Dispersant for dispersing carbon nanotubes in water and a carbon nanotube dispersion liquid

Abstract

To provide a dispersant that can disperse CNTs at high concentrations, and a dispersion in which CNTs are dispersed at high concentrations, by adding glucuronoxylan, a polymer dispersant, and a dispersant with a lower molecular weight than glucuronoxylan.SOLUTION: A dispersant for carbon nanotubes comprises glucuronoxylan and a monomer having a lower molecular weight than the glucuronoxylan. The mixing ratio of the monomer is smaller than that of the glucuronoxylan, and the monomer is one selected from naphthalene sulfonate, pyrene sulfonate, methyl-α-glucose, and xylose. In addition, the naphthalene sulfonate may be sodium naphthalene sulfonate. Also, the pyrene sulfonate may be sodium pyrene sulfonate.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dispersant for stably dispersing carbon nanotubes in water at a high concentration, and a carbon nanotube dispersion. [Background technology]

[0002] Carbon nanotubes (hereafter referred to as "CNTs") are cylindrical (tube-shaped) substances made entirely of carbon with a nanometer-sized diameter, and have a structure in which a sheet of benzene rings, in which carbon atoms are arranged in a hexagonal pattern, are all arranged side by side on a plane, is rolled into a cylinder. Those with one layer of this cylinder are called single-walled carbon nanotubes (hereafter referred to as "SWCNTs"), while those with multiple cylinders of different diameters stacked in layers are called multi-walled carbon nanotubes (hereafter referred to as "MWCNTs").

[0003] CNTs have high electrical conductivity and mechanical strength, and their applications in conductive paints, conductive resins, electromagnetic shielding sheets, and heater components are being considered, taking advantage of these properties. When applying them to these applications, it is important to develop a dispersant that can disperse CNTs uniformly and at high concentrations in a dispersion medium such as water. In the solid state, CNTs form bundle structures due to strong π-π interactions and van der Waals forces, making them difficult to disperse in many solvents. Therefore, to make CNTs dispersible in solvents and enable a variety of applications, a superior dispersant is needed to facilitate this. To achieve this, various dispersants have been developed.

[0004] For example, a dispersion liquid in which CNTs and / or graphene are dispersed in a solvent, the dispersion liquid containing a low molecular weight surfactant and a polymer surfactant, and the weight ratio of the sum of the content of the low molecular weight surfactant and the content of the polymer surfactant to the solvent is 0.3 to 1.5 times the weight ratio of the total content of CNTs and / or graphene to the solvent has been disclosed (see, for example, Patent Document 1).

[0005] Also disclosed is a CNT-containing acidic aqueous dispersion containing CNTs (A) with a specific shape and a polymer compound (B) having acidic groups in its side chains, further containing a nonvolatile organic acid. The acidic groups contained in the polymer compound (B) are disclosed as carboxyl groups, sulfonic acid groups, and phosphate groups, with specific examples including carboxymethyl cellulose and polystyrene sulfonic acid. It is also disclosed that the dispersion may further contain a nonvolatile organic acid, which is a low-molecular-weight acidic compound (see, for example, Patent Document 2).

[0006] Furthermore, it has been discovered that the affinity of a solvent to the surface of a poorly soluble or insoluble substance can be improved by using water-soluble xylan, and a solution containing water-soluble xylan, a substance, and a solvent has been disclosed, wherein the substance is poorly soluble or insoluble in the solvent in the absence of the water-soluble xylan (see, for example, Patent Document 3).

[0007] Furthermore, researchers including the present inventors have discovered that the hemicellulose 4-O-methylglucuronoxylan has the ability to disperse hydrophobic substances in water, and as a result of elucidating the dispersion mechanism of CNTs, they have disclosed that they have developed a dispersion solution that is most suitable for dispersion in water and is stable for a long period of time (see, for example, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2019-119775 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-152296 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-215542 [Non-patent literature]

[0009] [Non-Patent Document 1] Applied Glycoscience, Vol. 12, No. 1, 27-32 (2022) Summary of the Invention [Problem to be solved by the invention]

[0010] The invention described in Patent Document 1 aims to develop a dispersion liquid that can highly disperse CNTs in a solution and stably maintain that dispersion state. The dispersion liquid contains a specific ratio of a low-molecular-weight surfactant and a polymeric surfactant. The low-molecular-weight surfactant and the polymeric surfactant have hydrophobic and hydrophilic structural portions within their molecules, and are used to have affinity for both the dispersion medium and CNTs and to disperse CNTs in the dispersion medium. The polymeric surfactant is described as a physical adsorption solubilizer, such as a pendant copolymer polymer incorporating an aromatic unit such as carboxymethylcellulose or pyrene. The combination of a polymeric surfactant and a low-molecular-weight surfactant is described as enabling CNT dispersion on a large scale of 1 kg or more. However, the invention does not disclose or suggest the use of glucuronoxylan as a dispersant.

[0011] The invention described in Patent Document 2 is for forming a conductive film on the substrate surface of a film, and the conductive film produced using an acidic aqueous dispersion containing CNTs that satisfy a specific relationship formula and a polymer compound with acidic groups in the side chain is intended to have excellent conductivity and transparency, as well as improved adhesion between the conductive film and the substrate, but may be difficult to apply to uses other than conductive films. Furthermore, this invention does not disclose or suggest the use of glucuronoxylan as a dispersant.

[0012] The invention described in Patent Document 3 discloses a solution in which CNTs are dispersed in water using water-soluble xylan as a dispersant. The specification also discloses an example in which glucuronoxylan is used as the water-soluble xylan. It is described that water-soluble xylan exhibits a maximum absorbance at a wavelength of 500 nm at a concentration of 0.2 mg / mL, and that the absorbance did not change even when the concentration of water-soluble xylan was subsequently increased. In other words, the use of water-soluble xylan poses the problem of not being able to increase the dispersion concentration of CNTs in the dispersion. Furthermore, it is stated that the dispersion solvent can be not only water, but also a mixture of water and an organic solvent, and that organic solvents such as methanol, ethanol, and N-methylpyrrolidone can be used. It is also stated that the dispersion can contain raw materials for substrates such as films, pigments, solubilizers, and storage stabilizers, but there is no specific disclosure about adding a dispersant in addition to the water-soluble xylan.

[0013] The invention described in Non-Patent Document 1 shows an example of application to electronic materials in which a dispersion of SWCNTs is prepared using water-soluble xylan, a natural product, as a dispersant, and the dispersion is used as a paint. However, this disclosure does not disclose or suggest the use of dispersants other than water-soluble xylan. In order to utilize CNTs in various applications, a dispersant and dispersion that can disperse CNTs at high concentrations in aqueous dispersions and maintain a stable dispersion state for a long period of time are desired.

[0014] The present invention aims to provide a dispersant capable of dispersing CNTs at high concentrations and a dispersion in which CNTs are dispersed at high concentrations by adding a dispersant with a lower molecular weight than glucuronoxylan to the polymeric dispersant glucuronoxylan. [Means for solving the problem]

[0015] In order to solve the above-mentioned conventional problems, the CNT dispersant of the present invention is used to disperse CNTs in water, and is characterized by comprising glucuronoxylan (hereinafter sometimes referred to as "GX") and a monomer that has a lower molecular weight than GX and has hydrophobic and hydrophilic properties in its molecular structure, the mixing ratio of the monomer being smaller than the mixing ratio of GX, and the monomer being one type selected from naphthalenesulfonate, pyrenesulfonate, methyl-α-glucose, and xylose.

[0016] In the above-mentioned configuration, the naphthalene sulfonate may be sodium naphthalene sulfonate, and the pyrene sulfonate may be sodium pyrene sulfonate.

[0017] Next, the CNT dispersion of the present invention is a dispersion containing water as a dispersion solvent, a dispersant, and CNTs, wherein the dispersant is any of the CNT dispersants described above. In this case, the CNTs may be either SWCNTs or MWCNTs. [Effects of the Invention]

[0018] The CNT dispersant of the present invention and a CNT dispersion liquid using the same are highly effective in a wide range of fields, such as noise prevention in electronic devices, application to secondary batteries, and application in the semiconductor field. DETAILED DESCRIPTION OF THE INVENTION

[0019] (Embodiment)

[0020] The CNT dispersant and CNT dispersion according to the embodiments of the present invention will be described in detail below. To solve the above-mentioned problems of the related art, the CNT dispersant of the present invention is used to disperse CNTs in water, and contains GX and a monomer that has a lower molecular weight than GX and has hydrophobic and hydrophilic properties in its molecular structure, the monomer mixing ratio being lower than the GX mixing ratio, and the monomer is one selected from naphthalenesulfonate, pyrenesulfonate, methyl-α-glucose, and xylose.

[0021] Furthermore, sodium naphthalenesulfonate can be used as the naphthalenesulfonate, and sodium pyrenesulfonate can be used as the pyrenesulfonate. The present invention uses the above-mentioned monomers, and the terms "monomer" and "polymer" are defined as follows: a polymer is formed by repeatedly linking the same monomers, and when a monomer is "M," a polymer is defined as "(M)n, where n is the number of bonded Ms and is 3 or more."

[0022] The inventors investigated the effect of GX concentration on dispersing CNTs at high concentrations. When CNTs are brought into contact with GX, GX acts between the CNT surface and the solvent, improving the affinity of the CNT surface for water. To disperse CNTs at high concentrations, the GX concentration must also be increased. However, they found that increasing the GX concentration alone does not result in high CNT dispersion.

[0023] Next, the dispersibility of CNTs was investigated by adding various other dispersants to GX. As a result, it was found that CNTs could be dispersed at a high concentration by using a dispersant with a lower molecular weight than GX, a monomer content lower than that of GX, and one selected from naphthalenesulfonate, pyrenesulfonate, methyl-α-glucose, and xylose. This led to the completion of the present invention.

[0024] The monomer used in the present invention has both hydrophobic and hydrophilic properties in its molecular structure, and therefore has affinity for both the dispersant GX, the dispersion medium water, and carbon nanotubes, and has the effect of dispersing carbon nanotubes at high concentrations in water.

[0025] Although sodium naphthalenesulfonate is preferably used as the naphthalenesulfonate, potassium naphthalenesulfonate, ammonium naphthalenesulfonate, etc. can also be used. Furthermore, sodium pyrenesulfonate is preferably used as the pyrenesulfonate, but potassium pyrenesulfonate, ammonium pyrenesulfonate, etc. can also be used.

[0026] The GX used in the present invention has, for example, one 4-O-methyl-α-D-glucuronic acid bonded to approximately 10 xylose residues, and has a weight-average molecular weight of approximately 20,000. However, since the degree of branching of GX extracted from plants varies depending on the plant's origin, it is not limited to the above bond, and materials commonly referred to as glucuronoxylan can be used in the same way. Furthermore, even if a xylan other than glucuronoxylan is contained, it can also be used as long as glucuronoxylan is the main component. Note that "main component" refers to a situation in which glucuronoxylan is at least 60 wt%, preferably 75 wt% or more, and more preferably 90 wt% or more.

[0027] Sodium naphthalenesulfonate is a polycyclic aromatic compound with a molecular weight of 230.2, and because it has both hydrophobic and hydrophilic properties in its molecular structure, it not only has an affinity for CNTs and water, but also for GX. Furthermore, because its molecular weight is smaller than that of GX, it is more easily adsorbed onto the surface of CNTs, further enhancing the dispersibility of CNTs with GX.

[0028] Sodium pyrenesulfonate has a molecular weight of 304.2 and is an ionically dissociable polycyclic aromatic compound with functional groups that undergo ion dissociation in water. This allows polycyclic aromatic compounds to more selectively stack on CNTs through π-π bonding and has affinity for the solvent water and GX. This allows for greater dispersibility of CNTs in GX.

[0029] Methyl-α-glucose is α-D-glucose that has been methylated. α-D-glucose has an affinity for water molecules because it has a hydroxyl group in its molecular structure, while the methyl group is hydrophobic.

[0030] Xylose has a molecular weight of 150.1 and contains hydroxyl groups, giving it an affinity for water molecules, but it is also known to exhibit hydrophobicity depending on the orientation of the hydroxyl groups. In other words, sugar molecules have strong hydrophilicity and weak hydrophobicity, and these properties depend on the orientation of the OH groups (or conversely, CH groups) in each molecule. Specifically, D-xylose is more hydrophobic than D-glucose.

[0031] The effect of further adding the above-mentioned monomer to GX has not been clearly elucidated, but it is believed to be due to the following mechanism. Specifically, when the dispersant is GX alone, gelation is likely to occur, making it impossible to prepare a highly concentrated, highly fluid dispersion. This is thought to be because a dispersant containing only GX has a strong interaction between water, GX, and CNT, which makes it prone to gelation. However, when the above-mentioned monomer is added to GX in an amount less than the amount of GX mixed, the monomer penetrates between the CNT molecules and GX molecules, weakening the interaction and suppressing gelation, which is thought to result in a significant improvement in dispersibility.

[0032] In this way, by using a dispersant that is primarily composed of GX but has a lower molecular weight than GX and a lower mixing ratio than GX, and that uses one monomer selected from naphthalenesulfonate, pyrenesulfonate, methyl-α-glucose, and xylose as the monomer, it is possible to disperse CNTs at a higher concentration than when GX alone is used as a dispersant, and yet the dispersibility is maintained stably. Therefore, when CNTs are used in a variety of applications, higher performance products than before can be realized.

[0033] In the above-mentioned configuration, GX may be contained in wood; for example, it is known that GX is the main component of hemicellulose contained in hardwood. Such GX may be used. GX is a xylose polymer to which a 4-O-methylglucuronic acid residue and an acetyl group are bound, and may be extracted from wood or chemically synthesized. Note that GX of the present invention also includes arabinoglucuronoxylan and glucuronoarabinoxylan.

[0034] The CNT dispersion of the present invention contains water as a dispersion solvent, a dispersant, and CNTs, and is characterized in that the dispersant is the CNT dispersant described above. In this case, the CNTs may be either SWCNTs or MWCNTs.

[0035] Although it is more difficult to disperse SWCNTs than MWCNTs, the use of the dispersant of the present invention makes it possible to obtain a dispersion in which SWCNTs are dispersed more uniformly than conventional methods. Furthermore, when CNTs are synthesized, a mixture of SWCNTs and MWCNTs is produced, which is then purified as necessary. In the present invention, purified SWCNTs or MWCNTs are used, but they can also be used even if trace amounts of other CNTs remain. Depending on the application, CNTs that are a mixture of SWCNTs and MWCNTs can also be used. A detailed description will be given below based on examples. Example 1

[0036] This Example 1 describes the results of a comparison of the dispersibility of MWCNTs when GX alone is used as a dispersant to disperse MWCNTs, and when a monomer is further added to GX. The MWCNTs used were NC7000 from Nanosyl. These MWCNTs had an average diameter of 9.5 nm, an average length of 1.5 μm, a carbon purity of 90%, and a specific surface area of ​​250 to 300 m / g.

[0037] Table 1 shows the results of evaluating dispersibility when only GX was used as a dispersant. CNT dispersions were prepared as follows. For example, in Table 1, when GX is 1.0 wt% and MWCNT is 2.9 wt%, 1 mg of GX, 2.9 mg of MWCNT, and 96.1 mL of water were prepared. GX and MWCNT were added to the water and dispersed using a 600 W ultrasonic homogenizer. The dispersion time was 1 hour. Dispersibility was evaluated by visual inspection to determine whether the CNT dispersion containing MWCNT had fluidity. A visual evaluation of fluidity indicated a ○, and a lack of fluidity indicated an ×. Dispersions were prepared using the same method for the other conditions listed in Table 1. Specifically, the dispersibility of MWCNT was evaluated by varying the GX concentration from 1.0 wt% to 3.7 wt% and the MWCNT concentration from 2.8 wt% to 4.7 wt%.

[0038] As can be seen from Table 1, when GX was added at 1.9 wt% to 2.4 wt%, dispersibility was rated as good when MWCNT was added at 2.8 wt% to 2.9 wt%, but dispersibility was rated as bad at other GX addition ratios. As the amount of MWCNT added increased, dispersibility decreased; when MWCNT was 3.8 wt%, dispersibility was rated as good only when the GX concentration was 1.9 wt%, and when MWCNT was 4.7 wt%, dispersibility was rated as bad for all GX concentrations from 1.0 wt% to 3.7 wt%. In other words, it was found that MWCNTs could not be dispersed in an amount of more than 3.8 wt% using a dispersant containing only GX.

[0039] [Table 1]

[0040] Table 2 shows the results of determining the effect of adding the monomers according to the present invention in addition to GX as a dispersant. The added monomers were sodium naphthalenesulfonate, methyl-α-glucose, sodium pyrenesulfonate, and xylose.

[0041] Specifically, sodium naphthalenesulfonate was 2-sodium naphthalenesulfonate (Fujifilm Wako Pure Chemical Industries, Ltd., product code: 148-04632, molecular weight: 230.22). Methyl-α-glucose was methyl-α-D-glucose (Tokyo Chemical Industry Co., Ltd., product code M0228, molecular weight: 194.18). Sodium pyrenesulfonate was 1-sodium pyrenesulfonate (Frinton Laboratories Inc., catalog No. FR-1003). Xylose was D-xylose (Fujifilm Wako Pure Chemical Industries, Ltd., product code 244-00302, molecular weight: 150.13). The same was used in Examples 2 and 3 described below.

[0042] In Table 2, the CNT mixing ratio was set to 8.6 wt%, which is even higher than the CNT mixing ratio that resulted in a dispersibility rating of × in Table 1, and the GX mixing ratio was set to 4.0 wt%, and the monomer mixing ratio was set to 1.0 wt%, correspondingly, to confirm the effect of mixing monomers in improving dispersibility. The CNT dispersion liquid was prepared using the same method as in Table 1.

[0043] In Table 2, when the GX concentration was 5 wt%, the dispersant did not contain any monomer, and the dispersibility of the CNT dispersion was evaluated as "×". This is a result that was also expected from Table 1. On the other hand, when the GX concentration was 4.0 wt% and the monomer was 1.0 wt%, the dispersibility of the CNT dispersion was evaluated as "O" for all the monomers used. From these results, it was found that adding a monomer has a significant effect on improving the dispersibility of MWCNTs.

[0044] [Table 2] Example 2

[0045] This Example 2 describes the results of a detailed investigation into the effects of the mixing ratio of GX and the monomer dispersant added to MWCNT. The CNTs used were the same MWCNTs as in Example 1. The monomers used were sodium naphthalenesulfonate, methyl-α-glucose, xylose, and sodium pyrenesulfonate, as used in Example 1.

[0046] Table 3 shows the mixing ratio of GX and monomer and the mixing ratio of MWCNT in the dispersant according to Example 2. Four types of MWCNT were used: 3.0 wt%, 5.0 wt%, 8.0 wt%, and 10.0 wt%. The dispersant was GX only (i.e., without mixing monomer, GX only was used at 1.3 wt%, 2.0 wt%, 4.2 wt%, and 6.0 wt%); the total dispersant concentration was 1.3 wt% (GX: 1.2 wt%, monomer: 0.1 wt%); the total dispersant concentration was 2.0 wt% (GX: 1.9 wt%, monomer: 0.1 wt%); the total dispersant concentration was 4.2 wt% (GX: 3.7 wt%, monomer: 0.5 wt% and GX: 3.2 wt%, monomer: 1.0 wt%); and the total dispersant concentration was 6.0 wt% (GX: 5.0 wt%, monomer: 1.0 wt% and GX: 4.0 wt%, monomer: 2.0 wt%).

[0047] In addition, when a monomer was mixed, the GX mixing ratio was reduced by the amount of the monomer to match the dispersant mixing ratio when only GX was used. The shaded areas in Table 3 represent cases where the dispersant was a mixed dispersant of GX and a monomer. The dispersant notation includes both GX alone and cases where a monomer was added to GX. Table 3 also assigns a symbol to each condition, which corresponds to the symbol for the viscosity and dispersibility evaluation results for each monomer shown in Table 4.

[0048] [Table 3]

[0049] In this Example 2, the dispersibility of CNTs was evaluated by both viscosity measurement and CNT dispersibility. Viscosity was measured using an SV-type viscometer SV-1A (manufactured by A&D Co., Ltd.). This viscometer is a tuning fork vibration type that resonates an oscillator in the liquid and determines the viscosity from the excitation force required to move the oscillator at a constant amplitude.

[0050] Dispersibility was evaluated based on the results of viscosity measurements. A good rating was given for a measured viscosity of less than 1000 mPa·s and the CNT dispersion was easily deformed, while an unsatisfactory rating was given for a viscosity of 1000 mPa·s or more or for a CNT dispersion that did not deform and appeared to be in a solid state. (1) When sodium naphthalenesulfonate is used as the monomer

[0051] A CNT dispersion using sodium naphthalenesulfonate was prepared as follows. For example, in Table 3, when the MWCNT content is 5.0 wt%, GX content is 1.9 wt%, and the monomer (sodium naphthalenesulfonate) content is 0.1 wt% (condition (D)), 5.0 mg of MWCNT, 1.9 mg of GX, 0.1 mg of sodium naphthalenesulfonate, and 93.0 mL of water were prepared. GX and sodium naphthalenesulfonate were added to the water, and then the MWCNT was added and dispersed using a 600 W ultrasonic homogenizer. The dispersion time was 1 hour. Dispersions were also prepared using the same method for the other conditions shown in Table 3. That is, dispersions of MWCNT with various concentrations were prepared by varying GX from 1.3 wt% to 6.0 wt%, sodium naphthalenesulfonate from 0.1 wt% to 2.0 wt%, and MWCNT from 3.0 wt% to 10.0 wt%.

[0052] The viscosity measurements and dispersibility evaluation results when sodium naphthalenesulfonate was used as the monomer are shown in Table 4. Table 4 shows the viscosity and dispersibility evaluation results of the CNT dispersion liquid when the four types of monomers of Example 2 were used.

[0053] As can be seen from Table 4, when only GX was used as a dispersant, the viscosity increased by 1000 under all conditions, and the dispersibility was evaluated as × (conditions (A), (C), (E), and (H)). For example, when the dispersant contained 1.3 wt% GX, the viscosity increased by 1000 even when the MWCNT concentration was 3.0 wt%, and the dispersibility was evaluated as × (condition (A)). These are the same results as in Table 1.

[0054] In contrast, when a dispersant containing GX and sodium naphthalenesulfonate was further added, the viscosity was a maximum of 740 mPa·s (condition (I)), and all dispersibility evaluations were rated as good. For example, when a dispersant containing 3.7 wt% GX and 0.5 wt% sodium naphthalenesulfonate was added, the viscosity was 290 mPa·s even when 8.0 wt% MWCNT was added, and the dispersibility evaluation was good (condition (F)). Similarly, when a dispersant containing 5.0 wt% GX and 1.0 wt% sodium naphthalenesulfonate was added, the viscosity was 740 mPa·s even when 10.0 wt% MWCNT was added, and the dispersibility evaluation was good (condition (I)). Furthermore, a tendency was observed in which the viscosity decreased and the dispersibility improved as the amount of sodium naphthalenesulfonate added increased (conditions (F) and (G) and conditions (I) and (J)).

[0055] As described above, the dispersant obtained by adding sodium naphthalenesulfonate to GX was able to improve the dispersibility of MWCNTs, and even at 10.0 wt%, a CNT dispersion liquid with sufficient dispersibility was obtained.

[0056] Although not shown in Tables 3 and 4, further experimental testing was carried out under various conditions with respect to the amounts of GX and sodium naphthalenesulfonate added, and it was confirmed that good dispersibility was achieved even when GX was added up to 10 wt%. However, a concentration of approximately 5.0 wt% or less is preferable, as this further improves viscosity and dispersibility. Furthermore, it is preferable to add less sodium naphthalenesulfonate than the amount of GX added, and more preferably to add less than half the amount of GX added.

[0057] Although sodium naphthalenesulfonate was used in this example, similar results can be obtained with any naphthalenesulfonate, such as potassium naphthalenesulfonate, calcium naphthalenesulfonate, or ammonium naphthalenesulfonate. (2) When methyl-α-glucose is used as the monomer

[0058] This section describes a CNT dispersion using methyl-α-glucose as the monomer. The preparation method is the same as for sodium naphthalenesulfonate, so a detailed explanation is omitted. The evaluation of CNT dispersibility, as well as the mixing ratio of the dispersant GX to the monomer and the MWCNT mixing ratio, are shown in Tables 3 and 4.

[0059] As can be seen from Table 4, when only GX was used as a dispersant, the viscosity increased by 1000 under all conditions, and the dispersibility was evaluated as × (conditions (A), (C), (E), and (H)). These are the same results as in Table 1. As an example, when the dispersant contained 1.3 wt% GX, the viscosity increased by 1000 when the MWCNT concentration was 3.0 wt%, and the dispersibility was evaluated as × (condition (A)).

[0060] In contrast, when a dispersant containing GX and methyl-α-glucose was further added, the viscosity was a maximum of 810 mPa·s (condition (I)), and all dispersibility evaluations were rated as good. To give a specific example, when a dispersant containing 3.7 wt% GX and 0.5 wt% methyl-α-glucose was added, the viscosity was 400 mPa·s even when 8.0 wt% MWCNT was added, and the dispersibility evaluation was good (condition (F)). Similarly, when a dispersant containing 5.0 wt% GX and 1.0 wt% methyl-α-glucose was added, the viscosity was 810 mPa·s even when 10.0 wt% MWCNT was added, and the dispersibility evaluation was good (condition (I)). Furthermore, a tendency was observed in which the viscosity decreased and the dispersibility improved as the amount of methyl-α-glucose added increased (conditions (F) and (G) and conditions (I) and (J)).

[0061] As described above, the dispersant obtained by adding methyl-α-glucose to GX was able to improve the dispersibility of MWCNTs, and even at 10.0 wt%, a CNT aqueous dispersion with sufficient dispersibility was obtained.

[0062] Although not shown in Tables 3 and 4, further experimental testing was carried out under various conditions with respect to the amounts of GX and methyl-α-glucose added, and it was confirmed that good dispersibility was achieved even when GX was added up to 10 wt%. However, a concentration of approximately 4.5 wt% or less is preferable, as this further improves viscosity and dispersibility. Furthermore, it is preferable to add less methyl-α-glucose than GX, and more preferably to add less than half the amount of GX. (3) When xylose is used as a monomer

[0063] The method for preparing a CNT dispersion using xylose as a monomer is the same as the method described above, and therefore its explanation is omitted. In this example, the dispersibility of CNTs was evaluated by both viscosity measurement and CNT dispersibility, but the viscosity measurement and dispersibility evaluation methods were the same as those described above, and therefore their explanation is omitted.

[0064] As can be seen from Table 4, when only GX was used as a dispersant, the viscosity increased by 1000 under all conditions, and the dispersibility was evaluated as × (conditions (A), (C), (E), and (H)). These are the same as the results in Table 1. As an example, when the dispersant contained 1.3 wt% GX, the viscosity increased by 1000 even when the MWCNT concentration was 3.0 wt%, and the dispersibility was evaluated as × (condition (A)).

[0065] In contrast, when a dispersant containing GX and xylose was further added, the viscosity was a maximum of 840 mPa·s (condition (I)), and all dispersibility evaluations were rated as good. To give a specific example, when a dispersant containing 3.7 wt% GX and 0.5 wt% xylose was added, the viscosity was 830 mPa·s even when 8.0 wt% MWCNT was added, and the dispersibility evaluation was good (condition (F)). Similarly, when a dispersant containing 5.0 wt% GX and 1.0 wt% xylose was added, the viscosity was 840 mPa·s even when 10.0 wt% MWCNT was added, and the dispersibility evaluation was good (condition (I)). Furthermore, a tendency was observed in which the viscosity decreased and the dispersibility improved as the amount of xylose added increased (conditions (F) and (G) and conditions (I) and (J)).

[0066] As described above, the dispersant obtained by adding xylose to GX was able to improve the dispersibility of MWCNTs, and even at 10.0 wt%, a CNT dispersion liquid with sufficient dispersibility was obtained.

[0067] Although not shown in Tables 3 and 4, further experiments were carried out under various conditions with regard to the amount of GX and xylose added, and it was confirmed that good dispersibility was achieved even when GX was added up to 10 wt%. However, a concentration of approximately 4.0 wt% or less is preferable, as this further improves viscosity and dispersibility. Furthermore, it is preferable to add less xylose than the amount of GX, and more preferably less than half the amount of GX. (4) When sodium pyrenesulfonate is used as the monomer

[0068] The method for preparing a CNT dispersion using sodium pyrenesulfonate as a monomer is the same as that described above, and therefore a detailed description thereof will be omitted. In this example, the CNT dispersibility was evaluated by both viscosity measurement and CNT dispersibility. The viscosity measurement and dispersibility evaluation were performed using the same methods as those described above, and therefore a detailed description thereof will be omitted.

[0069] As can be seen from Table 4, when only GX was used as a dispersant, the viscosity increased by 1000 under all conditions, and the dispersibility was evaluated as × (conditions (A), (C), (E), and (H)). These are the same results as in Table 1. As an example, when the dispersant contained 1.3 wt% GX, the viscosity increased by 1000 even when the MWCNT concentration was 3.0 wt%, and the dispersibility was evaluated as × (condition (A)).

[0070] In contrast, when a dispersant containing GX and sodium pyrenesulfonate was further added, the viscosity was a maximum of 620 mPa·s (condition (I)), and all dispersibility evaluations were rated as good. To give a specific example, when a dispersant containing 3.7 wt% GX and 0.5 wt% sodium pyrenesulfonate was added, the viscosity was 520 mPa·s even when 8.0 wt% MWCNT was added, and the dispersibility evaluation was good (condition (F)). Similarly, when a dispersant containing 5.0 wt% GX and 1.0 wt% sodium pyrenesulfonate was added, the viscosity was 620 mPa·s even when 10.0 wt% MWCNT was added, and the dispersibility evaluation was good (condition (I)). Furthermore, a tendency was observed in which the viscosity decreased and the dispersibility improved as the amount of sodium pyrenesulfonate added increased (conditions (F) and (G) and conditions (I) and (J)).

[0071] As described above, the dispersant obtained by adding sodium pyrenesulfonate to GX was able to improve the dispersibility of MWCNTs, and even at 10.0 wt%, a CNT dispersion liquid with sufficient dispersibility was obtained.

[0072] Although not shown in Tables 3 and 4, further experimental testing was carried out under various conditions with respect to the amounts of GX and sodium pyrenesulfonate added, and it was confirmed that good dispersibility was achieved even when GX was added up to 10 wt%. However, a concentration of approximately 4.5 wt% or less is preferable, as this further improves viscosity and dispersibility. Furthermore, it is preferable to add less sodium pyrenesulfonate than the amount of GX added, and more preferably to add less than half the amount of GX added.

[0073] Although sodium pyrenesulfonate was used as the monomer, similar results can be obtained with pyrenesulfonate salts, such as potassium pyrenesulfonate, calcium pyrenesulfonate, and ammonium pyrenesulfonate.

[0074] In this Example 2, four types of monomers were added to GX, the dispersant of the present invention, and the viscosity and dispersibility of the MWCNT dispersions were evaluated. When 10 wt% MWCNT was added, the lowest viscosity was obtained with sodium naphthalenesulfonate, followed by methyl-α-glucose and then sodium pyrenesulfonate. Xylose exhibited a relatively high viscosity. Furthermore, in the case of sodium naphthalenesulfonate and methyl-α-glucose, increasing the monomer mixing ratio reduced the viscosity to more than half (330 mPa·s and 350 mPa·s, respectively), whereas the degree of viscosity reduction was small in the case of xylose.

[0075] In this Example 2, NC7000 manufactured by NANOSYL was used as the MWCNT, but the present invention is not limited to this material. MWCNT manufactured by companies that manufacture and sell CNT, such as Meijo Nanocarbon Co., Ltd., Hamamatsu Carbonix Co., Ltd., and Zeon Corporation, may also be used.

[0076] [Table 4] Example 3

[0077] Next, we will describe the viscosity and dispersibility evaluation results of CNT dispersions prepared by varying the mixing ratio of GX and the monomer dispersant added to SWCNT. The monomers used in this Example 3 were sodium naphthalenesulfonate, methyl-α-glucose, xylose, and sodium pyrenesulfonate, as in Examples 1 and 2.

[0078] The SWCNTs used in this Example 3 were MEIJO eDIPS2.0P from Meijo Nanocarbon Co., Ltd., with a central diameter of 2 to 3 nm and a carbon purity of 98 wt% or more.

[0079] CNT dispersions were prepared as follows. For example, for a 1.0 wt% GX and 0.4 wt% SWCNT dispersion, 1 mg of GX, 0.4 mg of SWCNT, and 98.6 mL of water were prepared. GX and SWCNT were added to the water and dispersed using a 600 W ultrasonic homogenizer. The dispersion time was 1 hour. When a monomer dispersant was added, for example, for a 0.8 wt% GX, 0.2 wt% monomer dispersant, and 0.4 wt% SWCNT dispersion, 0.8 mg of GX, 0.2 mg of monomer dispersant, 0.4 mg of SWCNT, and 98.6 mL of water were prepared. GX and the monomer dispersant were added to the water, and then SWCNT was added and dispersed using a 600 W ultrasonic homogenizer. The dispersion time was 1 hour. In other words, the total amount of dispersant added was the same whether GX alone was used as the dispersant or GX plus the monomer dispersant was added.

[0080] In this Example 3, the dispersibility of CNTs was evaluated by both viscosity measurement and CNT dispersibility. The viscosity was measured using an SV-type viscometer SV-1A (manufactured by A&D Co., Ltd.). This viscometer is a tuning fork vibration type that resonates an oscillator in the liquid and determines the viscosity from the excitation force required to move the oscillator at a constant amplitude.

[0081] Dispersibility was evaluated based on the results of viscosity measurements. A good rating was given for a measured viscosity of less than 1000 mPa·s and the CNT dispersion was easily deformed, while an unsatisfactory rating was given for a viscosity of 1000 mPa·s or more or for a CNT dispersion that did not deform and appeared to be in a solid state.

[0082] Table 5 shows the mixing ratios of GX, monomer, and SWCNT in the CNT dispersion liquid according to Example 3. Four types of SWCNT were used: 0.4 wt%, 0.6 wt%, 0.8 wt%, and 1.0 wt%. The dispersant was GX only (i.e., without mixing monomer, GX alone was 1.0 wt%, 1.7 wt%, 2.6 wt%, and 3.5 wt%), and when the total dispersant concentration was 1.0 wt% (GX: 0.8 wt%, monomer: 0.2 wt%), the total dispersant concentration was 1.7 wt% (GX: 1.4 wt%, monomer: 0.3 wt%, and GX: 1.2 wt%, monomer: 0.2 wt%). The following 11 conditions were tested: a total dispersant concentration of 2.6 wt% (GX: 1.8 wt%, monomer: 0.8 wt% and GX: 1.6 wt%, monomer: 1.0 wt%); a total dispersant concentration of 3.5 wt% (GX: 2.5 wt%, monomer: 1.0 wt% and GX: 2.0 wt%, monomer: 1.5 wt%).

[0083] In addition, when a monomer was mixed, the GX mixing ratio was reduced by the amount of the monomer to match the dispersant mixing ratio when only GX was used. The shaded areas in Table 5 represent cases where the dispersant was a mixture of GX and a monomer. Table 5 also assigns a symbol to each condition, which corresponds to the symbol for the viscosity and dispersibility evaluation results for each monomer shown in Table 6.

[0084] [Table 5] (1) When sodium naphthalenesulfonate is used as the monomer

[0085] The total dispersant concentrations were 1.0 wt%, 1.7 wt%, 2.6 wt%, and 3.5 wt%, and the SWCNT concentrations were 0.4 wt%, 0.6 wt%, 0.8 wt%, and 1.0 wt%, respectively, to match the dispersant concentrations. The specific mixing ratios are shown in Table 5. The shaded areas in Table 5 represent dispersants containing GX plus the monomer sodium naphthalenesulfonate.

[0086] Table 6 shows the viscosity and dispersibility evaluation results when sodium naphthalenesulfonate was used. As can be seen from Table 6, when only GX was used as a dispersant, the viscosity increased by 1000 under all conditions, and the dispersibility was evaluated as × (condition (K), condition (M), condition (P), condition (S)). These are the same results as in Tables 1 and 4. As an example, when the dispersant contained 1.0 wt% GX, the viscosity increased by 1000 even when the SWCNT concentration was 0.4 wt%, and the dispersibility was evaluated as × (condition (K)).

[0087] In contrast, when a dispersant containing GX and sodium naphthalenesulfonate was further added, the viscosity was a maximum of 790 mPa·s (condition Q), and all dispersibility evaluations were rated as good. To give a specific example, when a dispersant containing 1.8 wt% GX and 0.8 wt% sodium naphthalenesulfonate was added, the viscosity was 790 mPa·s, even when 0.8 wt% SWCNT was added, and the dispersibility evaluation was good (condition (Q)). Similarly, when a dispersant containing 2.5 wt% GX and 1.0 wt% sodium naphthalenesulfonate was added, the viscosity was 750 mPa·s, even when 1.0 wt% SWCNT was added, and the dispersibility evaluation was good (condition (T)). Furthermore, the greater the amount of sodium naphthalenesulfonate added, the lower the viscosity and the better the dispersibility tended to be (conditions (N) and (O), conditions (Q) and (R), and conditions (T) and (U)).

[0088] As described above, the dispersant GX containing sodium naphthalenesulfonate was able to improve the dispersibility of SWCNTs, and even at 1.0 wt% it was possible to obtain a CNT dispersion with sufficient dispersibility.

[0089] Although not shown in Tables 5 and 6, further testing of the amounts of GX and sodium naphthalenesulfonate confirmed that good dispersibility was achieved even when GX was added up to 4.0 wt%. However, a concentration of approximately 3.0 wt% or less is preferred, as this further improves viscosity and dispersibility. Furthermore, the amount of sodium naphthalenesulfonate added is preferably less than the amount of GX, and more preferably less than half the amount of GX.

[0090] Although sodium naphthalenesulfonate was used in this example, similar results can be obtained with any naphthalenesulfonate, such as potassium naphthalenesulfonate, calcium naphthalenesulfonate, or ammonium naphthalenesulfonate. (2) When methyl-α-glucose is used as the monomer

[0091] The mixing ratios of SWCNT, GX, and methyl-α-glucose are as shown in Table 5. The method for preparing the CNT dispersion has already been explained, so a detailed description is omitted. The dispersibility of the CNTs was evaluated by both viscosity measurement and CNT dispersibility. The viscosity measurement and dispersibility evaluation methods have also already been explained, so a detailed description is omitted.

[0092] Table 6 shows the viscosity and dispersibility evaluation results for CNT dispersions using methyl-α-glucose as the monomer. The total dispersant concentrations were 1.0 wt%, 1.7 wt%, 2.6 wt%, and 3.5 wt%, and the SWCNT concentrations were 0.4 wt%, 0.6 wt%, 0.8 wt%, and 1.0 wt%, respectively, to match the dispersant concentrations. The shaded areas in Tables 5 and 6 represent dispersants in which the monomer methyl-α-glucose was added in addition to GX.

[0093] As can be seen from Table 6, when only GX was used as a dispersant, the viscosity increased by 1000 under all conditions, and the dispersibility was evaluated as × (condition (K), condition (M), condition (P), condition (S)). As an example, when the dispersant contained 1.0 wt% GX, the viscosity increased by 1000 even when the SWCNT concentration was 0.4 wt%, and the dispersibility was evaluated as × (condition (K)).

[0094] In contrast, when a dispersant containing GX and methyl-α-glucose was further added, the viscosity was a maximum of 870 mPa·s (condition (Q)), and all dispersibility evaluations were rated as good. To give a specific example, when a dispersant containing 1.8 wt% GX and 0.8 wt% methyl-α-glucose was added, the viscosity was 870 mPa·s even when 0.8 wt% SWCNT was added, and the dispersibility evaluation was good (condition (Q)). Similarly, when a dispersant containing 2.5 wt% GX and 1.0 wt% methyl-α-glucose was added, the viscosity was 850 mPa·s even when 1.0 wt% SWCNT was added, and the dispersibility evaluation was good (condition (T)). Furthermore, a tendency for the viscosity to decrease with increasing amounts of methyl-α-glucose was observed (conditions (N) and (O), condition (Q) and (R), and condition (T) and (U)).

[0095] As described above, the dispersant obtained by adding methyl-α-glucose to GX was able to improve the dispersibility of SWCNTs, and even at 1.0 wt% it was possible to obtain a CNT aqueous dispersion with sufficient dispersibility.

[0096] Although not shown in Tables 5 and 6, further testing of the amounts of GX and methyl-α-glucose confirmed that good dispersibility was achieved even when GX was added up to 4.0 wt%. However, a concentration of approximately 2.5 wt% or less is preferred, as this further improves viscosity and dispersibility. Furthermore, it is preferable to add less methyl-α-glucose than GX, and more preferably less than half the amount of GX. (3) When xylose is used as a monomer

[0097] The mixing ratios of SWCNT, GX, and xylose are as shown in Table 5. The method for preparing the CNT dispersion has already been explained, so it will not be repeated here. The dispersibility of the CNTs was evaluated by both viscosity measurement and CNT dispersibility. The viscosity measurement and dispersibility evaluation methods have also been explained, so they will not be repeated here.

[0098] Table 6 shows the viscosity and dispersibility evaluation results for CNT dispersions using xylose as the monomer. The total dispersant concentrations were 1.0 wt%, 1.7 wt%, 2.6 wt%, and 3.5 wt%, and the SWCNT concentrations were 0.4 wt%, 0.6 wt%, 0.8 wt%, and 1.0 wt%, respectively, to match the dispersant concentrations. The shaded areas in Tables 5 and 6 represent dispersants in which the monomer xylose was added in addition to GX.

[0099] As can be seen from Table 6, when only GX was used as a dispersant, the viscosity increased by 1000 under all conditions, and the dispersibility was evaluated as × (condition (K), condition (M), condition (P), condition (S)). As an example, when the dispersant contained 1.0 wt% GX, the viscosity increased by 1000 even when the SWCNT concentration was 0.4 wt%, and the dispersibility was evaluated as × (condition (K)).

[0100] In contrast, when a dispersant containing GX and xylose was further added, the viscosity was a maximum of 950 mPa·s (condition (T)), and all dispersibility evaluations were rated as good. To give a specific example, when a dispersant containing 1.8 wt% GX and 0.8 wt% xylose was added, the viscosity was 940 mPa·s, even with 0.8 wt% SWCNTs added, and the dispersibility evaluation was good (condition (Q)). Similarly, when a dispersant containing 2.5 wt% GX and 1.0 wt% xylose was added, the viscosity was 950 mPa·s, even with 1.0 wt% SWCNTs added, and the dispersibility evaluation was good (condition (T)). Furthermore, a tendency for the viscosity to decrease with increasing amounts of xylose was observed, but the degree of viscosity decrease was smaller than with other monomers (conditions (N) and (O), conditions (Q) and (R), and conditions (T) and (U)).

[0101] As described above, the dispersant obtained by adding xylose to GX was able to improve the dispersibility of SWCNTs, and even at 10.0 wt% xylose, a CNT aqueous dispersion with sufficient dispersibility was obtained.

[0102] Although not shown in Tables 5 and 6, further testing of the amounts of GX and xylose confirmed that GX maintained good dispersibility even when added up to 4.0 wt%. However, a concentration of about 2.0 wt% or less is preferred, as this further improves viscosity and dispersibility. Furthermore, it is preferable to add less xylose than the amount of GX, and more preferably less than half the amount of GX. (4) When sodium pyrenesulfonate is used as the monomer

[0103] The mixing ratios of SWCNT, GX, and sodium pyrenesulfonate are as shown in Table 5. The method for preparing the CNT dispersion has already been explained, so it will not be repeated here. The dispersibility of the CNTs was evaluated by both viscosity measurement and CNT dispersibility. The viscosity measurement and dispersibility evaluation methods have already been explained, so they will not be repeated here.

[0104] Table 6 shows the viscosity and dispersibility evaluation results for CNT dispersions when sodium pyrenesulfonate was used as the monomer. The total dispersant concentrations were 1.0 wt%, 1.7 wt%, 2.6 wt%, and 3.5 wt%, and the SWCNT concentrations were 0.4 wt%, 0.6 wt%, 0.8 wt%, and 1.0 wt%, respectively, to match the dispersant concentrations. The shaded areas in Tables 5 and 6 represent dispersants in which the monomer sodium pyrenesulfonate was added in addition to GX.

[0105] As can be seen from Table 6, when only GX was used as a dispersant, the viscosity increased by 1000 under all conditions, and the dispersibility was evaluated as × (condition (K), condition (M), condition (P), condition (S)). As an example, when the dispersant contained 1.0 wt% GX, the viscosity increased by 1000 even when the SWCNT concentration was 0.4 wt%, and the dispersibility was evaluated as × (condition (K)).

[0106] In contrast, when a dispersant containing GX and sodium pyrenesulfonate was further added, the viscosity was a maximum of 800 mPa·s (condition (Q)), and all dispersibility evaluations were rated as good. To give a specific example, when a dispersant containing 1.8 wt% GX and 0.8 wt% sodium pyrenesulfonate was added, the viscosity was 800 mPa·s, even with 0.8 wt% SWCNTs added, and the dispersibility evaluation was good (condition (Q)). Similarly, when a dispersant containing 2.5 wt% GX and 1.0 wt% sodium pyrenesulfonate was added, the viscosity was 620 mPa·s, even with 1.0 wt% SWCNTs added, and the dispersibility evaluation was good (condition (T)). Furthermore, a tendency for the viscosity to decrease with increasing amounts of sodium pyrenesulfonate was observed (conditions (N) and (O), conditions (Q) and (R), and conditions (T) and (U)).

[0107] As described above, the dispersant GX containing sodium pyrenesulfonate was able to improve the dispersibility of SWCNTs, and even at 1.0 wt% it was possible to obtain a CNT aqueous dispersion with sufficient dispersibility.

[0108] Although not shown in Tables 5 and 6, further testing of the amounts of GX and sodium pyrenesulfonate confirmed that good dispersibility was achieved even when GX was added up to 4.0 wt%. However, a concentration of approximately 2.5 wt% or less is preferred, as this further improves viscosity and dispersibility. Furthermore, the amount of sodium pyrenesulfonate added is preferably less than the amount of GX added, and more preferably less than half the amount of GX added.

[0109] Although sodium pyrenesulfonate was used as the monomer in this example, similar results can be obtained with pyrenesulfonate salts, such as potassium pyrenesulfonate, calcium pyrenesulfonate, and ammonium pyrenesulfonate.

[0110] [Table 6]

[0111] In this Example 3, we described the amount of SWCNT added, and the results for viscosity and dispersibility when sodium naphthalenesulfonate, methyl-α-glucose, xylose, and sodium pyrenesulfonate were used as monomers added to GX. When evaluating dispersibility depending on the monomer material based on viscosity and dispersibility evaluation results, we found that sodium naphthalenesulfonate, sodium pyrenesulfonate, and methyl-α-glucose were preferable, as they showed low viscosity values ​​even when 1.0 wt% SWCNT was added, and that caution was required when using xylose, as its viscosity was close to the allowable value of 1000 mPa s.

[0112] In this Example 3, MEIJO eDIPS2.0P from Meijo Nanocarbon Co., Ltd. was used as the SWCNT, but the present invention is not limited to this material. SWCNT from companies that manufacture and sell CNT, such as NANOSYL Corporation and Zeon Corporation, may also be used.

[0113] As described above, it was discovered that a dispersant containing GX and one monomer selected from naphthalenesulfonate, pyrenesulfonate, methyl-α-glucose, and xylose, which has a lower molecular weight than GX and possesses both hydrophobic and hydrophilic properties in its molecular structure, can disperse MWCNTs and SWCNTs at high concentrations using water as the dispersion medium, and also has excellent stability.

[0114] The glucuronoxylan of the present invention includes arabinoglucuronoxylan (sometimes called glucuronoarabinoxylan) and arabinoxylan. Although the present embodiment and examples have described the use of glucuronoxylan as a dispersant, the present invention is not limited thereto, and arabinoxylan, arabinoglucuronoxylan, and the like may also be used. Furthermore, the dispersant may contain a xylan other than glucuronoxylan.

[0115] The CNT dispersion of the present invention can be used in a wide range of applications, such as electrode materials for lithium-ion batteries and all-solid-state secondary batteries, transparent electrode materials, antistatic materials, conductive rubber sheets, conductive paints, electromagnetic wave shielding materials, and heater components. [Industrial Applicability]

[0116] The CNT dispersant and CNT dispersion of the present invention are highly effective in a wide range of fields, such as noise prevention in electronic devices, application to secondary batteries, and application in the semiconductor field.

Claims

1. A dispersant for carbon nanotubes for dispersing carbon nanotubes in water, comprising: The present invention relates to a method for producing a cellulose ester copolymer comprising: a glucuronoxylan; and a monomer having a lower molecular weight than the glucuronoxylan and having hydrophobic and hydrophilic properties in its molecular structure; the mixing ratio of the monomer is smaller than the mixing ratio of the glucuronoxylan, The dispersant for carbon nanotubes is characterized in that the monomer is one selected from the group consisting of naphthalenesulfonate, pyrenesulfonate, methyl-α-glucose, and xylose.

2. 2. The dispersant for carbon nanotubes according to claim 1, wherein the naphthalenesulfonate is sodium naphthalenesulfonate.

3. 2. The dispersant for carbon nanotubes according to claim 1, wherein the pyrenesulfonate is sodium pyrenesulfonate.

4. A carbon nanotube dispersion liquid containing water as a dispersion solvent, a dispersant, and carbon nanotubes, A carbon nanotube dispersion liquid, wherein the dispersant is the carbon nanotube dispersant according to any one of claims 1 to 3.

5. 5. The carbon nanotube dispersion according to claim 4, wherein the carbon nanotubes are either single-walled carbon nanotubes or multi-walled carbon nanotubes.

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