Method for manufacturing spun yarn made of carbon nanotubes and spun yarn made of carbon nanotubes

Abstract

To provide means to produce a spun yarn formed of a high-strength carbon nanotube.SOLUTION: An aspect of the invention is a manufacturing method of a spun yarn formed of carbon nanotube and related to the method including following steps: a spun yarn precursor α producing step to produce the spun yarn precursor α formed of carbon nanotube by extracting a plurality of carbon nanotubes from carbon nanotube forest and spinning the plurality of carbon nanotubes while applying tension of 6 mN or less per 1 cm of width of the carbon nanotube forest to the plurality of carbon nanotubes; a spun yarn precursor β producing step to produce the spun yarn precursor β by applying higher tension than that of the spun yarn precursor α producing step to the spun yarn precursor α to densify the spun yarn precursor α; and a spun yarn producing step to produce a spun yarn formed of carbon nanotube by applying tension to and energizing and heating the spun yarn precursor β. Another aspect of the invention is related to the spun yarn formed of carbon nanotube.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for producing a spun yarn made of carbon nanotubes and to a spun yarn made of carbon nanotubes. [Background technology]

[0002] Carbon nanotubes (hereinafter also referred to as "CNTs") have high mechanical strength, thermal conductivity, and electrical conductivity. In addition, multiple CNTs can be spun to produce spun yarns made of CNTs (hereinafter also referred to as "CNT spun yarns"). CNT spun yarns also have high mechanical strength, thermal conductivity, and electrical conductivity, and therefore are being developed as materials for various products.

[0003] For example, Non-Patent Document 1 describes that by performing an electrical heating treatment under conditions of a temperature of 2450°C, a heating time (voltage pulse width) of 12 milliseconds, and a tension of 60 mN, the strength of the resulting CNT spun yarn is improved to a breaking stress of 3.2 GPa and a Young's modulus of 123 GPa.

[0004] Patent document 1 describes a method for manufacturing a structure spun from a spinning source member having a CNT forest, in which the entire end of the open portion of the CNT forest, which has a cylindrical opening substrate, is made into a spinnable portion, and the method includes a spinning process in which the CNTs are pulled out from the spinnable portion and spun.The method comprises a method for manufacturing a cylindrical web-like structure having an inner surface and an outer surface and comprising a plurality of carbon nanotubes entangled with each other. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6667848 [Non-patent literature]

[0006] [Non-Patent Document 1] Y. Song et al., Nanoscale 11, 13909-13917 (2019) Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, methods for producing CNT spun yarn have been developed. However, the conventional methods have had some problems. For example, in the case of CNT spun yarn obtained by spinning multiple CNTs extracted from a CNT forest, the yarn is spun by the van der Waals forces between CNT bundles, and therefore the yarn is usually spun at a density of 0.7 g / cm. 3 The density is about 1 / 2 of the original density. CNT spun yarns with this density may have insufficient strength. It is known that densification by applying tension and structural change from amorphous carbon to graphene by heating are effective in improving the strength of CNT spun yarns. However, in the case of CNT spun yarns with this density, if the temperature and applied tension of the electric current heating treatment are increased, the spun yarns cannot withstand the applied tension at high temperatures and break. On the other hand, if the electric current heating treatment is performed for an extremely short time to avoid breakage of the CNT spun yarns, although breakage of the CNT spun yarns can be avoided, there is a problem that the structural change from amorphous carbon to graphene is insufficient and the improvement in strength is also insufficient.

[0008] Therefore, the present invention aims to provide a means for producing high strength CNT spun yarns. [Means for solving the problem]

[0009] The present inventors have investigated various means for solving the above problems. They have found that by applying a high tension to a CNT spun yarn preliminarily within a range that does not cause the CNT spun yarn to break before subjecting the CNT spun yarn to an electrical heat treatment, thereby densifying the CNT spun yarn, it is possible to increase the temperature and applied tension of the electrical heat treatment compared to conventional methods. The present inventors have found that by producing CNT spun yarn using this procedure, the resulting CNT spun yarn has high crystallinity and high strength. Based on these findings, the present inventors have completed the present invention.

[0010] That is, the present invention includes the following aspects and embodiments. (1) A method for producing a spun yarn made of carbon nanotubes, comprising the following steps: a step of producing a spun yarn precursor α, drawing out a plurality of carbon nanotubes from the carbon nanotube forest, and spinning the plurality of carbon nanotubes while applying a tension of 6 mN or less per 1 cm width of the carbon nanotube forest to the plurality of carbon nanotubes, thereby producing a spun yarn precursor α made of carbon nanotubes; a spun yarn precursor β production step in which a higher tension is applied to the spun yarn precursor α than in the spun yarn precursor α production step, thereby producing a spun yarn precursor β by densifying the spun yarn precursor α; a spun yarn production step in which the spun yarn precursor β is electrically heated while applying tension to produce a spun yarn made of carbon nanotubes; The method comprising: (2) The method according to embodiment (1), wherein in the step of producing the spun yarn precursor β, tension is applied to the spun yarn precursor α while the spun yarn precursor α is brought into contact with a liquid selected from the group consisting of methanol, ethanol, acetone, water, paraffin, toluene, and mixtures thereof. (3) The method according to the above embodiment (1) or (2), wherein tension is applied to the spun yarn precursor α in stages over multiple times in the step of producing the spun yarn precursor β. (4) The method according to any one of the above embodiments (1) to (3), wherein the spun yarn is heated by electrical current at a temperature of 3200 K or less in the spun yarn production step. (5) The method according to any one of the above embodiments (1) to (4), wherein in the spun yarn production step, the spun yarn precursor β is electrically heated while being subjected to a tension of less than 480 MPa. (6) The method according to any one of the above embodiments (1) to (5), further comprising a crosslinking step of impregnating the spun yarn made of carbon nanotubes obtained in the spun yarn preparation step with an aqueous solution containing a sulfide salt. (7) The method of embodiment (6), wherein the sulfide salt is sodium tetrasulfide or sodium disulfide. (8) A spun yarn made of carbon nanotubes, The ratio (IG / ID) of the G-band peak intensity (IG) to the D-band peak intensity (ID) of the spectrum obtained by Raman spectroscopy is 5 or more, and Graphene is present in at least some of the carbon nanotubes. A spun yarn made of the carbon nanotubes. (9) The spun yarn according to the above embodiment (8), wherein the carbon nanotubes are cross-linked by disulfide bonds, trisulfide bonds, or tetrasulfide bonds. [Effects of the Invention]

[0011] The present invention makes it possible to provide a means for producing high-strength CNT spun yarn. [Brief explanation of the drawings]

[0012] [Figure 1] Figure 1 shows the Young's modulus of the CNT spun yarn obtained in Test I-4 by carrying out the spun yarn precursor β production process while applying tension at different loads, and then carrying out the spun yarn production process without electrical heating. In the figure, the horizontal axis represents the load (mN) in the spun yarn precursor β production process, and the vertical axis represents Young's modulus (GPa). The values ​​in the figure represent the average and standard deviation of the results of three tests. [Figure 2]Figure 2 shows the breaking stress of CNT spun yarns obtained in Test I-4 by carrying out the spun yarn precursor β production process while applying tension at different loads, and then carrying out the spun yarn production process without electrical heating. In the figure, the horizontal axis represents the load (mN) in the spun yarn precursor β production process, and the vertical axis represents the breaking stress (GPa). The values ​​in the figure represent the average and standard deviation of the results of three tests. [Figure 3] Figure 3 shows the density of CNT spun yarns obtained in Test I-4 by carrying out the spun yarn precursor β production process while applying tension at different loads, and then carrying out the spun yarn production process without electrical heating. In the figure, the horizontal axis represents the load (mN) in the spun yarn precursor β production process, and the vertical axis represents the density (g / cm3). The values ​​in the figure represent the average and standard deviation of the test results obtained from cross-sectional area measurements at six locations. [Figure 4] Figure 4 shows the density of CNT spun yarns obtained under various processing conditions in Test II-1. In the figure, the horizontal axis represents the processing conditions (tension and temperature of electrical heating) in the spun yarn production process, and the vertical axis represents density (g / cm3). The open bars represent the results when the spun yarn precursor β production process was carried out under no load, and the solid bars represent the results when the spun yarn precursor β production process was carried out under load. The values ​​in the figure represent the average and standard deviation of the test results obtained from cross-sectional area measurements at six locations. [Figure 5] Figure 5 shows the Raman spectrum in the range of 1000 to 2000 cm-1 of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under load in Test II-2. In the figure, the horizontal axis represents the Raman shift (cm-1), and the vertical axis represents the intensity of Raman scattered light (au). [Figure 6] Figure 6 shows the Raman spectrum in the range of 2200 to 3400 cm-1 of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under no load in Test II-2. In the figure, the horizontal axis represents the Raman shift (cm-1), and the vertical axis represents the intensity of Raman scattered light (au). [Figure 7]Figure 7 shows the Raman spectra in the range of 2200 to 3400 cm-1 of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under load in Test II-2. In the figure, A shows the Raman spectra of the untreated CNT spun yarn as a control and the CNT spun yarn obtained by electrical heating at 2500 K, and B shows the Raman spectra of the untreated CNT spun yarn as a control and the CNT spun yarn obtained by electrical heating at 3000 K. In the figure, the horizontal axis represents the Raman shift (cm-1), and the vertical axis represents the intensity of Raman scattered light (au). [Figure 8] FIG. 8 shows an image of the CNT spun yarn observed with a transmission electron microscope in Test II-3. In the figure, A is a transmission electron microscope image of an untreated CNT spun yarn (control); B is a transmission electron microscope image of a CNT spun yarn obtained by carrying out the spun yarn precursor β production process without load and then electrically heating at 2500 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β); C is a transmission electron microscope image of a CNT spun yarn obtained by carrying out the spun yarn precursor β production process with load and then electrically heating at 2500 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β); and D is a transmission electron microscope image of a CNT spun yarn obtained by carrying out the spun yarn precursor β production process with load and then electrically heating at 3000 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β). The scale bar in the figure is 10 nm. [Figure 9] Figure 9 shows the relationship between the temperature of electrical heating in the spun yarn production process and the Young's modulus of the resulting CNT spun yarn in Test II-4. In the figure, the horizontal axis represents the temperature (K) of electrical heating in the spun yarn production process, and the vertical axis represents the Young's modulus (GPa) of the CNT spun yarn. The dotted line in the figure also represents the Young's modulus of the untreated control CNT spun yarn, in which the spun yarn precursor β production process was carried out with or without load. The values ​​in the figure represent the average and standard deviation of the results of three tests. [Figure 10]Figure 10 shows the relationship between the temperature of electrical heating in the spun yarn production process and the breaking stress of the resulting CNT spun yarn in Test II-4. In the figure, the horizontal axis represents the temperature (K) of electrical heating in the spun yarn production process, and the vertical axis represents the breaking stress (GPa) of the CNT spun yarn. The dotted line in the figure also represents the breaking stress of the untreated control CNT spun yarn, which was subjected to the spun yarn precursor β production process with or without load. The values ​​in the figure represent the average and standard deviation of the results of three tests. [Figure 11] Figure 11 shows scanning electron microscope images of the surface of CNT spun yarn obtained by the method including the crosslinking step in Test III-2. In the figure, A is a scanning electron microscope image of a CNT spun yarn obtained by a 2-hour impregnation treatment in the crosslinking step, B is a scanning electron microscope image of a CNT spun yarn obtained by a 24-hour impregnation treatment in the crosslinking step, and C is a scanning electron microscope image of a CNT spun yarn obtained by a 48-hour impregnation treatment in the crosslinking step. The scale bar in the figure is 10 μm. [Figure 12] Figure 12 shows the diameter and density of the CNT spun yarn obtained in Test III-2 using a method including a crosslinking step. In the figure, graph A shows the diameter of the CNT spun yarn, and graph B shows the density of the CNT spun yarn. The horizontal axis represents the impregnation time in the crosslinking step, and the vertical axis represents the diameter (μm) or density (g / cm3) of the CNT spun yarn. [Figure 13] Figure 13 shows scanning electron microscope images of the cross section of a CNT spun yarn obtained in Test III-3 using a method including a crosslinking step. In the figure, A is a scanning electron microscope image of a CNT spun yarn obtained after a 2-hour impregnation treatment in the crosslinking step, B is a scanning electron microscope image of a CNT spun yarn obtained after a 24-hour impregnation treatment in the crosslinking step, and C is a scanning electron microscope image of a CNT spun yarn obtained after a 48-hour impregnation treatment in the crosslinking step. The dots in the images represent sulfur atoms present in the cross section of the CNT spun yarn, as mapped using an energy dispersive X-ray analyzer (EDS). [Figure 14]Figure 14 shows the quantitative results of sulfur atoms present in the cross section of a CNT spun yarn obtained by a method including a crosslinking step, as determined using EDS in Test III-3. In the figure, graph A shows the percentage of the number of sulfur atoms relative to the total number of atoms present in the cross section of the CNT spun yarn, and graph B shows the percentage of sulfur atomic mass relative to the total mass of atoms present in the cross section of the CNT spun yarn. The horizontal axis represents the impregnation time in the crosslinking step, and the vertical axis represents the percentage (%) of the number of sulfur atoms or the percentage (%) of sulfur atomic mass. [Figure 15] 15 shows the stress-strain curve of the CNT spun yarn obtained in Test III-4 using a method including a crosslinking step. In the figure, the horizontal axis represents the strain rate (%), and the vertical axis represents the breaking stress (GPa) of the CNT spun yarn. [Figure 16] 16 shows the stress-strain curve of the CNT spun yarn obtained in Test III-5 using a method including a crosslinking step. In the figure, the horizontal axis represents the strain rate (%), and the vertical axis represents the breaking stress (GPa) of the CNT spun yarn. [Figure 17] 17 shows the stress-strain curve of the CNT spun yarn obtained by the method including the crosslinking step in Test III-5. In the figure, the horizontal axis represents the strain rate (%), and the vertical axis represents the breaking stress (GPa) of the CNT spun yarn. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments of the present invention will now be described in detail.

[0014] 1. Method for producing spun yarn made from carbon nanotubes The present inventors have discovered that by applying a high tension to a spun yarn made of CNTs (CNT spun yarn) before subjecting it to an electrical heating treatment, within a range that does not cause the CNT spun yarn to break, to densify the CNT spun yarn, it is possible to increase the temperature and applied tension of the electrical heating treatment compared to conventional methods. The present inventors have discovered that by producing CNT spun yarn using this procedure, the resulting CNT spun yarn has high crystallinity and high strength. Therefore, one aspect of the present invention relates to a method for producing a spun yarn made of CNTs.

[0015] In each aspect of the present invention, CNT refers to a carbon material in which a single layer of graphite has a cylindrical structure. Typically, CNTs having a single-layer cylindrical structure are classified as single-walled CNTs, and CNTs having two or more cylindrical layers are classified as multi-walled CNTs. The CNTs applied to each aspect of the present invention may be either single-walled CNTs or multi-walled CNTs.

[0016] The method of this embodiment includes at least a step of preparing a spun yarn precursor α, a step of preparing a spun yarn precursor β, and a step of preparing a spun yarn. Each step will be described in detail below.

[0017] [1-1. CNT forest preparation process] The method of this embodiment may include a CNT forest preparation step of preparing a CNT forest.

[0018] In each embodiment of the present invention, a CNT forest refers to an aggregate of CNTs having a structure in which a plurality of CNTs are oriented in a certain direction for at least a portion of their longitudinal axes.

[0019] The shape and dimensions of the CNT forest prepared in this step are not particularly limited and may be any shape and size. The CNT forest is, for example, a quadrangle with a side length in the range of 5 to 1000 mm, preferably 10 to 40 mm.

[0020] The CNT forest prepared in this process can be prepared by various methods known in the art. For example, a CNT forest can be formed by placing catalyst particles that serve as growth nuclei on the surface of a metal substrate and contacting the surface of the substrate with a carbon-containing raw material gas in a reactor. In this process, the CNT forest can be prepared by hand using various methods known in the art, or it can be purchased.

[0021] [1-2. Spun yarn precursor α production process] This process involves pulling out multiple CNTs from a CNT forest, spinning the multiple CNTs while applying tension to the multiple CNTs, and producing a spun yarn precursor α (hereinafter also referred to as "CNT spun yarn precursor α") made of CNTs.

[0022] In this process, various means commonly used in the art can be used to extract multiple CNTs from the CNT forest. For example, a combing blade with multiple blades can be placed on top of the CNT forest substrate, and a CNT web consisting of multiple CNTs can be extracted from between the blades. In this embodiment, the combing blade preferably has three or more blades.

[0023] In this process, the formed CNT spun yarn precursor α is collected by winding it around the circumferential surface of a rotor. The rotor is, for example, a bobbin or a roller. By winding the CNT spun yarn precursor α around the circumferential surface of the rotor, multiple CNTs can be pulled out from the CNT forest at a desired pulling speed and a desired tension can be applied to the multiple CNTs.

[0024] In this step, the pulling speed for pulling out multiple CNTs from the CNT forest is preferably in the range of 100 to 1000 mm / min, and more preferably in the range of 200 to 500 mm / min.

[0025] In this process, it is preferable to spin multiple CNTs by rotating the CNT forest at a predetermined rotational speed. In this embodiment, the rotational speed of the CNT forest is preferably less than 2000 rpm, more preferably in the range of 100 to 1000 rpm, and even more preferably in the range of 200 to 500 rpm. Furthermore, the ratio of the rotational speed of the CNT forest to the pulling speed of the multiple CNTs is preferably in the range of more than 0.25 rev / mm and less than 25 rev / mm.

[0026] In this step, the tension applied to the CNTs is typically 6 mN or less per cm of CNT forest width. The tension applied to the CNTs is preferably in the range of 0.1 to 6 mN per cm of CNT forest width, more preferably 0.3 to 3 mN per cm of CNT forest width, and even more preferably 0.3 to 1 mN per cm of CNT forest width. For example, when the CNT forest has the shape and dimensions exemplified above, the tension applied to the CNTs is typically 10 mN or less (30 MPa per CNT), preferably in the range of 0.15 to 10 mN, more preferably in the range of 0.5 to 5 mN (1.6 to 16 MPa per CNT), and even more preferably in the range of 0.5 to 2 mN (1.6 to 6.4 MPa per CNT). If the tension is less than the lower limit, the density of the resulting CNT spun yarn precursor α may be low. Furthermore, if the tension exceeds the upper limit, the CNTs may break and it may not be possible to obtain the CNT spun yarn precursor a. Therefore, by carrying out this step while applying a tension within the above range to multiple CNTs, it is possible to obtain a high-density CNT spun yarn precursor a.

[0027] In this process, tension can usually be applied to the multiple CNTs drawn from the CNT forest by applying a load using a tensioning rod, a slider system, a motor, or the like.

[0028] In this process, tension is preferably applied to the CNTs extracted from the CNT forest while they are in contact with a liquid. In this embodiment, the liquid is preferably selected from the group consisting of methanol, ethanol, acetone, water, paraffin, toluene, and mixtures thereof, and more preferably selected from the group consisting of methanol, ethanol, acetone, water, and mixtures thereof. The liquid may contain one or more additional components, such as metal salts (e.g., iron chloride or nickel chloride) or metal oxides (e.g., iron oxide). The liquid is particularly preferably methanol, ethanol, acetone, or water. In this embodiment, means for contacting the CNTs with the liquid include, but are not limited to, impregnating the CNTs with the liquid, spraying the CNTs with the liquid, dripping the liquid onto the CNTs, and exposing the CNTs to the vapor of the liquid. It is preferable to contact the CNTs with the liquid by impregnating them with the liquid. In this embodiment, it is preferable to dry the CNTs that have been contacted with the liquid at room temperature or higher. By bringing multiple CNTs into contact with a liquid using the above method, the multiple CNTs can be aggregated using the aggregating force caused by vaporization of the liquid, thereby improving the density of the resulting CNT spun yarn precursor α.

[0029] The twist angle of the CNT spun yarn precursor α formed in this step is usually about 4°. The density of the CNT spun yarn precursor α is usually 0.7 g / cm 3 The Young's modulus of the CNT spun yarn precursor α is usually less than 100 GPa. The breaking stress of the CNT spun yarn precursor α is usually less than 1.4 GPa. By using the CNT spun yarn precursor α having the above properties in the following steps, a high-strength CNT spun yarn can be obtained in the method of this embodiment.

[0030] [1-3. Spun yarn precursor β production process] This step involves applying a higher tension to the spun yarn precursor α than in the spun yarn precursor α production step, thereby producing a spun yarn precursor β by densifying the spun yarn precursor α. The purpose of this step is to densify the spun yarn precursor α by preliminarily applying a high tension within a range that does not cause the spun yarn precursor α to break, before subjecting the spun yarn precursor β to an electrical heating treatment in the spun yarn production step.

[0031] This step can be carried out, for example, by drawing the spun yarn precursor α obtained in the spun yarn precursor α production step from the circumferential surface of a rotor and applying tension. The formed spun yarn precursor β is recovered by winding it around the circumferential surface of a rotor. The rotor is, for example, a bobbin or a roller. By winding the spun yarn precursor β around the circumferential surface of the rotor, the spun yarn precursor α can be drawn out at a desired drawing speed and a desired tension can be applied to the spun yarn precursor α.

[0032] In this step, the drawing speed for drawing out the spun yarn precursor α is preferably less than 4000 mm / min, and more preferably in the range of 1000 to 3000 mm / min.

[0033] In this step, the tension applied to the spun yarn precursor α is higher than that in the step of producing the spun yarn precursor α. The tension applied to the spun yarn precursor α is, for example, less than 150 mN (480 MPa for the spun yarn precursor α), preferably in the range of 0.5 to 120 mN (1.6 to 380 MPa for the spun yarn precursor α), and more preferably in the range of 1 to 100 mN (3 to 300 MPa for the spun yarn precursor α). If the tension is below the lower limit, the density of the resulting CNT spun yarn precursor β may be low. If the tension exceeds the upper limit, the spun yarn precursor α may break, making it impossible to obtain the CNT spun yarn precursor β. Therefore, by performing this step while applying a tension within the above range to the spun yarn precursor α, the spun yarn precursor α can be densified, resulting in a CNT spun yarn precursor β with high density. This also allows for the production of a CNT spun yarn with high strength.

[0034] In this step, it is preferable to apply tension to the spun yarn precursor α in stages multiple times. In this embodiment, the tension is increased stepwise from substantially the same tension as in the step of producing the spun yarn precursor α, and the tension is repeatedly applied stepwise to the spun yarn precursor α multiple times. In this case, the number of repeated tension applications is preferably two or more, more preferably two to five, and even more preferably three. The tension applied the first time is preferably in the range of 0.5 to 10 mN (1.6 to 30 MPa for the spun yarn precursor α), and more preferably 1 to 10 mN (3 to 30 MPa for the spun yarn precursor α). The tension applied in the final stage is preferably in the range of 10 to 120 mN (30 to 380 MPa for spun yarn precursor α), more preferably in the range of 20 to 100 mN (64 to 300 MPa for spun yarn precursor α), and even more preferably in the range of 50 to 100 mN (160 to 300 MPa for spun yarn precursor α). In a specific embodiment, it is preferable to apply tension to the spun yarn precursor α in a stepwise manner, increasing the tension in the order of 1 mN, 50 mN, or 100 mN (3 MPa, 160 MPa, or 300 MPa for spun yarn precursor α), three times. If the number of repetitions is less than the lower limit or if the tension applied in the first step exceeds the upper limit, the tension may increase rapidly, causing the spun yarn precursor α to break and preventing the production of CNT spun yarn precursor β. Furthermore, if the number of repetitions exceeds the upper limit, the processing time may become longer, potentially increasing the cost of the method of this embodiment. Therefore, by carrying out this step under the above conditions, the spun yarn precursor α can be densified, and a CNT spun yarn precursor β with a stable high density can be obtained, thereby producing a CNT spun yarn with high strength.

[0035] In this step, tension can usually be applied to the spun yarn precursor α drawn out from the circumferential surface of the rotor by applying a load using a tensioning rod, a slider system, a motor, or the like.

[0036] In this step, tension is preferably applied to the spun yarn precursor α while it is being brought into contact with a liquid. In this embodiment, the liquid is preferably selected from the group consisting of methanol, ethanol, acetone, water, paraffin, toluene, and mixtures thereof, and more preferably selected from the group consisting of methanol, ethanol, acetone, water, and mixtures thereof. The liquid may contain one or more additional components, such as metal salts (e.g., iron chloride or nickel chloride) or metal oxides (e.g., iron oxide). The liquid is particularly preferably methanol, ethanol, acetone, or water. In this embodiment, means for bringing the spun yarn precursor α into contact with the liquid include, but are not limited to, impregnating the spun yarn precursor α with the liquid, spraying the liquid onto the spun yarn precursor α, dripping the liquid onto the spun yarn precursor α, and exposing the spun yarn precursor α to the vapor of the liquid. Preferably, the spun yarn precursor α is brought into contact with the liquid by impregnating the spun yarn precursor α with the liquid. In this embodiment, the spun yarn precursor a that has been brought into contact with the liquid is preferably dried at room temperature or a temperature higher than room temperature. By bringing the spun yarn precursor a into contact with the liquid by this means, the coagulation force caused by the vaporization of the liquid is utilized to aggregate multiple CNTs, thereby improving the density of the resulting CNT spun yarn precursor β.

[0037] By carrying out this step under the above conditions, the spun yarn precursor α can be densified, and a CNT spun yarn precursor β with a stable high density can be obtained. The density of the spun yarn precursor β formed in this step is usually 1.0 g / cm 3 or more, for example, 1.0 to 1.2 g / cm 3 The Young's modulus of the CNT spun yarn precursor β is usually 100 GPa or more, for example, in the range of 100 to 150 GPa. The breaking stress of the CNT spun yarn precursor β is usually 1.4 GPa or more, for example, in the range of 1.4 to 2 GPa. By using the spun yarn precursor β having the above properties in the following steps, a high-strength CNT spun yarn can be obtained in the method of this embodiment.

[0038] [1-4. Spun yarn production process] This step involves applying tension to the spun yarn precursor β while electrically heating it, to produce a spun yarn made of carbon nanotubes.

[0039] This step can be carried out, for example, by drawing the spun yarn precursor β obtained in the spun yarn precursor β production step from the circumferential surface of a rotor and subjecting it to an electrical heating treatment while applying tension. The formed CNT spun yarn is recovered by winding it around the circumferential surface of a rotor. The rotor is, for example, a bobbin or roller. By winding the CNT spun yarn around the circumferential surface of the rotor, the spun yarn precursor α can be drawn out at a desired drawing speed and the desired tension can be applied to the spun yarn precursor α.

[0040] In this step, the drawing speed for drawing out the spun yarn precursor α is preferably in the range of more than 60 and 6000 mm / min, more preferably in the range of 100 to 1000 mm / min, and even more preferably in the range of 100 to 600 mm / min.

[0041] In this step, the tension applied to the spun yarn precursor β may be the same as or greater than that in the step of producing the spun yarn precursor β. The tension applied to the spun yarn precursor β is, for example, less than 150 mN (480 MPa for the spun yarn precursor β), preferably in the range of 0.5 to 120 mN (1.6 to 380 MPa for the spun yarn precursor β), and more preferably in the range of 1 to 100 mN (3 to 300 MPa for the spun yarn precursor β). If the tension is less than the lower limit, the density of the resulting CNT spun yarn may be low. If the tension exceeds the upper limit, the spun yarn precursor β may break, making it impossible to obtain a CNT spun yarn. Therefore, by performing this step while applying a tension within the above range to the spun yarn precursor β, the spun yarn precursor β can be densified, resulting in a CNT spun yarn with high density. This also allows for the production of a CNT spun yarn with high strength.

[0042] In this step, tension can usually be applied to the spun yarn precursor β drawn out from the circumferential surface of the rotor by applying a load using a tensioning rod, a slider system, a motor, or the like.

[0043] In this step, the means for electrically heating the spun yarn precursor β is not particularly limited, and various means commonly used in the art can be applied. This step may be carried out, for example, using a heater (e.g., a quartz heater) in an inert gas atmosphere (e.g., argon gas), or using an atmospheric furnace equipped with a tension application mechanism and capable of heating to ultra-high temperatures. In this embodiment, the distance between the electrodes of the heater is preferably in the range of 1 to 50 mm, and more preferably in the range of 1 to 10 mm.

[0044] In this step, the temperature of the electrical heating is preferably 3200 K or less, more preferably a temperature above room temperature and not exceeding 3200 K, even more preferably in the range of 1000 to 3200 K, and particularly preferably in the range of 2000 to 3000 K. If the temperature of the electrical heating is below the lower limit, the conversion of amorphous carbon in the CNTs contained in the spun yarn precursor β to graphene may not proceed sufficiently. If the temperature of the electrical heating exceeds the upper limit, the spun yarn precursor β may break, making it impossible to obtain a CNT spun yarn. Therefore, by performing this step under the above conditions, at least a portion of the amorphous carbon in the CNTs contained in the spun yarn precursor β can be converted to graphene, resulting in a high-strength CNT spun yarn.

[0045] In this step, the duration of the electrical heating is preferably greater than 0.1 and less than 10 seconds, more preferably between 0.5 and 10 seconds, and even more preferably between 0.5 and 1 second. If the duration of the electrical heating is less than the lower limit, the graphene conversion of the amorphous carbon in the CNTs contained in the spun yarn precursor β may not proceed sufficiently. If the duration of the electrical heating exceeds the upper limit, the spun yarn precursor β may break, making it impossible to obtain a CNT spun yarn. Therefore, by performing this step under the above conditions, at least a portion of the amorphous carbon in the CNTs contained in the spun yarn precursor β can be graphene converted, resulting in a high-strength CNT spun yarn.

[0046] In this step, tension is preferably applied to the spun yarn precursor β while it is being brought into contact with a liquid. In this embodiment, the liquid is preferably selected from the group consisting of methanol, ethanol, acetone, water, paraffin, toluene, and mixtures thereof, and more preferably selected from the group consisting of methanol, ethanol, acetone, water, paraffin, and mixtures thereof. The liquid may contain one or more additional components, such as metal salts (e.g., iron chloride or nickel chloride) or metal oxides (e.g., iron oxide). The liquid is particularly preferably methanol, ethanol, acetone, water, paraffin, or an ethanol solution of iron chloride. In this embodiment, means for bringing the spun yarn precursor β into contact with the liquid include, but are not limited to, impregnating the spun yarn precursor β with the liquid, spraying the liquid onto the spun yarn precursor β, dripping the liquid onto the spun yarn precursor β, and exposing the spun yarn precursor β to the vapor of the liquid. Preferably, the spun yarn precursor β is brought into contact with the liquid by impregnating the spun yarn precursor β with the liquid. In this embodiment, the spun yarn precursor β that has been in contact with the liquid is preferably dried at room temperature or higher. By contacting the spun yarn precursor β with the liquid by this means, the coagulation force caused by the vaporization of the liquid is utilized to aggregate multiple CNTs, thereby improving the density of the resulting CNT spun yarn.

[0047] By carrying out this step under the above conditions, the spun yarn precursor β can be densified and / or at least a portion of the amorphous carbon contained in the spun yarn precursor β can be converted into graphene, thereby obtaining a CNT spun yarn with high density and strength.

[0048] [1-5. Crosslinking process] The method of this embodiment may further include a crosslinking step of impregnating the spun yarn made of carbon nanotubes obtained in the spun yarn preparation step with an aqueous solution containing a sulfide salt.

[0049] In each embodiment of the present invention, the sulfide salt used in the crosslinking step may be referred to as the "sulfurizing agent." Simulations have predicted that treating a CNT spun yarn with a sulfurizing agent crosslinks the CNTs via disulfide bonds. Applying tensile force to this crosslinked CNT spun yarn results in the disulfide bonds repeatedly rebonding, improving tensile strength (Composite Science and Technology, 2018, Vol. 166, pp. 3-9). In the method of this embodiment, treating the CNT spun yarn obtained in the spun yarn preparation step with an aqueous solution containing a sulfurizing agent crosslinks the CNTs constituting the CNT spun yarn via disulfide bonds, trisulfide bonds, or tetrasulfide bonds, reducing voids and increasing the density of the CNT spun yarn. Therefore, performing the crosslinking step can further improve the density and strength of the resulting CNT spun yarn.

[0050] In this process, the sulfide salt used as the sulfiding agent is preferably a salt of tetrasulfide, trisulfide, or disulfide, more preferably a salt of tetrasulfide or disulfide, even more preferably a salt of tetrasulfide or disulfide with sodium ions, potassium ions, calcium ions, or magnesium ions, and particularly preferably sodium tetrasulfide or sodium disulfide. When the sulfide salt is a salt of tetrasulfide with one of the counterions listed above, particularly sodium tetrasulfide, performing this process can further improve the strain tolerance of the CNT spun yarn. Furthermore, when the sulfide salt is a salt of disulfide with one of the counterions listed above, particularly sodium disulfide, performing this process can further improve the breaking stress of the CNT spun yarn. Therefore, performing this process using one of the sulfide salts listed above can further improve the strength of the resulting CNT spun yarn.

[0051] In this step, the concentration of the sulfide salt in the aqueous sulfide salt solution is preferably 1 mmol / L or higher, more preferably 1 to 500 mmol / L, even more preferably 1 to 200 mmol / L, and particularly preferably 1 to 100 mmol / L. If the sulfide salt concentration is below the lower limit, disulfide bonds and the like will not be sufficiently introduced between the CNTs that make up the CNT spun yarn, which may result in insufficient improvement in the density and / or strength of the resulting CNT spun yarn. Therefore, by performing this step under the above conditions, the density and strength of the resulting CNT spun yarn can be further improved.

[0052] The aqueous solution of sulfide salt used in this step may optionally contain one or more additional components such as a water-miscible organic solvent, such as methanol, ethanol, and acetone.

[0053] In this step, the impregnation time for impregnating the CNT spun yarn with an aqueous solution containing a sulfide salt is typically 1 hour or longer, preferably 2 hours or longer, more preferably 24 hours or longer, and even more preferably 48 hours or longer. The upper limit of the impregnation time is not particularly limited, but is typically 72 hours or shorter, for example, 60 hours or shorter, and particularly 48 hours or shorter. If the impregnation time is shorter than the lower limit, disulfide bonds and the like will not be sufficiently introduced between the CNTs that make up the CNT spun yarn, which may result in insufficient improvement in the density and / or strength of the resulting CNT spun yarn. Therefore, by performing this step under the above conditions, the density and strength of the resulting CNT spun yarn can be further improved.

[0054] In this step, the impregnation temperature at which the CNT spun yarn is impregnated with an aqueous solution containing a sulfide salt is typically room temperature or higher, preferably 10°C or higher, and more preferably in the range of 10 to 60°C. If the impregnation temperature is below the lower limit mentioned above, the introduction of disulfide bonds between the CNTs that make up the CNT spun yarn may be insufficient, resulting in insufficient improvement in the density and / or strength of the resulting CNT spun yarn. Therefore, by carrying out this step under the above conditions, the density and strength of the resulting CNT spun yarn can be further improved.

[0055] In this step, it is preferable to dry the CNT spun yarn impregnated with the aqueous solution containing the sulfide salt. In this embodiment, the drying temperature is usually room temperature or higher, preferably 20°C or higher, and more preferably in the range of 20 to 100°C. The drying time is usually several minutes or longer, preferably 5 minutes or longer and several days or shorter, more preferably in the range of 5 minutes to 1 day, and even more preferably in the range of 5 minutes to 1 hour. In a specific embodiment, it is preferable to air-dry the CNT spun yarn impregnated with the aqueous solution containing the sulfide salt at room temperature for 1 day, or vacuum-dry it at 80°C for 1 hour. If the impregnation temperature and / or impregnation time are below the above-mentioned lower limit, the CNT spun yarn may not be sufficiently dried. Therefore, by performing this step under the above-mentioned conditions, it is possible to obtain a CNT spun yarn with the desired properties.

[0056] In the method of this embodiment, the steps described above may be performed sequentially or continuously. In the method of this embodiment, it is preferable to perform the steps described above continuously. By performing the steps of the method of this embodiment continuously, a CNT spun yarn with high density and strength can be produced efficiently and at low cost.

[0057] 2. Spun yarn made from carbon nanotubes As explained above, the manufacturing method of one embodiment of the present invention can provide a CNT spun yarn with high density and strength. Therefore, another embodiment of the present invention relates to a spun yarn (CNT spun yarn) obtainable by the manufacturing method of one embodiment of the present invention, and preferably made of carbon nanotubes obtained by said method.

[0058] In each embodiment of the present invention, the density of the CNT spun yarn precursor α, the CNT spun yarn precursor β, and the CNT spun yarn can be measured as bulk density, for example, by the following procedure, although this is not limited thereto. Using a microbalance, the weight per unit length of the CNT spun yarn precursor α, the CNT spun yarn precursor β, or the CNT spun yarn is measured. Using a scanning electron microscope, the cross-sectional area of ​​the CNT spun yarn precursor α, the CNT spun yarn precursor β, or the CNT spun yarn is measured. The bulk density is then calculated from the weight per unit length and the cross-sectional area obtained.

[0059] In each embodiment of the present invention, the strength of the CNT spun yarn precursor α, CNT spun yarn precursor β, and CNT spun yarn can be evaluated using, for example, Young's modulus and breaking stress as indicators. The Young's modulus and breaking stress of the CNT spun yarn precursor α, CNT spun yarn precursor β, and CNT spun yarn can be measured, for example, based on ISO11566:1996 (JIS R 7606:2000), under conditions of a test speed of 1 mm / min and a grip distance of 25 mm, without being limited thereto.

[0060] The CNT spun yarn of this embodiment typically has a density of 1.6 g / cm 3 Less than, for example, 1.0 g / cm 3 Over 1.6 g / cm 3 less than 1.2-1.5 g / cm 3 In contrast, CNT spun yarns obtained by a conventional method in which no preliminary tension is applied in the process of producing the spun yarn precursor β typically have a density in the range of 1.0 g / cm 3 Therefore, the CNT spun yarn of this embodiment can have a denser structure than CNT spun yarns obtained by methods of the prior art.

[0061] In the CNT spun yarn of this embodiment, the ratio (IG / ID) of the G-band peak intensity (IG) to the D-band peak intensity (ID) in the spectrum obtained by Raman spectroscopic analysis is usually 5 or more, for example, in the range of 5 to 35, and particularly in the range of 5 to 25. In contrast, in a CNT spun yarn obtained by a conventional method in which preliminary tension is not applied in the step of producing the spun yarn precursor β, IG / ID is usually less than 2, for example, less than 1.2. In the technical field, in a spectrum obtained by Raman spectroscopic analysis of CNTs and spun yarns made of CNTs (hereinafter also referred to as "Raman spectrum"), the G-band peak is due to the crystalline sp 2 The D band peak is due to the sp 3 It is known that this is due to the structure. Therefore, in the Raman spectra of CNTs and spun yarns made from CNTs, the I / I ratio serves as an indicator of the crystallinity of the CNTs. Furthermore, the structural change from amorphous carbon to graphene in CNTs can be confirmed, for example, by the presence of a flake-like crystalline structure, indicating the presence of graphene, in an image obtained by observing the CNTs with a transmission electron microscope. Since the CNT spun yarn of this embodiment has a higher I / I ratio than CNT spun yarns obtained by conventional methods, the CNT spun yarn of this embodiment has higher CNT crystallinity than CNT spun yarns obtained by conventional methods. Furthermore, since the CNT spun yarn of this embodiment has a flake-like crystalline structure confirmed in transmission electron microscope images, graphene may be present in at least a portion of the CNTs. Therefore, the CNT spun yarn of this embodiment has high crystallinity and a graphene structure not observed in CNT spun yarns obtained by conventional methods.

[0062] The CNT spun yarn of this embodiment has high strength due to its high crystallinity and graphene structure. The CNT spun yarn of this embodiment typically has a Young's modulus of 100 GPa or more, for example, in the range of 100 to 300 GPa, preferably in the range of 120 to 260 GPa, and particularly in the range of 190 to 260 GPa. The CNT spun yarn of this embodiment also typically has a breaking stress of 1.4 GPa or more, for example, in the range of 1.4 to 3.6 GPa, preferably in the range of 1.6 to 3.4 GPa, and particularly in the range of 2.2 to 3.2 GPa. In contrast, CNT spun yarns obtained by conventional methods that do not apply preliminary tension in the step of producing the spun yarn precursor β typically have a Young's modulus of less than 100 GPa and a breaking stress of less than 1.4 GPa. Therefore, the CNT spun yarn of this embodiment can have a strength greater than that of CNT spun yarns obtained by conventional methods.

[0063] In a specific embodiment, the CNTs in the CNT spun yarn of this embodiment may be cross-linked by disulfide bonds, trisulfide bonds, or tetrasulfide bonds. The CNT spun yarn of this embodiment has one or more bonds selected from the group consisting of disulfide bonds, trisulfide bonds, and tetrasulfide bonds between the CNTs. The CNT spun yarn of this embodiment can be obtained by the production method of one embodiment of the present invention, which includes the cross-linking step described above. The CNT spun yarn of this embodiment has higher density and strength.

[0064] The CNT spun yarn of this embodiment has high strength in addition to thermal conductivity and electrical conductivity, and therefore can be used as a high-strength carbon material to replace carbon fiber reinforced plastics (CFRP). The CNT spun yarn of this embodiment can be used, for example, as a material for automobile parts (e.g., high-pressure tanks or bodies), wind turbine parts (e.g., blades), aircraft parts (e.g., bodies), and the like. [Example]

[0065] The present invention will be described in more detail below using examples, although the technical scope of the present invention is not limited to these examples.

[0066] <Manufacture of Spun Yarn Composed of CNT (1)> [I-1: Process for Producing Spun Yarn Precursor α] A commingling blade having three blades was placed on the upper surface of a 18×18 mm CNT forest formed on the surface of a metal substrate. From between the blades, a CNT web composed of a plurality of CNTs was drawn out under the conditions of a substrate rotation speed of 500 rpm and a drawing speed of 500 mm / min. The CNT web was spun while applying a tension thereto with a load of less than 1 mN (3 MPa with respect to the CNT web composed of a plurality of CNTs), and a spun yarn precursor α composed of CNTs having a twist angle of about 4° was wound around the circumferential surface of a rotating body. In the above procedure, the load of less than 1 mN (3 MPa with respect to the CNT web composed of a plurality of CNTs) corresponds to a tension of 0.55 mN per 1 cm width of the CNT forest. By the above procedure, the spun yarn precursor α was produced. The substrate rotation speed was in the range of less than 200 rpm, the ratio of the substrate rotation speed / drawing speed was in the range of more than 0.25 rev / mm and less than 25 rev / mm, and the load was in the range of a tension of less than 10 mN (5.5 mN per 1 cm width of the CNT forest, 30 MPa with respect to the CNT web composed of a plurality of CNTs), and each was changed. Also, this step was carried out by a procedure in which the CNT web drawn from the CNT forest was impregnated with methanol, ethanol, acetone or water while applying a load thereto, and then wound around the circumferential surface of a rotating body.

[0067] [I-2: Process for Producing Spun Yarn Precursor β] Spun yarn precursor α was drawn from the circumferential surface of the rotor at a drawing speed of 2000 mm / min. After impregnating the spun yarn precursor α with ethanol while applying a higher tension than in the spun yarn precursor α production process, it was wound around the circumferential surface of the rotor. This procedure was repeated three times, applying a stepwise tension with increasing loads of 1 mN, 50 mN, or 100 mN (3 MPa, 160 MPa, or 300 MPa for spun yarn precursor α). This procedure densified the spun yarn precursor α to produce spun yarn precursor β. The drawing speed was varied within a range of less than 4000 mm / min, and the load was varied within a range of less than 150 mN (480 MPa for spun yarn precursor α). This process was also performed using a procedure in which the spun yarn precursor α was impregnated with methanol, acetone, or water instead of ethanol.

[0068] [I-3: Spun yarn production process] Spun yarn precursor β was drawn from the circumferential surface of the rotor at a drawing speed of 600 mm / min. The spun yarn precursor β was subjected to electrical heating at a temperature of 1500 to 3000 K for 1 second with an electrode distance of 10 mm while applying a tension of 1 mN, 10 mN, or 100 mN (3 MPa, 30 MPa, or 300 MPa for spun yarn precursor β), and then wound around the circumferential surface of the rotor. Using this procedure, CNT spun yarn was produced. The drawing speed was varied between more than 60 and 6000 mm / min, the load was varied between less than 150 mN (480 MPa for spun yarn precursor β), the electrical heating temperature was varied between above room temperature and 3200 K or less, and the electrical heating time was varied between more than 0.1 and less than 10 seconds. This process was also carried out by impregnating the spun yarn precursor β with methanol, ethanol, acetone, water, paraffin, or an ethanol solution of iron chloride, and then electrically heating the impregnated yarn precursor β and winding it around the circumferential surface of a rotating body.

[0069] [I-4: Effect of load on the spun yarn precursor β production process] In the spun yarn precursor β production step, spun yarn precursor β was produced by spinning while applying a tension of 1 mN, 50 mN, or 100 mN (3 MPa, 160 MPa, or 300 MPa for spun yarn precursor α). Next, in the spun yarn production step, a CNT spun yarn was produced without applying electrical heating. As a control, a CNT spun yarn was produced using the same procedure as above, except that spun yarn precursor β was produced by spinning without applying a load in the spun yarn precursor β production step. The Young's modulus and breaking stress of the obtained spun yarn were measured at a test speed of 1 mm / min and a grip distance of 25 mm according to ISO 11566:1996 (JIS R 7606:2000). The density of the obtained spun yarn was also measured using the following procedure. The weight per unit length of the spun yarn was measured using a microbalance. The cross-sectional area of ​​the spun yarn (at six locations) was measured using a scanning electron microscope. The bulk density was then calculated from the weight per unit length and cross-sectional area obtained. The Young's modulus, breaking stress, and density of the obtained spun yarn are shown in Figures 1, 2, and 3, respectively. In the figures, the horizontal axis represents the load (mN) in the process of producing spun yarn precursor β. In Figures 1 and 2, the values ​​in the figures represent the average and standard deviation of the test results obtained from the cross-sectional area measurements at six locations.

[0070] As shown in Figures 1 to 3, when spinning was performed while applying a load of 1 mN, 50 mN, or 100 mN (3 MPa, 160 MPa, or 300 MPa for spun yarn precursor α) in the process of producing spun yarn precursor β, the Young's modulus, breaking stress, and density of the resulting CNT spun yarn were all significantly higher than those of the control spun yarn.

[0071] [I-5: Effect of electrical heating treatment in the spun yarn production process] In the spun yarn precursor β production step, spun yarn precursor β was produced by spinning while applying a tension of either no load or 100 mN (300 MPa for spun yarn precursor α). Next, in the spun yarn production step, spun yarn precursor β was subjected to electrical heating at a temperature of 1500, 2000, 2500, 3000, or 3500 K for 1 second with an electrode distance of 10 mm while applying a tension of 1 mN, 10 mN, or 100 mN (3 MPa, 30 MPa, or 300 MPa for spun yarn precursor β), to produce a CNT spun yarn. Table 1 shows the relationship between the electrical heating temperature in the spun yarn precursor β production step and the CNT spun yarn when the spun yarn precursor β production step was performed without a load, and Table 2 shows the relationship between the electrical heating temperature in the spun yarn precursor β production step and the CNT spun yarn when the spun yarn precursor β production step was performed with a load. In the table, × indicates that the spun yarn precursor β was broken during the electrical heating treatment, and ◯ indicates that a CNT spun yarn was successfully produced.

[0072] [Table 1]

[0073] [Table 2]

[0074] As shown in Table 1, when the spun yarn precursor β production step was performed under no load conditions, the spun yarn precursor β broke during the electrical heating treatment when electrically heated at a temperature of 3000 K or higher, and a CNT spun yarn could not be obtained. In contrast, when the spun yarn precursor β production step was performed under load conditions while applying tension to the spun yarn precursor α, the spun yarn precursor β did not break even when electrically heated at 3000 K, and a good CNT spun yarn could be obtained. As explained below, the higher the electrical heating temperature in the spun yarn production step, the stronger the resulting spun yarn. Therefore, by performing the spun yarn precursor β production step while applying tension to the spun yarn precursor α, the strength of the resulting spun yarn can be improved.

[0075] <II: Property Analysis of Spun Yarn Composed of CNT> [II-1: Density of CNT Spun Yarn] In the process of producing the spun yarn precursor β, the spun yarn precursor β was produced by spinning while applying tension without load or with a load of 100 mN (300 MPa with respect to the spun yarn precursor α). Next, in the process of producing the CNT spun yarn, while applying a tension to the spun yarn precursor β with a load of 1 mN, 10 mN or 100 mN (3 MPa, 30 MPa or 300 MPa with respect to the spun yarn precursor β), electric current heating was carried out under the conditions of a temperature of 2500 or 3000 K, a time of 1 second, and an electrode distance of 10 mm to produce a CNT spun yarn. As a control, a CNT spun yarn was produced under the condition of non-treatment of electric current heating. The density of the CNT spun yarns obtained under various treatment conditions is shown in Fig. 4. In the figure, the horizontal axis is the treatment conditions (tension and temperature of electric current heating) in the process of producing the spun yarn, and the vertical axis is the density (g / cm 3 ). Also, the white bars are the results when the process of producing the spun yarn precursor β was carried out under the condition of no load, and the black bars are the results when the process of producing the spun yarn precursor β was carried out under the condition of having a load. The values in the figure show the average value and standard deviation of the test results obtained from the measured cross-sectional area values at 6 locations.

[0076] As shown in Figure 4, when the spun yarn precursor β production step was performed without load, the density of the CNT spun yarn obtained by electrical heating at a temperature of 2500 K was substantially the same as the density of the untreated CNT spun yarn. Furthermore, when electrical heating was performed at temperatures of 3000 K or higher, the spun yarn precursor β broke during the electrical heating treatment, making it impossible to obtain a CNT spun yarn. In contrast, when the spun yarn precursor β production step was performed with load while applying tension to the spun yarn precursor α, the density of the CNT spun yarn obtained by electrical heating at a temperature of 2500 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β) was significantly higher than the density of the untreated spun CNT yarn. Furthermore, the density of the CNT spun yarn obtained by electrical heating at a temperature of 3000 K was significantly higher than that of the untreated control CNT spun yarn, regardless of whether a tension load of 1 mN, 10 mN, or 100 mN (3 MPa, 30 MPa, or 300 MPa for the spun yarn precursor β) was applied.

[0077] [II-2: Analysis of peaks observed in the Raman spectrum of CNT-spun yarn] The spun yarn made of CNTs obtained in II-1 was subjected to Raman spectroscopy. The CNT spun yarn obtained by carrying out the spun yarn precursor β production process under load was analyzed using a Raman spectroscopic method. -1 Figure 5 shows the Raman spectrum in the range of 2200–3400 cm for the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under no load. -1 Figure 6 shows the Raman spectrum in the range of 2200–3400 cm for the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under load. -1 The Raman spectra for the range are shown in Figure 7. In the figure, the horizontal axis represents the Raman shift (cm -1 ), and the vertical axis represents the intensity (au) of Raman scattered light. In Fig. 7, A represents the Raman spectra of the untreated control CNT spun yarn and the CNT spun yarn obtained by electrical heating at a temperature of 2500 K, and B represents the Raman spectra of the untreated control CNT spun yarn and the CNT spun yarn obtained by electrical heating at a temperature of 3000 K.

[0078] As shown in Figure 5, the Raman spectrum of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under load revealed crystalline sp 2 G band peak due to the structure and sp 3 A D-band peak due to the structure was observed. The ratio of the G-band peak intensity (IG) to the D-band peak intensity (ID), which is an indicator of CNT crystallinity, (IG / ID) was 1.2 for the untreated CNT spun yarn and 2.0 for the CNT spun yarn obtained by electrical heating at 2500 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β). The ratio was 13 for the CNT spun yarn obtained by electrical heating at 3000 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β). Multiple experiments performed under similar conditions showed that the IG / ID ratio for the untreated CNT spun yarn was in the range of greater than 0.8 and less than 1.2, whereas for the CNT spun yarn obtained by electrical heating while applying tension, the ratio was greater than 1.2 and less than 35, particularly less than 25.

[0079] In the Raman spectrum, G * The band peak is known to originate from graphene (N. Ferralis, J. Mater. Sci. 45, 5135-5149 (2010), and M.S. Dresselhaus, et al., Nano Lett. 10 (3), 751-758 (2010)). As shown in Figures 6 and 7, the Raman spectra of the CNT yarns obtained under all conditions show a 2D band peak, which is a secondary D band peak, and a G band peak, which originates from graphene. * In particular, the G band peak of the CNT spun yarn obtained by electrical heating at 3000 K * The band peak corresponds to the G of the untreated control CNT yarn. * The intensity was more than twice as high as that of the band peak.

[0080] [II-3: Crystal structure analysis of CNT spun yarn] Figure 8 shows an image of the CNT spun yarn obtained in II-1 observed with a transmission electron microscope. In the figure, A is a transmission electron microscope image of an untreated CNT spun yarn (control); B is a transmission electron microscope image of a CNT spun yarn obtained by carrying out the spun yarn precursor β production process without load and then electrically heating at 2500 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β); C is a transmission electron microscope image of a CNT spun yarn obtained by carrying out the spun yarn precursor β production process with load and then electrically heating at 2500 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β); and D is a transmission electron microscope image of a CNT spun yarn obtained by carrying out the spun yarn precursor β production process with load and then electrically heating at 3000 K while applying a tension of 100 mN (300 MPa for the spun yarn precursor β). The scale bar in the figure is 10 nm.

[0081] As shown in Figure 8A, amorphous carbon (arrows a and C in Figure 8A) was observed in the untreated control CNT spun yarn. In contrast, no amorphous carbon was observed in the CNT spun yarns obtained by carrying out the spun yarn precursor β production process under load or without load, followed by electrical heating under tension (Figures 8B-D). Furthermore, in the case of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under load, flake-like crystalline structures indicating the presence of graphene were observed (arrows in Figures 8C and 8D). This result suggests that graphene may be present in at least some of the CNTs. Since more flake-like crystalline structures were observed in the CNT spun yarn obtained by electrical heating at 3000 K, it is inferred that electrical heating at 3000 K effectively promoted the structural transformation from amorphous carbon to graphene.

[0082] [II-4: Strength analysis of CNT spun yarn] Figure 9 shows the relationship between the electrical heating temperature in the spun yarn production process and the Young's modulus of the resulting CNT spun yarn for the CNT spun yarn obtained in II-1, and Figure 10 shows the relationship between the electrical heating temperature in the spun yarn production process and the breaking stress of the resulting CNT spun yarn. In the figure, the horizontal axis represents the electrical heating temperature (K) in the spun yarn production process, and the vertical axis represents the Young's modulus (GPa) or breaking stress (GPa) of the CNT spun yarn. The dotted line in the figure also represents the Young's modulus or breaking stress of the untreated control CNT spun yarn, which was subjected to the spun yarn precursor β production process with or without load. The values ​​in the figure represent the average and standard deviation of three test results.

[0083] As shown in Figure 9, the Young's modulus of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under no load conditions was substantially similar to that of the untreated CNT spun yarn. Furthermore, even when the electrical heating temperature in the spun yarn production process increased, no significant change in the Young's modulus of the resulting CNT spun yarn was observed. In contrast, the Young's modulus of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under load conditions significantly improved as the electrical heating temperature in the spun yarn production process increased. In particular, the Young's modulus of the CNT spun yarn obtained by electrical heating at a temperature of 3000 K reached a range of 190 to 220 GPa.

[0084] As shown in Figure 10, the breaking stress of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under unloaded conditions was substantially similar to the breaking stress of the untreated CNT spun yarn. Furthermore, even when the electrical heating temperature in the spun yarn production process increased, no significant change in the breaking stress of the resulting CNT spun yarn was observed. In contrast, the breaking stress of the CNT spun yarn obtained by carrying out the spun yarn precursor β production process under loaded conditions significantly increased as the electrical heating temperature in the spun yarn production process increased. In particular, the breaking stress of the CNT spun yarn obtained by electrical heating at a temperature of 3000 K reached a range of 2.0 to 2.8 GPa.

[0085] From the results of this example, it was revealed that by performing the production process of the spun yarn precursor β while applying a high tension to the spun yarn precursor α under the condition of having a load, and then performing electric heating while applying a tension, a CNT spun yarn having a high strength can be obtained. Further, it was revealed that the obtained CNT spun yarn has an IG / ID of the Raman spectrum of 5 or more, and graphene exists in at least a part of the CNTs.

[0086] <III: Production of Spun Yarn Composed of CNT (2)> [III-1: Crosslinking Process] In the production process of the spun yarn precursor α, a plurality of CNTs were spun while applying a tension of 1 mN per 1 cm width of the CNT forest to produce the spun yarn precursor α. Next, in the production process of the spun yarn precursor β, the spun yarn precursor β was produced by spinning while applying a load of 100 mN (300 MPa with respect to the spun yarn precursor α) and applying a tension. Further, in the production process of the spun yarn, while applying a load of 1 mN (3 MPa with respect to the spun yarn precursor β) and applying a tension to the spun yarn precursor β, electric heating was performed under the conditions of a temperature of 3000 K, a time of 1 second, and an electrode distance of 10 mm to remove residual oxygen, residual catalytic metal, and amorphous carbon, and a CNT spun yarn was produced.

[0087] By subjecting pure water to nitrogen bubbling treatment for 30 minutes, oxygen in the pure water was removed to produce ultrapure water. Na2S4 powder (sulfurizing agent) was dissolved in ultrapure water to prepare an aqueous solution containing 100 mmol / L (17.4 mg / mL) Na2S4. The CNT spun yarn produced by the above procedure was impregnated in an aqueous solution containing Na2S4 at 20 °C for a predetermined time, and then naturally dried at 20 °C for 1 day to obtain a CNT spun yarn in which the CNTs were crosslinked by disulfide bonds. As a non-treated control, a CNT spun yarn obtained by performing only the electric heating treatment in the spun yarn production process and not performing the crosslinking process was used.

[0088] [III-2: Surface Observation and Density Measurement of Crosslinked CNT Spun Yarn] The surface of the CNT spun yarn obtained by the above procedure was observed with a scanning electron microscope. The obtained images are shown in Figure 11. In the figure, A is a scanning electron microscope image of a CNT spun yarn obtained after 2 hours of impregnation treatment in the crosslinking step, B is a scanning electron microscope image of a CNT spun yarn obtained after 24 hours of impregnation treatment in the crosslinking step, and C is a scanning electron microscope image of a CNT spun yarn obtained after 48 hours of impregnation treatment in the crosslinking step. In the figure, the scale bar is 10 μm. The diameter and weight of the CNT spun yarn were also measured to calculate the density (bulk density). The diameter and density of the CNT spun yarn obtained under various treatment conditions are shown in Figure 12. In the figure, A is a graph showing the diameter of the CNT spun yarn, and B is a graph showing the density of the CNT spun yarn. The horizontal axis is the impregnation time in the crosslinking step, and the vertical axis is the diameter (μm) or density (g / cm) of the CNT spun yarn. 3 )

[0089] As shown in Figures 11 and 12, the diameter of the CNT yarn decreased significantly with increasing impregnation time during the cross-linking process, and the density of the CNT yarn increased accordingly. For example, the diameter of the untreated CNT yarn was 18.4 μm, while the diameter of the CNT yarn obtained after 48 hours of impregnation treatment was 16.8 μm.

[0090] [III-3: Cross-sectional observation and atomic analysis of cross-linked CNT yarn] The CNT spun yarn obtained by the above procedure was cut using a focused ion beam (FIB). The sulfur atoms present in the cross section of the obtained CNT spun yarn were quantified using an energy dispersive X-ray analyzer (EDS). Scanning electron microscope images of the cross section of the cut CNT spun yarn are shown in Figure 13. In the figure, A is a scanning electron microscope image of a CNT spun yarn obtained after 2 hours of impregnation treatment in the cross-linking process, B is a scanning electron microscope image of a CNT spun yarn obtained after 24 hours of impregnation treatment in the cross-linking process, and C is a scanning electron microscope image of a CNT spun yarn obtained after 48 hours of impregnation treatment in the cross-linking process. The dots in the images represent sulfur atoms present in the cross section of the CNT spun yarn, as mapped using EDS. The quantitative results of the sulfur atoms present in the cross section of the cut CNT spun yarn, as quantified using EDS, are shown in Figure 14. In the figure, A is a graph showing the percentage of the number of sulfur atoms relative to the total number of atoms present in the cross section of the CNT spun yarn, and B is a graph showing the percentage of the mass of sulfur atoms relative to the total mass of atoms present in the cross section of the CNT spun yarn. The horizontal axis is the impregnation time in the cross-linking step, and the vertical axis is the percentage (%) of the number of sulfur atoms or the percentage (%) of the mass of sulfur atoms.

[0091] 13 and 14, it was confirmed that sulfur atoms were introduced into the CNT spun yarn obtained by the method including the crosslinking step. Furthermore, as the impregnation time in the crosslinking step increased, the number and mass of sulfur atoms introduced into the CNT spun yarn significantly increased.

[0092] [III-4: Strength analysis of cross-linked CNT yarn] The breaking stress of the CNT spun yarn obtained by the above procedure was measured at a test speed of 1 mm / min and a grip distance of 10 mm according to ISO11566:1996 (JIS R 7606:2000). The stress-strain curves of the CNT spun yarn obtained under various processing conditions are shown in Figure 15. In the figure, the horizontal axis represents the strain rate (%), and the vertical axis represents the breaking stress (GPa) of the CNT spun yarn.

[0093] As shown in Figure 15, the CNT spun yarn obtained by the method including the crosslinking step had improved strain resistance and breaking stress compared to the control CNT spun yarn. In particular, when the impregnation time in the crosslinking step was 48 hours, both the strain resistance and breaking stress were significantly improved.

[0094] [III-5: Strength analysis of CNT yarns crosslinked with different sulfurizing agents] Crosslinked CNT spun yarns were obtained using the same procedure as above, except that the sulfiding agent used in the crosslinking step was changed to Na2S4, Na2S3, or Na2S2, and the impregnation time was changed to 48 or 24 hours. The breaking stress of the resulting CNT spun yarns was measured according to ISO 11566:1996 (JIS R 7606:2000) at a test speed of 1 mm / min and a grip distance of 10 mm. Figures 16 and 17 show the stress-strain curves of the CNT spun yarns obtained under various processing conditions. In the figures, the horizontal axis represents the strain rate (%), and the vertical axis represents the breaking stress (GPa) of the CNT spun yarns.

[0095] As shown in Figures 16 and 17, the strain tolerance and break stress of the CNT yarns obtained using either sulfiding agent were significantly improved compared to the untreated control CNT yarn. The CNT yarn obtained by the crosslinking process using Na2S4 exhibited higher strain tolerance than the CNT yarn obtained by the crosslinking process using Na2S2 (Figure 16). The CNT yarn obtained by the crosslinking process using Na2S2 also exhibited higher break stress than the CNT yarn obtained by the crosslinking process using Na2S4 (Figure 16). Furthermore, the CNT yarn obtained by the crosslinking process using Na2S3 exhibited high break stress and strain tolerance after 24 hours of impregnation treatment (Figure 17). The CNT yarn obtained by the crosslinking process using Na2S3 exhibited higher strain tolerance than the CNT yarn obtained by the crosslinking process using Na2S4 (Figures 16 and 17).

[0096] Simulations have predicted that treating CNT spun yarn with a sulfurizing agent crosslinks the CNTs via disulfide bonds and that applying tensile force to this crosslinked CNT spun yarn increases the tensile strength due to repeated recombination of disulfide bonds (Composite Science and Technology, 2018, Vol. 166, pp. 3-9). The results of this example demonstrate that the crosslinking process crosslinks the CNTs constituting the CNT spun yarn via disulfide, trisulfide, or tetrasulfide bonds, reducing voids and increasing the density of the CNT spun yarn. Furthermore, the resulting CNT spun yarn exhibited significantly improved strain tolerance and breaking stress, demonstrating high strength, compared to yarns without the crosslinking process.

[0097] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to add, delete, and / or replace part of the configuration of each embodiment with other configurations.

Claims

1. A method for producing a spun yarn made of carbon nanotubes, comprising the following steps: a step of producing a spun yarn precursor α, in which a plurality of carbon nanotubes are drawn out from the carbon nanotube forest, and the plurality of carbon nanotubes are spun while applying a tension of 6 mN or less per 1 cm width of the carbon nanotube forest to the plurality of carbon nanotubes, thereby producing a spun yarn precursor α made of carbon nanotubes; a spun yarn precursor β production step in which a higher tension than that in the spun yarn precursor α production step is applied to the spun yarn precursor α to produce a spun yarn precursor β by densifying the spun yarn precursor α; a spun yarn production step in which the spun yarn precursor β is electrically heated while applying tension to produce a spun yarn made of carbon nanotubes; The method comprising:

2. 2. The method according to claim 1, wherein in the step of producing the spun yarn precursor β, tension is applied to the spun yarn precursor α while the spun yarn precursor α is brought into contact with a liquid selected from the group consisting of methanol, ethanol, acetone, water, paraffin, toluene, and mixtures thereof.

3. 3. The method according to claim 1, wherein tension is applied to the spun yarn precursor α in stages over a plurality of times in the step of producing the spun yarn precursor β.

4. The method according to any one of claims 1 to 3, wherein electrical heating is performed at a temperature of 3200 K or less in the spun yarn production step.

5. The method according to any one of claims 1 to 4, wherein in the spun yarn production step, the spun yarn precursor β is electrically heated while being subjected to a tension of less than 480 MPa.

6. The method according to any one of claims 1 to 5, further comprising a crosslinking step of impregnating the spun yarn made of carbon nanotubes obtained in the spun yarn preparation step with an aqueous solution containing a sulfide salt.

7. 7. The method of claim 6, wherein the sulfide salt is sodium tetrasulfide or sodium disulfide.

Images