Cellulose-based fiber and method for producing cellulose-based fiber

Abstract

To provide a cellulose-based fiber that has an excellent mechanical property and can be efficiently produced.SOLUTION: There is provided a cellulose-based fiber that is a cellulose-based fiber in which carbon nanotube particles formed by aggregation of carbon nanotubes are contained in cellulose, the carbon nanotube particles are obtained from a dispersion liquid in which carbon nanotube powder, which is an agglomerate of the carbon nanotubes, is dispersed in an ionic liquid, an average particle size of the carbon nanotube particles measured by centrifugal sedimentation particle size distribution measurement of the dispersion is set to 800 nm or less, and when viewed in cross section in the fiber diameter direction, a number of carbon nanotube particles per unit area is set to 170 to 350 particles / 100 μm2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cellulosic fiber in which carbon nanotube particles formed by aggregation of carbon nanotubes are contained in cellulose, and to a method for producing a cellulosic fiber. [Background technology]

[0002] Conventionally, composite fibers have been used that combine multiple fiber materials to improve mechanical properties, etc., and cellulosic fibers made by incorporating carbon nanotubes into cellulose have been used as such composite fibers.

[0003] As this type of cellulose-based fiber, carbon nanotube-containing cellulose fibers containing chemically modified carbon nanotubes and cellulose fibers have been proposed (Patent Document 1). The cellulose-based fiber can be obtained by carrying out the following steps: a carbon nanotube dispersion preparation step in which a mixed liquid containing chemically modified carbon nanotubes, water, and water-soluble xylan is dispersed by ultrasonic treatment to prepare a carbon nanotube dispersion; a spinning dope preparation step in which the prepared carbon nanotube dispersion is mixed with a cellulose fiber raw material and at least one of an aprotic polar solvent and an ionic liquid capable of dissolving the cellulose fiber raw material to prepare a spinning dope; and a spinning step in which the prepared spinning dope is coagulated by a wet coagulation method and then spun. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-21151 Summary of the Invention [Problem to be solved by the invention]

[0005] The cellulose-based fiber of Patent Document 1 cannot be said to have sufficiently excellent mechanical properties such as tensile strength, breaking elongation, tensile modulus, and tensile toughness. Moreover, the method for producing the cellulose-based fiber of Patent Document 1 has difficulty in increasing the spinning speed, and therefore it is difficult to say that the production efficiency is excellent.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a cellulose-based fiber that can be efficiently produced while having excellent mechanical properties, and a method for producing a cellulose-based fiber that can efficiently produce a cellulose-based fiber having excellent mechanical properties. [Means for solving the problem]

[0007] To solve the above problems, the present inventors conducted extensive research as described below. Carbon nanotubes are typically traded in the form of carbon nanotube powder, which is a mass of carbon nanotubes aggregated into bundles. When using such carbon nanotube powder to produce cellulose-based fibers incorporating carbon nanotubes into cellulose, it has been thought that, in order to improve mechanical properties, it is preferable to disperse the carbon nanotube powder in an ionic liquid so that the carbon nanotubes are defibrated as much as possible into individual fibers, i.e., completely defibrated, before mixing it with cellulose. However, the present inventors discovered that over-defibrating cellulose powder tends to actually decrease mechanical properties. Specifically, they discovered that neither under-defibrating nor over-defibrating carbon nanotube powder completely improves mechanical properties, and that a certain degree of incomplete defibration (i.e., carbon nanotube particles composed of aggregated carbon nanotubes) is necessary. Furthermore, the degree of defibration that can improve mechanical properties can be determined using the average particle size of carbon nanotube particles measured by centrifugal sedimentation particle size distribution measurement of the dispersion liquid and the number of carbon nanotube particles per unit area in a cross-sectional view in the fiber diameter direction as indicators, and the present invention was completed based on the discovery that by appropriately setting these, mechanical properties can be improved and manufacturing efficiency can be increased.

[0008] That is, the characteristic configuration of the cellulosic fiber of the present invention for solving the above problems is as follows: A cellulose-based fiber in which carbon nanotube particles formed by aggregation of carbon nanotubes are contained in cellulose, The carbon nanotube particles are obtained from a dispersion liquid in which carbon nanotube powder, which is an agglomerate of the carbon nanotubes, is dispersed in an ionic liquid, the average particle size of the carbon nanotube particles measured by centrifugal sedimentation particle size distribution measurement of the dispersion is set to 800 nm or less; When viewed in cross section in the fiber diameter direction, the number of carbon nanotube particles per unit area is 170 to 350 particles / 100 μm 2 The reason is that it is set to

[0009] According to the cellulose-based fiber of this configuration, the average particle size of the carbon nanotube particles measured by centrifugal sedimentation particle size distribution measurement of the dispersion is set to 800 nm or less, and the number of carbon nanotube particles per unit area in the cross section in the fiber diameter direction is 170 to 350 particles / 100 μm 2 Furthermore, when spinning a stock solution prepared by mixing the dispersion, cellulose, and an ionic liquid, the spinnability of the stock solution is improved, allowing for an increased spinning speed and resulting in excellent production efficiency.

[0010] In the cellulosic fiber according to the present invention, The carbon nanotube particles preferably have an average particle size of 450 to 800 nm.

[0011] According to the cellulose-based fiber of this configuration, by setting the average particle size of the carbon nanotube particles within the above range, the mechanical properties become more excellent.

[0012] In the cellulosic fiber according to the present invention, The following conditions: (1) Temperature: 20±2℃ (2) Relative humidity: 65±4% (3) Fiber diameter: 10 to 20 μm (4) Fineness: 1.2~4.7dtex (5) Grip width: 2.0 cm (6) Tensile speed: 20 mm / min It is preferable that the tensile toughness calculated from the breaking elongation-tensile strength curve measured by the tensile test of the yarn performed in the above is 40 MPa or more.

[0013] By setting the tensile toughness within the above range, the cellulosic fiber of this configuration can have more excellent mechanical properties.

[0014] The characteristic configuration of the method for producing cellulosic fibers of the present invention for solving the above problems is as follows: a preparation step of adding carbon nanotube powder, which is a mass of carbon nanotubes, to an ionic liquid to obtain a dispersion; a liquid preparation step of mixing cellulose, an ionic liquid, and the dispersion to prepare a stock solution; a spinning step of spinning the stock solution to produce cellulosic fibers; A method for producing cellulosic fibers comprising: In the preparation step, the carbon nanotube powder is defibrated to produce carbon nanotube particles, which are aggregates of the carbon nanotubes, in the dispersion liquid.

[0015] According to the method for producing cellulose-based fibers of this configuration, when the above-mentioned preparation step, solution preparation step, and spinning step are performed, the preparation step is performed so that carbon nanotube particles, which are aggregates of carbon nanotubes, are produced in the dispersion by defibrating the carbon nanotube powder, thereby producing cellulose-based fibers with excellent mechanical properties. In addition, since the spinnability of the raw solution is improved, the spinning speed can be increased, resulting in excellent production efficiency.

[0016] In the method for producing cellulosic fibers according to the present invention, the average particle size of the carbon nanotube particles measured by centrifugal sedimentation particle size distribution measurement of the dispersion is set to 800 nm or less; When viewed in cross section in the fiber diameter direction, the number of carbon nanotube particles per unit area is 170 to 350 particles / 100 μm 2 It is preferable that it is set to .

[0017] According to the method for producing cellulose-based fibers of this configuration, the average particle size of the carbon nanotube particles measured by centrifugal sedimentation particle size distribution measurement of the dispersion is set to 800 nm or less, and the number of carbon nanotube particles per unit area in a cross section in the fiber diameter direction is set to 170 to 350 particles / 100 μm 2 By setting the temperature at 100°C to 120°C, it is possible to obtain cellulosic fibers with superior mechanical properties. In addition, since the spinnability of the dope is further improved, the spinning speed can be further increased, resulting in superior production efficiency. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a scanning electron microscope photograph showing the state of carbon nanotube particles in the dispersion liquid in Example 3. [Figure 2] FIG. 2 is a scanning electron microscope photograph showing the state of carbon nanotube particles in the dispersion liquid in Comparative Example 5. [Figure 3] FIG. 3 is a scanning electron microscope photograph showing the state of carbon nanotube particles in the dispersion liquid in Comparative Example 6. [Figure 4] FIG. 4 is a scanning electron microscope cross-sectional photograph showing carbon nanotube particles in the cellulosic fibers in Examples 3, 4, and 5. [Figure 5] FIG. 5 is a scanning electron microscope cross-sectional photograph showing carbon nanotube particles in cellulosic fibers in Comparative Examples 2, 4, and 5. [Figure 6] FIG. 6 is a scanning electron microscope cross-sectional photograph showing carbon nanotube particles in cellulosic fibers in Comparative Examples 6, 7, and 8. [Figure 7]FIG. 7 is a graph showing the relationship between the average particle size (Stokes diameter) of carbon nanotube particles and tensile toughness. [Figure 8] FIG. 8 is a graph showing the relationship between the number of carbon nanotube particles per unit area (number of CNT particles) in cellulosic fibers and tensile toughness. DETAILED DESCRIPTION OF THE INVENTION

[0019] The cellulosic fiber of the present invention and its manufacturing method will be described below. However, the present invention is not intended to be limited to the configurations described below or the examples described later.

[0020] [Cellulosic fiber] The cellulose-based fiber of this embodiment is a cellulose-based fiber in which carbon nanotube particles (hereinafter also referred to as "CNT particles") formed by an aggregation of carbon nanotubes (hereinafter also referred to as "CNTs") are contained in cellulose.

[0021] <Cellulose> The cellulose is not particularly limited and can be appropriately selected from known cellulose materials. Examples include naturally occurring cellulose such as cotton, cotton linter, flax (linen), hemp, ramie, banana, bamboo, kenaf, shell ginger, hemp, and kapok, as well as wood pulp and non-wood pulp obtained by refining naturally occurring cellulose. Regenerated cellulose obtained by dissolving and regenerating cellulose using various dissolution methods such as the viscose method, the cupric ammonium method, the NMMO method, and the ionic liquid method may also be used. The form of these cellulose materials (naturally occurring cellulose, wood pulp, non-wood pulp, regenerated cellulose, etc.) is not particularly limited, and various forms such as sheet, granular, and fibrous forms may be used.

[0022] (CNT) CNTs are graphene sheets in which carbon atoms are arranged in a hexagonal honeycomb pattern, formed into a single-layer or multi-layer coaxial tube shape. There are no particular limitations on the CNTs, and single-walled CNTs and / or multi-walled CNTs can be used, but single-walled CNTs are preferred. The use of single-walled CNTs can increase the strength of cellulosic fibers compared to the use of multi-walled CNTs.

[0023] The CNTs used preferably have a ratio (3σ / Av) of the diameter distribution (3σ) to the average diameter (Av) greater than 0.20 and less than 0.60, more preferably greater than 0.25, and even more preferably greater than 0.50. By using CNTs with a 3σ / Av in the above range, the strength of the cellulosic fiber can be increased and fiber breakage and fibrillation can be suppressed, even with a relatively small amount of CNTs incorporated. The average diameter (Av) and diameter distribution (3σ) of the CNTs can be adjusted by appropriately setting the CNT manufacturing method (manufacturing procedure, manufacturing conditions, etc.). Alternatively, they can also be adjusted by appropriately combining multiple types of CNTs obtained by different manufacturing methods.

[0024] In this embodiment, the CNTs that are normally used are those that exhibit a normal distribution when plotted on a graph with diameter on the horizontal axis and frequency on the vertical axis and approximated by Gaussian.

[0025] When evaluated using Raman spectroscopy, CNTs preferably have a radial breathing mode (RBM) peak. Note that RBM does not exist in the Raman spectrum of multi-walled CNTs with three or more walls.

[0026] The CNTs preferably have a ratio of the G-band peak intensity to the D-band peak intensity (G / D ratio) in the Raman spectrum of 1 to 20. By setting the G / D ratio within the above range, the strength of the cellulosic fiber can be increased even if the blending amount of CNTs is relatively small.

[0027] The average diameter (Av) of the CNTs is preferably 0.5 nm or more, more preferably 1 nm or more, and is preferably 15 nm or less, more preferably 10 nm or less. By setting the average diameter (Av) of the CNTs to the above lower limit or more, excessive aggregation (aggregation) of the CNTs can be suppressed, thereby obtaining CNT particles with a moderate aggregation of the CNTs. By setting the average diameter (Av) of the CNTs to the above upper limit or less, it is possible to suppress insufficient aggregation of the CNTs, thereby obtaining CNT particles with a moderate aggregation of the CNTs.

[0028] The specific surface area of CNT is 600m 2 / g or more is preferable, and 800m 2 / g or more is more preferable, while 2500m 2 When the CNTs are mainly open-ended, the specific surface area is preferably 1300 m 2 / g or more is preferred. By setting the specific surface area of the CNTs to the above lower limit or more, it is possible to prevent insufficient aggregation of the CNTs, thereby obtaining CNT particles with a moderate aggregation of the CNTs. By setting the specific surface area of the CNTs to the above upper limit or less, it is possible to prevent excessive aggregation (aggregation) of the CNTs, thereby obtaining CNT particles with a moderate aggregation of the CNTs. In this specification, "specific surface area" means the BET specific surface area measured using the BET method.

[0029] The mass density of CNTs is 0.002 g / cm 3 or more is preferred, while 0.2 g / cm 3 The following is preferred. By setting the mass density to the above lower limit or higher, the integrity of the CNTs can be improved and separation can be suppressed, making it possible to obtain CNT particles in which the CNTs are appropriately aggregated. By setting the mass density to the above upper limit or lower, it is possible to suppress excessive bonding (aggregation) between the CNTs, making it possible to obtain CNT particles in which the CNTs are appropriately aggregated.

[0030] The CNT preferably has a structure length of 100 to 5000 μm during synthesis.

[0031] CNTs preferably have multiple micropores. The diameter of the micropores is preferably less than 2 nm. The volume of the micropores in the CNTs (volume per unit mass (1 g)) is preferably 0.40 mL / g or more, more preferably 0.43 mL / g or more, and even more preferably 0.45 mL / g or more, and is typically 0.65 mL / g or less. When CNTs have such micropores, excessive aggregation of CNTs is suppressed, allowing CNT particles with a moderate aggregation of CNTs to be obtained. The diameter and volume of the micropores can be adjusted, for example, by appropriately setting the CNT manufacturing method (manufacturing procedure, manufacturing conditions, etc.). The "micropore volume (Vp)" can be calculated using the following formula (1) by measuring the nitrogen adsorption / desorption isotherm of the CNTs at liquid nitrogen temperature (77 K) and defining the amount of nitrogen adsorption at a relative pressure P / P0 = 0.19 as V: Vp=(V / 22414) × (M / ρ) ··· (1) P is the measured pressure at adsorption equilibrium, P0 is the saturated vapor pressure of liquid nitrogen at the time of measurement, M is the molecular weight of the adsorbate (nitrogen) (28.010), and ρ is the density of the adsorbate (nitrogen) at 77 K (0.808 g / cm 3 The volume of the micropores can be measured using, for example, BELSORP (registered trademark)-mini (manufactured by BEL Japan Co., Ltd.).

[0032] CNTs with the above-described properties can be efficiently produced by the super-growth method, a method for producing carbon nanotube bulk structures described in, for example, Japanese Patent No. 4621896 (European Patent Application Publication No. 1787955) and Japanese Patent No. 4811712 (U.S. Patent Application Publication No. 2009 / 297846). This method involves forming a catalyst layer on the substrate surface using a wet process and using a source gas containing acetylene as the main component (e.g., a gas containing 50% or more by volume of acetylene). The super-growth method is a CVD method in which a catalyst activation material such as water is brought into contact with the catalyst along with the source gas, thereby significantly increasing the activity and lifespan of the catalyst.

[0033] The CNT may be an unchemically modified CNT or a chemically modified CNT (chemically modified CNT). Examples of the chemically modified CNT include those having at least either a nitrogen-carbon bond or an oxygen-carbon bond on the CNT surface described in JP-A-2021-21151.

[0034] <CNT particles> The CNT particles are an aggregate of CNTs and are obtained from a dispersion in which carbon nanotube powder (CNT powder), which is a lump of CNTs, is dispersed in an ionic liquid. Originally, CNT powder is an aggregate in which fibrous CNTs aggregate with each other and are intertwined in a complex and disorderly manner, and it is difficult to specify its structure. Furthermore, the formation mechanism of CNT particles has not yet been fully elucidated. It is considered that the CNT powder and the ionic liquid that are the source of the CNT particles act on each other in a complex manner in the dispersion and are formed in accordance with the law of entropy increase in the process of transitioning from a non-equilibrium state to an equilibrium state. Therefore, it is impossible or not practical to specify the properties of the CNT particles obtained from the CNT powder and the ionic liquid by their structure. The degree of aggregation of the CNT particles can be indicated by the average particle diameter of the CNT particles (hereinafter also referred to as the "Stokes diameter") measured by centrifugal sedimentation particle size distribution measurement of the above dispersion, and also by the number of particles per unit area of the CNT particles (hereinafter also referred to as the "CNT particle number") in a cross-sectional view in the fiber diameter direction.

[0035] (CNT powder) CNT powder is a lump of CNTs. CNTs usually circulate in an aggregated lump state.

[0036] (Stokes diameter, and CNT particle number) The Stokes diameter of the CNT particles is set to 800 nm or less. The Stokes diameter is measured under the following conditions using a centrifugal sedimentation particle size distribution measuring device (for example, a centrifugal nano-particle analyzer: Partica CENTRIFUGE manufactured by Horiba, Ltd.). Measurement mode: Uniform sedimentation Rotation speed: 18000 rpm Light source: 470nm Temperature: 30℃ CNT particle density: 1.8g / cm 3 Reference solvent: 1-butyl-3-methylimidazolium chloride (BMIMCl) Solvent density: 1.08 g / cm 3 Solvent viscosity: 1600 mPa·s Dilution solvent: 1-butyl-3-methylimidazolium chloride (BMIMCl) Dilution rate: 2x Standard particles: Silica particles (Sicastar TMS 300 nm, manufactured by Corefront Co., Ltd.)

[0037] In the cross-sectional view of the fiber diameter, the number of CNT particles is 170 to 350 per 100 μm 2 The number of CNT particles was determined by cutting the cellulose fiber in the fiber diameter direction (perpendicular to the longitudinal direction) and counting the number of CNT particles per unit area (100 μm) on the cut surface. 2 The cutting of the cellulose-based fibers is carried out by embedding the cellulose-based fibers in an appropriate resin (for example, epoxy resin) and using an ion milling device (for example, Hitachi ion milling device: IM4000Plus manufactured by Hitachi High-Tech Corporation) under the following conditions: Ion source: Argon (Ar) gas Accelerating voltage: 4.0 kV Temperature: -50℃

[0038] The Stokes diameter is set to 800 nm or less, and the number of CNT particles is set to 170 to 350 per 100 μm. 2 By setting the above, the cellulosic fiber has excellent mechanical properties. In addition, when spinning a stock solution prepared by mixing the dispersion, cellulose, and an ionic liquid, the spinnability of the stock solution is improved, which allows for an increase in spinning speed and excellent production efficiency.

[0039] The Stokes diameter is preferably set to 450 to 800 nm. By setting the Stokes diameter within the above range, the cellulosic fiber will have better mechanical properties.

[0040] The Stokes diameter and number of CNT particles can be adjusted by appropriately setting the conditions for obtaining a dispersion by adding CNT powder to an ionic liquid in the preparation step described below, depending on the characteristics of the CNTs used, and by appropriately setting the conditions for preparing a stock solution by mixing cellulose, an ionic liquid, and a dispersion in the liquid preparation step, depending on the characteristics of the CNTs used.

[0041] (ionic liquid) Ionic liquids are liquids that can dissolve cellulose, and examples thereof include 1-butyl-3-methylimidazolium chloride (BMIMCl), 1-butyl-3-methylimidazolium acetate (BMIMAc), 1-butyl-3-methylimidazolium phosphinate (BMIMH2PO2), 1-butyl-3-methylimidazolium methylphosphonate (BMIMMeOHPO2), 1-ethyl-3-methylimidazolium chloride (EMIMCl), N,N-dimethyl-N-(2-methoxyethyl)-N-methylammonium, 2-methoxyacetate, etc. Ionic liquids can be used alone or as a mixture of two or more types.

[0042] (CNT particle content in cellulosic fibers) The content of CNT particles in the cellulose-based fibers (i.e., the CNT content) is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and preferably 5 parts by mass or less, more preferably 1 part by mass or less, per 100 parts by mass of cellulose. Furthermore, the content of CNT particles in the cellulose-based fibers is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and preferably 5% by mass or less, more preferably 1% by mass or less. By setting the content of CNT particles in the cellulose-based fibers within the above range, it is possible to suppress insufficient or excessive aggregation of the CNTs, thereby obtaining CNT particles with a moderate aggregation of the CNTs.

[0043] <Other ingredients> The cellulosic fibers may contain components other than cellulose and CNT particles, such as dispersion stabilizers (water-soluble polymers such as polyvinyl alcohol), alcohols, water, dispersants, and polymers other than dispersion stabilizers.

[0044] <Characteristics of cellulosic fibers> Cellulosic fibers meet the following criteria: (1) Temperature: 20±2℃ (2) Relative humidity: 65±4% (3) Fiber diameter: 10 to 20 μm (4) Fineness: 1.2~4.7dtex (5) Grip width: 2.0 cm (6) Tensile speed: 20 mm / min Preferably, the tensile toughness calculated from the breaking elongation-tensile strength curve measured by a tensile test of the yarn conducted in the above manner is 40 MPa or more. By setting the tensile toughness within the above range, the cellulosic fiber has better mechanical properties. The tensile toughness is calculated as the area under the curve in a graph with the breaking elongation (%) on the horizontal axis and the tensile strength (cN / dtex) on the vertical axis. The tensile test is conducted on a single cellulosic fiber having a fiber diameter and fineness within the above ranges, and the fiber diameter is preferably 10 to 15 μm and the fineness is preferably 1.2 to 2.6 dtex.

[0045] <Method of manufacturing cellulose-based fibers> The method for producing a cellulose-based fiber of the present embodiment is the method for producing the cellulose-based fiber described above, a preparation step of adding CNT powder, which is a mass of CNTs, to an ionic liquid to obtain a dispersion; a liquid preparation step of mixing cellulose, an ionic liquid, and the dispersion to prepare a stock solution; a spinning step of spinning the dope to produce cellulosic fibers; Includes.

[0046] (preparation process) In the preparation step, CNT powder, which is a mass of CNTs, is added to an ionic liquid to obtain a dispersion. In this preparation step, the CNT powder is defibrated to produce CNT particles, which are aggregates of CNTs, in the dispersion. In this preparation, the CNT powder is added to the ionic liquid and dispersed using a bead mill, high-speed stirrer, or the like.

[0047] Examples of bead mills include batch-type bead mills and continuous-type bead mills. Examples of batch-type bead mills include the Easy Nano RMBII model manufactured by Aimex Co., Ltd., where the rotation speed can be set to approximately 2,000 rpm and the dispersion time can be set to approximately 1 to 150 minutes. Examples of continuous bead mills include the Start Lab RMH-01 model manufactured by Aimex Co., Ltd., where the peripheral speed can be set to approximately 4 to 8 m / s and the number of passes can be set to approximately 1 to 5 passes. When using a bead mill, zirconia beads with a diameter φ of approximately 0.3 to 1.0 mm can be used. Examples of high-speed mixers include the Filmix FM-56-L model, a thin-film swirl high-speed mixer manufactured by Primix Corporation, where the rotation speed can be set to approximately 22,000 rpm. The dispersion conditions for these bead mills and high-speed mixers can be appropriately set so that the CNT powder is adequately disintegrated and the Stokes diameter and number of CNT particles described above are obtained.

[0048] The ionic liquid may be any of the ionic liquids exemplified above. The content of CNTs (i.e., CNT powder or CNT particles) in the dispersion is preferably 0.01 to 5 mass %, more preferably 0.02 to 1 mass %. By setting the CNT content in the dispersion within the above range, CNT particles in which the CNTs are more appropriately aggregated can be obtained.

[0049] (liquid preparation process) In the liquid preparation step, a known mixing device such as a planetary mixer is used to mix cellulose, an ionic liquid, and a dispersion to prepare a stock solution. The ionic liquids listed above can be used. It is preferable to use the same type of ionic liquid in the preparation step and the liquid preparation step. As described above, the blending ratio of cellulose, ionic liquid, and dispersion can be set so that the CNT particles are present in the cellulosic fiber at a ratio of preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and preferably 5 parts by mass or less, more preferably 1 part by mass or less, per 100 parts by mass of cellulose. Furthermore, the blending ratio can be set so that the CNT particle content in the cellulosic fiber is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and preferably 5% by mass or less, more preferably 1% by mass or less. In addition to the cellulose, ionic liquid, and dispersion, an antioxidant may be added in the liquid preparation step.

[0050] (Spinning process) In the spinning process, the stock solution is spun to produce cellulosic fibers. Specifically, for example, a conventionally known dry jet wet spinning device is used, the stock solution is discharged from the spinneret into a coagulation bath, and the coagulated material is wound around a roller rotating at high speed to obtain cellulosic fibers.

[0051] According to this method for producing cellulose-based fibers, when the above-mentioned preparation step, solution preparation step, and spinning step are performed, the preparation step is performed so that CNT particles, which are aggregates of CNTs, are produced in the dispersion by defibrating the CNT powder, thereby producing cellulose-based fibers with excellent mechanical properties. In addition, since the spinnability of the raw solution is improved, the spinning speed can be increased, resulting in excellent production efficiency.

[0052] In the method for producing the cellulose-based fiber, as described above, the Stokes diameter is set to 800 nm or less, and the number of CNT particles is 170 to 350 particles / 100 μm 2 It is preferable that the Stokes diameter is set to 800 nm or less and the number of CNT particles is set to 170 to 350 particles / 100 μm.2 By setting the temperature at 100°C to 120°C, it is possible to obtain cellulosic fibers with superior mechanical properties. In addition, since the spinnability of the dope is further improved, the spinning speed can be further increased, resulting in superior production efficiency. [Example]

[0053] Cellulose-based fibers (Examples 1 to 9) having the characteristic features of the present invention were produced, and various properties were measured. For comparison, cellulose-based fibers (Comparative Examples 1 to 8) not having the characteristic features of the present invention were produced, and properties were similarly measured. The measurement items were the Stokes diameter of the CNT particles, the number of CNT particles, and the tensile toughness of the cellulose-based fibers. Furthermore, as a reference example, a cellulose-based fiber not containing CNTs (Reference Example 1) was produced, and tensile toughness was measured.

[0054] The raw materials used are as follows: CNT powder: ZEONAN SG101 (manufactured by Zeon Nano Technology Co., Ltd.) Ionic liquid: 1-butyl-3-methylimidazolium chloride (BMIMCl) Cellulose: Cellulose pulp (Georgia Pacific, trade name "VFC", DP630)

[0055] Example 1 As shown in Table 1, CNT powder was added to the ionic liquid so that the CNT concentration in the dispersion was 0.1% by mass. A batch-type bead mill, Easy Nano RMB II model manufactured by Imex Co., Ltd., was used. Zirconia beads with a diameter of 1.0 mm were used as the beads. The rotation speed was set to 2000 rpm, and the dispersion time was set to 1 minute to obtain a dispersion. Cellulose, ionic liquid, and the dispersion were mixed in a planetary mixer so that the CNT content in the cellulosic fiber was 0.1% by mass (cellulose was 99.9% by mass), to obtain a spinning dope. The resulting spinning dope was discharged from the spinneret (diameter: 0.26 mm) into a coagulation bath using a dry-jet wet spinning apparatus. The coagulated material was wound around a high-speed rotating roller at a winding speed of 100 m / min, yielding cellulosic fibers with a fiber diameter of 12 μm.

[0056] Examples 2 to 5 Cellulose-based fibers of Examples 2 to 5 were obtained in the same manner as in Example 1, except that the dispersions were obtained by setting the dispersion times as shown in Table 1. Of these, the state of CNT particles in the dispersion of Example 3 is shown in Figure 1. Figure 1(a) is a scanning electron microscope photograph showing the state of carbon nanotube particles in the dispersion of Example 3, and Figure 1(b) is a scanning electron microscope photograph that is a partial enlargement of Figure 1(a).

[0057] (Comparative Examples 1 to 5) Cellulose-based fibers of Comparative Examples 1 to 5 were obtained in the same manner as in Example 1, except that zirconia beads with a diameter of 0.3 mm were used as the beads and dispersions were obtained by setting the dispersion time as shown in Table 1. The state of the CNT particles in the dispersion of Comparative Example 5 is shown in Figure 2. Figure 2(a) is a scanning electron microscope photograph showing the state of the carbon nanotube particles in the dispersion of Comparative Example 5, and Figure 2(b) is a scanning electron microscope photograph that is a partial enlargement of Figure 2(a).

[0058] Examples 6 to 8 The cellulose-based fibers of Examples 6 to 8 were obtained in the same manner as in Example 1, except that zirconia beads with a diameter of φ0.3 mm were used as the beads, a Start Lab RMH-01 model manufactured by Imex Co., Ltd. was used as the continuous bead mill, and the peripheral speed, number of passes, temperature (jacket temperature), and liquid delivery (speed) were set as shown in Table 1 to obtain the dispersion.

[0059] Example 9 The cellulose-based fibers of Example 9 were obtained in the same manner as in Example 1, except that zirconia beads with a diameter of φ1.0 mm were used as the beads, a Start Lab RMH-01 model manufactured by Imex Co., Ltd. was used as the continuous bead mill, and the peripheral speed, number of passes, temperature (jacket temperature), and liquid delivery (speed) were set as shown in Table 1 to obtain the dispersion.

[0060] (Comparative Examples 6 to 8) The cellulose-based fibers of Comparative Examples 6 to 8 were obtained in the same manner as in Example 1, except that zirconia beads with a diameter of 0.5 mm were used, a Start Lab RMH-01 continuous bead mill manufactured by Imex Co., Ltd. was used, and the peripheral speed, number of passes, temperature (jacket temperature), and liquid feed (speed) were set as shown in Table 1 to obtain the dispersions. The state of the CNT particles in the dispersion of Comparative Example 6 is shown in Figure 3. Figure 3(a) is a scanning electron microscope photograph showing the state of the carbon nanotube particles in the dispersion of Comparative Example 6, and Figure 3(b) is a scanning electron microscope photograph that partially enlarges Figure 3(a).

[0061] (Reference example 1) The cellulose-based fiber of Reference Example 1, which did not contain CNTs, was obtained in the same manner as in Example 1, except that a dispersion liquid was not prepared and cellulose and an ionic liquid were mixed in a planetary mixer to obtain a spinning solution.

[0062] (Stokes diameter) The Stokes diameters of the CNT particles in the dispersions of Examples 1 to 9 and Comparative Examples 1 to 8 were measured under the following conditions using a centrifugal sedimentation particle size distribution analyzer (a centrifugal nanoparticle analyzer: Partica CENTRIFUGE, manufactured by Horiba, Ltd.) The results are shown in Table 1. Measurement method: uniform sedimentation Rotation speed: 18,000 rpm Light source: 470nm Temperature: 30℃ CNT particle density: 1.8g / cm 3 Reference solvent: 1-butyl-3-methylimidazolium chloride (BMIMCl) Solvent density: 1.08 g / cm 3 Solvent viscosity: 1600 mPa·s Dilution solvent: 1-butyl-3-methylimidazolium chloride (BMIMCl) Dilution rate: 2x Standard particles: Silica particles (Sicastar TMS 300 nm, manufactured by Corefront Co., Ltd.)

[0063] (Number of CNT particles) The cellulose fibers of Examples 3 to 9 and Comparative Examples 1 to 8 were cut in the fiber diameter direction (direction perpendicular to the longitudinal direction), and an arbitrary unit area (100 μm 2 The number of CNT particles contained in the cellulose-based fibers was measured by counting the number of CNT particles contained in the cellulose-based fibers. Note that the number of CNT particles in the cellulose-based fibers of Examples 1 and 2 was not measured. The cellulose-based fibers were embedded in epoxy resin and cut using an ion milling device (Hitachi ion milling device: IM4000Plus, manufactured by Hitachi High-Technologies Corporation) under the following conditions: Ion source: Argon (Ar) gas Accelerating voltage: 4.0 kV Temperature: -50℃ Of Examples 3 to 9 and Comparative Examples 1 to 8, cross-sectional photographs of Examples 3, 4, and 5 are shown in Figure 4. Figures 4(a), (b), and (c) are scanning electron microscope cross-sectional photographs showing carbon nanotube particles in the cellulosic fibers of Examples 3, 4, and 5, respectively. Cross-sectional photographs of Comparative Examples 2, 4, and 5 are shown in Figure 5. Figures 5(a), (b), and (c) are scanning electron microscope cross-sectional photographs showing carbon nanotube particles in the cellulosic fibers of Comparative Examples 2, 4, and 5, respectively. Cross-sectional photographs of Comparative Examples 6, 7, and 8 are shown in Figure 6. Figures 6(a), (b), and (c) are scanning electron microscope cross-sectional photographs showing carbon nanotube particles in the cellulosic fibers of Comparative Examples 6, 7, and 8, respectively.

[0064] (tensile toughness) For the cellulose-based fibers of Examples 1 to 9, Comparative Examples 1 to 8, and Reference Example 1, a tensile test was performed on 15 cellulose-based fiber threads using a tensile tester (Shimadzu Corporation, EZ Test Series EZ-SX 5N load cell) under the following conditions. The area under the curve of the breaking elongation (%)-tensile strength (cN / dtex) curve was measured, and the average value was obtained as the tensile toughness (MPa) (n=15). (1) Temperature: 20±2℃ (2) Relative humidity: 65±4% (3) Fiber diameter: 10 to 20 μm (4) Fineness: 1.2~4.7dtex (5) Grip width: 2.0 cm (6) Tensile speed: 20 mm / min The results are shown in Table 1. The tensile toughness of Examples 1 to 9 and Comparative Examples 1 to 8 is shown as the difference from the tensile toughness of Reference Example 1 (the tensile toughness of Examples 1 to 9 and Comparative Examples 1 to 8 minus the tensile toughness of Reference Example 1), and the relationship with the Stokes diameter is shown in FIG. 7. The tensile toughness of Examples 3 to 9 and Comparative Examples 1 to 8 is shown as the difference from the tensile toughness of Reference Example 1 (the tensile toughness of Examples 1 to 9 and Comparative Examples 1 to 8 minus the tensile toughness of Reference Example 1), and the relationship with the number of CNT particles is shown in FIG. 8. FIG. 7 is a graph showing the relationship between the average particle size (Stokes diameter) of carbon nanotube particles and tensile toughness in the Examples and Comparative Examples. FIG. 8 is a graph showing the relationship between the number of carbon nanotube particles per unit area (the number of CNT particles) in cellulosic fibers and tensile toughness in the Examples and Comparative Examples. 7 and 8, when the difference is a positive value, it indicates that the tensile toughness is increased from that of Reference Example 1, and when the difference is a negative value, it indicates that the tensile toughness is decreased from that of Reference Example 1.

[0065] [Table 1]

[0066] As shown in Table 1, Figure 7, and Figure 8, the Stokes diameter is 800 nm or less and the number of CNT particles is 170 to 350 / 100 μm. 2 It was shown that the cellulose-based fibers of Examples 1 to 9, which satisfied the above condition, had improved tensile toughness compared to the cellulose-based fiber of Reference Example 1, which did not contain CNTs.

[0067] In contrast, although the Stokes diameter is 800 nm or less, the number of CNT particles is 170 to 350 per 100 μm 2 The cellulose-based fibers of Comparative Examples 1 to 5 did not satisfy the above condition, and the Stokes diameter did not satisfy the condition of 800 nm or less and the number of CNT particles was 170 to 350 / 100 μm 2It was shown that the cellulose-based fibers of Comparative Examples 6 to 8, which did not satisfy the above condition, did not have improved tensile toughness compared to the cellulose-based fiber of Reference Example 1, which did not contain CNTs. [Industrial Applicability]

[0068] The cellulosic fibers of the present invention have improved mechanical properties and can therefore be used in a variety of applications.

Claims

1. A cellulose-based fiber in which carbon nanotube particles formed by aggregation of carbon nanotubes are contained in cellulose, The carbon nanotube particles are obtained from a dispersion liquid in which carbon nanotube powder, which is an agglomerate of the carbon nanotubes, is dispersed in an ionic liquid, the average particle size of the carbon nanotube particles measured by centrifugal sedimentation particle size distribution measurement of the dispersion is set to 800 nm or less; When viewed in cross section in the fiber diameter direction, the number of carbon nanotube particles per unit area is 170 to 350 particles / 100 μm ２ Cellulosic fibers that are set to.

2. 2. The cellulose fiber according to claim 1, wherein the carbon nanotube particles have an average particle size of 450 to 800 nm.

3. The following conditions: (1) Temperature: 20±2℃ (2) Relative humidity: 65±4% (3) Fiber diameter: 10 to 20 μm (4) Fineness: 1.2 to 4.7 dtex (5) Grip width: 2.0 cm (6) Tensile speed: 20 mm / min 3. The cellulose fiber according to claim 1, wherein the tensile toughness calculated from the breaking elongation-tensile strength curve measured by a tensile test of the yarn is 40 MPa or more.

4. a preparation step of adding carbon nanotube powder, which is a mass of carbon nanotubes, to an ionic liquid to obtain a dispersion; a liquid preparation step of mixing cellulose, an ionic liquid, and the dispersion to prepare a stock solution; a spinning step of spinning the stock solution to produce cellulosic fibers; A method for producing cellulosic fibers comprising: A method for producing cellulose-based fibers, wherein the preparation step is carried out so that carbon nanotube particles, which are aggregates of carbon nanotubes, are produced in the dispersion liquid by defibrating the carbon nanotube powder.

5. the average particle size of the carbon nanotube particles measured by centrifugal sedimentation particle size distribution measurement of the dispersion is set to 800 nm or less; When viewed in cross section in the fiber diameter direction, the number of carbon nanotube particles per unit area is 170 to 350 particles / 100 μm ２ The method for producing cellulosic fibers according to claim 4, wherein the temperature is set to

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