Electric wave absorbing sheet

Abstract

The present application provides an electromagnetic wave absorbing sheet having a small variation in the amount of electromagnetic wave absorption caused by temperature change. A first electromagnetic wave absorbing sheet includes a substrate composed of an organic substance and a powder supported in the substrate, the powder being composed of a MnZn ferrite powder, an aluminum powder, and a silicon carbide powder, when a volume ratio of the MnZn ferrite powder is set to V M , a volume ratio of the aluminum powder is set to V A , and a volume ratio of the silicon carbide powder is set to V S , a silicon carbide occupancy ratio R S represented by V M / (V A + V S + V S1 ) is 1.5% or more and 41% or less.

Description

Technical Field

[0001] This invention relates to electromagnetic wave absorbing sheets. Background Technology

[0002] With the rapid development of communications, devices using radio waves in the 3–80 GHz frequency band are becoming increasingly common. For example, in Japan's fifth-generation (5G) communication systems, which have been used commercially since 2020, applications are being promoted in the sub-6 GHz band (3–5 GHz) and the millimeter-wave band (28–40 GHz). Furthermore, in the automotive sector, with the rapid development of autonomous driving systems, quasi-millimeter-wave radar using frequencies around 24 GHz and millimeter-wave radar using frequencies around 76–79 GHz are becoming increasingly prevalent. On the other hand, in such electronic devices, the problem of internal and external electromagnetic interference is becoming increasingly prominent. Therefore, electromagnetic wave absorbing sheets that function at frequencies that cause electromagnetic interference problems are becoming more useful.

[0003] Electromagnetic wave absorbing sheets function by being mounted on a conductive substrate such as metal, or by having a conductive layer such as metal disposed on the back side of the absorbing sheet. Specifically, the surface-reflected wave reflected at the surface of the absorbing sheet and the secondary-reflected wave, which passes through the interior of the absorbing sheet and undergoes total internal reflection on the back side and radiates from the surface of the absorbing sheet, are half a wavelength out of phase. These surface-reflected waves and secondary-reflected waves cancel each other out, thus exhibiting electromagnetic wave absorption (i.e., the so-called λ / 4 type absorbing sheet).

[0004] Electromagnetic wave absorbing sheets typically have the following structure: a soft resin and / or rubber as a substrate, with fillers thereon used to generate the electromagnetic wave absorption effect. Furthermore, by controlling the material constants (dielectric constant, permeability) and thickness of the sheet, a resonant peak value for electromagnetic wave absorption can be obtained at a specific frequency. In addition, the material constants of the electromagnetic wave absorbing sheet are adjusted by the material of the substrate and the amount of filler added. Therefore, controlling the amount of filler added within the necessary range is crucial.

[0005] As a representative example of the aforementioned radio wave absorbing sheet, one can cite a radio wave absorbing sheet that uses flexible resins such as rubber and elastomers as the base material and adds carbonyl iron powder and spinel ferrite powder as fillers.

[0006] In recent years, with the miniaturization of electronic devices using electromagnetic wave absorbing sheets, the accumulation of heat from the IC chips in the drive circuitry has become a frequent cause of high temperatures within the electronic devices. As a result, the electromagnetic wave absorbing sheets are also exposed to high-temperature environments, exceeding 100°C. This presents the following problem: for electromagnetic wave absorbing sheets designed to maximize absorption at room temperature, exposure to high temperatures alters the material constant of the filler, leading to a decrease in absorption and consequently weakening the electromagnetic wave response within the electronic devices.

[0007] As a technology to address this problem, for example, Patent Document 1 discloses a magnetic material comprising ε-iron oxide and hexagonal ferrite.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent No. 7105435. Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, the difference between the frequency at which the magnetic material disclosed in Patent Document 1 achieves its optimal absorption characteristics (in decibels) at 20°C (equivalent to a normal temperature environment) and the frequency at which it achieves its optimal absorption characteristics at 120°C (equivalent to a high temperature environment) is as high as 2.0 GHz or more.

[0013] Furthermore, the sheet containing the magnetic material disclosed in Patent Document 1 is a magnetic loss type electromagnetic wave absorbing sheet. Compared with dielectric loss type electromagnetic wave absorbing sheets, this magnetic loss type electromagnetic wave absorbing sheet has a greater frequency dependence; once it deviates from the target frequency band by a certain range, the electromagnetic wave absorption effect will weaken. Therefore, this magnetic loss type electromagnetic wave absorbing sheet lacks versatility.

[0014] Therefore, the objective of this invention is to provide an electromagnetic wave absorbing sheet with minimal variation in electromagnetic wave absorption due to temperature changes.

[0015] Methods for solving problems

[0016] In order to solve the above-mentioned problems, the inventors of the present invention conducted in-depth research and found that by using fillers with a real part of dielectric constant that increases with temperature and fillers with a real part of dielectric constant that decreases with temperature in a prescribed manner, it is possible to obtain an electromagnetic absorbing sheet with small variation in electromagnetic absorption caused by temperature changes.

[0017] This invention is based on the above insights. Specifically, the main components of this invention are as follows.

[0018] [1] An electromagnetic wave absorbing sheet comprising a substrate made of organic matter and powder supported in said substrate, characterized in that,

[0019] The powder is composed of MnZn ferrite powder, aluminum powder, and silicon carbide powder.

[0020] When the volume ratio of MnZn ferrite powder relative to the entire electromagnetic wave absorbing sheet is set to V M Let the volume ratio of aluminum powder be V. A The volume ratio of silicon carbide powder is set as V. S At that time, by V S / (V M +V A +V S The percentage of silicon carbide represented by ) R S1 It is between 1.5% and 41%.

[0021] [2] An electromagnetic wave absorbing sheet comprising a substrate made of organic matter and powder supported in said substrate, characterized in that,

[0022] The powder is composed of MnZn ferrite powder and silicon carbide powder.

[0023] When the volume ratio of MnZn ferrite powder relative to the entire electromagnetic wave absorbing sheet is set to V M The volume ratio of silicon carbide powder is set as V. S At that time, by V S / (V M +V S The percentage of silicon carbide represented by ) R S2 It is between 0.5% and 29%.

[0024] [3] According to the electromagnetic wave absorbing sheet described in [1], wherein, V M +V A +V S The total volume of packing material, V, is represented. P1 It is between 35% and 60%.

[0025] [4] According to the electromagnetic wave absorbing sheet described in [2], wherein, V M +V S The total volume of packing material, V, is represented. P2 It is between 30% and 60%.

[0026] [5] The radio wave absorbing sheet according to any one of [1] to [4], wherein the average particle size of the MnZn ferrite powder, the average particle size of the silicon carbide powder, and the average particle size of the aluminum powder in the case of containing the aluminum powder are all 1 μm or more and 60 μm or less.

[0027] [6] The electromagnetic wave absorbing sheet according to any one of [1] to [5], wherein the electromagnetic wave absorbing sheet is of dielectric loss type.

[0028] [7] The radio wave absorbing sheet according to any one of [1] to [6], wherein the frequency at which the reflection attenuation reaches its peak at 25°C is set as f. 25 The frequency at which the reflection attenuation reaches its peak at 120℃ is set as f. 120 At that time, f 25 with f 120 The absolute value of the difference, i.e., |f 120 -f 25 |Below 2.0GHz, and,

[0029] Frequency f at 25℃ 25 The absolute value of reflection attenuation A 25 and the frequency f at 120℃ 25 The absolute value of reflection attenuation A 120 All are above 10dB.

[0030] [8] An electromagnetic wave absorbing sheet, characterized in that it comprises dielectric fillers having a positive temperature dependence of the real part of the dielectric constant and dielectric fillers having a negative temperature dependence of the real part of the dielectric constant, mixed together.

[0031] When the frequency at which the reflection attenuation reaches its peak at 25℃ is set as f 25 The frequency at which the reflection attenuation reaches its peak at 120℃ is set as f. 120 At that time, f 25 with f 120 The absolute value of the difference, i.e., |f 120 -f 25 |Below 2.0GHz, and,

[0032] Frequency f at 25℃ 25 The absolute value of reflection attenuation A 25 and the frequency f at 120℃ 25 The absolute value of reflection attenuation A 120 All are above 10dB.

[0033] Invention Effects

[0034] According to the present invention, it is possible to provide an electromagnetic wave absorbing sheet with small variation in electromagnetic wave absorption due to temperature changes. Attached Figure Description

[0035] Figure 1 These are the measured data of the reflection attenuation of the radio wave absorbing sheet in Example 5.

[0036] Figure 2 These are the measured data of the reflection attenuation of the radio wave absorbing sheet in Comparative Example 1. Detailed Implementation

[0037] Hereinafter, embodiments (first embodiment, second embodiment, and third embodiment) of the electromagnetic wave absorbing sheet of the present invention will be described. However, this description is intended to illustrate the present invention and is not intended to limit the present invention in any way.

[0038] (First wave absorbing sheet)

[0039] The first embodiment of the present invention relates to an electromagnetic wave absorbing sheet (hereinafter, sometimes referred to as "the first sheet") comprising a substrate made of an organic material and powder supported thereon, wherein the powder is composed of MnZn ferrite powder, aluminum powder, and silicon carbide powder. That is, the filler contained in the first sheet comprises three types of filler (powders). Furthermore, the first sheet is characterized in that, when the volume ratio of the MnZn ferrite powder relative to the entire electromagnetic wave absorbing sheet is set to V... M Let the volume ratio of aluminum powder be V. A The volume ratio of silicon carbide powder is set as V. S At that time, by V S / (V M +V A +V S The percentage of silicon carbide represented by ) R S1 It is between 1.5% and 41%.

[0040] According to the inventors' in-depth research, for electromagnetic wave absorbing sheets containing only MnZn ferrite and / or aluminum as fillers, the real part of its dielectric constant decreases as the temperature rises. That is, it is known that, for example, MnZn ferrite and aluminum are fillers whose real part of the dielectric constant decreases with increasing temperature. This is presumably due to electron scattering caused by lattice vibrations, leading to an increase in the resistance of the filler. Therefore, for electromagnetic wave absorbing sheets containing only MnZn ferrite and / or aluminum as fillers, as the temperature rises, the peak value of the electromagnetic wave absorption shifts towards the higher frequency side, resulting in a decrease in the electromagnetic wave absorption at the target frequency.

[0041] Furthermore, according to the inventors' in-depth research, for an electromagnetic wave absorbing sheet containing only silicon carbide as a filler, the real part of its dielectric constant increases with increasing temperature. That is, it is known that silicon carbide, for example, is a filler whose real part of the dielectric constant increases with increasing temperature. This is presumably due to the increased carrier density and decreased resistance of the filler caused by the increased temperature. Therefore, for an electromagnetic wave absorbing sheet containing only silicon carbide as a filler, the peak value of electromagnetic wave absorption shifts to the lower frequency side when the temperature rises, resulting in a decrease in electromagnetic wave absorption at the target frequency.

[0042] Based on the inventors' insights described above, in the first sheet, by mixing three fillers—MnZn ferrite powder and aluminum powder, which are fillers whose real part of dielectric constant decreases with increasing temperature, and silicon carbide powder, which is a filler whose real part of dielectric constant increases with increasing temperature—and adjusting their volume ratio, it is possible to suppress the phenomenon that the frequency at which the electromagnetic wave absorption (reflection attenuation) reaches its peak (hereinafter, sometimes referred to as the "peak frequency") shifts with temperature changes. As a result, in the first sheet, even with temperature changes, the electromagnetic wave absorption at the target frequency can be maintained at a certain level or higher. In this way, the first sheet is manufactured based on the structure of the three fillers (MnZn ferrite powder, aluminum powder, and silicon carbide powder) and by discovering the correlation between the volume ratio of these fillers and the electromagnetic wave absorption at the target frequency.

[0043] Specifically, in the first sheet, as described above, when the volume ratio of MnZn ferrite powder to the entire sheet is set as V... M The volume ratio of aluminum powder to the entire sheet is V. A Let the volume ratio of silicon carbide powder to the entire sheet be V. S At that time, it is necessary to satisfy V S / (V M +V A +V S The percentage of silicon carbide represented by ) R S1 The content is between 1.5% and 41%. In sheets based on the above three filler structures, if the silicon carbide content R... S1 If the proportion of silicon carbide is less than 1.5%, the peak frequency will shift significantly towards higher frequencies as the temperature increases. Specifically, if the proportion of silicon carbide R... S1 If it is less than 1.5%, then the peak frequency at 25℃ is set to f. 25 Set the peak frequency at 120℃ as f 120 At that time, f 25 with f 120 The absolute value of the difference is |f 120 -f 25 (Hereinafter, this absolute value will sometimes be referred to as the "frequency change".) Exceeding 2.0 GHz. As a result, the variation in electromagnetic wave absorption due to temperature changes becomes larger. Furthermore, in sheets based on the above three filler structures, if the proportion of silicon carbide R... S1 If the silicon carbide content exceeds 41%, the peak frequency will shift significantly towards lower frequencies as temperature increases. Specifically, if the silicon carbide content R... S1 If the change exceeds 41%, the aforementioned frequency variation exceeds 2.0 GHz. As a result, the variation in radio wave absorption caused by temperature changes becomes larger.

[0044] In particular, from the viewpoint of further reducing the variation in electromagnetic wave absorption caused by temperature changes, the silicon carbide content R in the first sheet... S1 Preferably, it is 6% or more and 37% or less, more preferably 12% or more and less than 32%.

[0045] Furthermore, in the first sheet, V is preferred. M +V A +V S The total volume of packing material, V, is represented. P1 The content is between 35% and 60%. In the first sheet, if the total volume of filler V... P1 If the content is between 35% and 60%, the resonant frequency of electromagnetic wave absorption can be adjusted from the quasi-millimeter wave band to the millimeter wave band. Additionally, if the total volume V of the filler... P1 If the filler content is below 60%, then when wet methods such as scraper forming are used to prepare sheets, the formed sheets shrink and increase during heat treatment, making them prone to cracking on the sheet surface. Furthermore, if the total filler volume V... P1 If the filler content is below 60%, the flexibility of the resulting electromagnetic wave absorbing sheet tends to decrease. However, when there are no problems in the manufacturing process of the electromagnetic wave absorbing sheet and the flexibility of the resulting electromagnetic wave absorbing sheet is not required, the total filler volume V... P1 It can also exceed 60%.

[0046] In this specification, the volume ratio of each filler relative to the entire sheet (or, if it is the first sheet, the volume ratio V of the MnZn ferrite powder) is specified. M Volume ratio V of aluminum powder A The volume ratio V of silicon carbide powder S The following steps are followed: First, the electromagnetic absorbing sheet is cut in a direction perpendicular to the in-plane direction. After ion milling polishing of the cross-section, a reflected electron image is captured using a scanning electron microscope. Next, using the captured reflected electron image, the colors of the organic substrate and each filler (MnZn ferrite powder, aluminum powder, and silicon carbide powder if it is the first sheet) are multi-valued to distinguish the materials. After differentiation, the area ratio of each filler is calculated and defined as the volume ratio of the filler relative to the entire sheet (sometimes also called the amount added). Furthermore, during multi-valued processing, appropriate settings can be made to ensure clear boundaries between the materials.

[0047] Next, we will explain the various materials that may be contained in the sheet.

[0048] <Substrate>

[0049] The organic material constituting the substrate is not particularly limited. However, since electromagnetic wave absorbing sheets typically require flexibility and processability, the organic material constituting the substrate is preferably selected from one or more of rubber, elastomers, and resins. Specifically, considering its excellent resistance to cold and heat, insulation resistance, and wide use in electromagnetic wave absorbing sheets, the organic material constituting the substrate is preferably selected from one or more of silicone resins and acrylic resins. This resin can be a compounded resin or a liquid resin.

[0050] The following explanation uses silicone resins as an example. Liquid silicone resins can be commercially available products for general industrial use. From a liquid form perspective, silicone resins exist in single-component and two-component forms; from a curing form perspective, they exist in condensation reaction and addition reaction types, allowing for the use of any type. Furthermore, condensation reaction silicone resins require curing time, while addition reaction silicone resins can be expected to cure in a shorter time by incorporating a heating process. Therefore, from a productivity perspective, addition reaction silicone resins are preferred. For liquid silicones, if the viscosity is too low, the shape retention during sheet molding deteriorates; if the viscosity is too high, uniform dispersion of the filler becomes difficult. Therefore, a viscosity of 1–10 Pa·s is preferred.

[0051] <Powder>

[0052] The first sheet contains powder supported on the aforementioned substrate, which is composed of three fillers: MnZn ferrite powder, aluminum powder, and silicon carbide powder.

[0053] The average particle size of the MnZn ferrite powder contained in the sheet is preferably 1 μm or more and 60 μm or less. If the average particle size of the MnZn ferrite powder is 1 μm or more, the flowability and dispersibility of the filler can be well maintained, suppressing manufacturability deterioration. Furthermore, if the average particle size of the MnZn ferrite powder is 60 μm or less, the smoothness of the surface of the molded sheet can be well maintained. From the same viewpoint, the average particle size of the MnZn ferrite powder is more preferably 2 μm or more, further preferably 3 μm or more, and even more preferably 50 μm or less, and even more preferably 40 μm or less.

[0054] The average particle size of the aluminum powder (i.e., elemental aluminum powder) contained in the first sheet is preferably 1 μm or more and 60 μm or less. If the average particle size of the aluminum powder is 1 μm or more, the flowability and dispersibility of the filler can be well maintained, suppressing deterioration in manufacturability. Furthermore, if the average particle size of the aluminum powder is 60 μm or less, the smoothness of the surface of the formed sheet can be well maintained. From the same viewpoint, the average particle size of the aluminum powder is more preferably 2 μm or more, further preferably 3 μm or more, even more preferably 50 μm or less, and even more preferably 40 μm or less.

[0055] The average particle size of the silicon carbide powder contained in the sheet is preferably 1 μm or more and 60 μm or less. If the average particle size of the silicon carbide powder is 1 μm or more, the flowability and dispersibility of the filler can be well maintained, suppressing manufacturability deterioration. Furthermore, if the average particle size of the silicon carbide powder is 60 μm or less, the smoothness of the surface of the molded sheet can be well maintained. From the same viewpoint, the average particle size of the silicon carbide powder is more preferably 2 μm or more, further preferably 3 μm or more, even more preferably 50 μm or less, and even more preferably 40 μm or less.

[0056] Furthermore, in this specification, the average particle size of each filler can be measured using a particle size distribution meter. Additionally, the average particle size of each filler can also be measured from the manufactured electromagnetic absorbing sheet. Specifically, firstly, after ion milling and polishing the cross-section of the electromagnetic absorbing sheet, a reflected electron image is captured using a scanning electron microscope. To improve measurement accuracy, the magnification is set to 500x to 5000x according to the filler particle size; 5000x is preferred when the filler particle size is predominantly small (e.g., 1 μm), and 500x is preferred when the filler particle size is predominantly large (e.g., 60 μm). Next, in the captured reflected electron image, each filler (for the first sheet, the filler is MnZn ferrite powder, aluminum powder, or silicon carbide powder) is distinguished by multi-value processing of the image color. After distinction, the equivalent circle diameter of each filler is taken as its particle size, and the average value of all particle sizes of that filler in the captured field of view is defined as the average particle size of that filler contained in the electromagnetic absorbing sheet. In addition, fillers near the end of the captured electron image, or fillers with a particle size of less than 0.1 μm in the captured electron image, are removed from the test object.

[0057] As silicon carbide powder, industrially available silicon carbide powder can be used. Examples of industrially available silicon carbide powders include those for grinding and polishing applications, which include a high-purity green type and a lower-purity black type. The black type is characterized by a higher content of impurity elements Al and Fe compared to the green type. Typically, black type silicon carbide powder contains 0.1–0.2 mass% Al and 0.1–0.3 mass% Fe, while green type silicon carbide powder contains approximately 0.01–0.1 mass% Al and about 0.02–0.03 mass% Fe.

[0058] In particular, as silicon carbide powder, it is preferable to use low-purity black type silicon carbide powder as a loss filler. Here, the content of Al and Fe, which are impurity elements of silicon carbide, can be detected, for example, by surface analysis of the silicon carbide powder based on EPMA (Electron Probe X-ray Micro-Analyzer) (WDS: Wavelength Dispersive X-ray Spectroscopy) on the polished surface (ion milled surface, etc.) of the electromagnetic wave absorbing sheet.

[0059] Furthermore, the crystal structure of silicon carbide powder is mainly based on the tetrahedron as the smallest structural unit. According to the layered structure of this tetrahedron, the 4H and 6H types are predominant. In high-purity green silicon carbide, the 6H structure is dominant, while the 4H type is less common. Conversely, in low-purity black silicon carbide, the 4H and 6H types coexist, with the 4H type being more prevalent.

[0060] Furthermore, in silicon carbide powder, the preferred content ratio of 4H type to 6H type is I. 4H / I 6H High, specifically, I 4H / I 6H Preferably, it is 0.1 or more, more preferably 0.2 or more. If I 4H / I 6H If the dielectric constant is 0.1 or higher, materials with a high dielectric loss tangent tanδ (=ε" / ε'), which is an indicator of energy loss and is expressed by the real part ε' and the imaginary part ε" of the dielectric constant, can be obtained, thus making them more practical electromagnetic wave absorbers. On the other hand, I 4H / I 6H There is no particular upper limit, but it is preferred to be below 0.5.

[0061] In addition, the characteristics of the silicon carbide powder contained in the electromagnetic wave absorbing sheet, especially I... 4H / I 6H It can be identified by X-ray diffraction using Cu-Kα as the radiation source on the surface of the absorbing sheet. The X-ray diffraction measurement conditions are as follows.

[0062] <device>

[0063] Manufacturer: Rigaku Corporation, Japan

[0064] Device Name: SmartLab (9kW) Fully Automated Horizontal Multifunctional High-Power X-ray Diffraction System

[0065] Tube ball: Cu

[0066] <Optical System Conditions>

[0067] CBO selects a narrow slot: BB

[0068] Incident parallel slit (Soller / PSC): 5.0 deg

[0069] Length limiting slit (IS length): 10.0mm

[0070] Optical receiver (PSA): None

[0071] Optical receiving parallel slit (Soller): 5.0deg

[0072] <Measurement Conditions>

[0073] Scan axis: 2θ / θ, Mode: Continuous, Range specification: Absolute

[0074] Speed ​​counting time: 3.0 degrees / min

[0075] Scan: 20 degrees to 80 degrees

[0076] Data collection interval: 0.01 degrees

[0077] IS: 1 / 2 degree

[0078] Optical receiving slit RS1: 8.0mm

[0079] Optical receiving slit RS2: 13.0mm

[0080] Attenuator: Open

[0081] The following steps were taken to analyze the measured data. Using Rigaku's comprehensive powder X-ray analysis software PDXL, to remove the background effects from the obtained data, the value yobs-bkg was obtained by subtracting bkg from the diffraction intensity data yobs. Within the range of 2θ = 34.4–35°, the value obtained by subtracting the minimum value from the maximum value of yobs-bkg was taken as the peak intensity I originating from 4H-SiC. 4H Similarly, within the range of 2θ = 35–36°, the value obtained by subtracting the minimum value from the maximum value of yobs-bkg is taken as the peak intensity I originating from 6H-SiC. 6H Then, we can use these I... 4H and I 6H To find I 4H / I 6H .

[0082] <Other Additives>

[0083] In addition to the aforementioned substrate and powder, the sheet material may contain other additives within a range that does not reduce electromagnetic absorption or affect the curing properties of the substrate. Examples of such additives include flame retardants, flame retardant auxiliaries, thermal conductivity improvers, bulking agents, plasticizers, dispersants, and antioxidants. These additives may be used individually or in combination of two or more. For example, as flame retardants, materials that do not cause environmental burden are preferred, such as hydroxide compounds like aluminum hydroxide and magnesium hydroxide; and nitrogen compounds like melamine cyanurate. Additionally, examples of flame retardant auxiliaries include red phosphorus. Furthermore, these additives may be in powder form, but in this case, the powdered additive is not included in the powder composed of MnZn ferrite powder, silicon carbide powder, etc., as described in this invention.

[0084] <Various Properties of Sheets>

[0085] The thickness of the sheet is preferably 0.10 mm or more and 1 mm or less. If the sheet thickness is 0.10 mm or more, sufficient strength for handling can be achieved. Furthermore, if the thickness is 1 mm or less, it is possible to accommodate the thinning and miniaturization of electronic devices. Moreover, although affected by the relative permittivity of the substrate, if the sheet thickness is 0.10 mm or more and 1 mm or less, a resonant sheet with electromagnetic wave absorption in the frequency range of 18–90 GHz can be manufactured.

[0086] In the high-frequency band above 18 GHz, MnZn ferrite exhibits no magnetic loss due to the snooker limit. Therefore, MnZn ferrite functions as a dielectric loss type filler in the high-frequency band above 18 GHz. Furthermore, silicon carbide also lacks magnetic loss and thus functions as a dielectric loss type filler. Therefore, since the sheet contains both silicon carbide and MnZn ferrite, it is a dielectric loss type electromagnetic wave absorbing sheet. That is, it becomes an electromagnetic wave absorbing sheet used in the 18–90 GHz range (frequency band).

[0087] The sheet material achieves a rational proportion of silicon carbide powder relative to the total filler (silicon carbide content), thus resulting in minimal variation in electromagnetic wave absorption due to temperature changes, and a relatively large inherent electromagnetic wave absorption. Specifically, when the frequency at which the reflection attenuation of the sheet reaches its peak at 25°C is set as f... 25 The frequency at which the reflection attenuation of the sheet reaches its peak at 120°C is set as f. 120 At that time, f 25 with f 120 The absolute value of the difference, i.e., |f 120 -f 25 The frequency change is preferably below 2.0 GHz, and the frequency f at 25°C is... 25 The absolute value of reflection attenuation A25 and the frequency f at 120℃ 25 The absolute value of reflection attenuation A 120 All are preferably 10dB or higher. Furthermore, the above-mentioned |f of the sheet material 120 -f 25 The frequency change is more preferably 1.5 GHz or less, and even more preferably 1.0 GHz or less. Furthermore, the absolute value A of the sheet material mentioned above... 25 and A 120 More preferably, it is 15dB or more, and even more preferably, it is 18dB or more.

[0088] In addition, in this specification, the absolute value of the reflection attenuation is sometimes referred to as the "electromagnetic wave absorption amount".

[0089] Furthermore, the reflection attenuation of the electromagnetic wave absorbing sheet can be measured by scanning the frequency using a reflection attenuation measuring device while the sheet is bonded to an aluminum plate and heated to a specified temperature. Specifically, the measurement can be performed using the method described in the embodiments.

[0090] <Other Components>

[0091] Typically, electromagnetic wave absorbing sheets are used by attaching them to an object. Therefore, the sheet can have an adhesive layer on one side (back side). Furthermore, when the object to which the electromagnetic wave absorbing sheet is attached is not conductive, the sheet can also have a conductive layer on one side (back side). The material of the conductive layer is not particularly limited, but metallic materials are generally used. Examples of metals include brass, copper, iron, nickel, stainless steel, and aluminum. Furthermore, the conductive layer can be a layer composed of a single metallic substance, but it can also be a layer other than that; for example, a laminate obtained by vapor-depositing a metal such as aluminum onto a thin film can be used. The thickness of the conductive layer should be set to ensure that the electromagnetic waves incident on the electromagnetic wave absorbing sheet are reflected and that the layer has good flexibility. Specifically, it is preferably 10 nm to 300 μm, more preferably 50 nm to 100 μm. If the thickness of the conductive layer is less than 10 nm, the electromagnetic waves incident on the electromagnetic wave absorbing sheet may pass through the conductive layer, resulting in a decrease in the reflectance of the conductive layer. Furthermore, if the thickness of the conductive layer exceeds 300 μm, not only will the total thickness of the electromagnetic wave absorbing sheet become undesirably thicker, but the sheet may also lose its flexibility.

[0092] To improve weather resistance or ensure high surface resistivity, the sheet may also have a protective layer on one side (surface) made of resin materials such as PET resin, PEN resin, or polyvinyl chloride resin. The thickness of the protective layer is not particularly limited as long as it does not reduce electromagnetic absorption; specifically, it is preferably 10 μm to 200 μm, more preferably 30 μm to 130 μm. However, from a flexibility perspective, the sheet preferably does not have the aforementioned protective layer.

[0093] <Sheet Manufacturing>

[0094] There is no particular limitation on the method of manufacturing sheet material. As an example, a sheet material manufacturing method includes: a mixing process, in which organic matter (substrate) and a mixing material containing various fillers are mixed to prepare a mixture; and a molding process, in which the mixture is formed into a sheet material.

[0095] Regarding the aforementioned mixing process, when using, for example, liquid silicone resin as the organic material, it can be mixed with a compounding material containing various fillers using a planetary mixer and then mixed. Alternatively, when using, for example, a compounded silicone resin as the organic material, it can be mixed with a compounding material containing various fillers using a pressure kneader or an open mill and then mixed. In this case, it is preferable to mix while cooling to below 100°C to prevent vulcanization due to heat generated during the mixing process. Furthermore, when using a scraper molding method as the molding process described later, a solvent can be added to the mixture to adjust its viscosity, enabling scraper molding. Examples of such solvents include organic solvents with good solubility in organic materials (substrate), specifically toluene and methyl ethyl ketone.

[0096] Examples of methods for the above-mentioned forming process (methods for producing sheets) include compression molding, extrusion molding, calendering, calendering roll forming, and doctor blade forming. As an example, in the case of compression molding, the compounded material is placed into a mold with grooves to achieve a specified thickness for the formed radio wave absorbing sheet, and compression molding is performed for 5 to 30 minutes at a temperature of 120–200°C to promote vulcanization.

[0097] After the above molding process, heat treatment can also be performed to remove the solvent and solidify the organic matter.

[0098] The first sheet has been described above, but this disclosure is not limited to the above description and can be modified as appropriate.

[0099] (Second radio wave absorbing sheet)

[0100] The second embodiment of the present invention relates to an electromagnetic wave absorbing sheet (hereinafter, sometimes referred to as "the second sheet") comprising a substrate made of an organic material and powder supported on the substrate, wherein the powder is composed of MnZn ferrite powder and silicon carbide powder. That is, the filler contained in the second sheet is composed of two types of filler (powder). In other words, the second sheet differs from the first sheet in that it does not contain aluminum powder. Furthermore, the second sheet is characterized in that, when the volume ratio of the MnZn ferrite powder relative to the entire electromagnetic wave absorbing sheet is set to V... MThe volume ratio of silicon carbide powder is V S At that time, by V S / (V M +V S The percentage of silicon carbide represented by ) R S2 It is between 0.5% and 29%.

[0101] Based on the inventors' insights from the first sheet already described, in the second sheet, by mixing two fillers—MnZn ferrite powder (which has a lower real part of dielectric constant with increasing temperature) and silicon carbide powder (which has a higher real part of dielectric constant with increasing temperature) and adjusting their volume ratio, it is possible to suppress the phenomenon of peak frequency shifting with temperature. As a result, in the second sheet, even with temperature changes, the absorption of electromagnetic waves at the target frequency can be maintained above a certain level. Thus, the second sheet is manufactured based on two filler structures (MnZn ferrite powder and silicon carbide powder) and by discovering the correlation between the volume ratio of these fillers and the absorption of electromagnetic waves at the target frequency.

[0102] Specifically, in the second sheet, as described above, when the volume ratio of MnZn ferrite powder to the entire sheet is set to V... M Let the volume ratio of silicon carbide powder to the entire sheet be V. S At that time, it is necessary to satisfy V S / (V M +V S The percentage of silicon carbide represented by ) R S2 The content is between 0.5% and 29%. In sheets based on the above two filler structures, if the silicon carbide content R... S2 If the proportion of silicon carbide is less than 0.5%, the peak frequency will shift significantly towards higher frequencies as the temperature increases. Specifically, if the silicon carbide content R... S2 If it is less than 0.5%, then the peak frequency at 25℃ will be set to f. 25 The peak frequency at 120℃ is f 120 At that time, f 25 with f 120 The absolute value of the difference, i.e., |f 120 -f 25 The frequency variation exceeds 2.0 GHz. As a result, the variation in electromagnetic wave absorption due to temperature changes becomes larger. Furthermore, in sheets based on the two filler structures mentioned above, if the proportion of silicon carbide R... S2 If the silicon carbide content exceeds 29%, the peak frequency will shift significantly towards lower frequencies as temperature increases. Specifically, if the silicon carbide content R... S2If the change exceeds 29%, the aforementioned frequency variation exceeds 2.0 GHz. As a result, the variation in radio wave absorption caused by temperature changes becomes larger.

[0103] In particular, from the viewpoint of further reducing the variation in electromagnetic wave absorption caused by temperature changes, the silicon carbide content R in the second sheet is... S2 Preferably, it is 4% or more and 25% or less, more preferably 8% or more and 22% or less.

[0104] Furthermore, in the second sheet, V is preferred. M +V S The total volume of packing material, V, is represented. P2 The content is between 30% and 60%. In the second sheet, if the total volume of filler V... P2 If the concentration is between 30% and 60%, the resonant frequency of electromagnetic wave absorption can be adjusted from the quasi-millimeter wave band to the millimeter wave band. Additionally, if the total volume V of the filler... P2 If the filler content is below 60%, then when wet methods such as scraper forming are used to prepare sheets, the formed sheets will shrink more during the heat treatment process, making them prone to surface cracking. Furthermore, if the total filler volume V... P2 If the filler content is below 60%, the flexibility of the resulting electromagnetic wave absorbing sheet tends to decrease. However, when there are no problems in the manufacturing process of the electromagnetic wave absorbing sheet and the flexibility of the resulting electromagnetic wave absorbing sheet is not required, the total filler volume V... P2 It can also exceed 60%.

[0105] In the second sheet, the descriptions of details or preferred embodiments other than those described above, specifically regarding the substrate, powder (including MnZn ferrite powder and silicon carbide powder), other additives, various properties of the sheet, other components, and details or preferred embodiments of sheet manufacturing, are the same as in the first sheet. Therefore, repeated descriptions are omitted, and reference is made to the description in the first sheet.

[0106] The second sheet has been described above, but this disclosure is not limited to the above description and can be modified as appropriate.

[0107] (Third radio wave absorbing sheet)

[0108] The electromagnetic wave absorbing sheet (hereinafter, sometimes referred to as the "third sheet") according to the third embodiment of the present invention comprises dielectric fillers having a temperature dependence on the real part of their dielectric constant and dielectric fillers having a temperature dependence on the real part of their dielectric constant. These dielectric fillers are mixed and contained in the third sheet. Furthermore, the third sheet is characterized in that the frequency at which the reflection attenuation reaches its peak at 25°C is f. 25 The frequency at which the reflection attenuation reaches its peak at 120℃ is f. 120At that time, f 25 with f 120 The absolute value of the difference, i.e., |f 120 -f 25 |Below 2.0 GHz, and at 25°C, the frequency f 25 The absolute value of reflection attenuation A 25 and the frequency f at 120℃ 25 The absolute value of reflection attenuation A 120 All are above 10dB.

[0109] In this specification, "dielectric filler with a positive temperature dependence of the real part of the dielectric constant" refers to filler whose real part of the dielectric constant increases with increasing temperature (25℃~120℃), and is sometimes simply referred to as "positive dielectric filler". Specifically, filler whose real part of the dielectric constant measured at 25℃, 60℃, 90℃, and 120℃ satisfies (real part of dielectric constant at 25℃) < (real part of dielectric constant at 60℃) < (real part of dielectric constant at 90℃) < (real part of dielectric constant at 120℃) is defined as "dielectric filler with a positive temperature dependence of the real part of the dielectric constant".

[0110] In this specification, "dielectric filler with a negative temperature dependence of the real part of the dielectric constant" refers to filler whose real part of the dielectric constant decreases as the temperature increases (25℃~120℃), and is sometimes simply referred to as "negative dielectric filler". Specifically, filler whose real part of the dielectric constant measured at 25℃, 60℃, 90℃, and 120℃ satisfies (real part of dielectric constant at 25℃) > (real part of dielectric constant at 60℃) > (real part of dielectric constant at 90℃) > (real part of dielectric constant at 120℃) is defined as "dielectric filler with a negative temperature dependence of the real part of the dielectric constant".

[0111] Based on the inventors' understanding of the invention as described in the first sheet, in the third sheet, by mixing the negative dielectric filler with the positive dielectric filler and making |f 120 -f 25 | For frequencies below 2.0 GHz, the absolute value of the reflection attenuation A 25 and A 120 All values ​​are above 10dB, thereby suppressing the phenomenon of peak frequency shift with temperature changes. As a result, even with temperature changes, the absorption of electromagnetic waves at the target frequency can be maintained at a certain level in the third sheet. Furthermore, in the third sheet, the aforementioned |f 120 -f 25 The frequency change is preferably 1.5 GHz or less, more preferably 1.0 GHz or less. Furthermore, in the third sheet, the absolute value A mentioned above... 25 and A 120Preferably, it is 15dB or more, and more preferably 18dB or more.

[0112] In addition, it should be noted that the scope of the invention of the third sheet may overlap with the scope of the invention of the first sheet and / or the second sheet.

[0113] Examples of positive dielectric fillers, besides silicon carbide, include boron carbide and gallium nitride. The third sheet may contain one type of positive dielectric filler or a combination of two or more types. In particular, silicon carbide powder is preferred as the positive dielectric filler, and I0 powder is more preferred. 4H / I 6H The silicon carbide powder described above has a particle size of 0.1 or higher. In this case, it is possible to further suppress the variation in electromagnetic wave absorption caused by temperature changes while further improving electromagnetic wave absorption performance.

[0114] Examples of negative dielectric fillers include, in addition to MnZn ferrite and aluminum, graphite, copper, and silver. The third sheet may contain one type of negative dielectric filler or a combination of two or more types.

[0115] Positive dielectric fillers tend to exhibit a greater rate of change of the real part of their dielectric constant with temperature compared to negative dielectric fillers. Considering this, in the third sheet, when the volume ratio of the positive dielectric filler to the entire sheet is set as V... + Let V be the volume ratio of the negative dielectric filler to the entire sheet. - When, it is preferred to use V + / (V + +V - R represents the proportion of positive dielectric filler. + It is below 50%.

[0116] Furthermore, in the third sheet, V is preferred. + +V - The total volume of packing material, V, is represented. P3 The content is between 30% and 60%. In the third sheet, if the total volume of filler V... P3 If the concentration is between 30% and 60%, the resonant frequency of electromagnetic wave absorption can be adjusted from the quasi-millimeter wave band to the millimeter wave band. Additionally, if the total volume V of the filler... P3 If the filler content is below 60%, then when wet methods such as scraper forming are used to prepare sheets, the formed sheets will shrink more during the heat treatment process, making them prone to surface cracking. Furthermore, if the total filler volume V... P3 If the filler content is below 60%, the flexibility of the resulting electromagnetic wave absorbing sheet tends to decrease. However, when there are no problems in the manufacturing process of the electromagnetic wave absorbing sheet and the flexibility of the resulting electromagnetic wave absorbing sheet is not required, the total filler volume V... P3It can also exceed 60%.

[0117] The average particle size of the positive dielectric filler contained in the third sheet is preferably 1 μm or more and 60 μm or less. If the average particle size of the positive dielectric filler is 1 μm or more, the flowability and dispersibility of the filler can be well maintained, suppressing deterioration in manufacturability. Furthermore, if the average particle size of the positive dielectric filler is 60 μm or less, the smoothness of the surface of the molded sheet can be well maintained. From the same viewpoint, the average particle size of the positive dielectric filler is more preferably 2 μm or more, further preferably 3 μm or more, and even more preferably 50 μm or less, and even more preferably 40 μm or less.

[0118] The average particle size of the negative dielectric filler contained in the third sheet is preferably 1 μm or more and 60 μm or less. If the average particle size of the negative dielectric filler is 1 μm or more, the flowability and dispersibility of the filler can be well maintained, suppressing manufacturability deterioration. Furthermore, if the average particle size of the negative dielectric filler is 60 μm or less, the smoothness of the surface of the molded sheet can be well maintained. From the same viewpoint, the average particle size of the negative dielectric filler is more preferably 2 μm or more, further preferably 3 μm or more, and even more preferably 50 μm or less, and even more preferably 40 μm or less.

[0119] The third sheet preferably comprises a substrate made of organic material, in which positive dielectric fillers and negative dielectric fillers are supported. In this case, the details or preferred embodiments of the organic material constituting the substrate are the same as those in the first sheet. Therefore, repeated descriptions are omitted, and reference is made to that description in the first sheet.

[0120] In the third sheet, the descriptions of details or preferred embodiments other than those described above, specifically regarding other additives, various properties of the sheet, other components, and details or preferred embodiments of sheet manufacturing, are the same as in the first sheet. Therefore, repeated descriptions are omitted, and reference is made to the description in the first sheet.

[0121] The third sheet has been described above, but this disclosure is not limited to the above description and can be modified as appropriate.

[0122] Example

[0123] The present invention will be described in more detail below with reference to embodiments, but these embodiments are intended to illustrate the present invention and are not intended to limit the present invention in any way.

[0124] (Fabrication of radio wave absorbing sheet)

[0125] A coating solution (mixture) is prepared by mixing silicone resin (as the substrate), various fillers (MnZn ferrite powder, aluminum powder, silicon carbide powder), and toluene (as the solvent) using a planetary mixer. Using this coating solution, the film is formed into a sheet on a PET film using a doctor blade molding method. After heat treatment, the toluene is removed and the silicone resin is cured, producing an electromagnetic absorbing sheet of the specified thickness.

[0126] The volume ratios of various fillers relative to the overall electromagnetic wave absorbing sheet in each example are shown in Tables 1 and 2. Table 1 compares electromagnetic wave absorbing sheets (corresponding to the first sheet) using MnZn ferrite powder, aluminum powder, and silicon carbide powder as fillers, while Table 2 compares electromagnetic wave absorbing sheets (corresponding to the second sheet) using MnZn ferrite powder and silicon carbide powder as fillers instead of aluminum powder. In the example shown in Table 1, MnZn ferrite powder with an average particle size of 20.5 μm, aluminum powder with an average particle size of 25.4 μm, and silicon carbide powder with an average particle size of 13.2 μm were used. In the example shown in Table 2, MnZn ferrite powder with an average particle size of 34.6 μm and silicon carbide powder with an average particle size of 7.9 μm were used. Furthermore, as the silicon carbide powder, the I obtained according to the above steps was used in all examples. 4H / I 6H Powder exceeding 0.2.

[0127] Next, the following measurements and judgments were performed on the radio wave absorbing sheets produced in each example.

[0128] <Determination of the thickness of the electromagnetic wave absorbing sheet>

[0129] [Measuring Instruments]

[0130] Manufacturer: TECLOCK Co., Ltd.

[0131] Product Name: Digital Thickness Gauge

[0132] Model: SMD-565A-L

[0133] [Determination Method]

[0134] Ten points were randomly selected from the radio wave absorbing sheet, and their thickness was measured. The average value was taken as the thickness of the radio wave absorbing sheet. The results are shown in Tables 1 and 2.

[0135] <Determination of Reflection Attenuation (Electromagnetic Absorption) of Electromagnetic Absorbing Sheets>

[0136] [Device]

[0137] Manufacturer: KEYSIGHT TECHNOLOGY

[0138] Device Name: Vector Network Analyzer M9374A (60–90 GHz)

[0139] Device Name: Vector Network Analyzer P5008A (18-40GHz)

[0140] as well as

[0141] Manufacturer: KEYCOM

[0142] Device Name: Lens Antenna Type Oblique Incident Reflection Attenuation Measurement Device LAF-26.5A

[0143] [software]

[0144] Manufacturer: KEYSIGHT TECHNOLOGY

[0145] Software Name: VNA Soft Front Panel

[0146] as well as

[0147] Manufacturer: KEYCOM

[0148] Software Name: Free Space Type Radio Wave Absorption Measurement Program

[0149] [Measurement Conditions]

[0150] According to JIS R 1679:2007 standard. However, the conditions set forth in this specification shall prevail.

[0151] Dielectric lens antenna method - parallel beam method -

[0152] Vertical incidence

[0153] Frequency range: 60–90 GHz, 26.5–40 GHz, and 18–26.5 GHz

[0154] Data count: 1601

[0155] Port Power (Port1): 2dBm

[0156] Bandwidth: 1kHz

[0157] The time-domain method is used to remove the influence of reflected and scattered waves from outside the vicinity of the sample.

[0158] Time gate span: 0.5ns

[0159] [Determination Method]

[0160] A 2mm thick aluminum plate is placed on the heating plate of the reflection attenuation measuring device, and the reflection attenuation A is measured as a reference. M (25℃). Subsequently, the fabricated electromagnetic wave absorbing sheet was bonded to the aluminum plate using 0.1mm double-sided adhesive tape. While bonded, the sample was heated to the specified temperatures (25℃, 120℃) while simultaneously scanning frequencies and measuring the reflection attenuation A. S Calculate the difference A between the reflection attenuation of the sample and the reflection attenuation of the reference. S -A M absolute value | A S -A M | This is used as the amount of electromagnetic wave absorption. Additionally, a thermocouple is placed between the double-sided tape and the aluminum plate, and the temperature indicated by the thermocouple is defined as the temperature at the time of measurement.

[0161] For reference only. Figure 1 The reflection attenuation A of the radio wave absorbing sheet in Example 5 is shown. S -A M The measured data, Figure 2 The reflection attenuation A of the radio wave absorbing sheet in Comparative Example 1 is shown. S -A M The measured data.

[0162] <Measurement and Judgment of Frequency Changes>

[0163] In each example, the scanning frequency at 25°C was determined and the reflection attenuation A was measured. S Reflection attenuation at (25℃) [A] S (25℃)-A M (At 25℃) The frequency f at which peak absorption (radio wave absorption reaches its peak) is reached. 25 ; and scanning frequency at 120℃ and measuring reflection attenuation A. S Reflection attenuation at (120℃) [A] S (120℃)-A M (25℃) The frequency f that reaches its peak value 120 Additionally, find these f values. 25 with f 120 The absolute value of the difference, i.e., |f 120 -f 25 | (Frequency change). Sheets with a frequency change of less than 1.0 GHz were rated A, those exceeding 1.0 GHz but less than 1.5 GHz were rated B, those exceeding 1.5 GHz but less than 2.0 GHz were rated C, and those exceeding 2.0 GHz were rated NG. The results are shown in Tables 1 and 2. A smaller frequency change indicates a smaller variation in electromagnetic wave absorption due to temperature changes.

[0164] <f25 Measurement of electromagnetic wave absorption >

[0165] In each example, determine the frequency f at 25°C. 25 The absolute value of reflection attenuation A 25 and the frequency f at 120℃ 25 The absolute value of reflection attenuation at point A 120 The results are shown in Tables 1 and 2.

[0166] [Table 1]

[0167]

[0168] [Table 2]

[0169]

[0170] According to Table 1, when using MnZn ferrite powder, aluminum powder, and silicon carbide powder as fillers, V S / (V M +V A +V S The percentage of silicon carbide represented by ) R S1 The frequency variation of the radio wave absorbing sheets in Examples 1 to 10, which have a content of 1.5% or more and 41% or less, is all below 2.0 GHz (see also...). Figure 1 In other words, it can be seen that the electromagnetic wave absorbing sheets of Examples 1 to 10 show little variation in electromagnetic wave absorption due to temperature changes. Furthermore, the electromagnetic wave absorbing sheets of Examples 1 to 10 also correspond to the third sheet material.

[0171] In contrast, the proportion of silicon carbide R S1 The frequency variation of the radio wave absorbing sheet in Comparative Example 1, which was less than 1.5%, exceeded 2.0 GHz (see also [reference]). Figure 2 ).

[0172] In addition, the proportion of silicon carbide R S1 More than 41% of the radio wave absorbing sheets in Comparative Example 2 had a frequency variation exceeding 2.0 GHz.

[0173] Furthermore, as shown in Table 2, when using MnZn ferrite powder and silicon carbide powder as fillers, the V S / (V M +V S The percentage of silicon carbide represented by ) R S2The frequency variation of the radio wave absorbing sheets in Examples 11 to 19, which are between 0.5% and 29%, is all below 2.0 GHz. In other words, it can be seen that the radio wave absorption of the radio wave absorbing sheets in Examples 11 to 19 varies little with temperature changes. Furthermore, the radio wave absorbing sheets in Examples 11 to 19 also correspond to the third sheet material.

[0174] In contrast, the proportion of silicon carbide R S2 The frequency variation of the radio wave absorbing sheet in Comparative Example 3, which was less than 0.5%, exceeded 2.0 GHz.

[0175] In addition, the proportion of silicon carbide R S2 More than 29% of the radio wave absorbing sheets in Comparative Example 4 exhibited frequency variations exceeding 2.0 GHz.

[0176] Industrial availability

[0177] The electromagnetic wave absorbing sheet of the present invention is installed in electronic devices and is particularly effective as an electromagnetic noise response component that absorbs electromagnetic waves generated within these electronic devices. Compared with conventional products, it is an electromagnetic wave absorbing sheet with less variation in electromagnetic wave absorption due to temperature rise.

Claims

1. An electromagnetic wave absorbing sheet comprising a substrate made of organic matter and powder supported in said substrate, characterized in that, The powder is composed of MnZn ferrite powder, aluminum powder, and silicon carbide powder. When the volume ratio of MnZn ferrite powder relative to the entire electromagnetic wave absorbing sheet is set to V M Let the volume ratio of aluminum powder be V. A The volume ratio of silicon carbide powder is set as V. S At that time, by V S / (V M +V A +V S The percentage of silicon carbide represented by ) R S1 It is between 1.5% and 41%.

2. An electromagnetic wave absorbing sheet comprising a substrate made of organic matter and powder supported in said substrate, characterized in that, The powder is composed of MnZn ferrite powder and silicon carbide powder. When the volume ratio of MnZn ferrite powder relative to the entire electromagnetic wave absorbing sheet is set to V M The volume ratio of silicon carbide powder is set as V. S At that time, by V S / (V M +V S The percentage of silicon carbide represented by ) R S2 It is between 0.5% and 29%.

3. The electromagnetic wave absorbing sheet according to claim 1, wherein, By V M +V A +V S The total volume of packing material, V, is represented. P1 It is between 35% and 60%.

4. The electromagnetic wave absorbing sheet according to claim 2, wherein, By V M +V S The total volume of packing material, V, is represented. P2 It is between 30% and 60%.

5. The radio wave absorbing sheet according to any one of claims 1 to 4, wherein, The average particle size of the MnZn ferrite powder, the average particle size of the silicon carbide powder, and the average particle size of the aluminum powder (in the case of containing the aluminum powder) are all greater than 1 μm and less than 60 μm.

6. The radio wave absorbing sheet according to any one of claims 1 to 4, wherein, The electromagnetic wave absorbing sheet is of dielectric loss type.

7. The radio wave absorbing sheet according to any one of claims 1 to 4, wherein, When the frequency at which the reflection attenuation reaches its peak at 25℃ is set as f 25 The frequency at which the reflection attenuation reaches its peak at 120℃ is set as f. 120 At that time, f 25 with f 120 The absolute value of the difference, i.e., |f 120 -f 25 |Below 2.0GHz, and, Frequency f at 25℃ 25 The absolute value of reflection attenuation A 25 and the frequency f at 120℃ 25 The absolute value of reflection attenuation A 120 All are above 10dB.

8. An electromagnetic wave absorbing sheet, characterized in that, It comprises dielectric fillers with a positive temperature dependence of the real part of the dielectric constant and dielectric fillers with a negative temperature dependence of the real part of the dielectric constant, mixed together. When the frequency at which the reflection attenuation reaches its peak at 25℃ is set as f 25 The frequency at which the reflection attenuation reaches its peak at 120℃ is set as f. 120 At that time, f 25 with f 120 The absolute value of the difference, i.e., |f 120 -f 25 |Below 2.0GHz, and, Frequency f at 25℃ 25 The absolute value of reflection attenuation A 25 and the frequency f at 120℃ 25 The absolute value of reflection attenuation A 120 All are above 10dB.

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