Composite material containing carbon nanotubes and ionic liquid, and method for manufacturing the same

Abstract

To provide a composite material and a method for producing the same, which can maintain a defibrated state for a long period of time by bringing carbon nanotubes into a sufficiently defibrated state and suppressing re-aggregation. [Solution] A composite material comprising carbon nanotubes and an ionic liquid, wherein the ionic liquid comprises nitrogen-containing heteroaromatic ring cations and anions, the nitrogen-containing heteroaromatic ring cation having a specific cationic structure in which at least two substituents having hydroxyl groups at their terminal ends, and the content ratio of carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less.

Description

[Technical Field]

[0001] This disclosure belongs to the field of molecular nanotechnology and, in particular, relates to novel materials that incorporate carbon nanotubes (CNTs) and exhibit properties derived from carbon nanotubes over a long period of time. [Background technology]

[0002] Carbon nanotubes are used to impart functionalities such as conductivity and reinforcement, but they tend to aggregate due to intermolecular forces, and in order to impart sufficient functionality, the aggregated carbon nanotubes need to be in a loosened state (fibrillated state). For example, Patent Document 1 discloses a method of fragmenting (defibrillating) carbon nanotubes by mixing them with an ionic liquid. Patent Document 2 presents a characteristic structure among the cations of imidazolium salts as an ionic liquid to be mixed with carbon nanotubes. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2004-142972 [Patent Document 2] Japanese Patent Publication No. 2013-244673 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, according to the inventors' research, it can be difficult to achieve a sufficiently defibrated state of carbon nanotubes or to maintain that state using conventional techniques. As a result, it can be difficult to continuously exhibit the properties derived from carbon nanotubes over a long period of time. According to the first invention of the present disclosure, a composite material is provided that can maintain a defibrated state for a long time by making carbon nanotubes in a sufficient defibrated state and suppressing re-aggregation. Further, according to the second invention of the present disclosure, a method for manufacturing a composite material is provided that can form a sufficient defibrated state of carbon nanotubes, suppress re-aggregation, and maintain the defibrated state for a long time.

Means for Solving the Problems

[0005] According to at least one aspect of the present disclosure, a composite material containing carbon nanotubes and an ionic liquid, where the ionic liquid contains a nitrogen-containing heteroaromatic cation and an anion, the nitrogen-containing heteroaromatic cation has a cation structure having at least two substituents having a hydroxyl group at the terminal, represented by the following formula (1), a composite material is provided, wherein the content ratio of the carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less.

Chemical formula

[0006] Further, according to at least one aspect of the present disclosure, a method for manufacturing a composite material, where the composite material is containing carbon nanotubes and an ionic liquid, the ionic liquid contains a nitrogen-containing heteroaromatic cation and an anion, the nitrogen-containing heteroaromatic cation has a cation structure having at least two substituents having a hydroxyl group at the terminal, represented by the above formula (1), the content ratio of the carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less, and the manufacturing method is A step of obtaining a mixture of the carbon nanotube and the ionic liquid, A step of applying a shear force to the mixture and defibrating the carbon nanotubes in the presence of the ionic liquid, A method for producing a composite material is provided, characterized by including the following: [Effects of the Invention]

[0007] According to at least one aspect of this disclosure, a composite material can be obtained that can maintain a defibrillated state for a long period of time by bringing carbon nanotubes into a sufficiently defibrillated state and suppressing re-aggregation. Furthermore, according to at least one aspect of this disclosure, a method for producing a composite material can be obtained that can form a sufficiently defibrated state of carbon nanotubes, suppress re-aggregation, and maintain the defibrated state for a long period of time. [Modes for carrying out the invention]

[0008] In this disclosure, descriptions of numerical ranges such as "XX or greater and YY or less" or "XX to YY" mean a numerical range that includes the lower and upper limits, unless otherwise specified. When numerical ranges are described in steps, the upper and lower limits of each numerical range can be combined in any way.

[0009] Furthermore, in this disclosure, any statement such as "at least one selected from the group consisting of XX, YY, and ZZ" means any of the following: XX, YY, ZZ, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ. Note that if XX is a group, multiple elements may be selected from XX, and the same applies to YY and ZZ. Furthermore, in this specification, for the sake of explanation, carbon nanotubes may be referred to as "carbon nanotubes" or abbreviated as "CNT," but these references do not distinguish between the two.

[0010] The composite material comprises carbon nanotubes and an ionic liquid, wherein the ionic liquid comprises nitrogen-containing heteroaromatic ring cations and anions, the nitrogen-containing heteroaromatic ring cations having at least two substituents having hydroxyl groups at their terminal ends, and the carbon nanotube content in the composite material is 3% by mass or more and 30% by mass or less.

[0011] As is generally known, the aggregation of carbon nanotubes (CNTs) occurs due to adsorption between CNTs caused by π-π interactions between π-orbital electrons on the CNTs. Although the thickness (length in the short side direction) of a single CNT is only a few nanometers, adsorption can cause tens of thousands of CNTs to aggregate, and the size of the aggregate can reach tens of micrometers. Furthermore, it is known that adsorption occurs through π-π interactions between the π-orbital electrons in the heteroaromatic ring and the π-orbital electrons on the CNT. Patent Document 1 utilizes this adsorption effect to insert an ionic liquid containing a nitrogen-containing heteroaromatic ring as a cation backbone into the spaces between aggregated CNTs. This process is used to subdivide the carbon nanotubes (CNTs). However, since the π-π interactions between the nitrogen-containing heteroaromatic ring and the CNTs are energetically equivalent to the π-π interactions between CNTs themselves, when CNTs come into close proximity, re-adsorption between CNTs is induced, and re-aggregation of CNTs is likely to occur.

[0012] Regarding the above problem, the inventors speculate as follows that the remarkable effect of suppressing the re-aggregation of defibrated CNTs is obtained when the ionic liquid contained in the composite material contains nitrogen-containing heteroaromatic ring cations having at least two substituents with hydroxyl groups at their ends. The ionic liquid contains nitrogen-containing heteroaromatic ring cations, each of which has at least two substituents with hydroxyl groups at its terminal ends. When the ionic liquid is in close proximity to a CNT, in addition to the π-π interaction between the CNT and the ionic liquid, the hydroxyl groups on the ionic liquid molecules form hydrogen bonds with the hydroxyl groups of adjacent ionic liquid molecules. In other words, hydrogen bonding occurs between the ionic liquids.

[0013] This combined effect forms a network of CNT-ionic liquid-(one or more ionic liquids)-ionic liquid-CNT, allowing CNTs to maintain a certain distance from each other without coming into close proximity. Here, since hydrogen bonds have a higher bond energy and are stronger than π-π interactions, competitive π-π interactions between CNTs are less likely to occur. As a result, the re-aggregation of CNTs can be suppressed over the long term.

[0014] Furthermore, according to one aspect of the present disclosure, a method for producing a composite material is provided, comprising carbon nanotubes and an ionic liquid, wherein the ionic liquid comprises nitrogen-containing heteroaromatic ring cations and anions, the nitrogen-containing heteroaromatic ring cations having at least two substituents having hydroxyl groups at their terminal ends, and the content of the carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less, the method comprising a step of applying a shear force to the carbon nanotubes in the presence of the ionic liquid to defibrate them. By the above production method, a composite material can be obtained in which the defibration of CNTs is promoted and the re-aggregation of the defibrated CNTs is suppressed. The inventors speculate on the reason for this as follows.

[0015] As previously described, the ionic liquid and CNTs form a network such as CNT-ionic liquid-(one or more ionic liquids)-ionic liquid-CNT. In particular, in the case of aggregated CNTs, the network becomes CNT-CNT-ionic liquid-(one or more ionic liquids)-ionic liquid-CNT-CNT. However, according to the above manufacturing method, when an external shear force is applied and energy is applied to this network, the bonds between CNTs, which have weaker bond energy than the hydrogen bonds between ionic liquids, and the bonds between ionic liquids due to π-π interactions between CNTs are preferentially broken.

[0016] Furthermore, by keeping the CNT content within the above range, the ionic liquid, which is present in a larger quantity than the CNTs, enters the spaces between broken CNTs and forms new bonds. This repeated process gradually eliminates the interaction between CNTs, leading to the defibrillation of the CNTs. Additionally, as mentioned earlier, the presence of ionic liquid molecules between defibrillated CNTs maintains a certain distance, thus suppressing the re-aggregation of CNTs.

[0017] <Carbon nanotubes (CNTs)> As is well known, CNTs refer to materials in which graphene sheets, which consist of a network of six-membered rings of carbon atoms, are arranged in single or multi-layered coaxial tubes. Generally, carbon nanotubes (CNTs) are classified into single-walled and multi-walled types based on the number of components in the coaxial tubular surrounding wall, and further classified into zigzag, armchair, and chiral types based on differences in the composition of the graphene sheet. Various structures are known, such as [examples of structures]. In this disclosure, any of these CNT structures is applicable.

[0018] The CNTs preferably include single-walled carbon nanotubes (WYSIWNs), and more preferably are WYSIWNs. Because WYSIWNs are thinner than multiwalled carbon nanotubes (DWNs), they are more likely to form a dense network via ionic liquids, and the aforementioned effect of keeping CNTs at a certain distance from each other without coming into close proximity is more likely to occur. Therefore, using WYSIWNs makes it easier to suppress CNT re-aggregation.

[0019] In composite materials, it is preferable that the average number of CNTs in the short-side direction is 2 nm to 50 nm, and the average number of CNTs in the long-side direction is 10 μm to 2 mm. This is because the formation of the aforementioned network via the ionic liquid, which keeps the CNTs at a certain distance from each other, is more likely to occur when the length in the long-side direction is greater than the length in the short-side direction, i.e., the aspect ratio is larger, and thus the re-aggregation of CNTs is more easily suppressed.

[0020] The average number of lengths in the short-side direction of the CNTs is more preferably 2 nm to 40 nm, even more preferably 3 nm to 30 nm, and even more preferably 5 nm to 10 nm. The average length of the long side of a CNT is usually between 5 μm and 2 mm. More preferably, the average length of the long side is between 30 μm and 500 μm, even more preferably between 50 μm and 300 μm, and even more preferably between 100 μm and 200 μm.

[0021] The ratio of the length in the long side direction to the length in the short side direction of the CNT (average value of the length in the long side direction / average value of the length in the short side direction) is preferably, for example, 3000 to 40000, more preferably 4000 to 35000, and even more preferably 5000 to 30000.

[0022] <Ionic liquid> Ionic liquids are salts that are liquid at room temperature and composed of ions such as anions and cations. Ionic liquids include nitrogen-containing heteroaromatic ring cations and anions. In other words, ionic liquids have a nitrogen-containing heteroaromatic ring structure, and this nitrogen-containing heteroaromatic ring structure is a cation structure formed by nitrogen-containing heteroaromatic rings. A nitrogen-containing heteroaromatic ring structure refers to a chemical structure in which nitrogen, in addition to carbon, constitutes the aromatic ring.

[0023] <Cationes in ionic liquids> Nitrogen-containing heteroaromatic ring cations have a cationic skeleton containing a cationic nitrogen-containing heteroaromatic ring. The cationic skeleton has a nitrogen-containing heteroaromatic ring, and on the nitrogen-containing aromatic ring, there are at least two (preferably two or three, more preferably two) substituents having hydroxyl groups at their terminal ends. Nitrogen-containing heteroaromatic ring cations have a structure represented by the following formula (1). [ka] In formula (1) above, Z represents a cationic skeleton containing a cationic nitrogen-containing heteroaromatic ring. A1 and A2 are each independent linking groups, each having a hydroxyl group (-OH) at its terminus to form a substituent.

[0024] The nitrogen-containing heteroaromatic ring cation has the structure shown in formula (1) above, thus providing an ionic solution. The hydroxyl groups on the CNT molecules form hydrogen bonds with the hydroxyl groups of adjacent ionic liquid molecules, creating the aforementioned network of CNT-ionic liquid-(one or more ionic liquids)-ionic liquid-CNT. This allows the CNTs to maintain a certain distance from each other without coming into close proximity. Furthermore, since hydrogen bonds have a higher and stronger bond energy than the π-π interactions between CNTs, competitive π-π interactions between CNTs are less likely to occur. As a result, the re-aggregation of CNTs can be suppressed over the long term.

[0025] The cation skeleton can be any heteroaromatic ring cation containing a nitrogen atom. Examples of nitrogen-containing heteroaromatic ring cations include imidazolium cations, pyrazolium cations, pyridinium cations, and condensed ring cations such as benzimidazolium cations and quinolinium cations, which are formed by the condensation of one or more aromatic rings onto these nitrogen-containing heteroaromatic rings. In addition, cations such as oxazolium cations, thiazolium cations, benzoxazolium cations, and benzothiazolium cations may have one or more heteroatoms other than a nitrogen atom. The nitrogen-containing heteroaromatic ring cation is preferably at least one selected from the group consisting of imidazolium cation, pyridinium cation, pyrazolium cation, quinolinium cation, thiazolium cation, and oxazolium cation.

[0026] The cation skeleton is preferably at least one selected from the group consisting of a cationic imidazolium skeleton and a cationic pyridinium skeleton. In other words, the nitrogen-containing heteroaromatic ring cation is preferably at least one selected from the group consisting of imidazolium cations and pyridinium cations.

[0027] The ionic liquid is preferably at least one selected from the group consisting of the ionic liquid represented by formula (2) and the ionic liquid represented by formula (3) below. The ionic liquid is preferably represented by formula (2) or formula (3) below. [ka] The ionic liquid shown in formula (2) above contains an imidazolium cation as a nitrogen-containing heteroaromatic ring cation. In formula (2) above, R1 to R4 each represent a substituent or a hydrogen atom. On the nitrogen-containing heterocycle, R1 is bonded as a substituent to the carbon atoms adjacent to the two nitrogen atoms, R2 and R3 are bonded to the nitrogen atoms, and R4 is bonded as a substituent to the other carbon atoms. At least two of R1 to R3 or R4 have a hydroxyl group at the terminal. - This represents an anion. Note that, as with typical imidazolium cations, formulas (2) and (3) conveniently include a "+" sign indicating cationicity on one of the nitrogen atoms in the heterocycle; however, this does not indicate that the cation properties are localized solely to this nitrogen atom.

[0028] [ka] The ionic liquid shown in formula (3) above contains a pyridinium cation as a nitrogen-containing heteroaromatic ring cation. In formula (3) above, R5 to R9 each represent a substituent or a hydrogen atom. R5 is bonded to the nitrogen atom, R6 and R9 are bonded to the carbon atoms adjacent to the nitrogen atom, and R7 and R8 are bonded to the carbon atoms adjacent to those atoms. A hydrogen atom is bonded to the carbon atom diagonally opposite the nitrogen atom on its ring. At least two of these R5 to R9 have hydroxyl groups at their ends. - This represents an anion.

[0029] In composite materials, cations in ionic liquids represented by formula (2) or formula (3) above undergo charge delocalization within the cation due to their chemical structure. As a result, the interaction between nitrogen-containing heteroaromatic ring portions is weak, and the effect of hydroxyl groups at the terminals, i.e., the effect of hydrogen bonding between hydroxyl groups on one ionic liquid molecule and hydroxyl groups on adjacent ionic liquid molecules, becomes larger. Therefore, the defibrillation of CNTs and the suppression of re-aggregation are further promoted. Furthermore, more preferably, the nitrogen-containing heteroaromatic ring cation is an imidazolium cation. That is, the composite material more preferably contains the ionic liquid represented by formula (2) above. The ionic liquid represented by formula (2) above is preferred because it makes charge delocalization within the cation more likely and the effect of hydrogen bonding described above is greater.

[0030] In the cationic skeleton of a nitrogen-containing heteroaromatic ring cation, substituents having a hydroxyl group at their terminus are hydrocarbon groups, polyalkylene ether groups, etc., that act as linking groups between the hydroxyl group and the cationic skeleton. The hydrocarbon groups included in the linking group along with the oxygen atom of the hydroxyl group are linear or cyclic, saturated or unsaturated hydrocarbon groups having 1 to 30 carbon atoms, such as methylene groups, ethylene groups, propylene groups, butylene groups, pentylene groups, hexylene groups, and phenylene groups, and may have one or more heteroatoms such as oxygen atoms, nitrogen atoms, or sulfur atoms.

[0031] Furthermore, the compound may contain one or more substituents that do not have hydroxyl groups (for example, hydrocarbon groups having 1 to 30 carbon atoms, halogen groups such as fluorine, chlorine, bromine, and iodine, alkoxy groups such as methoxy and ethoxy groups, substituents containing heteroatoms such as amide and cyano groups, and haloalkyl groups such as trifluoromethyl groups). Examples of oxyalkylene groups that are formed together with the polyalkylene ether group and the oxygen atom of the hydroxyl group contained in the linking group include poly(ethylene glycol), poly(propylene glycol), and poly(tetramethylene glycol).

[0032] The substituents in the cation skeleton of the nitrogen-containing heteroaromatic ring cation that do not have a hydroxyl group are not particularly limited and may include, for example, hydrocarbon groups having 1 to 30 carbon atoms; halogen groups such as fluorine, chlorine, bromine, and iodine; alkoxy groups such as methoxy and ethoxy groups; substituents containing heteroatoms such as amide and cyano groups; haloalkyl groups such as trifluoromethyl groups, or hydrogen atoms.

[0033] As a result of their investigation, the inventors found that, in substituents containing a hydroxyl group, the length of the linking group connecting the hydrogen atom of the hydroxyl group to the cationic skeleton is preferably such that the number of atoms counted along the shortest distance from the cationic skeleton to the hydrogen atom of the hydroxyl group is 7 or less (the number of atoms counted along the shortest distance from the cationic skeleton to the hydroxyl group is 6 or less). For example, when the linking group portion is composed of a hydrocarbon group and the oxygen atom of the hydroxyl group, if the hydrocarbon group is a hexyl group, the number of atoms counted along the shortest distance from the cationic skeleton to the hydroxyl group is 7.

[0034] In formula (1) above, the linking groups A1 and A2 are preferably each independently a hydrocarbon group or polyalkylene ether group having 2 to 12 carbon atoms. The number of carbon atoms in A1 and A2 is more preferably 2 to 8, and even more preferably 2 to 6.

[0035] Furthermore, it was found that for substituents in the cation skeleton of nitrogen-containing heteroaromatic ring cations that do not contain hydroxyl groups, those with a maximum number of atoms counted from the cation skeleton to the terminal atom of 6 or less are preferable. The substituents that do not contain hydroxyl groups are preferably hydrogen atoms or hydrocarbon groups having 1 to 6 carbon atoms.

[0036] In formula (2) above, R1 is preferably a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, or an alkyl group having 1 to 2 carbon atoms with a hydroxyl group at its terminus. R2 and R3 are preferably alkyl groups having 1 to 12 carbon atoms with a hydroxyl group at its terminus, or an ethyl group or a butyl group. R4 is preferably a hydrogen atom or an alkyl group having 2 to 6 carbon atoms with a hydroxyl group at its terminus.

[0037] As a result of the investigation, the inventors found that it is preferable that R1 in formula (2) above is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, R2 and R3 are alkyl groups having 1 to 6 carbon atoms with a hydroxyl group at the terminal, and R4 is a hydrogen atom. More preferably, R1 is a hydrogen atom. Having such a structure in the ionic liquid prevents the loss of structural planarity throughout the nitrogen-containing heteroaromatic ring cation, making it easier to maintain a certain distance when present between adjacent CNTs.

[0038] Furthermore, R2 and R3 in formula (2) above may be the same substituent or different substituents. It is preferable that R2 and R3 are the same substituent represented by the same chemical formula. More preferably, R2 and R3 are -CH2CH2OH. When R2 and R3 are -CH2CH2OH, the sites where hydrogen bonds are formed when forming a network via an ionic liquid are closer together, and the variation in bonding strength is reduced due to molecular symmetry, thereby strengthening the bonding of the entire network. This further promotes the defibration of CNTs and suppresses re-aggregation.

[0039] In formula (3) above, R5 to R7 are preferably hydrogen atoms or alkyl groups having 2 to 12 carbon atoms with a hydroxyl group at the terminal end. R8 is preferably a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, or an alkyl group having 1 to 2 carbon atoms with a hydroxyl group at the terminal end. R9 is preferably a hydrogen atom or a methyl group. Furthermore, three of R5 to R9 may have hydroxyl groups at their terminal ends. For example, R6, R7, and R8 may have hydroxyl groups at their terminal ends.

[0040] In addition to the structures shown in formulas (2) and (3) above, ionic liquids may also be those shown in formulas (4) to (8) below. [ka]

[0041] The structure of the cation skeleton and the anions in ionic liquids can be controlled by the materials and synthesis methods used to synthesize them. The synthesis methods and materials used for ionic liquids will be described later.

[0042] <Anions in ionic liquids> Ionic liquids contain anions. X in formula (2) above. - , Y in equation (3) - The symbol represents anion. Examples of anions in ionic liquids include sulfonate fluoride anions, carboxylate fluoride anions, sulfonylimide fluoride anions, sulfonylmethide fluoride anions, alkylfluoroborate fluoride anions, alkylfluorophosphate fluoride anions, halide ions, carboxylate anions, sulfonate anions, tetrafluoroborate anions, hexafluorophosphate anions, hexafluoroarsenate anions, hexafluoroantimonate anions, dicyanamide anions, bis(oxalato)borate anions, nitrate anions, and perchlorate anions.

[0043] Examples of fluorinated sulfonate anions include trifluoromethanesulfonate anion, fluoromethanesulfonate anion, perfluoroethylsulfonate anion, perfluoropropylsulfonate anion, perfluorobutylsulfonate anion, perfluoropentylsulfonate anion, perfluorohexylsulfonate anion, and perfluorooctylsulfonate anion.

[0044] Examples of fluoride carboxylic acid anions include trifluoroacetate anion, perfluoropropionate anion, perfluorobutyrate anion, perfluorovalerate anion, and perfluorocaproate anion.

[0045] Examples of fluorinated sulfonylimide anions include anions such as trifluoromethanesulfonylimide anion, perfluoroethylsulfonylimide anion, perfluoropropylsulfonylimide anion, perfluorobutylsulfonylimide anion, perfluoropentylsulfonylimide anion, perfluorohexylsulfonylimide anion, perfluorooctylsulfonylimide anion, fluorosulfonylimide anion, and fluorosulfonylimide anion, as well as cyclic anions such as cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide.

[0046] Examples of fluoride sulfonylmethide anions include trifluoromethanesulfonylmethide anion, perfluoroethylsulfonylmethide anion, perfluoropropylsulfonylmethide anion, perfluorobutylsulfonylmethide anion, perfluoropentylsulfonylmethide anion, perfluorohexylsulfonylmethide anion, and perfluorooctylsulfonylmethide anion.

[0047] Examples of alkyl fluoroborate anions include trifluoromethyltrifluoroborate anion and perfluoroethyltrifluoroborate anion. Examples of alkyl fluorophosphate anions include tris-trifluoromethyl-trifluorophosphate anion and tris-perfluoroethyl-trifluorophosphate anion. Examples of halide ions include fluoride ions, chloride ions, bromide ions, and iodide ions.

[0048] Examples of the carboxylic acid anion include alkyl carboxylic acid anions such as acetate anion, propionate anion, butyrate anion, hexanoate anion, and aromatic carboxylic acid anions such as benzoate anion. The anion may have one or more substituents such as a hydrocarbon group having 1 to 30 carbon atoms, a halogen group such as fluorine, chlorine, bromine, iodine, an alkoxy group such as a methoxy group and an ethoxy group, a substituent containing a hetero atom such as an amide group and a cyano group, and a haloalkyl group such as a trifluoromethyl group.

[0049] Examples of the sulfonic acid anion include alkyl sulfonic acid anions such as methanesulfonic acid anion and ethanesulfonic acid anion and aromatic sulfonic acid anions such as benzenesulfonic acid and para-toluenesulfonic acid anion. The anion may be substituted by one or more substituents such as a hydrocarbon group having 1 to 30 carbon atoms, a halogen group such as fluorine, chlorine, bromine, iodine, an alkoxy group such as a methoxy group and an ethoxy group, a substituent containing a hetero atom such as an amide group and a cyano group, and a haloalkyl group such as a trifluoromethyl group.

[0050] Among the anions listed above, sulfonic acid fluoride anion and sulfonyl imide fluoride anion are preferred. Among them, bis(trifluoromethanesulfonyl)imide anion ((CF3SO2)2N - ) or bis(sulfonyl fluoride)imide anion ((FSO2)2N - ) is preferred.

[0051] The anion X - in the above formula (2) is, for example, (CF3SO2)2N - , (FSO2)2N - , ClO4 - , (C2O4)2B - and (C4F9SO2)2N - and at least one selected from the group consisting of. The anion X - is (CF3SO2)2N - or (FSO2)2N -This is preferable. The above anion is preferable because, due to its chemical structure, it is chemically stable and can remain stable as an ionic liquid even under harsh conditions such as high temperature and high humidity.

[0052] Anion Y in equation (3) above - For example, (CF3SO2)2N - Cl - CF3COO - , C3F7SO3 - , N(CN)2 - , (FSO2)2N - At least one selected from the group consisting of the following is anion Y. - (CF3SO2)2N - Or (FSO2)2N - It is preferable that this be the case.

[0053] <Method for synthesizing ionic liquids> Ionic liquids having the structure described above can be synthesized by the following method. Ionic liquids can be obtained by synthesizing an ionic liquid precursor using one or more known nucleophilic substitution reactions, such as the Menschtkin reaction, and then carrying out a known ion exchange reaction. For example, by using the following materials as a nucleophile and electrophile for nucleophilic substitution reactions, and as an alkali metal salt for ion exchange reactions, and by combining known methods, an ionic liquid having the above-mentioned specific structure can be synthesized.

[0054] As nucleophiles, compounds having a nucleophilic nitrogen atom, such as imidazole compounds, can be used. Examples of nucleophiles that can be used include imidazole, 2-ethylimidazole, 2-methylbenzimidazole, 2-pyridineethanol, 6-methyl-2-pyridinemethanol, 5-ethyl-2-pyridineethanol, 3-bromopyridine, pyrazole, 3-bromoquinoline, 2-bromothiazole, 5-bromo-4-methyl-2-phenyl-1,3-oxazole, 4,5-dibromoimidazole, and 3,5-dibromopyridine.

[0055] Furthermore, as electrophiles, for example, 2-bromoethanol, 4-bromo-1-butanol, 6-bromo-1-hexanol, 12-bromo-1-dodecanol, 8-bromo-1-octanol, 10-bromo-1-decanol, 4-bromobutane, iodoethane, 2-bromoethoxy-tert-butyldimethylsilane, 6-bromohexyloxy-tert-butyldimethylsilane, etc. can be used.

[0056] For the alkali metal salt used in the ion exchange reaction, alkali metal salts containing the aforementioned anions, such as lithium alkylsulfonate salt and potassium alkylsulfonylimide salt, can be used.

[0057] Examples of anion exchange salts that can be used include lithium bis(trifluoromethanesulfone)imide, potassium N,N-bis(fluorosulfonyl)imide, lithium perchlorate, lithium bis(oxalato)borate, potassium bis(nonafluorobutanesulfonyl)imide, sodium dicyanamide, potassium hexafluoroarsenate, lithium trifluoroacetate, potassium heptafluoropropanesulfonate, potassium trifluoro(trifluoromethyl)borate, lithium hexafluorophosphate, lithium hexafluoroantimonate, etc.

[0058] <Composite materials> The composite material includes carbon nanotubes and ionic liquids. The carbon nanotube content in the composite material is 3% by mass or more and 30% by mass or less. Preferably, the above percentage is 5% by mass or more and 20% by mass or less, and preferably 5% by mass or more and 15% by mass or less.

[0059] If the CNT content is higher than 30% by mass, the number of ionic liquid molecules that can penetrate between CNT molecules decreases, making it difficult to achieve the aforementioned effects. Conversely, if the CNT content is less than 3% by mass, the amount of CNTs in the composite material is insufficient, and the properties of the CNTs cannot be fully obtained. By controlling the CNT content within the above range, the properties can be fully exhibited without the CNTs re-aggregating.

[0060] The content of ionic liquid in the composite material is preferably 70% by mass or more and 97% by mass or less, more preferably 80% by mass or more and 95% by mass or less, and even more preferably 85% by mass or more and 95% by mass or less.

[0061] The composite material may contain, if necessary, general resins, rubber materials, conductivity imparters, compounding agents, fillers, crosslinking agents, catalysts, etc., other than CNTs and ionic liquids, to the extent that the effects of the present invention are not impaired.

[0062] <Method for manufacturing composite materials> The composite material can be manufactured by the following manufacturing method. That is, the manufacturing method for the composite material comprises carbon nanotubes and an ionic liquid, wherein the ionic liquid has a cation structure represented by the above formula (1) having at least two substituents having hydroxyl groups at their ends, and the content of the carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less, and comprises the following steps (1) and (2). (1) Steps to obtain a mixture of the carbon nanotubes and the ionic liquid. (2) A step of applying a shear force to the mixture and defibrating the carbon nanotubes in the presence of the ionic liquid.

[0063] As previously described, an ionic liquid containing a nitrogen-containing heteroaromatic ring cation having at least two substituents bonded to a hydroxyl group forms a network of CNT-ionic liquid-(one or more ionic liquids)-ionic liquid-CNT with a carbon nanotube (CNT). According to the above manufacturing method, when an external shear force is applied and energy is exerted on this network, the bonds between CNTs with weaker bond energies than hydrogen bonds and the bonds between ionic liquids due to π-π interactions between CNTs are preferentially broken.

[0064] Furthermore, by setting the CNT content in the composite material within the above range, the ionic liquid, which is present in a larger amount than the CNTs, enters the spaces between the broken CNTs and forms new bonds, thereby promoting CNT defibration. As described above, the defibrated CNTs have ionic liquid molecules present between them, maintaining a certain distance, thus suppressing the re-aggregation of CNTs. The above manufacturing method further promotes CNT defibration, and the defibrated CNTs This allows for the creation of composite materials in which re-aggregation is further suppressed.

[0065] The methods for applying shear force are not particularly limited and include kneading methods using equipment such as kneaders, roller kneaders, and twin-screw kneaders; granulation methods that collide solid components (CNTs) and liquid components (ionic liquids); and even simple methods such as kneading with a pestle on a mortar. Of these, the method of applying shear force through kneading using a roller kneader is preferred because it can apply shear force for defibrillation while preventing the cutting of CNTs, and defibrillation can be easily controlled from the operating conditions of the equipment.

[0066] As a method for applying shear force, it is preferable to perform the mixing process using a roll kneader. As a roll kneader, for example, an open roll device can be used. An open roll device is a device that applies shear force to an object by passing the object through the gap between two rotating rolls. The rotation speed of the rolls during the mixing process is not particularly limited, but for example, when using an open roll device, it is preferable to set the rotation speed of the front roll to 5 to 20 rpm and the rotation speed of the rear roll to 1 to 10 rpm. The duration of the mixing process is not particularly limited, but it is preferably carried out for 10 to 60 minutes, and more preferably for 20 to 40 minutes.

[0067] The method for manufacturing the composite material only needs to include a step of applying shear force to defibrate the CNTs, and it is possible to appropriately introduce auxiliary operations such as temperature control during the aforementioned step, a pre-process such as contacting the CNTs with an ionic liquid beforehand, and a post-process such as putting the material into a mold and molding it afterward.

[0068] When obtaining a mixture of carbon nanotubes and an ionic liquid, it is preferable to perform vacuum degassing. The method for producing the composite material may include, for example, the following steps. (1) A process of placing carbon nanotubes and an ionic liquid into a container and degassing them under vacuum to obtain a mixture. (2) A process of kneading the mixture using a roll kneader, applying shear force to defibrate the carbon nanotubes, and obtaining a composite material.

[0069] Composite materials can be used as materials such as resins. Examples include urethane materials and polyester materials that use composite materials. As resins using composite materials, urethane materials which are reaction products of composite materials, polyols, and isocyanates are preferred. Furthermore, composite materials can be used, for example, as conductive agents in conductive components or as heat dissipation components that take advantage of their high thermal conductivity. For instance, composite materials can be used as conductive agents in conductive components of electrophotographic image forming apparatuses, or as reinforcing agents for resins and the like.

[0070] <Confirmation of the composition of composite materials> The following describes various analytical methods for composite materials.

[0071] (Mass ratio of CNTs to ionic liquid) The ratio of CNTs to ionic liquid can be determined by measuring the total mass of the CNTs and ionic liquid, and then selectively acquiring or removing one of them using physical or chemical methods and measuring the mass of the removed component. Examples include centrifugation and washing with organic solvents. For example, carbon nanotubes (CNTs) can be separated from a composite material by centrifuging it at 6000 rpm for 60 minutes using a centrifuge. The CNT content (mass %) can then be calculated from the mass of the composite material before separation and the mass of the CNTs after separation.

[0072] (Structural analysis of ionic liquids) The structure of ionic liquids in composite materials can be confirmed by methods such as liquid chromatography-mass spectrometry (LC / MS), gas chromatography-GC / MS, evolved gas analysis (EGA-MS), FT-IR, or NMR. For example, ionic liquids selected from composite materials using the methods described above can be used as analytical samples. for example, 1 H nuclear magnetic resonance spectroscopy ( 1 ¹H-NMR spectrometer (AVANCE III 500, Bruker Biospin), and LC / MS (UltiMate 3000) The structure of ionic liquids can be analyzed using the LCQ FLEET instrument (manufactured by Thermo Fisher Scientific). Details of the analytical conditions when using the above instrument will be described later.

[0073] (Length of CNT) The size of carbon nanotubes (CNTs), specifically their length in the long and short directions, can be measured by directly observing the CNTs themselves or by indirectly obtaining information from their physical properties. Observation methods include, for example, selecting an appropriate optical microscope or electron microscope based on the measurement scale. Another method involves using an atomic force microscope, where the CNTs are pre-treated to expose their surface, then brought into contact with a probe to form a surface image for analysis. For example, after obtaining a surface image of a carbon nanotube (CNT) using a scanning electron microscope, the lengths in the long and short directions can be measured by image analysis. Specific measurement methods using a scanning electron microscope will be described later. [Examples]

[0074] The present disclosure will be described in further detail below using examples and comparative examples, but the embodiments of the present disclosure are not limited thereto.

[0075] <Synthesis of ionic liquids> An ionic liquid precursor was synthesized using the method described above, and an ionic liquid was synthesized by carrying out an ion exchange reaction with an alkali metal salt containing anions. The nucleophile and electrophile used in the synthesis of the ionic liquid precursor and the alkali metal salt used in the ion exchange reaction are shown in Tables 1, 2, and 7.

[0076] (Synthesis of ionic liquid precursor P-1) A stirring bar and 50 ml of tetrahydrofuran (THF, manufactured by Kanto Chemical Co., Ltd.) were placed in a round-bottom flask fitted with a Liebig condenser. 12.5 g (0.52 mol) of sodium hydride (manufactured by Kanto Chemical Co., Ltd.) was dispersed in the mixture, and the flask was cooled in an ice bath. A solution of 8.9 g (0.13 mol) of the nucleophile N-1 (imidazole, manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 50 ml of THF was slowly added dropwise. After removing the ice bath, the mixture was stirred at room temperature for 2 hours. After stirring, 41.1 g (0.33 mmol) of the electrophile Q-1 (2-bromoethanol) (manufactured by Tokyo Chemical Industry Co., Ltd.) was added at room temperature, and the mixture was heated under reflux at 70°C for 7 hours. The reaction mixture was filtered, insoluble matter was washed away with THF, and the solvent from the resulting filtrate was removed under reduced pressure. The mixture was then dissolved again in dichloromethane, filtered, and the filtrate was collected. The solvent was then removed under reduced pressure to obtain a concentrate. The obtained concentrate was washed with diethyl ether and dried under reduced pressure to obtain 28 g of ionic liquid precursor P-1.

[0077] [Table 1] [Table 2]

[0078] (Synthesis of ionic liquid precursors P-2, P-3, P-4, P-5, and P-12) Ionic liquid precursors P-2, P-3, P-4, P-5, and P-12 were obtained in the same manner as the synthesis of ionic liquid precursor P-1, except that the types and amounts of nucleophiles and electrophiles used as raw materials were changed as shown in Table 3.

[0079] [Table 3]

[0080] (Synthesis of ionic liquid precursor P-6) In a flask fitted with a Liebig condenser, 4.6 g (0.07 mol) of the nucleophile N-1 (imidazole, manufactured by Tokyo Chemical Industry Co., Ltd.), 21.3 g (0.10 mol) of the electrophile Q-5 (8-bromo-1-octanol, manufactured by Tokyo Chemical Industry Co., Ltd.), 25 g (0.18 mol) of potassium carbonate (manufactured by Kanto Chemical Co., Ltd.), and 200 ml of acetone were added, and the mixture was heated under reflux at 65°C overnight. After the reaction, the reaction mixture was filtered, and the solvent in the filtrate was removed by reduced pressure. The mixture was then purified by silica gel column chromatography (ethyl acetate) to obtain a compound in which the nucleophile had been tertiarily converted. Next, the obtained compound was dissolved in 50 ml of dichloromethane, and 24.1 g (0.10 mol) of the electrophile Q-6 (10-bromo-1-decanol, manufactured by Tokyo Chemical Industry Co., Ltd.) was added. The mixture was heated under reflux at 40°C for 18 hours. After the reaction, the solvent was removed by distillation under reduced pressure, washed with diethyl ether, and dried to obtain the quaternized ionic liquid precursor P-6.

[0081] (Synthesis of ionic liquid precursor P-7) 500 ml of distilled THF and 1 g of 2,6-di-tert-butylpyridine (Sigma Aldrich) were placed in a round-bottom flask and cooled to 0°C under a nitrogen atmosphere. Subsequently, 3.6 g (22 mmol) of methyl trifluoromethanesulfonate (Tokyo Chemical Industries) was added as an initiator. To stop polymerization, 5.87 g (44.5 mmol) of the nucleophile N-3 (2-methylbenzimidazole, Tokyo Chemical Industries) was added, and the polymer was precipitated and purified in water and diethyl ether. After drying under reduced pressure, tetramethylene glycol-substituted imidazole was obtained as a white powder. Next, to quaternize the polymer, the obtained polymer was dissolved in 200 ml of dichloromethane, 12.1 g (67 mmol) of the electrophile Q-3 (6-bromo-1-hexanol, manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was heated under reflux at 40°C for 18 hours. After the reaction, the solvent was removed by distillation under reduced pressure, washed with diethyl ether, and dried to obtain a white powder. To exchange the anion for a chloride ion, the obtained polymer was stirred for 2-3 hours in methanol dispersed with the ion exchange resin Dowex (manufactured by Wako Pure Chemical Industries, Ltd.). The ion exchange resin was removed by filtration, and after drying, the quaternized ionic liquid precursor P-7 was obtained. The anion of P-7 is a chloride ion.

[0082] (Synthesis of ionic liquid precursor P-8) 12.0 g (0.15 mol) of the nucleophile N-4 (2-pyridineethanol, manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 200 ml of dichloromethane, and 38 g (0.3 mol) of the electrophile Q-1 (2-bromoethanol, manufactured by Tokyo Chemical Industry Co., Ltd.) was added. The mixture was heated under reflux at 40°C for 18 hours. After the reaction, the solvent was removed by distillation under reduced pressure, and after washing with diethyl ether, the quaternized ionic liquid precursor P-8 was obtained as a white powder.

[0083] (Synthesis of ionic liquid precursors P-9 and P-10) Except for the changes made to the types and amounts of nucleophiles and electrophiles used in the reaction as shown in Table 4, Ionic liquid precursors P-9 and P-10 were synthesized in the same manner as ionic liquid precursor P-8. [Table 4]

[0084] (Synthesis of ionic liquid precursor P-11) 19 g (80 mmol) of the electrophile Q-6 (10-bromo-1-decanol, manufactured by Tokyo Chemical Industry Co., Ltd.) was mixed with tert-butyldimethylsilyl chloride in N,N-dimethylformamide in the presence of imidazole. The mixture was reacted at room temperature for 3 hours, then separated in ethyl acetate / water and dried to obtain a compound in which the hydroxyl group of Q-6 was silylated. 8.55 g (54 mmol) of the nucleophile N-7 (3-bromopyridine, Tokyo Chemical Industry Co., Ltd.) was dissolved in 400 ml of distilled THF under an inert atmosphere, and the mixture was cooled to -78°C in a dry ice / methanol bath. Subsequently, 23 ml (60 mmol) of n-butyllithium / hexane 2.6 mol / l solution (Kanto Chemical Co., Ltd.) was slowly added dropwise, and the mixture was stirred for 30 minutes. Then, 50 ml of silylated Q-6 THF solution was slowly added dropwise. After reacting at -78°C for 3 hours and overnight at room temperature, hydrochloric acid was added to the reaction solution, and the mixture was stirred at room temperature for 1 hour to desilylate it. After removing the solvent under reduced pressure, the mixture was separated with dichloromethane / water, and after drying, 3-(10-hydroxydecyl)pyridine was obtained as a white powder. This was dissolved in 50 ml of dichloromethane, and 15.8 g (60 mmol) of Q-8 (12-bromo-1-dodecanol, manufactured by Tokyo Chemical Industry Co., Ltd.), an electrophile for quaternization, was added. The mixture was heated under reflux at 40°C for 18 hours. After the reaction, the solvent was removed by distillation under reduced pressure, washed with diethyl ether, and dried to obtain the quaternized ionic liquid precursor P-11 as a white powder. The anion of P-11 is a bromide ion.

[0085] (Synthesis of ionic liquid precursors P-13, P-14, and P-15) Ionic liquid precursors P-13, P-14, and P-15 were synthesized in the same manner as ionic liquid precursor P-11, except that the nucleophile and electrophile used in the reaction were changed as shown in Table 5. [Table 5]

[0086] (Preparation of ionic liquid precursor P-16) 15.5 g (73 mmol) of the nucleophile N-12 (4,5-dibromoimidazole, manufactured by Sigma Aldrich), 15.2 g (0.11 mol) of the electrophile Q-7 (1-bromobutane, manufactured by Tokyo Chemical Industry Co., Ltd.), 27.8 g (0.2 mol) of potassium carbonate (manufactured by Kanto Chemical Co., Ltd.), and 100 ml of acetone were added, and the mixture was heated under reflux at 65°C overnight. After the reaction, the reaction mixture was filtered, and the solvent of the filtrate was removed by vacuum distillation. Then, silica gel column chromatography was performed. The compound was purified with ethyl acetate to obtain a compound in which the nucleophile was tertiarily converted. Next, the obtained compound was dissolved in 50 ml of dichloromethane, and 17.1 g (0.11 mmol) of Q-8 (iodoethane, manufactured by Tokyo Chemical Industry Co., Ltd.) was added as the electrophile B. The mixture was heated under reflux at 40°C for 18 hours. After the reaction, the solvent was removed by distillation under reduced pressure, and after washing with diethyl ether, 4,5-dibromoethylbutylimidazolium iodide was obtained as a white powder. Next, this compound was dissolved in 300 ml of distilled THF under a nitrogen atmosphere and cooled to -78°C in a dry ice / methanol bath. Then, 80 ml of n-butyllithium / hexane 2.6 M solution (manufactured by Kanto Chemical Co., Ltd.) was slowly added dropwise and stirred for 30 minutes. Subsequently, 100 ml of THF solution containing 52.3 g (0.22 mmol) of Q-9 (2-bromoethoxy-tert-butyldimethylsilane, manufactured by Sigma Aldrich) as the electrophile C was slowly added dropwise. After reacting at -78°C for 3 hours and overnight at room temperature, hydrochloric acid was added to the reaction solution and the mixture was stirred at room temperature for 1 hour to desilylate it. After removing the solvent under reduced pressure, the mixture was separated with ethyl acetate / water to obtain the ionic liquid precursor P-16 as a white powder. The anion of P-16 is the iodide ion.

[0087] (Preparation of ionic liquid precursors P-17, P-18, P-19, and P-20) Ionic liquid precursors P-17, P-18, P-19, and P-20 were synthesized in the same manner as ionic liquid precursor P-16, except that the nucleophiles and electrophiles A-C used in the reaction were changed as shown in Table 6. [Table 6]

[0088] (Synthesis of ionic liquid C-1) 7.7 g (33 mmol) of the ionic liquid precursor P-1 was dissolved in 50 ml of dichloromethane, and then an aqueous solution containing 10.3 g (36 mmol) of the anion exchange salt A-1 (bis(trifluoromethanesulfone)imide lithium, manufactured by Tokyo Chemical Industry Co., Ltd.) was added and the mixture was stirred for 24 hours. The resulting solution was separated to obtain the organic layer. After two liquid-liquid extractions of this organic layer with water, dichloromethane was removed under reduced pressure to obtain ionic liquid C-1, in which the anion is bis(trifluoromethanesulfone)imide anion. The synthesis of the ionic liquid precursor and ionic liquid was repeated until the mass of the obtained ionic liquid was 27 g or more.

[0089] [Table 7]

[0090] (Synthesis of ionic liquids C-2 to C-23) Ionic liquids C-2 to C-23 were synthesized in the same manner as ionic liquid C-1, except that the type of ionic liquid precursor and anion exchange salt used in the reaction was changed as shown in Table 8, and the amount of solvent was changed accordingly. In each case, the synthesis of the ionic liquid precursor and ionic liquid was repeated until the mass of the obtained ionic liquid was 27 g or more. [Table 8]

[0091] The synthesized ionic liquids C-1 to C-9 and C-19 to C-21 are represented by the following formula (2), where R1 to R4 in the cation structure and anion X - These were as shown in Table 9. Furthermore, C-11 to C-14, C-22 and C-23 are represented by the following formula (3), and R5 to R9 in the cation structure and the anion Y -This was as shown in Table 10.

[0092] [Table 9] In the table, for example, "C2H4OH" indicates CH2CH2OH. [ka]

[0093] [Table 10] [ka]

[0094] The structures of the ionic liquids C-10 and C-15 to C-18 were as shown in formulas (4) to (8) below, respectively. (C-10) [ka] (C-15) [ka] (C-16) [ka] (C-17) [ka] (C-18) [ka]

[0095] (Example 1) <Fabrication of composite materials> The manufacturing method for composite materials is described below. The composite material includes CNT-containing materials. The following weighing was performed so that the content was 10% by mass. • CNT: Zeon ZEONANO SG101 3.0g • Ionic liquid: Ionic liquid C-1 27.0g To allow the CNTs and ionic liquid to come into contact and blend without applying shear force, the above materials were placed in a plastic container, and the container was vacuum-degassed to obtain the mixture. To defibrate the carbon nanotubes (CNTs) in the aforementioned mixture by applying shear force, an open-roll apparatus (manufactured by Kansai Roll, with 6-inch front and rear rolls) was used. This apparatus applies shear force to the object by passing it through the gap between the two front and rear rolls while they rotate. 30g of the mixture was kneaded for 30 minutes under conditions of a 1mm roll gap, a front roll rotation speed of 10rpm, and a rear roll rotation speed of 8rpm to obtain composite material M-1.

[0096] <Structural analysis of ionic liquids in composite materials> Ionic liquids in composite materials are 1 H nuclear magnetic resonance spectroscopy ( 1 The analysis was performed using a 1H-NMR spectrometer (AVANCE III 500, Bruker Biospin) and an LC / MS spectrometer (UltiMate 3000 / LCQ FLEET, Thermo Fisher Scientific). Specifically, the analysis was conducted under the following conditions. 1 H nuclear magnetic resonance spectroscopy was performed using DMSO-d6 solvent, a resonance frequency of 500 MHz, and a sample volume of 100 mg. LC / MS was performed using an Acclaim Trinity P1 3μm 2.1×100mm column (Thermo Fisher Scientific), with a column temperature of 30°C, mobile phase A: acetonitrile, mobile phase B: 100mM aqueous solution of ammonium formate (pH 5.0), mobile phase C: pure water, flow rate: 0.5 mL / min, and detector: Corona Veo& Measurements were taken using PDA (190-800 nm), an injection volume of 10 μL, and ionized ESI. The resulting charts were analyzed using the instrument's dedicated software. The structure of the ionic liquid in composite material M-1 was found to be identical to that of ionic liquid C-1, and was confirmed to have the structure shown in formula (1) above.

[0097] <Observation and length evaluation of CNTs in composite materials> This analysis was performed to determine the lengths of the carbon nanotubes (CNTs) in the short and long side directions. (Measurement of length in the shorter direction) The length in the short direction was measured by obtaining surface images of the CNTs using a scanning electron microscope (Zeiss FE-SEM ULTRA55) and then calculating the length through image analysis. For observation, the composite material was cooled to -100°C and cut into 1 μm thick sections using a cryomicrotome (product name: UC-6, Leica Microsystems).

[0098] In this process, to ensure accurate measurement regardless of the orientation of the internal CNTs, three thin sections were cut from the observation sample, each containing three mutually perpendicular planes (i.e., the XY, YZ, and ZX planes, with XYZ and YYZ planes in place). Five locations on each thin section were observed using an in-lens SE detector in measurement mode with an exposure time of 4 minutes. An image for analysis was obtained by converting a 500 nm square area into image information with 1024 pixels or more. During this observation and image acquisition, the images were taken in a way that created a difference in brightness and contrast between the CNTs and the surrounding areas.

[0099] The images obtained here were imported into image processing software (product name "Image-Pro Plus": manufactured by Planetron Co., Ltd.), and the carbon nanotubes (CNTs) were automatically extracted as fibers using the "Fiber Separation" process. The angle deviation was set to 60° to count curved CNTs as fibers, and the fiber length corresponding to the length in the short side direction was calculated using the "Measure Thickness" process. Since the length in the short side direction of the CNT is calculated as the fiber width, the fiber width data from all five locations on all thin sections was read into a spreadsheet, and the average of all values ​​was taken as the numerical average of the lengths in the short side direction of the CNTs. .

[0100] (Method for confirming the fibrillation of carbon nanotubes (CNTs)) As defibration progresses in composite materials, the length of the short side of carbon nanotubes (CNTs) decreases, approaching the short side length of a single CNT, which is approximately 5 nm. If the length in the short side direction is 50 nm or less, it can be considered that defibration has progressed. In this disclosure, it is determined that the defibrillation of the CNT is progressing if the length in the short-side direction of the CNT is 50 nm or less, and that the defibrillation is not progressing if the length in the short-side direction exceeds 50 nm. In composite material M-1, the length of the CNTs in the short-side direction was 5.1 nm, confirming that defibration was progressing.

[0101] (Measurement of length in the longer direction) The length of the CNTs in the long-side direction was calculated by obtaining CNT images using a scanning electron microscope (Zeiss FE-SEM ULTRA55) and then analyzing the images. The measurement of the long-side length was performed to confirm whether or not CNT cleavage occurred. Therefore, since aggregation during pretreatment or measurement was not a particular problem, only CNTs were extracted from the composite material by centrifugation and used as the sample. CNTs were separated and extracted from composite material M-1 using a centrifuge (Hitachi Koki HIMAC CR22G) at 6000 rpm for 60 minutes. After centrifugation, CNTs were collected from the CNT accumulation area by attaching them to the tip of a 2mm diameter resin rod, and then placed on a glass substrate to be used as a measurement sample. To ensure that measurements could be taken even if the CNTs were oriented in random directions, 15 samples were obtained during observation, which is more than the length of the short side being measured. For each of these, a 200 μm square image was observed using an in-lens SE detector in measurement mode with an exposure time of 4 minutes, and images with a resolution of 1024 pixels or higher were obtained. During this observation and image acquisition, the images were taken in a way that created a difference in brightness and contrast between the CNTs and the surrounding areas.

[0102] The obtained images were imported into image processing software (product name "Image-Pro Plus": manufactured by Planetron Co., Ltd.), and the carbon nanotubes (CNTs) were automatically extracted as fibers using the "Fiber Separation" process. The angle deviation was set to 60° to count curved CNTs as fibers, and the fiber length corresponding to the length in the long direction was calculated. To account for cases where the entire CNT was not visible in the SEM image, the top 50% of the fiber length data, starting with the longest, was extracted. Similarly, data was extracted for all 15 locations, and the average of all extracted data was used as the numerical average length in the long side direction of the CNTs.

[0103] <Exposure of composite materials to high temperature and high humidity> To evaluate the degree of re-aggregation of CNTs in composite materials, the length of CNTs when left in a harsh environment and the conductivity of evaluation samples prepared using the composite material were assessed.

[0104] As an accelerated test, the composite material was left for 14 days in a high-temperature, high-humidity environment of 55°C and 95% RH (harsh environment), which increases molecular mobility and promotes CNT aggregation. The composite material left under the above conditions was designated as M-1b. To confirm whether or not CNT re-aggregation occurred in the composite material, the following two evaluation methods were performed. The evaluation involved leaving the composite material in the harsh environment described above, then leaving it at room temperature (25°C) for 24 hours to allow the environmental influences to dissipate before performing the two evaluations described below.

[0105] <Length of the short side of the CNT after standing> To check the state of CNTs in composite materials after storage, the stored composite material M-1b was used. The length of the short side of the CNT was measured using the method described above and compared with the length in the short side before storage. In other words, the ratio of the length in the short side after storage (after storage / before storage) to the length in the short side before storage was calculated. If the above ratio was 2.00 or less, it was determined that aggregation was suppressed, and therefore no re-aggregation was detected. On the other hand, if it exceeded 2.00, it was determined that re-aggregation had occurred. M-1b had the above ratio of 1.00, and therefore no re-aggregation was detected.

[0106] <Fabrication of urethane sheets using composite materials and measurement of resistivity> To ensure that the mass of CNTs was 0.2 parts by mass per 100 parts by mass of polyol (Actcall EP-550N, manufactured by Mitsui Chemicals), 10 g of composite material M-1 and 500 g of polyol were added to a 2 L plastic container. The blades of a stirring-type disperser (YY, manufactured by Primix Corporation) were placed inside the plastic container and stirred at 3200 rpm for 20 minutes. 40 g of this stirred solution was measured out, and more polyol was added to achieve a CNT concentration of 0.1 parts by mass per 100 parts by mass of polyol. The mixture was then stirred at 2000 rpm for 3 minutes while degassing using a rotation-revolution type mixer (Awatori Rentaro ARV-931TWIN, manufactured by Thinky Co., Ltd.).

[0107] After stirring, the following dispersants and catalysts 1 and 2 were added. Silicone (NIAX SILICONE L-3640, manufactured by Momentive Performance Materials Japan LLC) was added as a dispersant for urethane formation at a rate of 0.4 parts by mass per 100 parts by mass of polyol, N-methylmorpholine (manufactured by Tokyo Chemical Industry Co., Ltd.) was added as catalyst 1 at a rate of 1.0 part by mass per 100 parts by mass of polyol, and DABCO 33-LV (manufactured by Sigma-Aldrich) was added as catalyst 2 at a rate of 0.5 parts by mass per 100 parts by mass of polyol to obtain a slurry. Furthermore, the amount of isocyanate (Cosmonate TM-20, manufactured by Mitsui Chemicals) was calculated to be equivalent to the amount of NCO derived from the polyol in the obtained slurry, and the required amount was added. This isocyanate-added slurry was poured into a 10cm × 10cm × 2mmt steel mold that had been preheated to 80°C, and subjected to primary curing treatment at 80°C for 10 minutes. After curing, the solidified sample was removed from the mold and subjected to secondary curing treatment at 140°C for 30 minutes to obtain urethane sheet T-1. Furthermore, urethane sheet T-1b was obtained using the same method as described above for creating urethane sheet T-1, except that composite material M-1 was replaced with the left-as-is composite material M-1b.

[0108] The urethane sheets T-1 and T-1b were left at room temperature (25°C) for 24 hours, and then their resistivity was measured. The resistivity was measured by sandwiching the urethane sheet between Φ10mm electrodes and applying a 20V DC voltage. The current value was measured using a tester (Fluke Digital Multimeter 177), and the resistivity was calculated. The resistivity R of urethane sheet T-1b using the composite material after standing was compared to the resistivity R of urethane sheet T-1 using the composite material before standing. b Ratio (R b The resistance fluctuation ratio ( / R) was calculated.

[0109] As mentioned above, under harsh conditions, re-aggregation of CNTs in composite materials is more likely to occur. Re-aggregated CNTs form aggregates, making it easier for regions without CNTs to occur within the composite material. As a result, the conductive pathways become limited and the resistivity increases. That is, the resistance fluctuation ratio (R b A smaller value of / R indicates that the re-aggregation of CNTs in the composite material after standing is suppressed. The evaluation results for Example 1 are shown in Tables 12 and 13.

[0110] (Examples 2-23) Except for using the ionic liquids shown in Table 10, composite materials M2 to M23 were prepared using the same manufacturing method as composite material M-1 in Example 1, and evaluated in the same manner as in Example 1. The structure of the ionic liquids in composite materials M-2 to M-23 is as follows: Ionic liquids C-1 to C-23 It was confirmed that there was no difference and that it had the structure of formula (1) above. In each case, defibration of CNTs was confirmed, and re-aggregation was suppressed even after being left in a harsh environment for a long period of time. Furthermore, it was confirmed that the resistivity of the urethane sheet made using the composite material showed only a slight change in resistivity even when using the composite material after being left for a long period of time. The evaluation results of Examples 2 to 23 are shown in Tables 12 and 13.

[0111] [Table 11] In the table, the CNT content ratio indicates the percentage (by mass) of carbon nanotubes relative to the total content of carbon nanotubes and ionic liquid. The defibrillation method refers to the method used to apply shear force in the manufacturing method of the composite material. [Table 12] In the table, "cationic skeleton" refers to the cationic skeleton of a nitrogen-containing heteroaromatic ring cation. The "long side length" and "short side length" of CNTs represent the average length in each direction. Regarding the "fibrillation determination," "present" indicates that fibrillation was progressing, and "absent" indicates that fibrillation was not progressing. "Change in durability of CNT short side length" refers to the ratio of the length of the short side of a CNT after storage (after storage / before storage) to the length of the short side of a CNT before storage. [Table 13] Regarding the resistivity notation in the table, for example, the notation "1.70E+04" means "1.70 × 10 4 This indicates ".

[0112] (Example 24) The composite material M-24 was prepared using half C-1 and half C-2 (13.5 g each) as ionic liquids, except that the evaluation was carried out in the same manner as in Example 1.

[0113] (Example 25) The composite material M-25 was fabricated using OCSiAl TUBALL 01RW02, a single-walled carbon nanotube (CNT), as the CNT, except that the evaluation was performed in the same manner as in Example 1.

[0114] (Examples 26, 27) The composite material was prepared and evaluated in the same manner as in Example 1, except that the mixing ratio of CNTs and ionic liquid was changed as shown in Table 11.

[0115] (Comparative Example 1) As the ionic liquid C-C1, 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (manufactured by Tokyo Chemical Industry Co., Ltd.) was prepared. This ionic liquid is represented by formula (2) above, where R2 of the cation structure is C2H5OH and R3 is CH3, and the terminal end of R3 does not have an OH group. That is, the nitrogen-containing heteroaromatic ring cation of ionic liquid C-C1 has one substituent with a hydroxyl group at its terminal in the cation structure. The evaluation was performed in the same manner as in Example 1, except that C-C1 was used as the ionic liquid. The ionic liquid in the obtained composite material M-C1 had the same structure as C-C1, with R2 being C2H5OH and R3 being CH3, and one of the terminals lacking an OH group. Composite material M-C1 is C The average length of the NTs in the short-side direction exceeded 50 nm, and CNT defibration could not be confirmed. Furthermore, CNT re-aggregation was observed in composite material M-C1b after standing. The resistivity of urethane sheet T-C1b, which was made using the composite material after standing, changed by more than 10 times compared to urethane sheet T-C1, which was made using the composite material before standing.

[0116] (Comparative Example 2) In preparing the composite material, the same CNTs and ionic liquid C-1 as in Example 1 were used in the same proportions. In the manufacturing process, the CNTs and carbon nanotubes were simply degassed under vacuum and mixed, without kneading using an open-roll device that applies shear force, to obtain the composite material M-C2. The CNTs in the composite material M-C2 had not undergone significant defibration. Therefore, in this comparative example only, when measuring the length of the CNTs in the short-side direction, the average number of lengths in the short-side direction was calculated from analytical images obtained by converting 5 μm squares into image information. Despite using the same ionic liquid and CNTs as in Example 1, the composite material M-C2 in Comparative Example 2 showed no progress in CNT defibration. Furthermore, the resistivity R of the urethane sheet made using composite material M-C2 was more than 100 times higher than that of Example 1, confirming the effect of the insufficient CNT defibration. Therefore, the composite material had not reached a level suitable for evaluation after standing, and the evaluation was terminated.

[0117] This disclosure relates to the following configuration and method. (Composition 1) A composite material containing carbon nanotubes and an ionic liquid, The ionic liquid contains nitrogen-containing heteroaromatic ring cations and anions, The nitrogen-containing heteroaromatic ring cation has a cationic structure having at least two substituents having hydroxyl groups at their terminal ends, as shown in formula (1) below. A composite material characterized in that the content ratio of carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less. TIFF2026131465000026.tif18153 (In formula (1), Z represents a cationic skeleton containing a cationic nitrogen-containing heteroaromatic ring. A1 and A2 are each independent linking groups, each having a hydroxyl group (OH) at its terminus as a substituent.) (Configuration 2) The composite material according to configuration 1, wherein the ionic liquid is at least one selected from the group consisting of the ionic liquid represented by the following formula (2) and the ionic liquid represented by the following formula (3). TIFF2026131465000027.tif44153(In formula (2), R1 to R4 represent substituents or hydrogen atoms, and at least two of R1 to R3 or R4 have a hydroxyl group at the terminal. X - (This represents an anion.) TIFF2026131465000028.tif49153(In formula (3), R5 to R9 represent substituents or hydrogen atoms, and at least two of R5 to R9 have hydroxyl groups at their terminal ends. Y - (This represents an anion.) (Composition 3) The ionic liquid is the composite material according to configuration 2 represented by formula (2). (Composition 4) The R1 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms. R2 and R3 are alkyl groups having 1 to 6 carbon atoms and a hydroxyl group at the end. The aforementioned R4 is a hydrogen atom. The composite material described in Composition 3. (Composition 5) Anion X in equation (2) above - (CF3SO2)2N - Or (FSO2)2N - The composite material according to configuration 3 or 4. (Composition 6) The composite material according to any one of configurations 3 to 5, wherein R2 and R3 are -CH2CH2OH. (Composition 7) The carbon nanotube has a number average length in the short-side direction of 2 nm or more and 50 nm or less, and a number average length in the long-side direction of 10 μm or more and 2 mm or less. A composite material as described in any of configurations 1 to 6. (Composition 8) The composite material according to any one of configurations 1 to 7, wherein the carbon nanotube is a single-walled carbon nanotube. (Method 1) A method for manufacturing composite materials, The composite material is It contains carbon nanotubes and ionic liquids, The ionic liquid contains nitrogen-containing heteroaromatic ring cations and anions, The nitrogen-containing heteroaromatic ring cation has a cationic structure having at least two substituents having hydroxyl groups at their terminal ends, as shown in formula (1) below. The carbon nanotube content in the composite material is 3% by mass or more and 30% by mass or less. The manufacturing method is A step of obtaining a mixture of the carbon nanotube and the ionic liquid, A step of applying a shear force to the mixture and defibrating the carbon nanotubes in the presence of the ionic liquid, A manufacturing method characterized by including the following. TIFF2026131465000029.tif18153 (In formula (1), Z represents a cationic skeleton containing a cationic nitrogen-containing heteroaromatic ring. A1 and A2 are each independently linking groups, each having a hydroxyl group (OH) at its terminus as a substituent.) (Method 2) The method for producing a composite material according to Method 1, wherein the ionic liquid is at least one selected from the group consisting of ionic liquids represented by the following formula (2) and ionic liquids represented by the following formula (3). TIFF2026131465000030.tif44153(In formula (2), R1 to R4 represent substituents or hydrogen atoms, and at least two of R1 to R3 or R4 have a hydroxyl group at the terminal. X - (This represents an anion.) TIFF2026131465000031.tif49153(In formula (3), R5 to R9 represent substituents or hydrogen atoms, and at least two of R5 to R9 have hydroxyl groups at their terminal ends. Y - (This represents an anion.) (Method 3) The ionic liquid is the method for producing a composite material according to method 2 represented by formula (2). (Method 4) The R1 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms. R2 and R3 are alkyl groups having 1 to 6 carbon atoms and a hydroxyl group at the end. The aforementioned R4 is a hydrogen atom. A method for producing a composite material as described in Method 3. (Method 5) Anion X in equation (2) above - (CF3SO2)2N - Or (FSO2)2N - A method for producing a composite material according to method 3 or 4. (Method 6) A method for producing a composite material according to any one of methods 3 to 5, wherein R2 and R3 are -CH2CH2OH. (Method 7) The number average length of the carbon nanotube in the short-side direction is between 2 nm and 50 nm. A method for producing a composite material according to any one of methods 1 to 6, wherein the average number of lengths in the long side direction is 10 μm or more and 2 mm or less. (Method 8) A method for producing a composite material according to any one of methods 1 to 7, wherein the carbon nanotube is a single-walled carbon nanotube.

Claims

1. A composite material containing carbon nanotubes and an ionic liquid, The ionic liquid contains nitrogen-containing heteroaromatic ring cations and anions, The nitrogen-containing heteroaromatic ring cation has a cationic structure having at least two substituents having hydroxyl groups at their terminal ends, as shown in formula (1) below. A composite material characterized in that the content ratio of carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less. 【Chemistry 1】 (In formula (1), Z represents a cationic skeleton containing a cationic nitrogen-containing heteroaromatic ring. A1 and A2 are each independent linking groups, each having a hydroxyl group (OH) at its terminus to form a substituent.)

2. The composite material according to claim 1, wherein the ionic liquid is at least one selected from the group consisting of the ionic liquid represented by the following formula (2) and the ionic liquid represented by the following formula (3). 【Chemistry 2】 (In formula (2), R1 to R4 represent substituents or hydrogen atoms, and at least two of R1 to R3 or R4 have a hydroxyl group at the terminal end. X － (This represents an anion.) 【Transformation 3】 (In formula (3), R5 to R9 represent substituents or hydrogen atoms, and at least two of R5 to R9 have hydroxyl groups at their terminal ends. － (This represents an anion.)

3. The composite material according to claim 2, wherein the ionic liquid is represented by formula (2).

4. The R1 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms. R2 and R3 are alkyl groups having 1 to 6 carbon atoms and a hydroxyl group at the end. can be, The aforementioned R4 is a hydrogen atom. The composite material according to claim 3.

5. The anion X in the formula (2) － is (CF ３ SO ２ ), ２ N － or (FSO ２ ), ２ N － The composite material according to claim 3

6. R2 and R3 are -CH ２ CH ２ The composite material according to claim 3, which is OH.

7. The composite material according to claim 1, wherein the number average length of the carbon nanotubes in the short-side direction is 2 nm or more and 50 nm or less, and the number average length in the long-side direction is 10 μm or more and 2 mm or less.

8. The composite material according to any one of claims 1 to 7, wherein the carbon nanotube is a single-walled carbon nanotube.

9. A method for manufacturing composite materials, The composite material is It contains carbon nanotubes and ionic liquids, The ionic liquid contains nitrogen-containing heteroaromatic ring cations and anions, The nitrogen-containing heteroaromatic ring cation has a cationic structure having at least two substituents having hydroxyl groups at their terminal ends, as shown in formula (1) below. The carbon nanotube content in the composite material is 3% by mass or more and 30% by mass or less. The manufacturing method is A step of obtaining a mixture of the carbon nanotube and the ionic liquid, A step of applying a shear force to the mixture and defibrating the carbon nanotubes in the presence of the ionic liquid, A manufacturing method characterized by including the following. 【Chemistry 4】 (In formula (1), Z represents a cationic skeleton containing a cationic nitrogen-containing heteroaromatic ring. A1 and A2 are each independent linking groups, each having a hydroxyl group (OH) at its terminus to form a substituent.)

10. The method for producing a composite material according to claim 9, wherein the ionic liquid is at least one selected from the group consisting of ionic liquids represented by the following formula (2) and ionic liquids represented by the following formula (3). 【Transformation 5】 (In formula (2), R1 to R4 represent substituents or hydrogen atoms, and at least two of R1 to R3 or R4 have a hydroxyl group at the terminal end. X － (This represents an anion.) 【Transformation 6】 (In formula (3), R5 to R9 represent substituents or hydrogen atoms, and at least two of R5 to R9 have hydroxyl groups at their terminal ends. － (This represents an anion.)

11. The method for producing a composite material according to claim 10, wherein the ionic liquid is represented by formula (2).

12. The R1 is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms. R2 and R3 are alkyl groups having 1 to 6 carbon atoms and a hydroxyl group at the end. The aforementioned R4 is a hydrogen atom. A method for producing a composite material according to claim 11.

13. Anion X in equation (2) above － (CF ３ SO ２ ) ２ N － or (FSO ２ ) ２ N － The method for producing a composite material according to claim 11.

14. R2 and R3 are -CH ２ CH ２ A method for producing a composite material according to claim 11, wherein the composite material is OH.

15. The method for producing a composite material according to claim 9, wherein the number average length of the carbon nanotube in the short-side direction is 2 nm or more and 50 nm or less, and the number average length in the long-side direction is 10 μm or more and 2 mm or less.

16. A method for producing a composite material according to any one of claims 9 to 15, wherein the carbon nanotube is a single-walled carbon nanotube.

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