Carbon nanotube dispersion and method for producing same

Abstract

[Problem] To obtain a carbon nanotube dispersion which can be suitably used for various applications, maintains a fiber length and has excellent electrical properties. [Solution] This carbon nanotube dispersion is characterized by having: a volume resistivity value of 90 (Ωcm) or less when the concentration of carbon nanotubes is adjusted to 2.50 wt%; an average length of carbon nanotubes in the dispersion of 18 μm or more; and an absorbance at 500 nm of 0.20-0.70 when the concentration of carbon nanotubes is diluted to 0.001 wt%.

Description

Carbon nanotube dispersion and method for producing the same

[0001] The present invention relates to a carbon nanotube dispersion liquid with excellent electrical properties, suitable as a conductive material for batteries and the like, and a method for producing the same.

[0002] In recent years, with the advancement of various communication technologies such as autonomous driving and spatial recognition technology, there has been a growing need for electromagnetic shielding materials to protect objects from various electromagnetic waves emitted by devices. On the other hand, electromagnetic waves have also been suggested to pose a risk to the human body, making the role of electromagnetic shielding materials significant. To ensure the stable operation of devices and other equipment affected by electromagnetic waves, metal and carbon materials are known as electromagnetic shielding materials. Metal materials shield electromagnetic waves but do not absorb them, and they are heavy, which are disadvantages. Carbon materials, on the other hand, have the challenge of not being able to achieve sufficient electromagnetic shielding effects.

[0003] In recent years, carbon nanotubes (hereinafter referred to as CNTs) have attracted attention as a material that is lightweight and has excellent conductivity and mechanical properties. As an electromagnetic wave shielding material, CNTs are attracting attention as a component that possesses electromagnetic wave shielding and absorption properties, is lightweight, highly moldable with flexibility, and can handle a wide absorption range. CNTs are fibrous nanocarbons with a high aspect ratio, having a diameter of 1 nm to 150 nm and a length of several μm to several mm. Manufactured CNTs are in a form where the fibers are entangled or aggregated, and in this state, it is difficult to exhibit sufficient conductivity and electromagnetic wave shielding properties. It is necessary to separate the CNTs one by one from this aggregated state, and for this purpose, a dispersion process is considered indispensable.

[0004] Generally, when dispersing carbon nanotubes (CNTs), it is known that dispersal is performed by physical energy such as bead milling, high-pressure dispersion, or ultrasound. For example, Patent Documents 1 and 2 attempt to improve dispersibility by selecting a dispersant used when dispersing carbon nanotubes in a liquid medium. Patent Document 3 attempts to improve dispersibility by chemically modifying the carbon nanotubes themselves. Patent Document 4 attempts to improve dispersibility by selecting the pH of the carbon nanotubes. Patent Document 5 attempts to improve dispersibility by optimizing the dispersion conditions. Patent Document 6 attempts to improve dispersibility by producing carbon nanotubes with a specific swelling rate using a catalyst of a specific particle size and using them.

[0005] Furthermore, attempts have been made to prepare CNT dispersions using so-called high-pressure homogenizers. For example, Patent Document 7 proposes using a high-pressure homogenizer equipped with a multi-stage pressure control device (multi-stage step-down converter) that applies back pressure during dispersion to disperse CMC aqueous solution, SGCNTs, and graphite, and then further dispersing them with liquid paraffin and electrode active material to attach CNTs to the graphite surface for use as a battery material. Patent Document 8 also proposes using a multi-stage step-down high-pressure homogenizer equipped with a high-pressure dispersion processing unit having a 200 μm diameter narrow tube channel and a multi-stage pressure control device (multi-stage step-down converter) connected to the high-pressure dispersion processing unit, to obtain a CNT dispersion as a fibrous carbon nanostructure dispersion by processing sodium deoxycholate and CNTs multiple times as a dispersant. Patent documents 9 and 10 propose preparing a CNT dispersion by preparing a multilayer emulsion subjected to high-pressure shear emulsification and dispersion treatment, mixing it with a CNT organic solvent mixture, and then emulsifying it by further high-pressure shear emulsification and dispersion treatment.

[0006] Japanese Patent Publication No. 2003-238126, Japanese Patent Publication No. 2004-276232, Japanese Patent Publication No. 2008-517863, Japanese Patent Publication No. 2007-297255, Japanese Patent Publication No. 2007-169120, Japanese Patent Publication No. 2014-001083, Japanese Patent Publication No. 2021-118135, WO2016 / 189873, Japanese Patent Publication No. 2020-176052, Japanese Patent Publication No. 2016-153367

[0007] However, the inventors' research revealed that these conventional methods did not provide sufficient dispersibility or sufficient conductive performance. In particular, when carbon nanotubes with long fiber lengths were used, the CNTs were finely cut and fragmented during the dispersion process. The fragmented CNTs could not fully utilize the properties of carbon nanotubes with long fiber lengths, resulting in insufficient formation of a network structure between CNTs in the molded product, and thus inadequate performance.

[0008] Therefore, the inventors conducted further studies and found that by applying physical energy under specific conditions to disperse the CNTs, the length of the dispersed CNTs could be maintained for a long time, resulting in good conductive performance. The conductive network of molded products made of CNTs with maintained length is also considered to be effective in shielding electromagnetic waves. More specifically, the inventors arrived at the present invention by finding that by processing a pipe of a specific structure at a specific flow rate, the destruction of carbon nanotubes with long fiber lengths is minimized, and the carbon nanotube fibers can be loosened while maintaining their long fiber lengths.

[0009] In other words, the present invention provides: (1) a method for producing a carbon nanotube dispersion, comprising the step of passing a mixed solution containing at least carbon nanotubes and a dispersion medium, which contains 0.01 to 10% by weight of carbon nanotubes, through a tubular section, characterized in that the flow path does not have any sections where turbulence occurs; (2) a method for producing a carbon nanotube dispersion, comprising the step of passing a mixed solution containing at least carbon nanotubes and a dispersion medium, which contains 0.01 to 10% by weight of carbon nanotubes, through a tubular section, characterized in that the flow path does not have any nozzle sections; (3) A method for producing a carbon nanotube dispersion, comprising the step of passing a mixed solution containing at least carbon nanotubes and a dispersion medium, which contains 0.01 to 10% by weight of carbon nanotubes, through a tubular section, characterized in that the flow path does not have a structure in which a portion has an inner diameter (d0) of 0.20 mm or less and a portion has an inner diameter of 6 times or more of d0 is at a distance of d0 × 3 or less in the direction of the flow path axis, (4) A method for producing a carbon nanotube dispersion, comprising the step of passing a mixed solution containing at least carbon nanotubes and a dispersion medium, which contains 0.01 to 10% by weight of carbon nanotubes, through a tubular section, characterized in that the average flow rate Q when passing through the tubular section is 0.05 (liters / minute) or more and is a flow rate that does not generate turbulence, according to any one of (1) to (3) above, (5) A method for producing a carbon nanotube dispersion according to any one of (1) to (3) above, characterized in that the flow channel has a portion with an inner diameter d of 0.1 to 0.5 mm, (6) the flow channel has a portion with an inner diameter piping minimum diameter d of 0.1 to 0.A method for producing a carbon nanotube dispersion according to any one of (1) to (3) above, characterized in that it has a portion of 5 mm and the length of said portion is 1 mm or more; (7) A method for producing a carbon nanotube dispersion according to any one of (1) to (3) above, characterized in that the step of passing through the tubular portion is media-less; (8) A method for producing a carbon nanotube dispersion according to any one of (1) to (3) above, characterized in that the carbon nanotubes are single-walled carbon nanotubes; (9) A carbon nanotube dispersion characterized in that the volume resistivity when the concentration of carbon nanotubes in the coating film is adjusted to 1.29 wt% and the remainder is carboxymethylcellulose is 90 (Ωcm) or less, the average length of the carbon nanotubes in the dispersion is 18 μm or more, and the absorbance at 500 nm when the concentration of carbon nanotubes is diluted to 0.001 wt% is 0.20 to 0.70; (10) A carbon nanotube dispersion according to (9) above, characterized in that the concentration of carbon nanotubes is 0.01 to 10% by weight; and (11) The carbon nanotube dispersion described in (9) above is characterized in that the carbon nanotubes are single-walled carbon nanotubes.

[0010] The present invention provides a CNT dispersion containing CNTs that maintain their length and exhibit excellent conductive properties. Various molded products made using the dispersion containing CNTs with maintained length according to the present invention maintain a conductive network, and are expected to improve performance in various applications such as antistatic and conductive coatings, electromagnetic shielding materials, conductive paints, lithium-ion batteries, reinforcing materials, and thermoelectric conversion materials for semiconductor applications.

[0011] A conceptual diagram of the apparatus used in the present invention. A conceptual diagram showing the configuration of the module used in the embodiment. A schematic diagram showing the configuration of the nozzle used in the comparative example. A micrograph of the slurry obtained in Embodiment 3. A micrograph of the slurry obtained in Embodiment 9. A micrograph of the slurry obtained in Embodiment 10. A micrograph of the slurry obtained in Embodiment 11. A micrograph of the slurry obtained in Embodiment 13. A micrograph of the slurry obtained in Embodiment 14. A micrograph of the slurry obtained in Embodiment 15. A micrograph of the slurry obtained in Comparative Example 2. A micrograph of the slurry obtained in Comparative Example 3. Figures showing micrographs of the obtained slurry, Figures showing micrographs of the slurry obtained in Comparative Example 4, Figures showing micrographs of the premixing liquid in Comparative Example 9, Figures showing micrographs of the slurry obtained in Example 16, Figures showing micrographs of the slurry obtained in Example 17, Figures showing micrographs of the slurry obtained in Example 18, Figures showing micrographs of the slurry obtained in Example 19, Figures showing micrographs of the slurry obtained in Example 20, Figures showing micrographs of the slurry obtained in Example 21, Figures showing micrographs of the slurry obtained in Comparative Example 11, Figures showing micrographs of the slurry obtained in Comparative Example 12.

[0012] The present invention will be described in detail below. [Carbon Nanotubes] Examples of carbon nanotubes (CNTs) include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Among the multi-walled nanotubes, those with two walls are sometimes called double-walled carbon nanotubes (DWCNTs). One of these CNTs may be used alone, or two or more may be used in combination. Generally, MWCNTs are considered to have an excellent balance of cost and performance, and SWCNTs are considered to have high performance. The present invention can use either type, but SWCNTs having the following physical properties are particularly desirable because they can achieve unprecedentedly high performance.

[0013] [Average Diameter] The average diameter of CNTs is not particularly limited, but from the viewpoint of conductivity and dispersibility, it is preferably 0.5 nm or more, and more preferably 1 nm or more. There is no upper limit to the length, but it is usually 25 nm or less, particularly preferably 15 nm or less, and more preferably 10 nm or less. Even more preferably it is 2 to 6 nm, and most preferably 3 to 5 nm. Within this range, aggregation of CNTs is particularly suppressed, and dispersibility can be particularly improved.

[0014] The average diameter is measured by observing and imaging carbon nanotubes using a transmission electron microscope. Next, 300 random carbon nanotubes are selected from the observed images, and their outer diameters are measured. Then, the average outer diameter (nm) of the carbon nanotubes is calculated as the number average of the outer diameters. When purchasing and using carbon nanotubes (CNTs), catalog values ​​may be used.

[0015] [CNT Length] CNTs come in a wide variety of lengths, ranging from tens of nanometers to tens of millimeters, and their distribution is also diverse. Therefore, they should be selected appropriately depending on the application. In any case, the present invention makes it possible to dissolve the aggregation of fibers while maintaining the length relatively well. The length of the CNTs that can be used in the present invention is not particularly limited. Longer CNTs, especially those exceeding 100 μm, have particularly excellent electrical properties. There are moderately long fiber lengths of 300-500 μm and short fiber lengths of 100-300 μm, but the invention is not limited to these. For example, "SG101" (100-600 μm, manufactured by Nippon Zeon Co., Ltd.) has a considerably long fiber length, and multi-walled carbon nanotubes manufactured by High Pressure Gas Industry Co., Ltd. have a maximum fiber length of about 3 mm, both of which can be used in the present invention. In addition to manual measurement using SEM images or TEM images or automatic measurement using image analysis programs, measurement by far-infrared absorption spectroscopy and measurement using AFM are also known methods.

[0016] [Specific surface area] The specific surface area of ​​CNTs is not particularly limited, but is between 1 and 2000 m². 2 / g is preferred, and 500 to 1600m 2 / g is more preferable. Electrical characteristics are particularly excellent in this range.

[0017] The specific surface area is measured using the BET (Brunauer-Emmet-Teller) method. This method involves using a gas adsorption specific surface area meter to adsorb nitrogen as the adsorbent gas onto the surface of the CNT. The amount of adsorbed nitrogen is then measured using the BET formula based on the relationship between pressure and the amount of adsorbed nitrogen, and the specific surface area is calculated. When using commercially available CNTs, catalog values ​​may be used.

[0018] [Concentration] In this invention, a carbon nanotube dispersion can be obtained by dispersing a mixture containing at least carbon nanotubes and a dispersion medium under the conditions described later. The concentration of CNTs in the mixture subjected to dispersion treatment is not limited, but if the concentration is too high, the viscosity will be high and it will be difficult to pass it through the tubular portion of the dispersion apparatus described later. On the other hand, if the concentration is too low, it will be difficult to secure a sufficient amount to allow the CNTs to perform their function, and complicated operations such as removal of the dispersion medium will be required. Therefore, the concentration is generally 0.01 to 10% by weight, preferably 0.01 to 2% by weight, more preferably 0.03 to 1.5% by weight, even more preferably 0.1 to 1.3% by weight, and most preferably 0.3 to 1.3% by weight.

[0019] [Dispersion Medium] The dispersion medium can be water, organic solvents, or various other dispersion mediums without particular restriction. From the viewpoint of safety and ease of removal, aqueous media such as water and water-soluble organic solvents are preferred. Water and other aqueous dispersion mediums also have the advantage of being easy to remove in subsequent processes. For example, they are suitable for applications where freeze-drying is performed for molding or for use in combination with water-compatible materials (such as cellulose nanofibers). On the other hand, depending on the application of the CNT dispersion, organic solvents may be preferred from the viewpoint of affinity with components other than the CNT dispersion. For example, in applications such as lithium-ion batteries and non-aqueous electrolyte secondary batteries, organic solvents such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, propylene glycol monomethyl ether, and methanol are suitably used.

[0020] [Dispersant] The mixture may contain a dispersant. The dispersant is not particularly limited as long as it has the function of dispersing and stabilizing the CNTs, and generally includes surfactants, resin-type dispersants, etc. Surfactants mainly include anionic, cationic, nonionic, and amphoteric types, and these known dispersants can be appropriately selected according to the application and required characteristics of the CNT dispersion.

[0021] Examples of resin-type dispersants include acrylic resins (poly(meth)acrylic acid or salts thereof, poly(meth)acrylate, etc.), polyester resins, epoxy resins, polyether resins, alkyd resins, urethane resins, silicone resins, polycarbonate resins, silicate resins, chlorine-based resins, fluoropolymer resins, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyvinyl acetal, polyvinyl butyral, cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethylcellulose, ethyl hydroxyethylcellulose, nitrocellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, etc., or salts thereof), polyacrylonitrile, polyacrylonitrile polymers (polymers of polyacrylonitrile and acrylic acid, etc.), nitrile rubbers (acrylonitrile butadiene rubber, hydrogenated acrylonitrile butadiene rubber, copolymers of hydrogenated nitrile rubber and hydrogenated butadiene acrylonitrile, etc.), and composite resins thereof. Polymers in which other substituents have been introduced into some of these polymers, or modified polymers, may also be used.

[0022] Particularly preferred are methylcellulose, ethylcellulose, carboxymethylcellulose, or salts thereof, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile polymers, copolymers of acrylonitrile and acrylic acid, (meth)acrylic acid, or salts thereof, and hydrogenated nitrile rubber and hydrogenated butadiene acrylonitrile copolymers. Among these, methylcellulose, ethylcellulose, carboxymethylcellulose, or salts thereof are particularly preferred in terms of maintaining the fiber length of CNTs, and carboxymethylcellulose or its salts, more specifically sodium carboxymethylcellulose, is the best in terms of maintaining the fiber length.

[0023] The amount of dispersant is 10 to 700 parts by weight, preferably 10 to 600 parts by weight, and most preferably 50 to 300 parts by weight, per 100 parts by weight of CNT. If the amount is less than 10 parts by weight, aggregation tends to occur, and if it is more than 700 parts by weight, the resistance tends to increase.

[0024] [Production of Dispersion] 1. Apparatus The present invention is characterized by including a step of passing a mixed liquid, which is a mixture of the components described above, that is, a mixed liquid containing at least carbon nanotubes and a dispersion medium, through a tubular section arranged horizontally. To carry out this step, any apparatus that has a tubular section arranged horizontally and is capable of passing a liquid from one end of the tubular section to the other is used. Typically, a valve, nozzle, etc. are equipped at one end of the tubular section, and the liquid is pressurized and passed through the tubular section, where emulsification, homogenization, pulverization, and micronization are performed by back pressure. This is a typical apparatus known as a high-pressure homogenizer or high-pressure disperser. By applying high pressure to the liquid and flowing it at high speed through a narrow channel, shear force, cavitation, impact force, etc. are applied to disperse the liquid, and this is a type of so-called medialess disperser. They are broadly classified into variable valve type and chamber type. In the former, the fluid that passes through the gap of a valve opened by pressurization collides with an impact ring. In the latter, the fluid is injected at high pressure into a narrow tube inside a chamber. Depending on the configuration of the chamber and flow path, there are single-chamber type, oblique impact chamber type, ball impact type, separation chamber type, slit type, etc., and the part that is pressed into the narrow tube can be valve type, nozzle type, or a combination of these. Specifically, examples include the "BERYU MINI" (product name) from Miryu Co., Ltd., the "Starburst" (product name) from Sugino Machine Co., Ltd., the high-pressure disperser from Yoshida Machinery Industry Co., Ltd., the ultra-high-pressure homogenizer from Jokou Co., Ltd., the MST pressure homogenizer, the high-pressure homogenizers "H3-1D", "H3-2D", "HC3-4", and "HC3-5" from Sanmaru Machinery Industry Co., Ltd., and the "Microfluidizer" from Powrec Co., Ltd. There are no limitations on the types that can be used as long as they can be equipped with the tubular part that meets the conditions described below.

[0025] These can be selected and used as appropriate, but the present invention is characterized by dispersion without the use of a nozzle, as will be described later. For this reason, a structure that can be used without attaching a nozzle part is preferred. In particular, "BERYU MINI" from Biryu Co., Ltd. is preferred because it has a flow path consisting of a tubular part, and furthermore, as defined in the present invention, it can pass through the tubular part without going through a nozzle.

[0026] 2. Tubular Section The tubular section (piping portion) can be typically linear, helical, or any other shape, and can be used without problems. The cross-sectional shape of the tubular section is also not limited and can be selected from circles, ellipses, polygons, etc. Preferably, the minimum diameter (d) of the tubular section is 0.1 to 0.5 mm, more preferably 0.1 to 0.4 mm, and even more preferably 0.15 to 0.35 mm. The inventors' research has shown that within this range, carbon nanotube aggregates can be broken up most efficiently, and the CNT fiber length is easily maintained, thus improving performance such as conductivity. The length (L) of the minimum diameter portion of the tubular section is 0.2 mm or more, preferably 0.3 mm to 150 cm, more preferably 0.4 mm to 130 cm, and even more preferably 0.4 mm to 90 cm. If it is smaller than this range, the carbon nanotube aggregates may not be broken up sufficiently, and although there is no problem if it is larger than this range, there is no particular advantage. As long as the tubular section satisfies the above conditions, it is acceptable to have a tubular section with a larger diameter.

[0027] In this invention, it is particularly preferable that the flow path through which the CNT dispersion, which is the material to be processed, passes does not have any locations where turbulence occurs. Furthermore, the flow path through which the CNT dispersion, which is the material to be processed, passes is characterized by not having any orifice sections. So-called high-pressure dispersers, which pass the material to be processed through a tubular section, generally have a section where the inner diameter rapidly expands from a very small part called a nozzle or orifice. The aim was to accelerate the movement of the material to be processed through the tube by passing it through this section, generate turbulence (jet phenomenon), and then break it down by utilizing the shear force, cavitation, and impact force generated thereby. However, the inventors' research revealed that, surprisingly, such conventional high-pressure dispersion methods do not bring out the full performance of CNTs. The inventors also discovered that this is because the CNTs break due to the jet phenomenon.

[0028] Unlike conventional high-pressure dispersion methods, the present invention does not involve parts where the inner diameter rapidly expands, such as nozzles or orifices. Therefore, turbulence is not generated, and it is believed that the applied pressure dissolves the bundle of CNTs while maintaining their fiber length. Here, a nozzle generally refers to a device used in high-pressure dispersers, high-pressure homogenizers, etc., that has the function of generating turbulence by passing high pressure through a pore. In particular, an embodiment of the present invention that does not have the following "specific nozzle structure" is more preferable. Here, a "specific nozzle structure" refers to a structure in which the flow path has a portion with an inner diameter (d0) of 0.20 mm or less, and the distance between the portion with an inner diameter (d0) of 0.20 mm or less and the portion with an inner diameter of 6 times or more d0 is d0 × 3 or less in the flow path axis direction. Without such a specific nozzle structure, turbulence is less likely to occur, which is particularly preferable for the processing in the present invention, as it allows for the disintegration to proceed while maintaining the fibers of relatively long CNTs, and the performance of the CNTs can be fully extracted.

[0029] 3. The aforementioned mixed liquid is passed through the tubular section having the characteristics described above for processing conditions. The flow rate at this time is preferably an average flow rate (Q) of 0.05 liters / min or more, more preferably 0.1 liters / min or more, and more preferably 0.2 liters / min or more. If the flow rate is less than 0.05 liters / min, the conductivity of the resulting carbon nanotube dispersion tends not to increase sufficiently. This is presumed to be because the aggregates of carbon nanotubes are not sufficiently broken down. Furthermore, the upper limit of the flow rate should be within a range where turbulence does not occur. All other conditions being equal, as the flow rate increases, the Reynolds number Re increases and turbulence occurs. Preferably, it is 1 liter / min or less, and preferably 0.5 liters / min or less. CNT dispersion processing can be performed efficiently within this range.

[0030] The number of processing passes (n) is not limited, but is 1 to 20 times, preferably 2 to 15 times, and most preferably 3 to 10 times. Too many passes will increase the rate at which CNTs break, so the number should be selected according to the application.

[0031] [Physical Properties of Carbon Nanotube Dispersion] The surface resistance value of the carbon nanotube dispersion of the present invention is 1.0×10 8 (Ω / sq) or less when the concentration of carbon nanotubes in the coating film is adjusted to 1.29 wt% and the balance is carboxymethyl cellulose. The average length of the carbon nanotubes in the dispersion is 18 μm or more, and the absorbance at 500 nm when the concentration of the carbon nanotubes is diluted to 0.001 wt% can be 0.20 to 0.70. The surface resistance value and absorbance can be measured by the methods described in the examples.

[0032] The concentration of the carbon nanotubes in the carbon nanotube dispersion is 0.01 to 10% by weight, preferably 0.01 to 2% by weight, more preferably 0.03 to 1.5% by weight, still more preferably 0.1 to 1.3% by weight, and most preferably 0.3 to 1.3% by weight.

[0033] The carbon nanotube dispersion of the present invention can make the surface resistance value extremely low when the CNT concentration is lowered. Specifically, the surface resistance value when measured with the CNT concentration at 2.50 wt% can be 2×10 4 to 7×10 4 (Ω / sq), and can also be 2×10 4 to 4×10 4 Further, the surface resistance value when measured with the CNT concentration at 1.29 wt% can be 2×10 5 to 5×10 7 (Ω / sq), and can also be 2×10 5 to 4×10 5It can also be set as (Ω / □). The surface resistance value is the resistance value of the coating film prepared using the carbon nanotube dispersion liquid, and is also called the sheet resistance value. The surface resistance value in the present invention is the value measured by the method described in the examples. Also, the volume resistance value of the carbon nanotube dispersion liquid of the present invention can be 0.3 to 3 (Ωcm). Furthermore, the volume resistance value when the CNT concentration is lowered can be extremely low. Specifically, the volume resistance value measured when the CNT concentration is 2.50 wt% can be 0.7 to 20 (Ωcm). Also, the volume resistance value measured when the CNT concentration is 1.29 wt% can be 7 to 90 (Ωcm), and can also be 7 to 20 (Ωcm).

[0034] In the present invention, the average length of the carbon nanotubes in the carbon nanotube dispersion liquid can also be 25 μm or more. Furthermore, it can be 40 μm or more, 60 μm or more. The average length of the carbon nanotubes in the dispersion liquid can be measured by the method described in the examples.

[0035] The carbon nanotube dispersion liquid of the present invention can have a TI value of 5.6 or less. This TI value is the value of 3 rpm / 30 rpm. The TI value can be obtained by the following method. (1) Measure the viscosity after rotating for 1 minute at 3 rpm. (2) Measure the viscosity after rotating for 1 minute at 30 rpm. (3) The value obtained by dividing the value measured in (1) by the value measured in (2) is defined as the TI value. As shown in the examples, a small TI value indicates that the carbon nanotubes are not cut very much. Therefore, it is considered that the length is maintained as described above and the conductivity is excellent.

[0036] 〔Applications〕The carbon nanotube dispersion liquid of the present invention can be suitably used for various applications. For example, conductive materials in various batteries, electromagnetic wave shielding / absorbing materials, etc. are typical. In battery applications, a typical method is to prepare an electrode paste by mixing the carbon nanotube dispersion liquid of the present invention with a binder and an active material as needed, and then coating this on a substrate to form an electrode.

[0037] The present invention will be further described in detail by the following examples and comparative examples. 'parts' indicates parts by weight, and '%' indicates weight percent.

[0038] (1) Preparation of premixing solution 4.0 g of CNT ("SG101" (CNT manufactured by Nippon Zeon Co., Ltd.)), 6 g of carboxymethylcellulose sodium (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 990 g of deionized water were placed in a 2-liter container and processed at 11,000 rpm for 5 minutes using a "Robomix" (product name; homomixer manufactured by Primix Corporation) to obtain a premixing solution.

[0039] (2) Preparation of slurry (high-pressure dispersion treatment of premixing liquid) The premixing liquid obtained in (1) above was processed using a high-pressure disperser (an overview is shown in Figure 1) equipped with the module shown in Figure 2 alone or in combination with the nozzle shown in Figure 3, using the modules used and the number of passes shown in Table 1 to obtain a slurry. In Figure 1-1, 1 is a hopper, 2 is a high-pressure air pump, 3 is a module, 4 is a liquid receiving section such as a beaker, 5 is a regulator, and 6 is a compressor. The high-pressure air pump is equipped with a regulator and is connected to the compressor via the regulator. The compressor pumps air to the high-pressure air pump via the regulator at a maximum discharge pressure of 0.7 to 0.8 MPa. Figure 1-2 shows an overview of the structure of the high-pressure air pump. In Figure 1-2, 7 is the air piston, 8 is the plunger, and 9 and 10 are check valves. The high-pressure air pump is a plunger-type reciprocating pump that pressurizes the air supplied from the compressor using an air piston that moves from side to side, and intermittently pumps the material to be processed dropped from the hopper through a check valve that repeatedly opens and closes due to the movement of a plunger that is linked to the air piston. It is structured to pressurize the air supplied from the compressor by 265 times to pressurize the material to be processed and pump it into the flow path. A nozzle can be interposed between the high-pressure air pump and the module, as will be explained below.

[0040] As shown in Fig. 2, each module has a structure in which three spiral or circular pipes with different inner diameters and lengths are built into a cylindrical casing with a flow path connected by unions to each other. The end of the flow path consists of a pipe with an inner diameter of 1.7 mm, and one of the pipes at this end can be connected to a pressure pump either via a nozzle or without a nozzle. Among the pipes 1 to 12 built into each module, the pipes 1 to 3 and 10 to 12 built into the large module and the small module all have a structure with a spiral part having a spiral diameter of 1.4 cm and 8 turns, and straight parts of 2 cm before and 4 cm after the spiral part. The pipes 4 and 6 built into the micro-module, and the pipe 8 built into the ultra-micro-module all have a structure with a spiral part having a spiral diameter of 1.3 cm and 8 turns, and straight parts of 2 cm before and 4 cm after the spiral part. The pipe 5 built into the micro-module has a structure with a spiral part having a spiral diameter of 1.3 cm and 9 turns, and straight parts of 2 cm before and after the spiral part respectively. The pipe 7 of the ultra-micro-module consists of a spiral with a diameter of 1.3 cm and 1 turn, and the pipe 9 has a structure with a spiral part having a spiral diameter of 1.3 cm and 16 turns, and straight parts of 2 cm before and 4 cm after the spiral part.

[0041] Figure 3-1 is a schematic diagram showing a cross-section of the nozzle, and Figure 3-2 is a schematic diagram showing the relationship between the axial position from the orifice to the nozzle outlet and the inner diameter. In Figure 3, 11 is the orifice plate and 12 is the nozzle body. As shown in Figure 3-1, the nozzle has a structure in which an orifice plate, which is a disc with an orifice (hole), is fixed in the center of the nozzle body. The orifice plate has a tapered section on both the inlet and outlet sides, and the narrowest part of the orifice is the part with the smallest diameter of the nozzle. The tapered section is relatively short in the direction of the flow path axis, and the structure generates turbulence by rapidly expanding the inner diameter. In the nozzle used in the comparative example, a diamond orifice plate is incorporated into a stainless steel nozzle body, and as shown in Figure 3-2, the orifice plate has a minimum diameter (d0) of 0.17 mm and a tapered section of 0.12 mm in the direction of the flow path axis. In other words, as shown in Figure 3-2, if we let x be the axial coordinate of the position with the smallest diameter of the orifice plate and closest to the nozzle outlet, then the orifice outlet is at the position x = 0.12 (mm).

[0042] The inner diameter of the nozzle body at the orifice outlet (x = 0.12 mm) is 1.108 mm, and after maintaining the same inner diameter up to x = 2.614 mm, a tapered section is formed, and the inner diameter at the nozzle outlet (x = 4.548 mm) is 6.780 mm. Therefore, the minimum nozzle diameter (d0) is 0.20 mm or less, and the portion where the inner diameter is 6 times or more d0 is d0 × 3 or less in the flow path axis direction from the position of the minimum nozzle diameter (d0), and the inner diameter d at the nozzle outlet e The minimum diameter of the nozzle (d0) is approximately 39.9 times, i.e., 20 times or more, and even 30 times or more. The length in the axial direction of the flow path from the position of the minimum diameter of the nozzle (d0) to the nozzle outlet is approximately 27.5 times, i.e., 20 times or more and 30 times or less, which corresponds to a specific nozzle structure.

[0043] In Table 1, "Large," "Small," "Micro," and "Extra Micro" refer to the large, small, micro, and extra-micro modules in Figure 2, respectively. "Large Nozzle" and "Micro Nozzle" indicate the installation of a nozzle with the large module and a nozzle with the micro module, respectively. P indicates the number of passes. For example, "Small 1P" indicates one pass of processing with the small module, and "Small 3P + Micro 3P" indicates three passes of processing with the small module followed by three passes of processing with the micro module. Comparative Example 9 shows a premixing liquid that has not undergone high-pressure disperser processing. The pressure during processing was measured at the regulator position and was 0.4 MPa. Therefore, the pressurization by the high-pressure air pump was 0.4 × 265 = 106 MPa. The flow rate through the flow path was calculated from the weight of the slurry that came out after passing through the module and the time required for passage. The results are shown in Table 1. In the case of multiple processing (multiple passes, etc., where the slurry passes through the flow path multiple times), the flow rate at the final pass is shown. Table 1 Processing conditions (modules used and number of passes), flow rate for each example

[0044]

[0045] (3) Measurement of the physical properties of the slurry The physical properties of each obtained slurry were measured using the following method. [Viscosity and TI value] Using the E-type viscometer "TV-25" manufactured by Toki Sangyo Co., Ltd., 1.1 mL of slurry was placed in a sample cup, and the viscosity was measured at 25°C using the standard included "1°34'×R24" cone rotor. The viscosity values ​​(unit: mPa・s) measured after 1 minute of rotation at 3 rpm, 6 rpm, 30 rpm, and 60 rpm, and the TI values ​​calculated from these values ​​for 3 rpm / 30 rpm and 6 rpm / 60 rpm are shown in Table 2.

[0046]

[0047] [Absorbance Measurement] A slurry (CNT concentration 0.4 wt%) was diluted 20 times with deionized water, and this was further diluted 20 times with deionized water to obtain a diluted solution with a CNT concentration of 0.001 wt%. The absorbance at 500 nm of this diluted solution with a CNT concentration of 0.001 wt% was measured using a Shimadzu UV-1850 spectrophotometer. The results are shown in Table 3.

[0048] [CNT Length] For Examples 1-15 and Comparative Examples 1-8, the slurry was diluted to 0.001 wt% with deionized water, and for Comparative Example 9, the slurry was diluted to 0.04 wt% with deionized water. The slurry was dropped onto a glass slide, a coverslip was placed on top, and a photograph was taken with a microscope. The field of view was adjusted from 100 to 700 times depending on the length of the CNTs. The length of each individual CNT was measured, and the average length of at least 100 CNTs was calculated. This is shown in Table 3 as "CNT Length".

[0049]

[0050] [Evaluation of Conductivity] 1. Surface Resistivity Value 2g of slurry (CNT concentration 0.4wt%) and 2g of deionized water were added to a 100mL container and mixed at 2000rpm for 1 minute using an "Awatori Rentaro" (rotation / revolution mixer manufactured by Thinky Co., Ltd.). 3g of a 5wt% CMC solution was added to this and mixed again at 2000rpm for 1 minute using the "Awatori Rentaro". This mixture was coated onto a glass substrate at a concentration of 1mil and dried at 100°C. The surface resistance value of the coating film at a CNT concentration of approximately 4.7wt% was measured using a "Loresta-GXII" (low-resistivity resistivity meter manufactured by Nitto Seikou Analytech Co., Ltd.). The surface resistance value at a CNT concentration of approximately 1.3wt% in the film was measured in the same manner as above, except that the amount of slurry was 0.5g and the amount of deionized water was 3.5g (equivalent to a CNT concentration of 1.3wt%). The surface resistance value at a CNT concentration of 2.5 wt% was measured in the same manner as above, except that the amount of slurry was 1 g and the amount of deionized water was 3 g (equivalent to a CNT concentration of 2.5 wt%). The results are shown in Table 4.

[0051] 2. Volume Resistivity For each coating film prepared using the surface resistance measurement method described above, the film thickness was measured using a "BirdScan" (a 3D roughness meter manufactured by Ryoka Systems Co., Ltd.). The volume resistance was calculated by multiplying the surface resistance value measured above by the film thickness and dividing the result by 10,000. The results are shown in Table 4.

[0052]

[0053] [Measurement of TT and HAZE] For each coating film prepared using the surface resistance measurement method described above, TT and HAZE were measured using a "Haze Meter NDH-500" (manufactured by Nippon Denshoku Industries Co., Ltd.). The results are shown in Table 5.

[0054]

[0055] (4) Photographic observation: A drop of the slurry obtained in Examples 3, 9-11, 13-15 and Comparative Examples 2-4, 9 was placed onto a glass slide using a dropper, a cover slip was placed on top and pressed down, and the results were shown in Figures 4-13 under an optical microscope.

[0056] From the above results, it can be seen that in Comparative Example 9, which was not subjected to high-pressure dispersion, most of the bundles remained intact even in the microscopic image, whereas in Examples 1 to 15, which were subjected to high-pressure dispersion without the use of a nozzle, the bundles were separated into thin fibers. In addition, the absorbance in Comparative Example 9 was extremely low, which also indicates that the CNTs were not dispersed. Furthermore, in Comparative Examples 1 to 8, which were subjected to high-pressure dispersion using a nozzle, the length of the CNTs was 2.1 to 16.8 μm, while in Examples 1 to 15, which were subjected to high-pressure dispersion without the use of a nozzle, the length of the CNTs was 21 to 48.1 μm, indicating a tendency to maintain the length. Also, in Examples 3 to 15, in particular, which were processed in two or more passes with small modules, the surface resistance at a CNT concentration of 1.29% was 2.0 × 10⁻⁶. 5 ~5.0 x 10 7 While (Ω / □) is the case, in Comparative Examples 1-8, where high-pressure dispersion was performed using a nozzle, the surface resistance at a CNT concentration of 0.1% was 6.0 × 10⁻⁶. 9 ~2.0×10 11 (Ω / □) indicates that, according to the present invention, a low surface resistance can be obtained by high-pressure dispersion without using a nozzle. As described above, it can be seen that, according to the present invention, the length of the CNT can be maintained and a low surface resistance can be obtained.

[0057] (Examples 16-18) (1) Preparation of premixing solution 3.6 g of CNT ("6A" (CNT manufactured by JEIO Co., Ltd.)), 36 g of a solution (equivalent to 0.6 wt%) of "Butyl 268" (butyl rubber composition manufactured by Nippon Butyl Co., Ltd.) dissolved in toluene at 10 wt%, and 560.4 g of toluene were placed in a 1 liter container and processed at 9000 rpm for 5 minutes using "Robomix" (trade name; homomixer manufactured by Primix Co., Ltd.) to obtain a premixing solution (equivalent to 0.6 wt% CNT).

[0058] (2) Preparation of slurry (high-pressure dispersion treatment of premixing liquid) The premixing liquid obtained in (1) above was treated with a high-pressure disperser (an overview is shown in Figure 1, which is a combination of "Biryu MINI" (high-pressure homogenizer manufactured by Biryu Co., Ltd.) and a compressor manufactured by Hitachi Industrial Systems, Ltd. (model: POD-11MA6, 11kW)) equipped with the module shown in Figure 2 alone or in combination with the nozzle shown in Figure 3) using the module and number of passes shown in the "Pretreatment" column of Table 6, and then treated with the module or nozzle and number of passes shown in the "Number of Passes" column to obtain a slurry. In addition, the notation in the "Pretreatment" column and "Number of Passes" column is the same as in Table 1, where "Small" means that it was treated with a small module, "Extremely Fine" means that it was treated with an extremely fine module, and "Large Nozzle" means that it was treated with a combination of a nozzle and a large module, and the number before P indicates the number of passes for treatment.

[0059] (Examples 19-21, Comparative Examples 10-12) (1) Preparation of premixing solution 1.8 g of CNT ("SG101" (CNT manufactured by Nippon Zeon Co., Ltd.)), 120 g of a solution (equivalent to 2 wt%) in which "Butyl 268" (butyl rubber composition manufactured by Nippon Butyl Co., Ltd.) was dissolved in toluene at 10 wt%, and 478.2 g of toluene were placed in a 1 liter container and processed at 9000 rpm for 5 minutes using "Robomix" (trade name; homomixer manufactured by Primix Co., Ltd.) to obtain a premixing solution (equivalent to 0.3 wt% CNT).

[0060] (2) Preparation of slurry (high-pressure dispersion treatment of premixing liquid) The premixing liquid obtained in (1) above was treated with the same apparatus as in Examples 16 to 18, using the module and number of passes shown in the "Pretreatment" column of Table 6, and then treated with the module or nozzle and number of passes shown in the "Number of passes" column to obtain a slurry.

[0061]

[0062] (Viscosity, average CNT length, SD) Measurements were performed on some of the slurries obtained in Examples 16-21 and Comparative Examples 10-12. Each was measured using the following method. The results are shown in Table 6.

[0063] (Viscosity) The viscosity of a dispersion in a 50 mL metal can was measured using a Type B viscometer "TVB-10M" manufactured by Toki Sangyo Co., Ltd. at 25°C after rotating at 60 rpm for 1 minute (unit: mPa・s).

[0064] (Average CNT Length) For Comparative Examples 11 and 12, the slurry was diluted to 0.01 wt% with toluene, dropped onto a glass slide, a coverslip was placed on top, and a photograph was taken with a microscope. The field of view was adjusted from 500 to 1000 times depending on the length of the CNTs. The length of each individual CNT was measured, and the standard deviation (SD) of the average length SD of at least 100 CNTs was calculated.

[0065] (Evaluation of conductivity) (I) The slurries of Examples 16 to 18 were evaluated at concentrations of 0.5%, 0.75%, and 1% (each in weight percent of CNTs). (1) In the case of 0.5%, 9.90 g of a solution of Butyl 268 pre-dissolved in toluene at 12 wt% (hereinafter referred to as "12 wt% Butyl 268 solution") and 1 g of slurry were added to a 20 mL container and mixed at 2000 rpm for 1 minute using an "Awatori Rentaro" (a rotating / intersecting mixer manufactured by Thinky Co., Ltd.). This mixture was coated onto a glass substrate at a thickness of 3 mil, and the film thickness of the coating, dried at 100°C, was measured using a "BirdScan" (a 3D roughness meter manufactured by Ryoka Systems Co., Ltd.). The volume resistance at a CNT concentration of approximately 0.5 wt% in the film was measured using a "Loresta-GXII" (a low-resistivity resistivity meter manufactured by Nitto Seikou Analytech Co., Ltd.). (2) In the case of 0.75 wt%, the measurement was performed in the same manner except that 6.57 g of 12 wt% Butyl 268 solution was used. (3) In the case of 1 wt%, the measurement was performed in the same manner except that 4.9 g of 12 wt% Butyl 268 solution was used. The results are shown in Table 6.

[0066] (II) The slurries of Examples 19-21 and Comparative Examples 10-12 were evaluated at concentrations of 0.4%, 0.5%, 0.6%, 0.75%, and 1% (each in weight percent of CNTs). (1) In the case of 0.4%, 6.06 g of a solution of Butyl 268 pre-dissolved in toluene at 12 wt% (hereinafter referred to as "12 wt% Butyl 268 solution") and 1 g of slurry were added to a 20 mL container and mixed at 2000 rpm for 1 minute using an "Awatori Rentaro" (rotating / intersecting mixer manufactured by Thinky Co., Ltd.). This mixture was coated onto a glass substrate at a thickness of 3 mil, and the film thickness of the coating, dried at 100°C, was measured using a "BirdScan" (3D roughness meter manufactured by Ryoka Systems Co., Ltd.), and the volume resistance at a CNT concentration of approximately 0.4 wt% in the film was measured using a "Loresta-GXII" (low resistance resistivity meter manufactured by Nitto Seikou Analytech Co., Ltd.). (2) In the case of 0.5 wt%, the measurement was carried out in the same manner except that 4.81 g of 12 wt% Butyl 268 solution was used. (3) In the case of 0.6 wt%, the measurement was carried out in the same manner except that 3.98 g of 12 wt% Butyl 268 solution was used. (4) In the case of 0.75 wt%, the measurement was carried out in the same manner except that 3.14 g of 12 wt% Butyl 268 solution was used. (5) In the case of 1 wt%, the measurement was carried out in the same manner except that 2.31 g of 12 wt% Butyl 268 solution was used. The results are shown in Table 6.

[0067] (Photographic Observation) The slurries obtained in Comparative Examples 11 and 12 were diluted with toluene to a CNT concentration of 0.01 wt%, a drop was placed on a glass slide using a dropper, a coverslip was placed on top and pressed down, and the images were taken with an optical microscope at 1000x magnification. These are shown in Figures 21-22. The slurries from Examples 16-21 were diluted 10 to 100 times with a 10 wt% Butyl 268 toluene solution, a drop was placed on a glass slide using a dropper, a coverslip was placed on top and pressed down, and the images were taken with an optical microscope (500x magnification). These are shown in Figures 15-20. These results also show that the present invention provides superior effects.

[0068] The present invention provides a carbon nanotube dispersion that maintains fiber length and exhibits excellent electrical properties, making it suitable for a variety of applications.

[0069] 1. Hopper 2. High-pressure air pump 3. Module 4. Liquid receiving section 5. Regulator 6. Compressor 7. Air piston 8. Plunger 9. Check valve 10. Check valve 11. Orifice plate 12. Nozzle body

Claims

1. A method for producing a carbon nanotube dispersion, comprising the step of passing a mixed liquid containing at least carbon nanotubes and a dispersion medium, which contains 0.01 to 10% by weight of carbon nanotubes, through a tubular section, characterized in that the flow path does not have any sections where turbulence occurs.

2. A method for producing a carbon nanotube dispersion, comprising the step of passing a mixed liquid containing at least carbon nanotubes and a dispersion medium, which contains 0.01 to 10% by weight of carbon nanotubes, through a tubular section, characterized in that the flow path does not have a nozzle section.

3. A method for producing a carbon nanotube dispersion, comprising the step of passing a mixed liquid containing at least carbon nanotubes and a dispersion medium, which contains 0.01 to 10% by weight of carbon nanotubes, through a tubular section, characterized in that the flow channel does not have a structure in which a portion has an inner diameter (d0) of 0.20 mm or less and a portion with an inner diameter of 0.20 mm or less and a portion with an inner diameter of 6 times or more d0 are at a distance of d0 × 3 or less in the direction of the flow channel axis.

4. A method for producing a carbon nanotube dispersion, comprising the step of passing a mixed liquid containing at least carbon nanotubes and a dispersion medium, which contains 0.01 to 10% by weight of carbon nanotubes, through a tubular section, characterized in that the average flow rate Q when passing through the tubular section is 0.05 (liters / minute) or more and is a flow rate that does not generate turbulence, according to any one of claims 1 to 3.

5. A method for producing a carbon nanotube dispersion according to any one of claims 1 to 3, characterized in that the flow channel has a portion with an inner diameter d of 0.1 to 0.5 mm.

6. A method for producing a carbon nanotube dispersion according to any one of claims 1 to 3, characterized in that the flow path has a portion with a minimum inner diameter d of 0.1 to 0.5 mm, and the length of said portion is 1 mm or more.

7. A method for producing a carbon nanotube dispersion according to any one of claims 1 to 3, characterized in that the step of passing the material through the tubular portion is media-free.

8. A method for producing a carbon nanotube dispersion according to any one of claims 1 to 3, characterized in that the carbon nanotubes are single-walled carbon nanotubes.

9. A carbon nanotube dispersion characterized in that, when the concentration of carbon nanotubes in the coating film is adjusted to 1.29 wt% with the remainder being carboxymethylcellulose, the volume resistivity is 90 (Ωcm) or less, the average length of carbon nanotubes in the dispersion is 18 μm or more, and the absorbance at 500 nm when the concentration of carbon nanotubes is diluted to 0.001 wt% is 0.20 to 0.

70.

10. The carbon nanotube dispersion according to claim 9, characterized in that the concentration of carbon nanotubes is 0.01 to 10% by weight.

11. The carbon nanotube dispersion according to claim 9, characterized in that the carbon nanotubes are single-walled carbon nanotubes.

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