Hexagonal magnetoplumbite-type ferrite powder, ferrite resin composite material, ferrite resin composite, and electromagnetic wave absorber

Abstract

The present invention is a hexagonal magnetoplumbite-type ferrite powder containing 50.0-65.0 mass% of iron (Fe), 6.0-9.0 mass% of strontium (Sr), and 0.3-14.0 mass% of zirconium (Zr), wherein the content of divalent iron ions (Fe2+) is 0.5-5.5 mass%, the content of a magnetite (Fe3O4) phase is 5.0-20.0 mass%, the saturation magnetization is 50-75 emu / g, and the volume resistivity is 1.0×109Ω·cm or less.

Description

Hexagonal magnetoplanvite-type ferrite powder, ferrite resin composite material, ferrite resin composite, and electromagnetic wave absorber

[0001] The present invention relates to hexagonal magnetoplanvite-type ferrite powder, ferrite resin composite materials, ferrite resin composites, and electromagnetic wave absorbers.

[0002] Recent advancements in information and communication technology have led to the development and utilization of a wide variety of information and communication devices. Furthermore, the frequency bands used are shifting towards higher frequencies, including microwaves. In particular, the 8-12 GHz frequency band known as the X-band (classified by the IEEE) is seeing increasing use in a diverse range of applications, primarily military satellites, weather satellites, Earth observation satellites, navigation radars, surface operation radars, air search radars, fire control radars, and amateur radio.

[0003] The use of information and communication equipment generates unintended electromagnetic waves. These unintended electromagnetic waves can cause electromagnetic interference (EMI). Specifically, they can cause malfunctions or failures in other equipment, or have adverse effects on the human body. Therefore, the importance of electromagnetic compatibility (EMC) measures to improve the electromagnetic environment is strongly recognized. As a concrete means of EMC countermeasures, methods are used to absorb unwanted electromagnetic waves using electromagnetic wave absorbers to suppress their effects.

[0004] Magnetic materials, dielectric materials, and / or conductive materials are used as electromagnetic wave absorbers. In magnetic materials, magnetic resonance occurs with respect to electromagnetic waves of specific frequencies. In this case, magnetic materials exhibit large magnetic losses, and much of the electromagnetic wave energy is absorbed by the material and converted into thermal energy. Therefore, electromagnetic wave absorption is possible by utilizing magnetic loss. In dielectric materials, dielectric loss occurs due to the phase difference between the phase of the electromagnetic wave and the phase difference of the dielectric polarization, and electromagnetic wave absorption is possible by utilizing this dielectric loss.

[0005] Ferrite has been proposed as a magnetic material for electromagnetic wave absorbers, and among them, sintered bodies such as spinel-type ferrite and magnetic composites are widely used. Patent document 1 discloses such technology, specifically regarding Fe... ２ O ３ A radio wave absorber has been proposed that consists of a spinel main phase containing 40.0 to 49.9 mol% of nitrile, 4.0 to 26.5 mol% of ZnO, and the remainder being MnO, and a subphase containing CaO as the main component, wherein the mass ratio of the spinel main phase is 50 to 99 mass% of the total mass of the spinel main phase and the subphase (Claim 1 of Patent Document 1).

[0006] Japanese Patent Application Publication No. 2004-247603

[0007] While the use of spinel-type ferrite as a magnetic material for electromagnetic wave absorbers has been proposed for some time, there was room for improvement in conventional technology. Specifically, a theory known as the Snake's limit is known regarding magnetism. According to this theory, for materials with low magnetic anisotropy such as spinel-type ferrite, the product of the upper limit of magnetic permeability and the resonance frequency is constant. Therefore, it is not possible to increase the resonance frequency while maintaining high magnetic permeability, and consequently, it has been difficult to obtain excellent electromagnetic wave absorption performance in the high-frequency range, including microwaves.

[0008] In view of these problems, the inventors conducted diligent research. As a result, they found that a hexagonal magnetoplanbite-type ferrite powder containing predetermined amounts of iron, strontium, and zirconium, with divalent iron ions and magnetite phase content within predetermined ranges, and further having saturation magnetization and volume resistivity within predetermined ranges, exhibits excellent electromagnetic wave absorption performance in the microwave frequency band, particularly in the 7-13 GHz frequency band.

[0009] The present invention was completed based on such findings, and aims to provide a ferrite powder that exhibits excellent electromagnetic wave absorption performance in the microwave frequency band, particularly in the 7-13 GHz frequency band, as well as a ferrite resin composite material, a ferrite resin composite, and an electromagnetic wave absorber containing the ferrite powder.

[0010] The present invention encompasses the following embodiments (1) to (7). In this specification, the expression "~" includes the numerical values ​​at both ends. That is, "X~Y" is synonymous with "X or more and Y or less".

[0011] (1) A hexagonal magnetoplanbite-type ferrite powder containing iron (Fe) in amounts of 50.0% to 65.0% by mass, strontium (Sr) in amounts of 6.0% to 9.0% by mass, and zirconium (Zr) in amounts of 0.3% to 14.0% by mass, wherein divalent iron ions (Fe ２＋ The content of ) is 0.5% by mass or more and 5.5% by mass or less, and magnetite (Fe ３ O ４ The phase content is 5.0% by mass or more and 20.0% by mass or less, the saturation magnetization is 50 emu / g or more and 75 emu / g or less, and the volume resistivity is 1.0 × 10⁻⁶ ９ Ferrite powder with a density of Ω·cm or less.

[0012] (2) The ferrite powder of the above (1), wherein the average particle size (D50) is 3.0 μm or more and 35.0 μm or less.

[0013] (3) The ferrite powder according to (1) or (2) above, having a resonant frequency in the frequency range of 7 GHz to 13 GHz, and having an imaginary component (μ'') of the complex relative permeability at the resonant frequency of 1.0 or more.

[0014] (4) The ferrite powder according to (3) above, wherein the imaginary component (ε'') of the complex relative permittivity at the resonance frequency is 30 or more.

[0015] (5) A ferrite resin composite material comprising any of the ferrite powders and resins described in (1) to (4) above.

[0016] (6) A ferrite resin composite, which is a molded body of the ferrite resin composite material described in (5) above.

[0017] (7) An electromagnetic wave absorber comprising the ferrite resin composite described in (6) above.

[0018] According to the present invention, there are provided ferrite powders exhibiting excellent electromagnetic wave absorption performance in the microwave frequency band, particularly in the frequency band of 7 to 13 GHz, and ferrite resin composite materials, ferrite resin composites, and electromagnetic wave absorbers containing the ferrite powders.

[0019] Specific embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described below. However, the present invention is not limited to the following embodiments, and various modifications are possible without changing the gist of the present invention. Also, in this specification, as long as technical consistency can be achieved, any combination of suitable aspects can be adopted. For example, one and the other of suitable numerical ranges can be arbitrarily combined. <(

[0020] <<1. Ferrite Powder>> The hexagonal magnetoplumbite-type ferrite powder of the present embodiment (hereinafter sometimes simply referred to as "ferrite powder") contains iron (Fe) in an amount of 50.0 mass% or more and 65.0 mass% or less, strontium (Sr) in an amount of 6.0 mass% or more and 9.0 mass% or less, and zirconium (Zr) in an amount of 0.3 mass% or more and 14.0 mass% or less. Also, the content of divalent iron ions (Fe ２＋ ) in this ferrite powder is 0.5 mass% or more and 5.5 mass% or less, and the content of the magnetite (Fe ３ O ４ ) phase is 5.0 mass% or more and 20.0 mass% or less. Further, the saturation magnetization of the ferrite powder is 50 emu / g or more and 75 emu / g or less, and the volume resistivity is 1.0×10 ９ Ω·cm or less. Such ferrite powder exhibits excellent electromagnetic wave absorption performance in the microwave frequency band.

[0021] The ferrite powder of the present embodiment mainly contains a hexagonal magnetoplumbite-type ferrite phase (hereinafter sometimes referred to as "M-type ferrite phase"). The M-type ferrite phase has a composition represented by the general formula: AFe １２ O １９ (where A is a metal element such as strontium (Sr) or barium (Ba)), and is a ferromagnetic material having a hexagonal crystal structure (space group: P63 / mmc). A (Sr, Ba, etc.) is usually a divalent ion (M２＋ It is contained in the M-type ferrite phase in the form of ). Iron (Fe) is usually a trivalent ion (Fe ３＋ It is included in the form of iron ions (Fe ３＋ ) may also be substituted with other transition metal ions of similar size.

[0022] By using an M-type ferrite phase as the main phase, it becomes possible to impart excellent electromagnetic wave absorption performance in the high-frequency band to the ferrite powder. That is, ferromagnetic materials exhibit high magnetic loss at a specific frequency (resonance frequency) due to ferromagnetic resonance (FMR). It is also known that the resonance frequency at which magnetic loss is exhibited (FMR frequency) is proportional to the magnitude of the magnetic anisotropy of the material (magnetic anisotropy constant). In this respect, the M-type ferrite phase is a ferromagnetic material. Furthermore, it has uniaxial magnetic anisotropy and high magnetic anisotropy. Therefore, by using such an M-type ferrite phase as the main component, it is possible to obtain a ferrite powder with a high FMR frequency and excellent electromagnetic wave absorption performance (EMI shielding performance) in the high-frequency band. Specifically, FMR can be induced in the frequency band from 7 GHz to 13 GHz.

[0023] In this specification, the main phase refers to the crystalline phase with the largest mass in the ferrite powder. That is, the ferrite powder contains 50% or more by mass of the M-type ferrite phase. From the viewpoint of taking advantage of the excellent effects based on the M-type ferrite phase, a higher proportion of the M-type ferrite phase is preferable. On the other hand, if the proportion of the M-type ferrite phase is excessively high, other ferromagnetic materials such as magnetite (Fe) ３ O ４ The proportion of the ) phase decreases. Therefore, it becomes difficult to take advantage of the effects based on the magnetite phase. From the viewpoint of further improving electromagnetic wave absorption performance, the content of the M-type ferrite phase is preferably 75.0% by mass or more and 95.0% by mass or less, more preferably 75.0% by mass or more and 90.0% by mass or less, and even more preferably 75.0% by mass or more and 85.0% by mass or less. The content of the M-type ferrite phase and other crystalline phases can be determined by analyzing the ferrite powder by X-ray diffraction and performing Rietveld analysis on the obtained X-ray diffraction pattern. Specifically, it can be determined by the method described in the examples below or a similar method.

[0024] The ferrite powder of this embodiment contains iron (Fe) in an amount of 50.0% by mass or more and 65.0% by mass or less. Ferrite powder containing an appropriate amount of Fe has electromagnetic wave absorption performance suitable for the desired application. If the amount of Fe is less than 50.0% by mass, the magnetic properties, especially saturation magnetization and permeability, become low, and the electromagnetic wave absorption performance decreases. If the amount of Fe exceeds 65.0% by mass, it becomes an Fe excess composition. Hematite (α-Fe ２ O ３ Because other phases, such as the ) phase, are formed in the ferrite powder, the electromagnetic wave absorption performance is also reduced. From the viewpoint of further improving the electromagnetic wave absorption performance, the Fe content is preferably 53.0% by mass or more and 63.0% by mass or less, and more preferably 55.0% by mass or more and 60.0% by mass or less. In one preferred embodiment, the Fe content in the ferrite powder is preferably 50.0% by mass or more and 63.0% by mass or less, and more preferably 50.0% by mass or more and 60.0% by mass or less. In one preferred embodiment, the Fe content in the ferrite powder is preferably 53.0% by mass or more and 65.0% by mass or less, more preferably 53.0% by mass or more and 63.0% by mass or less, and even more preferably 53.0% by mass or more and 60.0% by mass or less. In a preferred embodiment, the Fe content in the ferrite powder is preferably 55.0% by mass or more and 65.0% by mass or less, more preferably 55.0% by mass or more and 63.0% by mass or less, and even more preferably 55.0% by mass or more and 60.0% by mass or less.

[0025] The ferrite powder of this embodiment contains strontium (Sr) in an amount of 6.0% by mass or more and 9.0% by mass or less. Ferrite powder containing an appropriate amount of Sr has electromagnetic wave absorption performance suitable for the desired application. If the amount of Sr is less than 6.0% by mass, the magnetic properties (saturation magnetization, coercivity) will decrease, which may reduce the electromagnetic wave absorption performance. If the amount of Sr exceeds 9.0% by mass, it will be an Sr excess composition. Other phases such as Sr-Fe oxide and Sr oxide (SrO) will be formed in the ferrite powder, which may also reduce the electromagnetic wave absorption performance. From the viewpoint of further improving the electromagnetic wave absorption performance, the Sr content is preferably 6.0% by mass or more and 8.0% by mass or less, and more preferably 6.0% by mass or more and 7.0% by mass or less.

[0026] The ferrite powder of this embodiment contains zirconium (Zr) in an amount of 0.3% by mass or more and 14.0% by mass or less. Ferrite powder containing an appropriate amount of Zr can further enhance electromagnetic wave absorption performance. Although this should not be interpreted restrictively, the following mechanism can be cited as the reason.

[0027] Zirconium (Zr) is usually found in tetravalent ions (Zr) in oxides. ４＋ The state of ) is stable. Also, the zirconium ion (Zr ４＋ ) is a trivalent iron ion (Fe) whose size (ionic radius) ３＋ ) is close to. Therefore, Zr is in M-type ferrite. ４＋ Fe ３＋ It is thought that Zr will be substituted. However, ４＋ and Fe ３＋ The valencies are different. Zr ４＋ Along with the substitution, Fe ３＋ A portion of it is divalent iron ions (Fe ２＋ It is thought that this changes to ) or that oxygen vacancies (VO) are formed. Fe ２＋ This is because the formation of oxygen vacancies satisfies the charge neutrality condition, thereby stabilizing the crystal structure.

[0028] On the other hand, divalent iron ions (Fe ２＋When vacancies (V) or oxygen vacancies (VO) are formed, a charge imbalance occurs in the crystal, which induces electric dipoles and dielectric polarization. The induction of dielectric polarization increases dielectric properties and the resulting losses (dielectric loss), and it is thought that this dielectric loss can be utilized for electromagnetic wave absorption. In fact, the inventors have confirmed that incorporating zirconium (Zr) into ferrite powder increases the dielectric constant (ε) and decreases the electrical resistance (volume resistivity). All of these are related to Fe ２＋ This supports the formation of oxygen vacancies. When ferrite powder contains an appropriate amount of Zr, Fe ２＋ Because oxygen vacancies are induced, it is believed that this imparts excellent electromagnetic wave absorption performance to the ferrite powder.

[0029] If the Zr content is less than 0.3 mass%, the dielectric properties will not be sufficiently expressed. Therefore, there is a risk that the electromagnetic wave absorption performance will decrease. If the Zr content exceeds 14.0 mass%, the Zr content is excessive. Since other phases such as Zr-Fe oxides other than ferrite are formed in the ferrite powder, there is a risk that the electromagnetic wave absorption performance will decrease. From the viewpoint of further improving the electromagnetic wave absorption performance, a Zr content of 5.0 mass% to 14.0 mass% is preferable, and 10.0 mass% to 14.0 mass% is more preferable.

[0030] The ferrite powder of this embodiment contains divalent iron ions (Fe ２＋ ) contains in an amount of 0.5% by mass or more and 5.5% by mass or less. That is, a portion of the iron (Fe) contained in the ferrite powder is Fe ２＋ Fe in ferrite powder ２＋ The presence of Fe induces dielectric polarization, increasing dielectric loss which contributes to electromagnetic wave absorption performance. ２＋ Magnetite (Fe) has high magnetic properties (saturation magnetization, permeability). ３ O ４ It is also a constituent ion of the phase. Fe ２＋ The presence of this element improves the magnetic properties, allowing for effective utilization of magnetic loss, and consequently, improving electromagnetic wave absorption performance.

[0031] Fe ２＋If the quantity is within the range described above, the effect of increasing dielectric loss can be enhanced, and the effect of improving magnetic properties and magnetic loss based on the magnetite phase can be sufficiently enhanced, resulting in further improvement of electromagnetic wave absorption performance. Fe ２＋ If the amount is less than 0.5 mass%, the effects of increased dielectric loss and improved permeability cannot be fully utilized. Fe ２＋ If the amount exceeds 5.5% by mass, the ferrite powder may oxidize further, potentially leading to a decrease in magnetic properties. From the perspective of further improving electromagnetic wave absorption performance, Fe ２＋ The amount is preferably 1.5% by mass or more and 5.5% by mass or less, and more preferably 2.5% by mass or more and 5.5% by mass or less. ２＋ The amount varies depending on the composition of the ferrite powder, especially the amount of Zr. It also varies depending on the manufacturing conditions, especially the calcination conditions. Therefore, by adjusting the blending composition and manufacturing conditions, Fe ２＋ The amount can be controlled. Also, Fe ２＋ The quantity can be determined by redox titration. Specifically, it can be measured using the method described in the examples below or a similar method.

[0032] The ferrite powder of this embodiment is an oxide containing strontium (Sr), zirconium (Zr), and iron (Fe) as essential components. That is, the total content of strontium (Sr), zirconium (Zr), iron (Fe), and oxygen (O) is 100.0% by mass or less. The ferrite powder may contain elements other than Sr, Zr, Fe, and O, but it is preferable that the amount of these elements is not excessively large. The total content of Sr, Zr, Fe, and O is preferably 90.0% by mass or more, more preferably 95.0% by mass or more, even more preferably 99.0% by mass or more, and particularly preferably 99.9% by mass or more.

[0033] The ferrite powder of this embodiment contains magnetite (Fe) in addition to the main M-type ferrite phase. ３ O ４ ) Contains the phase in an amount of 5.0% by mass or more and 20.0% by mass or less. Fe ３ O ４ The phase is Fe ２＋ Fe ３＋ ２ O ２－４ It is a type of spinel-type ferrite with the chemical formula and a cubic crystal structure (space group: Fd-3m). As can be seen from this chemical formula, Fe ３ O ４ The phase is trivalent iron ions (Fe ３＋ ) along with divalent iron ions (Fe ２＋ ) contains. Also, like other spinel-type ferrites, Fe ３ O ４ The phase is a ferromagnetic material. A suitable amount of Fe is added to the ferrite powder. ３ O ４ By incorporating a phase, the magnetic properties, particularly saturation magnetization and permeability, are enhanced, further improving electromagnetic wave absorption performance. Fe ３ O ４ If the phase amount is less than 5.0 mass%, the effect of improving magnetic properties cannot be fully utilized. Fe ３ O ４ When the phase amount exceeds 20.0 mass%, the proportion of the M-type ferrite phase becomes relatively low, making it difficult to fully utilize the effects based on the M-type ferrite phase. From the perspective of further improving electromagnetic wave absorption performance, Fe ３ O ４ The phase amount is preferably 10.0% by mass or more and 20.0% by mass or less, and more preferably 15.0% by mass or more and 20.0% by mass or less.

[0034] The ferrite powder of this embodiment consists of an M-type ferrite phase and Fe ３ O ４ Separately from the phase, zirconium oxide (ZrO ２ ) It may or may not include the phase. ZrO ２ The phase is a nonmagnetic material with a monoclinic crystal structure (space group: P21 / c). ZrO ２ If the amount of phase is excessive, the M-type ferrite phase and Fe, which are the main components of the magnetic properties, ３ O ４ Because the proportion of phases decreases, there is a risk that the electromagnetic wave absorption performance will decrease. From the perspective of further improving the electromagnetic wave absorption performance, ZrO ２ The phase content is preferably 0.0% by mass or more and 10.0% by mass or less, more preferably 3.0% by mass or more and 10.0% by mass or less, and even more preferably 5.0% by mass or more and 10.0% by mass or less.

[0035] The ferrite powder of this embodiment is an M-type ferrite phase, Fe ３ O ４ Phase and ZrO ２ Other phases (different phases) may be included besides the current phase. These different phases may include raw materials or intermediate products (SrFe) used during the production of ferrite powder. ２ O ４ , SrZrO ３ Examples include M-type ferrite phase and Fe ３ O ４ From the viewpoint of fully utilizing the excellent magnetic properties of the phase, it is preferable to have a small amount of the other phase. M-type ferrite phase, Fe ３ O ４ Phase and ZrO ２ The amount of non-phases other than the current phase is preferably 30.0% by mass or less, more preferably 10.0% by mass or less, even more preferably 5.0% by mass or less, and particularly preferably 1.0% by mass or less.

[0036] The ferrite powder of this embodiment has a saturation magnetization (Ms) of 50 emu / g or more and 75 emu / g or less. By increasing Ms to a certain extent, it is possible to obtain excellent electromagnetic wave absorption performance. To explain this point, the imaginary part (μ'') of the complex permeability is used as an indicator of magnetic loss, and the higher this value, the faster the electromagnetic waves are attenuated. Furthermore, the permeability (μ) is proportional to the saturation magnetization (Ms), as shown in equation (1) below. In equation (1) below, HA is the anisotropic magnetic field.

[0037]

[0038] Therefore, the larger the saturation magnetization (Ms) of the ferrite powder, the larger the magnetic permeability (μ) and its imaginary part (μ’’). Therefore, it becomes possible to obtain excellent electromagnetic wave absorption performance based on magnetic loss. When Ms is less than 50 emu / g, the effect of improving the electromagnetic wave absorption performance based on the improvement of the magnetic permeability cannot be expected. When Ms exceeds 75 emu / g, the electromagnetic wave absorption performance may rather decrease. From the viewpoint of improving the electromagnetic wave absorption performance, Ms is preferably 60 emu / g or more and 75 emu / g or less, and more preferably 70 emu / g or more and 75 emu / g or less. Note that Ms is the magnetization value measured under an external magnetic field of 10 kOe (800 kA / m).

[0039] Regarding magnetic properties other than the saturation magnetization (Ms), the residual magnetization (Mr) of the ferrite powder is preferably 5 emu / g or more and 35 emu / g or less, more preferably 10 emu / g or more and 30 emu / g or less, and even more preferably 15 emu / g or more and 25 emu / g or less. As a preferred embodiment, the residual magnetization (Mr) of the ferrite powder is preferably 5 emu / g or more and 30 emu / g or less, and more preferably 5 emu / g or more and 25 emu / g or less. As a preferred embodiment, the residual magnetization (Mr) of the ferrite powder is preferably 10 emu / g or more and 35 emu / g or less, more preferably 10 emu / g or more and 30 emu / g or less, and even more preferably 10 emu / g or more and 25 emu / g or less. As a preferred embodiment, the residual magnetization (Mr) of the ferrite powder is preferably 15 emu / g or more and 35 emu / g or less, more preferably 15 emu / g or more and 30 emu / g or less, and even more preferably 15 emu / g or more and 25 emu / g or less. The coercive force (Hc) is preferably 200 Oe or more and 350 Oe or less, more preferably 200 Oe or more and 300 Oe or less, and even more preferably 200 Oe or more and 250 Oe or less.

[0040] The volume resistivity of the ferrite powder of the present embodiment is 1.0×10 ９It is less than or equal to Ω·cm. By maintaining the volume resistivity (electrical resistance) at a low level, the electromagnetic wave absorption performance in the high-frequency band can be further improved. That is, as described above, the ferrite powder of this embodiment has oxygen vacancies. Furthermore, the presence of these oxygen vacancies is thought to lower the electrical resistance (volume resistivity) and increase dielectric loss, which contributes to the improvement of electromagnetic wave absorption performance. More specifically, the imaginary part (ε'') of the complex dielectric constant is used as an indicator of dielectric loss, and the higher this value, the faster the electromagnetic wave attenuates. Also, ε'' is inversely proportional to the volume resistivity (ρV), as shown in equation (2) below. Note that in equation (2) below, ε ０ ρV is the permittivity of vacuum, ρV is the volume resistivity, and ω is the angular frequency of the applied electric field.

[0041]

[0042] Therefore, the lower the electrical resistance of the ferrite powder, the better the electromagnetic wave absorption performance based on dielectric loss can be obtained. From the viewpoint of improving electromagnetic wave absorption performance, a low volume resistivity is desirable. Specifically, a volume resistivity of 1.0 × 10⁻⁶ is desirable. ８ It is more preferable to have a value of Ω·cm or less, and 1.0 × 10 ７ A value of Ω·cm or less is even more preferable.

[0043] Preferably, the average particle size (D50) of the ferrite powder is 3.0 μm or more and 35.0 μm or less. In many cases, ferrite powder is used as a filler and mixed with resin to produce a composite material, which is then molded to produce a composite (such as an electromagnetic wave absorber). If the average particle size is within the above range, the fluidity and metering / handling properties of the ferrite powder and composite material are improved. As a result, the filler filling rate of the composite material is improved.

[0044] On the other hand, if the average particle size of the ferrite powder is too small, the fluidity of the ferrite powder and the composite material decreases, and the particles (ferrite particles) constituting the ferrite powder tend to aggregate. Therefore, it becomes difficult to obtain a composite with a high filler filling rate. Also, if the average particle size is too large, the voids between the ferrite particles become large. Therefore, it also becomes difficult to obtain a composite with a high filler filling rate. From the viewpoint of improving the filler filling rate, the average particle size is more preferably 3.0 μm or more and 25.0 μm or less, and even more preferably 3.0 μm or more and 15.0 μm or less. The average particle size may be measured using a particle size analyzer. Specifically, it may be measured by the method of the examples described later or a method analogous thereto.

[0045] The ferrite powder of the present embodiment containing Fe, Sr, and Zr in specific amounts has an M-type ferrite phase with a large magnetic anisotropy as the main phase, and thus exhibits excellent electromagnetic wave absorption performance in the high-frequency band. Also, since it contains Zr, Fe ２＋ and Fe ３ O ４ phases in appropriate amounts, the dielectric loss and magnetic loss are large. As a result of these acting in combination, the electromagnetic wave absorption performance in the high-frequency band, particularly in the frequency band of 7 GHz or more and 13 GHz or less, becomes even higher.

[0046] Preferably, the ferrite powder has a resonance frequency in the frequency range of 7 GHz or more and 13 GHz or less. Also, preferably, the imaginary component (μ'') of the complex relative permeability at the resonance frequency is 1.0 or more. The ferrite powder of the present embodiment preferably has a resonance frequency in the frequency range of 7 GHz or more and 13 GHz or less, and the imaginary component (μ'') of the complex relative permeability at the resonance frequency is 1.0 or more. Here, the resonance frequency is the magnetic loss (tanδ Ｍ) is the frequency at which the frequency is maximized. On the other hand, μ'' is an indicator of magnetic loss, and the larger it is, the greater the loss based on ferromagnetic resonance. Therefore, ferrite powder with a large μ'' has high electromagnetic wave absorption performance based on magnetic loss. From the viewpoint of improving electromagnetic wave absorption performance, a larger μ'' is desirable. Specifically, μ'' is more preferably 2.0 or higher, and even more preferably 3.0 or higher. There is no particular upper limit to μ''. For example, it may be 50 or less, 30 or less, or 10 or less. In one preferred embodiment, μ'' is preferably 1.0 or more and 50 or less, more preferably 1.0 or more and 30 or less, and even more preferably 1.0 or more and 10 or less. In one preferred embodiment, μ'' is preferably 2.0 or more and 50 or less, more preferably 2.0 or more and 30 or less, and even more preferably 2.0 or more and 10 or less. In one preferred embodiment, μ'' is preferably 3.0 or more and 50 or less, more preferably 3.0 or more and 30 or less, and even more preferably 3.0 or more and 10 or less.

[0047] Preferably, the imaginary component (ε'') of the complex relative permittivity at the resonance frequency is 30 or more. The ferrite powder of this embodiment preferably has a resonance frequency in the frequency range of 7 GHz to 13 GHz, and the imaginary component (ε'') of the complex relative permittivity at the resonance frequency is 30 or more. ε'' is the dielectric loss (tanδ Ｅε'' is an indicator of dielectric loss, and the larger it is, the greater the dielectric loss. Therefore, ferrite powder with a large ε'' has high electromagnetic wave absorption performance based on dielectric loss. From the viewpoint of improving electromagnetic wave absorption performance, a larger ε'' is desirable. Specifically, ε'' is more preferably 40 or more, and even more preferably 50 or more. There is no particular upper limit to ε''. For example, it may be 500 or less, 300 or less, or 100 or less. In one preferred embodiment, ε'' is preferably 30 or more and 500 or less, more preferably 30 or more and 300 or less, and even more preferably 30 or more and 100 or less. In one preferred embodiment, ε'' is preferably 40 or more and 500 or less, more preferably 40 or more and 300 or less, and even more preferably 40 or more and 100 or less. In one preferred embodiment, ε'' is preferably 50 or more and 500 or less, more preferably 50 or more and 300 or less, and even more preferably 50 or more and 100 or less.

[0048] <<2. Method for Producing Ferrite Powder>> The method for producing the ferrite powder of this embodiment is not limited as long as it satisfies the requirements described above. However, preferably, the method includes the following steps: a step of mixing a strontium (Sr) source, a zirconium (Zr) source, an iron (Fe) source, water, and optionally a binder, dispersant, defoaming agent and / or pH adjuster to produce a slurry (raw material mixing step); a step of spray granulation of the obtained slurry to produce granules (granulation step); and a step of calcining the obtained granules to produce a calcined product (calcination step). Optionally, a step of post-treatment of the obtained calcined product (post-treatment step) may also be provided. Details of each step are described below.

[0049] <Raw Material Mixing Process> In the mixing process, a strontium (Sr) source, a zirconium (Zr) source, an iron (Fe) source, water, and, if necessary, a binder, dispersant, defoamer and / or pH adjuster are prepared as raw materials, and these raw materials are mixed to produce a slurry. Known ferrite raw materials such as oxides, carbonates, and hydroxides may be used as the Sr source, Zr source, and Fe source. Preferably, strontium carbonate (SrCO3) ３ ), zirconium oxide (ZrO２ ), and iron oxide (Fe ２ O ３ It is preferable to use these materials. They are inexpensive, stable at room temperature and humidity, and have excellent handling properties.

[0050] If necessary, additives such as binders, dispersants, defoamers, and pH adjusters may be added to the raw material mixture (slurry). Binders are added to improve the strength of the granules obtained after spray granulation. As binders, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and / or acrylic resin binders can be used, and the amount added is 0.05% by mass or more and 1.0% by mass or less in terms of solid content relative to the raw material mixture.

[0051] The mixing of raw materials (Sr source, Zr source, Fe source, water, etc.) can be carried out by known methods. For example, the raw materials can be mixed and formed into a slurry using a mixing and grinding machine such as a wet bead mill. The solid content concentration of the resulting slurry is preferably 30% by mass or more and 75% by mass or less, more preferably 45% by mass or more and 65% by mass or less, and even more preferably 50% by mass or more and 60% by mass or less. In one preferred embodiment, the solid content concentration of the slurry is preferably 30% by mass or more and 65% by mass or less, and more preferably 30% by mass or more and 60% by mass or less. In one preferred embodiment, the solid content concentration of the slurry is preferably 45% by mass or more and 75% by mass or less, more preferably 45% by mass or more and 65% by mass or less, and even more preferably 45% by mass or more and 60% by mass or less. In a preferred embodiment, the solid content concentration of the slurry is preferably 50% by mass or more and 75% by mass or less, more preferably 50% by mass or more and 65% by mass or less, and even more preferably 50% by mass or more and 60% by mass or less.

[0052] <Granulation Process> In the granulation process, the obtained slurry is spray-granulated to produce granules. Spray granulation can be performed using a spray dryer. Granulation can be performed under known conditions. For example, conditions such as slurry discharge rate: 200 g / min or more and 500 g / min or less, atomizer disc rotation speed: 1000 rpm or more and 12000 rpm or less, and drying temperature: 100°C or more and 500°C or less can be used. The average particle size of the granules formed in the granulation process is preferably 20 μm or more and 120 μm or less.

[0053] In the granulation process, the obtained granules may be subjected to a debinder treatment. In the debinder treatment, the granules are heated to decompose and remove organic components such as binders, thereby obtaining a defatted material. The debinder treatment can be carried out using a known heating furnace. The heating should be carried out under conditions that remove organic components, for example, at a temperature of 650°C to 1050°C for 0.5 hours to 12 hours. However, the debinder treatment is not essential. Even without the debinder treatment, organic components will be decomposed and removed in the subsequent calcination process.

[0054] <Casturing Process> In the calcination process, the obtained granules or defatted material are calcined (main calcination) to obtain a calcined product. The calcination temperature is preferably 1100°C to 1300°C, more preferably 1200°C to 1300°C, and even more preferably 1220°C to 1260°C. In one preferred embodiment, the calcination temperature is preferably 1100°C to 1260°C. In one preferred embodiment, the calcination temperature is preferably 1200°C to 1300°C, and more preferably 1200°C to 1260°C. In one preferred embodiment, the calcination temperature is preferably 1220°C to 1300°C, and more preferably 1220°C to 1260°C. When the calcination temperature is within the above range, ferrite powder exhibiting electromagnetic wave absorption performance suitable for the desired application can be obtained. Conversely, if the firing temperature is too low, the resonance frequency may shift excessively to the low-frequency side, potentially reducing absorption performance. If the firing temperature is too high, the resonance frequency may shift excessively to the high-frequency side, potentially reducing absorption performance. Firing should be performed for 3 to 6 hours.

[0055] Firing can be carried out under a nitrogen atmosphere. ２ The concentration is preferably 10.0% by volume or less, more preferably 5.0% by volume or less, and even more preferably 1.0% by volume or less. ２ By reducing the concentration, oxygen vacancies and divalent iron ions (Fe) are formed in the resulting ferrite powder. ２＋ The formation of oxygen vacancies and Fe is promoted. ２＋ This makes it possible to fully utilize the effects of improved dielectric properties (dielectric loss) and magnetic properties (saturation magnetization, permeability) resulting from this. ２ If the concentration is too high, oxygen vacancies and Fe ２＋ This could lead to a decrease in absorption performance.

[0056] <Post-processing> If necessary, the calcined product may be subjected to post-processing. Examples of post-processing include crushing, heat treatment, and classification. Post-processing may be performed individually or in combination. In this way, the ferrite powder of this embodiment can be obtained.

[0057] <<3. Ferrite Resin Composite Material>> The ferrite resin composite material of this embodiment (hereinafter sometimes referred to as "composite material") includes the ferrite powder and resin described above. The composite material is a precursor material for the ferrite resin composite, which is a component of the electromagnetic wave absorber. That is, the composite is made by molding the composite material.

[0058] Examples of resins constituting the composite material include epoxy resins, urethane resins, acrylic resins, silicone resins, polyamide resins, polyimide resins, polyamide-imide resins, fluororesins, or combinations thereof. The silicone resin may be a modified silicone resin modified with acrylic, urethane, epoxy, and / or fluorine.

[0059] The composite material may contain components other than ferrite powder and resin. Examples of such components include solvents, fillers (organic fillers, inorganic fillers), plasticizers, antioxidants, dispersants, colorants such as pigments, and / or thermally conductive particles.

[0060] The proportion of ferrite powder to the total solid content in the composite material is preferably 50% to 95% by mass, and more preferably 80% to 95% by mass. The proportion of resin to the total solid content in the composite material is preferably 5% to 50% by mass, and more preferably 5% to 20% by mass. By setting the proportions of ferrite powder and resin within the above ranges, the dispersion stability of the ferrite powder, as well as the storage stability and moldability of the composite material, are improved, and the properties such as mechanical strength and magnetic properties of the composite obtained by molding the composite material are also improved.

[0061] <<4. Ferrite Resin Composite>> The ferrite resin composite of this embodiment (hereinafter sometimes referred to as "composite") is a molded body of the ferrite resin composite material described above. That is, the composite is produced by molding the composite material. The molding method is not particularly limited and examples include compression molding, extrusion molding, injection molding, blow molding, or calendering. Alternatively, a method of forming a coating film of the composite material on a substrate may also be used.

[0062] The filler filling rate of the composite is preferably 70% by volume or more, more preferably 80% by volume or more, and even more preferably 90% by volume or more. The filler filling rate is an indicator of the proportion of ferrite particles (particles constituting the ferrite powder) in the composite. Setting the filler filling rate within the above range results in excellent dispersion stability of the ferrite particles, storage stability of the composite, and moldability. Conversely, if the filler filling rate is excessively low, the strength of the composite may decrease. The filler filling rate can be determined by observing the cross-section of the composite with an SEM and determining the proportion of ferrite particles in the resulting cross-sectional SEM image. Specifically, it can be measured using the method described in the examples below or a similar method. However, the magnification during SEM observation should be selected according to the particle size of the ferrite powder and the thickness of the composite.

[0063] <<5. Electromagnetic Wave Absorber>> The electromagnetic wave absorber of this embodiment comprises the ferrite resin composite described above. The electromagnetic wave absorber may consist only of the composite, or other members may be provided. For example, an impedance matching layer or a surface protection layer may be provided on the surface of the composite. A reflective member may also be provided on the back surface. An example of an impedance matching layer is a layer in which magnetic powder or dielectric powder is dispersed in resin. An example of a surface protection layer is a layer made of resin or glass. Examples of reflective members include film-like, foil-like, or mesh-like metal members.

[0064] It is desirable that the electromagnetic wave absorber has a peak in the frequency characteristics of the attenuation Rtp. The peak frequency of Rtp is preferably 7 GHz or more and 13 GHz or less, more preferably 8 GHz or more and 12 GHz or less, and even more preferably 9 GHz or more and 11 GHz or less. In one preferred embodiment, the peak frequency of Rtp is preferably 7 GHz or more and 12 GHz or less, and more preferably 7 GHz or more and 11 GHz or less. In one preferred embodiment, the peak frequency of Rtp is preferably 8 GHz or more and 13 GHz or less, more preferably 8 GHz or more and 12 GHz or less, and even more preferably 8 GHz or more and 11 GHz or less. In one preferred embodiment, the peak frequency of Rtp is preferably 9 GHz or more and 13 GHz or less, more preferably 9 GHz or more and even more preferably 9 GHz or more and 11 GHz or less. Furthermore, the attenuation Rtp at the peak frequency is preferably 20 dB or more, more preferably 40 dB or more, and even more preferably 60 dB or more. If the attenuation Rtp and peak frequency are within the above-mentioned range, suitable absorption performance for the desired application can be obtained. The attenuation Rtp is measured using the microstrip line method or the free-space method. Specifically, it can be measured using the method described in the examples below or a similar method.

[0065] The applications of electromagnetic wave absorbers are not limited as long as their purpose is to absorb electromagnetic waves. For example, they can be applied to transmission lines, high-frequency circuits, electronic components, and / or electronic equipment. The electromagnetic wave absorber of this embodiment exhibits excellent electromagnetic wave absorption performance in the microwave frequency band, particularly in the 7 to 13 GHz frequency band.

[0066] The present invention will be described in more detail using the following examples and comparative examples. However, the present invention is not limited to the following examples. (1) Preparation of ferrite powder and ferrite resin composite [Example 1] In Example 1, ferrite powder and ferrite resin composite were prepared and evaluated.

[0067] <Raw material mixing> As a raw material, iron oxide (Fe ２ O ３ ), strontium carbonate (SrCO ３ ), and zirconium oxide (ZrO ２ Prepare these, and use Fe ２ O ３ :73.1% by mass, SrCO ３ : 10.8% by mass, ZrO ２ The material was weighed to a proportion of 16.1% by mass. Next, water was added to the weighed material, and it was finely ground using a wet bead mill equipped with 0.65 mmφ zirconia beads to obtain a slurry.

[0068] <Granulation> To the obtained slurry, polyvinyl alcohol (PVA, 15% aqueous solution) was added as a binder, acrylic copolymer ammonium salt (BASF, AA-4040, 40% aqueous solution) as a dispersant, and ammonia aqueous solution (25% aqueous solution) as a pH adjuster. At this time, the amount of binder (PVA) added was 1% by mass in terms of solid content, and the amount of dispersant (acrylic copolymer ammonium salt) added was 0.3% by mass in terms of solid content. The concentration (solid content) of the obtained slurry was 55% by mass. Subsequently, the slurry with the binder, dispersant and pH adjuster added was spray-granulated using a spray dryer to obtain granules. The average particle size of the obtained granules was 60 μm.

[0069] <Casturing> Next, the obtained granules were calcined (main calcination) to obtain calcined products. Calcination was carried out using oxygen (O ２ The process was carried out under conditions of 1240°C for 5 hours in a nitrogen atmosphere with a concentration of 0.0 volume%. Subsequently, the resulting calcined material was pulverized using a hammer mill to obtain calcined powder with an average particle size (D50) of 14.3 μm. In this way, ferrite powder was prepared. The manufacturing conditions for the ferrite powder are summarized in Table 1 below.

[0070] <Preparation of Composite> A ferrite resin composite material was prepared by mixing and kneading 90 parts by mass of filler (ferrite powder) and 10 parts by mass of binder resin. Powdered fluororesin was used as the binder resin. The mixing was performed using a sample mill. Next, the obtained ferrite resin composite material was filled into a mold and heated at 180°C for 2 hours while being press-molded in a press machine to produce a resin molded body. The obtained sheet (resin molded body) had a thickness of 3 mm. The obtained sheet was used as the ferrite resin composite for evaluation.

[0071] [Examples 2 to 14] Raw materials (Fe ２ O ３ SrCO ３ , and ZrO ２ The mixing ratio and firing conditions of the ferrite powder were changed as shown in Table 1 below. Otherwise, the composite was prepared in the same manner as in Example 1. Examples 1 to 6 are example samples, and Examples 7 to 14 are comparative example samples.

[0072]

[0073] (2) The ferrite powders and composites obtained in Evaluation Examples 1 to 14 were evaluated for various properties as follows.

[0074] <Chemical Analysis> The Fe, Sr, and Zr content in the ferrite powder was measured by ICP emission spectrometry. Specifically, 0.2 g of the ferrite powder to be measured was weighed. Then, 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid were added to 60 ml of pure water and heated, and the weighed ferrite powder was added and completely dissolved to prepare an aqueous solution. The prepared aqueous solution was used as the sample for measurement and was set in an ICP emission spectrometer (Shimadzu Corporation, ICPS-1000IV) to measure the Fe, Sr, and Zr content.

[0075] <Redox Titration> Fe in ferrite powder ２＋ The quantity was determined by redox titration with potassium permanganate solution. The redox titration was performed in accordance with JIS M 8213-1995, using potassium permanganate solution instead of potassium dichromate solution.

[0076] <XRD> Using ferrite powder as a sample, a powder X-ray diffraction pattern was obtained, and the obtained pattern was subjected to Rietveld analysis to determine each crystalline phase (M-type ferrite phase, Fe) in the ferrite powder. ３ O ４ Phase, ZrO ２ The content of each phase was determined. While it can be difficult to identify and quantify each crystalline phase using waveform separation of powder X-ray diffraction patterns, Rietveld analysis based on a crystal structure model makes it possible to identify and quantify each phase.

[0077] A Panalytical "X'PertPRO MPD" X-ray diffractometer was used. A Co-ionized tube (CoKα) was used as the X-ray source. Furthermore, a focusing optical system and a high-speed detector "X'Celarator" were employed. The measurement conditions were as follows:

[0078] - Scan speed: 0.08° / sec - Divergence slit: 1.0° - Scattering slit: 1.0° - Receiving slit: 0.15mm - Voltage and current values ​​of the sealed tube: 40kV / 40mA - Measurement range: 2θ = 15° to 90° - Number of integrations: 5

[0079] Based on the obtained measurement results, the crystal structure was identified as follows.

[0080] • Magnetoplanbite-type ferrite (M-type ferrite) Space group: P63 / mmc (No. 194) • Magnetite (Fe ３ O ４ ) Space group: Fd-3m (No. 227) ・Zirconium oxide (ZrO ２ ) Space group: P21 / c (No. 14)

[0081] Next, the following parameters were optimized using the analysis software "RIETAN-FP v2.83," and based on the optimization results, the M-type ferrite phase and Fe in the ferrite powder were analyzed. ３ O ４ Phase and ZrO ２The content of each phase was determined. During optimization, a pseudo-Voigt function of Thompson, Cox, and Hasting was used as the profile function, and asymmetricalization was performed using Howard's method. Furthermore, the following parameters were optimized so that the Rwp value and S value, which represent the accuracy of the fitting, were Rwp: 2% or less and S value: 1.5 or less, respectively.

[0082] (Parameters to optimize) - Shift factor - Scale factor - Background parameter - Gaussian functions U, V, W - Lorentz functions X, Y - Asymmetric parameter As - Lattice constant - Atomic coordinates

[0083] <Volume-average particle size> The volume-average particle size (D50) of the ferrite powder was measured using a Microtrac particle size analyzer (Nikkiso Co., Ltd., Model 9320-X100). Specifically, 10 g of ferrite powder and 80 ml of water were placed in a 100 ml beaker, and 2 to 3 drops of a dispersant (sodium hexametaphosphate) were added. Next, the resulting mixture was subjected to dispersion treatment using an ultrasonic homogenizer (SMT.Co.LTD., UH-150 type) to prepare a sample for measurement. The output level of the ultrasonic homogenizer was set to 4. The dispersion treatment was performed for 20 seconds. After the dispersion treatment, the bubbles formed on the surface of the beaker were removed to prepare the sample for measurement. The obtained sample for measurement was subjected to the particle size analyzer described above to measure D50.

[0084] <Volume Resistivity> The volume resistivity of ferrite powder was measured. First, the cross-sectional area was 4 cm². ２ A sample for measurement was prepared by filling a fluororesin cylinder with ferrite powder to a height of 4 mm. Next, electrodes were attached to both ends (top and bottom) of the sample, and a 1 kg weight was placed on top to measure the electrical resistance. For resistance measurement, an electrometer (KEITHLEY, insulation resistance meter, model 6517A) was used to calculate the resistance value at an applied voltage of 100 V. The volume resistance was calculated from the obtained resistance value.

[0085] <Magnetic Properties> The saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) of ferrite powder were measured. Specifically, ferrite powder was packed into a cell with an inner diameter of 5 mm and a height of 2 mm, and set in a vibrating sample type magnetic measuring device (Toei Kogyo Co., Ltd., VSM-C7-10A). An applied magnetic field was swept up to 10 kOe, and then the applied magnetic field was decreased to generate a hysteresis curve. Ms, Mr, and Hc were read from the data of the obtained curve.

[0086] <Complex Permittivity and Complex Permeability> For Examples 1-6 and 8-14, the complex permittivity (relative permittivity) and complex permeability (relative permeability) were measured using the following procedure. First, a sample for measurement was prepared. Specifically, 9.0 g of magnetic powder (ferrite powder) and 1.0 g of binder resin (Kynar301F: polyvinylidene fluoride) were weighed using a 50 cc glass bottle, and the weighed magnetic powder and binder resin were stirred and mixed in a ball mill at a rotation speed of 100 rpm for 30 minutes. After stirring, the stirred mixture was weighed, and about 1.2 g of the weighed stirred mixture was placed in a die with a diameter of 6.8 mm and pressed in a press machine at a pressure of 40 MPa for 3 minutes. The resulting molded body was left to stand in a hot air dryer at 140°C for 2 hours. A sample for measuring dielectric constant and magnetic permeability was prepared by drilling a 3.25 mm diameter hole in the center of the dried molded body.

[0087] Next, the complex permittivity (relative permittivity) and complex permeability (relative permeability) of the measurement sample were measured using an ENA vector network analyzer (Keysight Technologies E5071C) and an adapter (11533A / APC-7). Prior to measurement, the diameter, thickness, and inner diameter of the sample molded body were measured and input into the measuring device. Then, under an amplitude of 10 mA, the range from 300 MHz to 18 GHz was swept on a logarithmic scale to determine the complex relative permittivity (real part relative permittivity ε′, imaginary part relative permittivity ε′′) and complex relative permeability (real part relative permeability μ′, imaginary part relative permeability μ′′). Based on the obtained data, the permeability loss (magnetic loss; tanδ) was calculated according to equations (3) and (4) below. Ｍ ) and dielectric loss (dielectric loss; tanδ Ｅ The tanδ obtained was calculated. ＭTherefore, the resonance frequency (tanδ Ｍ The frequency at which the value is maximized was determined.

[0088]

[0089] For Example 7, the complex permittivity and complex permeability were measured using the free-space method with the composite material as the measurement sample. The composite material used as the measurement sample was prepared by heat molding a composite material containing 90 parts by mass of ferrite powder and 10 parts by mass of fluororesin (binder resin), as described above. The measurements were performed using a network analyzer (Keysight Technologies, E5253E2) and a free-space measurement device (EM Labs, FS-330). Specifically, using one port, an input wave of a predetermined frequency (20-45 GHz) was irradiated onto the composite material through a dielectric lens from a transmitting and receiving antenna. The reflection and transmission characteristics (S-parameters) of the electromagnetic waves were then measured, and the complex permittivity and complex permeability were calculated from the obtained characteristics. The analysis was performed using the Keysight material measurement suite N1500A attached to the device. The analysis was performed using the Nicholson-Ross-Weir (NRW method) model.

[0090] <Filler Packing Ratio> The filler packing ratio in the composite was determined by observing the cross-section of the composite with a scanning electron microscope (SEM). Specifically, the composite was processed using an ion milling apparatus (Hitachi High-Tech Corporation, IM-4000) to dimensions of 5 mm x 5 mm and a thickness of 3 mm. The processed composite was then set on a stage with its cross-section facing upwards and used as a sample for measurement. The composite used as the sample for measurement was prepared by heat molding a composite material containing 90 parts by mass of ferrite powder and 10 parts by mass of fluororesin (binder resin), as described above. The ion milling process was performed under the following conditions.

[0091] - Discharge voltage: 1.5kV - Acceleration voltage: 6kV - Stage control: C3 - Discharge current inside the ion gun: 380-450μA - Ion beam current: 110-140μA - Argon gas flow rate: 0.07-0.10cm ３ / min - Processing time: 60 minutes

[0092] Next, the prepared sample for measurement was observed using a SEM (Hitachi High-Technologies Corporation, SU-8020). SEM observation was performed under the conditions of acceleration voltage: 1 kV and magnification: 500 to 10000x (magnification that allows approximately 30 particles to fit in one field of view), and cross-sectional SEM images of three fields of view were taken in LA mode. Subsequently, the obtained cross-sectional SEM images were binarized to determine the proportion of ferrite powder, and the filler packing rate was calculated. The filler packing rate calculated as the average of the three fields of view was rounded to two decimal places.

[0093] <Electromagnetic Wave Absorption Performance> To evaluate the electromagnetic wave absorption performance of Examples 1-6 and 8-14, the composite was used as a measurement sample and the attenuation Rtp in the frequency range of 3-14 GHz was measured. The composite used as the measurement sample was prepared by heat molding a composite material containing 90 parts by mass of ferrite powder and 10 parts by mass of fluororesin (binder resin), as described above. The measurement was performed using the microstrip line method in accordance with IEC 62333. Rtp was calculated according to the following equation (5). In the equation, S １１ is the reflection coefficient, S ２１ This is the transmission coefficient.

[0094]

[0095] The attenuation value Rtp (unit: dB) is an indicator of electromagnetic wave absorption performance; a higher value indicates higher electromagnetic wave absorption performance. The relationship between the Rtp value and the actual electromagnetic wave absorption performance (electromagnetic wave suppression ability) is as follows.

[0096] 3 dB: 50% absorption 6 dB: 75% absorption 10 dB: 90% absorption 20 dB: 99% absorption 30 dB: 99.9% absorption

[0097] For Example 7, the attenuation was measured using the free-space method with the composite material as the measurement sample. The composite material used as the measurement sample was obtained by heat molding a composite material containing 90 parts by mass of ferrite powder and 10 parts by mass of fluororesin (binder resin), as described above. A network analyzer (Keysight Technologies, E5253E2) and a free-space measuring device (EM Lab Co., Ltd., FS-330) were used as the measurement equipment. The incident angle was set to 0° and the sweep frequency to 20 GHz to 45 GHz, and the S-parameter (S １１ and S ２１ The following parameters were measured. Then, from the obtained S-parameters, the attenuation Rtp of the composite in the 20–45 GHz range was measured. The S-parameter analysis was performed using the Keysight material measurement suite N1500A attached to the instrument. The same formula as the microstrip line method described above was used for the attenuation.

[0098] (3) Evaluation Results The results obtained for the ferrite powder and composite are summarized in Tables 2 and 3 below. In Table 3 below, the volume resistivity is expressed in E notation. That is, the number before "E" represents the mantissa, and the number after "E" represents the exponent. The attenuation Rtp in Table 3 indicates the attenuation at the peak frequency. The peak frequency (GHz) in Table 3 is also the resonance frequency, and μ′′ and ε′′ in Table 3 are values ​​at the resonance frequency.

[0099] Composition (Fe amount, Sr amount, Zr amount, Fe ２＋ amount), crystalline phase (Fe ３ O ４ In the example samples (Examples 1 to 6) where the phase, magnetic properties (saturation magnetization Ms), and volume resistance all satisfy the range specified in this embodiment, the peak frequency of the attenuation Rtp was in the range of 7 to 13 GHz in the electromagnetic wave absorption performance evaluation. Furthermore, the attenuation Rtp was 20 dB or more.

[0100] In contrast, comparative examples (Examples 7 to 14) in which the composition, crystal phase, magnetic properties, and volume resistivity did not satisfy the range specified in this embodiment had an attenuation Rtp of less than 20 dB.

[0101] From the above results, it is understood that this embodiment provides a ferrite powder that exhibits excellent electromagnetic wave absorption performance in the microwave band, particularly in the 7-13 GHz frequency band, as well as a ferrite resin composite material, a ferrite resin composite, and an electromagnetic wave absorber containing the ferrite powder.

[0102]

[0103]

[0104] The present invention provides a ferrite powder that exhibits excellent electromagnetic wave absorption performance in the microwave frequency band, particularly in the 7 to 13 GHz frequency band, as well as a ferrite resin composite material, a ferrite resin composite, and an electromagnetic wave absorber containing the ferrite powder.

[0105] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2024-176061, filed on 7 October 2024, the contents of which are incorporated herein by reference.

Claims

1. A hexagonal magnetoplanvite-type ferrite powder containing iron (Fe) in amounts of 50.0% to 65.0% by mass, strontium (Sr) in amounts of 6.0% to 9.0% by mass, and zirconium (Zr) in amounts of 0.3% to 14.0% by mass, wherein divalent iron ions (Fe) ２＋ The content of ) is 0.5% by mass or more and 5.5% by mass or less, and magnetite (Fe ３ O ４ The phase content is 5.0% by mass or more and 20.0% by mass or less, the saturation magnetization is 50 emu / g or more and 75 emu / g or less, and the volume resistivity is 1.0 × 10⁻⁶ ９ Ferrite powder with a density of Ω·cm or less.

2. The ferrite powder according to claim 1, wherein the average particle size (D50) is 3.0 μm or more and 35.0 μm or less.

3. The ferrite powder according to claim 1 or 2, wherein the resonant frequency is in the frequency range of 7 GHz to 13 GHz, and the imaginary component (μ'') of the complex relative permeability at the resonant frequency is 1.0 or more.

4. The ferrite powder according to claim 3, wherein the imaginary component (ε'') of the complex relative permittivity at the resonance frequency is 30 or more.

5. A ferrite resin composite material comprising the ferrite powder and resin according to claim 1 or 2.

6. A ferrite resin composite, which is a molded article of the ferrite resin composite material according to claim 5.

7. An electromagnetic wave absorber comprising the ferrite resin composite described in claim 6.

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