Resin composition, molded body, electromagnetic wave absorber, and method for producing resin composition

Abstract

To provide a resin composition that has a high electromagnetic wave absorption rate, a molded body, an electromagnetic wave absorber, and a method for manufacturing the resin composition.SOLUTION: A resin composition contains a polybutylene telephthalate resin, a polystyrene resin, and carbon nanotubes. There are also provided a molded body of the resin composition, and an electromagnetic wave absorber, and a method for manufacturing the resin composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition, a molded article, an electromagnetic wave absorber, and a method for producing a resin composition. [Background technology]

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

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-197048 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-155993 Summary of the Invention [Problem to be solved by the invention]

[0004] In millimeter-wave radar, the electromagnetic waves that pass through it are the biggest cause of malfunction, so there is a demand for resin compositions that have a high absorption rate of electromagnetic waves. The present invention aims to solve such problems and to provide a resin composition, a molded article, an electromagnetic wave absorber, and a method for producing a resin composition, which have a high absorption rate of electromagnetic waves. [Means for solving the problem]

[0005] In view of the above problems, the present inventors have conducted research and found that the above problems can be solved by blending a polystyrene resin and carbon nanotubes with a polybutylene terephthalate resin. Specifically, the above problems were solved by the following means. <1> A resin composition comprising a polybutylene terephthalate resin, a polystyrene-based resin, and carbon nanotubes. <2> The content of carbon nanotubes in the resin composition is 0.01 to 10% by mass. <1> The resin composition according to claim 1. <3> the resin composition exhibits 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-based resin, 30 mass% or more of the resin component contained in the resin composition is polybutylene terephthalate resin, and the content of carbon nanotubes contained in the sea region is greater than the content of carbon nanotubes contained in the island region; <1> or <2> The resin composition according to claim 1. <4> the polystyrene-based resin is derived from the carbon nanotube masterbatch; <1> ~ <3> The resin composition according to any one of the above. <5> When the resin composition is molded into a thickness of 2 mm, the absorption rate calculated according to formula (A) at a frequency of 76.5 GHz is 50.0 to 100%. <1> ~ <4> The resin composition according to any one of the above. Formula (A)

number

number

number

[0006] According to the present invention, it is possible to provide a resin composition, a molded article, an electromagnetic wave absorber, and a method for producing a resin composition, which have a high absorption rate of electromagnetic waves. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, an embodiment for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to only this embodiment. In this specification, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit. In this specification, various physical properties and characteristic values ​​are those at 23°C unless otherwise specified. In this specification, the weight average molecular weight and number average molecular weight are values ​​measured by GPC (gel permeation chromatography) in terms of polystyrene. In this specification, the unit of return loss and transmission loss is "dB" (decibels). If the standards shown in this specification differ depending on the year and the measurement method, etc., they will be based on the standards as of January 1, 2021, unless otherwise stated.

[0008] The resin composition of the present invention is characterized by containing a polybutylene terephthalate resin, a polystyrene-based resin, and carbon nanotubes. This configuration results in a resin composition with high absorption. The reason for this is presumed to be as follows: By blending carbon nanotubes into the polybutylene terephthalate resin, a certain level of electromagnetic wave absorption is achieved. In this embodiment, it is presumed that further blending a styrene-based resin allows the carbon nanotubes to be more effectively dispersed in the polybutylene terephthalate resin, thereby increasing the absorption rate of the resulting resin composition. Furthermore, by adopting the configuration of this embodiment, the reflectance and transmittance of the resin composition to electromagnetic waves can be reduced, and the tensile properties, particularly the tensile strain, can be improved. Furthermore, the above effect can be achieved more effectively by forming carbon nanotubes into a masterbatch with a styrene-based resin and blending it with a polybutylene terephthalate resin. The mechanism is speculative, but it is speculated that when the polybutylene terephthalate resin and the styrene-based resin masterbatch of carbon nanotubes are melt-kneaded, the carbon nanotubes leave the styrene-based resin and penetrate into the polybutylene terephthalate resin, where they diffuse. The driving force at this time breaks up the aggregation of the carbon nanotubes, allowing them to diffuse more effectively in the polybutylene terephthalate resin.

[0009] <Polybutylene terephthalate resin> The resin composition of the present embodiment contains a polybutylene terephthalate resin. By using the polybutylene terephthalate resin, a resin composition having excellent mechanical properties can be obtained. Polybutylene terephthalate resin is a polyester resin having a structure in which terephthalic acid units and 1,4-butanediol units are ester-bonded, and includes not only polybutylene terephthalate resin (homopolymer), but also polybutylene terephthalate copolymers containing other copolymerization components other than terephthalic acid units and 1,4-butanediol units, and mixtures of homopolymers and polybutylene terephthalate copolymers.

[0010] The polybutylene terephthalate resin may contain one or more dicarboxylic acid units other than terephthalic acid. Specific examples of other 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 the polybutylene terephthalate resin used in this embodiment, terephthalic acid units preferably account for 80 mol % or more, and more preferably 90 mol % or more, of all dicarboxylic acid units.

[0011] The diol unit may contain one or more other diol units in addition to 1,4-butanediol. Specific examples of other diol units include aliphatic or alicyclic diols having 2 to 20 carbon atoms, bisphenol derivatives, etc. 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 adduct diol of bisphenol A. In addition to the above-mentioned bifunctional monomers, small amounts of trifunctional monomers such as trimellitic acid, trimesic acid, pyromellitic acid, pentaerythritol, and trimethylolpropane can also be used in combination to introduce a branched structure, or monofunctional compounds such as fatty acids to adjust the molecular weight. In the polybutylene terephthalate resin used in this embodiment, 1,4-butanediol units preferably account for 80 mol % or more, and more preferably 90 mol % or more, of all diol units.

[0012] As described above, the polybutylene terephthalate resin is preferably a polybutylene terephthalate homopolymer obtained by polycondensation of terephthalic acid and 1,4-butanediol. Alternatively, the polybutylene terephthalate copolymer may contain, as the carboxylic acid unit, one or more dicarboxylic acids other than the above-mentioned terephthalic acid and / or, as the diol unit, one or more diols other than the above-mentioned 1,4-butanediol. 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, polyester ether resins copolymerized with polytetramethylene glycol are preferred. These copolymers refer to those in which the copolymerization amount is 1 mol% or more and less than 50 mol% of all 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%. By setting the copolymerization amount in this range, fluidity, toughness, and tracking resistance tend to be easily improved, which is preferable.

[0013] The amount of terminal carboxyl groups in the polybutylene terephthalate resin may be appropriately selected and determined, but is typically 60 eq / ton or less, preferably 50 eq / ton or less, and more preferably 30 eq / ton or less. By setting the amount below the upper limit, alkali resistance and hydrolysis resistance tend to be improved. The lower limit of the amount of terminal carboxyl groups is not particularly specified, but is typically 10 eq / ton or more, taking into account the productivity of polybutylene terephthalate resin production.

[0014] The amount of terminal carboxyl groups in the polybutylene terephthalate resin is determined by dissolving 0.5 g of the polybutylene terephthalate resin in 25 mL of benzyl alcohol and titrating the solution with a 0.01 mol / L benzyl alcohol solution of sodium hydroxide. The amount of terminal carboxyl groups can be adjusted by any conventional method, such as adjusting the polymerization conditions, such as the raw material charge ratio, polymerization temperature, and pressure reduction, or by reacting a terminal blocking agent.

[0015] The intrinsic viscosity of the polybutylene terephthalate resin is preferably 0.5 to 2 dL / g. From the viewpoint of moldability and mechanical properties, an intrinsic viscosity in the range of 0.6 to 1.5 dL / g is more preferable. By making the intrinsic viscosity 0.5 dL / g or more, the mechanical strength of the resulting resin composition tends to be further improved. Furthermore, by making the intrinsic viscosity 2 dL / g or less, the fluidity of the resin composition tends to be further improved, and moldability tends to be improved. The intrinsic viscosity of the polybutylene terephthalate resin is a value measured at 30° C. in a mixed solvent of tetrachloroethane and phenol in a 1:1 (mass ratio).

[0016] Polybutylene terephthalate resin can be produced by batch or continuous melt polymerization of a dicarboxylic acid component containing terephthalic acid as the main component or an ester derivative thereof with a diol component containing 1,4-butanediol as the main component. 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-state polymerization under a nitrogen gas flow or reduced pressure. The polybutylene terephthalate resin is preferably one obtained by a production method in which a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of 1,4-butanediol are subjected to continuous melt polycondensation.

[0017] The catalyst used in carrying out the esterification reaction may be a conventionally known catalyst, such as a titanium compound, a tin compound, a magnesium compound, or a calcium compound. Among these, titanium compounds are particularly preferred. Specific examples of titanium compounds used as esterification catalysts include titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, and titanium phenolates such as tetraphenyl titanate.

[0018] The content of polybutylene terephthalate resin in the resin composition of this embodiment 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. In particular, when a reinforcing material is not contained, the content of polybutylene terephthalate resin in the resin composition is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and may even be 90% by mass or more. By setting the content to be equal to or greater than the above lower limit, chemical resistance tends to be further improved. Furthermore, the content of polybutylene terephthalate resin in the resin composition is preferably 98% by mass or less. In particular, when a reinforcing material is contained, the content of polybutylene terephthalate resin in the resin composition is preferably 80% by mass or less, more preferably 75% by mass or less. By setting the content to be equal to or less than the above upper limit, the amount of warpage of the molded article tends to be more effectively reduced. The resin composition of the present embodiment may contain only one type of polybutylene terephthalate resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0019] <Polystyrene resin> The resin composition of the present embodiment contains a polystyrene-based resin. By using a polystyrene-based resin, carbon nanotubes can be more easily diffused into the polybutylene terephthalate resin, which tends to improve the electromagnetic wave absorption of the resin composition. Furthermore, the electromagnetic wave transmittance and reflectance of the resin composition tend to be lower.

[0020] Examples of polystyrene-based resins include homopolymers of styrene-based monomers and copolymers of styrene-based monomers and monomers copolymerizable with styrene-based monomers. Examples of styrene-based monomers include styrene, α-methylstyrene, chlorostyrene, methylstyrene, and tert-butylstyrene. In the styrene-based resin of this embodiment, 50 mol % or more of the monomer units are styrene-based monomers. More specific examples of polystyrene resins include polystyrene resin, acrylonitrile-styrene copolymer (AS resin), high impact polystyrene resin (HIPS, butadiene rubber-containing polystyrene), 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), and styrene-IPN type rubber copolymer. In this embodiment, the styrene-based resin is preferably an acrylonitrile-styrene copolymer (AS resin), high-impact polystyrene resin (HIPS, butadiene rubber-containing polystyrene), 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, and more preferably a high-impact polystyrene resin (HIPS, butadiene rubber-containing polystyrene). It is believed that such a polystyrene-based resin acts as a driving force for the diffusion of carbon nanotubes into the polybutylene terephthalate resin, thereby breaking down carbon nanotube aggregation. As a result, it is believed that the dispersion of carbon nanotubes is effectively promoted. In particular, when the polystyrene-based resin is derived from a carbon nanotube masterbatch, the diffusion of the carbon nanotubes tends to be more effectively promoted.

[0021] When the polystyrene resin contains a rubber component, the content of the rubber component 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, and a rubber component content of 50% by mass or less is preferred because it tends to improve flame retardancy. The average particle size of the rubber component 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, and an average particle size of 10 μm or less tends to improve appearance, which is preferred.

[0022] The weight-average molecular weight of the polystyrene resin is usually 50,000 or more, preferably 100,000 or more, more preferably 150,000 or more, and usually 500,000 or less, preferably 400,000 or less, more preferably 300,000 or less. The number-average molecular weight is usually 10,000 or more, preferably 30,000 or more, more preferably 50,000 or more, and preferably 500,000 or less, more preferably 300,000 or less.

[0023] The melt flow rate (MFR) of the polystyrene resin, measured in accordance with JIS K7210 (temperature 200°C, load 5 kgf), is preferably 0.1 to 30 g / 10 min, more preferably 0.5 to 25 g / 10 min. An MFR of 0.1 g / 10 min or more tends to improve fluidity, while an MFR of 30 g / 10 min or less tends to improve impact resistance.

[0024] Examples of methods for producing such polystyrene resins include known methods such as emulsion polymerization, solution polymerization, suspension polymerization, and bulk polymerization.

[0025] The content of the polystyrene-based resin in the resin composition of this embodiment is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 3.0 parts by mass or more, even more preferably 4.0 parts by mass or more, and even more preferably 4.5 parts by mass or more, relative to 100 parts by mass of the polybutylene terephthalate resin. By setting the content at or above the lower limit, the electromagnetic wave absorption performance tends to be improved and the warpage of the resulting molded article tends to be effectively reduced. Furthermore, the content of the polystyrene-based resin is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10.0 parts by mass or less, even more preferably 7 parts by mass or less, and even more preferably 5.0 parts by mass or less, relative to 100 parts by mass of the polybutylene terephthalate resin. By setting the content at or below the upper limit, the chemical resistance tends to be further improved. The resin composition of the present embodiment may contain only one type of styrene-based resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0026] <Carbon nanotubes> The resin composition of the present embodiment contains carbon nanotubes, which can impart electromagnetic wave absorbing properties to the resin composition. The carbon nanotubes used in this embodiment are single-walled carbon nanotubes and / or multi-walled carbon nanotubes, and preferably contain at least multi-walled carbon nanotubes. Carbon materials partially having a carbon nanotube structure can also be used. The carbon nanotubes are not limited to a cylindrical shape, and may have a coiled shape with a spiral at a pitch of 1 μm or less. Carbon nanotubes are commercially available, and examples thereof include carbon nanotubes available from Bayer MaterialScience, Nanosil, Showa Denko K.K., and Hyperion Catalysis International, Inc. In addition to the name carbon nanotubes, they are also called graphite fibrils, carbon fibrils, etc. The diameter (number average fiber diameter) of the carbon nanotubes is preferably 0.5 to 100 nm, more preferably 1 to 30 nm. From the viewpoint of imparting good electromagnetic wave absorption properties, the aspect ratio of the carbon nanotubes is preferably 5 or more, more preferably 50 or more. There is no particular upper limit, but it is, for example, 500 or less. The carbon nanotubes may be blended as a masterbatch. In this case, the content of the carbon nanotubes in the masterbatch is preferably 1% by mass or more, more preferably 5% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and even more preferably 20% by mass or less. By adjusting the content to within the above upper and lower limits, the dispersibility of the carbon nanotubes in the polybutylene terephthalate resin tends to be further improved. The resin used in the masterbatch is a polyester resin (preferably a polybutylene terephthalate resin) or a polystyrene-based resin, and a polystyrene-based resin is more preferred.

[0027] The content of 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, and may be 0.2% by mass or more, or even 0.4% by mass or more. By making the content equal to or greater than the lower limit, electromagnetic wave absorption properties are effectively exhibited. Furthermore, the content of 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, or even 1% by mass or less. By making the content equal to or less than the upper limit, the fluidity of the resin tends to be further improved.

[0028] The resin composition of this embodiment preferably contains 0.1 parts by mass or more of carbon nanotubes per 100 parts by mass of polybutylene terephthalate resin. By setting the content at or above the lower limit, electromagnetic wave absorption properties are effectively exhibited. The resin composition of this embodiment preferably contains 10.0 parts by mass or less of carbon nanotubes per 100 parts by mass of polybutylene terephthalate 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 2.5 parts by mass or less, particularly 1.5 parts by mass or less. Setting the content at or below the upper limit tends to further improve the fluidity of the resin. The resin composition of the present embodiment may contain only one type of carbon nanotube, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0029] <Reinforcement material> The resin composition of the present embodiment may contain a reinforcing material, which can improve the mechanical strength of the resulting molded article. The reinforcing material that can be used in this embodiment is not particularly limited in terms of type, and may be any of fibers, fillers, beads, etc., with fibers being preferred.

[0030] When the reinforcing material is a fiber, it may be a short fiber or a long fiber. When the reinforcing material is short fibers, fillers, beads, or the like, the resin composition of this embodiment may be in the form of pellets, powdered pellets, or a film formed from the pellets. When the reinforcing material is a long fiber, examples of the reinforcing material include so-called long fiber for unidirectional (UD) materials, sheet-like long fiber such as woven fabric and knitted fabric, etc. When using these long fibers, the components other than the reinforcing material of the resin composition of the present embodiment can be impregnated into the sheet-like long fiber reinforcing material to form a sheet-like resin composition (for example, a prepreg).

[0031] 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, polyparaphenylene benzobisoxazole, and ultra-high molecular weight polyethylene, with glass being preferred.

[0032] The resin composition of the present embodiment preferably contains glass fibers as a reinforcing material. The glass fiber is 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 fiber refers to a fibrous material whose cross section, cut perpendicular to the longitudinal direction, is circular or polygonal. The number-average fiber diameter of the single fiber of the glass fiber is usually 1 to 25 μm, preferably 5 to 17 μm. By making the number-average fiber diameter 1 μm or more, the molding processability of the resin composition tends to be further improved. By making the number-average fiber diameter 25 μm or less, the appearance of the obtained molded article tends to be improved, and the reinforcing effect also tends to be improved. The glass fiber may be a single fiber or a plurality of single fibers twisted together. The glass fiber may be in the form of a glass roving obtained by continuously winding a single fiber or a plurality of twisted fibers, a chopped strand cut to a length of 1 to 10 mm (i.e., glass fiber having a number average fiber length of 1 to 10 mm), or a milled fiber pulverized to a length of about 10 to 500 μm (i.e., glass fiber having a number average fiber length of 10 to 500 μm), but chopped strand cut to a length of 1 to 10 mm is preferred. Glass fibers of different forms can also be used in combination. Glass fibers having an irregular cross-sectional shape are also preferred. The irregular cross-sectional shape has an oblateness, which is the ratio of the major axis to the minor axis of the cross section perpendicular to the longitudinal direction of the fiber, of, for example, 1.5 to 10, preferably 2.5 to 10, more preferably 2.5 to 8, and even more preferably 2.5 to 5.

[0033] The glass fiber may be surface-treated with, for example, a silane-based compound, an epoxy-based compound, a urethane-based compound, or the like, or may be oxidized, in order to improve its affinity with the resin component, as long as the properties of the resin composition of this embodiment are not significantly impaired.

[0034] When the resin composition of this embodiment contains a reinforcing material (preferably glass fiber), the content thereof 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, relative to 100 parts by mass of the polybutylene terephthalate resin. By ensuring that the content is equal to or greater than the above-mentioned lower limit, the mechanical strength of the resulting molded article tends to be further increased. 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, relative to 100 parts by mass of the polybutylene terephthalate resin. By ensuring that the content is equal to or less than the above-mentioned upper limit, the appearance of the molded article tends to be improved, and the flowability of the resin composition tends to be further improved.

[0035] The content of the reinforcing material (preferably glass fiber) in the resin composition of this embodiment 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 in the resin composition. The content of the reinforcing material (preferably glass fiber) in the resin composition 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. By setting the content at or above the lower limit, mechanical strength tends to be further increased. By setting the content at or below the upper limit, the appearance of the molded article tends to be improved, and the fluidity of the resin composition when melted tends to be further improved. The resin composition of the present embodiment may contain only one type of reinforcing material (preferably glass fiber), or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0036] <Other ingredients> The resin composition of this embodiment may contain other components in addition to those described above, as necessary, as long as the desired physical properties are not significantly impaired. Examples of other components include thermoplastic resins other than polybutylene terephthalate resin and styrene-based resin, various resin additives, etc. Note that one type of other component may be contained, or two or more types may be contained in any combination and ratio. Examples of other thermoplastic resins include polyamide resins, polycarbonate 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, and polymethacrylate resins. However, in this embodiment, a configuration that is substantially free of other thermoplastic resins may also be used. "Substantially free" means that the content of other thermoplastic resins per 100 parts by mass of polybutylene terephthalate resin is 5.00 parts by mass or less, preferably 2.80 parts by mass or less, more preferably 2.00 parts by mass or less, and even more preferably 1.00 parts by mass or less.

[0037] Examples of various resin additives include stabilizers, mold release agents, flame retardants, reactive compounds, pigments, dyes, UV absorbers, antistatic agents, antifogging agents, antiblocking agents, flow improvers, plasticizers, dispersants, antibacterial agents, etc. The resin composition of the present embodiment preferably contains at least one of stabilizers and mold release agents. The resin composition of this embodiment is prepared so that the total of the polybutylene terephthalate resin, polystyrene-based resin, carbon nanotubes, and other optional components is 100% by mass. In the resin composition of this embodiment, the total of the polybutylene terephthalate resin, styrene-based resin, carbon nanotubes, and reinforcing material (preferably glass fiber) preferably accounts for 95% by mass or more of the resin composition. Furthermore, in the resin composition of this embodiment, the total of the polybutylene terephthalate resin, styrene-based resin, carbon nanotubes, reinforcing material (preferably glass fiber), stabilizer, and mold release agent preferably accounts for 99% by mass or more of the resin composition.

[0038] <<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 preferred to use a hindered phenol compound and a phosphorus compound in combination. As the stabilizer, specifically, the descriptions in paragraphs 0046 to 0057 of JP 2018-070722 A, the descriptions in paragraphs 0030 to 0037 of JP 2019-056035 A, and the descriptions in paragraphs 0066 to 0078 of WO 2017 / 038949 A can be referred to, the contents of which are incorporated herein by reference.

[0039] The resin composition of this embodiment preferably contains 0.01 parts by mass or more of the stabilizer relative to 100 parts by mass of the polybutylene terephthalate resin, more preferably 0.05 parts by mass or more, and even more preferably 0.08 parts by mass or more. The upper limit of the amount of the stabilizer contained 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, relative to 100 parts by mass of the polybutylene terephthalate resin. The resin composition of the present embodiment may contain only one stabilizer, or may contain two or more stabilizers. When two or more stabilizers are contained, the total amount is preferably in the above range.

[0040] <<Release Agent>> The resin composition of the present embodiment preferably contains a release agent. As the release agent, a wide variety of known release agents can be used, and preferred are esters of aliphatic carboxylic acids, paraffin wax, polystyrene wax, and polyolefin wax, with polyethylene wax being more preferred. For details of the release agent, please refer to the descriptions in paragraphs 0115 to 0120 of JP-A No. 2013-007058, paragraphs 0063 to 0077 of JP-A No. 2018-070722, and paragraphs 0090 to 0098 of JP-A No. 2019-123809, the contents of which are incorporated herein by reference.

[0041] The resin composition of this embodiment preferably contains 0.01 parts by mass or more of the release agent relative to 100 parts by mass of the polybutylene terephthalate resin, more preferably 0.08 parts by mass or more, and even more preferably 0.2 parts by mass or more. The upper limit of the amount of the release agent contained relative to 100 parts by mass of the polybutylene terephthalate resin 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. The resin composition may contain only one type of release agent, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

[0042] <Sea-island structure> On the other hand, the resin composition of this embodiment typically exhibits a sea-island structure having a sea region rich in polybutylene terephthalate resin and island regions rich in polystyrene-based resin, in which 30% by mass or more (preferably 45% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 85% by mass or more) of the resin components contained in the resin composition is polybutylene terephthalate resin, and the content of carbon nanotubes in the sea region is higher than the content of carbon nanotubes in the island regions. This type of structure tends to enhance the electromagnetic wave absorption of the resin composition. It is believed that this sea-island structure is due to the poor compatibility between polybutylene terephthalate resin and polystyrene-based resin and the fact that carbon nanotubes are inherently more compatible with polybutylene terephthalate resin than polystyrene-based resin.

[0043] <Physical properties of resin composition> The resin composition of this embodiment preferably has a high absorption rate of electromagnetic waves. Specifically, the resin composition of this embodiment preferably has an absorption rate of 50.0 to 100% at a frequency of 76.5 GHz calculated according to formula (A) when molded into a 2 mm thickness (preferably, 100 mm × 100 mm × 2 mm thickness). Formula (A)

number

[0044] The absorbency is preferably 53.0% or more, more preferably 55.0% or more, even more preferably 58.0% or more, and even more preferably 60.0% or more. The upper limit is ideally 100%, but even if it is 90.0% or less, the required performance is sufficiently met.

[0045] The resin composition of this embodiment preferably has low reflectance of electromagnetic waves. Specifically, the resin composition of this embodiment preferably has a reflectance of 40.0% or less at a frequency of 76.5 GHz, as calculated according to formula (B), when molded to a thickness of 2 mm (preferably, 100 mm x 100 mm x 2 mm). Formula (B)

number

[0046] The reflectance is preferably 35.0% or less, more preferably 30.0% or less, and even more preferably 26.0% or less. The lower limit is ideally 0%, but even if it is 5.0% or more, or even 10.0% or more, the required performance is sufficiently met.

[0047] The resin composition of the present embodiment preferably has low transmittance. The resin composition of this embodiment preferably has a transmittance of 25.0% or less at a frequency of 76.5 GHz as determined according to formula (C) when molded into a 2 mm thick piece (preferably 100 mm x 100 mm x 2 mm thick piece). Formula (C)

number

[0048] The transmittance is preferably 23.0% or less, and more preferably 20.0% or less. The lower limit is ideally 0%, but even if it is 5.0% or more, the required performance is sufficiently met.

[0049] The resin composition of the present embodiment preferably satisfies all of the absorptance calculated according to the above formula (A), the reflectance calculated according to the above formula (B), and the transmittance calculated according to the above formula (C).

[0050] The resin composition of this embodiment preferably has a relative dielectric constant of 4.50 or more, more preferably 5.00 or more, at a frequency of 76.5 GHz. The upper limit of the relative dielectric constant is practically 8.00 or less. The resin composition of this embodiment preferably has a dielectric loss tangent of 0.10 or more, more preferably 0.18 or more, at a frequency of 76.5 GHz. The lower limit of the dielectric loss tangent is not particularly limited, but may be, for example, 0.50 or less, or even 0.40 or less.

[0051] The resin composition of the present embodiment preferably has excellent mechanical strength. The resin composition of this embodiment preferably has particularly excellent tensile properties. For example, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (thickness 4 mm), the tensile strength at maximum point measured according to ISO 527-1 and ISO 527-2 is preferably 40 MPa or more, more preferably 50 MPa or more. There is no particular upper limit for the tensile strength at maximum point, but for example, even a value of 200 MPa or less is still practical. Furthermore, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (thickness 4 mm), the tensile modulus measured in accordance with ISO 527-1 and ISO 527-2 is preferably 1500 MPa or more, more preferably 1800 MPa or more, and even more preferably 2000 MPa or more. There is no particular upper limit to the tensile modulus, but, for example, even a value of 12000 MPa or less is within a practical level. Furthermore, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (thickness 4 mm), 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 3.0% or more. There is no particular upper limit for the tensile strain, but, for example, a value of 30% or less is also practical.

[0052] Furthermore, the resin composition of the present embodiment preferably has excellent bending properties. Specifically, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (thickness 4 mm), the bending strength is preferably 50 MPa or more, more preferably 70 MPa or more. The upper limit of the bending strength is not particularly specified, but for example, 300 MPa or less is practical. Furthermore, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (thickness 4 mm), the flexural modulus is preferably 1,500 MPa or more, more preferably 2,000 MPa or more. The upper limit of the flexural modulus is not particularly specified, but for example, 15,000 MPa or less is practical.

[0053] Furthermore, the resin composition of the present embodiment preferably has excellent impact resistance. Specifically, when the resin composition of this embodiment is molded into an ISO multipurpose test piece (thickness 4 mm), the notched Charpy impact strength according to the ISO179 standard is 2.0 kJ / m 2 It is preferable that the concentration is 3.0 kJ / m or more. 2 The upper limit of the notched Charpy impact strength is not particularly limited, but is preferably 50 kJ / m or more. 2 The following is practical:

[0054] The resin composition of the present embodiment also has a surface resistance of 1.0×10 when molded into a test piece having a thickness of 2 mm (preferably, 100 mm×100 mm×2 mm) according to IEC 60093. 11 Ω or more, and 1.0 × 10 16 It is preferably Ω or less. The resin composition of the present embodiment further has a volume resistivity of 1.0×10 in accordance with IEC 60093 on a test piece of 2 mm thickness (preferably, 100 mm×100 mm×2 mm thickness). 10 It is preferable that the resistivity is Ω·cm or more, and 1.0×10 17 It is preferable that the resistivity is Ω·cm or less. The details of the measurement method are as described in the Examples.

[0055] <Method of manufacturing resin composition> The resin composition of this embodiment can be produced by a conventional method for producing a resin composition containing a thermoplastic resin. For example, it can be obtained by melt-kneading a polybutylene terephthalate resin, a styrene-based resin, and carbon nanotubes. The method for producing the resin composition of this embodiment preferably includes melt-kneading a polybutylene terephthalate resin and a styrene-based resin masterbatch of carbon nanotubes. More specifically, the resin composition of this embodiment is produced by feeding polybutylene terephthalate resin, a styrene-based resin, and carbon nanotubes (preferably a styrene-based resin masterbatch of polybutylene terephthalate resin and carbon nanotubes), and other components (glass fibers, etc.) that are blended as needed, into an extruder and melt-kneading them. The components may be mixed in advance and fed all at once to the extruder, or the components may be mixed in advance without mixing, or only a portion of the components may be mixed in advance, and then fed to the extruder using a feeder. The extruder may be a single-screw extruder or a twin-screw extruder. When glass fibers are compounded, they are preferably fed from a side feeder midway through the cylinder of the extruder. The heating temperature during melt-kneading can usually be appropriately selected from the range of 170 to 350°C.

[0056] <Method of manufacturing molded body> A molded article, particularly an electromagnetic wave absorber, is formed from the resin composition of this embodiment. The method for producing the molded article in this embodiment is not particularly limited, and any molding method commonly used for resin compositions containing thermoplastic resins can be used. Examples include injection molding, ultra-high speed injection molding, injection compression molding, two-color molding, gas-assisted hollow molding, molding using a heat-insulating mold, molding using a rapidly heated mold, foam molding (including supercritical fluid), insert molding, IMC (in-mold coating molding), extrusion molding, sheet molding, thermoforming, rotational molding, lamination molding, press molding, blow molding, etc., and among these, injection molding is preferred.

[0057] <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 used for an electromagnetic wave absorber (also referred to as an electromagnetic wave absorbing member), more preferably for an electromagnetic wave absorber having a frequency of at least 60 to 90 GHz, and even more preferably for an electromagnetic wave absorber having a frequency of at least 70 to 80 GHz. Such an electromagnetic wave absorber is preferably used for radar applications. Specifically, it is used for housings, covers, etc. for millimeter-wave radar. The electromagnetic wave absorber of this embodiment can be suitably used for in-vehicle millimeter-wave radars used in automatic brake control devices, inter-vehicle distance control devices, pedestrian accident reduction steering devices, erroneous transmission suppression control devices, devices for suppressing acceleration when pedal misapplication occurs, devices for warning of approaching vehicles, lane keeping assist devices, rear-end collision prevention warning devices, parking assist devices, devices for warning of obstacles around the vehicle, etc.; railway and aviation millimeter-wave radars used in platform monitoring / railroad crossing obstacle detection devices, in-train content transmission devices, tram / railroad collision prevention devices, foreign object detection devices in runways, etc.; millimeter-wave radars for transportation infrastructure such as intersection monitoring devices and elevator monitoring devices; millimeter-wave radars for various security devices; millimeter-wave radars for medical and nursing care such as systems for watching over children and the elderly; millimeter-wave radars for transmitting various information content; etc. [Example]

[0058] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed without departing 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 the like, measurements can be made using other instruments with equivalent performance.

[0059] raw material The following raw materials were used: In Table 1 below, HIPS stands for high impact polystyrene (polystyrene containing butadiene rubber), PBT stands for polybutylene terephthalate resin, PA stands for polyamide resin, and CNT stands for carbon nanotubes. [Table 1]

[0060] Examples 1 to 3, Comparative Examples 1 and 2 <Production of Resin Composition (Pellets)> The components listed in Table 1, excluding the reinforcing material, were placed in a stainless steel tumbler and mixed for 1 hour. The resulting mixture was fed into a co-rotating intermeshing twin-screw extruder (Japan Steel Works, Ltd., "TEX-30α," 32 mm screw diameter, L / D = 42) through the main feed port. The barrel temperature of the first mixing section was set to 260°C for plasticization. The reinforcing material (glass fiber) was fed through a side feeder in the proportions shown in Table 2. The barrel temperature after adding the reinforcing material was set to 250°C, and the mixture was melt-mixed at a discharge rate of 40 kg / h and a screw rotation speed of 200 rpm. The mixture was then extruded as a strand using a four-hole nozzle (circular, 4 mm diameter, 1.5 cm long). The extruded strand was introduced into a water bath for cooling and then cut into a pelletizer to obtain a resin composition (pellets).

[0061] <76.5GHz electromagnetic wave absorption rate, reflectance, transmittance> The pellets obtained above were injection molded in an injection molding machine ("NEX80" manufactured by Nissei Plastic Industrial Co., Ltd.) at a cylinder temperature of 260°C and a mold temperature of 80°C to obtain test pieces measuring 100 mm x 100 mm x 2 mm thick. Using the test pieces obtained, the absorptance calculated according to formula (A), the reflectance calculated according to formula (B), and the transmittance calculated according to formula (C) at a frequency of 76.5 GHz were measured as follows. For the measurements, a Keysight network analyzer "N5252A" was used. The measurement was performed by placing the test piece so that the TD (transverse direction) direction of the injection molded article was parallel to the direction of the electric field. Formula (A)

number

[0062] Formula (B)

number

[0063] Formula (C)

number

[0064] <Electromagnetic wave absorption performance evaluation> The electromagnetic wave absorption performance was evaluated as follows: A if all three of the absorbance, reflectance, and transmittance were satisfied; B if at least the absorbance met the following criteria (except for cases that fell under A); and C if neither A nor B was satisfied. Judgment criteria Absorption rate is 50.0% or more Reflectivity is 40.0% or less Transmittance is 25.0% or less

[0065] <Relative permittivity and dielectric loss tangent> The pellets obtained above were injection molded in an injection molding machine (NEX80 manufactured by Nissei Plastic Industrial Co., Ltd.) at a cylinder temperature of 260°C and a mold temperature of 80°C to obtain test pieces measuring 100 mm x 100 mm x 2 mm thick. The dielectric constant and dielectric loss tangent at a frequency of 76.5 GHz were determined using the obtained test specimen. The test specimen was placed so that the TD (transverse direction) direction of the injection-molded article was parallel to the electric field direction. The measurements were performed using a Keysight network analyzer "N5252A," and the values ​​of the relative permittivity and dielectric loss tangent were estimated using Keysight's "N1500A Materials Measurement Suite," with each value calculated using the "NIST Precision" calculation model.

[0066] <Tensile properties> The resin pellets obtained above were dried at 120°C for 5 hours, and then ISO multipurpose test specimens (thickness 4 mm) were injection molded using an injection molding machine ("J85AD" manufactured by The Japan Steel Works, Ltd.) under conditions of a cylinder temperature of 250°C and a mold temperature of 80°C. Using the molded multipurpose ISO multipurpose test specimens, the maximum tensile strength (unit: MPa), tensile modulus (unit: MPa), and tensile strain (unit: %) were measured in accordance with ISO527-1 and ISO527-2.

[0067] <Bending properties> The resin pellets obtained above were dried at 120°C for 5 hours, and then ISO multipurpose test specimens (thickness 4 mm) were injection molded using an injection molding machine ("J85AD" manufactured by The Japan Steel Works, Ltd.) under conditions of a cylinder temperature of 250°C and a mold temperature of 80°C. The flexural strength (unit: MPa) and flexural modulus (unit: MPa) were measured using the molded multipurpose ISO multipurpose test specimens in accordance with ISO178.

[0068] <Notched Charpy impact strength> The resin pellets obtained above were dried at 120°C for 5 hours, and then ISO multipurpose test specimens (thickness 4 mm) were injection molded using an injection molding machine ("J85AD" manufactured by The Japan Steel Works, Ltd.) under conditions of a cylinder temperature of 250°C and a mold temperature of 80°C. According to ISO179 standard, the ISO multipurpose test piece obtained above was cut to a specified size and shape, and the Charpy impact strength (notched) was measured. The unit is kJ / m 2 As shown.

[0069] <Surface resistance> The pellets obtained above were injection molded in an injection molding machine (NEX80 manufactured by Nissei Plastic Industrial Co., Ltd.) at a cylinder temperature of 260°C and a mold temperature of 80°C to obtain test pieces measuring 100 mm x 100 mm x 2 mm thick. The surface resistance (unit: Ω) of the obtained test piece was measured in accordance with IEC60093. For the measurements, an "R8340 ULTRA HIGH RESISTANCE METER" manufactured by ADVANTEST was used.

[0070] <Volume resistance> The pellets obtained above were injection molded in an injection molding machine (NEX80 manufactured by Nissei Plastic Industrial Co., Ltd.) at a cylinder temperature of 260°C and a mold temperature of 80°C to obtain test pieces measuring 100 mm x 100 mm x 2 mm thick. Using the obtained test pieces, the volume resistivity (unit: Ω·cm) was measured in accordance with IEC60093. For the measurements, an "R8340 ULTRA HIGH RESISTANCE METER" manufactured by ADVANTEST was used.

[0071] [Table 2]

[0072] In Table 2 above, the CNT content refers to the blending ratio (mass%) of CNTs (carbon nanotubes) in the resin composition, and the GF content refers to the blending ratio (mass%) of glass fibers 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 also had low electromagnetic wave transmittance and reflectance. Furthermore, molded articles formed from the resin composition of the present invention had excellent mechanical strength, particularly excellent bending strain characteristics. Furthermore, these properties were particularly effectively achieved when the resin composition of the present invention was produced using a styrene-based resin masterbatch of carbon nanotubes.

Claims

1. A resin composition comprising a polybutylene terephthalate resin, a polystyrene-based resin, and carbon nanotubes, wherein the polystyrene-based resin comprises a butadiene rubber-containing polystyrene.

2. The resin composition according to claim 1, wherein the content of carbon nanotubes in the resin composition is 0.01 to 10% by mass.

3. The resin composition according to claim 1 or 2, wherein the absorptivity calculated according to formula (A) at a frequency of 76.5 GHz when the resin composition is molded to a thickness of 2 mm is 50.0 to 100%. Formula (A) [Equation 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.)

4. The resin composition according to any one of claims 1 to 3, wherein the reflectance calculated according to formula (B) at a frequency of 76.5 GHz when the resin composition is molded to a thickness of 2 mm is 40.0% or less. Formula (B) [Equation 2] (In the above formula (B), R represents the return loss measured by the free space method.)

5. The resin composition according to any one of claims 1 to 4, wherein the transmittance calculated according to formula (C) at a frequency of 76.5 GHz when molded to a thickness of 2 mm is 25.0% or less. Formula (C) [Equation 3] (In the above formula (C), T represents the transmission attenuation measured by the free space method.)

6. The resin composition according to any one of claims 1 to 5, wherein the carbon nanotubes include multi-walled carbon nanotubes.

7. The resin composition according to any one of claims 1 to 6, which is used for an electromagnetic wave absorber.

8. A molded article formed from the resin composition according to any one of claims 1 to 7.

9. An electromagnetic wave absorber formed from the resin composition according to any one of claims 1 to 7.

10. A method for producing a resin composition, comprising melt-kneading a polybutylene terephthalate resin and a styrene-based resin masterbatch of carbon nanotubes, The method for producing a resin composition, wherein the resin composition is the resin composition according to any one of claims 1 to 7.

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