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

Abstract

Provided are: a composite material in which a defibrated state can be maintained for a long period of time by making carbon nanotubes sufficiently defibrated and suppressing reaggregation; and a method for producing same. The composite material contains carbon nanotubes and an ionic liquid, wherein the ionic liquid contains nitrogen-containing heterocyclic aromatic cations and anions, the nitrogen-containing heterocyclic aromatic cations have a specific cation structure having at least two substituents having a hydroxyl group at terminal ends thereof, and the content of the carbon nanotubes in the composite material is 3-30 mass%.

Description

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

[0001] The present disclosure belongs to the technical field of molecular nanotechnology, and particularly relates to a novel material that incorporates carbon nanotubes (CNTs) and exhibits properties derived from carbon nanotubes over a long period of time.

[0002] Carbon nanotubes are used for imparting functionalities such as conductivity and reinforcement. However, due to intermolecular forces and the like, aggregation tends to proceed, and in order to impart sufficient functionality, it is necessary to have the aggregated carbon nanotubes in a disaggregated state (defibrillated state). For example, Patent Document 1 discloses mixing carbon nanotubes with an ionic liquid to subdivide (defibrillate) the carbon nanotubes. Further, Patent Document 2 presents a characteristic structure among the cations of imidazolium salts as the ionic liquid to be mixed with carbon nanotubes.

[0003] Japanese Patent Application Laid-Open No. 2004-142972 Japanese Patent Application Laid-Open No. 2013-244673

[0004] However, according to the studies by the present inventors, in the prior art, it may be difficult to achieve a sufficient defibrillated state of carbon nanotubes or to maintain the defibrillated state. As a result, it may be difficult to continuously exhibit the properties derived from carbon nanotubes over a long period of time. According to the first invention according to the present disclosure, a composite material is provided that can maintain the defibrillated state over a long period of time by achieving a sufficient defibrillated state of carbon nanotubes and suppressing re-aggregation. Further, according to the second invention according to the present disclosure, a method for producing a composite material is provided that can form a sufficient defibrillated state of carbon nanotubes, suppress re-aggregation, and maintain the defibrillated state over a long period of time.

[0005] According to at least one aspect of the present disclosure, 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 cation having a cationic structure having at least two substituents having hydroxyl groups at their terminal ends, represented by the following formula (1), and the content of carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less. (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.)

[0006] Furthermore, according to at least one aspect of the present disclosure, a method for producing a composite material is provided, wherein the composite material comprises carbon nanotubes and an ionic liquid, the ionic liquid comprises 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), the content of the carbon nanotubes in the composite material is 3% by mass or more and 30% by mass or less, and the production method comprises the steps of: obtaining a mixture of the carbon nanotubes and the ionic liquid; and applying a shear force to the mixture to defibrate the carbon nanotubes in the presence of the ionic liquid.

[0007] According to at least one aspect of this disclosure, a composite material can be obtained in which carbon nanotubes are sufficiently defibrated and re-aggregated, thereby maintaining the defibrated state for a long period of time. Furthermore, according to at least one aspect of this disclosure, a method for producing a composite material can be obtained in which carbon nanotubes are sufficiently defibrated, re-aggregated, and the defibrated state can be maintained for a long period of time.

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

[0009] Furthermore, in this disclosure, a 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. Also, in this specification, for explanatory purposes, carbon nanotubes may be referred to as "carbon nanotubes" or abbreviated as CNT, but these descriptions 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 CNTs occurs due to adsorption between CNTs caused by π-π interactions between π-orbital electrons on the CNTs. The thickness (length in the short side direction) of a single CNT is only a few nanometers, but due to adsorption, tens of thousands of CNTs can aggregate, and the size of the aggregate can reach tens of micrometers. It is also known that adsorption occurs between π-π interactions between π-orbital electrons in heteroaromatic rings and π-orbital electrons on CNTs. Patent Document 1 utilizes this adsorption effect to subdivide CNTs by inserting an ionic liquid containing a nitrogen-containing heteroaromatic ring as a cation backbone between aggregated CNTs. However, since the π-π interaction between the nitrogen-containing heteroaromatic ring and the CNT and the π-π interaction between CNTs are energetically similar, when CNTs are in close proximity to each other, re-adsorption of CNTs is induced, and re-aggregation of CNTs is likely to occur.

[0012] Regarding the above problem, the inventors speculate as follows on why the remarkable effect of suppressing the re-aggregation of defibrated CNTs is obtained by the ionic liquid contained in the composite material containing nitrogen-containing heteroaromatic ring cations having at least two substituents with hydroxyl groups at their terminals: The ionic liquid contains nitrogen-containing heteroaromatic ring cations, and these nitrogen-containing heteroaromatic ring cations have at least two substituents with hydroxyl groups at their terminals. When the ionic liquid is in close proximity to the CNTs, in addition to the π-π interaction between the CNTs and the ionic liquid, the hydroxyl groups on the ionic liquid molecules form hydrogen bonds with the hydroxyl groups of adjacent ionic liquid molecules. That is, hydrogen bonds are formed between the ionic liquids.

[0013] This combined effect forms a network of CNT-ionic liquid-(one or more ionic liquids)-ionic liquid-CNT, allowing the 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 the ionic liquids, and the bonds between the ionic liquids due to π-π interactions, are preferentially broken.

[0016] Furthermore, by keeping the CNT content 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. This repeated process gradually eliminates the interaction between the CNTs, leading to the defibration of the CNTs. In addition, as previously described, the presence of ionic liquid molecules between the defibrated CNTs maintains a certain distance, thus suppressing the re-aggregation of the CNTs.

[0017] <Carbon Nanotubes (CNTs)> As is well known, CNTs refer to materials in which graphene sheets, which consist of a six-membered ring network of carbon atoms, are formed into single-layer or multi-layer coaxial tubes. Generally, they are classified into single-walled CNTs and multi-walled CNTs based on the number of components in the surrounding walls of the coaxial tube, and further classified into zigzag type, armchair type, and chiral type based on differences in the composition of the graphene sheet, and various other structures are known. In this disclosure, any of these CNT structures is applicable.

[0018] The CNTs preferably include single-walled carbon nanotubes (WYNS), and more preferably are single-walled CNTs. Because single-walled CNTs are thinner than multi-walled CNTs, they readily 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 occurs more easily. Therefore, using single-walled CNTs makes it easier to suppress the re-aggregation of CNTs.

[0019] In the composite material, it is preferable that the number average length of the CNTs in the short-side direction is 2 nm to 50 nm, and the number average length of the long-side direction is 10 μm to 2 mm. This is because the effect of forming a network via the aforementioned 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., when 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 CNT 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 number of lengths in the long-side direction of the CNT is usually 5 μm to 2 mm. The average number of lengths in the long-side direction is more preferably 30 μm to 500 μm, even more preferably 50 μm to 300 μm, and even more preferably 100 μm to 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, 3,000 to 40,000, more preferably 4,000 to 35,000, and even more preferably 5,000 to 30,000.

[0022] <Ionic Liquids> Ionic liquids are salts that are liquid at room temperature and composed of ions such as anions and cations. Ionic liquids contain nitrogen-containing heteroaromatic ring cations and anions. That is, 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] <Cations 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). 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, so that the hydroxyl group on the ionic liquid molecule forms a hydrogen bond with the hydroxyl group of an adjacent ionic liquid molecule, forming the aforementioned CNT-ionic liquid-(one or more ionic liquids)-ionic liquid-CNT network. As a result, the CNTs can maintain a certain distance from each other without coming into close proximity. Furthermore, since hydrogen bonds have a much higher bond energy and are stronger than the π-π interactions between CNTs described above, 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 may be a 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 heterocycles. They may also have one or more heteroatoms other than a nitrogen atom, such as oxazolium cations, thiazolium cations, benzoxazolium cations, and benzothiazolium cations. Preferably, the nitrogen-containing heteroaromatic ring cation is at least one selected from the group consisting of imidazolium cations, pyridinium cations, pyrazolium cations, quinolinium cations, thiazolium cations, and oxazolium cations.

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

[0027] The ionic liquid is preferably 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). The ionic liquid is preferably represented by the following formula (2) or the following formula (3). The ionic liquid represented by formula (2) above contains an imidazolium cation as a nitrogen-containing heteroaromatic ring cation. In formula (2), R1 to R4 each represent a substituent or a hydrogen atom. On the nitrogen-containing heteroaromatic ring, R1 is bonded as a substituent to carbon atoms adjacent to 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 their terminal end. － The symbol represents an anion. Note that, as with typical imidazolium cations, formulas (2) and (3) conveniently include a "+" indicating cationicity on one of the nitrogen atoms of the heterocycle, but this does not indicate that the cation properties are localized only on this nitrogen atom.

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

[0029] In composite materials, cations in the ionic liquid represented by formula (2) or formula (3) above undergo charge delocalization within the cation due to their chemical structure, and because the interaction between nitrogen-containing heteroaromatic ring portions is small, 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 promotion of defibration and suppression of re-aggregation of CNTs is further promoted. Furthermore, more preferably, the nitrogen-containing heteroaromatic ring cation is an imidazolium cation. In other words, it is more preferable for the composite material to contain the ionic liquid represented by formula (2) above. The ionic liquid represented by formula (2) above is preferable because charge delocalization within the cation occurs more easily, and the effect of hydrogen bonding described above becomes larger.

[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 cation skeleton is preferably such that the number of atoms counted along the shortest distance from the cation skeleton to the hydrogen atom of the hydroxyl group is 7 or less (the number of atoms counted along the shortest distance from the cation 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 cation 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 six or fewer atoms counted along the longest distance from the cation skeleton to the terminal atom 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 -CH ２ CH ２ It is OH. R2 and R3 are -CH ２ CH ２ Being an OH group brings the sites where hydrogen bonds are formed closer together when forming a network through an ionic liquid. Furthermore, molecular symmetry reduces the variation in bonding strength, resulting in stronger bonds throughout the network. This further promotes the defibrillation 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 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 end. R9 is preferably a hydrogen atom or a methyl group. Furthermore, three of R5 to R9 may have hydroxyl groups at the end. For example, R6, R7 and R8 may have hydroxyl groups at the end.

[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.

[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 anion, carboxylate anion, sulfonylimide anion, sulfonylmethide anion, alkylfluoroborate anion, alkylfluorophosphate anion, 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 trifluoromethanesulfonylimide anions, perfluoroethylsulfonylimide anions, perfluoropropylsulfonylimide anions, perfluorobutylsulfonylimide anions, perfluoropentylsulfonylimide anions, perfluorohexylsulfonylimide anions, perfluorooctylsulfonylimide anions, fluorosulfonylimide anions, and cyclic anions such as cyclohexafluoropropane-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 the alkylfluoroborate anion include trifluoromethyltrifluoroborate anion, perfluoroethyltrifluoroborate anion, and the like. Examples of the alkylfluorophosphate anion include tris-trifluoromethyl-trifluorophosphate anion, tris-perfluoroethyl-trifluorophosphate anion, and the like. Examples of the halide ion include fluoride ion, chloride ion, bromide ion, iodide ion, and the like.

[0048] Examples of the carboxylic acid anion include alkylcarboxylic 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, an ethoxy group, a substituent containing a hetero atom such as an amide group, a cyano group, and a haloalkyl group such as a trifluoromethyl group.

[0049] Examples of the sulfonic acid anion include alkylsulfonic acid anions such as methanesulfonic acid anion, ethanesulfonic acid anion, and aromatic sulfonic acid anions such as benzenesulfonic acid, para-toluenesulfonic acid anion, and the like. It 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, an ethoxy group, a substituent containing a hetero atom such as an amide group, a cyano group, and a haloalkyl group such as a trifluoromethyl group.

[0050] Among the anions mentioned above, sulfonic acid fluoride anion and sulfonylimide fluoride anion are preferred. Among them, bis(trifluoromethanesulfonyl)imide anion ((CF ３ SO ２ ), ２ N － ), or bis(fluorosulfonyl)imide anion ((FSO ２ ), ２ N － )) is preferred.

[0051] Anion X in equation (2) above － For example (CF ３ SO ２ ) ２ N － (FSO ２ ) ２ N － , ClO ４ － , (C ２ O ４ ) ２ B － and (C ４ F ９ SO ２ ) ２ N － At least one selected from the group consisting of the following is anion X. － (CF ３ SO ２ ) ２ N － or (FSO ２ ) ２ N － It is preferable that the above anion is chemically stable due to its chemical structure 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 (CF ３ SO ２ ) ２ N － , Cl － CF ３ COO － , C ３ F ７ SO ３ － , N (CN) ２ － (FSO ２ ) ２ N － At least one selected from the group consisting of the following is anion Y. － (CF ３ SO ２ ) ２ N － or (FSO ２ ) ２ N － It is preferable that this be the case.

[0053] <Method for synthesizing ionic liquids> Ionic liquids having the above-described structure 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 performing a known ion exchange reaction. For example, by using the following materials as the nucleophile and electrophile used in the nucleophilic substitution reaction and the alkali metal salt used in the ion exchange reaction, and by combining known methods, an ionic liquid having the above-described 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 Material> The composite material contains carbon nanotubes and an ionic liquid. 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. Furthermore, 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 other than CNTs and ionic liquids, rubber materials, conductivity imparters, compounding agents, fillers, crosslinking agents, catalysts, etc., insofar as the effects of the present invention are not impaired.

[0062] <Method for Manufacturing Composite Materials> Composite materials can be manufactured by the following manufacturing method. That is, the method for manufacturing composite materials 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 ratio of 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) A step of obtaining 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 described above, 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 applied to this network, the bonds between CNTs with weaker bond energy than hydrogen bonds and the bonds between ionic liquids and CNTs due to π-π interactions 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 the defibration of the CNTs. As described above, the defibrated CNTs are separated from adjacent CNTs by ionic liquid molecules, which maintain a certain distance, thus suppressing the re-aggregation of the CNTs. The above manufacturing method yields a composite material in which the defibration of CNTs is further promoted and the re-aggregation of the defibrated CNTs 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 rolls while rotating the front and rear 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 time for performing the mixing process is not particularly limited, but for example, it is preferable to perform it 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, vacuum degassing is preferable. The method for producing the composite material may include, for example, the following steps: (1) A step of placing carbon nanotubes and an ionic liquid into a container and obtaining a mixture by vacuum degassing; (2) A step 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 also be used, for example, as conductive agents in conductive members or as heat dissipation members that take advantage of their high thermal conductivity. For example, composite materials can be used as conductive agents in conductive members of electrophotographic image forming apparatuses or as reinforcing agents for resins.

[0070] <Confirmation of Composite Material Components> 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 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, 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 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 structural analysis of ionic liquids in composite materials can be confirmed by methods such as liquid chromatography-mass spectrometry (LC / MS), gas chromatography-GC / MS, generated gas analysis (EGA-MS), FT-IR, or NMR. For example, an ionic liquid selected from the composite material using the above methods can be used as an analytical sample. For example, １ H nuclear magnetic resonance spectroscopy ( １ The structure of ionic liquids can be analyzed using an H-NMR spectrometer (AVANCE III 500, manufactured by Bruker Biospin) and an LC / MS spectrometer (UltiMate 3000 / LCQ FLEET, manufactured by Thermo Fisher Scientific). Details of the analytical conditions when using the above instruments will be described later.

[0073] (Length of CNTs) The size of a CNT, i.e., its length in the long and short sides, can be measured by directly observing the CNT itself or by indirectly obtaining information from its physical properties. One observation method involves appropriately selecting an optical microscope or electron microscope depending on the measurement scale. Another method involves using an atomic force microscope, where the CNT is pre-treated to expose it to the surface, then brought into contact with a probe to form a surface image, which is then analyzed. For example, a scanning electron microscope can be used to obtain a CNT surface image, after which the lengths in the long and short sides can be measured by image analysis. Specific measurement methods using a scanning electron microscope will be described later.

[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> Ionic liquid precursors were synthesized using the method described above, and ionic liquids were synthesized by carrying out an ion exchange reaction with an alkali metal salt containing anions. The nucleophiles and electrophiles used in the synthesis of the ionic liquid precursors and the alkali metal salts 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, and 12.5 g (0.52 mol) of sodium hydride (manufactured by Kanto Chemical Co., Ltd.) was dispersed. The round-bottom flask was then 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 solution was filtered, insoluble matter was washed away with THF, and the solvent of the resulting filtrate was removed by vacuum distillation. Subsequently, the solution was 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]

[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]

[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 of the filtrate was removed by reduced pressure distillation. The mixture was then purified by silica gel column chromatography (ethyl acetate) to obtain a compound in which the nucleophile had been tertiarily converted. Subsequently, 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, and the mixture was heated under reflux at 40°C for 18 hours. After the reaction, the solvent was removed by vacuum distillation, 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. 5.87 g (44.5 mmol) of the nucleophile N-3 (2-methylbenzimidazole, Tokyo Chemical Industries) was added to stop polymerization, 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 in which the ion exchange resin Dowex (manufactured by Wako Pure Chemical Industries, Ltd.) was dispersed. 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) Ionic liquid precursors P-9 and P-10 were synthesized in the same manner as ionic liquid precursor P-8, except that the types and amounts of nucleophiles and electrophiles used in the reaction were changed as shown in Table 4.

[0084] (Synthesis of ionic liquid precursor P-11) 19 g (80 mmol) of 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, and the mixture was reacted at room temperature for 3 hours. After liquid-liquid extraction in ethyl acetate / water and drying, a compound was obtained in which the hydroxyl group of Q-6 was silylated. 8.55 g (54 mmol) of nucleophile N-7 (3-bromopyridine, manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 400 ml of distilled THF under an inert atmosphere and cooled to -78°C in a dry ice / methanol bath. Subsequently, 23 ml (60 mmol) of n-butyllithium / hexane 2.6 mol / l solution (manufactured by Kanto Chemical Co., Ltd.) was slowly added dropwise and stirred for 30 minutes. Subsequently, 50 ml of THF solution of silylated Q-6 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 dried to obtain 3-(10-hydroxydecyl)pyridine 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 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 the synthesis of ionic liquid precursor P-11, except that the nucleophile and electrophile used in the reaction were changed as shown in 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 reduced pressure distillation. The mixture was then purified by silica gel column chromatography (ethyl acetate) to obtain a compound in which the nucleophile had been tertiarily converted. Subsequently, the obtained compound was dissolved in 50 ml of dichloromethane, and 17.1 g (0.11 mmol) of the electrophile Q-8 (iodoethane, 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 vacuum distillation, and after washing with diethyl ether, 4,5-dibromoethylbutylimidazolium iodide was obtained as a white powder. This compound was then dissolved in 300 ml of distilled THF under a nitrogen atmosphere and cooled to -78°C in a dry ice / methanol bath. Subsequently, 80 ml of n-butyllithium / hexane 2.6 M solution (manufactured by Kanto Chemical Co., Ltd.) was slowly added dropwise, and the mixture was stirred for 30 minutes. Next, 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 by vacuum distillation, the mixture was separated with ethyl acetate / water, and ionic liquid precursor P-16 was obtained as a white powder. The anion of P-16 is an 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 the synthesis of ionic liquid precursor P-16, except that the nucleophiles and electrophiles A to C used in the reaction were changed as shown in Table 6.

[0088] (Synthesis of Ionic Liquid C-1) 7.7 g (33 mmol) of ionic liquid precursor P-1 was dissolved in 50 ml of dichloromethane. 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. This organic layer was separated twice with water, and the dichloromethane was removed by vacuum distillation 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]

[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 according to the volume. In all cases, 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.

[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 anion Y － This was as shown in Table 10.

[0092] For example, in the table, "C ２ H ４ The notation "OH" is CH ２ CH ２ It shows OH.

[0093]

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

[0095] (Example 1) <Preparation of Composite Material> The manufacturing method of the composite material is described below. The following materials were weighed to constitute the composite material, with a CNT content of 10% by mass: ・CNT: 3.0 g of ZEONANO SG101 manufactured by Zeon ・Ionic liquid: 27.0 g of ionic liquid C-1 In order to bring the CNT and ionic liquid into contact and blend them without applying shear force, the above materials were placed in a plastic container and the container was vacuum-degassed to obtain a mixture. To defibrate the CNT by applying shear force to the mixture, an open roll device (6 inches each of the front and rear rolls manufactured by Kansai Roll) was used. This device applies shear force to the object by passing it through the gap between the two front and rear rolls while they rotate. 30 g of the mixture was kneaded for 30 minutes under conditions of a roll gap of 1 mm, a front roll rotation speed of 10 rpm, and a rear roll rotation speed of 8 rpm 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 an H-NMR spectrometer (AVANCE III 500, Bruker Biospin) and an LC / MS spectrometer (UltiMate 3000 / LCQ FLEET, Thermo Fisher Scientific). Specifically, the analysis was performed under the following conditions. １H 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 Acclam Trinity P1 3 μm 2.1 × 100 mm column (Thermo Fisher Scientific), with a column temperature of 30°C, mobile phase A: acetonitrile, mobile phase B: 100 mM ammonium formate aqueous solution (pH 5.0), mobile phase C: pure water, flow rate: 0.5 mL / min, detector: Corona Veo & PDA (190–800 nm), injection volume: 10 μL, and ionization ESI. The obtained charts were analyzed using the instrument's dedicated software. It was confirmed that the structure of the ionic liquid in composite material M-1 was identical to that of ionic liquid C-1 and possessed the structure of formula (1) above.

[0097] <Observation and length evaluation of CNTs in composite materials> This analysis was performed to confirm the lengths of CNTs in the short and long side directions. (Measurement of length in the short side direction) The length in the short side direction was measured by obtaining surface images of 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 at a resolution of 1024 pixels or higher. 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° so that curved CNTs were also counted 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 program, 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 CNT fibrillation) As fibrillation progresses in the composite material, the length in the short-side direction of the 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 fibrillation has progressed. In this disclosure, it was determined that fibrillation of the CNTs had progressed if the length in the short-side direction of the CNTs was 50 nm or less, and that fibrillation had not progressed if the length in the short-side direction exceeded 50 nm. In composite material M-1, the length in the short-side direction of the CNTs was 5.1 nm, confirming that fibrillation had progressed.

[0101] (Measurement of length in the long side direction) The length in the long side direction of the CNTs was calculated by obtaining CNT images using a scanning electron microscope (Zeiss FE-SEM ULTRA55) and then performing image analysis. The measurement of the length in the long side direction was performed to confirm whether or not CNT breakage 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 samples. 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 attached to the tip of a 2 mm diameter resin rod and collected from the CNT aggregate area, and placed on a glass substrate 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, more than the measurement of the short side length. 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 such a way that there was 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 from 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 of the lengths in the long side direction of the CNTs.

[0103] <Storage of composite materials under high temperature and high humidity conditions> To evaluate the degree of re-aggregation of CNTs in composite materials, the length of CNTs and the conductivity of evaluation samples made using the composite material were evaluated when the materials were left in a harsh environment.

[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 (a harsh environment) where molecular mobility is high and CNT aggregation is likely to progress. The composite material left under the above conditions was designated as M-1b. Two evaluation methods were performed to confirm whether or not CNT re-aggregation occurred in the composite material. The evaluation was performed after leaving the composite material in the harsh environment above, and then leaving it at room temperature of 25°C for 24 hours to allow the environmental influence to dissipate.

[0105] <Short-side length of CNTs after standing> To check the state of CNTs in the composite material after standing, the short-side length of the CNTs in the standing composite material M-1b was measured using the method described above and compared with the short-side length before standing. That is, the ratio of the short-side length after standing (after standing / before standing) to the short-side length before standing was calculated. If the above ratio is 2.00 or less, it can be judged that aggregation has been suppressed and therefore no re-aggregation was determined. On the other hand, if it exceeds 2.00, it was judged that re-aggregation has occurred. In M-1b, the above ratio was 1.00, and there was no re-aggregation.

[0106] <Preparation of urethane sheets using composite materials and measurement of resistivity> 10 g of composite material M-1 and 500 g of polyol (Actcol EP-550N, manufactured by Mitsui Chemicals) were added to a 2 L plastic container so that the mass of CNTs was 0.2 parts by mass per 100 parts by mass of polyol. 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 liquid was measured out, and more polyol was added so that the CNT concentration was 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. As a dispersant for urethane formation, silicone (NIAX SILICONE L-3640, manufactured by Momentive Performance Materials Japan LLC) was added in an amount of 0.4 parts by mass per 100 parts by mass of polyol. As catalyst 1, N-methylmorpholine (manufactured by Tokyo Chemical Industry Co., Ltd.) was added in an amount of 1.0 part by mass per 100 parts by mass of polyol. As catalyst 2, DABCO 33-LV (manufactured by Sigma-Aldrich) was added in an amount of 0.5 parts by mass per 100 parts by mass of polyol to obtain a slurry. Furthermore, isocyanate (Cosmonate™-20, manufactured by Mitsui Chemicals) was added in an amount calculated to be equivalent to the amount of NCO derived from the polyol in the obtained slurry. After the curing treatment, the solidified sample was removed from the mold and subjected to a secondary curing treatment at 140°C for 30 minutes to obtain urethane sheet T-1. In addition, urethane sheet T-1b was obtained using the same method as described above for the preparation of urethane sheet T-1, except that composite material M-1 was replaced with the previously left-to-set composite material M-1b.

[0108] The resistivity of the urethane sheets T-1 and T-1b was measured after leaving them at room temperature (25°C) for 24 hours. The resistivity was calculated by sandwiching the urethane sheet between Φ10 mm electrodes and measuring the current value when a 20 V DC voltage was applied using a tester (Fluke Digital Multimeter 177). The resistivity R of the urethane sheet T-1b after leaving the composite material was compared to the resistivity R of the urethane sheet T-1b before leaving the composite material. 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) ｂA 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 M2-23 were manufactured using the same 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-M-23 was found to be no different from that of ionic liquids C-1-C-23, and it was confirmed that they had the structure of formula (1) above. Defibration of CNTs was confirmed in each case, 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 it had been left to stand. The evaluation results for Examples 2-23 are shown in Tables 12 and 13.

[0111] 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. 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 the CNTs represent the numerical average of the lengths in each direction. For "fibrillation judgment," "present" indicates that fibrillation had progressed, and "absent" indicates that fibrillation had not progressed. "CNT short side length durability change" shows the ratio of the short side length of the CNTs after storage (after storage / before storage) to the short side length of the CNTs before storage. Regarding the resistivity notation in the table, for example, the notation "1.70E+04" means "1.70 × 10 ４ This indicates ".

[0112] (Example 24) 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 prepared using OCSiAl TUBALL 01RW02, which is a single-walled CNT, as the CNT, except that the evaluation was carried out in the same manner as in Example 1.

[0114] (Examples 26 and 27) Composite materials were 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 the above formula (2), and the cation structure R2 is C ２ H ５ OH, R3 is CH ３ Therefore, the R3 terminus does not have an OH group. That is, the nitrogen-containing heteroaromatic ring cation of the ionic liquid C-C1 has one substituent with a hydroxyl group at its terminus in the cation structure. 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 has the same structure as C-C1, and R2 is C ２ H ５ OH, R3 is CH ３ In this case, one end lacked an OH group. In composite material M-C1, the average number of CNT lengths 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 the urethane sheet T-C1b made using the composite material after standing was more than 10 times greater than that of the urethane sheet T-C1 made using the composite material before standing.

[0116] (Comparative Example 2) In creating 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 an analysis image created 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 of Comparative Example 2 showed no significant defibration of the CNTs. Furthermore, the resistivity R of the urethane sheet made using the composite material M-C2 was more than 100 times higher than that of Example 1, confirming the effect of the lack of CNT defibration. Therefore, the composite material had not reached a level where it was necessary to conduct an evaluation after standing, and the evaluation was terminated.

[0117] This disclosure is not limited to the embodiments described above, and various modifications and alterations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of this disclosure public. This application claims priority based on Japanese Patent Application No. 2025-016341, filed on 3 February 2025, the entire contents of which are incorporated herein by reference.

Claims

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 the following formula (1): 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. (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.) 　 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). (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.) (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.) 　 The composite material according to claim 2, wherein the ionic liquid is represented by formula (2). 　 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 according to claim 3. 　 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 or 4. 　 R2 and R3 are -CH ２ CH ２ The composite material according to any one of claims 3 to 5, wherein the composite material is OH. 　 The composite material according to any one of claims 1 to 6, 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 of the carbon nanotubes in the long-side direction is 10 μm or more and 2 mm or less. 　 The composite material according to any one of claims 1 to 7, wherein the carbon nanotube is a single-walled carbon nanotube. 　 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 the following formula (1): 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. (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.) 　 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). (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.) (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.) 　 The method for producing a composite material according to claim 10, wherein the ionic liquid is represented by formula (2). 　 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. 　 Anion X in equation (2) above － (CF ３ SO ２ ) ２ N － or (FSO ２ ) ２ N － A method for producing a composite material according to claim 11 or 12. 　 R2 and R3 are -CH ２ CH ２ A method for producing a composite material according to any one of claims 11 to 13, wherein the material is OH. A method for producing a composite material according to any one of claims 9 to 14, wherein the number average value of the length in the short-side direction of the carbon nanotube is 2 nm or more and 50 nm or less, and the number average value of the length in the long-side direction is 10 μm or more and 2 mm or less. 　 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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