JP6108658B2 - Transparent conductive composite manufacturing method and transparent conductive composite - Google Patents

Description

  The present invention relates to a transparent conductive composite material using carbon nanotubes as a conductive material and a method for producing the same.

  Carbon nanotubes and conductive polymers are known as organic materials for forming the conductive layer of the transparent conductive composite material. These materials can be applied with a conductive layer at room temperature and atmospheric pressure, and can be formed by a simple process. Moreover, since it is rich in flexibility, even when a conductive layer is formed on a flexible film, it can follow the flexibility of the film. Furthermore, when a film is used as the substrate, the conductive layer can be continuously formed, so that the process cost can be reduced. These conductive layers can improve transparency by reducing the film thickness. In particular, since carbon nanotubes are black, a neutral color tone can be obtained.

  Conventionally, carbon nanotubes have been difficult to disperse in a solvent, but in recent years, compositions containing a solvent and carbon nanotubes have been proposed as compositions with improved dispersibility of carbon nanotubes (for example, patent documents). 1). A carbon nanotube transparent conductive composite material having excellent transparency and conductivity is obtained by such a dispersion method (for example, Patent Document 2).

  Non-Patent Document 1 describes an example in which the dispersibility and conductivity of a carbon nanotube dispersion using polyacrylic acid as a dispersant are improved. By increasing the pH of the dispersion, the carboxyl groups of polyacrylic acid are ionized and the electrostatic repulsion between the carboxyl groups is utilized to improve the dispersibility of the carbon nanotubes. As a result, the polyacrylic acid-carbon nanotube composite polymer prepared by drying this dispersion has improved conductivity compared to a polymer having a relatively low pH of the dispersion.

JP-A-2005-97499 JP 2009-252713 A

Nano Letters, 2006 vol. 6 No. 5,911-915

  However, a carbon nanotube composite polymer in which carbon nanotubes are dispersed in a polymer using a method of adjusting the pH and improving the dispersibility of the carbon nanotube dispersion as in Non-Patent Document 1 provides high transparent conductivity. Was difficult.

  An object of the present invention is to provide a transparent conductive composite material having high transparent conductivity in a transparent conductive composite material using carbon nanotubes as a conductive material, and a method for producing the same.

In the carbon nanotube composite polymer in which carbon nanotubes are dispersed in a polymer using a technique for adjusting the pH and improving the dispersibility of the carbon nanotube dispersion liquid as in Non-Patent Document 1, the present inventors have high transparent conductivity. The reason why it is difficult to obtain is a phenomenon that if the pH is sufficiently high to ensure dispersibility, the surface tension of the dispersion increases and the wettability to the substrate decreases, so that it cannot be applied uniformly. And the present invention has been reached. That is, this invention consists of the following structures. That is,
(1) A method for producing a transparent conductive composite material in which a dispersion liquid in which carbon nanotubes are dispersed in a solvent is applied onto a transparent substrate, and then the solvent in the dispersion liquid is removed by evaporation to form a carbon nanotube-containing layer. There,
The concentration of the carbon nanotubes adjusted to satisfy the following characteristics (A) and / or (B) on the transparent substrate adjusted so that the water contact angle of the surface on which the dispersion is applied is 35 to 55 ° is A method for producing a transparent conductive composite material, wherein 0.02 to 0.15% by mass of a carbon nanotube dispersion is applied.
(A) pH is 7.1 to 10
(B) The zeta potential of the dispersion obtained by diluting the carbon nanotube concentration to 0.003% by mass is −60 mV to −40 mV.
(2) The method for producing a transparent conductive composite material according to (1), wherein the characteristics of the dispersion liquid are adjusted to satisfy (A) and / or (B) by adding nitric acid and / or ammonia.
(3) The method for producing a transparent conductive composite material according to (1) or (2), wherein a water contact angle of a surface to which the dispersion liquid of the transparent substrate is applied is adjusted by corona treatment.
(4) The method for producing a transparent conductive composite material according to (1) or (2), wherein a water contact angle of a surface to which the dispersion liquid of the transparent base material is applied is adjusted by plasma treatment .

  According to the present invention, it becomes possible to uniformly fix carbon nanotubes on a transparent substrate with improved dispersibility of carbon nanotubes, and to provide a transparent conductive composite material having high transparent conductivity. it can.

It is the schematic which shows an example of the apparatus which manufactures a carbon nanotube by a chemical vapor deposition method. It is the schematic which shows an example of the apparatus used for the corona treatment in this invention.

Embodiments of the present invention will be described below.
[Method for producing transparent conductive composite]
In the method for producing a transparent conductive composite material of the present invention, a dispersion liquid in which carbon nanotubes are dispersed in a solvent is applied on a transparent substrate, and then the solvent in the dispersion liquid is removed by evaporation to form a carbon nanotube-containing layer. A method for producing a transparent conductive composite comprising applying a dispersion liquid having a specific hydrogen ion concentration and / or a charged state of a dispersion onto a transparent substrate having specific surface characteristics. is there.

  That is, the water contact angle of the surface on which the dispersion liquid of the transparent substrate is applied is adjusted to 35 to 55 °, and the dispersion liquid is adjusted so that (A) pH is 6 to 10 and / or (B) carbon nanotube concentration is 0 A combination of the dispersion diluted to 0.003 mass% and having a zeta potential (hereinafter sometimes simply referred to as a zeta potential) adjusted to a range of −60 mV to −40 m is combined.

Hereinafter, each configuration of the present invention will be described.
[Transparent substrate]
The optical properties required for the transparent substrate used in the present invention are required to have a high visible light transmittance, as in the case of ordinary transparent conductive composite materials. A rate of 50% or more, preferably 90% or more is applied. Examples of such a transparent substrate include resin and glass. The form may be a film that can be rolled up with a thickness of 250 μm or less, or a substrate with a thickness of more than 250 μm. Examples of the resin include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate, polyimide, polyphenylene sulfide, aramid, polypropylene, polyethylene, polylactic acid, polyvinyl chloride, polycarbonate, polymethyl methacrylate, alicyclic acrylic resin, and cycloolefin. Examples thereof include a resin and triacetyl cellulose. As the glass, ordinary soda glass can be used. Moreover, these several base materials can also be used in combination. For example, a composite substrate such as a substrate in which a resin and glass are combined and a substrate in which two or more kinds of resins are laminated may be used. There are various purposes for laminating two or more kinds of resins. For example, surface hardness is improved, surface tension is controlled to improve coating properties, surface material refractive index is controlled to improve optical properties, and the like. .

  In the present invention, as described above, it is important to adjust the water contact angle of the surface on which the dispersion liquid of the transparent substrate is applied to 35 to 55 °.

In the present invention, a carbon nanotube dispersion liquid in which the pH and / or the zeta potential of the dispersion liquid are adjusted to a specific range is used. However, as described later, the range of such characteristics is more basic than the conventional conditions. . And when the carbon nanotube dispersion became more basic, it was found that the surface tension of the carbon nanotube dispersion became larger. For this reason, it is considered that even if a carbon nanotube dispersion liquid having a range of such characteristics is applied on a normal polyester base material, it cannot be applied uniformly and repelling occurs. In order to apply a carbon nanotube dispersion liquid having such a characteristic range on a substrate, a hydrophilic functional group is exposed on the surface, and the surface tension of the substrate is improved and / or the interfacial tension at the gas-liquid interface is increased. A reduced transparent substrate is preferred. Examples of the hydrophilic functional group include a carboxyl group, a carbonyl group, a hydroxyl group, a sulfone group, and a silanol group. Examples of surface hydrophilization methods for this purpose include physical treatment such as corona treatment, plasma treatment and flame treatment, and chemical treatment such as acid treatment and alkali treatment. Of these, corona treatment and plasma treatment are preferred. The corona treatment can be performed using, for example, an apparatus configured as shown in FIG. A high voltage imprinting device 201 generates a DC voltage of 10 to 100 kV between the ground and the electrode 202, and the transparent substrate 204 and the transparent substrate 204 (for example, PET film) 204 have a transparent substrate 204 of 50 to 200 μm. A partition wall 203 is provided so as to be separated from the distance, and the electrode is moved in the A direction at a speed of 1 to 10 cm / second. By these treatments, it is possible to achieve a substrate surface water contact angle of 35 ° to 55 ° or less where carbon nanotubes having such characteristics can be applied.
[carbon nanotube]
A carbon nanotube has a shape in which one surface of graphite is wound into a cylindrical shape, and a single-walled carbon nanotube is formed by winding one layer, a double-walled carbon nanotube is formed by winding two layers, and three or more layers are formed. The rolled material is called multi-walled carbon nanotube. The carbon nanotubes used in the present invention may be any of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes having three or more layers. To obtain high conductivity, single-walled carbon nanotubes or double-walled carbon nanotubes are used. It is preferable to use it.

  The carbon nanotube used in the present invention is produced, for example, as follows. A powdery catalyst in which iron is supported on magnesia is present in the entire horizontal cross-sectional direction of the reactor in a vertical reactor, methane is circulated in the vertical direction in the reactor, and methane and the catalyst are mixed in 500 to 1200. After making the carbon nanotubes contact with each other at 0 ° C., the carbon nanotubes are oxidized. Since the carbon nanotube usually forms a bundle, the dispersibility is low. This is presumably because the amorphous carbon produced as a by-product plays the role of glue and strengthens the bundle. Therefore, the amorphous carbon can be removed by performing an oxidation treatment in order to improve the dispersibility of the carbon nanotubes. Examples of the oxidation treatment method include a baking treatment method and treatment with an acid having strong oxidizing power such as hydrogen peroxide, mixed acid, nitric acid. The carbon nanotube oxidized with an acid has a surface of the carbon nanotube modified with an acidic functional group such as carboxylic acid, and a liquid suspended in ion-exchanged water exhibits acidity. By using carbon nanotubes oxidized by an acid, a dispersion having improved dispersibility and high conductivity can be obtained. The treatment of carbon nanotubes with nitric acid means that the carbon nanotubes are mixed, for example, in commercially available nitric acid 40 to 80% by mass so as to be 0.1 mg / mL to 100 mg / mL, and at a temperature of 60 to 150 ° C. It means reacting for 5 to 48 hours. By performing such an oxidation treatment, impurities such as amorphous carbon in the product can be selectively removed. These oxidation treatments may be performed immediately after the synthesis of the carbon nanotubes or after another purification treatment. For example, when iron / magnesia is used as a catalyst, after the calcination treatment, a purification treatment for removing the catalyst may be performed with an acid such as hydrochloric acid, or a purification treatment for removing the catalyst with an acid such as hydrochloric acid may be performed first. After performing, you may oxidize. In any case, it is preferable to adjust the oxidation strength and time appropriately according to the characteristics of the carbon nanotubes, and to perform sufficient oxidation treatment until a desired dispersibility is obtained.

The carbon nanotubes thus obtained are highly dispersible and can be unwound relatively easily. In the present invention, it is more preferable to use the carbon nanotubes in a state containing a solvent without purifying the carbon nanotubes after purification. Once the carbon nanotubes are dried, the carbon nanotubes are intertwined or strongly aggregated, making it difficult to disperse compared to a state containing a solvent without passing through a drying step. In addition, when the aggregation is strong in this way, when the entanglement is released, the carbon nanotubes are cut without being easily solved, and the particle size becomes too small. Thus, by dispersing the carbon nanotubes in a state containing the solvent, the carbon nanotubes can be further easily dispersed and at the same time, the dispersibility is improved.
[Carbon nanotube dispersion]
The carbon nanotubes used in the present invention are dispersed in a solvent to form a dispersion and then applied to a transparent substrate. The dispersion is adjusted, for example, as follows. The synthesized carbon nanotube aggregate is usually subjected to removal of the catalyst and, if necessary, subjected to purification, the above-described oxidation treatment, and the like to produce a dispersion.

  The solvent for producing the dispersion is preferably an aqueous solvent, in which the dispersant is dissolved and the carbon nanotubes are dispersed. By dispersing in an aqueous solvent, electrostatic repulsion can be utilized and carbon nanotubes can be highly dispersed. An aqueous solvent refers to a solvent in which the main component of the solvent is water, and specifically refers to a solvent having a water mass ratio of 50 to 100%.

  The concentration of carbon nanotubes in the carbon nanotube dispersion used in the present invention is 0.02 to 0.15% by mass. If it is less than 0.02 mass%, the coating property to a base material will fall and it will become difficult to apply a carbon nanotube layer uniformly. On the other hand, if it exceeds 0.15% by mass, the carbon nanotubes are likely to aggregate and the pot life of the carbon nanotube dispersion is reduced.

  When dispersing the carbon nanotubes in a solvent, it is preferable to use a dispersant. As the dispersant that can be used in the present invention, surfactants, various polymer materials (water-soluble polymer materials, etc.) and the like can be used. The dispersant is useful for improving the dispersibility and dispersion stabilization ability of the aggregate of carbon nanotubes or fine particles. Surfactants are classified into ionic surfactants and nonionic surfactants. In the present invention, any surfactant can be used, but ionic surfactants are used because of their high dispersibility. Is preferred. Examples of the surfactant include the following surfactants. Such surfactants can be used alone or in admixture of two or more.

  The ionic surfactant is classified into a cationic surfactant, an amphoteric surfactant and an anionic surfactant. Examples of the cationic surfactant include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine surfactants and amine oxide surfactants. Examples of anionic surfactants include alkylbenzene sulfonates such as dodecylbenzene sulfonic acid, aromatic sulfonic acid surfactants such as dodecyl phenyl ether sulfonate, monosoap anionic surfactants, ether sulfate-based interfaces Examples thereof include an activator, a phosphate surfactant, and a carboxylic acid surfactant. Among them, those containing an aromatic ring, that is, aromatic ionic surfactants are preferable because they are excellent in dispersibility, dispersion stability, and high concentration, and in particular, aromatics such as alkylbenzene sulfonate and dodecyl phenyl ether sulfonate. Group ionic surfactants are preferred.

  Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters, fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl , Polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, ether surfactants such as polyoxyethylene / polypropylene glycol, polyoxyalkylene octyl phenyl ether, polyoxyalkylene nonyl phenyl ether, polyoxyalkyl dibutyl phenyl ether, poly Oxyalkyl styryl phenyl ether, polyoxyalkyl benzyl phenyl ether, polyoxyalkyl bisphenyl ether, polyoxyalkyl alkyl Aromatic anionic surfactants such as phenyl ether and the like. In the above, alkyl is preferably alkyl having 1 to 20 carbon atoms. Among them, a nonionic surfactant is preferable because of its excellent dispersibility, dispersion stability, and high concentration, and polyoxyethylene phenyl ether which is an aromatic nonionic surfactant is particularly preferable.

  Examples of various polymer materials include water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, polystyrene sulfonate ammonium salt, polystyrene sulfonate sodium salt, carboxymethyl cellulose and its salts (sodium salt, ammonium salt, etc.), methyl cellulose, hydroxyethyl cellulose, and the like. Sugar polymers such as amylose, cycloamylose and chitosan. In addition, conductive polymers such as polythiophene, polyethylenedioxythiophene, polyisothianaphthene, polyaniline, polypyrrole, polyacetylene, and derivatives thereof can also be used. In the present invention, a water-soluble polymer is preferable, and among them, carbon is obtained by using a water-soluble polymer such as carboxymethyl cellulose and its salt (sodium salt, ammonium salt, etc.), polystyrene sulfonate ammonium salt, polystyrene sulfonate sodium salt. It is preferable because the conductive properties of the aggregate of nanotubes can be efficiently exhibited.

  As an apparatus used for producing the dispersion used in the present invention, a conventional mixing and dispersing machine (for example, a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, an ultrasonic homogenizer, a high pressure homogenizer, an ultrasonic apparatus, an attritor, a resolver, a paint) A shaker or the like can be applied. Especially, the dispersibility of the carbon nanotube of the dispersion liquid obtained by disperse | distributing using an ultrasonic wave is high and preferable. The carbon nanotubes to be dispersed may be in a dry state or in a state containing a solvent, but it is preferable to disperse the carbon nanotubes in a state containing a solvent without drying after purification because the dispersibility is improved. As an ultrasonic irradiation method in the case of dispersing using ultrasonic waves, it is preferable to use an ultrasonic homogenizer. The bundle diameter of the carbon nanotubes may be adjusted by optimally adjusting the ultrasonic irradiation output, the processing amount, and the dispersion time. The bundle diameter of the carbon nanotubes refers to the diameter when each carbon nanotube is formed into a bundle shape due to the high π-electron interaction. Usually, the thickness of a single-walled or double-walled carbon nanotube is 1 to 2 nm, but the diameter becomes 2 nm or more by assembling a bundle. The diameter of the carbon nanotube bundle in the carbon nanotube dispersion is determined by observing means having a sub-nm order resolution such as an atomic force microscope (AFM) after applying and drying a 0.02 mass% dispersion on PET. It can be measured with respect to the substrate surface. Specifically, the carbon nanotubes that directly lie on the surface of the base material without overlapping with other carbon nanotubes are selected, and the surface farthest from the base material surface of one carbon nanotube bundle with respect to the base material surface (Hereinafter also referred to as the height of the bundle of carbon nanotubes). In the present invention, the height of the bundle of 100 carbon nanotubes observed on the substrate is obtained, and the average of 100 is defined as the bundle diameter of the carbon nanotubes of the sample.

The ultrasonic radiation output in the case of dispersion using ultrasonic waves can be adjusted as appropriate depending on the amount of treatment and the dispersion time, but is preferably 20 to 1000 W. If the irradiation output is too large, the carbon nanotubes may be defective, or the carbon nanotubes may be cut and the transparent conductivity of the dispersion will be reduced. For example, when the dispersion processing amount is 20 mL or less, 20 to 50 W is preferable, and when the dispersion processing amount is 100 to 500 mL, 100 W to 400 W is preferable. It is possible to control the carbon nanotubes to the optimum bundle diameter and length by adjusting, for example, shortening the dispersion time when the output of the ultrasonic wave is large and increasing the dispersion time when the output is small. In order to prevent the liquid temperature from increasing during dispersion, the temperature during the dispersion is preferably such that the liquid temperature does not increase by cooling in a continuous flow manner so that the liquid temperature does not increase during dispersion. The liquid temperature during ultrasonic irradiation is preferably 0 ° C to 50 ° C, more preferably 0 ° C to 30 ° C, and further preferably 0 ° C to 20 ° C. By being in this range, the carbon nanotube and the dispersant can interact stably and can be dispersed well. The frequency is preferably 20 to 100 kHz.
[Characteristics of carbon nanotube dispersion]
The dispersion used in the present invention satisfies the following (A) and / or (B).
(A) pH is 6-10
(B) The zeta potential of the dispersion obtained by diluting the carbon nanotube concentration to 0.003% by mass is −60 mV to −40 mV.
When the pH of the carbon nanotube dispersion is 6 to 10, an acidic functional group such as carboxylic acid that modifies the surface of the carbon nanotube, or an acidic functional group such as carboxylic acid contained in the dispersant located around the carbon nanotube. The ionization degree of the group is improved, and as a result, the carbon nanotube or the dispersant around the carbon nanotube is negatively charged. This is because the carbon nanotubes or the dispersing agent around the carbon nanotubes are electrostatically repulsive to each other, so that the dispersibility of the carbon nanotubes can be further increased and the bundle diameter can be reduced. The pH adjustment is preferably performed in a step of mixing and dispersing with a dispersant using the mixing and dispersing machine, but the same effect can be obtained even if the adjustment is performed after the dispersion step.

The pH of the carbon nanotube dispersion can be adjusted by adding an acidic substance or a basic substance according to the definition of Arrhenius to the carbon nanotube dispersion. Acidic substances include, for example, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, borohydrofluoric acid, hydrofluoric acid, perchloric acid, organic carboxylic acids, phenols, organic sulfonic acids, etc. Is mentioned. Furthermore, examples of the organic carboxylic acid include formic acid, acetic acid, succinic acid, benzoic acid, phthalic acid, maleic acid, fumaric acid, malonic acid, tartaric acid, citric acid, lactic acid, succinic acid, monochloroacetic acid, dichloroacetic acid, and trichloroacetic acid. Trifluoroacetic acid, nitroacetic acid, triphenylacetic acid and the like. Examples of the organic sulfonic acid include alkylbenzene sulfonic acid, alkyl naphthalene sulfonic acid, alkyl naphthalene disulfonic acid, naphthalene sulfonic acid formalin polycondensate, melamine sulfonic acid formalin polycondensate, naphthalene disulfonic acid, naphthalene trisulfonic acid, dinaphthylmethane. Examples include disulfonic acid, anthraquinone sulfonic acid, anthraquinone disulfonic acid, anthracene sulfonic acid, and pyrene sulfonic acid. Among these, preferred are volatile acids that volatilize during coating and drying, such as hydrochloric acid and nitric acid.
Examples of the basic substance include sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia and the like. Among these, preferred is a volatile base that volatilizes during coating and drying, such as ammonia.

In addition, the carbon nanotube dispersion can be prepared by adjusting the carbon nanotube dispersion so that the zeta potential is −60 mV to −40 mV when the carbon nanotube concentration is diluted to 0.003% by mass. good. This is based on the negative charge of the carbon nanotubes or the dispersant around the carbon nanotubes when adjusting the pH of the carbon nanotube dispersion. In the present invention, the range of the zeta potential in which the dispersibility of the carbon nanotube is a preferable range is in the range of −60 to −40 mV.
[PH adjustment of carbon nanotube dispersion]
The pH of the carbon nanotube dispersion is adjusted by adding the acidic substance and / or basic substance to a desired pH while measuring the pH. Examples of the pH measurement method include a method using a pH test paper such as litmus test paper, a hydrogen electrode method, a quinhydrone electrode method, an antimony electrode method, a glass electrode method, etc. Among them, the glass electrode method is simple and requires the required accuracy. Is preferable. In addition, when an excessive amount of acidic substance or basic substance is added to exceed a desired pH value, a substance having the opposite characteristics may be added to adjust the pH. Nitric acid is preferable as an acidic substance applied for such adjustment, and ammonia is preferable as a basic substance.
[Adjustment of zeta potential of carbon nanotube dispersion]
The zeta potential is adjusted by sampling a part of the carbon nanotube dispersion liquid to which an acidic substance or a basic substance has been added and diluting it to 0.003% by mass, and measuring the zeta potential. Repeat the addition of acidic and / or basic substances until the value is reached. As a zeta potential measurement method, an electrophoresis method for measuring the mobility of charged particles when a potential is applied to a solution is generally used. The concentration is a concentration suitable for measuring the zeta potential by electrophoresis. The concentration at which the zeta potential is measured is not necessarily limited to this value, and a concentration suitable for the measurement method is selected. Addition of an acidic substance increases the zeta potential to the + side, and addition of a basic substance decreases it to the-side. Similar to pH adjustment, when an excessive amount of an acidic substance or basic substance is added and the desired zeta potential is exceeded, a substance having the opposite characteristics may be added to adjust the zeta potential. Nitric acid is preferable as an acidic substance applied for such adjustment, and ammonia is preferable as a basic substance.
[Formation of carbon nanotube-containing layer]
In the present invention, the carbon nanotube dispersion is applied on the surface of the transparent substrate adjusted to have a water contact angle of 35 to 55 °, and then the solvent in the dispersion is evaporated and removed. A carbon nanotube-containing layer is formed. At this time, the method for applying the carbon nanotube dispersion liquid is not particularly limited. Known application methods such as spray coating, dip coating, spin coating, knife coating, kiss coating, gravure coating, screen printing, ink jet printing, pad printing, other types of printing, or roll coating can be used. The application may be performed any number of times, and two different application methods may be combined. The solvent is removed by evaporation with increasing temperature. As a method for increasing the solvent temperature, there are a method of blowing hot air from the outside, a method of irradiating infrared rays, a method of irradiating microwaves, etc., but it is preferable to use hot air.

The coating thickness (wet thickness) of the dispersion liquid also depends on the concentration of the dispersion liquid. Therefore, if the desired light transmittance and surface resistance value can be obtained, it is not necessary to specify, but it is 0.1 to 50 μm. preferable. More preferably, it is 1 μm to 20 μm.
By adjusting the pH and / or zeta potential within a predetermined range, the diameter of the carbon nanotube bundle in the carbon nanotube-containing layer can be reduced. The carbon nanotube bundle diameter in the carbon nanotube-containing layer is selected from carbon nanotubes that lie directly on the surface of the transparent substrate without overlapping with other carbon nanotubes, using observation means with sub-nm height resolution such as AFM. Measure the distance from the transparent base material surface to the surface farthest from the transparent base material surface of the carbon nanotube bundle (hereinafter sometimes referred to as the height of the carbon nanotube bundle). Measured in In the present invention, the height of the bundle of 100 carbon nanotubes observed on the transparent substrate is obtained, and the average of 100 is defined as the bundle diameter of the carbon nanotubes of the sample. By using the present invention, the bundle diameter can be reduced to 1 to 4 nm. By reducing the bundle diameter of carbon nanotubes, the number of carbon nanotube contacts can be increased even when the carbon nanotube application amount is the same when the carbon nanotubes are applied on the base material. Transparent conductivity can be improved.

  The transparent conductive composite of the present invention thus obtained preferably has a surface resistance value of 500 to 1000 Ω / □ at a total light transmittance of 87.0% because of high transparency and conductivity. Usually, transparency and conductivity are in a trade-off relationship, but the transparent conductive composite of the present invention can achieve both at a high level. In addition, the surface resistance value in the total light transmittance of 87.0% is that the sample having the total light transmittance of 87.0% or more and 89.0% or less and the sample of 84.0% or more and less than 87.0%, respectively. One level is prepared, and the surface resistance value at the total light transmittance of 87.0% is interpolated and calculated from the data obtained by measuring each surface resistance value and the total light transmittance. As described above, the transparency and the conductivity are usually in a trade-off relationship as described above by interpolating from the two samples of the total light transmittance range as described above. This is because it is difficult to obtain a sample having a total light transmittance of 87.0% with an accuracy of ± 0.1%. That is, the surface resistance value at the total light transmittance of 87.0% is obtained by interpolating from the data obtained within the controllable range of the total light transmittance.

By adopting a preferred embodiment in the present invention, it is possible to obtain a conductive film having both transparency and conductivity. By being in this range, it can be preferably used as a substrate with a transparent conductive film such as a touch panel, a liquid crystal display, organic electroluminescence, and electronic paper. That is, if it is 1 × 10 ⁰ Ω / □ or more, the substrate can have high transmittance and low power consumption, and if it is 1 × 10 ³ Ω / □ or less, the resistive touch panel An electric signal sufficient for position detection can be obtained.

  The transparent conductive composite of the present invention is used as a display-related transparent electrode such as a touch panel, a liquid crystal display, organic electroluminescence, and electronic paper.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these Examples.
The measurement method used in this example is shown below. Unless otherwise specified, the number of measurements n was 1.

(i) Surface Resistance Value at a Total Light Transmittance of 87.0% The surface resistance value was measured by the 4-terminal method at the center of the conductive surface of the transparent conductive composite sampled to 5 cm × 10 cm. The measuring instrument used was a resistivity meter MCP-T360 type manufactured by Dia Instruments Co., Ltd., and the MCP-TPO 3P manufactured by Dia Instruments Co., Ltd. was used as the 4-probe probe.
Samples to be used for measuring the surface resistance value were prepared with one level each of a sample having a total light transmittance of 87.0% or more and 89.0% or less and a sample of 84.0% or more and less than 87.0%. The resistance value and the total light transmittance were measured, and the surface resistance value at a total light transmittance of 87.0% was interpolated and calculated.

(ii) Total light transmittance Based on JIS-K7361 (1997), it was measured using a turbidimeter NDH2000 manufactured by Nippon Denshoku Industries Co., Ltd.

(iii) Carbon nanotube bundle-layer carbon nanotube-containing layer The carbon nanotube-containing layer was observed with AFM (SPM-9600, manufactured by Shimadzu Corporation). 100 carbon nanotubes are randomly selected from the carbon nanotubes that do not overlap with other carbon nanotubes (directly lying on the surface of the transparent substrate), and the transparent base at the highest point of the bundle of carbon nanotubes based on the surface of the transparent substrate The distance from the material surface was measured, and the average height was calculated by taking the arithmetic average, and this value was taken as the bundle diameter of the carbon nanotubes on the film.

(iv) Zeta potential
From the carbon nanotube dispersion, 1 ml was sampled and diluted to 0.003% by mass. The zeta potential of the diluted solution was measured using ELS-Z2 manufactured by Otsuka Electronics Co., Ltd. At that time, the refractive index and viscosity of water were input in advance, the measurement was performed three times at a setting of 25 ° C., and the average value was obtained.
(Catalyst preparation example)
2.46 g of ammonium iron citrate (Wako Pure Chemical Industries, Ltd.) was dissolved in 500 mL of methanol (Kanto Chemical Co., Ltd.). To this solution, 100.0 g of magnesium oxide (MJ-30 manufactured by Iwatani Chemical Industry Co., Ltd.) was added, vigorously stirred for 60 minutes with a stirrer, and the suspension was concentrated and solidified at 40 ° C. under reduced pressure. The obtained powder was heated and dried at 120 ° C. to remove methanol, and a catalyst body in which a metal salt was supported on magnesium oxide powder was obtained. The obtained solid content was collected on a sieve and the particle size in the range of 20 to 32 mesh (0.5 to 0.85 mm) was collected while being finely divided in a mortar. The iron content contained in the obtained catalyst body was 0.38 wt%. The bulk density was 0.61 g / mL. The above operation was repeated and subjected to the following experiment.
(Example of carbon nanotube-containing composition production)
Carbon nanotubes were synthesized using the apparatus shown in FIG. The reactor 103 is a cylindrical quartz tube having an inner diameter of 75 mm and a length of 1100 mm. A quartz sintered plate 102 is provided at the center, a mixed gas introduction pipe 108 serving as an inert gas and source gas supply line is provided at the lower part of the quartz pipe, and a waste gas pipe 106 is provided at the upper part. Further, three electric furnaces 101 are provided as heaters surrounding the circumference of the reactor so that the reactor can be maintained at an arbitrary temperature. A thermocouple 105 is provided for detecting the temperature in the reaction tube.

  The catalyst layer 104 was formed by taking 132 g of the solid catalyst body prepared in the catalyst preparation example and introducing the solid catalyst body onto the quartz sintered plate at the center of the reactor installed in the vertical direction. While heating the catalyst layer until the temperature in the reaction tube reaches about 860 ° C., nitrogen gas is supplied from the bottom of the reactor toward the top of the reactor using the mass flow controller 107 at 16.5 L / min. It was circulated through the layers. Thereafter, while supplying nitrogen gas, methane gas was further introduced at 0.78 L / min for 60 minutes using the mass flow controller 107, and the gas was passed through the catalyst body layer for reaction. The contact time (W / F) obtained by dividing the mass of the solid catalyst body by the flow rate of methane at this time was 169 min · g / L, and the linear velocity of the gas containing methane was 6.55 cm / sec. The introduction of methane gas was stopped, and the quartz reaction tube was cooled to room temperature while supplying nitrogen gas at 16.5 L / min.

  The heating was stopped and the mixture was allowed to stand at room temperature. After the temperature reached room temperature, the carbon nanotube-containing composition containing the catalyst body and the carbon nanotubes was taken out from the reactor.

(Purification of carbon nanotube aggregate and oxidation treatment)
118 g of the carbon nanotube-containing composition containing the catalyst body and carbon nanotube obtained in the production example of the carbon nanotube-containing composition was transferred to an evaporating dish and left in an electric furnace preheated to a preset temperature of 446 ° C. for 3 hours. Heat oxidation treatment was performed.

  The carbon nanotube-containing composition obtained as described above was stirred in an aqueous 4.8N hydrochloric acid solution for 1 hour to dissolve the catalyst metal iron and the carrier MgO. The obtained black suspension was filtered, and the filtered product was again put into a 4.8N hydrochloric acid aqueous solution, treated with MgO, and collected by filtration. This operation was repeated 3 times (de-MgO treatment). The carbon nanotube-containing filter residue finally obtained was heat-dried overnight at 120 ° C. to obtain 0.374 g of a carbon nanotube-containing composition.

About 300 times as much concentrated nitric acid (first grade assay 60-61%, manufactured by Wako Pure Chemical Industries, Ltd.) was added to the dry mass of the obtained carbon nanotube-containing composition. Thereafter, the mixture was heated to reflux with stirring in an oil bath at about 140 ° C. for 5 hours. After heating to reflux, a nitric acid solution containing the carbon nanotube-containing composition was diluted with ion-exchanged water three times and suction filtered. The carbon nanotube composition was stored in a wet state containing water after washing with ion-exchanged water until the suspension of the filtered material became neutral. At this time, the mass of the wet carbon nanotube composition containing water was 4.65 g (carbon nanotube-containing composition concentration: 7.47 wt%).
Example 1
i) Preparation of carbon nanotube dispersion liquid 15 mg of a carbon nanotube aggregate in a wet state obtained in the carbon nanotube-containing composition production example and 1 wt% sodium carboxymethylcellulose (Daicel Finechem Co., Ltd., Daicel 1140) ) 1.5 g of aqueous solution was weighed and ion exchange water was added to make 10 g. A 28% aqueous ammonia solution (manufactured by Kishida Chemical Co., Ltd.) was added thereto to adjust the pH to 10, and then an ultrasonic homogenizer was used for dispersion treatment under ice-cooling at an output of 20 W for 1.5 minutes. During the dispersion treatment using an ultrasonic homogenizer, the temperature was controlled so that the liquid temperature was 1 to 20 ° C. The resulting treatment solution was centrifuged at 10,000 G for 15 minutes in a high-speed centrifuge, then ion-exchanged water was added to prepare a carbon nanotube aggregate concentration of 0.02% by mass, and carbon A nanotube dispersion was obtained. This dispersion had a zeta potential of −60 mV and a pH of 7.1.
ii) Adjustment of water contact angle of transparent substrate Corona treatment was performed on Lumirror (registered trademark) U46 manufactured by Toray Industries, Inc. using the apparatus shown in FIG. A DC voltage of 10 kV was generated between the ground and the electrode 202 using a type H pinhole tester manufactured by DENSOK PRECISION INDUSTRY CORP. Used as the high voltage device application device 201. Then, a partition wall 203 is provided between the electrode 202 and the transparent base material (Lumirror (registered trademark) U46 manufactured by Toray Industries, Inc.) 204 so as to be separated from the transparent base material by a distance of 150 μm, and at a speed of about 2 cm / second. The operation of moving the electrode in the A direction was performed three times. The water contact angle of the corona-treated film was 53 °.
iii) Formation and Evaluation of Carbon Nanotube-Containing Layer After applying a carbon nanotube dispersion using a bar coater on the surface subjected to corona treatment, the solvent is evaporated and removed in a dryer at 125 ° C. for 1 minute. A containing layer was formed. The obtained transparent conductive composite had a surface resistance value of 6.0 × 10 ² Ω / □ at a total light transmittance of 87.0%. The bundle diameter of the carbon nanotubes in the carbon nanotube-containing layer was 3.3 nm.
( Reference Example 2)
i) Preparation of carbon nanotube dispersion liquid 15 mg of a carbon nanotube aggregate in a wet state obtained in the carbon nanotube-containing composition production example and 1 wt% sodium carboxymethylcellulose (Daicel Finechem Co., Ltd., Daicel 1140) ) 1.5 g of aqueous solution was weighed, and ion exchange water was added to make 10 g. Concentrated nitric acid (1st grade Assay 60-61%, manufactured by Wako Pure Chemical Industries, Ltd.) was added to this to adjust the pH to 5.5, and then an ultrasonic homogenizer was used for dispersion treatment under ice-cooling at an output of 20 W for 1.5 minutes. Otherwise, a carbon nanotube dispersion was prepared in the same manner as in Example 1. The dispersion had a zeta potential of −45 mV and a pH of 6.0.
Except for using the above dispersion, ii) adjustment of the water contact angle of the transparent substrate, and iii) formation and evaluation of the carbon nanotube-containing layer were carried out in the same manner as in Example 1.
The resulting transparent conductive composite had a surface resistance value of 1.0 × 10 ³ Ω / □ at a total light transmittance of 87.0%. The bundle diameter of the carbon nanotubes in the carbon nanotube-containing layer was 4.0 nm.
(Example 3)
i) Preparation of carbon nanotube dispersion liquid 15 mg of a carbon nanotube aggregate in a wet state obtained in the carbon nanotube-containing composition production example and 1 wt% sodium carboxymethylcellulose (Daicel Finechem Co., Ltd., Daicel 1140) ) 1.5 g of aqueous solution was weighed and ion exchange water was added to make 10 g. A 28% aqueous ammonia solution (manufactured by Kishida Chemical Co., Ltd.) was added thereto to adjust the pH to 10, and then an ultrasonic homogenizer was used for dispersion treatment under ice-cooling at an output of 20 W for 1.5 minutes. During the dispersion treatment using an ultrasonic homogenizer, the temperature was controlled so that the liquid temperature was 1 to 20 ° C. The resulting treatment solution was centrifuged at 10,000 G for 15 minutes in a high-speed centrifuge, and then ion-exchanged water was added to prepare a carbon nanotube aggregate concentration of 0.03% by mass. In this state, the pH was 7.1. Further, a 28% aqueous ammonia solution (manufactured by Kishida Chemical Co., Ltd.) was added to adjust the pH to 9.4 to obtain a carbon nanotube dispersion.
Except for using the above dispersion, ii) adjustment of the water contact angle of the transparent substrate, and iii) formation and evaluation of the carbon nanotube-containing layer were carried out in the same manner as in Example 1.
When the carbon nanotube dispersion liquid was applied to the transparent substrate, the coating could be applied without unevenness and repellency. The resulting conductive film had a surface resistance value of 8.0 × 10 ² Ω / □ at a total light transmittance of 87.0%.
Example 4
i) Preparation of carbon nanotube dispersion liquid A carbon nanotube dispersion liquid was prepared in the same manner as in Example 3.
ii) Adjustment of water contact angle of transparent substrate Corona treatment was performed on Lumirror (registered trademark) U46 manufactured by Toray Industries, Inc. using the apparatus shown in FIG. A DC voltage of 10 kV was generated between the ground and the electrode 202 using a type H pinhole tester manufactured by DENSOK PRECISION INDUSTRY CORP. Used as the high voltage device application device 201. Then, a partition wall 203 is provided between the electrode 202 and the transparent base material (Lumirror (registered trademark) U46 manufactured by Toray Industries, Inc.) 204 so as to be separated from the transparent base material by a distance of 150 μm, and at a speed of about 2 cm / second. The operation of moving the electrode in the A direction was performed once. The water contact angle of the corona-treated film was 55 °.
iii) Formation and Evaluation of Carbon Nanotube-Containing Layer When a carbon nanotube dispersion was applied on a corona-treated surface using a bar coater, coating could be performed without unevenness and repelling (Example 5)
i) Preparation of carbon nanotube dispersion liquid A film dispersion liquid was prepared in the same manner as in Example 3.
ii) Adjustment of water contact angle of transparent base material Toray Co., Ltd. Lumirror (registered trademark) U46 was subjected to vacuum plasma treatment for 60 seconds using a plasma processing apparatus YHS-R manufactured by Sakai Semiconductor Co., Ltd. . The water contact angle of the film after the plasma treatment was 35 °.
iii) Formation and Evaluation of Carbon Nanotube-Containing Layer When a carbon nanotube dispersion was applied onto the surface subjected to plasma treatment using a bar coater, coating could be performed without unevenness and repelling. The obtained transparent conductive composite had a surface resistance value of 7.5 × 10 ² Ω / □ at a total light transmittance of 87.0%.
(Comparative Example 1)
Wet carbon nanotube aggregates obtained in the production examples of carbon nanotube-containing compositions were weighed 15 mg in terms of dry mass and 1.5 g of 1 wt% sodium carboxymethylcellulose (Daicel Finechem Co., Ltd., Daicel 1140) aqueous solution. Then, ion exchange water was added to make 10 g. Concentrated nitric acid (1st grade Assay 60-61%, manufactured by Wako Pure Chemical Industries, Ltd.) was added to this to adjust the pH to 4.0, and then an ultrasonic homogenizer was used for dispersion treatment under ice-cooling at an output of 20 W for 1.5 minutes. Otherwise, a carbon nanotube dispersion was prepared in the same manner as in Example 1. This dispersion had a zeta potential of −20 mV and a pH of 4.9.
Except for using the above dispersion, ii) adjustment of the water contact angle of the transparent substrate, and iii) formation and evaluation of the carbon nanotube-containing layer were carried out in the same manner as in Example 1.
The resulting transparent conductive composite had a surface resistance value of 1.3 × 10 ³ Ω / □ at a total light transmittance of 87.0%. The bundle diameter of the carbon nanotubes in the carbon nanotube-containing layer was 4.4 nm.
(Comparative Example 2)
i) Preparation of carbon nanotube dispersion liquid 15 mg of a carbon nanotube aggregate in a wet state obtained in the carbon nanotube-containing composition production example and 1 wt% sodium carboxymethylcellulose (Daicel Finechem Co., Ltd., Daicel 1140) ) 1.5 g of aqueous solution was weighed and ion exchange water was added to make 10 g. A 28% aqueous ammonia solution (manufactured by Kishida Chemical Co., Ltd.) was added thereto to adjust the pH to 10, and then an ultrasonic homogenizer was used for dispersion treatment under ice-cooling at an output of 20 W for 1.5 minutes. During the dispersion treatment using an ultrasonic homogenizer, the temperature was controlled so that the liquid temperature was 1 to 20 ° C. The resulting treatment solution was centrifuged at 10,000 G for 15 minutes in a high-speed centrifuge, and then ion-exchanged water was added to prepare a carbon nanotube aggregate concentration of 0.03% by mass. In this state, the pH was 7.1. Furthermore, concentrated nitric acid (1st grade Assay 60-61%, manufactured by Wako Pure Chemical Industries, Ltd.) was added to adjust the pH to 5.5 to obtain a carbon nanotube dispersion on a transparent substrate.
Except for using the above dispersion, ii) adjustment of the water contact angle of the transparent substrate, and iii) formation and evaluation of the carbon nanotube-containing layer were carried out in the same manner as in Example 1.
The resulting conductive film had a surface resistance value of 1.1 × 10 ³ Ω / □ at a total light transmittance of 87.0%.
(Comparative Example 3)
ii) Except that the corona treatment was not performed in adjusting the water contact angle of the transparent substrate, i) preparation of the carbon nanotube dispersion and iii) formation and evaluation of the carbon nanotube-containing layer were performed in the same manner as in Comparative Example 2. .
Since no corona treatment was performed, the water contact angle was 62 °. Although an attempt was made to produce a transparent conductive composite material by applying a carbon nanotube dispersion, repelling occurred and a uniform conductive layer could not be produced.
(Comparative Example 4)
ii) Except that no corona treatment was performed in adjusting the water contact angle of the transparent substrate, i) preparation of the carbon nanotube dispersion and iii) formation and evaluation of the carbon nanotube-containing layer were performed in the same manner as in Example 3. .
Since no corona treatment was performed, the water contact angle was 62 °. Although an attempt was made to produce a transparent conductive composite material by applying a carbon nanotube dispersion, repelling occurred and a uniform conductive layer could not be produced.
(Comparative Example 5)
i) Preparation of carbon nanotube dispersion liquid 15 mg of a carbon nanotube aggregate in a wet state obtained in the carbon nanotube-containing composition production example and 1 wt% sodium carboxymethylcellulose (Daicel Finechem Co., Ltd., Daicel 1140) ) 1.5 g of aqueous solution was weighed and ion exchange water was added to make 10 g. A 28% aqueous ammonia solution (manufactured by Kishida Chemical Co., Ltd.) was added thereto to adjust the pH to 10, and then an ultrasonic homogenizer was used for dispersion treatment under ice-cooling at an output of 20 W for 1.5 minutes. During the dispersion treatment using an ultrasonic homogenizer, the temperature was controlled so that the liquid temperature was 1 to 20 ° C. The resulting treatment solution was centrifuged at 10,000 G for 15 minutes in a high-speed centrifuge, and then ion-exchanged water was added to prepare a carbon nanotube aggregate concentration of 0.03% by mass. In this state, the pH was 7.1. Furthermore, concentrated nitric acid (1st grade Assay 60-61%, manufactured by Wako Pure Chemical Industries, Ltd.) was added and adjusted to pH 5.8 to obtain a carbon nanotube dispersion.
ii) Adjustment of water contact angle of transparent base material Lumirror U46 manufactured by Toray Industries, Inc. was subjected to vacuum plasma treatment in the same manner as in Example 5. The water contact angle of the plasma treated surface was 35 °.
iii) Formation and Evaluation of Carbon Nanotube-Containing Layer When a carbon nanotube dispersion was applied onto this film using a bar coater, it could be applied without unevenness and repellency. The resulting transparent conductive composite had a surface resistance value of 1.2 × 10 ³ Ω / □ at a total light transmittance of 87.0%.
The results are summarized in Table 1. It should be noted that in the item of the table, the card must be installed carbon nanotubes abbreviated as CNT.

As described above, the coating properties of the dispersion liquids of Example 1 , Reference Example 2, Examples 3 to 5 and Comparative Examples 1 to 5, the pH of the carbon nanotube dispersion liquid, the bundle diameter of carbon nanotubes in the carbon nanotube-containing layer ( nm) and the surface resistance value (Ω / □) at a total light transmittance of 87.0%. In the examples, the surface resistance value at a total light transmittance of 87.0% was 1000Ω / □ or less, and a transparent conductivity that can be applied to touch panel applications was obtained.

DESCRIPTION OF SYMBOLS 101 Electric furnace 102 Sintered quartz plate 103 Reactor 104 Catalyst layer 105 Thermocouple 106 Waste gas pipe 107 Mass flow controller 108 Mixed gas introduction pipe 201 High voltage loading apparatus 202 Electrode 203 Partition wall 204 Transparent base material

Claims (4)

A method for producing a transparent conductive composite material, wherein a carbon nanotube-containing layer is formed by applying a dispersion liquid in which carbon nanotubes are dispersed in a solvent containing carboxymethyl cellulose on a transparent substrate and then removing the solvent in the dispersion liquid by evaporation. Because
The concentration of the carbon nanotubes adjusted to satisfy the following characteristics (A) and / or (B) on the transparent substrate adjusted so that the water contact angle of the surface on which the dispersion is applied is 35 to 55 ° is A method for producing a transparent conductive composite material, wherein 0.02 to 0.15% by mass of a carbon nanotube dispersion is applied.
(A) pH is 7.1-10
(B) zeta potential of the dispersion was diluted to a concentration of carbon nanotubes to 0.003 mass% -60M V The method for producing a transparent conductive composite material according to claim 1, adjusted so meet the characteristics of the dispersion (A) and / or (B) by adding ammonia. The manufacturing method of the transparent conductive composite material of Claim 1 or 2 which adjusts the water contact angle of the surface which applies the dispersion liquid of the said transparent base material by corona treatment. The manufacturing method of the transparent conductive composite material of Claim 1 or 2 which adjusts the water contact angle of the surface which apply | coats the dispersion liquid of the said transparent base material by plasma processing.

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