Resin composition, molded article, and electromagnetic wave absorber

Abstract

To provide a resin composition that has a high electromagnetic wave absorption rate, a molded body, and an electromagnetic wave absorber.SOLUTION: A resin composition contains a thermoplastic resin and a conductive substance. When the resin composition is cut into a test piece having a thickness of 2 mm and its cross-section is observed with a digital microscope, the aggregate that is derived from the conductive substance and has a circle equivalent diameter of at least 30 μm has an area ratio of at most 0.80%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a resin composition, a molded article, and an electromagnetic wave absorber. [Background technology]

[0002] Millimeter-wave radar emits radio waves in the millimeter-wave band with wavelengths of 1 to 10 mm and frequencies of 30 to 300 GHz, particularly 60 to 90 GHz. By receiving the reflected waves that collide with an object and return, it detects the presence of obstacles, as well as the distance and relative speed to the object. Millimeter-wave radar is being considered for use in a wide range of fields, including collision avoidance sensors in automobiles, autonomous driving systems, road information systems, security systems, and medical and nursing care devices. A resin composition for such millimeter-wave radar is known, as described in Patent Document 1. Furthermore, Patent Document 2 discloses a multifunctional resin composition that can be used for electromagnetic interference shielding or radio frequency interference shielding. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-197048 [Patent Document 2] Japanese Patent Publication No. 2010-155993 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In millimeter-wave radar, the most significant cause of malfunction is transmitted electromagnetic waves. Therefore, resin compositions with high electromagnetic wave absorption rates are required. The present invention aims to solve these problems and to provide a resin composition, a molded article, and an electromagnetic wave absorber with high electromagnetic wave absorption rates. [Means for solving the problem]

[0005] Based on the above-mentioned problems, the inventors conducted research and found that in a resin composition in which a conductive substance is blended with a thermoplastic resin, the absorption rate of electromagnetic waves can be reduced by reducing the large aggregates derived from the conductive substance. Specifically, the above problem was solved by the following means. <1-1> A resin composition comprising a thermoplastic resin and a conductive substance, wherein when the resin composition is molded into a test piece with a thickness of 2 mm and its cross-section is observed with a digital microscope, the area ratio of aggregates derived from the conductive substance with an equivalent circular diameter of 30 μm or more is 0.80% or less. <1-2> The conductive material is the resin composition described in <1-1>, which contains carbon nanotubes. <1-3> The resin composition according to <1-1> or <1-2>, wherein the thermoplastic resin comprises a polybutylene terephthalate resin. <1-4> The resin composition according to any one of <1-1> to <1-3>, wherein the content of the conductive substance in the resin composition is 0.01 to 10% by mass. <1-5> The resin composition according to <1-1>, wherein the thermoplastic resin comprises a polybutylene terephthalate resin, the conductive substance comprises carbon nanotubes, and the content of the conductive substance in the resin composition is 0.01 to 10% by mass. <1-6> The resin composition according to <1-1>, wherein the thermoplastic resin comprises a polybutylene terephthalate resin and a polystyrene-based resin, and the conductive substance comprises carbon nanotubes. <1-7> The resin composition according to <1-6>, wherein the carbon nanotube content in the resin composition is 0.01 to 10% by mass. <1-8> The resin composition has a sea-island structure having a sea region containing a large amount of the polybutylene terephthalate resin and an island region containing a large amount of the polystyrene resin, wherein 30% by mass or more of the resin components contained in the resin composition is polybutylene terephthalate resin, and the carbon nanotube content in the sea region is greater than the carbon nanotube content in the island region, as described in <1-6> or <1-7>. <1-9> The resin composition according to any one of <1-6> to <1-8>, wherein the polystyrene resin is derived from a carbon nanotube masterbatch. <1-10> The resin composition according to any one of <1-1> to <1-9>, wherein the conductive material contains carbon nanotubes and the relative permittivity of the resin composition at a frequency of 76.5 GHz is 4.50 or higher. <1-11> The resin composition according to <1-10>, wherein the dielectric loss tangent of the resin composition at a frequency of 76.5 GHz is 0.10 or more. <1-12> The resin composition according to <1-10> or <1-11>, wherein the carbon nanotube content in the resin composition is 0.01 to 10% by mass. <1-13> The thermoplastic resin comprises thermoplastic resin (A) and thermoplastic resin (B), The resin composition according to any one of <1-10> to <1-12>, wherein the thermoplastic resin (B) is present in an amount of 1.0 to 100 parts by mass per 100 parts by mass of the thermoplastic resin (A). <1-14> The resin composition according to <1-13>, wherein the thermoplastic resin (A) comprises a polyester resin. <1-15> The resin composition according to <1-14>, wherein the polyester resin comprises a polybutylene terephthalate resin. <1-16> The resin composition according to any one of <1-13> to <1-15>, wherein the thermoplastic resin (B) comprises a polystyrene-based resin. <1-17> The resin composition according to any one of <1-13> to <1-16>, wherein at least a portion of the thermoplastic resin (B) is derived from the masterbatch of carbon nanotubes. <1-18>The resin composition according to <1-17>, wherein the concentration of carbon nanotubes in the masterbatch is 1 to 50% by mass. <1-19>The resin composition according to any one of <1-1> to <1-18>, wherein the absorption rate determined according to formula (A) at a frequency of 76.5 GHz when the resin composition is formed into a thickness of 2 mm is 50.0 to 100%. Formula (A)

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[0006] A resin composition described in any one of <1-29>, <1-10>, to <1-23>, which satisfies the requirements described in any one of <4-1> to <4-12> described later.

[0007] <2-1> A resin composition comprising polybutylene terephthalate resin, polystyrene resin, and carbon nanotubes. <2-2> The resin composition according to <2-1>, wherein the carbon nanotube content in the resin composition is 0.01 to 10% by mass. <2-3> The resin composition has a sea-island structure having a sea region containing a large amount of the polybutylene terephthalate resin and an island region containing a large amount of the polystyrene resin, wherein 30% by mass or more of the resin components contained in the resin composition is polybutylene terephthalate resin, and the carbon nanotube content in the sea region is greater than the carbon nanotube content in the island region, as described in <2-1> or <2-2>. <2-4> The resin composition according to any one of <2-1> to <2-3>, wherein the polystyrene resin is derived from the carbon nanotube masterbatch. <2-5> The resin composition according to any one of <2-1> to <2-4>, wherein when the resin composition is molded to a thickness of 2 mm, the absorption rate determined according to formula (A) at a frequency of 76.5 GHz is 50.0 to 100%. Formula (A)

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[0008] <3-1> A resin composition comprising a thermoplastic resin and carbon nanotubes, wherein the relative permittivity of the resin composition at a frequency of 76.5 GHz is 4.50 or higher. <3-2> The resin composition according to <3-1>, wherein the dielectric loss tangent of the resin composition at a frequency of 76.5 GHz is 0.10 or more. <3-3> The resin composition according to <3-1> or <3-2>, wherein the carbon nanotube content in the resin composition is 0.01 to 10% by mass. <3-4> The resin composition according to any one of <3-1> to <3-3>, wherein the thermoplastic resin comprises thermoplastic resin (A) and thermoplastic resin (B), and the thermoplastic resin (B) is present in an amount of 1.0 to 100 parts by mass per 100 parts by mass of thermoplastic resin (A). <3-5> The resin composition according to <3-4>, wherein the thermoplastic resin (A) comprises a polyester resin. <3-6> The resin composition according to <3-5>, wherein the polyester resin comprises a polybutylene terephthalate resin. <3-7> The resin composition according to any one of <3-4> to <3-6>, wherein the thermoplastic resin (B) comprises a polystyrene-based resin. <3-8> The resin composition according to any one of <3-4> to <3-7>, wherein at least a portion of the thermoplastic resin (B) is derived from the masterbatch of carbon nanotubes. <3-9> The resin composition according to <3-8>, wherein the concentration of carbon nanotubes in the masterbatch is 1 to 50% by mass. <3-10> The resin composition according to any one of <3-1> to <3-9>, wherein when the resin composition is molded to a thickness of 2 mm, the absorption rate determined according to formula (A) at a frequency of 76.5 GHz is 50.0 to 100%. Formula (A)

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[0009] <4-1> A resin composition comprising a thermoplastic resin (A), a thermoplastic resin (B), and carbon nanotubes, wherein at least a portion of the thermoplastic resin (B) is derived from a masterbatch of carbon nanotubes, and the SP value of thermoplastic resin (A) ≥ the SP value of thermoplastic resin (B) (where the SP value is a solubility parameter). <4-2> The resin composition according to <4-1>, wherein the concentration of carbon nanotubes in the masterbatch is 1 to 50% by mass. <4-3> The resin composition according to <4-1> or <4-2>, wherein the thermoplastic resin (A) is selected from polyester resin, polycarbonate resin, and polyamide resin. <4-4> The resin composition according to any one of <4-1> to <4-3>, wherein the thermoplastic resin (B) is selected from polyester resin, polystyrene resin, and polyolefin resin. <4-5> The resin composition according to any one of <4-1> to <4-4>, wherein the difference between the SP value of the thermoplastic resin (A) and the SP value of the thermoplastic resin (B) is 0 to 8.0. <4-6> The resin composition according to any one of <4-1> to <4-4>, wherein the difference between the SP value of the thermoplastic resin (A) and the SP value of the thermoplastic resin (B) is 0.1 to 8.0. <4-7> The resin composition according to any one of <4-1> to <4-6>, wherein the carbon nanotube content in the resin composition is 0.01 to 10% by mass. <4-8> The resin composition according to any one of <4-1> to <4-7>, wherein when the resin composition is molded to a thickness of 2 mm, the absorption rate determined according to formula (A) at a frequency of 76.5 GHz is 50.0 to 100%. Formula (A)

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[0010] The present invention makes it possible to provide a resin composition, a molded article, and an electromagnetic wave absorber with high electromagnetic wave absorption rates. [Brief explanation of the drawing]

[0011] [Figure 1] The electron microscope images of the test specimens observed in the examples are shown. [Modes for carrying out the invention]

[0012] The following describes in detail embodiments for carrying out the present invention (hereinafter simply referred to as "this embodiment"). Note that the following embodiment is illustrative for explaining the present invention, and the present invention is not limited to this embodiment. In this specification, "~" is used to mean that the numbers before and after it are included as the lower and upper limits, respectively. In this specification, all physical properties and characteristic values ​​shall be those at 23°C unless otherwise specified. In this specification, the weight-average molecular weight and number-average molecular weight are polystyrene-equivalent values ​​measured by GPC (gel permeation chromatography). In this specification, the units for reflection loss and transmission loss are "dB" (decibels). If the standards described herein differ in measurement methods, etc., from year to year, unless otherwise specified, the standards as of January 1, 2021 shall apply.

[0013] The resin composition of this embodiment is a resin composition comprising a thermoplastic resin and a conductive substance, characterized in that when the resin composition is molded into a test piece with a thickness of 2 mm and its cross-section is observed with a digital microscope, the area ratio of aggregates derived from the conductive substance with an equivalent circular diameter of 30 μm or more is 0.80% or less. By reducing the proportion of aggregates derived from the conductive substance that are larger than a predetermined size, electromagnetic wave absorption can be significantly improved. Furthermore, electromagnetic wave transmittance and reflectance can be reduced. Moreover, the molded article formed from the resin composition of this embodiment can have excellent mechanical strength.

[0014] One way to reduce the proportion of aggregates derived from conductive materials is to sufficiently disperse the conductive material in the thermoplastic resin. More specifically, this can be achieved by more thoroughly melt-kneading the thermoplastic resin and conductive material together, supplying the conductive material in multiple stages during melt-kneading, incorporating a dispersant into the thermoplastic resin to improve the dispersibility of the conductive material, forming a masterbatch of the conductive material and mixing it with the thermoplastic resin, and utilizing the driving force when the conductive material diffuses from the masterbatch into the thermoplastic resin during melt-kneading to improve dispersibility, or selecting a conductive material with a shape that is easily dispersed. In particular, it is desirable to select two or more of these methods to achieve effective dispersion.

[0015] In this embodiment, the area ratio of aggregates derived from conductive material with an equivalent circular diameter of 30 μm or more is preferably 0.70% or less, more preferably 0.60% or less, even more preferably 0.50% or less, and even more preferably 0.42% or less. The lower limit of the area ratio is ideally 0%, but 0.01% or more is practical, and even 0.10% or more sufficiently satisfies the required performance. The area ratio is measured according to the description in the examples described later.

[0016] <Thermoplastic resin> The resin composition of this embodiment includes a thermoplastic resin. Examples of thermoplastic resins used in this embodiment include polyester resin (thermoplastic polyester resin); polyamide resin; polycarbonate resin; polystyrene resin; polyolefin resin such as polyethylene resin, polypropylene resin, and cyclic cycloolefin resin; polyacetal resin; polyimide resin; polyetherimide resin; polyurethane resin; polyphenylene ether resin; polyphenylene sulfide resin; polysulfone resin; and polymethacrylate resin, with polyester resin (thermoplastic polyester resin), polyamide resin, polycarbonate resin, and polyphenylene ether resin being preferred.

[0017] In this embodiment, the thermoplastic resin (for example, polyester resin (thermoplastic polyester resin), polyamide resin, polycarbonate resin, and polyphenylene ether resin) may be a linear polymer or a branched polymer having a branched structure. In this embodiment, it is preferable that the thermoplastic resin has a small branching structure. For example, the thermoplastic resin used in this embodiment has a degree of branching DB (degree of branching) of preferably less than 10%, more preferably 5% or less, and even more preferably 3% or less. Here, the degree of branching is defined as DB (%) = 100 × (T + Z) / (T + Z + L), where T is the average number of end-bonded monomer units, Z is the average number of monomer units forming branches, and L is the average number of linearly bonded monomer units (within the macromolecule of each substance).

[0018] In this embodiment, the thermoplastic resin preferably contains a polyester resin, and more preferably contains a polybutylene terephthalate resin. Furthermore, in this embodiment, preferably 90% by mass or more, and more preferably 93% by mass or more, of the thermoplastic resin is polyester resin. The thermoplastic resin may also preferably contain a polyester resin (preferably polybutylene terephthalate resin) and a polystyrene resin. In this embodiment, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more of the total thermoplastic resin consists of a polyester resin (preferably polybutylene terephthalate resin) and a polystyrene resin (preferably HIPS, more preferably butadiene rubber-containing polystyrene).

[0019] The details of each thermoplastic resin are described below.

[0020] <<Polyester resin>> As the polyester resin, known thermoplastic polyester resins can be used, with polyethylene terephthalate resin and polybutylene terephthalate resin being preferred, and more preferably containing at least polybutylene terephthalate resin. The polybutylene terephthalate resin used in the resin composition of this embodiment is a polyester resin having a structure in which terephthalic acid units and 1,4-butanediol units are ester-bonded, and includes, in addition to the polybutylene terephthalate resin (homopolymer), a polybutylene terephthalate copolymer containing other copolymer components other than terephthalic acid units and 1,4-butanediol units, or a mixture of the homopolymer and the polybutylene terephthalate copolymer.

[0021] Polybutylene terephthalate resin may contain one or more dicarboxylic acid units other than terephthalic acid. Other specific examples of dicarboxylic acids include aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, biphenyl-2,2'-dicarboxylic acid, biphenyl-3,3'-dicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, bis(4,4'-carboxyphenyl)methane, anthracenedicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and 4,4'-dicyclohexyldicarboxylic acid; and aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, and dimer acid. In this embodiment, the polybutylene terephthalate resin preferably contains terephthalic acid units accounting for 80 mol% or more of the total dicarboxylic acid units, more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 97 mol% or more, and even more preferably 99 mol% or more.

[0022] The diol unit may include one or more other diol units in addition to 1,4-butanediol. Other specific examples of diol units include aliphatic or alicyclic diols with 2 to 20 carbon atoms, and bisphenol derivatives. Specific examples include ethylene glycol, propylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, decamethylene glycol, cyclohexanedimethanol, 4,4'-dicyclohexylhydroxymethane, 4,4'-dicyclohexylhydroxypropane, and ethylene oxide addition diols of bisphenol A. In addition to the bifunctional monomers mentioned above, small amounts of trifunctional monomers such as trimellitic acid, trimesic acid, pyromellitic acid, pentaerythritol, and trimethylolpropane can be used to introduce branched structures, and small amounts of monofunctional compounds such as fatty acids can be used to adjust molecular weight. In this embodiment, the polybutylene terephthalate resin preferably contains 1,4-butanediol units accounting for 80 mol% or more of the total diol units, more preferably 90 mol% or more, even more preferably 95 mol% or more, even more preferably 97 mol% or more, and even more preferably 99 mol% or more.

[0023] As described above, the polybutylene terephthalate resin is preferably a polybutylene terephthalate homopolymer obtained by polycondensation of terephthalic acid and 1,4-butanediol. Alternatively, it may be a polybutylene terephthalate copolymer containing one or more dicarboxylic acids other than terephthalic acid as the carboxylic acid unit and / or one or more diols other than 1,4-butanediol as the diol unit. When the polybutylene terephthalate resin is a polybutylene terephthalate resin modified by copolymerization, specific preferred copolymers include polyester ether resins copolymerized with polyalkylene glycols, particularly polytetramethylene glycol, dimer acid copolymerized polybutylene terephthalate resins, and isophthalic acid copolymerized polybutylene terephthalate resins. Among these, it is preferable to use a polyester ether resin copolymerized with polytetramethylene glycol. These copolymers refer to those with a copolymerization amount of 1 mol% or more and less than 50 mol% of the total segments of the polybutylene terephthalate resin. In particular, the copolymerization amount is preferably 2 mol% or more and less than 50 mol%, more preferably 3 to 40 mol%, and even more preferably 5 to 20 mol%. Such copolymerization ratios tend to improve fluidity, toughness, and tracking resistance, and are therefore preferable.

[0024] The amount of terminal carboxyl groups in polybutylene terephthalate resin can be appropriately selected and determined, but is usually 60 eq / ton or less, preferably 50 eq / ton or less, and more preferably 30 eq / ton or less. Keeping it below the above upper limit tends to improve alkali resistance and hydrolysis resistance. There is no specific lower limit for the amount of terminal carboxyl groups, but considering the productivity of polybutylene terephthalate resin production, it is usually 10 eq / ton or more.

[0025] The amount of terminal carboxyl groups in polybutylene terephthalate resin is measured by dissolving 0.5 g of polybutylene terephthalate resin in 25 mL of benzyl alcohol and titrating it with a 0.01 mol / L benzyl alcohol solution of sodium hydroxide. The amount of terminal carboxyl groups can be adjusted by any conventionally known method, such as adjusting polymerization conditions like the raw material ratio, polymerization temperature, and reduced pressure method during polymerization, or by reacting with a chelating agent.

[0026] The intrinsic viscosity of the polybutylene terephthalate resin is preferably 0.5 dL / g or higher, and more preferably 0.6 dL / g or higher. Setting the intrinsic viscosity to 0.5 dL / g or higher tends to further improve the mechanical strength of the resulting resin composition. The intrinsic viscosity is preferably 2.00 dL / g, more preferably 1.50 dL / g or lower, even more preferably 1.30 dL / g or lower, even more preferably 1.26 dL / g or lower, even more preferably 1.23 dL / g or lower, and may also be 1.20 dL / g or lower, 1.17 dL / g or lower, 1.15 dL / g or lower, 1.13 dL / g or lower, 1.07 dL / g or lower, 1.05 dL / g or lower, 1.00 dL / g or lower, or 0.97 dL / g or lower. Setting it to 2.0 dL / g or lower tends to further improve the fluidity of the resin composition and improve its moldability. In particular, when a masterbatch of conductive material (especially carbon nanotubes) with polybutylene terephthalate resin is incorporated into a resin composition in which polybutylene terephthalate resin is the main component of the thermoplastic resin (for example, 80% or more by mass of the resin component), the lower the intrinsic viscosity of the main component polybutylene terephthalate resin, the easier it is for the conductive material to disperse. As a result, the electromagnetic wave absorption characteristics tend to improve. The intrinsic viscosity of polybutylene terephthalate resin is measured at 30°C in a 1:1 (mass ratio) mixed solvent of tetrachloroethane and phenol.

[0027] Polybutylene terephthalate resin can be produced by melt polymerization of a dicarboxylic acid component mainly composed of terephthalic acid or ester derivatives thereof, and a diol component mainly composed of 1,4-butanediol, in a batch or continuous manner. Furthermore, after producing a low molecular weight polybutylene terephthalate resin by melt polymerization, the degree of polymerization (or molecular weight) can be increased to a desired value by further solid-phase polymerization under a nitrogen atmosphere or reduced pressure. The polybutylene terephthalate resin is preferably obtained by a manufacturing method in which a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of 1,4-butanediol are continuously melt-polycondensed.

[0028] The catalyst used in carrying out the esterification reaction may be one of the conventionally known ones, such as titanium compounds, tin compounds, magnesium compounds, and calcium compounds. Among these, titanium compounds are particularly preferred. Specific examples of titanium compounds as esterification catalysts include titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, and titanium phenolates such as tetraphenyl titanate.

[0029] In addition to the above, the description in paragraphs 0013 to 0016 of Japanese Patent Publication No. 2010-174223 can be given to the polyester resin, and its contents are incorporated herein by reference.

[0030] <<Polystyrene resin>> Examples of polystyrene resins include homopolymers of styrene monomers and copolymers of styrene monomers and monomers copolymerizable with styrene monomers. Examples of styrene monomers include styrene, α-methylstyrene, chlorostyrene, methylstyrene, and tert-butylstyrene. In this embodiment, the styrene resin contains styrene monomers at a concentration of 50 mol% or more of the monomer units. More specifically, polystyrene-based resins include polystyrene resin, acrylonitrile-styrene copolymer (AS resin), high-impact polystyrene resin (HIPS), acrylonitrile-butadiene-styrene copolymer (ABS resin), acrylonitrile-acrylic rubber-styrene copolymer (AAS resin), acrylonitrile-styrene-acrylic rubber copolymer (ASA resin), acrylonitrile-ethylene propylene-rubber-styrene copolymer (AES resin), styrene-IPN type rubber copolymer, and other resins. In this embodiment, the styrene-based resin is preferably acrylonitrile-styrene copolymer (AS resin), high-impact polystyrene resin (HIPS), acrylonitrile-butadiene-styrene copolymer (ABS resin), acrylonitrile-acrylic rubber-styrene copolymer (AAS resin), acrylonitrile-styrene-acrylic rubber copolymer (ASA resin), acrylonitrile-ethylene propylene rubber-styrene copolymer (AES resin), or styrene-IPN type rubber copolymer, more preferably high-impact polystyrene resin (HIPS), and even more preferably butadiene rubber-containing polystyrene.

[0031] When a polystyrene resin contains rubber components, the content of rubber components in the polystyrene resin is preferably 3 to 70% by mass, more preferably 5 to 50% by mass, and even more preferably 7 to 30% by mass. A rubber component content of 3% by mass or more tends to improve impact resistance, while a content of 50% by mass or less tends to improve flame retardancy, which is preferable. Furthermore, the average particle size of the rubber components is preferably 0.05 to 10 μm, more preferably 0.1 to 6 μm, and even more preferably 0.2 to 3 μm. An average particle size of 0.05 μm or more tends to improve impact resistance, while an average particle size of 10 μm or less tends to improve appearance, which is preferable.

[0032] The weight-average molecular weight of polystyrene resins is typically 50,000 or more, preferably 100,000 or more, more preferably 150,000 or more, and also typically 500,000 or less, preferably 400,000 or less, and more preferably 300,000 or less. The number-average molecular weight is typically 10,000 or more, preferably 30,000 or more, more preferably 50,000 or more, and also preferably 500,000 or less, and more preferably 300,000 or less.

[0033] The melt flow rate (MFR) of polystyrene resins, measured in accordance with JIS K7210 (temperature 200°C, load 5 kgf), is preferably 0.1 to 30 g / 10 min, and more preferably 0.5 to 25 g / 10 min. When the MFR is 0.1 g / 10 min or higher, fluidity tends to improve, and when it is 30 g / 10 min or lower, impact resistance tends to improve.

[0034] Known methods for producing such polystyrene resins include emulsion polymerization, solution polymerization, suspension polymerization, and bulk polymerization.

[0035] <<Polycarbonate resin>> Polycarbonate resin is a branched homopolymer or copolymer obtained by reacting a dihydroxy compound, or a small amount thereof, with a polyhydroxy compound with phosgene or a diester carbonate. The method for producing polycarbonate resin is not particularly limited, and conventionally known methods such as the phosgene method (interfacial polymerization) or the melting method (transesterification) can be used.

[0036] As the raw material dihydroxy compound, aromatic dihydroxy compounds are preferred, including 2,2-bis(4-hydroxyphenyl)propane (=bisphenol A), tetramethylbisphenol A, bis(4-hydroxyphenyl)-p-diisopropylbenzene, hydroquinone, resorcinol, 4,4-dihydroxydiphenyl, and others, with bisphenol A being preferred. In addition, compounds in which one or more tetraalkylphosphonium sulfonates are bonded to the above aromatic dihydroxy compounds can also be used.

[0037] Among the polycarbonate resins mentioned above, aromatic polycarbonate resins derived from 2,2-bis(4-hydroxyphenyl)propane, or aromatic polycarbonate copolymers derived from 2,2-bis(4-hydroxyphenyl)propane and other aromatic dihydroxy compounds are preferred. Alternatively, copolymers mainly composed of aromatic polycarbonate resins, such as copolymers with polymers or oligomers having a siloxane structure, may also be used. Furthermore, two or more of the above-mentioned polycarbonate resins may be mixed and used.

[0038] To adjust the molecular weight of polycarbonate resin, monovalent aromatic hydroxy compounds can be used, such as m- and p-methylphenol, m- and p-propylphenol, p-tert-butylphenol, and p-long-chain alkyl-substituted phenols.

[0039] The viscosity-average molecular weight (Mv) of the polycarbonate resin is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 13,000 or more. Using a resin with a viscosity-average molecular weight of 5,000 or more tends to improve the mechanical strength of the resulting resin composition. Furthermore, the viscosity-average molecular weight (Mv) of the polycarbonate resin is preferably 60,000 or less, more preferably 40,000 or less, and even more preferably 30,000 or less. Using a resin with a viscosity-average molecular weight of 60,000 or less tends to improve the fluidity of the resin composition and improve its moldability. When the mixture contains two or more types of polycarbonate resin, it is preferable that the mixture satisfies the above range (the same consideration applies to molecular weight below).

[0040] In this embodiment, the viscosity-average molecular weight (Mv) of the polycarbonate resin is calculated using an Ubbelohde viscometer to determine the intrinsic viscosity ([η]) of the methylene chloride solution of the polycarbonate resin at 20°C, and the value is derived from Schnell's viscosity formula. [η] = 1.23 × 10 -4 Mv0.83

[0041] The method for producing the polycarbonate resin is not particularly limited, and polycarbonate resin produced by either the phosgene method (interfacial polymerization method) or the melting method (transesterification method) can be used. Furthermore, polycarbonate resin produced by the melting method and then subjected to post-treatment to adjust the amount of terminal OH groups is also preferred.

[0042] <<Polyphenylene ether resin>> In this embodiment, known polyphenylene ether resins can be used, for example, polymers having a main chain of structural units represented by the following formula (preferably polymers in which the structural units represented by the following formula account for 90 mol% or more of all structural units excluding terminal groups). The polyphenylene ether resin may be either a homopolymer or a copolymer.

[0043] [ka] (In the formula, two R a Each of these independently represents a hydrogen atom, a halogen atom, a primary or secondary alkyl group, an aryl group, an aminoalkyl group, a halogenated alkyl group, a hydrocarbon oxy group, or a halogenated hydrocarbon oxy group, and the two R b Each of these independently represents a hydrogen atom, a halogen atom, a primary or secondary alkyl group, an aryl group, a halogenated alkyl group, a hydrocarbon oxy group, or a halogenated hydrocarbon oxy group. However, two R a (They cannot both become hydrogen atoms.)

[0044] R a and R bIndependently, a hydrogen atom, a primary or secondary alkyl group, or an aryl group is preferred. Preferred examples of the primary alkyl group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-amyl group, an isoamyl group, a 2-methylbutyl group, a 2,3-dimethylbutyl group, a 2-, 3- or 4-methylpentyl group, or a heptyl group. Preferred examples of the secondary alkyl group include, for example, an isopropyl group, a sec-butyl group, or a 1-ethylpropyl group. In particular, R a is preferably a primary or secondary alkyl group having 1 to 4 carbon atoms or a phenyl group. R b is preferably a hydrogen atom.

[0045] Preferred homopolymers of the polyphenylene ether resin include, for example, polymers of 2,6-dialkylphenylene ether such as poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-diethyl-1,4-phenylene ether), poly(2,6-dipropyl-1,4-phenylene ether), poly(2-ethyl-6-methyl-1,4-phenylene ether), poly(2-methyl-6-propyl-1,4-phenylene ether). Examples of the copolymer include 2,6-dialkylphenol / 2,3,6-trialkylphenol copolymers such as 2,6-dimethylphenol / 2,3,6-trimethylphenol copolymer, 2,6-dimethylphenol / 2,3,6-triethylphenol copolymer, 2,6-diethylphenol / 2,3,6-trimethylphenol copolymer, 2,6-dipropylphenol / 2,3,6-trimethylphenol copolymer; graft copolymers obtained by graft-polymerizing styrene onto poly(2,6-dimethyl-1,4-phenylene) ether; graft copolymers obtained by graft-polymerizing styrene onto 2,6-dimethylphenol / 2,3,6-trimethylphenol copolymer, and the like.

[0046] In this embodiment, poly(2,6-dimethyl-1,4-phenylene) ether and 2,6-dimethylphenol / 2,3,6-trimethylphenol random copolymers are particularly preferred as the polyphenylene ether resin. Polyphenylene ether resins with specified terminal group counts and copper content, as described in Japanese Patent Application Publication No. 2005-344065, can also be suitably used.

[0047] The polyphenylene ether resin is preferably one with an intrinsic viscosity of 0.2 to 0.8 dL / g, and more preferably 0.3 to 0.6 dL / g, measured in chloroform at 30°C. A viscosity of 0.2 dL / g or higher tends to improve the mechanical strength of the molded article, while a viscosity of 0.8 dL / g or lower tends to improve the fluidity of the resin composition, making molding easier. Alternatively, two or more polyphenylene ether resins with different intrinsic viscosities may be used in combination to achieve this viscosity range.

[0048] The method for producing the polyphenylene ether resin used in this embodiment is not particularly limited, and a known method can be employed, for example, by oxidative polymerization of a monomer such as 2,6-dimethylphenol in the presence of an amine copper catalyst. In this case, the intrinsic viscosity can be controlled to a desired range by selecting the reaction conditions. Control of the intrinsic viscosity can be achieved by selecting conditions such as polymerization temperature, polymerization time, and catalyst amount.

[0049] <<Polyamide resin>> The polyamide resin is a polymer whose constituent units are acid amides obtained by ring-opening polymerization of lactams, polycondensation of aminocarboxylic acids, or polycondensation of diamines and dibasic acids, and may be an aliphatic polyamide resin or a semi-aromatic polyamide resin. Specifically, examples include polyamides 6, 11, 12, 46, 66, 610, 612, 6I, 6 / 66, 6T / 6I, 6 / 6T, 66 / 6T, 66 / 6T / 6I, 9T, 10T, xylylenediamine-based polyamide resins (details to be described later), polytrimethylhexamethylene terephthalamide, polybis(4-aminocyclohexyl)methanedodecamamide, polybis(3-methyl-4-aminocyclohexyl)methanedodecamamide, and polyundemethylenehexahydroterephthalamide. Note that "I" indicates the isophthalic acid component and "T" indicates the terephthalic acid component. Furthermore, for polyamide resins, reference can be made to paragraphs 0011-0013 of Japanese Patent Application Publication No. 2011-132550, which are incorporated herein by reference.

[0050] The polyamide resin used in this embodiment is composed of diamine-derived structural units and dicarboxylic acid-derived structural units, and a xylylenediamine-based polyamide resin is preferred in which 50 mol% or more of the diamine-derived structural units are derived from xylylenediamine. More preferably, 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 95 mol% or more of the diamine-derived structural units of the xylylenediamine-based polyamide resin are derived from at least one of meta-xylylenediamine and para-xylylenediamine. More preferably, 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 95 mol% or more, the dicarboxylic acid-derived structural units of the xylylenediamine-based polyamide resin are derived from α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms. Suitable α,ω-linear aliphatic dibasic acids having 4 to 20 carbon atoms include adipic acid, sebacic acid, suberic acid, dodecanediic acid, and eicodionic acid, with adipic acid and sebacic acid being more preferred.

[0051] Diamines other than meta-xylylenediamine and para-xylylenediamine that can be used as raw material diamine components for xylylenediamine-based polyamide resins include aliphatic diamines such as tetramethylenediamine, pentamethylenediamine, 2-methylpentanediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, dodecamethylenediamine, 2,2,4-trimethyl-hexamethylenediamine, and 2,4,4-trimethylhexamethylenediamine, as well as 1,3-bis( Examples include alicyclic diamines such as aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane, bis(aminomethyl)decalin, and bis(aminomethyl)tricyclodecane, as well as aromatic ring-containing diamines such as bis(4-aminophenyl) ether, paraphenylenediamine, and bis(aminomethyl)naphthalene. One or more of these can be used in combination.

[0052] Examples of dicarboxylic acid components other than the above-mentioned α,ω-linear aliphatic dicarboxylic acids having 4 to 20 carbon atoms include phthalate compounds such as isophthalic acid, terephthalic acid, and orthophthalic acid, and isomers of naphthalenedicarboxylic acids such as 1,2-naphthalenedicarboxylic acid, 1,3-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,6-naphthalenedicarboxylic acid, 1,7-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid. One or more of these can be used in combination.

[0053] In the resin composition of this embodiment, the content of thermoplastic resin is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, even more preferably 45% by mass or more, and even more preferably 50% by mass or more. If the resin composition does not contain a reinforcing material, the content of thermoplastic resin is more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. Setting it above the lower limit tends to further improve fluidity during injection molding. Furthermore, the content of thermoplastic resin is preferably 99% by mass or less. If the resin composition contains a reinforcing material, the content of thermoplastic resin is more preferably 90% by mass or less, even more preferably 85% by mass or less, and even more preferably 80% by mass or less. Setting it below the upper limit tends to more effectively reduce the amount of warpage of the molded article. The resin composition of this embodiment may contain only one type of thermoplastic resin, or it may contain two or more types. When it contains two or more types, it is preferable that the total amount is within the above range.

[0054] <Conductive material> The resin composition of this embodiment contains a conductive substance. By including a conductive substance, electromagnetic wave absorbing properties can be imparted to the resin composition. Examples of conductive materials used in this embodiment include metals, metal oxides, conductive carbon compounds, and conductive polymers, with conductive carbon compounds being preferred. Examples of metals include copper, nickel, silver, and stainless steel, with metal fillers, stainless steel fibers, and magnetic fillers being preferred. Examples of metal oxides include alumina and zinc oxide, with alumina fibers and zinc oxide nanotubes being preferred. Preferred conductive carbon compounds include carbon black, ketjencarbon, graphene, graphite, fullerene, carbon nanocoils, carbon nanotubes, and carbon fibers, with carbon nanotubes being more preferred. Fibers coated with metals, metal oxides, or conductive carbon compounds are also preferred. Examples include carbon-coated potassium titanate whiskers and metal-coated fibers.

[0055] In this embodiment, the conductive material is preferably in a relatively thin and long shape, such as fibrous, tubular, or whisker-like. The diameter (number-average fiber diameter) of the conductive material (preferably carbon nanotubes) is preferably 0.5 nm or more, more preferably 1 nm or more, and even more preferably 5 nm or more. Furthermore, the diameter (number-average fiber diameter) of the carbon nanotubes is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 30 nm or less, and even more preferably 10 nm or less. From the viewpoint of providing good electromagnetic wave absorption, the aspect ratio of the conductive material is preferably 5 or more, and more preferably 50 or more. There is no particular upper limit, but for example, it is 500 or less.

[0056] The conductive material used in this embodiment is preferably carbon nanotubes. The carbon nanotubes are single-walled carbon nanotubes and / or multi-walled carbon nanotubes, and it is preferable that they include at least multi-walled carbon nanotubes. Carbon materials having a partially carbon nanotube structure can also be used. Furthermore, the carbon nanotubes are not limited to a cylindrical shape, but may have a coiled shape in which a helix completes one turn with a pitch of 1 μm or less. Carbon nanotubes are commercially available, and examples include those from Bayer MaterialScience, NanoSil, Showa Denko Corporation, and Hyperion Catalysis International. They are also sometimes referred to as graphite fibrils or carbon fibrils.

[0057] The content of conductive material (preferably carbon nanotubes) in the resin composition of this embodiment is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, may be 0.2% by mass or more, and may even be 0.4% by mass or more. Setting it above the lower limit allows for effective electromagnetic wave absorption. Furthermore, the content of (preferably carbon nanotubes) in the resin composition of this embodiment is preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, even more preferably 4% by mass or less, even more preferably 3% by mass or less, may be 2% by mass or less, and may even be 1% by mass or less. Setting it below the upper limit tends to further improve the fluidity of the resin.

[0058] The resin composition of this embodiment preferably also contains a conductive substance (preferably carbon nanotubes) in an amount of 0.1 parts by mass or more per 100 parts by mass of the thermoplastic resin. By setting it above the lower limit, the electromagnetic wave absorption properties are effectively exhibited. Furthermore, the resin composition of this embodiment preferably contains a conductive substance (preferably carbon nanotubes) in an amount of 10.0 parts by mass or less per 100 parts by mass of the thermoplastic resin, more preferably 8.0 parts by mass or less, even more preferably 6.0 parts by mass or less, even more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and even more preferably 2.5 parts by mass or less, and particularly 1.5 parts by mass or less. Setting it below the upper limit tends to further improve the fluidity of the resin. The resin composition of this embodiment may contain only one conductive substance or two or more. When it contains two or more, it is preferable that the total amount is within the above range.

[0059] <Other ingredients> The resin composition of this embodiment may contain other components as needed, as long as they do not significantly impair the desired physical properties. Examples of other components include reinforcing agents and various resin additives. Note that the other components may be present individually, or two or more in any combination and ratio.

[0060] Examples of various resin additives include stabilizers, release agents, flame retardants, pigments, dyes, UV absorbers, antistatic agents, antifogging agents, antiblocking agents, flow improvers, plasticizers, dispersants, and antibacterial agents. The resin composition of this embodiment preferably contains at least one of a stabilizer and a release agent. The resin composition of this embodiment is prepared so that the total of the thermoplastic resin, conductive material, and other selectively blended components is 100% by mass. Preferably, the total of the thermoplastic resin, conductive material, stabilizer, and release agent in the resin composition of this embodiment is 99% by mass or more. Furthermore, preferably, the total of the thermoplastic resin, conductive material, reinforcing material (preferably glass fiber), stabilizer, and release agent in the resin composition of this embodiment is 99% by mass or more.

[0061] <<Stabilizer>> The resin composition of this embodiment may contain a stabilizer. Examples of stabilizers include hindered phenol compounds, hindered amine compounds, phosphorus compounds, and sulfur-based stabilizers. Among these, hindered phenol compounds are preferred. It is also preferable to use a combination of hindered phenol compounds and phosphorus compounds. Specifically, as stabilizers, reference can be made to paragraphs 0046-0057 of Japanese Patent Publication No. 2018-070722, paragraphs 0030-0037 of Japanese Patent Publication No. 2019-056035, and paragraphs 0066-0078 of International Publication No. 2017 / 038949, the contents of which are incorporated herein by reference.

[0062] The resin composition of this embodiment preferably contains 0.01 parts by mass or more of stabilizer per 100 parts by mass of thermoplastic resin, more preferably 0.05 parts by mass or more, and even more preferably 0.08 parts by mass or more. Furthermore, the upper limit of the stabilizer content is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less per 100 parts by mass of thermoplastic resin. The resin composition of this embodiment may contain only one stabilizer or two or more stabilizers. When two or more stabilizers are included, it is preferable that the total amount is within the above range.

[0063] <<Release agent>> The resin composition of this embodiment preferably contains a mold release agent. A wide range of known release agents can be used as the release agent, with aliphatic carboxylic acid esters, paraffin wax, polystyrene wax, and polyolefin wax being preferred, and polyethylene wax being more preferred. Specifically, as a mold release agent, reference can be given to the descriptions in paragraphs 0115 to 0120 of Japanese Patent Publication No. 2013-007058, paragraphs 0063 to 0077 of Japanese Patent Publication No. 2018-070722, and paragraphs 0090 to 0098 of Japanese Patent Publication No. 2019-123809, the contents of which are incorporated herein by reference.

[0064] The resin composition of this embodiment preferably contains 0.01 parts by mass or more of a release agent per 100 parts by mass of thermoplastic resin, more preferably 0.08 parts by mass or more, and even more preferably 0.2 parts by mass or more. Furthermore, the upper limit of the release agent content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less, and even more preferably 0.8 parts by mass or less per 100 parts by mass of thermoplastic resin. The resin composition may contain only one type of release agent or two or more types. If it contains two or more types, it is preferable that the total amount is within the above range.

[0065] <<Reinforcement material>> The resin composition of this embodiment may or may not contain a reinforcing material. By including a reinforcing material, the mechanical strength of the resulting molded article can be improved. The reinforcing material that can be used in this embodiment is not particularly specified in terms of type, and may be any of the following: fibers, fillers, beads, etc., but fibers are preferred. In particular, the use of glass fibers is preferable because they also function as a dispersant for conductive materials. Furthermore, in this invention, any substance that falls under both the category of conductive material and a reinforcing material is referred to as a conductive material.

[0066] If the reinforcing material is fiber, it may be short fiber or long fiber. When the reinforcing material is short fibers, fillers, beads, etc., the resin composition of this embodiment may include pellets, powdered pellets, and films formed from the pellets. When the reinforcing material is long fiber, examples of the reinforcing material include so-called UD (Uni-Directional) long fiber, sheet-like long fiber such as woven and knitted fabrics. When using these long fiber, components other than the reinforcing material of the resin composition of this embodiment can be impregnated into the sheet-like long fiber reinforcing material to form a sheet-like resin composition (e.g., a prepreg).

[0067] The raw materials for the reinforcing material include inorganic materials such as glass, carbon (carbon fiber, etc.), alumina, boron, ceramics, and metals (steel, etc.), and organic materials such as plants (including kenaf, bamboo, etc.), aramid, polyoxymethylene, aromatic polyamide, poly(p-phenylenebenzobisoxazole), and ultra-high molecular weight polyethylene, with glass being preferred.

[0068] The resin composition of this embodiment preferably contains glass fibers as a reinforcing material. The glass fibers are selected from glass compositions such as A glass, C glass, E glass, R glass, D glass, M glass, and S glass, with E glass (alkali-free glass) being particularly preferred. Glass fibers refer to fibrous materials whose cross-sectional shape, when cut perpendicular to the length, is circular or polygonal. Glass fibers typically have a number-average fiber diameter of 1 to 25 μm, preferably 5 to 17 μm. A number-average fiber diameter of 1 μm or more tends to improve the moldability of the resin composition. A number-average fiber diameter of 25 μm or less tends to improve the appearance of the resulting molded article and enhance its reinforcing effect. Glass fibers may be single fibers or multiple single fibers twisted together. The glass fibers may take any form, such as glass roving made by continuously winding single fibers or multiple strands twisted together, chopped strands cut to a length of 1 to 10 mm (i.e., glass fibers with a number-average fiber length of 1 to 10 mm), or milled fibers crushed to a length of approximately 10 to 500 μm (i.e., glass fibers with a number-average fiber length of 10 to 500 μm), but chopped strands cut to a length of 1 to 10 mm are preferred. Glass fibers with different forms can also be used in combination. Furthermore, glass fibers having an irregular cross-sectional shape are also preferred. This irregular cross-sectional shape refers to a flattening ratio, which is indicated by the major axis / minor axis ratio of the cross-section perpendicular to the length direction of the fiber, and is, for example, 1.5 to 10, more preferably 2.5 to 10, even more preferably 2.5 to 8, and particularly preferably 2.5 to 5.

[0069] The glass fibers may be surface-treated with, for example, silane compounds, epoxy compounds, or urethane compounds, or oxidized, in order to improve their affinity with the resin components, as long as the properties of the resin composition of this embodiment are not significantly impaired.

[0070] In this embodiment, if the resin composition contains a reinforcing material (preferably glass fiber), the content is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of the thermoplastic resin. Setting the content above the lower limit tends to further increase the mechanical strength of the resulting molded article. Furthermore, the content of the reinforcing material (preferably glass fiber) is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 85 parts by mass or less, even more preferably 80 parts by mass or less, and even more preferably 75 parts by mass or less, per 100 parts by mass of the thermoplastic resin. Setting the content below the upper limit tends to improve the appearance of the molded article and further improve the fluidity of the resin composition.

[0071] If the resin composition of this embodiment contains a reinforcing material (preferably glass fiber), its content is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and even more preferably 25% by mass or more. Furthermore, the content of the reinforcing material (preferably glass fiber) is more preferably 50% by mass or less, even more preferably 45% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less. Setting the content above the lower limit tends to further increase the mechanical strength. Furthermore, setting the content below the upper limit tends to improve the appearance of the molded article and further improve the fluidity of the resin composition when melted. The resin composition of this embodiment may contain only one type of reinforcing material (preferably glass fiber) or two or more types. When two or more types are included, it is preferable that the total amount is within the above range.

[0072] <Physical properties of resin compositions> The resin composition of this embodiment preferably has a high electromagnetic wave absorption rate. Specifically, the resin composition of this embodiment preferably has an absorption rate of 50.0 to 100% when molded to a thickness of 2 mm (preferably 100 mm × 100 mm × 2 mm) and determined according to formula (A) at a frequency of 76.5 GHz. Formula (A)

number

[0073] The absorption rate (2mm thickness) is preferably 53.0% or higher, more preferably 55.0% or higher, even more preferably 58.0% or higher, even more preferably 60.0% or higher, and even more preferably 64.0% or higher. Ideally, the upper limit is 100%, but even 90.0% or lower will sufficiently satisfy the required performance.

[0074] Furthermore, the resin composition of this embodiment preferably has an absorption rate of 63.0 to 100% when molded to a thickness of 3 mm (preferably 100 mm × 100 mm × 3 mm) and determined according to formula (A) at a frequency of 76.5 GHz. The absorption rate (at a thickness of 3 mm) is preferably 57.0% or higher, more preferably 59.0% or higher, even more preferably 64.0% or higher, even more preferably 66.0% or higher, and even more preferably 70.0% or higher. Ideally, the upper limit is 100%, but even 90.0% or lower will sufficiently satisfy the required performance.

[0075] The resin composition of this embodiment preferably has a low reflectivity of electromagnetic waves. Specifically, the resin composition of this embodiment preferably has a reflectance of 40.0% or less when molded to a thickness of 2 mm (preferably 100 mm × 100 mm × 2 mm) and determined according to formula (B) at a frequency of 76.5 GHz. Formula (B)

number

[0076] The reflectance (2mm thickness) is preferably 35.0% or less, more preferably 30.0% or less, even more preferably 26.0% or less, even more preferably 22.0% or less, and even more preferably 18.5% or less. The lower limit is ideally 0%, but even 5.0% or more, and even 10.0% or more, will sufficiently satisfy the required performance.

[0077] Furthermore, it is preferable that the resin composition of this embodiment, when molded to a thickness of 3 mm (preferably 100 mm × 100 mm × 3 mm), has a reflectance of 38.0% or less, as determined by formula (B) at a frequency of 76.5 GHz. The reflectance (at 3mm thickness) is preferably 33.0% or less, more preferably 28.0% or less, even more preferably 24.0% or less, even more preferably 20.0% or less, and even more preferably 16.5% or less. The lower limit is ideally 0%, but even 3.0% or more, and even 8.0% or more, will sufficiently satisfy the required performance.

[0078] The resin composition of this embodiment preferably has low transmittance. The resin composition of this embodiment preferably has a transmittance of 25.0% or less when molded to a thickness of 2 mm (preferably 100 mm × 100 mm × 2 mm) and determined according to formula (C) at a frequency of 76.5 GHz. Formula (C)

number

[0079] The aforementioned transmittance (at a thickness of 2 mm) is preferably 23.0% or less, and more preferably 20.0% or less. Ideally, the lower limit should be 0%, but even if it is 5.0% or more, it will still sufficiently meet the required performance.

[0080] Furthermore, it is preferable that the resin composition of this embodiment has a transmittance of 26.0% or less when molded to a thickness of 3 mm (preferably 100 mm × 100 mm × 3 mm) and calculated according to formula (C) at a frequency of 76.5 GHz. The aforementioned transmittance (at a 3mm thickness) is preferably 24.0% or less, and more preferably 21.0% or less. Ideally, the lower limit should be 0%, but even if it is 4.0% or more, it will still sufficiently meet the required performance.

[0081] The resin composition of this embodiment preferably satisfies all of the following: the absorption rate determined according to formula (A), the reflectance determined according to formula (B), and the transmittance determined according to formula (C).

[0082] The resin composition of this embodiment preferably has a high dielectric constant. Furthermore, the resin composition of this embodiment also preferably has a high dielectric loss tangent. The resin composition of this embodiment preferably has a relative permittivity of 4.50 or higher at a frequency of 76.5 GHz, more preferably 4.60 or higher, even more preferably 4.75 or higher, even more preferably 4.90 or higher, even more preferably 5.00 or higher, and even more preferably 5.10 or higher. Setting it above the lower limit tends to result in a higher electromagnetic wave absorption rate for the resulting molded article. Furthermore, the upper limit of the relative permittivity is preferably 8.00 or lower, more preferably 6.00 or lower, even more preferably 5.50 or lower, even more preferably 5.30 or lower, and even more preferably 5.20 or lower. Setting it below the upper limit tends to result in a lower electromagnetic wave reflectivity for the resulting molded article. The resin composition of this embodiment preferably has a dielectric loss tangent of 0.10 or higher at a frequency of 76.5 GHz, more preferably 0.12 or higher, even more preferably 0.14 or higher, even more preferably 0.16 or higher, even more preferably 0.18 or higher, and even more preferably 0.21 or higher. Setting it above the lower limit tends to increase the electromagnetic wave absorption rate of the resulting molded article. Furthermore, the lower limit of the dielectric loss tangent is not particularly defined, but for example, it may be 0.50 or lower, and even more preferably 0.40 or lower. By setting the value below the aforementioned upper limit, the electromagnetic wave reflectivity of the resulting molded body tends to be lower.

[0083] The resin composition of this embodiment preferably has excellent mechanical strength. The resin composition of this embodiment is preferably particularly excellent in tensile properties. For example, when the resin composition of this embodiment is molded into an ISO multipurpose test specimen (4 mm thick), the maximum tensile strength measured according to ISO 527-1 and ISO 527-2 is preferably 40.0 MPa or higher, and more preferably 50.0 MPa or higher. There is no particular upper limit for the maximum tensile strength, but for example, even 200.0 MPa or lower is at a practical level. Furthermore, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (4 mm thick), the tensile modulus measured according to ISO 527-1 and ISO 527-2 is preferably 1500 MPa or higher, more preferably 1800 MPa or higher, and even more preferably 2000 MPa or higher. There is no particular upper limit to the tensile modulus, but for example, 12000 MPa or less is at a practical level. Furthermore, when the resin composition of this embodiment is molded into an ISO multipurpose test specimen (4 mm thick), the tensile strain measured according to ISO 527-1 and ISO 527-2 is preferably 1.0% or more, more preferably 2.0% or more, and even more preferably 3.5% or more. While there is no specific upper limit for the tensile strain, for example, 30% or less is still within a practical range.

[0084] Furthermore, the resin composition of this embodiment is preferably excellent in terms of bending properties. Specifically, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (4 mm thick), the flexural strength is preferably 50.0 MPa or higher, and more preferably 70.0 MPa or higher. Furthermore, there is no upper limit to the flexural strength, but for example, 300.0 MPa or less is practical. Furthermore, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (4 mm thick), the flexural modulus is preferably 1,500 MPa or higher, and more preferably 2,000 MPa or higher. While there is no specific upper limit for the flexural modulus, for example, 15,000 MPa or less is practical.

[0085] Furthermore, it is preferable that the resin composition of this embodiment has excellent impact resistance. Specifically, when the resin composition of this embodiment is molded into an ISO multipurpose test specimen (4 mm thick), the notched Charpy impact strength according to ISO 179 standard is 2.0 kJ / m². 2 Preferably, it is 3.0 kJ / m 2 It is more preferable that the value be greater than or equal to 3.2 kJ / m³. 2 It is even more preferable that the above values ​​are met. Furthermore, there is no upper limit specified for the notched Charpy impact strength, but for example, 50 kJ / m 2 The following is practical.

[0086] The resin composition of this embodiment also has a surface resistance of 1.0 × 10⁻¹⁰ when molded to a thickness of 2 mm (preferably 100 mm × 100 mm × 2 mm), in accordance with IEC60093. 8 It is preferable that the value be Ω or greater, and 1.0 × 10 9 It is more preferable that it be Ω or greater, 1.0 × 10 10 It is even more preferable that it be Ω or greater, 1.0 × 10 11 It is even more preferable that it be Ω or greater, 1.0 × 10 12 It is even more preferable that it be Ω or greater, 1.0 × 10 13 It is even more preferable that it be greater than or equal to Ω, specifically 1.0 × 10⁻⁶. 14 It is especially preferable that it be greater than or equal to Ω, and also 1.0 × 10 16 It is preferable that it be less than or equal to Ω, and 1.0 × 10 15 It is more preferable that the value be less than or equal to Ω. By setting the value within this range, the resulting molded body tends to have a higher electromagnetic wave absorption rate. The resin composition of this embodiment further has a volume resistivity of 1.0 × 10⁻¹⁰ in a 2 mm thick (preferably 100 mm × 100 mm × 2 mm thick) test specimen in accordance with IEC60093. 10 It is preferable that the density be Ω·cm or greater, and 1.0 × 10 11 It is more preferable that the value be Ω·cm or greater, and 1.0 × 10 12 It is even more preferable that the density be Ω·cm or greater, and 1.0 × 10 13 It is even more preferable that it be Ω·cm or less, and 1.0 × 10 14 It is even more preferable that it be Ω·cm or greater, and 1.0 × 10 15 It is even more preferable that it be Ω·cm or greater, and also 1.0 × 10 17 It is preferable that the value be Ω·cm or less, and 1.0 × 10 16 It is more preferable that the value be Ω·cm or less. By setting it within this range, the electromagnetic wave absorption rate of the resulting molded body tends to be higher. The details of the above measurement method are measured according to the description in the examples.

[0087] <Other specific examples of resin compositions (1)> Another specific example (1) of the resin composition of this embodiment is a resin composition comprising a polybutylene terephthalate resin, a polystyrene-based resin, and carbon nanotubes. This configuration yields a resin composition with high absorption. The reason for this is presumed to be as follows: By incorporating carbon nanotubes into the polybutylene terephthalate resin, a certain level of electromagnetic wave absorption is achieved. In this embodiment, it is presumed that by further incorporating a styrene-based resin, the carbon nanotubes can be dispersed more effectively in the polybutylene terephthalate resin, resulting in an even higher absorption rate for the resulting resin composition. Furthermore, by adopting the configuration of this embodiment, the reflectivity and transmittance of electromagnetic waves of the resin composition can be reduced. In addition, the tensile properties, particularly the tensile strain, can be increased. Furthermore, the above effects can be achieved more effectively by forming a masterbatch of carbon nanotubes with a styrene-based resin and blending it with polybutylene terephthalate resin. Although this mechanism is speculative, it is presumed that when polybutylene terephthalate resin and a styrene-based resin masterbatch of carbon nanotubes are melt-mixed, the carbon nanotubes emerge from the styrene-based resin and enter the polybutylene terephthalate resin, where they diffuse. The driving force at this time breaks down the aggregation of carbon nanotubes, allowing them to diffuse more effectively within the polybutylene terephthalate resin. On the other hand, another specific example of a resin composition (1) typically exhibits a sea-island structure having a sea region containing a large amount of polybutylene terephthalate resin and an island region containing a large amount of polystyrene resin, where 30% or more by mass (preferably 45% or more by mass, more preferably 65% ​​or more by mass, and even more preferably 85% or more by mass) of the resin components contained in the resin composition is polybutylene terephthalate resin, and the carbon nanotube content in the sea region is greater than the carbon nanotube content in the island region. By exhibiting such a structure, the electromagnetic wave absorption of the resin composition tends to be high. It is presumed that such a sea-island structure is based on the fact that polybutylene terephthalate resin and polystyrene resin are not easily compatible, and that carbon nanotubes are inherently more compatible with polybutylene terephthalate resin than with polystyrene resin.

[0088] <Other specific examples of resin compositions (2)> Another specific example (2) of the resin composition of this embodiment is a resin composition comprising a thermoplastic resin and carbon nanotubes, wherein the relative permittivity of the resin composition at a frequency of 76.5 GHz is 4.50 or higher. By increasing the relative permittivity at a frequency of 76.5 GHz, the electromagnetic wave absorption rate of the resulting resin composition at around 76.5 GHz can be increased. Furthermore, by adopting the configuration of this embodiment, the reflectance and transmittance of electromagnetic waves of the resin composition at a frequency of 76.5 GHz can be reduced. The reason why increasing the relative permittivity improves the electromagnetic wave absorption rate is presumed to be because the shielding effect of the resin composition against electric fields improves. It is surprising that increasing the relative permittivity of a resin composition improves its absorption rate. Furthermore, increasing the dielectric loss tangent also improves the absorption rate. The reason why increasing the dielectric loss tangent improves the absorption rate is presumed to be because the efficiency of converting electromagnetic waves into thermal energy within the resin composition improves. Methods for increasing the dielectric constant of a resin composition include selecting materials with high dielectric constants, minimizing the use of materials that lower the dielectric constant, ensuring good dispersion of materials with high dielectric constants within the resin, and increasing the volume separation of materials with high dielectric constants. In particular, a resin composition with a high dielectric constant can be obtained by incorporating additives with high dielectric constants into a composition consisting of two or more thermoplastic resins. Methods for increasing the dielectric loss tangent of a resin composition are basically the same as those for increasing the dielectric constant, but some materials may increase the dielectric constant but decrease the dielectric loss tangent, so selection may be necessary. In this embodiment, the thermoplastic resin preferably comprises thermoplastic resin (A) and thermoplastic resin (B). However, thermoplastic resin (A) and thermoplastic resin (B) may be the same resin.

[0089] The content of thermoplastic resin (B) in the resin composition of this embodiment is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, per 100 parts by mass of thermoplastic resin (A). Setting it above the lower limit tends to further improve the electromagnetic wave absorption performance. Furthermore, the content of thermoplastic resin (B) is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, even more preferably 10.0 parts by mass or less, and even more preferably 8.0 parts by mass or less, 7.0 parts by mass or less, or 6.0 parts by mass or less, per 100 parts by mass of thermoplastic resin (A). Setting it below the upper limit tends to further lower the transmittance of the resulting molded article. In this embodiment, it is preferable that the thermoplastic resin (A) is the main resin constituting the molded article (for example, the component with the highest content). Furthermore, in this embodiment, it is preferable that at least a portion of the thermoplastic resin (B) is derived from the carbon nanotube masterbatch. With such a configuration, the effects of the present invention tend to be exhibited more effectively. The resin composition of this embodiment may contain only one type of thermoplastic resin (A) and one type of thermoplastic resin (B), or it may contain two or more types. When two or more types are included, it is preferable that the total amount is within the above range.

[0090] In this embodiment, the thermoplastic resin (A) preferably contains a polyester resin (preferably a polybutylene terephthalate resin). Furthermore, in this embodiment, preferably 95% by mass or more, more preferably 99% by mass or more, of the thermoplastic resin (A) is polyester resin.

[0091] In this embodiment, a preferred example of the thermoplastic resin is that thermoplastic resin (A) and thermoplastic resin (B) each contain a polyester resin (preferably polybutylene terephthalate resin), and that 90% or more by mass (preferably 95% or more by mass, more preferably 99% or more by mass) of the thermoplastic resin is polyester resin (preferably polybutylene terephthalate resin).

[0092] In this embodiment, a preferred example of the thermoplastic resin is that thermoplastic resin (A) contains a polyester resin (preferably polybutylene terephthalate resin), and thermoplastic resin (B) contains a polystyrene-based resin. In this embodiment, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more of the thermoplastic resin consists of polyester resin (preferably polybutylene terephthalate resin) and polystyrene-based resin (preferably HIPS, more preferably butadiene rubber-containing polystyrene).

[0093] <Other specific examples of resin compositions (3)> Another specific example (3) of the resin composition of this embodiment comprises a thermoplastic resin (A), a thermoplastic resin (B), and carbon nanotubes, wherein at least a portion of the thermoplastic resin (B) is derived from the masterbatch of carbon nanotubes, and the SP value of thermoplastic resin (A) ≥ the SP value of thermoplastic resin (B) (where the SP value is a solubility parameter). This configuration makes it possible to provide a resin composition with high electromagnetic wave absorption. The reason for this is presumed to be as follows: Resins with high SP values ​​have a relatively large number of polar groups. On the other hand, when carbon nanotubes are melt-kneaded with two or more resins, they tend to be attracted to the resin with polar groups. Therefore, it was presumed that if the SP value of the resin used to make the carbon nanotubes into a masterbatch is greater than the SP value of the main thermoplastic resin, the carbon nanotubes will not disperse easily in the main thermoplastic resin even if the carbon nanotube masterbatch and the main thermoplastic resin are melt-kneaded. In this embodiment, by setting the SP value of the thermoplastic resin (B) used to make the carbon nanotubes into a masterbatch to be less than or equal to the SP value of thermoplastic resin (A), it is presumed that during melt-kneading, the carbon nanotubes can be more easily dispersed in thermoplastic resin (A) by correlated migration from thermoplastic resin (B) to thermoplastic resin (A). In particular, it was presumed that by setting the difference between the SP value of thermoplastic resin (A) and the SP value of thermoplastic resin (B) to 0.1 or more, the dispersion of carbon nanotubes in thermoplastic resin (A) can be improved more significantly. Furthermore, by improving the dispersibility of carbon nanotubes in thermoplastic resin (A), a high electromagnetic wave absorption rate was achieved. In another specific example (3) of the resin composition of this embodiment, the SP value of thermoplastic resin (A) is greater than or equal to the SP value of thermoplastic resin (B) (where SP is a solubility parameter). With this configuration, the dispersibility of carbon nanotubes in thermoplastic resin (A) tends to improve. The difference between the SP value of thermoplastic resin (A) and the SP value of thermoplastic resin (B) is 0 or greater, preferably 0.1 or greater, more preferably 0.3 or greater, even more preferably 0.5 or greater, even more preferably 0.7 or greater, and even more preferably 1.0 or greater. Furthermore, the difference between the SP value of thermoplastic resin (A) and the SP value of thermoplastic resin (B) is preferably 8.0 or less, more preferably 7.0 or less, even more preferably 6.0 or less, even more preferably 5.0 or less, and even more preferably 4.0 or less. Keeping the difference below the above upper limit tends to improve compatibility during melt mixing. Another specific example (3) of the resin composition of this embodiment may contain only one type of thermoplastic resin (A) and one or more types of thermoplastic resin (B). When two or more types are included, it is preferable that the SP value of the mixture satisfies the above range. In this embodiment, the solubility of a solvent with a known SP value can be determined, and then calculated using the Hansen Solubility Parameter in Practice ver. 5.0.

[0094] In another specific example (3) of the resin composition of this embodiment, the thermoplastic resin (A) is typically the main component of the resin components included in the resin composition. The thermoplastic resins used in this embodiment are preferably polyester resins (thermoplastic polyester resins); polyamide resins; polycarbonate resins; polystyrene resins; polyolefin resins such as polyethylene resins, polypropylene resins, and cyclic cycloolefin resins; polyacetal resins; polyimide resins; polyetherimide resins; polyurethane resins; polyphenylene ether resins; polyphenylene sulfide resins; polysulfone resins; polymethacrylate resins; and are more preferably selected from polyester resins, polycarbonate resins, and polyamide resins, even more preferably containing polyester resins, and even more preferably containing polybutylene terephthalate resins.

[0095] In another specific example (3) of the resin composition of this embodiment, the content of thermoplastic resin (A) is preferably 30% by mass or more, more preferably 35% by mass or more, even more preferably 40% by mass or more, even more preferably 45% by mass or more, and even more preferably 50% by mass or more. If the resin composition does not contain a reinforcing material, the content of thermoplastic resin (A) is more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. Setting it above the lower limit tends to further improve fluidity during injection molding. Furthermore, the content of the thermoplastic resin is preferably 99% by mass or less. If the resin composition contains a reinforcing material, the content of thermoplastic resin (A) is more preferably 90% by mass or less, even more preferably 80% by mass or less, and even more preferably 75% by mass or less. Setting it below the upper limit tends to further improve the mechanical strength of the resulting molded article.

[0096] Another specific example (3) of the resin composition of this embodiment includes a thermoplastic resin (B). At least a portion of the thermoplastic resin (B) is derived from the carbon nanotube masterbatch. With this configuration, during melt mixing, the carbon nanotubes are more easily transferred from the thermoplastic resin (B) to the thermoplastic resin (A), improving the dispersibility of the carbon nanotubes in the resin composition. Furthermore, a portion of the thermoplastic resin (B) does not necessarily have to be derived from a carbon nanotube masterbatch.

[0097] Thermoplastic resin (B) is determined in relation to thermoplastic resin (A). That is, as long as the relationship between the SP value of thermoplastic resin (A) and the SP value of thermoplastic resin (B) described above is satisfied, the type of thermoplastic resin (B) is not predetermined and can be selected as appropriate. The thermoplastic resin (B) used in this embodiment is preferably exemplified by polyester resin (thermoplastic polyester resin); polyamide resin; polycarbonate resin; polystyrene resin; polyolefin resin such as polyethylene resin, polypropylene resin, and cyclic cycloolefin resin; polyacetal resin; polyimide resin; polyetherimide resin; polyurethane resin; polyphenylene ether resin; polyphenylene sulfide resin; polysulfone resin; polymethacrylate resin; and is more preferably selected from polyester resin, polystyrene resin, and polyolefin resin, even more preferably selected from polyester resin and polystyrene resin, even more preferably containing polystyrene resin, and even more preferably containing HIPS (preferably butadiene rubber-containing polystyrene).

[0098] In another specific example (3) of the resin composition of this embodiment, the content of thermoplastic resin (B) is preferably 1.0 part by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, per 100 parts by mass of thermoplastic resin (A). Setting it above the lower limit tends to further improve the electromagnetic wave absorption performance. Furthermore, the content of thermoplastic resin (B) is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 50 parts by mass or less, even more preferably 30 parts by mass or less, even more preferably 10.0 parts by mass or less, and even more preferably 8.0 parts by mass or less, 7.0 parts by mass or less, or 6.0 parts by mass or less, per 100 parts by mass of thermoplastic resin (A). Setting it below the upper limit tends to further lower the transmittance and reflectance of the resulting molded article.

[0099] In another specific example (3) of the resin composition of this embodiment, at least a portion of the thermoplastic resin (B) is blended as a resin for masterbatching. The concentration of thermoplastic resin (B) in the masterbatch is preferably 99% by mass or less, preferably 95% by mass or less, preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more. By setting the concentration within the above upper and lower limits, the dispersibility of carbon nanotubes in thermoplastic resin (A) tends to improve.

[0100] In another specific example (3) of the resin composition of this embodiment, an example of a preferred blend form of thermoplastic resin is that thermoplastic resin (A) contains a polyester resin (preferably polybutylene terephthalate resin) and thermoplastic resin (B) contains a polystyrene resin. In this embodiment, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more of the resin components contained in the resin composition consist of polyester resin (preferably polybutylene terephthalate resin) and polystyrene resin (preferably HIPS). In another specific example (3) of the resin composition of this embodiment, a preferred other example of the thermoplastic resin is that thermoplastic resin (A) contains a polyester resin (preferably polybutylene terephthalate resin), and thermoplastic resin (B) contains a polyester resin (preferably polybutylene terephthalate resin). In another specific example (3) of the resin composition of this embodiment, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more of the resin components contained in the resin composition consist of polyester resin (preferably polybutylene terephthalate resin).

[0101] <Method for producing resin compositions> The resin composition of this embodiment can be manufactured by a conventional method for manufacturing resin compositions containing a thermoplastic resin. For example, it can be obtained by melt-kneading a thermoplastic resin, a conductive substance, and other components as needed. It is preferable to incorporate the conductive substance by forming a masterbatch with the thermoplastic resin. By forming a masterbatch with the conductive substance using the thermoplastic resin, the dispersibility of the conductive substance in the thermoplastic resin can be effectively improved. The concentration of the conductive substance in the masterbatch is preferably 1% by mass or more, preferably 5% by mass or more, preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and most preferably 20% by mass or less. By setting the concentration within the above upper and lower limits, the dispersibility of the conductive substance in the thermoplastic resin tends to be further improved.

[0102] The components may be pre-mixed and supplied to the extruder all at once, or they may be supplied to the extruder using a feeder, either without pre-mixing them, or with only some of them pre-mixed. The extruder may be a single-screw extruder or a twin-screw extruder. Furthermore, when incorporating glass fibers, it is preferable to supply them from a side feeder located midway through the extruder cylinder. The heating temperature during melting and kneading can usually be appropriately selected from the range of 170 to 350°C.

[0103] <Method for manufacturing molded articles> The molded article, in particular the electromagnetic wave absorber, is formed from the resin composition of this embodiment. The method for manufacturing the molded article in this embodiment is not particularly limited, and any molding method commonly used for resin compositions containing thermoplastic resins can be arbitrarily employed. Examples include injection molding, ultra-high-speed injection molding, injection compression molding, two-color molding, hollow molding methods such as gas-assisted molding, molding using insulated molds, molding using rapidly heated molds, foam molding (including supercritical fluids), insert molding, IMC (in-mold coating) molding, extrusion molding, sheet molding, thermoforming, rotational molding, lamination molding, press molding, blow molding, etc., with injection molding being preferred among them.

[0104] <Application> The electromagnetic wave absorber of this embodiment is formed from the resin composition of this embodiment. That is, the resin composition of this embodiment is preferably for electromagnetic wave absorbers (also called for electromagnetic wave absorbing members), more preferably for electromagnetic wave absorbers with a frequency of at least 60 to 90 GHz, and even more preferably for electromagnetic wave absorbers with a frequency of at least 70 to 80 GHz. Such electromagnetic wave absorbers are preferably used in radar applications. Specifically, they are used in housings, covers, etc., for millimeter-wave radars. The electromagnetic wave absorber of this embodiment can be suitably used in: on-board millimeter-wave radar used in automatic brake control devices, inter-vehicle distance control devices, pedestrian accident reduction steering devices, unintended acceleration suppression devices, pedal misapplication acceleration suppression devices, approaching vehicle warning devices, lane keeping assist devices, rear-end collision prevention warning devices, parking assist devices, vehicle surrounding obstacle warning devices, etc.; railway and aviation millimeter-wave radar used in platform monitoring / level crossing obstacle detection devices, in-train content transmission devices, tram / railway collision avoidance devices, runway foreign object detection devices, etc.; millimeter-wave radar for traffic infrastructure such as intersection monitoring devices and elevator monitoring devices; millimeter-wave radar for various security devices; medical and nursing care millimeter-wave radar such as child and elderly monitoring systems; millimeter-wave radar for various information content transmission; and the like. [Examples]

[0105] The present invention will be described in more detail below with reference to examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate, as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. If the measuring instruments used in the examples are difficult to obtain due to discontinuation or other reasons, measurements can be taken using other instruments with equivalent performance.

[0106] raw material The following raw materials were used. In Table 1 below, PBT refers to polybutylene terephthalate resin, HIPS refers to high-impact polystyrene, PA refers to polyamide resin, and CNT refers to carbon nanotubes (the same applies to Table 2).

[0107] [Table 1] The diameter (number-average fiber diameter) of the above CNT is 9 nm.

[0108] Examples 1, 2, Comparative Example 1 <Manufacturing of resin compositions (pellets)> As shown in Table 2, each component listed in Table 1 was placed in a stainless steel tumbler and stirred and mixed for 1 hour. The resulting mixture was supplied from the main feed port to a coaxial twin-screw extruder (TEX-30α, manufactured by Japan Steel Works, Ltd., screw diameter 32 mm, L / D = 42). The barrel temperature of the first kneading section was set to 250°C, and the mixture was melt-kneaded under conditions of a discharge rate of 40 kg / h and a screw rotation speed of 200 rpm. The mixture was then extruded as strands using 4 nozzles (circular (φ4 mm), length 1.5 cm). The extruded strands were cooled in a water tank and inserted into a pelletizer to cut them, thereby obtaining resin compositions (pellets).

[0109] <76.5GHz electromagnetic wave absorption rate, reflectance rate, transmittance rate> Using the pellets obtained above, injection molding was performed using an injection molding machine (NEX80, manufactured by Nissei Plastic Industrial Co., Ltd.) with a cylinder temperature of 260°C and a mold temperature of 80°C to obtain test specimens of 100mm × 100mm × 2mm thickness and 100mm × 100mm × 3mm thickness. Using the obtained test specimens, the absorptivity determined according to equation (A), the reflectivity determined according to equation (B), and the transmittance determined according to equation (C) at a frequency of 76.5GHz were measured as follows. For the measurements, we used a Keysight N5252A network analyzer. Furthermore, the test specimen was positioned so that the transverse direction (TD) of the injection-molded body was parallel to the direction of the electric field, and measurements were taken. Formula (A)

number

[0110] Formula (B)

number

[0111] Formula (C)

number

[0112] <Relative permittivity and dielectric loss tangent> Using the pellets obtained above, injection molding was performed using an injection molding machine (NEX80, manufactured by Nissei Plastic Industrial Co., Ltd.) with a cylinder temperature of 260°C and a mold temperature of 80°C to obtain test specimens measuring 100 mm x 100 mm x 2 mm in thickness. Using the obtained test specimens, the relative permittivity and dielectric loss tangent were determined at a frequency of 76.5 GHz. The test specimens were positioned so that the transverse direction (TD) of the injection-molded body was parallel to the electric field direction during the measurements. For the measurements, a Keysight N5252A network analyzer was used. The relative permittivity and dielectric loss tangent values ​​were estimated using the Keysight N1500A materials measurement suite, and the NIST Precision calculation model was used to calculate each value.

[0113] <Agglutinate area ratio> Using the pellets obtained above, injection molding was performed using an injection molding machine (NEX80, manufactured by Nissei Plastic Industrial Co., Ltd.) with a cylinder temperature of 260°C and a mold temperature of 80°C to obtain a test specimen measuring 100 mm × 100 mm × 2 mm in thickness. A rectangular, mechanically polished cross-section was prepared, including the center point of the obtained test specimen, perpendicular to the MD direction (resin flow direction) during injection molding, with dimensions of 15 mm in the TD direction (direction perpendicular to the MD direction) and 2 mm in the thickness direction. In preparing the cross-section, the specimen was pre-embedded in a curable epoxy resin and polished to maintain its condition and obtain a smooth surface suitable for light microscopy observation. The aforementioned cross-section was observed using a Keyence VHX-7000 digital microscope. For the observation and photography, the illumination method and image contrast were adjusted as needed to ensure that the carbon nanotube-derived aggregates appeared clearly and darkly. A high-resolution (HR) head medium-magnification equal-objective lens, VHX-E100, was used, and images of four fields of view were acquired per sample at a magnification of 100. From the images obtained above, the equivalent circular diameter and area ratio of carbon nanotube aggregates were determined using the image processing software "WinROOF 2018" manufactured by Mitani Corporation, following the procedure in 1.2.3 below. 1. Monochrome conversion of observed images 2. Automatic binarization (select carbon nanotube aggregates) (The threshold value is set by the measurer using the discriminant classification method, at any value.) 3. The equivalent diameter and area ratio were calculated, and the average value of 4 fields of view per sample was shown. (Note that samples with an equivalent circle diameter of less than 30 μm were removed.) In this context, the equivalent diameter of a circle is defined as: Equivalent diameter of a circle = (Area value of the aggregate image / π) 1 / 2 The area ratio was calculated using the following formula, multiplied by 2. Area percentage (%) = (Sum of areas of CNT aggregates) / (Area of ​​the observed cross-section) × 100

[0114] <Tensile properties> The resin pellets obtained above were dried at 120°C for 5 hours, and then ISO multipurpose test specimens (4 mm thick) were injection molded using an injection molding machine (Japan Steel Works, Ltd. "J85AD") under the conditions of a cylinder temperature of 250°C and a mold temperature of 80°C. Using molded multi-purpose ISO test specimens, the maximum point tensile strength (in MPa), tensile modulus (in MPa), and tensile strain (in %) were measured in accordance with ISO 527-1 and ISO 527-2.

[0115] <Bending properties> The resin pellets obtained above were dried at 120°C for 5 hours, and then ISO multipurpose test specimens (4 mm thick) were injection molded using an injection molding machine (Japan Steel Works, Ltd. "J85AD") under the conditions of a cylinder temperature of 250°C and a mold temperature of 80°C. Using molded multi-purpose ISO test specimens, flexural strength (in MPa) and flexural modulus (in MPa) were measured in accordance with ISO 178.

[0116] <Charpy impact strength with notch> The resin pellets obtained above were dried at 120°C for 5 hours, and then ISO multipurpose test specimens (4 mm thick) were injection molded using an injection molding machine (Japan Steel Works, Ltd. "J85AD") under the conditions of a cylinder temperature of 250°C and a mold temperature of 80°C. In accordance with the ISO 179 standard, the ISO multipurpose test specimens obtained above were cut to the specified size and shape, and the Charpy impact strength (with notch) was measured. The unit is kJ / m 2 As shown.

[0117] <Surface resistance> Using the pellets obtained above, injection molding was performed using an injection molding machine (NEX80, manufactured by Nissei Plastic Industrial Co., Ltd.) with a cylinder temperature of 260°C and a mold temperature of 80°C to obtain test specimens measuring 100 mm x 100 mm x 2 mm in thickness. The surface resistance (in Ω) of the obtained test specimens was measured in accordance with IEC60093. For the measurements, we used the ADVANTEST R8340 ULTRA HIGH RESISTANCE METER.

[0118] <Volume Resistivity> Using the pellets obtained above, injection molding was performed using an injection molding machine (NEX80, manufactured by Nissei Plastic Industrial Co., Ltd.) with a cylinder temperature of 260°C and a mold temperature of 80°C to obtain test specimens measuring 100 mm x 100 mm x 2 mm in thickness. The volume resistivity (unit: Ω·cm) was measured using the obtained test specimens in accordance with IEC60093. For the measurements, we used the ADVANTEST R8340 ULTRA HIGH RESISTANCE METER.

[0119] [Table 2]

[0120] In Table 2 above, the CNT content indicates the amount of carbon nanotubes in the resin composition. As is clear from the above results, the resin composition of the present invention had a high electromagnetic wave absorption rate. Furthermore, it had low electromagnetic wave transmittance and reflectance. In addition, the molded articles formed from the resin composition of the present invention had excellent mechanical strength.

[0121] <Heat resistance> For the pellets obtained in Example 1, test specimens measuring 100 mm × 100 mm × 2 mm thick were prepared according to the above-mentioned <76.5 GHz electromagnetic wave absorption rate, reflectance, and transmittance>, and the absorption rate, reflectance, and transmittance were measured. Furthermore, the 100 mm × 100 mm × 2 mm thick test specimens were heat-treated at 180°C in a hot air oven (Yamato Scientific Co., Ltd. "DNE400"). The absorption rate, reflectance, and transmittance were measured for the test specimens after 500 hours, 1000 hours, 1500 hours, and 2000 hours, respectively, according to the above-mentioned <76.5 GHz electromagnetic wave absorption rate, reflectance, and transmittance>. The data before treatment (0 hours) and the results are shown in Table 3.

[0122] <Hydrolysis resistance> For the pellets obtained in Example 1, test specimens measuring 100 mm × 100 mm × 2 mm thick were prepared according to the above-mentioned <76.5 GHz electromagnetic wave absorption rate, reflectance, and transmittance>, and the absorption rate, reflectance, and transmittance were measured. Furthermore, the 100 mm × 100 mm × 2 mm thick test specimens were left standing in an accelerated life testing apparatus (ESPEC Corporation "EHS-221M") at 121°C, 100% relative humidity, and 2 atm. The absorption rate, reflectance, and transmittance were measured for the test specimens after 50 hours, 100 hours, and 200 hours of processing, respectively, according to the above-mentioned <76.5 GHz electromagnetic wave absorption rate, reflectance, and transmittance>. The data before processing (0 hours) and the results are shown in Table 3.

[0123] [Table 3]

[0124] As is clear from the results above, the resin composition of the present invention showed almost no change in electromagnetic wave properties even after prolonged heating. Furthermore, the resin composition of the present invention also exhibited excellent hydrolysis resistance.

[0125] Examples 3-6 In Example 1, the components in the above-mentioned <Production of Resin Composition (Pellets)> were changed as shown in Table 4, and pellets were obtained by proceeding in the same manner otherwise. Next, the obtained pellets were used to measure the absorptive rate, reflectance, and transmittance according to the above-mentioned <76.5GHz electromagnetic wave absorptive rate, reflectance, and transmittance>. Next, the relative permittivity and dielectric loss tangent were measured according to the above-mentioned <relative permittivity and dielectric loss tangent>. Furthermore, the aggregate area ratio was measured according to the above-mentioned <aggregate area ratio>.

[0126] [Table 4]

[0127] The resin composition of the present invention exhibited excellent electromagnetic wave absorption properties regardless of the intrinsic viscosity of the thermoplastic resin, but a lower intrinsic viscosity resulted in a higher electromagnetic wave absorption rate.

Claims

1. Thermoplastic resin and A resin composition containing a conductive substance, The content of the conductive substance is 4.0 parts by mass or less per 100 parts by mass of the thermoplastic resin. The thermoplastic resin includes a polyester resin, When the resin composition was molded into a 2 mm thick test piece and its cross-section was observed with a digital microscope, the area ratio of aggregates derived from the conductive material with an equivalent circular diameter of 30 μm or more was 0.80% or less. A resin composition in which, when molded to a thickness of 2 mm, the absorption rate determined according to formula (A) at a frequency of 76.5 GHz is 50.0 to 100%. Formula (A) [Math 1] (In the above formula (A), R represents the return loss measured by the free-space method, and T represents the transmission loss measured by the free-space method.)

2. The resin composition according to claim 1, wherein the conductive material includes carbon nanotubes.

3. The resin composition according to claim 1 or 2, wherein the thermoplastic resin comprises a polybutylene terephthalate resin.

4. The resin composition according to any one of claims 1 to 3, wherein the content of the conductive substance in the resin composition is 0.01 to 3% by mass.

5. The thermoplastic resin includes a polybutylene terephthalate resin. The conductive material includes carbon nanotubes, The resin composition according to claim 1, wherein the content of the conductive substance in the resin composition is 0.01 to 3% by mass.

6. The thermoplastic resin comprises a polybutylene terephthalate resin and a polystyrene-based resin. The resin composition according to claim 1, wherein the conductive material includes carbon nanotubes.

7. The resin composition according to claim 6, wherein the carbon nanotube content in the resin composition is 0.01 to 3% by mass.

8. The resin composition has a sea-island structure having a sea region containing a large amount of the polybutylene terephthalate resin and an island region containing a large amount of the polystyrene resin, wherein 30% by mass or more of the resin components contained in the resin composition is polybutylene terephthalate resin. The total carbon nanotube content in the aforementioned sea region is greater than the total carbon nanotube content in each of the aforementioned island regions. The resin composition according to claim 6 or 7.

9. The conductive material includes carbon nanotubes, The resin composition according to any one of claims 1 to 8, wherein the relative permittivity of the resin composition at a frequency of 76.5 GHz is 4.50 or higher.

10. The resin composition according to claim 9, wherein the dielectric loss tangent of the resin composition at a frequency of 76.5 GHz is 0.10 or more.

11. The resin composition according to claim 9 or 10, wherein the carbon nanotube content in the resin composition is 0.01 to 3% by mass.

12. The thermoplastic resin comprises thermoplastic resin (A) and thermoplastic resin (B), The resin composition according to any one of claims 9 to 11, wherein the thermoplastic resin (B) is present in an amount of 1.0 to 100 parts by mass per 100 parts by mass of the thermoplastic resin (A).

13. The resin composition according to claim 12, wherein the polyester resin comprises a polybutylene terephthalate resin.

14. The resin composition according to any one of claims 11 to 13, wherein the thermoplastic resin (B) comprises a polystyrene resin.

15. The resin composition according to any one of claims 1 to 14, wherein the reflectance determined according to formula (B) at a frequency of 76.5 GHz is 40.0% or less when the resin composition is molded to a thickness of 2 mm. Formula (B) [Math 2] (In equation (B) above, R represents the return loss measured by the free-space method.)

16. The resin composition according to any one of claims 1 to 15, wherein when the resin composition is molded to a thickness of 2 mm, the transmittance determined according to formula (C) at a frequency of 76.5 GHz is 25.0% or less. Formula (C) [Math 3] (In the above formula (C), T represents the transmission attenuation measured by the free-space method.)

17. When the aforementioned resin composition is molded to a thickness of 2 mm, the surface resistance according to IEC 60093 is 1.0 × 10⁻⁶. ８ A resin composition according to any one of claims 1 to 16, wherein the Ω value is 1 or greater.

18. A resin composition according to any one of claims 1 to 17, for use as an electromagnetic wave absorber.

19. A molded article formed from the resin composition according to any one of claims 1 to 18.

20. An electromagnetic wave absorber formed from the resin composition according to any one of claims 1 to 18.

21. A method for producing a resin composition, comprising melt-kneading a polybutylene terephthalate resin and a styrene-based resin masterbatch of carbon nanotubes.

22. The method for producing the resin composition according to claim 21, wherein the resin composition is the resin composition according to any one of claims 5 to 8.

23. This involves melt-kneading a thermoplastic resin with carbon nanotubes that have been master-batched with the thermoplastic resin. A method for producing the resin composition according to any one of claims 9 to 15.

24. A method for producing a resin composition according to any one of claims 21 to 23, wherein the concentration of carbon nanotubes in the masterbatch is 1 to 50% by mass.

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