Electromagnetic wave absorber

Abstract

To provide a technology for improving the magnetic wave absorbing performance of an electromagnetic wave absorber using a resin foam. [Solution] An electromagnetic wave absorber is provided, which comprises a resin foam containing a silicone resin and one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles, which are contained in the resin foam. The particles used in the electromagnetic wave absorber according to the present technology may have an average aspect ratio of 1 to 5. The resin foam used in the electromagnetic wave absorber according to the present technology may be a resin foam having closed cells.

Description

[Technical Field]

[0001] The present technology relates to an electromagnetic wave absorber, and more particularly to an electromagnetic wave absorber having a resin foam. [Background technology]

[0002] Foams made from resin components are widely used in a variety of fields, including construction, machinery, home appliances, transportation, packaging, daily necessities, toys, and miscellaneous goods. Various developments are underway to improve quality and add new functions to them according to each field and purpose.

[0003] For example, Patent Document 1 discloses a radio wave absorber that is lightweight and does not generate toxic gases when burned, by forming a porous structure from a rubber composition in which conductive carbon black, a radio wave absorbing material, is mixed with nitrile rubber, which is the raw rubber.

[0004] Furthermore, for example, Patent Document 2 discloses a technology for a radio wave absorber including a foam, the foam comprising a base material containing an elastomer and nanocarbon dispersed in the foam, and the content of the nanocarbon being 5 to 45 parts by mass per 100 parts by mass of the base material, thereby making it possible to change the radio wave absorption band. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-73760 [Patent Document 2] Japanese Patent Application Publication No. 2019-106421 Summary of the Invention [Problem to be solved by the invention]

[0006] Resin foams can be applied to a variety of products by taking advantage of their physical properties such as flexibility. However, because electromagnetic wave absorbers using resin foams have voids, they have generally been thought to have inferior electromagnetic wave absorbing performance compared to electromagnetic wave absorbers using non-foamed resins.

[0007] Therefore, a main object of the present technology is to provide a technology for improving the electromagnetic wave absorbing performance of an electromagnetic wave absorber using a resin foam. [Means for solving the problem]

[0008] The inventors of the present application have conducted extensive research into technology for improving the electromagnetic wave absorption performance of electromagnetic wave absorbers that use resin foam, and as a result have unexpectedly discovered that by using a specific resin and an electromagnetic wave absorbing material having a specific form, the electromagnetic wave absorption performance is improved compared to electromagnetic wave absorbers that use non-foamed resin, and have thus completed the present technology.

[0009] That is, in the present technology, first, a resin foam containing a silicone resin; one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles, which are contained in the resin foam; The present invention provides an electromagnetic wave absorber having the following structure. The particles used in the electromagnetic wave absorber according to the present technology may have an average aspect ratio of 1-5. The resin foam used in the electromagnetic wave absorber according to the present technology may be a resin foam having closed cells. The density of the resin foam used in the electromagnetic wave absorber according to the present technology is 0.5 g / cm 3 It can be more than that. The particles used in the electromagnetic wave absorber according to the present technology may be one or more particles selected from carbon-containing particles and metal particles. The electromagnetic wave absorber according to the present technology may have at least one electromagnetic wave absorption peak in a frequency range of 1 GHz or higher, and the absorption amount is −20 dB or less. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph showing the results of electromagnetic wave absorption measurements carried out in Examples. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, preferred embodiments for carrying out the present technology will be described with reference to the drawings. The embodiments described below are examples of typical embodiments of the present technology, and any of the embodiments can be combined. Furthermore, the scope of the present technology is not to be interpreted narrowly by these embodiments.

[0012] 1.Electromagnetic wave absorber The electromagnetic wave absorber according to the present technology has a resin foam. The resin foam used in the present technology contains a silicone resin and one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles. That is, the resin foam used in the present technology is a foam of a foamable resin composition containing a silicone resin and one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles. The foamable resin composition used in the present technology for producing the resin foam (hereinafter also referred to as a "resin foam-producing composition") can contain resins other than silicone resin, a blowing agent, a crosslinking agent, and various other components that can be used to produce resin foams depending on the purpose. Each component will be described in detail below.

[0013] (1) Silicone resin The silicone resin used in this technology is a resin having organopolysiloxane as the main chain.

[0014] The type of silicone resin used in the present technology is not particularly limited as long as it does not impair the function and effect of the present technology. Examples of silicone resins used in the present technology include solid raw material type silicone resins (such as millable silicone resins) and liquid raw material type silicone resins (such as one-component silicone resins and two-component silicone resins). Among these, it is preferable to use millable silicone resins as the silicone resin used in the present technology.

[0015] Millable silicone resin is a silicone resin made from organopolysiloxane as the main raw material, which is obtained by compounding and kneading various additives (fillers, dispersants, vulcanizing agents, etc.) and then thermally curing the mixture.

[0016] The resin foam used in the present technology may contain resins other than silicone resin as described below, as long as the action and effect of the present technology are not impaired. However, it is preferable that the resin foam be primarily composed of silicone resin. In the present technology, a resin foam primarily composed of silicone resin means that the resin component contains 50% by mass or more of silicone resin. In the present technology, the content of silicone resin in the resin component is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It is particularly preferable that the resin component be composed solely of silicone resin.

[0017] (2) Resins other than silicone resins The resin foam used in this technology may contain resins other than silicone resins, as long as the function and effect of this technology are not impaired. In this technology, resin is a resin in the broad sense, and includes not only resin in the narrow sense but also rubber, elastomer, etc. In this technology, as long as the function and effect of this technology are not impaired, one or more resins in the broad sense that can be used in foams with electromagnetic wave absorption properties can be used in any combination.

[0018] Resins in the narrow sense include, for example, acrylic resins, polyolefin resins, polyurethane resins, and the like.

[0019] Examples of rubber include silicone rubber, urethane rubber (U), ethylene-propylene rubber (EPM, EPDM), nitrile rubber (NBR), chloroprene rubber (CR), natural rubber (NR), isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), 1,2-polybutadiene rubber (1,2-BR), butyl rubber (IIR), chlorosulfonated polyethylene rubber (CSM), acrylic rubber (ACM, ANM), epichlorohydrin rubber (CO, ECO), polysulfide rubber (T), and fluororubber (FKM).

[0020] Examples of the elastomer include olefin elastomer (TPO), styrene elastomer (TPS), polyurethane elastomer (TPU), polyester elastomer (TPEE), and polyvinyl chloride elastomer (TPVC).

[0021] (3) One or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles The resin foam used in the present technology contains one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles. This technology is characterized by using particulate components as one or more components selected from the group consisting of conductive, dielectric, and magnetic materials to impart electromagnetic wave absorption performance. As mentioned above, electromagnetic wave absorbers using resin foam have voids, and therefore are generally thought to have inferior electromagnetic wave absorption performance compared to electromagnetic wave absorbers using non-foamed resins. However, the present inventors have surprisingly discovered that by using a silicone resin as the resin component and one or more components selected from the group consisting of particulate conductive materials, particulate dielectric materials, and particulate magnetic materials, the electromagnetic wave absorption performance is improved compared to electromagnetic wave absorbers using non-foamed resins.

[0022] In this technology, "conductive particles" are defined as particles with a surface resistivity of 1.0 x 10 12 The upper limit of the surface resistivity of the conductive particles that can be used in this technology is 1.0 × 10 12There is no particular limitation as long as it is Ω / □ or less, but it is preferably 1.0×10 10 Ω / □ or less, more preferably 1.0×10 8 Ω / □ or less, more preferably 1.0×10 7 Ω / □ or less, and even more preferably 1.0×10 6 Ω / □ or less, particularly preferably 1.0×10 5 Ω / □ or less. Using conductive particles with a surface resistivity in this range can contribute to further improving the electromagnetic wave absorption performance of the electromagnetic wave absorber to be manufactured. The lower limit of the surface resistivity of the conductive particles that can be used in the present technology is not particularly limited, and is, for example, 1 Ω / □ or more, preferably 10 Ω / □ or more, and more preferably 100 Ω / □ or more.

[0023] In the present technology, "dielectric particles" refer to particles having a dielectric constant of 1 F / m or more. The lower limit of the dielectric constant of the dielectric particles that can be used in the present technology is not particularly limited as long as it is 1 F / m or more, but is preferably 1.5 F / m or more, more preferably 2.0 F / m or more, even more preferably 2.5 F / m or more, and even more preferably 3.0 F / m or more. The use of dielectric particles with a dielectric constant in this range can contribute to further improvement of the electromagnetic wave absorption performance of the electromagnetic wave absorber to be manufactured. The upper limit of the dielectric constant of the dielectric particles that can be used in the present technology is not particularly limited, and is, for example, 30 F / m or less, preferably 20 F / m or less, and more preferably 10 F / m or less.

[0024] In the present technology, "magnetic particles" refer to particles having a magnetic permeability of 1 H / m or more. The lower limit of the magnetic permeability of magnetic particles that can be used in the present technology is not particularly limited as long as it is 1 H / m or more, but is preferably 1.5 H / m or more, more preferably 2.0 H / m or more, even more preferably 2.5 H / m or more, and even more preferably 3.0 H / m or more. The use of magnetic particles with a magnetic permeability in this range can contribute to further improvement of the electromagnetic wave absorption performance of the electromagnetic wave absorber to be manufactured. The upper limit of the magnetic permeability of magnetic particles that can be used in the present technology is not particularly limited, and is, for example, 30 H / m or less, preferably 20 H / m or less, and more preferably 10 H / m or less.

[0025] The shape of the one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles that can be used in the present technology is not particularly limited as long as it is particulate and does not impair the functions and effects of the present technology. The particle shape can be expressed by the average aspect ratio. The aspect ratio is the ratio of the major axis (long axis diameter) to the minor axis (minor axis diameter) of a particle, and in the present technology, it indicates a value calculated as aspect ratio = major axis (long axis diameter) / minor axis (minor axis diameter).

[0026] The lower limit of the aspect ratio of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles that can be used in the present technology is, for example, 1 or more. Furthermore, the upper limit of the average aspect ratio of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles is, for example, 8.0 or less, preferably 7.0 or less, more preferably 6.0 or less, even more preferably 5.0 or less, even more preferably 4.0 or less, particularly preferably 3.5 or less, and most preferably 3.0 or less. Setting the upper limit of the average aspect ratio of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles within this range can improve the dispersibility of the particles in the composition for producing a resin foam, contributing to further improvement of the electromagnetic wave absorption performance of the produced electromagnetic wave absorber. Furthermore, a low aspect ratio can also reduce the influence of orientation.

[0027] Examples of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles that can be used in the present technology include particles containing carbon such as conductive carbon black; metal particles made of metal compounds such as iron, silver, nickel, copper, tin, or alloys thereof, copper sulfide, copper iodide, zinc sulfide, and cadmium sulfide; and the like.

[0028] The amount of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles used in the composition for producing a resin foam can be freely set as long as it does not impair the functions and effects of the present technology. In the present technology, the lower limit of the amount of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles in the composition for producing a resin foam is, for example, 100 parts by mass or more, preferably 120 parts by mass or more, more preferably 130 parts by mass or more, and even more preferably 140 parts by mass or more, per 100 parts by mass of the resin component. Setting the lower limit of the amount of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles to this range can contribute to further improving the electromagnetic wave absorption performance of the produced electromagnetic wave absorber.

[0029] In the present technology, the upper limit of the amount of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles in the composition for producing a resin foam is, for example, 450 parts by mass or less, preferably 400 parts by mass or less, more preferably 350 parts by mass or less, and even more preferably 300 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles to be used within this range, it is possible to prevent a decrease in the physical properties of the produced resin foam. It is also possible to suppress a decrease in foamability.

[0030] (4) Foaming agent A foaming agent can be used in the composition for producing a resin foam. As the foaming agent that can be used in the present technology, one or more foaming agents that can be used for resin foams can be freely selected and used as long as the action and effect of the present technology are not impaired.

[0031] Examples of blowing agents that can be used in this technology include organic and inorganic thermal decomposition type chemical blowing agents. Examples of organic blowing agents include azo compounds such as azodicarbonamide (ADCA), metal azodicarboxylates (e.g., barium azodicarboxylate), and azobisisobutyronitrile (AIBN); nitroso compounds such as N,N'-dinitrosopentamethylenetetramine (DPT); hydrazine derivatives such as hydrazodicarbonamide, 4,4'-oxybis(benzenesulfonylhydrazide) (OBSH), and toluenesulfonylhydrazide (TSH); and semicarbazide compounds such as toluenesulfonylsemicarbazide. Examples of inorganic blowing agents include ammonium carbonate, sodium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and anhydrous monosodium citrate.

[0032] Among these, in the present technology, it is preferable to use an organic blowing agent as the blowing agent, and among organic blowing agents, it is preferable to use azodicarbonamide (ADCA) because ADCA is easy to handle and has little impact on the human body and the environment.

[0033] The amount of blowing agent used in the composition for producing a resin foam can be freely set as long as it does not impair the functions and effects of the present technology. In the present technology, the lower limit of the amount of blowing agent in the composition for producing a resin foam is, for example, 1.0 part by mass or more, preferably 3.0 parts by mass or more, more preferably 5.0 parts by mass or more, and even more preferably 10.0 parts by mass or more, per 100 parts by mass of the resin component. Setting the lower limit of the amount of blowing agent used within this range can improve foamability, which can contribute to further improving the electromagnetic wave absorption performance of the produced electromagnetic wave absorber.

[0034] In the present technology, the upper limit of the amount of blowing agent in the composition for producing a resin foam, relative to 100 parts by mass of the resin component, is, for example, 40 parts by mass or less, preferably 35 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less. Setting the upper limit of the amount of blowing agent used within this range can prevent molding defects due to excessive foaming and also contribute to cost reduction.

[0035] (5) Crosslinking agent A crosslinking agent can be used in the composition for producing a resin foam. As the crosslinking agent that can be used in the present technology, one or more crosslinking agents that can be used for resin foams can be freely selected and used, as long as the action and effect of the present technology are not impaired.

[0036] Examples of crosslinking agents that can be used in the present technology include crosslinking agents having a chemical structure such as a silane group, a peroxide, a hydroxyl group, an amide group, an ester group, etc. Among these, in the present technology, it is preferable to use an organic peroxide as the crosslinking agent.

[0037] Examples of organic peroxides include 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, dicumyl peroxide, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide, di-t-butylperoxy-3,3,5-trimethylcyclohexane, and t-dibutyl hydroperoxide. Among these, in the present technology, it is preferable to use 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane as a crosslinking agent.

[0038] The amount of crosslinking agent used in the composition for producing a resin foam can be freely set as long as it does not impair the functions and effects of the present technology. In the present technology, the lower limit of the amount of crosslinking agent in the composition for producing a resin foam is, for example, 0.1 parts by mass or more, preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more, per 100 parts by mass of the resin component. By setting the lower limit of the amount of crosslinking agent used within this range, the viscosity of the composition can be increased, thereby improving foamability. Furthermore, the mechanical properties of the produced foam, such as durability, can be improved.

[0039] In the present technology, the upper limit of the amount of crosslinking agent in the composition for producing a resin foam is, for example, 20 parts by mass or less, preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, relative to 100 parts by mass of the resin component. By setting the upper limit of the amount of crosslinking agent used within this range, it is possible to prevent cracking and the like from occurring during foaming and improve moldability.

[0040] (6) Other In the composition for producing resin foam, one or more of various components that can be used in resin foams can be freely selected and used as other components depending on the purpose, as long as the action and effect of the present technology are not impaired.

[0041] Examples of components that can be used in the resin foam according to the present technology include foaming aids, foam stabilizers, crosslinking accelerators, crosslinking accelerator assistants, fillers, softeners, processing aids, stabilizers, colorants, antioxidants, dispersants, ultraviolet absorbers, and flame retardants.

[0042] (7) Method for manufacturing resin foam The resin foam used in the present technology can be produced by any commonly-used method for producing resin foams, for example, by carrying out a composition preparation step of preparing a resin foam-producing composition, a crosslinking and foaming step of crosslinking and foaming the prepared resin foam-producing composition, a molding step, etc.

[0043] [Composition preparation process] The composition preparation step is a step of kneading the raw materials for the resin foam-producing composition described above. Specifically, all or part of the raw materials for the resin foam-producing composition can be kneaded using a kneading machine such as a kneader, a Banbury mixer, or a roll mixer.

[0044] The composition preparation step can be carried out in a plurality of stages. Specifically, for example, the components other than the crosslinking agent, crosslinking accelerator, foaming agent, foaming auxiliary, etc. are first kneaded primarily, and then the crosslinking agent, crosslinking accelerator, crosslinking accelerator auxiliary, foaming agent, foaming auxiliary, etc. are added to the obtained primary kneaded mixture and kneaded secondarily.

[0045] [Crosslinking foaming process] The crosslinking and foaming step is a step of crosslinking and foaming the prepared resin foam-producing composition. Specifically, for example, crosslinking and foaming can be performed by applying heat and, if necessary, pressure.

[0046] The crosslinking and foaming step can be carried out in multiple stages. Specifically, for example, after first crosslinking and foaming is carried out under first heating (and pressurizing as needed) conditions, the resulting primary crosslinked foam can be further subjected to second crosslinking and foaming under second heating (and pressurizing as needed) conditions, thereby carrying out crosslinking and foaming in multiple stages.

[0047] [Molding process] The molding step is a step of processing the resin foam that has been subjected to the above-described cross-linking and foaming step into a desired shape by trimming or slicing the edges. The specific method of the molding step is not particularly limited as long as it does not impair the functions and effects of the present technology, and any molding method that can be used to produce a general resin foam can be freely combined.

[0048] (8) Physical properties of resin foam [density] The density of the resin foam used in the present technology can be freely set as long as it does not impair the function and effect of the present technology. The lower limit of the density of the resin foam used in the present technology is, for example, 0.1 g / cm 3or more, preferably 0.3 g / cm 3 More preferably, 0.5 g / cm 3 More preferably, 0.7 g / cm 3 That's all. By setting the lower limit of the density of the resin foam within this range, it is possible to prevent electromagnetic waves from passing through. The upper limit of the density of the resin foam used in this technology is, for example, 3.5 g / cm. 3 or less, preferably 3.0 g / cm 3 or less, more preferably 2.5 g / cm 3 More preferably 2.0 g / cm or less 3 By setting the upper limit of the density of the resin foam within this range, it is possible to improve the electromagnetic wave absorption performance. Note that in this technology, the density is a value measured in accordance with the method based on JIS K6767:1999.

[0049] [Expansion ratio] The expansion ratio of the resin foam used in the present technology can be freely set as long as it does not impair the functions and effects of the present technology. The lower limit of the expansion ratio of the resin foam used in the present technology is, for example, more than 1.0 times, preferably 1.1 times or more, more preferably 1.2 times or more, and even more preferably 1.3 times or more. Setting the lower limit of the expansion ratio of the resin foam within this range can improve the electromagnetic wave absorption performance. The upper limit of the expansion ratio of the resin foam used in the present technology is, for example, 3.5 times or less, preferably 3.0 times or less, more preferably 2.5 times or less, and even more preferably 2.0 times or less. Setting the upper limit of the expansion ratio of the resin foam within this range can prevent electromagnetic waves from passing through. Note that in the present technology, the expansion ratio of the resin foam is a value calculated by the method described in the Examples below.

[0050] [Average cell diameter] The average cell diameter of the resin foam used in the present technology can be freely set as long as it does not impair the function and effect of the present technology. The lower limit of the average cell diameter of the resin foam used in the present technology is, for example, 15 μm or more, preferably 20 μm or more, and more preferably 25 μm or more. The upper limit of the average cell diameter of the resin foam used in the present technology is, for example, 70 μm or less, preferably 60 μm or less, and more preferably 50 μm or less. In the present technology, the average cell diameter of the resin foam is a value calculated by the method described in the Examples below.

[0051] [Cell morphology] The cell shape of the resin foam used in the present technology is not particularly limited as long as it does not impair the function and effect of the present technology, but it is preferable that the resin foam have closed cells. The presence of closed cells can contribute to further improving the electromagnetic wave absorption performance of the electromagnetic wave absorber. Although the mechanism of action of the high electromagnetic wave absorption performance of the electromagnetic wave absorber according to the present technology has not been elucidated, it is presumed that the electromagnetic waves are attenuated by multiple scattering in the closed cells of the foam.

[0052] 2. Performance of electromagnetic wave absorbers [Electromagnetic wave absorption peak] The electromagnetic wave absorption peak of the electromagnetic wave absorber according to the present technology may be present in any frequency range, but in the present technology, it is preferable that the electromagnetic wave absorber has at least one electromagnetic wave absorption peak in a frequency range of 1 GHz or more, preferably in a frequency range of 10 GHz or more. The absorption amount is also not particularly limited, but is, for example, −15 dB or less, preferably −20 dB or less.

[0053] Furthermore, the electromagnetic wave absorber according to the present technology may have at least one electromagnetic wave absorption peak, but preferably has multiple peaks. Specifically, the electromagnetic wave absorber according to the present technology preferably has two or more, more preferably three or more electromagnetic wave absorption peaks. Having multiple electromagnetic wave absorption peaks makes it possible to realize applications in a variety of uses.

[0054] [Surface resistivity] The surface resistivity of the electromagnetic wave absorber according to the present technology can be freely set as long as it does not impair the function and effect of the present technology. The lower limit of the surface resistivity of the electromagnetic wave absorber according to the present technology is, for example, 1 Ω / □ or more, preferably 10 Ω / □ or more, and more preferably 100 Ω / □ or more. By setting the lower limit of the surface resistivity within this range, it is possible to prevent electromagnetic wave reflection and further improve the electromagnetic wave absorption performance. The upper limit of the surface resistivity of the electromagnetic wave absorber according to the present technology is not particularly limited, and can be, for example, 1.0 × 10 18 Ω / □ or less, preferably 1.0×10 17 Ω / □ or less, more preferably 1.0×10 16 Ω / □ or less, more preferably 1.0×10 15 Ω / □ or less. Depending on the application of the electromagnetic wave absorber, for example, 1.0×10 14 Ω / □ or less, 1.0×10 12 Ω / □ or less, 1.0×10 10 Ω / □ or less, 1.0×10 8 Ω / □ or less, 1.0×10 7 Ω / □ or less, 1.0×10 6 Ω / □ or less, 1.0×10 5 It may be Ω / □ or less.

[0055] [Dielectric constant] The dielectric constant of the electromagnetic wave absorber according to the present technology can be freely set as long as it does not impair the function and effect of the present technology. The lower limit of the dielectric constant of the electromagnetic wave absorber according to the present technology is, for example, 1 F / m or more, preferably 2 F / m or more, and more preferably 3 F / m or more. By setting the lower limit of the dielectric constant of the electromagnetic wave absorber within this range, it is possible to further improve the electromagnetic wave absorption performance. The upper limit of the dielectric constant of the electromagnetic wave absorber according to the present technology is, for example, 30 F / m or less, preferably 20 F / m or less, and more preferably 10 F / m or less. By setting the upper limit of the dielectric constant of the electromagnetic wave absorber within this range, it is possible to prevent variations in the electromagnetic wave absorption performance at the target frequency. Note that, in the present technology, the dielectric constant of the electromagnetic wave absorber is a value measured by the method described in the examples below.

[0056] [Magnetic permeability] The magnetic permeability of the electromagnetic wave absorber according to the present technology can be freely set as long as it does not impair the function and effect of the present technology. The lower limit of the magnetic permeability of the electromagnetic wave absorber according to the present technology is, for example, 1 H / m or more, preferably 2 H / m or more, and more preferably 3 H / m or more. By setting the lower limit of the magnetic permeability of the electromagnetic wave absorber within this range, it is possible to further improve the electromagnetic wave absorption performance. The upper limit of the magnetic permeability of the electromagnetic wave absorber according to the present technology is, for example, 30 H / m or less, preferably 20 H / m or less, and more preferably 10 H / m or less. By setting the upper limit of the magnetic permeability of the electromagnetic wave absorber within this range, it is possible to prevent variations in the electromagnetic wave absorption performance at the target frequency. Note that in the present technology, the magnetic permeability of the electromagnetic wave absorber is a value measured by the method described in the examples below.

[0057] The present technology can also take the following forms. [1] a resin foam containing a silicone resin; one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles, which are contained in the resin foam; An electromagnetic wave absorber having: [2] The electromagnetic wave absorber according to [1], wherein the particles have an average aspect ratio of 1 to 5. [3] The electromagnetic wave absorber according to [1] or [2], wherein the resin foam has closed cells. [4] The density of the resin foam is 0.5 g / cm 3 The electromagnetic wave absorber according to any one of [1] to [3] above. [5] The electromagnetic wave absorber according to any one of [1] to [4], wherein the resin foam has an expansion ratio of 1.1 or more. [6] The density of the resin foam is 2.0 g / cm 3 An electromagnetic wave absorber according to any one of [1] to [5], which is: [7] The electromagnetic wave absorber according to any one of [1] to [6], wherein the particles are one or more particles selected from the group consisting of carbon-containing particles and metal particles. [8] The electromagnetic wave absorber according to any one of [1] to [7], which has at least one electromagnetic wave absorption peak in a frequency range of 1 GHz or more. [9] The electromagnetic wave absorber according to any one of [1] to [8], which has at least one electromagnetic wave absorption peak in a frequency range of 10 GHz or higher.

[10] The electromagnetic wave absorber according to any one of [1] to [9], wherein the absorption amount at the electromagnetic wave absorption peak is −20 dB or less. [Example]

[0058] The present technology will be described in more detail below based on examples. Note that the examples described below are examples of typical examples of the present technology, and the scope of the present technology should not be construed as being narrow.

[0059] (1) Manufacturing of electromagnetic wave absorbers [Example 1] The raw materials shown in Table 1 below were mixed and roll-kneaded, and then heated under the conditions shown in Table 1 below to carry out primary crosslinking and foaming and secondary crosslinking and foaming, thereby producing an electromagnetic wave absorber.

[0060] [Comparative Example 1] The raw materials shown in Table 1 below were mixed and roll-kneaded, and then heated under the conditions shown in Table 1 below to carry out primary crosslinking, thereby producing an electromagnetic wave absorber.

[0061] (2) Measurement of physical properties The physical properties of the produced electromagnetic wave absorbers were evaluated using the following methods.

[0062] [density] The density was measured in accordance with the method based on JIS K6767:1999.

[0063] [Expansion ratio] The expansion ratio was calculated using the formula: expansion ratio (times) = density before expansion / density after expansion.

[0064] [Average cell diameter] The diameters of 10 cells were measured using a microscope, and the average of the measured values ​​was calculated as the average cell diameter.

[0065] [Surface resistivity] The surface resistivity was measured in accordance with the double ring method of JIS K6271.

[0066] [Dielectric constant / permeability] The permittivity and permeability were measured using a vector network analyzer (Keysight Technologies P5007A) and a 7 mm coaxial sample holder by the transmission line method under the following conditions. Frequency range: 500MHz~18GHz Sample shape: Cylindrical Sample size: inner diameter φ3.04 mm, outer diameter φ7.00 mm, thickness 5 mm Jig model number: CSH2-APC7 (Kanto Electronics Application Development)

[0067] [Electromagnetic wave absorption performance (500MHz~18GHz)] Electromagnetic wave absorption was measured using a vector network analyzer (Keysight Technologies "P5007A") and a 7 mm coaxial sample holder by the transmission line method under the following conditions. Frequency range: 500MHz~18GHz Sample shape: Cylindrical Sample size: inner diameter φ3.04 mm, outer diameter φ7.00 mm, thickness 5 mm Jig model number: CSH2-APC7 (Kanto Electronics Application Development) Measurement method: A brass plate was attached to the sample surface opposite to the side where the electromagnetic wave was incident. Measure return loss using the metal back method (S11 in S parameters)

[0068] [Electromagnetic wave absorption performance (55GHz~95GHz)] Electromagnetic wave absorption was measured using a vector network analyzer (Keysight Technologies "N5290A") under the following conditions using the free space method. Frequency range: 55GHz to 95GHz (E band) Sample size: 100mm x 100mm x 5mm thick Measurement method: A brass plate was attached to the sample surface opposite to the side where the electromagnetic wave was incident. Measure return loss using the metal back method (S11 in S parameters)

[0069] (3) Results The results are shown in Table 1 below and in FIG. [Table 1]

[0070] (4) Discussion 1, the electromagnetic wave absorber of Comparative Example 1, in which a non-foamed resin was used, did not have an electromagnetic wave absorption peak with an absorption amount of −20 dB or less in a frequency range of 1 GHz or more. On the other hand, the electromagnetic wave absorber of Example 1, in which a resin foam was used, had four electromagnetic wave absorption peaks with absorption amounts of −20 dB or less in a frequency range of 1 GHz or more.

Claims

1. a resin foam containing a silicone resin; one or more particles selected from the group consisting of conductive particles, dielectric particles, and magnetic particles, which are contained in the resin foam; An electromagnetic wave absorber having the above structure.

2. 2. The electromagnetic wave absorber according to claim 1, wherein the particles have an average aspect ratio of 1 to 5.

3. The electromagnetic wave absorber according to claim 1 , wherein the resin foam has closed cells.

4. The density of the resin foam is 0.5 g / cm ３ The electromagnetic wave absorber according to claim 1 .

5. 2. The electromagnetic wave absorber according to claim 1, wherein the particles are one or more particles selected from the group consisting of particles containing carbon and metal particles.

6. 2. The electromagnetic wave absorber according to claim 1, which has at least one electromagnetic wave absorption peak in a frequency range of 1 GHz or more, and the absorption amount is −20 dB or less.

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