volume average particle diameter" refers to the particle size (D50) at 50% of the cumulative value in the particle size distribution measured using a particle size distribution measuring device based on the laser scattering/diffraction method. Note that "D50 of ferrite particles (A)" refers to the D50 of all particulate matter contained in ferrite particles (A), and "D50 of magnetic particles (B)" refers to the D50 of all particulate matter contained in magnetic particles (B).

"90% volume average particle diameter" refers to the particle size (D90) at 90% of the cumulative value in the particle size distribution measured using a particle size distribution measuring device based on the laser scattering/diffraction method. Note that "D90 of ferrite particles (A)" refers to the D90 of all particulate matter contained in ferrite particles (A), and "D90 of magnetic particles (B)" refers to the D90 of all particulate matter contained in magnetic particles (B).

<Ferrite particles (A)>
The ferrite particles (A) have a D50 of 0.05 μm or more and 0.50 μm or less. By including fine ferrite particles (A) in the magnetic resin composition in this way, the viscosity of the magnetic resin composition can be reduced.

The ferrite particles (A) contain at least one type of ferrite. Ferrite is a ceramic filler whose main component is iron oxide. Ferrite includes soft ferrite, which exhibits soft magnetic properties, and hard ferrite, which exhibits hard magnetic properties. Ferrite is classified into spinel ferrite, hexagonal ferrite, garnet ferrite, etc., depending on its crystal structure.

Spinel ferrite has a spinel-type crystal structure. The composition formula of spinel ferrite is expressed as AFe ₂ O ₄ (A is Mn, Co, Ni, Cu, Zn, etc.). Most spinel ferrites are soft ferrites. Spinel ferrites include, for example, manganese zinc ferrite (Mn-Zn ferrite), nickel zinc ferrite (Ni-Zn ferrite), copper zinc ferrite (Cu-Zn ferrite), etc. Spinel ferrite has high magnetic permeability and electrical resistance, resulting in low eddy current loss in the high frequency band. Magnetite is also a type of spinel ferrite. The composition formula of magnetite is expressed as Fe ₃ O ₄ .

Hexagonal ferrite has a magnetoplumbite-type hexagonal crystal structure. The composition formula of hexagonal ferrite is expressed as AFe ₁₂ O ₁₉ (A is Ba, Sr, Pb, etc.). Hexagonal ferrite is also called magnetoplumbite-type ferrite or M-type ferrite. Hexagonal ferrite has a larger magnetic anisotropy than spinel ferrite, and therefore exhibits a larger coercive force. Hexagonal ferrite is a typical hard ferrite.

Garnet ferrite has a garnet-type crystal structure. The composition formula of garnet ferrite is expressed as RFe ₅ O ₁₂ (R is a rare earth element). Garnet ferrite is also called rare-earth iron garnet (RIG). A typical example of garnet ferrite is yttrium iron garnet (YIG). Garnet ferrite has small magnetic loss at high frequencies.

By containing at least one type of ferrite in the ferrite particles (A), the magnetic permeability of the processed product at high frequencies can be increased.

The ferrite particles (A) preferably contain at least one selected from the group consisting of Mn ferrite (manganese ferrite), Mn-Zn ferrite (manganese zinc ferrite), and magnetite, and more preferably contain at least one selected from the group consisting of Mn ferrite and magnetite.

Manganese-based ferrite is a ferrite containing manganese. Examples of manganese-based ferrites include, but are not limited to, manganese ferrite (Mn ferrite), manganese zinc ferrite (Mn-Zn ferrite), iron-manganese ferrite (Fe-Mn ferrite), manganese magnesium ferrite (Mn-Mg ferrite), and magnesium manganese strontium ferrite (Mg-Mn-Sr ferrite). When the ferrite particles (A) contain at least one type selected from the group consisting of manganese-based ferrite and magnetite, the processed product has a good balance of magnetic permeability and loss factor (tan δ). In other words, the processed product can be made to have a high magnetic permeability and a low loss factor (tan δ). Furthermore, by including magnetite in the magnetic resin composition, the viscosity of the magnetic resin composition can be reduced.

The ferrite particles (A) preferably contain spherical particles, and more preferably, at least one of Mn ferrite, Mn-Zn ferrite, and magnetite contains spherical particles. This improves the fluidity of the magnetic resin composition, making it easier to mold processed products. It also allows for a high loading of the ferrite particles (A). High loading of the ferrite particles (A) in particular allows for a high magnetic permeability of the processed product. It also improves the drillability of the processed product. Drillability is a measure of the ease with which a processed product can be machined when drilling holes in the processed product. Drillability is evaluated using wear rates and other parameters. The ferrite particles (A) may contain particles with shapes other than spherical. Shapes other than spherical are not particularly limited, but examples include ellipsoids, flattened shapes, crushed shapes, and amorphous shapes.

The content of ferrite particles (A) is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 1% by mass or more and 10% by mass or less, relative to the total mass of the magnetic resin composition. By keeping the content within this range, the viscosity and thixotropy of the magnetic resin composition can be reduced.

It is preferable that the magnetic resin composition be substantially free of sendust and amorphous alloys (non-crystalline alloys). Here, sendust is a ternary alloy (Fe-Si-Al alloy) composed of iron, silicon, and aluminum. The basic composition of sendust is Fe-10Si-5Al. On the other hand, amorphous alloys are disordered alloys with no regularity in the arrangement of elements. As described above, if the magnetic resin composition is substantially free of sendust and amorphous alloys, deterioration in machinability can be suppressed. However, at least one of sendust and amorphous alloys may be contained in the magnetic resin composition as an unavoidable impurity.

<Magnetic particles (B)>
The D50 of the magnetic particles (B) is 3.0 μm or more, and the D90 of the magnetic particles (B) is 5.0 μm or more. Preferably, the D50 of the magnetic particles (B) is 3.0 μm or more and 6.0 μm or less, and the D90 of the magnetic particles (B) is 10.0 μm or more and 20.0 μm or less. By keeping the D50 within these ranges, the drilling processability of the cured product can be further improved.

The magnetic particles (B) contain at least one type of ferrite. The crystal structure, properties, and preferred shape of the ferrite in the magnetic particles (B) are the same as those of the ferrite particles (A) described above.

The magnetic particles (B) preferably contain Mn ferrite and/or Mn-Zn ferrite, and more preferably contain Mn ferrite. In this specification, "X and/or Y" means "X," "Y," or "X and Y."

The magnetic particles (B) preferably contain spherical particles, and it is more preferable that the Mn ferrite and/or Mn-Zn ferrite contain spherical particles. This improves the fluidity of the magnetic resin composition, making it easier to mold processed products. It also allows for a high packing density of the magnetic particles (B). In particular, a high packing density of the magnetic particles (B) can increase the magnetic permeability of the processed product. It also improves the drillability of the processed product. The magnetic particles (B) may also contain particles with shapes other than spherical.

The content of magnetic particles (B) is preferably 75% by mass or more and 95% by mass or less, and more preferably 80% by mass or more and 90% by mass or less, relative to the total mass of the magnetic resin composition. By keeping the content within this range, it is possible to increase magnetic permeability while reducing viscosity.

(1.2) Resin Material The resin material can function as a binder. As described above, the resin material contains a liquid epoxy compound (C) and a curing agent (D). The resin material may contain additives and/or solvents. When the resin material contains the liquid epoxy compound (C), it becomes easier to mold a processed product from the magnetic resin composition. Furthermore, when the resin material contains a self-polymerizing material, the pot life (usable time) of the magnetic resin composition can be extended. Furthermore, a processed product exhibiting a high glass transition temperature with excellent heat resistance can be obtained by thermal curing in a short time.

<Liquid Epoxy Compound (C)>
The liquid epoxy compound (C) is liquid at 25°C and includes a liquid epoxy compound (C-1) having two or less epoxy groups in the molecule and a polyfunctional liquid epoxy compound (C-2) having three or more epoxy groups in the molecule.

The liquid epoxy compound (C) preferably contains at least one selected from the group consisting of bisphenol F type epoxy resin, bisphenol A type epoxy resin, alkyl diglycidyl ether, alkyl monoglycidyl ether, and alkylphenol monoglycidyl ether.

The epoxy equivalent of the liquid epoxy compound (C) is not particularly limited, but is preferably 90 g/eq or more and 200 g/eq or less.

The liquid epoxy compound (C-1) is a liquid epoxy compound that is liquid at 25°C and has two or less (one or two) epoxy groups per molecule. It is particularly preferable that the liquid epoxy compound (C-1) has two epoxy groups per molecule. The liquid epoxy compound (C-1) may be used alone or in combination with two or more types.

The viscosity of the liquid epoxy compound (C-1) at 25°C is not particularly limited. For example, the viscosity of the liquid epoxy compound (C-1) at 25°C may be 500 mPa·s or less, or may exceed 500 mPa·s.

The liquid epoxy compound (C-1) preferably contains an epoxy-based reactive diluent (C-3). This reduces the viscosity of the magnetic resin composition.

Here, the epoxy-based reactive diluent (C-3) is a liquid epoxy compound that is liquid at 25°C and has a viscosity of 500 mPa·s or less. The viscosity of the epoxy-based reactive diluent (C-3) is not particularly limited as long as it is 500 mPa·s or less, but a viscosity of 10 mPa·s or more and 500 mPa·s or less is preferable. In other words, the epoxy-based reactive diluent (C-3) refers to a liquid epoxy compound (C-1) that has a viscosity of 500 mPa·s or less at 25°C. Thus, because the epoxy-based reactive diluent (C-3) has a viscosity of 500 mPa·s or less at 25°C, it reduces the viscosity and thixotropy of the magnetic resin composition.

The epoxy-based reactive diluent (C-3) has two or less epoxy groups per molecule. It is particularly preferable that the epoxy-based reactive diluent (C-3) has two epoxy groups per molecule.

The polyfunctional liquid epoxy compound (C-2) is a polyfunctional liquid epoxy compound that is liquid at 25°C and has three or more epoxy groups per molecule. The upper limit of the number of epoxy groups per molecule of the polyfunctional liquid epoxy compound (C-2) is preferably four, and more preferably three. The polyfunctional liquid epoxy compound (C-2) may be used alone or in combination with two or more types. By including the polyfunctional liquid epoxy compound (C-2) in the liquid epoxy compound (C), the glass transition temperature of the cured product of the magnetic resin composition can be increased, thereby improving heat resistance.

The viscosity of the polyfunctional liquid epoxy compound (C-2) at 25°C is not particularly limited, but is, for example, 10 mPa·s or more and 1,300 mPa·s or less.

The content of the polyfunctional liquid epoxy compound (C-2) is preferably 10% by mass or more and 80% by mass or less, and more preferably 25% by mass or more and 70% by mass or less, based on the total mass of the liquid epoxy compound (C). By keeping the content within this range, it is possible to achieve both low viscosity and good thixotropy of the magnetic resin composition. Furthermore, the cured product of the magnetic resin composition can have an increased glass transition temperature and improved heat resistance.

In particular, when the liquid epoxy compound (C) contains a liquid epoxy compound (C-1) with a viscosity of greater than 500 mPa·s, a polyfunctional epoxy resin compound (C-2), and an epoxy-based reactive diluent (C-3), the content of the polyfunctional liquid epoxy compound (C-2) is preferably 25% by mass or more and 70% by mass or less, based on the total mass of the liquid epoxy compound (C). By keeping the content within this range, the magnetic resin composition can achieve both low viscosity and good thixotropy. Furthermore, the cured product of the magnetic resin composition can have an increased glass transition temperature and improved heat resistance.

<Curing Agent (D)>
The curing agent (D) is not particularly limited, but examples thereof include phenol compounds, acid anhydride compounds, amine compounds, and imidazole compounds. Among these, imidazole compounds are preferred. Imidazole compounds are a type of curing accelerator and are effective in improving the storage stability and reducing the viscosity of the magnetic resin composition. Thus, the curing agent (D) may contain a curing accelerator.

The curing agent (D) is preferably liquid. If the curing agent (D) is liquid, it is easier to make the magnetic resin composition into a paste.

The curing accelerator is not particularly limited, but examples include the imidazole compounds mentioned above. The curing accelerator is preferably encapsulated in a capsule. If the curing accelerator is encapsulated in a capsule, the storage stability of the magnetic resin composition can be improved. Furthermore, by changing the capsule thickness, the curing initiation temperature of the magnetic resin composition can be controlled, and the curing behavior can be adjusted to suit the usage form. For example, by making the capsule thickness thin, the reaction can be initiated at a low temperature. On the other hand, by making the capsule thickness thick, the reaction can be initiated at a high temperature and storage stability at low temperatures and room temperature can be improved.

<Additives>
The magnetic resin composition may contain additives within the range that does not impair the effects of this embodiment.

Additives are not particularly limited, but examples include silane coupling agents, dispersants, leveling agents, adhesion promoters, and antistatic agents. In particular, when a silane coupling agent and a dispersant are contained in the magnetic resin composition, they can improve the dispersibility of the ferrite particles (A) and magnetic powder (B) in the magnetic resin composition.

Silane coupling agents are not particularly limited, but examples include epoxy group-containing alkoxysilane compounds such as γ-glycidoxypropyltrimethoxysilane, mercapto group-containing alkoxysilane compounds such as γ-mercaptopropyltriethoxysilane, and amino group-containing alkoxysilane compounds such as γ-(2-aminoethyl)aminopropylmethyldimethoxysilane.

A variety of dispersants commonly used can be used as dispersants. Specific examples of dispersants include hyperbranched polyesters, hydroxyl-containing carboxylic acid esters, and alkylammonium salts and phosphate ester salts of polymeric copolymers. Commercially available dispersants include the DISPERBYK series manufactured by BYK Chemie Corporation.

<Solvent>
The solvent is not particularly limited, but examples thereof include methyl ethyl ketone (MEK), N,N-dimethylformamide (DMF), acetone, and methyl isobutyl ketone (MIBK).

(1.3) Manufacturing Method The magnetic resin composition can be manufactured by uniformly mixing the raw materials, ferrite particles (A), magnetic particles (B), liquid epoxy compound (C), and curing agent (D). A known mixer can be used to mix the raw materials.

(1.4) Material Forms Obtained Using the Magnetic Resin Composition Examples of material forms obtainable using the magnetic resin composition according to this embodiment include paste, slurry, sheet, powder, prepreg, and the like. These material forms may include the magnetic resin composition or a semi-cured product of the magnetic resin composition. A "semi-cured product" refers to a magnetic resin composition that has been partially cured to the extent that it can be further cured. In other words, a semi-cured product is a magnetic resin composition that has been semi-cured (B-staged). These material forms can be obtained by coating, heat drying, heat curing, pressurizing, kneading, and impregnation.

(1.5) Uses The processed product according to this embodiment includes a cured product of the magnetic resin composition described above. The processed product may be used to manufacture inductor components and embedded substrate components.

The inductor component comprises a coiled wiring and an insulating layer that covers the coiled wiring. The insulating layer has electrical insulation properties and includes the processed product according to this embodiment. This makes it easier for the inductor component to control noise in the high frequency band. Inductor components include coils, inductors, filters, reactors, and transformers. Applications for inductor components are not particularly limited, but examples include noise filter components and impedance matching circuit components. Examples of noise filters include low-pass filters and common choke coils.

The embedded-substrate component comprises a substrate and an insulating layer covering the substrate. The insulating layer includes the processed product according to this embodiment. This makes it easier to impart magnetic properties to the embedded-substrate component. Applications for the embedded-substrate component are not particularly limited, but examples include inductors.

The present disclosure will be specifically explained below using examples. However, the present disclosure is not limited to these examples.

(1) Preparation of Magnetic Resin Composition A magnetic resin composition in paste form (hereinafter also referred to as "magnetic paste") was prepared. The raw materials of the magnetic paste are shown below.

(1.1) Magnetic Filler Ferrite Particles (A)
Mn ferrite (D50: 0.3 μm)
・Mn-Zn ferrite (D50: 0.3 μm)
Magnetite (D50: 0.3 μm)
Magnetic particles (B)
Mn ferrite (D50: 5.0 μm, D90: 15 μm)
・Mn-Zn ferrite (D50: 5.0 μm, D90: 15 μm)
Mn ferrite (D50: 3.5 μm, D90: 9.0 μm)
・Mn-Zn ferrite (D50: 3.5 μm, D90: 9.0 μm)
Others: Mn ferrite (D50: 0.6 μm, D90: 2.0 μm).

(1.2) Resin Material Liquid Epoxy Compound (C)
Liquid epoxy compound (C-1)
Bisphenol F type epoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., product name "YDF-8170C", liquid, number of epoxy groups per molecule: 2, viscosity at 25°C: 1300 mPa s, epoxy equivalent: 155 to 165 g/eq)
Multifunctional liquid epoxy compound (C-2)
- Multifunctional epoxy resin (manufactured by ADEKA Corporation, product name "EP-3950S", glycidylamine type, number of epoxy groups in molecule: 3, viscosity at 25°C: 650 mPa s, epoxy equivalent: 95 g/eq)
Epoxy-based reactive diluent (C-3)
Reactive diluent (manufactured by Mitsubishi Chemical Corporation, trade name "YED216D", liquid, number of epoxy groups in molecule: 2, viscosity at 25°C: 10 mPa·s, epoxy equivalent: 110 to 130 g/eq).

Curing agent (D)
Imidazole compound (manufactured by Shikoku Chemicals Corporation, trade name "2MAOK-PW", imidazole-based epoxy resin curing agent, fine powder).

<Additives>
Silane coupling agent (manufactured by Momentive Performance Materials Japan, LLC, product name "Silquest A-187")
Dispersant (manufactured by BYK Japan Co., Ltd., product name "DISPERBYK-2152").

(2) Evaluation Items (2.1) Viscosity The viscosity of the magnetic paste was measured using an E-type viscometer (TA Instruments, Rheometer, model "AR2000ex"). Specifically, the gap between upper and lower parallel plates with a diameter of 25 mm was set to 300 μm, and the magnetic paste was filled into this gap. After a temperature equilibration time of 2 minutes was allowed to pass at room temperature, the viscosity was measured at a rotation speed of 5.0 rpm. The E-type viscosities of the magnetic pastes are shown in Tables 1 to 3.

(2.2) Thixotropy Index Using the above-mentioned E-type viscometer, viscosity measurements were performed at rotation speeds of 0.5 rpm and 5.0 rpm. Settings other than the rotation speed were the same as in (2.1). The thixotropy index was then calculated using the following formula (2). The thixotropy indexes of the magnetic pastes are shown in Tables 1 to 3. In formula (2), the denominator on the right side is the E-type viscosity at a rotation speed of 5.0 rpm, and the numerator is the E-type viscosity at a rotation speed of 0.5 rpm.

(2.3) Magnetic Properties The magnetic paste was heated and cured in the atmosphere to obtain a ring-shaped evaluation product (outer diameter 7.0 mm, inner diameter 3.5 mm, thickness 1.0 mm). The heating conditions were 130° C. for 2 hours.

Next, the complex permeability (μ) of the above-mentioned evaluation processed product at 70 MHz was measured using a Hewlett-Packard Model 4291ARF Impedance/Material Analyzer. The measurement was carried out at room temperature with a current frequency of 1 MHz to 500 MHz. From the initial magnetization curve obtained by measurement, the permeability (real part (μr') of complex relative permeability (μr)) and imaginary part (μr") were obtained, and the loss factor (tan δ) was calculated from these. The permeability and loss factor of the above-mentioned evaluation processed product are shown in Tables 1 to 3.

(2.4) Glass transition temperature (Tg)
The glass transition temperature of the cured magnetic paste was measured using a viscoelasticity spectrometer, model "DMS100," manufactured by Seiko Instruments Inc. Dynamic mechanical analysis (DMA) was performed using a bending module at a frequency of 10 Hz, and the temperature at which the loss tangent (tan δ) reached a maximum when the temperature was raised from room temperature to 280°C at a heating rate of 5°C/min was taken as the glass transition temperature. The glass transition temperatures of the cured magnetic pastes are shown in Tables 1 to 3.

Claims (9)

A magnetic resin composition,
The magnetic resin composition is
Ferrite particles (A) having a particle size (D50) at 50% cumulative particle size distribution of 0.05 μm or more and 0.50 μm or less;
magnetic particles (B) having a D50 of 3.0 μm or more and 6.0 μm or less and a particle size at 90% cumulative value in the particle size distribution (D90) of 10.0 μm or more and 20.0 μm or less;
a liquid epoxy compound (C) that is liquid at 25°C;
and a curing agent (D),
The content of the ferrite particles (A) is 0.1% by mass or more and 20.0% by mass or less relative to the total mass of the magnetic resin composition,
The content of the magnetic particles (B) is 75% by mass or more and 95% by mass or less with respect to the total mass of the magnetic resin composition,
the magnetic particles (B) are made of Mn ferrite and/or Mn—Zn ferrite,
The liquid epoxy compound (C) comprises a liquid epoxy compound (C-1) having two or less epoxy groups in the molecule and a polyfunctional liquid epoxy compound (C-2) having three or more epoxy groups in the molecule,
The liquid epoxy compound (C-1) contains an epoxy-based reactive diluent (C-3).
Magnetic resin composition. The ferrite particles (A) contain at least one selected from the group consisting of Mn ferrite, Mn—Zn ferrite, and magnetite.
The magnetic resin composition according to claim 1 . The ferrite particles (A) and/or the magnetic particles (B) include spherical particles.
The magnetic resin composition according to claim 1 or 2. The liquid epoxy compound (C) contains at least one selected from the group consisting of bisphenol F epoxy resins, bisphenol A epoxy resins, alkyl diglycidyl ethers, alkyl monoglycidyl ethers, and alkylphenol monoglycidyl ethers.
The magnetic resin composition according to any one of claims 1 to 3. The content of the polyfunctional liquid epoxy compound (C-2) is 10% by mass or more and 80% by mass or less based on the total mass of the liquid epoxy compound (C).
The magnetic resin composition according to any one of claims 1 to 4. The content of the polyfunctional liquid epoxy compound (C-2) is 25% by mass or more and 70% by mass or less based on the total mass of the liquid epoxy compound (C).
The magnetic resin composition according to any one of claims 1 to 5. The magnetic resin composition has an E-type viscosity of 50 Pa s or less at a rotation speed of 5.0 rpm.
The magnetic resin composition according to any one of claims 1 to 6. The magnetic resin composition has a thixotropy index (E-type viscosity at a rotation speed of 0.5 rpm/E-type viscosity at a rotation speed of 5.0 rpm) of 5.0 or less.
The magnetic resin composition according to any one of claims 1 to 7. A cured product of the magnetic resin composition according to any one of claims 1 to 8,
Processed products.