Method for producing fibrous structure

Abstract

The present invention improves the handleability of a fibrous structure and ensures sufficient dispersibility thereof.　A method for producing a fibrous structure according to the present invention comprises: a preparation step for preparing a fibrous structure A that is aggregated in a state in which voids are formed between a plurality of fibrous materials; and a void removal step for removing some of the voids in the fibrous structure A to form a fibrous structure B, wherein when the bulk density of the fibrous structure A is ρA (g / mL), and the bulk density of the fibrous structure B is ρB (g / ml), 1.3≤ρB / ρA≤200 is satisfied.

Description

Method for manufacturing fibrous structures

[0001] This invention relates to a method for manufacturing a fibrous structure.

[0002] In recent years, carbon nanotubes (hereinafter sometimes referred to as "CNTs") have attracted attention as a fibrous nanostructure material, a type of fibrous structure, due to their lightweight nature and excellent conductivity and mechanical properties. CNTs are known to improve electrical conductivity, thermal conductivity, and mechanical strength when added to polymers such as resins and rubbers.

[0003] Although individual carbon nanotubes (CNTs) possess excellent properties, their small outer diameter makes them prone to forming bundled carbon nanotube structures due to van der Waals forces. This presents challenges in dispersion, such as difficulty in dispersing them in solvents. Furthermore, CNTs have low bulk density and are easily dispersed, resulting in poor handling during use and inefficient storage and transport.

[0004] Therefore, there is a need for a technology that can increase the bulk density of CNTs to improve their handling and efficiency, while not reducing their dispersibility in media such as polymers and solvents. This problem is not limited to CNTs, but also occurs with other fibrous nanomaterials such as cellulose nanofibers and fibrous materials such as carbon fibers. For example, Patent Document 1 discloses a technology to reduce the volume of CNTs and improve their handling.

[0005] Japanese Patent Publication No. 2017-119792

[0006] However, according to the technology shown in Patent Document 1, there was room for improvement in achieving both volume reduction and dispersibility of CNTs.

[0007] The object of the present invention is to provide a method for manufacturing a fibrous structure that improves the handling of a fibrous structure in which fibrous materials such as CNTs are aggregated with voids formed between the fibrous materials, and that can sufficiently ensure the dispersibility of the fibrous material in a solvent or the like.

[0008] The inventors diligently conducted research with the aim of solving the above problems. As a result, the inventors newly discovered that by setting the ratio of bulk density before and after processing of the fibrous structure to a specific range, it is possible to achieve both improved handling properties of the resulting fibrous structure and improved dispersibility when dispersed in a solvent, and thus completed the present invention.

[0009] In other words, the present invention aims to advantageously solve the above problems, and the present invention is a method for manufacturing a fibrous structure comprising: [1] a preparation step of preparing a fibrous structure A which is aggregated with voids formed between a plurality of fibrous materials; and a void removal step of removing a part of the voids in the fibrous structure A to form a fibrous structure B, wherein the bulk density of the fibrous structure A is ρA (g / ml) and the bulk density of the fibrous structure B is ρB (g / ml), satisfying 1.3 ≤ ρB / ρA ≤ 200. According to the present invention, by setting the ratio of the bulk density of the fibrous structure before and after processing to a specific range, the obtained fibrous structure has the effect of being sufficiently excellent in both handling and dispersibility when dispersed in a solvent, etc. Here, normally, a gas such as air is present in the voids. And it is preferable that the air does not contain liquid such as condensation.

[0010] [2] In the method for manufacturing the fibrous structure described in [1], it is preferable that ρB / ρA ≤ 20 is satisfied. [3] In addition, in the method for manufacturing the fibrous structure described in [1] or [2], it is preferable that the fibrous material includes at least one of fibrous nanomaterial and carbon fiber. [4] In addition, in the method for manufacturing the fibrous structure described in [3], it is preferable that the fibrous nanomaterial includes at least one of carbon nanotube and cellulose nanofiber. [5] In addition, in the method for manufacturing the fibrous structure described in [4], it is preferable that the carbon nanotube includes single-walled carbon nanotube. In such a configuration, for example, by using carbon nanotube, particularly single-walled carbon nanotube, as the fibrous material, it is possible to efficiently impart conductivity to insulating materials such as polymers with only a small amount of additive, and it becomes possible to develop various applications such as battery electrodes. [6] Here, in any of the methods for manufacturing the fibrous structure described in [1] to [5], it is preferable that the fibrous structure consists substantially only of fibrous material. With such a configuration, no materials other than fibrous material are included, and the versatility of applications is increased without being restricted in subsequent processes. Furthermore, "consisting substantially of fibrous material" means not only that the material is composed solely of fibrous material, but also that it may unintentionally contain other materials such as impurities in addition to the fibrous material.

[0011] [7] In any of the methods for manufacturing the fibrous structure described in [1] to [6] above, an apparatus can be used that includes a filter that allows gas to pass through but substantially blocks the fibrous material, and a ventilation mechanism that moves the gas inside the filter to the outside. In the preparation step, the fibrous structure A is supplied to the inside of the filter, and in the void removal step, the ventilation mechanism is used to vent the gas in the voids in the fibrous structure A supplied to the inside of the filter to the outside of the filter, thereby forming the fibrous structure B inside the filter. With such an apparatus, the bulk density can be adjusted relatively easily by simply preparing the filter and adjusting the conditions of the ventilation mechanism, and both the handling and dispersibility of the fibrous structure can be achieved relatively easily. Note that substantially blocking means blocking 90% or more by mass.

[0012] [8] In any of the methods for manufacturing a fibrous structure described in [1] to [6] above, an apparatus can be used that includes a cylindrical filter formed in a cylindrical shape that allows gas to pass through but substantially prevents the fibrous material from passing through, a ventilation mechanism for moving the gas inside the cylindrical filter to the outside, and a transport mechanism for transporting the fibrous structure A supplied to the inner space of the cylindrical filter from one end to the other of the cylindrical filter. The apparatus can be configured such that in the preparation step, the fibrous structure A is supplied to the inside of the cylindrical filter, and in the void removal step, the gas in the voids in the fibrous structure A supplied to the inside of the cylindrical filter is vented to the outside of the cylindrical filter by the ventilation mechanism, while the fibrous structure A inside the cylindrical filter is transported to the other end of the cylindrical filter by the transport mechanism to form the fibrous structure B. With this configuration, fibrous material is supplied from one end (input side) of the cylindrical filter, and this fibrous material is conveyed to the other end (discharge side) of the cylindrical filter by a conveying mechanism to form a fibrous structure B on the inner surface of the cylindrical filter, thereby forming the fibrous structure B. This makes it possible to relatively easily input fibrous material, form the fibrous structure, and discharge it. Note that "substantially impermeable" means that 90% or more by mass is impermeable.

[0013] [9] In the method for manufacturing the fibrous structure described in [8] above, the void removal step preferably includes a preliminary step of forming a fibrous material layer on the surface of the cylindrical filter by collecting the fibrous material A on the surface of the cylindrical filter, while using the ventilation mechanism to allow the gas in the voids in the fibrous structure A supplied to the inside of the cylindrical filter to be vented to the outside of the cylindrical filter, and using the transport mechanism to transport the fibrous structure A on the inside of the cylindrical filter to the other end, and after the preliminary step, forming the fibrous structure B by using the ventilation mechanism to allow the gas in the voids in the fibrous structure A supplied to the inside of the fibrous material layer to be vented to the outside of the cylindrical filter through the fibrous material layer, and using the transport mechanism to transport the fibrous structure A on the inside of the fibrous material layer to the other end of the cylindrical filter. With this configuration, by performing a preliminary step to form a fibrous material layer on the surface of the cylindrical filter (the inner and / or outer circumferential surfaces of the cylindrical filter), it is possible to suppress clogging of the fibrous material in the cylindrical filter and the resulting poor transport of the fibrous structure, and to efficiently form the fibrous structure with a relatively simple procedure.

[0014]

[10] A method for manufacturing a fibrous structure according to any one of [1] to [6] above, using an apparatus having a cylindrical filter formed in a cylindrical shape that allows gas to pass through but substantially prevents the fibrous material from passing through, a ventilation mechanism that moves the gas inside the cylindrical filter outwards, and a transport mechanism that transports the fibrous structure A supplied to the inner space of the cylindrical filter from one end to the other of the cylindrical filter, in the preparation step, the fibrous structure A is supplied to the inside of the cylindrical filter, and in the void removal step, the ventilation mechanism is used to... The apparatus is configured to form a fibrous structure C by conveying the fibrous structure A inside the cylindrical filter to the other end of the cylindrical filter by the conveying mechanism, while the gas in the voids in the fibrous structure A supplied to the inside of the cylindrical filter is passed out to the outside of the cylindrical filter. The apparatus further comprises a filling device that fills a packaging bag with the fibrous structure C discharged by the conveying mechanism. Preferably, the filling device performs a void removal step 2 to remove a portion of the voids in the fibrous structure C inside the packaging bag to form a fibrous structure B. Note that "substantially impermeable" means that 90% or more by mass is impermeable.

[0015]

[11] In the method for manufacturing a fibrous structure according to any of [1] to

[10] above, it is preferable that the bulk density ρA of the fibrous structure A is 0.005 (g / ml) or more and 0.2 (g / ml) or less.

[0016] The present invention provides a method for manufacturing fibrous structures that improves the handling of fibrous structures containing fibrous materials and ensures sufficient dispersibility in solvents and the like.

[0017] This is a cross-sectional view showing the main parts of an example of an apparatus capable of carrying out the method for producing the carbon nanotube dispersion of the present invention.

[0018] A method for manufacturing a fibrous structure according to the present invention will now be described. Each component disclosed in this embodiment, as well as preferred embodiments, numerical ranges, and thresholds defining such numerical ranges, can be independently combined with each other in any manner. The manufacturing method of the present invention comprises a preparation step of preparing a fibrous structure A in which a plurality of fibrous materials are aggregated with voids formed between the fibrous materials, and a void removal step of removing a portion of the voids in the fibrous structure A to form a fibrous structure B. Here, when the bulk density of the fibrous structure A is ρA (g / ml) and the bulk density of the fibrous structure B is ρB (g / ml), the relationship 1.3 ≤ ρB / ρA ≤ 200 is satisfied.

[0019] <Fibrous Structures> Fibrous structures are formed by the aggregation of multiple fibrous materials with voids formed between them. Examples of fibrous materials include fibrous nanomaterials and carbon fibers. Examples of fibrous nanomaterials include carbon nanotubes (CNTs) and cellulose nanofibers. Among these, CNTs are preferred as fibrous nanomaterials because they can impart conductivity to insulating materials such as polymers with only a small amount of addition. Furthermore, it is preferable that the fibrous material consists substantially of fibrous materials. "Substantially consisting of fibrous materials" includes not only cases where the material consists solely of fibrous materials, but also cases where other materials such as impurities are unintentionally included in addition to the fibrous materials. The proportion of other materials such as impurities is usually 20% by mass or less, preferably 10% by mass or less, more preferably 1.0% by mass or less, and most preferably 0.5% by mass or less. This configuration has the advantage of not including extra materials, which can be advantageous for subsequent application development.

[0020] <CNTs> The multiple CNTs may include single-walled CNTs and / or multi-walled CNTs, but it is preferable to include single-walled to five-walled CNTs, more preferably single-walled to two-walled CNTs, and even more preferably single-walled CNTs. Furthermore, it is preferable that the multiple CNTs contain more than 50% single-walled CNTs, more preferably more than 70%, and may contain 80% or more. In addition, CNTs that have undergone surface treatment or post-treatment after synthesis can also be used.

[0021] CNT has a BET specific surface area of ​​400 m². ２ / g or more, 600m ２ / g or more, 800m ２ It can be set to 1 / g or more, and 2000m ２ / g or less, 1800m ２ / g or less, 1600m ２ / g or less, 1300m ２ / g or less, 1200m ２ It can be less than or equal to / g. In this invention, "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET (Brunauer-Emmett-Teller) method.

[0022] The average diameter of the CNTs is preferably 1 nm or more, more preferably 1.5 nm or more, and can also be 2 nm or more, or 3 nm or more. Furthermore, the average diameter of the CNTs is preferably 60 nm or less, more preferably 30 nm or less, even more preferably 10 nm or less, particularly preferably 6 nm or less, and can also be 5 nm or less. In this invention, the "average diameter of the CNTs" can be determined by measuring the diameter (outer diameter) of, for example, 20 CNTs on a transmission electron microscope (TEM) image and calculating the numerical average value.

[0023] The average length of the CNTs is preferably 10 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, particularly preferably 100 μm or more, and also preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 400 μm or less. CNTs with an average length within the above range intertwine with each other due to their length, so the structure of the fibrous structure is less likely to change over time, and a stable fibrous structure can be provided.

[0024] CNTs typically have an aspect ratio (length / diameter) greater than 10, and can be 100 or more, or even 1000 or more. By setting the aspect ratio as described above, the CNTs intertwine with each other, making the structure of the fibrous structure less susceptible to changes over time and providing a stable fibrous structure. The aspect ratio of CNTs can be determined by measuring the diameter and length of 100 randomly selected CNTs using a scanning electron microscope or transmission electron microscope, and calculating the average value of the ratio of diameter to length (length / diameter).

[0025] When evaluated using Raman spectroscopy, CNTs preferably have a Radial Breathing Mode (RBM) peak. Note that RBM is not present in the Raman spectra of multilayer CNTs with three or more layers.

[0026] Furthermore, the ratio of the G-band peak intensity to the D-band peak intensity in the Raman spectrum (G / D ratio) of the CNT is preferably 0.5 or higher, more preferably 2.0 or higher, even more preferably 3.0 or higher, preferably 150 or lower, more preferably 50 or lower, and can also be 10 or lower.

[0027] Furthermore, CNTs can be manufactured using known CNT synthesis methods such as arc discharge, laser ablation, and chemical vapor deposition (CVD), without any particular limitations. Specifically, CNTs can be efficiently manufactured, for example, by supplying raw material compounds and a carrier gas onto a substrate having a catalyst layer for CNT production on its surface, and synthesizing CNTs by chemical vapor deposition (CVD), while dramatically improving the catalytic activity of the catalyst layer by introducing a small amount of oxidizing agent (catalyst activator) into the system (Supergrowth method; see International Publication No. 2006 / 011655).

[0028] Next, a method for manufacturing a fibrous structure according to one embodiment of the present invention will be described in detail using Figure 1 as an example, using an auger-type powder filling apparatus. Figure 1 shows a cross-sectional view of the main part of the powder filling apparatus used when carrying out the method for manufacturing a fibrous structure according to one embodiment of the present invention. Note that the method for manufacturing a fibrous structure of the present invention is not limited to being carried out using the apparatus shown in Figure 1.

[0029] As shown in Figure 1, the powder filling device 10 is a so-called auger-type powder filling device, comprising a cylindrical filter 1, an outer cylinder 2 arranged with a vacuum chamber 4 as a gap on the outer circumference of the cylindrical filter 1, and an auger 3 arranged inside the cylindrical filter 1. Carbon nanotube structures 6A are fed in as fibrous structures A from one end 1A of the cylindrical filter 1 and discharged from the other end 1B of the cylindrical filter 1. The carbon nanotube structures 6A are formed by the aggregation of multiple carbon nanotubes with voids formed inside, and gases such as air are usually present in these voids. The cylindrical filter 1, outer cylinder 2, and auger 3 are arranged coaxially, and both ends of the vacuum chamber 4 are hermetically sealed.

[0030] The cylindrical filter 1 is a cylindrical filter with a mesh portion 1X formed on its outer surface. A carbon nanotube structure 6A is supplied to the inside of the cylindrical filter 1, specifically to the space 5 between the inner surface of the cylindrical filter 1 and the auger 3. The mesh portion 1X is formed with an opening that substantially blocks the carbon nanotubes constituting the carbon nanotube structure 6A, while allowing gas to pass through. "Substantially blockable" means that 90% or more by mass of the introduced carbon nanotubes are blocked.

[0031] The outer cylinder 2 has an exhaust port 2A formed therein for discharging the gas inside the outer cylinder 2 to the outside. A ventilation mechanism (not shown) draws in the gas (air) inside the cylindrical filter 1 and the gas inside the vacuum chamber 4, and discharges them through the exhaust port 2A, thereby creating a reduced pressure or vacuum state inside the outer cylinder 2.

[0032] The auger 3 is formed as a screw that rotates by a transport mechanism (not shown) and transports the carbon nanotube structure 6A, which has been introduced into the cylindrical filter 1 from one end 1A of the cylindrical filter 1, to the other end 1B of the cylindrical filter 1.

[0033] An example of a method for manufacturing a fibrous structure according to the present invention will be described. First, a carbon nanotube structure 6A is prepared as a fibrous structure A formed by aggregating multiple carbon nanotubes with voids formed between them (preparation step). Next, in the powder filling apparatus 10, the internal gas is discharged from the exhaust port 2A by a ventilation mechanism (not shown) to reduce the pressure (vacuum) inside the outer cylinder 2, and the auger 3 is driven by a conveying mechanism (not shown), while the carbon nanotube structure 6A is supplied into the cylindrical filter 1 from one end 1A (upper end in the figure).

[0034] Initially, when the carbon nanotube structure 6A is supplied, a roughly cylindrical carbon nanotube layer (not shown) is formed on the surface of the cylindrical filter 1 by the carbon nanotubes constituting the carbon nanotube structure 6A, and this carbon nanotube layer acts as a filter. In other words, the cylindrical filter 1 functions as a multilayer filter with an additional filter formed on its surface (preliminary procedure).

[0035] Next, the subsequently supplied carbon nanotube structure 6A is biased toward the inner circumferential surface side of the cylindrical filter 2 (the carbon nanotube layer side mentioned above) by the ventilation mechanism, and transported to the other end side 1B (lower end in the figure) of the cylindrical filter 1 by the drive of the auger 3. This removes the voids within the carbon nanotube structure 6A, forming a carbon nanotube structure 6B as a fibrous structure B with a higher bulk density than the carbon nanotube structure 6A (void removal step). By following the above procedure, the desired carbon nanotube structure 6B with increased bulk density can be obtained.

[0036] In this embodiment, when the bulk density of the carbon nanotube structure 6A as fibrous structure A is ρA (g / ml) and the bulk density of the carbon nanotube structure 6B as fibrous structure B is ρB (g / ml), the relationship 1.3 ≤ ρB / ρA ≤ 200 is satisfied. Here, ρB / ρA can be 100 or less, 80 or less, 50 or less, 30 or less, 20 or less, or 10 or less.

[0037] The bulk density ρA of the carbon nanotube structure 6A can be 0.005 (g / ml) or more and 0.2 (g / ml) or less, 0.01 (g / ml) or more, 0.1 (g / ml) or more, less than 0.1 (g / ml), or less than 0.01 (g / ml).

[0038] When the bulk density ρA of the carbon nanotube structure 6A is 0.005 (g / ml) or more and 0.01 (g / ml) or less, it is preferable that ρB / ρA is 3 or more. When the bulk density ρA is greater than 0.01 (g / ml) and less than 0.1 (g / ml), it is preferable that ρB / ρA is 1.5 or more. When the bulk density ρA is 0.1 (g / ml) or more and 0.2 (g / ml) or less, it is preferable that ρB / ρA is 1.3 or more.

[0039] <Modification> In this embodiment, CNTs were used as the fibrous structure for the explanation, but CNTs are merely examples, and fibrous structures made of other fibrous materials such as cellulose nanofibers or carbon fibers may also be used.

[0040] In this embodiment, a mode using a screw-type powder filling device has been described as an example. However, the present invention is not limited to this mode. For example, modes implemented using a rotary valve-type filling device, modes implemented by performing a decompression process inside a bag using a compression bag, and modes implemented by performing a decompression process inside a container using a bellows container are also included, and the devices to be implemented are not particularly limited. Note that, as the above-described decompression means, for example, a so-called compression mode in which the gas inside is pushed out by external pressure from the outside of the bag or container at a pressure within a range where the dispersibility of the fibrous structure is not impaired is also included, and modes of decompression alone, compression alone, and combinations of these are also included.

[0041] Further, in the screw-type powder filling device in this embodiment, the volume reduction of CNTs has been achieved only by the decompression means (device), but it is not limited thereto, and a configuration combining a decompression part and a compression part can be adopted. Specifically, separately from the decompression means (device), a compression means (device) may be prepared, and a configuration combining a decompression device and a compression device may be adopted. Also, the screw-type powder filling device may be configured by dividing it into a plurality of zones, and a configuration in which a compression zone and a decompression zone are appropriately combined can be adopted. Considering miniaturization of the device and the like, a configuration in which one screw-type powder filling device is composed of a plurality of zones and a compression zone and a decompression zone are combined is preferable.

[0042] Also, in this embodiment, the desired carbon nanotube structure 6B was obtained by a one-step process as described above. However, for example, when the bulk density is not within the desired range in a single process or when a higher bulk density is required, the carbon nanotube structure 6A may be processed multiple times in the void removal step to obtain the carbon nanotube structure 6B. For example, a further pressure reduction treatment may be performed on the carbon nanotube structure subjected to the pressure reduction treatment to obtain a carbon nanotube structure having a higher bulk density than the carbon nanotube structure. Specifically, in the void removal step, a carbon nanotube structure C obtained by subjecting the carbon nanotube structure 6A to a pressure reduction treatment (void removal step 1) using an auger-type powder filling device or the like is filled into a packaging bag using a filling device that fills the carbon nanotube structure C discharged from the device into the packaging bag, and a pressure reduction treatment (void removal step 2) is performed inside the filled packaging bag to reduce the voids inside the carbon nanotube structure C and form a carbon nanotube structure 6B as a fibrous structure B having a higher bulk density than the carbon nanotube structure C. Here, it is preferable that the bulk density ρC (g / ml) of the carbon nanotube structure C satisfies the relationship of 1 ≦ ρB / ρC ≦ 2.

[0043] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were performed by the following methods.

[0044] <Bulk density> Using a bulk density measuring instrument (manufactured by Tsutsui Rikagaku Kikai Co., Ltd., tap-type densely packed bulk density measuring machine 'TPM-3A'), a 150-ml graduated cylinder (capacity 150 ml, outer diameter 35 mmφ) was filled with 150 ml of CNT as a fibrous material. Then, after performing a total of 300 tap operations at a tapping width of 20 mm and a tap speed of 36 times / minute, the mass and volume of the fibrous material were measured. Bulk density (g / ml) = mass of CNT (g) / volume after tapping <Evaluation of dispersibility> 0.4 g of CNT, 0.8 g of carboxymethyl cellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Cellogen 5A), and 98.8 g of pure water were placed in a glass bottle container and mixed to obtain a crude CNT dispersion. Next, the obtained crude CNT dispersion was subjected to a dispersion treatment at 42 MPa for 10 passes using a wet jet mill (manufactured by Yoshida Kikai Kogyo Co., Ltd., model number 'NVL-ES008A-D10', product name 'Nanovator (registered trademark)') to obtain a CNT dispersion. Pure water was added to the obtained CNT dispersion and diluted so that the CNT concentration became 0.001% by mass to obtain a CNT dispersion for measurement. The obtained CNT dispersion for measurement was measured using a Zetasizer Nano (manufactured by Malvern, product name 'Nano ZS') under the conditions of a temperature of 25°C, a scanning number of 3 times, and a scanning time of 60 seconds, and the harmonic mean diameter (Z average diameter) was determined, and the quality was judged according to the following criteria. Good dispersibility: The harmonic mean diameter (Z average diameter) is 5000 nm or less Poor dispersibility: The harmonic mean diameter (Z average diameter) exceeds 5000 nm Also, as an index indicating that the dispersibility does not decrease before and after performing a volume reduction treatment on the used CNT, the harmonic mean diameter (nm) before the treatment / harmonic mean diameter (nm) after the treatment was calculated. It is preferably 0.5 to 1.5, and more preferably 0.8 to 1.2, that the harmonic mean diameter (nm) before the treatment / harmonic mean diameter (nm) after the treatment is 0.5 to 1.5.

[0045] <Example 1> A carbon nanotube structure A1 containing single-walled carbon nanotubes (CNT1) as a fibrous nanomaterial was manufactured according to the method disclosed in Example 4 of International Publication No. 2022 / 114237. The average diameter of CNT1 is 5.9 nm, the average length is 221 μm, and the BET specific surface area is 854 m ２The g / g and G / D ratio were 1.4. The bulk density ρA of carbon nanotube structure A1 was 0.0176 (g / ml). Dispersibility evaluation of carbon nanotube structure A1 showed that the harmonic mean diameter was 3700 nm, which is less than 5000 nm, indicating good dispersibility. Next, 29 g of carbon nanotube structure A1 was placed in a compression bag with a check valve, and after closing the double zipper, the air inside the compression bag was removed through the check valve. The vacuum pressure at that time was approximately 30 kPa. After depressurizing for 2 minutes to remove the air inside, the double zipper was opened, and carbon nanotube structure B1 was obtained inside the compression bag. The bulk density and dispersibility of the obtained carbon nanotube structure B1 were evaluated, and the bulk density (ρB) of carbon nanotube structure B1 was 0.0481 (g / ml), with ρB / ρA = 2.73. Therefore, the bulk density ratio ρB / ρA of the carbon nanotubes before and after treatment satisfied the relationship 1.3 ≤ ρB / ρA ≤ 200. When the dispersibility of such carbon nanotube structure B1 was evaluated, the harmonic mean diameter was 4300 nm, which is less than or equal to 5000 nm, indicating good dispersibility. Furthermore, the harmonic mean diameter before treatment / harmonic mean diameter after treatment = 1.14, which satisfies the above index of 0.8 to 1.2, indicating that the dispersibility does not decrease due to the treatment. In addition, the bulk density (ρB) of carbon nanotube structure B1 was greater than the bulk density (ρA) of carbon nanotube structure A1, resulting in improved handling without scattering or other issues.

[0046] <Example 2> A carbon nanotube structure A2 containing single-walled carbon nanotubes (CNT2) as a fibrous nanomaterial was manufactured according to the method disclosed in Example 4 of International Publication No. 2022 / 114237. The average diameter of the CNT2 was 6.2 nm, the average length was 160 μm, and the BET specific surface area was 844 m². ２The g / g and G / D ratio were 1.2. The bulk density ρA of carbon nanotube structure A2 was 0.0192 (g / ml). Dispersibility evaluation of carbon nanotube structure A2 showed that the harmonic mean diameter was 3700 nm, which is less than 5000 nm, indicating good dispersibility. 45 g of carbon nanotube structure A2 was placed in a 3 L bellows container, and the air inside the container was removed by folding the container. The vacuum pressure at that time was approximately 30 kPa. After removing the air inside by depressurizing for 2 minutes, the container opening was opened, and carbon nanotube structure B2 was obtained inside the container. The bulk density and dispersibility of the obtained carbon nanotube structure B2 were evaluated, and the bulk density (ρB) of carbon nanotube structure B2 was 0.0258 (g / ml), and ρB / ρA = 1.34. Therefore, the bulk density ratio ρB / ρA of the carbon nanotube before and after treatment satisfied the relationship 1.3 ≤ ρB / ρA ≤ 200. When the dispersibility of this carbon nanotube structure B was evaluated, the harmonic mean diameter was 4000 nm and less than or equal to 5000 nm, indicating good dispersibility. Furthermore, the harmonic mean diameter before treatment / harmonic mean diameter after treatment = 1.09, satisfying the above index of 0.8 to 1.2, indicating that the dispersibility did not decrease due to the treatment. In addition, the bulk density (ρB) of carbon nanotube structure B2 was greater than the bulk density (ρA) of carbon nanotube structure A2, resulting in improved handling without scattering or other issues.

[0047] As shown in Examples 1 and 2, the bulk density ratio ρB / ρA of carbon nanotubes before and after treatment satisfies the relationship 1.3 ≤ ρB / ρA ≤ 200, indicating that the bulk density of carbon nanotubes can be increased to improve handling while maintaining sufficient dispersibility. Furthermore, as shown in Examples 1 and 2, the harmonic mean diameter before treatment / harmonic mean diameter after treatment is in the range of 0.8 to 1.2, indicating that the dispersibility does not decrease as a result of this treatment.

[0048] According to the present invention, it is possible to provide a method for manufacturing a fibrous structure that improves the handling of the fibrous structure and ensures sufficient dispersibility in solvents and the like.

[0049] 1...Cylindrical filter 1A...One end 1B...Other end 1X...Mesh section 2...Outer cylinder 2A...Exhaust port 3...Auger 4...Vacuum chamber 5...Space 6A, 6B...Carbon nanotube structure

Claims

1. A method for manufacturing a fibrous structure, comprising: a preparation step of preparing a fibrous structure A formed by aggregating multiple fibrous materials with voids formed between them; and a void removal step of removing a portion of the voids in the fibrous structure A to form a fibrous structure B, wherein the bulk density of the fibrous structure A is ρA (g / ml) and the bulk density of the fibrous structure B is ρB (g / ml), satisfying 1.3 ≤ ρB / ρA ≤ 200.

2. A method for manufacturing a fibrous structure according to claim 1, satisfying ρB / ρA ≤ 20.

3. The method for producing a fibrous structure according to claim 1 or 2, wherein the fibrous material comprises at least one of a fibrous nanomaterial and a carbon fiber.

4. The method for producing a fibrous structure according to claim 3, wherein the fibrous nanomaterial comprises at least one of carbon nanotubes and cellulose nanofibers.

5. The method for producing a fibrous structure according to claim 4, wherein the carbon nanotubes include single-walled carbon nanotubes.

6. A method for manufacturing a fibrous structure according to claim 1 or 2, wherein the fibrous structure consists substantially only of a fibrous material.

7. A method for manufacturing a fibrous structure according to claim 1 or 2, wherein an apparatus is used having a filter that allows gas to pass through but substantially prevents the fibrous material from passing through, and a ventilation mechanism that moves the gas inside the filter to the outside, wherein in the preparation step, the fibrous structure A is supplied to the inside of the filter, and in the void removal step, the ventilation mechanism is used to vent the gas in the voids in the fibrous structure A supplied to the inside of the filter to the outside of the filter, thereby forming the fibrous structure B inside the filter.

8. A method for manufacturing a fibrous structure according to claim 1 or 2, wherein the apparatus comprises: a cylindrical filter formed in a cylindrical shape that allows gas to pass through but substantially prevents the fibrous material from passing through; a ventilation mechanism for moving the gas inside the cylindrical filter to the outside; and a transport mechanism for transporting the fibrous structure A supplied to the inner space of the cylindrical filter from one end to the other of the cylindrical filter, wherein in the preparation step, the fibrous structure A is supplied to the inside of the cylindrical filter; and in the void removal step, the gas in the voids of the fibrous structure A supplied to the inside of the cylindrical filter is vented to the outside of the cylindrical filter by the ventilation mechanism, and the fibrous structure A inside the cylindrical filter is transported to the other end of the cylindrical filter by the transport mechanism to form the fibrous structure B.

9. A method for manufacturing a fibrous structure according to claim 8, wherein the void removal step comprises a preliminary step of forming a fibrous material layer on the surface of the cylindrical filter by collecting the fibrous material A on the surface of the cylindrical filter, while the ventilation mechanism allows the gas in the voids in the fibrous structure A supplied to the inside of the cylindrical filter to be vented to the outside of the cylindrical filter, and the transport mechanism transports the fibrous structure A on the inside of the cylindrical filter to the other end, and after the preliminary step, forming the fibrous structure B by allowing the gas in the voids in the fibrous structure A supplied to the inside of the fibrous material layer to be vented to the outside of the cylindrical filter via the fibrous material layer, and the transport mechanism transports the fibrous structure A on the inside of the fibrous material layer to the other end of the cylindrical filter, 10. A method for manufacturing a fibrous structure according to claim 1 or 2, wherein the apparatus comprises: a cylindrical filter formed in a cylindrical shape that allows gas to pass through but substantially prevents the fibrous material from passing through; a ventilation mechanism for moving the gas inside the cylindrical filter to the outside; and a transport mechanism for transporting the fibrous structure A supplied to the inner space of the cylindrical filter from one end to the other of the cylindrical filter, wherein in the preparation step, the fibrous structure A is supplied to the inside of the cylindrical filter; in the void removal step, the gas in the voids in the fibrous structure A supplied to the inside of the cylindrical filter is vented to the outside of the cylindrical filter by the ventilation mechanism, and the fibrous structure A inside the cylindrical filter is transported to the other end of the cylindrical filter by the transport mechanism to form a fibrous structure C; and the apparatus further comprises a filling device for filling the fibrous structure C discharged by the transport mechanism into a packaging bag. A method for manufacturing a fibrous structure, wherein the filling apparatus performs a void removal step 2 to remove a portion of the voids in the fibrous structure C within the packaging bag to form a fibrous structure B.

11. The method for producing a fibrous structure according to claim 1 or 2, wherein the bulk density ρA of the fibrous structure A is 0.005 (g / ml) or more and 0.2 (g / ml) or less.

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