JP6822124B2 - Method for producing surface-modified carbon nanotubes and its dispersion - Google Patents

Description

The present invention relates to a method for producing surface-modified carbon nanotubes in which the mixed acid treatment temperature is controlled to increase conductivity, and a dispersion liquid thereof.

Carbon nanotubes were first widely reported in 1991. The carbon nanotube has a shape in which one surface of graphite is wound into a tubular shape, and the one wound in one layer is called a single-walled carbon nanotube, and the one wound in multiple layers is called a multi-walled carbon nanotube. Among the multi-walled carbon nanotubes, those wound in two layers are called double-walled carbon nanotubes. Carbon nanotubes themselves have excellent intrinsic conductivity and are expected to be used as conductive materials.

As a method for producing carbon nanotubes, an arc discharge method, a laser evaporation method, a chemical vapor deposition method and the like are known. Among the chemical vapor deposition methods, a catalytic chemical vapor deposition method in which a catalyst is supported on a carrier is known.

Among carbon nanotubes, single-walled carbon nanotubes are known to have high properties such as conductivity and thermal conductivity because they have a high graphite structure. However, since the single-walled carbon nanotubes have a strong and very thick bundle structure, the nano-effects of each carbon nanotube cannot be exhibited, and it is difficult to develop various applications. In particular, since it is extremely difficult to disperse in a resin or a solvent, it is not possible to exhibit the expected high characteristics, and the current situation is that development into various applications is hindered. In particular, it has been difficult to demonstrate practical performance by using carbon nanotubes for applications such as transparent conductive films, molded products, and membranes.

Among multi-walled carbon nanotubes, 2-5-walled carbon nanotubes, which have a relatively small number of layers, have the characteristics of both single-walled carbon nanotubes and multi-walled carbon nanotubes, and therefore are attracting attention as promising materials in various applications. Are collecting. Among them, two-walled carbon nanotubes are considered to have the best characteristics, and several synthetic methods have been developed. Recently, the method of Endo et al. Is known as a method for synthesizing high-purity two-walled carbon nanotubes (Non-Patent Documents 1, 2 and 3) (Patent Document 1). In this method, a two-walled carbon nanotube is synthesized by arranging an iron salt as a main catalyst and a molybdate as an auxiliary catalyst and reacting the carbon sources. Further, as the use of the two-walled carbon nanotubes obtained here, the use as a field emitter used at a high current is described because the two-walled carbon nanotubes have high thermal stability.

However, it is difficult to disperse carbon nanotubes because high-quality two-walled carbon nanotubes form a strong bundle due to hydrophobic interactions between tubes and interactions between π electrons, similar to single-walled carbon nanotubes. It is believed that. It is considered that the two-walled carbon nanotubes of Endo et al. Also form a strong and thick bundle. Indirect evidence of having a strong and thick bundle structure is the heat resistance of the carbon nanotube aggregate. It is presumed that the carbon nanotube aggregate having high heat resistance forms a thicker bundle structure (Non-Patent Document 3). The heat resistance of carbon nanotubes can be determined by the peak combustion temperature in air. Combustion in air is considered to be an oxidation reaction due to the attack of oxygen molecules.

Even if the carbon nanotubes are the same one by one, in a bundle with a thick bundle, that is, a bundle in which more carbon nanotubes are gathered, the inner carbon nanotubes are less susceptible to oxygen attack, so that an oxidation reaction occurs. It becomes difficult and the peak combustion temperature of the carbon nanotube aggregate rises. On the contrary, in a bundle in which the bundle is thin, that is, in which a small number of carbon nanotubes are aggregated, it is considered that the combustion peak temperature of the carbon nanotube aggregate is lowered because the inner carbon nanotubes are also easily attacked by oxygen.

The carbon nanotubes described in Non-Patent Documents 1, 2, 3 and 1 are manufactured by the same synthetic method, and as described in Non-Patent Document 2, their combustion peak temperature is as high as 717 ° C. These carbon nanotubes are considered to form a tightly thick bundle, which is not satisfactory when a high degree of dispersibility is required.

On the other hand, multi-walled carbon nanotubes having a larger number of layers than the above generally have a large diameter, many defects in the graphite layer, and are more difficult to bundle than carbon nanotubes having a smaller number of layers, and thus have excellent dispersibility. However, since such multi-walled carbon nanotubes are inferior in quality, it is difficult to demonstrate practical performance in applications such as transparent conductive films, molded products, and films that require excellent light transmittance and surface resistance. there were.

Currently, various carbon nanomaterials typified by carbon nanotubes are being developed. For example, conductive fillers, heat conductive materials, light emitting elements, electrode materials for batteries and capacitors, wiring materials, electrode bonding materials for wiring, and reinforcing materials. , Black pigment, etc., are promising as materials having various functions in various applications.

However, in general, carbon nanomaterials form aggregates in the as-manufactured state, and it is very difficult to make them sufficiently dispersed in a solvent. Therefore, there is a problem that the characteristics cannot be sufficiently exhibited when the product is made.

Conventionally, as a means for improving the dispersibility of carbon nanomaterials, for example, an acidic suspension of fine carbon fibers to which an oxidizing agent is added to oxidize the surface (Patent Document 2), nitric acid or nitric acid and sulfuric acid are used. A COOM group introduced by wet oxidation using a mixed acid (Patent Document 3), or a nitro group introduced by ultrasonic treatment in fuming nitric acid or a mixed acid of fuming nitric acid and concentrated sulfuric acid (Patent Document 4). ), Mixed acid oxidation treatment at 100 ° C. or higher (Patent Document 5) and the like are known.

However, these conventional examples have problems that the conductivity deteriorates due to the cutting of carbon nanotubes by excessive oxidation treatment, the oxidation treatment is insufficient and the dispersibility is inferior, and the dispersion medium is organic in nitration. There is a problem that the dispersibility of carbon nanotubes is not sufficient when the concentration is high as a solvent, and the carbon nanotubes are destroyed by the oxidation treatment at high temperature, and the dispersibility is improved but the conductivity is lowered. there were.

Japanese Unexamined Patent Publication No. 2005-343726 Japanese Unexamined Patent Publication No. 2008-270204 Japanese Unexamined Patent Publication No. 2008-251272 Japanese Unexamined Patent Publication No. 2010-24127 International release WO2013 / 047871

Nature, vol. 433,476 (2005) Chemical Physics Letters, 414 (2005) 444-448 Journal of the American Chemical Society, 128 (2006) 12 636-12637

The present invention solves the above-mentioned problems, and comprises a surface-modified carbon nanotube having excellent dispersibility and high conductivity, a dispersion liquid containing the surface-modified carbon nanotube and not requiring a dispersant, and further. Is to provide a coating composition and a paste composition produced by these dispersions.

That is, the present invention is a surface-modified carbon nanotube that is an oxide of carbon nanotubes, and has an average particle diameter D50 of 1 to 50 μm and a volume resistivity of 0.1 to 0.01 Ω · cm. Regarding.

The present invention also relates to a method for producing surface-modified carbon nanotubes, in which carbon nanotubes are oxidized at a temperature of 60 ° C. or lower using a mixed acid composed of nitric acid and sulfuric acid having a concentration of 60 to 70% by mass.

The present invention also relates to a carbon nanotube dispersion liquid containing the above-mentioned surface-modified carbon nanotubes and one or more dispersion media composed of a polar solvent.

The present invention also relates to a composition containing the above-mentioned carbon nanotube dispersion liquid and a binder.

The present invention also relates to a coating film formed from the above composition.

Compared with the conventional case, the surface-modified carbon nanotube of the present invention can be uniformly dispersed even at a high concentration, particularly when dispersed in a polar solvent. Further, by using a coating composition or a paste composition using the dispersion liquid of the surface-modified carbon nanotubes, a conductive coating film having excellent conductivity can be easily formed.

Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following examples.

The surface-modified carbon nanotubes of the present invention are characterized in that they are oxidized at 60 ° C. or lower using a mixed acid composed of nitric acid and sulfuric acid having a concentration of 60 to 70% by mass, and have an average particle diameter D50 of 1 to 50 μm and volume resistivity. It is a surface-modified carbon nanotube characterized by having a ratio of 0.1 to 0.01 Ω · cm.

When the carbon nanotubes are oxidized using a mixed acid of nitric acid and sulfuric acid, the higher the mixed acid temperature, the more the carbon nanotubes are decomposed, the average particle size D50 becomes smaller, and the dispersibility in a polar solvent is improved.

However, when the decomposition of carbon nanotubes progresses and the average particle size D50 becomes smaller, there is an adverse effect that the conductivity is lowered. In order to maintain conductivity, it is necessary to set the average particle size D50 to 1 μm or more, and as a result of examining the mixed acid oxidation conditions for maintaining this particle size, the average particle size D50 was obtained by performing the mixed acid treatment at 60 ° C. or lower. Can be maintained at 1 μm or more.

The mixed acid treatment temperature may be such that the carbon nanotube raw material is immersed in a mixed acid of nitric acid and sulfuric acid and reacted at a temperature of 60 ° C. or lower. The liquid temperature is preferably 60 to 20 ° C, more preferably 60 to 40 ° C. At a liquid temperature of 100 ° C. or higher, the decomposition of carbon nanotubes proceeds, and the average particle size D50 tends to be 1 μm or less.

The preferable reaction time of the mixed acid treatment is, for example, 2 to 8 hours, but the reaction time is not limited to this range. The mixture during the oxidation treatment is preferably kept agitated.

In the above oxidation treatment, the mass ratio of the mixed acid of nitric acid and sulfuric acid to the carbon nanotube raw material is appropriately in the range of 50 to 100 parts by mass of the mixed acid with respect to 1 part by mass of the carbon nanotube raw material.

By performing the oxidation treatment in which the treatment temperature conditions of the mixed acid are adjusted as described above, the surface of the carbon nanotubes is subjected to a carboxyl group (-COOH), a carbonyl group (> C = O), an ether group (CO-C), and phenol. A sex hydroxyl group (-OH) or the like is introduced.

The surface-modified carbon nanotube of the present invention refers to a carbon nanotube in which a carboxyl group (-COOH) and a phenolic hydroxyl group (-OH), which are acidic substituents, are bonded to the surface of the carbon nanotube.

During the production of carbon nanotubes, they exist in the form of separate nanotubes or aggregates of nanotubes, which are randomly entwined with each other to form entangled balls similar to bird's nests. Further details regarding the formation of this carbon nanotube agglomerate were filed in Tennent's US Pat. No. 5,165,909, Moy et al., US Pat. No. 5,456,897, and Snyder et al., May 1, 1991. US Pat. Nos. 5,707,916, and PCT Application Nos. US89 / 00322, WO89 / 07163, filed January 28, 1989, and Moy et al., Filed August 2, 1994. US Pat. Nos. 5,456,897 and PCT Application US90 / 05489, WO91 / 05089, filed September 27, 1990, and Mandeville et al., US Pat. No. 5,500, filed June 7, 1995, Explained in the disclosure of US Pat. Nos. 200 and US Pat. No. 5,456,897 filed August 2, 1994 and US Pat. No. 5,569,635 filed October 11, 1994 by Moy et al. ing.

The average particle size D50 shown in the specification of the present application indicates not the diameter of carbon nanotubes but the size of aggregates. Carbon nanotubes generally exist in the form of aggregates. This can be solved by treating it with a mixed acid.

The size of the aggregates of the carbon nanotubes can be measured by a laser diffraction type particle size distribution measuring device. Specifically, there is an analyzer such as Mastersizer2000.

When the average particle size D50 of the carbon nanotubes is 1 μm or more, the connection between the carbon nanotubes in the dispersion liquid or the coating film state is maintained, and the conductivity becomes good. Therefore, the average particle size D50 of the surface-modified carbon nanotubes is preferably 1 to 50 μm as the average particle size D50 that maintains the conductivity in the dispersion liquid or the coating film state and maintains the dispersibility in the polar solvent.

Carbon nanotubes are characterized by high structural conductivity. For example, the volume resistivity of FloTube9100 (multi-walled carbon nanotubes manufactured by CNano) measured by Lorester GP manufactured by Mitsubishi Chemical Corporation is 0.015 Ω · cm. ..

However, the volume resistivity of the surface-modified carbon nanotubes produced by the oxidation treatment using a mixed acid composed of nitric acid and sulfuric acid increases as the average particle size D50 decreases. Therefore, the volume resistivity of the surface-modified carbon nanotubes that maintain the dispersibility in the polar solvent and maintain the conductivity in the dispersion liquid or the coating film state is 0.1 Ω · cm or less.

By dispersing the surface-modified carbon nanotubes in one or more dispersion media selected from polar solvents such as alcohol, a dispersion liquid having excellent dispersibility of carbon nanotubes can be obtained.

As an apparatus used to obtain the dispersion liquid of the present invention, a disperser or a mixer usually used for pigment dispersion or the like can be used.

For example, mixers such as disper, homomixer, or planetary mixer; homogenizers such as "Clearmix" manufactured by M-Technique or "Philmix" manufactured by PRIMIX; Scandex (manufactured by Scandex Co., Ltd.), Paint Media type disperser such as conditioner (manufactured by Red Devil), ball mill, sand mill (manufactured by Simmal Enterprises "Dyno mill", etc.), attritor, pearl mill (manufactured by Erich "DCP mill", etc.), or coball mill; Mills ("Genus PY" manufactured by Genus, "Starburst" manufactured by Sugino Machine, "Nanmizer" manufactured by Nanomizer, etc.), "Claire SS-5" manufactured by M-Technique, or "MICROS" manufactured by Nara Machinery Co., Ltd. Medialess disperser; or other roll mills and the like, but are not limited thereto.

As a method for producing the dispersion liquid, when a media type disperser is used, a method using a disperser in which the agitator and the vessel are made of ceramic or resin, or a method in which the surface of the metal agitator and the vessel is sprayed with tungsten carbide or resin. It is preferable to use a disperser that has been treated with a coating or the like. As the medium, it is preferable to use glass beads, zirconia beads, or ceramic beads such as alumina beads. Also, when a roll mill is used, it is preferable to use a ceramic roll. As the disperser, only one type may be used, or a plurality of types of devices may be used in combination.

A coating composition or a paste composition can be obtained by adding a binder component (resin component) to the carbon nanotube dispersion liquid of the present invention. In such a composition, since the resin component is insulating, if the amount of the resin component is large and the amount of the surface-modified carbon nanotubes is small, the conductivity of the composition decreases, but the surface-modified carbon nanotubes of the present invention Since it has good dispersibility, it exhibits high conductivity even with a small content, and a good conductive coating film can be obtained.

Preferred compositions of the coating composition or paste composition include, for example, a composition containing 30 to 94% by mass of a polar solvent, 1 to 8% by mass of surface-modified carbon nanotubes, and 5 to 60% by mass of a binder component. In addition to the polar solvent, a non-polar solvent may be contained if necessary, or other components necessary for a coating composition or a paste composition may be added.

As the wet mixing device, for example, mixers such as a dispenser, a homomixer, or a planetary mixer;
Homogenizers such as "Clearmix" manufactured by M-Technique or "Philmix" manufactured by PRIMIX;
Scandex (manufactured by Scandex Co., Ltd.), paint conditioner (manufactured by Red Devil), ball mill, sand mill (manufactured by Simmal Enterprises "Dyno Mill", etc.), Atwriter, Pearl Mill (manufactured by Erich, etc. "DCP Mill") Or a media type disperser such as a coball mill;
Wet jet mill (Genus PY manufactured by Genus, Starburst manufactured by Sugino Machine, Nanomizer manufactured by Nanomizer, etc.), Claire SS-5 manufactured by M-Technique, Micros manufactured by Nara Machinery Co., Ltd. Medialess disperser such as "; other roll mills, kneaders, etc., but are not limited to these. Further, as the wet mixing apparatus, it may be preferable to use an apparatus that has been subjected to a metal contamination prevention treatment from the apparatus.

For example, when using a media type disperser, a method of using a disperser in which the agitator and the vessel are made of ceramic or resin, or a disperser in which the surface of the metal agitator and the vessel is treated with tungsten carbide spraying or a resin coating or the like. Is preferably used. As the medium, it is preferable to use glass beads, zirconia beads, or ceramic beads such as alumina beads. When a roll mill is used, it is preferable to use a ceramic roll. As the disperser, only one type may be used, or a plurality of types of devices may be used in combination. Further, in order to improve the wettability and dispersibility of the raw material in the solvent, a dispersant having a general hydrophilic functional group can be added together, dispersed and mixed.

In the case where each raw material does not dissolve uniformly during wet mixing, a commercially available dispersant is added together, dispersed and mixed in order to improve the wettability and dispersibility of each raw material in a solvent. May be good. As the dispersant, an aqueous dispersant and a solvent-based dispersant can be used, and specific examples thereof include the following.

Commercially available aqueous dispersants are not particularly limited, and examples thereof include the following.
Examples of the dispersant manufactured by Big Chemie include Disperbyk-180, 183, 184, 185, 187, 190, 191 and 192, 193, 198, 2090, 2091, 2095, 2096, and BYK-154.
Examples of the dispersant manufactured by Japan Lubrizol Co., Ltd. include SOLPERSE 12000, 20000, 27000, 41000, 41090, 43000, 44000, 45000 and the like.
Examples of the dispersant manufactured by Fuka Additives include EFKA1101, 1120, 1125, 1500, 1503, 4500, 4510, 4520, 4530, 4540, 4550, 4560, 4570, 4580, and 5071.
BASF Japan's dispersants include JONCRYL67, 678, 586, 611, 680, 682, 683, 690, 52J, 57J, 60J, 61J, 62J, 63J, 70J, HPD-96J, 501J, 354J, 6610, PDX-6102B, 7100, 390, 711, 511, 7001, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX-7630, 352J, 252D, 538J, 7640, Examples thereof include 7641, 631, 790, 780, 7610, JDX-C3000, JDX-3020, or JDX-6500. In addition, Luvitec K17, K30, K60, K80, K85, K90, K115, VA64W, VA64, VPI55K72W, VPC55K65W and the like can be mentioned.
Examples of the dispersant manufactured by Kawaken Fine Chemicals Co., Ltd. include Hinoact A-110, 300, 303, 501 and the like.
Examples of the dispersant manufactured by Nittobo Medical Co., Ltd. include PAA series, PAS series, amphoteric series PAS-410C, 410SA, 84, 2451, 2351 and the like.
Examples of the dispersant manufactured by ASP Japan include polyvinylpyrrolidone PVP K-15, K-30, K-60, K-90, K-120 and the like.
Examples of the dispersant manufactured by Maruzen Petrochemical Co., Ltd. include polyvinyl imidazole PVI.

The commercially available solvent-based dispersant is not particularly limited, and examples thereof include the following.
Dispersants manufactured by Big Chemie include Anti-Terra-U, U100, 203, 204, 205, Disperbyk-101, 102, 103, 106, 107, 108, 109, 110, 111, 112, 116, 130, 140. , 142, 161, 162, 163, 164, 166, 167, 168, 170, 171, 174, 180, 182, 183, 184, 185, 2000, 2001, 2050, 2070, 2096, 2150, BYK-P104, P104S , P105, 9076, 9077, 220S and the like.
Dispersants manufactured by Japan Lubrizol Co., Ltd. include SOLSERSE3000, 5000, 9000, 13240, 13650, 13940, 17000, 18000, 19000, 21000, 22000, 24000SC, 24000GR, 26000, 28000, 31845, 32000, 32500, 32600, 33500. 34750, 35100, 35200, 36600, 37500, 38500, or 53095.
Dispersants manufactured by Fuka Additives include EFKA1500, 1501, 1502, 1503, 4008, 4009, 4010, 4015, 4020, 4046, 4047, 4050, 4055, 4060, 4080, 4300, 4330, 4400, 4401, Examples thereof include 4402, 4403, 4406, 4510, 4520, 4530, 4570, 4800, 5010, 5044, 5054, 5055, 5063, 5064, 5065, 5066, 5070, 5071, 5207, or 5244.
Examples of the dispersant manufactured by Ajinomoto Fine-Techno Co., Ltd. include Azisper PB711, PB821, PB822, PN411, or PA111.
Examples of the dispersant manufactured by Kawaken Fine Chemicals Co., Ltd. include Hinoact KF-1000, 1300M, 1500, 1700, T-6000, 8000, 8000E, 9100 and the like. Examples of the dispersant manufactured by BASF Japan Ltd. include Lavaca and the like.

In the present invention, the carbon nanotubes used have a multi-walled structure in which carbon nanotubes having a planar structure in which carbon atoms form a hexagon are weakly bonded by van der Waals force. Since carbon nanotubes have a planar structure with few defects, they exhibit high electron conductivity, high thermal conductivity, and high mechanical strength.
The thickness of the multi-walled carbon nanotube is not particularly limited, but is preferably a single-walled or more. If it is too thick, the electron conductivity and specific surface area will be low, which may be unfavorable.

Single-walled carbon nanotubes have a seamless cylindrical shape with a diameter in the nanometer region, and can be imagined as a rounded graphene sheet (two-dimensional graphite plane). The structure of the nanotube is defined by the diameter and the relative orientation of the 6-membered ring of carbon with respect to the axis of the tube. For example, Meijo Nanocarbon (EC1.0, EC1.5, EC2.0, EC1.5-P) and the like can be mentioned.

Multi-walled carbon nanotubes are composed of these concentric cylindrical tubes, and it is thought that several single-walled tubes are nested. They have a concentric multi-walled structure of 6 layers when there are few and about 25 layers when there are many. .. Therefore, the diameter of the multi-walled carbon nanotube shows a large value of 30 nm with respect to 0.7-2.0 nm of a typical single-walled carbon nanotube. The excellent and unique properties of carbon nanotubes make it possible to develop new applications and improve performance in existing applications. For example, CNano (FloTube9000, FloTube9100, FloTube9110, FloTube9200), Nanocycle (NC7000), Knano (100T) and the like can be mentioned.

The binder is preferably an aqueous resin, and examples thereof include acrylic urethane resin, isocyanate-based polyester resin, styrene acrylic resin, acrylic resin, polyester resin, polyurethane resin, polyolefin resin, and epoxy resin, but the binder is not limited thereto.

Examples of the water-based acrylic urethane resin include NeoPac: R-9699, R-9029, E-123, E-125 manufactured by DSM Coating Resins, and WEM-031U, WEM-200U, WEM-321U manufactured by Taisei Fine Chemicals Co., Ltd. , WEM-3000, WEM-290A and the like.
Examples of the isocyanate-based polyester resin include 11-408, D-210-80, D-161, J-517, D-128-65BA, D-144-65BA, and D-145-55BA manufactured by Dai Nippon Printing Co., Ltd. Can be mentioned.
Examples of the styrene acrylic resin include Almatex: 785-5, 749.5M, 749-17AE, 749-16AE manufactured by Mitsui Chemicals, Inc.
Examples of the acrylic resin include water-based acrylic resin emulsions such as Polymaron manufactured by Arakawa Chemical Industries, Ltd.
Examples of the polyurethane resin include Hydran manufactured by Dai Nippon Printing Co., Ltd .: HW-171, COR-70, HW-350 and the like.
Examples of the aqueous dispersion of the polyester resin include Byronal MD1245 (manufactured by Toyobo Co., Ltd.).
Examples of the polyolefin resin include surflen manufactured by Mitsubishi Chemical Corporation.
Examples of the epoxy resin include 825, 827, 828, 828EL, 828US, 828XA, 834 manufactured by Mitsubishi Chemical Corporation.

As the dispersion medium, water or a polar solvent having a high affinity for water is preferable, and alcohol is particularly preferable. As such an alcohol, for example, a monohydric alcohol or a polyhydric alcohol having a boiling point of about 80 to 200 ° C. can be used, and an alcohol solvent having 4 or less carbon atoms is preferable. Specific examples thereof include 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, propylene glycol and ethylene glycol.

Further, it is preferable to use one or more kinds of polar solvents, and specific examples thereof include a mixed solvent of water and ethanol, a mixed solvent of water and 2-propanol, a mixed solvent of water and propylene glycol, and a mixed solvent of water and dipropylene glycol. Examples thereof include a mixed solvent, a mixed solvent of water and DMF (N, N-dimethylformamide), a mixed solvent of water and NMP (N-methylpyrrolidone), and the like.

Hereinafter, examples of the present invention will be shown together with comparative examples. The present invention is not limited to these examples.

Example 1
As carbon nanotubes, multi-walled carbon nanotubes (FloTube9100) manufactured by CNano are used as raw materials, and commercially available concentrated nitric acid (concentration 60% by mass) and concentrated sulfuric acid (concentration 96% by mass) are used, and the surface is surfaced for 4 hours under the temperature conditions shown in Table 1. Oxidation treatment was performed to obtain surface-modified multilayer carbon nanotubes (hereinafter abbreviated as MW-CNT).
Table 1 shows the dispersed states of the 8% by mass aqueous dispersion and the 8% by mass DMF dispersion prepared by using the obtained surface-modified MW-CNT.

The 8 mass% aqueous dispersion was dispersed by Scandex, and its dispersibility was confirmed by a grind gauge. Good dispersion was rated as 〇, and poor dispersion was rated as x.

The 8 mass% DMF dispersion was dispersed by Scandex, and its dispersibility was confirmed by a grind gauge. Good dispersion was rated as 〇, and poor dispersion was rated as x.

Example 2
The test was carried out in the same manner as in Example 1 except that mixed acid oxidation was carried out at a reaction temperature of 50 ° C.

Comparative Example 1
The test was carried out in the same manner as in Example 1 except that mixed acid oxidation was carried out at a reaction temperature of 100 ° C.

Comparative Example 2
The test was carried out in the same manner as in Example 1 except that mixed acid oxidation was carried out at a reaction temperature of 120 ° C.

Table 1

Example 3
The surface-modified MW-CNT prepared in Example 1 was dispersed in water, and the average particle size D50 was measured. Table 2 shows the results of measuring the volume resistivity of the powder.
The average particle size D50 was measured by Mastersizer 2000 manufactured by Malvern. The volume resistivity (Ω · cm) was measured by Lorester GP manufactured by Mitsubishi Chemical Corporation.

Example 4
The test was carried out in the same manner as in Example 3 except that the surface-modified carbon nanotubes shown in Table 2 were used instead of the surface-modified MW-CNT prepared in Example 1.

Comparative Example 3
The test was carried out in the same manner as in Example 3 except that the surface-modified MW-CNT prepared in Comparative Example 1 was used.

Comparative Example 4
The test was carried out in the same manner as in Example 3 except that the surface-modified MW-CNT prepared in Comparative Example 2 was used.

Table 2

As shown in Table 2, when the oxidation treatment temperature with the mixed acid was 50 to 60 ° C., the average particle size D50 by the Mastersizer 2000 was 1 μm or more as shown in Examples 3 to 4. The volume resistivity of Lorester was 0.089 to 0.095 Ω · cm. However, when the oxidation treatment temperature with the mixed acid was 100 ° C., the average particle size D50 by the Mastersizer 2000 was 0.85 μm, which was 1 μm or less, as shown in Comparative Example 3. The volume resistivity of the lolester was 3.5 Ω · cm. Further, even when the oxidation treatment temperature with the mixed acid was 120 ° C., the average particle diameter D50 by the Mastersizer 2000 was 0.47 μm, which was 1 μm or less, as shown in Comparative Example 4. The volume resistivity of Lorester was 5.67 Ω · cm. This is because when the oxidation treatment temperature with the mixed acid was raised, the oxidation reaction proceeded, and as a result, the carbon nanotubes were decomposed and the average particle diameter D50 became smaller. As a result, it is considered that the volume resistivity of the powder increased.

Example 5
A carbon nanotube dispersion was prepared by dispersing 8 parts by mass of the surface-modified MW-CNT and 92 parts by mass of water prepared in Example 1 by scandex, and WEM-200U (Taisei Fine Chemical Co., Ltd.) was used as a binder in this carbon nanotube dispersion. (Acrylic urethane resin) was added in an amount of 10 parts by mass, and a composition was prepared with a paint conditioner. The composition thus obtained was applied to a PET (polyethylene terephthalate) film with a bar coater and dried to prepare a coating film having a film thickness of 2 μm. The results of measuring the volume resistivity of this coating film are shown in Table 3.
The volume resistivity (Ω · cm) was measured by Lorester GP manufactured by Mitsubishi Chemical Corporation.

In order to confirm the resolubility of the coating film in water, the coating film was cut into 2 cm squares, immersed in 100 ml of ion-exchanged water together with the PET film, and ultrasonic waves were applied at a frequency of 80 kHz for 1 minute. When the coating film did not dissolve in the ion-exchanged water, it was evaluated as ◯, and when the coating film dissolved in the ion-exchanged water, it was evaluated as x.

Example 6
The test was carried out in the same manner as in Example 5 except that the surface-modified carbon nanotubes shown in Table 3 were used instead of the surface-modified MW-CNT prepared in Example 1.

Comparative Example 5
The test was carried out in the same manner as in Example 5 except that the surface-modified MW-CNT prepared in Comparative Example 1 was used.

Comparative Example 6
The test was carried out in the same manner as in Example 5 except that the surface-modified MW-CNT prepared in Comparative Example 2 was used.

Table 3

As shown in Table 3, when the oxidation treatment temperature with the mixed acid is 50 to 60 ° C., as shown in Examples 5 to 6, the composition to which the binder is added is applied to the PET film and dried in a thin film state. The volume resistivity of the coating film was 0.76 to 0.57 Ω · cm. However, when the oxidation treatment temperature with the mixed acid was 100 ° C., the volume resistivity was 12.2 Ω · cm as shown in Comparative Example 5. Further, even when the oxidation treatment temperature with the mixed acid was 120 ° C., the volume resistivity was 17.6 Ω · cm as shown in Comparative Example 6. This is because when the oxidation treatment temperature with the mixed acid was raised, the oxidation reaction proceeded, and as a result, the carbon nanotubes were decomposed and the average particle diameter D50 became smaller. As a result, it is considered that the volume resistivity of the coating film increased. Moreover, in the re-dissolution test, it was confirmed that the coating film did not dissolve in the ion-exchanged water.

From these results, the effect of preventing the decomposition of carbon nanotubes was exhibited by setting the mixed acid treatment temperature to 60 ° C. or lower, and as a result, it was possible to prevent a decrease in conductivity while maintaining dispersibility in a polar solvent.

The surface-modified carbon nanotubes of the present invention can be uniformly dispersed even at a high concentration, particularly when dispersed in a polar solvent. Further, by using a coating composition or a paste composition using the dispersion liquid of carbon nanotubes, a conductive coating film having excellent conductivity can be easily formed, so that it can be industrially used. ..

Claims (5)

Surface-modified carbon nanotubes, which are oxides of carbon nanotubes,
The average particle size D50 is 1 to 50 μm.
Surface-modified carbon nanotubes having a volume resistivity of 0.1 to 0.01 Ω · cm. A method for producing surface-modified carbon nanotubes, which is oxidized at a temperature of 60 ° C. or lower using 50 to 100 parts by mass of a mixed acid composed of nitric acid and sulfuric acid having a concentration of 60 to 70% by mass with respect to 1 part by mass of carbon nanotubes. .. A composition containing the surface-modified carbon nanotubes according to claim 1, a polar solvent, and a binder, wherein the polar solvent is 30 to 94% by mass and the surface-modified carbon nanotubes are 1 based on the mass of the composition. A composition containing ~ 8% by mass and 5-60% by mass of a binder. The coating film of the composition according to claim 3. A method for producing a composition containing a surface-modified carbon nanotube, a polar solvent, and a binder, wherein the surface-modified carbon nanotube contains nitric acid having a concentration of 60 to 70% by mass with respect to 1 part by mass of the carbon nanotube. , using a mixed acid 50 to 100 parts by mass consisting of sulfuric acid, which has been oxidized at 60 ° C. below the temperature, based on the weight of the composition, the polar solvent 30 to 94 wt%, the surface-modified carbon nanotubes 1 to 8% by mass and 5 to 60% by mass of a binder.