Fiber containing carbon nanotubes and cellulose and method for producing the same

Abstract

To provide a composite fiber of carbon nanotubes and cellulose having high conductivity and a low elastic modulus, and a method for producing the same.SOLUTION: A fiber provided by the present disclosure comprises cellulose and carbon nanotubes dispersed in the cellulose, wherein a G / D of the carbon nanotubes is 3 or more and 150 or less, and the fiber contains the carbon nanotubes in an amount of more than 50.0 mass% and 90.0 mass% or less based on a total mass of the fiber. Also, the method for producing the fiber provided by the present disclosure includes a step of preparing a mixed dispersion by mixing a specific carbon nanotube dispersion and a cellulose solution at a mass ratio of 5:95 to 99:1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to fibers comprising carbon nanotubes and cellulose and methods for making the same. [Background technology]

[0002] In recent years, there has been active development of smart textiles that are endowed with electrical functions such as wiring, heaters, sensors, and actuators. Conductive fibers are used as components in smart textiles to impart electrical functionality to textiles. However, the lack of conductive fibers that combine the required conductivity with the processability of knitting and weaving has hindered the development of smart textiles. Therefore, there is a demand for conductive fibers that offer both high conductivity and processability.

[0003] Conductive fibers made from various materials with high electrical conductivity have been reported. Examples include conductive fibers made from highly conductive materials such as metals like stainless steel or carbon materials like carbon nanotubes. While these fibers have high electrical conductivity, their metal and carbon components make them very stiff and have a high modulus of elasticity. Stiff fibers are prone to breakage during processing on looms or knitting machines, resulting in textiles that feel uncomfortable against the skin. To address this issue, composite fibers have been developed in which organic fibers, such as synthetic fibers, are coated with conductive materials like metals or carbon materials. However, increasing the amount of coating to achieve high electrical conductivity is difficult due to the risk of coating peeling. On the other hand, a method has been developed in which conductive materials are dispersed in organic fibers by blending them with organic polymers and then fabricating them into fibers, achieving both electrical conductivity and softness.

[0004] For example, Patent Document 1 below describes a method for obtaining fibers with high electrical conductivity by kneading a carbon nanotube dispersion into an aqueous cellulose solution and wet-spinning the mixture, but the carbon nanotube content of the fibers is limited to 50% by weight.

[0005] In Patent Document 2, a solution in which polyvinyl alcohol and carbon nanotubes are mixed is used to obtain fibers containing nearly 70% by weight of a conductive material, but the conductivity of the fibers is low.

[0006] In Patent Document 3, fibers containing 50% by weight or more of carbon nanotubes and having high electrical conductivity are obtained. However, because the weight ratio of carbon nanotubes is high, the fibers have a high elastic modulus and are hard.

[0007] In Non-Patent Document 1, a solution of cellulose nanofibers and carboxylated carbon nanotubes is processed into fibers to obtain fibers containing nearly 50% by weight of a conductive material and having a low elastic modulus. However, because the conductive material is dispersed using cellulose nanofibers, it is necessary to use carbon nanotubes with low conductivity whose G / D ratio has been reduced by carboxylation, and the conductivity of the resulting fibers is low. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2023-19716 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-281024 [Patent Document 3] Special Publication No. 2014-530964

[0009] [Non-Patent Document 1] Heather et al., Acs Appl.Mater.Interfaces 2023, 15, 30 Summary of the Invention [Problem to be solved by the invention]

[0010] In the above-mentioned conventional techniques, it is difficult to obtain fibers in which carbon nanotubes are dispersed in cellulose at a high concentration, and as a result, it has only been possible to obtain fibers that have either high electrical conductivity or low elastic modulus.

[0011] An object of the present disclosure is to provide a composite fiber of carbon nanotubes and cellulose having high electrical conductivity and low elastic modulus, and a method for producing the same. [Means for solving the problem]

[0012] Examples of embodiments of the present disclosure are listed in the following items [1] to

[16] . [1] A fiber comprising cellulose and carbon nanotubes dispersed in the cellulose, The carbon nanotubes have a G / D ratio of 3 or more and 150 or less, The fibers contain more than 50.0 mass % and 90.0 mass % or less of the carbon nanotubes, based on the total mass of the fibers. [2] Item 2. The fiber according to item 1, wherein the fiber has a peak in the diffraction angle 2θ range of 10° to 17° in wide-angle X-ray scattering measured by setting the fiber so that the fiber axis is oriented in the equator direction. [3] 3. The fiber according to item 1 or 2, wherein the degree of orientation of the carbon nanotubes in the fiber is 0.20 or more and 0.90 or less. [4] The specific conductivity of the above fiber is 1000Scm 2 / g or more 6000Scm 2 / g or less. [5] 5. The fiber according to any one of items 1 to 4, wherein the fiber has an elastic modulus of 10 GPa or more and 100 GPa or less. [6] 6. The fiber according to any one of items 1 to 5, wherein the G / D of the carbon nanotubes is 30 or more and 150 or less. [7] 1. A method for producing a fiber, the method comprising: A step of preparing a carbon nanotube dispersion in which more than 3.0 mass % and not more than 20.0 mass % of carbon nanotubes are dispersed in water; preparing a cellulose solution in which cellulose is dissolved in a solvent; a step of mixing the carbon nanotube dispersion liquid and the cellulose solution at a mass ratio (mass of the carbon nanotube dispersion liquid:mass of the cellulose solution) of 5:95 to 99:1 to prepare a mixed dispersion liquid containing the carbon nanotubes and the cellulose; wet-spinning the obtained mixed dispersion in a liquid to obtain cellulose fibers containing the carbon nanotubes; drying the obtained cellulose fibers to obtain fibers; A method for producing a fiber, comprising: [8] 8. The method according to Item 7, wherein the cellulose solution contains the cellulose in an amount of 1.0% by mass or more and 30.0% by mass or less based on the total mass of the cellulose solution. [9] Item 9. The method according to item 7 or 8, wherein in the step of preparing the mixed dispersion, the mass ratio of the carbon nanotube dispersion to the cellulose solution (mass of the carbon nanotube dispersion:mass of the cellulose solution) is 50:50 to 99:1.

[10] 10. The method according to any one of items 7 to 9, wherein the fibers contain more than 50.0 mass % and 90.0 mass % or less of the carbon nanotubes based on the total mass of the fibers.

[11] 11. The method according to any one of items 7 to 10, wherein the G / D of the carbon nanotubes is 3 or more and 150 or less.

[12] 12. The method according to any one of items 7 to 11, wherein the fiber has a peak in the diffraction angle 2θ range of 10° to 17° in wide-angle X-ray scattering measured by setting the fiber so that the fiber axis is oriented in the equator direction.

[13] 13. The method according to any one of items 7 to 12, wherein the degree of orientation of the carbon nanotubes in the fiber is 0.20 or more and 0.90 or less.

[14] The specific conductivity of the above fiber is 1000Scm 2 / g or more 6000Scm 2 / g or less.

[15] 15. The method according to any one of items 7 to 14, wherein the fiber has an elastic modulus of 10 GPa or more and 100 GPa or less.

[16] 16. The method according to any one of items 7 to 15, wherein the solvent is a cuprammonium method dissolution system.

[17] A textile comprising the fiber according to any one of items 1 to 6. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide a composite fiber of carbon nanotubes and cellulose having high electrical conductivity and low elastic modulus, and a method for producing the same. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is an example of an X-ray measurement chart having a peak at a diffraction angle 2θ of 10° or more and 17° or less due to wide-angle X-ray scattering. [Figure 2] FIG. 2 is an example of an X-ray measurement chart in which there is no peak at a diffraction angle 2θ of 10° or more and 17° or less due to wide-angle X-ray scattering. [Figure 3] FIG. 3 is a graph showing the relationship between the CNT concentration in the entire fiber calculated from the charge amount (charge amount CNT concentration) and the CNT residual index in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments. The upper and lower limit values ​​of each numerical range in the following embodiments can be arbitrarily combined to form any numerical range.

[0016] "fiber" The fibers of the present disclosure contain cellulose and carbon nanotubes (hereinafter simply referred to as "CNTs") dispersed in the cellulose. In the present disclosure, the term "fiber" refers to a structure having a ratio of the major axis direction to the minor axis direction (major axis length / minor axis length) of 1000 or more. Specifically, the term refers to continuous long fibers, short fibers, etc. The CNTs contained in the fibers have a G / D ratio of 3 or more and 150 or less, and are contained in the fibers at a content of more than 50.0 mass% and 90.0 mass% or less. The fibers of the present disclosure, with the above configuration, can provide CNT-cellulose composite fibers with high electrical conductivity and low modulus of elasticity. The inventors speculate that the reason for this is as follows, without being limited by theory. Specifically, fibers containing a high concentration of CNTs with a high G / D ratio in cellulose can produce fibers with high electrical conductivity. However, CNTs with a high G / D ratio generally have strong intermolecular interactions and tend to aggregate. Therefore, it is believed that aggregation of CNTs in fibers increases the modulus of elasticity of the fibers. In this regard, as described below, the present inventors have discovered a method for dispersing CNTs with a high G / D ratio in cellulose at a high concentration while maintaining the high G / D ratio, and have succeeded for the first time in obtaining CNT-cellulose composite fibers with high electrical conductivity and a low elastic modulus, something that could not be achieved with conventional technology. Therefore, in the present disclosure, by "dispersing" CNTs with a high G / D ratio in cellulose at a high concentration, it is possible to provide CNT-cellulose composite fibers that contain a high concentration of CNTs with a high G / D ratio but have a low elastic modulus.

[0017] Wide-angle X-ray scattering The inventors have found that the dispersion state of CNTs in cellulose can be confirmed using wide-angle X-ray scattering. Preferably, in wide-angle X-ray scattering measurements performed with the fibers set so that the fiber axis is oriented in the equatorial direction, the fibers have a peak at a diffraction angle 2θ in the range of 10° to 17°. The peak is preferably present at a diffraction angle 2θ in the range of 10° to 16°, even more preferably 11° to 15°, and even more preferably 12° to 14°. This peak is believed to be derived from type II crystals of cellulose. The inventors have found that the presence of the peak at a diffraction angle 2θ in the range of 10° to 17° further improves the dispersion state of CNTs in cellulose, making it easier to obtain fibers with a low modulus even at high CNT concentrations. While not limited by theory, the inventors speculate that the reason for this is as follows. That is, this peak is not observed in fibers composed solely of cellulose or cellulose fibers with a CNT coating (CNTs not dispersed in the cellulose), and the peak is small in CNT-cellulose composite fibers in which the CNTs are not well dispersed in the cellulose. Therefore, this peak is thought to reflect the interaction between the cellulose and the CNT surface. More specifically, when this peak exists in the diffraction angle 2θ range of 10° to 17°, it is thought that the presence of type II cellulose crystals wrapped around the surface of the CNTs in the fiber effectively reduces the strong intermolecular interaction between the CNTs and maintains a certain distance between the CNTs. This is thought to enable the production of fibers with a lower elastic modulus, even when the CNT concentration in the fiber is high.

[0018] In the present disclosure, whether or not the peak exists is determined by the peak intensity ratio X, as will be described in detail in the Examples section below. More specifically, if the peak intensity ratio X is 0.20 or more, it is determined that the peak exists. The peak intensity ratio X may be preferably 0.25 or more, more preferably 0.30 or more. The higher the peak intensity ratio X, the better the dispersion state of the CNTs is considered to be. The upper limit of the peak intensity ratio X is not particularly limited, but may be, for example, 0.50 or less.

[0019] Carbon nanotubes Carbon nanotubes (CNTs) are carbon-based materials consisting of graphene sheets rolled into a cylindrical shape. Various types of CNTs are known, but they can be broadly classified into single-wall carbon nanotubes (SWCNTs), double-wall carbon nanotubes (DWCNTs), and multi-wall carbon nanotubes (MWCNTs) based on the number of walls. Furthermore, they can be classified into chiral (spiral), zigzag, and armchair types based on the structure of the graphene sheets. The physical properties of individual CNTs are said to be approximately 150 GPa in strength, 100,000 S / cm or more in conductivity, 0.9 TPa in Young's modulus, and 3,000 W / m·K in thermal conductivity.

[0020] Any type of carbon nanotube may be used as long as it is so-called CNT. For example, even if multi-walled carbon nanotubes (MWCNT) with three or more walls are contained, high electrical conductivity and specific conductivity can be achieved. The carbon nanotube is preferably at least one selected from the group consisting of single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT). Fibers with higher electrical conductivity can be obtained by using SWCNT and / or DWCNT as raw materials. The diameter of SWCNT and DWCNT is preferably 5 nm or less. From the viewpoint of obtaining fibers with higher electrical conductivity, the ratio of CNTs with a diameter of 5 nm or less among the CNTs is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and may even be 100%.

[0021] The spectrum obtained by resonance Raman scattering measurement of carbon nanotubes is 1550-1650 cm -1 The maximum peak intensity in the range of G is 1300-1400 cm -1 When the maximum peak intensity within this range is defined as D, the G / D ratio of the CNTs in the fiber may be 3 or more, preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more, for example, 40 or more, 50 or more, 60 or more, or 70 or more. The G / D ratio of the CNTs in the fiber may be 150 or less, for example, 140 or less, 130 or less, 120 or less, 110 or less, 100 or less, 90 or less, or 80 or less. -1 The peak in the range of 1300 to 1400 cm is called the G band and is a peak derived from the graphite structure. -1The peak within this range is called the D band and is a peak derived from lattice defects in amorphous carbon, graphene, or CNT. The relative occurrence rate of defects in graphene and CNT can be quantified using the G / D ratio. A G / D ratio of 3 or more for the CNTs in the fiber means that the fiber is composed of high-quality graphene or CNT with few lattice defects, and a fiber with high conductivity can be obtained. In particular, a G / D ratio of 10 or more, further 20 or more, or 30 or more means that the fiber is composed of higher-quality CNTs, resulting in a fiber with higher conductivity and superior thermal conductivity and heat resistance. The method for producing CNTs is not particularly limited.

[0022] <CNT content> The CNT content in the fiber is 50.0% by mass or more and 90.0% by mass or less, based on the total mass of the fiber. The lower limit of the CNT content may be, for example, 55.0% by mass or more, 60.0% by mass or more, 65.0% by mass or more, 70.0% by mass or more, 75.0% by mass or more, or 80% by mass or more. The upper limit of the CNT content may be, for example, 80.0% by mass or less, 75.0% by mass or less, 70.0% by mass or less, 65.0% by mass or less, or 60.0% by mass or less. By having the CNT content in the fiber in these ranges, the fiber can be suitably used for various applications. The CNT content in the fiber in the present application can be calculated from the CNT residual index obtained by dividing the weight of the fiber after sulfuric acid immersion described in the Examples by the weight of the fiber before sulfuric acid immersion and multiplying the result by 100, using the following formula: CNT content (mass%) = CNT residual index x 0.71 The value is defined by

[0023] <CNT orientation> The degree of orientation of the CNTs in the fiber is preferably 0.20 or more and 0.90 or less. The lower limit of the degree of orientation of the CNTs is more preferably 0.30 or more, even more preferably 0.40 or more, 0.50 or more, or more than 0.50. The upper limit of the degree of orientation of the CNTs may be, for example, 0.80 or less, or 0.70 or less. When the degree of orientation of the CNTs is 0.20 or more, it is easier to obtain fibers with high electrical conductivity due to the CNTs oriented in the longitudinal direction of the fiber. Furthermore, it is more preferable that the CNTs in the fiber have the above-mentioned G / D ratio of 3 or more and 150 or less, and an orientation degree of 0.20 or more and 0.90 or less. This allows type II cellulose crystals, which have the same orientation direction as the CNTs, to be wrapped around the surface of the CNTs oriented in the longitudinal direction of the fiber, thereby effectively reducing the strong intermolecular interaction between the CNTs and maintaining a certain distance between the CNTs. This is thought to enable fibers with a lower elastic modulus to be obtained even when the CNT concentration in the fiber is high.

[0024] <cellulose> Cellulose is a type of polysaccharide, a polymer in which many glucose units are linked in a linear chain by β-1,4-glycosidic bonds. Because cellulose has low water solubility and high water resistance, it has long been used in recycled fibers and paper.

[0025] Cellulose raw materials include so-called wood pulps such as softwood pulp and hardwood pulp, as well as non-wood pulps. Non-wood pulps include cotton-derived pulps such as cotton linter pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp. Cotton-derived pulp, hemp-derived pulp, bagasse-derived pulp, kenaf-derived pulp, bamboo-derived pulp, and straw-derived pulp refer to purified pulps obtained from raw materials such as cotton lint or cotton linter, hemp-based abaca (e.g., often produced in Ecuador or the Philippines), zaisal, bagasse, kenaf, bamboo, and straw, respectively, through a cooking treatment for delignification, a refining process for removing hemicellulose, and a bleaching process. In addition, purified products such as seaweed-derived cellulose and sea squirt cellulose can also be used as raw materials for cellulose fine fibers. Furthermore, cut yarns of regenerated cellulose fibers and cut yarns of cellulose derivative fibers can also be used as cellulose raw materials, and cut yarns of ultrafine regenerated cellulose or cellulose derivatives obtained by electrospinning can also be used as cellulose. Among these, refined pulp derived from cotton lint or cotton linter, hemp-based abaca, zaisal, bagasse, kenaf, bamboo, straw, etc. is particularly preferred.

[0026] Cellulose can be detected by common methods, such as spectral analysis using XRD or IR. Furthermore, if it can be decomposed with cellulase, it can be determined to be cellulose. The crystal structure of cellulose can be determined to be type II by observing the crystal structure specific to type II using wide-angle X-ray scattering.

[0027] The cellulose content of the fibers is more than 0% by mass and less than 50.0% by mass, based on the total mass of the fibers. From the viewpoint of easily obtaining fibers with a lower modulus while increasing the CNT concentration to achieve higher electrical conductivity, the lower limit of the cellulose content may more preferably be 10.0% by mass or more, 15.0% by mass or more, 20.0% by mass or more, 25.0% by mass or more, 30.0% by mass or more, 35.0% by mass or more, or 40.0% by mass or more. The upper limit of the cellulose content may preferably be 45.0% by mass or less, 40.0% by mass or less, 35.0% by mass or less, 30.0% by mass or less, 25.0% by mass or less, 20.0% by mass or less, 15.0% by mass or less, or 10.0% by mass or less.

[0028] <Fineness> The fiber may be a monofilament or a multifilament. When the fiber is a monofilament, the fineness (single yarn fineness) is preferably 0.5 dtex or more and 500 dtex or less, more preferably 1 dtex or more and 300 dtex or less, and even more preferably 1.5 dtex or more and 200 dtex or less. When the fiber is a multifilament, the single yarn fineness is preferably 0.5 dtex or more and 500 dtex or less, more preferably 1 dtex or more and 300 dtex or less, and even more preferably 1.5 dtex or more and 200 dtex or less.

[0029] When the fiber is a multifilament, the total fiber fineness is preferably 1.0 dtex or more and 1000 dtex or less, more preferably 5 dtex or more and 1000 dtex or less, even more preferably 10 dtex or more and 900 dtex or less, and even more preferably 20 dtex or more and 750 dtex or less. In the case of a monofilament, the single yarn fineness and the total fiber fineness are the same.

[0030] <Specific conductivity> The specific conductivity of the fiber is 1000 Scm 2 / g or more 6000Scm 2 / g or less. 2 / g or more 6000Scm 2 / g or less, the material can be suitably used in applications such as smart textiles. 2 / g or more, more preferably 2000 Scm 2 / g or more, and even more preferably 2500 Scm 2 / g or more. The upper limit of the specific conductivity is, for example, 5500 Scm 2 / g or less, or 5000Scm 2 / g or less.

[0031] <Elastic modulus> The elastic modulus of the fiber is preferably 10 GPa or more and 100 GPa or less. When the elastic modulus is 100 GPa or less, weaving and knitting properties are good. The lower limit of the elastic modulus of the fiber may be, for example, 15 GPa or more, or 20 GPa or more. The upper limit of the elastic modulus of the fiber may be, for example, 90 GPa or less, 80 GPa or less, 70 GPa or less, 60 GPa or less, 50 GPa or less, or 45 GPa or less.

[0032] <Breaking strength> The breaking strength of the fiber is preferably 50 MPa or more and 600 MPa or less. A breaking strength of 50 MPa or more results in good weaving and knitting properties. The lower limit of the breaking strength is more preferably 60 MPa or more, even more preferably 70 MPa or more, and even more preferably 80 MPa or more, for example, 100 MPa or more, 110 MPa or more, 120 MPa or more, 130 MPa or more, 140 MPa or more, 150 MPa or more, 160 MPa or more, or 170 MPa or more. The upper limit of the breaking strength may be, for example, 500 MPa or less, 400 MPa or less, 300 MPa or less, or 200 MPa or less. The elongation of the fiber at break may be 0.2% or more and 3.0% or less.

[0033] <Fiber Uses> The fibers of the present disclosure have high electrical conductivity and low elastic modulus, and therefore are not limited to specific applications, but can be suitably used as textiles. For example, the fibers of the present disclosure can be suitably used in smart textiles for electrodes for acquiring bioelectric potentials such as electrocardiograms, electromyograms, and electroencephalograms, electrodes for electrical stimulation, wiring for wearable devices, electromagnetic wave shielding materials, stretch sensors, humidity sensors, heaters, etc. "Smart textiles" refer to textile materials with new functions that cannot be obtained with ordinary textile materials, or textile materials that can obtain existing functions using new technology.

[0034] In smart textiles, highly conductive and flexible fibers are preferred, such as wearable wiring for connecting electronic devices. Wearable wiring requires high conductivity to reduce power loss during power transmission, and fibers with low elasticity and easy processability are preferred for incorporation into textiles.

[0035] <<Fiber manufacturing method>> The fiber manufacturing method includes the steps of dispersing more than 3.0 mass% but not more than 20.0 mass% carbon nanotubes (CNTs) in water to prepare a CNT dispersion, preparing a cellulose solution in which cellulose is dissolved in cuprammonium, mixing the CNT dispersion and the cellulose solution under predetermined conditions to prepare a mixed dispersion containing CNTs and cellulose, wet-spinning the mixed dispersion to obtain cellulose fibers containing CNTs, and drying the cellulose fibers to obtain fibers. The CNT dispersion and the cellulose solution are mixed under the conditions such that the mass ratio (mass of the CNT dispersion:mass of the cellulose solution) is 5:95 to 99:1.

[0036] The above production method can produce CNT-cellulose composite fibers with high electrical conductivity and low elastic modulus. The inventors speculate that the reason for this is as follows, without being limited by theory. Generally, to obtain fibers with high electrical conductivity, it is necessary to incorporate a high concentration of CNTs into the fibers. However, in this case, the strong intermolecular interactions between the CNTs in the fibers cause the CNTs to aggregate, resulting in a fiber with a high elastic modulus. Therefore, to obtain fibers with a low elastic modulus, it is preferable to reduce the strong intermolecular interactions between CNTs. However, spinning fibers with a high CNT concentration using a mixed dispersion containing CNTs and cellulose as a raw material is difficult for the following reasons. First, when spinning high-concentration CNT fibers by increasing the CNT concentration in the mixed dispersion, the cellulose concentration in the mixed dispersion decreases. A decrease in the cellulose concentration leads to poor spinnability, such as thread breakage, making spinning difficult. Furthermore, if the mass ratio of the CNT dispersion and cellulose solution to be kneaded is kept constant by increasing the CNT concentration in the CNT dispersion, which is the raw material for the mixed dispersion, CNT agglomerates occur due to poor dispersion, resulting in poor spinnability. In this regard, the present disclosure limits the CNT concentration in the CNT dispersion to more than 3.0 mass% and 20.0 mass% or less, and mixes the CNT dispersion and cellulose solution at a mass ratio of 5:95 to 99:1, thereby suppressing the generation of CNT agglomerates due to poor dispersion and preventing poor spinnability. Therefore, even if the CNT concentration of the resulting fiber is high, a uniform CNT network can be formed within the fiber, resulting in a CNT-cellulose composite fiber with high electrical conductivity and low elastic modulus.

[0037] <Preparation of CNT dispersion liquid> The CNT concentration in the CNT dispersion is greater than 3.0% by mass and less than or equal to 20.0% by mass. The lower limit of the CNT amount in the CNT dispersion is preferably greater than 3.0% by mass, for example, greater than or equal to 3.5% by mass, or greater than or equal to 4.0% by mass. The upper limit of the CNT amount in the CNT dispersion is preferably less than or equal to 15.0% by mass, more preferably less than or equal to 10.0% by mass, and even more preferably less than or equal to 8.0% by mass. A CNT concentration of greater than 3.0% by mass in the CNT dispersion makes it easier to adjust the CNT concentration of the resulting fibers to a high level, resulting in fibers with high electrical conductivity. Furthermore, a CNT concentration of 20.0% by mass or less in the CNT dispersion is believed to suppress the generation of CNT agglomerates due to poor dispersion and result in fibers with a low elastic modulus. The CNTs preferably used are those described above in the section on "Carbon Nanotubes."

[0038] CNTs can be dispersed in water. A dispersant may be used for the dispersion. The dispersant may be any of a nonionic surfactant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and an aromatic ring-containing compound.

[0039] Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, sorbitan fatty acid esters, sucrose fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, and polyoxyethylene polyoxypropylene block copolymers. Specific examples include poly(oxyethylene) octylphenyl ether (e.g., Triton (registered trademark) X-100) and polyoxyethylene sorbitan monolaurate (e.g., Tween (registered trademark) 20).

[0040] Examples of anionic surfactants include alkylbenzenesulfonates (e.g., sodium dodecylbenzenesulfonate, etc.), alkyl alcohol sulfates (e.g., sodium dodecyl sulfate, etc.), sodium alkyldiphenyletherdisulfonate, sodium polyoxyethylene alkylether sulfate, sodium dialkylsulfosuccinate, sodium alkylallyl sulfosuccinate, sodium N-lauroylsarcosine, sodium polyoxyethylene alkylphenylether sulfate, sodium (meth)acryloylpolyoxyalkylene sulfate, alkyl alcohol phosphates, and bile salts (e.g., sodium cholate, sodium deoxycholate, etc.), and preferred examples include bile salts such as sodium cholate.

[0041] From the viewpoint of improving electrical conductivity while maintaining high mechanical properties by reducing defects in the CNTs contained in the obtained fibers and uniformly dispersing the CNTs in the fibers, the surfactant is preferably a bile salt, more preferably sodium deoxycholate, and even more preferably sodium taurodeoxycholate. In particular, when using CNTs, sodium taurodeoxycholate is particularly preferred in order to suppress the occurrence of defects and obtain a CNT dispersion and composite fibers in which the CNTs are uniformly dispersed while maintaining their length.

[0042] Examples of cationic surfactants include tetraalkylammonium halides, alkylpyridinium halides, alkylimidazoline halides, etc. Examples of amphoteric surfactants include alkylbetaines, alkylimidazolinium betaines, lecithin, etc.

[0043] Examples of aromatic ring-containing compounds include naphthalene derivatives, anthracene derivatives, tetracene derivatives, phenanthrene derivatives, pyrene derivatives, acridine-containing compounds, and isoalloxazine-containing compounds.

[0044] The amount of dispersant in the CNT dispersion is preferably 3.0 mass % or more and 15 mass % or less, more preferably 3.0 mass % or more and 10.0 mass % or less, and even more preferably 3.0 mass % or more and 6.0 mass % or less.

[0045] The method for dispersing CNTs is not particularly limited. However, CNT dispersions have high viscosity due to the CNT network formed in the liquid, making them prone to the incorporation of air bubbles. Furthermore, depending on the kneading method, CNTs may be destroyed and the G / D ratio may decrease. In this regard, in the present disclosure, a media-less disperser that does not use media such as balls or beads is preferably used to suppress the incorporation of air bubbles and the generation of aggregates during CNT dispersion. Furthermore, from the viewpoint of suppressing the decrease in G / D ratio of CNTs, it is preferable to use a disperser that causes less damage to CNTs. Examples of such dispersers include a roll mill and a nanovater. Furthermore, a multi-stage dispersion process is preferably performed, including dispersing CNTs at a first shear force and then dispersing CNTs at a second shear force higher than the first high shear force. For example, by pre-dispersing CNTs using a three-roll mill and then performing the main dispersion at high shear using a nanovater while adjusting the conditions, a CNT dispersion suitable for spinning can be prepared while suppressing the decrease in G / D ratio.

[0046] <Preparation of cellulose solution> Many solvent systems that dissolve cellulose are generally known. Examples of such dissolution systems include cuprammonium dissolution systems, viscose dissolution systems, 4-methylmorpholine N-oxide / water systems, dimethyl sulfoxide / carbon disulfide / amine systems, dimethylformamide / nitrogen tetroxide systems, dimethyl sulfoxide / paraformaldehyde systems, dimethylformamide / chloral / pyridine systems, N-ethylpyridinium chloride systems, dimethylacetamide / lithium chloride systems, hydrazine systems, trifluoroacetic acid / dichloromethane systems, formic acid / lithium chloride systems, urea / sodium hydroxide / water systems, liquid ammonia / ammonium thiocyanate systems, calcium thiocyanate / water systems, zinc chloride / water systems, dimethylformamide / sulfur trioxide systems, aqueous sulfuric acid systems, sulfuric acid / polyphosphoric acid / water systems, caustic soda / water systems, dimethyl sulfoxide / tetrabutylammonium acetate systems, 1-ethyl-3-methylimidazolium diethylphosphate systems, and 1-ethyl-3-methylimidazolium acetate systems.

[0047] In the fiber manufacturing method, preferred are cuprammonium dissolution systems, viscose dissolution systems, 4-methylmorpholine N-oxide / water systems, sulfuric acid / water systems, sulfuric acid / polyphosphoric acid / water systems, caustic soda / water systems, dimethyl sulfoxide / tetrabutylammonium acetate systems, 1-ethyl-3-methylimidazolium diethylphosphate systems, and 1-ethyl-3-methylimidazolium acetate systems. More preferred are cuprammonium dissolution systems, viscose dissolution systems, 4-methylmorpholine N-oxide / water systems, caustic soda / water systems, dimethyl sulfoxide / tetrabutylammonium acetate systems, 1-ethyl-3-methylimidazolium diethylphosphate systems, and 1-ethyl-3-methylimidazolium acetate systems. Most preferred is the cuprammonium dissolution system.

[0048] The concentration of each component in the solvent for dissolving cellulose is determined by the combination of the solvent, additive, and cellulose, and can be set to any desired concentration. The cellulose concentration in the cellulose solution is preferably 1.0% by mass or more and 30.0% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less. When the cellulose concentration in the cellulose solution is 1.0% by mass or more and 30.0% by mass or less, deterioration of spinnability can be further suppressed.

[0049] <Preparation of Mixed Dispersion> By mixing the CNT dispersion obtained above with the cellulose solution, a mixed dispersion (spinning dope) in which CNT and cellulose are uniformly kneaded can be obtained.

[0050] The mixing conditions are preferably controlled by controlling at least one condition selected from the group consisting of oxygen concentration, degree of vacuum (pressure), and liquid temperature (temperature of the mixed liquid). For example, the oxygen concentration is preferably 1000 ppm or less. The degree of vacuum is preferably -0.1 MPa or more and -0.01 MPa or less. The liquid temperature is preferably 20°C to 40°C. By satisfying at least one of these conditions, it becomes easier to uniformly disperse CNTs in the resulting fibers. Without being limited by theory, in the process of mixing the CNT dispersion and the cellulose solution, the mixed dispersion has high viscosity due to the CNT network and cellulose formed in the liquid, and air bubbles are easily mixed in. Furthermore, when components contained in the solution, such as ammonia, volatilize, cellulose aggregates are generated, which makes it easy for foreign matter to be contained, making spinning difficult. In this regard, reducing the oxygen concentration during kneading reduces cellulose decomposition by oxygen and suppresses the generation of foreign matter associated with decomposition. Furthermore, by controlling the degree of pressure reduction, degassing by pressure reduction can be promoted, and volatilization of components contained in the dissolution system due to excessive pressure reduction can be suppressed, thereby suppressing the generation of aggregates. Furthermore, by controlling the temperature during kneading, volatilization of components contained in the dissolution system can be suppressed, and degassing can be promoted by adjusting the viscosity of the cellulose solution.

[0051] The mass ratio of the CNT dispersion to the cellulose solution when mixed (mass of CNT dispersion:mass of cellulose solution) is preferably 5:95 to 99:1. In addition to the CNT concentration in the CNT dispersion being greater than 3.0 mass% and not more than 20.0 mass%, a mass ratio within the range of 5:95 to 99:1 makes it easier to uniformly disperse the CNTs in the resulting fibers. From a similar perspective, it is more preferable to adjust the cellulose concentration in the cellulose solution to one of the above-mentioned preferred ranges. The mass ratio of the CNT dispersion to the cellulose solution is more preferably 50:50 to 99:1, even more preferably 50:50 to 95:5, even more preferably 60:40 to 95:5, and particularly preferably 70:30 to 90:10.

[0052] The concentration of cellulose contained in the mixed dispersion is preferably 0.1% by mass or more and 20% by mass or less, based on the total mass of the mixed dispersion. The lower limit of the concentration of cellulose contained in the mixed dispersion is more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. The upper limit of the concentration of cellulose contained in the mixed dispersion is more preferably 15% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less. The concentration of CNT contained in the mixed dispersion is preferably 0.1% by mass or more and 50% by mass or less, based on the total mass of the mixed dispersion. The lower limit of the concentration of CNT contained in the mixed dispersion may be, for example, 0.5% by mass or more, 1.0% by mass or more, 2.0% by mass or more, or 3.0% by mass or more. The upper limit of the concentration of CNT contained in the mixed dispersion may be, for example, 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, 8% by mass or less, or 6% by mass or less. The concentration of CNT contained in the mixed dispersion is correlated with the CNT residual index in the fiber, and the mass percentage of CNT relative to the total mass of the fiber can be calculated by multiplying the CNT residual index by 0.71.

[0053] The CNT concentration (also referred to as the CNT concentration) based on the total mass of CNT and cellulose in the mixed dispersion is preferably 50.0% by mass or more and 90.0% by mass or less. The lower limit of the CNT concentration may be, for example, 55.0% by mass or more, 60.0% by mass or more, 65.0% by mass or more, 70.0% by mass or more, 75.0% by mass or more, or 80% by mass or more. The upper limit of the CNT concentration may be, for example, 80.0% by mass or less, 75.0% by mass or less, 70.0% by mass or less, 65.0% by mass or less, or 60.0% by mass or less. By having the CNT concentration in these ranges, it is easy to adjust the mass% of CNT relative to the total mass of the fiber to within the preferred range of the present application.

[0054] <Wet spinning process> CNT-containing cellulose fibers can be obtained by wet-spinning the mixed dispersion. Typically, the mixed dispersion is discharged into a coagulation bath from a syringe, spinneret, or the like during the spinning process, producing a composite gel containing CNTs and cellulose in the form of a thread (hereinafter simply referred to as the "composite gel"). In the spinning process, the composite gel is preferably continuously withdrawn from the coagulation bath to prevent it from loosening. The diameter of the syringe, spinneret, or the like used for discharging is preferably 5 μm to 5,000 μm, more preferably 10 μm to 3,000 μm, and even more preferably 15 μm to 1,000 μm. Adjusting this diameter allows for adjustment of the coagulation rate and fiber diameter. The dispersion is discharged directly from the spinneret into the coagulation bath in the direction of gravity or perpendicular to gravity. The direction is changed using a deflection roll or deflection rod, and the composite gel is continuously withdrawn from the coagulation bath by a rotating roll such as a Nelson roll. When the dispersion is discharged in the direction of gravity, it may also be discharged from the spinneret into the coagulation bath via the air. Alternatively, the syringe or spinneret may be submerged in the bottom of the coagulation bath and the composite gel may be extruded in the direction of a rotating roll that pulls the composite gel out of the coagulation bath. In either case, it is preferable that the fibrous composite gel is continuously pulled out of the coagulation bath so that it does not slacken. The composite gel may also be stretched in the coagulation bath.

[0055] The solvent for the coagulation bath is preferably water. Acids and salts may be added to the water used in the coagulation bath. If the cellulose type, one of the components constituting the fiber, does not contain acids or salts, the fibrous composite gel cannot be coagulated so that it can be continuously pulled up from the coagulation bath without loosening. Examples of acids include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid; carboxylic acids such as formic acid, acetic acid, benzoic acid, citric acid, and oxalic acid; and organic acids such as sulfonic acids such as toluenesulfonic acid. The salts may be either inorganic or organic, but inorganic salts are preferred. The salts are water-soluble. The salts are preferably alkali metal salts or alkaline earth metal salts, more preferably sodium salts, potassium salts, lithium salts, calcium salts, magnesium salts, barium salts, and strontium salts, and even more preferably sodium salts, calcium salts, and magnesium salts. Examples of anions of salts include chloride ions, fluoride ions, bromide ions, iodide ions, sulfate ions, sulfite ions, phosphate ions, nitrate ions, nitrite ions, methanesulfonate ions, benzenesulfonate ions, toluenesulfonate ions, citrate ions, oxalate ions, malate ions, tartrate ions, maleate ions, fumarate ions, and acetate ions.

[0056] Preferred salts include sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride, sodium bromide, potassium bromide, calcium bromide, magnesium bromide, sodium sulfate, potassium sulfate, sodium nitrate, potassium nitrate, calcium nitrate, magnesium nitrate, sodium acetate, calcium acetate, sodium phosphate, disodium monohydrogen phosphate, monosodium dihydrogen phosphate, sodium phosphate, disodium monohydrogen phosphate, monosodium dihydrogen phosphate, potassium phosphate, dipotassium monohydrogen phosphate, monopotassium dihydrogen phosphate, potassium phosphate, dipotassium monohydrogen phosphate, monopotassium dihydrogen phosphate, and the like.

[0057] In another embodiment, the solvent for the coagulation bath may be an organic solvent. The organic solvent in the coagulation bath is preferably a water-miscible organic solvent, such as lower alcohols such as ethanol, methanol, propanol, and isopropanol; ketones such as acetone, methyl ethyl ketone, and 4-methyl-2-pentanone (MIBK); ethers such as tetrahydrofuran and dioxane; esters such as propylene carbonate; amides such as dimethylformamide, acetamide, formamide, dimethylacetamide, N-methylpyrrolidone, and 1,3-dimethyl-2-imidazolidinone; glycols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and glycerin; alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether; dimethyl sulfoxide; and acetonitrile. The solvent for the coagulation bath is preferably a water-containing organic solvent. Even when an organic solvent is used as the coagulation bath, salts can be added to the coagulation bath.

[0058] The concentration of the salts added to the coagulation bath is preferably 0% by mass or more and 40% by mass or less, preferably 0% by mass or more and 35% by mass or less, and more preferably about 0% by mass or less and 30% by mass or less. The salts are dissolved in the coagulation bath either alone or in combination of two or more kinds of salts.

[0059] The temperature of the coagulation bath is not particularly limited, but is determined by the combination of salts and salt concentrations so that the fibrous composite gel is in a coagulated state in which it can be continuously pulled up from the coagulation bath without loosening. A temperature of 5°C to 80°C is preferred from the viewpoint of ease of temperature control.

[0060] The immersion time of the discharged composite gel in the coagulation bath varies depending on the conditions of the coagulation bath, and is not particularly limited as long as the fibrous composite gel is in a coagulated state in which it can be continuously pulled up from the coagulation bath without loosening. The coagulation bath may be a stationary bath or a fluidized bath using a tube or the like.

[0061] The fibrous composite gel removed from the coagulation bath can be further immersed in water or the same organic solvent as used in the coagulation bath to wash away the surfactant, transition metals, and salts. When a transition metal is used, it is preferable to wash using an acid with a pH of 3 or less. The temperature of the water or organic solvent in this washing step is not particularly limited, but can be, for example, 5°C to 80°C, preferably around room temperature. The immersion time is also not particularly limited, but can be, for example, 2 hours or more, preferably 24 hours or more. This water immersion step allows for the production of CNT-containing fibers from which the surfactant, or the surfactant, transition metal, and salts have been appropriately removed.

[0062] The fibrous composite gel may be subjected to the subsequent stretching step in a wet state. Stretching is performed between rotating rolls such as Nelson rolls, with the stretching occurring at different rotation speeds. The stretching ratio is preferably between 5% and 500%, more preferably between 10% and 300%. This promotes the alignment of CNTs in the fiber along the fiber axis and the orientation of cellulose, improving electrical and mechanical properties. The stretching ratio is defined by the following formula: Stretching ratio (%)= [{(length after stretching) - (length before stretching)} / (length before stretching)] x 100

[0063] After drawing, the obtained fibers may be further washed with water or the same organic solvent as used in the coagulation bath, if necessary.

[0064] <Drying process> After wet spinning, the resulting fibers can be dried to obtain fibers containing CNTs. When drying, the resulting fibers may be heated as needed. The heating temperature may be determined depending on the type of cellulose and is not limited. When a polysaccharide is used, the heating temperature may be, for example, 100°C or higher and 300°C or lower, or 150°C or higher and 250°C or lower. [Example]

[0065] The present disclosure will be specifically described below using examples and comparative examples. However, the present disclosure is not limited to the following examples. The physical properties of the fibers were measured and evaluated as follows.

[0066] <<Measurement and Evaluation Methods>> [Content of CNTs with a diameter of 5 nm or less] The percentage of CNTs with diameters of 5 nm or less was determined by observation using a transmission electron microscope at 200,000 to 1,000,000 magnifications, which allows the diameter of a single CNT to be measured by image analysis. One hundred locations were selected from the field of view where the CNT bundles had loosened and single CNTs existed. The diameters of these 100 CNTs were evaluated using image analysis software, and the number of CNTs with diameters of 5 nm or less was counted to determine the percentage of CNTs with diameters of 5 nm or less. In this case, if a portion of a CNT present in a single state in the field of view is visible, it is counted as one CNT; both ends (the entire CNT) do not necessarily have to be visible. Furthermore, even if two CNTs are recognized in the field of view, they may be connected outside the field of view to form a single CNT, in which case they are counted as two CNTs.

[0067] [Fineness] The single yarn fineness and total fineness were measured as follows. The spun fiber was left to stand in an environment of 23°C and 50.5% RH for at least 24 hours, and then a 10 m sample was measured. The weight of the sample was measured using a precision balance (XPE205) manufactured by METTLER TOLEDO. The single yarn fineness and total fineness were measured by calculating the weight per 10,000 m from the weight.

[0068] [Specific conductivity] The specific conductivity was calculated using the four-terminal method by measuring the voltage when a specified current was applied to the fiber. The voltage was measured and calculated from the resistance value obtained from the slope of the current-voltage curve and the weight of the fiber. Ten test pieces were taken from the fiber and repeatedly measured using a potentio-galvanostat (Biologic, SP-50) measuring jig with a fixed terminal distance of 5.6 cm to obtain resistance values. The linear resistance (resistance per cm) was calculated using the obtained resistance value and the distance between the terminals of the measuring jig, and the reciprocal of the linear resistance was calculated by taking its reciprocal. The weight of the fiber per 10 m was measured using a precision balance (METTLER TOLEDO, XPE205), and the weight per cm was calculated from the weight and length. Finally, the specific conductivity was calculated by dividing the reciprocal of the linear resistance by the weight per cm. On the other hand, for fibers with a resistance value per 1 cm exceeding 10,000 Ω, the resistance value at 1 cm between the terminals was calculated using a resistance meter (HIOKI, RM3544). For fibers with a resistance value per 1 mm exceeding 3.5 MΩ, the linear resistance was calculated as 35 MΩ or more, and the specific conductivity was calculated as the reciprocal of the linear resistance of 35 MΩ divided by the mass per 1 cm.

[0069] [Measurement of CNT residual index and calculation of CNT content] The fibers were dried in an oven (AVO-250SB, AS ONE Corporation) at 105°C in the atmosphere for 5 hours, and then their weight was measured using a precision balance (XPE205, METTLER TOLEDO). After the weight measurement, the fibers were immersed in 95% sulfuric acid in the atmosphere at room temperature for 72 hours. After the sulfuric acid immersion, water replacement and water immersion were performed, and the fibers were then dried in an oven at 105°C in the atmosphere for 5 hours, and their weight was measured. The CNT residual index was calculated by dividing the weight of the fibers after sulfuric acid immersion by the weight of the fibers before sulfuric acid immersion and multiplying the result by 100. The CNT content was calculated using the following formula: CNT content (mass%) = CNT residual index x 0.71 is defined as:

[0070] [Breaking strength and elongation] The breaking strength was measured in accordance with the test method for tensile strength and elongation of JIS L 1013. More specifically, stress-strain measurements were performed, and the strength (cN / dtex) was calculated from the stress at the breaking position and the fineness. The elongation is the elongation (%) at break.

[0071] Elasticity Modulus The elongation-stress curve was measured according to JIS-L-1013. The stress at each point on the obtained elongation-stress curve was differentiated by the elongation to determine the elastic modulus.

[0072] [Wide-angle X-ray scattering spectrum measurement method] Using an X-ray diffractometer (Rigaku NANOPIX), the fiber was set so that the fiber axis was oriented in the equatorial direction, and a diffraction curve was drawn from a diffraction angle 2θ of 5 to 35 degrees. The measurement conditions are as follows: ·Incoming X-ray wavelength 0.154nm Detector: HyPix-6000 (2D semiconductor detector) Measurement time: 30 minutes Camera length: 86.1mm Point collimation: 1st slit: 0.55mmφ, guard slit: 0.35mmφ Beam stopper: 2mmφ When the structure is oriented, the X-ray scattering pattern becomes anisotropic. Instead of a circular average, which takes an average over all azimuthal angles φ, we used a fan-shaped average Iφs<φ<φe(2θ), which takes an average only for scattering at a specific azimuthal angle. Iφs<φ<φe(2θ) refers to the fan-shaped average in the azimuthal angle range φs<φ<φe, and is calculated using the following formula (1). The fan-shaped average range was ±10°. The azimuthal angle φ was defined clockwise, with the 12 o'clock direction of the 2D scattering pattern being set to 0°. Empty cell correction was also performed.

[0073]

number

[0074] [How to confirm the peak at a diffraction angle of 2θ=13° in wide-angle X-ray scattering] Cellulose crystals oriented in the fiber axis direction in cellulose fibers can be confirmed as a peak near 2θ = 13° on the WAXS spectrum obtained by performing sector averaging based on the above formula (1). The presence of the peak near 2θ = 13° can be confirmed by the following method. First, the WAXS profile obtained by performing sector averaging based on the above formula (1) is fitted with a function that combines a background assumed to be linear in the range of 10° < 2θ < 17° and a Lorentzian function, and the peak intensity I (1-10) The peak position is determined. A line is drawn connecting the two points at 2θ = 10 deg and 2θ = 17 deg, and the value at the determined peak position is taken as the background intensity I (1-10)B The intensity ratio X of the obtained peaks is calculated using the following formula (2). If X is 0.20 or more, it can be confirmed that there is a peak near 2θ=13°. Note that, because the way to draw the line is uniquely defined as above, the peak intensity ratio X may be a negative value, in which case it is determined that there is no peak. X=[I (1-10) -I (1-10)B ] / I (1-10) ···(2) FIG. 1 is an example of an X-ray measurement chart having a peak in the range of diffraction angle 2θ of 10° or more and 17° or less, and FIG. 2 is an example of an X-ray measurement chart having no peak in the range of diffraction angle 2θ of 10° or more and 17° or less.

[0075] [G / D] The G / D of the CNTs in the fiber was measured using a confocal Raman microscope (Renishaw inVia) TM The Raman spectrum was measured at 10 points with an excitation wavelength of 532 nm, and the peak intensity was 1593 ± 5 cm -1 The area of ​​the G band peak fitted in the range of 1345±10cm -1The ratio of the area of ​​the D band obtained by peak fitting within the range was calculated for 10 points, and G / D was calculated from the average value.

[0076] [CNT orientation in fiber] Confocal Raman microscope (Renishaw inVia TM The degree of CNT orientation in the fiber was evaluated using a 532 nm circularly polarized light source. The resulting Raman signal was detected by detecting the polarization components parallel and perpendicular to the fiber. Parallel and perpendicular Raman spectra were obtained for 10 points, and the areas of the G bands calculated by peak fitting in the same manner as above were calculated as I G(0) , I G(90) The degree of orientation is then (I G(0) -I G(90) / (I G(0) +I G(90) The degree of orientation was calculated from the average value of 10 points calculated by

[0077] Examples and Comparative Examples [Example 1] 40 g of Tuball-CNT (Tuball, manufactured by OCSiAl; hereafter also referred to as Tuball-CNT) and 40 g of sodium taurodeoxycholate (TDOC, manufactured by Sigma-Aldrich) as a dispersant were added to 920 g of water, and the mixture was processed in two passes using a three-roll mill (BR-150VIII, manufactured by Imex Co., Ltd.) with the motor rotation speed set to 300 rpm, the gap between the feed roll and the intermediate roll set to 40 μm, and the gap between the intermediate roll and the finishing roll set to 10 μm. Next, the mixture was filtered through a 0.3 mm plain-woven stainless steel mesh to remove coarse CNTs. Thereafter, a 0.2 mm diameter nozzle was attached to a Nanovater (manufactured by Yoshida Kikai Kogyo Co., Ltd.), and the filtered dispersion was subjected to 20-pass dispersion treatment at 100 MPa, followed by degassing for 30 minutes using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro ARE-310), to obtain a Tuball-CNT dispersion with a Tuball-CNT weight concentration of 4.0 mass%.

[0078] Copper hydroxide was dissolved in a 6.1% by mass aqueous ammonia solution so that the copper content was 3.6% by mass, and cellulose was added thereto so that the content was 10.15% by mass, followed by kneading to prepare a cuprammonium cellulose solution.

[0079] The inside of a flask equipped with a stirring unit was purged with nitrogen to adjust the oxygen concentration to 992 ppm, and then the above Tuball-CNT dispersion and cuprammonium cellulose solution were mixed at a mass ratio (mass of Tuball-CNT dispersion:mass of cuprammonium cellulose solution) of 80:20, and the Tuball-CNT concentration (CNT concentration in the entire fiber calculated from the charged amount, denoted as "charged CNT concentration" in the table) based on the total mass of Tuball-CNT and cellulose was 61.2 mass%, and then charged into the flask. The inside of the flask was adjusted to -0.08 MPa and 30°C, and the mixture was kneaded with a helical ribbon impeller for 5 hours, and then left to stand for 10 hours to degas, yielding a uniform Tuball-CNT / cuprammonium cellulose dispersion.

[0080] This Tuball-CNT / cuprammonium cellulose dispersion was used for wet spinning. A spinneret with a 0.2 mm hole diameter and one hole was used as a spinning nozzle. The dispersion was extruded in the direction of gravity at a rate of 0.23 ml / min while the spinneret was immersed in a coagulation bath filled with 40°C warm water. After coagulation, the yarn was deflected by a rotating roll in the warm water and then lifted out of the water bath using a rotating roll traveling at 3.0 m / min. A washing treatment was then performed by running the yarn through a 2.0% by mass sulfuric acid bath at 40°C and a water bath at 40°C in that order. The resulting coagulated yarn was then dried in a dryer at 200°C and wound up at a speed of 3.0 m / min to obtain a Tuball-CNT / cellulose composite fiber.

[0081] [Example 2] A Tuball-CNT dispersion and a cuprammonium cellulose solution were obtained in the same manner as in Example 1, except that the Tuball-CNT dispersion and the cuprammonium cellulose solution were kneaded at a mass ratio of 85:15 to give a Tuball-CNT concentration of 69.1 mass% relative to the cellulose. Spinning was performed under the same conditions as in Example 1, and a Tuball-CNT / cellulose composite fiber was obtained.

[0082] [Example 3] A Tuball-CNT dispersion and a cuprammonium cellulose solution were obtained in the same manner as in Example 1, except that the Tuball-CNT dispersion and the cuprammonium cellulose solution were kneaded at a mass ratio of 90:10 to give a Tuball-CNT concentration of 78.0 mass% relative to the cellulose. Spinning was performed under the same conditions as in Example 1, and a Tuball-CNT / cellulose composite fiber was obtained.

[0083] [Example 4] Dispersion was carried out in the same manner as in Example 1, except that 50 g of Tuball-CNT and 50 g of TDOC were added to 900 g of water, to obtain a Tuball-CNT dispersion with a Tuball-CNT weight concentration of 5.0 mass%. The Tuball-CNT dispersion and the cuprammonium cellulose solution were kneaded in a mass ratio of 70:30, to obtain a Tuball-CNT dispersion and a cuprammonium cellulose solution in the same manner as in Example 1, except that the Tuball-CNT concentration relative to the cellulose was 53.4 mass%.

[0084] This Tuball-CNT / cuprammonium cellulose dispersion was used for wet spinning. A spinneret with a 0.15 mm hole diameter and 10 holes was used as a spinning nozzle. The dispersion was extruded in the direction of gravity at a rate of 0.72 ml / min while the spinneret was immersed in a coagulation bath filled with 40°C warm water. After coagulation, the yarn was deflected by a rotating roll in the warm water and then lifted from the water bath using a rotating roll traveling at 5.6 m / min. A washing treatment was then performed by running the yarn through a 40°C 2.0% by mass sulfuric acid bath and a 40°C water bath, in that order. The resulting coagulated yarn was then dried in a dryer at 200°C and wound up at a speed of 5.6 m / min to obtain a Tuball-CNT / cellulose composite fiber.

[0085] [Example 5] A Tuball-CNT dispersion and a cuprammonium cellulose solution were obtained in the same manner as in Example 4, except that the Tuball-CNT dispersion and the cuprammonium cellulose solution were kneaded in a mass ratio of 85:15 to give a Tuball-CNT concentration of 73.6 mass% relative to the cellulose.

[0086] This Tuball-CNT / cuprammonium cellulose dispersion was used for wet spinning. A spinneret with a 0.15 mm hole diameter and 10 holes was used as a spinning nozzle. The dispersion was extruded in the direction of gravity at a rate of 1.44 ml / min while the spinneret was immersed in a coagulation bath filled with 40°C warm water. After coagulation, the yarn was deflected by a rotating roll in the warm water and then lifted from the water bath using a rotating roll traveling at 10.3 m / min. A washing treatment was then performed by running the yarn through a 40°C 2.0% by mass sulfuric acid bath and a 40°C water bath, in that order. The resulting coagulated yarn was then dried in a dryer at 200°C and wound up at a speed of 10.3 m / min to obtain a Tuball-CNT / cellulose composite fiber.

[0087] [Example 6] Dispersion was carried out in the same manner as in Example 1, except that 60 g of Tuball-CNT and 60 g of TDOC were added to 880 g of water, to obtain a Tuball-CNT dispersion with a Tuball-CNT weight concentration of 6.0 mass%. The Tuball-CNT dispersion and the cuprammonium cellulose solution were kneaded in a mass ratio of 90:10, to obtain a Tuball-CNT dispersion and a cuprammonium cellulose solution in the same manner as in Example 1, except that the Tuball-CNT concentration relative to the cellulose was 84.2 mass%.

[0088] This Tuball-CNT / cuprammonium cellulose dispersion was used for wet spinning. A spinneret with a 0.15 mm hole diameter and 10 holes was used as a spinning nozzle. The dispersion was extruded in the direction of gravity at a rate of 0.72 ml / min while the spinneret was immersed in a coagulation bath filled with 40°C warm water. After coagulation, the yarn was deflected by a rotating roll in the warm water and then lifted from the water bath using a rotating roll traveling at 5.6 m / min. A washing treatment was then performed by running the yarn through a 40°C 2.0% by mass sulfuric acid bath and a 40°C water bath, in that order. The resulting coagulated yarn was then dried in a dryer at 200°C and wound up at a speed of 5.6 m / min to obtain a Tuball-CNT / cellulose composite fiber.

[0089] [Comparative Example 1] Dispersion was carried out in the same manner as in Example 1, except that 30 g of Tuball-CNT and 30 g of TDOC were added to 940 g of water, to obtain a Tuball-CNT dispersion with a Tuball-CNT weight concentration of 3.0 mass%. The Tuball-CNT dispersion and the cuprammonium cellulose solution were kneaded in a mass ratio of 67:33, to obtain a Tuball-CNT dispersion and a cuprammonium cellulose solution in the same manner as in Example 1, except that the Tuball-CNT concentration relative to the cellulose was 37.2 mass%. Spinning was carried out under the same conditions as in Example 4, to obtain a Tuball-CNT / cellulose composite fiber.

[0090] Comparative Example 2 Dispersion was performed in the same manner as in Example 1, except that 30 g of Tuball-CNT and 30 g of TDOC were added to 940 g of water, to obtain a Tuball-CNT dispersion with a Tuball-CNT weight concentration of 3.0 mass%. The Tuball-CNT dispersion and the cuprammonium cellulose solution were kneaded in a mass ratio of 80:20, to obtain a Tuball-CNT dispersion and a cuprammonium cellulose solution in the same manner as in Example 1, except that the Tuball-CNT concentration relative to the cellulose was 53.1 mass%. Spinning was performed under the same conditions as in Example 4, but thread breakage occurred and threads could not be obtained.

[0091] Comparative Example 3 A 100% CNT fiber (manufactured by DexMat, hereinafter also referred to as DexMat) was coated by running it through a cuprammonium cellulose solution bath with the same composition as in Example 1 at 1.0 m / min. The fiber was then pulled out of the bath using a rotating roll and then fed into a coagulation bath filled with warm water at 40°C using a rotating roll at 1.1 m / min. After coagulation, the fiber was deflected using a rotating roll in the warm water and then pulled out of the hot water bath using a rotating roll running at 1.1 m / min. The fiber was then washed by running it through a 2.0% by mass sulfuric acid bath at 40°C and then a water bath at 40°C. The resulting coagulated fiber was then dried in a dryer at 200°C to obtain a cellulose-coated CNT fiber with a CNT concentration of 55.6% by mass.

[0092] Comparative Example 4 Wet spinning was performed using a cuprammonium cellulose solution in the same manner as in Example 1. A spinning nozzle with a 0.15 mm hole diameter and 10 holes was used as a spinning nozzle. The dispersion was discharged in the direction of gravity at a rate of 1.44 ml / min while the spinning nozzle was immersed in a coagulation bath filled with 40°C warm water. After coagulation, the yarn was deflected by a rotating roll in the warm water and then lifted from the hot water bath using a rotating roll traveling at 10.3 m / min. A washing process was then performed by running the yarn through a 2.0% by mass sulfuric acid bath at 40°C and a water bath at 40°C. The resulting coagulated yarn was then dried in a dryer at 200°C and wound up at a speed of 10.3 m / min to obtain cellulose fiber.

[0093] 10 g of Tuball-CNT and 20 g of TDOC as a dispersant were added to 970 g of water, and the mixture was dispersed for 10 hours using an in-line mixer (IKA, magic LAB). After that, a degassing operation was carried out for 10 minutes using a planetary centrifugal mixer, and a Tuball-CNT dispersion liquid with a Tuball-CNT weight concentration of 1.0 mass% was obtained.

[0094] The cellulose fibers obtained above were coated by running them through a 1.0% by mass Tuball-CNT dispersion bath at 1.0 m / min, then pulled out of the bath using a rotating roll, and then sent out at 1.1 m / min using a rotating roll into a coagulation bath filled with 1,3-dimethyl-2-imidazolidinone at 25°C. After coagulation, the fibers were turned using a rotating roll in warm water, then pulled out of the coagulation bath using a rotating roll running at 1.1 m / min, and then washed by running the fibers through a 40°C water bath. The resulting coagulated fibers were then dried in a dryer at 200°C to obtain CNT-coated cellulose fibers with a CNT concentration of 19.6% by mass.

[0095] Comparative Example 5 The raw material used was 20 g of CNTs (Zeonano, manufactured by Zeon Corporation, hereafter referred to as SG) produced by the super-growth method, and 40 g of sodium taurodeoxycholate (TDOC, manufactured by Sigma-Aldrich) as a dispersant, added to 940 g of water, and the mixture was dispersed for 10 hours using an in-line mixer. After that, the mixture was degassed for 10 minutes using a planetary mixer, yielding an SG-CNT dispersion with a weight concentration of 2.0 mass% SG-CNT.

[0096] An SG-CNT dispersion and a cuprammonium cellulose solution were obtained in the same manner as in Example 1, except that the SG-CNT dispersion and the cuprammonium cellulose solution were mixed in a mass ratio of 85:15 to give an SG-CNT concentration of 52.8 mass% relative to the cellulose. Spinning was performed under the same conditions as in Example 1 to obtain SG-CNT / cellulose composite fibers.

[0097] The physical properties of the conjugate fibers obtained in the examples and comparative examples are shown in the following Table 1. In Table 1, the symbol "-" for each physical property value indicates that the value was not measured.

[0098] [Table 1]

[0099] The CNT concentration in the entire fiber calculated from the charge amount in the examples (charge amount CNT concentration), the carbon nanomaterial residual index, and the CNT concentration in the fiber calculated from the carbon nanomaterial residual index are shown in Table 2. Figure 3 is a graph showing the relationship between the CNT concentration in the entire fiber calculated from the charge amount in the examples (charge amount CNT concentration) and the CNT residual index.

[0100] [Table 2] [Industrial Applicability]

[0101] The fibers of the present disclosure have high electrical conductivity and low elastic modulus, and are therefore suitable for components used in applications such as electrodes for acquiring bioelectric potentials such as electrocardiograms, electromyograms, and electroencephalograms in smart textiles, electrodes for electrical stimulation, wiring for wearable devices, heaters, stretch sensors, temperature and humidity sensors, electromagnetic shielding, anti-static agents, filters, etc.

Claims

1. A fiber comprising cellulose and carbon nanotubes dispersed in the cellulose, the G / D of the carbon nanotubes is 3 or more and 150 or less; The fibers contain more than 50.0 mass % and 90.0 mass % or less of the carbon nanotubes, based on the total mass of the fibers.

2. 2. The fiber according to claim 1, wherein the fiber has a peak in the diffraction angle 2θ range of 10° or more and 17° or less in wide-angle X-ray scattering measured by setting the fiber so that the fiber axis is oriented in the equator direction.

3. The fiber according to claim 1 or 2, wherein the degree of orientation of the carbon nanotubes in the fiber is 0.20 or more and 0.90 or less.

4. The specific conductivity of the fiber is 1000 Scm ２ / g or more 6000Scm ２ The fiber according to claim 1 or 2, wherein the fiber has a viscosity of 1 / g or less.

5. The fiber according to claim 1 or 2, wherein the fiber has an elastic modulus of 10 GPa or more and 100 GPa or less.

6. The fiber according to claim 1 or 2, wherein the G / D of the carbon nanotubes is 30 or more and 150 or less.

7. 1. A method for producing a fiber, the method comprising: preparing a carbon nanotube dispersion in which more than 3.0 mass % and not more than 20.0 mass % of carbon nanotubes are dispersed in water; preparing a cellulose solution in which cellulose is dissolved in a solvent; a step of mixing the carbon nanotube dispersion liquid and the cellulose solution at a mass ratio (mass of the carbon nanotube dispersion liquid:mass of the cellulose solution) of 5:95 to 99:1 to prepare a mixed dispersion liquid containing the carbon nanotubes and the cellulose; wet-spinning the obtained mixed dispersion in a liquid to obtain cellulose fibers containing the carbon nanotubes; drying the obtained cellulose fibers to obtain fibers; A method for producing a fiber, comprising:

8. The method according to claim 7 , wherein the cellulose solution contains 1.0% by mass or more and 30.0% by mass or less of the cellulose based on the total mass of the cellulose solution.

9. 9. The method according to claim 7, wherein the mass ratio of the carbon nanotube dispersion to the cellulose solution (mass of the carbon nanotube dispersion:mass of the cellulose solution) in the step of preparing the mixed dispersion is 50:50 to 99:

1.

10. 9. The method according to claim 7, wherein the concentration of carbon nanotubes in the mixed dispersion is greater than 50.0 mass% and not more than 90.0 mass%, based on the total mass of carbon nanotubes and cellulose.

11. The method according to claim 7 or 8, wherein the G / D of the carbon nanotubes is 3 or more and 150 or less.

12. 9. The method according to claim 7, wherein the fiber has a peak in the diffraction angle 2θ range of 10° or more and 17° or less in wide-angle X-ray scattering measured by setting the fiber so that the fiber axis is oriented in the equator direction.

13. The method according to claim 7 or 8, wherein the degree of orientation of the carbon nanotubes in the fiber is 0.20 or more and 0.90 or less.

14. The specific conductivity of the fiber is 1000 Scm ２ / g or more 6000Scm ２ The method according to claim 7 or 8, wherein the saturation coefficient is 1 / g or less.

15. The method according to claim 7 or 8, wherein the elastic modulus of the fiber is 10 GPa or more and 100 GPa or less.

16. 9. The method of claim 7 or 8, wherein the solvent is a cuprammonium process dissolution system.

17. A textile comprising the fiber of claim 1 or 2.

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