Resin composition and molded article

Abstract

To provide a resin composition and a molded article that can achieve a bluish black hue. [Solution] A resin composition containing a thermoplastic resin and carbon nanotubes, wherein the carbon nanotubes are entangled carbon nanotubes whose bulk density and tap density satisfy specific values, the content of the carbon nanotubes is 0.1% by mass or more and 2% by mass or less relative to 100% by mass of the resin composition, and the aggregation area ratio is 0.4% or more.

Description

[Technical Field]

[0001] The present invention relates to a resin composition and a molded article. [Background technology]

[0002] When coloring a resin composition black, black pigments such as carbon black or perylene black are usually used, as well as black dyes such as azo compounds or azine compounds. However, when polypropylene resin or the like is used as the base resin, black dyes may bleed, so carbon black, which does not bleed, is generally used. However, moldings using resin compositions containing carbon black tend to have a reddish-black hue, although they have excellent physical properties. Therefore, there is a demand for improving this reddish-black hue to a bluish-black hue. For example, a molded article formed from a resin composition containing a thermoplastic resin and carbon nanotubes has been described (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-6918 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the molded article described in Patent Document 1 is still not satisfactory in terms of the required bluish black hue.

[0005] Therefore, an object of the present invention is to provide a resin composition and a molded article that can achieve a bluish-black hue. [Means for solving the problem]

[0006] According to the present invention, there are provided the following resin compositions and molded articles. [1] A resin composition containing a thermoplastic resin and carbon nanotubes, The carbon nanotubes are entangled carbon nanotubes that satisfy both of the following requirements (1) and (2), and the content of the carbon nanotubes is 0.1% by mass or more and 2% by mass or less with respect to 100% by mass of the resin composition; The aggregation area rate is 0.4% or more. Resin composition. (1) The bulk density of the carbon nanotubes is 28 kg / m 3 More than 106kg / m 3 The following is the result. (2) The tap density of the carbon nanotubes is 38 kg / m 3 More than 168kg / m 3 The following is the result. [2] The average diameter of the carbon nanotubes is 5 nm or more and 25 nm or less. The resin composition according to [1]. [3] The resin composition according to [1] or [2], wherein the thermoplastic resin is at least one selected from the group consisting of polypropylene and polyethylene. [4] A resin composition according to any one of [1] to [3], Molded body. [Effects of the Invention]

[0007] According to one aspect of the present invention, it is possible to provide a resin composition that can achieve a bluish-black hue, and a molded article thereof. [Brief explanation of the drawings]

[0008] [Figure 1] 1 shows photographs of the measurement samples obtained in Test Examples 4 and 6 taken at 300x magnification. [Figure 2] This is a scanning electron microscope photograph of the surface of an entangled carbon nanotube, magnified 2000 times. [Figure 3] This is a scanning electron microscope photograph of the surface of a bundled carbon nanotube, magnified 2000 times. [Figure 4] 3 is a photograph of the molded bodies obtained in Example 1 and Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Carbon nanotubes] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. First, the carbon nanotubes used in the present embodiments will be described. Carbon nanotubes (hereinafter also referred to as "CNTs") refer to carbon materials in which a single layer of graphite has a cylindrical structure. CNTs with a single-layer cylindrical structure are usually classified as single-walled CNTs, CNTs with two-layered cylindrical structures as double-walled CNTs, and CNTs with three or more layers as multi-walled CNTs. Carbon nanotubes are important colorants for imparting blackness. Commercially available carbon nanotubes can be used. The average diameter of the carbon nanotubes is preferably 5 nm or more and 25 nm or less, more preferably 6 nm or more and 22 nm or less, and particularly preferably 8 nm or more and 20 nm or less. Carbon nanotubes with an average diameter of less than 5 nm are difficult to disperse due to the very strong intermolecular forces between the carbon nanotubes, resulting in excessive agglomerates, which causes strong scattered light and makes it impossible to obtain a jet-black tone, which is undesirable.On the other hand, those with an average diameter of more than 25 nm have a small number of nanotubes per unit volume, which reduces the coloring power and makes it impossible to obtain a jet-black tone.

[0010] The average diameter of the carbon nanotubes can be determined by image analysis.

[0011] The average diameter is determined by observing carbon nanotubes at an accelerating voltage of 3 kV using, for example, a field emission scanning electron microscope (Hitachi High-Technologies Corporation, S-4800) and taking an image at 100,000 magnification. Next, for any 20 carbon nanotubes in the image, the number average of the minor axis lengths of each is taken as the average diameter of the carbon nanotubes.

[0012] The bulk density of the carbon nanotubes used in this embodiment is 28 kg / m 3 More than 106kg / m 3 The tap density of carbon nanotubes is 38 kg / m 3 More than 168kg / m 3 The following is required: The bulk density of carbon nanotubes is 28 kg / m 3 If the bulk density is less than 106 kg / m, the properties of the entangled carbon nanotubes cannot be realized, and the molded article made of the resin composition cannot achieve a bluish black color. 3 If the density exceeds 32 kg / m, the carbon nanotube units that make up the entangled carbon nanotubes are too densely packed together and are therefore not easy to disperse. In this case, a large number of agglomerates are formed on the surface of the molded body, which tends to cause light scattering, resulting in an increase in brightness and making it impossible to obtain a jet-black molded body. From the same perspective, the bulk density of carbon nanotubes is 32 kg / m 3 More than 90kg / m 3 It is preferable that the saturation is 36 kg / m or less. 3 More than 80kg / m 3 More preferably, it is: The tap density of carbon nanotubes is 38 kg / m 3 If the tap density is less than 168 kg / m, the properties of the entangled carbon nanotubes cannot be realized, and therefore, a bluish black color cannot be achieved in a molded article made from the resin composition. 3If the tap density of the carbon nanotubes exceeds 42 kg / m, the carbon nanotube units that make up the entangled carbon nanotubes are too densely packed together and are therefore not easy to disperse. In this case, a large number of agglomerates are formed on the surface of the molded body, which tends to cause light scattering, resulting in an increase in brightness and making it impossible to obtain a jet-black molded body. From the same perspective, the tap density of carbon nanotubes is 42 kg / m 3 More than 158kg / m 3 It is preferable that the saturation is 46 kg / m or less. 3 More than 148kg / m 3 More preferably, it is:

[0013] In this specification, the bulk density and tap density of carbon nanotubes were measured under the following conditions. Most carbon nanotubes are commercially available in compressed pellet form, so these were powdered and used as measurement samples. To ensure uniform test conditions, the same process was also performed on powdered, non-compressed pelletized carbon nanotubes. The powdering process involved a 30-second pulverization process using a mixing device (Kyoritsu Riko's "Sample Mill SK-M10"). Note that this process only converts the carbon nanotubes from pellets to powder; it does not actually pulverize them. The bulk density and tap density were measured using a Tsutsui Rikagaku Kikaisha "A·B·D Powder Property Measuring Instrument." The bulk density was calculated by loading the material into a sample hopper, pouring it into a sample container over a period of approximately 30–60 seconds, and then leveling it off when the sample reached a mound. The volume and mass were then used to calculate the bulk density. The tap density is calculated from the ratio of the volume to the mass when a measurement sample is placed in a container and subjected to a specific vibration or tapping (for example, mechanical tapping for 3 minutes). Further, examples of carbon nanotubes whose bulk density and tap density satisfy the above conditions include entangled carbon nanotubes.

[0014] The term "entangled" used in this specification refers to a configuration in which multiple CNT units are entangled without being restricted to a specific orientation, such as in a bundle or rope. A scanning electron microscope photograph of an entangled carbon nanotube is shown in Figure 2. Unless otherwise specified, the term "bundle-type" used in this specification refers to a secondary shape in which multiple CNT units are arranged side by side or entangled in a helical shape, like a bundle or rope. A scanning electron microscope photograph of a bundle-type carbon nanotube is shown in Figure 3.

[0015] [Thermoplastic resin] Next, the thermoplastic resin used in this embodiment will be described. Thermoplastic resins are the base resins that serve as binders for resin compositions. Examples of thermoplastic resins include polyolefin resins (such as polypropylene, high-density polyethylene, low-density polyethylene, and linear low-density polyethylene), polyphenylene sulfide, liquid crystal polymers, polyurethanes, polyether ether ketones, polyether sulfones, polystyrene resins, polyphenylene ethers, acrylonitrile-butadiene-styrene (ABS) resins, polyvinyl chloride, polyacetals, polycarbonate resins, polyamide resins, unsaturated polyester resins, polymethyl methacrylate resins (PMMA), ethylene-vinyl acetate copolymer resins, ethylene-vinyl alcohol copolymer resins, acrylonitrile-styrene copolymers, and polysulfone resins. Among these, polyolefin resins are preferred. The polyolefin resin may be a polypropylene resin or a polyethylene resin. These may be used alone or in combination.

[0016] The content of the thermoplastic resin is preferably within a range that allows the carbon nanotubes to be maintained in a dispersed state. From this viewpoint, the content of the thermoplastic resin is preferably 80% by mass or more, and more preferably 90% by mass or more, relative to 100% by mass of the resin composition. If the content is less than 80% by mass, moldability may decrease.

[0017] [Other ingredients] The resin composition according to the present embodiment may contain carbon black, color pigments, inorganic fillers (such as silica and titanium), ester wax, polyethylene wax, antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, surfactants, and the like, as long as the effects of the present invention are not impaired.

[0018] [Resin composition] The resin composition according to this embodiment will be described. The resin composition according to this embodiment contains a thermoplastic resin and entangled carbon nanotubes.

[0019] The present inventors speculate that the reason why the resin composition according to this embodiment can achieve a bluish black hue is as follows. Specifically, the resin composition according to this embodiment uses carbon nanotubes (entangled carbon nanotubes) whose bulk density and tap density satisfy the above-mentioned conditions. The present inventors have surprisingly discovered for the first time that when entangled carbon nanotubes are dispersed in a thermoplastic resin at a relatively low concentration (e.g., in the range of 0.1% by mass to 2% by mass), a bluish-black hue can be achieved, depending on the dispersion state of the carbon nanotubes. In the case of a resin composition containing bundled carbon nanotubes, the carbon nanotubes are oriented parallel to the resin flow direction during molding. However, entangled carbon nanotubes are less likely to have a consistent orientation. This is believed to be due to the structure of the carbon nanotube particles in the molded product, which makes it difficult for reflected light from the carbon nanotube particles to escape to the outside of the molded product and facilitates the trapping of incident light within the carbon nanotube particles. At a relatively high concentration (e.g., greater than 2.0% by mass), the frequency of aggregates on the surface of the molded product increases, which not only impairs the appearance but also easily causes scattered light. Conversely, a high concentration increases the brightness. As a result of extensive research, the inventors have found an appropriate range for the dispersion state of carbon nanotubes, and have completed the present invention. The inventors believe that the effects of the present invention can be achieved in this way.

[0020] Furthermore, in the resin composition according to this embodiment, the content of carbon nanotubes must be 0.1% by mass or more and 2% by mass or less, relative to 100% by mass of the resin composition. If the carbon nanotube content is less than 0.1% by mass, the resin composition cannot be sufficiently colored. On the other hand, if the carbon nanotube content exceeds 2% by mass, the amount of aggregates present on the surface of the molded article made of the resin composition increases, not only deteriorating the appearance but also increasing the likelihood of scattered light and increasing brightness. From the same perspective, the carbon nanotube content is preferably 0.1% to 2% by mass, and more preferably 0.2% to 1.5% by mass.

[0021] Furthermore, the resin composition according to this embodiment must have an aggregation area ratio of 0.4% or more. If the aggregation area ratio is less than 0.4%, when the carbon nanotube content is 0.1% by mass or more and 2% by mass or less, a bluish-black hue may not be achieved in a molded article made from the resin composition. The aggregation area ratio is an index representing the dispersion state of the carbon nanotubes. The smaller the aggregation area ratio, the more finely the carbon nanotubes are dispersed in the resin composition. The upper limit of the agglomeration area ratio is, for example, 3%. If it exceeds 3%, the toughness and ductility of the material will be impaired, which is undesirable.

[0022] The measurement sample was prepared with a carbon nanotube content of 1% by mass relative to 100% by mass of the resin composition. This was done to increase the contrast between aggregates and other components by observing them under transmitted light, facilitating image analysis. A content exceeding 1% by mass is undesirable as it reduces light transmission through a 0.04 mm thickness, making observation difficult. When the carbon nanotube content exceeds 1% by mass relative to 100% by mass of the resin composition, dilution to 1% by mass or less is required. To minimize changes in the dispersion state within the sample, dilution is preferably performed using equipment with peptization capabilities but limited dispersion capabilities. For example, this can be done using a single-screw extruder or a single-screw injection molding machine. Twin-screw extruders, plastographs, Banbury mixers, rolls, or kneaders are undesirable dilution devices due to the strong shear stress they generate and the significant changes in the dispersion state. When the carbon nanotube content relative to 100% by mass of the resin composition is less than 1% by mass, the agglomeration area ratio for a thickness of 0.04 mm is multiplied by a constant to convert to 1% by mass. For example, when the carbon nanotube content relative to 100% by mass of the resin composition is 0.5% by mass, the agglomeration area ratio is multiplied by 2.

[0023] The resin composition according to the present embodiment contains a thermoplastic resin and carbon nanotubes, and may contain a relatively high concentration of carbon nanotubes. The resin composition may be used as a masterbatch that is diluted with a thermoplastic resin during molding, or may be a compound that is used for molding as is without diluting with a thermoplastic resin. From the viewpoints of additive costs and inventory costs, a masterbatch that can be made highly concentrated is preferred. The masterbatch is preferably in the form of pellets, which are easy to handle.

[0024] [Analysis method] In this specification, the maximum diameter and the aggregation area ratio are values ​​measured under the following conditions. First, if the carbon nanotube content exceeds 1% by mass relative to 100% by mass of the resin composition or molded product to be measured, it must be diluted to 1% by mass or less using a single-screw extruder or an injection molding machine equipped with a single screw. Exceeding 1% by mass not only makes observation difficult due to poor light transmission at a thickness of 0.04 mm, but also results in a low contrast ratio between aggregates and non-aggregates, making image processing difficult. Furthermore, twin-screw extruders, plastographs, and Banbury mixers have stronger mixing capabilities than single-screw extruders or single-screw extruders, and the dispersion state changes significantly during the dilution process, making it difficult to accurately measure the dispersion state before dilution. When diluting using a single-screw extruder or an injection molding machine equipped with a single-screw extruder, mixing can be performed up to three times without changing the dispersion state. Next, a measurement sample with a concentration of 1% by mass or less was press-molded with the resin composition at or above the melting point of the thermoplastic resin to prepare a measurement sample with a thickness of 0.04 mm, which was then analyzed. Specifically, the measurement sample was observed at 300x magnification using an image analyzer (VHX-7100, manufactured by Keyence Corporation), and the total area of ​​aggregates with a maximum diameter of 5 μm or more present within an observation area (5 mm × 5 mm) was calculated using a digital microscope (VHX-7100, manufactured by Keyence Corporation). In this case, if the carbon nanotube content relative to 100% by mass of the resin composition is less than 1%, it can be multiplied by a constant to obtain 1% by mass. For example, if the carbon nanotube content relative to 100% by mass of the resin composition is 0.5% by mass, it can be multiplied by two. When the content of carbon nanotubes relative to 100% by mass of the resin composition or molded article to be measured is 1% by mass or less, dilution is not required and analysis can be carried out according to the above method.

[0025] In this specification, "maximum diameter" refers to the longest part observed when an aggregate is observed with an image analyzer. "Total area of ​​aggregates" refers to the sum of the areas of aggregates with a maximum diameter of 5 μm or more observed in the observation range. "Agglomeration area ratio" refers to the total area of ​​aggregates divided by the area of ​​the observation range (25 mm 2 ) The agglomeration area ratio was determined by observation, analysis, and calculation according to the procedure of the above-mentioned analytical method, and is a value when the carbon nanotube content is 1% by mass relative to 100% by mass of the resin composition. In this specification, the term "aggregate" refers to a material resulting from the aggregation of carbon nanotubes, and refers to both a material consisting only of carbon nanotubes and a material containing a thermoplastic resin in addition to carbon nanotubes.

[0026] [Method of producing resin composition] Next, a method for producing the resin composition according to the present embodiment will be described. The resin composition according to the present embodiment can be produced, for example, by melt-kneading carbon nanotubes and a thermoplastic resin.

[0027] Examples of methods for producing the resin composition include melt-kneading using a kneading device such as a Banbury mixer, a roll, a plastograph, a single-screw extruder, a twin-screw extruder, and a kneader. However, in the melt-kneading, it is preferable to use an extruder capable of continuous production rather than a batch type, as this can improve production efficiency. Furthermore, it is preferable to use a twin-screw extruder as the extruder. The components are melt-kneaded using a kneading device such as an extruder, and the kneaded mixture is extruded in the form of strands, after which the kneaded mixture extruded in the form of strands can be processed into a desired form such as pellets or flakes. Before melt-kneading, the components may be mixed in various mixers such as a high-speed mixer (e.g., a Henschel mixer) or a tumbler, or they may be melt-kneaded by using multiple feeders in an extruder to feed the components at multiple points without mixing.

[0028] [Molded body] The molded article according to this embodiment is obtained by molding the resin composition according to this embodiment described above. The molded article according to this embodiment uses the resin composition according to this embodiment described above, and therefore can be adjusted to have an excellent bluish black hue with a luxurious feel. The molded article according to this embodiment is for use in a housing. The housing refers to a box or the like that forms the exterior of a machine or electrical device having some function, and there is no particular limitation on the type of housing, and it can be used for housings such as smartphone or personal computer cases, or the outer panels of automobiles or airplanes. The molded article itself may be used as a housing, or it may be further painted and used as a housing. [Example]

[0029] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are by mass unless otherwise specified.

[0030] [Preparing materials] The following carbon nanotubes and thermoplastic resins were prepared. Note that the parts by mass of the carbon nanotubes and thermoplastic resins in the table indicate the solid content. (carbon nanotubes) CNT-1: Entangled carbon nanotubes (average diameter 15 nm), product name "FT9100N", manufactured by Cnano CNT-2: Entangled carbon nanotubes (average diameter 16 nm), product name "FT9120N", manufactured by Cnano CNT-3: Bundled carbon nanotubes (average diameter 12 nm), product name "FT7000", manufactured by Cnano [Thermoplastic resin] Thermoplastic resin-1: Homopolypropylene (MFR 45g / 10min), product name "Prime Polypro J108PN", manufactured by Prime Polymer Co., Ltd. Thermoplastic resin-2: Homopolypropylene (MFR 45g / 10min), product name "Prime Polypro J108M", manufactured by Prime Polymer Co., Ltd.

[0031] [Test Examples 1 to 3] The bulk density and tap density of carbon nanotubes (Test Example 1: CNT-1, Test Example 2: CNT-2, Test Example 3: CNT-3) were measured under the following conditions. Specifically, the carbon nanotubes were powdered and used as the measurement sample. The powdering was carried out for 30 seconds using a mixer (Kyoritsu Riko Co., Ltd.'s "Sample Mill SK-M10"). The bulk density and tap density were measured using an "A·B·D powder property measuring instrument" manufactured by Tsutsui Scientific Instruments Co., Ltd. The bulk density was calculated from the volume and mass of the sample placed in the sample hopper at the top of the measurement container, poured into the sample container in about 30 to 60 seconds, and then leveled off when the sample was heaped. The tap density was calculated from the volume and mass of the sample after it was placed in a container and subjected to a specific vibration or tapping (mechanical tapping for 3 minutes). The results are shown in Table 1.

[0032] [Table 1]

[0033] [Test Examples 4, 7 and 10] 95 parts of thermoplastic resin-1 and 5 parts of carbon nanotubes (Test Example 4: CNT-1, Test Example 7: CNT-2, Test Example 10: CNT-3) were mixed for 2 minutes at 900 rpm using a Henschel mixer (FM75L / I, manufactured by Nippon Coke Co.). This mixture was melt-mixed and granulated at 180 to 230°C using a twin-screw extruder (TEX30-α, manufactured by The Japan Steel Works) to produce a pelletized masterbatch (mixing method A). 20 parts of the resulting masterbatch were dry-blended with 80 parts of thermoplastic resin-2 and molded at 220°C using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co., Ltd.) to obtain a test material.

[0034] [Test Examples 5 and 8] 95 parts of thermoplastic resin-1, 5 parts of carbon nanotubes (Test Example 5: CNT-1, Test Example 8: CNT-2), and 5 parts of water were mixed for 2 minutes at 900 rpm using a Henschel mixer (FM75L / I, manufactured by Nippon Coke Co.). This mixture was melt-mixed and granulated at 180 to 230°C using a twin-screw extruder (TEX30-α, manufactured by The Japan Steel Works) to produce a pelletized masterbatch (mixing method B). 20 parts of the resulting masterbatch were dry-blended with 80 parts of thermoplastic resin-2, and the mixture was molded at 220°C using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co., Ltd.) to obtain a test material.

[0035] [Test Examples 6 and 9] 95 parts of thermoplastic resin-1, 5 parts of carbon nanotubes (Test Example 6: CNT-1, Test Example 9: CNT-2), and 5 parts of water were mixed for 2 minutes at 900 rpm using a Henschel mixer (FM75L / I, Nippon Coke Co.). This mixture was melt-mixed and granulated at 180°C to 230°C using a twin-screw extruder (TEX30-α, Japan Steel Works). A masterbatch was then produced. 100 parts of the resulting masterbatch were melt-mixed and granulated at 120°C to 220°C using a Banbury mixer (BR-type Banbury mixer 1.7L, Kobe Steel, Ltd.) to produce a pelletized masterbatch (mixing method C). 20 parts of the resulting masterbatch and 80 parts of thermoplastic resin-2 were dry-blended and molded at 220°C using an injection molding machine (NS-40 5A, Nissei Plastic Industrial Co., Ltd.).

[0036] [Preparation and evaluation of measurement samples] The test material obtained as described above was press-molded at 220°C to prepare a measurement sample with a thickness of 0.04 mm. This measurement sample was observed at 300x magnification using a digital microscope (VHX-7100, manufactured by Keyence Corporation), and the area ratio of agglomerates with a maximum diameter of 5 μm or more present within the observation area (5 mm x 5 mm) was calculated using the digital microscope (VHX-7100, manufactured by Keyence Corporation). The results are shown in Table 2. Photographs of the measurement samples obtained in Test Examples 4 and 6 taken at 300x magnification are shown in Figure 1.

[0037] [Table 2]

[0038] [Example 1] 95 parts of thermoplastic resin-1 and 5 parts of CNT-1 were mixed for 2 minutes at 900 rpm using a Henschel mixer (FM75L / I, manufactured by Nippon Coke Co.). This mixture was kneaded at 180 to 230°C using a twin-screw extruder (TEX-30, manufactured by The Japan Steel Works) to produce a pellet-shaped masterbatch (kneading method A). 10 parts of the resulting masterbatch and 90 parts of thermoplastic resin-2 were dry-blended and molded using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co., Ltd.) to produce a molded body with a thickness of 2 mm.

[0039] [Examples 2, 5, and 6, and Comparative Examples 1, 4, and 7 to 9] Resin compositions and molded articles were prepared in the same manner as in Example 1, except that the brand and blending amount of carbon nanotubes were changed as shown in Table 3.

[0040] [Example 3] 95 parts of thermoplastic resin-1, 5 parts of CNT-1, and 5 parts of water were mixed for 2 minutes at 900 rpm using a Henschel mixer (FM75L / I, manufactured by Nippon Coke Co.). This mixture was kneaded at 180 to 230°C using a twin-screw extruder (TEX-30, manufactured by The Japan Steel Works) to produce a pelletized masterbatch (kneading method B). 10 parts of the resulting masterbatch and 90 parts of thermoplastic resin-2 were dry-blended and molded using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co.) to produce a 2 mm thick molded body.

[0041] [Examples 4, 7 and 8, and Comparative Examples 2 and 5] Resin compositions and molded articles were produced in the same manner as in Example 3, except that the brand and blending amount of carbon nanotubes were changed as shown in Table 3.

[0042] [Comparative Examples 3 and 6] 95 parts of thermoplastic resin-1, 5 parts of carbon nanotubes (Comparative Example 3: CNT-1, Comparative Example 6: CNT-2), and 5 parts of water were mixed at 900 rpm for 2 minutes using a Henschel mixer (FM75L / I, manufactured by Nippon Coke Co.). This mixture was melt-mixed and granulated at 180°C to 230°C using a twin-screw extruder (TEX30-α, manufactured by The Japan Steel Works) to produce a pellet-shaped masterbatch. 100 parts of the resulting masterbatch were melt-mixed and granulated at 120°C to 220°C using a Banbury mixer (BR-type Banbury mixer 1.7L, manufactured by Kobe Steel, Ltd.) to produce a masterbatch (mixing method C). 10 parts of the resulting masterbatch were dry-blended with 90 parts of thermoplastic resin-2 and molded at 220°C using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co., Ltd.) to obtain a test material.

[0043] [Evaluation of molded products] The molded articles obtained in the examples and comparative examples were evaluated for color tone and appearance by the following methods. The results of Examples 1 to 8 and Comparative Examples 1 to 9 are shown in Table 3. The brand name, bulk density, and tap density of the CNTs used in each example are also shown in Table 3. Table 3 also shows the CNT content, kneading method, and agglomeration area ratio in the resin composition. (i) Color tone A spectrophotometer (CM-36dG, manufactured by Konica Minolta) was used to measure the brightness and saturation using the SCE method. (ii) Appearance The surface condition of the molded body was observed under an optical microscope (20x magnification), and surface irregularities with a longitudinal width of 5 μm or more present within an observation area (1 cm × 1 cm) were analyzed by image analysis (using an image analyzer "VHX-7100" manufactured by Keyence Corporation), the surface irregularity area ratio was calculated, and the appearance was evaluated. The appearance was evaluated according to the following criteria. Photographs of the molded bodies obtained in Example 1 and Comparative Example 3 are shown in Figure 4. ⊚: The surface irregularity area ratio is less than 0.1%, and the appearance of the molded product surface is extremely beautiful. ◯: The surface irregularity area ratio is 0.1% or more and less than 1.0%, and the appearance of the molded product surface is beautiful. Δ: The surface irregularity area ratio is 1.0% or more and less than 2.0%, and there is a problem with the appearance of the molded product surface. ×: The surface irregularity area ratio is 2.0% or more, and there is a significant problem with the appearance of the molded product surface. In this specification, "surface irregularities" refers to poor appearance caused by aggregates present on the surface of a molded product. "Longitudinal width" refers to the longest part observed when the surface irregularities are observed with an image analyzer. "Total area of ​​surface irregularities" refers to the sum of the areas of irregularities resulting from aggregates with a maximum diameter of 5 μm or more observed within the observed range. "Surface irregularity area ratio" refers to the total area of ​​surface irregularities divided by the area (1 cm2) of the observed range. 2 ) can be found by dividing by

[0044] Colorimetric values ​​(color values) measured by a colorimeter are greatly affected by the geometric conditions of the lighting and light reception. The geometric conditions of colorimeters can be broadly divided into 45-degree lighting systems and diffuse lighting systems using an integrating sphere. Diffuse lighting systems are further divided into SCI (Specular Component Include) and SCE (Specular Component Exclude) systems depending on the method of processing the specular reflection component using a light trap. In SCI, all specular reflection components from the sample are integrated. In SCE, the specular reflection component is removed using a light trap installed on the wall of the integrating sphere.

[0045] The molded article of the present invention has an excellent appearance and is characterized by its tendency to specularly reflect incident light from a colorimeter. When such a molded article is measured using the SCI method, it may appear jet black to the naked eye, but its brightness may be measured as high, which may not match the visual impression. Therefore, the molded article of the present invention was evaluated using the SCE method, which excludes the specular reflection component.

[0046] [Table 3]

[0047] As a method of expressing color tone, the International Commission on Illumination (CIE) established the CIE L color space, which expresses the colors we see with our eyes. * a * b* There is a color space (CIE L) * a * b * In the color system, color is expressed by three coordinates, and lightness is "L * ", red to green is "a * (positive is reddish, negative is greenish), yellow to blue is "b * " (positive is yellowish, negative is blueish) and the bluish black color tone is b * The value is negative, a * A value close to 0 is displayed as ideal. When the resin compositions according to the present invention (Examples 1 to 8) are used, the L * The value is sufficiently small, 2.80 or less, and b * It was found that the value was negative, and a bluish black hue could be achieved. It was also found that there was no problem in terms of the appearance of the molded article when the resin compositions according to the present invention (Examples 1 to 8) were used. Therefore, it was confirmed that the present invention can achieve a bluish black hue.

Claims

1. A resin composition containing a thermoplastic resin and carbon nanotubes, The carbon nanotubes are entangled carbon nanotubes that satisfy both of the following requirements (1) and (2), and the content of the carbon nanotubes is 0.1% by mass or more and 2% by mass or less with respect to 100% by mass of the resin composition; The aggregation area rate is 0.4% or more. Resin composition. (1) The bulk density of the carbon nanotubes is 28 kg / m ３ More than 106kg / m ３ The following is the result. (2) The tap density of the carbon nanotubes is 38 kg / m ３ More than 168kg / m ３ The following is the result.

2. The average diameter of the carbon nanotubes is 5 nm or more and 25 nm or less. The resin composition according to claim 1.

3. The resin composition according to claim 1 or 2, wherein the thermoplastic resin is at least one selected from the group consisting of polypropylene and polyethylene.

4. A molded product obtained by molding the resin composition according to claim 1 or claim 2. Molded body.

Images