Production method for n-type nanocarbon yarn

Abstract

A production method for N-type nanocarbon yarn comprising: a first step in which an N-type dopant is added to a nanocarbon dispersion to dope the nanocarbon; and a second step in which the doped nanocarbon dispersion is extruded to generate nanocarbon yarn.

Description

Manufacturing method of N-type nanocarbon yarn

[0001] The present disclosure relates to a method for producing N-type nanocarbon yarn.

[0002] In recent years, thermoelectric power generation elements have become known as solid-state devices that convert thermal energy into electrical energy. Thermoelectric power generation elements have also been applied to, for example, space power supplies and thermoelectric conversion modules (wristwatches, wearable devices, etc.) that operate on body heat. Furthermore, nanocarbon yarns, such as carbon nanotube yarns, are sometimes used in thermoelectric conversion elements, and various studies on nanocarbon yarns have been conducted.

[0003] For example, Patent Document 1 discloses "a method for producing an aggregated thread structure, comprising: a step (a) of preparing a dispersion in which carbon nanotubes are dispersed in a first solvent, which is either water alone or a mixed solvent containing an organic solvent and water, using a surfactant; and a step (b) of injecting the dispersion in which the carbon nanotubes are dispersed into an aggregate liquid, which is a second solvent different from the first solvent, and aggregate-spinning the carbon nanotubes."

[0004] Patent Document 2 discloses "a carbon nanotube-containing body, characterized by having a carbon nanotube composite yarn obtained by impregnating or coating a part or all of a substrate formed into a thread shape with a dispersion liquid containing carbon nanotubes having semiconducting properties and then drying the same, and a conductive yarn having electrical conductivity, the semiconducting carbon nanotube composite yarn and the conductive yarn being woven together so as to be electrically connected to each other." Patent Document 3 discloses "a method for producing carbon nanotube yarns by spinning a carbon nanotube dispersion liquid containing a carbon nanotube dispersion, wherein the carbon nanotubes have an equivalent spherical size of 25 nm to 1.3 μm as measured with a disk-type frequency-based centrifugal sedimentation device." Patent Document 4 discloses a heat transport device comprising: a first composite yarn, which is a single-walled carbon nanotube composite yarn obtained by impregnating or coating a dispersion liquid containing single-walled carbon nanotubes into a yarn of natural origin or a yarn of synthetic fiber, or a blend of these, and a second composite yarn, which is a multi-walled carbon nanotube composite yarn obtained by impregnating or coating the blended yarn with a dispersion liquid containing multi-walled carbon nanotubes; a single-layer-multi-layer series-connected body of heterogeneous composite yarns, which is formed by connecting the first and second composite yarns in series in the order of second composite yarn-first composite yarn-second composite yarn-second composite yarn, or first composite yarn-second composite yarn-first composite yarn; and a heat transport device characterized in that by passing a direct current through the series-connected body, a temperature difference is generated between one connection point and the other connection point due to the Peltier effect.

[0005] JP 2012-126635 A JP 2013-155058 A JP 2016-216863 A JP 2018-186260 A

[0006] Conventionally, including Patent Documents 1 to 4, the mainstream method for producing N-type nanocarbon yarn is to dope a completed nanocarbon yarn with an N-type dopant. However, doping a completed nanocarbon yarn with an N-type dopant requires many steps, including a vacuum heating step that is time-consuming for mass production.

[0007] Therefore, an object of the present invention is to provide a method for producing N-type nanocarbon yarns that can produce N-type nanocarbon yarns at low cost.

[0008] Means for solving the problems include the following aspects. <1> A method for producing N-type nanocarbon yarns, comprising: a first step of adding an N-type dopant to a nanocarbon dispersion to dope the nanocarbon; and a second step of extruding the doped nanocarbon dispersion to produce nanocarbon yarns. <2> A method for producing N-type nanocarbon yarns according to <1>, wherein the nanocarbon dispersion is an aqueous dispersion, and the N-type dopant is a non-ionic compound. <3> A method for producing N-type nanocarbon yarns according to <2>, wherein the non-ionic compound is a polyalkyleneimine.

[0009] According to the present disclosure, a method for producing N-type nanocarbon yarns is provided that can produce N-type nanocarbon yarns at low cost.

[0010] Hereinafter, an embodiment that is an example of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiments and do not limit the scope of the invention. In the numerical ranges described in stages in this specification, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. Each component in the composition may contain multiple corresponding substances. When referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the total amount of those multiple substances present in the composition is meant, unless otherwise specified.

[0011] <Method for manufacturing N-type nanocarbon yarn> The method for manufacturing N-type nanocarbon yarn of the present disclosure includes a first step of adding an N-type dopant to a nanocarbon dispersion liquid to dope the nanocarbon, and a second step of extruding the doped nanocarbon dispersion liquid to produce nanocarbon yarn.

[0012] In the method for producing N-type nanocarbon yarns of the present disclosure, an N-type dopant is added to a nanocarbon dispersion liquid before producing the nanocarbon yarns, thereby doping the nanocarbons. Nanocarbon yarns are then produced from the doped nanocarbons. Therefore, the method for producing N-type nanocarbon yarns of the present disclosure can simplify steps such as a vacuum heating step, allowing N-type nanocarbon yarns to be produced at low cost.

[0013] Furthermore, in the method for producing N-type nanocarbon yarns disclosed herein, nanocarbon yarns are produced from doped nanocarbons, allowing the N-type dopant to penetrate deep into the nanocarbon yarns. This results in stable N-type nanocarbon yarns with little change in conductivity over time. Specifically, for example, stable N-type nanocarbon yarns with little change in electrical resistivity and Seebeck coefficient can be obtained.

[0014] Here, we will explain the dimensionless figure of merit ZT, which is one of the indices used to evaluate the thermoelectric conversion performance of nanocarbon yarn. ZT is expressed by the following formula (1): Dimensionless figure of merit ZT = S2 × σ × T / κ (1) In formula (1), S (V / K) represents the Seebeck coefficient, σ (S / m) represents the electrical conductivity, κ (W / mK) represents the thermal conductivity, and T (K) represents the absolute temperature.

[0015] The nanocarbon yarn manufacturing method according to this embodiment will be described in detail below.

[0016] (First Step) In the first step, an N-type dopant is added to the nanocarbon dispersion liquid to dope the nanocarbon.

[0017] -Dispersion Medium- From the viewpoint of reducing the environmental load, the dispersion medium of the nanocarbon dispersion preferably contains water as the main component. In other words, the nanocarbon dispersion is preferably an aqueous dispersion. The aqueous dispersion may contain a water-soluble organic solvent such as alcohol (methanol, ethanol, propanol, etc.). Note that "water is the main component" refers to, for example, the proportion of water being 50% by mass (preferably 70% by mass or 90% by mass) or more relative to the total dispersion medium. However, the dispersion medium of the nanocarbon may be mainly composed of an organic solvent. Examples of organic solvents include alcohol (ethanol, propanol, etc.), acetone, methyl ethyl ketone, and butyl acetate. "An organic solvent is the main component" refers to, for example, the proportion of the organic solvent being 50% by mass (preferably 70% by mass or 90% by mass) or more relative to the total dispersion medium.

[0018] Nanocarbons Examples of nanocarbons include carbon nanotubes (CNTs). The carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) in which one carbon film (graphene sheet) is wound into a cylindrical shape. The carbon nanotubes may also be multi-walled carbon nanotubes (MWCNTs), such as double-walled carbon nanotubes, triple-walled carbon nanotubes, and four-walled carbon nanotubes, in which two graphene sheets are wound concentrically. In consideration of thermoelectric properties, carbon nanotubes preferably have 10 or fewer walls. Single-walled carbon nanotubes are preferred because they are more likely to achieve high thermoelectric properties. Multi-walled carbon nanotubes are preferred because they are inexpensive and easy to mass-produce. Single-walled carbon nanotubes and multi-walled carbon nanotubes can also be used in combination. Furthermore, the carbon nanotubes may be metallic carbon nanotubes, semiconducting carbon nanotubes, or a mixture thereof. The method for producing carbon nanotubes is not particularly limited. Carbon nanotubes can be produced by arc discharge, chemical vapor deposition (CVD), laser ablation, etc. Commercially available carbon nanotubes may also be used.

[0019] The nanocarbon may be graphene. By inserting a carrier between two layers of graphene, graphene can be used as a semiconductor material.

[0020] Other examples of nanocarbons include carbon nanorods, carbon nanowires, graphene, and fullerenes.

[0021] -N-Type Dopant- Examples of the N-type dopant include nonionic compounds and ionic compounds. In particular, when the nanocarbon dispersion is an aqueous dispersion, the N-type dopant is preferably a nonionic compound. On the other hand, when the nanocarbon dispersion is an organic solvent-based dispersion, the N-type dopant is preferably an ionic compound.

[0022] As the nonionic compound, a polyalkyleneimine is preferred. As the polyalkyleneimine, a polyalkyleneimine having a structural unit with an alkylene group having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms) is preferred, and polyethyleneimine is more preferred.

[0023] Examples of the ionic compound include alkali metal salts (salts of lithium, sodium, potassium, cesium, etc.) and alkylammonium salts (salts of tetraethylammonium ion, tetrabutylammonium ion, etc.). Among these, alkylammonium halide salts are preferred as the ionic compound, and examples thereof include the following compounds:

[0024]

[0025] The amount of the N-type dopant added is preferably 2 to 20 mass % relative to the nanocarbon, and more preferably 5 to 15 mass %.

[0026] Other Components The nanocarbon dispersion (nanocarbon dispersion before addition of the N-type dopant) may contain well-known additives such as surfactants.

[0027] (Second step) In the second step, the doped nanocarbon dispersion is extruded to produce nanocarbon yarns. Specifically, for example, the doped nanocarbon dispersion is extruded into an agglomerate, and the nanocarbon is agglomerated and spun to produce nanocarbon yarns.

[0028] The coagulating liquid is selected depending on the dispersion medium of the nanocarbon dispersion. When the main component of the dispersion medium of the nanocarbon dispersion is water, examples of the coagulating liquid include N-methylpyrrolidone, N,N-dimethylacetamide, propylene carbonate, formamide, and N-methylformamide. When the main component of the dispersion medium of the nanocarbon dispersion is an organic solvent, examples of the coagulating liquid include water and alcohol (methanol, ethanol, propanol, etc.).

[0029] (Applications) The N-type nanocarbon yarn obtained by the N-type nanocarbon yarn manufacturing method of the present disclosure can be applied to various applications. For example, the N-type nanocarbon yarn can be suitably used as an N-type nanocarbon yarn that connects thermoelectric conversion elements of a thermoelectric conversion module. In addition, the N-type nanocarbon yarn can also be suitably used in semiconductor applications.

[0030] Examples will be described below, but the present disclosure is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0031] Example 1: 5% by mass of polyethyleneimine was added to a 0.2% by mass aqueous dispersion of carbon nanotubes (CNTs) and mixed by ultrasonic treatment. The CNT aqueous dispersion was then extruded into a propanol aggregating solution, and the CNTs were aggregated and spun. In this way, N-type carbon nanotube yarns were produced.

[0032] Comparative Example 1: A 0.2% by mass aqueous dispersion of carbon nanotubes (CNTs) was extruded into a propanol aggregating solution, and the CNTs were aggregated and spun. The resulting CNT yarn was then vacuum heated and immersed in a 1000 mmol / L aqueous solution of the following chloroalkylammonium salt, followed by drying. Thus, an N-type carbon nanotube yarn was produced.

[0033] <Evaluation> The N-type carbon nanotube yarn obtained in each example was subjected to the following evaluation.

[0034] (Electrical Resistivity) The electrical resistivity of the N-type carbon nanotube yarn was measured. The measurement method was as follows. Four electrodes were placed in contact with the N-type carbon nanotube yarn, and the resistance value was measured using a four-terminal measurement method. The distance between the electrodes and the cross-sectional area of ​​the sample were then measured, and the electrical resistivity was calculated using these values.

[0035] (Seebeck Coefficient / Conductivity Type) The Seebeck coefficient of the N-type carbon nanotube yarn was measured as follows: One end of the N-type carbon nanotube yarn was heated to generate a temperature difference between both ends of the sample, and the generated thermoelectric power was measured and calculated using a thermoelectric property measuring device.

[0036] From the above results, it can be seen that in this example, N-type nanocarbon yarn can be obtained at low cost.

[0037] The disclosure of Japanese Patent Application No. 2024-004104 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A method for manufacturing an N-type nanocarbon fiber, comprising: a first step of adding an N-type dopant to a nanocarbon dispersion to dope the nanocarbon; and a second step of extruding the nanocarbon dispersion after the doping to produce a nanocarbon fiber.

2. The method for manufacturing an N-type nanocarbon fiber according to claim 1, wherein the nanocarbon dispersion is an aqueous dispersion, and the N-type dopant is a nonionic compound.

3. The method for manufacturing an N-type nanocarbon fiber according to claim 2, wherein the nonionic compound is a polyalkyleneimine.

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