JP7018661B2 - Method for manufacturing carbon nanotube dispersion liquid, carbon nanotube dispersion liquid, and method for manufacturing carbon nanotube composite film - Google Patents

Description

The present invention relates to a carbon nanotube composite membrane and a carbon nanotube dispersion liquid.

Carbon nanotubes (hereinafter, also referred to as CNTs) have attracted a great deal of attention as new materials capable of exhibiting various new functions, and are being actively researched and developed all over the world. In the future, in order to effectively use CNTs for various industrial applications, it is an indispensable task to form CNTs into a homogeneous thin film or thick film by a simple method. Further, when this film is used as a conductive film or an electrode, it is necessary to impart sufficient conductivity to the film.

In order to form a film of CNT easily and at low cost, a method of dispersing CNT, which is originally insoluble, in a solution such as a surfactant and forming a film by coating has been proposed (Non-Patent Document 1). Further, for example, by using gelatin or a cellulose derivative as a matrix polymer (Patent Document 1), a CNT-containing thin film in which a plurality of CNTs are separated from each other and dispersed in a good state has been proposed.

In order for the CNT-containing thin film to exhibit the high conductivity and semiconductor characteristics of CNT, it is necessary to prevent the mixture in the thin film from interfering with the electrical characteristics. However, in the above method, it is necessary to mix a large amount of surfactant and matrix polymer for dispersion, but since these are electrically insulators, a sufficient amount of current can be passed through the thin film. Have difficulty. Therefore, there is known a method of decomposing and removing a non-conductive substance by washing or heating and firing these thin films (Non-Patent Document 2) after producing the thin films.

However, in this method, since it is necessary to put the thin film in a high temperature furnace, there is a problem in sequentially processing the roll sheet-like thin film. Further, since it is heated at a high temperature, there is a problem that a substrate such as a plastic substrate which may be softened or decomposed at a high temperature cannot be used.

Further, in order to improve the conductivity of the CNT-containing thin film, a soluble polyphenylene vinylene substitute or a copolymer thereof, or a conductive polymer such as a soluble polythiophene substitute is used as the matrix polymer (Patent). Document 2) has been proposed.

However, even in this method, since it is necessary to insert a large amount of the conductive polymer for dispersion, the conductive polymer is sandwiched between the CNTs or between the CNT bundles. Therefore, since the conductivity and semiconductor characteristics of the film are defined by the electrical characteristics of the conductive polymer, the high conductivity and semiconductor characteristics inherent in CNT are not exhibited. That is, it is clear that such a thin film cannot fully utilize the electronic functions originally possessed by CNTs.

Therefore, it has also been proposed to further dope the dispersant contained in the thin film using a dopant solution (Patent Document 3). However, since the conductivity of the conductive polymer is inferior to the electronic function of the CNT even if it is doped, the conductivity of the entire membrane is defined by the electrical characteristics of the inferior conductive polymer, which is sufficient. It is not possible to ensure sufficient conductivity. Further, a step of immersing in the dopant solution, a step of cleaning the remaining dopant, and a step of drying the cleaned CNT-containing thin film are required.

Further, in order to improve the adhesion of the CNT-containing thin film to the substrate, a method of mixing polyacrylic acid or carboxymethyl cellulose as a matrix polymer together with a surfactant to produce a transparent conductive film has been proposed (non-). Patent Document 3).

However, in this method, sodium dodecyl sulfate and Triton-X100 are added as surfactants at about 10 times the weight of CNT to disperse the CNT, and then polyacrylic acid or carboxymethyl cellulose is added. For this reason, CNTs are covered with a surfactant, and polyacrylic acid and carboxymethyl cellulose do not come into direct contact with CNTs, and simply function as a binder for increasing the adhesive strength. Further, in order to improve the conductivity of the film, it is necessary to wash the film after forming the film to remove the surfactant, and then immerse the film in an aqueous nitric acid solution for doping.

Further, a method for producing a stretchable conductive film using polyacrylic acid as a CNT dispersant has been proposed (Non-Patent Document 4).

However, in this method, sufficient conductivity cannot be obtained by CNT alone, and a step of mixing with expensive silver nanoparticles and further mixing with the polyurethane matrix is required in order to impart conductivity to the film.

Further, in order to improve the flatness of the surface of the thin film of CNT alone and the adhesion to the substrate, a method of forming a thin film of a mixture of CNT and polyacrylic acid on the upper or lower part of the CNT single film has been proposed. (Patent Document 4).

However, in this method, it is necessary to separately form the layer of the CNT single film and the layer of the mixed film of CNT and polyacrylic acid, and the surfactant required for dispersion is washed and removed from the layer of the CNT single film. The manufacturing process is complicated because it requires a step to be performed.

International Publication No. 2005/082775 Pamphlet Japanese Unexamined Patent Publication No. 2006-265035 Japanese Unexamined Patent Publication No. 2008-10339 U.S. Patent Publication No. 2009/0225967

Michael J. O'Connel et al., "Band gap fluorescence from individual single-walled carbon nanotubes", Science, 2002, 297, 593-596. Annamalai Karthigenan et al., "Highly sensitive, room-temperature gas sensors prepared from cellulose derivative assisted dispersions of single-wall carbon nanotubes", Jpn. J. Appl. Phys., 2008, 47, 7440-7443. Yan Wang et al. "Fabrication and evaluation of adhesion enhanced flexible carbon nanotube transparent conducting films", J. Mater. Chem. C, 2015, 3, 3796-3802. Hangil Ki et al., "Chemically Driven, Water-Soluble Composites of Carbon Nanotubes and Silver Nanoparticles as Stretchable Conductors", ACS Macro Lett. 2015, 4, 769-773.

As described above, CNT composite films that disperse CNTs well and the dispersants do not interfere with the electrical connection between the CNTs, i.e. the dispersants do not need to be removed after film formation, and such composite films. If a CNT composite dispersant or a dispersion method for producing CNTs can be developed, flexible conductive films and conductive sheets can be produced by utilizing the flexibility of CNTs. For example, when this is a thin film, it can be used as a transparent electrode such as a touch panel, an electrode of an organic EL or an organic solar cell, and can be used as an electromagnetic wave absorbing sheet. Further, when this is a thick film, it can be used as a flexible electrode or wiring that surpasses a metal film or a metal foil. As described above, the industrial utility value is extremely large, but the present situation is that a composite membrane that meets such a demand and a CNT dispersion liquid for producing the composite membrane have not yet been developed.

The present invention has been made in view of such a situation, and provides a CNT composite film and a CNT dispersion liquid having good electrical connection in a CNT network, excellent electrical performance, and excellent durability. The purpose is to do.

[A] A carbon nanotube dispersion liquid containing a polymer acid that functions as a dispersant and a dopant for carbon nanotubes, wherein the concentration of the carbon nanotubes is 0.005% by weight or more and 1% by weight or less, and the polymer. The concentration of the acid is 0.005% by weight or more and 5% by weight or less, and the weight ratio of the carbon nanotube to the polymer acid is 1: 1 to 1: 5. The carbon nanotube is a region where the carbon nanotubes are in contact with each other. A carbon nanotube dispersion liquid in which the polymer acid surrounds the carbon nanotubes except for.
[B] The carbon nanotube dispersion liquid according to [A], wherein the polymer acid is at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid and poly (p-styrene sulfonic acid).
[C] The carbon nanotube dispersion liquid according to [B], wherein the polyacrylic acid has a weight average molecular weight of 500 or more and 250,000 or less.
[D] A carbon nanotube composite film formed by providing the carbon nanotube dispersion liquid according to any one of [A] to [C] on a substrate.
[E] The carbon nanotube composite membrane according to [D], wherein the carbon nanotube composite membrane has a conductivity of 400 S / cm or more.
[F] The area ratio of the part containing the polymer acid and the carbon nanotube and the part where the polymer acid is attached to a single carbon nanotube or a bundle of carbon nanotubes and the part where the carbon nanotube is exposed is 1: 1. From 10 to 1 carbon nanotube composite film.
[G] A carbon nanotube composite film containing a polymer acid and carbon nanotubes, wherein the ratio of the number of atoms of carbon to oxygen on the surface layer of the carbon nanotube composite film is 12: 1 to 2.5: 1.
[H] A carbon nanotube composite film containing a polymer acid and a carbon nanotube, the weight ratio of the polymer acid to the carbon nanotube is 0.8: 1 to 5: 1, and the conductivity of the carbon nanotube composite film. A carbon nanotube composite film with a rate of 400 S / cm or more.
[I] The carbon nanotube composite according to [F] to [H], wherein the polymer acid is at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid and poly (p-styrene sulfonic acid). film.
[J] The carbon nanotube composite membrane according to [F] to [H], wherein the polymer acid has a weight average molecular weight of 500 or more and 250,000 or less.
[K] The carbon nanotube composite membrane according to [I], wherein the repeating unit of the polyacrylic acid is 8 or more and 3,500 or less.
[L] The absorbance of carbon nanotube-based absorption in the carbon nanotube composite film at a wavelength of 1550 nm is the same at a wavelength of 550 nm including polyvinylpyrrolidone and carbon nanotubes at a wavelength of 1550 nm. The carbon nanotube composite film according to any one of [F] to [K], which decreases by 50% or more with respect to the absorbance.
[M] A carbon nanotube composite film containing a polymer acid and a carbon nanotube, wherein the weight ratio of the polymer acid to the carbon nanotube is 0.8: 1 to 5: 1 and the wavelength is 550 nm. A carbon nanotube composite film having a permeability of 90% or more and a sheet resistance of the carbon nanotube composite film of 500 Ω / □ or less.
[N] A carbon nanotube composite film containing a polymer acid and carbon nanotubes, wherein the weight ratio of the polymer acid to the carbon nanotubes is 0.8: 1 to 5: 1, and the film thickness of the carbon nanotube composite film. A carbon nanotube composite film in which the sheet resistance of the carbon nanotube composite film is 10 Ω / □ or less when is 1 μm.
[O] The carbon nanotube composite film according to any one of [F] to [N], wherein an acid or an oxidizing agent adheres to the carbon nanotubes contained in the carbon nanotube composite film.
[P] A carbon nanotube dispersion containing a polymer acid, a carbon nanotube, and a solvent, wherein the weight ratio of the polymer acid to the carbon nanotube is 0.8: 1 to 5: 1, and the carbon nanotube is used. The permeability of the carbon nanotube composite film at a wavelength of 550 nm, which was evaluated as the carbon nanotube composite film from which the solvent was removed from the dispersion liquid, was 90% or more, and the sheet resistance of the carbon nanotube composite film was 500 Ω / □. The following carbon nanotube dispersion liquid.
[Q] A carbon nanotube dispersion containing a polymer acid, a carbon nanotube, and a solvent, wherein the weight ratio of the polymer acid to the carbon nanotube is 0.8: 1 to 5: 1, and the carbon nanotube. The sheet resistance of the carbon nanotube composite film when the thickness of the carbon nanotube composite film is 1 μm, which was evaluated as the carbon nanotube composite film obtained by removing the solvent from the dispersion liquid, is 10 Ω / □ or less. liquid.
[R] A method for producing a carbon nanotube dispersion liquid in which a polymer acid and carbon nanotubes are dispersed in a solvent in a weight ratio of 0.8: 1 to 5: 1.
[S] The method for producing a carbon nanotube dispersion liquid according to [R], wherein the polymer acid and carbon nanotubes are dispersed in the solvent while being cooled to 5 ° C. or lower.
[T] The carbon nanotube dispersion according to [R] or [S], wherein the polymer acid is at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid and poly (p-styrene sulfonic acid). Liquid manufacturing method.
[U] The method for producing a carbon nanotube dispersion liquid according to any one of [R] to [T], wherein the polymer acid has a weight average molecular weight of 500 or more and 250,000 or less.
[V] The method for producing a carbon nanotube dispersion liquid according to [T], wherein the repeating unit of the polyacrylic acid is 8 or more and 3,500 or less.
[W] The method for producing a carbon nanotube dispersion liquid according to any one of [R] to [V], wherein the carbon nanotubes are treated with an acid or an oxidizing agent before the carbon nanotubes are dispersed in the solvent.
[X] A carbon nanotube composite in which a carbon nanotube dispersion is produced by the method for producing a carbon nanotube dispersion according to any one of [R] to [W] and the solvent is removed from the produced carbon nanotube dispersion. How to manufacture the membrane.
[Y] The method for producing a carbon nanotube composite film according to [X], wherein the carbon nanotube composite film is treated with an acid or an oxidizing agent.
[Z] The method for producing a carbon nanotube composite membrane according to [X], wherein the carbon nanotube composite membrane is heated or treated with an alkali to remove a part or all of the polymer acid.

According to the present invention, there is provided a CNT composite film and a CNT dispersion liquid which are excellent in electrical performance and durability by improving electrical connection in a CNT network.

CNTs can be uniformly dispersed with a small amount of polymer acid to obtain a homogeneous composite film, and a conductive film can be obtained without removing the dispersant after film formation, which simplifies the post-treatment process and manufactures. It is advantageous in the process. Further, since the polymer acid itself exhibits a doping effect, it is not necessary to add a separate dopant, and since the polymer acid is stable and has no volatility, a conductive film exhibiting stable conductivity over a long period of time can be obtained. Furthermore, since the molecular structure of not only CNTs but also polymer acids is flexible, it is possible to obtain a film that is extremely resistant to bending.

It is a schematic diagram explaining the CNT composite film 10 which concerns on one Embodiment of this invention. It is a figure which shows the relationship between the sheet resistance value of the CNT composite film which concerns on one Example of this invention, and the transmittance (relative value when the transmittance of a substrate is 100%) at a wavelength of 550 nm. It is a figure which shows the relationship between the sheet resistance value of the CNT composite film which concerns on one Example of this invention, and the transmittance (relative value when the transmittance of a substrate is 100%) at a wavelength of 550 nm. It is a figure which shows the transmittance with respect to the wavelength of the transmitted light of the CNT composite film which concerns on one Example of this invention. A transmission electron microscope according to an embodiment of the present invention is shown, and (b) shows an enlarged view of (a). An atomic force microscope image according to an embodiment of the present invention is shown, and (b) shows an enlarged view of (a). A transmission electron microscope according to an embodiment of the present invention is shown, and (b) shows an enlarged view of (a). An atomic force microscope image according to an embodiment of the present invention is shown, and (b) shows an enlarged view of (a). The XPS spectrum of the CNT composite film which concerns on one Example of this invention is shown. The XPS spectrum of the CNT composite film which concerns on one Example of this invention is shown. The fitting of the XPS spectrum of the CNT composite film which concerns on one Example of this invention is shown. The fitting of the XPS spectrum of the CNT composite film which concerns on one Example of this invention is shown. The XPS spectrum of the CNT composite film which concerns on one Example of this invention is shown. The XPS spectrum of the CNT composite film which concerns on one Example of this invention is shown.

Hereinafter, the carbon nanotube composite membrane (hereinafter, also referred to as CNT composite membrane) and the carbon nanotube dispersion liquid (hereinafter, also referred to as CNT dispersion liquid) according to the present invention will be described with reference to the drawings. The CNT composite membrane and the CNT dispersion liquid of the present invention are not construed as being limited to the description contents of the embodiments and examples shown below. In the drawings referred to in the present embodiment and the embodiments described later, the same parts or parts having the same functions are designated by the same reference numerals, and the repeated description thereof will be omitted.

[CNT composite membrane]
FIG. 1 is a schematic diagram illustrating a CNT composite membrane 10 according to an embodiment of the present invention. The CNT composite membrane 10 according to the embodiment of the present invention contains the polymer acid 1 and the CNT 3. The area ratio of the portion where the polymer acid 1 is attached to one CNT 3 alone or the CNT bundle 5 and the portion where the CNT 3 is exposed is 1: 1 to 10: 1. The polymer acid 1 adheres by a van der Waals force so as to surround the simple substance of the CNT 3 or the bundle 5 of the CNT.

The CNT bundle 5 is a bundle-like structure in which the CNTs 3 are aggregated, and the CNTs 3 are locally oriented, but the bundle 5 may have a structure in which the CNTs 3 are partially separated from each other. Further, it includes one or more of a portion where the CNTs 3 are in contact with each other (contact portion 7a), a portion where the CNT bundles 5 are in contact with each other (contact portion 7b), and a portion where the CNT 3 and the CNT bundle 5 are in contact with each other (contact portion 7c). .. As a result, the CNT 3 constitutes a network as a whole. In this CNT network, the electrical connection between the CNT 3 and the CNT 3 at the contact portion 7a, the electrical connection between the bundle 5 and the bundle 5 at the contact portion 7b, and the electrical connection between the CNT 3 and the CNT bundle 5 at the contact portion 7c. And imparts conductivity to the entire network.

The CNT composite film 10 includes a network of the polymer acid 1 and the CNT, and the polymer acid 1 is arranged around the CNT 3 while the contact between the CNTs 3 is ensured. Therefore, in the CNT composite film 10, the electrical connection between the CNT 3 and the CNT 3, the electrical connection between the bundle 5 and the bundle 5, and the electrical connection between the CNT 3 and the bundle 5 of the CNT are not hindered by the polymer acid 1. Therefore, the CNT composite film 10 improves the electrical connection in the CNT network and is excellent in electrical performance.

Here, the area ratio of the portion where the polymer acid 1 is attached to one CNT 3 alone or the CNT bundle 5 and the portion where the CNT 3 is exposed is, for example, a transmission electron microscope (TEM) image and an energy dispersive X. It can be calculated by combining the area ratio of oxygen atom and carbon atom on the image of CNT alone or CNT bundle in combination with line spectroscopy (EDX). Alternatively, by utilizing the fact that X-ray photoelectron spectroscopy (XPS) can observe only a region (hereinafter referred to as a surface layer) at a depth of several nanometers to 10 nanometers on the sample surface, carbon and oxygen on the surface layer of the composite film can be observed. It can be calculated from the intensity ratio of.

Further, the area ratio of oxygen atom to carbon atom corresponds to the ratio of the number of carbon to oxygen atoms on the surface of the CNT composite film 10. The CNT composite film 10 has a surface carbon to oxygen atom number ratio of 12: 1 to 2.5: 1. If the ratio of the number of atoms of carbon and oxygen on the surface of the CNT composite film 10 is within this range, a sufficient doping effect can be obtained. The ratio of the number of atoms of carbon to oxygen on the surface layer of the CNT composite film 10 can be calculated based on the XPS spectrum.

In the present invention, the type of CNT3 is not particularly limited, and conventionally known ones can be used. For example, any of single-walled CNT (hereinafter, also referred to as SWNT), double-walled CNT (hereinafter, also referred to as DWNT), multi-walled CNT (hereinafter, also referred to as MWNT), rope-shaped CNT, and ribbon-shaped CNT is used. Further, it is also possible to use the metallic CNT, the metallic CNT that has undergone the separation step of the semiconductor CNT, or the semiconductor CNT alone.

Although the length and diameter of the CNTs are not particularly limited, in order to obtain a highly conductive CNT composite film, a diameter of 0.4 nm or more and 2.0 nm or less and a length of 0.5 μm or more and 20 μm or less are preferable. Further, a single-walled CNT having excellent crystallinity and a long length is preferable. Furthermore, it is preferable to use a high-quality single-layer CNT synthesized by the direct-injection pyrolysis synthesis (DIPS) method because a more homogeneous dispersion can be obtained, and thus a highly conductive composite film can be obtained.

In one embodiment, the polymer acid 1 is at least one selected from the group consisting of a polymer carboxylic acid such as polyacrylic acid and polymethacrylic acid, and a polymer sulfonic acid such as poly (p-styrene sulfonic acid). Can be preferably used, but is not limited thereto.

In one embodiment, the weight average molecular weight of the polymer acid 1 is preferably 500 or more and 250,000 or less, and preferably 1,800 or more and 25,000 or less. Further, it is preferable that the average value of the repeating unit of polyacrylic acid (hereinafter, also referred to as PAA) is 8 or more and 3,500 or less, and 25 or more and 350 or less. A polymer acid having a large molecular weight disperses CNTs better, but as shown in Examples described later, a polymer acid having a small molecular weight tends to have a larger doping effect.

When polyacrylic acid is used, the molecular weight is not particularly limited, but if the weight of the polyacrylic acid is the same, it is better to use the polyacrylic acid having a smaller molecular weight to have a higher doping effect. When polyacrylic acid having a weight average molecular weight (MW) of 25,000 or less is used, the doping effect is large. It is presumed that this is because polyacrylic acid having a large molecular weight partially self-aggregates, the area in contact with CNTs decreases, and the doping effect is not sufficiently exhibited.

PAA is generally considered to be a macromolecule with a relatively large molecular weight dispersion. The company's PAA with a weight average molecular weight of 50,000 is said to contain macromolecules with a molecular weight of 1000 to 1000000. In addition, the company's sodium polyacrylate with a weight average molecular weight of 20000 is said to contain macromolecules with a molecular weight of 100 to 300,000. (MR Dubay: "The Molecular Weight Effects of Poly (acrylic acid) on Calcium Carbonate Inhibition in the Kraft Pulping Process" Dissertation, the University of Minnesota, May, 2011, https://conservancy.umn.edu/handle/11299/ 107782). Therefore, the PAA shown by the weight average molecular weight in the present specification may contain a PAA having a molecular weight of about 1/10 to 1/100 times the weight average molecular weight to a PAA having a molecular weight of about 10 to 100 times. Intended to be.

In one embodiment, the weight ratio of the polymeric acid 1 to CNT 3 is 0.8: 1 to 5: 1. When the weight ratio of the polymer acid 1 and CNT3 is in this range, the electrical connection between CNT3 and CNT3, the electrical connection between bundle 5 and bundle 5, and the electrical connection between CNT3 and CNT bundle 5 are high. Not hindered by molecular acid 1.

For example, the weight ratio of polyacrylic acid to CNT is preferably 1: 1 to 5: 1, and more preferably 1: 1 to 3: 1. In this range, the polymer acid is adsorbed so as to cover the circumference of the CNT or the CNT bundle and disperses the CNT well, but the polymer acid cannot completely cover the surface of the CNT or the CNT bundle, and the CNT or the CNT bundle is not covered. There is a part where the CNT bundle is exposed. Therefore, the CNT composite film exhibits good conductivity because it does not interfere with the electrical connection between the CNTs or the CNT bundles. On the other hand, if the amount of the polymer acid is too small, the CNTs cannot be sufficiently dispersed. Further, if the amount of the polymer acid is too large, the polymer acid completely covers the periphery of the CNT. In such a state, the contact between the CNTs or the CNT bundles is hindered, so that the CNT composite film does not show good conductivity.

In one embodiment, the conductivity of the CNT composite film 10 is 400 S / cm or more, preferably 1,000 S / cm or more. The CNT composite film 10 is excellent in electrical performance because it has a good electrical connection in the CNT network.

In one embodiment, the CNT composite membrane 10 has the same absorbance at a wavelength of 550 nm, including polyvinylpyrrolidone (hereinafter also referred to as PVP) and CNT3, for the absorbance of absorption based on CNT3 at a wavelength near 1550 nm. It is reduced by more than 50% with respect to the absorbance of the indicated film at a wavelength of 1550 nm. That is, in the CNT composite film 10, the absorption intensity of the semiconducting CNTs existing in the near-infrared region is reduced, and the transmittance in the near-infrared region is increased. Specifically, the absorbance of the absorption peak of the semiconductor CNT having a wavelength around 1500 nm (the wavelength depends on the diameter of the CNT used) is reduced by about 50%. This is because the doping effect of the polymer acid 1 causes charge carriers to be generated in the semiconducting CNTs, resulting in metallic behavior. Such a decrease in the absorbance in the near-infrared region is a phenomenon related to the phenomenon in which the conductivity of the CNT composite film 10 according to the present embodiment is improved.

In one embodiment, when the CNT composite film 10 is manufactured with a thickness such that the transmittance is 90% or more at a wavelength of 550 nm, the sheet resistance of the CNT composite film 10 is 500 Ω / □ or less. Further, in one embodiment, the CNT composite film 10 has a sheet resistance of 10 Ω / □ or less when the film thickness is 1 μm. As described above, the CNT composite film 10 can achieve the world's top level performance in the CNT transparent conductive film. It also has excellent durability.

In one embodiment, the CNT composite film 10 has a change in sheet resistance of 20% or less before and after an environmental durability test (treatment in an environment of humidity 85% and temperature 85 ° C. for 1000 hours).

Further, in one embodiment, the CNT composite film 10 has a change in sheet resistance of 20% or less before and after heating at 100 ° C., 200 ° C., and 280 ° C. for 2 hours, respectively.

Further, in one embodiment, the CNT composite film 10 may be arranged on the substrate. When producing a transparent conductive film using the CNT composite film 10, a transparent substrate can be selected as needed. As the transparent substrate, for example, in addition to a hard substrate such as glass or quartz glass, a flexible substrate and a transparent and flexible substrate can be used. Specifically, a substrate selected from the group consisting of polyethylene naphthalate (PEN), polyimide (PI), polyethylene terephthalate (PET), polyether sulfone (PES), polyethylene (PE), polycarbonate (PC) and the like is used. It can, but is not limited to these. Further, the CNT composite membrane 10 may be a self-supporting membrane.

[CNT dispersion liquid]
The above-mentioned CNT composite film according to the present invention can be obtained by using the CNT dispersion liquid described below. In one embodiment, the CNT dispersion liquid according to the present invention contains a polymer acid that functions as a CNT dispersant and a dopant. The CNT dispersion has a CNT concentration of 0.005% by weight or more and 1% by weight or less, a polymer acid concentration of 0.005% by weight or more and 5% by weight or less, and a weight ratio of CNT to polymer acid of 1: 1 to 1: 1: 1. Equipped with 5. In the CNT dispersion liquid, the polymer acid surrounds the CNTs except for the region where the CNTs come into contact with each other. The polymer acid adheres so as to surround the simple substance of CNT or the bundle of CNT.

In one embodiment, the CNTs and the polymeric acid in the CNT dispersion have a structure similar to the structure in the CNT composite membrane 10 shown in FIG. That is, in the portion of the CNT 3 to which the polymer acid 1 is attached, the CNTs 3 do not come into contact with each other and are well dispersed. On the other hand, in the portion of the CNTs 3 to which the polymer acid 1 is not attached, the CNTs are likely to aggregate with each other due to the van der Waals force, resulting in stronger contact. Therefore, it is presumed that the following three local states exist in the CNT dispersion liquid.
A High molecular weight acid adheres to CNTs and CNTs do not come into contact with each other (stable dispersion state)
The CNTs do not come into direct contact with each other, the intermolecular force in the CNT dispersion is weak, and it is difficult for the CNTs to be electrically connected.
B CNTs are in contact with each other (CNTs are aggregated)
It is an unstable dispersed state of CNTs, the intramolecular force of CNTs is strong, and CNTs are electrically connected.
C A state in which the polymer acid adheres to a part of the CNTs and the CNTs are in contact with each other. .. The intramolecular force is strong at the portion where the CNTs are in contact with each other, and the CNTs are electrically connected.

In the CNT dispersion liquid, the CNT bundle 5 is a bundle-like structure in which the CNTs 3 are aggregated, and the CNTs 3 are locally oriented, but the CNTs 3 may have a structure in which the CNTs 3 are partially separated from each other. .. Further, it includes one or more of a portion where the CNTs 3 are in contact with each other (contact portion 7a), a portion where the CNT bundles 5 are in contact with each other (contact portion 7b), and a portion where the CNT 3 and the CNT bundle 5 are in contact with each other (contact portion 7c). .. As a result, the CNT 3 constitutes a network as a whole.

On the other hand, regardless of the state of the CNTs, at the stage where the CNT dispersion liquid is formed into a CNT composite film (the solvent is dried and removed), the intermolecular force of the CNTs causes the CNTs to selectively polymerize each other. Contact at the part where the acid does not adhere.

Since the above-mentioned polymer acid and CNT are dispersed in the CNT dispersion liquid, detailed description of the polymer acid and CNT will be omitted. The solvent for dispersing the high molecular acid and CNT is a solvent selected from the group consisting of water, methanol, ethanol, 2-propanol, glycerin, ethylene glycol, water and ethanol mixed solution, ethanol and 2-propanol mixed solution, and the like. Can be preferably used.

In one embodiment, the concentration of CNTs in the CNT dispersion is 0.005% by weight or more and 1% by weight or less, preferably 0.01% by weight or more and 0.5% by weight or less. The concentration of the polymer acid in the CNT dispersion is 0.005% by weight or more and 5% by weight or less, preferably 0.01% by weight or more and 1.5% by weight or less.

In one embodiment, the weight ratio of the polymeric acid 1 to CNT 3 is 0.8: 1 to 5: 1. When the weight ratio of the polymer acid 1 and the CNT 3 is in this range, in the CNT composite membrane 10, the electrical connection between the CNT 3 and the CNT 3, the electrical connection between the bundle 5 and the bundle 5, and the bundle 5 between the CNT 3 and the CNT 5 The electrical connection is not hindered by the polymer acid 1.

The physical characteristics of the CNT dispersion liquid can be evaluated as a CNT composite membrane in which the solvent is removed from the CNT dispersion liquid. The CNT composite film from which the solvent has been removed from the CNT dispersion has a sheet resistance of 500 Ω / □ or less when the transmittance of the CNT composite film at a wavelength of 550 nm is 90% or more. That is, when the CNT dispersion liquid according to the present embodiment is evaluated as a CNT composite film having a thickness of 90% or more at a wavelength of 550 nm, the sheet resistance of the CNT composite film is 500. It is a CNT dispersion liquid having Ω / □ or less.

Further, when the film thickness of the CNT composite film from which the solvent is removed from the CNT dispersion liquid is 1 μm, the sheet resistance of the CNT composite film is 10 Ω / □ or less.

(Manufacturing method of CNT dispersion liquid)
In one embodiment, the CNT dispersion liquid according to the present invention can be produced as follows.

(1) Pre-doping step CNT powder is added to a solution in which a dopant such as an oxidizing agent is dissolved, and the mixture is vigorously stirred with a magnetic stirrer or the like for several tens of minutes to one day. Then, the dispersion is filtered and the CNT powder remaining on the filter paper is washed to obtain a doped CNT powder. The pre-doping step is a step arbitrarily performed in the method for producing a CNT dispersion liquid according to the present invention.

It is also possible to improve the conductivity of CNTs by pre-doping CNTs with an acid, an oxidizing agent, or the like before dispersing them in a solvent. In the predoping step, a dopant selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, iodine, bromine, chlorosulfonic acid (superacid), hydroiodic acid, hydrobromic acid and mixtures thereof can be used. ..

As the solvent for dissolving the dopant, the solvent for dispersing the above-mentioned polymer acid and CNT can be used. Further, these solvents can also be used for cleaning the CNT powder remaining on the filter paper.

(2) Pre-dispersion step CNT powder is added to a solution in which a polymer acid as a dispersant is dissolved, and the mixture is vigorously stirred with a magnetic stirrer or the like for several tens of minutes to one day. As the solvent for dispersing CNTs, the above-mentioned solvent can be used. The pre-dispersion step is an essential step in the method for producing a CNT dispersion liquid according to the present invention.

(3) This dispersion step Using the pre-dispersed liquid, CNTs are dispersed more finely by an ultrasonic homogenizer, an ultrasonic bath, jet mill high-pressure dispersion, etc. to obtain a CNT dispersion liquid in which CNTs do not easily aggregate and settle. .. This dispersion step is an essential step in the method for producing a CNT dispersion liquid according to the present invention.

In this dispersion step, the ultrasonic homogenizer strongly disperses the CNT, but if it takes too much time, the CNT and the polymer acid may be damaged. Further, when the polymer acid solution is heated when the CNT dispersion liquid is prepared, the polymer acid is partially self-aggregated in the CNT dispersion liquid, the area where the polymer acid comes into contact with the CNT is reduced, and the doping is performed. It is presumed that the effect will be smaller. Generally, in the dispersion treatment of CNT with an ultrasonic homogenizer, high heat is locally generated by vibrating solvent molecules and polymer acid molecules, so that the polymer acid aggregates violently. In that case, the doping effect becomes small and the contact between the CNTs is hindered.

Therefore, it is effective to minimize the processing time with the ultrasonic homogenizer or to irradiate the ultrasonic waves while cooling the pre-dispersed liquid. For example, by performing pre-dispersion for about 12 hours, a uniform dispersion can be obtained even if the ultrasonic homogenizer irradiation time in this dispersion is shortened, and damage to CNTs and polymer acids due to ultrasonic homogenizer irradiation is minimized. It can be suppressed to the limit. Further, when the uniform dispersion liquid can be obtained in this way, the next ultracentrifugal treatment can be omitted, which is very advantageous in the manufacturing process. Further, in order to shorten the processing time with the ultrasonic homogenizer, it is also effective to perform the treatment with the ultrasonic bus prior to the processing with the ultrasonic homogenizer.

(4) Centrifugation step The CNT dispersion liquid obtained by this dispersion is stretched and separated by an ultracentrifugation device, and the obtained supernatant is used as a dispersion liquid for membrane formation. The centrifugation step is an arbitrary step in the method for producing a CNT dispersion liquid according to the present invention.

In the centrifugation, the rotation speed of the rotor is 2,000 rpm or more and 60,000 rpm or less, preferably 45,000 rpm, and the centrifugation time is about 2 hours. When a CNT dispersion is prepared using high-quality SWNTs, a homogeneous CNT dispersion can be prepared, so that the ultracentrifugation treatment can be omitted.

(Manufacturing method of CNT composite film)
In one embodiment, the CNT composite membrane according to the present invention can be produced as follows using the above-mentioned CNT dispersion liquid.

(5) Film forming process The CNT dispersion obtained by the above-mentioned production method is formed by a method such as spin coating, bar coating, or spray coating, and if necessary, a drying step such as heating is performed to form a CNT composite film. obtain.

The film forming method is not particularly limited, but the casting method, dip coating method, spin coating method, bar coating method, blade coating method, die coating method, spray coating method, inkjet method, screen printing method, etc. can be freely selected. can. In the film forming step, the above-mentioned transparent substrate can be used. Further, after the film is formed, it can be peeled off from the substrate, or a self-standing film can be formed by a method such as using a gas-liquid interface or a liquid-liquid interface without using a substrate from the time of film formation.

If a thick film is required, the CNT concentration in the dispersion is increased, or the film is formed once, the solvent is distilled off, and then the film is formed again (overcoating) to obtain an arbitrary film thickness. Thick film can be made.

(6) Cleaning step When it is desired to obtain a conductive CNT composite film, the dispersant may interfere with the conductivity of CNT. In this case, the dispersant is removed from the CNT composite membrane by a method such as washing. The cleaning step is an arbitrary step in the method for producing a CNT composite film according to the present invention.

Generally, when a non-conductive dispersant is used, electrical connections between CNTs or CNT bundles are provided, and in order to make the CNT composite film exhibit conductivity, the CNT composite film is not conductive after film formation. The dispersant needs to be removed. For this, for example, a method of immersing in a solvent to remove the substance can be considered. However, in the present application, although the polymer acid used for dispersion is non-conductive, it can be dispersed in a small amount, so that if the weight of the polymer acid with respect to CNT is up to several times, it is not removed. The high conductivity of CNT is exhibited as it is.

(7) Post-Doping Step The CNT composite film obtained by the above method is doped by exposing it to the vapor of an oxidizing agent or immersing it in a solution containing an oxidizing agent. The post-doping step is an arbitrary step in the method for producing a CNT composite film according to the present invention.

Further, in general, since the conductivity of a film composed of only CNTs is not sufficient, a method of doping with an oxidizing agent such as nitric acid is often adopted. At this time, generally, a step of immersing the membrane in the solution of the oxidant or exposing the film to the vapor of the oxidant is required. Further, when a volatile oxidizing agent such as nitric acid is used, the conductivity of the obtained film is unstable. However, in the method for producing a CNT composite film according to the present invention, since the polymer acid itself, which is a dispersant, functions as a doping agent, it is not necessary to go through a doping step again after the film formation, and the polymer acid is used. Since it is non-volatile, the conductivity of the obtained CNT composite film is extremely stable.

In the method for producing a CNT composite membrane according to the present invention, the polymer acid as a dispersant may be added in a very small amount of about 1: 1 to 5: 1 with respect to CNT, and the polymer acid itself becomes a dopant. Therefore, the above-mentioned (6) cleaning step and (7) post-doping step, which are usually required, can be omitted, which is advantageous in the manufacturing process. Further, by optimizing the (2) pre-dispersion step and (3) the present dispersion step according to the method for manufacturing the CNT composite film according to the present invention, (4) the centrifugation step can be omitted, which is advantageous in the manufacturing process. Is. Furthermore, the conductivity of the obtained film is stable for a long period of time.

As described above, in the method for producing a CNT composite film according to the present invention, a highly conductive film can be obtained without removing the polymer acid as a dispersant after the film formation, but if necessary. It is also possible to remove a part or all of the polymer acid after the film formation. The method for removing the polymer acid is not particularly limited, but heat firing (heat treatment), pulsed light firing (heat treatment), cleaning with a solvent, cleaning with an alkaline developer (alkali treatment), and the like are preferably used.

The method for producing a CNT composite film of the present invention can be used for various purposes because it can produce a self-supporting film regardless of the type of substrate, can increase the area, is simple, and is low in cost. It is expected. Specifically, it is expected as a transparent conductive film material, an electromagnetic wave shielding film, a flexible electrode material, etc., in place of ITO.

Next, the present invention will be described in more detail based on Examples. The following description is for facilitating the understanding of the present invention, and is not limited thereto. That is, modifications, embodiments, and other examples based on the technical idea of the present invention are all included in the present invention.

In the following examples, single-walled CNTs synthesized by the improved direct-injection pyrolysis synthesis (eDIPS) method of Meijo Nanocarbon Co., Ltd. or single-walled CNTs synthesized by the National Institute of Advanced Industrial Science and Technology Super Growth (SG) method are used. Using. For polyacrylic acid (PAA, weight average molecular weight 5,000, 25,000, 1,000,000), a reagent manufactured by Wako Pure Chemical Industries, Ltd. was used. For PAA with a weight average molecular weight of 1,800 and 450,000, a reagent manufactured by Sigma-Aldrich was used.

First, the measurement method / apparatus used in the examples will be described.

[Surface resistance]
The surface resistivity of the CNT conductive film was measured at room temperature and in the atmosphere by a four-deep needle resistivity measuring device (Lorester, manufactured by Mitsubishi Chemical Corporation).

[Film thickness]
The film thickness of the produced CNT-containing thin film was measured with a Dektak8 stylus type film thickness step / surface shape measuring instrument (manufactured by ULVAC, Inc.).

[Ultraviolet-visible-near infrared transmission spectrum]
The ultraviolet-visible-near-infrared transmission spectrum was measured with a V-670 ultraviolet-visible-near-infrared spectrophotometer (manufactured by JASCO Corporation). Hereinafter, unless otherwise specified, the transmittance is a relative value at a wavelength of 550 nm when the transmittance of the substrate is 100%. The infrared absorption change rate is a value (a) obtained by converting the relative transmittance of the CNT composite film at a wavelength of 1550 nm (0.8 eV) when the transmittance of the substrate is 100% into absorbance. And the absorbance value estimated at 1550 nm in a film formed by adjusting the transmittance so that the transmittance is the same at 550 nm using polyvinylpyrrolidone (PVP) instead of polymer acid as a dispersant ( It is a value calculated as a ÷ b using b).

[Transmission electron microscope]
The transmission electron microscope was measured with LEO EM922 (manufactured by Carl Zeiss).

[X-ray photoelectron spectroscopy]
The X-ray photoelectron spectrum (XPS) was measured at an incident angle of 45 ° using PHI 5000 VersaProbe (manufactured by ULVAC) and Al Kα ray (1486.6 eV) as the X-ray source. PHI SUMMIT XPS, which is the analysis software attached to the device, was used to calculate the intensity ratio of the obtained X-ray photoelectron spectrum.

[Curve fitting]
ERDwards et al. (EREdwards, EFAntunes, ECBotelhoa MRBaldan EJCoratb, Evaluation of residual iron in carbon nanotubes purified by acid treatments, Applied Surface Science Volume 258, Issue 2, 1 November 2011, Pages 641- Fitted according to 648).

[Ratio of atomic numbers]
Using X-ray photoelectron spectra, P. Beccat et al. (P. Beccat, P. Da Silva, Y. Huiban, S. Kasztelan, Quantitative Surface Analysis by XPS: Application to Hydrotreating Catalysts, Oil & Gas Science and Technology --Rev The ratio of the number of carbon and oxygen atoms in the surface layer of the composite film was calculated according to IFP, Vol. 54 (1999), No. 4, pp. 487-496).

A_CNT：ＣＮＴの原子数の比、A_PAA：ＰＡＡの原子数の比、O_CP：ＣＮＴ複合膜表層の酸素原子の比、O_C：ＣＮＴ中の欠陥部分などに含まれる酸素原子の比。
なお、式中、０．４０はＰＡＡに含まれる酸素原子の比である（水素原子を除く）。[Ratio of atomic numbers of CNT and PAA]
The ratio of the atomic numbers of CNTs and PAA exposed on the surface layer of the composite film was calculated by the following formula, assuming that the atomic number of PAA was 1.

A _CNT : Ratio of CNT atoms, A _PAA : Ratio of PAA atoms, _OCP : Ratio of oxygen atoms on the surface of the CNT composite film, OC: Ratio of oxygen _atoms contained in defective parts in CNT.
In the formula, 0.40 is the ratio of oxygen atoms contained in PAA (excluding hydrogen atoms).

[Atomic force microscope]
The atomic force microscope was measured by combining the SPA300 and SPI3800 manufactured by Seiko Instruments.

(Example 1)
Dissolve 14 mg, 20 mg or 50 mg of polyacrylic acid (PAA, weight average molecular weight 5,000) in 30 mL of a 9: 1 mixed solvent of 2-propanol and ethanol, and then add 10 mg of CNT (eDIPS, unpurified sample). And mixed. The mixture was stirred overnight at a rotation speed of 1,500 rpm (pre-dispersion step). After that, as the main dispersion, ultrasonic irradiation was performed while cooling so that the treatment temperature was maintained at around 5 ° C. using bath-type ultrasonic treatment. The obtained mixed solution was further finely dispersed by ultrasonic irradiation using an ultrasonic homogenizer while cooling so that the treatment temperature was maintained at about 5 ° C. to obtain a uniform CNT dispersion of CNT and PAA. .. In this way, as the CNT dispersion liquid of Example 1, a CNT dispersion liquid having a weight ratio of CNT: PAA of 1: 1.4, 1: 2 and 1: 5 was obtained.

The obtained CNT dispersion liquid was formed on one side of a glass substrate using a spin coater. The film thickness and transmittance were adjusted by changing the rotation speed of the spin coater. Then, the CNT composite film of Example 1 was obtained by completely drying on a hot plate (100 ° C., 10 minutes).

FIG. 2 shows the relationship between the sheet resistance value of the CNT composite film of Example 1 and the transmittance (relative value when the transmittance of the substrate is 100%) at a wavelength of 550 nm. These values were sufficient transparency and conductivity to be used as a transparent electrode. A CNT composite film having a composition ratio of 1: 5 between CNT and PAA has a higher sheet resistance than a CNT composite film having a composition ratio of 1: 2, but when the amount of PAA relative to CNT is large, PAA covers the entire circumference of the CNT. It is presumed that this is because the CNTs are exhausted and the contact between the CNTs is hindered.

(Example 2)
In this example, the mixing ratio of CNT and PAA was changed in more detail to form a film, and the relationship with the sheet resistance was examined. That is, the amount of PAA added to 30 mL of solvent was 14 mg to 100 so that the mixing ratio of CNT (eDIPS, unpurified sample) and PAA (weight average molecular weight 5,000) was 1: 1.4 to 1:10. The dispersion was changed to mg in the same manner as in Example 1 above, and a CNT composite film was prepared on a glass substrate. At this time, the film thickness was adjusted so that the transmittance of the CNT composite film at a wavelength of 550 nm was 90% to 91%.

(Comparative Example 1)
As Comparative Example 1, a CNT composite membrane was prepared using polyvinylpyrrolidone (PVP) instead of PAA. That is, 50 mg of PVP was dissolved in 30 mL of a 9: 1 mixed solvent of water and ethanol, and 10 mg of CNT (eDIPS, unpurified sample) was added thereto to prepare a CNT dispersion liquid in the same manner as in Example 2, and CNT was prepared. A composite film was formed.

Table 1 shows the relationship between the CNT / PAA composition ratio of the obtained CNT composite films of Examples 2 and 1 and the sheet resistance and the infrared absorption change rate.

In the CNT composite film of Example 2, the sheet resistance is relatively small at 250 Ω / □ to 400 Ω / □ at a composition ratio of 1: 1.4 to 1: 3, but when the PAA is larger than the composition ratio of 1: 3. It was proved that the seat resistance was high. On the other hand, the CNT composite film of Comparative Example 1 had a high sheet resistance of 3,000 Ω / □, and it was shown that the CNT composite film of Comparative Example 1 had no doping effect.

FIG. 3 is a diagram showing the relationship between the sheet resistance value of the CNT composite film of Example 2 and Comparative Example 1 and the transmittance (relative value when the transmittance of the substrate is 100%) at a wavelength of 550 nm. be. Further, FIG. 4 is a diagram showing the transmittance of the transmitted light of the CNT composite film of Example 2 and Comparative Example 1 with respect to the wavelength. As shown in FIG. 4, it was proved that the CNT composite film of Example 2 had a high transmittance near near infrared rays. This indicates that the doping from PAA to CNT changed the semiconducting CNT to metallic CNT. On the other hand, it was proved that the CNT composite film of Comparative Example 1 had a low transmittance near near infrared and did not show a doping effect.

(Example 3)
In this example, the relationship between the molecular weight of PAA used and the sheet resistance of the CNT composite film was investigated. That is, PAA having a weight average molecular weight of 5,000, 25,000, 450,000, and 1,000,000 was weighed in 20 mg each and dissolved in 30 mL of a 9: 1 mixed solvent of 2-propanol and ethanol, and CNT (eDIPS, unpurified) was dissolved therein. Sample) was added in an amount of 10 mg and dispersed in the same manner as in Example 1. Further, 50 mg of PAA having a weight average molecular weight of 1,800 was weighed and dissolved in 30 mL of a 9: 1 mixed solvent of 2-propanol and ethanol, and 10 mg of CNT (eDIPS, unpurified sample) was added thereto to carry out Example 1. Dispersed in the same manner. Using these dispersions, a CNT composite film was prepared on a glass substrate by the same method as in Example 1. At this time, the film thickness was adjusted so that the transmittance of the CNT composite film at a wavelength of 550 nm was 90% to 91%.

Table 2 shows the relationship between the weight average molecular weight of PAA and the sheet resistance and the rate of change in infrared absorption of the obtained CNT composite film. That is, it was proved that the smaller the molecular weight of PAA, the lower the sheet resistance of the CNT composite film can be obtained even if the same weight of PAA is used.

(Comparative Example 2)
The effect of temperature on preparing the CNT dispersion was investigated. As Comparative Example 2, 20 mg of polyacrylic acid (PAA, weight average molecular weight 5,000) was dissolved in 30 mL of a 9: 1 mixed solvent of 2-propanol and ethanol, and then 10 mg of CNT (eDIPS, unpurified sample) was added. Mixed. When this mixed solution was dispersed using an ultrasonic homogenizer, CNTs were dispersed without performing a cooling operation. A film was formed by the method of Example 1 using this CNT dispersion liquid.

Table 3 shows the sheet resistance and the infrared absorption change rate of the CNT composite films of Example 1 and Comparative Example 2. As shown in Table 3, in the CNT composite film of Comparative Example 2, the sheet resistance of the CNT composite film having a transmittance of about 90% at a wavelength of 550 nm is about 930 Ω / □, and cooling is performed as in Example 1. It was higher than the sheet resistance (about 360 Ω / □) of the CNT composite film performed. From this, it was proved that the temperature at the time of preparing the dispersion liquid may affect the sheet resistance value.

(Example 4)
In this example, the influence of the presence or absence of CNT pretreatment was examined. That is, using purified eDIPS (sample treated with acid or the like) manufactured by Meijo Nanocarbon Co., Ltd. as CNT, the mixing ratio of PAA (weight average molecular weight 5,000) is changed from 1: 1 to 1:10. The amount of PAA added to a 30 mL solvent was changed from 10 mg to 100 mg to prepare a dispersion by the same method as in Example 1 above, and then the CNT composite was formed on a glass substrate by the same method as in Example 1 above. A film was prepared. At this time, the film thickness was adjusted so that the transmittance of the thin film at a wavelength of 550 nm was 90% to 91%.

Table 4 shows the relationship between the CNT / PAA composition ratio, the sheet resistance, and the infrared absorption change rate of the CNT composite film of Example 4. That is, the sheet resistance was relatively small at 250 Ω / □ to 300 Ω / □ when the composition ratio was 1: 1 to 1: 3, but the sheet resistance became higher when the PAA was larger than the composition ratio of 1: 3. Further, as compared with the case of using the unpurified eDIPS sample shown in Example 2, the CNT composite membrane having a PAA composition smaller than 1: 3 has a lower sheet resistance than the unpurified CNT composite membrane. It has been proven that it can be obtained.

(Example 5)
In this example, a CNT composite film having a film thickness of more than 1 μm was produced. That is, 250 mg of polyacrylic acid (PAA, weight average molecular weight 5,000 or 25,000) was dissolved in 100 mL of water, and then 250 mg of CNT (SG) was added and mixed. A dispersion was prepared for this mixture by the same method as in Example 1.

Next, this CNT dispersion liquid was formed on one side of a glass substrate or a resin substrate by moving the bar at a constant speed by an automatic device using a bar coater. The film thickness was adjusted by changing the count of the wire wound around the bar and recoating. Then, the CNT composite film was obtained by drying on a hot plate (70 ° C., 30 minutes).

Table 5 shows the relationship between the weight average molecular weight and film thickness of the polyacrylic acid of the CNT composite film of Example 5 and the sheet resistance and conductivity.

In addition, as a comparative experiment, PAA was prepared by heating a CNT composite membrane prepared with a weight average molecular weight of 5,000 PAA to a film thickness of 3 μm at 300 ° C. for 2 hours, and then treating with an aqueous solution of tetramethylammonium hydroxide. When removed, the sheet resistance changed to 28 Ω / □ (110 S / cm in terms of conductivity) as shown in Table 5, demonstrating that the doping effect disappears when PAA is lost.

(Example 6)
In this example, the effect of further doping the CNT composite film prepared using PAA (post-doping step) was examined. 15 mg of polyacrylic acid (PAA, weight average molecular weight 25,000) was dissolved in 30 mL of water, and then 10 mg of CNT (SG) was added and mixed. A dispersion was prepared for this mixture by the same method as in Example 1.

Next, this CNT dispersion liquid was formed on one side of the glass substrate by moving the bar at a constant speed by an automatic device using a doctor blade. The film thickness was adjusted to 3 μm by changing the count of the wire wound around the bar and recoating. After the film was formed, it was dried on a hot plate (70 ° C., 30 minutes) to obtain a CNT composite film. This CNT composite film was immersed in concentrated nitric acid, iodine solution, hydrogen iodide solution, bromine solution, and hydrobromic acid for 30 minutes each, pulled up, washed with water, and the sheet resistance was measured. Separately, the substrate on which the CNT composite film is formed coexists with a container containing concentrated nitric acid, iodine solution, hydrogen iodide solution, bromine solution, and hydrobromic acid, and is sealed and left at room temperature for 2 hours. Thereby, they were exposed to the steam generated from each solution. After pulling this up and drying it at room temperature, the sheet resistance was measured.

Table 6 shows the relationship between the dopant and film thickness of Example 6 CNT composite film and the sheet resistance and conductivity. From this result, it was clarified that the sheet resistance is lowered and the conductivity is improved by post-doping.

(Example 7)
In this example, the effect of doping the CNT powder (pre-doping step) before preparing the mixed dispersion with PAA was examined. First, CNT (unpurified eDIPS) was added to a mixed solution of nitric acid and hydrochloric acid and stirred. Next, this was filtered, washed and dried to obtain CNT powder.

15 mg of polyacrylic acid (PAA, weight average molecular weight 5,000) was dissolved in 30 mL of water, and then 10 mg of CNT obtained by acid treatment was added and mixed. This mixed liquid was subjected to ultrasonic homogenizer treatment in the same manner as in Example 1 to prepare a dispersion liquid.

Next, this CNT dispersion liquid was formed on one side of the glass substrate by moving the bar at a constant speed by an automatic device using a doctor blade. The film thickness was adjusted to 1 μm and 10 μm by changing the count of the wire wound around the bar and recoating. After the film was formed, it was dried on a hot plate (70 ° C., 30 minutes) to obtain a CNT composite film.

Table 7 shows the pre-doping step of the CNT composite film of Example 7 and the measurement results of the sheet resistance and the conductivity. As shown in Table 7, 1.3 Ω / □ (7,700 S / cm when converted to conductivity) when the film thickness is 1 μm, 0.12 Ω / □ (8,300 S / cm when converted to conductivity) when the film thickness is 10 μm. It became.

Next, the PAA was removed by heating the CNT composite film having a film thickness of 1 μm at 300 ° C. for 2 hours and then treating it with an aqueous solution of tetramethylammonium hydroxide. As shown in Table 7, the sheet resistance was 12 It was Ω / □ (830 S / cm when converted to conductivity).

Further, the CNT obtained by the above acid treatment was added to the iodine solution, ultrasonically treated, washed with water, mixed with the PAA aqueous solution, and the dispersion prepared by the same method as in Example 1 was used. When the sheet resistance of the CNT composite film formed so as to have a film thickness of 1 μm and 10 μm was measured by the same method as in Example 7, as shown in Table 7, when the film thickness was 1 μm, 0.7 Ω / □ (14,000 S / cm when converted to conductivity), 0.06 Ω / □ when the film thickness is 10 μm (17,000 S / cm when converted to conductivity), and the sheet resistance is about 1 / compared to the case without iodine solution treatment. It was proved to be 2.

(Example 8)
In this example, the mixed state in the CNT composite membrane was investigated. That is, a dispersion liquid (composition ratio of CNT and PAA of 1: 1) prepared by the same method as in Example 4 was applied to a copper mesh and observed with a transmission electron microscope (TEM). Further, the dispersion was applied to glass and observed with an atomic force microscope (AFM). FIG. 5 shows a transmission electron microscope (TEM) image, and FIG. 5 (b) shows an enlarged view of FIG. 5 (a). Further, FIG. 6 shows an atomic force microscope (AFM) image, and FIG. 6 (b) shows an enlarged view of FIG. 6 (a). As shown in FIGS. 5 and 6, it was proved that the PAA clung to and covered a part of the surface of the CNT.

The same was observed for the CNT composite membrane using the CNT dispersion having a composition ratio of CNT and PAA of 1: 5. FIG. 7 shows a transmission electron microscope (TEM) image, and FIG. 7 (b) shows an enlarged view of FIG. 7 (a). Further, FIG. 8 shows an atomic force microscope (AFM) image, and FIG. 8 (b) shows an enlarged view of FIG. 8 (a). As shown in FIGS. 7 and 8, it was proved that the PAA completely covered the circumference of the CNT in the CNT composite membrane having a composition ratio of CNT and PAA of 1: 5.

(Example 9)
In this example, the difference in the molecular structure of the polymer acid, which is a dispersant, was examined. Using polymethacrylic acid (PMAA) instead of PAA in Example 1, a dispersion liquid of CNT (unpurified eDIPS) was prepared by the same production method as in Example 1, and a CNT composite membrane was formed.

Table 8 shows the relationship between the composition ratio of CNT / PMAA of the CNT composite film of Example 9 and the sheet resistance and the rate of change in infrared absorption.

(Example 10)
In this example, the environmental durability of the CNT composite membrane prepared using PAA was measured. As CNT, eDIPS and SG-CNT were used. The change in sheet resistance before and after 1000 hours of treatment was measured in an environment with a humidity of 85% and a temperature of 85 ° C. using an electronic cold / thermo-hygrostat made by Advantech.

Table 9 shows the sheet resistance of the CNT composite film of Example 10 before and after the environmental durability test.

(Example 11)
In this example, the heat resistance of the CNT conductive film prepared by using PAA was measured. EDIPS was used as the CNT. The CNT film was heated at 100 ° C., 200 ° C., and 280 ° C. for 2 hours by a hot plate, and the sheet resistance was measured. Table 10 shows the sheet resistance.

(Example 12)
The XPS spectrum of the CNT composite film after each step described above was measured. FIG. 9 shows an XPS spectrum of a CNT composite film prepared by using PAA having a molecular weight of 5000 and varying the mixing ratio of CNT and PAA as in Example 4. In the region where the peak derived from the carbon atom is seen shown in the left figure of Fig. 9, peaks are observed near 284.8 eV, 285.6 eV and 289.5 eV, respectively, and carbon due to sp2 C = C, CC and C = O bonds, respectively. Derived from the atom. The peak near 532 eV shown on the right of FIG. 9 is derived from the oxygen atom. The 284.8 eV (C = C) peaks are derived from CNTs, and the 285.6 eV (CC) and 289.5 eV (C = O) peaks are derived from PAA. Also, the peak of oxygen atoms near 532 eV is mainly derived from PAA, except for oxygen in the defect in the CNT present in a very small amount.

From the XPS spectrum of FIG. 9, it was clarified that as the mixing ratio of PAA to CNT increased, the peak intensity of oxygen atoms increased, and the XPS spectrum reflected the amount of PAA present on the surface layer of the CNT composite film. ..

FIG. 10 shows the XPS spectrum of the CNT composite film prepared by fixing the mixing ratio to 1: 1 and changing the molecular weight of PAA as in Example 3. From the XPS spectrum of FIG. 10, it was clarified that as the molecular weight of the added PAA increased, the peak intensity of the oxygen atom increased, and the XPS spectrum reflected the molecular weight of PAA existing on the surface layer of the CNT composite film. Due to the increase in peak intensity derived from oxygen atoms near 532 eV shown on the right of FIG. 10, the surface layer of the CNT composite film to which PAA having a weight average molecular weight of 450000 and 1000000 was added had more PAA than the mixing ratio of PAA to CNT. Was observed, suggesting that significant aggregation of PAA occurred.

FIG. 11 shows the result of curve fitting for the XPS spectrum of CNT (eDIPS) only. FIG. 12 shows the result of curve fitting for the XPS spectrum of the CNT composite film having a composition ratio of CNT and PAA of 1: 1. The area of each fitted peak was compared as the peak intensity. The peak intensity is proportional to the number of atoms in each state in the measurement range. As the mixing ratio of PAA in the composite membrane is increased, the peak intensities of carbon C-C and carbon C-O increase, and the peaks derived from oxygen atoms also increase accordingly.

The ratio of the number of carbon and oxygen atoms in the CNT composite film was calculated from the X-ray photoelectron spectrum. The ratio of oxygen atoms contained in the CNTs used in the examples was 0.04. Since XPS measures from the surface of the CNT composite film to the surface layer region to a depth of about several nm to 10 nm, the XPS spectrum reflects the components exposed on the surface layer of the CNT composite film. Therefore, the area ratio of CNT and PAA exposed on the surface layer of the CNT composite film can be estimated from the ratio of the number of atoms of CNT and PAA calculated based on the ratio of oxygen calculated from the XPS spectrum.

Table 11 shows the ratio of the number of atoms of CNT obtained from the XPS spectrum of the CNT composite film prepared by variously changing the mixing ratio of PAA to CNT, where the number of atoms of PAA is 1.

As shown in FIG. 7, in the CNT composite film having a composition ratio of CNT and PAA of 1: 5, PAA completely covers the periphery of CNT. From Table 10, it was clarified that the ratio of the number of atoms of CNT to PAA in the surface layer of the CNT composite film in the state where PAA completely covered the circumference of CNT was 0.8: 1. Further, in the CNT composite film having a composition ratio of CNT and PAA of 1:10 or more, PAA aggregates on the surface of CNT, and the amount of PAA adhered on the surface of CNT is saturated. From the results of the sheet resistance shown in Table 1, when the composition ratio of CNT and PAA is 1 to 10 or more, the conductivity due to the contact between CNT and CNT cannot be obtained. Therefore, PAA aggregated on the surface of CNT is formed. It was suggested that the contact between CNTs would be hindered. From Table 11, it was shown that the doping effect was obtained when the ratio of the number of atoms of carbon to oxygen on the surface layer of the CNT composite film was 12: 1 to 2.5: 1.

Table 12 shows the ratio of the number of atoms of CNT obtained from the XPS spectrum of the CNT composite film prepared by changing the molecular weight of PAA, where the number of atoms of PAA is 1.

From Table 12, it was clarified that when PAA having a molecular weight of 4.500000 or more was added, PAA aggregated on the surface of CNT. From the results of the sheet resistance shown in Table 2, when PAA having a molecular weight of 4.500000 or more was added, the conductivity due to the contact between CNT and CNT decreased, so that PAA aggregated on the surface of CNT became CNT and CNT. It was suggested that the contact would be hindered.

(Example 13)
In Example 13, the uniformity in the depth direction of the CNT composite film prepared with a mixing ratio of 1: 1 with CNT was evaluated using PAA having a molecular weight of 5000 and a molecular weight of 1000000 by changing the incident angle of XPS. .. The larger the angle of incidence, the more the composition of the portion closer to the surface of the composite film is reflected, and the smaller the angle of incidence, the more the composition from the surface to the deep portion is reflected. The CNT composite film using PAA having a molecular weight of 5000 shown in FIG. 13 did not change the peak of XPS even when the incident angle was changed, and showed high uniformity in the depth direction. On the other hand, in the CNT composite film using PAA having a molecular weight of 1000000 shown in FIG. 14, the peak intensities of carbon CC and carbon C = O increase as the incident angle increases, and the peaks derived from oxygen atoms also increase accordingly. do. That is, a part of the PAA of the CNT composite film aggregated, and the uniformity of the components deteriorated in the depth direction. Table 13 shows the ratio of the number of atoms calculated from the XPS measurement. From the results in Table 13, in the CNT composite membrane using PAA having a molecular weight of 1000000, many oxygen atoms are distributed on the surface layer of the composite membrane, and the aggregation of PAA is increased and unevenly distributed on the surface of the CNT composite membrane. Suggested that there is.

(Example 14)
In Example 14, the CNT composite film prepared in Example 4 was immersed in water for about 2 hours to evaluate the water resistance. Table 14 shows the ratio of the number of atoms calculated from the sheet resistance and XPS.

From Table 14, it was clarified that by immersing the CNT composite membrane in water, a part of PAA was removed from the CNT composite membrane and the doping effect was reduced, but the undoped CNT membrane (for example, comparison). Compared with Example 1), the CNT composite film after immersion in water showed a low sheet resistance value.

1: Polymer acid, 3: CNT, 5: Bundle, 7a: Contact part, 7b: Contact part, 7c: Contact part, 10: CNT composite membrane

Claims (11)

A carbon nanotube dispersion liquid containing a polymer acid that functions as a dispersant and a dopant for carbon nanotubes.
The polymer acid is at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid and poly (p-styrene sulfonic acid).
The carbon nanotube dispersion liquid has a concentration of the carbon nanotubes of 0.005% by weight or more and 1% by weight or less, a concentration of the polymer acid of 0.005% by weight or more and 5% by weight or less, and a weight of the carbon nanotubes and the polymer acid. With a ratio of 1: 1 to 1: 5,
In the carbon nanotubes, the polymer acid surrounds the carbon nanotubes except for a region where the carbon nanotubes are in contact with each other.
When the carbon nanotube composite film from which the solvent was removed from the carbon nanotube dispersion was evaluated, the portion where the polymer acid was attached to a single carbon nanotube or a bundle of carbon nanotubes and the portion where the carbon nanotubes were exposed. A carbon nanotube dispersion liquid characterized by an area ratio of 1: 1 to 10: 1. The carbon nanotube dispersion liquid according to claim 1, wherein the polyacrylic acid has a weight average molecular weight of 500 or more and 250,000 or less. A carbon nanotube dispersion containing a polymer acid, carbon nanotubes, and a solvent.
The polymer acid is at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid and poly (p-styrene sulfonic acid).
The carbon nanotube dispersion liquid has a carbon nanotube concentration of 0.005% by weight or more and 1% by weight or less, and a polymer acid concentration of 0.005% by weight or more and 5% by weight or less.
The weight ratio of the polymer acid to the carbon nanotubes is 0.8: 1 to 5: 1.
In the carbon nanotubes, the polymer acid surrounds the carbon nanotubes except for a region where the carbon nanotubes are in contact with each other.
The permeability of the carbon nanotube composite film at a wavelength of 550 nm, which was evaluated as the carbon nanotube composite film obtained by removing the solvent from the carbon nanotube dispersion liquid, is 90% or more, and the sheet resistance of the carbon nanotube composite film is 500. A carbon nanotube dispersion liquid characterized by being Ω / □ or less. The sheet resistance of the carbon nanotube composite film when the thickness of the carbon nanotube composite film is 1 μm, which is evaluated as the carbon nanotube composite film obtained by removing the solvent from the carbon nanotube dispersion liquid, is 10 Ω / □ or less. The carbon nanotube dispersion liquid according to claim 3 , wherein the carbon nanotube dispersion liquid is characterized by the above. The weight ratio of the polymer acid to the carbon nanotube is 0.8: 1 so that the concentration of the carbon nanotube is 0.005% by weight or more and 1% by weight or less and the concentration of the polymer acid is 0.005% by weight or more and 5% by weight or less . Perform the first dispersion step of dispersing in the solvent in the range of 5 to 1.
A second dispersion step of dispersing the polymer acid and the carbon nanotubes in a solution while irradiating the solution with ultrasonic waves is further performed.
The implementation time of the first dispersion step is made longer than that of the second dispersion step, or in the second dispersion step, the polymer acid and the carbon nanotube are used in the solvent while being cooled to 5 ° C. or lower. Disperse,
The method for producing a carbon nanotube dispersion liquid, wherein the polymer acid is at least one selected from the group consisting of polyacrylic acid, polymethacrylic acid and poly (p-styrene sulfonic acid). The method for producing a carbon nanotube dispersion liquid according to claim 5 , wherein the weight average molecular weight of the polymer acid is 500 or more and 250,000 or less. The method for producing a carbon nanotube dispersion liquid according to claim 5 , wherein the repeating unit of the polyacrylic acid is 8 or more and 3,500 or less. The method for producing a carbon nanotube dispersion liquid according to claim 5 , wherein the carbon nanotubes are treated with an acid or an oxidizing agent before the first dispersion step of dispersing the carbon nanotubes in the solvent. A method for producing a carbon nanotube composite membrane, wherein a carbon nanotube dispersion is produced by the method for producing a carbon nanotube dispersion according to any one of claims 5 to 8 , and the solvent is removed from the produced carbon nanotube dispersion. The method for producing a carbon nanotube composite film according to claim 9 , wherein the carbon nanotube composite film is treated with an acid or an oxidizing agent. The method for producing a carbon nanotube composite membrane according to claim 9 , wherein the carbon nanotube composite membrane is heated or treated with an alkali to remove a part or all of the polymer acid.

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