Composition for electromagnetic wave absorption and method for producing the same

Abstract

A composition for electromagnetic wave absorption, characterized by comprising (A) an electromagnetic wave absorbing filler: 6% by mass to 30% by mass relative to the total composition for electromagnetic wave absorption, and (B) an organic resin: 70% by mass to 94% by mass relative to the total composition for electromagnetic wave absorption, and by the (A) electromagnetic wave absorbing filler being one in which when a free-space method using a vector network analyzer is used to measure the dielectric loss tangent and relative permittivity, at 60 GHz to 90 GHz, of cured products obtained by molding, into sheet form, three or more types of filler selection compositions containing different amounts of a selection filler compounded with the (B) organic resin, and the obtained measured values are plotted with the relative permittivity on the X-axis and the dielectric loss tangent on the Y-axis, the slope of a linearly approximated straight line is 0.050 or greater. Thereby, a composition for electromagnetic wave absorption is provided that exhibits a low relative permittivity and a high dielectric loss tangent, and demonstrates excellent absorption characteristics in the high-frequency band of 60 GHz to 90 GHz.

Description

Composition for electromagnetic wave absorption and method for producing the same 【0001】 The present invention relates to a composition for electromagnetic wave absorption and a method for producing the same, which are suitably used for semiconductor devices used in high-speed large-capacity communication-compatible devices and in-vehicle applications. 【0002】 High-speed large-capacity communication using radio waves in the so-called millimeter wave band with frequencies from 30 GHz to 300 GHz is expected to be utilized in multiple fields such as 5G-compatible communication devices, automotive autonomous driving systems, and remote medical systems. Among them, electromagnetic wave shielding materials are known as sheets that absorb unnecessary radio wave leakage and reflection, and play a role in maintaining a stable communication environment and preventing malfunction. 【0003】 Electromagnetic wave shielding materials include so-called electromagnetic wave shielding materials that utilize only the reflection of electromagnetic waves, and electromagnetic wave absorption materials that suppress the reflection and transmission of irradiated electromagnetic waves. Electromagnetic wave shielding materials can highly suppress the transmission of electromagnetic waves, but due to their high conductivity, resonance and re-emission of electromagnetic waves occur, causing problems such as unexpected electromagnetic waves like harmonics. On the other hand, electromagnetic wave absorption materials can suppress both the reflection and transmission of unnecessary electromagnetic waves. Therefore, for the stable operation of next-generation high-speed large-capacity communication technologies, the development of electromagnetic wave absorption materials with higher absorption performance is required. 【0004】 In the field of developing electromagnetic wave absorption materials for millimeter waves, the development of λ / 4 type electromagnetic wave absorption sheets in which a dielectric layer filled with a carbon-based filler in a resin and a reflection layer composed of a conductive material are attached thereto has been reported many times. However, in these electromagnetic wave absorption sheets, a method of controlling the phase of electromagnetic waves by adjusting the dielectric constant is used. However, due to reasons of principle, only narrow-band absorption characteristics can be obtained, and most of them are limited to a performance with an attenuation amount of 20 dB or more in the order of 5 GHz (Patent Document 1 and Patent Document 2). In addition, there remains a problem that the absorption characteristics change greatly due to slight changes in the film thickness, dielectric constant, and incident angle. 【0005】On the other hand, a sheet exhibiting low relative permittivity and high dielectric loss tangent can directly convert electromagnetic waves into heat in addition to attenuating them due to phase differences, thus providing stable absorption characteristics against the changes described above. However, generally, when attempting to obtain a high dielectric loss tangent by filling a resin with a high amount of dielectric filler, the relative permittivity also increases simultaneously. Therefore, there is still room for improvement in developing sheets with both low relative permittivity and high dielectric loss tangent. 【0006】 To improve these, the use of Ketjenblack is being considered. For example, an electromagnetic wave absorber consisting of a dielectric layer made of a thermosetting resin blended with conductive titanium oxide and / or Ketjenblack and an electromagnetic wave absorbing layer made of a wire mesh has been reported (Patent Document 3). However, it has problems such as lack of flexibility such as bendability, a complex structure and a long manufacturing process. In addition, an electromagnetic wave shielding resin composition and molded product consisting of a thermoplastic resin, Ketjenblack and carbon fibers has also been reported (Patent Document 4). However, there is a problem that anisotropy occurs due to the carbon fibers, making it difficult to exhibit uniform electromagnetic wave absorption. 【0007】 Therefore, while an electromagnetic wave absorbing sheet with a low dielectric constant and high dielectric loss tangent could solve the above problem, there is still much room for improvement in its development. 【0008】 International Publication No. 2018 / 168859, Japanese Patent Publication No. 2023-129145, Japanese Patent Publication No. 2004-278226, Japanese Patent Publication No. 2022-048145 【0009】 The present invention has been made to solve the above problems and aims to provide an electromagnetic wave absorbing composition and a method for manufacturing the same that exhibits a low relative permittivity and a high dielectric loss tangent, and shows excellent absorption characteristics in the high frequency band of 60 GHz to 90 GHz. 【0010】To solve the above problems, the present invention provides an electromagnetic wave absorbing composition comprising: (A) an electromagnetic wave absorbing filler: 6% to 30% by mass of the entire electromagnetic wave absorbing composition; and (B) an organic resin: 70% to 94% by mass of the entire electromagnetic wave absorbing composition, wherein the (A) electromagnetic wave absorbing filler is a cured product obtained by molding three or more filler selection compositions with different amounts of selected filler blended with the (B) organic resin into a sheet, and measuring the dielectric loss tangent and relative permittivity at 60 GHz to 90 GHz using the free-space method with a vector network analyzer, and plotting the relative permittivity on the X axis and the dielectric loss tangent on the Y axis for the obtained measured values, the slope of the linearly approximated line is 0.050 or higher. 【0011】 The electromagnetic wave absorbing composition of the present invention exhibits a low relative permittivity and a high dielectric loss tangent, and provides an electromagnetic wave absorbing composition that shows excellent absorption characteristics in the high frequency band of 60 GHz to 90 GHz. 【0012】 Furthermore, it is preferable that component (A) is carbon black produced by the furnace process. 【0013】 Such a component (A) is preferred from the viewpoint of compatibility with organic resins, wettability, dispersibility, etc. 【0014】 Furthermore, it is preferable that component (A) is Ketjenblack. 【0015】 Ketjenblack is preferred because it blends well with resins, offers excellent workability, and has good electromagnetic wave absorption properties. 【0016】 Furthermore, it is preferable that component (B) is one or more selected from thermosetting resins and thermoplastic resins. 【0017】 Such a component (B) is preferred as component (B) of the present invention. 【0018】Preferably, the thermosetting resin is one or more selected from silicone resins, epoxy resins, maleimide resins, bismaleimide resins, amine resins, styrene resins, methacrylic resins, acrylic resins, allyl resins, benzoxazine resins, phenolic resins, cyanate resins, polyimide resins, melamine resins, and polyamideimide resins. 【0019】 Such thermosetting resins are more preferred as component (B) of the present invention. 【0020】 It is preferable that the thermoplastic resin is one or more selected from polyethylene resin, polypropylene resin, polystyrene resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polycarbonate resin, polyurethane resin, polyphenylene sulfide resin, polyamide resin, and fluororesin. 【0021】 Such thermoplastic resins are more preferred as component (B) of the present invention. 【0022】 Furthermore, the present invention provides a method for manufacturing the electromagnetic wave absorbing composition, characterized in that the (A) electromagnetic wave absorbing filler to be blended into the electromagnetic wave absorbing composition is selected by the following steps: (1) Prepare three or more filler selection compositions by blending the (B) organic resin with the selection filler in different filling amounts, and mold the filler selection compositions into a sheet to produce a cured filler selection product; (2) Measure the dielectric loss tangent and relative permittivity of the cured filler selection product at 60 GHz to 90 GHz using the free-space method with a vector network analyzer; (3) Plot the relative permittivity on the X axis and the dielectric loss tangent on the Y axis for the measurements obtained in (2), and select the selection filler that satisfies the condition that the slope of the linearly approximated line is 0.050 or more as the (A) electromagnetic wave absorbing filler. 【0023】 Using the method for producing the electromagnetic wave absorbing composition of the present invention, an electromagnetic wave absorbing composition can be produced that has a low relative permittivity and a high dielectric loss tangent in the millimeter wave band such as 60 GHz to 90 GHz, and exhibits stable absorption performance over a wide frequency band. 【0024】 As described above, an electromagnetic wave absorbing composition using the electromagnetic wave absorbing filler of the present invention exhibits low dielectric constant and high dielectric loss tangent in the millimeter wave band such as 60 GHz to 90 GHz, and therefore can show stable absorption performance over a wide frequency band. For this reason, it is extremely useful as an electromagnetic wave absorbing material installed in semiconductor devices. Furthermore, the method for manufacturing the electromagnetic wave absorbing composition of the present invention allows for the selection of an appropriate electromagnetic wave absorbing filler from among multiple selectable fillers, and the electromagnetic wave absorbing composition of the present invention can be reliably manufactured. 【0025】 As mentioned above, there was a need for the development of electromagnetic wave absorbing compositions with low dielectric constant and high dielectric loss tangent. 【0026】 As a result of diligent research to achieve the above objective, the inventors of the present invention have discovered that an electromagnetic wave absorbing composition consisting of an electromagnetic wave absorbing filler and an organic resin exhibits excellent absorption characteristics in the high-frequency range, provided that when the electromagnetic wave absorbing filler is filled into an organic resin, the slope of the approximate straight line plotting the dielectric loss tangent (Y axis) and relative permittivity (X axis) is 0.050 or higher. 【0027】 In other words, the present invention relates to an electromagnetic wave absorbing composition comprising: (A) an electromagnetic wave absorbing filler: 6% to 30% by mass of the entire electromagnetic wave absorbing composition; and (B) an organic resin: 70% to 94% by mass of the entire electromagnetic wave absorbing composition, wherein the (A) electromagnetic wave absorbing filler is a cured product obtained by molding three or more filler selection compositions with different amounts of the selected filler blended with the (B) organic resin into a sheet, and measuring the dielectric loss tangent and relative permittivity at 60 GHz to 90 GHz using the free-space method with a vector network analyzer, and plotting the relative permittivity on the X axis and the dielectric loss tangent on the Y axis for the obtained measured values, the slope of the linearly approximated line is 0.050 or higher. 【0028】 The present invention will be described in detail below, but the present invention is not limited to these descriptions. 【0029】<(A) Electromagnetic wave absorbing filler> The electromagnetic wave absorbing composition of the present invention contains 6% to 30% by mass of the electromagnetic wave absorbing filler, which is component (A), relative to the entire electromagnetic wave absorbing composition. The (A) electromagnetic wave absorbing filler is a cured product obtained by molding three or more filler selection compositions, each with a different amount of the selected filler blended with the (B) organic resin, into a sheet. The dielectric loss tangent and relative permittivity at 60 GHz to 90 GHz are measured using the free-space method with a vector network analyzer. The obtained measured values ​​are plotted with the relative permittivity on the X axis and the dielectric loss tangent on the Y axis, and the slope of the linearly approximated line is 0.050 or higher. 【0030】 The above-mentioned component (A) can be used regardless of the type of filler, as long as the slope of the approximate straight line of the dielectric loss tangent (Y axis) and relative permittivity (X axis) when the amount of component (A) added is changed after filling with the organic resin which is component (B) is 0.050 or higher. 【0031】 The method for measuring the slope of the approximate straight line involves measuring the relative permittivity and dielectric loss tangent of the cured electromagnetic wave absorbing composition at 60 GHz to 90 GHz using the free-space method with a vector network analyzer. The relative permittivity obtained from the measurement is plotted on the X-axis and the dielectric loss tangent on the Y-axis, and the slope of the linearly approximated straight line is calculated. The slope of the approximate straight line is 0.050 or higher, preferably 0.060 or higher, and more preferably 0.100 or higher. A slope below 0.050 has the disadvantage of not obtaining sufficient dielectric loss tangent, resulting in a decrease in absorption rate, or even if the dielectric loss tangent is satisfied, the relative permittivity is too high, resulting in a disadvantage of high surface reflectivity. There is no particular upper limit to the slope of the approximate straight line, but for example, it can be 1.00 or lower. 【0032】 The aforementioned component (A) is preferably a carbon-based filler from the viewpoint of compatibility with organic resins, wettability, dispersibility, etc., and can be used alone or in combination of two or more types. 【0033】Examples of the carbon-based fillers mentioned above include carbon black such as furnace black, channel black, acetylene black, or thermal black, graphite, carbon fibers, carbon nanotubes, graphene, graphene oxide, graphite, and fullerene. Among these, furnace black, i.e., carbon black produced by the furnace method, is preferred as a carbon-based filler in which the slope of the approximate straight line of dielectric loss tangent (Y axis) and relative permittivity (X axis) when the amount added is changed is 0.050 or more. In particular, Ketjenblack is preferred because it blends well with resin, has excellent workability, and has good electromagnetic wave absorption properties. 【0034】 The amount of the above-mentioned filler added is 6% to 30% by mass relative to the entire composition, with 6% to 20.0% by mass being preferable. If the amount falls outside the range of 6% to 30% by mass, viscosity and workability may be inferior, and electromagnetic wave absorption characteristics may become problematic. 【0035】 The above carbon black has a specific surface area of ​​400 to 1,500 m² according to JIS K 6217-2:2017, considering its compatibility with resin, dispersibility, and electromagnetic wave absorption. ２ A carbon black of / g is preferred. Specific surface area of ​​400 m² is preferred. ２ If the concentration is 1 / g or higher, there are no problems with dispersibility in organic resins, and electromagnetic wave absorption is excellent, allowing for an average reflectivity of 40% or an average electromagnetic wave absorption rate of 30% or higher. Furthermore, the specific surface area is 1,500 m². ２ If the viscosity is less than / g, the viscosity does not increase, the dispersibility is good, and the electromagnetic wave absorption is excellent. In addition, an electromagnetic wave absorbing sheet with a constant thickness can be molded. 【0036】 <(B) Organic resin> The electromagnetic wave absorbing composition of the present invention contains 70% to 94% by mass of the organic resin, which is component (B), relative to the entire electromagnetic wave absorbing composition. 【0037】 The above (B) organic resin is preferably one or more selected from thermosetting resins and thermoplastic resins. 【0038】Examples of the above-mentioned thermosetting resins include epoxy resins, phenolic resins, cyanate resins, melamine resins, silicone resins, maleimide resins, bismaleimide resins, cyclic imide resins, urea resins, thermosetting polyimide resins, modified polyphenylene ether resins, thermosetting acrylic resins, methacrylic resins, and epoxy-silicone hybrid resins. Preferably, it is one or more selected from silicone resins, epoxy resins, maleimide resins, bismaleimide resins, amine resins, styrene resins, methacrylic resins, acrylic resins, allyl resins, benzoxazine resins, phenolic resins, cyanate resins, polyimide resins, melamine resins, and polyamideimide resins. Silicone resins, epoxy resins, and bismaleimide resins are particularly preferred from the viewpoint of dielectric properties. 【0039】 The thermoplastic resin is preferably one or more selected from polyethylene resin, polypropylene resin, polystyrene resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polycarbonate resin, polyurethane resin, polyphenylene sulfide resin, polyamide resin, and fluororesin. Polyethylene resin, polystyrene resin, and polyamide resin are particularly preferred from the viewpoint of dielectric properties. 【0040】 The relative permittivity of the (B) organic resin affects the relative permittivity of the entire electromagnetic wave absorbing composition. Therefore, the relative permittivity of the (B) organic resin is preferably 1 to 5, and more preferably 1 to 4. If the relative permittivity of the (B) organic resin is within this range, it becomes easy to satisfy the slope of the approximate straight line plotting the dielectric loss tangent (Y axis) and relative permittivity (X axis) with respect to the amount of filler added as 0.050 or more, and it becomes easy to make the average reflectivity of the electromagnetic wave absorbing composition 40% or less. 【0041】<Method for Manufacturing an Electromagnetic Wave Absorbing Composition> The present invention provides a method for manufacturing an electromagnetic wave absorbing composition, wherein the (A) electromagnetic wave absorbing filler to be incorporated into the electromagnetic wave absorbing composition is selected by the following steps: (1) Prepare three or more filler selection compositions by incorporating the (B) organic resin with the selection filler in different amounts, and mold the filler selection compositions into a sheet to produce a cured filler selection product; (2) Measure the dielectric loss tangent and relative permittivity of the cured filler selection product at 60 GHz to 90 GHz using the free-space method with a vector network analyzer; (3) Plot the relative permittivity on the X axis and the dielectric loss tangent on the Y axis for the measurements obtained in (2), and select the selection filler that satisfies the condition that the slope of the linearly approximated line is 0.050 or more as the (A) electromagnetic wave absorbing filler. 【0042】 With this manufacturing method, it is possible to produce an electromagnetic wave absorbing composition that has a low relative permittivity and a high dielectric loss tangent in the millimeter wave band, such as 60 GHz to 90 GHz, and exhibits stable absorption performance over a wide frequency band. Furthermore, by selecting an appropriate electromagnetic wave absorbing filler from among several selectable fillers, the electromagnetic wave absorbing composition of the present invention can be reliably manufactured. 【0043】<Optional Components> In addition to the components (A) and (B) above, the electromagnetic wave absorbing composition can be appropriately blended with optional components according to the object of the present invention. For example, for the purpose of appropriately adjusting reactivity, shrinkage rate during curing, coefficient of thermal expansion of the obtained cured product, mechanical strength, heat resistance, chemical resistance, flame retardancy, gas permeability, thermal conductivity, oxidation resistance, dielectric constant, etc., various optional components may be added. Such optional components include non-conductive inorganic fillers such as silica, fumed silica, quartz powder, glass fiber, titanium dioxide, calcium carbonate, magnesium carbonate, aluminum hydroxide, alumina (aluminum oxide), aluminum nitride, magnesium oxide, boron nitride, etc., and antioxidants such as hydroquinone, 2,6-tert-butyl-p-cresol, etc. Among them, aluminum oxide, aluminum nitride, magnesium oxide, boron nitride, etc. can be preferably used for the purpose of improving heat dissipation. These additives can be used by appropriately combining one or more of them. 【0044】 The electromagnetic wave absorbing composition of the present invention is obtained by mixing the above-mentioned (B) organic resin, the above-mentioned (A) electromagnetic wave absorbing filler having the above characteristics, and optional components as required. The mixing method is not particularly limited, but it can be mixed with a known kneader. Examples of kneaders include kneaders, Banbury mixers, two-roll mills, three-roll mills, planetary mixers, gate mixers, rotating and revolving mixers, etc. 【0045】 <Molding Method> The electromagnetic wave absorbing composition of the present invention can be molded into any shape. The molding method is not particularly limited, but it can be molded by a known method, and examples include press molding, coating molding, extrusion molding, etc. For example, each component can be mixed and extruded into a sheet shape using a melt kneader and used as it is. Also, it can be melt-mixed by a hot two-roll mill to produce a resin composition, pulverized into tablets or granules, and then heat-cured by a hot press machine to be formed into a sheet shape. Further, the organic resin can be dissolved in an organic solvent to be made into a varnish and handled. Examples of the varnish coating method include a spin coater, a slit coater, a spray, a dip coater, a bar coater, etc., but there is no particular limitation. 【0046】As the organic solvent, any solvent can be used without limitation as long as it can dissolve the above-mentioned (B) organic resin. For example, anisole, tetralin, mesitylene, xylene, toluene, tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), N-methyl-2-pyrrolidone (NMP), etc. can be mentioned. Among them, aromatic organic solvents such as anisole, tetralin, mesitylene, xylene, and toluene are preferred. These may be used alone or in combination of two or more. 【0047】 As the method for applying the varnish, a spin coater, a slit coater, a spray, a dip coater, a bar coater, etc. can be mentioned, but there is no particular limitation. 【0048】 <Curing method> When a thermosetting resin is used as the above-mentioned (B) organic resin, it is cured according to the curing method of the resin. The curing may proceed partially or may be completely cured. As the curing method, curing at room temperature is possible, but heating may be performed as necessary. As the heating conditions when heating is performed, it is preferably about 1 to 240 minutes at 50 to 200°C. 【0049】 <Composition for electromagnetic wave absorption> The composition for electromagnetic wave absorption of the present invention preferably has an average electromagnetic wave reflectance in the frequency range of 60 GHz to 90 GHz of the cured product of 40% or less, more preferably 30% or less, and even more preferably 20% or less. 【0050】 At the same time, it is preferably that the average electromagnetic wave absorption rate of the cured product is 30% or more, more preferably 50% or more, and even more preferably 80% or more. If the electromagnetic wave reflectance is 40% or less and the electromagnetic wave absorption rate is 30% or more, it becomes an electromagnetic wave absorption material that can sufficiently absorb malfunction prevention due to electromagnetic wave noise and leakage or reflection of unnecessary electromagnetic waves. 【0051】The electromagnetic wave absorbing composition of the present invention can be formed into an electromagnetic wave absorbing sheet by the molding method described above. In this case, it is preferable to laminate electromagnetic wave absorbing sheets with different carbon-based filler contents. Furthermore, it is even more preferable to have an electromagnetic wave absorbing sheet in which a layer having a lower dielectric constant than the electromagnetic wave absorbing sheet is laminated on the electromagnetic wave incident surface side, or a layer that reflects electromagnetic waves is laminated on the opposite side of the electromagnetic wave incident surface, or both are laminated. 【0052】 By laminating sheets with different electromagnetic wave absorption characteristics, or by combining a low dielectric constant layer, a reflective layer, or both, surface reflection can be reduced and absorption characteristics can be improved. 【0053】 The low dielectric constant layer described above is not particularly limited as long as it has a lower dielectric constant than the electromagnetic wave absorbing composition, and examples include silicone resin, epoxy resin, maleimide resin, bismaleimide resin, polyetherketone resin, phenolic resin, polyethylene resin, polypropylene resin, polystyrene resin, polyimide resin, polyamide resin, polyethylene terephthalate resin, polyurethane resin, polyester resin, polyvinyl chloride resin, etc. These resins may be used individually or in mixtures of two or more. Furthermore, fillers such as carbon black may be added to control the dielectric constant, as long as the dielectric constant does not exceed that of the electromagnetic wave absorbing sheet. 【0054】 The reflective layer described above can be any sheet that has sufficient properties to reflect incident electromagnetic waves, and is preferably one with a transmission attenuation of 20 dB or more. Examples of such reflective layers include metallic materials such as silver, copper, and aluminum, and carbon materials such as carbon fibers, carbon nanotubes, graphene, and graphite. Carbon nanosheets made of carbon nanotubes are particularly preferred because they have a transmission attenuation of 20 dB or more in the high-frequency range of 60 to 90 GHz, are lightweight, and have excellent strength and flexibility. 【0055】 Such carbon nanosheets can be manufactured by directly stretching and compressing carbon nanotubes. Alternatively, carbon nanotubes can be suspended in water or an organic solvent, and a sheet can be made using methods such as filtration or papermaking, which can then be dried to produce a nonwoven fabric. 【0056】 Carbon nanosheets produced by direct stretching or processing stretch in the direction of stretching, resulting in a nonwoven fabric where the fibers intertwine. On the other hand, nonwoven fabrics produced by filtration or papermaking can be made without anisotropy, resulting in a nonwoven fabric where the fibers are intertwined. 【0057】 Since the reflective layer used in this invention has uniform electromagnetic wave reflectivity even for electromagnetic waves with different directions, it is preferable that the entanglement of the fibers is uniform in all directions. 【0058】 Furthermore, the lamination of these low dielectric constant layers and reflective layers with the electromagnetic wave absorbing sheet may be continuous or discontinuous. A simple lamination method by pressure bonding without chemical bonding such as adhesives is preferred to simplify the manufacturing process and to enable the thinning of the electromagnetic wave absorbing sheet. 【0059】 <Semiconductor Devices> Because the above electromagnetic wave absorbing sheet exhibits excellent electromagnetic wave absorption characteristics, it can be suitably used in semiconductor devices for high-speed, high-capacity communication equipment and automotive applications. In particular, it is suitable for semiconductor devices used in millimeter-wave radar and ECUs. 【0060】 The present invention will be described in detail below, but the present invention is not limited to these descriptions. 【0061】 Table 1 below shows the fillers used. "(A) Electromagnetic wave absorbing fillers" (a-1): Ketjenblack EC600JD (manufactured by Lion Specialty Chemicals Co., Ltd.) (a-2): Ketjenblack EC300J (manufactured by Lion Specialty Chemicals Co., Ltd.) (a-3): Vulcan XC-72 (manufactured by Cabot Corporation); for comparative example (a-4): Mitsubishi Carbon Black #3230B (manufactured by Mitsubishi Chemical Group Corporation); for comparative example (a-5): Denka Black Li-100 (manufactured by Denka Co., Ltd.); for comparative example (a-6): iGraphene α (manufactured by ITEC Co., Ltd.); for comparative example (a-7): Carbon fiber: ZY-300-25M (manufactured by Nippon Graphite Fiber Co., Ltd.); for comparative example 【0062】 *CB: Carbon Black 【0063】The following resins were used as organic resins: (B) Organic Resins (b-1) Addition-curing silicone resin (product name: KE-106F / CAT-106F (100 parts by mass / 10 parts by mass), manufactured by Shin-Etsu Chemical Co., Ltd.) (b-2) Thermosetting bismaleimide resin (product name: SLK-3000, manufactured by Shin-Etsu Chemical Co., Ltd. / Dicumyl peroxide (product name: Perkmyl D, manufactured by NOF Corporation) (100 parts by mass / 1.0 part by mass) (b-3) Thermosetting epoxy resin (product name: ZX1059 (manufactured by Nippon Steel Chemical & Material Co., Ltd.) / Reactive diluent (product name: ED-523L (manufactured by ADEKA Corporation) / Hardener (product name: Kayahard AA, manufactured by Nippon Kayaku Co., Ltd.) (100 parts by mass / 50 parts by mass / 120 parts by mass) (b-4) Polyethylene terephthalate (product name: TRN-8580FCS, manufactured by Teijin Limited) 【0064】 <Manufacturing of Electromagnetic Wave Absorbing Sheets> The formulations of (A) and (B) were carried out in the amounts shown in Tables 2 to 6 below (Preparation Examples 1 to 24, Examples 1 to 9, and Comparative Examples 1 to 6). The electromagnetic wave absorbing filler of (A) above was mixed with the organic resin of (B) above in a planetary mixer for 1 hour to obtain an electromagnetic wave absorbing resin composition. The obtained electromagnetic wave absorbing composition was press-molded into a sheet of 120 mm in length x 120 mm in width, and then heat-cured at 150°C for 2 hours to obtain an electromagnetic wave absorbing sheet. The thickness of the sheet was 0.6 mm for Preparation Examples 1 to 24 in Tables 2 to 4, and for Examples 1 to 9 and Comparative Examples 1 to 6 in Tables 5 and 6, the thickness was as indicated in the table. Furthermore, when a low dielectric constant layer and a reflective layer were to be installed on this electromagnetic wave absorbing sheet, the sheets were manufactured by bonding each layer together and applying pressure at 1 MPa for 10 minutes. 【0065】 <Measurement of Dielectric Properties and Electromagnetic Wave Absorption Properties> The relative permittivity, dielectric loss tangent, and electromagnetic wave absorption properties from 60 GHz to 90 GHz were measured using the free-space method with the electromagnetic wave absorption sheet described above as the measurement target. Specifically, a network analyzer (manufactured by Keycom Co., Ltd.), a horn antenna (manufactured by Keycom Co., Ltd.), and a dielectric lens (manufactured by Keycom Co., Ltd.) were used to irradiate the electromagnetic wave absorption sheet with electromagnetic waves incident perpendicularly, and the properties were calculated from the incident and reflected waves. The results are shown in Tables 2 to 6. 【0066】Dielectric properties slope: The dielectric properties of the sheets prepared according to Tables 2 to 4 below were measured using the method described above. The dielectric loss tangent was plotted on the Y axis and the relative permittivity on the X axis when the amount of filler added was varied, and the slope of the approximate straight line was calculated. From Tables 2 to 4 below, the fillers whose approximate straight line slope was 0.05 or higher were (a-1) and (a-2). (a-1) and (a-2) were used as components (A) in Examples 1 to 9 for evaluation. 【0067】 Absorption rate: The absorption rate (%) was calculated using equation (3) from the reflectance (%) and transmittance (%) obtained from the reflection loss (dB) and transmission loss (dB) obtained from the measurement, using equations (1) and (2) below. (In equations (1) and (2) above, R represents the return loss (dB) measured by the free-space method, and T represents the transmission loss (dB).) 【0068】 【0069】 【0070】 【0071】 【0072】 【0073】 The electromagnetic wave absorbing compositions of Examples 1 to 9 exhibit higher dielectric loss tangents in the frequency range of 60 GHz to 90 GHz and a larger slope of dielectric properties compared to Comparative Examples 1 to 6. In the conventional technology, increasing the filler concentration to increase the dielectric loss tangent also increases the relative permittivity. On the other hand, as shown in Examples 2 and 7, the electromagnetic wave absorbing compositions of the present invention can increase only the dielectric loss tangent while maintaining a low relative permittivity, even at relatively high filler concentrations. 【0074】The unique dielectric properties of the present invention demonstrate their performance in electromagnetic wave absorbing sheets. As can be seen from Tables 5 and 6 above, in Examples 1 to 9, the reflectance was all 40% or less and the absorption rate was all 30% or more, showing lower electromagnetic wave reflectance and higher electromagnetic wave absorption compared to Comparative Examples 1 to 6. In Comparative Example 6, which used carbon fiber as a filler, the relative permittivity was high. Generally, when carbon-based fillers are used, the relative permittivity is high, and reflection at the sheet surface becomes a problem. In contrast, the present invention has a low relative permittivity, so surface reflection is suppressed, and due to the high dielectric loss tangent, the sheet can efficiently absorb electromagnetic waves, demonstrating that the unique dielectric properties of the present invention are extremely useful as an electromagnetic wave absorbing sheet. Furthermore, as shown in Comparative Example 6, carbon fiber is a filler with excellent absorption rate, but it has the disadvantage of being difficult to fill and mix, resulting in a sheet that does not exhibit uniform electromagnetic wave absorption. The low relative permittivity and high dielectric loss tangent of the present invention demonstrate stable absorption characteristics for a wide frequency range. 【0075】 [Industrial Applicability] The electromagnetic wave absorbing sheet obtained from the electromagnetic wave absorbing composition of the present invention has low reflectivity and excellent electromagnetic wave absorption properties, making it suitable for use in semiconductor devices used in high-speed, high-capacity communication equipment and automotive applications. 【0076】This specification includes the following embodiments: [1]: An electromagnetic wave absorbing composition comprising: (A) an electromagnetic wave absorbing filler: 6% to 30% by mass of the entire electromagnetic wave absorbing composition, and (B) an organic resin: 70% to 94% by mass of the entire electromagnetic wave absorbing composition, wherein the (A) electromagnetic wave absorbing filler is a cured product obtained by molding three or more filler selection compositions with different amounts of the selected filler blended with the (B) organic resin into a sheet, and measuring the dielectric loss tangent and relative permittivity at 60 GHz to 90 GHz using the free-space method with a vector network analyzer, and plotting the relative permittivity on the X axis and the dielectric loss tangent on the Y axis for the obtained measured values, the slope of the linearly approximated line is 0.050 or higher. [2]: The electromagnetic wave absorbing composition according to [1], wherein the (A) component is carbon black manufactured by the furnace method. [3]: The electromagnetic wave absorbing composition according to [2], characterized in that the (A) component is Ketjenblack. [4]: ​​The electromagnetic wave absorbing composition according to any one of [1] to [3], characterized in that the (B) component is one or more selected from thermosetting resins and thermoplastic resins. [5]: The electromagnetic wave absorbing composition according to [4], characterized in that the thermosetting resin is one or more selected from silicone resin, epoxy resin, maleimide resin, bismaleimide resin, amine resin, styrene resin, methacrylic resin, acrylic resin, allyl resin, benzoxazine resin, phenol resin, cyanate resin, polyimide resin, melamine resin, and polyamideimide resin. [6]: The electromagnetic wave absorbing composition according to [4], characterized in that the thermoplastic resin is one or more selected from polyethylene resin, polypropylene resin, polystyrene resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polycarbonate resin, polyurethane resin, polyphenylene sulfide resin, polyamide resin, and fluororesin. [7]: A method for producing an electromagnetic wave absorbing composition according to any one of [1] to [6], characterized in that the (A) electromagnetic wave absorbing filler to be incorporated into the electromagnetic wave absorbing composition is selected by the following steps.(1) A step of preparing three or more filler selection compositions by blending a selection filler with the (B) organic resin in different filling amounts, and molding the filler selection compositions into sheets to produce a cured product for filler selection; (2) A step of measuring the dielectric loss tangent and relative permittivity of the cured product for filler selection at 60 GHz to 90 GHz using the free-space method with a vector network analyzer; (3) A step of selecting the selection filler as the (A) electromagnetic wave absorbing filler, which satisfies the condition that the slope of the linearly approximated line is 0.050 or more, based on the measurements obtained in (2). 【0077】 It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. An electromagnetic wave absorbing composition comprising: (A) an electromagnetic wave absorbing filler: 6% to 30% by mass of the entire electromagnetic wave absorbing composition; and (B) an organic resin: 70% to 94% by mass of the entire electromagnetic wave absorbing composition, wherein the (A) electromagnetic wave absorbing filler is a cured product obtained by molding three or more filler selection compositions with different amounts of the selected filler blended with the (B) organic resin into a sheet, and measuring the dielectric loss tangent and relative permittivity at 60 GHz to 90 GHz using the free-space method with a vector network analyzer, and plotting the relative permittivity on the X axis and the dielectric loss tangent on the Y axis for the obtained measured values, the slope of the linearly approximated line is 0.050 or higher.

2. The electromagnetic wave absorbing composition according to claim 1, characterized in that the component (A) is carbon black produced by the furnace method.

3. The electromagnetic wave absorbing composition according to claim 2, characterized in that the component (A) is Ketjenblack.

4. The electromagnetic wave absorbing composition according to any one of claims 1 to 3, characterized in that the (B) component is one or more selected from thermosetting resins and thermoplastic resins.

5. The electromagnetic wave absorbing composition according to claim 4, characterized in that the thermosetting resin is one or more selected from silicone resin, epoxy resin, maleimide resin, bismaleimide resin, amine resin, styrene resin, methacrylic resin, acrylic resin, allyl resin, benzoxazine resin, phenol resin, cyanate resin, polyimide resin, melamine resin, and polyamideimide resin.

6. The electromagnetic wave absorbing composition according to claim 4, characterized in that the thermoplastic resin is one or more selected from polyethylene resin, polypropylene resin, polystyrene resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polycarbonate resin, polyurethane resin, polyphenylene sulfide resin, polyamide resin, and fluororesin.

7. A method for manufacturing an electromagnetic wave absorbing composition according to any one of claims 1 to 3, characterized in that the (A) electromagnetic wave absorbing filler to be blended into the electromagnetic wave absorbing composition is selected by the following steps: (1) Prepare three or more filler selection compositions by blending the (B) organic resin with the selection filler in different filling amounts, and mold the filler selection compositions into a sheet to produce a cured filler selection product; (2) Measure the dielectric loss tangent and relative permittivity of the cured filler selection product at 60 GHz to 90 GHz using the free-space method with a vector network analyzer; (3) Plot the relative permittivity on the X axis and the dielectric loss tangent on the Y axis for the measurements obtained in (2), and select the selection filler that satisfies the condition that the slope of the linearly approximated line is 0.050 or more as the (A) electromagnetic wave absorbing filler.

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