Carbon nanotube dispersants and carbon nanotube dispersions

Abstract

By using alkylated xylan, which is obtained by alkylating xylan, we provide a dispersant that can disperse carbon nanotubes (CNTs) at a high concentration in the organic solvent N-methyl-2-pyrrolidone (NMP), and a dispersion liquid with a high concentration of CNTs dispersed in it. [Solution] The present invention provides a CNT dispersant for dispersing CNTs in an organic solvent called NMP, characterized by using alkylated xylan, which is soluble in NMP, obtained by alkylating xylan. In the above configuration, the alkyl group to be alkylated may consist of any one group selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group. By alkylating xylan, it becomes soluble in NMP, and the dispersion in which alkylated xylan is dissolved in NMP can disperse CNTs at a high concentration.

Description

Technical Field

[0001] The present invention relates to a dispersant and a dispersion liquid for dispersing carbon nanotubes at a high concentration and stably.

Background Art

[0002] Carbon nanotubes (hereinafter referred to as "CNT") are substances in the form of cylindrical (tube) with a diameter on the nanometer scale composed only of carbon, and have a structure in which benzene rings in which carbon atoms are arranged in a hexagonal shape are arranged adjacent to each other on a plane and rolled into a cylindrical shape. A single layer of this tube is a single-walled carbon nanotube (hereinafter referred to as "SWCNT"), and a structure in which a plurality of tubes with different diameters are stacked in layers is called a multi-walled carbon nanotube (hereinafter referred to as "MWCNT").

[0003] CNT has high conductivity and high mechanical strength, and its application to conductive paints, conductive resins, electromagnetic shielding sheets, or heater members has been studied by taking advantage of these characteristics. CNT can be expected to exhibit various physical properties by taking advantage of its structural characteristics of an extremely large aspect ratio and an extremely small diameter.

[0004] In recent years, in consideration of environmental measures, etc., it has been required to disperse CNT at a high concentration to reduce the amount of solvent used and to reduce the energy used during drying. However, when the CNT concentration becomes high, the viscosity of the CNT dispersion liquid increases and the fluidity decreases, so the workability and homogeneity decrease when used as a paint. Therefore, a CNT dispersion liquid having sufficient dispersibility, good storage stability, high concentration and low viscosity is required.

[0005] In the solid state, CNT forms a bundle (bundle) structure due to strong π-π interaction and van der Waals force, so it is difficult to disperse in many solvents. Therefore, in order to make CNT dispersible in a solvent and enable various applications, an excellent dispersant to assist this is required. Therefore, various dispersants have been developed.

[0006] For example, a CNT dispersion composition comprising CNTs, a dispersant, and an amide-based polar solvent is disclosed, wherein ethylcellulose can be used as a resin-type dispersant cellulose derivative, and N-methylpyrrolidone (NMP) can be used as the amide-based polar organic solvent (see, for example, Patent Document 1).

[0007] Furthermore, a CNT dispersion solution comprising CNTs, an amide-based polar organic solvent, and polyvinylpyrrolidone (PVP) has been disclosed in which the amide-based polar organic solvent is N-methylpyrrolidone (NMP) and the CNTs are single-walled carbon nanotubes (SWNTs) (see, for example, Patent Document 2).

[0008] Furthermore, a method for producing a carbonaceous material dispersion, wherein a carbonaceous material is dispersed in a non-aqueous solvent consisting of a nitrogen-containing heterocyclic amide compound with a solvent purity of 99.9% or higher, wherein the amine component concentration in the non-aqueous solvent is 3 × 10⁻⁶ by mass fraction. -6 A amine control concentration confirmation step to confirm that it is less than 5 × 10⁻¹⁰, and the water concentration in the non-aqueous solvent is confirmed to be less than 5 × 10⁻¹⁰ by mass fraction. -4 A method for producing a carbonaceous material dispersion is disclosed, comprising a moisture control concentration confirmation step to confirm that the concentration is less than a certain amount, and a dispersion step in which a carbonaceous material is added to a non-aqueous solvent that satisfies the conditions in the amine control concentration confirmation step and the moisture control concentration confirmation step, and stirred and mixed so that the carbonaceous material concentration relative to the total mass is 15 to 30% by mass. The nitrogen-containing heterocyclic amide compound is N-methyl-2-pyrrolidone, and a resin-based dispersant is added as a dispersant, with methylcellulose or ethylcellulose being used as the resin-based dispersant (see, for example, Patent Document 3).

[0009] Furthermore, a semiconducting CNT dispersion containing semiconducting CNTs, alkylcellulose, and an organic solvent is disclosed. Specific alkylcelluloses described include methylcellulose and ethylcellulose, and the alkyl group may be linear or branched. These alkylcelluloses have hydrophobic alkyl groups, allowing for good dispersion of CNTs. As for the organic solvent, for example, toluene and 1-methyl-2-pyrrolidone, an organic solvent containing a nitrogen atom, are described (see, for example, Patent Document 4).

[0010] Furthermore, a solution is disclosed comprising an added water-soluble xylan, a substance, and a solvent, wherein the substance is sparingly soluble or insoluble in the solvent in the absence of the water-soluble xylan. In this solution, CNTs are used as the substance, and the water-soluble xylan is disclosed to consist of a xylose residue or an acetylated xylose residue, an arabinose residue, and a 4-O-methylglucuronic acid residue, or a xylose residue or an acetylated xylose residue, and a 4-O-methylglucuronic acid residue (see, for example, Patent Document 5). [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2023-69017 [Patent Document 2] Japanese Patent Publication No. 2005-162877 [Patent Document 3] Japanese Patent Publication No. 2022-22739 [Patent Document 4] Japanese Patent Publication No. 2021-134123 [Patent Document 5] Japanese Patent Publication No. 2007-215542 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] The invention described in Patent Document 1 aims to realize a CNT dispersion composition with high dispersibility and to obtain an electrode film with high adhesion and conductivity. This is achieved by having the CNTs contain a specific amount of cobalt, setting the G / D ratio and BET specific surface area within a specific range, and setting the water content of the CNT dispersion within a specific range.

[0013] The invention described in Patent Document 2 has found that an amide-based polar organic solvent, particularly a mixed solvent consisting of N-methylpyrrolidone and polyvinylpyrrolidone, functions as an excellent dispersant for CNTs, and has obtained a dispersion solvent that can effectively disperse CNTs in polar organic solvents useful as polymer solvents. However, this invention does not disclose or suggest the use of alkylated xylan as a dispersant, as polyvinylpyrrolidone functions as the dispersant.

[0014] The invention described in Patent Document 3 found that nitrogen-containing heterocyclic amide compounds such as N-methyl-2-pyrrolidone often contain amine components as impurities, and when attempting to form electrodes for lithium-ion secondary batteries using a carbonaceous material dispersion, the viscosity can vary from lot to lot due to these amine components, resulting in coating problems. The invention developed a manufacturing method to prevent this. Although carbon nanotubes (CNTs) are also described as carbonaceous materials in the specification, no specific explanation or suggestion regarding CNTs is disclosed.

[0015] The invention described in Patent Document 4 addresses the need to selectively extract semiconducting CNTs from other CNTs in order to use them in integrated circuits and the like. Specifically, alkylcellulose selectively adsorbs onto and encapsulates the CNTs. At this time, metallic CNTs rapidly aggregate in the dispersion, but semiconducting CNTs exhibit high dispersibility and disperse in the solvent, resulting in the selective extraction of semiconducting CNTs into the dispersion. In this invention, the use of 1-methyl-2-pyrrolidone as an organic solvent is also described, but there is no disclosure or suggestion regarding the use of alkylated xylan as a dispersant.

[0016] The invention described in Patent Document 5 is characterized in that water is mainly used as a solvent, and water-soluble xylan is used as a dispersant for dispersing CNTs in this solvent. Water-soluble xylan is not a pure xylose polymer, but a molecule in which at least some of the hydroxyl groups in the xylose polymer are replaced by other substituents (for example, acetyl groups, glucuronic acid residues, arabinose residues, etc.), and is soluble in water. Therefore, it seems difficult to use NMP, which is an organic solvent, as a dispersion solvent and water-soluble xylan as a dispersant.

[0017] In order to apply CNTs, for example, as a conductive material for secondary batteries, it may be preferable to use an organic solvent as a dispersion liquid. And what is desired is a dispersant and a dispersion liquid that can disperse CNTs at a high concentration in the dispersion liquid and maintain the dispersed state stably for a long time.

[0018] An object of the present invention is to provide a dispersant that imparts solubility to NMP, which is an organic solvent, by using alkylated xylan obtained by alkylating xylan, and can disperse CNTs at a high concentration, and a dispersion liquid in which CNTs are dispersed at a high concentration.

Means for Solving the Problems

[0019] In order to solve the above conventional problems, the CNT dispersant of the present invention is a CNT dispersant for dispersing CNTs in N-methyl-2-pyrrolidone (hereinafter referred to as "NMP"), which is an organic solvent, and is characterized by using alkylated xylan having solubility in NMP by alkylating xylan.

[0020] In the above configuration, the alkyl group for alkylation treatment may be composed of any one group selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group.

[0021] By subjecting xylan to alkylation treatment, it becomes soluble in NMP. The present invention has been achieved by finding that a dispersion in which alkylated xylan is dissolved in NMP can disperse CNT at a high concentration.

[0022] Next, the method for producing the CNT dispersant of the present invention is a method for producing a dispersant for dispersing CNT in NMP, which is an organic solvent, and includes a step of suspending xylan in dimethyl sulfoxide, a step of adding sodium hydroxide and an alkyl iodide compound, replacing with nitrogen gas, and then performing heat treatment, and a step of recovering alkylated xylan, which is a reaction product, by a chloroform extraction method.

[0023] In this case, as the alkyl iodide compound, any one of methyl iodide, ethyl iodide, propyl iodide, isopropyl iodide or butyl iodide may be used. Also, the mixing ratio of sodium hydroxide and the alkyl iodide compound is preferably 1:5 by weight, but may be in the range of 1:(5 to 10).

[0024] Whether the alkylated xylan after alkylation treatment is soluble in NMP can be determined visually, for example, after mixing alkylated xylan with NMP and applying ultrasonic waves. When it is recognized that the solubility is insufficient, the steps of suspending xylan in dimethyl sulfoxide, adding sodium hydroxide and an alkyl iodide compound, replacing with nitrogen gas, performing heat treatment, and recovering alkylated xylan, which is a reaction product, by a chloroform extraction method may be repeated a plurality of times, for example, 2 to 3 times. By repeating the steps in this way, the degree of substitution with an alkyl group can be increased, and solubility can be ensured. The number of repetitions is preferably about 2 to 5 times. If it is 6 times or more, the complexity of the process increases compared to the degree of improvement in the degree of substitution, and the production cost rises, which is not preferable.

[0025] Next, the CNT dispersion of the present invention comprises NMP as a dispersion solvent, a dispersant, and CNTs, wherein the dispersant is the CNT dispersant described above. In this case, the CNTs may be either SWCNTs or MWCNTs. In other words, SWCNTs alone may be used, MWCNTs alone may be used, or a mixture of SWCNTs and MWCNTs may be used. By using the CNT dispersion of the present invention, for example, when applied to conductive materials for lithium-ion batteries, it is possible to manufacture batteries with higher performance than conventional ones. [Effects of the Invention]

[0026] The CNT dispersant of the present invention and the CNT dispersion liquid using the same will have a significant effect in a wide range of fields, including noise suppression in electronic equipment, applications in secondary batteries, and applications in the semiconductor field. [Brief explanation of the drawing]

[0027] [Figure 1] Table 2 shows a graph of the degree of variance. [Figure 2] Table 2 shows a graph of the viscosity values. [Figure 3] Table 3 shows a graph of the variance. [Figure 4] Table 3 shows a graph of the viscosity values. [Figure 5] Table 4 shows a graph of the variance. [Figure 6] Table 4 shows a graph of the viscosity values. [Modes for carrying out the invention]

[0028] (Embodiment)

[0029] The following describes in detail the CNT dispersant and CNT dispersion according to embodiments of the present invention. The CNT dispersant according to this embodiment is for dispersing CNTs in an organic solvent called NMP, and is characterized by using alkylated xylan which is soluble in NMP obtained by alkylating xylan.

[0030] In this case, the alkyl group to be alkylated may consist of any one group selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group.

[0031] In this invention, xylan refers to a molecule containing two or more xylose residues linked by β-1,4 bonds. In this invention, the concept includes not only molecules composed solely of xylose residues (i.e., pure xylose polymers), but also modified molecules thereof, and molecules in which other residues, such as arabinose residues, are bonded to pure xylose polymers.

[0032] Alkylation treatment of xylan makes it soluble in NMP. The solution in which alkylated xylan is dissolved in NMP allows for high-concentration dispersion of carbon nanotubes (CNTs).

[0033] Alkyl groups are hydrocarbons formed by removing one hydrogen (H) atom from an alkane molecule. The main alkyl groups are methyl, ethyl, propyl, isopropyl, and butyl groups, but there are various other alkyl groups as well. The present invention was completed by discovering that when alkylated xylan, obtained by alkylating xylan using the above alkyl groups, is used as a dispersant, CNTs can be dispersed in NMP at a high concentration. However, the present invention is not limited to the above alkyl groups, and other alkyl groups can be used as long as they are soluble in NMP.

[0034] By using alkylated xylan as a dispersant, CNTs can be dispersed at a high concentration in the organic solvent NMP, and the dispersion state can be maintained for a long period of time.

[0035] The NMP used in this invention is a nitrogen-containing five-membered ring compound that is highly polar, completely miscible with most organic solvents (such as alcohols), and highly soluble in organic and inorganic substances. Furthermore, it can be mixed with water in any proportion. It is safer than other similar solvents because it has a higher flash point. It is easy to handle because it has a high boiling point and a low freezing point. It is chemically and thermally stable and non-corrosive. Note that NMP is a general term that includes N-methyl-2-pyrrolidone, 1-methyl-2-pyrrolidone, 1-methylpyrrolidine-2-one, and N-methyl-2-pyrrolidinone, and this invention also encompasses these compounds.

[0036] Next, the method for producing a CNT dispersant according to this embodiment is a method for producing a dispersant for dispersing CNTs in an organic solvent called NMP, and includes the steps of: suspending xylan in dimethyl sulfoxide; adding sodium hydroxide and an alkyl iodide compound, purging with nitrogen gas, and then heat-treating; and recovering the alkylated xylan, which is a reaction product, by chloroform extraction.

[0037] In this case, any one of methyl iodide, ethyl iodide, propyl iodide, isopropyl iodide, or butyl iodide may be used as the alkyl iodide compound. Furthermore, the mixing ratio of sodium hydroxide to the alkyl iodide compound is preferably 1:5 by weight, but may be in the range of 1:(5~10).

[0038] After this, it is checked whether xylan is soluble in NMP. If solubility is found to be insufficient, the steps of suspending xylan in dimethyl sulfoxide, adding sodium hydroxide and an alkyl iodide compound, purging with nitrogen gas, and then heat-treating, and recovering the alkylated xylan reaction product by chloroform extraction may be repeated multiple times, for example, twice. By repeating the steps in this way, the degree of substitution with alkyl groups can be increased, and solubility can be ensured. The number of repetitions is preferably around 2 to 3 times, but it may be carried out up to around 5 times. Repeating it 6 times or more is undesirable because the complexity of the process increases compared to the degree of improvement in the degree of substitution, and the manufacturing cost increases. This section describes a specific example of alkylation treatment of xylan. For example, it describes the case of producing methylated xylan by methylating the xylan shown in Formula 1.

[0039] [ka]

[0040] However, in Formula 1, n represents the degree of polymerization. There are no particular restrictions on the degree of polymerization n, but 10 to 500 is preferred, and 40 to 500 is more preferred. A may have a hydroxyl group (-OH), an acetylated hydroxyl group (-OCOCH3), or at least one arabinose residue forming a side chain attached to it. B may have a hydroxyl group (-OH), an acetylated hydroxyl group (-OCOCH3), a 4-O-methylglucuronic acid residue of Formula 2 (structural formula (2) below) forming a side chain attached to it, or at least one arabinose residue forming a side chain attached to it. In addition, the carboxyl group (-COOH) of the 4-O-methylglucuronic acid residue shown in Formula 2 (structural formula (2)) may be the sodium salt (-COONa).

[0041] [ka]

[0042] It should be noted that the xylan shown in structural formula (1) in chemical formula 1 is not limited to those formed by the polymerization of a single monomer. For example, in A shown in structural formula (1), one monomer is a hydroxyl group, another monomer is an acetylated hydroxyl group, and yet another monomer is at least one arabinose residue forming a side chain, and xylan may be formed by the polymerization of monomers containing these. The same applies to B shown in structural formula (1). For example, one monomer is a hydroxyl group, another monomer is an acetylated hydroxyl group, and yet another monomer is a 4-O-methylglucuronic acid residue of structural formula (2) forming a side chain, at least one arabinose residue forming a side chain, and the carboxyl group of the 4-O-methylglucuronic acid residue is a sodium salt, and xylan may be formed by the polymerization of monomers containing these. Thus, A and B are not limited to hydroxyl groups, and may be xylan polymers in which monomers with different sugar residues are polymerized and mixed. Therefore, this also includes naturally occurring xylan extracted from plants, etc.

[0043] One g of xylan shown in Formula 1 was suspended in 50 mL of dimethyl sulfoxide (DMSO), and 5 g of sodium hydroxide and 25 mL of methyl iodide were added. The mixture was then purged with nitrogen gas and heated at 110°C for 2 hours. The reaction product was then recovered by chloroform extraction. This procedure was repeated twice to obtain methylated xylan. The methylated xylan prepared in this way was examined for solubility in NMP and confirmed to dissolve well.

[0044] Since solubility was confirmed in this way, it was determined that all or any of the hydroxyl groups (-OH) in the skeleton and the hydroxyl groups (-OH) and carboxyl groups (-COOH) in the side chains shown in Formula 1 were methylated. In this invention, it is sufficient that the methylated xylan obtained by methylating the xylan shown in Formula 1 is soluble in NMP, and it is not necessary for all of the hydroxyl groups (-OH) in the skeleton, the hydroxyl groups (-OH) in the side chains, and the carboxyl groups (-COOH) to be methylated.

[0045] It should be noted that the chemical structure of xylan is not limited to the above and various other structures exist. We have found that these can also be treated in the same way to make them soluble in NMP.

[0046] Next, the ethylation treatment method will be described. 1 g of xylan was suspended in 50 mL of dimethyl sulfoxide (DMSO), 5 g of sodium hydroxide and 25 mL of ethyl iodide were added, and the mixture was purged with nitrogen gas. The mixture was then heated at 110°C for 2 hours. The reaction product was then recovered by chloroform extraction. This procedure was repeated twice to obtain ethylated xylan. The ethylated xylan produced in this way was examined for solubility in NMP and was found to be well soluble.

[0047] Next, the propylation treatment method will be described. 1 g of xylan was suspended in 50 mL of dimethyl sulfoxide (DMSO), 5 g of sodium hydroxide and 25 mL of propyl iodide were added, and the mixture was purged with nitrogen gas. The mixture was then heated at 110°C for 2 hours. The reaction product was then recovered by chloroform extraction. This procedure was repeated twice to obtain propylated xylan. The propylated xylan produced in this way was examined for solubility in NMP and was found to be well soluble.

[0048] Next, the method for isopropylation treatment will be described. 1 g of xylan was suspended in 50 mL of dimethyl sulfoxide (DMSO), 5 g of sodium hydroxide and 25 mL of isopropyl iodide were added, and the mixture was purged with nitrogen gas. The mixture was then heated at 110°C for 2 hours. The reaction product was then recovered by chloroform extraction. This procedure was repeated twice to obtain isopropylated xylan. The solubility of the isopropylated xylan produced in this way was examined in NMP and confirmed to be good.

[0049] Next, the butylation treatment method will be described. 1 g of xylan was suspended in 50 mL of dimethyl sulfoxide (DMSO), 5 g of sodium hydroxide and 25 mL of butyl iodide were added, and the mixture was purged with nitrogen gas. The mixture was then heated at 110°C for 2 hours. The reaction product was then recovered by chloroform extraction. This procedure was repeated twice to obtain butylated xylan. The solubility of the butylated xylan produced in this way was examined in NMP and it was confirmed to dissolve very well.

[0050] The differences between alkylated xylan, which has undergone alkylation treatment in this manner, and commonly used water-soluble xylan were investigated. Table 1 shows the results of a comparative evaluation of the CNT dispersion of ethylated xylan, which has undergone ethylation treatment as part of the alkylation treatment, and water-soluble xylan. Table 1 also includes a comparison when ethyl cellulose, which is commonly used as a dispersant, is used. Ethylated xylan is obtained by ethylating water-soluble xylan.

[0051] [Table 1]

[0052] Table 1 shows two types of carbon nanotubes (CNTs): SWCNTs EC2.0P (Meijo Nanocarbon Co., Ltd.) and SG101 (Nippon Zeon Co., Ltd.), and MWCNTs NC-7000 (Nippon Zeon Co., Ltd.). The values ​​in Table 1 indicate the degree of dispersion.

[0053] Table 1 shows the results of preparing dispersions as follows and comparing their dispersion degrees. A fixed amount of CNTs was weighed according to each method. Simultaneously, 50 mL each of mixed solutions containing ethylated xylan, ethylcellulose, and water-soluble xylan in NMP was prepared, and CNTs were added to each. Then, each was dispersed using an ultrasonic homogenizer (60 W). Next, the solutions were separated using a centrifuge (Eppendorf Hi-Mac Technologies, CT18R) at 10,000 G for 1 hour, and the supernatant was used as the sample for dispersion degree measurement. This supernatant was diluted to a measurable concentration using a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900), and the absorbance at a wavelength of 500 nm was measured to determine the absorbance. The dispersion degree was then calculated based on the obtained absorbance and the diluted volume. Note that the purpose of Table 1 is to compare water-soluble xylan and ethylated xylan, so the concentration of CNTs was set to 0.1 wt%.

[0054] As can be seen from Table 1, water-soluble xylan does not dissolve in NMP, and the dispersion degree was 0 for SWCNTs and a very small value of 0.3 for MWCNTs. In contrast, when ethylated xylan, which has been ethylated, was used, a greater dispersion degree was obtained than when ethylcellulose was used. As a result, it was confirmed that alkylation treatment of xylan increases its solubility in NMP and also increases the dispersion degree of CNTs.

[0055] Next, the CNT dispersion of the present invention is a CNT dispersion comprising NMP as a dispersion solvent, a dispersant, and CNTs, characterized in that the dispersant is the CNT dispersant described above. In this case, the CNTs may be either SWCNTs or MWCNTs. That is, only SWCNTs may be used, only MWCNTs may be used, or a mixture of SWCNTs and MWCNTs may be used.

[0056] Next, the results of measuring the dispersion and viscosity of alkylated xylanes, including methylated xylan, ethylated xylan, propylated xylan, isopropylated xylan, and butylated xylan, will be explained by example. (Example 1)

[0057] In Example 1, methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) were used as dispersants for alkylated xylan. Ethyl cellulose was also used as a dispersant in the comparative example.

[0058] This Example 1 describes the results of dispersing SWCNTs using the above-mentioned dispersant. ZEONANO SG101 (hereinafter referred to as "SWCNT1") from Nippon Zeon Co., Ltd. was used as the SWCNT. SWCNT1 has a specific surface area of ​​800 m². 2 The material must be 1 / g or larger, have an average diameter of 3-5 nm, and a carbon purity of 99% or higher.

[0059] The dispersions were prepared as follows: A fixed amount of CNTs was weighed according to the preparation conditions for each dispersion. Simultaneously, alkylated xylans such as methylated xylan were quantified and mixed into NMP to prepare 50 mL of each mixed solution. CNTs were then added to these solutions. Subsequently, each solution was dispersed using an ultrasonic homogenizer (60 W). Next, the solutions were separated using a centrifuge (Eppendorf Hi-Mac Technologies, CT18R) at 10,000 G for 1 hour, and the supernatant was used as the sample for dispersion measurement.

[0060] The supernatant was diluted to a concentration measurable with a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900), and the absorbance at a wavelength of 500 nm was measured to determine the absorbance. The degree of dispersion was then calculated based on the obtained absorbance and the amount of dilution. Dispersibility was evaluated as good when gelation did not occur even at high CNT concentrations, the degree of dispersion was high, and the viscosity was low.

[0061] Note that the concentration of CNTs is expressed as a percentage of the dispersion containing CNTs, with the dispersion being set to 100. For example, if the amount of CNTs is 0.05 g and the amount of the mixed solution of methylated xylan and NMP is 49.95 g, the CNT concentration is 0.1 wt%.

[0062] Furthermore, viscosity was measured using an SV-type viscometer SV-1A (manufactured by A&D Company, Limited). This viscometer is a tuning fork vibration type, which resonates a vibrator in a liquid and determines viscosity from the excitation force required to move the vibrator at a constant amplitude.

[0063] Table 2 shows the results of determining the degree of dispersion and viscosity with respect to CNT concentration when SWCNT1 is used as a dispersant, with methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) as alkylated xylans, as examples, and the case when ethyl cellulose is used as a comparative example.

[0064] [Table 2]

[0065] Figure 1 is a graph of the dispersion shown in Table 2, and Figure 2 is a graph of the viscosity shown in Table 2. In Figure 1, the horizontal axis represents the concentration of SWCNTs and the vertical axis represents the dispersion. In Figure 2, the horizontal axis represents the concentration of SWCNTs and the vertical axis represents viscosity.

[0066] As shown in Table 2, when methylated xylan (A), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) were used as dispersants, gelation occurred at CNT concentrations of 0.7 wt% or higher. In the case of ethylated xylan (B), gelation did not occur up to a CNT concentration of 0.8 wt%, and even at 0.8 wt%, the dispersion degree was 496.8, indicating high concentration dispersion, and a sufficiently low viscosity of 109 mPa·s was obtained. On the other hand, in the comparative example, ethylcellulose (F) gelation occurred at a CNT concentration of 0.4 wt% or higher.

[0067] As can be seen from Figure 1, the dispersion degree of methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) all show almost the same value and slope. On the other hand, as shown in Figure 2, the viscosity of methylated xylan (A), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) is almost the same value and slope, but ethylated xylan (B) is found to have a lower viscosity than the others. From these results, it can be seen that better results can be obtained by using ethylated xylan as a dispersant among alkylated xylans.

[0068] In contrast, when ethyl cellulose (F) was used as a dispersant, as can be seen from Figures 1 and 2, the degree of dispersion was greater even at lower CNT concentrations compared to alkylated xylan, and the viscosity also increased. From these results, it was found that alkylated xylan, obtained by alkylating xylan, yields a dispersion with better dispersion characteristics than conventional methods using ethyl cellulose when NMP is used as the solvent.

[0069] Both SWCNTs and MWCNTs have a very large aspect ratio. Therefore, when mixing CNTs into a dispersion, the fluidity of the dispersion decreases significantly at a certain concentration. In other words, the viscosity increases sharply and gelation occurs. Since such gelation makes the dispersion unusable, the concentration of CNTs must be limited to a range where gelation does not occur.

[0070] In this Example 1, it was found that alkylated xylans, including methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E), could suppress gelation and achieve low viscosity even when dispersed at higher concentrations than conventionally used ethyl cellulose. (Example 2)

[0071] This second example describes the case where EC2.0P (hereinafter referred to as "SWCNT2") from Meijo Nanocarbon Co., Ltd. is used as the SWCNT. EC2.0P from Meijo Nanocarbon Co., Ltd. has a central diameter of 2-3 nm and a carbon purity of 98% or higher. Since the comparison between the dispersant of the present invention and conventional dispersants when using SWCNTs was explained in Example 1, this example only provides examples for five types of alkylated xylan.

[0072] The dispersions were prepared as follows: A fixed amount of CNTs was weighed according to the preparation conditions for each dispersion. Simultaneously, alkylated xylans such as methylated xylan were quantified and mixed into NMP to prepare 50 mL of each mixed solution. CNTs were then added to these solutions. Subsequently, each solution was dispersed using an ultrasonic homogenizer (60 W). Next, the solutions were separated using a centrifuge (Eppendorf Hi-Mac Technologies, CT18R) at 10,000 G for 1 hour, and the supernatant was used as the sample for dispersion measurement.

[0073] The supernatant was diluted to a concentration measurable with a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900), and the absorbance at a wavelength of 500 nm was measured to determine the absorbance. The degree of dispersion was then calculated based on the obtained absorbance and the amount of dilution. Dispersibility was evaluated as good when gelation did not occur even at high CNT concentrations, the degree of dispersion was high, and the viscosity was low.

[0074] Note that the concentration of CNTs is expressed as a percentage of the dispersion containing CNTs, with the dispersion being set to 100. For example, if the amount of CNTs is 0.05 g and the amount of the mixed solution of methylated xylan and NMP is 49.95 g, the CNT concentration is 0.1 wt%.

[0075] Furthermore, viscosity was measured using an SV-type viscometer SV-1A (manufactured by A&D Company, Limited). This viscometer is a tuning fork vibration type, which resonates a vibrator in a liquid and determines viscosity from the excitation force required to move the vibrator at a constant amplitude.

[0076] Table 3 shows the results of determining the degree of dispersion and viscosity with respect to CNT concentration when alkylated xylanes, specifically methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E), were used as dispersants.

[0077] [Table 3] Figure 3 is a graph of the dispersion in Table 3, and Figure 4 is a graph of the viscosity in Table 3.

[0078] As shown in Table 3, when methylated xylan (A), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) were used as dispersants, gelation occurred at CNT concentrations of 0.4 wt% or higher. However, with ethylated xylan (B), gelation did not occur even at a CNT concentration of 0.4 wt%, and dispersion was achieved at a high concentration of 250.8, with a viscosity of 105 mPa·s.

[0079] Figure 3 shows the relationship between CNT concentration and dispersion. Unlike the case using SWCNT1, it was found that the dispersion was affected by the dispersant. Specifically, butylated xylan (E) and isopropylated xylan (D) showed almost the same dispersion characteristics, and propylated xylan (C) and methylated xylan (A) also showed almost the same dispersion characteristics. However, the dispersion characteristics of propylated xylan (C) and methylated xylan (A) were slightly better than those of butylated xylan (E) and isopropylated xylan (D). The best dispersion characteristics were obtained when ethylated xylan (B) was used, with a dispersion of 250.8 at a CNT concentration of 0.4 wt%.

[0080] Figure 4 shows the relationship between CNT concentration and viscosity, and it showed a similar trend to that observed when SWCNT1 was used. Specifically, ethylated xylan (B) had the lowest viscosity, at 105 mPa·s even with a CNT concentration of 0.4 wt%. In contrast, methylated xylan (A), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) showed higher viscosity compared to ethylated xylan (B). The viscosity tended to increase in the order of methylated xylan (A), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E).

[0081] In this Example 2, it was found that no gelation occurred in any of the alkylated xylans, including methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E), up to a CNT concentration of 0.3 wt%, and that low viscosity could be achieved even when dispersed at high concentrations. (Example 3)

[0082] In this third example, we will describe the case in which methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) are used as dispersants. For comparison, ethylcellulose was also used as a dispersant.

[0083] This third example describes the results of dispersing MWCNTs using the above-described dispersant. As the MWCNTs, we used NC-7000 from Nanocyl, handled by Nippon Zeon Co., Ltd. (hereinafter referred to as "MWCNT"). These MWCNTs have an average diameter of 9.5 nm, an average length of 1.5 μm, and a purity of 90%.

[0084] The dispersions were prepared as follows: A fixed amount of CNTs was weighed according to the preparation conditions for each dispersion. Simultaneously, alkylated xylans, such as methylated xylan, were quantified and mixed into NMP, and 50 mL of each mixed solution was prepared. CNTs were then added to these solutions. Subsequently, each solution was dispersed using an ultrasonic homogenizer (60 W). Next, the solutions were separated using a centrifuge (Eppendorf Hi-Mac Technologies, CT18R) at 10,000 G for 1 hour, and the supernatant was used as the sample for dispersion measurement.

[0085] The supernatant was diluted to a concentration measurable with a UV-Vis spectrophotometer (Shimadzu Corporation, UV-1900), and the absorbance at a wavelength of 500 nm was measured to determine the absorbance. The degree of dispersion was then calculated based on the obtained absorbance and the amount of dilution. Dispersibility was evaluated as good when gelation did not occur even at high CNT concentrations, the degree of dispersion was high, and the viscosity was low.

[0086] The concentration of CNTs is expressed as a percentage of the dispersion of CNTs, with the dispersion being set to 100%. For example, if the amount of CNTs is 0.05g and the amount of the mixed solution of methylated xylan and NMP is 49.95g, the CNT concentration is 0.1wt%.

[0087] Viscosity was measured using an SV-type viscometer SV-1A (manufactured by A&D Company, Limited). This viscometer is a tuning fork vibration type, which resonates a vibrator in a liquid and determines viscosity from the excitation force required to move the vibrator at a constant amplitude.

[0088] Table 4 shows the results of determining the degree of dispersion and viscosity with respect to CNT concentration when alkylated xylanes (A, B, C, D, and E) were used as dispersants, with MWCNTs being used as examples, and the results when ethyl cellulose was used as a comparative example.

[0089] [Table 4] Figure 5 is a graph of the dispersion in Table 4, and Figure 6 is a graph of the viscosity in Table 4.

[0090] As shown in Table 4, when methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) were used as dispersants, gelation did not occur up to a CNT concentration of 3.0 wt%. For these dispersants, the degree of dispersion and viscosity were almost the same. On the other hand, when ethyl cellulose (F) was used as a dispersant, gelation occurred at a CNT concentration of 2.5 wt%. Furthermore, in the range up to a CNT concentration of 2 wt%, the degree of dispersion tended to be slightly lower and the viscosity slightly higher than that of alkylated xylan.

[0091] Figure 5 shows the relationship between CNT concentration and dispersion. Methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) all showed almost the same values ​​and slopes. On the other hand, when ethyl cellulose (F) was used as a dispersant, the dispersion was lower than the others, and it was found that gelation occurred at CNT concentrations of 2.5 wt% or higher, making it unusable as a dispersion.

[0092] Figure 6 shows the relationship between CNT concentration and viscosity. It was found that the viscosity trend differed depending on the alkylated xylan. Ethylated xylan (B) had the lowest viscosity overall, at 115 mPa·s even with a CNT concentration of 3.0 wt%. In contrast, methylated xylan (A), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) showed higher viscosity compared to ethylated xylan (B). Viscosity tended to increase in the order of methylated xylan (A), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E).

[0093] On the other hand, when ethylcellulose (F) was used as a dispersant, the viscosity was slightly higher than the others, and it was found that gelation occurred when the CNT concentration was 2.5 wt% or higher, making it unusable as a dispersion.

[0094] As described above, when MWCNTs are used, it was found that using methylated xylan (A), ethylated xylan (B), propylated xylan (C), isopropylated xylan (D), and butylated xylan (E) as dispersants allows for a lower viscosity dispersion while dispersing MWCNTs at a higher concentration than when conventionally used ethyl cellulose as a dispersant.

[0095] The CNT dispersion of the present invention can disperse CNTs at a high concentration in NMP, an organic solvent, and can therefore be applied to various uses. For example, a conductive additive used in lithium-ion batteries transmits electrical energy to the active material, Li + It plays a role in causing the detachment and insertion of ions, and also reduces the resistance of the battery. Until now, carbon black has been the mainstream, but the use of CNTs is being promoted. By using CNTs as a conductive additive, higher capacity, higher output, and longer lifespan can be achieved. [Industrial applicability]

[0096] The CNT dispersant and CNT dispersion of the present invention have significant effects in a wide range of fields, including noise suppression in electronic equipment, applications in secondary batteries, and applications in the semiconductor field.

Claims

1. A carbon nanotube dispersant for dispersing carbon nanotubes in an organic solvent, N-methyl-2-pyrrolidone, A carbon nanotube dispersant characterized by using alkylated xylan that is soluble in N-methyl-2-pyrrolidone, obtained by alkylating xylan.

2. The carbon nanotube dispersant according to claim 1, characterized in that the alkyl group to be alkylated consists of one group selected from a methyl group, an ethyl group, a propyl group, an isopropyl group, and a butyl group.

3. A method for producing a carbon nanotube dispersant for dispersing carbon nanotubes in an organic solvent, N-methyl-2-pyrrolidone, The process involves suspending xylan in dimethyl sulfoxide, The process involves adding sodium hydroxide and an alkyl iodide compound, purging with nitrogen gas, and then heat-treating the mixture. A step to recover alkylated xylan, which is a reaction product, by chloroform extraction, A method for producing a carbon nanotube dispersant containing [the specified ingredient].

4. The method for producing a carbon nanotube dispersant according to claim 3, characterized in that methyl iodide, ethyl iodide, propyl iodide, isopropyl iodide, or butyl iodide is used as the alkyl iodide compound.

5. A carbon nanotube dispersion comprising N-methyl-2-pyrrolidone as a dispersion solvent, a dispersant, and carbon nanotubes, A carbon nanotube dispersion characterized in that the dispersant is the carbon nanotube dispersant described in claim 1 or 2.

6. The carbon nanotube dispersion according to claim 5, characterized in that the carbon nanotube is either a single-walled carbon nanotube or a multi-walled carbon nanotube.

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