Pellet blended product and molded article

Abstract

To provide a pellet blended product and a molded article which enable provision of a molded article that can suppress warpage when being formed into the molded article, and is excellent in electromagnetic shielding property.SOLUTION: A pellet blended product is a blended product of a pellet of a resin composition containing a crystalline thermoplastic resin, an amorphous resin and a carbon fiber, wherein an average value of a flat ratio of a pellet cross section defined by 1-a / b is 0.30 or more (provided that a is a minor axis of a pellet cross section, and b is a major axis of the pellet cross section).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to pellet blends and molded articles.

Background Art

[0002] In recent years, electronic devices have been used in all fields. In particular, communication devices are increasing in number from those using relatively long-wavelength radio waves such as radio to those using short-wavelength radio waves such as mobile phones, satellite broadcasts, and wireless LANs, and electromagnetic shielding has become an important technology.

[0003] As a resin composition having electromagnetic shielding properties, for example, Patent Document 1 discloses a polybutylene terephthalate resin composition prepared by blending 100 parts by mass of polybutylene terephthalate resin (A), 2 to 6 parts by mass of carbon black (B), 0.3 to 4 parts by mass of carbon fiber (C), and 0.05 to 5 parts by mass of glycerin fatty acid ester (D). The glycerin fatty acid ester (D) is a glycerin fatty acid ester having a hydroxyl value of 200 or more, which is composed of at least one selected from glycerin and its dehydration condensate and a fatty acid having 12 or more carbon atoms. The volume resistivity of the resin composition is 1×10 10 ~1×10 17 Ω·cm, the transmission loss is -30 dB or less in the band of 75 to 110 GHz, and the electromagnetic wave absorption rate is 30% or more.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, when manufacturing a molded article formed from a resin composition excellent in electromagnetic wave shielding properties, carbon fibers are blended with a crystalline thermoplastic resin. However, in a crystalline thermoplastic resin such as polybutylene terephthalate resin, the molded article may be warped. Therefore, in order to suppress such warping, an amorphous resin is blended. Regarding a molded article formed from a resin composition containing such a crystalline thermoplastic resin, an amorphous thermoplastic resin, and carbon fibers, it is required to further improve the electromagnetic wave shielding properties of the obtained molded article while effectively suppressing warping. An object of the present invention is to solve such problems, and to provide a pellet blend and a molded article capable of suppressing warping and providing a molded article excellent in electromagnetic wave shielding properties when formed into a molded article.

Means for Solving the Problems

[0006] As a result of investigations by the present inventors based on the above problems, it has been found that the above problems can be solved by setting the average value of the flatness ratio of the pellets to a predetermined value or more. Specifically, the above problems have been solved by the following means. <1>A blend of pellets of a resin composition containing a crystalline thermoplastic resin, an amorphous resin, and carbon fibers, The average value of the flatness ratio of the pellet cross-section defined by 1 - a / b is 0.30 or more (where a is the minor axis of the pellet cross-section and b is the major axis of the pellet cross-section), the pellet blend. <2>The pellet blend according to <1>, wherein the flatness ratio is 0.45 or more. <3>The pellet blend according to <1> or <2>, wherein the flatness ratio is 0.8 or less. <4>The pellet blend according to any one of <1> to <3>, wherein the crystalline thermoplastic resin contains polybutylene terephthalate resin. <5>The pellet blend according to any one of <1> to <4>, wherein the amorphous resin contains a polystyrene-based resin. <6>The pellet blend according to any one of <1> to <5>, which is for forming an electromagnetic wave shielding member. <7>The flatness ratio is 0.45 or more and 0.8 or less, The crystalline thermoplastic resin contains a polybutylene terephthalate resin, The amorphous resin contains a polystyrene-based resin, The pellet blend according to any one of <1> to <6>, which is for forming an electromagnetic wave shielding member. <8>A molded article formed from the pellet blend according to any one of <1> to <7>.

Advantages of the Invention

[0007] According to the present invention, when formed into a molded article, warpage can be suppressed, and a pellet blend and a molded article capable of providing a molded article excellent in electromagnetic wave shielding properties can be provided.

Brief Description of the Drawings

[0008]

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[0009] FIG. 1, FIG. 8, FIG. 15, and FIG. 22 are perspective views each showing an example of a single pellet included in the pellet blend of the present embodiment. The articles shown in each figure are pellets used for manufacturing automotive parts, parts for electric and electronic devices, building material parts, parts for other precision instruments, and the like. An example of the pellet has a horizontal length of approximately 2.8 mm when viewed from the front.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. Note that the following present embodiment is an exemplification for explaining the present invention, and the present invention is not limited to only the present embodiment. In this specification, "~" is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value. Also, any combination of the upper limit value and the lower limit value of the numerical values in this specification can be cited as an example of the present embodiment. In this specification, various physical property values and characteristic values are those at 23°C unless otherwise specified. In this specification, unless otherwise specified, the weight average molecular weight and the number average molecular weight are measured by the GPC (gel permeation chromatography) method using HLC-8320GPC EcoSEC manufactured by Tosoh Corporation, using tetrahydrofuran as the solvent, using Shodex KF-G, KF-805L×3, KF-800D as the columns, at a column temperature of 40°C and a flow rate of 1.2 mL / min, and detected at a detection wavelength of 254 nm, and are values in terms of polystyrene conversion. When the measurement methods and the like described in the standards shown in this specification differ depending on the year, unless otherwise specified, they are based on the standards as of January 1, 2023. When the measurement methods and the like described in the standards shown in this specification have been abolished as of January 1, 2023, they are based on the standards at the time of abolition.

[0011] The pellet blend of this embodiment is a blend of pellets of a resin composition containing a crystalline thermoplastic resin, an amorphous resin, and carbon fibers, and the average value of the flatness ratio of the pellet cross-section defined by 1 - a / b is 0.30 or more (where a is the minor axis of the pellet cross-section and b is the major axis of the pellet cross-section). By using such a pellet blend, warpage can be suppressed, and a molded article excellent in electromagnetic shielding properties can be provided.

[0012] When manufacturing a molded article excellent in electromagnetic shielding properties, carbon fibers are blended with a thermoplastic resin. Further, an amorphous resin may be blended to suppress warpage of a molded article formed from a resin composition containing a crystalline thermoplastic resin. And for a molded article formed from a resin composition containing a crystalline thermoplastic resin, an amorphous thermoplastic resin, and carbon fibers, it is required to further improve the electromagnetic shielding properties of the obtained molded article while effectively suppressing warpage. Under such circumstances, when the present inventors conducted studies, it was found that when forming a resin composition molded article in which an amorphous resin is blended with a crystalline thermoplastic resin and carbon fibers, the warpage is improved, but the electromagnetic shielding property may or may not be significantly improved. Further studies on this reason revealed that when manufacturing a molded article from a resin composition containing a crystalline thermoplastic resin, an amorphous resin, and carbon fibers, usually, it passes through pellets of the resin composition obtained by melt-kneading. When manufacturing these pellets, it was found that the electromagnetic shielding property is likely to be improved by intentionally suppressing the dispersion of carbon fibers and minimizing the fragmentation of carbon fibers. That is, it was found that by melt-kneading to such an extent that the carbon fibers in the pellets are not uniformly dispersed, the fiber length of the carbon fibers remains relatively long in the resulting molded article, and as a result, the electromagnetic shielding property is improved. And it was found that by making a pellet blend containing pellets with a large flatness ratio so that this non-uniform dispersion state of the carbon fibers is maintained, the electromagnetic shielding property of the resulting molded article can be improved. That is, in the process of cutting the strands, the ratio of carbon fibers to the resin is locally disturbed in a pellet blend containing pellets with a large flatness ratio. It was found that by locally disturbing the ratio of the two in this way, the fiber length of the carbon fibers is appropriately maintained.

[0013] The pellet blend of the present embodiment has an average value of the flatness ratio of the pellet cross-section defined by 1 - a / b of 0.30 or more (where a is the minor axis of the pellet cross-section and b is the major axis of the pellet cross-section). The pellet cross-section is, for example, in the case of pellets obtained by cutting a resin composition extruded in a strand shape, the cross-section in the extrusion direction (the longitudinal direction of the strand-shaped resin composition), that is, the cut surface. The cut surface is, for example, the surface shown in FIG. 4 or FIG. 5. By making the pellets have such a flat cross-sectional shape, the aggregated state of the carbon fibers is appropriately maintained in the pellets, and the electromagnetic shielding property when made into a molded article can be improved.

[0014] In the flatness ratio of the pellet cross-section defined by the above 1-a / b, a is the minor axis of the pellet cross-section, and b is the major axis of the pellet cross-section. Here, b (the major axis of the pellet cross-section) is the length of the line connecting two points on the outer periphery on one surface of the pellet cross-section, which is the longest in distance. Also, a (the minor axis of the pellet cross-section) is a line that perpendicularly bisects the major axis b and is the length of the line connecting two points on the outer periphery on one surface of the pellet cross-section. The average value of the flatness ratio in this embodiment is obtained by selecting any 100 pellets from the pellet blend, measuring the minor axis a and the major axis b for one cross-section of each pellet to calculate the flatness ratio, and taking the average value.

[0015] The average value of the flatness ratio is 0.30 or more, preferably 0.35 or more, more preferably 0.40 or more, still more preferably 0.45 or more, even more preferably 0.50 or more, and preferably 0.80 or less, more preferably 0.70 or less, still more preferably 0.65 or less, even more preferably 0.60 or less, and even more preferably 0.57 or less. By setting it to be not less than the lower limit value, the electromagnetic wave shielding property tends to be improved. Also, by setting it to be not more than the upper limit value, the injection molding efficiency tends to be improved.

[0016] The pellet blend of this embodiment preferably has an average length of the major axis b of the cross-section of 2.5 mm or more, more preferably 3.0 mm or more, still more preferably 3.3 mm or more, and preferably 3.5 mm or less, more preferably 3.8 mm or less, still more preferably 4.0 mm or less. The pellet blend of this embodiment preferably has an average length (cut length) in the longitudinal direction of 1.0 mm or more, more preferably 1.5 mm or more, still more preferably 2.0 mm or more, and preferably 8.0 mm or less, more preferably 6.0 mm or less, still more preferably 4.0 mm or less. The average length in the longitudinal direction shall be the average value of the lengths in the longitudinal direction of 100 pellets.

[0017] The pellet blend of the present embodiment has an average value of the flatness ratio of the pellet cross-section satisfying the above value, with 2 or more pellets, usually 100 or more pellets, and usually 10×10 10 grains or less aggregated. Examples of the aggregate here include a state packaged with a packaging material or the like.

[0018] The pellet blend of the present embodiment can be obtained by melt-kneading a resin composition containing a crystalline thermoplastic resin, an amorphous resin, and carbon fibers in an extruder, extruding it into strands, and cutting it. For the extruder, each component may be mixed in advance and supplied at once, or each component may be supplied to the extruder using a feeder without pre-mixing or only partially pre-mixing. The extruder may be a single-screw extruder or a twin-screw extruder. Also, it is preferable to supply the carbon fibers from a side feeder in the middle of the cylinder of the extruder. The cross-section of the die opening when extruding the resin composition into strands is usually substantially circular. Since the carbon fibers in the resin composition in the present embodiment are in a non-uniform state, the cross-section may become a flat shape when cutting the strand-shaped resin composition into pellets. Therefore, the average value of the flatness ratio of the pellet cross-section is 0.30 or more. The diameter (inner diameter) of the cross-section of the die opening is preferably 1.0 mm or more, more preferably 2.0 mm or more, further preferably 3.0 mm or more, and preferably 8.0 mm or less, more preferably 7.0 mm or less, and further preferably 6.0 mm or less.

[0019] In order to make the pellet blend of the present embodiment satisfy the flatness ratio of a desired cross section, an amorphous resin is blended, and after the crystalline thermoplastic resin and the amorphous resin are uniformly melt-kneaded in the first kneading section in the extruder, chopped strands of carbon fiber are supplied from a side feeder in the middle of the cylinder, and it is exemplified that the kneaded components of the crystalline resin and the amorphous resin and the carbon fiber are not sufficiently kneaded in the second kneading section. That is, in the resin composition in which the crystalline thermoplastic resin and the amorphous resin are present, the chopped strands of carbon fiber partially remain un-fibrillated. That is, by not sufficiently melt-kneading the resin component composed of the crystalline thermoplastic resin and the amorphous resin and the carbon fiber, it becomes easy to form regions with a large amount and a small amount of carbon fiber present. In addition, in order to make the pellet blend of the present embodiment satisfy the flatness ratio of a desired cross section, it is exemplified to use a slow compression screw, use a low shear screw, slow down the melt-kneading speed, use a twin-screw extruder, introduce carbon fiber from a side screw, widen the gap between the screw and the barrel, etc. Further, when cutting the strand-shaped pellets extruded from the extruder, it is exemplified to slow down the extrusion speed of the strand-shaped resin composition, increase the strand temperature during cutting, increase the extrusion temperature, etc. The heating temperature during melt-kneading can usually be appropriately selected from the range of 170 to 350°C.

[0020] <Crystalline thermoplastic resin> The resin composition in the present embodiment contains a crystalline thermoplastic resin. The crystalline thermoplastic resin refers to a resin having a clear melting point. Examples of the crystalline thermoplastic resin used in the present embodiment preferably include crystalline thermoplastic polyester resins; polyamide resins; polyethylene resins; polyolefin resins such as polypropylene resins and cyclic olefin resins; polyacetal resins; polyphenylene sulfide resins; polysulfone resins; etc. It is more preferable to contain at least one of a polyester resin and a polyamide resin, even more preferable to contain a polyester resin, and still more preferable to contain a polybutylene terephthalate resin.

[0021] In this embodiment, a preferred example of the crystalline thermoplastic resin is to contain a polyester resin (preferably, polybutylene terephthalate resin), and 40% by mass or more (preferably 50% by mass or more) of the resin composition is a polyester resin (preferably, polybutylene terephthalate resin).

[0022] The resin composition in this embodiment may also be an alloy obtained by blending two or more crystalline thermoplastic resins. When blending two or more crystalline thermoplastic resins, they usually do not dissolve completely and form a sea-island structure. Since it is difficult for carbon fibers to exist in the island part, as a result, the region where carbon fibers exist in the resin composition or pellets becomes narrow, and even if the blending amount of carbon fibers is reduced, electromagnetic wave shielding properties can be effectively achieved. Hereinafter, details of each crystalline thermoplastic resin will be described.

[0023] <<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 to contain at least polybutylene terephthalate resin. The polybutylene terephthalate resin used in the resin composition in this embodiment is a polyester resin having a structure in which terephthalic acid units and 1,4-butanediol units are ester-bonded. In addition to polybutylene terephthalate resin (homopolymer), it includes 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.

[0024] 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, 4,4'-diphenyletherdicarboxylic acid, etc.; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 4,4'-dicyclohexyldicarboxylic acid, etc.; and aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, dimer acid, etc. The polybutylene terephthalate resin used in this embodiment preferably has terephthalic acid units accounting for 80 mol% or more of all dicarboxylic acid units, and more preferably 90 mol% or more.

[0025] As the diol units, one or more other diol units may be included 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, ethylene oxide-added diol of bisphenol A, etc. In addition to the bifunctional monomers as described above, trifunctional monomers such as trimellitic acid, trimesic acid, pyromellitic acid, pentaerythritol, trimethylolpropane, etc. for introducing a branched structure and monofunctional compounds such as fatty acids for molecular weight adjustment can also be used in a small amount in combination. The polybutylene terephthalate resin used in this embodiment preferably has 1,4-butanediol units accounting for 80 mol% or more of all diol units, and more preferably 90 mol% or more.

[0026] As described above, the polybutylene terephthalate resin is preferably a polybutylene terephthalate homopolymer obtained by polycondensing terephthalic acid and 1,4-butanediol. Further, it may be a polybutylene terephthalate copolymer containing at least one dicarboxylic acid other than the terephthalic acid as a carboxylic acid unit and / or at least one diol other than the 1,4-butanediol as a diol unit. When the polybutylene terephthalate resin is a polybutylene terephthalate resin modified by copolymerization, specific preferred copolymers include polyester ether resins copolymerized with polyalkylene glycols, particularly polytetramethylene glycol, dimer acid copolymerized polybutylene terephthalate resins, and isophthalic acid copolymerized polybutylene terephthalate resins. Among them, it is preferable to use a polyester ether resin copolymerized with polytetramethylene glycol. Note that these copolymers refer to those having a copolymerization amount of 1 mol% or more and less than 50 mol% in all segments of the polybutylene terephthalate resin. Among them, the copolymerization amount is preferably 2 mol% or more and less than 50 mol%, more preferably 3 to 40 mol%, and even more preferably 5 to 20 mol%. By setting such a copolymerization ratio, fluidity, toughness, and tracking resistance tend to be easily improved, which is preferable.

[0027] The amount of terminal carboxyl groups in the polybutylene terephthalate resin may be appropriately selected and determined, but is usually 60 eq / ton or less, preferably 50 eq / ton or less, and more preferably 30 eq / ton or less. By setting it below the above upper limit value, the alkali resistance and hydrolysis resistance tend to be improved. The lower limit value of the amount of terminal carboxyl groups is not particularly defined, but considering the productivity of the production of the polybutylene terephthalate resin, it is usually 10 eq / ton or more.

[0028] The amount of terminal carboxyl groups in the polybutylene terephthalate resin is a value measured by titration using a 0.01 mol / L benzyl alcohol solution of sodium hydroxide after dissolving 0.5 g of the polybutylene terephthalate resin in 25 mL of benzyl alcohol. As a method for adjusting the amount of terminal carboxyl groups, any conventionally known method may be used, such as a method of adjusting polymerization conditions such as the raw material charging ratio, polymerization temperature, and decompression method during polymerization, or a method of reacting a terminal blocking agent.

[0029] The intrinsic viscosity of the polybutylene terephthalate resin is preferably 0.5 to 2 dL / g. From the viewpoints of moldability and mechanical properties, those having an intrinsic viscosity in the range of 0.6 to 1.5 dL / g are more preferable. 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. Further, by setting it to 2 dL / g or less, the fluidity of the resin composition is further improved, and the moldability tends to be improved. The intrinsic viscosity of the polybutylene terephthalate resin is a value measured at 30 °C in a mixed solvent of tetrachloroethane and phenol at a mass ratio of 1:1.

[0030] The polybutylene terephthalate resin can be produced by melt-polymerizing a dicarboxylic acid component mainly composed of terephthalic acid or an ester derivative thereof and a diol component mainly composed of 1,4-butanediol in a batch or continuous manner. Further, after producing a low molecular weight polybutylene terephthalate resin by melt polymerization, the degree of polymerization (or molecular weight) can also be increased to a desired value by solid-phase polymerization under a nitrogen stream 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 melt-polycondensed continuously.

[0031] The catalyst used when performing the esterification reaction may be a conventionally known one, and examples thereof include titanium compounds, tin compounds, magnesium compounds, calcium compounds, and the like. Among these, a particularly suitable one is a titanium compound. Specific examples of the titanium compound as an esterification catalyst include titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, tetrabutyl titanate, and titanium phenolates such as tetraphenyl titanate.

[0032] As the polyester resin, in addition to the above, the descriptions in paragraphs 0013 to 0016 of JP-A-2010-174223 can be referred to, and the content thereof is incorporated herein.

[0033] The crystalline thermoplastic resin used in this embodiment may be a recycled product (including recycled products, material recycled products, chemical recycled products, etc.), a defective product, or a scrap material during the molding of the crystalline thermoplastic resin.

[0034] In the resin composition in this embodiment, the content of the crystalline thermoplastic resin (preferably polybutylene terephthalate resin) is preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more in the resin composition. By setting the content to be equal to or higher than the lower limit value, the heat resistance tends to be further improved. Also, the content of the crystalline thermoplastic resin (preferably polybutylene terephthalate resin) is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less, still more preferably 65% by mass or less, even more preferably 60% by mass or less, and particularly preferably 55% by mass or less. By setting the content to be equal to or lower than the upper limit value, the dimensional stability of the molded product tends to be improved. The resin composition in this embodiment may contain only one type of crystalline thermoplastic resin or may contain two or more types. When containing two or more types, the total amount is preferably within the above range.

[0035] <Amorphous resin> The resin composition in this embodiment contains an amorphous resin. An amorphous resin refers to a resin that does not have a distinct melting point. The amorphous resin is usually a thermoplastic resin. Examples of the amorphous thermoplastic resin used in this embodiment include polycarbonate resin, polystyrene-based resins (HIPS, AS resin, ABS resin, etc.), polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), modified polyphenylene ether resin, polyethersulfone resin, polyetherimide resin, and polyamideimide resin. Polycarbonate resin, modified polyphenylene ether, and polystyrene-based resins are preferred, polycarbonate resin and polystyrene-based resins are more preferred, and polystyrene-based resins are even more preferred.

[0036] An example of the embodiment of the amorphous thermoplastic resin used in this embodiment is a form containing a polystyrene-based resin (for example, high-impact polystyrene, HIPS). In this case, the proportion of the polystyrene-based resin is preferably 90% by mass or more (preferably 95% by mass or more, more preferably 99% by mass or more) of the resin composition.

[0037] <<Polystyrene-based resin>> Examples of the polystyrene-based resin include a homopolymer of a styrene-based monomer and a copolymer of a styrene-based monomer and a monomer copolymerizable with the styrene-based monomer. Examples of the styrene-based monomer include styrene, α-methylstyrene, chlorostyrene, methylstyrene, and tert-butylstyrene. In the polystyrene-based resin in this embodiment, 50 mol% or more of the monomer units are styrene-based monomers. As polystyrene resins, more specifically, polystyrene resin, acrylonitrile-styrene copolymer (AS resin), high impact polystyrene resin (HIPS), acrylonitrile-butadiene-styrene copolymer (ABS resin), acrylonitrile-acrylic rubber-styrene copolymer (AAS resin), acrylonitrile-styrene-acrylic rubber copolymer (ASA resin), acrylonitrile-ethylene propylene rubber-styrene copolymer (AES resin), styrene-IPN type rubber copolymer and other resins can be mentioned. In this embodiment, the polystyrene 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), styrene-IPN type rubber copolymer, and more preferably high impact polystyrene resin (HIPS).

[0038] When the polystyrene resin contains a rubber component, the content of the rubber component in the polystyrene resin is preferably 3 to 70% by mass, more preferably 5 to 50% by mass, and even more preferably 7 to 30% by mass. By setting the content of the rubber component to 3% by mass or more, the impact resistance tends to improve, and by setting it to 50% by mass or less, the flame retardancy tends to improve, which is preferable. Also, the average particle diameter 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. When the average particle diameter is 0.05 μm or more, the impact resistance tends to be easily improved, and when it is 10 μm or less, the appearance tends to improve, which is preferable.

[0039] The weight-average molecular weight of the polystyrene resin is usually 50,000 or more, preferably 100,000 or more, more preferably 150,000 or more, and is usually 500,000 or less, preferably 400,000 or less, more preferably 300,000 or less. Also, the number-average molecular weight is usually 10,000 or more, preferably 30,000 or more, more preferably 50,000 or more, and is preferably 500,000 or less, more preferably 300,000 or less.

[0040] The melt flow rate (MFR) of the polystyrene resin measured in accordance with JIS K7210 (temperature 200 °C, load 5 kgf) is preferably 0.1 to 30 g / 10 min, more preferably 0.5 to 25 g / 10 min. When the MFR is 0.1 g / 10 min or more, the fluidity tends to improve, and when it is 30 g / 10 min or less, the impact resistance tends to improve.

[0041] Examples of such a method for producing a polystyrene resin include known methods such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization.

[0042] <<Polycarbonate resin>> The polycarbonate resin is a branched or unbranched homopolymer or copolymer obtained by reacting a dihydroxy compound or a small amount of a polyhydroxy compound with phosgene or a carbonic acid diester. The method for producing the polycarbonate resin is not particularly limited, and those produced by conventionally known phosgene methods (interfacial polymerization methods) or melting methods (transesterification methods) can be used.

[0043] As the starting dihydroxy compound, an aromatic dihydroxy compound is preferred, a bisphenol is more preferred, 2,2-bis(4-hydroxyphenyl)propane (= bisphenol A), tetramethyl bisphenol A, bis(4-hydroxyphenyl)-p-diisopropylbenzene, hydroquinone, resorcinol, 4,4-dihydroxydiphenyl, etc. are even more preferred, and bisphenol A is even more preferred. Further, a compound in which one or more tetraalkylphosphonium sulfonates are bonded to the above aromatic dihydroxy compound can also be used.

[0044] Among the above-described polycarbonate resins, an aromatic polycarbonate resin derived from 2,2-bis(4-hydroxyphenyl)propane (bisphenol A type polycarbonate resin) or an aromatic polycarbonate copolymer derived from 2,2-bis(4-hydroxyphenyl)propane and another aromatic dihydroxy compound is preferred. Further, a copolymer mainly composed of an aromatic polycarbonate resin, such as a copolymer with a polymer or oligomer having a siloxane structure, may also be used. Furthermore, two or more of the above-described polycarbonate resins may be mixed and used.

[0045] To adjust the molecular weight of the polycarbonate resin, a monohydric aromatic hydroxy compound may be used. For example, m- and p-methylphenol, m- and p-propylphenol, p-tert-butylphenol, p-long-chain alkyl-substituted phenol, etc. may be mentioned.

[0046] 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. Also, 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 fluidity of the resin composition is improved, and the moldability tends to be improved. When two or more polycarbonate resins are included, it is preferable that the mixture satisfies the above range.

[0047] In this embodiment, the viscosity average molecular weight (Mv) of the polycarbonate resin is a value calculated from the following Schnell viscosity formula by measuring the viscosity of a methylene chloride solution of the polycarbonate resin at 20 °C using an Ubbelohde viscometer to obtain the intrinsic viscosity ([η]). [η]=1.23×10 -4 Mv 0.83

[0048] The melt flow rate (MFR) of the polycarbonate resin measured in accordance with JIS K7210 (temperature 300 °C, load 1.2 kgf) is preferably 1 g / 10 min or more, more preferably 8 g / 10 min or more, even more preferably 10 g / 10 min or more, still more preferably 18 g / 10 min or more, yet more preferably 20 g / 10 min or more, and even still more preferably 30 g / 10 min or more. By setting the lower limit value or more, the electromagnetic wave absorption rate of the resulting resin composition or molded article tends to be further improved. Also, the upper limit of the MFR is, for example, 100 g / 10 min or less, and further may be 80 g / 10 min or less.

[0049] The method for producing the polycarbonate resin is not particularly limited, and polycarbonate resins produced by either the phosgene method (interfacial polymerization method) or the melt method (transesterification method) can be used. Further, a polycarbonate resin obtained by subjecting a polycarbonate resin produced by the melt method to a post-treatment for adjusting the amount of terminal OH groups is also preferable.

[0050] The amorphous resin used in this embodiment may be a recycled product (including recycled products, material recycled products, chemical recycled products, etc.), a defective product, or a scrap material during amorphous resin molding.

[0051] The content of the amorphous resin in the resin composition is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, further preferably 30 parts by mass or more, still more preferably 35 parts by mass or more, even more preferably 40 parts by mass or more, and even more preferably 45 parts by mass or more, based on 100 parts by mass in total of the crystalline thermoplastic resin and the amorphous resin. Also, it is preferably 70 parts by mass or less, more preferably 65 parts by mass or less, further preferably 60 parts by mass or less, and still more preferably 55 parts by mass or less. By setting it to be not less than the lower limit value, the dimensional stability of the molded product tends to be more improved. Also, by setting it to be not more than the upper limit value, the heat resistance tends to be more improved. The resin composition in this embodiment may contain only one kind of amorphous resin or two or more kinds of amorphous resins. When two or more kinds are contained, the total amount is preferably within the above range.

[0052] <Carbon fiber> The resin composition in this embodiment contains carbon fiber. By containing carbon fiber, the electromagnetic wave shielding property of the obtained molded product can be improved. The type of the carbon fiber is not particularly defined, and either polyacrylonitrile-based carbon fiber (PAN-based fiber) or pitch-based carbon fiber using pitch is preferably used, and polyacrylonitrile-based carbon fiber (PAN-based fiber) is more preferable. In addition, carbon fibers with a tensile strength of 5.0 GPa or less (preferably 3.5 to 5.0 GPa) as measured in accordance with JIS R7601 at 23°C can also be used.

[0053] The carbon fiber is preferably a chopped strand. The carbon fiber preferably has a lower limit of the number average fiber length (cut length) of 2 mm or more, more preferably 3 mm or more. The upper limit of the number average fiber length is preferably 10 mm or less, more preferably 8 mm or less, and even more preferably 7 mm or less. The carbon fiber preferably has a number average fiber diameter of 3 to 20 μm, more preferably 5 to 15 μm. By using carbon fibers within such a range, the resulting molded product can have an excellent balance between mechanical strength and appearance. Specific examples of the carbon fiber include, for example, Torayca manufactured by Toray Industries, Inc., Besfight Filament manufactured by Toho Tenax Co., Ltd., Pyrofil manufactured by Mitsubishi Chemical Corporation, and the like.

[0054] The carbon fiber may also be recycled products (including recycled products, material recycled products, chemical recycled products, etc.), defective products, or scrap materials such as carbon fiber rovings.

[0055] The content of carbon fiber in the resin composition is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, still more preferably 10 parts by mass or more, even more preferably 14 parts by mass or more, and even more preferably 24 parts by mass or more, with respect to a total of 100 parts by mass of the crystalline thermoplastic resin and the amorphous resin. Also, it is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, still more preferably 82 parts by mass or less, even more preferably 67 parts by mass or less, and even more preferably 45 parts by mass or less, and still even more preferably 40 parts by mass or less, and particularly even more preferably 35 parts by mass or less. By setting it to be not less than the lower limit value, the electromagnetic wave shielding property tends to be further improved. Also, by setting it to be not more than the upper limit value, the fluidity during injection molding tends to be further improved.

[0056] The content of carbon fiber in the resin composition is also preferably 5% by mass or more, more preferably 7.5% by mass or more, still more preferably 8% by mass or more, even more preferably 9% by mass or more, and even more preferably 11% by mass or more, in 100% by mass of the resin composition. Also, it is preferably 50% by mass or less, more preferably 45% by mass or less, still more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 25% by mass or less. The resin composition in this embodiment may contain only one kind of carbon fiber or may contain two or more kinds. When two or more kinds are contained, it is preferable that the total amount is within the above range.

[0057] In addition to the above, the resin composition in the present embodiment may contain other components. Examples of other components include electromagnetic wave absorbers other than carbon fibers, colorants (pigments, dyes), reactive compounds, flame retardants, flame retardant aids, stabilizers, mold release agents, ultraviolet absorbers, antistatic agents, antifogging agents, antiblocking agents, fluidity improvers, impact resistance improvers, plasticizers, dispersants, antibacterial agents, and the like. The content of these components is preferably 0% by mass or more and less than 20% by mass, more preferably less than 15% by mass, still more preferably less than 10% by mass, and may even be less than 1% by mass in 100% by mass of the resin composition. Details of these can be referred to the descriptions in paragraphs 0084 to 0141 of International Publication No. 2021 / 256488, and the contents thereof are incorporated herein.

[0058] In the resin composition of the present embodiment, it is preferable that the total of the crystalline thermoplastic resin, the amorphous resin, and the carbon fiber occupies 80% by mass or more of the resin composition, more preferably 85% by mass or more, and still more preferably 90% by mass or more. Also, the resin composition in the present embodiment can be configured to substantially not contain fillers other than carbon fibers. Substantially not containing means that the content of fillers other than carbon fibers contained in the resin composition is less than 15% by mass of the content of carbon fibers, preferably less than 10% by mass, more preferably less than 5% by mass, still more preferably less than 3% by mass, and may even be less than 1% by mass.

[0059] The pellet blend of the present embodiment is preferably used for forming an electromagnetic wave shielding member.

[0060] The molded article formed from the pellet blend of the present embodiment preferably has an electromagnetic wave shielding property of less than 0 dB. The lower limit of the electromagnetic wave shielding property is not particularly defined, but is preferably -100 dB or more in practice. The electromagnetic wave shielding property is measured according to the method described in the examples below.

[0061] The molded article of the present embodiment is formed from the pellet blend of the present embodiment. Such a molded article can achieve excellent electromagnetic wave shielding properties with appropriate aggregation of carbon fibers. The manufacturing method of the molded article in the present embodiment is not particularly limited, and any molding method generally adopted for molding pellets of resin compositions can be arbitrarily adopted. Examples thereof include injection molding method, ultra-high speed injection molding method, injection compression molding method, two-color molding method, hollow molding methods such as gas assist, molding method using an insulating mold, molding method using a rapid heating mold, foam molding (including supercritical fluids), insert molding, IMC (in-mold coating molding) molding method, extrusion molding method, sheet molding method, thermoforming method, rotational molding method, lamination molding method, press molding method, blow molding method, etc. Among them, injection molding is preferred.

[0062] The molded article of the present embodiment is preferably used as an electromagnetic wave shielding material, and specifically, it is used for automotive electrical component applications. For example, it is used for housings, covers, mounting members, etc. of electronic devices. The molded article of the present embodiment can be suitably used for in-vehicle millimeter-wave radars used in brake automatic control devices, inter-vehicle distance control devices, pedestrian accident reduction steering devices, false transmission suppression control devices, acceleration suppression devices when the pedal is misstepped, approaching vehicle warning devices, lane keeping support devices, rear-end collision prevention warning devices, parking support devices, vehicle peripheral obstacle warning devices, etc.; millimeter-wave radars for railways and aviation used in home monitoring / level crossing obstacle detection devices, in-train content transmission devices, tram / railway collision prevention devices, runway foreign object detection devices, etc.; millimeter-wave radars for traffic infrastructure such as intersection monitoring devices and elevator monitoring devices; millimeter-wave radars for various security devices; millimeter-wave radars for medical and nursing care such as child and elderly monitoring systems; millimeter-wave radars for transmitting various information contents; etc.

Examples

[0063] The present invention will be described in more detail with reference to the following examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not depart from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. When it is difficult to obtain the measuring instruments and the like used in the examples due to their being obsolete or the like, measurements can be made using other devices having equivalent performance.

[0064] 1. Raw materials The following raw materials were used. [Table 1]

[0065] 2. Example 1, Example 2, Comparative Example 1 <Manufacture of pellet blend> Among the components shown in Table 1 above, the crystalline resin and the amorphous resin were put into a stainless steel tumbler at the ratios shown in Table 2 and mixed for about 15 minutes. The obtained mixture was fed into a twin-screw extruder ("TEX-42αII" manufactured by Japan Steel Works, Ltd.) from the main feed port. Also, carbon fiber or glass fiber was supplied from a side feeder provided downstream of the first kneading section of the extruder so as to be at the ratios shown in Table 2. The barrel temperature of the first kneading section was set at 260 °C, the barrel temperature of the second kneading section was set at 270 °C, and melt kneading was performed under the conditions of a discharge of 150 kg / h and a screw rotation speed of 240 rpm. The extruded strands were cooled in a water tank using a die with 15 holes (Φ4.5 mm) and a land length of 9 mm, and then a pellet blend was produced using a pelletizer so that the pellet cut length was approximately 3 mm.

[0066] Four pellets of a typical shape were taken out from the obtained pellets of Example 2 and shown in FIGS. 29 to 32. For each drawing, one pellet was photographed from six directions.

[0067] <Average value of flatness ratio of pellet cross-section> One hundred pellets were randomly taken out from the pellets obtained above, and the major axis b and minor axis a of the pellet cross-section were measured using an electron microscope. The major axis b of the pellet cross-section was defined as the length of the line connecting two points on the outer periphery on one side of the pellet cross-section, which had the longest distance. Also, the minor axis a of the pellet cross-section was defined as the length of the line connecting two points on the outer periphery on one side of the pellet cross-section, which was perpendicular to and bisected the major axis b. For the 100 measured samples, the flatness ratio of the pellet cross-section defined by 1 - a / b was calculated, and the average value of the flatness ratio was measured.

[0068] <Low warpage property> After drying the pellet blend obtained by the above manufacturing method at 120°C for 5 hours, a disk-shaped test piece with a diameter of Φ100 mm and a thickness of 1.6 mm was molded using an injection molding machine (manufactured by Shibaura Machine Co., Ltd., "J50AD") under the conditions of a cylinder temperature of 260°C, a mold temperature of 80°C, and a cooling time of 15 seconds. As an evaluation of warpage, the warpage amount of the obtained molded product was measured. The warpage amount was calculated from the difference between the maximum height and the minimum height detected by scanning the solid of the plate test piece using a Keyence three-dimensional measuring machine VR-3000. A: Less than 1 mm B: 1 mm or more and less than 5 mm C: 5 mm or more

[0069] <Electromagnetic wave shielding property> Using the pellet blend obtained above, injection molding was performed using an injection molding machine (manufactured by Shibaura Machine Co., Ltd., "EC-160NII") at a cylinder set temperature of 260°C and a mold temperature of 80°C to obtain a flat plate-shaped test piece with dimensions of 150 mm × 150 mm × 2 mm thickness. For the obtained test piece, the electromagnetic wave shielding property (unit: dB) at 100 MHz was measured using an electromagnetic wave shielding property measuring device compliant with the KEC (Kansai Electronic Industry Promotion Center) method. Here, the electromagnetic wave shielding property is marked with a negative value, and 0 dB means that the transmission loss of the electromagnetic wave is 0%.

[0070]

Table 2

[0071] The unit of the amount of each component in Table 2 above is parts by mass. As is clear from the above results, the resin composition of this embodiment was able to effectively suppress warping and improve electromagnetic shielding properties (Examples 1 and 2). In contrast, Comparative Example 1 without a polystyrene-based resin had a large warping.

Claims

1. A blend of pellets of a resin composition containing a crystalline thermoplastic resin, an amorphous resin, and carbon fibers, wherein the average value of the flatness ratio of the pellet cross-section defined by 1 - a / b is 0.30 or more (where a is the minor axis of the pellet cross-section and b is the major axis of the pellet cross-section), the pellet blend.

2. The pellet blend according to Claim 1, wherein the flatness ratio is 0.45 or more.

3. The pellet blend according to Claim 1 or 2, wherein the flatness ratio is 0.8 or less.

4. The pellet blend according to Claim 1 or 2, wherein the crystalline thermoplastic resin contains a polybutylene terephthalate resin.

5. The pellet blend according to Claim 1 or 2, wherein the amorphous resin contains a polystyrene-based resin.

6. The pellet blend according to Claim 1 or 2, which is for forming an electromagnetic shielding member.

7. the flatness ratio is 0.45 or more and 0.8 or less, the crystalline thermoplastic resin contains a polybutylene terephthalate resin, the amorphous resin contains a polystyrene-based resin, and it is for forming an electromagnetic shielding member, the pellet blend according to Claim 1.

8. A molded article formed from the pellet blend according to Claim 1, 2, or 7.

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