JP5725799B2 - Nanocarbon aqueous dispersion, method for producing the same, and nanocarbon-containing structure - Google Patents

Description

  The present invention relates to a nanocarbon aqueous dispersion, a production method, and a nanocarbon-containing structure.

  Nanocarbons typified by carbon nanotubes are excellent in electrical conductivity, thermal conductivity, mechanical strength, thermal stability, and so on, and their application development research is actively conducted.

  However, since nanocarbon easily aggregates into bundles, entangled ropes or lumps due to strong van der Waals forces in the dispersion medium, there is a problem that separation, purification and handling are difficult. And especially in the carbon nanotube expected as a functional material, aggregation is remarkable and aggregation elimination is calculated | required strongly.

  Attempts have been made to isolate and disperse nanocarbons in the medium in order to eliminate aggregation in the dispersion medium and facilitate separation, purification and handling. The first approach is a method of facilitating dispersion in a medium by chemically modifying the end of the carbon nanotube with a hydrophilic group or a hydrophobic group. The second approach is a method using a substance (dispersant) that assists the affinity of the carbon nanotube in the medium.

  As the former, for example, a method is described in which a carbon nanotube is nitrated and then substituted with other groups and dispersed in water (Patent Document 1). The latter method is preferred because it may change physical properties.

  In the latter method, both an aqueous medium and a hydrophobic organic solvent have been studied as a medium, but the use of an aqueous medium is desired from the viewpoint of cost, toxicity, and environmental aspects.

  Examples of substances (dispersing agents) that assist the affinity of carbon nanotubes in an organic medium include polyimide (Non-patent Document 1), polybenzimidazole (Non-patent Document 2), and polyamic acid (Patent Document 1). Polymers are known.

  Examples of substances (dispersing agents) that help the affinity of carbon nanotubes in an aqueous medium include dodecylbenzenesulfonic acid, dodecylitaconate (Patent Document 3), and polycondensed aromatic surfactants (Patent Document). 4), surfactants such as nonionic surfactants containing a steroid skeleton (Patent Document 5); catechins (Patent Document 6), amphiphilic triphenylene derivatives (Patent Document 7), polyphenol-containing aqueous solutions (Patent Document 8) ), Amphiphilic π-conjugated compounds (Patent Document 9), pyrene derivatives (Non-Patent Document 3), porphyrin derivatives (Non-Patent Document 4) and other aromatic or heterocyclic compounds; polystyrene sulfonic acid (Patent Document 10), polysaccharides (Patent Document 11), hydrophilic polymers such as pyrene polymer (Non-Patent Document 5) and DNA (Non-Patent Document 6) are known.

  Carbon nanotubes isolated and dispersed in a medium using these dispersants are used for purification, separation of carbon nanotubes with different conductivity, formation of conductive films, etc., but the dispersant remains on the surface of the carbon nanotubes. There is a risk of reducing the electrical conductivity between the carbon nanotube and the carbon nanotube. Therefore, it is desirable to use a material that can be easily removed, does not adversely affect electrical conductivity even if it remains, or can disperse carbon nanotubes in a small amount, but can satisfy at least one of these. The substance has not been developed yet.

JP 2004-107657 A JP 2010-24127 A JP 2010-13312 A Japanese Patent Laying-Open No. 2005-263608 JP 2009-242126 A JP 2009-298625 A JP 2009-190940 A JP 2009-161393 A JP 2006-265151 A JP 2009-149832 A JP 2008-53607 A

Chem. Phys. Lett., 418, 115-118 (2006) Adv. Funct. Mater., 18. 1776 (2008). Chem. Lett., 6, 638-639 (2002). Chem. Phys. Lett. 378, 481-485 (2003). Trans. Mater. Research Soc. Jpn., 29, 525-528 (2004). Chem. Lett., 32, 456 (2003).

  An object of the present invention is to provide a nanocarbon aqueous dispersion that can disperse nanocarbons in an aqueous solvent by an extremely low concentration dispersant and a method for producing the same. It is another object of the present invention to provide a nanocarbon-containing structure having high electrical conductivity obtained by removing water from the nanocarbon aqueous dispersion.

  As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved when the polyamic acid salt is employed as a nanocarbon dispersant, and has completed the present invention.

That is, this invention relates to the following nanocarbon aqueous dispersion, its manufacturing method, and a nanocarbon containing structure.
1. An aqueous nanocarbon dispersion comprising a polyamic acid salt, nanocarbon and an aqueous solvent.
2. The polyamidate is a salt of a polycondensate composed of 9,9-bis (4-aminophenyl) fluorene and an aromatic tetracarboxylic dianhydride and an alkali metal or an organic amine. Nanocarbon water dispersion.
3. Item 3. The nanocarbon aqueous dispersion according to Item 1 or 2, wherein the nanocarbon is a single-walled or multi-walled carbon nanotube.
4). Step 1 for preparing a composition by mixing nanocarbon with an aqueous solvent containing a polyamic acid salt, and Step 2 for subjecting the composition to a physical dispersion treatment.
A method for producing a nanocarbon aqueous dispersion, comprising:
5). 4. A nanocarbon-containing structure, which is a dried product of the nanocarbon aqueous dispersion according to any one of Items 1 to 3.
6). Item 6. The nanocarbon-containing structure according to Item 5, wherein the dried body is heat-treated.

  Hereinafter, the present invention will be described in detail.

  The nanocarbon aqueous dispersion of the present invention is characterized by containing a polyamic acid salt, nanocarbon and an aqueous solvent.

  The nanocarbon aqueous dispersion of the present invention having the above-described characteristics can disperse nanocarbons in an aqueous solvent in an extremely low concentration by using a polyamic acid salt as a dispersant. In addition, since separation and purification of nanocarbon from the nanocarbon aqueous dispersion is easy, and nanocarbon can be uniformly mixed with other materials, it can be applied to nanocomposites containing nanocarbon. Furthermore, the nanocarbon-containing structure, which is a dried product of the nanocarbon aqueous dispersion, has high electrical conductivity even when the dispersant remains, and thus can be applied to various optical / electronic devices. .

Nanocarbon aqueous dispersion and production method thereof Nanocarbon used in the present invention is not limited, and known single-walled or multi-walled carbon nanotubes can be used. Specifically, for example, the following can be exemplified.
(i) single-walled carbon nanotubes,
(ii) amorphous nanoscale carbon tube,
(iii) a carbon tube selected from the group consisting of nano flake carbon tubes and nested multi-walled carbon nanotubes, or
(iv) An iron-carbon composite comprising the carbon tube of the above (iii) and iron carbide or iron, wherein iron carbide or iron is filled in a range of 10 to 90% of the space in the tube of the carbon tube.
<Carbon nanotube>
A carbon nanotube is a hollow carbon material in which a graphite sheet (that is, a carbon atom plane or graphene sheet of a graphite structure) is closed like a tube, its diameter is nanometer scale, and the wall structure has a graphite structure. . Among the carbon nanotubes, one with a single graphite sheet whose wall structure is closed in a tube shape is called a single-walled carbon nanotube, and a plurality of graphite sheets are each closed in a tube shape and are nested. It is called a multi-walled carbon nanotube with a nested structure. In the present invention, any of these single-walled or multi-walled carbon nanotubes can be used.

  The single-walled carbon nanotube preferably has a diameter of about 0.4 to 10 nm and a length of about 1 to 500 μm, more preferably has a diameter of about 0.7 to 5 nm and a length of about 1 to 100 μm. Those having a length of about 0.7 to 2 nm and a length of about 1 to 20 μm are preferable.

The multi-walled carbon nanotube preferably has a diameter of about 1 to 100 nm and a length of about 1 to 500 μm, more preferably has a diameter of about 1 to 50 nm and a length of about 1 to 100 μm. Those having a length of about 40 nm and a length of about 1-20 μm are preferred.
<Amorphous nanoscale carbon tube>
An amorphous nanoscale carbon tube is described in WO00 / 40509 (Patent No. 3355442), has a main skeleton made of carbon, has a diameter of 0.1 to 1000 nm, and has an amorphous structure. In the X-ray diffraction method (incident X-ray: CuKα), the plane interval (d002) of the carbon mesh plane (002) measured by the diffractometer method is 3.54 mm or more, particularly 3.7 mm. The diffraction angle (2θ) is 25.1 degrees or less, particularly 24.1 degrees or less, and the full width at half maximum of the 2θ band is 3.2 degrees or more, particularly 7.0 degrees or more.

  Amorphous nanoscale carbon tubes are nanoscale carbon nanotubes having an amorphous structure (amorphous structure), are hollow linear, and have highly controlled pores. The shape is mainly a cylinder, a quadrangular prism, etc., and at least one of the tips often has no cap (open). When the tip is closed, the shape is often flat.

  The outer diameter of the amorphous nanoscale carbon tube is usually in the range of about 1 to 1000 nm, preferably in the range of about 1 to 200 nm, and more preferably in the range of about 1 to 100 nm. The aspect ratio (tube length / diameter) is 2 times or more, preferably 5 times or more.

  Here, “amorphous structure” means a carbonaceous structure consisting of an irregular carbon network plane, not a graphite structure consisting of a continuous carbon layer of regularly arranged carbon atoms. The graphene sheets are irregularly arranged, and the atomic arrangement is irregular. From an image obtained by a transmission electron microscope, which is a typical analysis technique, the nanoscale carbon tube having an amorphous structure according to the present invention has a spread in the plane direction of the carbon network plane that is one time larger than the diameter of the amorphous nanoscale carbon tube. small. As described above, the amorphous nanoscale carbon tube has an amorphous structure in which a large number of fine graphene sheets (carbon network surface) are irregularly distributed instead of a graphite structure on the wall portion, and therefore constitutes the outermost layer. The carbon mesh surface is not continuous over the entire length in the tube longitudinal direction but is discontinuous. In particular, the length of the carbon network surface constituting the outermost layer is less than 20 nm, particularly less than 5 nm.

  Amorphous carbon generally does not exhibit X-ray diffraction, but exhibits broad reflection. In the graphitic structure, the carbon mesh planes are regularly stacked, so the carbon mesh plane spacing (d002) is narrowed, and the broad reflection shifts to the high angle side (2θ) and becomes gradually sharper (half the 2θ band). The value range becomes narrower), and it becomes observable as d002 diffraction lines (d002 = 3.354 mm if regularly stacked due to the graphite positional relationship).

  In contrast, an amorphous structure generally does not exhibit X-ray diffraction as described above, but partially exhibits very weak coherent scattering. The theoretical crystallographic properties of the amorphous nanoscale carbon tube according to the present invention measured by the diffractometer method in the X-ray diffraction method (incident X-ray = CuKα) are defined as follows: carbon network plane The interval (d002) is 3.54 mm or more, more preferably 3.7 mm or more; the diffraction angle (2θ) is 25.1 degrees or less, more preferably 24.1 degrees or less; the half width of the 2θ band is 3.2 degrees or more, and more preferably 7.0 degrees or more.

  Typically, the amorphous nanoscale carbon tube has a diffraction angle (2θ) by X-ray diffraction in the range of 18.9 to 22.6 degrees, the carbon network plane spacing (d002) is in the range of 3.9 to 4.7 mm, The full width at half maximum of the 2θ band is in the range of 7.6 to 8.2 degrees.

The term “linear”, which is one term representing the shape of the amorphous nanoscale carbon tube, is defined as follows. That is, when the length of the amorphous nanoscale carbon tube image obtained by a transmission electron microscope is L and the length when the amorphous nanoscale carbon tube is extended is L ₀ , L / L ₀ is 0.9 or more. It shall mean shape characteristics.
<Iron-carbon composite>
The iron-carbon composite is described in JP-A No. 2002-338220, and (a) a carbon tube selected from the group consisting of a nano flake carbon tube and a multi-walled carbon nanotube with a nested structure; and (b) iron carbide or iron. The iron tube or iron of (b) is filled in the range of 10 to 90% of the space in the tube of the carbon tube (a). That is, it is not completely filled in the range of 100% of the space in the tube, but the metal or alloy is filled in the range of 10 to 90% of the space in the tube (that is, partially) It is characterized in that it is filled). The wall portion is a patchwork-like or machete-like (so-called paper mache-like) nano-flake carbon tube.

  The “nano flake carbon tube” is an aggregate of graphite sheets composed of a plurality of (usually many) flake-like graphite sheets assembled in a patchwork shape or a paper mache shape. Refers to a carbon tube.

  In the present invention, a polyamic acid salt is used as a nanocarbon dispersant. The polyamic acid salt can be adsorbed on the surface of the nanocarbon to disperse the nanocarbon in an aqueous solvent. Further, the polyamic acid salt has an advantage that even if it remains on the nanocarbon surface, it hardly affects the electrical conductivity of the nanocarbon.

  The polyamic acid salt is not limited, but is a salt of a polycondensate composed of 9,9-bis (4-aminophenyl) fluorene and an aromatic tetracarboxylic dianhydride and an alkali metal or organic amine. Is preferred. When an alkali metal salt is used, it cannot be converted into a polyimide even if the nanocarbon-containing structure is heat-treated, but when an organic amine salt is used, it can be converted into a polyimide by heat-treating.

  Examples of the alkali metal salt include sodium salt, potassium salt, lithium salt and the like.

  Examples of the organic amine salt include triethanolamine salt, diethanolamine salt, dimethylaminoethanol salt, and the like. Among these organic amine salts, a triethanolamine salt is preferable in consideration of dispersibility in an aqueous solvent.

  The content of the polyamic acid salt in the nanocarbon aqueous dispersion is not limited, but is preferably 0.01 to 50 wt%, more preferably 0.1 to 20 wt%. Moreover, in order to disperse | distribute nanocarbon favorably, 1-1000 weight part is preferable with respect to 100 weight part of nanocarbon, and 10-100 weight part is more preferable. In this invention, since it is also possible to use a polyamic acid or its salt as a binder, in that case, the quantity of the polyamic acid salt with respect to nanocarbon is not limited to the said range.

  Further, the content of the nanocarbon in the nanocarbon aqueous dispersion is not limited, but in the present invention, it can be dispersed at a high concentration up to about 20 wt%, preferably 0.01 to 10 wt%.

  In the present invention, an aqueous solvent is used as the nanocarbon dispersion medium of the nanocarbon aqueous dispersion.

  As the aqueous solvent, for example, water, ethanol, methanol, ethylene glycol or the like can be used. The content of the aqueous solvent in the nanocarbon aqueous dispersion is not limited, but may be adjusted so as to be the contents of the nanocarbon and the dispersant.

  In the nanocarbon aqueous dispersion of the present invention, the polyamic acid salt as a dispersant is adsorbed on the nanocarbon surface, and the nanocarbon can be isolated and dispersed in an aqueous solvent. In addition, it is easy to separate and purify nanocarbon from the nanocarbon aqueous dispersion.

  The method for producing the nanocarbon aqueous dispersion of the present invention is not limited, and the nanocarbon aqueous dispersion can be produced by mixing the above components, but can be suitably produced by using the following production method of the present invention.

  That is, a nanocarbon aqueous dispersion comprising a step 1 of preparing a composition by mixing nanocarbon with an aqueous solvent containing a polyamic acid salt and a step 2 of subjecting the composition to a physical dispersion treatment It can manufacture suitably with a manufacturing method. About the kind and content of each component in the manufacturing method of this invention, it is as above-mentioned.

  The physical dispersion treatment in the above step 2 can be performed by a known stirrer such as an ultrasonic homogenizer, a homogenizer, or a ball mill.

Nanocarbon-containing structure The nanocarbon-containing structure of the present invention is a dried product of the nanocarbon aqueous dispersion.

  In order to obtain a dried product, the nanocarbon-containing structure is recovered by ordinary solid-liquid separation. As a method of performing this separation, for example, a method used for usual solid-liquid separation, for example, a method of filtering using a filter paper, a glass filter or the like; a method of filtering after centrifugation; a method of using a vacuum filter A method of filtering or centrifuging the nanocarbon after agglomerating nanocarbon from the dispersion by making the pH of the dispersion acidic, adding salt or the like to the dispersion, or adding a large amount of alcohol to the dispersion, etc. can be exemplified. . Next, it does not specifically limit as a drying method, For example, the method of drying for about 1 to 24 hours at about 50-200 degreeC using a warm air dryer etc. can be illustrated.

  The nanocarbon-containing structure of the present invention hardly affects the electrical conductivity even if the dispersant remains on the nanocarbon surface, but if necessary, the nanocarbon-containing structure can be washed with a dilute acid. Salt can be removed.

Washing for removing the salt is performed by bringing the nanocarbon-containing structure into contact with the diluted acid and then washing with water. The diluted acid is preferably 0.1 to 5% hydrochloric acid. The washing operation may be performed by bringing the diluted acid and the nanocarbon-containing structure into contact with each other. For example, it is preferable to gently immerse the nanocarbon-containing structure recovered from the nanocarbon aqueous dispersion or a dried product thereof in a dilute acid at room temperature. The immersion time is 30 minutes, preferably within 20 minutes. If immersed for longer than 30 minutes, the structure may collapse.
The amount of the dilute acid used is not particularly limited as long as it is an amount effective for cleaning, and can be appropriately selected from a wide range.In general, the cleaning solvent is used in an amount of 100 to 100 parts by weight of the nanocarbon-containing structure. Good results are obtained when about 100000 parts by weight, especially about 1000 to 5000 parts by weight are used.

  The nanocarbon-containing structure of the present invention may be subjected to heat treatment as necessary. When the dispersant is an organic amine salt, the polyamic acid salt becomes a polyimide by heat treatment, improving the heat resistance and mechanical properties of the nanocarbon-containing structure (composite of nanocarbon and polyimide). Can be made. Such a composite of nanocarbon and polyimide can be used as a heat-resistant conductive material having no anisotropy. The conditions for the heat treatment are not limited, but when polyimidizing, it is preferable to perform the heat treatment at about 200 to 300 ° C. for about 1 to 12 hours.

  The nanocarbon aqueous dispersion of the present invention can disperse nanocarbons in an aqueous solvent in an aqueous solvent at a very low concentration by using a polyamic acid salt as a dispersant. In addition, since separation and purification of nanocarbon from the nanocarbon aqueous dispersion is easy, and nanocarbon can be uniformly mixed with other materials, it can be applied to nanocomposites containing nanocarbon. Furthermore, the nanocarbon-containing structure, which is a dried product of the nanocarbon aqueous dispersion, has high electrical conductivity even when the dispersant remains, and thus can be applied to various optical / electronic devices. .

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples.

Example 1
(Synthesis of polyamic acid)
To the three-necked separable flask, 8.71 g of 9,9-bisaniline fluorene (BAF, manufactured by JFE Chemical Co., Ltd.) was added, and 75.04 g of dried N-methylpyrrolidone (NMP) was further added.

  This solution was bubbled with nitrogen, 5.74 g of pyromellitic anhydride (PMDA) was added with stirring at 0 ° C., stirred for 2 hours with a mechanical stirrer, and then stirred at room temperature for 17 hours.

The reaction solution was added dropwise to 1.5 liters of distilled water, and the resulting solid was washed with methanol and then dried to obtain 22.22 g of polyamic acid containing NMP. The weight average molecular weight of the polyamic acid was 37900, and the number average molecular weight was 6390.
(Preparation of polyamic acid salt)
0.5 g of polyamic acid was dissolved in 2 ml of 2-ethoxyethanol, and 0.1 g of triethanolamine was added thereto to precipitate a salt.

This salt was recovered by centrifugation and then dissolved in 100 ml of water.
(Dispersion of carbon nanotubes)
To 10 ml of the above polyamic acid aqueous solution, 0.1 g of carbon nanotubes (CNT) (NC7000 manufactured by Nanosil Co., Ltd.) was added and dispersed with an ultrasonic homogenizer (300 mA, 5 minutes).

  The resulting dispersion (CNT concentration 1wt% BPF weight: CNT weight = 0.5: 1) was diluted with water to prepare a CNT concentration 0.01wt% solution. When observed with a scanning electron microscope, CNTs were isolated and dispersed. Thus, it was confirmed that a small amount of the dispersant was 50 parts by weight with respect to 100 parts by weight of CNT.

Example 2
(Nanocarbon-containing structure)
A CNT aqueous dispersion (CNT concentration: 1 wt%, polyamic acid weight: CNT weight = 10: 1) obtained in the same manner as in Example 1 was applied on two glass plates, and then dried at 60 ° C. for 1 hour. Since the shrinkage of the coating film during drying was severe, when 5 wt% of ethylene glycol (EG) was added to the dispersion and dried, the shrinkage could be prevented. After drying at 60 ° C., it was further dried at 150 ° C. for 30 minutes. Furthermore, one sheet was heat-treated at 300 ° C. for 10 minutes.

  The surface resistance of the obtained cured film was measured with Loresta made by Mitsubishi Analitech.

  The surface resistance of the cured film was 1E + 03 Ω / □ when dried at 150 ° C, and 5E + 02 Ω / □ when heat-treated at 300 ° C. . From this result, it can be seen that good conductivity is maintained even when the degree of imidization increases at high temperatures.

Claims (5)

An aqueous nanocarbon dispersion comprising a polyamic acid salt, nanocarbon and an aqueous solvent, wherein the polyamic acid salt comprises 9,9-bis (4-aminophenyl) fluorene and an aromatic tetracarboxylic acid An aqueous nanocarbon dispersion which is a salt of a polycondensate comprising a dianhydride and an alkali metal or an organic amine. The nanocarbon aqueous dispersion according to claim 1, wherein the nanocarbon is a single-walled or multi-walled carbon nanotube. Step 1 for preparing a composition by mixing nanocarbon with an aqueous solvent containing a polyamic acid salt, and Step 2 for subjecting the composition to a physical dispersion treatment.
The method for producing an aqueous nanocarbon dispersion according to claim 1 or 2, wherein: A nanocarbon-containing structure, which is a dried product of the aqueous nanocarbon dispersion according to claim 1 or 2. The nanocarbon-containing structure according to claim 4, wherein the dried product is heat-treated.