Thermoplastic resin composition and molded article

Abstract

Disclosed is a thermoplastic resin composition which contains a photoluminescent pigment (A), carbon black (B), a polyolefin wax (C), and a polyolefin resin (D). The carbon black (B) is contained in an amount of 0.1-10 mass% based on 100 mass% of the thermoplastic resin composition, and the content mass ratio (B) / (C) of the carbon black (B) to the polyolefin wax (C) is 0.1 to 10. Also disclosed is a molded article.

Description

Thermoplastic resin composition and molded article

[0001] The present disclosure relates to a thermoplastic resin composition and a molded article.

[0002] Molded articles formed from thermoplastic resin compositions are relatively inexpensive and have excellent properties, and are therefore used in a wide range of fields, including automobile parts, home appliance parts, office supplies, building materials, and decorative items. However, the appearance and feel of such molded articles can sometimes give a cheap impression compared to molded articles made from metal materials, inorganic materials, or wood. Therefore, there is a demand for highly designed molded articles that have a metallic feel like metal. To achieve a metallic appearance, a method of painting using a metallic paint is known. However, in consideration of simplifying the manufacturing process and reducing the environmental impact, there is currently a demand for molded articles that can exhibit a good metallic appearance without painting.

[0003] As a material for eliminating the need for painting, a thermoplastic resin composition in which a lustrous pigment such as an aluminum pigment is kneaded into a thermoplastic resin is being investigated.

[0004] For example, Patent Document 1 describes that a resin composition with a metallic finish can be obtained by kneading an aluminum pigment into a synthetic resin. Patent Document 2 proposes a method of injection molding a polypropylene resin composition containing a lustrous material using a mold with a heat insulating layer on the inner surface of the cavity. Patent Document 3 describes a polypropylene resin composition with a flip-flop metallic finish obtained by using carbon black and aluminum flakes. Patent Document 4 discloses a masterbatch containing an aluminum pigment.

[0005] Japanese Patent Publication No. 51-63847 Japanese Patent Publication No. 2000-313747 Japanese Patent No. 6868090 Japanese Patent No. 4748541

[0006] By using such luster pigments, it is possible to achieve a metallic appearance without painting. However, molded products incorporating luster pigments tend to have noticeable molding defects such as weld lines and flow marks, making them difficult to use in large parts for building materials, automobiles, etc. Furthermore, these applications are often used outdoors, so the molded products also require light resistance and scratch resistance.

[0007] Conventional molded products, such as those disclosed in Patent Document 2, have the drawback of requiring time to cool the injection molding die provided with a special heat insulating layer, resulting in a long molding cycle. Patent Document 3 has problems of poor appearance due to color streaks and color unevenness caused by poor dispersion of carbon black, and insufficient scratch resistance of molded products. Patent Document 4 has problems with the mechanical strength and light resistance of molded products due to the large amount of polyethylene wax contained.

[0008] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a resin composition that has excellent pigment dispersibility, a metallic appearance, and fewer weld lines, and that can form molded articles with excellent appearance. It is also an object of the present disclosure to provide a thermoplastic resin composition that also has good mechanical properties, scratch resistance, and light resistance.

[0009] The present inventors have conducted extensive research and found that the above-mentioned problems can be solved by the following aspects, leading to the completion of the present invention. [1] A thermoplastic resin composition comprising a bright pigment (A), carbon black (B), a polyolefin wax (C), and a polyolefin resin (D), wherein the thermoplastic resin composition contains 0.1 to 10 mass% of carbon black (B), based on 100 mass% of the thermoplastic resin composition, and the mass ratio (B) / (C) of the carbon black (B) to the polyolefin wax (C) is 0.1 to 10. [2] The thermoplastic resin composition according to [1], which contains 15 to 55 mass% of the bright pigment (A), based on 100 mass% of the thermoplastic resin composition. [3] The thermoplastic resin composition according to [1] or [2], wherein the bright pigment (A) contains aluminum flakes. [4] The thermoplastic resin composition according to any one of [1] to [3], wherein the bright pigment (A) has an average particle size of 5 μm to 100 μm. [5] A molded article formed using the thermoplastic resin composition according to any one of [1] to [4].

[0010] The thermoplastic resin composition of one embodiment of the present invention can provide a molded article with excellent pigment dispersibility, reduced weld lines while maintaining a metallic appearance, and also has good mechanical properties, scratch resistance, and light resistance.

[0011] An example of an embodiment to which the present invention is applied will be described below. However, the present invention is not limited to this embodiment, and other embodiments may also fall within the scope of the present invention as long as they conform to the spirit of the present invention. Furthermore, the numerical values ​​"A to B" specified in this specification refer to a range that satisfies the following conditions: numerical value A is greater than numerical value A, and numerical value B is less than numerical value B. Furthermore, in this specification, "film," "sheet," and "plate" are synonymous and are not distinguished by thickness. Furthermore, "thermoplastic resin composition" may be referred to as "resin composition," "carbon black" as "CB," "polyolefin wax (C)" as "wax (C)," and "polyolefin resin (D)" as "resin (D)." Unless otherwise noted, the various components mentioned in this specification may be used independently, either singly or in combination of two or more types. The numerical values ​​specified in this specification are determined by the methods disclosed in the embodiments or examples.

[0012] Thermoplastic Resin Composition: A thermoplastic resin composition according to one embodiment of the present invention comprises a luster pigment (A), carbon black (B), a polyolefin wax (C), and a polyolefin resin (D). The thermoplastic resin composition contains 0.1 to 10 mass% of carbon black (B), based on 100 mass% of the thermoplastic resin composition, and the mass ratio (B) / (C) of the carbon black (B) to the polyolefin wax (C) is 0.1 to 10. Use of such a resin composition provides excellent dispersibility of pigments such as the luster pigment (A) and the carbon black (B), maintains a metallic appearance, and suppresses weld lines, which are molding defects that occur when molten resins join together in a mold during injection molding. Furthermore, the thermoplastic resin composition also exhibits excellent mechanical properties, scratch resistance, and light resistance.

[0013] <Brilliant Pigment (A)> A brilliant pigment is a pigment having a pearl-like luster or a metallic luster. Examples of the brilliant pigment (A) of the present disclosure include metal flakes such as aluminum flakes; metal foils such as aluminum foil; mica such as pearl mica, interference mica, and mica coated with metals such as titanium dioxide; metal powders such as zinc powder, Fronds powder, stainless steel powder, and aluminum powder; glass flakes coated with metals (such as silver and silver alloys) or metal oxides (such as titanium dioxide), preferably glass flakes coated with titanium dioxide. Preferably, the brilliant pigment is selected from the group consisting of metal flakes, pearl mica, interference mica, and glass flakes coated with metal oxides including titanium dioxide. From the viewpoints of excellent luster and suppression of weld lines, aluminum flakes are more preferred.

[0014] The average particle size of the luster pigment (A) is preferably 5 to 100 μm, more preferably 20 to 60 μm. When the average particle size is 5 μm or more, the occurrence of weld lines can be further suppressed. When the average particle size is 100 μm or less, the luster pigment is not too noticeable, and both brightness and weld lines can be achieved, which is preferable because the luxurious feel is not impaired. In addition, the deterioration of impact resistance can be further suppressed.

[0015] When the bright pigment (A) is in a flake form, the thickness in the thickness direction is preferably 0.2 to 10 μm, more preferably 0.2 to 4 μm, and even more preferably 0.7 to 3 μm. A thickness of 0.2 μm or more can further suppress the occurrence of weld lines. The thickness may be, for example, 0.2 μm or more or 0.7 μm or more. The thickness may be, for example, 10 μm or less, 4 μm or less, or 3 μm or less. A thickness of 10 μm or less is preferable because the bright pigment is not too noticeable, achieving both brightness and weld lines, and not impairing the luxurious feel. Furthermore, deterioration of impact resistance can be further suppressed. Preferably, the average particle size of the bright pigment (A) is 5 to 100 μm, and the thickness is 0.2 to 10 μm.

[0016] The average particle size and thickness of the bright pigment (A) can be determined by image analysis using a transmission electron microscope. The thickness can be determined as an average thickness. Specifically, these can be determined by the methods described in the examples.

[0017] The content of the luster pigment (A) is preferably 15 to 55 mass%, more preferably 20 to 45 mass%, and even more preferably 25 to 35 mass%, based on 100 mass% of the thermoplastic resin composition. When the content of the luster pigment (A) is 15 mass% or more, the molded article can exhibit a superior metallic appearance. When the content exceeds 55 mass%, the effect of adding the luster pigment (A) may become saturated. Furthermore, when the content is 55 mass% or less, the mechanical properties can be improved.

[0018] <Carbon Black (B)> Carbon black is an amorphous carbon having electrical conductivity produced by the incomplete combustion of oil or gas or the thermal decomposition of hydrocarbons. There are no particular limitations on the carbon black (B), and any of acetylene black, furnace black, hollow carbon black, ketjen black, etc. can be used.

[0019] The average particle size of carbon black (B) is preferably 15 nm or more. It is more preferably 20 to 90 nm, and even more preferably 30 to 40 nm. Generally, as the particle size of carbon black decreases, the specific surface area increases, which tends to improve the light resistance of molded articles. On the other hand, carbon black particles tend to aggregate, resulting in variations in the dispersion state of carbon black in molded articles, making them more susceptible to the formation of streaks and color unevenness. Therefore, an average particle size of 15 nm or more is preferred. Furthermore, an average particle size of 90 nm or less allows the coloring power of carbon black to be fully exerted. Furthermore, whitening due to the bright pigment and resin when the molded article is scratched is suppressed, further improving scratch resistance. The average particle size of carbon black can be determined by image analysis using a transmission electron microscope. Specifically, it can be determined by the method described in the Examples.

[0020] In an embodiment, the content of carbon black (B) is 0.1 to 10% by mass, based on 100% by mass of the thermoplastic resin composition. It is preferably 0.3 to 8% by mass, more preferably 0.5 to 5% by mass, and even more preferably 1.1 to 5% by mass. If the content is less than 0.1% by mass, light resistance is weakened, and when the molded product is scratched, whitening due to the luster pigment and resin becomes noticeable, and scratch resistance is also reduced. If the content is 1.1% by mass or more, the occurrence of weld lines can be further suppressed. If the content exceeds 10% by mass, the hiding power of carbon black (B) reduces the overall lightness and brightness.

[0021] <Polyolefin wax (C)> Wax is an organic substance that is solid at room temperature (25°C) and becomes liquid when heated. In the present disclosure, the polyolefin wax (C) is not particularly limited as long as it is a wax made of polyolefin.

[0022] From the viewpoint of processability and dispersibility, the melt flow rate (MFR) of the polyolefin wax (C) is preferably greater than 100 g / 10 min (MFR, also referred to as melt viscosity). The melt flow rate (MFR) can be determined in accordance with JIS K-7210. From the viewpoint of pigment dispersibility, the melting point of the polyolefin wax (C) is preferably 130°C or lower, more preferably 120°C or lower, and preferably 70°C or higher. By using a wax (C) exhibiting a melting point within the above range, the dispersibility of the carbon black (B) is further improved, and the processability when melt-kneading the thermoplastic resin and wax is also improved. The melting point can be determined using a differential scanning calorimeter. Specifically, for example, it can be determined by measuring using a Seiko Instruments Inc. DSC6200 differential scanning calorimeter at a temperature range of 40 to 200°C and a heating rate of 10°C / min using alumina as a standard substance.

[0023] The polyolefin wax (C) of the present disclosure is a polymer of an olefin monomer such as ethylene, propylene, or butylene, and may be a block or random copolymer or terpolymer. Specifically, it is a polymer of α-olefins such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), or polypropylene (PP). The waxes can be used alone or in combination of two or more.

[0024] The number average molecular weight of the polyolefin wax (C) is preferably 1,000 to 30,000, more preferably 2,000 to 25,000. The number average molecular weight can be measured by gel permeation chromatography (GPC) using polystyrene as a standard substance and tetrahydrofuran as an eluent.

[0025] The content of the polyolefin wax (C) is preferably 0.1 to 20 mass%, more preferably 0.5 to 15 mass%, and even more preferably 1 to 10 mass%, based on 100 mass% of the thermoplastic resin composition. When the content of the polyolefin wax (C) is within this range, the mechanical properties and light resistance can be improved.

[0026] The mass ratio (B) / (C) of the carbon black (B) to the polyolefin wax (C) is preferably 0.1 to 10, more preferably 0.3 to 8, and even more preferably 0.5 to 5. When the mass ratio is within this range, the occurrence of streaks and color unevenness due to poor dispersion of the carbon black (B) can be further reduced, and a molded product with superior appearance can be obtained.

[0027] <Polyolefin Resin (D)> Polyolefin resin (D) is a polymer primarily composed of olefins, and examples thereof include polyethylene, polypropylene, and polybutene. However, this does not include the polyolefin wax (C). The polyolefin resin (D) used in the present disclosure is not particularly limited. Specific examples include polypropylene, propylene-ethylene block copolymers and random copolymers thereof, high-density polyethylene, linear low-density polyethylene, and low-density polyethylene, which are widely available on the market for injection molding and extrusion molding. Among these, polypropylene resin is preferred, and propylene-ethylene block copolymers are more preferred, as they can provide molded articles with good mechanical strength.

[0028] The melt flow rate (MFR) of the polyolefin resin (D) is preferably 5 to 100 g / 10 min, more preferably 10 to 60 g / 10 min, from the viewpoints of processability and appearance. The melt flow rate (MFR) can be determined in accordance with JIS K-7210.

[0029] The melting point of the polyolefin resin (D) is preferably above 130°C. It is also preferably 180°C or lower, more preferably 170°C or lower. The melting point can be determined by a differential scanning calorimeter. Specifically, for example, the melting point can be determined by measurement using a differential scanning calorimeter DSC6200 manufactured by Seiko Instruments Inc., using alumina as a standard substance, at a temperature range of 40 to 200°C, and at a heating rate of 10°C / min.

[0030] In the present invention, the content of the polyolefin resin (D) is preferably 25% by mass or more, more preferably 40% by mass or more, based on 100% by mass of the thermoplastic resin composition. Also, it is preferably 80% by mass or less. By having the content of the polyolefin resin (D) within this range, the mechanical properties can be improved.

[0031] <Other Pigments> As long as the effects of the present invention are not impaired, other pigments such as organic pigments and inorganic pigments other than carbon black (B) and the luster pigment (A) can be used as needed to match the required hue. For example, organic pigments include azo-based, anthraquinone-based, phthalocyanine-based, quinacridone-based, isoindolinone-based, dioxazine-based, and quinophthalone-based pigments. Inorganic pigments include iron oxide, cobalt blue, ultramarine, yellow lead, talc, mica, calcium carbonate, barium sulfate, glass fiber, gypsum, magnesium carbonate, magnesium oxide, and titanium oxide. Among these, talc is preferred.

[0032] <Optional Components> The resin composition of the present invention may contain additives as optional components, such as metallic soaps of alkali metals, alkaline earth metals, or zinc, hydrotalcite, nonionic surfactants, cationic surfactants, anionic surfactants, amphoteric surfactants, antistatic agents, flame retardants such as halogen-based, phosphorus-based, or metal oxide flame retardants, antioxidants, ultraviolet absorbers, and fillers, within a range that does not impair the effects of the present invention.

[0033] <Method for producing resin composition> The resin composition can be produced by blending and mixing the above-mentioned components in the blending ratios described above, followed by melt-kneading. At this time, a known method for producing a resin composition can be used. For example, the melt-kneading can be performed using a conventional kneader such as a single-screw extruder, a twin-screw extruder, a Banbury mixer, a roll mixer, a Brabender plastograph, or a kneader, to knead and granulate the resin composition into pellets, powder, granules, or beads.

[0034] The resin composition may be used in the form of either a masterbatch or a compound. In the case of a compound, after the compound is produced, the compound can be used as it is to produce a molded article by the method described below.

[0035] In the case of a masterbatch, after the masterbatch is produced, a molded article can be produced by blending the masterbatch with, for example, the same polyolefin resin (D) used in the production of the masterbatch as the diluent resin, as the main component of the molded article. The masterbatch content is preferably 1 to 15 parts by mass, more preferably 3 to 10 parts by mass, per 100 parts by mass of the diluent polyolefin resin (D). The polyolefin resin (D) used as the diluent resin may be the same as or different from that used in the production of the masterbatch, but using the same polyolefin resin is preferred because of superior compatibility between the resins. When using the luster pigment (A), it is preferable to use a masterbatch as the diluent from the viewpoints of operability and dispersibility. The content of the luster pigment (A) is preferably 15 to 65% by mass, based on 100% by mass of the masterbatch, from the viewpoints of impact strength and dispersibility. It is more preferably 20 to 55% by mass.

[0036] The bright pigment (A), carbon black (B), polyolefin wax (C), and polyolefin resin (D) can be mixed by any known method, such as a method of stirring and mixing the pigment with the polyolefin wax (C) and polyolefin resin (D) using a dry grinder such as a fluid energy grinder or an impact grinder, or a high-speed mixer such as a Henschel mixer or a super mixer, or a method of melt-kneading using a kneader, a roll mill, a Banbury mixer, or the like.

[0037] Molded Articles Molded articles can be obtained by molding the thermoplastic resin composition of the embodiment. Molded articles formed using the thermoplastic resin composition are useful in various fields, such as automotive interior and exterior materials, building materials, and home appliance exteriors. The molding method is not particularly limited, and can be obtained by extrusion molding, compression molding, injection molding, blow molding, etc. When the thermoplastic resin composition of the embodiment is a masterbatch, it can be kneaded with a diluent resin at a specified ratio during molding to form a molded article. The diluent resin is preferably a polyolefin resin, more preferably the same polyolefin resin as the polyolefin resin (D) of the thermoplastic resin composition. The diluent resin may be blended with an inorganic filler to form a diluent resin composition before use. The type of inorganic filler is not particularly limited, and known inorganic materials can be used. Examples of inorganic fillers include talc. The content of the inorganic filler in the diluent resin composition is, for example, preferably 1 to 40 mass%, more preferably 10 to 30 mass%, based on 100 mass% of the diluent resin composition.

[0038] In the molded article, the content of the bright pigment (A) is preferably 0.5 to 3 mass%, more preferably 1 to 3 mass%, and even more preferably 1 to 2 mass%, based on 100 mass% of the molded article. In the molded article, the content of the carbon black (B) is preferably 0.05 to 0.5 mass%, more preferably 0.07 to 0.4 mass%, even more preferably 0.08 to 0.3 mass%, and even more preferably 0.09 to 0.2 mass%, based on 100 mass% of the molded article. In the molded article, the content of the polyolefin wax (C) is preferably 0.005 to 2 mass%, more preferably 0.02 to 1 mass%, and even more preferably 0.05 to 0.5 mass%, based on 100 mass% of the molded article. In the molded article, the total amount of the polyolefin resin (D) and the diluent resin is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on 100% by mass of the molded article.

[0039] Next, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. Hereinafter, "parts" means "parts by mass" and "%" means "% by mass." Furthermore, the blending amounts in the tables are "parts by mass," the content rates are "% by mass," and blank spaces in the tables indicate that no blending has been performed.

[0040] The number average molecular weight and melting point of the polyolefin wax were measured as follows: <Number average molecular weight of polyolefin wax> Measurement was carried out by gel permeation chromatography (GPC method) using polystyrene as a standard substance and tetrahydrofuran as an eluent.

[0041] <Melting Point of Polyolefin Wax> The melting point of polyolefin wax was measured using a differential scanning calorimeter DSC6200 manufactured by Seiko Instruments Inc., using alumina as a standard substance, in a temperature range of 40 to 200° C., and at a heating rate of 10° C. / min.

[0042] <Measurement of Average Particle Diameter and Thickness of Pigments> For the effective pigment (A), the particle diameter was determined by the longest axis, and the thickness was determined by the thinnest point, and the particle diameters and thicknesses of approximately 30 particles observable in a magnified image (e.g., 500x to 10,000x) taken with a transmission electron microscope (TEM) were measured and averaged. The average particle diameters of carbon black (CB) and inorganic pigments were determined by measuring the particle diameters or thicknesses of approximately 30 particles observable in a magnified image (e.g., 500x to 10,000x) taken with a transmission electron microscope (TEM) and averaged.

[0043] The raw materials used in the examples and comparative examples are shown below. <Brilliant pigments (A)> (A-1) Metax Neo NME040T3 (aluminum flakes, average thickness 0.9 μm, average particle diameter 40 μm, manufactured by Toyo Aluminum, aluminum concentration = 70%, carrier resin LDPE = 30%) (A-2) Iriodin 153 Flash Pearl (pearl mica, average particle diameter 100 μm, manufactured by Merck) (A-3) Metax Neo NME060T4 (aluminum flakes, average thickness 1.1 μm, average particle diameter 60 μm, manufactured by Toyo Aluminum, aluminum concentration = 70%, carrier resin LDPE = 30%) (A-4) Metax Neo NME005N1 (aluminum flakes, average thickness 0.2 μm, average particle diameter 5 μm, manufactured by Toyo Aluminum, aluminum concentration = 70%, carrier resin LDPE = 30%) <Carbon black (B)> (B-1) Mitsubishi Carbon Black #40, average particle size 24 nm

[0044] <Polyolefin Waxes (C)> (C-1) Sanwax 131P (polyethylene wax manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight 3,500, MFR = more than 100 g / 10 min, melting point 105°C) (C-2) Hiwax NP056 (polypropylene wax manufactured by Mitsui Chemicals, Inc., number average molecular weight 7,200, MFR = more than 100 g / 10 min, melting point 130°C)

[0045] <Polyolefin Resin (D)> (D-1) SunAllomer PMA60Z (manufactured by SunAllomer Co., Ltd., MFR=45 g / 10 min, propylene-ethylene block copolymer) (D-2) Prime Polypro J226T (manufactured by Prime Polymer Co., Ltd., melting point 141°C, MFR=20 g / 10 min, propylene-ethylene random copolymer) (D-3) Novatec PP BC03C (manufactured by Japan Polypropylene Corporation, melting point 161°C, MFR=30 g / 10 min, propylene-ethylene block copolymer)

[0046] <Other ingredients> (E-1) Dispersant, calcium stearate (manufactured by Nitto Kasei Kogyo Co., Ltd.) (E-2) Talc, Micro Ace P-3 (manufactured by Nippon Talc Co., Ltd., particle size: 5 μm)

[0047] [Production of diluent resin composition] 20 parts by mass of talc (E-2) (Microace P-3, manufactured by Nippon Talc Co., Ltd., average particle size 5 μm)) and 80 parts by mass of polyolefin resin (D-3) were blended, extruded at 220°C using a twin-screw extruder (manufactured by The Japan Steel Works, Ltd.), and granulated to obtain a pellet-shaped diluent resin composition.

[0048] Example 1 40 parts of the bright pigment (A-1) (28 parts of aluminum flakes), 2 parts of carbon black (B-1), 2 parts of polyolefin wax (C-1), and 56 parts of polyolefin resin (D-1) were blended and premixed in a Henschel mixer. The mixture was then melt-kneaded at 220°C in a single-screw extruder (manufactured by The Japan Steel Works, Ltd.) with a screw diameter of 30 mm, and then granulated to obtain a pellet-shaped resin composition (F-1).

[0049] [Examples 2 to 12, Examples 14 to 18, Comparative Examples 1 to 3, 5] Pellet-shaped resin compositions (F-2 to 12, F-14 to 21, F-23) were obtained in the same manner as in Example 1, except that the materials and blending amounts (parts by mass) were changed to those shown in Table 1.

[0050] Example 13 2 parts of the luster pigment (A-1), 0.1 parts of carbon black (B-1), 0.2 parts of polyolefin wax (C-1), 78.7 parts of polyolefin resin (D-1), and 19 parts of talc as an additional component (E-2) were blended and melt-kneaded at 220°C in a twin-screw extruder (manufactured by The Japan Steel Works, Ltd.), followed by granulation to obtain a pellet-shaped resin composition (F-13).

[0051] Comparative Example 4 40 parts of the bright pigment (A-1), 1 part of carbon black (B-1), 58 parts of the polyolefin resin (D-1), and 1 part of the optional component (E) were blended and premixed in a Henschel mixer. The mixture was melt-kneaded at 220°C in a single-screw extruder (manufactured by The Japan Steel Works, Ltd.) with a primary screw diameter of 30 mm, and then granulated to obtain a pellet-shaped resin composition (F-22).

[0052] In Table 1, "(A) content" is the content (%) of the bright pigment (A) based on 100% by mass of the thermoplastic resin composition, and "(B) content" is the content (%) of the carbon black (B) based on 100% by mass of the thermoplastic resin composition.

[0053]

[0054] [Evaluation Items and Evaluation Methods] The appearance, mechanical properties, scratch resistance, and light resistance of the thermoplastic resin compositions were evaluated using the following methods. The results are shown in Table 2. <Preparation of Test Molded Articles> (Test Piece 1) For Examples 1 to 12, Examples 14 to 18, and Comparative Examples 1 to 5, 5 parts of the obtained resin composition and 100 parts of the dilution resin composition were mixed and molded at 220°C using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) to obtain appearance test piece 1 measuring 150 mm in length, 125 mm in width, and 2.5 mm in thickness. The resin composition obtained in Example 13 was directly molded at 220°C using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) to obtain appearance test piece 1 measuring 150 mm in length, 125 mm in width, and 2.5 mm in thickness.

[0055] (Test Piece 2) For Examples 1 to 12, Examples 14 to 18, and Comparative Examples 1 to 5, 5 parts of the obtained resin composition and 100 parts of the diluting resin composition were mixed and molded at 220°C using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) to obtain a test piece 2 having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm. The resin composition obtained in Example 13 was molded as it was using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) at 220°C to obtain a test piece 2 having a length of 80 mm, a width of 10 mm, and a thickness of 4 mm.

[0056] (Test Piece 3) For Examples 1 to 12, Examples 14 to 18, and Comparative Examples 1 to 5, 5 parts of the obtained resin composition and 100 parts of a resin composition for dilution were mixed and molded at 220°C using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) to obtain a 45 mm long x 45 mm wide x 2.5 mm thick test piece 3. The resin composition obtained in Example 13 was molded directly at 220°C using an injection molding machine (manufactured by Toshiba Machine Co., Ltd.) to obtain a 45 mm long x 45 mm wide x 2.5 mm thick test piece 3.

[0057] <Appearance Evaluation> (Dispersibility) Test piece 1 was observed in a field of view at a magnification of 50x using an optical microscope "Digital Microscope VHX-100" (manufactured by Keyence Corporation). Dispersibility was evaluated based on the size of black spot agglomerates observed in the field of view. The fewer large particles present, the better the dispersibility and the more excellent the appearance. [Evaluation Criteria] A: No black spot agglomerates of 100 μm or more present, very good B: Black spot agglomerates of 100 μm or more present, but no black spot agglomerates of 200 μm or more present, good C: Black spot agglomerates of 200 μm or more present, but no black spot agglomerates of 300 μm or more present, practical level D: Black spot agglomerates of 300 μm or more present in the field of view, not practical

[0058] (Brightness) Using test piece 1, the metallic appearance (brightness) was visually evaluated based on the sparkle. [Evaluation criteria] A: Deep and strong sparkle, very good B: Sparkle, good C: Slightly less sparkle, practical level D: Almost no sparkle, not practical

[0059] (Weld line) Using test piece 1, weld lines were visually evaluated. [Evaluation criteria] A: Weld lines are not noticeable, very good B: Weld lines are visible depending on the viewing angle but are not noticeable, good C: Weld lines are noticeable as black streaks depending on the viewing angle, practical level D: Weld lines are clearly noticeable as black streaks, not practical

[0060] <Impact Strength Measurement> Mechanical properties were evaluated by Charpy impact strength. The Charpy impact strength of test piece 2 and a reference test piece, which was produced as a reference using only the dilution resin composition in the same manner as test piece 2, were measured in accordance with JIS K7171:2016. From the obtained measured values, the property retention for each measured value was calculated according to the following formula (1). The higher the property retention value, the better the strength, and the better it can be said to be. If the evaluation is "△" or higher, no destruction of the molded article occurs. Formula (1) Property retention (%) = [Charpy impact strength of test piece 2 / Charpy impact strength of reference test piece] × 100 [Evaluation Criteria] A: Property retention of 80% or more, very good B: Property retention of 75% or more but less than 80%, good C: Property retention of 70% or more but less than 75%, practical level D: Property retention of less than 70%, not practical

[0061] <Scratch Resistance Evaluation> Using a cross-cut coating peeling tester AD-1110 manufactured by Ueshima Seisakusho Co., Ltd., five scratches were made on the surface of test piece 1 in the machine direction (MD) with a scratching needle (a tungsten steel needle of SKS type 2 specified in JIS G4404) carrying a load of 175 g at a scratching speed of 500 mm / min and a pitch of 0.75 mm. A similar test was also performed in the transverse direction (TD), and then the scratch resistance was evaluated visually. [Evaluation Criteria] A: Scratches are not noticeable, very good B: Scratches are visible depending on the visual angle but are not noticeable, good C: Scratches are noticeable depending on the visual angle, practical level D: Scratches are clearly noticeable, not practical

[0062] <Lightfastness Evaluation> Test piece 3 was used to measure lightfastness using a Sunshine Weather Meter (Model S80, manufactured by Suga Test Instruments Co., Ltd.) under a radiation energy of 255 W / m ２ The color difference (ΔE) of the sample surface was measured under the conditions of 63°C, 63°C temperature, and 1000 hours test time. The smaller the ΔE, the better the lightfastness. The lightfastness was evaluated according to the following criteria. [Evaluation criteria] A: ΔE after 1000 hours = less than 0.5 Very good B: ΔE after 1000 hours = 0.5 or more but less than 1.0 Good C: ΔE after 1000 hours = 1.0 or more but less than 1.5 Practical level D: ΔE after 1000 hours = 1.5 or more Not practical

[0063]

[0064] As shown in Table 2, by using the resin composition of the present invention, molded articles with excellent dispersibility and metallic appearance but with inconspicuous weld lines were obtained. Furthermore, it was confirmed that the molded articles also had good mechanical properties, light resistance, scratch resistance, and impact resistance.

[0065] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-219811, filed December 26, 2023, the entire disclosure of which is incorporated herein by reference.

Claims

1. A thermoplastic resin composition comprising a bright pigment (A), carbon black (B), a polyolefin wax (C), and a polyolefin resin (D), wherein the carbon black (B) is contained in an amount of 0.1 to 10% by mass based on 100% by mass of the thermoplastic resin composition, and the mass ratio (B) / (C) of the carbon black (B) to the polyolefin wax (C) is 0.1 to 10.

2. The thermoplastic resin composition according to claim 1, wherein the bright pigment (A) is contained in an amount of 15 to 55% by mass based on 100% by mass of the thermoplastic resin composition.

3. The thermoplastic resin composition according to claim 1 or 2, wherein the bright pigment (A) contains aluminum flakes.

4. The thermoplastic resin composition according to any one of claims 1 to 3, wherein the average particle diameter of the bright pigment (A) is 5 μm to 100 μm.

5. A molded article formed using the thermoplastic resin composition according to any one of claims 1 to 4.

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