JP2013014448A - Carbon nanotube dispersion composition and carbon nanotubes containing composition using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon nanotube dispersion composition, having high dispersion stability of carbon nanotubes and capable of adding to other material conductivity, size stability and impact resistance with a small amount of addition.SOLUTION: The amount of a dispersant in the carbon nanotube dispersion composition is set to be at least 3 mg to at most 15 mg for a geometric surface area 1 mof the carbon nanotube. Also, using the carbon nanotube dispersion composition, and by removing a solvent therefrom, the carbon nanotubes containing composition is produced.

Description

  The present invention relates to a carbon nanotube dispersion composition having excellent dispersion stability, and a carbon nanotube-containing composition produced using the carbon nanotube dispersion composition.

  A carbon nanotube (CNT) is a form of carbon based on a structure in which a sheet of graphite in which carbon is arranged in a regular hexagonal shape is wound into a cylindrical shape, and a single-walled carbon nanotube (SWCNT) ), Those having a plurality of layers are called multi-walled carbon nanotubes (MWCNT). Since the basic structure is a graphite sheet, it has high conductivity and strength, and various applications utilizing its characteristics are considered. For example, Patent Documents 1 to 5 disclose conductive paints and transparent conductive films that utilize the fact that high conductivity can be obtained with a small amount of addition. Patent Document 6 discloses the use of a carbon nanotube as a heater member that takes advantage of the conductivity of carbon nanotubes. Patent Document 7 and Patent Document 8 also include resin materials that have increased dimensional stability by containing carbon nanotubes. , Respectively.

  The most important of these utilization forms is the dispersibility of the carbon nanotubes. Carbon nanotubes tend to agglomerate due to their fibrous form, in which the fibers are intertwined or gathered in bundles. In particular, when dispersed in a low-viscosity liquid, the carbon nanotubes can move freely. Therefore, even if they can be dispersed temporarily, the tendency to gradually aggregate increases. When such agglomeration occurs, the uniformity in the dispersion composition is impaired, leading to a decrease in conductivity, an increase in light scattering, a decrease in strength, and the like.

JP 2001-11344 A JP 2001-30200 A Japanese Patent No. 3665969 JP 2005-255985 A JP 2008-24568 A Special table 2010-517231 JP 2003-82202 A JP 2008-255256 A

  As described above, in order to apply the carbon nanotube to various members, its dispersibility, particularly dispersion stability capable of maintaining the dispersion state for a long time is required. An object of the present invention is to provide a carbon nanotube dispersion composition having such a high dispersion stability, and to provide a high-performance carbon nanotube-containing composition using the same.

  As a result of various studies to solve the above problems, the inventor has found that it is important to optimize the amount of the dispersant.

That is, the carbon nanotube dispersion composition comprises at least carbon nanotubes, a dispersant, and a solvent, and the amount of the dispersant is 3 mg or more and 15 mg or less per 1 m ² of the geometric surface area of the carbon nanotubes.

  Moreover, it is a carbon nanotube containing composition formed by removing a solvent from the said carbon nanotube dispersion composition.

  By using the present invention, a composition in which carbon nanotubes are stably dispersed over a long period of time can be obtained. Such a carbon nanotube dispersion composition having good dispersibility can impart conductivity, dimensional stability, impact resistance, etc. with a very small amount of addition to other materials. This is effective for enhancing the functionality of materials, resin compositions, and the like. Moreover, since the composition formed by removing the solvent from the resin composition of the present invention can exhibit conductivity even in an extremely thin film state, both transparency, high conductivity, and antistatic properties can be achieved.

The first invention constituting the present invention is characterized by comprising at least carbon nanotubes, a dispersant and a solvent, and the amount of the dispersant is 3 mg or more and 15 mg or less per 1 m ² of the geometric surface area of the carbon nanotubes. It is a carbon nanotube dispersion composition.

Since carbon nanotubes have an inert surface and tend to aggregate, various dispersing agents are used for stable dispersion in a solvent. In particular, in a non-aqueous solvent in which an electric repulsive force does not work, a polymer dispersant that is adsorbed on the surface and exhibits a steric repulsive effect is used. At that time, if the amount of the dispersant is less than 3 mg per 1 m ² of the geometric surface area of the carbon nanotube, an adsorption layer having a required thickness cannot be formed on the surface of the carbon nanotube, and the steric repulsive force is insufficient. Thus, a sufficient dispersion effect cannot be obtained. On the other hand, if there are too many dispersants and the geometric surface area is 15 mg or more per 1 m ² , not only the content of carbon nanotubes is lowered and the performance such as conductivity is impaired, but the excess dispersants act as crosslinking agents. On the contrary, it leads to aggregation.

In the dispersion of the carbon nanotubes, the reason why the optimum amount of the dispersing agent is 3 mg or more and 15 mg or less per 1 m ² of the geometric surface area of the carbon nanotube is considered as follows.

  First, the surface area is determined. As a method for determining the surface area of the powder sample, a BET method for calculating based on the amount of adsorption of nitrogen gas or the like is generally used. This is because a normal powder sample has a complicated shape and is often not constant, so that it is difficult to calculate from a particle diameter or the like. However, since the shape of the carbon nanotube is simple, the surface area can be obtained geometrically by regarding this as an ideal cylindrical shape. In addition, when determining the surface area by gas adsorption, it is difficult to obtain an accurate surface area when a so-called bundle is formed, in which carbon nanotubes are aggregated in a bundle. There is also a possibility that the area of the inner wall portion is not added to the actual situation. Therefore, the geometrically determined surface area is considered appropriate for a system in which carbon nanotubes are ideally dispersed.

  Next, considering how the dispersant contributes to the dispersion of the carbon nanotubes, the amount of the required dispersant is estimated.

  When electric repulsive force cannot be expected, it is the energy of thermal motion that contributes to the stable dispersion of carbon nanotubes, and the magnitude is about kT, where B is the Boltzmann constant and T is the absolute temperature. . On the other hand, the carbon nanotubes are aggregated mainly by van der Waals energy acting between the nanotubes, and the magnitude relationship between the two determines whether the dispersion system becomes stable. Since van der Waals energy increases rapidly as the distance approaches, it is important to prevent the carbon nanotubes from approaching each other and to ensure that the van der Waals energy does not greatly exceed the thermal kinetic energy in order to disperse stably. It is. This function is the adsorbing layer of the dispersant formed on the surface of the carbon nanotube.

The van der Waals energy that causes aggregation of carbon nanotubes can be calculated by setting the Hamaker constant, which is a constant related to the magnitude of this energy, as 5 × 10 ⁻¹³ erg, which is a general value of graphite. For example, as an example in which relatively thin carbon nanotubes are weakly aggregated, when carbon nanotubes having a diameter of 5 nm approach each other in a portion extending over a length of 10 nm, the van der Waals energy is 0.3 kT at a surface-to-surface distance of 5 nm. The distance is about 1 kT when the distance between the surfaces is 3 nm, and about 3 kT when the distance between the surfaces is 2 nm (when T = 298 degrees). This means that if an adsorption layer with a thickness of 1.5 nm or more is formed on the surface and the distance between the surfaces is kept at 3 nm or more, the cohesive energy can be suppressed to 1 kT or less, that is, the cohesive energy and the thermal kinetic energy are the same level. It means that dispersion by thermal motion becomes possible. As an example of a relatively strong interaction model, when an example in which a carbon nanotube with a diameter of 15 nm approaches in a portion extending over 100 nm is considered, the van der Waals energy at that time is 0.5 kT at a distance between surfaces of 20 nm, and a distance between surfaces. It is 1 kT at 15 nm and 3 kT at a surface-to-surface distance of 10 nm. This means that if a dispersion adsorbing layer having a thickness of 7.5 nm is formed on the surface and the distance between the surfaces is 15 nm, dispersion by thermal kinetic energy is still possible.

In order to prevent the above-mentioned weak aggregation by forming an adsorption layer having a thickness of 1.5 nm on the surface of the carbon nanotube, assuming that the specific gravity of the dispersant is 1, 1.5 mg of the dispersant is required per 1 m ^{2 of} the surface area. . Assuming that half of the dispersant present in the liquid is adsorbed on the surface, the amount of dispersant required is 3 mg per 1 m ^{2 of} carbon nanotube surface area. On the other hand, in order to form an adsorption layer having a thickness of 7.5 nm on the surface of the carbon nanotube to prevent the above-mentioned strong aggregation, 7.5 mg of a dispersant per 1 m ² of the surface area is required. Accordingly, assuming that half of the dispersant in the liquid is adsorbed, the required amount of dispersant is 15 mg per 1 m ² of the surface area of the carbon nanotube. However, if the amount of the dispersant is too large, as described above, the relative concentration of the carbon nanotubes may be reduced, and another type of aggregation may be caused by the crosslinking of the dispersant. It is considered undesirable to add a large amount of.

  The carbon nanotubes used in the present invention are not particularly limited, and single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes and the like synthesized by various methods can be applied, and the diameter is also calculated as described above. As shown in the example, a general one of about 5 nm to 15 nm can be used. Also, for nanotubes with a larger diameter, the van der Waals energy is increased in calculation, and a larger amount of dispersant is required. Therefore, it is expected that the amount of dispersant in this range can be adequately accommodated.

  The dispersant used in the present invention is not particularly limited as long as it has high solubility in the solvent to be used and has an ability to adsorb to the carbon nanotubes. For example, co-polymerization of acrylic monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, benzyl (meth) acrylate, hydroxyethyl (meth) acrylate, dimethylaminoethyl acrylate, acrylic acid and methacrylic acid Polymers such as coalescence, polyallylamine, polyethyleneimine, polyvinylpyrrolidone, polyacetal, polyester, and cellulose derivatives, or copolymers thereof, various surfactants such as polyethylene glycol alkyl ether, ammonium dodecylbenzenesulfonate, etc. Can be used.

  Solvents that are suitable for applications and dispersants may be used. Various solvents such as water, ethanol, isopropanol, methyl ethyl ketone, tetrahydrofuran, cyclohexanone, cellosolve acetate, and propylene glycol methyl ether acetate may be used alone or in combination. Can be used.

  The method for producing the dispersion composition is not particularly limited. For example, the carbon nanotubes are added to a solvent together with a dispersant, and the mixture is uniformly mixed by a method such as ultrasonic irradiation or bead mill. And a small amount of solvent are kneaded using a kneader or the like and then diluted to a predetermined concentration.

  Other components may be added to the carbon nanotube dispersion composition of the present invention. For example, resin components such as acrylic, epoxy, polyester, and urethane may be included to provide film formability and adhesion, and reactive monomers, crosslinking agents, and polymerization initiators for curing in later steps Etc. may be added. Further, inorganic fillers such as silica, alumina and barium sulfate, metal oxide sols such as silica sol, metal alkoxides and the like can be added. Further, it can be combined with other types of carbon materials such as carbon black and fullerene.

  The second invention constituting the present invention is a carbon nanotube-containing composition obtained by removing a solvent from the carbon nanotube dispersion composition of the first invention. Specific forms include a coating applied to a base material and dried, an independent thin film peeled from the base material, a molded product solidified with other components such as plastic and rubber, a powder and a sintered body, etc. And the like. As used herein, “removing the solvent” refers to removing the solvent used in the production to an extent suitable for each application, and does not necessarily mean that the solvent is completely removed. is not.

  Examples of the coating film include conductive films and antistatic films applied to films and molded articles such as polyethylene terephthalate (PET), polystyrene, polyvinyl chloride, and polycarbonate. In the case of a transparent substrate, the transparency can be imparted, and in the case of a colored substrate, the conductivity can be imparted without greatly detracting from the underlying color. It can be applied to packaging materials, trays, carrier tapes, cover tapes, spacer tapes for protecting members on which electronic circuits are formed, partition films having an antistatic function, and the like. It is also possible to produce a window material having electromagnetic wave shielding ability and a heater using a carbon nanotube as a heating element. Furthermore, if it is applied to a flexible substrate, it can also be used as an electrode material having flexibility and impact relaxation properties.

  As an independent thin film, the electroconductive sheet etc. which are obtained by apply | coating to a release film the carbon nanotube dispersion liquid which added resin, such as urethane, for example, and peeling after peeling can be mentioned. Such a thin film can be used for flexible electrode materials, electromagnetic wave shielding sheets, heater heating elements, and the like.

  When the carbon nanotube dispersion composition is hardened together with other components such as plastic and rubber, the carbon nanotube dispersion composition is added to the plastic or rubber that has been softened by heating, kneaded, molded, cooled. It is common to solidify. Alternatively, it can be added to a plastic or rubber precursor and kneaded, and a molding reaction can be caused after molding to obtain a molded product. These molded products can be expected to improve conductivity, strength, dimensional stability and the like due to the characteristics of carbon nanotubes. Or it can also mix with the adhesive material which has a certain amount of fluidity | liquidity, and can also be used as a functional adhesive agent. Such an adhesive has conductivity based on carbon nanotubes, and at the same time, the strength of carbon nanotubes can be improved after solidification.

  Examples of the composite with powder include addition to an electrode material. Electrode materials such as lithium ion batteries are made by mixing powders such as metal oxides and carbon with a binder and applying or molding them into a predetermined shape, but the electrical resistance between the material powders increases the internal resistance of the battery. The battery performance may be reduced. If the solvent is removed after the carbon nanotube dispersion composition of the present invention is applied to or impregnated with these electrode materials, the well-dispersed carbon nanotubes work to connect the material powder, thereby reducing the resistance inside the electrodes. It becomes possible to reduce.

  The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. In the following, “parts” represents parts by weight.

[Example 1]
In 100 parts of methyl ethyl ketone, 1.6 parts of methyl methacrylate, benzyl methacrylate, and dimethylaminoethyl acrylate copolymer (referred to as Dispersant A) were dissolved as a dispersant. To this solution, 3 parts of carbon nanotubes having an average diameter of 12 nm and an average number of layers of 10 (geometric specific surface area of 175 m ² / g) were added and irradiated with ultrasonic waves for 3 hours to prepare a carbon nanotube dispersion. . Under this condition, 3.0 mg of the dispersant is contained per 1 m ² of the geometric surface area of the carbon nanotube. The obtained dispersion had no aggregates that could be visually confirmed, and was uniformly dispersed. This dispersion was diluted 10 times with methyl ethyl ketone and applied to a PET film having a thickness of 0.1 mm using a No. 6 wire bar. The solvent was evaporated by heating at 80 ° C. for 10 minutes to obtain a carbon nanotube coating film. When the surface resistance of this coating film was measured by LorestaGP manufactured by Mitsubishi Chemical Corporation, it was 3 × 10 ⁵ Ω / sq.

[Examples 2 to 8]
A carbon nanotube dispersion was prepared in the same manner as in Example 1 except that the type of carbon nanotube (CNT) and the amount of the dispersant A were changed as shown in Table 1. The results of visual evaluation of the dispersion state and the results of measuring the surface resistance after coating by the same method as in Example 1 were as shown in Table 1. In Table 1, “dispersing agent amount” represents how many mg of dispersing agent per 1 m ² of the geometric surface area of the carbon nanotube is contained in the composition. The evaluation criteria for the dispersion state are as follows.
○ = There are no aggregates that can be visually confirmed, and the carbon nanotubes are uniformly dispersed. Δ = Agglomerates that can be visually confirmed are not present, but adhesion to the vessel wall is uneven and non-uniform. X = There are aggregates that can be visually confirmed.

Example 9
In 100 parts of ethanol, 1.6 parts of hydroxypropyl cellulose (referred to as Dispersant B) was dissolved as a dispersant. To this solution, 3 parts of carbon nanotubes having an average diameter of 12 nm and an average number of layers of 10 (geometric specific surface area of 175 m ² / g) were added and irradiated with ultrasonic waves for 3 hours to prepare a carbon nanotube dispersion. . Under this condition, 3.0 mg of the dispersant is contained per 1 m ² of the geometric surface area of the carbon nanotube. The obtained dispersion had no aggregates that could be visually confirmed, and was uniformly dispersed. This dispersion was diluted 10 times with ethanol and applied to a PET film having a thickness of 0.1 mm using a No. 6 wire bar. The solvent was evaporated by heating at 80 ° C. for 10 minutes to obtain a carbon nanotube coating film. When the surface resistance of this coating film was measured by LorestaGP manufactured by Mitsubishi Chemical Corporation, it was 5 × 10 ⁵ Ω / sq.

[Examples 10 to 13]
A carbon nanotube dispersion was prepared in the same manner as in Example 9 by combining the types of carbon nanotubes (CNT) and the amount of the dispersant as shown in Table 1. The results of visual evaluation of the dispersion state and the results of measuring the surface resistance after coating by the same method as in Example 9 were as shown in Table 1.

[Comparative Example 1]
In 100 parts of methyl ethyl ketone, 1.3 parts of dispersant A is dissolved. To this solution, 3 parts of carbon nanotubes having an average diameter of 12 nm and an average number of layers of 10 (geometric specific surface area of 175 m ² / g) were added and irradiated with ultrasonic waves for 3 hours to prepare a carbon nanotube dispersion. . Under this condition, 2.5 mg of the dispersant is contained per 1 m ² of the geometric surface area of the carbon nanotube. Aggregates were scattered in the obtained dispersion. The dispersion was diluted 10-fold with methyl ethyl ketone, applied to a PET film having a thickness of 0.1 mm using a No. 6 wire bar, and the surface resistance was measured. The result was 3 × 10 ⁷ Ω / sq.

[Comparative Example 2]
In 100 parts of methyl ethyl ketone, 9.0 parts of dispersant A is dissolved. To this solution, 3 parts of carbon nanotubes having an average diameter of 12 nm and an average number of layers of 10 (geometric specific surface area of 175 m ² / g) were added and irradiated with ultrasonic waves for 3 hours to prepare a carbon nanotube dispersion. . Under this condition, 17.1 mg of dispersant is contained per 1 m ² of the geometric surface area of the carbon nanotube. Although there was no aggregate that could be visually confirmed in the obtained dispersion, there was unevenness in adhesion to the wall of the container, and it was in a slightly non-uniform state. This dispersion was diluted 10-fold with methyl ethyl ketone, applied to a PET film having a thickness of 0.1 mm using a No. 6 wire bar, and the surface resistance was measured. The result was 9 × 10 ⁶ Ω / sq.

[Comparative Example 3]
Dispersant B1.3 parts is dissolved in 100 parts of ethanol. To this solution, 3 parts of carbon nanotubes having an average diameter of 12 nm and an average number of layers of 10 (geometric specific surface area of 175 m ² / g) were added and irradiated with ultrasonic waves for 3 hours to prepare a carbon nanotube dispersion. . Under this condition, 2.5 mg of the dispersant is contained per 1 m ² of the geometric surface area of the carbon nanotube. Aggregates were scattered in the obtained dispersion. When this dispersion was diluted 10 times with ethanol and applied to a PET film having a thickness of 0.1 mm using a No. 6 wire bar, the surface resistance was measured. As a result, it exceeded the measurable range of the apparatus.

[Comparative Example 4]
In 100 parts of ethanol, 9.0 parts of dispersant B is dissolved. To this solution, 3 parts of carbon nanotubes having an average diameter of 12 nm and an average number of layers of 10 (geometric specific surface area of 175 m ² / g) were added and irradiated with ultrasonic waves for 3 hours to prepare a carbon nanotube dispersion. . Under this condition, 17.1 mg of dispersant is contained per 1 m ² of the geometric surface area of the carbon nanotube. There was no aggregate that could be visually confirmed in the obtained dispersion, but unevenness was observed on the wall of the container. The dispersion was diluted 10-fold with ethanol, applied to a PET film having a thickness of 0.1 mm using a No. 6 wire bar, and the surface resistance was measured. The result was 5 × 10 ⁷ Ω / sq.

  The carbon nanotube dispersion composition of the present invention is effective as an additive material for enhancing the functions of various paints, electrode materials, resin compositions and the like. Moreover, the composition formed by removing the solvent from the resin composition of the present invention is a film material such as a packaging material for electronic parts, a carrier tape, a cover tape, a TAB spacer tape, a film material for partitioning, an electromagnetic shielding material, and a window. It can be suitably used for producing a transparent material. Furthermore, it can be applied to a highly efficient heater using a carbon nanotube-containing conductive solid composition as a heating element.

Claims (2)

A carbon nanotube dispersion composition comprising at least carbon nanotubes, a dispersant, and a solvent, wherein the amount of the dispersant is 3 mg or more and 15 mg or less per 1 m ² of the geometric surface area of the carbon nanotubes.   A carbon nanotube-containing composition obtained by removing a solvent from the carbon nanotube dispersion composition according to claim 1.