JP7806477B2 - Crushed material, material, compact, and method for manufacturing compact - Google Patents

Description

The present invention relates to crushed material, materials, molded bodies, and methods for manufacturing molded bodies. In particular, it relates to crushed material made from recycled thermoplastic resins.

Thermoplastic resins have traditionally been molded into various molded articles. However, in recent years, there has been a strong demand for the reuse of resources, and recycling of thermoplastic resins has also been studied (Patent Document 1).

Japanese Patent Application Laid-Open No. 2021-080428

Here, when a molded thermoplastic resin body is recycled and molded again, there is a problem that various physical properties are deteriorated compared to when virgin thermoplastic resin before recycling is used.
Meanwhile, the present inventors have been conducting research and development into resin compositions containing thermoplastic resins that have high electromagnetic wave absorption properties. It is predicted that there will be a demand for recycling of such resin compositions with high electromagnetic wave absorption properties in the future.
The present invention aims to solve such problems and to provide crushed materials, materials, molded articles, and a method for manufacturing molded articles of resin compositions containing thermoplastic resins that can maintain high electromagnetic wave absorption properties even when recycled.

In light of the above-mentioned problems, the present inventors have conducted research and found that the above-mentioned problems can be solved by using carbon nanotubes as the conductive material in a resin composition containing a thermoplastic resin and a conductive material for achieving electromagnetic wave absorption.
Specifically, the above problems were solved by the following means.
<1> A crushed material of a resin composition containing a thermoplastic resin and carbon nanotubes, wherein when the crushed material is molded into a 2 mm thick molded body, the absorption rate calculated according to formula (A) at a frequency of 76.5 GHz is 40.0 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.)
<2> The crushed material described in <1>, wherein the thermoplastic resin includes polybutylene terephthalate resin.
<3> The crushed material according to <1> or <2>, containing 0.1 to 10.0 parts by mass of the carbon nanotubes per 100 parts by mass of the thermoplastic resin.
<4> The crushed material according to any one of <1> to <3>, wherein the resin composition is a recycled resin composition containing a thermoplastic resin and carbon nanotubes.
<5> The crushed material according to any one of <1> to <4>, wherein the resin composition is a molded body formed from a resin composition containing a thermoplastic resin and carbon nanotubes.
<6> The crushed material according to any one of <1> to <5>, wherein the resin composition further contains 10 to 100 parts by mass of an inorganic filler per 100 parts by mass of the thermoplastic resin.
<7> A material comprising pellets obtained from a resin composition containing a thermoplastic resin and carbon nanotubes, and the crushed material according to any one of <1> to <6>.
<8> The material according to <7>, wherein the pellets are virgin pellets.
<9> The material according to <7> or <8>, wherein the mass ratio of the pellets to the crushed material is 10 to 90:90 to 10.
<10> The material according to any one of <7> to <9>, wherein the thermoplastic resin contained in the pellets includes a polybutylene terephthalate resin.
<11> The material according to any one of <7> to <10>, wherein the pellet further contains 0.1 to 10.0 parts by mass of the carbon nanotubes per 100 parts by mass of the thermoplastic resin.
<12> The material according to any one of <7> to <11>, wherein the pellets further contain 10 to 100 parts by mass of an inorganic filler per 100 parts by mass of the thermoplastic resin.
<13> A compact formed from the crushed material according to any one of <1> to <6> or the material according to any one of <7> to <12>.
<14> A method for producing a molded body, comprising molding the crushed material according to any one of <1> to <6> or the material according to any one of <7> to <12>.
<15> The method for producing a molded body according to <14>, wherein the material is formed by injection molding or extrusion molding.

The present invention makes it possible to provide crushed materials, materials, molded articles, and methods for manufacturing molded articles made from resin compositions containing thermoplastic resins that maintain high electromagnetic wave absorption properties even after recycling.

FIG. 1 is a schematic diagram showing a recycling flow of a resin composition (pellets) containing a thermoplastic resin and a conductive material.

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 term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.
If the measurement methods, etc. described in the standards shown in this specification differ from year to year, they will be based on the standards as of January 1, 2021, unless otherwise stated.

The crushed material of this embodiment is crushed material of a resin composition containing a thermoplastic resin and carbon nanotubes, and is characterized in that when the crushed material (or a material containing the crushed material) is molded into a 2 mm thick molded body, the absorption rate calculated according to formula (A) at a frequency of 76.5 GHz is 40.0 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.)

Such crushed material can maintain high electromagnetic wave absorption even after recycling, and can also maintain low electromagnetic wave reflectance and electromagnetic wave absorption even after recycling.
As described above, the present inventors have been investigating resin compositions that can provide molded articles with high electromagnetic wave absorption properties by blending a thermoplastic resin with a conductive material. Meanwhile, in recent years, there has been a demand for recycling thermoplastic resins in light of environmental impact. Therefore, the present inventors have investigated ways to make resin compositions that can provide molded articles with high electromagnetic wave absorption properties recyclable. Specifically, as shown in FIG. 1 , when a resin composition (pellets) 1 containing a thermoplastic resin and a conductive material is injection-molded using an injection molding machine 2, rejected articles 4 and scrap 5 are typically produced in addition to accepted articles 3. It is conceivable to crush such rejected articles 4 and scrap 5 using a crusher 6, and reuse the crushed material 7 obtained 8 for injection molding again.

However, the inventors have conducted research and found that when a resin composition containing a thermoplastic resin and a conductive material is recycled as described above, the electromagnetic wave absorption properties of the resulting molded article may be reduced.
The present inventors have surprisingly found that this problem can be solved by using carbon nanotubes as the conductive material, that is, by using carbon nanotubes, it is possible to maintain an extremely high level of electromagnetic wave absorption even when a resin composition containing a thermoplastic resin and a conductive material is recycled.
The reason why using carbon nanotubes as a conductive material can maintain high electromagnetic wave absorption properties even after recycling is believed to be as follows. First, when recycling a resin composition containing a thermoplastic resin and a conductive material, for example, as shown in Figure 1, rejected molded products 4 and scraps 5 formed from a resin composition 1 containing a thermoplastic resin and a conductive material are crushed by a crusher 6 to produce crushed material 7. It was assumed that ordinary conductive materials are cut or broken during molding or crushing, resulting in a decrease in electromagnetic wave absorption properties. In contrast, carbon nanotubes are thin and short, but have high individual strength, so they tend to be less likely to cut or break during molding or crushing. Therefore, it was believed that excellent electromagnetic wave absorption properties can be maintained even if a resin composition containing a thermoplastic resin and carbon nanotubes is crushed, etc., and then remolded.

The crushed material of this embodiment is a crushed material of a resin composition containing a thermoplastic resin and carbon nanotubes. Even when recycled into a molded product, such crushed material has excellent electromagnetic wave absorption properties. The crushed material is not particularly limited as long as it is a crushed material of the resin composition. For example, a recycled product of a resin composition containing a thermoplastic resin and carbon nanotubes can be used. In particular, a molded product formed from a resin composition containing a thermoplastic resin and carbon nanotubes can be used as the resin composition. Examples of the molded product include an injection molded product and an extrusion molded product. Furthermore, the molded product may be a flat molded product such as a film, or may be a molded product molded using a mold. Specifically, examples of the molded product include rejected products and scraps that are generated when molding a resin composition.

The crushed material of this embodiment is, as described above, crushed material of a resin composition containing a thermoplastic resin and carbon nanotubes, and is crushed , for example, by a crushed material molding machine for resin molded bodies. The size of the crushed material is not particularly specified, but for example, for 50% by mass or more, further 70% by mass or more, particularly 90% by mass or more of the crushed material, the longest portion is preferably 20.0 mm or less, more preferably 8.0 mm or less, and also preferably 1.0 mm or more, more preferably 2.0 mm or more.

In this embodiment, when the crushed material (preferably a material containing the crushed material) is molded into a 2 mm thick (preferably 100 mm × 100 mm × 2 mm thick) molded body, the absorption rate calculated according to formula (A) at a frequency of 76.5 GHz is 40.0 to 100%. The crushed material of this embodiment uses carbon nanotubes as the conductive material, making it possible to achieve such a high electromagnetic wave absorption rate.
In particular, even if the material contains 10% by mass or more, or even 20% by mass or more of the crushed material , a high electromagnetic wave absorption rate can be achieved. Furthermore, in this embodiment, even if 100% by mass of the material is made up of the crushed material of this embodiment, a high electromagnetic wave absorption rate can be achieved. However, from the viewpoint of other properties, the proportion of the crushed material in the material is preferably 50% by mass or less, and may be 45% by mass or less. The same applies to the reflectance calculated according to formula (B) and the transmittance calculated according to formula (C) described below.

The absorbency is preferably 53.0% or higher, more preferably 55.0% or higher, even more preferably 58.0% or higher, and even more preferably 60.0% or higher. Ideally, the upper limit is 100%, but even if it is 90.0% or lower, the required performance will be fully met.

In this embodiment, it is preferable that the crushed material (or a material containing the crushed material) has a low reflectance of electromagnetic waves when molded into a 2 mm thick molded body.
Specifically, in this embodiment, when the crushed material (or a material containing the crushed material) is molded into a molded body having a thickness of 2 mm (preferably, a thickness of 100 mm x 100 mm x 2 mm), it is preferable that the reflectivity 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 reflectance is preferably 35.0% or less, more preferably 30.0% or less, and even more preferably 26.0% or less. Ideally, the lower limit is 0%, but a reflectance of 5.0% or more, or even 10.0% or more, will fully satisfy the required performance.

In this embodiment, it is preferable that the crushed material (or a material containing the crushed material) has low transmittance when molded into a molded article having a thickness of 2 mm.
In this embodiment, when the crushed material (or a material containing the crushed material) is molded into a molded body having a thickness of 2 mm (preferably, a thickness of 100 mm x 100 mm x 2 mm), it is preferable that the transmittance calculated according to formula (C) at a frequency of 76.5 GHz is 25.0% or less.
Formula (C)
(In the above formula (C), T represents the transmission attenuation measured by the free space method.)

The transmittance is preferably 23.0% or less, and more preferably 20.0% or less. Ideally, the lower limit is 0%, but even if it is 5.0% or more, the required performance will be fully met.

In this embodiment, when the crushed material (or a material containing the crushed material) is molded into a 2 mm thick molded body, it is preferable that 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) all satisfy the above requirements.

Furthermore, with regard to the resin composition used in this embodiment (the resin composition before crushing , for example, virgin pellets, or the resin composition to be blended into the material described later), when molded into a molded article of 2 mm thickness (preferably, 100 mm × 100 mm × 2 mm thickness) in the same manner as above, it is preferable that the resin composition satisfies one or more 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), and it is more preferable that the resin composition satisfies all of them.

In particular, the absorption rate calculated according to formula (A) above when the crushed material (or a material containing the crushed material) is molded into a 2 mm-thick molded body relative to the absorption rate calculated according to formula (A) above when the resin composition (e.g., virgin pellets) used in this embodiment is molded into a 2 mm-thick (preferably, 100 mm x 100 mm x 2 mm) molded body, i.e., (absorption rate of material / absorption rate of resin composition) x 100 (unit: %), is preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, even more preferably 55% or more, and even more preferably 60% or more. Ideally, the upper limit is 100%, but it may be 99.9% or less.

In particular, the reflectance calculated according to formula (B) above when the crushed material (or a material containing the crushed material) is molded into a 2 mm thick molded body relative to the reflectance calculated according to formula (B) above when the resin composition (e.g., virgin pellets) used in this embodiment is molded into a 2 mm thick molded body (preferably 100 mm x 100 mm x 2 mm thick), i.e., (reflectance of material / reflectance of resin composition) x 100 (unit: %), is preferably 40% or less, more preferably 35% or less, even more preferably 30% or less, even more preferably 25% or less, and even more preferably 20% or less. The lower limit is ideally 0%, but may be 1% or more.

In particular, the transmittance calculated according to formula (C) when the crushed material (or a material containing the crushed material) is molded into a 2 mm thick molded body relative to the transmittance calculated according to formula (C) when the resin composition (e.g., virgin pellets) used in this embodiment is molded into a 2 mm thick molded body (preferably, 100 mm x 100 mm x 2 mm thick), i.e., (transmittance of material/transmittance of resin composition) x 100 (unit: %), is preferably 30% or less, more preferably 20% or less, even more preferably 15% or less, even more preferably 10% or less, and even more preferably 8% or less. The lower limit is ideally 0%, but may be 1% or more.

In this embodiment, when the crushed material (or a material containing the crushed material) is molded into a 2 mm thick molded body, the surface resistance according to IEC 60093 is preferably 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, even more preferably 1.0× ¹⁰ Ω or more, particularly preferably 1.0× ¹⁰ Ω or more, and preferably 1.0× ¹⁰ Ω or less, and more preferably 1.0× ¹⁰ Ω or less. By setting the surface resistance within such a range, the electromagnetic wave absorption rate of the obtained molded body tends to be higher.

Virgin pellets refer to materials that have been melt-kneaded and pelletized from thermoplastic resin, carbon nanotubes, and other ingredients added as needed. Virgin pellets that have been re-melted and pelletized are called re-pellets and are included in the recycled product category.

<Thermoplastic resin>
Next, the thermoplastic resin contained in the resin composition used in this embodiment will be described.
Preferred examples of the thermoplastic resin used in this embodiment include polyester resins (thermoplastic polyester resins); polyamide resins; polycarbonate resins; polystyrene-based 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, with polyester resins (thermoplastic polyester resins), polyamide resins, polycarbonate resins, and polyphenylene ether resins being preferred.
In this embodiment, the thermoplastic resin preferably includes a polyester resin, and more preferably includes a polybutylene terephthalate resin.

In this embodiment, the thermoplastic resin (for example, polyester resin (thermoplastic polyester resin), polyamide resin, polycarbonate resin, and polyphenylene ether resin) may be a linear polymer or a branched polymer having a branched structure. In this embodiment, the thermoplastic resin preferably has a small branched structure. For example, the thermoplastic 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).
Each thermoplastic resin will be described in detail below.

<<Polyester resin>>
As the polyester resin, known thermoplastic polyester resins can be used, and polyethylene terephthalate resin and polybutylene terephthalate resin are preferred, and it is more preferred that the polyester resin contains at least polybutylene terephthalate resin.
The polybutylene terephthalate resin used in the resin composition used in 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 this embodiment, terephthalic acid units preferably account for 80 mol % or more, and more preferably 90 mol % or more, of all dicarboxylic acid units.

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 this embodiment, 1,4-butanediol units preferably account for 80 mol % or more, and more preferably 90 mol % or more, of all diol units.

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, toughness, and tracking resistance 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.

The intrinsic viscosity of the polybutylene terephthalate resin is preferably 0.5 dL/g or more, more preferably 0.6 dL/g or more. By setting the intrinsic viscosity to 0.5 dL/g or more, the mechanical strength of the resulting resin composition tends to be further improved. The intrinsic viscosity is preferably 2.00 dL/g, more preferably 1.50 dL/g or less, even more preferably 1.30 dL/g or less, even more preferably 1.25 dL/g or less, even more preferably 1.23 dL/g or less, and may even be 1.19 dL/g or less, 1.17 dL/g or less, 1.15 dL/g or less, 1.13 dL/g or less, 1.07 dL/g or less, 1.05 dL/g or less, 1.00 dL/g or less, or 0.97 dL/g or less. By setting the intrinsic viscosity to 2.0 dL/g or less, the fluidity of the resin composition tends to be further improved, and moldability tends to be improved. In particular, when a masterbatch of carbon nanotubes with polybutylene terephthalate resin is blended into a resin composition in which polybutylene terephthalate resin is the main component of a thermoplastic resin (e.g., 80% by mass or more of the resin component), the carbon nanotubes are more easily dispersed when the intrinsic viscosity of the main component polybutylene terephthalate resin is lower, which tends to result in improved electromagnetic wave absorption properties.
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).

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 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 description of polyester resins in paragraphs 0013 to 0016 of JP 2010-174223 A can be referred to, the contents of which are incorporated herein by reference.

<<Polystyrene-based resin>>
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), 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), acrylonitrile-butadiene-styrene copolymer (ABS resin), acrylonitrile-acrylic rubber-styrene copolymer (AAS resin), acrylonitrile-styrene-acrylic rubber copolymer (ASA resin), acrylonitrile-ethylene propylene rubber-styrene copolymer (AES resin), or styrene-IPN type rubber copolymer, more preferably a high impact polystyrene resin (HIPS), and even more preferably a butadiene rubber-containing polystyrene.

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

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

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

Methods for producing such polystyrene-based resins include known methods such as emulsion polymerization, solution polymerization, suspension polymerization, and bulk polymerization.

<<Polycarbonate resin>>
Polycarbonate resins are homopolymers or copolymers, which may be branched, obtained by reacting a dihydroxy compound or a small amount of a polyhydroxy compound with phosgene or a carbonate diester. The method for producing the polycarbonate resin is not particularly limited, and polycarbonate resins produced by the conventionally known phosgene method (interfacial polymerization method) or melt method (ester interchange method) can be used.

The dihydroxy compound used as the raw material is preferably an aromatic dihydroxy compound, such as 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), tetramethylbisphenol A, bis(4-hydroxyphenyl)-p-diisopropylbenzene, hydroquinone, resorcinol, or 4,4-dihydroxydiphenyl, with bisphenol A being preferred. It is also possible to use compounds in which one or more tetraalkylphosphonium sulfonates are bonded to the above aromatic dihydroxy compounds.

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

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

The viscosity average molecular weight (Mv) of the polycarbonate resin is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 13,000 or more. By using a polycarbonate resin having a viscosity average molecular weight of 5,000 or more, the mechanical strength of the resulting resin composition tends to be further improved. Furthermore, the viscosity average molecular weight (Mv) of the polycarbonate resin is preferably 60,000 or less, more preferably 40,000 or less, and even more preferably 30,000 or less. By using a polycarbonate resin having a viscosity average molecular weight of 60,000 or less, the flowability of the resin composition tends to be improved, and moldability tends to be improved.
When two or more polycarbonate resins are contained, it is preferable that the mixture satisfies the above range (hereinafter, the same applies to molecular weight).

In this embodiment, the viscosity average molecular weight (Mv) of the polycarbonate resin is a value calculated from the intrinsic viscosity ([η]) obtained by measuring the viscosity of a methylene chloride solution of the polycarbonate resin at 20°C using an Ubbelohde viscometer, and then using the following Schnell viscosity formula:
[η]=1.23×10 ^-4 Mv ^0.83

There are no particular limitations on the method for producing polycarbonate resin, and polycarbonate resins produced by either the phosgene method (interfacial polymerization method) or the melt method (ester interchange method) can be used. Also preferred are polycarbonate resins produced by the melt method that have been post-treated to adjust the amount of terminal OH groups.

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

(In the formula, two R ^a 's each independently represent a hydrogen atom, a halogen atom, a primary or secondary alkyl group, an aryl group, an aminoalkyl group, a halogenated alkyl group, a hydrocarbonoxy group, or a halogenated hydrocarbonoxy group; and two R ^b 's each independently represent a hydrogen atom, a halogen atom, a primary or secondary alkyl group, an aryl group, a halogenated alkyl group, a hydrocarbonoxy group, or a halogenated hydrocarbonoxy group; provided that two R ^a's cannot both be hydrogen atoms.)

R ^a and R ^b are each independently preferably a hydrogen atom, a primary or secondary alkyl group, or an aryl group. Suitable examples of primary alkyl groups include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-amyl group, an isoamyl group, a 2-methylbutyl group, a 2,3-dimethylbutyl group, a 2-, 3-, or 4-methylpentyl group, or a heptyl group. Suitable examples of secondary alkyl groups include an isopropyl group, a sec-butyl group, or a 1-ethylpropyl group. In particular, R ^a is preferably a primary or secondary alkyl group having 1 to 4 carbon atoms or a phenyl group. R ^b is preferably a hydrogen atom.

Suitable homopolymers of polyphenylene ether resins include, for example, polymers of 2,6-dialkylphenylene ethers such as poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-diethyl-1,4-phenylene ether), poly(2,6-dipropyl-1,4-phenylene ether), poly(2-ethyl-6-methyl-1,4-phenylene ether), and poly(2-methyl-6-propyl-1,4-phenylene ether). Examples of copolymers include 2,6-dialkylphenol/2,3,6-trialkylphenol copolymers such as 2,6-dimethylphenol/2,3,6-trimethylphenol copolymer, 2,6-dimethylphenol/2,3,6-triethylphenol copolymer, 2,6-diethylphenol/2,3,6-trimethylphenol copolymer, and 2,6-dipropylphenol/2,3,6-trimethylphenol copolymer; graft copolymers in which styrene is graft polymerized onto poly(2,6-dimethyl-1,4-phenylene ether); and graft copolymers in which styrene is graft polymerized onto 2,6-dimethylphenol/2,3,6-trimethylphenol copolymer.

In this embodiment, poly(2,6-dimethyl-1,4-phenylene) ether and 2,6-dimethylphenol/2,3,6-trimethylphenol random copolymer are particularly preferred as polyphenylene ether resins. Polyphenylene ether resins with a specified number of terminal groups and copper content, such as those described in JP-A-2005-344065, can also be suitably used.

The polyphenylene ether resin preferably has an intrinsic viscosity of 0.2 to 0.8 dL/g, more preferably 0.3 to 0.6 dL/g, measured in chloroform at 30°C. An intrinsic viscosity of 0.2 dL/g or higher tends to improve the mechanical strength of the molded article, while an intrinsic viscosity of 0.8 dL/g or lower tends to improve the fluidity of the resin composition and facilitate molding. Two or more polyphenylene ether resins with different intrinsic viscosities may be used in combination to achieve this intrinsic viscosity range.

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

<<Polyamide resin>>
Polyamide resins are polymers whose constituent units are acid amides obtained by ring-opening polymerization of lactams, polycondensation of aminocarboxylic acids, or polycondensation of diamines and dibasic acids, and may be either aliphatic polyamide resins or semi-aromatic polyamide resins.
Specific examples include polyamide 6, 11, 12, 46, 66, 610, 612, 6I, 6/66, 6T/6I, 6/6T, 66/6T, 66/6T/6I, 9T, 10T, xylylenediamine-based polyamide resins (details of which will be described later), polytrimethylhexamethylene terephthalamide, polybis(4-aminocyclohexyl)methanedodecamide, polybis(3-methyl-4-aminocyclohexyl)methanedodecamide, and polyundecamethylene hexahydroterephthalamide. The "I" in the above text represents an isophthalic acid component, and the "T" represents a terephthalic acid component. For polyamide resins, see paragraphs 0011 to 0013 of JP 2011-132550 A, the contents of which are incorporated herein by reference.

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

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

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

The content of the thermoplastic resin in the resin composition used in 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. When the resin composition does not contain an inorganic filler, the content of the thermoplastic resin in the resin composition is more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. By setting the content to be equal to or greater than the lower limit, the fluidity during injection molding tends to be further improved. Furthermore, the content of the thermoplastic resin is preferably 99% by mass or less. When the resin composition contains an inorganic filler, the content of the thermoplastic resin in the resin composition is more preferably 90% by mass or less, even more preferably 85% by mass or less, and even more preferably 80% by mass or less. By setting the content to be equal to or less than the upper limit, the amount of warpage of the molded product tends to be more effectively reduced.
The resin composition used in the present embodiment may contain only one type of thermoplastic resin or may contain two or more types. When two or more types are contained, it is preferable that the total amount is in the above range.

<Carbon nanotubes>
The resin composition used in this embodiment contains carbon nanotubes.
The carbon nanotubes 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 perspective 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 content of carbon nanotubes in the resin composition used in 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 used in 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 used in this embodiment also preferably contains 0.1 parts by mass or more of carbon nanotubes relative to 100 parts by mass of the thermoplastic resin. By setting the carbon nanotubes at or above the lower limit, electromagnetic wave absorption properties are effectively exhibited. The resin composition used in this embodiment also preferably contains 10.0 parts by mass or less of carbon nanotubes relative to 100 parts by mass of the thermoplastic resin, more preferably 8.0 parts by mass or less, even more preferably 6.0 parts by mass or less, even more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less, and even 2.5 parts by mass or less, particularly 1.5 parts by mass or less. Setting the carbon nanotubes at or below the upper limit tends to further improve the fluidity of the resin.
The resin composition used in this 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 used in 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 inorganic fillers and various resin additives. 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 various resin additives include stabilizers, mold release agents, flame retardants, pigments, dyes, ultraviolet absorbers, antistatic agents, antifogging agents, antiblocking agents, flow improvers, plasticizers, dispersants, antibacterial agents, etc. The resin composition used in this embodiment preferably contains at least one of stabilizers and mold release agents.
The resin composition used in this embodiment is adjusted so that the total of the thermoplastic resin, carbon nanotubes, and other optional components is 100% by mass. It is also preferable that the total of the thermoplastic resin, carbon nanotubes, stabilizer, and release agent in the resin composition used in this embodiment is 99% by mass or more. It is also preferable that the total of the thermoplastic resin, carbon nanotubes, inorganic filler (preferably glass fiber), stabilizer, and release agent in the resin composition used in this embodiment is 99% by mass or more.

<<Stabilizers>>
The resin composition used in 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 used in this embodiment preferably contains 0.01 parts by mass or more of the stabilizer relative to 100 parts by mass of the thermoplastic 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 stabilizer content is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the thermoplastic resin.
The resin composition used in 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 used in this 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 used in this embodiment preferably contains 0.01 parts by mass or more of a release agent relative to 100 parts by mass of the thermoplastic 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 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 thermoplastic 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.

<<Inorganic fillers>>
The resin composition used in this embodiment may or may not contain an inorganic filler. By containing an inorganic filler, the mechanical strength of the obtained molded article can be improved.
The inorganic filler that can be used in this embodiment is not particularly limited in terms of type, etc., and may be any of fibers, fillers, beads, etc., with fibers being preferred.
In particular, glass fibers are preferable because they also function as a dispersant for carbon nanotubes.

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

Inorganic filler raw materials include inorganic substances such as glass, carbon (carbon fiber, etc.), alumina, boron, ceramic, and metal (steel, etc.), as well as organic substances 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 used in this embodiment preferably contains glass fiber as an inorganic filler.
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 used in this embodiment.

When the resin composition used in this embodiment contains an inorganic filler (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 thermoplastic 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 inorganic filler (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 thermoplastic 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.

When the resin composition used in this embodiment contains an inorganic filler (preferably glass fiber), its content in the resin composition is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and even more preferably 25% by mass or more. Furthermore, the content of the inorganic filler (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, the mechanical strength tends to be further increased. Furthermore, 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 used in this embodiment may contain only one type of inorganic filler (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.

The resin composition used in this embodiment can be produced by a conventional method for producing resin compositions containing a thermoplastic resin. For example, it can be obtained by melt-kneading a thermoplastic resin, carbon nanotubes, and other components as needed. The carbon nanotubes are preferably blended as a masterbatch with the thermoplastic resin. Masterbatching the carbon nanotubes with the thermoplastic resin effectively improves the dispersibility of the conductive material in the thermoplastic resin. The concentration of carbon nanotubes in the masterbatch is preferably 1% by mass or more, more preferably 5% by mass or more, and also 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 above upper and lower limit ranges, the dispersibility of the carbon nanotubes in the thermoplastic resin tends to be further improved.

The components may be mixed in advance and fed to the extruder all at once, 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.

<Materials>
Next, the materials of this embodiment will be described.
The material of this embodiment includes pellets obtained from a resin composition containing a thermoplastic resin and carbon nanotubes, and the crushed material of this embodiment.

The pellets obtained from the resin composition containing the thermoplastic resin and the carbon nanotubes may be virgin pellets or repellets. In this embodiment, the pellets are preferably virgin pellets.
In this embodiment, the mass ratio of the pellets (preferably virgin pellets) to the crushed material is preferably 10 to 90:90 to 10. Furthermore, when the total of the pellets and the crushed material is 100 parts by mass, the mass ratio of the crushed material is more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, and even more preferably 25 parts by mass or more. By setting the mass ratio at or above the lower limit, recycled resin can be used efficiently. The mass ratio of the crushed material is preferably 90 parts by mass or less, more preferably 75 parts by mass or less, even more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less. By setting the mass ratio at or below the upper limit, a decrease in the mechanical strength of the resulting molded body can be suppressed.

The material of the present embodiment may contain only one type of pellets and crushed material, or may contain two or more types. When two or more types are contained, it is preferable that the total amount is within the above range.
The material of this embodiment may contain pellets and crushed material in total, accounting for 90% by mass or more of the total, but may also contain other components. Examples of other components include virgin or recycled thermoplastic resins, inorganic fillers, and other resin additives. For details of these components, please refer to the descriptions of the thermoplastic resins, inorganic fillers, and resin additives described in the resin composition section above.

The thermoplastic resin contained in the pellets used in this embodiment preferably contains a polybutylene terephthalate resin.
The pellets used in this embodiment preferably further contain 0.1 to 10.0 parts by mass of the carbon nanotubes per 100 parts by mass of the thermoplastic resin.
The pellets used in this embodiment preferably further contain 10 to 100 parts by mass of an inorganic filler per 100 parts by mass of the thermoplastic resin.
Other than that, the pellets used in this embodiment are the same as those of the resin composition described above, and the preferred ranges are also the same.

<Molded body>
The compact of this embodiment is formed from the crushed material of this embodiment or the material of this embodiment.
Furthermore, the method for producing a molded body in this embodiment includes molding the crushed material of the embodiment or the material of the embodiment.
The manufacturing of molded body can be arbitrarily adopted molding method for resin composition containing thermoplastic resin.Examples thereof include injection molding, ultra-high speed injection molding, injection compression molding, two-color molding, gas-assisted hollow molding etc., molding method using heat-insulating mold, molding method using rapid heating mold, foam molding (including supercritical fluid), insert molding, IMC (in-mold coating molding) molding method, extrusion molding, sheet molding, thermoforming, rotational molding, lamination molding, press molding, blow molding etc., and injection molding or extrusion molding is preferred, and injection molding is more preferred.

In this embodiment, the shape of the molded product is not particularly specified, and examples include molded products such as injection molded products and extrusion molded products (e.g., films, etc.).

<Application>
The crushed material , material, or molded article 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 electromagnetic wave absorbers are preferably used for radar applications. Specifically, they are 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 performed using other instruments with equivalent performance.

1. Raw Materials The following raw materials were used: In Table 1 below, PBT stands for polybutylene terephthalate resin, and CNT stands for carbon nanotubes.

Example 1, Comparative Example 1
<Production of Resin Composition (Pellets)>
As shown in Table 2, each of the components listed in Table 1 (amounts in parts by mass) except for the inorganic filler 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 260°C for plasticization, and the inorganic filler (glass fiber) was fed from a side feeder in the proportions shown in Table 2. The barrel temperature after adding the inorganic filler 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 (virgin pellets).

<76.5 GHz electromagnetic wave absorption rate, reflectance, and transmittance>
The virgin pellets obtained above were injection molded in an injection molding machine ("NEX80" manufactured by Nissei Plastic Industrial Co., Ltd.) at a cylinder set 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.
The test pieces obtained above were crushed using a Granulator GSL180/180 manufactured by ZERMA to a size of approximately 3.0 mm x 3.0 mm x 2.0 mm for the majority of the crushed pieces , to obtain crushed pieces (referred to as crushed pieces A).
Furthermore, the crushed material A obtained above was used in the same manner as above to obtain test pieces measuring 100 mm x 100 mm x 2 mm thick. The crushed material obtained by crushing the test pieces was used again, and the process of obtaining test pieces was counted as one recycling process, and test pieces that had finally undergone up to five recycling processes were obtained. The electromagnetic wave absorption rate maintenance rate and electromagnetic wave reflectance maintenance rate after five recycling processes relative to the virgin product were calculated (100% absorption rate maintenance rate for crushed material , 100% reflectance maintenance rate for crushed material ). The closer to 100%, the better the maintenance rate.

The crushed material A and virgin pellets obtained above were mixed in a mass ratio of 30:70, and test pieces measuring 100 mm x 100 mm x 2 mm were obtained in the same manner as above. This constitutes one recycling process, and test pieces that had undergone up to five recycling processes were finally obtained. The test pieces obtained after the virgin product, the second recycling, and the fifth recycling were measured for the absorbance 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 as follows.
Furthermore, the electromagnetic wave absorption rate and electromagnetic wave reflectance rate after five recycling cycles were calculated relative to the virgin product.

A network analyzer "N5252A" manufactured by Keysight Corporation was used to measure various electromagnetic wave characteristics.
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.)

In Table 2 above, the content of the conductive material (CTN, carbon fiber) indicates the mass ratio (unit: mass %) of the conductive material in the resin composition.
As is clear from the above results, the crushed material of this embodiment was able to maintain excellent electromagnetic wave properties even after recycling. In contrast, the crushed material of the comparative example was significantly degraded in electromagnetic wave properties after recycling.

1. Resin composition (pellets)
2 Injection molding machine 3 Passed products 4 Rejected products 5 Scrap material 6 Crusher 7 Crushed material 8 Recycle

Claims (13)

pellets obtained from a resin composition containing a thermoplastic resin and carbon nanotubes;
The present invention relates to a crushed material of a resin composition containing a thermoplastic resin and carbon nanotubes, and when the crushed material is molded into a molded body having a thickness of 2 mm, the crushed material has an absorption rate of 40.0 to 100% at a frequency of 76.5 GHz calculated according to formula (A) ,
the thermoplastic resin contained in the pellets includes polybutylene terephthalate resin,
The mass ratio of the pellets to the crushed material is 10 to 90:90 to 10.
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 material of claim 1 , wherein the thermoplastic resin contained in the crushed material comprises polybutylene terephthalate resin. The material according to claim 1 or 2, wherein the resin composition constituting the crushed material contains 0.1 to 10.0 parts by mass of the carbon nanotubes per 100 parts by mass of the thermoplastic resin. The material according to any one of claims 1 to 3, wherein the resin composition constituting the crushed material is a recycled resin composition containing a thermoplastic resin and carbon nanotubes. The material according to any one of claims 1 to 4, wherein the resin composition constituting the crushed material is a molded body formed from a resin composition containing a thermoplastic resin and carbon nanotubes. The material according to any one of claims 1 to 5, wherein the resin composition constituting the crushed material further contains 10 to 100 parts by mass of an inorganic filler per 100 parts by mass of thermoplastic resin. In the resin composition constituting the crushed material, the thermoplastic resin contains polybutylene terephthalate resin,
The resin composition constituting the crushed material contains 0.1 to 10.0 parts by mass of the carbon nanotubes per 100 parts by mass of the thermoplastic resin,
the resin composition constituting the crushed material is a recycled product and/or a molded product of a resin composition containing a thermoplastic resin and carbon nanotubes,
The material according to any one of claims 1 to 6, wherein the resin composition constituting the crushed material further contains 10 to 100 parts by mass of an inorganic filler per 100 parts by mass of thermoplastic resin. The material according to any one of claims 1 to 7, wherein the pellets are virgin pellets.
9. The material according to claim 7 or 8. The material according to any one of claims 1 to 8 , wherein the pellet further contains 0.1 to 10.0 parts by mass of the carbon nanotubes per 100 parts by mass of the thermoplastic resin. The material according to any one of claims 1 to 9 , wherein the pellets further contain 10 to 100 parts by mass of an inorganic filler per 100 parts by mass of the thermoplastic resin. A molded article made from the material according to any one of claims 1 to 10 . A method for producing a molded body, comprising molding the material according to any one of claims 1 to 10 . The method for producing a molded article according to claim 12 , wherein the material is formed by injection molding or extrusion molding.