Resin composition and molded article

Abstract

To provide a resin composition and a molded product which can be used for a thin molded product, which has excellent mechanical strength and appearance, and which 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 0.6% by mass or more and 8% by mass or less relative to 100% by mass of the resin composition, and the aggregation area ratio is less than 0.4%.

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, molded articles made using resin compositions containing carbon black have excellent physical properties but tend to have a reddish-black hue. 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. Furthermore, carbon nanotubes are known to be difficult to disperse in a finely divided state due to their extremely strong intermolecular forces. Poor dispersion results in noticeable agglomerates on the surface of the molded product, leading to poor appearance. The presence of agglomerates becomes even more noticeable in relatively thin molded products such as films or sheets. Furthermore, when there are many carbon nanotube agglomerates in a molded product, the mechanical strength tends to be insufficient.

[0005] Therefore, the present invention aims to provide a resin composition and a molded article in which carbon nanotubes are highly miniaturized, resulting in a dispersion state that is suitable for molding into relatively thin forms such as films and sheets, achieving a bluish-black hue even at relatively high concentrations, and having excellent appearance and mechanical strength. [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 0.6% by mass or more and 8% by mass or less with respect to 100% by mass of the resin composition; The aggregation area rate is less than 0.4%. 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, a resin composition and a molded article can be provided that have a dispersion state that is compatible with relatively thin molded articles such as films or sheets, have excellent mechanical strength and appearance, and can achieve a bluish-black hue. [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 2 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 3It 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. 3 If 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. An SEM 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. An SEM 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. That is, 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 found for the first time that when entangled carbon nanotubes are dispersed in a thermoplastic resin at a relatively high concentration (for example, in the range of 0.6% by mass to 8% 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 using bundled carbon nanotubes, the carbon nanotubes are oriented parallel to the flow direction of the resin when a molded body is formed. However, entangled carbon nanotubes are unlikely to have a consistent orientation. This is thought to be due to the fact that reflected light from the carbon nanotube particles in the molded body is less likely to exit the molded body, and incident light is easily trapped within the carbon nanotube particles. In resin compositions containing black materials such as carbon nanotubes or carbon black, the brightness does not decrease in proportion to the amount of black material added, but rather generally reaches a minimum value at a certain amount, after which the brightness increases. At amounts below the minimum, light is absorbed by the black material, resulting in a decrease in brightness. However, above the minimum, the effect of light scattering due to aggregates of the black material in the resin composition increases. On the other hand, in the present invention, it was confirmed that the brightness decreased depending on the amount added. The inventors believe that this is because the dispersion state is extremely good and light scattering is unlikely to occur even when the amount added is relatively high (for example, 3% by mass or more). 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 0.6% by mass or more and 8% by mass or less, relative to 100% by mass of the resin composition. If the carbon nanotube content is less than 0.6% by mass, the resin composition cannot be sufficiently colored, while if the carbon nanotube content exceeds 8% by mass, the flowability is reduced and moldability is impaired. From the same viewpoint, the carbon nanotube content is preferably 0.7% to 7% by mass, and more preferably 0.8% to 6% by mass.

[0021] Furthermore, in the resin composition according to this embodiment, the aggregation area ratio must be less than 0.4%. If the aggregation area ratio is 0.4% or more, when the carbon nanotube content is relatively high (for example, more than 2% by mass), a bluish-black hue may not be achieved in the 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. An aggregation area ratio of 0% is particularly preferred, but it may be more than 0%.

[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 makes light transmission through a 0.04 mm thickness difficult, 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 necessary. 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 prone to generating strong shear stress, significantly altering the dispersion state, and are therefore undesirable as dilution devices. 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 viewpoint of additive costs or 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 aggregation area ratio of the resin composition 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, 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 resin composition or molded article to be measured has a carbon nanotube content of 1% by mass or less relative to 100% by mass, 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 this embodiment will be described. The resin composition according to this embodiment can be produced, for example, by a method including the following steps 1 to 3. Step 1: A step of mixing carbon nanotubes, a solvent, and the thermoplastic resin to obtain a carbon nanotube resin mixture. Step 2: A step of removing the solvent while kneading the carbon nanotube resin mixture. Step 3: A step of re-kneading the carbon nanotube resin composition.

[0027] In step 1, a resin to be used, carbon nanotubes in a specific mass ratio, and a solvent are mixed and dispersed to obtain a carbon nanotube resin mixture. The carbon nanotubes are as described above. The mixing and dispersion method is not particularly limited as long as it can achieve uniform mixing and dispersion. For example, a Henschel mixer, super mixer, ultrasonic homogenizer, spiral mixer, planetary mixer, disperser, or hybrid mixer can be used to perform dispersion processing by a known method. Two or more of these dispersers may be used in combination. In particular, from the viewpoints of high dispersibility of carbon nanotubes in thermoplastic resins and suppression of damage to the carbon nanotubes, it is preferable to use a Henschel mixer, super mixer, or ultrasonic homogenizer. Furthermore, after this processing, a ball mill, vibration mill, sand mill, roll mill, or the like may be used to further thoroughly disperse the carbon nanotubes, as long as it does not damage the carbon nanotubes. The processing temperature and processing time for mixing and dispersing are adjusted as appropriate.

[0028] Step 2 is a step of removing the solvent from the carbon nanotube resin mixture produced in the previous step while kneading it. The thermoplastic resin is as described above. 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. The treatment temperature and pressure vary depending on the thermoplastic resin, solvent, etc. used, and are therefore adjusted appropriately. However, as will be described later, treatment is preferably carried out at a high temperature, and the treatment temperature is preferably 100 to 370° C. In this step, after the pretreatment, a resin composition is finally obtained that has been granulated into pellets or flakes.

[0029] Step 3 is a step of re-kneading the resin composition prepared in the previous step. Examples of the re-kneading method include melt-kneading using a kneading device such as a Banbury mixer, roll, plastograph, single-screw extruder, twin-screw extruder, or kneader. However, in Step 3, it is preferable to use a batch-type kneader such as a Banbury mixer for melt-kneading, as this can improve dispersion efficiency. The treatment temperature and pressure are adjusted appropriately depending on the thermoplastic resin used, but the treatment temperature is preferably 100°C or higher and 370°C or lower.

[0030] [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 has a dispersion state that can be used for relatively thin molded articles such as films or sheets, and is excellent in mechanical strength and appearance, and can achieve a bluish-black hue. 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]

[0031] 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.

[0032] [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 (diameter 8nm to 20nm), product name "FT9100N", manufactured by Cnano CNT-2: Entangled carbon nanotubes (diameter 8nm to 20nm), product name "FT9120N", manufactured by Cnano CNT-3: Bundled carbon nanotubes (diameter 7nm to 11nm), product name "FT7000", manufactured by Cnano (thermoplastic resin) Thermoplastic resin-1: Homopolypropylene (MFR 45g / 10mm), product name "Prime Polypro J108PN", manufactured by Prime Polymer Co., Ltd. Thermoplastic resin-2: Homopolypropylene (MFR 45g / 10mm), product name "Prime Polypro J108M", manufactured by Prime Polymer Co., Ltd.

[0033] [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 powder was obtained by pulverizing the carbon nanotubes for 30 seconds using a mixer (Kyoritsu Riko Co., Ltd.'s "Sample Mill SK-M10" model). 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.

[0034] [Table 1]

[0035] [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 prepare a masterbatch (mixing method A). 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.

[0036] [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 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.

[0037] [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.). (Mixing Method C) 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, Nissei Plastic Industrial Co., Ltd.).

[0038] [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.

[0039] [Table 2]

[0040] [Example 1] 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 and granulated at 180-230°C using a twin-screw extruder (TEX-30, manufactured by The Japan Steel Works) to produce a pelletized resin composition. 100 parts of the resulting resin composition were re-mixed in a Banbury mixer at 220°C and 100 RPM for 10 minutes, and then granulated to produce a pelletized masterbatch (Kneading Method C). 20 parts of the resulting masterbatch were dry-blended with 80 parts of thermoplastic resin-2 and molded using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co., Ltd.) to produce a 2 mm thick molded body.

[0041] [Examples 2 to 6 and Comparative Examples 9 and 18] 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.

[0042] [Comparative 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 and granulated at 180°C to 230°C using a twin-screw extruder (TEX-30, manufactured by The Japan Steel Works) to produce a pelletized masterbatch (kneading method A). 10 parts of the resulting masterbatch were dry-blended with 90 parts of thermoplastic resin-2 and molded using an injection molding machine (NS-40 5A, manufactured by Nissei Plastic Industrial Co., Ltd.) to produce a 2 mm thick molded body.

[0043] [Comparative Examples 2 to 4, 10 to 13, and 19 to 22] Resin compositions and molded articles were prepared in the same manner as in Comparative Example 1, except that the brand and blending amount of carbon nanotubes were changed as shown in Table 3.

[0044] Comparative Example 5 95 parts of thermoplastic resin-1, 5 parts of CNT-1, and 5 parts of water (FM75L / I, manufactured by Nippon Coke Co.) were mixed at 900 rpm for 2 minutes. This mixture was kneaded at 180°C to 230°C using a twin-screw extruder (TEX-30, manufactured by The Japan Steel Works) to produce a resin kneaded product. (Kneading Method B)

[0045] [Comparative Examples 6 to 8 and 14 to 17] Resin compositions and molded articles were prepared in the same manner as in Comparative Example 5, except that the brand and blending amount of carbon nanotubes were changed as shown in Table 3.

[0046] [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 6 and Comparative Examples 1 to 22 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 2 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

[0047] 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.

[0048] 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.

[0049] [Table 3]

[0050] 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 composition of the present invention (Examples 1 to 4) is used, the L * The value is sufficiently small, 2.07 or less, and b * The values ​​were in the range of -0.28 to -0.44, and it was found that a bluish black hue could be achieved. It was also found that there were no problems with the appearance of the molded article when the resin compositions of the present invention (Examples 1 to 4) were used. Therefore, it was confirmed that the present invention can achieve a bluish black hue.

[0051] [Evaluation of physical properties of molded products] The masterbatches obtained in Examples 3 and 6 and Comparative Examples 4 and 13 were evaluated for strain at break and impact strength by the methods described below. The results of Examples 3 and 6 and Comparative Examples 4 and 13 are shown in Table 4. Table 4 also shows the CNT content, kneading method, and agglomeration area ratio in the master batch. (i) Breaking strain The masterbatches obtained in Examples 3 and 6 and Comparative Examples 4, 13, and 20 were molded into sheets with a thickness of 50 μm using a belt extruder (NV-20 mm L / D22 extruder, manufactured by Mars Seiki Co., Ltd.) set at 200°C, and test pieces were punched out into dumbbell shapes to prepare test pieces. The breaking strain (unit: %) was measured using a tensile tester (AG-X Refresh, manufactured by Shimadzu Corporation).

[0052] [Table 4]

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 0.6% by mass or more and 8% by mass or less, relative to 100% by mass of the resin composition: The aggregation area rate is less than 0.4%. 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