Electromagnetic wave-absorbing foam

Abstract

To provide an electromagnetic wave-absorbing foam capable of achieving superior electromagnetic wave absorption.SOLUTION: An electromagnetic wave-absorbing foam contains a polyolefin resin and carbon black. The BET specific surface area of the carbon black is 500 m2 / g or less. When the polyolefin resin is 100 pts.mass, the content of the carbon black is 15 pts.mass or more and 50 pts.mass or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to electromagnetic wave absorbing foams. [Background technology]

[0002] Patent Document 1 discloses a radio wave absorber that contains a specific resin component and carbon black.

[0003] Patent Document 2 discloses a conductive cross-linked polyethylene foam, which contains a low-density polyethylene resin, an ethylene-vinyl acetate copolymer resin, and carbon black. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-311586 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-183436 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a demand for electromagnetic wave absorbing foams that have excellent electromagnetic wave absorbing properties. The present disclosure has an object to provide an electromagnetic wave absorbing foam having excellent electromagnetic wave absorbing properties. The present disclosure can be realized in the following aspects. [Means for solving the problem]

[0006] [1] An electromagnetic wave absorbing foam containing a polyolefin resin and carbon black, The BET specific surface area of ​​the carbon black is 500 m 2 / g or less, The electromagnetic wave absorbing foam has a carbon black content of 15 parts by mass or more and 50 parts by mass or less when the polyolefin resin is taken as 100 parts by mass. [Effects of the Invention]

[0007] According to the present disclosure, an electromagnetic wave absorbing foam having excellent electromagnetic wave absorption properties can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0008] Here, a preferred example of the present disclosure will be described. [2] Surface resistivity measured at an applied voltage of 1 V in accordance with JIS C2139-3-2:2018 is 3.00 x 10 6 The electromagnetic wave absorbing foam according to [1], having a resistance of Ω or less. [3] The electromagnetic wave-absorbing foam according to [1] or [2], wherein the peak electromagnetic wave absorption in the frequency band of 0.5 GHz or more and 17 GHz or less measured in accordance with ASTM D4935-18 is 5 dB or more. [4] The electromagnetic-wave-absorbing foam according to [1] or [2], wherein the imaginary part ε" of the complex relative permittivity ε in a frequency band of 1 GHz measured in accordance with ASTM D4935-18 is 1.50 F / m or more. [5] An electromagnetic wave absorbing foam containing a polyolefin resin and carbon black, An electromagnetic wave absorbing foam with a peak electromagnetic wave absorption of 20 dB or more in the frequency band of 0.5 GHz to 17 GHz, measured in accordance with ASTM D4935-18.

[0009] The present disclosure will be described in detail below. In this specification, the upper and lower limit values ​​of each numerical range can be combined in any way. In this specification, when a numerical range is described using "-", it is meant to include both the lower limit value and the upper limit value unless otherwise specified. For example, the description "10-20" includes both the lower limit value "10" and the upper limit value "20". In other words, "10-20" has the same meaning as "10 or more and 20 or less".

[0010] 1. First embodiment The electromagnetic wave absorbing foam of the first embodiment contains a polyolefin resin and carbon black.

[0011] 1-1. Raw materials for electromagnetic wave absorbing foam (1) Polyolefin resin A polyolefin resin is a resin whose main component is an olefin component unit. A resin whose main component is an olefin component unit is a resin containing 50% by mass or more of an olefin component unit. The content of the olefin component unit in the resin is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and it is particularly preferable that the resin component is composed only of a polyolefin resin.

[0012] The polyolefin resin is preferably at least one selected from the group consisting of polyethylene resins, polypropylene resins, polybutene, polypentene, and copolymers of olefin monomers and monomers copolymerizable with the olefin monomers.

[0013] The polyethylene resin is preferably at least one selected from the group consisting of ethylene homopolymers such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), very low-density polyethylene (VLDPE), and high-density polyethylene (HDPE), ethylene-propylene random copolymers, ethylene-propylene block copolymers, ethylene-butene random copolymers, ethylene-butene block copolymers, ethylene-vinyl acetate copolymers (EVA), and ethylene-methyl methacrylate copolymers.

[0014] The polypropylene-based resin is preferably at least one selected from the group consisting of propylene homopolymers such as isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene, propylene-ethylene random copolymers, propylene-ethylene block copolymers, propylene-butene random copolymers, propylene-butene block copolymers, propylene-ethylene-butene terpolymers, propylene-acrylic acid copolymers, and propylene-maleic anhydride copolymers.

[0015] As the polyolefin-based resin, it is preferable to use a polyethylene-based resin, and as the polyethylene-based resin, it is preferable to use low-density polyethylene (LDPE).

[0016] The content of the polyolefin resin can be freely set as long as it does not impair the purpose and effect of the present technology.

[0017] In addition, the raw materials for the electromagnetic wave absorbing foam may contain, in addition to the polyolefin resin, other resins, resins other than polyolefin resins such as elastomers, rubber components, etc., as long as the purpose and effects of the present technology are not impaired. The resin other than polyolefin resin is preferably one or more selected from the group consisting of thermoplastic resins such as polystyrene resins, polyamide resins, and polyester resins. The elastomer other than polyolefin resin is preferably one or more selected from the group consisting of olefin thermoplastic elastomers and styrene thermoplastic elastomers. The rubber component is preferably one or more selected from the group consisting of ethylene-propylene-diene rubber (EPDM), natural rubber (NR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and silicone rubber (SI).

[0018] (2) Carbon black The carbon black is preferably one or more types selected from the group consisting of furnace black, ketjen black, and acetylene black, and particularly preferably furnace black.

[0019] The BET specific surface area of ​​the carbon black was set to 500 m from the viewpoint of ensuring a sufficient amount of addition without deteriorating foam molding properties. 2 / g or less, and 300m 2 / g or less is preferable, and 100m 2 / g or less is more preferable, and 70m 2The BET specific surface area of ​​the carbon black is preferably 50 m / g or less from the viewpoint of ensuring sufficient electrical conductivity of the electromagnetic wave absorbing foam. 2 / g or more is preferable, and 55m 2 / g or more is more preferable, and 60m 2 / g or more is more preferable, and 65m 2 From these viewpoints, the BET specific surface area of ​​carbon black is preferably 500 m 2 / g or less, and 50m 2 / g or more 500m 2 / g or less is preferable, and 55m 2 / g or more 300m 2 / g or less is more preferable, and 60m 2 / g or more 100m 2 / g or less is more preferable, and 65m 2 / g or more 70m 2 / g or less is particularly preferred. The BET specific surface area can be measured from the nitrogen adsorption isotherm in accordance with the BET method.

[0020] The volatile content of carbon black is preferably 0.01% to 1.0%, more preferably 0.03% to 0.5%, and even more preferably 0.05% to 0.1%. The volatile content of carbon black is the amount of volatilization (weight loss) when ozone-oxidized carbon black is heated to a high temperature, and refers to the amount of oxygen-containing groups volatilized on the carbon black. During heating at a high temperature, the chemisorbed oxygen-containing groups are decomposed, and carbon dioxide, carbon monoxide, moisture, and the like are volatilized as gases.

[0021] The pH of carbon black when contacted with water is preferably 6 or more and 13 or less, more preferably 7 or more and 12 or less, and even more preferably 8 or more and 11 or less.

[0022] The ash content of the carbon black is preferably 0.001% or more and 0.025% or less, more preferably 0.003% or more and 0.020% or less, and even more preferably 0.005% or more and 0.015% or less.

[0023] The amount of carbon black is 15 parts by mass or more, preferably 20 parts by mass or more, and more preferably 25 parts by mass or more, per 100 parts by mass of the polyolefin-based resin, from the viewpoint of ensuring sufficient conductivity. The amount of carbon black is 50 parts by mass or less, preferably 40 parts by mass or less, and more preferably 35 parts by mass or less, per 100 parts by mass of the polyolefin-based resin, from the viewpoint of maintaining foam moldability. From these viewpoints, the amount of carbon black is 15 parts by mass or more and 50 parts by mass or less, preferably 20 parts by mass or more and 40 parts by mass or less, and more preferably 25 parts by mass or more and 35 parts by mass or less, per 100 parts by mass of the polyolefin-based resin.

[0024] (3) Foaming agent The raw materials for the electromagnetic wave-absorbing foam preferably contain a blowing agent. The blowing agent is preferably a pyrolytic type that decomposes upon heating to generate gas, but is not particularly limited. The blowing agent is preferably one or more selected from the group consisting of azodicarbonamide (ADCA), 2,2'-azobisisobutyronitrile, diazoaminobenzene, benzenesulfonylhydrazide, benzene-1,3-sulfonylhydrazide, diphenyloxide-4,4'-disulfonylhydrazide, 4,4'-oxybisbenzenesulfonylhydrazide, paratoluenesulfonylhydrazide, N,N'-dinitrosopentamethylenetetramine, N,N'-dinitroso-N,N'-dimethylphthalamide, terephthalazide, pt-butylbenzazide, sodium bicarbonate, and ammonium bicarbonate. Among these, azodicarbonamide (ADCA) is particularly preferred.

[0025] The amount of the foaming agent is preferably 5.00 parts by mass or more and 15.00 parts by mass or less, more preferably 6.00 parts by mass or more and 10.00 parts by mass or less, and even more preferably 7.0 parts by mass or more and 8.00 parts by mass or less, based on 100 parts by mass of the polyolefin resin.

[0026] (4) Foaming aid The raw materials for the electromagnetic wave-absorbing foam preferably contain a foaming aid. The foaming aid is not particularly limited. The foaming aid is preferably one or more selected from the group consisting of metal oxides such as zinc oxide, zinc stearate, and lead oxide, lower or higher fatty acids or metal salts thereof, and urea and derivatives thereof.

[0027] The amount of urea as a foaming aid is preferably 0.03 parts by mass or more and 0.20 parts by mass or less, more preferably 0.05 parts by mass or more and 0.15 parts by mass or less, and even more preferably 0.08 parts by mass or more and 0.10 parts by mass or less, based on 100 parts by mass of the polyolefin resin.

[0028] The amount of zinc oxide as a foaming aid is preferably 0.05 parts by mass or more and 0.25 parts by mass or less, more preferably 0.08 parts by mass or more and 0.20 parts by mass or less, and even more preferably 0.10 parts by mass or more and 0.15 parts by mass or less, based on 100 parts by mass of the polyolefin resin.

[0029] (5) Crosslinking agent The raw materials of the electromagnetic wave absorbing foam preferably contain a crosslinking agent. The crosslinking agent is not particularly limited. The crosslinking agent is preferably used for chemical crosslinking. The crosslinking agent is preferably an organic peroxide. The crosslinking agent is preferably one or more selected from the group consisting of dicumyl peroxide, 2,5-dimethyl-2,5-bis-tert-butylperoxyhexane, and 1,3-bis-tert-peroxy-isopropylbenzene.

[0030] The amount of the crosslinking agent is preferably 0.1 to 2.0 parts by mass, more preferably 0.3 to 1.5 parts by mass, and even more preferably 0.5 to 1.0 parts by mass, based on 100 parts by mass of the polyolefin resin.

[0031] (6) Lubricants The raw materials of the electromagnetic wave absorbing foam preferably contain a lubricant. The lubricant is not particularly limited. The lubricant is preferably a sorbitan fatty acid ester such as sorbitan stearate or sorbitan laurate.

[0032] The amount of lubricant is preferably 0.10 parts by mass or more and 1.5 parts by mass or less, more preferably 0.20 parts by mass or more and 1.0 parts by mass or less, and even more preferably 0.30 parts by mass or more and 0.50 parts by mass or less, based on 100 parts by mass of the polyolefin resin.

[0033] (7) Other raw materials The raw materials of the electromagnetic wave absorbing foam may contain, as necessary, a surface tension adjuster, a filler (such as calcium carbonate), a pigment, a plasticizer, a function-imparting agent (such as a flame retardant), and the like.

[0034] 1-2. Composition of electromagnetic wave absorbing foam (1) Density (apparent density) The density of the electromagnetic wave absorbing foam is 30 kg / m 3 More than 50 kg / m is preferable. 3 More preferably, 70 kg / m 3 More preferably, the density of the electromagnetic wave absorbing foam is 150 kg / m 3 Preferably less than 100 kg / m 3 Less than 90 kg / m is more preferable. 3 Therefore, the density of the electromagnetic wave absorbing foam is preferably 30 kg / m or less. 3 More than 150kg / m 3 Less than 50 kg / m 3 More than 100kg / m 3 Less than 70 kg / m is more preferable. 3 More than 90kg / m 3 The following is even more preferred: The density of the electromagnetic wave absorbing foam can be measured based on JIS K 6767:2015.

[0035] (2)Surface resistivity The surface resistivity of the electromagnetic wave absorbing foam measured at an applied voltage of 1 V according to JIS C2139-3-2:2018 is 3.00 × 10 6 Ω or less is preferable, 1.00×10 5 Ω or less is preferable, and 1.00×10 4 The surface resistivity of the electromagnetic wave absorbing foam is more preferably 1.00×10 3Ω or more is preferable, 3.00×10 3 Ω or more is preferable, 5.00×10 3 Therefore, the surface resistivity of the electromagnetic wave absorbing foam is preferably 1.00×10 3 Ω or more 3.00×10 6 Ω or less is preferable, 3.00×10 3 Ω or more 1.00×10 5 Ω or less is preferable, 5.00×10 3 Ω or more 1.00×10 4 The surface resistivity of the electromagnetic wave absorbing foam can be calculated by setting a foam having a thickness of 10 mm in a testing machine and measuring the surface resistance value of the foam surface.

[0036] (3) Electromagnetic wave absorption The peak electromagnetic wave absorption of the electromagnetic wave-absorbing foam in the frequency band of 0.5 GHz or more and 17 GHz or less, measured in accordance with ASTM D4935-18, is preferably 5 dB or more, more preferably 10 dB or more, and even more preferably 20 dB or more. There is no particular restriction on the lower limit of the electromagnetic wave absorption of the electromagnetic wave-absorbing foam. The electromagnetic wave absorption of the electromagnetic wave-absorbing foam is measured in the frequency band of 0.5 GHz or more and 17 GHz or less by punching out a 10 mm thick foam into a cylindrical sample and setting it in a coaxial tube.

[0037] (4) Relative dielectric constant The imaginary part ε" of the complex relative permittivity ε of the electromagnetic wave absorbing foam in a frequency band of 1 GHz, measured in accordance with ASTM D4935-18, is preferably 1.50 F / m or more, more preferably 2.00 F / m or more, and even more preferably 3.00 F / m or more. The imaginary part ε" of the complex relative permittivity ε of the electromagnetic wave absorbing foam is preferably 7.00 F / m or less, more preferably 6.00 F / m or less, and even more preferably 5.00 F / m or less. Therefore, the imaginary part ε" of the complex relative permittivity ε of the electromagnetic-wave absorbing foam is preferably 1.50 F / m or more and 7.00 F / m or less, more preferably 2.00 F / m or more and 6.00 F / m or less, and even more preferably 3.00 F / m or more and 5.00 F / m or less. The imaginary part ε" of the complex relative permittivity ε of the electromagnetic-wave absorbing foam is measured by punching out a foam with a thickness of 10 mm into a cylindrical shape, setting the sample in a coaxial tube, and measuring S parameters in a frequency band of 0.5 GHz or more and 17 GHz or less. Then, the complex relative permittivity ε" is calculated from the obtained S parameters using the Reflection / Transmission Epsilon Precision Model formula.

[0038] (5) 25% compressive stress The 25% compressive stress of the electromagnetic wave-absorbing foam is preferably 0.100 MPa or more, more preferably 0.110 MPa or more, and even more preferably 0.120 MPa or more. The 25% compressive stress of the electromagnetic wave-absorbing foam is preferably 0.500 MPa or less, more preferably 0.300 MPa or less, and even more preferably 0.200 MPa or less. Therefore, the 25% compressive stress of the electromagnetic wave-absorbing foam is preferably 0.100 MPa or more and 0.500 MPa or less, more preferably 0.110 MPa or more and 0.300 MPa or less, and even more preferably 0.120 MPa or more and 0.200 MPa or less. The 25% compressive stress of the electromagnetic wave-absorbing foam can be measured in accordance with JIS K6767:2015. Specifically, a foam sample measuring 50 mm x 50 mm x 20 mm thick is compressed at a compression speed of 10 mm / min to determine the stress at 25% compression.

[0039] 1-3. Manufacturing method of electromagnetic wave absorbing foam The method for producing an electromagnetic wave-absorbing foam includes a raw material mixing step, a primary heating step, and a secondary heating step. In the raw material mixing step, a polyolefin resin, carbon black, and other raw materials are mixed to produce a resin mixture. For example, the polyolefin resin, carbon black, and other raw materials are heated and kneaded using a kneader at 120°C for 15 minutes to produce the resin mixture. In the primary heating step, the resin mixture is subjected to a primary heat press in a mold at 137°C for 60 minutes at 10 MPa to produce a primary pressed body. In the secondary heating step, the primary pressed body is subjected to a secondary heat press in a mold at 163°C for 90 minutes to produce an electromagnetic wave-absorbing foam.

[0040] 1-4. Effects of the First Embodiment The electromagnetic wave absorbing foam of the first embodiment has good moldability and excellent electromagnetic wave absorbing properties. The electromagnetic wave absorbing foam of the first embodiment is durable and can be used as a structure.

[0041] 2. Second embodiment The electromagnetic-wave-absorbing foam of the second embodiment contains a polyolefin resin and carbon black, and has a peak electromagnetic-wave absorption of 20 dB or more in a frequency band of 0.5 GHz or more and 17 GHz or less, measured in accordance with ASTM D4935-18.

[0042] 2-1. Raw materials for electromagnetic wave absorbing foam With regard to the raw materials of the electromagnetic wave absorbing foam, the explanations in the section "Raw materials for electromagnetic wave absorbing foam" in the first embodiment regarding "polyolefin resin," "foaming agent," "foaming aid," "crosslinking agent," "lubricant," and "other raw materials" apply as is, and descriptions thereof are omitted. In other words, the "polyolefin resin," "foaming agent," "foaming aid," "crosslinking agent," "lubricant," and "other raw materials" explained in the section "Raw materials for electromagnetic wave absorbing foam" in the first embodiment apply as is.

[0043] Carbon black Regarding carbon black, the descriptions other than the BET specific surface area and amount of "carbon black" explained in the section "raw material for electromagnetic wave absorbing foam" in the first embodiment are applied as is.

[0044] The BET specific surface area of ​​the carbon black was set to 500 m from the viewpoint of ensuring a sufficient amount of addition without deteriorating foam molding properties. 2 / g or less is preferable, and 300m 2 / g or less is more preferable, and 100m 2 / g or less is more preferable, and 70m 2 The BET specific surface area of ​​the carbon black is particularly preferably 50 m / g or less from the viewpoint of ensuring sufficient electrical conductivity of the electromagnetic wave absorbing foam. 2 / g or more is preferable, and 55m 2 / g or more is more preferable, and 60m 2 / g or more is more preferable, and 65m 2 From these viewpoints, the BET specific surface area of ​​carbon black is preferably 50 m 2 / g or more 500m 2 / g or less is preferable, and 55m 2 / g or more 300m 2 / g or less is more preferable, and 60m 2 / g or more 100m 2 / g or less is more preferable, and 65m 2 / g or more 70m 2 / g or less is particularly preferred. The BET specific surface area can be measured from the nitrogen adsorption isotherm in accordance with the BET method.

[0045] From the viewpoint of ensuring sufficient conductivity, the amount of carbon black is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 25 parts by mass or more, per 100 parts by mass of the polyolefin-based resin. From the viewpoint of maintaining foam moldability, the amount of carbon black is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less, per 100 parts by mass of the polyolefin-based resin. From these viewpoints, the amount of carbon black is preferably 15 parts by mass or more and 50 parts by mass or less, more preferably 20 parts by mass or more and 40 parts by mass or less, and even more preferably 25 parts by mass or more and 35 parts by mass or less, per 100 parts by mass of the polyolefin-based resin.

[0046] 2-2. Composition of electromagnetic wave absorbing foam In the configuration of the electromagnetic wave absorbing foam, the explanations in the section "Configuration of electromagnetic wave absorbing foam" in the first embodiment regarding "density (apparent density)," "surface resistivity," "dielectric constant," and "25% compressive stress" apply as is, and the description thereof will be omitted. In other words, the "density (apparent density)," "surface resistivity," "dielectric constant," and "25% compressive stress" explained in the section "Configuration of electromagnetic wave absorbing foam" in the first embodiment apply as is.

[0047] Electromagnetic wave absorption The peak electromagnetic wave absorption of the electromagnetic wave-absorbing foam in the frequency band of 0.5 GHz or more and 17 GHz or less, measured in accordance with ASTM D4935-18, is 20 dB or more, preferably 25 dB or more, and more preferably 30 dB or more. There is no particular upper limit to the electromagnetic wave absorption of the electromagnetic wave-absorbing foam. The electromagnetic wave absorption of the electromagnetic wave-absorbing foam is measured in the frequency band of 0.5 GHz or more and 17 GHz or less by punching a 10 mm thick foam into a cylindrical sample and setting it in a coaxial tube.

[0048] 2-3. Manufacturing method of electromagnetic wave absorbing foam In the method for producing the electromagnetic wave absorbing foam, the explanation in the section "Method for producing the electromagnetic wave absorbing foam" in the first embodiment is applied as is, and the description thereof will be omitted.

[0049] 2-4. Effects of the second embodiment The electromagnetic wave absorbing foam of the second embodiment has good moldability and excellent electromagnetic wave absorbing properties. The electromagnetic wave absorbing foam of the second embodiment is durable and can be used as a structure. [Example]

[0050] The present invention will be explained in more detail below with reference to examples. 1. Preparation of Electromagnetic Wave Absorbing Foam Electromagnetic wave-absorbing foams of Examples and Comparative Examples were produced using the blending ratios shown in Tables 1 and 2. Details of the raw materials of the electromagnetic wave-absorbing foams in Tables 1 and 2 are shown in Tables 3 and 4. In Tables 1 and 2, the blending ratios represent the blending ratios (parts by mass) when the polyolefin resin is taken as 100 parts by mass.

[0051] [Table 1]

[0052] [Table 2]

[0053] [Table 3]

[0054] [Table 4]

[0055] The electromagnetic wave-absorbing foams of Examples 1-4 and Comparative Examples 1-5 were produced by the same method as in the above-described embodiment. Specifically, a raw material mixing step, a primary heating step, and a secondary heating step were performed. In the raw material mixing step, polyolefin resin, carbon black, and other raw materials (foaming agent, foaming aid, crosslinking agent, and lubricant) were mixed to produce a resin mixture. The polyolefin resin, carbon black, and other raw materials were heated and kneaded using a kneader at 120°C for 15 minutes to produce a resin mixture. In the primary heating step, the resin mixture was subjected to a primary heat press at 137°C for 60 minutes at 10 MPa in a mold to produce a primary-pressed body. In the secondary heating step, the primary-pressed body was subjected to a secondary heat press at 163°C for 90 minutes in a mold to produce an electromagnetic wave-absorbing foam.

[0056] 2. Evaluation Method (1) Foam moldability The foam moldability of the electromagnetic wave absorbing foam was evaluated by visually inspecting the appearance, cutting the foam with a cutter, and visually inspecting the cells, based on the following criteria. A: No wrinkles or voids are observed, and the appearance is good. B: Wrinkles and voids are present, and the appearance is poor.

[0057] (2) Foam density (apparent density) The density of the electromagnetic wave absorbing foam was measured in accordance with JIS K 6767:2015.

[0058] (3)Surface resistivity The surface resistivity of the electromagnetic wave absorbing foam was measured in accordance with JIS C2139-3-2:2018 at an applied voltage of 1 V. Specifically, the surface resistivity was calculated by setting a foam with a thickness of 10 mm in a testing machine and measuring the surface resistance value of the foam surface.

[0059] (4) Electromagnetic wave absorption The peak electromagnetic wave absorption of the electromagnetic wave absorbing foam was measured in the frequency band of 0.5 GHz to 17 GHz in accordance with ASTM D4935-18. A sample (foam) made by punching out a 10 mm thick foam into a cylindrical shape was set in a coaxial tube, and the electromagnetic wave absorption was measured in the frequency band of 0.5 GHz to 17 GHz.

[0060] (5) Relative permittivity The imaginary part ε" of the complex relative permittivity ε of the electromagnetic wave absorbing foam was measured in the 1 GHz frequency band, measured in accordance with ASTM D4935-18. The imaginary part ε" of the complex relative permittivity ε of the electromagnetic wave absorbing foam was measured by punching out a 10 mm thick foam into a cylindrical sample, setting the sample in a coaxial tube, and measuring the S parameters in the frequency band from 0.5 GHz to 17 GHz. The complex relative permittivity ε" was then calculated from the obtained S parameters using the Reflection / Transmission Epsilon Precision Model formula.

[0061] (6) 25% compressive stress The 25% compression stress of the electromagnetic wave absorbing foam was measured based on JIS K6767: 2015. Specifically, a foam sample measuring 50 mm x 50 mm x 20 mm thick was compressed at a compression speed of 10 mm / min, and the stress at 25% compression was determined.

[0062] 3.Results The results are shown in Tables 1 and 2. In Example 1-4, the evaluation of foam moldability was "A", and it was found that an electromagnetic wave absorbing foam with good foamability (appearance) could be obtained.

[0063] In Example 1-4, the surface resistivity of the electromagnetic wave absorbing foam was 2.76 × 10 3 Ω-5.09×10 5 In Comparative Example 1-5, the surface resistivity of the electromagnetic wave absorbing foam was 4.36 × 10 6 Ω-6.01×10 6The resistance was Ω. Example 1-5 satisfies the following requirements (A) and (B), whereas Comparative Example 1-5 does not satisfy the following requirements (A) and (B). Requirement (A): The BET specific surface area of ​​carbon black is 500m 2 / g or less Requirement (A): When the polyolefin resin is 100 parts by mass, the carbon black content is 15 parts by mass or more and 50 parts by mass or less. It was found that in Examples 1-5, the surface resistivity of the electromagnetic wave absorbing foam could be reduced by satisfying the above requirements (a) and (b).

[0064] In Example 1-4, the peak electromagnetic wave absorption amount in the frequency band of 0.5 GHz or more and 17 GHz or less in the electromagnetic wave absorbing foam was 9.19 dB or more and 31.60 dB or less. In Comparative Example 1-5, the peak electromagnetic wave absorption amount in the frequency band of 0.5 GHz or more and 17 GHz or less in the electromagnetic wave absorbing foam was 0.66 dB or more and 7.40 dB or less. Example 1-4 satisfies the above requirements (A) and (B), whereas Comparative Example 1-5 does not satisfy the above requirements (A) and (B). It was found that in Example 1-4, by satisfying the above requirements (a) and (b), the peak electromagnetic wave absorption amount in the frequency band of 0.5 GHz or more and 17 GHz or less in the electromagnetic wave absorbing foam can be increased.

[0065] In Example 1-4, the imaginary part ε" of the complex relative permittivity ε in the 1 GHz frequency band of the electromagnetic wave absorbing foam was 2.85 F / m-6.58 F / m. In Comparative Example 1-5, the imaginary part ε" of the complex relative permittivity ε in the 1 GHz frequency band of the electromagnetic wave absorbing foam was 0.38 F / m-1.31 F / m. Example 1-4 satisfies the above requirements (a) and (b), whereas Comparative Example 1-5 does not satisfy the above requirements (a) and (b). It was found that in Examples 1-4, the imaginary part ε" of the complex relative permittivity ε, which indicates the degree of attenuation of electromagnetic waves inside a substance, can be increased by satisfying the above requirements (a) and (b). 4. Effects of the Example According to the above examples, it was possible to produce an electromagnetic wave absorbing foam that has good moldability and excellent electromagnetic wave absorbing properties.

[0066] The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible.

Claims

1. An electromagnetic wave absorbing foam comprising a polyolefin resin and carbon black, The BET specific surface area of ​​the carbon black is 500 m ２ / g or less, The electromagnetic wave absorbing foam has a carbon black content of 15 parts by mass or more and 50 parts by mass or less when the polyolefin resin is taken as 100 parts by mass.

2. The surface resistivity measured at an applied voltage of 1 V in accordance with JIS C2139-3-2:2018 is 3.00 × 10 ６ 2. The electromagnetic wave absorbing foam according to claim 1, wherein the resistance is Ω or less.

3. 3. The electromagnetic wave absorbing foam according to claim 1, wherein the peak electromagnetic wave absorption in the frequency band of 0.5 GHz or more and 17 GHz or less measured in accordance with ASTM D4935-18 is 5 dB or more.

4. 3. The electromagnetic wave absorbing foam according to claim 1, wherein the imaginary part ε" of the complex relative permittivity ε in a frequency band of 1 GHz measured in accordance with ASTM D4935-18 is 1.50 F / m or more.

5. An electromagnetic wave absorbing foam comprising a polyolefin resin and carbon black, An electromagnetic wave absorbing foam having a peak electromagnetic wave absorption of 20 dB or more in the frequency band of 0.5 GHz or more and 17 GHz or less, measured in accordance with ASTM D4935-18.

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