JP2014207116A - Transparent electroconductive film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, by using multilayer carbon nanotubes (CNT), a transparent electroconductive film capable of satisfying both light transmissivity and electroconductivity demands at high levels.SOLUTION: The provided transparent electroconductive film includes: a transparent substrate; and a transparent electroconductive layer including carbon nanotubes and a matrix material. The carbon nanotubes of the transparent electroconductive film, furthermore, are multilayer carbon nanotubes having lengths of 10-5000 [μm] and numbering in 1×10to 1×10[nanotubes/m] per unit area of the electroconductive layer. Both light transmissivity and electroconductivity demands of the transparent electroconductive film can be satisfied at high levels, despite the use of multi-walled carbon nanotubes (MWNT), by confining the CNT length and CNT number density respectively to the stipulated ranges.

Description

  The present invention relates to a transparent conductive film using multilayer carbon nanotubes and a method for producing the same.

  A transparent conductive film is a film provided with a conductive layer having a high transmittance on a transparent plastic substrate or the like, and is transparent and has electrical conductivity. Mainly used in liquid crystal panels and touch panels. As the material for forming the conductive layer, ITO is the mainstream, but since there is a concern about the supply of indium as a raw material, an alternative material is being studied. As an alternative material for ITO, carbon nanotubes are being studied along with conductive polymers and metal nanomaterials.

  A carbon nanotube (hereinafter sometimes abbreviated as “CNT”) is a tube-shaped material in which a graphene sheet composed of carbon atoms is wound in a cylindrical shape, usually with a diameter of 100 [μm] or less. . Since CNT is excellent in electrical characteristics and mechanical characteristics and has a small specific gravity, various applications are expected. It has been shown that the composite material can be used as various molded articles in many fields such as electronic parts and automobile parts. For example, it has been studied to impart conductivity to a resin, ceramics, or the like to prevent charging, and to impart thermal conductivity to suppress thermal expansion. As one of these composite materials, a transparent conductive film has been studied. For example, Patent Document 1 describes a transparent conductive film in which a layer containing CNTs is formed on at least one surface of a transparent substrate.

JP 2008-177143 A

  The CNTs can be classified into single-walled carbon nanotubes (SWNTs) having a single graphene sheet layer and multi-walled carbon nanotubes (MWNTs) having multiple layers. In addition, a graphene sheet having two layers may be particularly referred to as DWNT (double-walled carbon nanotube). CNTs with a small number of layers are usually manufactured using a laser ablation method or an arc method, and have a high crystallinity, and thus are often excellent in properties such as conductivity. On the other hand, a transparent conductive film is required to have particularly excellent light transmittance and conductivity. For this reason, SWNTs, or SWNTs and MWNTs with a small number of layers, were used in the conventional research on transparent conductive films using CNTs. Even in the transparent conductive film described in Patent Document 1, it is assumed that 50% or more of CNTs having an inner diameter of 3 [nm] or more have a single layer to five layers.

  However, SWNT has a problem that it is easy to break because of its high manufacturing cost and thin diameter. On the other hand, MWNTs, especially those with a large number of layers, are low in manufacturing cost but have a small aspect ratio (thick and short), low crystallinity and many defects. It was difficult to achieve both.

  The present invention has been made in consideration of the above points, and an object of the present invention is to provide a transparent conductive film that can achieve both light transmittance and conductivity at a high level using MWNT. Moreover, it aims at providing the manufacturing method of this transparent conductive film.

The transparent conductive film of the present invention has a transparent substrate and a transparent conductive layer containing carbon nanotubes and a matrix material. The carbon nanotubes are multi-walled carbon nanotubes, have a length of 10 to 5000 [μm], and the number is 1 × 10 ⁷ to 1 × 10 ¹⁴ [lines / m ² ] per unit area of the conductive layer. is there.

  Here, the number of CNTs per unit area of the conductive layer, that is, the number density can be obtained by observing a plurality of fields of view with a scanning electron microscope (SEM).

  By setting the CNT length and the CNT number density in such a range, the light transmittance and conductivity of the transparent conductive film can be compatible at a high level while using MWNT.

  Preferably, the transparent conductive film has a surface resistivity of 10,000 [Ω / □] or less and a total light transmittance of 80% or more. Here, the surface resistivity can be measured by a four-probe method defined in JISK7194. The total light transmittance refers to the ratio of the total transmitted light beam to the parallel incident light beam of the CIE standard light D65, and is defined by JIS K7361-1: 1997 (corresponding to ISO13468-1: 1996). This is the value measured by entering the light beam from the opposite side of the material. By making the characteristic of a transparent conductive film into such a range, it can utilize for more uses.

  Preferably, the carbon nanotube is a multi-walled carbon nanotube having 3 to 50 layers.

Also, preferably, the carbon nanotubes, the ratio G / D intensity I _D of the peak appearing in the intensity I _G and D bands peaks appearing in G-band in a Raman spectrum obtained at an excitation wavelength of 632.8 [nm] Is 0.7 or more. Here, the G band is a peak due to the graphite structure that appears in the vicinity of a wave number of 1580 [cm ⁻¹ ]. The D band is a peak due to various defects that appears in the vicinity of a wave number of 1360 [cm ⁻¹ ]. _IG and _ID mean the height of each peak.

  Preferably, the average number of bundles of the carbon nanotubes is 20 or less. Here, the average number of bundles of CNTs can be determined by observing multiple fields of view with SEM and the dynamic light scattering (DLS) method. Specifically, the pseudo diameter of the CNT can be obtained by obtaining the average length of the CNT by SEM and obtaining the particle size distribution by the DLS method.

Preferably, the amount of the carbon nanotube is 1.2 × 10 [μg / m ² ] to 1.2 [g / m ² ] per unit area of the conductive layer.

  By adopting one or more of the above preferred configurations, the light transmittance and conductivity of the transparent conductive film can be made compatible at a higher level.

  In the case where the carbon nanotubes are directly coated on the base material, preferably, the base material has a roughness Ra of the interface with the conductive layer of 5 [nm] or less. is there. Here, Ra is defined according to JISB0601: 2001.

The method for producing a transparent conductive film of the present invention is a method for producing a transparent conductive film having a surface resistance of 10,000 [Ω / □] or less and a total light transmittance of 80% or more, and preparing a transparent first substrate. A step of preparing a carbon nanotube dispersion containing multi-walled carbon nanotubes having a length of 10 to 250 [μm] and an amphoteric molecule as a dispersant, and the dispersion on the first transparent substrate A carbon nanotube layer in which the number of carbon nanotubes per unit area (number density) of the carbon nanotubes is 1 × 10 ⁷ to 1 × 10 ¹⁴ [lines / m ² ], and the carbon nanotubes A step of washing the layer to remove the dispersion, and a step of applying / curing the raw material liquid of the matrix material from the carbon nanotube layer.

Another method for producing a transparent conductive film of the present invention is a method for producing a transparent conductive film having a surface resistance of 10,000 [Ω / □] or less and a total light transmittance of 80% or more, and preparing a first substrate. A step of preparing a carbon nanotube dispersion containing multi-walled carbon nanotubes having a length of 10 to 250 [μm] and an amphoteric molecule as a dispersant, and the dispersion on the first substrate. A step of coating and drying to form a carbon nanotube layer in which the number of carbon nanotubes per unit area of the conductive layer (number density) is 1 × 10 ⁷ to 1 × 10 ¹⁴ [lines / m ² ], and the carbon nanotube layer Removing the dispersion liquid, preparing a transparent second base material, applying a matrix material raw material liquid onto the second base material, and curing the matrix material Before the said carbo And a step of crimping the nanotube layer a layer of said matrix material, and curing the matrix material, and a step of removing the first substrate.

  In any one of the above manufacturing methods, the surface roughness Ra of the first base material is preferably 5 [nm] or less. By coating the CNT dispersion on a smooth substrate in this way, the light transmittance and conductivity of the transparent conductive film can be made compatible at a higher level.

  According to the transparent conductive film or the method for producing the same of the present invention, it is possible to achieve both the light transmittance and the conductivity of the transparent conductive film at a high level using inexpensive multi-walled carbon nanotubes.

It is a SEM image of the transparent conductive film of Example 1 of this invention. It is a figure which shows typically the film | membrane structure of the transparent conductive film concerning one Embodiment of this invention. It is a figure which shows the manufacturing process of the transparent conductive film of the 1st Embodiment of this invention. It is a figure which shows the manufacturing process of the transparent conductive film of the 2nd Embodiment of this invention. It is a figure for demonstrating the principle of dispersion | distribution of the carbon nanotube by an amphoteric molecule.

  First, the structure of the transparent conductive film according to the first embodiment of the present invention will be described with reference to the drawings.

  FIG. 2 schematically shows a cross-sectional structure of the transparent conductive film of the present embodiment. The transparent conductive film 10 of the present embodiment includes a transparent base material 11 and a conductive layer 12. The conductive layer 12 includes a network structure 14 formed of multi-layered CNTs (MWNTs) 13 and a matrix material 15 that has entered the voids of the network structure 14. The CNT 13 is firmly fixed to the base material by the matrix material 15 and the strength of the network structure 14 is reinforced. FIG. 1 is a scanning electron microscope (SEM) image viewed from the conductive layer 12 side of the transparent conductive film 10 of the present embodiment. It can be confirmed that the long CNTs 13 are highly dispersed to form the network structure 14.

  The transparent conductive film 10 of the present embodiment has both high conductivity and transparency. Both are contradictory characteristics, and there is a relationship that increasing the density and the number of contacts of the CNTs 13 increases the conductivity but decreases the transparency. The characteristics of the transparent conductive film are preferably that the surface resistivity is 10000 [Ω / □] or less and the total light transmittance is 80% or more, more preferably the surface resistivity is 1000 [Ω / □] or less. The transmittance is 80% or more, and more preferably, the surface resistivity is 300 [Ω / □] or less and the total light transmittance is 85% or more. It becomes applicable to many uses whenever it has such preferable electroconductivity and transparency.

  If the base material 11 of this embodiment is transparent, the material will not be specifically limited, Various resin films, a glass sheet, etc. can be used. Further, when the CNT 13 is directly coated on the base material to form the network structure 14, the base material 11 preferably has a roughness Ra of the interface with the conductive layer 12 of 5 [nm] or less. It is. Thereby, the electroconductivity of the transparent conductive film 10 can be improved more.

  The conductive layer 12 of this embodiment is substantially composed of CNTs 13 and a matrix material 15. However, the present invention is not limited to this, and a material having some other function, for example, a small amount of inorganic oxide fine particles may be included to improve heat resistance. Moreover, even when it is substantially composed of CNT and a matrix material, it usually contains residues such as a solvent / dispersant derived from the production process. Further, the thickness of the CNT network structure 14 and the layer of the matrix material 15 is not particularly limited.

  The CNTs 13 included in the conductive layer 12 of the present embodiment are multilayer CNTs, and the number of layers is preferably 3 to 50 layers. If the number of layers is less than this, the manufacturing cost becomes high, and if it is more than this, the transparency tends to be impaired, and it becomes difficult to achieve both the required conductivity and transparency of the transparent conductive film. More preferably, the number of layers is 4-12. The number of CNT layers can be determined by observing a transmission electron microscope image (TEM image).

  The diameter of the CNT 13 depends largely on the number of layers, but is generally 1 to 80 [nm], preferably 5 to 20 [nm].

  The length of the CNT 13 needs to be 10 [μm] or more. This is because if the CNT 13 is shorter than this, it is necessary to increase the number density of the CNTs in order to obtain desired conductivity, and the transparency is impaired. On the other hand, the length of the CNT 13 needs to be 5000 [μm] or less. This is because if the CNT 13 is longer than this, it is difficult to disperse it to a high degree, and as a result, it becomes difficult to achieve both transparency and conductivity. Preferably, the length of the CNT 13 is 50 to 600 [μm].

The CNT13 the appearance preferably crystalline (linearity) is good, specifically, to the intensity I _G and D bands peaks appearing in G-band in a Raman spectrum obtained at an excitation wavelength of 632.8 [nm] The ratio G / D of the peak intensity _ID is preferably 0.7 or more, and more preferably 8.0 or more. Although sometimes splitting of peaks of CNT in the G band is observed, that case may be employed peak height higher as the peak intensity I _G. When CNTs with good crystallinity are used in this way, the resistance per unit length of CNTs is smaller than those with poor crystallinity, so the conductivity of the transparent conductive film is further improved when the same amount of CNTs is used. Can be made. Therefore, the light transmittance and conductivity of the transparent conductive film can be made compatible at a higher level. The value of G / D can be determined using a known Raman spectroscopic analyzer.

In the network structure 14 of the CNT 13, the number of the CNTs 13 needs to be 1 × 10 ⁷ to 1 × 10 ¹⁴ [lines / m ² ] per unit area of the conductive film. This is because it is difficult to obtain desired conductivity when the number density is smaller than this, and it is difficult to obtain desired transparency when the number density is larger than this. In the conductive layer 12 of the present embodiment, the CNTs 13 are electrically coupled to each other at the contact points, so that the conductivity of the entire network structure 14 is ensured. However, since the electrical resistance of the contacts is much larger than the resistance of the CNTs themselves, it is not preferable to increase the number of contacts using short CNTs. In this embodiment, by using a long CNT having a length of 10 [μm] or more, the conductivity of the conductive film can be ensured even if the number density is reduced.

The contact number density between CNTs is closely related to the amount per unit area of CNTs contained in the conductive layer 12. Furthermore, when the CNT length is the same, a large amount of CNT corresponds to a large number of contacts, and a small amount of CNT corresponds to a small number of contacts. Therefore, in the transparent conductive film of this embodiment, the amount of CNT per unit area is preferably 1.2 × [μg / m ² ] to 1.2 [g / m ² ].

  The average number of bundles of the CNTs 13 is preferably 20 or less, and more preferably 5 or less. In this embodiment, CNT is basically monodispersed as will be described later, but if a large bundle exists locally, the average number of bundles is preferably within this range. CNT has a strong cohesive force due to van der Waals force due to its shape, and is easily bundled. When CNT forms a thick bundle, the number of contacts per unit amount of CNT in the network structure 14 is reduced, and as a result, conductivity is deteriorated.

  The matrix material 15 included in the conductive layer 12 of the present embodiment enters the voids of the CNT network structure 14. Thereby, the network structure 14 itself is reinforced, and the adhesion between the CNT 13 and the base material 11 becomes stronger.

  As the matrix material 15, various transparent organic or inorganic materials can be used. When the base material 11 can be deformed flexibly, the matrix material 15 is also preferably flexible because the film structure is not destroyed at the time of deformation. Further, from the viewpoint of the ease of the manufacturing method, it is preferable that the material can be cured in situ after filling the voids of the network structure 14 in the state of a raw material liquid or the like. Moreover, when using the resin film etc. with a limit in heat resistance as the base material 11, it is more preferable that it is what hardens | cures with electromagnetic rays, such as UV. Specifically, various resins, organic-inorganic composite materials, and the like can be preferably used, and UV curable resins or thermosetting resins can be particularly preferably used.

  Next, a manufacturing method for the transparent conductive film of the first embodiment will be described.

  The manufacturing method of this embodiment is a method of sequentially forming a CNT layer and a matrix material layer on a transparent substrate. As shown in FIG. 3, this method schematically includes a step of preparing a transparent first substrate, a step of preparing a CNT dispersion, and a step of forming a CNT layer by applying the CNT dispersion. And a step of cleaning the CNT layer and a step of applying a matrix material.

  As a 1st base material, as mentioned above, various resin films, glass sheets, etc. which are transparent can be prepared. The surface of the first substrate on which CNT is applied is preferably smooth, and specifically, the average surface roughness Ra is preferably 5 [nm] or less. When such a base material is used, the conductivity of the transparent conductive film 10 can be further improved. Although the cause is not necessarily clear, when a base material having a smooth surface is used, even when the same CNT dispersion liquid is applied, the CNT 13 is less biased and a network structure 14 having a more uniform density and dispersion state is formed. This is probably because of this. The influence of the smoothness of the surface of the substrate was not dependent on the CNT coating method, and the same tendency was confirmed by the bar coating method and the gravure method.

  The long CNTs used in this embodiment can be manufactured by a method in which a plurality of CNTs are bundled and vertically aligned on a substrate. The method is not particularly limited, and a known method can be used. Specifically, a method of generating an arc discharge between carbon electrodes and growing it on the cathode surface of the discharge electrode (arc discharge method), a method of heating and sublimating silicon carbide with a laser beam (laser evaporation method) There are a method of carbonizing a hydrocarbon in a gas phase under a reducing atmosphere using a transition metal catalyst (chemical vapor deposition method: CVD method), a thermal decomposition method, a method using plasma discharge, and the like. Among these, a chemical vapor deposition method (CVD method) can be preferably used. Details of the method for producing long CNTs by the CVD method will be described later.

  The CNT dispersion used in this embodiment includes the long CNT, a dispersant, and a solvent. By using amphoteric molecules as the dispersant, the CNT bundle can be opened to obtain a highly dispersed state. The amphoteric molecule is not particularly limited as long as the CNT can be isolated and dispersed in the solution. For example, the amphoteric polymer such as 2-methacryloyloxyethyl phosphorylcholine polymer, polypeptide, and 3- (N, N -Dimethylstearylammonio) propanesulfonate, 3- (N, N-dimethylmyristylammonio) propanesulfonate, 3-[(3-cholamidopropyl) dimethylammonio] -1-propanesulfonate (CHAPS), 3- [ (3-Cholamidopropyl) dimethylammonio] -2-hydroxypropanesulfonate (CHAPSO), n-dodecyl-N, N′-dimethyl-3-ammonio-1-propanesulfonate, n-hexadecyl-N, N′- Dimethyl-3-ammonio-1-propanesulfonate , N-octylphosphocholine, n-dodecylphosphocholine, n-tetradecylphosphocholine, n-hexadecylphosphocholine, dimethylalkylbetaine, perfluoroalkylbetaine, lecithin and other amphoteric polymers and amphoteric surfactants can do. Details of the principle of obtaining a highly dispersed state by amphoteric molecules will be described later.

  The dispersion medium of the CNT dispersion is not particularly limited as long as it can disperse the CNT bundle in an isolated state in combination with the amphoteric molecules to be used. For example, water, alcohol, and an aqueous solvent such as a combination thereof In addition, non-aqueous solvents (oil-based solvents) such as silicon oil, carbon tetrachloride, chloroform, toluene, acetone, and combinations thereof can be used.

  Moreover, you may add the substance which forms hydrogen bonds, such as glycerol, a polyhydric alcohol, polyvinyl alcohol, an alkylamine, as a stabilizer to a CNT dispersion liquid.

  Moreover, when dispersing CNT, you may use together physical methods, such as an ultrasonic mill, a bead mill, a jet mill, and a wet pulverization apparatus.

  As a method for coating the CNT dispersion liquid on the first substrate, known methods such as gravure coating, die coating, spray coating, bar coating, casting, dip coating can be used. Then, the film by which the CNT layer which has a network structure was formed on the 1st base material can be obtained by drying using hot air oven etc.

  The obtained film still contains a dispersant, a stabilizer and the like. If such impurities remain, the conductivity of the transparent conductive film is impaired, and the film is washed. The washing method is preferably a combination of water washing and acid washing. Specifically, for example, the film can be immersed in water for about 1 minute, then immersed in a 3M aqueous nitric acid solution for about 1 minute, further washed with water, and then dried using a hot air oven or the like. . Other cleaning agents include hydrogen peroxide, persulfate reagents (potassium persulfate, sodium persulfate, ammonium persulfate, etc.), hydroxide reagents (sodium hydroxide, potassium hydroxide, calcium hydroxide, etc.), sodium bicarbonate Etc. can be used. Moreover, you may wash | clean several times using the same or different cleaning agent.

  As described above, as the matrix material, various kinds of transparent organic or inorganic materials can be used, and a UV curable resin or a thermosetting resin can be particularly preferably used. Specifically, a solution containing about 3% by weight of these resins as a solid content concentration can be used as a raw material liquid. As a method for applying the matrix material, known methods such as gravure coating, die coating, spray coating, bar coating, casting, dip coating, and the like can be used. After the coating of the raw material liquid, it is cured by a method according to the type of material such as UV irradiation, heating or the like.

  Next, the transparent conductive film of the 2nd Embodiment of this invention is demonstrated. The transparent conductive film of the present embodiment has basically the same structure and characteristics as the transparent conductive film of the first embodiment, and the manufacturing method is different.

  The manufacturing method according to the present embodiment is a method in which a CNT layer and a matrix material layer are formed on different bases, and are then pressed and transferred. The method generally includes a step of preparing a first substrate, a step of preparing a CNT dispersion, a step of coating a CNT dispersion on the first substrate to form a CNT layer, and a CNT layer. Cleaning step, preparing a transparent second base material, applying a matrix material onto the second base material, and crimping the CNT layer and the matrix material layer before the matrix material is cured A step of curing, a step of curing the matrix material, and a step of peeling the first substrate.

  Among the steps described above, the step of preparing the first base material to the step of cleaning the CNT layer are the same as those in the first embodiment except that the first base material may not be transparent. .

  Next, separately from the first substrate, a transparent second substrate is prepared, and a matrix material is applied to the surface thereof. The second substrate is not particularly limited as long as it is transparent, and the same material as the first substrate can be used. The matrix material and the coating method thereof are also the same as in the first embodiment. The first base material on which the CNT layer is formed and the second base material on which the matrix material liquid is applied are pressure-bonded with the CNT layer and the matrix material liquid layer inside before the matrix material is cured. Specifically, two films can be laminated at a pressure of 0.1 to 1 MPa. After lamination, the matrix material is cured and the first substrate is peeled off, whereby the transparent conductive film of the present embodiment is obtained.

  When the CNT layer is transferred in this manner, the degree of exposure of the CNT layer becomes uniform on the surface of the manufactured transparent conductive film, and the flatness of the CNT layer surface is improved. Therefore, the conductivity of the transparent conductive film is improved and stabilized.

  The present invention is not limited to the above embodiment. For example, a hard coat layer, an antireflection layer, or an easy-adhesion layer for fixing CNTs may be provided on the surface of the substrate used.

  Here, a method for producing long CNTs by the CVD method will be described in detail below.

  As a chemical vapor deposition method (CVD method), for example, a solution containing a complex of a metal such as nickel, cobalt, or iron is applied on at least one surface of a substrate (silicon substrate) with a spray or a brush, and then heated. By applying a general chemical vapor deposition method (CVD method) using an aliphatic hydrocarbon on the formed film or a film formed by striking with a cluster gun, a diameter of 0.5 to 50 It is possible to produce a long CNT base material including a CNT group in which a plurality of CNTs of about [nm] form a bundle and are vertically aligned with respect to the substrate.

  The length of the long CNT on the long CNT substrate can be adjusted by the amount of raw material added, the synthesis pressure, and the CVD reaction time. By making the CVD reaction time long, the length of the long CNT can be extended to several millimeters. The thickness of one long CNT constituting the long CNT base material can be controlled by the thickness of the catalyst film formed on the substrate. By making the catalyst film thinner, the catalyst particle diameter can be reduced, and the diameter of the long CNT formed by the CVD method is reduced. On the contrary, the catalyst particle diameter can be increased by increasing the thickness of the catalyst film, and the diameter of the long CNT is increased. By controlling the catalyst particle diameter uniformly and densely arranging, the number of CNTs per unit area can be increased, and a dense long CNT substrate can be obtained.

  A more specific method for producing a long CNT substrate is illustrated below.

  First, catalyst particles are formed on a substrate, and CNTs are grown from a raw material gas in a high temperature atmosphere using the catalyst particles as nuclei.

The substrate may be any material that supports catalyst particles, and is preferably a material having smoothness that does not hinder movement when the catalyst is fluidized / particulated. In particular, a crystalline silicon substrate is the most easily used material in terms of smoothness, cost, and heat resistance. It is desirable that the reactivity of the substrate material with respect to the catalytic metal is low. In the case of a silicon substrate, since a compound is formed, it is desirable that the surface is subjected to oxidation treatment or nitridation treatment. Further, it is desirable to form and use a catalytic metal film after forming a low-reactivity alumina or other metal oxide on the surface. For example, a substrate in which an oxide film (SiO ₂ ) is formed on the surface of a crystalline silicon substrate and a substrate in which a nitride film (Si ₃ N ₄ ) is formed can be given.

  Examples of the catalyst particles include metal particles such as nickel, cobalt, and iron. A solution of a compound such as these metals or a complex thereof is applied to the substrate by spin coating, spraying, bar coater, ink jet, slit coater, or hitting the substrate with a cluster gun. Then, it is dried and heated if necessary to form a film. The thickness of this film is preferably about 0.5 to 100 [nm], preferably about 0.5 to 15 [nm]. When it exceeds 15 [nm], it becomes difficult to form particles by heating at about 700 [° C.].

  Next, when this film is heated to 500 to 1000 [° C.], preferably 650 to 800 [° C.], preferably under reduced pressure or non-oxidizing atmosphere, catalyst particles having a diameter of about 0.5 to 50 [nm] are formed. The When catalyst particles are formed in this way and the particle diameter is made uniform, the density of CNTs increases.

  As the raw material gas for CNT, acetylene, methane, ethylene, and other aliphatic hydrocarbons are used as appropriate. Among them, acetylene gas is preferable, and acetylene gas having an acetylene concentration of 99.9999% is more preferable. preferable. The higher the raw material gas purity, the better the quality of CNT. In the case of acetylene, CNTs having a multilayer structure and a thickness of 0.5 to 50 [nm] are formed in a brush shape by being oriented and grown perpendicularly to the substrate in a certain direction from catalyst particles as nuclei.

  The CNT formation temperature in the chemical vapor deposition method (CVD method) is 500 to 1000 [° C.], preferably 650 to 800 [° C.].

Next, a method for dispersing long CNTs will be described in detail below.
The principle of obtaining a highly dispersed state of long CNTs by using amphoteric molecules as a dispersant will be described in detail below based on FIGS.

  First, the principle in which amphoteric molecules open carbon nanotube bundles (CNTB) in a dispersion and disperse them in a single CNT is explained.

  Amphoteric molecules adhere to at least a part of the CNTs constituting the plurality of CNTBs. Among a plurality of CNTBs, amphoteric molecules attached to CNTs constituting one CNTB are electrically attracted to amphoteric molecules attached to adjacent CNTBs, thereby isolating each CNT constituting the CNTB. Disperse.

  Amphoteric molecules have a positive charge and a negative charge, and these molecules form a self-assembled zwitterionic monolayer (hereinafter abbreviated as “SAZM”) on the surface of CNTB. The SAZM that covers the CNTB tends to electrostatically couple with the SAZM that covers the other CNTB due to the strong electrical interaction between the dipoles. When each CNTB in the mixture is pulled by this electrostatic force, the CNTs constituting the CNTB are peeled off, and a new surface of the CNTB is exposed. The newly exposed surface is newly covered with SAZM. Since the above reaction is repeated until the CNTs constituting the CNTB are completely isolated and dispersed, the CNTs are finally completely isolated and dispersed.

  When the CNTB 21, the amphoteric molecule 25, and the stabilizer are mixed, the amphoteric molecule 25 is first self-assembled by an electric attractive force between the amphoteric molecules to become a dimer or a tetramer. At this time, the stabilizer forms a hydrogen bond with the hydrophobic part of the amphoteric molecule 25 and stabilizes the bond between the amphoteric molecules constituting the dimer or tetramer. Since there is no need for a stabilizer, it is not shown here.

  These SAZM components (dimers or tetramers of amphoteric molecules) adhere to the surface of CNTB 21 and associate between the components to form SAZM on the surface of CNTB 21 (FIG. 5A). At this time, if a region having the same polarity approaches between adjacent amphoteric molecules 5, a repulsive force will work. Therefore, the amphoteric molecule 5 configures the SAZM so that positive charges and negative charges alternate as shown in FIGS. 5A to 5C.

  The SAZM that covers the CNTB 21 is electrostatically coupled to the SAZM that covers the other CNTB due to the strong electrical interaction between the dipoles. Such electrical interactions between the dipoles occur easily and it is sufficient to leave them standing. At this time, the respective CNTBs are pulled together by this electrostatic force, whereby the CNTs 23 constituting the CNTB 21 are peeled off, and the CNTs to which the amphoteric molecules are not adsorbed are exposed (FIG. 5B).

  This newly exposed surface is newly covered with amphoteric molecules 25. Since the above reaction is repeated until the CNTs constituting the CNTB are completely isolated and dispersed, the CNTs 23 are finally completely isolated and dispersed by the amphoteric molecules 25 (FIG. 5C).

  Examples of amphoteric molecules that can be used based on this principle are as described above.

  First, specific examples of the first embodiment will be described below.

[Step 1: Production of long CNT]
An iron catalyst was deposited to a thickness of 3.0 [nm] by sputtering on a 6-inch silicon substrate with an oxide film. N ₂ was introduced into a quartz reaction furnace, and the silicon substrate was heated to 720 [° C.] with an infrared heater in an inert atmosphere. When the silicon substrate reaches 720 [° C.], the _C 2 _{H 2} in a quartz _{reactor, C 2 H 2: N 2} = 45: introduced so that 55 was subjected to CVD treatment 60 seconds. As a result, long CNTs having a total weight of 68 [mg] and a height of 150 [μm] were obtained on a 6-inch silicon substrate.

[Step 2: Stripping long CNTs]
The long CNTs on the silicon substrate were peeled off and collected with a stainless steel scraper.

[Step 3: Annealing]
A part of the obtained long CNT was filled in a carbon crucible. A carbon crucible filled with long CNTs was inserted into a high temperature carbon electric furnace (manufactured by Marusho Denki Co., Ltd.), and the long CNTs were annealed at 2600 [° C.] for 2 hours.

[Step 4: Evaluation of crystallinity]
For long CNT and annealing the long CNT, measures the Raman spectrum, the intensity I _D of the peak appearing in the intensity I _G and D bands peaks appearing in G band obtained at an excitation wavelength of 632.8 [nm] G / D was measured from the ratio.

[Step 5: Preparation of CNT dispersion]
A sodium iodide aqueous solution 500 [mL] having a concentration of 1.0 [mmol] was prepared. As an amphoteric surfactant, 1.0 [g] of 3-[(3-cholamidopropyl) dimethylammonio] propanesulfonate (CHAPS) was prepared. Add 50 mg of amphoteric surfactant and long CNT to sodium iodide aqueous solution, perform dispersion treatment for 2 hours with an ultrasonic homogenizer (BRANSON SONIFIER 20 [kHz]), and add a long CNT concentration of 0.01 [weight] %] CNT dispersion.

[Step 6: Preparation of substrate]
A polyethylene terephthalate (PET) film having a thickness of 125 [μm] was prepared as a CNT coating substrate. In addition, the base material (The Teijin DuPont Films make, O4 grade) which did not perform the primer process was used.

[Step 7: Preparation of CNT dispersion for transparent conductive film]
In order to ensure wetting with the substrate, 20.9 [g] of the CNT dispersion was added 0.9 [g] of a wetting agent (E-202S, manufactured by NOF Corporation), and an ultrasonic homogenizer (Branson Ultrasonics). (BRANSON SONIFIER, 20 [kHz]) manufactured by Corporation for 2 minutes to obtain a CNT dispersion for transparent conductive film having a wetting agent concentration of 3.0 [wt%].

[Step 8: Preparation of CNT layer]
The CNT dispersion for transparent conductive film was applied to the substrate by a bar coating method using a wire bar (manufactured by Marukyo Giken Co., Ltd.). The base material coated with the long CNT dispersion liquid for transparent conductive film was inserted into an electric furnace heated to 120 [° C.] immediately after coating, and subjected to a drying treatment for 1 minute.

[Step 9: Removal of dispersant]
Ion exchange water heated to 40 [° C.] was prepared. The transparent conductive film that had been subjected to the drying treatment was immersed in the warm water, and the dispersant was removed by washing. The transparent conductive film treated with warm water was quickly inserted into an electric furnace heated to 120 [° C.] and subjected to secondary drying treatment for 1 minute. A 3 [mol / L] nitric acid aqueous solution heated to 40 [° C.] was prepared. The transparent conductive film subjected to the secondary drying treatment was immersed in the aqueous nitric acid solution, and the dispersant was removed by washing. The transparent conductive film after the nitric acid aqueous solution treatment was immersed in room temperature ion exchange water, and the nitric acid aqueous solution adhering to the transparent conductive film was removed by washing. The transparent conductive film was quickly inserted into an electric furnace heated to 120 [° C.] and subjected to a tertiary drying treatment for 1 minute.

[Step 10: Production of Matrix Layer]
A UV curable acrylic resin liquid was added to a mixed solvent of methyl ethyl ketone (MEK) and isopropyl alcohol (IPA) in an amount of 1% by weight in terms of solid part to prepare a coating liquid. This coating solution was applied from above the CNT layer by a bar coating method. The substrate after coating was dried at 80 [° C.] for 1 minute, and then the resin was cured by irradiation with ultraviolet rays. The thickness of the matrix layer was 50 [nm]. The sample of the transparent conductive film was obtained by the above process.

[Step 11: Measurement of total light transmittance]
About the produced transparent conductive film sample, a total light transmittance is measured by the method prescribed | regulated to JISK7361-1: 1997 (corresponding to ISO13468-1: 1996) using a haze meter (Nippon Denshoku Industries Co., Ltd. make, NDH4000). did.

[Step 12: Measurement of surface resistivity]
About the produced transparent conductive film sample, the surface resistivity was measured by the 4-probe method prescribed | regulated to JISK7194 using the low resistivity meter (the Mitsubishi Chemical Corporation make, Loresta GP-MCP-T610).

(Examples 1 and 2)
The transparent conductive film of Example 1 and Example 2 was obtained by changing the thickness of the bar coat in Step 8. The average solid layer thickness of the CNT layer after the drying treatment was 1.7 [nm] in Example 1 and 1.1 [nm] in Example 2.

(Examples 3 and 4)
Steps 1 to 5 and 7 to 12 were carried out in the same manner as in Example 1. In Step 6, transparent conductive films of Example 3 and Example 4 were produced using a substrate different from Example 1. In Example 3, the CNT dispersion was applied to the surface (Ra = 3 [nm]) on which a primer treatment of a PET film (O321, manufactured by Mitsubishi Plastics Co., Ltd.) having a thickness of 125 [μm] was performed. In Example 4, the CNT dispersion was applied to the surface (Ra = 5.8 [nm]) on which a primer treatment of a 125 [μm] thick PET film (Toray Industries, Inc., U347) was performed.

(Example 5)
Steps 2 and 4 to 12 are carried out in the same manner as in Example 1, and long CNTs with low crystallinity are produced in Step 1 (Step 1 ′), and Step 3 (annealing treatment) is not carried out. A transparent conductive film was produced. Step 1 ′ was performed as follows. An iron catalyst was deposited to a thickness of 3.0 [nm] by sputtering on a 6-inch silicon substrate with an oxide film. N ₂ was introduced into a quartz reaction furnace, and the silicon substrate was heated to 700 [° C.] with an infrared heater in an inert atmosphere. When the silicon substrate reaches 700 [° C.], the _C 2 _{H 2} in a quartz _{reactor, C 2 H 2: N 2} = 70: introduced so that the 30 were CVD process 90 seconds. As a result, long CNTs having a total weight of 57 [mg] and a height of 150 [μm] were obtained on a 6-inch silicon substrate.

(Comparative Examples 1 and 2)
Steps 3, 4 and 6-12 are carried out in the same manner as in Examples, and a commercially available MWNT is used in place of Steps 1 and 2, and in Step 5, the CNT concentration in the dispersion is changed, and Comparative Example 1 and Comparative Example 2 are used. A transparent conductive film was prepared. As the commercially available MWNT, Nanocyl-Nanocyl-7000 (average diameter φ 9.5 [nm], average length 1.5 [μm]: catalog value) was used. It was confirmed by SEM observation that the average diameter and average length were not different from the catalog values. The CNT concentration in the dispersion was 0.1 [wt%].

(Example 6 and Comparative Example 3)
Steps 1 to 4 and 6 to 12 were performed in the same manner as in Example 1, and a transparent conductive film of Example 6 and a transparent film of Comparative Example 3 were produced by using a different dispersant from Example 1 in Step 5. . In Example 6, 1.0 [g] sodium anionic surfactant sodium dodecyl sulfate (SDS) was used as a dispersant. In Comparative Example 4, 1.0 [g] of a polysaccharide water-soluble xylan as a coating dispersant was used as the dispersant.

  Table 1-1 and Table 1-2 show the production conditions and evaluation results of Examples 1 to 6 and Comparative Examples 1 to 3.

  From the results shown in Table 1-1 and Table 1-2, it was found that the light transmittance and conductivity of the transparent conductive film can be compatible at a high level under some preferable conditions. From the comparison of Examples 1, 3, and 4, the smoother the substrate surface, the lower the surface resistance with the same total light transmittance. From comparison between Examples 1 to 4 and Example 5, it was found that the greater the G / D, the higher the light transmittance and conductivity of the transparent conductive film. From comparison between Examples 1 to 5 and Comparative Examples 1 and 2, it was found that the light transmittance and conductivity of the transparent conductive film can be compatible at a high level by reducing the number density using a long MWNT. From comparison between Example 1, Example 6, and Comparative Example 3, by using an amphoteric molecule (CHAPS in Example 1) as a dispersant, a low surface resistance was obtained with the same total light transmittance. In Comparative Example 6, no conductivity was obtained.

  Next, specific examples of the second embodiment will be described below. Steps 1 to 9, 11, and 12 are the same as those in Examples 1 and 2, and the following steps A to E are performed in place of step 10.

[Step A: Preparation of second substrate]
A 188 [μm] polyethylene terephthalate (PET) film was prepared as a matrix material coating substrate. In addition, the base material (Teijin DuPont Films make, O4 grade) which used the primer process was used.

[Step B: Preparation of Matrix Layer]
A UV curable acrylic resin liquid was added to a mixed solvent of toluene and MEK in an amount of 10% by weight in terms of solid part to prepare a coating liquid. This coating solution was applied to the surface of the substrate by a bar coating method. The substrate after coating was dried at 80 [° C.] for 1 minute. The thickness of the matrix layer was 500 [nm].

[Process C: Crimping]
The first base material on which the CNT layer in Steps 1 to 9 is formed and the second base material on which the matrix layer in Steps A and B are formed are overlapped with the CNT layer and the matrix layer, and 80 [° C.] The sample was pressure-bonded at a pressure of 0.5 [Pa] for 1 minute while heating.

[Step D: Curing of Matrix Material]
The resin was cured by irradiating ultraviolet rays from the second substrate side.

[Step E: Peeling of first substrate]
The first substrate was peeled off. As mentioned above, the sample of the transparent conductive film was obtained by process 1-9 and AE. This sample was evaluated by steps 11 and 12.

(Examples 7 and 8)
The transparent conductive films of Examples 7 and 8 were obtained by changing the thickness of the bar coat in Step 8. The average solid layer thickness of the CNT layer after the drying treatment was 1.7 [nm] in Example 7 and 1.1 [nm] in Example 8.

  Table 2 shows production conditions and evaluation results of Examples 7 and 8. In Examples 7 and 8, as in Examples 1 and 2, the light transmittance and conductivity of the transparent conductive film were compatible at a high level.

DESCRIPTION OF SYMBOLS 10 Transparent conductive film 11 Base material 12 Conductive layer 13 Carbon nanotube 14 Carbon nanotube network structure 15 Matrix material 21 Carbon nanotube bundle 23 Carbon nanotube 25 Amphoteric molecule

Claims (10)

A transparent substrate;
Having a carbon nanotube and a transparent conductive layer containing a matrix material;
The carbon nanotubes are multi-walled carbon nanotubes, have a length of 10 to 5000 [μm], and the number is 1 × 10 ⁷ to 1 × 10 ¹⁴ [lines / m ² ] per unit area of the conductive layer.
Transparent conductive film. The transparent conductive film has a surface resistivity of 10,000 [Ω / □] or less and a total light transmittance of 80% or more.
The transparent conductive film according to claim 1. The carbon nanotube is a multi-walled carbon nanotube having 3 to 50 layers,
The transparent conductive film according to claim 1 or 2. The carbon nanotubes, excitation wavelength 632.8 [nm] by the ratio G / D intensity I _D of the peak appearing in the intensity I _G and D bands peaks appearing in G bands in the Raman spectrum obtained is 0.7 or higher Is,
The transparent conductive film as described in any one of Claims 1-3. The average number of bundles of the carbon nanotubes is 20 or less,
The transparent conductive film as described in any one of Claims 1-4. The amount of the carbon nanotube is 1.2 [μg / m ² ] to 1.2 [g / m ² ] per unit area of the conductive layer.
The transparent conductive film as described in any one of Claims 1-5. When the carbon nanotubes are directly coated on the substrate,
The substrate has a roughness Ra of 5 [nm] or less at the interface with the conductive layer.
The transparent conductive film as described in any one of Claims 1-6. A method for producing a transparent conductive film having a surface resistance of 10,000 [Ω / □] or less and a total light transmittance of 80% or more,
Preparing a transparent first substrate;
Preparing a carbon nanotube dispersion containing multi-walled carbon nanotubes having a length of 10 to 5000 [μm] and amphoteric molecules as a dispersant;
The dispersion liquid is applied and dried on the first transparent substrate to form a carbon nanotube layer in which the number of carbon nanotubes is 1 × 10 ⁷ to 1 × 10 ¹⁴ [lines / m ² ] per unit area. Process,
Washing the carbon nanotube layer to remove the dispersion;
Applying and curing a matrix material raw material solution from above the carbon nanotube layer;
The manufacturing method of the transparent conductive film which has this. A method for producing a transparent conductive film having a surface resistance of 10,000 [Ω / □] or less and a total light transmittance of 80% or more,
Preparing a first substrate;
Preparing a carbon nanotube dispersion containing multi-walled carbon nanotubes having a length of 10 to 5000 [μm] and amphoteric molecules as a dispersant;
The step of applying and drying the dispersion on the first substrate to form a carbon nanotube layer in which the number of carbon nanotubes is 1 × 10 ⁷ to 1 × 10 ¹⁴ [lines / m ² ] per unit area. When,
Washing the carbon nanotube layer to remove the dispersion;
Preparing a transparent second substrate;
Applying a raw material solution of a matrix material on the second substrate;
Crimping the carbon nanotube layer and the layer of matrix material before the matrix material is cured;
Curing the matrix material;
Peeling the first substrate;
The manufacturing method of the transparent conductive film which has this. The surface roughness Ra of the first substrate is 5 [nm] or less,
The manufacturing method of the transparent conductive film of Claim 8 or 9.