Thermoplastic resin composition for electromagnetic wave absorber and molded article

Abstract

One embodiment of the present invention relates to a thermoplastic resin composition for an electromagnetic wave absorber, said composition comprising a thermoplastic resin (A), carbon nanotubes (B) having an average diameter of 1-15 nm, and carbon black (C) having an average primary particle size of 20-50 nm, wherein one of (i)-(iv) is satisfied, and ΔRL expressed by formula (1) is 3 dB or less and ΔTL expressed by formula (2) is 5 dB or less.

Description

[Technical Field]

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

[0002] Plastics are easy to mold and process, and are used in a wide range of fields, including electrical and electronic equipment parts, automotive parts, medical parts, and food containers. Coloring of plastic molded products is widely used to enhance their decorative appeal and to impart functionality. In particular, in the automotive field, colored molded products are in circulation 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 application of electromagnetic wave absorbers installed far from the electromagnetic wave source is the use of electronic toll collection (ETC) systems on expressways. ETC is a system that uses microwaves at a frequency of 5.8 GHz between a roadside unit antenna installed at the toll booth and an onboard unit antenna to exchange toll information when a vehicle passes through a toll booth exit. At toll booths where ETC systems have been introduced, microwaves emitted from the antenna can be reflected by the toll booth roof or other surfaces, causing unwanted electromagnetic waves to leak from adjacent ETC lanes, resulting in communication problems. Therefore, electromagnetic wave absorbers are installed on the toll booth roof or between the ETC lanes to suppress communication problems.

[0005] In recent years, millimeter-wave radar has been used in the automotive field for the purposes of autonomous driving and collision prevention, and in many cases, millimeter-wave radar devices are 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 as part of security checks at airports, and video transmission from surveillance cameras on platforms during one-man train operations. Millimeter-wave radar devices emit 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 for automobiles and other vehicles. In the case of automobile 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 make up such electromagnetic wave absorbers include carbon-based, metal-carbon-based, and magnetic-based materials, and in recent years, carbon nanotubes (CNTs) have been attracting attention as a carbon-based material due to their high conductivity and relatively light weight. Resin compositions containing carbon nanotubes have high electrical conductivity and are therefore used in parts that require electrical conductivity in the fields of automobiles, home appliances, and building materials (Patent Document 1), as well as in electromagnetic wave absorbers that take advantage of their electromagnetic wave properties (Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-108524 [Patent Document 2] Special Publication No. 2017-512847 [Patent Document 3] Special Publication No. 2016-504471 Summary of the Invention [Problem to be solved by the invention]

[0009] However, molded articles using these conventional resin compositions do not have sufficient electromagnetic wave absorption performance in terms of electromagnetic wave reflection loss and transmission loss to adequately protect the radar from the surrounding environment and not interfere with radar signal transmission.

[0010] In addition, carbon nanotubes are difficult to disperse because they are a material with a relatively high aspect ratio, and if they are not dispersed sufficiently, bumps or welds (a phenomenon in which a wavy pattern appears) may appear on the surface of the molded product, damaging the appearance. Furthermore, there is also the problem of angle dependency, in which carbon nanotubes tend to be oriented in a specific direction during molding, and the electromagnetic wave absorption performance of the molded product varies depending on the angle of incidence of the electromagnetic wave.

[0011] As described above, it is difficult to achieve both high conductivity and dispersion stability of carbon nanotubes. Therefore, the object of the present invention is to provide a thermoplastic resin composition for electromagnetic wave absorbers that has excellent dispersibility, and a molded article that exhibits excellent radio wave absorption performance with low reflection loss and transmission loss, and further has little angular dependence of radio wave absorption performance. In particular, the object is to provide a molded article for a millimeter wave absorber that is excellent in reflection loss and transmission loss in the specific frequency band of 60 to 90 GHz known as millimeter waves. [Means for solving the problem]

[0012] 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.

[0013] That is, the present invention includes the following embodiments. One embodiment comprises a thermoplastic resin (A), carbon nanotubes (B) having an average diameter of 1 to 15 nm, and carbon black (C) having an average primary particle diameter of 20 to 50 nm, Satisfy any of the following (i) to (iv): ΔRL represented by the following formula (1) is 3 dB or less, and ΔTL represented by the following formula (2) is 5 dB or less, The present invention relates to a thermoplastic resin composition for an electromagnetic wave absorber. (i): The thermoplastic resin (A) contains a polyolefin resin (A1) having an MFR of 5.0 to 50 g / 10 min at a temperature of 230° C. and a load of 2.16 kgf. (ii): The thermoplastic resin (A) contains a polyamide resin (A2) having an MFR of 5.0 to 50 g / 10 min at a temperature of 240° C. and a load of 2.16 kgf. (iii): The thermoplastic resin (A) contains a polyester resin (A3) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. and a load of 1.2 kgf. (iv): The thermoplastic resin (A) contains a polycarbonate resin (A4) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. under a load of 1.2 kgf. Equation (1) ΔRL = |RL(MD) - RL(TD)| Equation (2) ΔTL = |TL(MD)-TL(TD)| (Note that RL(MD) and RL(TD) are the values ​​measured when an electromagnetic wave with a frequency of 76.5 GHz is incident on a molded body of 90 mm in length, 110 mm in width and 3 mm in thickness, which is molded from a thermoplastic resin composition for an electromagnetic wave absorber using an injection molding machine, after leaving it for one day, with the electric field direction of the electromagnetic wave being parallel to the injection direction (MD direction) or perpendicular to the injection direction (TD direction) in the thickness direction of the molded body.) reflection is the amount of attenuation. TL(MD) and TL(TD) are the values ​​measured when an electromagnetic wave with a frequency of 76.5 GHz is incident on a molded body of 90 mm in length, 110 mm in width and 3 mm in thickness, which is molded from a thermoplastic resin composition for an electromagnetic wave absorber using an injection molding machine, after leaving it for one day, with the electric field direction of the electromagnetic wave being parallel to the injection direction (MD direction) or perpendicular to the injection direction (TD direction). transparent is the amount of attenuation. The vertical direction of the molded body is the injection direction.) Another embodiment relates to a molded article formed from the thermoplastic resin composition for an electromagnetic wave absorber. [Effects of the Invention]

[0014] The thermoplastic resin composition for an electromagnetic wave absorber of the present invention has excellent dispersibility, and the electromagnetic wave absorber obtained therefrom exhibits excellent radio wave absorbing performance with low reflection loss and transmission loss, and further has small angle dependency of the radio wave absorbing performance. In particular, since it has excellent reflection loss and transmission loss in the specific frequency band of 60 to 90 GHz called millimeter waves, it can also be suitably used as a molded article for millimeter wave absorbers. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a conceptual diagram showing how transmission loss and return loss are measured using a millimeter wave transmitter. [Figure 2] FIG. 2 is a conceptual diagram of measuring the incidence angle dependency using a millimeter wave transmitter. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be 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 limit values ​​of the range. Carbon nanotubes are sometimes referred to as CNTs, and examples thereof include "carbon nanotubes (B) having an average diameter of 1 to 15 nm," "carbon black (C) having an average primary particle diameter of 20 to 50 nm," "polyolefin resin (A1) having an MFR of 5.0 to 50 g / 10 min at a temperature of 230°C and a load of 2.16 kgf," "polyamide resin (A2) having an MFR of 5.0 to 50 g / 10 min at a temperature of 240°C and a load of 2.16 kgf," and "polyamide resin (A3) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280°C and a load of 1.2 kgf." The "polyester resin (A3) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280°C and a load of 1.2 kgf," the "polycarbonate resin (A4) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280°C and a load of 1.2 kgf," and the "thermoplastic resin composition for an electromagnetic wave absorber" may be referred to as "carbon nanotubes (B)," "carbon black (C)," "polyolefin resin (A1)," "polyamide resin (A2)," "polyester resin (A3)," "polycarbonate resin (A4)," and the "thermoplastic resin composition," respectively. Unless otherwise noted, the various components appearing in this specification may be used independently either alone or in combination of two or more. The numerical values ​​specified in this specification are values ​​determined by the methods disclosed in the embodiments or examples.

[0017] The MFR in the embodiment of the present invention is a value obtained by measuring each thermoplastic resin as a melt mass flow rate value in accordance with JIS K7210.

[0018] <<Thermoplastic resin composition for electromagnetic wave absorber>> According to an embodiment of the present invention, the thermoplastic resin composition is used to form an electromagnetic wave absorber. The thermoplastic resin composition contains a thermoplastic resin (A), carbon nanotubes (B) having an average diameter of 1 to 15 nm, and carbon black (C) having an average primary particle diameter of 20 to 50 nm, and satisfies any one of the following (i) to (iv): (i): The thermoplastic resin (A) contains a polyolefin resin (A1) having an MFR of 5.0 to 50 g / 10 min at a temperature of 230° C. and a load of 2.16 kgf. (ii): The thermoplastic resin (A) contains a polyamide resin (A2) having an MFR of 5.0 to 50 g / 10 min at a temperature of 240° C. and a load of 2.16 kgf. (iii): The thermoplastic resin (A) contains a polyester resin (A3) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. and a load of 1.2 kgf. (iv): The thermoplastic resin (A) contains a polycarbonate resin (A4) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. under a load of 1.2 kgf.

[0019] In this way, by using carbon nanotubes with a small average diameter and carbon black with a small average primary particle diameter within a specific range, and combining these with a thermoplastic resin (A) that satisfies any one of (i) to (iv), it is possible to control the orientation of the carbon nanotubes in the molded product, resulting in excellent carbon nanotube stability in the thermoplastic resin composition and suppressing orientation when the molded product is formed.

[0020] Moreover, ΔRL expressed by the following formula (1) is 3 dB or less, and ΔTL expressed by the following formula (2) is 5 dB or less. Equation (1) ΔRL = |RL(MD) - RL(TD)| Equation (2) ΔTL = |TL(MD)-TL(TD)| (Note that RL(MD) and RL(TD) are the values ​​measured when an electromagnetic wave with a frequency of 76.5 GHz is incident on a molded body of 90 mm in length, 110 mm in width and 3 mm in thickness, which is molded from a thermoplastic resin composition for an electromagnetic wave absorber using an injection molding machine, after leaving it for one day, with the electric field direction of the electromagnetic wave being parallel to the injection direction (MD direction) or perpendicular to the injection direction (TD direction) in the thickness direction of the molded body.) reflection is the amount of attenuation. TL(MD) and TL(TD) are the values ​​measured when an electromagnetic wave with a frequency of 76.5 GHz is incident on a molded body of 90 mm in length, 110 mm in width and 3 mm in thickness, which is molded from a thermoplastic resin composition for an electromagnetic wave absorber using an injection molding machine, after leaving it for one day, with the electric field direction of the electromagnetic wave being parallel to the injection direction (MD direction) or perpendicular to the injection direction (TD direction). transparent is the amount of attenuation. The vertical direction of the molded body is the injection direction.)

[0021] The injection direction here refers to the direction in which the thermoplastic resin composition flows from the gate of the molding machine into the mold. That is, a molded body having a length of 90 mm, a width of 110 mm and a thickness of 3 mm is a molded body having a length of 90 mm in the injection direction, a length of 110 mm in the direction perpendicular to the injection direction and a thickness of 3 mm.

[0022] Furthermore, from the viewpoint of dispersibility and incidence angle dependency, the total content of the carbon nanotubes (B) and carbon black (C) is preferably 6 to 18 mass%, more preferably 6 to 15 mass%, and even more preferably 8 to 13 mass%, based on the thermoplastic resin composition (100 mass%).

[0023] In an embodiment of the present invention, it is important not only to ensure that ΔRL represented by formula (1) is 3 dB or less and ΔTL represented by formula (2) is 5 dB or less, but also to use a combination of carbon nanotubes (B) having a small average diameter and carbon black (C) having a relatively small average primary particle diameter within a specific particle size range, and a thermoplastic resin (A) that satisfies any of (i), (ii), (iii), or (iv). In addition, by further reducing the blending amounts of each component as much as possible and setting them within a specific range, it becomes possible to control the orientation of the carbon nanotubes and carbon black, and to exhibit sufficient radio wave absorption not only when electromagnetic waves are incident in a direction parallel to the injection direction of the molded body, but also when electromagnetic waves are incident in a direction perpendicular to the injection direction, thereby further suppressing the angle dependence of the electromagnetic wave absorber.

[0024] <Thermoplastic resin (A)> The thermoplastic resin (A) is a resin that can be molded by heating and melting, and the thermoplastic resin composition according to an embodiment of the present invention satisfies any one of the following (i) to (iii). (i): The thermoplastic resin (A) contains a polyolefin resin (A1) having an MFR of 5.0 to 50 g / 10 min at a temperature of 230° C. and a load of 2.16 kgf. (ii): The thermoplastic resin (A) contains a polyamide resin (A2) having an MFR of 5.0 to 50 g / 10 min at a temperature of 240° C. and a load of 2.16 kgf. (iii): The thermoplastic resin (A) contains a polyester resin (A3) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. and a load of 1.2 kgf. (iv): The thermoplastic resin (A) contains a polycarbonate resin (A4) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. under a load of 1.2 kgf.

[0025] The polyolefin resin (A1), the polyamide resin (A2), the polyester resin (A3), or the polycarbonate resin (A4) has high fluidity when melted. By selecting such a thermoplastic resin and using it in combination with the carbon black (C) and the carbon nanotubes (B), it is possible to suppress the orientation of the carbon nanotubes when a molded article is formed, and a thermoplastic resin composition having the effect of having small angle dependence of radio wave absorption can be obtained. On the other hand, when the fluidity during melting becomes higher than a certain level, a skin layer with a relatively low concentration of carbon nanotubes (B) and a core layer with a relatively high concentration of carbon nanotubes (B) are generated on the surface and inside of the molded body, resulting in a concentration gradient. Therefore, by selecting and using the above-mentioned thermoplastic resin, a molded body with a uniform carbon nanotube concentration can be obtained, and the angle dependency of radio wave absorption can be reduced.

[0026] In each of the embodiments (i), (ii), (iii) or (iv), it is preferable that the polyolefin resin (A1), the polyamide resin (A2), the polyester resin (A3) or the polycarbonate resin (A4) based on the thermoplastic resin (A) is used alone, and it is preferable that at least one of the polyolefin resin (A1), the polyamide resin (A2), the polyester resin (A3) and the polycarbonate resin (A4) is the main component. The main component refers to the component that is contained in the highest proportion among the thermoplastic resins that constitute the thermoplastic resin (A). Specifically, in each embodiment, the content of the polyolefin resin (A1), the polyamide resin (A2), the polyester resin (A3), or the polycarbonate resin (A4) is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass, based on the thermoplastic resin (A).

[0027] [Polyolefin resin (A1)] The polyolefin resin (A1) is a polyolefin resin having an MFR of 5.0 to 50 g / 10 min at a temperature of 230° C. and a load of 2.16 kgf. The polyolefin resin (A1) is a polymer composed of an olefin (monomer). Specific examples include polyethylene resins (PE) such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE), polypropylene resins (PP), ethylene-α-olefin copolymers, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, and ethylene-ethyl acrylate copolymers, as well as cyclic olefin resins such as cycloolefin polymers and cycloolefin copolymers. Low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and polypropylene resins (PP) are preferred from the viewpoints of versatility and fluidity. These polyolefin resins may also be oxidized polyolefins, in which polyolefins are partially oxidized. The polyolefin resins (A1) can be used alone or in combination.

[0028] The polyolefin resin (A1) according to the embodiment of the present invention has an MFR of 5.0 to 50 g / 10 min, preferably 15 to 40 g / 10 min, and particularly preferably 25 to 35 g / 10 min, at a temperature of 230° C. and a load of 2.16 kgf. A MFR within the above range is preferred in terms of incidence angle dependency.

[0029] [Polyamide resin (A2)] The polyamide resin (A2) is a polyamide resin having an MFR of 5.0 to 50 g / 10 min at a temperature of 240° C. and a load of 2.16 kgf. The polyamide resin (A2) is a polycondensate having an amide bond, and specific examples thereof include nylon 4,6, nylon 6, nylon 6,6, nylon 6,10, nylon 6,12, nylon 12, nylon 6,T, nylon 9,T, and aromatic nylon resins. From the viewpoints of versatility and fluidity, nylon 6 and nylon 6,6 are preferred. The polyamide resin (A2) can be used alone or in combination of two or more types.

[0030] Furthermore, the polyamide resin (A2) according to an embodiment of the present invention has an MFR of 5.0 to 50 g / 10 min, preferably 15 to 40 g / 10 min, and particularly preferably 25 to 35 g / 10 min, at a temperature of 240° C. and a load of 2.16 kgf. A MFR within the above range is preferred in terms of incidence angle dependency.

[0031] [Polyester resin (A3)] The polyester resin (A3) is a polyester resin having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. and a load of 1.2 kgf. The polyester resin (A3) is a polycondensate having an ester bond, and specific examples thereof include polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene naphthalate resin, and amorphous copolyester resin. In terms of versatility and fluidity, polyethylene terephthalate resin or polybutylene terephthalate resin is preferred. The polyester resin (A3) can be used alone or in combination of two or more types.

[0032] Furthermore, the polyester resin (A3) according to an embodiment of the present invention has an MFR of 5.0 to 50 g / 10 min, preferably 15 to 40 g / 10 min, and particularly preferably 25 to 35 g / 10 min, at a temperature of 280° C. and a load of 1.2 kgf. A MFR within the above range is preferred in terms of incidence angle dependency.

[0033] [Polycarbonate resin (A4)] The polycarbonate resin (A4) is a polycarbonate resin having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. and a load of 1.2 kgf. The polycarbonate resin (A4) is a polycondensate in which the bond between the monomer units is a carbonate group. Specifically, a resin that can be easily produced by reacting an aromatic dihydroxy compound with a carbonate precursor such as phosgene or a carbonate diester can be used. For example, the resin can be produced by an interfacial method when phosgene is used as the carbonate precursor, or by a transesterification method in which the two are reacted in a molten state when a carbonate diester is used.

[0034] Furthermore, the polycarbonate resin (A4) according to an embodiment of the present invention has an MFR of 5.0 to 50 g / 10 min, preferably 15 to 40 g / 10 min, and particularly preferably 25 to 35 g / 10 min, at a temperature of 280° C. and a load of 1.2 kgf. A MFR within the above range is preferred in terms of incidence angle dependency.

[0035] From the viewpoint of electromagnetic wave absorption performance, the content of the thermoplastic resin (A) is preferably 82% by mass or more, more preferably 84% by mass or more, and even more preferably 85% by mass or more, based on the thermoplastic resin composition (100% by mass). It is also preferably 94% by mass or less, more preferably 92% by mass or less, and even more preferably 90% by mass or less. The content of the thermoplastic resin (A) may be, for example, 82 to 94% by mass, 84 to 92% by mass, or 85 to 90% by mass.

[0036] <Carbon nanotubes (B)> The carbon nanotubes (B) have an average diameter of 1 to 15 nm as determined by a scanning electron microscope, preferably within the range of 1 to 10 nm. This range ensures high dispersibility of the carbon nanotubes in the thermoplastic resin composition, and excellent electromagnetic wave absorption performance of the molded article.

[0037] Specifically, the average diameter of carbon nanotubes is determined using, for example, a scanning electron microscope (e.g., JSM-6700M manufactured by JEOL Ltd.) Conditions are as follows: carbon nanotubes are observed at an accelerating voltage of 5 kV, and an image (1024 × 1280 pixels) is taken at 50,000 magnification. Next, the minor axis length of each of 20 random carbon nanotubes in the image is measured, and the number average of these minor axis lengths is calculated as the average diameter of the carbon nanotubes.

[0038] The carbon nanotubes (B) may be single-walled carbon nanotubes, multi-walled carbon nanotubes 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 rather than a graphite structure may also be used.

[0039] Carbon nanotubes (B) can generally be produced by laser ablation, arc discharge, chemical vapor deposition (CVD), combustion, etc., but any method may be used. In particular, CVD 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 support 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 usually 400 to 1000°C, and is also preferred as the carbon nanotubes used in the embodiment of the present invention.

[0040] From the viewpoint of radio wave absorption performance, the content of the carbon nanotubes (B) is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the thermoplastic resin composition (100% by mass). Also, it is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. The content of the carbon nanotubes (B) may be, for example, 0.1 to 5% by mass, 0.5 to 5% by mass, 1 to 3% by mass, or 1 to 2% by mass.

[0041] <Carbon black (C)> The carbon black (C) has an average primary particle diameter of 20 to 50 nm as determined by a scanning electron microscope, preferably 25 nm or more. It is also preferably 40 nm or less, and more preferably 35 nm or less. By using carbon black (C) having an average primary particle diameter within this range, the carbon nanotubes (B) incorporated into the molded product after injection molding or extrusion molding can effectively form conductive paths with each other, enabling stable development of high conductivity and electromagnetic wave absorption performance.

[0042] Specifically, the average primary particle diameter of carbon black is determined using, for example, a scanning electron microscope (e.g., JSM-6700M manufactured by JEOL Ltd.) The carbon black is observed at an accelerating voltage of 5 kV, and an image is taken at 50,000 magnification (1024 × 1280 pixels). Next, the particle diameter of each of 20 random carbon black particles in the image is measured, and the number average value is calculated as the average primary particle diameter of the carbon black.

[0043] When a thermoplastic resin composition containing only carbon nanotubes as a conductive material is injection-molded to produce a molded article, it is difficult to achieve high conductivity, even if the carbon nanotubes are sufficiently dispersed in the composition. The reason for this is thought to be that the resin content becomes high, resulting in the formation of a layer with a low carbon nanotube concentration (a so-called "skin layer") on the surface of the molded article. In other words, when a thermoplastic resin composition contains both a high resin content and a low carbon nanotube concentration and a low resin content and a high carbon nanotube concentration, the viscosity of each layer when melted (melt viscosity) differs. For example, during extrusion molding, the portion with a high resin content (low viscosity and high fluidity) is extruded first, resulting in the surface of the molded article being covered with a skin layer, which is thought to reduce the conductivity of the molded article.

[0044] On the other hand, carbon black generally has a lower specific surface area and oil absorption than carbon nanotubes, so a thermoplastic resin composition containing carbon black is less likely to have a high melt viscosity and form a skin layer on the surface of a molded article than a thermoplastic resin composition containing only carbon nanotubes. Furthermore, because carbon black has good affinity with carbon nanotubes, even if carbon nanotubes are incorporated into the molded article, a conductive path can be formed between the carbon black present on the surface of the molded article, and the molded article according to an embodiment of the present invention can exhibit high conductivity.

[0045] That is, according to an embodiment of the present invention, in a thermoplastic resin composition, by using a combination of carbon nanotubes (B) having a small average diameter and carbon black (C) having a relatively small average primary particle diameter within a specific range, it is possible to control the orientation of the carbon nanotubes and carbon black in the molded body, and to exhibit sufficient radio wave absorption properties not only when electromagnetic waves are incident in a direction parallel to the injection direction of the molded body, but also when electromagnetic waves are incident in a perpendicular direction.

[0046] Carbon black (C) can be any of a variety of materials, such as furnace black, which is produced by continuously pyrolyzing a gaseous or liquid raw material in a reactor, particularly ketjen black, which is made from ethylene heavy oil, channel black, which is produced by burning a raw material gas and then quenching it by applying the flame to the bottom surface of a channel steel to precipitate it, thermal black, which is obtained by periodically repeating combustion and pyrolysis of a gas as the raw material, and acetylene black, which is made from acetylene gas as the raw material, either alone or in combination. Conventional oxidation-treated carbon black and hollow carbon can also be used.

[0047] Examples of commercially available carbon black include furnace blacks manufactured by Nippon Steel Carbon Co., Ltd., such as Nitelon #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, 975 ULTRA, and PUER. Furnace blacks manufactured by Colombian such as BLACK100, 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 MONARCH1400, 1300, 900, VulcanXC-72R, and BlackPearls2000; Examples of suitable blacks include furnace black manufactured by Chabot Corporation; furnace blacks manufactured by Imerys such as Ensaco 250G, Ensaco 260G, Ensaco 350G, and Super P-Li; ketjen blacks manufactured by Akzo Chemical Industries such as Ketjen Black EC-300J and EC-600JD; and acetylene blacks manufactured by Denki Kagaku Kogyo Co., Ltd. such as Denka Black HS-100 and FX-35, but are not limited to these.

[0048] From the viewpoint of radio wave absorption performance, the content of carbon black (C) is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, based on the thermoplastic resin composition (100% by mass). It is also preferably 16% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less. The content of carbon black (C) may be, for example, 3 to 16% by mass, 5 to 15% by mass, or 7 to 12% by mass.

[0049] Furthermore, the content ratio of carbon nanotubes (B) to carbon black (C) (mass (%) / mass (%)) is preferably within the range of carbon nanotubes (B) / carbon black (C) = 1 / 2.5 to 1 / 20, more preferably within the range of 1 / 5 to 1 / 15.

[0050] <Other optional ingredients> The thermoplastic resin composition may contain other optional components such as electromagnetic wave absorbing materials, weather stabilizers, antistatic agents, dyes, pigments, coupling agents, crystal nucleating agents, and resin fillers, as required.

[0051] The thermoplastic resin composition preferably does not contain any volatile components. In 100% by mass of the thermoplastic resin composition, the amount of volatile components such as solvents and low-molecular-weight components is preferably 5% by mass or less, and more preferably 1% by mass or less.

[0052] The electromagnetic wave absorbing material may contain carbon nanotubes and carbon black other than the carbon nanotubes (B) and carbon black (C) as long as the effects of the present invention are not impaired. From the viewpoint of electromagnetic wave absorption performance, however, the greater the amount of carbon nanotubes (B) and carbon black (C) in 100% by mass of the electromagnetic wave absorbing material, the more preferable, more preferably 50 to 100% by mass, even more preferably 70 to 100% by mass, and particularly preferably 90 to 100% by mass. The content of the electromagnetic wave absorbing material other than the carbon nanotubes (B) and carbon black (C) is preferably 10% by mass or less, and more preferably 5% by mass or less, based on 100% by mass of the electromagnetic wave absorbing material.

[0053] If the carbon nanotubes are poorly dispersed, a high amount of carbon nanotubes is required to achieve practical electromagnetic wave absorption performance. Although high addition improves transmission loss, it also reflects electromagnetic waves, resulting in a decrease in electromagnetic wave absorption performance. Furthermore, when attempting to achieve electromagnetic wave absorption performance using carbon black, which has poorer electrical conductivity than carbon nanotubes, it is necessary to add a higher amount of carbon black than carbon nanotubes. When the concentration of these electromagnetic wave absorbing materials in the resin composition becomes high, the fluidity of the resin composition decreases, and poor distribution may prevent uniform electromagnetic wave absorption performance in the molded product.

[0054] However, in an embodiment of the present invention, the thermoplastic resin composition uses a combination of carbon nanotubes (B) having an average diameter of 1 to 15 nm and carbon black (C) having an average primary particle diameter of 20 to 50 nm, and further has a specific relationship between reflection loss and transmission loss, so that the molded body can achieve high electromagnetic wave absorption performance and suppressed angle dependency without adding a large amount of electromagnetic wave absorbing material.

[0055] <Method of producing thermoplastic resin composition> The method for producing the thermoplastic resin composition according to an embodiment of the present invention is not particularly limited. For example, thermoplastic resin (A), carbon nanotubes (B), carbon black (C), and, if necessary, additives, etc., are mixed in a Henschel mixer, tumbler, disper, etc., 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. In an embodiment of the present invention, it is preferable to use a twin-screw extruder for melt-kneading.

[0056] In an embodiment of the present invention, the thermoplastic resin composition may be a masterbatch containing carbon nanotubes (B) and carbon black (C) at a relatively high concentration and diluted with thermoplastic resin (A) before molding, or may be a compound containing carbon nanotubes (B) and carbon black (C) at a relatively low concentration and used for molding as is without diluting with thermoplastic resin (A). From the viewpoints of additive costs, inventory costs, etc., a masterbatch that can be made into a high concentration is preferred. The masterbatch is preferably in the form of pellets, which are easy to handle.

[0057] <<Molded body>> The molded article is formed from the thermoplastic resin composition according to an embodiment of the present invention and is used as an electromagnetic wave absorber. The molded article can be obtained by melt-mixing a compound or masterbatch, which is a thermoplastic resin composition, and a diluted resin in a molding machine usually set at 50° C. to 350° C., forming the shape of the molded article, and cooling it. The temperature of the molding machine does not matter as long as it is a temperature at which the thermoplastic resin (A) softens, but it should be at least 30° C. higher than the softening point of the thermoplastic resin that is the main component. The molded product can preferably be in the form of a plate, rod, fiber, tube, pipe, bottle, film, or the like.

[0058] 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. According to an embodiment of the present invention, the thermoplastic resin composition is capable of highly controlling the orientation of the carbon nanotubes (B), and therefore can exhibit excellent effects in terms of high electromagnetic wave absorption performance and suppression of angle dependency even in injection-molded or extrusion-molded articles in which orientation is likely to occur.

[0059] From the viewpoint of radio wave absorption performance, the content of carbon nanotubes (B) in the molded article is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the thermoplastic resin composition (100% by mass). Also, it is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. The content of carbon nanotubes (B) may be, for example, 0.1 to 5% by mass, 0.5 to 5% by mass, 1 to 3% by mass, or 1 to 2% by mass. From the viewpoint of radio wave absorption performance, the content of carbon black (C) in the molded article is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, based on the thermoplastic resin composition (100% by mass). It is also preferably 16% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less. The content of carbon black (C) may be, for example, 3 to 16% by mass, 5 to 15% by mass, or 7 to 12% by mass.

[0060] Electromagnetic wave absorbers convert the energy of incident electromagnetic waves into thermal energy and absorb it. Unlike electromagnetic wave shielding materials, the purpose of electromagnetic wave absorbers is to absorb radio waves within the molded body without reflecting them on the surface. Electromagnetic wave absorbers are used in expressway electronic toll collection systems (ETC), in-vehicle radar, full-body scanners that see under clothing as part of security checks at airports, etc., millimeter-wave radar devices used to transmit images from surveillance cameras on platforms when trains are operated by a single driver, and to prevent false radar images from ship masts. In particular, the molded article formed from the thermoplastic resin composition according to the embodiment of the present invention has excellent electromagnetic wave absorption performance in the millimeter wave band of 60 to 90 GHz, and can therefore be suitably used in millimeter wave radar devices.

[0061] Examples of embodiments of the present invention are given below: The present invention is not limited to the following. [1] A thermoplastic resin (A), carbon nanotubes (B) having an average diameter of 1 to 15 nm, and carbon black (C) having an average primary particle diameter of 20 to 50 nm, Satisfy any of the following (i) to (iv): ΔRL represented by the following formula (1) is 3 dB or less, and ΔTL represented by the following formula (2) is 5 dB or less, Thermoplastic resin composition for electromagnetic wave absorber. (i): The thermoplastic resin (A) contains a polyolefin resin (A1) having an MFR of 5.0 to 50 g / 10 min at a temperature of 230° C. and a load of 2.16 kgf. (ii): The thermoplastic resin (A) contains a polyamide resin (A2) having an MFR of 5.0 to 50 g / 10 min at a temperature of 240° C. and a load of 2.16 kgf. (iii): The thermoplastic resin (A) contains a polyester resin (A3) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. and a load of 1.2 kgf. (iv): The thermoplastic resin (A) contains a polycarbonate resin (A4) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. under a load of 1.2 kgf. Equation (1) ΔRL = |RL(MD) - RL(TD)| Equation (2) ΔTL = |TL(MD)-TL(TD)| (Note that RL(MD) and RL(TD) are the values ​​measured when an electromagnetic wave with a frequency of 76.5 GHz is incident on a molded body of 90 mm in length, 110 mm in width and 3 mm in thickness, which is molded from a thermoplastic resin composition for an electromagnetic wave absorber using an injection molding machine, after leaving it for one day, with the electric field direction of the electromagnetic wave being parallel to the injection direction (MD direction) or perpendicular to the injection direction (TD direction) in the thickness direction of the molded body.) reflection is the amount of attenuation. TL(MD) and TL(TD) are the values ​​measured when an electromagnetic wave with a frequency of 76.5 GHz is incident on a molded body of 90 mm in length, 110 mm in width and 3 mm in thickness, which is molded from a thermoplastic resin composition for an electromagnetic wave absorber using an injection molding machine, after leaving it for one day, with the electric field direction of the electromagnetic wave being parallel to the injection direction (MD direction) or perpendicular to the injection direction (TD direction). transparent is the amount of attenuation. The vertical direction of the molded body is the injection direction.) [2] The thermoplastic resin composition for an electromagnetic wave absorber according to [1], wherein the total content of the carbon nanotubes (B) and the carbon black (C) is 6 to 18 mass% based on the thermoplastic resin composition for an electromagnetic wave absorber. For example, the total content of the carbon nanotubes (B) and the carbon black (C) may be 6 to 15 mass%. [3] The thermoplastic resin composition for an electromagnetic wave absorber according to [1] or [2], wherein the content of the thermoplastic resin (A) is 82 to 94 mass% based on the thermoplastic resin composition for an electromagnetic wave absorber. For example, the content of the thermoplastic resin (A) may be 85 to 90 mass%. [4] The thermoplastic resin composition for an electromagnetic wave absorber according to any one of [1] to [3], wherein the content of the thermoplastic resin (A) is 82 to 94 mass%, the content of the carbon nanotubes (B) is 1 to 3 mass%, and the content of the carbon black (C) is 5 to 15 mass%, based on the thermoplastic resin composition for an electromagnetic wave absorber. For example, the content of the thermoplastic resin (A) may be 85 to 90 mass%, the content of the carbon nanotubes (B) may be 1 to 3 mass%, and the content of the carbon black (C) may be 5 to 12 mass%. [5] A molded article formed from the thermoplastic resin composition for an electromagnetic wave absorber according to any one of [1] to [4].

[0062] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2022-124303, filed on August 3, 2022, the entire disclosure of which is incorporated herein by reference. [Example]

[0063] 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 mass %, and blank spaces in the tables indicate that no blending was performed.

[0064] The average diameter of the carbon nanotubes, the average primary particle diameter of the carbon black, and the MFR of the thermoplastic resin (A) were measured by the following methods.

[0065] <Average diameter of carbon nanotubes> Carbon nanotubes were observed using a scanning electron microscope (JEOL, JSM-6700M) at an accelerating voltage of 5 kV, and images were taken at 50,000 magnifications (1024 × 1280 pixels). Next, the minor axis length of each of 20 randomly selected carbon nanotubes in the image was measured, and the number-average value of these minor axis lengths was used as the average diameter of the carbon nanotubes.

[0066] <Average primary particle size of carbon black> Carbon black was observed using a scanning electron microscope (JEOL, JSM-6700M) at an accelerating voltage of 5 kV, and an image was taken at 50,000 magnification (pixel count: 1024 × 1280). Next, the particle size of each of 20 randomly selected carbon black particles in the image was measured, and the number average value was taken as the average primary particle size of the carbon black.

[0067] <MFR (Melt Mass Flow Rate) of Thermoplastic Resin (A)> The MFR of the thermoplastic resin (A) was measured using a melt indexer manufactured by Toyo Seiki Seisakusho in accordance with JIS K7210. Measurements were performed under the following conditions: temperature 230°C, load 2.16 kgf for polyolefin resin, temperature 240°C, load 2.16 kgf for polyamide resin, temperature 280°C, load 1.2 kgf for polyester resin, and temperature 280°C, load 1.2 kgf for polycarbonate resin.

[0068] The materials used in the examples are as follows: <Thermoplastic resin (A)> (A1-1) Prime Polypro J107G (Polypropylene resin manufactured by Prime Polymer Co., Ltd.) (A1-2) Prime Polypro J106G (Polypropylene resin manufactured by Prime Polymer Co., Ltd.) (A1-3) SunAllomer PM802A (polypropylene resin manufactured by SunAllomer Co., Ltd.) (A2-4) Amilan CM1017 (Toray Nylon 6) (A3-5) Duranex 700FP (Polyplastics polybutylene terephthalate resin) (A4-6) Iupilon H3000 (polycarbonate resin manufactured by Mitsubishi Engineering Plastics Corporation) (A5-7) SunAllomer PMB60A (polypropylene resin manufactured by SunAllomer) (A5-8) SunAllomer PM472W (polypropylene resin manufactured by SunAllomer) (A5-9) Crystalline polyamide resin (MFR 0.1g / 10min or less at 240℃ x 1.2kgf, MFR 60g / 10min at 300℃ x 10kgf) Table 1 shows the MFR of the thermoplastic resin (A) under various conditions.

[0069] [Table 1]

[0070] <Carbon nanotubes (B), etc.> (B-1) Flotube 7000 (CNano, average diameter 6.0 nm) (B-2) SMW210 (SouthWest NanoTechnologies, average diameter 9.0 nm) (B-3) CM-130 (Hanhwa Chemical Hanos, average diameter 15.0 nm) (B'-1) NTP3121 (NTP, average diameter 30.0 nm) <Carbon black (C), etc.> (C-1) Mitsubishi Carbon #30B (manufactured by Mitsubishi Chemical Corporation, average primary particle diameter 30 nm) (C-2) Nitelon #10 (furnace black manufactured by Nippon Steel Carbon Co., Ltd., average primary particle diameter 39 nm) (C-3) Ensaco 250G (Imerys furnace black, average primary particle size 45 nm) (C'-1) Mitsubishi Carbon #3030B (manufactured by Mitsubishi Chemical Corporation, average primary particle diameter 55 nm) (C'-2) Mitsubishi Carbon #900B (manufactured by Mitsubishi Chemical Corporation, average primary particle size 16 nm)

[0071] (Production of Thermoplastic Resin Composition) Example 1 Thermoplastic resin (A1-1) 89% by mass, carbon nanotubes (B-1) 1% by mass, and carbon black (C-1) 10% by mass were mixed and 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.

[0072] (Examples 2 to 14) 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 2 and 3, respectively.

[0073] Example 15 The thermoplastic resin (A2-4) was 89% by mass, the carbon nanotubes (B-1) were 1% by mass, and the carbon black (C-1) were 10% by mass. The mixture was melt-kneaded, extruded at 280°C using a twin-screw extruder (manufactured by The Japan Steel Works, Ltd.), and granulated to obtain a thermoplastic resin composition.

[0074] Example 16 The thermoplastic resin (A3-5) was 89% by mass, the carbon nanotubes (B-1) were 1% by mass, and the carbon black (C-1) was 10% by mass. The mixture was melt-kneaded, extruded at 260°C using a twin-screw extruder (manufactured by The Japan Steel Works, Ltd.), and granulated to obtain a thermoplastic resin composition.

[0075] Example 17 The thermoplastic resin (A4-6) was 89% by mass, the carbon nanotubes (B-1) were 1% by mass, and the carbon black (C-1) was 10% by mass. The mixture was melt-kneaded, extruded at 280°C using a twin-screw extruder (manufactured by The Japan Steel Works, Ltd.), and granulated to obtain a thermoplastic resin composition.

[0076] (Comparative Example 1) The thermoplastic resin (A5-7) was 89% by mass, the carbon nanotubes (B-1) were 1% by mass, and the carbon black (C-1) was 10% by mass. The mixture was melt-kneaded, extruded at 230°C using a single-screw extruder (manufactured by The Japan Steel Works, Ltd.), and granulated to obtain a thermoplastic resin composition.

[0077] (Comparative Example 2, Comparative Examples 4 to 1 3 ) A thermoplastic resin composition was obtained in the same manner as in Comparative Example 1, except that the materials and blending amounts (mass %) were changed to those shown in Tables 3 and 4, respectively.

[0078] (Comparative Example 3) The thermoplastic resin (A5-9) was 89% by mass, the carbon nanotubes (B-1) were 1% by mass, and the carbon black (C-1) was 10% by mass. The mixture was melt-kneaded, extruded at 280°C using a single-screw extruder (manufactured by The Japan Steel Works, Ltd.), and granulated to obtain a thermoplastic resin composition.

[0079] <Physical properties and evaluation of thermoplastic resin composition> The physical properties and evaluation results of the obtained thermoplastic resin composition were determined by the following methods. The results are shown in Tables 2 to 4.

[0080] <Measurement of transmission loss and return loss> The thermoplastic resin compositions obtained in Examples 1 to 14 and Comparative Examples 1 to 13 were injection molded using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) with a cylinder set temperature of 220°C and a mold temperature of 40°C to produce molded bodies measuring 90 mm in length (injection direction), 110 mm in width (direction perpendicular to the injection direction), and 3 mm in thickness.

[0081] The thermoplastic resin compositions obtained in Examples 15 and 17 were injection molded using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) with a cylinder temperature set at 280°C and a mold temperature of 80°C to produce molded bodies measuring 90 mm in length (injection direction), 110 mm in width (direction perpendicular to the injection direction), and 3 mm in thickness.

[0082] The thermoplastic resin composition obtained in Example 16 was injection molded using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) with a cylinder temperature set at 260°C and a mold temperature of 40°C, to produce a molded body 90 mm long (injection direction), 110 mm wide (direction perpendicular to the injection direction), and 3 mm thick. The vertical direction of the molded body is the injection direction.

[0083] Using the obtained molded body, the return loss RL (TD) and transmission loss TL (TD) were measured in the direction parallel to the injection direction of the molded body (MD direction) and the direction perpendicular to the injection direction of the electromagnetic wave (TD direction) by the following method. Figure 1 shows the electromagnetic wave irradiation direction (x), electric field direction (y), and magnetic field direction (z) when an electromagnetic wave is incident in the thickness direction of a molded body, i.e., when the plane of the molded body is placed in the direction of electromagnetic wave injection. 1. is the transmission attenuation TL (MD), 2. is the return loss RL (MD), and 3. is the transmission attenuation TL (TD), 4. is a conceptual diagram of measurement of return loss RL(TD). As shown in Figure 1, 1 and 2, the obtained molded body was left standing for one day, and then the return loss RL (MD) and transmission loss TL (MD) were measured in a state where the electric field direction of the electromagnetic wave (y direction in the figure) was parallel to the injection direction (MD direction). Furthermore, as shown in 3 and 4 of Figure 1, after the obtained molded body was left to stand for one day, the return loss RL (TD) and transmission loss TL (TD) were measured in a state where the electric field direction of the electromagnetic wave (y direction in the figure) was perpendicular to the injection direction (TD direction). The millimeter-wave transmitter was E8257D+E8257DS12 (output: 4 dBm), the millimeter-wave receiver was N9030A+M1970V, and the horn antenna was AAHR015 (WR15, AET, INC) (all manufactured by Keysight Technologies). The return loss and transmission loss of the obtained molded body at a measurement frequency of 76.5 GHz were measured in an environment of a temperature of 24.8°C and a relative humidity of 48%. Based on the obtained return loss RL(MD), RL(TD) and transmission loss TL(MD), TL(TD), the incidence angle dependency ΔRL of the return loss and the incidence angle dependency ΔTL of the transmission loss were calculated using the following formulas (1) and (2). Equation (1) ΔRL = |RL(MD) - RL(TD)| Equation (2) ΔTL = |TL(MD)-TL(TD)|

[0084] <Dispersibility> The obtained thermoplastic resin composition for electromagnetic wave absorber was extrusion molded using a T-die molding machine (manufactured by Toyo Seiki) with a cylinder set temperature of 220°C and a mold temperature of 40°C to produce a T-die film with a width of 10 cm, a length of 5 m, and a thickness of 100 μm. The obtained T-die film was observed with an optical microscope (manufactured by Keyence Corporation), the number of particles having a size of 100 μm or more was counted, and dispersibility was evaluated according to the following criteria. [Evaluation criteria] Good: Less than 30 particles △ (Practical): Number of items: 30 or more, less than 50 × (Not practical): 50 or more items

[0085] <Electromagnetic wave absorption performance> (Reflection loss RL(MD)) As an index of electromagnetic wave absorption performance, the reflection loss (dB) in the millimeter wave frequency band was measured using the following method. Using E8257D+E8257DS12 (output: 4 dBm) as a millimeter-wave transmitter, N9030A+M1970V as a millimeter-wave receiver, and AAHR015 (WR15, AET, INC) as a horn antenna (all manufactured by Keysight Technologies), the reflection loss was measured for the molded bodies obtained in the examples and comparative examples in an environment of a temperature of 24.8°C and a relative humidity of 48% when the emission direction (MD direction) and the electric field direction of the electromagnetic wave (y direction in the figure) were parallel at a measurement frequency of 76.5 GHz. As the electromagnetic wave absorption performance, the return loss RL (MD) was evaluated according to the following criteria. [Evaluation criteria] Good: Return loss is less than -6dB △ (Practical): Return loss is -6dB or more, less than -5dB × (Not practical): Return loss is -5dB or more

[0086] (Transmission loss TL(MD)) As an index of electromagnetic wave absorption performance, the transmission loss (dB) in the millimeter wave frequency band was measured by the following method. Using E8257D+E8257DS12 (output: 4 dBm) as a millimeter-wave transmitter, N9030A+M1970V as a millimeter-wave receiver, and AAHR015 (WR15, AET, INC) as a horn antenna (all manufactured by Keysight Technologies), the transmission loss was measured for the molded bodies obtained in the examples and comparative examples in an environment of a temperature of 24.8°C and a relative humidity of 48% when the emission direction (MD direction) and the electric field direction of the electromagnetic wave (y direction in the figure) were parallel at a measurement frequency of 76.5 GHz. As the electromagnetic wave absorption performance, the transmission loss TL (MD) was evaluated according to the following criteria. [Evaluation criteria] Good: Transmission loss is less than -15dB △ (Practical): Transmission loss is -15dB or more, less than -10dB × (Not practical): Transmission loss is -10dB or more

[0087] <Incidence angle dependence> The angle dependency was evaluated based on the incidence angle dependency by the following method. Using E8257D+E8257DS12 (output: 4 dBm) as a millimeter-wave transmitter, N9030A+M1970V as a millimeter-wave receiver, and AAHR015 (WR15, AET, INC) as a horn antenna (all manufactured by Keysight Technologies), the reflection loss and transmission loss were measured for the molded bodies obtained in the examples and comparative examples in an environment of a temperature of 24.8°C and a relative humidity of 48% when the emission direction (MD direction) and the electric field direction of the electromagnetic wave (y direction in the figure) were parallel at a measurement frequency of 76.5 GHz. In addition, in this measurement, the molded body was placed at an angle of 20° to the direction of irradiation of the electromagnetic wave and the measurement was carried out (Figure 2 is a conceptual diagram showing an example of measuring transmission loss). As the incidence angle dependency, the return loss RL (MD) was evaluated according to the following criteria. [Evaluation criteria] Good: Return loss is less than -5dB △ (Practical): Return loss is -5dB or more, less than -3dB × (Not practical): Return loss is -3dB or more

[0088] Furthermore, as the incidence angle dependency, the transmission loss TL(MD) was evaluated according to the following criteria. [Evaluation criteria] Good: Transmission loss is less than -15dB △ (Practical): Transmission loss is -15dB or more, less than -10dB × (Not practical): Transmission loss is -10dB or more

[0089] [Table 2]

[0090] [Table 3]

[0091] [Table 4]

[0092] In addition, the thermoplastic resin compositions formed by replacing the thermoplastic resin (A1-1) with the thermoplastic resin (A2-4), the thermoplastic resin (A3-5), or the thermoplastic resin (A4-6) in Examples 2 to 12 showed evaluation results similar to those obtained when the thermoplastic resin (A1-1) was used. In other words, the effectiveness of all forms (i) to (iv) was confirmed.

[0093] From the above evaluation results, it was confirmed that the thermoplastic resin composition according to the embodiment of the present invention and the molded article using the same have excellent dispersibility as a resin composition, the molded article exhibits excellent radio wave absorption performance with low reflection loss and low transmission loss, and is able to stably exhibit electromagnetic wave absorption performance even when electromagnetic waves are incident at different angles of incidence, thereby resulting in excellent suppression of angle dependency. In particular, since the molded article has excellent reflection loss and transmission loss in the specific frequency band of 60 to 90 GHz known as millimeter waves, it can be said that the molded article can be suitably used as a millimeter wave absorber.

Claims

1. A thermoplastic resin composition for an electromagnetic wave absorber, comprising: a thermoplastic resin (A); carbon nanotubes (B) having an average diameter of 1 to 15 nm; and carbon black (C) having an average primary particle diameter of 20 to 50 nm, Based on the thermoplastic resin composition for an electromagnetic wave absorber, the content of the thermoplastic resin (A) is 82 to 94 mass%, and the total content of the carbon nanotubes (B) and the carbon black (C) is 6 to 18 mass% (excluding the case where the content of the thermoplastic resin (A) is 85 to 90 mass%, the content of the carbon nanotubes (B) is 0.1 to 5 mass%, and the content of the carbon black (C) is 5 to 12 mass%). Satisfy any of the following (i) to (iv): ΔRL represented by the following formula (1) is 3 dB or less, and ΔTL represented by the following formula (2) is 5 dB or less, Thermoplastic resin composition for electromagnetic wave absorber. (i): The thermoplastic resin (A) contains a polyolefin resin (A1) having an MFR of 5.0 to 50 g / 10 min at a temperature of 230° C. and a load of 2.16 kgf. (ii) The thermoplastic resin (A) contains a polyamide resin (A2) having an MFR of 5.0 to 50 g / 10 min at a temperature of 240° C. and a load of 2.16 kgf. (iii) The thermoplastic resin (A) contains a polyester resin (A3) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. and a load of 1.2 kgf. (iv) The thermoplastic resin (A) contains a polycarbonate resin (A4) having an MFR of 5.0 to 50 g / 10 min at a temperature of 280° C. and a load of 1.2 kgf. Formula (1) ΔRL=|RL(MD)−RL(TD)| Formula (2) ΔTL=|TL(MD)−TL(TD)| (Note that RL (MD) and RL (TD) are the return losses when a molded body having a length of 90 mm, a width of 110 mm and a thickness of 3 mm, which is molded from a thermoplastic resin composition for an electromagnetic wave absorber using an injection molding machine, is left standing for one day, and then an electromagnetic wave having a frequency of 76.5 GHz is incident on the thickness direction of the molded body with the electric field direction of the electromagnetic wave being parallel to the injection direction (MD direction) or perpendicular to the injection direction (TD direction). Furthermore, TL (MD) and TL (TD) are the transmission attenuation amounts measured when an electromagnetic wave having a frequency of 76.5 GHz is incident on a molded body having a length of 90 mm, a width of 110 mm and a thickness of 3 mm, which is molded from a thermoplastic resin composition for an electromagnetic wave absorber using an injection molding machine, after the molded body has been left standing for one day, with the electric field direction of the electromagnetic wave being parallel to the injection direction (MD direction) or perpendicular to the injection direction (TD direction). The vertical direction of the molded body is the injection direction.)

2. 2. The thermoplastic resin composition for an electromagnetic wave absorber according to claim 1, wherein the content of the carbon nanotubes (B) is 1 to 3 mass% and the content of the carbon black (C) is 5 to 15 mass% based on the thermoplastic resin composition for an electromagnetic wave absorber.

3. A molded article formed from the thermoplastic resin composition for electromagnetic wave absorber according to claim 1 or 2.

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