Carbon nanotube yarn, thermoelectric power generation module including the same, and method of producing the same

Abstract

To provide carbon nanotube yarn that can be used for obtaining a thermoelectric power generation module of a high electromotive force.SOLUTION: The band-shaped carbon nanotube yarn bent along the longitudinal direction of the band is provided with a position where a part of the band-shaped carbon nanotube yarn and another part thereof face each other in a cross section vertical to the longitudinal direction, and has a void formed on the position where a part and another part of the nanotube yarn face each other.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a carbon nanotube yarn, a thermoelectric power generation module including the same, and a method for manufacturing the same. [Background technology]

[0002] Conventionally, thermoelectric elements or thermoelectric conversion devices using carbon nanotubes have been proposed.

[0003] For example, Patent Document 1 describes a thermoelectric element that includes a fibrous first lead wire in which a p-type semiconductor made of carbon nanotubes and an n-type semiconductor made of carbon nanotubes are connected in series, and a fibrous second lead wire in which a p-type semiconductor made of carbon nanotubes and an n-type semiconductor made of carbon nanotubes are connected in series, the first lead wire and the second lead wire being twisted together. It also describes that by forming the thermoelectric element in a fibrous form in this way, it is possible to obtain the advantageous effect of realizing a small-sized thermoelectric element with excellent flexibility.

[0004] For example, Patent Document 2 describes a thermoelectric conversion device having a strip-shaped thermoelectric conversion material sheet that is a strip-shaped carbon nanotube nonwoven fabric, the strip-shaped thermoelectric conversion material sheet being wound in a spiral shape. It also describes that such a thermoelectric conversion device can be manufactured more simply and efficiently even if there is a greater thickness between the surface that serves as the heat source (or cooling source) during power generation and the surface on the opposite side of the axis from that surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-195232 A [Patent Document 2] JP 2016-207766 A Summary of the Invention [Problem to be solved by the invention]

[0006] A thermoelectric power generation module including carbon nanotubes preferably has a higher electromotive force.

[0007] The present invention provides a carbon nanotube yarn that can be used to obtain a thermoelectric power generation module with high electromotive force, a method for producing the same, and a thermoelectric power generation module including such a carbon nanotube yarn. [Means for solving the problem]

[0008] The present invention relates to the following (1) to (8). (1) A carbon nanotube yarn, characterized in that a band-shaped carbon nanotube yarn is bent along the longitudinal direction, and in a cross section perpendicular to the longitudinal direction, there are areas where one part of the carbon nanotube yarn faces another part, and a void is formed at the opposing area. (2) The carbon nanotube yarn according to (1) above, in which L / W is 15 to 50, where L is the length from one end to the other end of the band-shaped carbon nanotube yarn in the cross section and W is the width of the band-shaped carbon nanotube yarn. (3) The carbon nanotube yarn according to (2) above, wherein L / D is 3.1 to 4.7, where D is the average diameter of the cross section. (4) The carbon nanotube yarn according to any one of (1) to (3) above, which is made of single-walled, double-walled or multi-walled carbon nanotubes. (5) The carbon nanotube yarn according to any one of (1) to (4) above, in which P-type portions and N-type portions are alternately present in the longitudinal direction. (6) The carbon nanotube yarn according to any one of (1) to (5) above, which has a coating made of a heat insulating material and / or an insulating material on at least a part of its surface. (7) A thermoelectric power generation module comprising the carbon nanotube yarn according to any one of (1) to (6) above. (8) an initial step of drawing an initial web from a CNT array on a substrate and processing it with a blade to obtain a densified wide web; a preforming step of passing the wide web through a first die to preform the wide web to obtain a preformed web; a solvent step of adding a volatile solvent to at least one selected from the group consisting of the initial web, the wide web, and the preformed web; a main molding step of passing the preformed web containing the volatile solvent through a second mold to obtain the carbon nanotube yarn described in any one of (1) to (6) above; A method for producing a carbon nanotube yarn comprising the steps of: Effect of the Invention

[0009] According to the present invention, it is possible to provide a carbon nanotube yarn that can be used to obtain a thermoelectric power generation module with a high electromotive force and a manufacturing method thereof, and also to provide a thermoelectric power generation module including such a carbon nanotube yarn. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1(a) shows an SEM image (500x magnification) of a cross section perpendicular to the longitudinal direction of a carbon nanotube yarn corresponding to the yarn of the present invention, and FIG. 1(b) shows a copy of the outline of the yarn of the present invention in that cross section. [Diagram 2] FIG. 2(a) shows a SEM image (500x magnification) of a cross section of the carbon nanotube yarn of FIG. 1(a) perpendicular to its longitudinal direction in a different field of view, and FIG. 2(b) shows the outline of the yarn of the present invention in these cross sections. [Diagram 3]Figure 3(a) shows a different SEM image (500x magnification) of a cross section perpendicular to the longitudinal direction of the carbon nanotube yarn of Figure 1(a), and Figure 3(b) shows the outline of the yarn of the present invention in these cross sections. [Figure 4] 1 shows an SEM image (magnification: 500x) of a cross section perpendicular to the longitudinal direction of a conventionally known carbon nanotube yarn that does not correspond to the yarn of the present invention. [Diagram 5] FIG. 2 is a diagram illustrating a member used for obtaining a cross section for SEM observation in a direction perpendicular to the longitudinal direction of a carbon nanotube yarn corresponding to the yarn of the present invention. [Figure 6] FIG. 2 is a schematic diagram for explaining the manufacturing method of the present invention, showing members used in the manufacturing method of the present invention as viewed from above. [Figure 7] 1 is a diagram showing the relationship between the number of times a doping agent is applied to the outer surface of a yarn and the thermoelectromotive force for a carbon nanotube yarn corresponding to the yarn of the present invention and a conventionally known carbon nanotube yarn. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will now be described. The present invention is a carbon nanotube yarn characterized in that a band-shaped carbon nanotube yarn has a shape bent along the longitudinal direction, and in a cross-section perpendicular to the longitudinal direction, there are areas where one part of the carbon nanotube yarn faces another part, and a void is formed at the opposing points. Such a carbon nanotube yarn is hereinafter also referred to as "the yarn of the present invention."

[0012] The present invention is also a thermoelectric generating module comprising the yarn of the present invention. Such a thermoelectric power generation module will hereinafter be referred to as the "thermoelectric power generation module of the present invention."

[0013] Furthermore, the present invention is a method for producing carbon nanotube yarn, comprising: an initial step of drawing out an initial web from a CNT array on which carbon nanotubes have grown (or been arranged) on a substrate, and treating it with a blade to obtain a densified wide web; a preforming step of preforming the wide web by passing it through a first mold to obtain a preformed web; a solvent step of imparting a volatile solvent to at least one selected from the group consisting of the initial web, the wide web, and the preformed web; and a main forming step of passing the preformed web containing the volatile solvent through a second mold to form it, thereby obtaining the yarn of the present invention. Such a production method will be hereinafter referred to as the "production method of the present invention."

[0014] <Yarn of the present invention> The yarn of the present invention will be described with reference to the drawings. Figures 1(a), 2(a) and 3(a) are SEM images (magnification: 500x) of cross sections perpendicular to the longitudinal direction of a carbon nanotube yarn which corresponds to the yarn of the present invention, while Figures 1(b), 2(b) and 3(b) are copies of the outlines of the yarn of the present invention in these cross sections. In addition, the cross section of the yarn of the present invention in the direction perpendicular to its longitudinal direction refers to an SEM image (photograph or image) obtained by magnifying it 500 times using a scanning electron microscope. For comparison, FIG. 4 shows an SEM image (magnification: 500 times) of a cross section of a conventionally known carbon nanotube yarn in a direction perpendicular to its longitudinal direction.

[0015] As shown in FIG. 5, these cross sections are prepared by attaching the yarn of the present invention (or a conventionally known carbon nanotube yarn) 104 to the surface of an adhesive carbon tape 102 attached to the main surface of a Si substrate 100, and then covering the surface with copper tape 106 to fix the yarn of the present invention (or a conventionally known carbon nanotube yarn) 104, and then preparing the cross section using a cross section polisher (e.g., IB-19520CCP manufactured by JEOL).

[0016] As shown in Figures 1 to 3, the yarn of the present invention has a specific shape in cross section perpendicular to its longitudinal direction. Specifically, the band 1 meanders, spirals, or overlaps, that is, a single band 1 has a bent shape. And, between one part of the band 1 and another part, that is, between one part of the outer edge of the band 1 and another part of the outer edge, a gap 3 is formed.

[0017] The voids 3 are connected from the outer surface of the circularly or elliptically bent yarn toward the inside. In addition, in Figs. 1 to 3, there are some areas where the yarns are crushed and voids are blocked during the cross-section preparation process, but it is believed that before the cross-section preparation, the voids are connected from the outer surface to the inside. Therefore, when a doping agent is applied to the outer surface of the yarn of the present invention, the doping agent can easily permeate the entire desired range of the yarn of the present invention through the voids 3. As a result, the electromotive force of the thermoelectric power generation module of the present invention including the yarn of the present invention is high. This can also be confirmed by the fact that, as shown in Figure 7, the electromotive force of the thermoelectric power generation module using the yarn of the present invention is higher than that of conventional carbon nanotube yarns as the number of times the doping agent is applied to the outer surface of the yarn increases. In contrast, conventional carbon nanotube yarns such as the one shown in FIG. 4 do not have such voids 3. Conventional carbon nanotube yarns may have voids such as cracks in some places, but these voids are in the longitudinal direction and do not connect from the outer surface to the inside. Therefore, it is difficult for the doping agent to penetrate into the entire desired range. As a result, the electromotive force of a thermoelectric power generation module using this yarn is low.

[0018] As shown in Figs. 1(b), 2(b), and 3(b), L is the length from one end S of band 1 to the other end E, that is, the length of the dotted lines in these figures. The length L is measured using Segmented Line in the image processing software "ImageJ," memorizing how many pixels are in 1 μm using Set Scale, and marking points at any intervals along the center of the width of band 1 from one end S to the other end E (or from the other end E to the one end S). The length L is preferably from 160 to 700 μm, more preferably from 240 to 470 μm, and further preferably from 300 to 400 μm.

[0019] As shown in FIGS. 1 to 3, the cross section of the yarn of the present invention has a shape close to a circle or ellipse when the outer edges are joined, and D is the average diameter of this cross section. Here, the average diameter D means the average value of the longest diameter in the cross section defined as the major diameter and the shortest diameter defined as the minor diameter. The average diameter D is preferably from 50 to 150 μm, more preferably from 50 to 125 μm, and further preferably from 50 to 100 μm.

[0020] When L and D are defined in this way, L / D is preferably 3.1 to 4.7, more preferably 3.4 to 4.7, and even more preferably 4.0 to 4.7. When such a relationship is satisfied, the size of the voids 3 in the cross section perpendicular to the longitudinal direction falls within a preferred range, so that when a doping agent is permeated into the yarn of the present invention, the doping agent can easily permeate into the entire desired range through the voids 3, and in addition, the strength required for the yarn of the present invention is also satisfied.

[0021] Also, as shown in Figures 1(b), 2(b), and 3(b), the width of band 1 is W. As is clear from these figures, the width W of band 1 is not constant. Therefore, using Segmented Line in the image processing software "ImageJ," store how many pixels 1 μm has by using Set Scale, and measure W1 to W10 at 10 points at approximately equal intervals from one end S of band 1 to the other end E (or from the other end E to the one end S) perpendicular to the line passing through the center of W, and use the measure to determine the average of the obtained values ​​as the width W of band 1. In this case, L / W is preferably 15-50, more preferably 20-50, and further preferably 30-50. When this relationship is satisfied, the size of the voids 3 in the cross section perpendicular to the longitudinal direction falls within a preferred range, so that when a doping agent is permeated into the yarn of the present invention, the doping agent can easily permeate into all of the desired range through these voids 3, and in addition, the strength required of the yarn of the present invention is also satisfied.

[0022] The width W of the band 1 is preferably 3 to 47 μm, more preferably 3 to 25 μm, and even more preferably 3 to 15 μm.

[0023] As shown in Figures 1 to 3, the cross section of the yarn of the present invention has a shape close to a circle or ellipse when the outer edges are connected, and the area ratio of the voids 3 shown therein is preferably 10 to 50%, more preferably 20 to 50%, and even more preferably 30 to 50%. The area ratio of the voids 3 in the cross section of the yarn of the present invention is determined as follows. Assuming that the cross section of the yarn of the present invention is an ellipse (including a circle), the area of ​​the ellipse (π × major axis × minor axis / 4) is calculated using the major axis and minor axis measured when calculating the average diameter R of the cross section as described above. The area of ​​the ellipse calculated here is S 1 Let us assume that. Next, using the length from the start point to the end point of the aforementioned band, L, and the width of the band, W, L×W is the area S of band 1. 2 Let us assume that. And, (S 1 -S 2 ) / S1 The value calculated from x 100 is the area ratio of the voids 3 in the cross section of the yarn of the present invention.

[0024] The yarn of the present invention has the same characteristics (material, crystal structure, etc.) as conventionally known carbon nanotubes.

[0025] The yarn of the present invention may be formed from any of single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT) and multi-walled carbon nanotubes (MWCNT). The number of walls of the multi-walled carbon nanotubes is preferably 3 to 8.

[0026] There are no particular limitations on the length of the yarn of the present invention in the longitudinal direction, and it is, for example, preferably 1 to 3000 m, more preferably 1 to 2000 m, and even more preferably 1 to 1000 m.

[0027] It is preferable that the yarn of the present invention has P-type portions and N-type portions alternately present in the longitudinal direction. Here, the P-type portion means a portion that can move holes toward a portion away from the heat when heat is applied. The P-type portion may be, for example, a portion doped with a P-type dopant. Here, the N-type portion means a portion that can move electrons toward a portion away from the heat when heat is applied. The N-type portion may be, for example, a portion doped with an N-type dopant. Such a yarn of the present invention can be preferably used as a member (thermoelectric element) for obtaining a thermoelectric power generation module of the present invention, which will be described later. In addition, since carbon nanotubes usually exhibit the same characteristics as P-type portions, the yarn of the present invention may have an embodiment in which N-type portions and untreated portions are alternately present. In addition, there may be a portion between the P-type portion and the N-type portion that does not fall into either category. Even in such a case, the yarn of the present invention is included.

[0028] The method of doping with the P-type dopant or N-type dopant is not particularly limited. For example, various dopants are dissolved in a solvent capable of dissolving them, a dopant solution is prepared, and the solution is applied to the desired position of the yarn of the present invention, and then dried. In this case, the dopant solution is likely to uniformly penetrate into all the desired portions of the yarn of the present invention, even to the inside.

[0029] The yarn of the present invention preferably has a coating made of a heat insulating material and / or an insulating material on at least a part of its surface. In this case, there is an effect of preventing leakage current from occurring between the yarns or between the yarn and a contact object. Examples of the heat insulating material include silicone rubber, styrene butadiene rubber, and acrylic resin. Examples of insulating materials include aluminum oxide, aluminum nitride, boron nitride, zinc oxide, and composites of the above materials with thermal insulating materials. The coating locations of the coating made of a heat insulating material and / or an insulating material are not particularly limited, and for example, when obtaining the thermoelectric power generation module of the present invention described below, the coating can be provided on surfaces other than the parts where the yarn of the present invention comes into contact with the rod material.

[0030] When the yarn of the present invention has a coating made of a heat insulating material and / or an insulating material, the thickness of the coating is preferably 1 μm to 0.5 mm.

[0031] The method for covering the yarn of the present invention with the heat insulating material and / or insulating material is not particularly limited, and for example, the yarn can be covered by a method of spraying the heat insulating material diluted in a solvent.

[0032] The yarn of the present invention is preferably a non-twist yarn. This allows the yarn of the present invention to be preferably used as a member (thermoelectric element) for obtaining a thermoelectric power generation module of the present invention, which will be described later.

[0033] <Thermoelectric power generation module of the present invention> The thermoelectric power generation module of the present invention will now be described. The thermoelectric power generation module of the present invention is not particularly limited as long as it contains the yarn of the present invention. The thermoelectric power generation module of the present invention may be, for example, a fabric knitted using the yarn of the present invention. The fabric (hereinafter simply referred to as "fabric") that is the thermoelectric power generation module of the present invention may be similar to fabrics used in general clothing, formed using cotton, chemical fibers, etc. as necessary, so long as it uses the yarn of the present invention as at least a part thereof. Here, the fabric has a front and a back surface, and it is preferable that the boundaries between the P-type and N-type portions of the yarn of the present invention are exposed on the front and back surfaces. In this case, clothing made of this fabric can generate electricity by utilizing the difference in heat between the front surface (e.g., the heat of the human body wearing it) and the back surface (e.g., the heat of the outside air). Furthermore, if an electric current is passed through such a fabric, heat transfer such as cooling or heating can occur, allowing the wearer's body temperature to be regulated. By winding the yarn of the present invention around a flexible rod material such as silicone rubber, and doping the yarn of the present invention present on any one surface of the rod material (excluding the end surface of the rod material) with an N-type dopant, a thermoelectric power generation module having a structure in which P-type portions and N-type portions exist alternately can be manufactured. If the center-to-center distance between a pair of P-type and N-type portions and an adjacent pair of P-type and N-type portions is defined as the pitch, the pitch of the thermoelectric power generation module of the present invention is preferably 100 μm to 450 μm. This thermoelectric power generation module is made of the yarn of the present invention and a flexible rod material, and therefore can be made to conform to structures with curved surfaces, such as pipes through which hot water passes.

[0034] <Production Method of the Present Invention> The manufacturing method of the present invention will be described with reference to FIG. FIG. 6 is a schematic diagram for explaining the manufacturing method of the present invention, and shows members used in the manufacturing method of the present invention as viewed from above.

[0035] The manufacturing method of the present invention is a method for manufacturing carbon nanotube yarns, which includes an initial step, a preforming step, a solvent step, and a main forming step, which will be described below. In the manufacturing method of the present invention, it is preferable that the treatments in each step are carried out continuously as shown in FIG.

[0036] <Initial process> In the initial step, an initial web 23 is first drawn from the CNT array 21 .

[0037] The CNT array 21 is formed by growing carbon nanotubes on a substrate. The carbon nanotubes are grown on the substrate so that their longitudinal direction is parallel to the perpendicular line of the main surface of the substrate. In the CNT array 21, the carbon nanotubes are grown very densely on the substrate, with a density of 1 cm 2 This can range from tens of billions to hundreds of billions of pieces per unit. In the CNT array 21, it is believed that the carbon nanotubes are attracted to adjacent carbon nanotubes by van der Waals forces. The configuration and manufacturing method of the CNT array are described, for example, in JP 2019-199676 A.

[0038] The carbon nanotube may be a single-walled carbon nanotube (SWCNT), a double-walled carbon nanotube (DWCNT), or a multi-walled carbon nanotube (MWCNT). The number of walls of the multi-walled carbon nanotube is preferably 3 to 8.

[0039] From such a CNT array 21 an initial web 23 is drawn and processed by a blade 30 . The initial web 23 is in a sheet shape, and is subjected to a process of pressing its main surface against the cutting edge 301 of the blade 30. As in the embodiment shown in Fig. 6, it is preferable to continuously pull out the initial web 23 from the CNT array 21 and continuously perform a process of pressing its main surface against the cutting edge 301 of the blade 30. The blade 25 may be similar to that shown in JP 2019-199676 A. In this way, the carbon nanotubes constituting the initial web 23 are densified, and a wide web 25 having a width of about 0.5 mm to 30 mm can be obtained.

[0040] The initial web 23 before being treated with the blade 30 and / or the wide web 25 after being treated with the blade 30 may be consolidated by passing it between two rollers to apply stress in the thickness direction of the initial web 23 and / or the wide web 25. Furthermore, trash adhering to the initial web 23 before being treated with the blade 30 and / or the wide web 25 after being treated with the blade 30 may be removed by air blowing or the like.

[0041] <Preforming process> Next, the wide web 25 obtained as described above is passed through a first mold 32 . In the initial step, it is preferable to continuously pull out the initial web 23 from the CNT array 21 and continuously press its main surface against the cutting edge 301 of the blade 30 , and further to continuously pass the wide web 25 through the first mold 32 . The first die 32 has a circular or elliptical through hole through which the wide web 25 passes. Here, the width of the wide web 25 is made longer than the diameter in the case of a circular through hole, and the major axis in the case of an elliptical through hole. By doing this, a preformed web 27 is obtained in which the cross section perpendicular to the longitudinal direction has a specific shape, i.e., a shape in which the band-shaped carbon nanotube yarn is bent along the longitudinal direction, and in which the cross section perpendicular to the longitudinal direction has points where one part of the carbon nanotube yarn faces another part, and voids are formed at the opposing points.

[0042] <Solvent process> The manufacturing method of the present invention includes a solvent step of making at least one selected from the group consisting of the initial web 23, the wide web 25 and the preformed web 27 obtained as described above contain a volatile solvent. That is, the initial web 23 drawn from the CNT array 21 may be subjected to a treatment to impregnate it with a volatile solvent before being treated with the blade 30 . Furthermore, the wide web 25 obtained in the initial step may be subjected to a treatment to impart a volatile solvent thereto before being subjected to the preforming step. Furthermore, the preformed web 27 obtained through the preforming step may be subjected to a treatment to impregnate it with a volatile solvent. Furthermore, these processes may be performed in an overlapping manner. It is sufficient that the preformed web 27 immediately before the main forming described below contains a volatile solvent.

[0043] Volatile solvents include organic solvents. Examples of the volatile solvent include ethanol, acetone, methyl ethyl ketone, propanol, methanol, and methyl isobutyl ketone.

[0044] There is no particular limitation on the method for impregnating at least one selected from the group consisting of the initial web 23, the wide web 25, and the preformed web 27 with a volatile solvent. For example, there may be mentioned a method of spraying at least one selected from the group consisting of the initial web 23, the wide web 25, and the preformed web 27 with a volatile solvent or passing the web (continuously) through a pool of a volatile solvent.

[0045] The inventors have discovered that when the preformed web 27 containing a volatile solvent is subjected to the main forming process described below, the shape of the preformed web 27 is largely retained when the volatile solvent subsequently dries, and a yarn of the present invention having the intended cross-sectional shape is obtained. In contrast, the inventors have discovered that even if a preformed web that does not contain a volatile solvent is subjected to the actual forming process described below, the shape of the preformed web 27 changes over time, making it difficult to obtain the voids that the yarn of the present invention has.

[0046] <Main molding process> Next, the preformed web 27 containing the volatile solvent obtained as described above is passed through a second mold 34 . As shown in FIG. 6, in the initial step, it is preferable to continuously pull out the initial web 23 from the CNT array 21 and continuously press its main surface against the cutting edge 301 of the blade 30, continuously pass the wide web 35 through the first die 32, and further continuously pass the preformed web 27 containing the volatile solvent through the second die 34.

[0047] The second die 34 has circular or elliptical through holes, similar to the first die 32, through which the preformed web 27 containing a volatile solvent is passed. Here, the width of the preformed web 27 containing a volatile solvent is made longer than the diameter of the circular through-holes, and the major axis of the elliptical through-holes. Furthermore, the cross-sectional area (the cross-sectional area in a direction perpendicular to the longitudinal direction) of the portion of the preformed web 27 passing through the through hole is preferably 50 to 90% of the cross-sectional area of ​​the through hole of the second mold 34, more preferably 50 to 80%, and even more preferably 50 to 70%. By doing this, the cross section perpendicular to the longitudinal direction has a specific shape, i.e., a shape in which a band-shaped carbon nanotube yarn is bent along the longitudinal direction, and in the cross section perpendicular to the longitudinal direction, there are points where one part of the carbon nanotube yarn faces another part, and a void is formed at the opposing points, resulting in the yarn of the present invention.

[0048] The yarn of the present invention obtained by the manufacturing method of the present invention is preferably wound as shown in FIG.

Claims

1. A carbon nanotube yarn, characterized in that the band-shaped carbon nanotube yarn has a shape bent along the longitudinal direction, and in a cross section perpendicular to the longitudinal direction, there are areas where one part of the band-shaped carbon nanotube yarn faces another part, and a void is formed at the opposing area.

2. The carbon nanotube yarn according to claim 1, wherein L / W is 15 to 50, where L is the length from one end to the other end of the band-shaped carbon nanotube yarn in the cross section and W is the width of the band-shaped carbon nanotube yarn.

3. 3. The carbon nanotube yarn according to claim 2, wherein L / D is 3.1 to 4.7, where D is the average diameter of the cross section.

4. 3. The carbon nanotube yarn of claim 1 or 2, which is made of single-walled, double-walled or multi-walled carbon nanotubes.

5. 3. The carbon nanotube yarn according to claim 1, wherein P-type portions and N-type portions alternate in the longitudinal direction.

6. The carbon nanotube yarn according to claim 5 , which has a coating made of a heat insulating material and / or an insulating material on at least a part of its surface.

7. A thermoelectric power generation module comprising the carbon nanotube yarn of claim 5 .

8. An initial step of drawing an initial web from a CNT array in which carbon nanotubes are arranged on a substrate and treating it with a blade to obtain a densified wide web; a preforming step of passing the wide web through a first die to preform the wide web to obtain a preformed web; a solvent step of adding a volatile solvent to at least one selected from the group consisting of the initial web, the wide web, and the preformed web; a main forming step of passing the preformed web containing the volatile solvent through a second mold to form the carbon nanotube yarn according to claim 1 or 2; A method for producing a carbon nanotube yarn comprising the steps of:

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