Method for producing a conductive resin composition, method for producing a conductive resin molded article, and use of a conductive resin molded article

Abstract

To provide a method for producing a conductive resin composition that exhibits superior mechanical properties compared to conventional methods by highly dispersing a carbon material in a thermoplastic resin. [Solution] The present invention provides a method for producing a conductive resin composition, comprising: a mixing and dispersion step of mixing each component containing an aqueous medium to obtain a mixture; a kneading and solvent removal step of removing the aqueous medium while kneading the obtained mixture in an extruder to obtain a primary kneaded product; and a re-kneading step of shear-melt kneading the obtained primary kneaded product in a Banbury mixer.

Description

Technical Field

[0001] The present invention relates to a method for producing a resin composition that exhibits excellent mechanical properties by highly dispersing fibrous carbon compounds in a thermoplastic resin.

Background Art

[0002] Thermoplastic resins are indispensable materials in our daily lives, but they are colorless, have low mechanical strength, and are insulating when used alone. Therefore, resin compositions with various fillers added to impart functionality are actively being developed. For applications that require conductivity, carbon black and other materials are generally used as conductive materials and are used as resin compositions with antistatic functions in the field of electronic components. However, in the automotive field and other areas, high conductivity, mechanical properties, and moldability are often required, and there are many cases where carbon black cannot meet these requirements.

[0003] In recent years, carbon nanotubes have attracted attention as materials that may be able to provide high conductivity while ensuring other physical properties. Carbon nanotubes have a structure in which a planar graphene sheet is rolled into a cylinder, with a diameter of several nanometers to several tens of nanometers and a length of several micrometers, and a high aspect ratio. Due to this structure, they exhibit extremely high mechanical strength, electrical conductivity, and thermal conductivity, and are expected to be applied in various fields.

[0004] On the other hand, the application of carbon nanotubes has been difficult for the following reasons. This is because carbon nanotubes have an elongated shape and strong van der Waals forces, causing them to aggregate strongly with each other, making dispersion extremely difficult. In the field of thermoplastic resins, studies have been conducted to improve mechanical properties by dispersing carbon nanotubes in resins, but it is not possible to enhance mechanical properties unless the carbon nanotubes are uniformly dispersed. If they are not uniformly dispersed, the stress applied to the resin composition will concentrate near the aggregates of carbon nanotubes, causing fracture to occur easily. Therefore, uniformly dispersing carbon nanotubes, which have strong cohesive forces, has been a challenge.

[0005] Against this backdrop, methods are being investigated for uniformly dispersing fibrous carbon compounds such as carbon nanotubes and cellulose fibers using kneaders with high production speeds. One such method involves a hydrolysis method in which the material is pretreated with a wetting agent and kneaded in a twin-screw extruder, enabling high dispersion of carbon nanotubes (Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2013-201117 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The method described in Patent Document 1 significantly improves conductivity and mechanical properties compared to not pre-treating the material. However, this method still has its challenges; while it improves dispersibility in olefin-based resins, such as polypropylene resin, it does not achieve a sufficiently dispersed state.

[0008] The present invention aims to provide a method for producing a conductive resin composition, a conductive resin composition, a conductive resin molded article, and a method for using a conductive resin molded article, particularly when using carbon nanotubes, by highly dispersing fibrous carbon compounds in a thermoplastic resin, thereby exhibiting superior mechanical properties compared to conventional techniques. [Means for solving the problem]

[0009] [1] A method for producing a conductive resin composition containing a thermoplastic resin and a fibrous carbon compound, A method for producing a conductive resin composition comprising the following steps 1, 2, and 3. Step 1: A step of mixing a thermoplastic resin with an average particle size of 0.01 mm or more and 3 mm or less, a fibrous carbon compound in an amount of 0.3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the thermoplastic resin, and an aqueous medium in an amount of 10 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the fibrous carbon compound to obtain a mixture. Step 2: The mixture is melt-kneaded using a single-screw or twin-screw extruder at a peripheral speed of 5 m / min or more and 150 m / min or less, and the aqueous medium is removed to obtain a primary kneaded product. Step 3: A step to obtain a secondary mixture by shear-melt kneading the primary mixture using a Banbury mixer at a temperature set to be below the melting or softening point of the thermoplastic resin, and at a screw peripheral speed of 1 m / min or more and 150 m / min or less. Step 4: A step to obtain a conductive resin composition by melt-kneading the secondary kneaded material at a temperature set to be above the melting point or softening point of the thermoplastic resin and making it homogenized. [2] A method for producing a conductive resin composition according to [1], wherein the fibrous carbon compound is a carbon nanotube. [3] The method for producing a conductive resin composition according to [1] or [2], wherein the aqueous medium is at least one selected from the group consisting of water and hydrophilic organic solvents. [4] A method for producing a conductive resin composition according to any one of [1] to [3], wherein the thermoplastic resin is at least one selected from the group consisting of polypropylene resin, low-density polyethylene resin, linear low-density polyethylene resin, and thermoplastic polyurethane. A conductive resin composition prepared by the method for producing a conductive resin composition described in any of [5] [1] to [4]. [6] The conductive resin composition according to [5], further comprising a surfactant. [7] The conductive resin composition according to [6], wherein the surfactant is at least one selected from the group consisting of acetylene glycol compounds and alkanesulfonic acid compounds. A conductive resin molded article using the conductive resin composition described in [8] [5]. A conductive resin molded article using the conductive resin composition described in [9] [6] or [7]. Use of conductive resin molded articles as described in

[10] [8] in automotive parts, building material parts, machine parts, electrical parts, electronic parts, furniture parts, home appliance parts, containers, or packaging materials. Use of conductive resin molded articles as described in

[11] [9] in automotive parts, building material parts, machine parts, electrical parts, electronic parts, furniture parts, home appliance parts, containers, or packaging materials. [Effects of the Invention]

[0010] According to the present invention, by highly dispersing fibrous carbon compounds in a thermoplastic resin, it is possible to provide a method for producing a conductive resin composition that exhibits superior mechanical properties compared to those obtained using conventional techniques, a conductive resin composition, a conductive resin molded article, and a method for using the conductive resin molded article. [Modes for carrying out the invention]

[0011] The embodiments of the present invention will be described below, but the present invention is not limited to the embodiments described below, and various modifications are possible without departing from the spirit of the invention.

[0012] <Method for producing conductive resin composition> The method for producing the conductive resin composition according to this embodiment comprises: step 1 (hereinafter also referred to as the "mixing and dispersion step"), which involves mixing each component containing an aqueous medium to obtain a mixture; step 2 (hereinafter also referred to as the "kneading and solvent removal step"), which involves kneading the obtained mixture in an extruder while removing the aqueous medium to obtain a primary kneaded product; and step 3 (hereinafter also referred to as the "re-kneading step"), which involves kneading the obtained primary kneaded product in a Banbury mixer. The details thereof will be described below. In the method for producing the conductive resin composition according to this embodiment, a step of kneading the fibrous carbon compound into a thermoplastic resin was investigated, enabling high dispersion of the fibrous carbon compound. Furthermore, compared to the conventional method, the mechanical properties of the resulting conductive resin molded article were significantly improved.

[0013] (Process 1 (mixing and dispersion process)) In the mixing and dispersion step, a mixture is obtained by mixing a thermoplastic resin with an average particle size of 0.01 mm to 3 mm, a fibrous carbon compound in an amount of 1 to 30 parts by mass per 100 parts by mass of the thermoplastic resin, and at least one aqueous medium selected from the group consisting of 10 to 500 parts by mass per 100 parts by mass of the fibrous carbon compound and a hydrophilic organic solvent.

[0014] In the mixing and dispersion process, it is also preferable to use dispersers such as Henschel mixers, super mixers, ultrasonic homogenizers, spiral mixers, planetary mixers, dispersers, hybrid mixers, and kneaders. Two or more dispersers may be used in combination. In particular, from the viewpoint of dispersing carbon nanotubes in thermoplastic resin or suppressing damage to carbon nanotubes, it is preferable to use a Henschel mixer, super mixer, or ultrasonic homogenizer. Furthermore, as necessary, within a range that does not damage the carbon nanotubes, the mixture may be further dispersed using a ball mill, vibration mill, sand mill, or roll mill.

[0015] As the thermoplastic resin, it is necessary to use a powdery or pellet状 one with an average particle size of 0.01 mm or more and 3 mm or less. By using the thermoplastic resin with the above average particle size, the fibrous carbon compound is easily loosened by the thermoplastic resin, and the kneading process becomes easy. The average particle size of the thermoplastic resin can be measured using a microscope or a digital microscope. As the thermoplastic resin, those generally used in various molding methods such as injection molding method and extrusion molding method can be used. Examples of the thermoplastic resin include polyethylene-based resins, polypropylene-based resins, polystyrene-based resins, acrylic-based resins, polyolefin-based resins, acrylonitrile-butadiene-styrene copolymer (ABS resin), polyamide resins, polycarbonate resins, and thermoplastic polyurethane resins. These resins can be used alone or in combination of two or more. Examples of the polyethylene-based resin include ethylene homopolymer (high-density polyethylene, low-density polyethylene, linear low-density polyethylene), ethylene-propylene copolymer, and ethylene-vinyl acetate copolymer. Examples of the polypropylene-based resin include propylene homopolymer (polypropylene resin) and propylene-butene copolymer. Examples of the polystyrene-based resin include styrene homopolymer, acrylonitrile-styrene copolymer, and styrene-butadiene copolymer. Examples of the acrylic-based resin include acrylate ester homopolymer, methyl methacrylate homopolymer, and ethylene-ethyl acrylate copolymer. Examples of the polyolefin-based resin include α-olefin homopolymer and ethylene-α-olefin copolymer. Among them, it is preferable to use low-density polyethylene, linear low-density polyethylene, polypropylene resin, or thermoplastic polyurethane resin.

[0016] The thermoplastic resin may contain additives. Examples of the additives include primary antioxidants, secondary antioxidants, lubricants, ultraviolet absorbers, light stabilizers, weather resistance improvers, fluidity improvers, plasticizers, mold release agents, flame retardants, crystal nucleating agents, foaming agents, antibacterial agents, antifungal agents, or surfactants, which can be appropriately used.

[0017] As the fibrous carbon compound, from the viewpoint of improving the strength of the resin composition, carbon nanotubes, carbon nanofibers, cellulose nanofibers, cellulose microfibers, chitin / chitosan nanofibers, or chitin / chitosan microfibers can be used. Among them, from the viewpoint of improving conductivity, it is preferable to use carbon nanotubes or carbon nanofibers. These materials can also be used in combination of two or more.

[0018] As the carbon nanotubes (hereinafter also referred to as "CNT"), appropriately known ones can be used. The amount of the carbon nanotubes needs to be 0.3 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin. If the amount of the carbon nanotubes is less than 0.3 parts by mass with respect to 100 parts by mass of the thermoplastic resin, the conductivity will be low. On the other hand, if the amount of the carbon nanotubes exceeds 30 parts by mass with respect to 100 parts by mass of the thermoplastic resin, the dispersibility will decrease, and it may not be possible to obtain the conductive resin composition depending on the kneading apparatus, which is not preferable. The amount of the carbon nanotubes is preferably 0.5 parts by mass or more and 25 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin, and more preferably 1 part by mass or more and 20 parts by mass or less.

[0019] Cellulose microfibers function as reinforcing materials when dispersed in a resin matrix. Such cellulose fibers are obtained by defibrating and finely refining cellulose-containing fiber raw materials (e.g., various types of pulp). Suitable defibration equipment used in the defibration process includes high-speed defibrators, grinders (stone mill type pulverizers), high-pressure homogenizers or ultra-high-pressure homogenizers, high-pressure impact pulverizers, ball mills, bead mills, disc refiners, conical refiners, twin-screw kneaders, vibrating mills, homomixers under high-speed rotation, ultrasonic dispersers, or beaters, or wet grinding equipment. Cellulose microfibers can be used alone, but it is preferable to use them in combination with CNTs to improve conductivity. When using cellulose microfibers as a fibrous carbon compound, the amount blended is preferably 1 to 70 parts by mass per 100 parts by mass of thermoplastic resin.

[0020] The aqueous medium is preferably at least one selected from the group consisting of water and a hydrophilic organic solvent. The aqueous medium is preferably mainly water (50% or more of the total) and further contains a hydrophilic organic solvent. As water, it is preferable to use ion-exchanged water, distilled water, and purified water. As the hydrophilic organic solvent, it is preferable to use one that has a boiling point that evaporates easily in the subsequent kneading and solvent removal step and does not remain in the resulting conductive resin composition. Considering the impact on the working environment, cost, and handling ease, an alcohol-based solvent or a glycol-based solvent can be used, with ethanol being particularly preferred. The amount of the aqueous medium should be greater than or equal to the amount that can disperse the carbon nanotubes, and less than or equal to the amount that can be removed by kneading. The amount of the aqueous medium must be 10 parts by mass or more and 500 parts by mass or less, and preferably 20 parts by mass or more and 400 parts by mass or less, per 100 parts by mass of carbon nanotubes.

[0021] In the mixing and dispersion step, it is preferable to further mix the surfactant to obtain a mixture. By adding a surfactant, the aqueous medium containing the surfactant can easily penetrate the entangled aggregates of fibrous carbon compounds, thereby improving the effect of loosening the fibrous carbon compounds. As surfactants, anionic surfactants such as anionic surfactants, cationic surfactants, and amphoteric surfactants, as well as nonionic surfactants, can be used. Examples of anionic surfactants include sulfate ester type, phosphate ester type, and sulfonic acid type surfactants. Examples of cationic surfactants include quaternary ammonium salt type surfactants. Examples of amphoteric surfactants include alkyl betaine type, amide betaine type, and amine oxide type surfactants. Examples of nonionic surfactants include fatty acid esters and sorbitan fatty acid esters. Among these, the use of acetylene glycol-based compounds or alkane sulfonic acid-based compounds is preferred because they have a high effect in loosening carbon nanotubes. Examples of acetylene glycol compounds include the Surfinol series (manufactured by Nisshin Chemical Industry Co., Ltd.), the Orfin series (manufactured by Nisshin Chemical Industry Co., Ltd.), and the Acetyleneol series (manufactured by Kawaken Fine Chemical Co., Ltd.). Examples of alkanesulfonic acid compounds include HOSTAPUR SAS93 (manufactured by Clariant Japan Co., Ltd.) and Latemul PS (manufactured by Kao Corporation).

[0022] The amount of surfactant should be within a range that does not degrade the physical properties of the resulting conductive resin composition. Specifically, the amount of surfactant may be 0 parts by mass, more than 0 parts by mass but 40 parts by mass or less, or 0.02 parts by mass or more but 10 parts by mass or less, per 100 parts by mass of the total of the fibrous carbon compound and the surfactant.

[0023] The conductive resin composition may optionally contain other components besides those mentioned above. Examples of other components include flame retardants, fillers, plasticizers, antioxidants, ultraviolet absorbers, light stabilizers, dispersants, antistatic agents, conductivity imparters, mold release agents, lubricants, dyes, and pigments.

[0024] (Process 2 (Mixing and Solvent Removal Process)) In the mixing and solvent removal process, the solvent in the mixture obtained in the mixing and dispersion process is removed while the mixture is being kneaded. Then, a conductive resin composition (primary kneaded product) in pellet or flake form can be obtained by granulation as needed. Alternatively, a high-concentration product (masterbatch) with a high content of fibrous carbon compounds may be mixed with the raw resin in a predetermined ratio, and then granulation may be performed using a kneader such as an extruder or roll.

[0025] In this process, it is necessary to remove the aqueous medium, so it is necessary to use a single-screw or twin-screw extruder (hereinafter also referred to as "extruder") for kneading the mixture. Furthermore, kneading may be performed twice, in which case different equipment may be combined. For example, it is preferable to first use a pressure kneader to remove some of the aqueous medium by kneading under reduced pressure, and then remove the aqueous medium with an extruder, as this allows for better dispersion of the fibrous carbon compound. If a Banbury mixer or a kneader without a vacuum function is used first, the heating is limited to the jacket section, making it difficult to heat the mixture and resulting in a longer removal of the aqueous medium. This is undesirable because it can cause the thermoplastic resin to yellow. Also, because of the presence of the aqueous medium, shear force is difficult to apply to the mixture, hindering dispersion, which is undesirable. The processing temperature and pressure should be set appropriately according to the type of thermoplastic resin and aqueous medium. However, it is preferable to process at a high temperature to remove the solvent, and while the appropriate temperature varies depending on the thermoplastic resin used, it is generally preferable to process at 100°C to 370°C.

[0026] The extruder must have a peripheral speed of 5 m / min to 150 m / min, preferably between 20 m / min and 100 m / min. If the peripheral speed is below the lower limit, the resulting resin composition will yellow. If the peripheral speed is above the upper limit, the amount of heat generated due to shearing will increase, causing the resulting resin composition to burn and yellow.

[0027] (Step 3 (Re-mixing step)) In the re-mixing process, the mixture obtained in the mixing and solvent removal process is re-mixed using a Banbury mixer. Then, a conductive resin composition (secondary mixture) in pellet or flake form can be obtained by granulation as needed using a two-roll or square pelletizer. In this process, fibrous carbon compounds are loosened and dispersed in the thermoplastic resin by melt-mixing under shear force. For shear-melt mixing to be effective, the temperature must be within the range from when the thermoplastic resin begins to melt or soften until just before it completely melts or softens. This allows for shear-melt mixing while maintaining a high viscosity state, efficiently loosening the fibrous carbon compounds. If the temperature significantly exceeds the melting or softening point, the viscosity decreases, and the shear force also decreases, resulting in the fibrous carbon compounds remaining aggregated and not loosened even with prolonged melt-mixing. In a Banbury mixer, shear heat generation occurs during shear-melt mixing, causing a natural temperature rise even without heating; therefore, it is important to cool the mixture appropriately to maintain the aforementioned temperature range. The shear-melt mixing time required in a high-viscosity state is approximately 2 to 5 minutes using the Banbury mixer (capacity 1.7L) used in this invention. The optimal shear-melt mixing time varies depending on the size of the apparatus, and the optimal time increases or decreases in proportion to the capacity. For example, if the capacity increases, the required mixing time increases. For crystalline resins, the melting point is used as a guideline for management, and for amorphous resins, the softening point is used as a guideline.

[0028] For re-mixing the kneaded material, for example, a Banbury mixer can be used. Banbury mixers (internal mixers) include tangential types where the rotating circles of the left and right rotors do not overlap, and meshing types where the rotating circles overlap. In this embodiment, it is preferable to use the meshing type, which provides a greater shear force.

[0029] The processing temperature and pressure can be set appropriately depending on the type of thermoplastic resin. However, in order to achieve proper dispersion, it is preferable to knead at the lowest possible temperature, specifically at a temperature below the melting point of the thermoplastic resin. By heating with shear heat and kneading at a temperature near the melting point of the thermoplastic resin, kneading can be performed in a high-viscosity state, thereby improving the dispersibility of the fibrous carbon compound.

[0030] In step 3, the peripheral speed of the screw in the kneader, such as a Banbury mixer, must be 1 m / min or more and 150 m / min or less, preferably 5 m / min or more and 130 m / min or less, more preferably 8 m / min or more and 100 m / min or less, even more preferably 9 m / min or more and 80 m / min or less, even more preferably 10 m / min or more and 70 m / min or less, and particularly preferably 11 m / min or more and 50 m / min or less. If the peripheral speed is less than 1 m / min, no shear force is applied and dispersibility decreases. If the peripheral speed is greater than 150 m / min, the fibrous carbon compound is fragmented, dispersibility deteriorates, and conductivity or mechanical properties decrease.

[0031] The mixing time in the Banbury mixer may be 1 minute or more, 1 minute or more and 30 minutes or less, 2 minutes or more and 15 minutes or less, or 3 minutes or more and 10 minutes or less.

[0032] (Process 4 (uniformization process)) In the homogenization process, it is necessary to uniformly disperse the fibrous carbon compound in the thermoplastic resin in a melted or softened state at a temperature setting above the melting point or softening point. For homogenization of the kneaded material, for example, a two-roll kneader, a kneader, an extruder, or a Banbury mixer can be used. In step 4, the peripheral speed of the screw in the kneader, extruder, or Banbury mixer used in kneading is preferably 1 m / min or more and 150 m / min or less, more preferably 5 m / min or more and 130 m / min or less, even more preferably 8 m / min or more and 100 m / min or less, even more preferably 9 m / min or more and 80 m / min or less, even more preferably 10 m / min or more and 70 m / min or less, and particularly preferably 11 m / min or more and 50 m / min or less. If the peripheral speed is less than 1 m / min, there is not enough force applied to the kneading, and the dispersibility will decrease. If the peripheral speed exceeds 150 m / min, the fibrous carbon compound becomes fragmented, worsening its dispersibility and reducing its conductivity or mechanical properties.

[0033] According to the method for producing a conductive resin composition of this embodiment, it is possible to disperse fibrous carbon compounds in a good state without impairing the inherent physical properties of the thermoplastic resin, such as its mechanical strength, and to produce a conductive resin composition with excellent conductivity while maintaining the inherent physical properties of the thermoplastic resin, such as its mechanical strength.

[0034] <Conductive resin composition and conductive resin molded article> The conductive resin composition according to this embodiment was prepared by the method for manufacturing the conductive resin composition according to this embodiment described above. Furthermore, the conductive resin molded article according to this embodiment uses the conductive resin composition according to this embodiment described above. Furthermore, the conductive resin molded article according to this embodiment can be suitably used for automotive parts, building material parts, machine parts, electrical parts, electronic parts, furniture parts, home appliance parts, containers, or packaging materials. The thickness of films and sheets is defined in JIS Z0108:2012. In this application, a film is defined as a plastic membrane with a thickness of less than 0.25 mm (less than 250 μm), and a sheet is defined as a thin plastic plate with a thickness of 0.25 mm or more (250 μm or more). [Examples]

[0035] 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 "%" refer to mass unless otherwise specified. The average particle size of the thermoplastic resin was obtained by observing 30 randomly selected particles using a digital microscope (Keyence Corporation, model number VHX-600) at a magnification of 100x and averaging the result.

[0036] <Manufacturing of conductive resin compositions> (Example 1) 1.5 parts of carbon nanotubes (product name "Knanos 100T", manufactured by Kunho Petrochemical) and 98.5 parts of polypropylene powder (PP, product name "Prime Polypro J229E", manufactured by Prime Polymer) with an average particle size of 0.05 to 1.1 mm were placed in a mixer and stirred and mixed for 3 minutes at 25°C. 5 parts of a 1% surfactant aqueous solution prepared by diluting acetylene glycol-based surfactant (product name "Surfinol #465", manufactured by Nisshin Chemical Co., Ltd.) with water were added and stirred and mixed for 2 minutes at 25°C to obtain a mixture. Using a twin-screw extruder (product name "TEX30", manufactured by Japan Steel Works, Ltd.), the obtained mixture was melt-kneaded at a peripheral speed of 38 m / min and a processing temperature of 200°C, while the solvent (water) was evaporated and removed from the vent of the twin-screw extruder to obtain a pellet-shaped primary kneaded product. Using a Banbury mixer, the primary mixture was melt-kneaded at a peripheral speed of 20 m / min and a processing temperature of 160°C. After confirming the sound of gas escaping at the start of melting, mixing was continued while cooling water was flowed through the jacket to obtain a conductive resin composition (secondary mixture). The obtained secondary mixture was kneaded using a two-roll mixer (product name "MX-0X12", manufactured by Inoue Seisakusho Co., Ltd.) at a processing temperature of 25°C to produce a 1 cm thick sheet. The obtained sheet was then used with a square pelletizer (product name "GHP-220", manufactured by Tomorai Tekkosho Co., Ltd.) to obtain a secondary mixture in the form of square pellets.

[0037] (Examples 2-21 and Comparative Examples 9-12) The conductive resin composition was obtained in the same manner as in Example 1 described above, except that the formulation was changed as shown in Tables 1-4. Details of the materials used are shown below.

[0038] • LLDPE: Linear low-density polyethylene (average particle size 0.01-1.2 mm, product name "US370GN", manufactured by Nippon Polyethylene Co., Ltd.) • LDPE: Low-density polyethylene (average particle size 0.01-1.0 mm, product name "Suntec F2270", manufactured by Asahi Kasei Chemicals Corporation) • TPU: Thermoplastic polyurethane (average particle size 0.01~1.0 mm, product name "Rezamin P-880" crushed product, manufactured by Dainichi Seika Kogyo Co., Ltd.) • FT9000: Carbon nanotube (product name "FT9000", manufactured by Canno Inc.) • VGCF-X: Carbon nanotube (product name "VGCF-X", manufactured by Showa Denko Corporation) • B800: Cellulose microfiber (product name "ARBOCEL B800", manufactured by Rettenmeyer) • Hostapure SAS93: Alkanesulfonic acid-based surfactant (product name "HostaPure SAS93", manufactured by Clariant Japan Co., Ltd.)

[0039] (Comparative Example 1) 95.5 parts of polypropylene powder (product name "Prime PolyPro J229E", manufactured by Prime Polymer Co., Ltd.) with an average particle size of 0.05 to 1.1 mm were mixed with 4.5 parts of carbon nanotubes (product name "Knanos 100T", manufactured by Kunho Petrochemical Co., Ltd.) and stirred and mixed in the same manner as in Example 1 to obtain a mixture. Using a twin-screw extruder, the obtained mixture was melt-kneaded at a peripheral speed of 38 m / min and a processing temperature of 200°C, while the water was evaporated and removed from the vent of the twin-screw extruder to obtain a pellet-shaped kneaded product.

[0040] (Comparative Examples 2-4, 7, 8, and 13-20) A conductive resin composition was obtained in the same manner as in Comparative Example 1, except that the formulation was changed as shown in Tables 1-4.

[0041] (Comparative Example 5) A conductive resin composition was obtained in the same manner as in Example 2, except that step 2 was performed using a Banbury mixer and step 3 using a twin-screw extruder.

[0042] (Comparative Example 6) A conductive resin composition was obtained in the same manner as in Example 2, except that both steps 2 and 3 were performed using a twin-screw extruder.

[0043] (Reference examples A~D) The four thermoplastic resins used in the examples and comparative examples—polypropylene resin, low-density linear polyethylene resin, low-density polyethylene resin, and thermoplastic polyurethane resin—were each evaluated individually using the same physical properties. The results are shown in Table 4 as Reference Examples A to D.

[0044] <Rating> (Surface resistivity) An extruder equipped with a belt die (product name "NV-20", manufactured by Mars Seiki Co., Ltd.) was used to mold the obtained conductive resin composition to produce evaluation sheets with a thickness of approximately 0.1 mm and a width of 50 mm. The surface resistivity (Ω / □) of the manufactured evaluation sheets was then measured using a low resistivity meter (product name "Loresta GP", manufactured by Mitsubishi Chemical Corporation) and a high resistivity meter (product name "Hiresta UP", manufactured by Mitsubishi Chemical Corporation). The results are shown in Tables 1 to 4. Note that in the tables, "3.5E+05" etc. are equivalent to "3.5 × 10 5 This indicates things like ".

[0045] (Distributed state) A conductive resin composition was pressed into a sheet to obtain a sheet approximately 20 μm thick. The dispersion state of carbon nanotubes in the obtained sheet was then observed using an optical microscope or digital microscope at a magnification of 100x, and the dispersion state of carbon nanotubes was evaluated according to the evaluation criteria shown below. The results are shown in Tables 1 to 4. [Criteria for evaluating the distributed state]: S: No aggregates larger than 1 μm are present. A: Aggregate size is 1 μm or more and less than 5 μm. B: Aggregate size is 5 μm or more and less than 10 μm C: Aggregate size is between 10 μm and 20 μm D: Aggregate size is 20 μm or more and less than 50 μm E: Aggregate size is 50 μm or larger

[0046] (Tensile elongation at fracture) In accordance with ASTM D638, the obtained conductive resin compositions were molded into dumbbells using an injection molding machine, and then the tensile elongation at break was measured using a tensile testing machine. The tensile elongation at break was then evaluated for each type of thermoplastic resin according to the evaluation criteria shown below. The results are shown in Tables 1 to 4. [Evaluation Criteria for Tensile Elongation at Breaking] PP S: Tensile elongation at break of 400% or more A: Tensile elongation at break 300% or more but less than 400% B: Tensile elongation at break 200% or more but less than 300% C: Tensile elongation at break 150% or more but less than 200% D: Tensile elongation at break 100% or more but less than 150% E: Tensile elongation at break is less than 100% LLDPE S: Tensile elongation at break of 500% or more A: Tensile elongation at break 400% or more but less than 500% B: Tensile elongation at break 300% or more but less than 400% C: Tensile elongation at break 200% or more but less than 300% D: Tensile elongation at break 100% or more but less than 200% E: Tensile elongation at break is less than 100% LDPE S: Tensile elongation at break of 600% or more A: Tensile elongation at break 500% or more but less than 600% B: Tensile elongation at break 400% or more but less than 500% C: Tensile elongation at break 300% or more but less than 400% D: Tensile elongation at break 200% or more but less than 300% E: Tensile elongation at break less than 200% TPU S: Tensile elongation at break of 750% or more A: Tensile elongation at break 650% or more but less than 750% B: Tensile elongation at break 550% or more but less than 650% C: Tensile elongation at break 450% or more but less than 550% D: Tensile elongation at break 350% or more but less than 450% E: Tensile elongation at break less than 350%

[0047] [Table 1]

[0048] [Table 2]

[0049] [Table 3]

[0050] [Table 4]

[0051] (Application Example 1: Use as a masterbatch) In Example 6, 20 parts of the square pellet-shaped secondary kneaded material obtained in Example 6 and 80 parts of polypropylene powder (product name "Prime Polypro J229E", manufactured by Prime Polymer Co., Ltd.) with an average particle size of 0.05 to 1.1 mm were placed in a mixer and stirred and mixed for 3 minutes at 25°C. Next, using a twin-screw extruder (product name "TEX30", manufactured by Japan Steel Works Co., Ltd.), the resulting mixture was melt-kneaded at a peripheral speed of 38 m / min and a processing temperature of 200°C to obtain a pellet-shaped kneaded material. When the obtained kneaded material was evaluated, the dispersion state was B, the tensile elongation at break was A, and the conductivity was excellent, similar to Example 2.

[0052] (Application Example 2: T-die method) The compound prepared in Example 19 was extruded at 200°C using a Laboplast Mill (Toyo Seiki Co., Ltd.) equipped with a T-die to produce a sheet-like evaluation sample with a thickness of approximately 50 μm and a width of 100 mm. The volume resistivity of the produced evaluation sample was measured using a Loresta GX-11 (Nitto Seiko Analytech Co., Ltd.). The volume resistivity was 8.2 × 10⁻⁶. 3 The film was confirmed to have high conductivity at Ω·cm.

[0053] (Application Example 3: Inflation Molding Method) An inflation film with a thickness of 20 μm was fabricated from the compound prepared in Example 4 using an inflation molding machine (manufactured by Thermoplastics Industry Co., Ltd.) at a molding temperature of 230°C. The volume resistivity of the manufactured evaluation sample was measured using a Loresta GX-11 (manufactured by Nitto Seikou Analytech Co., Ltd.). The volume resistivity was 1.2 × 10⁻⁶. 2 The film was confirmed to have high conductivity at Ω·cm.

Claims

1. A method for producing a conductive resin composition containing a thermoplastic resin and carbon nanotubes, A method for producing a conductive resin composition comprising the following steps 1, 2, 3, and 4. Step 1: A step of obtaining a mixture by mixing a thermoplastic resin with an average particle size of 0.01 mm or more and 3 mm or less, 0.3 parts by mass or more and 30 parts by mass or less of carbon nanotubes per 100 parts by mass of the thermoplastic resin, and at least one aqueous medium selected from the group consisting of 10 parts by mass or more and 500 parts by mass or less of water per 100 parts by mass of the carbon nanotubes and ethanol. Step 2: The mixture is melt-kneaded using a single-screw or twin-screw extruder at a peripheral speed of 5 m / min or more and 150 m / min or less, and the aqueous medium is removed to obtain a primary kneaded product. Step 3: A step to obtain a secondary mixture by shear-melt kneading the primary mixture using a Banbury mixer at a temperature set to be below the melting or softening point of the thermoplastic resin, and at a screw peripheral speed of 11 m / min or more and 150 m / min or less. Step 4: A step to obtain a conductive resin composition by melt-kneading the secondary kneaded material at a temperature set to be above the melting point or softening point of the thermoplastic resin and making it homogenized.

2. A method for producing a conductive resin composition according to claim 1, wherein the thermoplastic resin is at least one selected from the group consisting of polypropylene resin, low-density polyethylene resin, linear low-density polyethylene resin, and thermoplastic polyurethane.

3. The method for producing the conductive resin composition according to claim 1, wherein the conductive resin composition further contains a surfactant.

4. The method for producing a conductive resin composition according to claim 3, wherein the surfactant is at least one selected from the group consisting of acetylene glycol compounds and alkanesulfonic acid compounds.

5. A method for producing a conductive resin molded article using a conductive resin composition obtained by the method for producing a conductive resin composition according to any one of claims 1 to 4.

6. Use of a conductive resin molded article obtained by the method for manufacturing a conductive resin molded article described in claim 5 in automobile parts, building material parts, machine parts, electrical parts, electronic parts, furniture parts, home appliance parts, containers, or packaging materials.

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