Resin composition and molded body

Abstract

A resin composition comprising a thermoplastic resin and carbon nanotubes, wherein the carbon nanotubes are entangled carbon nanotubes having a bulk density and a tap density satisfying specific values, and the carbon nanotubes are contained in an amount of 0.1-2 mass% with respect to 100 mass% of the resin composition and exhibits an agglomeration area ratio of 0.4% or more.

Description

Resin composition and molded article

[0001] This invention relates to resin compositions and molded articles.

[0002] When coloring a resin composition black, black pigments such as carbon black or perylene black, as well as black dyes such as azo compounds or azine compounds, are usually used. However, when using polypropylene resin or similar as the base resin, black dyes may bleed, so it is common to use carbon black, which does not pose a risk of bleeding. However, while molded products using resin compositions containing carbon black generally have excellent physical properties, they tend to have a reddish-black hue. Therefore, there is a need to improve this reddish-black hue to a bluish-black hue. Accordingly, for example, a molded article formed from a resin composition containing a thermoplastic resin and carbon nanotubes has been described (see Patent Document 1).

[0003] Japanese Patent Publication No. 2023-6918

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

[0005] Therefore, the present invention aims to provide a resin composition and a molded article that can achieve a bluish-black hue.

[0006] The present invention provides the following resin composition and molded article: [1] A resin composition containing a thermoplastic resin and carbon nanotubes, wherein the carbon nanotubes are entangled carbon nanotubes that satisfy all of the following requirements (1) and (2), 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, and the aggregated area ratio is 0.4% or more. (1) The bulk density of the carbon nanotubes is 28 kg / m³ ３ More than 106kg / m ３ The following applies: (2) The tap density of the carbon nanotubes is 38 kg / m³ ３ More than 168kg / m ３The following: [2] The resin composition according to [1], wherein the average diameter of the carbon nanotubes is 5 nm or more and 25 nm or less. [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 molded article obtained by molding the resin composition according to any one of [1] to [3].

[0007] According to one aspect of the present invention, a resin composition and a molded article capable of achieving a bluish-black hue can be provided.

[0008] These are photographs of the measurement samples obtained in Test Example 4 and Test Example 6, taken at 300x magnification. These are scanning electron microscope images of the surface of entangled carbon nanotubes observed at 2000x magnification. These are scanning electron microscope images of the surface of bundled carbon nanotubes observed at 2000x magnification. These are photographs of the molded articles obtained in Example 1 and Comparative Example 3.

[0009] [Carbon Nanotubes] The embodiments of the present invention will be described below, but the present invention is not limited to the embodiments described below. First, the carbon nanotubes used in this embodiment will be described. Carbon nanotubes (hereinafter also referred to as "CNTs") refer to carbon materials in which a single layer of graphite has a tubular structure. Usually, CNTs having a single layer of tubular structure are classified as single-walled CNTs, CNTs having two layers of tubular structure are classified as double-walled CNTs, and CNTs having three or more layers of tubular structure are classified as multi-walled CNTs. Carbon nanotubes are an important coloring agent 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. If the average diameter of the carbon nanotubes is less than 5 nm, the intermolecular forces between the carbon nanotubes are very strong, making dispersion difficult, and too many aggregates are formed, resulting in strong scattered light generation, which is undesirable as it is not possible to obtain a jet black finish. On the other hand, for those with an average diameter exceeding 25 nm, the number of fibers per unit volume decreases, resulting in lower coloring power and making it impossible to achieve a jet-black finish.

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

[0011] The average diameter is determined, for example, by observing carbon nanotubes with a field emission scanning electron microscope (Hitachi High-Technologies Corporation, S-4800) at an accelerating voltage of 3 kV and taking images at 100,000x magnification. Then, for 20 arbitrary carbon nanotubes in the captured images, the average of the number of short axis lengths of each nanotube 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 / m³. ３ More than 106kg / m ３ The tap density of carbon nanotubes is as follows: 38 kg / m³ ３ More than 168kg / m ３It is necessary that the bulk density of carbon nanotubes is 28 kg / m ３ or less. When the bulk density is less than this value, the characteristics of entangled carbon nanotubes cannot be exhibited, so that a blue-black hue cannot be achieved in a molded article made of the resin composition. On the other hand, when the bulk density exceeds 106 kg / m ３ , the spaces between the carbon nanotube units constituting the entangled carbon nanotubes are too densely packed, so dispersion is not easy. In this case, a large number of aggregates are formed on the surface of the molded article, which easily causes light scattering, resulting in increased lightness, and a jet-black molded article cannot be obtained. From the same viewpoint, the bulk density of the carbon nanotubes is 32 kg / m ３ or more and 90 kg / m ３ or less, preferably 36 kg / m ３ or more and 80 kg / m ３ or less. It is necessary that the tap density of the carbon nanotubes is 38 kg / m ３ or more. When the tap density is less than this value, the characteristics of entangled carbon nanotubes cannot be exhibited, so that a blue-black hue cannot be achieved in a molded article made of the resin composition. On the other hand, when the tap density exceeds 168 kg / m ３ , the spaces between the carbon nanotube units constituting the entangled carbon nanotubes are too densely packed, so dispersion is not easy. In this case, a large number of aggregates are formed on the surface of the molded article, which easily causes light scattering, resulting in increased lightness, and a jet-black molded article cannot be obtained. From the same viewpoint, the tap density of the carbon nanotubes is 42 kg / m ３ or more and 158 kg / m ３ or less, preferably 46 kg / m ３ or more and 148 kg / m ３ or less.

[0013] In this specification, the bulk density and tap density of carbon nanotubes are values ​​measured under the following conditions. Since carbon nanotubes are mostly sold in compressed pellet form, powdered versions of these pellets were used as the measurement samples. To ensure consistent test conditions, the same treatment was also performed on powdered carbon nanotubes that were not compressed pelletized. For powdering, a mixing device ("Sample Mill SK-M10" manufactured by Kyoritsu Riko Co., Ltd.) was used to process the material for 30 seconds. Note that this powdering process only changes the carbon nanotubes from pellet form to powder form and does not finely grind the carbon nanotubes. The bulk density and tap density were measured using the "A・B・D Powder Properties Measuring Instrument" manufactured by Tsutsui Rikagaku Kikai Co., Ltd. The bulk density was calculated by placing the material into a sample hopper, pouring it into a sample container after approximately 30 to 60 seconds, leveling off the sample when it was overflowing, and then calculating the volume-to-mass ratio. Tap density is calculated by placing the sample in a container, applying a specific vibration or tapping (e.g., mechanical tapping for 3 minutes), and then determining the ratio of volume to mass at that time. Entangled carbon nanotubes are examples of carbon nanotubes whose bulk density and tap density satisfy the above conditions.

[0014] As used herein, the term "entangled" refers to a form in which multiple CNT units are intertwined in a bundle or rope-like manner without being limited to a specific orientation. A scanning electron microscope image of an entangled carbon nanotube is shown in Figure 2. As used herein, the term "bundle" refers to a secondary shape in which multiple CNT units are arranged side by side or intertwined in a helical manner, such as a bundle or rope. A scanning electron microscope image of a bundled carbon nanotube is shown in Figure 3.

[0015] [Thermoplastic Resin] Next, the thermoplastic resin used in this embodiment will be described. The thermoplastic resin is a base resin that serves as a binder for the resin composition. Examples of thermoplastic resins include polyolefin resins (polypropylene, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, etc.), polyphenylene sulfide, liquid crystal polymers, polyurethanes, polyether ether ketones, polyether sulfones, polystyrene resins, polyphenylene ethers, acrylonitrile butadiene styrene (ABS) resins, polyvinyl chloride, polyacetal, 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 individually or in combination of two or more.

[0016] The thermoplastic resin content is preferably within a range that can maintain the dispersion state of carbon nanotubes. From this viewpoint, the thermoplastic resin content is preferably 80% by mass or more, and more preferably 90% by mass or more, based on 100% by mass of the resin composition. If it is less than 80% by mass, the moldability may decrease.

[0017] [Other components] The resin composition according to this embodiment may contain carbon black, coloring pigments, inorganic fillers (such as silica and titanium), ester waxes, polyethylene waxes, antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, and surfactants, to the extent that they do not impair the effects of the present invention.

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

[0019] The inventors surmise 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 conditions. Furthermore, the inventors have discovered for the first time that, surprisingly, a bluish-black hue can be achieved depending on the dispersion state of the carbon nanotubes when entangled carbon nanotubes are dispersed in a thermoplastic resin at a relatively low concentration (for example, in the range of 0.1% to 2% by mass). In the case of resin compositions using bundled carbon nanotubes, the carbon nanotubes are oriented parallel to the flow direction of the resin when forming the molded body, but entangled carbon nanotubes do not tend to have a certain orientation. Therefore, it is considered that reflected light from the carbon nanotube particles in the molded body does not easily escape to the outside of the molded body, or that the incident light is easily trapped inside the carbon nanotube particles. At relatively high concentrations (for example, in the range greater than 2.0 mass%), aggregates are frequently present on the surface of the molded body, which not only impairs the appearance but also easily generates scattered light. It is hypothesized that, conversely, brightness increases at higher concentrations. As a result of diligent research, the inventors have found an appropriate range for the dispersion state of carbon nanotubes and have completed the present invention. The inventors surmise that the effects of the present invention described above are achieved in this manner.

[0020] Furthermore, in the resin composition according to this embodiment, the carbon nanotube content must be 0.1% by mass or more and 2% by mass or less based on 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 body made of the resin composition increases, which not only worsens the appearance but also makes it easier for scattered light to occur, increasing the brightness. From a similar viewpoint, the carbon nanotube content is preferably 0.1% by mass or more and 2% by mass or less, and more preferably 0.2% by mass or more and 1.5% by mass or less.

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

[0022] The reason for preparing the measurement sample with a carbon nanotube content of 1% by mass per 100% by mass of the resin composition is to increase the contrast ratio between aggregates and other parts by observing with transmitted light, thereby facilitating image analysis. Content exceeding 1% by mass is undesirable as a measurement condition because the 0.04 mm thickness makes it difficult to transmit light and observe. When the carbon nanotube content exceeds 1% by mass per 100% by mass of the resin composition, dilution to 1% by mass or less is necessary. When diluting, it is preferable to use a device with plastination ability but low dispersion ability to minimize changes in the dispersion state within the sample. For example, this can be done with a single-screw extruder or an injection molding machine equipped with a single screw. Twin-screw extruders, plastographs, Banbury mixers, rolls, or kneaders are undesirable as dilution devices because they generate strong shear stress and cause large changes in the dispersion state. If the carbon nanotube content is less than 1% by mass per 100% by mass of the resin composition, the aggregation area ratio when the thickness is 0.04 mm should be multiplied by a constant to convert it to 1% by mass. For example, if the carbon nanotube content is 0.5% by mass relative to 100% by mass of the resin composition, then you should double the amount.

[0023] The resin composition according to this embodiment contains a thermoplastic resin and carbon nanotubes, and may be used as a masterbatch containing a relatively high concentration of carbon nanotubes, which is diluted with the thermoplastic resin during molding, or as a compound that is used for molding in its original composition without dilution with the thermoplastic resin. From the viewpoint of addition costs or inventory costs, a masterbatch that can be made highly concentrated is preferable. The masterbatch is preferably in pellet form for easy handling.

[0024] [Analysis Method] In this specification, the maximum diameter and aggregation area ratio are values ​​measured under the following conditions. First, if the carbon nanotube content per 100% by mass of the resin composition or molded article to be measured exceeds 1% by mass, it is necessary to dilute it to 1% by mass or less using a single-screw extruder or an injection molding machine equipped with a single screw. If it exceeds 1% by mass, light transmission becomes difficult at a thickness of 0.04 mm, making observation difficult, and there is also the problem that the contrast ratio between aggregated and non-aggregated areas is small, making image processing difficult. Furthermore, when diluting, twin-screw extruders, plastographs, Banbury mixers, etc., have stronger kneading capabilities compared to single-screw extruders or those equipped with single screws, causing a large change in the dispersion state 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, kneading can be performed without changing the dispersion state for up to three passes. Next, the measurement sample, which had been reduced to 1% by mass or less, was press-molded at a temperature above the melting point of the thermoplastic resin to prepare a measurement sample with a thickness of 0.04 mm, and then analyzed. Specifically, the sample was observed at 300x magnification using a digital microscope (VHX-7100, Keyence Corporation), and the total area of ​​aggregates 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, Keyence Corporation). In this case, if the carbon nanotube content per 100% by mass of the resin composition is less than 1% by mass, it should be converted by multiplying by a constant so that it becomes 1% by mass. For example, if the carbon nanotube content per 100% by mass of the resin composition is 0.5% by mass, it should be multiplied by 2. If the carbon nanotube content per 100% by mass of the resin composition or molded article to be measured is 1% by mass or less, dilution is not necessary, and the analysis should be performed according to the method described above.

[0025] In this specification, "maximum diameter" refers to the longest portion of the aggregate observed with an image analyzer. "Total aggregate area" refers to the sum of the areas of aggregates with a maximum diameter of 5 μm or more observed within the observation range. "Agglomeration area ratio" refers to the total aggregate area multiplied by the area of ​​the observation range (25 mm²). ２can be obtained by dividing by ). The values described herein are obtained through observation, analysis, and calculation in accordance with the procedure of the above analysis method. The aggregate area ratio is a value obtained when the content of carbon nanotubes relative to 100% by mass of the resin composition is 1% by mass. The term "agglomerate" as used herein refers to those derived from agglomeration of carbon nanotubes, and includes both those consisting only of carbon nanotubes and those containing a thermoplastic resin in addition to carbon nanotubes.

[0026] [Method for 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 the method for producing the resin composition include a method of melt-kneading using a kneading apparatus such as a Banbury mixer, a roll, a plastograph, a single-screw extruder, a twin-screw extruder, and a kneader. However, in melt-kneading, use of an extruder or the like capable of continuous production instead of a batch process is preferable because it can improve production efficiency. Further, as the extruder, it is preferable to use a twin-screw extruder. Each component is melt-kneaded using a kneading apparatus such as an extruder, and after extruding the kneaded product into a strand shape, the kneaded product extruded into the strand shape can be processed into a desired form such as a pellet shape or a flake shape. Before melt-kneading, the components may be mixed in various mixers such as a high-speed mixer (such as a Henschel mixer) or a tumbler, or may be melt-kneaded by using a plurality of feeders in an extruder and performing multi-point feeding without mixing.

[0028] [Molded Article] The molded article according to the present embodiment is obtained by molding the resin composition according to the present embodiment described above. Since the molded article according to the present embodiment uses the resin composition according to the present embodiment described above, it can be adjusted to have an excellent bluish black hue with a high-grade feel. The molded article according to the present embodiment is for a housing. The term "housing" refers to a box or the like that forms the outside of a machine or electrical device having some function, and there is no particular limitation on the type of housing. It can be used for housings such as smartphone or personal computer cases, and outer panels of automobiles or airplanes. Further, the molded article itself may be used as a housing, or may be further subjected to coating or the like and then used as a housing.

[0029] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" in Examples and Comparative Examples are based on mass.

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

[0031] [Test Examples 1-3] 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, powdered carbon nanotubes were used as the measurement sample. For powdering, a powdering process was performed for 30 seconds using a mixing device ("Sample Mill SK-M10" manufactured by Kyoritsu Riko Co., Ltd.). The bulk density and tap density were measured using the "A・B・D Powder Properties Measuring Instrument" manufactured by Tsutsui Rikagaku Kikai Co., Ltd. The bulk density was calculated by placing the sample in the sample hopper at the top of the measurement container, pouring it into the sample container after approximately 30-60 seconds, leveling it off when the sample was overflowing, and calculating the volume and mass at that time. The tap density was calculated by applying a specific vibration or tapping (mechanical tapping for 3 minutes) to the measurement sample after it was placed in the container, and calculating the volume and mass at that time. The obtained results are shown in Table 1.

[0032]

[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., Ltd.). This mixture was melt-kneaded and granulated at 180°C to 230°C using a twin-screw extruder (TEX30-α, manufactured by Japan Steel Works, Ltd.) to produce a pellet-shaped masterbatch (Kneading Method A). 20 parts of the obtained masterbatch and 80 parts of thermoplastic resin-2 were dry-blended and molded at 220°C using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co., Ltd.) to obtain test materials.

[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., Ltd.). This mixture was melt-kneaded and granulated at 180°C to 230°C using a twin-screw extruder (TEX30-α, manufactured by Japan Steel Works, Ltd.) to produce a pellet-shaped masterbatch (kneading method B). 20 parts of the obtained masterbatch and 80 parts of thermoplastic resin-2 were dry-blended and molded at 220°C using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co., Ltd.) to obtain test materials.

[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, manufactured by Nippon Coke Co., Ltd.). This mixture was melt-kneaded and granulated using a twin-screw extruder (TEX30-α, manufactured by Japan Steel Works) at 180°C to 230°C to produce a masterbatch. 100 parts of the obtained masterbatch were melt-kneaded and granulated using a Banbury mixer (BR type Banbury mixer 1.7L, manufactured by Kobe Steel, Ltd.) at 120°C to 220°C to produce a pellet-shaped masterbatch (Kneading Method C). 20 parts of the obtained masterbatch and 80 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.) at 220°C to obtain a test material.

[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, Keyence Corporation), and the percentage of aggregated areas with a maximum diameter of 5 μm or more present within the observation area (5 mm × 5 mm) was calculated using the digital microscope (VHX-7100, Keyence Corporation). The results obtained are shown in Table 2. Figure 1 shows photographs of the measurement samples obtained in Test Examples 4 and 6 taken at 300x magnification.

[0037]

[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., Ltd.). This mixture was kneaded at 180°C to 230°C using a twin-screw extruder (TEX-30, manufactured by Japan Steel Works, Ltd.) to produce a pellet-shaped masterbatch (Kneading Method A). 10 parts of the obtained 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 7-9] Resin compositions and molded articles were prepared in the same manner as in Example 1, except that the brand and 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., Ltd.). This mixture was kneaded at 180°C to 230°C using a twin-screw extruder (TEX-30, manufactured by Japan Steel Works, Ltd.) to produce a pellet-shaped masterbatch (Kneading Method B). 10 parts of the obtained 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.

[0041] [Examples 4, 7, and 8, and Comparative Examples 2 and 5] Resin compositions and molded articles were prepared in the same manner as in Example 3, except that the brand and 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 for 2 minutes at 900 rpm using a Henschel mixer (FM75L / I, manufactured by Nippon Coke Co., Ltd.). This mixture was melt-kneaded and granulated using a twin-screw extruder (TEX30-α, manufactured by Japan Steel Works) at 180°C to 230°C to produce a pellet-shaped masterbatch. 100 parts of the obtained masterbatch were melt-kneaded and granulated using a Banbury mixer (BR type Banbury mixer 1.7L, manufactured by Kobe Steel, Ltd.) at 120°C to 220°C to produce a masterbatch (Kneading Method C). 10 parts of the obtained 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.) at 220°C to obtain a test material.

[0043] [Evaluation of Molded Articles] The color tone and appearance of the molded articles obtained in the examples and comparative examples were evaluated using the following methods. The results for 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. Furthermore, the CNT content, mixing method, and aggregation area ratio in the resin composition are also shown in Table 3. (i) Brightness and saturation were measured using the SCE method with a color spectrophotometer (CM-36dG, Konica Minolta). (ii) Appearance The surface condition of the molded articles was observed with an optical microscope (20x magnification), and surface irregularities with a long side width of 5 μm or more present in the observation area (1 cm × 1 cm) were analyzed using image analysis (using a digital microscope "VHX-7100" manufactured by Keyence Corporation), and the surface irregularity area ratio was calculated to evaluate the appearance. The appearance was evaluated according to the following criteria. Photographs of the molded articles obtained in Example 1 and Comparative Example 3 are shown in Figure 4. AA: The surface irregularity area ratio is less than 0.1%, and the appearance of the molded surface is extremely beautiful. A: The surface irregularity area ratio is 0.1% or more and less than 1.0%, and the appearance of the molded surface is beautiful. B: The surface irregularity area ratio is 1.0% or more and less than 2.0%, and there are problems with the appearance of the molded surface. C: The surface irregularity area ratio is 2.0% or more, and there are significant problems with the appearance of the molded surface. In this specification, "surface irregularity" means appearance defects caused by aggregates present on the surface of the molded body. "Longest width" means the longest part observed when the surface irregularities are viewed with an image analysis device. "Total surface irregularity area" means the sum of the areas of irregularities originating from aggregates with a maximum diameter of 5 μm or more observed within the observation range. "Surface irregularity area ratio" means the total surface irregularity area multiplied by the area of ​​the observation range (1 cm²). ２ It can be found by dividing by ).

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

[0045] The molded article according to the present invention has 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 the measured brightness may be high, which does not match the visual impression. Therefore, the molded article according to the present invention was evaluated using the SCE method, which excludes the specular reflection component.

[0046]

[0047] As a method for representing color tones, the International Commission on Illumination (CIE) has formulated the CIE L color space, which represents visible colors as a color space. ＊ a ＊ b ＊ There is a color system (color space). This CIE L ＊ a ＊ b ＊ In color systems, color is represented by three coordinates, and lightness is "L". ＊ ", red to green is "a ＊ (Positive indicates reddish tint, negative indicates greenish tint), yellow to blue is "b ＊ (Positive corresponds to yellowish, negative to bluish.) And the bluish-black color tone is b ＊ When the value is in the negative direction, a ＊ Values ​​close to 0 are displayed as ideal. Using the resin composition according to the present invention (Examples 1 to 8), the L of the molded body ＊ The value is 2.80 or less, which is sufficiently small, and b ＊The value was found to be negative, indicating that a bluish-black hue could be achieved. Furthermore, it was found that there were no problems in terms of the appearance of the molded article when using the resin composition according to the present invention (Examples 1 to 8). Therefore, it was confirmed that a bluish-black hue can be achieved according to the present invention.

Claims

1. A resin composition containing a thermoplastic resin and carbon nanotubes, wherein the carbon nanotubes are entangled carbon nanotubes that satisfy all of the following requirements (1) and (2), the content of the carbon nanotubes is 0.1% by mass or more and 2% by mass or less based on 100% by mass of the resin composition, and the aggregated area ratio is 0.4% or more. (1) The bulk density of the carbon nanotubes is 28 kg / m³ ３ More than 106kg / m ３ The following applies: (2) The tap density of the carbon nanotubes is 38 kg / m³ ３ More than 168kg / m ３ The following applies:

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

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

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

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