JP7790136B2 - Resin composition, pellets, molded body, electromagnetic wave absorber, and method for producing resin composition - Google Patents

Description

The present invention relates to a resin composition, pellets, molded articles, electromagnetic wave absorbers, and a method for producing a resin composition.

Millimeter-wave radar emits millimeter-wave radio waves with wavelengths of 1 to 10 mm at frequencies of 30 to 300 GHz, particularly 60 to 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.

Japanese Patent Application Laid-Open No. 2019-197048 JP 2010-155993 A

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 these problems and to provide a resin composition, pellets, molded body, electromagnetic wave absorber, and method for producing the resin composition, which have a high absorption rate of electromagnetic waves.

In light of the above-mentioned problems, the present inventors have conducted research and found that the electromagnetic wave absorption rate of a resin composition obtained by blending carbon nanotubes with a polyester resin having an intrinsic viscosity of 0.87 to 2.00 dL/g can be improved by blending a polyamide resin therewith.
Specifically, the above problems were solved by the following means.
<1> 0.1 to 10.0 parts by mass of a polyamide resin relative to 100 parts by mass of a polyester resin having an intrinsic viscosity of 0.87 to 2.00 dL/g;
A resin composition comprising carbon nanotubes.
<2> The resin composition according to <1>, wherein the carbon nanotubes are derived from carbon nanotubes masterbatched with a polyamide resin.
<3> The resin composition according to <2>, wherein the concentration of carbon nanotubes in the masterbatch is 1 to 50 mass%.
<4> The resin composition according to any one of <1> to <3>, wherein the polyester resin contains a polybutylene terephthalate resin.
<5> The resin composition according to any one of <1> to <4>, wherein the polyamide resin includes an aliphatic polyamide resin.
<6> The resin composition according to any one of <1> to <5>, wherein the content of carbon nanotubes in the resin composition is 0.01 to 10 mass%.
<7> The resin composition according to any one of <1> to <6>, 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 43.0 to 100%.
Formula (A)
(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.)
<8> The resin composition according to any one of <1> to <7>, 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)
(In the above formula (B), R represents the return loss measured by the free space method.)
<9> The resin composition according to any one of <1> to <8>, wherein the transmittance calculated according to formula (C) at a frequency of 76.5 GHz when the resin composition is molded to a thickness of 2 mm is less than 43.0%.
Formula (C)
(In the above formula (C), T represents the transmission attenuation measured by the free space method.)
<10> The resin composition according to any one of <1> to <9>, which is for use in an electromagnetic wave absorber.
<11> Pellets formed from the resin composition according to any one of <1> to <10>.
<12> A molded article formed from the resin composition according to any one of <1> to <10>.
<13> An electromagnetic wave absorber formed from the resin composition according to any one of <1> to <10>.
<14> A method for producing the resin composition according to any one of <1> to <10>, comprising melt-kneading a polyester resin having an intrinsic viscosity of 0.87 to 2.00 dL/g and a carbon nanotube masterbatched with a polyamide resin.

The present invention makes it possible to provide resin compositions, pellets, molded articles, electromagnetic wave absorbers, and methods for producing resin compositions that have high electromagnetic wave absorption rates.

Hereinafter, an embodiment of 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 word "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 unit of reflection 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.

The resin composition of this embodiment is characterized by containing 0.1 to 10.0 parts by mass of a polyamide resin and carbon nanotubes, per 100 parts by mass of a polyester resin having an intrinsic viscosity of 0.87 to 2.00 dL/g (hereinafter sometimes referred to as a "specific polyester resin"). By using such a configuration, it is possible to increase the electromagnetic wave absorption rate of a molded article formed from the resin composition.
In particular, by masterbatching carbon nanotubes with polyamide resin and blending them with a specific polyester resin, a molded product with high electromagnetic wave absorption can be obtained. The reason for this is presumed to be as follows. Specifically, when carbon nanotubes masterbatched with polyamide resin are blended with polyester resin, the polyamide resin has many polar groups, which causes strong interactions with the carbon nanotubes and makes them difficult to disperse. Here, poor dispersibility of the carbon nanotubes results in poor electromagnetic wave absorption. In this embodiment, by using a polyester resin with an intrinsic viscosity of 0.87 to 2.00 dL/g, the polyamide resin is strongly blended during melt blending, resulting in fine dispersion of the polyamide resin containing aggregates of carbon nanotubes in the polyester resin, presumably improving the dispersibility of the carbon nanotubes.

<Polyester Resin Having Intrinsic Viscosity of 0.87 to 2.00 dL/g>
The resin composition of this embodiment contains a polyester resin (specific polyester resin) having an intrinsic viscosity of 0.87 to 2.00 dL/g. By containing such a specific polyester resin, when a resin composition containing a polyamide resin and carbon nanotubes is used, particularly when carbon nanotubes masterbatched with the polyamide resin are used, the carbon nanotubes can be effectively dispersed in the specific polyester resin.

The intrinsic viscosity of the specific polyester resin is 0.87 dL/g or more, preferably 0.90 dL/g or more, more preferably 0.95 dL/g or more, even more preferably 0.98 dL/g or more, even more preferably 1.00 dL/g or more, and even more preferably 1.05 dL/g or more. By making the intrinsic viscosity equal to or greater than the lower limit, the electromagnetic wave absorption property tends to be improved.
The intrinsic viscosity is 2.00 dL/g or less, preferably 1.80 dL/g or less, more preferably 1.50 dL/g or less, even more preferably 1.40 dL/g or less, still more preferably 1.30 dL/g or less, and even more preferably 1.26 dL/g or less. By making the intrinsic viscosity 2.00 dL/g or less, the flowability of the resin composition is further improved, and moldability tends to be improved.
The intrinsic viscosity of the specific polyester resin is a value measured at 30° C. in a mixed solvent of tetrachloroethane and phenol in a 1:1 (mass ratio).
When the resin composition of the present embodiment contains two or more polyester resins, the intrinsic viscosity is the intrinsic viscosity of the mixture.

As the specific polyester resin used in this embodiment, any known thermoplastic polyester resin can be used as long as it satisfies the above-mentioned intrinsic viscosity. Polyethylene terephthalate resin and polybutylene terephthalate resin are preferred, and it is more preferred that the specific polyester resin contains at least polybutylene terephthalate resin.
The polybutylene terephthalate resin used in the resin composition of the present 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 polybutylene terephthalate resin (homopolymer), 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.

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 the present embodiment, terephthalic acid units preferably account for 80 mol % or more of all 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.

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 addition 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 the present embodiment, 1,4-butanediol units preferably account for 80 mol % or more of all diol units, more preferably 90 mol % or more, even more preferably 95 mol % or more, still more preferably 97 mol % or more, and even more preferably 99 mol % or more.

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 terephthalic acid and/or, as the diol unit, one or more diols other than 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 achieving such a copolymerization ratio, fluidity and toughness tend to be improved, which is preferred.

The amount of terminal carboxyl groups in polybutylene terephthalate resins can be determined as appropriate, but is typically 60 eq/ton or less, preferably 50 eq/ton or less, and more preferably 30 eq/ton or less. By keeping the amount below the upper limit, alkali resistance and hydrolysis resistance tend to be improved. There is no particular lower limit for the amount of terminal carboxyl groups, but taking into account the productivity of polybutylene terephthalate resin production, it is typically 10 eq/ton or more.

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 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 during polymerization, such as the raw material charge ratio, polymerization temperature, and pressure reduction method, or by reacting with a terminal blocking agent.

In this embodiment, the specific polyester resin may be a linear polymer or a branched polymer having a branched structure. In this embodiment, the specific polyester resin preferably has a small branched structure. For example, the specific polyester resin used in this embodiment preferably has a degree of branching (DB) of 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 terminally bonded monomer units, Z is the average number of monomer units that form branches, and L is the average number of linearly bonded monomer units (within the macromolecules of each substance).

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. Alternatively, 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.

The catalyst used in carrying out the esterification reaction may be a conventional 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 that can be used as esterification catalysts include titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, and titanium phenolates such as tetraphenyl titanate.

In addition to the above, the specific polyester resins may be found in paragraphs 0013 to 0016 of JP 2010-174223 A, the contents of which are incorporated herein by reference.

The content of the specific polyester resin in the resin composition of this embodiment is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, when the total amount of the resin composition is 100% by mass. When the resin composition does not contain a reinforcing material, it is even more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. By setting the content at or above the lower limit, the mechanical strength of the resin composition tends to be improved. Furthermore, the upper limit of the content of the specific polyester resin is preferably 99% by mass or less, when the total amount of the resin composition is 100% by mass. By setting the content at or below the upper limit, the stability of the resin during processing tends to be further improved.

Furthermore, the content of the specific polyester resin in the resin composition of this embodiment is preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, when the total amount of resin components contained in the resin composition is 100% by mass. By making the content equal to or greater than the lower limit, the effect of suppressing the water absorption of the resin tends to be further improved. Furthermore, the upper limit of the content of the specific polyester resin is preferably such that, when the total amount of resin components contained in the resin composition is 100% by mass, all components other than the polyamide resin are the specific polyester resin. By making the content equal to or less than the upper limit, the electromagnetic wave absorption rate of the obtained molded product tends to be further improved.
The resin composition of the present embodiment may contain only one specific polyester resin, or may contain two or more specific polyester resins. When two or more specific polyester resins are contained, the total amount is preferably in the above range.

<Polyamide resin>
The resin composition of this embodiment contains 0.1 to 10.0 parts by mass of a polyamide resin relative to 100 parts by mass of the specific polyester resin. By blending the polyamide resin with the specific polyester resin and melt-kneading them, the dispersibility of the polyamide resin can be improved compared to when the intrinsic viscosity of the polyester resin is low, and the dispersibility of the carbon nanotubes can also be improved.
The polyamide resin is a polymer having, as a constituent unit, an acid amide obtained by ring-opening polymerization of lactam, polycondensation of aminocarboxylic acid, or polycondensation of diamine and dibasic acid, and may be an aliphatic polyamide resin or a semi-aromatic polyamide resin, with an aliphatic polyamide resin being preferred.
Specific examples include polyamide 6, 11, 12, 46, 66, 666, 610, 612, 6I, 6/66, 6T/6I, 6/6T, 66/6T, 66/6T/6I, 9T, 10T, polyamide resin (MXD6) synthesized from metaxylylenediamine and adipic acid, polyamide resin (MP10) synthesized from metaxylylenediamine, paraxylylenediamine and sebacic acid, polyamide resin (MXD610) synthesized from metaxylylenediamine, adipic acid and sebacic acid, polyamide resin (MXD10) synthesized from metaxylylenediamine and sebacic acid, polytrimethylhexamethylene terephthalamide, polybis(4-aminocyclohexyl)methanedodecamide, polybis(3-methyl-4-aminocyclohexyl)methanedodecamide, and polyundecamethylenehexahydroterephthalamide. The above "I" represents an isophthalic acid component, and "T" represents a terephthalic acid component. Regarding polyamide resins, the description in paragraphs 0011 to 0013 of JP 2011-132550 A can be referred to, the contents of which are incorporated herein by reference.

In this embodiment, as described above, the polyamide resin is preferably an aliphatic polyamide resin, more preferably polyamide 6, 11, 12, 46, 66, 666, 610, or 612, even more preferably polyamide 6, 66, or 666, and even more preferably polyamide 6.
The polyamide 6 herein is a ring-opening polymer of caprolactam, but is intended to include those containing units derived from monomers other than caprolactam (dicarboxylic acid units, diamine units, aminocarboxylic acid units) and terminal groups, etc., within the scope of the present invention. The polyamide 6 used in this embodiment preferably contains 99% by mass or more of units derived from caprolactam, excluding the terminal groups. The same applies to other polyamide resins such as polyamide 66.

The content of the polyamide resin in the resin composition of this embodiment is 0.1 parts by mass or more, preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, even more preferably 1.5 parts by mass or more, even more preferably 2.0 parts by mass or more, and even more preferably 2.5 parts by mass or more, relative to 100 parts by mass of the specific polyester resin. The upper limit of the content of the polyamide resin is 10.0 parts by mass or less, preferably 9.5 parts by mass or less, more preferably 8.5 parts by mass or less, even more preferably 6.5 parts by mass or less, even more preferably 6.2 parts by mass or less, and even more preferably 5.0 parts by mass or less, relative to 100 parts by mass of the specific polyester resin. By setting the content below the upper limit, the effect of suppressing the moisture absorption of the resin composition tends to be further improved.
The resin composition of the present embodiment may contain only one type of polyamide resin, or may contain two or more types. When two or more types are contained, the total amount is preferably in the above range.

<Carbon nanotubes>
The resin composition of the present embodiment contains carbon nanotubes. By containing carbon nanotubes, a resin composition or molded article having a high electromagnetic wave absorption rate can be obtained.
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 may also be 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.

In this embodiment, the carbon nanotubes are preferably derived from carbon nanotubes masterbatched with a polyamide resin, which tends to further improve the electromagnetic wave absorption properties of the resulting resin composition or molded article.
As described above, the carbon nanotubes may be blended in the form of a masterbatch, and in this case, the concentration of the carbon nanotubes in the masterbatch is preferably 1% by mass or more, more preferably 5% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less. By setting the concentration within the range of the above upper limit or less and the above lower limit or more, the dispersibility of the carbon nanotubes in the specific polyester resin tends to be further improved.

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 above 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 below the upper limit, the fluidity of the resin tends to be further improved.

The resin composition of this embodiment preferably contains 0.1 parts by mass or more of carbon nanotubes per 100 parts by mass of the specific polyester 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 the specific polyester 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.

<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 the specific polyester resin and polyamide resin, reinforcing materials, 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.

Preferred examples of the other thermoplastic resins include 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 the like.

Examples of various resin additives include stabilizers, mold release agents, flame retardants, reactive compounds, pigments, dyes, ultraviolet 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 specific polyester resin, polyamide resin, carbon nanotubes, and other components that are selectively blended is 100% by mass. In one example of the resin composition of this embodiment, the total of the specific polyester resin, polyamide resin, and reinforcing material (preferably glass fiber) accounts for 95% by mass or more of the resin composition. In another example of the resin composition of this embodiment, the total of the specific polyester resin, polyamide resin, carbon nanotubes, stabilizer, and release agent accounts for 99% by mass or more of the resin composition. In yet another example of the resin composition of this embodiment, the total of the specific polyester resin, polyamide resin, carbon nanotubes, reinforcing material (preferably glass fiber), stabilizer, and release agent accounts for 99% by mass or more of the resin composition.

<<Stabilizers>>
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.
Specific examples of stabilizers include the following: JP 2018-070722 A, paragraphs 0046 to 0057; JP 2019-056035 A, paragraphs 0030 to 0037; and WO 2017/038949 A, paragraphs 0066 to 0078. These contents are incorporated herein by reference.

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 specific polyester 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 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 specific polyester resin.
The resin composition of the present embodiment may contain only one stabilizer or two or more stabilizers. When two or more stabilizers are contained, the total amount is preferably in the above range.

<<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.
Specific examples of the release agent include the descriptions in paragraphs 0115 to 0120 of JP-A-2013-007058, the descriptions in paragraphs 0063 to 0077 of JP-A-2018-070722, and the descriptions in paragraphs 0090 to 0098 of JP-A-2019-123809. The contents of these descriptions are incorporated herein by reference.

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 specific polyester 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 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 relative to 100 parts by mass of the specific polyester resin.
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.

<<Reinforcement material>>
The resin composition of the present embodiment may or may not contain a reinforcing material. By containing 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 limited in terms of type, and may be any of fibers, fillers, beads, etc., with fibers being preferred.

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 long fibers for so-called unidirectional (UD) materials, sheet-like long fibers such as woven fabrics and knitted fabrics, etc. When using these long fibers, the 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 (for example, a prepreg).

Reinforcing materials include inorganic materials such as glass, carbon (carbon fiber, etc.), alumina, boron, ceramics, and metals (steel, etc.), as well as organic materials such as plants (including kenaf and bamboo), aramid, polyoxymethylene, aromatic polyamide, polyparaphenylene benzobisoxazole, and ultra-high molecular weight polyethylene, with glass being preferred.

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 form of the glass fiber may be any of glass roving obtained by continuously winding single fibers or multiple twisted fibers, chopped strands cut to a length of 1 to 10 mm (i.e., glass fibers having a number average fiber length of 1 to 10 mm), and milled fibers pulverized to a length of about 10 to 500 μm (i.e., glass fibers having 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 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 a flattening ratio, which is the ratio of the major axis to the minor axis of a 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.

The glass fibers may be surface-treated with, for example, silane-based compounds, epoxy-based compounds, or urethane-based compounds, or may be oxidized to improve their affinity with the resin components, as long as this does not significantly impair the properties of the resin composition of this embodiment.

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 specific polyester resin. By setting the content at or above the 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 specific polyester resin. By setting the content at or below the upper limit, the appearance of the molded article tends to be improved, and the flowability of the resin composition tends to be further improved.

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.

<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 the present embodiment, when molded into a thickness of 2 mm (preferably, 100 mm × 100 mm × 2 mm), preferably has an absorption rate calculated according to formula (A) at a frequency of 76.5 GHz of 43.0 to 100%.
Formula (A)
(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.)

The absorbency is preferably 45.0% or higher, more preferably 47.0% or higher, even more preferably 49.0% or higher, and even more preferably 50.0% or higher. Ideally, the upper limit is 100%, but even if it is 90.0% or lower, the required performance will be fully met.

The resin composition of this embodiment preferably has low reflectance of electromagnetic waves.
Specifically, the resin composition of this embodiment, when molded to a thickness of 2 mm (preferably, 100 mm × 100 mm × 2 mm), preferably has a reflectance calculated according to formula (B) at a frequency of 76.5 GHz of 40.0% or less.
Formula (B)
(In the above formula (B), R represents the return loss measured by the free space method.)

The reflectance 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. Ideally, the lower limit is 0%, but a reflectance of 1.0% or more, or even 5.0% or more, will fully satisfy the required performance.

The resin composition of the present embodiment preferably has low transmittance.
The resin composition of this embodiment preferably has a transmittance calculated according to formula (C) at a frequency of 76.5 GHz of less than 43.0% when molded into a thickness of 2 mm (preferably, 100 mm × 100 mm × 2 mm).
Formula (C)
(In the above formula (C), T represents the transmission attenuation measured by the free space method.)

The transmittance is preferably 42.0% or less, and more preferably 40.0% or less. Ideally, the lower limit is 0%, but even if it is 5.0% or more, the required performance will be fully met.

The resin composition of this embodiment preferably satisfies all of the absorbance 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).

The resin composition of this embodiment, when molded to a thickness of 2 mm (preferably 100 mm × 100 mm × ² mm), preferably has a surface resistance according to IEC 60093 of 1.0 × 10 Ω or more, more preferably 1.0 × ¹⁰ Ω or more, even more preferably 1.0 × ¹⁰ Ω or more, even more preferably 1.0 × ¹⁰ Ω or more, still more preferably 1.0 × ¹⁰ Ω or more, still more preferably 1.0 × ¹⁰ Ω or more, particularly preferably 1.0 × ¹⁰ Ω or more, and preferably 1.0 × ¹⁰ Ω or less, more preferably 1.0 × ¹⁰ Ω or less. By setting the surface resistance within these ranges, the electromagnetic wave absorption rate of the obtained molded article tends to be higher.
The surface resistance is a value obtained by measuring the surface resistance (unit: Ω) in accordance with IEC60093 using a test piece of 100 mm×100 mm×2 mm thick formed from the resin composition.

The resin composition of this embodiment has a relative dielectric constant at a frequency of 76.5 GHz of 4.00 or more, preferably 4.20 or more, more preferably 4.45 or more, even more preferably 4.60 or more, even more preferably 4.70 or more, and even more preferably 5.10 or more. By setting the relative dielectric constant at or above the lower limit, the electromagnetic wave absorption rate of the obtained molded article tends to be higher. Furthermore, the upper limit of the relative dielectric constant is preferably 8.00 or less, more preferably 6.00 or less, even more preferably 5.50 or less, even more preferably 5.30 or less, and even more preferably 5.20 or less. By setting the relative dielectric constant at or below the upper limit, the electromagnetic wave reflectivity of the obtained molded article tends to be lower.
The resin composition of this embodiment preferably has a dielectric loss tangent of 0.05 or more, more preferably 0.10 or more, at a frequency of 76.5 GHz. By making the dielectric loss tangent equal to or greater than the lower limit, the electromagnetic wave absorption rate of the resulting molded article tends to be higher. The lower limit of the dielectric loss tangent is not particularly specified, but may be, for example, 0.50 or less, or even 0.40 or less.

<Method of producing 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 specific polyester resin, a polyamide resin, and carbon nanotubes (preferably carbon nanotubes masterbatched with a polyamide resin). More specifically, it can be produced by feeding the specific polyester resin, the carbon nanotubes masterbatched with a polyamide resin, and other components (such as glass fibers) that are optionally blended into an extruder and melt-kneading them. One form formed from such a resin composition is a pellet.
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 a reinforcing material such as glass fiber is compounded, it is preferable to feed it 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.

<Method of manufacturing molded body>
A molded article, particularly an electromagnetic wave absorber, is formed from the resin composition of this embodiment.
The manufacturing method of the molded article in this embodiment is not particularly limited, and any molding method generally used for resin compositions containing thermoplastic resins can be used. Examples thereof 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 rapid heating 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.

<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 radar 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 the driver mis-depresses the pedal, devices for warning about approaching vehicles, lane keeping assist devices, rear-end collision prevention warning devices, parking assist devices, devices for warning about obstacles around the vehicle, etc.; railway and aviation millimeter-wave radar 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 radar for transportation infrastructure such as intersection monitoring devices and elevator monitoring devices; millimeter-wave radar for various security devices; millimeter-wave radar for medical and nursing care such as systems for watching over children and the elderly; millimeter-wave radar for transmitting various information contents; etc.

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.

Raw Materials The following raw materials were used: In Table 1 below, PBT stands for polybutylene terephthalate resin, and CNT stands for carbon nanotubes (the same applies to Table 2).

Example 1, Comparative Example 1
<Production of Resin Composition (Pellets)>
As shown in Table 2, each component listed in Table 1 was placed in a stainless steel tumbler and mixed with stirring for 1 hour. The resulting mixture was fed into an intermeshing co-rotating twin-screw extruder ("TEX-30α" manufactured by The Japan Steel Works, Ltd., screw diameter 32 mm, L/D = 42) through the main feed port. The barrel temperature of the first kneading section was set to 250°C, and the mixture was melt-kneaded 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 (φ4 mm), length 1.5 cm). The extruded strand was introduced into a water bath, cooled, and then inserted into a pelletizer and cut to obtain a resin composition (pellets).

<76.5 GHz electromagnetic wave absorption rate, reflectance, and 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 obtained test pieces, the absorptivity calculated according to formula (A), the reflectivity 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 measurement, a network analyzer "N5252A" manufactured by Keysight Corporation was used.
The measurement was carried out 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)
(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.)

Formula (B)
(In the above formula (B), R represents the return loss measured by the free space method.)

Formula (C)
(In the above formula (C), T represents the transmission attenuation measured by the free space method.)

<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 specimens, which were placed so that the transverse direction (TD) of the injection-molded article was parallel to the electric field direction.
The measurements were performed using a Keysight N5252A network analyzer, and the values of the relative permittivity and dielectric loss tangent were estimated using a Keysight N1500A material measurement suite and calculated using the NIST Precision calculation model.

In Table 2 above, the CNT content indicates the content 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, and further had low electromagnetic wave transmittance and reflectance.

Claims (11)

0.1 to 10.0 parts by mass of a polyamide resin relative to 100 parts by mass of a polyester resin having an intrinsic viscosity of 0.87 to 2.00 dL/g;
and carbon nanotubes ,
the polyester resin comprises a polybutylene terephthalate resin,
the content of carbon nanotubes in the resin composition is 0.01 to 10% by mass,
A resin composition, wherein the polyamide resin comprises at least one of polyamide 6, polyamide 66, and polyamide 6/66. The resin composition described in claim 1, wherein the carbon nanotubes are derived from carbon nanotubes masterbatched with a polyamide resin. The resin composition according to claim 2, wherein the concentration of carbon nanotubes in the masterbatch is 1 to 50 mass%. The resin composition according to any one of claims 1 to 3 , wherein 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 43.0 to 100%.
Formula (A)
(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.) The resin composition according to any one of claims 1 to 4 , wherein when the resin composition is molded into a thickness of 2 mm, the reflectance calculated according to formula (B) at a frequency of 76.5 GHz is 40.0% or less.
Formula (B)
(In the above formula (B), R represents the return loss measured by the free space method.) The resin composition according to any one of claims 1 to 5 , wherein when the resin composition is molded into a thickness of 2 mm, the transmittance calculated according to formula (C) at a frequency of 76.5 GHz is less than 43.0%.
Formula (C)
(In the above formula (C), T represents the transmission attenuation measured by the free space method.) The resin composition according to any one of claims 1 to 6 , which is used for an electromagnetic wave absorber. A pellet formed from the resin composition according to any one of claims 1 to 6 . A molded article formed from the resin composition according to any one of claims 1 to 6 . An electromagnetic wave absorber formed from the resin composition according to any one of claims 1 to 6 . A method for producing the resin composition according to any one of claims 1 to 7 , comprising melt-kneading a polyester resin having an intrinsic viscosity of 0.87 to 2.00 dL/g and carbon nanotubes masterbatched with a polyamide resin ,
the polyester resin comprises a polybutylene terephthalate resin,
the content of carbon nanotubes in the resin composition is 0.01 to 10% by mass,
The method for producing a resin composition, wherein the polyamide resin comprises at least one of polyamide 6, polyamide 66, and polyamide 66/6.