Thermoplastic resin composition for electromagnetic wave absorbers, and molded body

Abstract

One embodiment of the present invention relates to a thermoplastic resin composition for electromagnetic wave absorbers, the thermoplastic resin composition containing: 50% by mass to 80% by mass of an olefin-based elastomer (A) that has a tensile elongation at break of 400% to 700% as determined in accordance with ISO 37; 15% by mass to 35% by mass of an elastomer (B) that includes at least one elastomer which is selected from the group consisting of a styrene-based elastomer (B1) and an olefin-based elastomer (B2) that has a tensile elongation at break of 800% or more as determined in accordance with ISO 37; 0.5% by mass to 5% by mass of carbon nanotubes (C); and 3% by mass to 15% by mass carbon black (D).

Description

Thermoplastic resin composition for electromagnetic wave absorber and molded article

[0001] An embodiment of the present invention relates to a thermoplastic resin composition for an electromagnetic wave absorber and a molded article thereof.

[0002] Plastics are easy to mold and process, and are therefore used in a wide range of fields, including electrical and electronic equipment parts, automotive parts, medical parts, and food containers. Plastic molded products are often colored to enhance their decorativeness or to impart functionality. In particular, in the automotive field, colored molded products are widely distributed for the purpose of imparting functionality, such as electromagnetic wave absorption.

[0003] Electromagnetic waves are emitted from communication devices such as radios, televisions, and wireless communication devices, but also from electronic devices such as mobile phones and personal computers, which have rapidly increased in number due to recent advances in information technology. Conventionally, one method for preventing malfunctions of electronic devices and communication devices due to electromagnetic waves has been to install electromagnetic wave absorbers, which efficiently absorb electromagnetic waves and convert the absorbed electromagnetic waves into thermal energy, near or far from the electromagnetic wave generating device.

[0004] An example of an electromagnetic wave absorber installed far from the electromagnetic wave generating point is its application in an electronic toll collection system (ETC) on expressways. ETC is a system that exchanges billing information and other information using microwaves at a frequency of 5.8 GHz between a roadside unit antenna installed at the toll booth and an on-board unit antenna when a vehicle passes through a toll booth exit on an expressway. At toll booths where this ETC system has been introduced, microwaves emitted from the antenna are reflected by the toll booth roof or the like, causing unwanted electromagnetic waves to leak from adjacent ETC lanes, which can cause communication abnormalities. Therefore, electromagnetic wave absorbers are installed on the toll booth roof or between the ETC lanes to suppress communication abnormalities.

[0005] In recent years, millimeter-wave radar has been used in the automotive field for the purposes of autonomous driving and collision prevention, and millimeter-wave radar devices are often installed inside automobiles. Millimeter waves are electromagnetic waves with wavelengths of 1 to 10 mm and frequencies of 30 to 300 GHz. They are currently used in vehicle radar, full-body scanners that see under clothing for security checks at airports, and video transmission from surveillance cameras on platforms during train operation with a single driver. Millimeter-wave radar devices transmit millimeter waves and receive the reflected waves to recognize obstacles. Due to their long detectable distance and resistance to interference from sunlight, rain, and fog, they are now being used in autonomous driving technologies, such as automobiles. In the case of automotive sensors, millimeter-wave radar devices transmit and receive millimeter waves from an antenna to detect the relative distance and relative speed of obstacles.

[0006] The transmitting and receiving antennas of these millimeter-wave radar devices may receive signals reflected from road surfaces other than the target obstacle, which can reduce the detection accuracy of the device. To solve this problem, millimeter-wave radar devices are equipped with an electromagnetic wave absorber between the antenna and control circuit as a shielding member to block electromagnetic waves.

[0007] Known millimeter-wave band electromagnetic wave absorbing materials that constitute such electromagnetic wave absorbers include carbon-based, metal-carbon-based, and magnetic-based materials. For example, carbon-based electromagnetic wave absorbers containing carbon nanotubes (CNTs) are used because of their high conductivity and relatively light weight (Patent Document 1).

[0008] Special table 2017-512847 publication

[0009] Patent Document 1 discloses a method of adding carbon nanotubes instead of conductive carbon black to an electromagnetic wave absorber in order to improve conductivity while reducing the amount of conductive filler added, and according to Patent Document 1, a composite material containing carbon nanotubes has been shown to have excellent conductivity while also improving mechanical properties. However, in recent years, further improvements in electromagnetic wave absorbers are desired for use in the automotive field and the like.

[0010] Therefore, an object of some embodiments of the present invention is to provide a thermoplastic resin composition for an electromagnetic wave absorber, which can provide an electromagnetic wave absorber having good electromagnetic wave absorbency and flexibility, and also excellent heat resistance. Another object of some embodiments of the present invention is to provide a molded article having good electromagnetic wave absorbency and flexibility, and also excellent heat resistance.

[0011] As a result of extensive research, the present inventors have found that the problems of the present invention can be solved by the following aspects, and have thus completed the present invention.

[0012] One embodiment of the present invention relates to a thermoplastic resin composition for an electromagnetic wave absorber, comprising 50 to 80% by mass of an olefin-based elastomer (A) having a tensile elongation at break of 400 to 700% measured in accordance with ISO 37: 2017, 15 to 35% by mass of an elastomer (B) containing at least one selected from the group consisting of a styrene-based elastomer (B1) and an olefin-based elastomer (B2) having a tensile elongation at break of 800% or more measured in accordance with ISO 37: 2017, 0.5 to 5% by mass of carbon nanotubes (C), and 3 to 15% by mass of carbon black (D). Another embodiment of the present invention relates to a molded article molded using the thermoplastic resin composition for an electromagnetic wave absorber.

[0013] According to some embodiments of the present invention, the thermoplastic resin composition for an electromagnetic wave absorber can be used to produce an electromagnetic wave absorber having good electromagnetic wave absorbency and flexibility, and also having excellent heat resistance. According to some embodiments of the present invention, the molded article has good electromagnetic wave absorbency and flexibility, and also has excellent heat resistance.

[0014] FIG. 1 is a conceptual diagram showing how transmission loss and return loss are measured using a millimeter wave transmitting device.

[0015] The present invention is described in detail below. In this specification, a numerical range specified using "to" includes the numerical values ​​before and after "to" as the lower and upper limits. Furthermore, "an olefin-based elastomer (A) having a tensile elongation at break of 400 to 700% measured in accordance with ISO 37:2017" may be referred to as "olefin-based elastomer (A)," an olefin-based elastomer (B2) having a tensile elongation at break of 800% or more measured in accordance with ISO 37:2017 may be referred to as "olefin-based elastomer (B2)," an "elastomer (B) comprising at least one member selected from the group consisting of a styrene-based elastomer (B1) and an olefin-based elastomer (B2)" may be referred to as "elastomer (B)," a thermoplastic resin composition for electromagnetic wave absorbers may be referred to as "thermoplastic resin composition," and "carbon nanotubes" may be referred to as "CNT." Unless otherwise noted, the various components mentioned in this specification may be used independently, either singly or in combination. The numerical values ​​specified in this specification are values ​​determined by the methods disclosed in the embodiments or examples.

[0016] <Thermoplastic resin composition for electromagnetic wave absorber> According to an embodiment of the present invention, the thermoplastic resin composition for an electromagnetic wave absorber contains 50 to 80 mass% of an olefin-based elastomer (A) having a tensile elongation at break of 400 to 700% measured in accordance with ISO 37:2017 (hereinafter referred to as "ISO37"), 15 to 35 mass% of an elastomer (B) including at least one selected from the group consisting of a styrene-based elastomer (B1) and an olefin-based elastomer (B2) having a tensile elongation at break of 800% or more measured in accordance with ISO37, 0.5 to 5 mass% of carbon nanotubes (C), and 3 to 15 mass% of carbon black (D).

[0017] [Olefin-Based Elastomer (A)] The olefin-based elastomer (A) has a tensile elongation at break of 400 to 700% measured in accordance with ISO 37. A tensile elongation at break of 400% or more is preferable in terms of electromagnetic wave absorption and flexibility, as it improves the electromagnetic wave transmission efficiency between conductive fillers such as carbon nanotubes and carbon black. The tensile elongation at break is preferably 500% or more, more preferably 550% or more, and even more preferably 600% or more. A tensile elongation at break of 700% or less is preferable in terms of heat resistance. The tensile elongation at break is preferably 680% or less, more preferably 650% or less. The tensile elongation at break may be, for example, 400 to 700%, 500 to 680%, or 550 to 650%.

[0018] In an embodiment of the present invention, the tensile elongation at break is a value obtained by measurement in accordance with ISO 37. Specifically, the measurement is performed on a test piece (a dumbbell-shaped No. 3 test piece prepared in accordance with JIS K 6251:2017) using a materials testing machine (for example, "3367" manufactured by Instron Corporation) under conditions of an atmosphere at a temperature of 23°C and a tensile speed of 500 mm / min.

[0019] The melt mass-flow rate (MFR) of the olefin-based elastomer (A) is, for example, 0.1 to 50 g / 10 min. The MFR is preferably 5 g / 10 min or more, more preferably 15 g / 10 min or more, and even more preferably 20 g / 10 min or more. An MFR of 5 g / 10 min or more is particularly preferable in terms of electromagnetic wave absorption and moldability, as it allows the conductive filler to be uniformly dispersed in the molded article. The MFR is preferably 45 g / 10 min or less, more preferably 40 g / 10 min or less, and even more preferably 30 g / 10 min or less. An MFR of 50 g / 10 min or less is preferable in terms of heat resistance. The melt mass-flow rate (MFR) may be, for example, 5 to 45 g / 10 min, 15 to 40 g / 10 min, or 20 to 30 g / 10 min.

[0020] In an embodiment of the present invention, the MFR is a value of the melt mass flow rate measured in accordance with JIS K 7210: 1999. Specifically, the measurement is performed using a melt flow rate measuring device (for example, "Melt Indexer" manufactured by Toyo Seiki Seisakusho) under conditions of a temperature of 230°C and a load of 2.16 kgf.

[0021] The olefinic elastomer (A) is preferably a mixed material in which an elastic rubber component is dispersed in a polyolefin, which is a molecular restraining component that prevents plastic deformation. The rubber component may be an uncrosslinked rubber component, a partially crosslinked rubber component, or a fully crosslinked rubber component. The crosslinking may be, for example, dynamic crosslinking that occurs during mixing and kneading of the polyolefin and the rubber component. In the mixed material, the polyolefin and a portion of the rubber component may be graft polymerized.

[0022] Examples of polyolefins that are molecular restraining components include crystalline polyolefins such as polyethylene and polypropylene. Examples of rubber components include ethylene propylene rubbers such as ethylene-propylene copolymer (EPM), ethylene-butylene copolymer (EBM), and ethylene-propylene-diene terpolymer (EPDM), and acrylonitrile butadiene rubber (NBR).

[0023] From the viewpoint of heat resistance, the olefin elastomer (A) is preferably a dynamically crosslinked olefin thermoplastic elastomer, and is preferably a dynamically crosslinked elastomer using crystalline polypropylene as a molecular restraining component and ethylene-propylene-diene terpolymer (EPDM) as a rubber component.

[0024] Commercially available olefin elastomers (A) include, for example, Milastomer 9070NS, Milastomer L900NS, and Milastomer A970B manufactured by Mitsui Chemicals, Inc.; Actima GA-1075N and Actima LVG9541S manufactured by Riken Technos Corporation; Santoprene 201-87 and Santoprene 203-40 manufactured by Exxon Mobil Corporation; Sarlink 4190, Sarlink 3190, and Sarlink 4155 manufactured by Toyobo Co., Ltd.; and Excellink 1300B, Excellink 1404B, and Excellink 1309B manufactured by JSR Corporation.

[0025] The content of the olefinic elastomer (A) is 50 to 80% by mass, based on the mass of the thermoplastic resin composition. A content of 50% by mass or more is preferred in terms of the manufacturability of the thermoplastic resin composition and the molded article. The content is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more. A content of 80% by mass or less is preferred in terms of electromagnetic wave absorption. The content is preferably 75% by mass or less, more preferably 70% by mass or less, and even more preferably 70% by mass or less. The content may be, for example, 55 to 75% by mass, 60 to 70% by mass, or 65 to 70% by mass.

[0026] [Elastomer (B)] The thermoplastic resin composition contains at least one elastomer (B) selected from the group consisting of a styrene-based elastomer (B1) and an olefin-based elastomer (B2). The elastomer (B) may be the styrene-based elastomer (B1), the olefin-based elastomer (B2), or both the styrene-based elastomer (B1) and the olefin-based elastomer (B2).

[0027] (Styrene-based elastomer (B1)) The styrene-based elastomer (B1) may be a block copolymer of styrene and at least one selected from the group consisting of α-olefins and diolefins. The styrene may be substituted or unsubstituted, and is preferably unsubstituted. Examples of α-olefins are as described below. Examples of diolefins (dienes) include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. The styrene-based elastomer (B1) may be a styrene-based thermoplastic elastomer or a hydrogenated styrene-based thermoplastic elastomer.

[0028] In the styrene-based elastomer (B1), the content of the styrene structure is, for example, 10 to 50% by mass, preferably 15 to 35% by mass, and more preferably 20 to 32% by mass, based on the mass of the styrene-based elastomer (B1). A styrene structure content of 15% by mass or more increases the proportion of styrene structures as hard segments, which is preferable in terms of heat resistance. The styrene structure content is preferably 18% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. A styrene structure content of 35% by mass or less increases the proportion of α-olefin structures as soft segments, which is preferable in terms of flexibility. Furthermore, compatibility with the olefin-based elastomer (A) is improved, which is preferable in terms of electromagnetic wave absorption. The styrene structure content is preferably 34% by mass or less, more preferably 32% by mass or less, and even more preferably 30% by mass or less.

[0029] The styrene-based elastomer (B1) contains, for example, a styrene structure and at least one selected from the group consisting of an α-olefin structure and a diolefin structure. The diolefin structure may be hydrogenated or may not be hydrogenated.

[0030] In the styrene-based elastomer (B1), the content of the α-olefin structure and the diolefin structure is, for example, 50 to 85% by mass, based on the mass of the styrene-based elastomer (B1). From the viewpoint of flexibility, it is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 65% ​​by mass or more. From the viewpoint of heat resistance, it is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less. The content may be, for example, 50 to 80% by mass, 55 to 75% by mass, or 60 to 70% by mass. When the styrene-based elastomer (B1) contains an α-olefin structure and a diolefin structure, the "content of the α-olefin structure and the diolefin structure" refers to the total content of both structures, and when only one structure is contained, it refers to the content of the one structure.

[0031] The solution viscosity of the styrene-based elastomer (B1) is, for example, 30 mPa·s or more, preferably 50 mPa·s or more, more preferably 100 mPa·s or more, and even more preferably 200 mPa·s or more. A solution viscosity of 30 mPa·s or more is preferred in terms of heat resistance. There is no particular upper limit to the solution viscosity, but from the perspective of compatibility with the olefin-based elastomer (A), it may be 1,000 mPa·s or less or 500 mPa·s or less. The solution viscosity may be, for example, 30 to 1,000 mPa·s, 50 to 1,000 mPa·s, 100 to 500 mPa·s, or 200 to 500 mPa·s.

[0032] In an embodiment of the present invention, the solution viscosity of the styrene-based elastomer (B1) is a value measured using a toluene solution obtained by dissolving the styrene-based elastomer (B1) in a toluene solvent to a concentration of 5% by mass, using a Brookfield viscometer in an atmosphere at a temperature of 30° C. As the Brookfield viscometer, for example, a "VISCOMETER TVB-10" manufactured by Toki Sangyo Co., Ltd. can be used.

[0033] The weight-average molecular weight of the styrene-based elastomer (B1) is, for example, 10,000 or more. From the viewpoint of heat resistance, it is preferably 50,000 or more, more preferably 80,000 or more, and even more preferably 100,000 or more. Furthermore, from the viewpoint of compatibility with the olefin-based elastomer (A), it is preferably 800,000 or less, more preferably 600,000 or less, and even more preferably 500,000 or less. The weight-average molecular weight is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene. The weight-average molecular weight may be, for example, 50,000 to 800,000, 80,000 to 600,000, or 100,000 to 500,000.

[0034] From the viewpoint of flexibility, the Shore A hardness of the styrene-based elastomer (B1) is preferably not more than 80, more preferably not more than 70, and even more preferably not more than 60. Unless otherwise specified in this specification, the Shore A hardness is a value measured using a durometer with a type A indenter in accordance with JIS K6253.

[0035] The styrene-based elastomer (B1) may be, for example, any of the following block copolymers. From the viewpoint of heat resistance, the styrene-based elastomer (B1) is preferably a block copolymer of a styrene structure as a hard segment and an α-olefin structure as a soft segment. From the viewpoint of heat resistance, the styrene-based elastomer (B1) is preferably a block copolymer of a styrene structure as a hard segment and an α-olefin structure and a diolefin (diene) structure as a soft segment. The diolefin (diene) structure may be hydrogenated or not, and is preferably a hydrogenated diolefin (diene) structure. From the viewpoint of heat resistance, the styrene-based elastomer (B1) is preferably a block copolymer of a styrene structure as a hard segment and a hydrogenated polydiene structure as a soft segment.

[0036] Examples of the styrene elastomer (B1) include styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene block copolymer (SEP), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-butadiene-styrene block copolymer (SBS), styrene-butadiene-styrene-butadiene block copolymer (SBSB), styrene-butadiene-butylene-styrene block copolymer (SBBS), etc. The styrene elastomer (B1) preferably contains at least one selected from the group consisting of styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene block copolymer (SEP), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS). From the viewpoints of heat resistance, electromagnetic wave absorption, and moldability, the thermoplastic resin composition more preferably contains at least one selected from the group consisting of styrene-ethylene-butadiene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), and further preferably contains at least one selected from the group consisting of styrene-ethylene-butylene-styrene block copolymer (SEBS) and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

[0037] Commercially available styrene-based elastomers (B1) include, for example, Septon 4077, Septon 4055, Septon 8006, Septon 4044, and Septon 2005 manufactured by Kuraray Co., Ltd.; Tuftec H1221, Tuftec H1041, and Tuftec H1051 manufactured by Asahi Kasei Chemicals Corporation; and Kraton G1643M, Kraton G1645M, and Kraton G1652H manufactured by Kraton Polymers.

[0038] The content of the styrene-based elastomer (B1) is 15 to 35% by mass, based on the mass of the thermoplastic resin composition. A content of 15% by mass or more is preferred in terms of flexibility. The content is preferably 16% by mass or more, more preferably 18% by mass or more, and even more preferably 20% by mass or more. A content of 35% by mass or less is preferred in terms of heat resistance and electromagnetic wave absorption. The content is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 23% by mass or less. When the thermoplastic resin composition contains the styrene-based elastomer (B1), heat resistance is improved. The content may be, for example, 16 to 30% by mass, 18 to 25% by mass, or 20 to 23% by mass.

[0039] (Olefin-based elastomer (B2)) The olefin-based elastomer (B2) has a tensile elongation at break of 800% or more, measured in accordance with ISO 37. A tensile elongation at break of 800% or more is preferred in terms of flexibility and electromagnetic wave absorption. The tensile elongation at break is preferably 1,000% or more. There is no particular upper limit to the tensile elongation at break, but it may be 1,500% or less. The tensile elongation at break may be 800 to 1,500%, or 1,000 to 1,500%.

[0040] The olefin elastomer (B2) is preferably an uncrosslinked or partially crosslinked elastomer, more preferably an uncrosslinked elastomer, and may be, for example, an olefin homopolymer or an olefin copolymer. The olefin copolymer is, for example, a copolymer of at least two types of α-olefins, and may be a copolymer of ethylene and an α-olefin, or may be a copolymer of ethylene and at least one α-olefin having 3 or more carbon atoms. The olefin elastomer (B2) may be a copolymer of an olefin and maleic acid, a copolymer of an olefin and a (meth)acrylic acid ester, or the like.

[0041] Examples of α-olefins include ethylene, propylene, 1-butene, 2-methyl-1-propene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 1-heptene, methyl-1-hexene, and dimethyl 1-pentene, ethyl-1-pentene, trimethyl-1-butene, methylethyl-1-butene, 1-octene, methyl-1-pentene, ethyl-1-hexene, dimethyl-1-hexene, propyl-1-heptene, methylethyl-1-heptene, trimethyl-1-pentene, propyl-1-pentene, diethyl-1-butene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, and the like.

[0042] The α-olefin preferably contains 1-butene, which is readily available commercially and has excellent flexibility.

[0043] The melt mass flow rate (MFR) of the olefinic elastomer (B2) is, for example, 0.1 to 50 g / 10 min. The MFR is preferably 3 g / 10 min or more, more preferably 5 g / 10 min or more, and may even be 20 g / 10 min or more. An MFR of 3 g / 10 min or more is particularly preferred in terms of electromagnetic wave absorption. The MFR is also preferably 20 g / 10 min or less, more preferably 10 g / 10 min or less. An MFR of 20 g / 10 min or less is particularly preferred in terms of moldability and heat resistance. The MFR may be, for example, 3 to 20 g / 10 min or 5 to 10 g / 10 min.

[0044] Examples of the olefin elastomer (B2) include ethylene-propylene copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-octene-1 copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylate copolymer, propylene-ethylene-1-butene copolymer, ethylene-1-butene copolymer, polybutene, polyisobutylene, and maleic acid modified versions thereof. As the olefin elastomer (B2), propylene-ethylene-1-butene copolymer is preferred because it is easily available.

[0045] Commercially available olefin elastomers (B2) include, for example, Tafmer PN-3560, MH-5010, PN-20300, MA9015, and XM-7090 manufactured by Mitsui Chemicals; and ENGAGE 8130, ENGAGE 8200, and ENGAGE 8400 manufactured by Dow Chemical.

[0046] The content of the olefin elastomer (B2) is 15 to 35% by mass, based on the mass of the thermoplastic resin composition. A content of 15% by mass or more is preferred in terms of flexibility. The content is preferably 16% by mass or more, more preferably 18% by mass or more, and even more preferably 20% by mass or more. A content of 35% by mass or less is preferred in terms of heat resistance and electromagnetic wave absorption. The content is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 23% by mass or less. The content may be, for example, 16 to 30% by mass, 18 to 25% by mass, or 20 to 23% by mass.

[0047] The styrene-based elastomer (B1) and the olefin-based elastomer (B2) can be used in combination. When they are used in combination, in terms of flexibility and heat resistance, the amount of the olefin-based elastomer (B2) is preferably less than 100% by mass, and more preferably 50% by mass or less, relative to 100% by mass of the styrene-based elastomer (B1).

[0048] The content of elastomer (B) is 15 to 35% by mass, based on the mass of the thermoplastic resin composition. A content of 15% by mass or more is preferable in terms of flexibility. The content is preferably 16% by mass or more, more preferably 18% by mass or more, and even more preferably 20% by mass or more. A content of 35% by mass or less is preferable in terms of heat resistance and electromagnetic wave absorption. The content is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 23% by mass or less. When the elastomer (B) contains a styrene-based elastomer (B1) and an olefin-based elastomer (B2), the "content of elastomer (B)" refers to the total content of both. When only one of the elastomers is contained, the "content of elastomer (B)" refers to the content of the single elastomer. The content may be, for example, 16 to 30% by mass, 18 to 25% by mass, or 20 to 23% by mass.

[0049] [Carbon nanotubes (C)] The carbon nanotubes (C) may be single-walled carbon nanotubes, multi-walled carbon nanotubes wound with two or more layers, or a mixture of these, but multi-walled carbon nanotubes are preferred from the standpoints of cost and strength. Furthermore, carbon nanotubes whose sidewalls have an amorphous structure instead of a graphite structure may also be used.

[0050] Carbon nanotubes (C) can generally be produced by laser ablation, arc discharge, chemical vapor deposition (CVD), combustion, etc., but any method may be used. In particular, the CVD method is a method that can inexpensively and mass-produce carbon nanotubes by contacting catalyst fine particles, which are formed by supporting a metal catalyst such as iron or nickel on a carrier such as silica, alumina, magnesium oxide, titanium oxide, silicate, diatomaceous earth, alumina silica, silica titania, or zeolite, with a carbon-containing gas as a raw material at a high temperature of typically 400 to 1000° C., and is also preferred as the carbon nanotubes used in the embodiments of the present invention.

[0051] The carbon nanotubes (C) preferably have an average diameter of 1 to 30 nm, more preferably 2 to 25 nm, and even more preferably 5 to 20 nm, as determined by scanning electron microscopy. This range ensures high dispersibility of the carbon nanotubes in the thermoplastic resin composition, and excellent electromagnetic wave absorption performance of the molded article.

[0052] The average diameter of carbon nanotubes is determined using a scanning electron microscope (e.g., JSM-6700M manufactured by JEOL Ltd.) by observing carbon nanotubes at an accelerating voltage of 5 kV, taking a 50,000-magnification image (1024 × 1280 pixels), measuring the minor axis length of any 20 carbon nanotubes in the image, and calculating the number average of the minor axis lengths as the average diameter of the carbon nanotubes.

[0053] Examples of commercially available carbon nanotubes include CM-130 and CM-250 manufactured by Hanhwa Chemical Hanos; SNW210 manufactured by SouthWest NanoTechnologies; Flotube 7000 and Flotube 3100 manufactured by CNano; and Graphistrength C100 manufactured by Arkema.

[0054] The content of carbon nanotubes (C) is 0.5 to 5% by mass based on the mass of the thermoplastic resin composition. A content of 0.5% by mass or more is preferable in terms of electromagnetic wave absorption (particularly transmission loss) because electromagnetic waves are transmitted smoothly within the molded body, and is also preferable in terms of heat resistance. A content of 5% by mass or less is preferable in terms of electromagnetic wave absorption (particularly reflection loss) because electromagnetic waves are easily captured at the surface of the molded body, and is also preferable in terms of flexibility. The content is preferably 1% by mass or more, more preferably 1.5% by mass or more. The content is preferably 4% by mass or less, more preferably 3% by mass or less. The content may be, for example, 1 to 4% by mass or 1.5 to 3% by mass.

[0055] [Carbon Black (D)] Carbon black (D) can be any of a variety of materials, such as furnace black produced by continuous thermal decomposition of a gaseous or liquid raw material in a reactor, particularly ketjen black made from ethylene heavy oil, channel black produced by burning a raw material gas and quenching it by applying the flame to the bottom surface of a channel steel, thermal black obtained by periodically repeating combustion and thermal decomposition of a gas as the raw material, and acetylene black, particularly acetylene gas as the raw material, which can be used alone or in combination of two or more types. Conventional oxidation-treated carbon black and hollow carbon can also be used.

[0056] The carbon black (D) preferably has an average primary particle diameter of 20 to 60 nm, more preferably 30 to 50 nm, and even more preferably 35 to 45 nm, as determined by scanning electron microscopy. By having this range, the carbon nanotubes (C) incorporated into the molded article after injection molding or extrusion molding can effectively form conductive paths with each other, enabling stable development of high electrical conductivity and electromagnetic wave absorption properties.

[0057] Specifically, the average primary particle diameter of carbon black is determined using, for example, a scanning electron microscope (JSM-6700M, manufactured by JEOL Ltd.) The conditions are as follows: the carbon black is observed at an acceleration voltage of 5 kV, an image is taken at 50,000 magnification (1024 × 1280 pixels), and then the particle diameter of each of 20 random carbon black particles in the taken image is measured, and the number average value thereof is calculated as the average primary particle diameter of the carbon black.

[0058] Examples of commercially available carbon black include furnace blacks manufactured by Shin-Nichika Carbon Co., Ltd., such as Niteron #10, #200, and #300; furnace blacks manufactured by Tokai Carbon Co., Ltd., such as Toka Black #4300, #4400, #4500, and #5500; furnace blacks manufactured by Degussa Corporation, such as Printex L; Raven 7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, Conductex SC ULTRA, 975ULTRA, and PUER. Furnace blacks manufactured by Columbian, such as BLACK 100, 115, and 205; furnace blacks manufactured by Mitsubishi Chemical, such as #30B, #45, #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, and #5400B; furnace blacks manufactured by Cabot, such as MONARCH 1400, 1300, 900, Vulcan XC-72R, and BlackPearls 2000; Ensaco 250G , Ensacco 260G, Ensacco 350G, and Super P-Li, and other furnace blacks manufactured by Imerys; Ketjenblack EC-300J and EC-600JD, and other Ketjenblacks manufactured by Akzo Chemical Industry; acetylene blacks such as Denka Black HS-100 and FX-35, and other Ketjenblacks manufactured by Denki Kagaku Kogyo Co., Ltd.; and Ketjenblacks such as Carbon ECP and Carbon ECP600JD, and other Ketjenblacks manufactured by Lion Specialty Chemicals, but are not limited to these.

[0059] The content of carbon black (D) is 3 to 15% by mass based on the mass of the thermoplastic resin composition. A content of 3% by mass or more is preferable in terms of electromagnetic wave absorption (particularly transmission loss) because electromagnetic waves are transmitted smoothly within the molded article, and is also preferable in terms of heat resistance. A content of 15% by mass or less is preferable in terms of electromagnetic wave absorption (particularly reflection loss) because electromagnetic waves are easily captured at the surface of the molded article, and is also preferable in terms of flexibility. The content is preferably 5% by mass or more, more preferably 7% by mass or more. The content is preferably 12% by mass or less, more preferably 10% by mass or less. The content may be, for example, 5 to 12% by mass or 7 to 12% by mass.

[0060] Furthermore, the content ratio of carbon nanotubes (C) to carbon black (D) is preferably carbon nanotubes (C) / carbon black (D) = 1 / 2 to 1 / 7, and more preferably 1 / 3 to 1 / 5. By being within this range, it becomes possible to achieve both low reflection loss and low transmission loss in electromagnetic wave absorption.

[0061] [Other Optional Components] The thermoplastic resin composition may contain other optional components, such as polymers other than the olefin-based elastomer (A) and the elastomer (B), electromagnetic wave absorbing materials, weather stabilizers, antistatic agents, dyes, pigments, coupling agents, crystal nucleating agents, and resin fillers, as needed.

[0062] The thermoplastic resin composition preferably does not contain any volatile components. The content of volatile components such as solvents and low-molecular-weight components in 100% by mass of the thermoplastic resin composition is preferably 5% by mass or less, more preferably 1% by mass or less.

[0063] [Method for Producing Thermoplastic Resin Composition] The method for producing the thermoplastic resin composition is not particularly limited. For example, the olefin-based elastomer (A), the elastomer (B), the carbon nanotubes (C), the carbon black (D), and optionally additives are mixed in a Henschel mixer, tumbler, disperser, or the like, and then mixed or melt-kneaded in a batch mixer such as a kneader, roll mill, super mixer, Henschel mixer, Schuggie mixer, vertical granulator, high-speed mixer, Farmatrix, ball mill, steel mill, sand mill, vibration mill, attritor, or Banbury mixer, a twin-screw extruder, a single-screw extruder, or a rotor-type twin-screw kneader, to obtain a resin composition in the form of pellets, powder, granules, beads, or the like. It is preferable to use a twin-screw extruder for melt-kneading.

[0064] <Molded Article> According to an embodiment of the present invention, a molded article is formed using the thermoplastic resin composition of the above embodiment and is used as an electromagnetic wave absorber. The molded article can be obtained by melting the thermoplastic resin composition in a molding machine, forming the shape of the molded article, and cooling it. The temperature of the molding machine is not critical as long as it is a temperature at which the olefin-based elastomer (A) and the elastomer (B) soften, but is preferably a temperature 30°C or more higher than the softening points of both. It is preferable that the molded article can be in the shape of a plate, rod, fiber, tube, pipe, bottle, film, or the like.

[0065] Examples of molding methods that can be used include extrusion molding, injection molding, blow molding, compression molding, transfer molding, film molding such as T-die molding and inflation molding, calendar molding, and spinning.

[0066] Electromagnetic wave absorbers convert the energy of incident electromagnetic waves into thermal energy and absorb them. Unlike electromagnetic wave shielding materials, electromagnetic wave absorbers are intended to absorb electromagnetic waves within the molded body without reflecting them on the surface of the molded body. Electromagnetic wave absorbers are used in the automotive field, such as electronic toll collection systems (ETC) on highways and on-board radar, full-body scanners that see under clothing as security checks at airports, millimeter-wave radar devices used for transmitting images from surveillance cameras on platforms during one-man train operation, and for preventing false radar images on ship masts. In particular, molded articles formed from the thermoplastic resin composition according to an embodiment of the present invention have excellent electromagnetic wave absorption performance in the millimeter-wave band of 60 to 90 GHz, making them suitable for use in millimeter-wave radar devices.

[0067] <Examples of Embodiments> The present invention includes, for example, the following embodiments. The embodiments of the present invention are not limited to the following examples. (1) A thermoplastic resin composition for an electromagnetic wave absorber, comprising: 50 to 80 mass% of an olefin-based elastomer (A) having a tensile elongation at break of 400 to 700% measured in accordance with ISO 37:2017, 15 to 35 mass% of an elastomer (B) containing at least one selected from the group consisting of a styrene-based elastomer (B1) and an olefin-based elastomer (B2) having a tensile elongation at break of 800% or more measured in accordance with ISO 37:2017, 0.5 to 5 mass% of carbon nanotubes (C), and 3 to 15 mass% of carbon black (D). (2) The thermoplastic resin composition for an electromagnetic wave absorber according to (1) above, wherein the elastomer (B) comprises the styrene-based elastomer (B1), and the styrene-based elastomer (B1) comprises at least one selected from the group consisting of styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene block copolymer (SEP), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS). (3) The thermoplastic resin composition for an electromagnetic wave absorber according to (1) or (2) above, wherein the elastomer (B) comprises the styrene-based elastomer (B1), and the content of the styrene structure in the styrene-based elastomer (B1) is 15 to 35 mass%. (4) The thermoplastic resin composition for an electromagnetic wave absorber according to any one of (1) to (3) above, wherein the elastomer (B) comprises the olefin-based elastomer (B2), and the olefin-based elastomer (B2) comprises an ethylene-α-olefin copolymer. (5) A molded article molded using the thermoplastic resin composition for an electromagnetic wave absorber according to any one of (1) to (4) above.

[0068] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-116232, filed on July 14, 2023, the entire disclosure of which is incorporated herein by reference.

[0069] The present invention will be described in more detail below with reference to examples, but the following examples do not limit the present invention in any way. In the examples, "parts" means "parts by mass" and "%" means "% by mass." The blending amounts in the tables are in % by mass, and blank spaces in the tables indicate that no blending is performed.

[0070] The tensile elongation at break and MFR of the olefin-based elastomer (A) and the olefin-based elastomer (B2), the solution viscosity and weight-average molecular weight of the styrene-based elastomer (B1), the average diameter of the carbon nanotubes (C), and the average primary particle diameter of the carbon black (D) were measured by the following methods.

[0071] (Tensile elongation at break of olefin-based elastomer (A) and olefin-based elastomer (B2)) The tensile elongation at break was measured in accordance with ISO 37. Specifically, the measurement was carried out on test pieces (dumbbell-shaped No. 3 test pieces prepared in accordance with JIS K 6251:2017) prepared using the elastomers using a material testing machine "3367" manufactured by Instron Corporation under conditions of an atmosphere at a temperature of 23°C and a pulling speed of 500 mm / min.

[0072] (MFR (Melt Mass Flow Rate) of Olefin-Based Elastomer (A) and Olefin-Based Elastomer (B2)) The MFR was measured in accordance with JIS K 7210: 1999. Specifically, the measurement was carried out using a "Melt Indexer" manufactured by Toyo Seiki Seisakusho, Ltd., under conditions of a temperature of 230°C and a load of 2.16 kgf.

[0073] (Solution Viscosity of Styrene-Based Elastomer (B1)) The solution viscosity was measured using a solution obtained by dissolving the styrene-based elastomer (B1) in a toluene solvent to a concentration of 5% by mass, in an atmosphere at a temperature of 30°C, using a "B-type viscometer VISCOMETER TVB-10" manufactured by Toki Sangyo Co., Ltd.

[0074] (Weight-average molecular weight of styrene-based elastomer (B1)) The weight-average molecular weight was measured using LC Solution (manufactured by Shimadzu Corporation). THF was used as an eluent to adjust the concentration to 2 mg / mL, and 10 μL of the measurement sample solution was injected into the apparatus. The column oven temperature was 40°C, the THF flow rate was 1 mL / min, and a differential refractometer RID-10A (manufactured by Shimadzu Corporation) was used as the detector. Two TSKgel G4000Hxl columns in series (manufactured by Tosoh Corporation) and a TSKguard column Hxl-L (manufactured by Tosoh Corporation) were used as the guard column.

[0075] (Average Diameter of Carbon Nanotubes (C)) Carbon nanotubes were observed using a scanning electron microscope (JSM-6700M, manufactured by JEOL Ltd.) at an acceleration voltage of 5 kV, and an image was taken at 50,000 magnification (1024 × 1280 pixels). Next, the minor axis length of each of 20 random carbon nanotubes in the taken image was measured, and the number average value of these minor axis lengths was taken as the average diameter of the carbon nanotubes.

[0076] (Average Primary Particle Diameter of Carbon Black (D)) Carbon black was observed using a scanning electron microscope (JSM-6700M, manufactured by JEOL Ltd.) at an accelerating voltage of 5 kV, and an image was taken at 50,000 magnification (1024 × 1280 pixels). Next, the particle diameter of each of 20 randomly selected carbon black particles in the taken image was measured, and the number average value was taken as the average primary particle diameter of the carbon black.

[0077] The materials used in the examples and comparative examples are as follows: (Olefin-based elastomer (A))

[0078] (Styrene-based elastomer (B1))

[0079] (Olefin-based elastomer (B2))

[0080] (Carbon nanotubes (C))

[0081] (Carbon Black (D))

[0082] <Production of Thermoplastic Resin Composition> [Example 1] An olefin-based elastomer (A-1), a styrene-based elastomer (B1-1), carbon nanotubes (C-1), and carbon black (D-1) were mixed to obtain the blending amounts (mass %) shown in Table 5, melt-kneaded, extruded at 230°C using a twin-screw extruder (manufactured by The Japan Steel Works, Ltd.), and granulated to obtain a thermoplastic resin composition.

[0083] Examples 2 to 22 and Comparative Examples 1 to 8 Thermoplastic resin compositions were obtained in the same manner as in Example 1, except that the materials and blending amounts (mass %) were changed to those shown in Tables 5 to 7, respectively.

[0084] <Evaluation of Thermoplastic Resin Composition> The obtained thermoplastic resin composition was evaluated by the following methods. The results are shown in Tables 5 to 7.

[0085] [Preparation of Molded Article] The thermoplastic resin composition was injection molded using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) with a cylinder temperature set at 220°C and a mold temperature of 40°C to prepare a molded article measuring 90 mm in length (injection direction), 110 mm in width (direction perpendicular to the injection direction), and 3 mm in thickness.

[0086] [Electromagnetic wave absorption performance] Figure 1 shows a conceptual diagram of measurement of transmission attenuation TL (MD) and return attenuation RL (MD) when electromagnetic waves are incident in the thickness direction of a molded article, with the irradiation direction (x), electric field direction (y), and magnetic field direction (z) of the electromagnetic waves. As shown in Figures 1 and 2, after the obtained molded article was left to stand for one day, the return attenuation RL (MD) and transmission attenuation TL (MD) were measured in a state where the electric field direction of the electromagnetic waves (y direction in the figure) was parallel to the injection direction (MD direction).

[0087] (Return Loss RL) As an index of electromagnetic wave absorption performance, the return loss (dB) in the millimeter wave frequency band was measured by the following method. A VNA (Vector Network Analyzer) was used as a measuring instrument, an APC-7 (manufactured by Kanto Electronics Application Development Co., Ltd.) was used as a measuring jig, and an E-band antenna (WR-12) was used as an antenna. Measurements were carried out by the free space method. Specifically, the return loss was measured for the molded articles obtained in the examples and comparative examples under an environment of a temperature of 24.8°C and a relative humidity of 48%, with the injection direction (MD direction) at a measurement frequency of 76.5 GHz parallel to the electric field direction of the electromagnetic waves (y direction in FIG. 1 ).

[0088] (Transmission Loss TL) As an index of electromagnetic wave absorption performance, the transmission loss (dB) in the millimeter wave frequency band was measured by the following method. A VNA (Vector Network Analyzer) was used as a measuring instrument, an APC-7 (manufactured by Kanto Electronics Application Development Co., Ltd.) was used as a measuring jig, and an E-band antenna (WR-12) was used as an antenna, and the measurement was performed by the free space method. Specifically, the transmission loss was measured for the molded articles obtained in the examples and comparative examples under an environment of a temperature of 24.8°C and a relative humidity of 48%, with the injection direction (MD direction) at a measurement frequency of 76.5 GHz and the electric field direction of the electromagnetic waves (y direction in FIG. 1 ) being parallel to each other.

[0089] The electromagnetic wave absorption performance was evaluated according to the following criteria: ◯ (good): reflection loss of -5 dB or less and transmission loss of -15 dB or less △ (suitable for practical use): reflection loss of -4 dB or less and transmission loss of -10 dB or less × (not suitable for practical use): reflection loss greater than -4 dB or transmission loss greater than -10 dB

[0090] [Flexibility] As an index of flexibility, Shore D hardness was measured using a durometer (D type) manufactured by Kobunshi Keiki Co., Ltd. in accordance with ISO 7619-1:2010. An indenter was brought into contact with a test piece consisting of two stacked 3 mm thick molded articles obtained by the above method, and the Shore D hardness (after 5 seconds) was measured by reading the scale after 5 seconds. (Evaluation criteria) ◯ (Good): Shore D hardness (after 5 seconds) is less than 40 △ (Suitable for practical use): Shore D hardness (after 5 seconds) is 40 or more but less than 50 × (Not suitable for practical use): Shore D hardness (after 5 seconds) is 50 or more

[0091] [Heat Resistance] As an index of heat resistance, the deflection temperature under load was measured in accordance with ISO 178:2019 using a heat destation tester manufactured by Yasuda Seiki. The thermoplastic resin composition was injection molded using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) with a cylinder setting temperature of 220°C and a mold temperature of 40°C, and a multipurpose test piece (thickness 4 mm) was prepared according to ISO 10724-1:1998. The deflection temperature under load was measured using the multipurpose test piece under a load of 0.45 MPa. (Evaluation Criteria) ◯ (Good): Deflection temperature under load of 50°C or more △ (Suitable for practical use): Deflection temperature under load of 40°C or more, but less than 50°C × (Not suitable for practical use): Deflection temperature under load of less than 40°C

[0092]

[0093]

[0094]

[0095] The above evaluation results confirmed that the thermoplastic resin composition of the present invention and a molded article made therefrom have good electromagnetic wave absorption properties and flexibility, and also have excellent heat resistance. In particular, they have excellent reflection loss and transmission loss in the specific frequency band of 60 to 90 GHz known as millimeter waves, and therefore can be suitably used as a molded article for a millimeter wave absorber.

Claims

1. A thermoplastic resin composition for electromagnetic wave absorbers, comprising: 50 to 80 mass% of an olefin-based elastomer (A) having a tensile elongation at break of 400 to 700% as measured in accordance with ISO 37:2017; 15 to 35 mass% of an elastomer (B) including at least one selected from the group consisting of a styrene-based elastomer (B1) and an olefin-based elastomer (B2) having a tensile elongation at break of 800% or more as measured in accordance with ISO 37:2017; 0.5 to 5 mass% of carbon nanotubes (C); and 3 to 15 mass% of carbon black (D).

2. The thermoplastic resin composition for electromagnetic wave absorber according to claim 1, wherein the elastomer (B) comprises the styrene-based elastomer (B1), and the styrene-based elastomer (B1) comprises at least one selected from the group consisting of styrene-ethylene-butylene-styrene block copolymers, styrene-ethylene-propylene block copolymers, styrene-ethylene-propylene-styrene block copolymers, and styrene-ethylene-ethylene-propylene-styrene block copolymers.

3. A thermoplastic resin composition for an electromagnetic wave absorber according to claim 1 or 2, wherein the elastomer (B) comprises the styrene-based elastomer (B1), and the content of the styrene structure in the styrene-based elastomer (B1) is 15 to 35 mass %.

4. A thermoplastic resin composition for an electromagnetic wave absorber according to any one of claims 1 to 3, wherein the elastomer (B) comprises the olefin-based elastomer (B2), and the olefin-based elastomer (B2) comprises an ethylene-α-olefin copolymer.

5. A molded article obtained by molding the thermoplastic resin composition for electromagnetic wave absorbers according to any one of claims 1 to 4.

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