JP6917642B2 - Carbon nanotube composite membrane - Google Patents

Description

The present invention relates to a carbon nanotube composite membrane in which carbon nanotubes are dispersed in an elastomer. In particular, the present invention relates to a carbon nanotube composite thin film having a film thickness of 100 μm or less.

Carbon nanotubes composed of only carbon atoms are materials with excellent electrical properties, thermal conductivity, and mechanical properties. Carbon nanotubes are extremely lightweight, extremely tough, and have excellent elasticity and resilience. Carbon nanotubes having such excellent properties are extremely attractive and important substances as industrial materials.

Carbon nanotube composites and conductive materials, which are polymer foams and elastomers with conductive fillers, are used in a variety of applications, such as electronic products, computers, medical equipment, etc., to provide gaskets and seals for electromagnetic shielding and / or static electricity dissipation. Widely used as. In the past, electrical conductivity was usually given by using fine particles such as metal and carbon black. As the miniaturization of electronic components and the use of plastic components progress, carbon nanotube composite materials and conductive materials having higher conductivity have been required, especially in consumer electronic devices. Therefore, carbon nanotubes having excellent conductivity are attracting attention as conductive fillers.

For example, when carbon nanotubes in which carbon fibers extend three-dimensionally (radially) from the central portion are blended in the elastomer, the specific carbon nanotubes are derived from the three-dimensional shape and uniformly dispersed in the elastomer. As a result, a continuous conductive path (conductive path) is formed in the entire elastomer, and a flexible electrode having excellent conductivity is realized (Patent Document 1).

Further, a carbon nanotube composite material or a conductive material containing a carbon nanotube rubber composition composed of carbon nanotubes, an ionic liquid, and rubber having miscibility with the ionic liquid is 1S / S sufficient to be used as a constituent material of an electronic circuit. It has a conductivity of cm or more and an elongation rate of 10% or more, and has been used as wiring in an expandable electronic device capable of realizing flexible electronics (Patent Document 2).

In order to apply it to flexible electronics, it is necessary to form a thin film of carbon nanotube composite material on a substrate and pattern it using photolithography. Further, when a thin film is formed of a carbon nanotube composite material applicable to flexible electronics, it is necessary to disperse long carbon nanotubes in order to obtain high conductivity. However, long carbon nanotubes make the thin film bulky and cause irregularities on the main surface. With carbon nanotube composite materials and conductive materials according to the prior art, when a thin film of 100 μm or less is formed, unevenness is generated on the surface, and it is difficult to apply a resist. Further, even if the conductive layer is formed of the carbon nanotube composite material, the conductivity becomes non-uniform due to such unevenness, and it is difficult to satisfy the electrical characteristics required for the formation of the electronic device. ..

Japanese Unexamined Patent Publication No. 2008-198425 International release WO2009 / 102077

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a carbon nanotube composite film having a high flatness of a main surface of 1 mm or less.

According to one embodiment of the present invention, it contains carbon nanotubes and an elastomer, has a film thickness of 0.01 μm or more and 1 mm or less, and has an arithmetic mean roughness of the main surface of 50% or less of the film thickness and / or 5 μm or less. The carbon nanotube composite film is provided, wherein the compounding amount of the carbon nanotubes is 0.001% by weight or more and 40% by weight or less.

The carbon nanotube composite film has a residual water content of 5% or less.

The carbon nanotube composite film contains carbon nanotubes having a conductivity of 1 S / cm or more, and the carbon nanotube composite film has a conductivity of 0.01 S / cm or more.

In the carbon nanotube composite film, the length of the carbon nanotube is 0.1 μm or more.

In the carbon nanotube composite film, the average diameter of the carbon nanotubes is 1 nm or more and 30 nm or less.

In the carbon nanotube composite film, the carbon purity of the carbon nanotubes by analysis using fluorescent X-rays is 90% by weight or more.

In the carbon nanotube composite film, the elastomer includes nitrile rubber, chloroprene rubber, chlorosulfonated polyethylene, urethane rubber, acrylic rubber, epichlorohydrin rubber, fluororubber, styrene-butadiene rubber, isoprene rubber, butadiene rubber, butyl rubber, silicone rubber, and the like. It contains one or more selected from ethylene-propylene copolymer and ethylene-propylene-diene ternary copolymer.

The carbon nanotube composite film according to the present invention is a thin film having a film thickness of 0.01 μm or more and 1 mm or less while ensuring high conductivity by dispersing long fibrous carbon nanotubes in an elastomer. It can be a thin film having excellent flatness. The carbon nanotube composite film according to the present invention having excellent flatness can be used as a conductive film applicable to flexible electronics.

It is a schematic diagram of the carbon nanotube composite film 100 which concerns on one Embodiment of this invention. It is a flowchart which shows the manufacturing process of the carbon nanotube composite film which concerns on one Embodiment of this invention. It is a flowchart which shows the manufacturing process of the carbon nanotube composite film which concerns on one Embodiment of this invention. It is a flowchart which shows the manufacturing process of the carbon nanotube composite film which concerns on one Embodiment of this invention. It is a schematic diagram which shows the press of the carbon nanotube composite film which concerns on one Embodiment of this invention. It is a scanning electron microscope (SEM) image of the main surface of the carbon nanotube composite film which concerns on one Example of this invention, (a) shows Example, (b) shows Comparative Example 1. It is a laser microscope image of the main surface of the carbon nanotube composite film which concerns on one Example of this invention, (a) shows Comparative Example 2, and (b) shows Example.

The carbon nanotube composite film according to the present invention is a thin film formed by dispersing carbon nanotubes in an elastomer. In the prior art, when long carbon nanotubes are dispersed in order to obtain high conductivity, a thin film having a bulky surface and an uneven surface is formed, which is not suitable for forming an electronic device. The carbon nanotube composite film of the present invention has excellent flatness as described later, and can be used as a conductive layer of an electronic device. FIG. 1 is a schematic view of the carbon nanotube composite film 100 according to the embodiment of the present invention, and FIG. 1 (a) is a schematic view of the carbon nanotube composite film 100 arranged on the substrate 1. FIG. b) is a diagram in which a part of the carbon nanotube composite film 100 is cut out to expose the inside. In the carbon nanotube composite film 100, the carbon nanotubes 10 are dispersed in the elastomer 30. In FIG. 1, as an example, a carbon nanotube composite film 100 having a carbon nanotube composite film 100 arranged on a substrate 1 is shown.

The substrate 1 used for forming the carbon nanotube composite film 100 is not particularly limited as long as it has a high flatness with an arithmetic mean roughness of the main surface of less than 500 nm, and is not particularly limited. For example, silicon, sapphire, and the like. Those generally used for electronic devices such as polyimide and dimethylpolysiloxane (PDMS) may be used.

The carbon nanotube composite film according to the present invention has a film thickness of 0.01 μm or more and 1 mm or less, and the arithmetic mean roughness of the main surface is 50% or less of the film thickness and / or 5 μm or less. The carbon nanotube composite film according to the present invention has a lower limit of the film thickness of preferably 0.1 μm or more, more preferably 1 μm or more, further preferably 3 μm or more, still more preferably 5 μm or more, and an upper limit of 1 mm or less, preferably 500 μm. Below, it is more preferably 300 μm or less, still more preferably 100 μm or less, still more preferably 70 μm or less, still more preferably 40 μm or less, still more preferably 20 μm or less, still more preferably 15 μm or less. If the lower limit of the film thickness is less than the bundle size of CNT, it becomes difficult to ensure flatness and uniformity.

In the carbon nanotube composite film according to the present invention, the arithmetic roughness of the film surface is preferably 20% or less or 2 μm or less, more preferably 10% or less or 1 μm or less, still more preferably 5% or less or 0.5 μm of the film thickness. Below, it is more preferably 2% or less or 0.2 μm or less, further preferably 1% or less or 0.1 μm or less, still more preferably 0.1% or less or 0.01 μm or less. There is no particular lower limit to the surface roughness of the film, but it is difficult to make the unevenness of the film surface less than the CNT bundle size and the film thickness.

The carbon nanotube composite film according to the present invention has an arithmetic average roughness of 50% or less of the film thickness of the main surface with respect to a film thickness of 0.01 μm or more and 1 mm or less, which is within a practical range as a conductive layer of an electronic device. Moreover, excellent flatness of 5 μm or less can be realized. If the arithmetic mean roughness of the main surface exceeds 50% or 5 μm of the film thickness, it becomes difficult to apply a resist, and even if a conductive layer is formed, the conductivity becomes non-uniform, so that the reliability required for electronic devices is required. Is difficult to secure.

Here, the arithmetic mean roughness (Ra) of the main surface of the carbon nanotube composite film according to the present invention can be obtained by calculation based on JIS B 0601-2001 from the measured value of the atomic force microscope (AFM). .. The arithmetic mean roughness is expressed by extracting the reference length l from the roughness curve in the direction of the average line, summing the absolute values of the deviations from the average line of the extracted portion to the measurement curve, and averaging the values.

In the carbon nanotube composite membrane according to the present invention, the length of the carbon nanotube is 0.5 mm or more, more preferably 1 μm or more. When such carbon nanotubes are dispersed in an elastomer, they can form a network of carbon nanotubes and impart excellent conductivity to the carbon nanotube composite film.

Further, the blending amount of the carbon nanotubes is 0.001% by weight or more and 40% by weight or less when the total weight of the carbon nanotube composite material is 100% by weight. The lower limit is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, further preferably 1% by weight or more, still more preferably 2% by weight or more, and the upper limit is preferably 40% by weight or less. It is preferably 15% by weight or less, more preferably 8% by weight or less, still more preferably 5% by weight or less. If the blending amount of the carbon nanotubes exceeds 70% by weight, favorable permanent elongation and elastic modulus cannot be obtained in flexible electronics. If the blending amount of the carbon nanotubes is less than 0.001% by weight, favorable conductivity cannot be obtained in electronics applications. Such a carbon nanotube orientation amount is preferable for obtaining a carbon nanotube composite film having high flatness.

Further, as the carbon nanotube composite film according to the present invention, carbon nanotubes having high purity and almost no defects can be preferably used as described later. When such high-quality carbon nanotubes are used in the above-mentioned blending amount and formed with the above-mentioned film thickness, the carbon nanotube composite film according to the present invention has a residual water content of 5% or less, preferably 1%. It is less than or equal to, more preferably 0.5% or less, further preferably 0.2% or less, still more preferably 0.1% or less, still more preferably 0.01% or less. In order to form the carbon nanotube composite film according to the present invention, it is necessary to apply the carbon nanotube composite material to the base material and remove the solvent by a drying step, as will be described later. When the residual water content exceeds 5%, the carbon nanotubes agglomerate with each other, which hinders flattening. Further, when the elastomer solidifies, the water contained in the carbon nanotube composite material becomes blisters, and when the water evaporates in the drying step, unevenness is formed on the main surface of the carbon nanotube composite film. In the carbon nanotube composite film according to the present invention, the arithmetic mean roughness of the main surface is 50% of the film thickness and 5 μm or less by controlling the water content in the manufacturing process so that the residual water content is 5% or less. Excellent flatness can be realized.

The longer the carbon nanotubes, the easier it is to form large bundles, the more difficult it is to flatten, and the more difficult it is to evenly distribute the carbon nanotubes in the membrane. Further, the larger the content of carbon nanotubes, the more difficult it is to flatten. In the present invention, the flatness is ensured by filling the gaps between the carbon nanotubes with an elastomer. Further, the thicker the thickness of the carbon nanotube composite film, the greater the roughness of the film immediately after the film formation. Therefore, the flatness of the main surface of the carbon nanotube composite film becomes more difficult as the film thickness approaches the bundle size of the carbon nanotubes. In order to produce the carbon nanotube composite film according to the present invention, it is necessary to overcome these problems, and high flatness can be realized by the following solutions.

[Carbon nanotube rubber paste manufacturing process]
In order to reduce the amount of water in the carbon nanotube rubber paste to 5% or less, it is preferable to remove the water adsorbed on the carbon nanotubes by a method such as vacuum heating and drying. Further, it is preferable to prevent the adsorption and absorption of water in the solvent used for the dispersion of carbon nanotubes and the dispersion of the elastomer. In order to prevent the adsorption and absorption of water on the carbon nanotubes and the solvent, it is preferable to carry out the pre-dispersion step in an inert gas atmosphere with a small amount of water.

[Formation of carbon nanotube composite film]
In the film formation of the carbon nanotube composite film, it is important that the carbon nanotubes are uniformly distributed in the film and that the film thickness can be controlled. In order to uniformly distribute the carbon nanotubes in the film, it is necessary to uniformly disperse the carbon nanotubes in the solvent. However, the amount of water adsorbed on the carbon nanotubes reduces the dispersibility, so that the amount of water is suppressed. Is also important for the dispersion of carbon nanotubes. When the residual water content of the film after film formation is 5% or less, it is considered that the dispersion of carbon nanotubes in the solvent is sufficient for forming a flat film. Further, in order to uniformly distribute the carbon nanotubes in the film, it is also necessary to prevent the carbon nanotubes from agglomerating during solvent drying during the film formation.

When a solution in which carbon nanotubes are dispersed in an elastomer is applied by a spray coating method, if the spray coating amount is too large, the carbon nanotubes agglomerate before the solvent dries. What is effective in preventing agglomeration is that the spray droplets are uniformly applied to the substrate by optimizing the spray amount, and that the substrate is heated to promote the evaporation of the solvent. For example, when the carbon nanotube concentration is 2% by weight, 5% by weight, 8% by weight, or 12% by weight, the carbon nanotubes are uniformly dispersed by applying the spray amount to a silicon substrate heated to 100 ° C. with a spray amount of 50 μL to 200 μL. The carbon nanotube composite film can be produced.

In the spray coating method, a carbon nanotube composite film can be formed on an arbitrary substrate, and the influence of wettability between the substrate and the solvent can be minimized by adjusting the spray pressure and the amount of spray. In the present invention, for example, a carbon nanotube composite film having carbon nanotube concentrations of 2% by weight, 8% by weight, and 12% by weight can be obtained on a substrate such as silicon, sapphire, polyimide, or dimethylpolysiloxane (PDMS).

Since the spray coating method can control the film thickness by the number of sprays, it is suitable for controlling the film thickness of a thin film of 50 μm or less. The accuracy of film thickness control depends on the amount applied by spray coating and the solvent concentration of the elastomer paste of carbon nanotubes. When applied by the spin coating method, the centrifugal force applied differs depending on the mass of the carbon nanotube and the elastomer, so that the carbon nanotube and the elastomer are easily separated and it is difficult to uniformly disperse the carbon nanotube in the film. Further, it is difficult to suppress the influence of the wettability between the substrate and the solvent by the spin coating method.

When applied by the casting method, the solvent is dried in a container such as a beaker or a petri dish, but the distribution of carbon nanotubes can be made uniform and the film thickness distribution can be made uniform by swirling the container. In film formation by the casting method, the film thickness is controlled by the amount of solvent. In principle, it is possible to form a film of 50 μm or less, and it is possible to control the film thickness with an accuracy of several microns, but it is actually difficult to estimate the dry amount of the solvent. Therefore, the thickness of the film produced by the prior art was 50 μm or more. The flatness of the film formed by the casting method was 5 to 20 μm in arithmetic roughness when the film thickness was 50 to 100 μm, which was coarser than that of the carbon nanotube composite film according to the present invention.

[Flatration of carbon nanotube composite film]
The arithmetic mean roughness of the surface of the carbon nanotube composite film after film formation is 10 to 50% of the film thickness regardless of the film thickness, but by pressing the film surface with a flat plate at a temperature at which the elastomer softens. , The arithmetic mean roughness of the film can be improved to 50% or less of the film thickness and 5 μm or less. In order to prevent the film from peeling off in the flattening step, it is necessary that the adhesion between the carbon nanotube composite film and the substrate is sufficiently higher than the adhesion between the carbon nanotube composite film and the plate for pressing. When the substrate is a silicon or polyimide sheet, the PDMS coating on the press plate is effective in preventing the film from peeling off. The flatness of the press plate is important in the flattening process. In order to prevent the flatness of the press plate from being lowered by the PDMS coating for preventing peeling, it is effective to dilute PDMS with toluene to make it thin, or to use PDMS having low viscosity and high hardness.

The higher the content of carbon nanotubes, the higher the conductivity, which is advantageous when used as an electronic wiring material, but flattening becomes difficult. The surface roughness immediately after film formation increases as the film thickness increases, but it is difficult to flatten the carbon nanotubes under conditions where the aggregate size and film thickness are close to each other, and the difficulty of flattening is higher for thinner films.

For the carbon nanotube composite film whose water content is adjusted to 5% or less, for example, when the carbon nanotube concentration is 2% by weight, 5% by weight, or 8% by weight, the film thickness is in the range of 5 μm to 25 μm, and the arithmetic mean coarseness is coarse. It has been confirmed that flatness of 50% or less of the thickness and 5 μm or less can be realized. When the carbon nanotube concentration is 10% by weight or more, a film having a thickness of 1 μm or more or a carbon nanotube composite film having a carbon nanotube concentration of 2% by weight or less is applied to the surface to form a film having a thickness of 25 μm or less. It is possible to realize an arithmetic average roughness of 50% or less of the film thickness and 5 μm or less.

[Measurement of water content]
The residual water content of the carbon nanotube composite film according to the present invention can be determined by the Karl Fischer reaction method. The carbon nanotube aggregate was measured by the Karl Fischer reaction method (Mitsubishi Chemical Analytech Co., Ltd., coulometric titration type trace moisture measuring device CA-200). After drying the carbon nanotube aggregate under predetermined conditions (holding at 200 ° C. for 1 hour under vacuum), the vacuum is released in a glove box in a dry nitrogen gas stream, and about 30 mg of the carbon nanotube aggregate is taken out and a moisture meter is used. Transfer the glass boat. The glass boat moves to a vaporizer, where it is heated at 150 ° C. for 2 minutes, during which the vaporized water is carried by nitrogen gas and reacts with iodine by the adjacent Karl Fischer reaction. The amount of water is detected by the amount of electricity required to generate an amount of iodine equal to the amount of iodine consumed at that time. In the examples described later, by this method, the carbon nanotube aggregate before drying contained 0.8% by weight of water. After drying, the carbon nanotube aggregate was reduced to 0.1% by weight of water.

The carbon nanotube composite membrane according to the present invention is obtained by dispersing carbon nanotubes having the following characteristics in an elastomer, and only carbon nanotubes can be extracted from the carbon nanotube composite membrane and evaluated as buckypaper.

[Raman spectrum]
A carbon nanotube composite material containing carbon nanotubes in which peaks are observed in the regions of ^{110 ± 10 cm -1} , 190 ± 10 cm ^-1 , and 200 cm ^-1 or more by Raman spectroscopy at a wavelength of 633 nm has the effect of the present invention. Suitable for obtaining. The structure of carbon nanotubes can be evaluated by Raman spectroscopy. There are various laser wavelengths used in Raman spectroscopy, but here, wavelengths of 532 nm and 633 nm are used. The region of 350 cm ^-1 or less in the Raman spectrum is called radial breathing mode (hereinafter referred to as RBM), and the peak observed in this region correlates with the diameter of carbon nanotubes.

The carbon nanotubes and carbon nanotube composite films according to the present invention have a wide range of peaks observed in the regions of ^{110 ± 10 cm -1} , 190 ± 10 cm ^-1 , and 200 cm ^{-1 or more by Raman spectroscopic analysis at a wavelength of 633 nm.} It has a peak over the wavelength range. In addition to the above, it is more preferable to have peaks at ^{135 ± 10 cm -1} , 250 ± 10 cm ^-1 , and 280 ± 10 cm ^-1. That is, since carbon nanotubes having such Raman peaks are composed of carbon nanotubes having greatly different diameters, carbon nanotubes having greatly different diameters cannot be packed closely between the carbon nanotubes, and the carbon nanotubes cannot be packed closely. The interaction between them is relatively weak and shows extremely good dispersibility. Therefore, since the carbon nanotubes can be easily dispersed in the elastomer without cutting the carbon nanotubes by ultrasonic waves or the like, the characteristics originally possessed by the carbon nanotubes can be sufficiently imparted to the elastomer. That is, when the carbon nanotubes are dispersed in the elastomer, damage to the carbon nanotubes can be minimized, so that a carbon nanotube composite film having high conductivity can be obtained with a small amount of the carbon nanotubes blended.

Since the wave number of Raman spectroscopic analysis may fluctuate depending on the measurement conditions, the wave number specified here shall be specified in the range of ^{wave number ± 10 cm -1.} In the above, for example, if there is a peak at exactly ^{200 cm -1} , it falls within the range of ^{190 ± 10 cm -1} and 200 cm ^{-1 or more.} In such a case, it is considered that the peak exists in both the range of ^{190 ± 10 cm -1} and 200 cm ^{-1 or more.} When considering the attribution of the peak by the correlation between the peak of the Raman spectrum and the diameter of the carbon nanotube according to the following idea, it may be interpreted that it belongs to only one of the ranges in relation to the other peaks. For example there is a peak already 190 ± 10 cm ^-1, further peak exists in 200 cm ^-1, if there is no peak other than 200 cm ^-1 to 200 cm ^-1 or more peaks of 200 cm ^-1 is 200 cm ^-1 or more It can be interpreted as a peak.

[Conductivity of carbon nanotube composite film]
The carbon nanotube composite material of the present invention preferably has a conductivity of 0.01 S / cm or more, more preferably 0.1 S / cm or more, and more preferably 1 S / cm or more. The upper limit of the electrical conductivity not particularly but not able to surpass the conductive 10 ⁴ S / cm of the carbon material.

[Conductivity of carbon nanotubes]
The conductivity of the carbon nanotubes used in the carbon nanotube composite film of the present invention is 1 S / cm or more, more preferably 10 S / cm or more, still more preferably 50 S / cm or more. Carbon nanotubes having such conductivity are preferable in order to obtain a highly conductive carbon nanotube composite film.

[Characteristics of carbon nanotubes]
The characteristics of the carbon nanotubes used in the carbon nanotube composite membrane of the present invention can be evaluated by extracting only the carbon nanotubes from the carbon nanotube composite membrane and using, for example, buckypaper. For extraction, known means such as dissolving the elastomer with a solvent can be appropriately used.

The average diameter of the carbon nanotubes used in the carbon nanotube composite film of the present invention is in the range of 1 nm or more and 30 nm or less, preferably 1 nm or more and 10 nm or less. If the average diameter is too small, it will be too cohesive and will not disperse. On the other hand, if the average diameter is too large, the carbon nanotubes become hard and form a bulky network structure in the elastomer, which is not preferable. The average diameter of the carbon nanotubes used in the carbon nanotube composite film of the present invention is outside the individual carbon nanotubes from the transmission electron microscope (hereinafter referred to as TEM) image of the carbon nanotube oriented aggregate before being dispersed in the elastomer. A histogram is created by measuring the diameter, that is, the diameter, and is obtained from this histogram.

The carbon purity of the carbon nanotubes used in the carbon nanotube composite membrane of the present invention by analysis using fluorescent X-rays is preferably 90% by weight or more, more preferably 95% by weight or more, still more preferably 98% by weight or more. Is. Such high-purity carbon nanotubes have excellent conductivity and are suitable as a conductive layer for electronic devices. The carbon purity indicates what percentage of the weight of the carbon nanotubes is composed of carbon, and the carbon purity of the carbon nanotubes used in the carbon nanotube composite film of the present invention is obtained from element analysis by fluorescent X-rays.

Carbon nanotubes used in the carbon nanotube composite film of the present invention, the maximum peak intensity in the range 1560 cm ^-1 or 1600 cm ^-1 The following spectrum obtained by measurement of the resonance Raman scattering measurement method G, 1310cm ^-1 or 1350cm ^When the maximum peak intensity in the range of -1 or less is D, the G / D ratio is preferably 3 or more. The carbon nanotubes used in the carbon nanotube composite film of the present invention are preferable because the fewer defects in the graphene sheet, the better the quality and the higher the conductivity. Defects in this graphene sheet can be evaluated by Raman spectroscopy. There are various laser wavelengths used in Raman spectroscopy, but here, wavelengths of 532 nm and 633 nm are used. In the Raman spectrum, the ^{Raman shift seen near 1590 cm -1} is called the G band derived from ^{graphite, and the Raman shift seen near 1350 cm -1} is called the D band derived from defects in amorphous carbon or graphite. In order to measure the quality of carbon nanotubes, the height ratio (G / D ratio) of G band and D band by Raman spectroscopy is used. The higher the G / D ratio, the higher the degree of graphitization and the higher the quality. Here, when evaluating the Raman G / D ratio, a wavelength of 532 nm is used. The higher the G / D ratio, the better, but if it is 3 or more, the carbon nanotubes contained in the carbon nanotube composite film have sufficiently high conductivity, which is preferable for obtaining a carbon nanotube composite film having high electrical conductivity. The G / D ratio is preferably 4 or more and 200 or less, and more preferably 5 or more and 150 or less. Raman spectroscopy of solids such as carbon nanotubes may also vary by sampling. Therefore, it is assumed that at least three places and other places are subjected to Raman spectroscopic analysis and their arithmetic mean is taken.

The carbon nanotubes used in the carbon nanotube composite film of the present invention are preferably single-walled carbon nanotubes. The single-walled carbon nanotubes have excellent deformability, and high flatness of the main surface of the carbon nanotube composite film can be obtained.

[Elastomer]
The elastomer used for the carbon nanotube composite film of the present invention is preferably an elastomer. Elastomers are preferred because they have excellent deformability. Examples of the elastomer applicable to the carbon nanotube composite film of the present invention include nitrile rubber (NBR), chloroprene rubber (CR), chlorosulfonated polyethylene, urethane rubber, and acrylic in terms of flexibility, conductivity, and durability. Rubber, epichlorohydrin rubber, fluororubber, styrene-butadiene rubber (SBR), isoprene rubber (IR), butadiene rubber (BR), butyl rubber, silicone rubber, ethylene-propylene copolymer, ethylene-propylene-diene ternary copolymer One or more selected from (EPDM) can be mentioned. The elastomer used for the carbon nanotube composite membrane of the present invention may be crosslinked with one or more selected from the above group.

As the elastomer used for the carbon nanotube composite film of the present invention, fluororubber is particularly preferable. Fluororubber is particularly preferable because it has high dispersibility with carbon nanotubes and can realize both high conductivity and flatness of the carbon nanotube composite film at the same time.

The cross-linking agent varies depending on the type of the above-mentioned elastomer, but for example, an isocyanate group-containing cross-linking agent (isocyanate, blocked isocyanate, etc.), a sulfur-containing cross-linking agent (sulfur, etc.), a peroxide cross-linking agent (peroxide, etc.). , Hydrosilyl group-containing cross-linking agent (hydrosilyl curing agent), urea resin such as melamine, epoxy curing agent, polyamine curing agent, photo-crosslinking agent that generates radicals by energy such as ultraviolet rays and electron beams, and the like. These may be used alone or in combination of two or more.

In the carbon nanotube composite membrane of the present invention, an ionic liquid can also be used in order to improve the dispersibility of the carbon nanotubes in the elastomer. Known ionic liquids can be used for the carbon nanotube composite film of the present invention. For example, the following general formulas (I) to (IV) disclosed by the present inventors in Japanese Patent Application Laid-Open No. 2010-0977794 can be used. (preferably, an imidazolium ion, a quaternary ammonium ion) cation represented as, anion ^- are those composed of (X).

In the above formulas (I) to (IV), R ₁ contains an alkyl group or an ether bond having a linear or branched carbon number of 1 to 12, and the total number of carbon and oxygen is 3 to 12 linear or fractionated. It represents an alkyl group having a branch, and in the formula (I), R ₂ represents a linear or branched alkyl group or a hydrogen atom having 1 to 4 carbon atoms. In formula (I), _{it is preferable that R 1} and R ₂ are not the same. In formulas (III) and (IV), x is an integer of 1 to 4, respectively.

In addition to the above-mentioned components, the carbon nanotube composite membrane of the present invention may contain, for example, an ionic conductive agent (surfactant, ammonium salt, inorganic salt), plasticizer, oil, cross-linking agent, cross-linking accelerator, anti-aging agent. , Flame retardant, colorant and the like may be used as appropriate.

[Use of carbon nanotube composite material]
Since the carbon nanotube composite film of the present invention has high conductivity and high flatness of the main surface, it can be used as a conductive layer of an electronic device. It can be used for organic EL and the like.

[Production method]
The method for producing the carbon nanotube composite film of the present invention will be described below. The carbon nanotube composite film of the present invention can be obtained by dispersing carbon nanotubes having the above-mentioned characteristics in an elastomer and applying the carbon nanotubes to a substrate to remove the solvent. The carbon nanotubes used in the carbon nanotube composite film of the present invention may have the above-mentioned characteristics and can be obtained by a known production method. The present inventors disclose, for example, a method for producing the same in Japanese Patent Application No. 2011-191502.

[Dispersion of carbon nanotubes]
FIG. 2 is a flowchart showing a manufacturing process of a carbon nanotube composite film according to an embodiment of the present invention. A drying step is performed on the exfoliated carbon nanotube aggregate (S101). Since the carbon nanotubes constituting the carbon nanotube aggregate used in the carbon nanotube composite film of the present invention are composed of carbon nanotubes having a plurality of diameters that differ greatly, they can be easily stored in the atmosphere and transported between the carbon nanotubes in the atmosphere. Adsorbs the water inside. The carbon nanotube composite film according to the present invention preferably has a residual water content of 5% or less in order to have an arithmetic mean roughness of the main surface of 50% or less and 5 μm or less. Therefore, the step of drying the carbon nanotube aggregate is an indispensable step in the manufacturing step of the carbon nanotube composite film according to the present invention. Further, in such a state where water is adsorbed, the carbon nanotubes are attached to each other due to the surface tension of water, so that the carbon nanotubes are very difficult to unravel, and good dispersibility in the elastomer cannot be obtained. Therefore, it is preferable to carry out a drying step of the carbon nanotubes before the dispersion step to remove the water contained in the carbon nanotubes and improve the dispersibility in the dispersion medium. For the drying step, for example, heat drying or vacuum drying can be used, and heat vacuum drying is suitable.

The classified carbon nanotube aggregate is mixed with an organic solvent in an atmosphere of an inert gas having a low water content (S103). At this time, an ionic liquid may be added in order to improve the dispersibility of the carbon nanotubes. Here, the atmosphere of an inert gas having a small amount of water is an environment filled with an inert gas containing water of 0.1 ppm or less, and nitrogen, argon, or the like can be used as the inert gas.

Prior to the next dispersion step, it is preferable to carry out the pre-dispersion step in an atmosphere of an inert gas having a small amount of water (S105). The pre-dispersion step is a step of stirring and dispersing the carbon nanotube aggregate in a solvent. As described later, the carbon nanotubes used in the carbon nanotube composite material of the present invention preferably have a dispersion method using a jet mill, but by carrying out a pre-dispersion step, the jet mill can be prevented from being clogged with carbon nanotubes. , The dispersibility of carbon nanotubes can be improved. It is preferable to use a stirrer in the pre-dispersion step.

A dispersion step is performed on the dispersion liquid of the carbon nanotube aggregate that has been subjected to the pre-dispersion step (S107). In the step of dispersing the carbon nanotube aggregate in the dispersion liquid, a method of dispersing the carbon nanotubes by shear stress is preferable, and a jet mill is preferable. In particular, a wet jet mill can be preferably used. In a wet jet mill, a mixture in a solvent is pumped as a high-speed flow from a nozzle arranged in a pressure-resistant container in a closed state. Carbon nanotubes are dispersed in a pressure-resistant container by collisions between countercurrents, collisions with container walls, turbulence caused by high-speed flow, shear flow, and the like. When, for example, Nanojet Pal Co., Ltd. (JN10, JN100, JN1000) is used as the wet jet mill, the processing pressure in the dispersion step is preferably in the range of 10 MPa or more and 150 MPa or less. The dispersion step is preferably carried out in an inert gas atmosphere having a small amount of water, but may be carried out in an atmosphere in which the humidity is controlled to be low due to the scale of the apparatus.

The carbon nanotube dispersion liquid dispersed in this way can provide a highly dispersible and stable dispersion liquid while maintaining the excellent electrical characteristics, thermal conductivity, and mechanical properties of the carbon nanotubes.

Next, the elastomer is mixed with the solvent in an inert gas atmosphere with a low water content (S111), and the elastomer is dissolved in the solvent in an inert gas atmosphere with a low water content (S113). The elastomer solution prepared in such an environment with a small amount of water is added to the carbon nanotube dispersion liquid and sufficiently stirred to disperse the carbon nanotubes in the elastomer (S121). As described above, in the carbon nanotube composite membrane of the present invention, when the mass of the entire carbon nanotube composite membrane is 100% by weight, it is 0.001% by weight or more and 40% by weight or less. It is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, still more preferably 1% by weight or more, still more preferably 2% by weight or more, preferably 40% by weight or less, and more preferably 15% by weight. Below, it is preferable to mix the carbon nanotube dispersion liquid and the elastomer solution so as to be more preferably 8% by weight or less, still more preferably 5% by weight or less.

A well-mixed solution is prepared by concentrating or diluting with a solvent to a predetermined concentration under an atmosphere of an inert gas having a low water content (S123). The prepared carbon nanotube composite material is preferably used immediately in the film forming process, but when stored, it should be stored in an inert gas atmosphere with a small amount of water. By performing the carbon nanotube dispersion step according to the present invention under the condition of inactivity of water, it is possible to suppress the mixing of water into the carbon nanotube composite material and form a carbon nanotube composite film having high flatness.

[Formation of carbon nanotube composite film]
The prepared carbon nanotube composite material can be formed into a film by a known film forming method. For example, a printing method, a spray coating method, a spin coating method, or the like can be used. Above all, when forming a carbon nanotube composite film according to the present invention having a film thickness of 0.01 μm or more and 1 mm or less, it is preferable to use a spray coat that is thin and can be uniformly formed over a relatively large area. can.

When the film is formed by spray coating, for example, the film can be formed by the following steps. FIG. 3 is a flow chart showing a film forming process of the carbon nanotube composite film by the spray coating method. The spray-coated substrate is heated to a temperature at which the solvent volatilizes (S201). The prepared carbon nanotube composite material is spray-coated on the heated substrate surface (S203). The solvent in the carbon nanotube composite material is removed by heat drying to form a film (S205). The steps of spray coating and heat drying are repeated until the desired thickness is reached. These film forming steps are preferably performed in an inert gas atmosphere with a small amount of water, but may be performed in an atmosphere in which the humidity is controlled to be low due to the scale of the apparatus. When the film is formed in the air, the carbon nanotube composite film is preferably further heated and dried (S207). In the film forming process, it is important to sufficiently remove water and prevent it from being mixed. The substrate used for film formation is not particularly limited as long as it has a high flatness with an arithmetic mean roughness of the main surface smaller than 500 nm. For example, silicon, sapphire, polyimide, or dimethylpolysiloxane (PDMS). ), Etc., which are generally used for electronic devices.

[Flatration of carbon nanotube composite film]
Since a carbon nanotube composite material in which long carbon nanotubes are dispersed is used, the formed carbon nanotube composite film is bulky and the main surface is not sufficiently flat. In the production of the carbon nanotube composite film according to the present invention, a flattening step is further carried out. FIG. 4 is a flow chart showing a flattening step of the carbon nanotube composite film according to the present invention.

The carbon nanotube composite film is pressed using a press machine equipped with a heating mechanism (S301). FIG. 5 is a schematic view showing a press of the carbon nanotube composite film 100. The main surface of the carbon nanotube composite film 100 formed on the substrate 1 is pressed by another substrate 7. The substrate 7 is not particularly limited as long as it has a high flatness with an arithmetic mean roughness of the main surface smaller than 500 nm, and may be generally used for electronic devices such as silicon and sapphire, for example. Further, since the substrate 7 presses the carbon nanotube composite film 100 under high temperature and high pressure conditions, an adhesion prevention layer for preventing the carbon nanotube composite film 100 from adhering to the surface of the substrate 7 in contact with the carbon nanotube composite film 100 It is preferable to form 9. For the adhesion prevention layer 9, it is preferable to use a material having a low affinity with the elastomer used for the carbon nanotube composite film 100, and for example, dimethylpolysiloxane (PDMS) can be preferably used.

The pressed carbon nanotube composite film 100 is heated to a temperature equal to or higher than the softening point of the elastomer by a heating mechanism (S303). As a result, the elastomer, which is the matrix of the carbon nanotube composite film 100, is softened and compressed together with the bulky carbon nanotubes. In the pressed state, the temperature is raised to room temperature to solidify the elastomer (S305). By this flattening step, the main surface of the carbon nanotube composite film 100 can also be flattened so that the arithmetic average roughness is 50% or less of the film thickness and 5 μm or less.

[solvent]
The dispersion medium of the carbon nanotubes used in the carbon nanotube composite membrane of the present invention and the solvent used for dissolving the elastomer may be any organic solvent capable of dissolving the elastomer, and can be appropriately selected depending on the elastomer used. For example, toluene, xylene, acetone, carbon tetrachloride and the like can be used. In particular, as the solvent used for the carbon nanotube composite film of the present invention, methyl isobutyl ketone (hereinafter referred to as MIBK), which is soluble in many rubbers including fluororubber and silicone rubber and is a good solvent for carbon nanotubes, is preferable.

The dispersant may be added to the carbon nanotube dispersion. The dispersant is useful for improving the dispersibility and dispersion stabilizing ability of carbon nanotubes.

In this way, the carbon nanotube composite film of the present invention having high conductivity and excellent flatness can be produced. The manufactured carbon nanotube composite film of the present invention can be used as a conductive layer of an electronic device. For example, when used for electronic devices such as actuators, sensors and transducers, solar cells, organic EL and the like, each of them. Further processing suitable for the application can be performed. Since the processing method for each application can be appropriately selected by a known technique, detailed description thereof will be omitted.

[Characteristics of carbon nanotubes produced in Examples]
The characteristics of the carbon nanotube aggregate depend on the details of the production conditions, but in the production conditions of Example 1, the length is 100 μm and the average diameter is 3.0 nm as a typical value.

[Purity of carbon nanotube aggregate]
The carbon purity of the carbon nanotube aggregate was determined from the results of elemental analysis using fluorescent X-rays. Elemental analysis of the carbon nanotube aggregates exfoliated from the substrate by fluorescent X-ray revealed that the weight percent of carbon was 99.98% and the weight percentage of iron was 0.013%, and other elements were not measured. From this result, the carbon purity was measured to be 99.98%.

[Raman spectrum evaluation of carbon nanotube aggregates]
The Raman spectrum of the carbon nanotube aggregate obtained in Example 1 was measured. A sharp G-band peak is ^{observed in the vicinity of 1590 cm -1} , which indicates that the carbon nanotubes constituting the carbon nanotube aggregate of the present invention have a graphite crystal structure.

In addition, the D-band peak derived from the defect structure and the like is ^{observed in the vicinity of 1340 cm -1} , indicating that the carbon nanotubes contain significant defects. Since the RBM mode caused by the plurality of single-walled carbon nanotubes was ^{observed on the low wavelength side (100 to 300 cm -1} ), it can be seen that this graphite layer is a single-walled carbon nanotube. The G / D ratio was 8.6.

[Dispersion of carbon nanotubes]
For the obtained carbon nanotube aggregate, the oriented carbon nanotube aggregate was sucked by using a vacuum pump and peeled off from the base material 501, and the carbon nanotube aggregate adhering to the filter was recovered. At that time, the oriented carbon nanotube aggregates were dispersed to obtain a massive carbon nanotube aggregate.

The classified carbon nanotube aggregate was accurately weighed in 100 mg, placed in a 100 ml flask (three mouths: for vacuum, for temperature control), held under vacuum at 200 ° C. for 24 hours, and dried. After the drying was completed, 20 ml of the dispersion medium MIBK (methyl isobutyl ketone) (manufactured by Sigma-Aldrich Japan Co., Ltd.) was injected in the state of heating and vacuum treatment to prevent the carbon nanotube aggregates from coming into contact with the atmosphere (drying step).

Further, in an argon atmosphere with a water content of 0.1 ppm or less, MIBK (manufactured by Sigma-Aldrich Japan Co., Ltd.) and an ionic liquid are added to make 300 ml. A stirrer was placed in the beaker, the beaker was sealed with aluminum foil to prevent the MIBK from volatilizing, and the beaker was stirred at 600 RPM for 24 hours at room temperature with a stirrer.

In the dispersion step, a wet jet mill (Nanojet Pal (registered trademark) JN10 manufactured by Jokko Co., Ltd.) was used to pass a 200 μm flow path at a pressure of 60 MPa to disperse the carbon nanotube aggregates in MIBK, and the weight concentration was 0. A 033 wt% carbon nanotube dispersion was obtained. The dispersion step was carried out in the air.

[Carbon nanotube rubber paste manufacturing process]
In this example, fluororubber (Daiel-G912, manufactured by Daikin Industries, Ltd.) was used as the elastomer. The fluororubber was mixed with MIBK (manufactured by Sigma-Aldrich Japan) under an argon atmosphere and dissolved in 2 days. When the total mass of the carbon nanotube composite material is 100% by weight, 150 ml of the carbon nanotube dispersion is added to 50 ml of the fluororubber solution so that the carbon nanotube content is 8%, and the stirrer is used under the condition of about 300 rpm. The mixture was stirred at room temperature for 16 hours and concentrated until the total volume reached about 50 ml. The obtained carbon nanotube composite material contains 100 mg of single-phase carbon nanotubes, 100 cc of MIBK, and 1150 mg of fluororubber.

As another example, a carbon nanotube composite film having a carbon nanotube content of 2, 8 or 12% by weight was prepared.

[Carbon nanotube composite film forming process]
A well-mixed solution was spray-coated on a silicon substrate heated to 100 ° C. in an amount of 50 to 200 μl each. The solvent in the carbon nanotube composite material was removed by heat drying to form a film. Spray coating and heat drying were repeated 40 times to obtain a carbon nanotube composite film having a film thickness of 15 μm. Then, it was further dried at 150 ° C. for 5 hours.

[Flatification process]
The carbon nanotube composite film was pressed on a silicon substrate coated with PDMS and heated to 150 ° C. The temperature was lowered to room temperature while being pressed and flattened to obtain the carbon nanotube composite film of the example. The water content of the obtained carbon nanotube composite film of this example was measured by the above-mentioned Karl Fischer reaction method. The water content of the carbon nanotube composite film of this example was 0.065%.

(Comparative Example 1)
As Comparative Example 1, a carbon nanotube composite film dispersed and formed in the air was produced using carbon nanotubes prepared in the air, not under moisture control as in the examples. The water content of the carbon nanotube composite film of Comparative Example 1 was 0.300%.

FIG. 6 is a scanning electron microscope (SEM) image of the main surface of the carbon nanotube composite film according to the present embodiment. FIG. 6A shows Example 1, and FIG. 6B shows Comparative Example 1. In Comparative Example 1, blistering irregularities in which the water contained in the carbon nanotube composite film has evaporated are observed. On the other hand, in the carbon nanotube composite film of Example 1, such unevenness is not observed, and it can be seen that the flatness is ensured. Although not shown, similar results were obtained in other examples.

(Comparative Example 2)
As Comparative Example 2, a carbon nanotube composite film which had not been subjected to a flattening step after film formation was prepared. FIG. 7 is a laser microscope image of the main surface of the carbon nanotube composite film according to this embodiment. FIG. 7 (a) shows Comparative Example 2, and FIG. 8 (b) shows Example 1. It can be seen that in Comparative Example 2 which is not flattened, the unevenness of the main surface is large. On the other hand, in the carbon nanotube composite film of Example 1, the unevenness of the main surface is significantly suppressed. In addition, the surface was measured using AFM, and the arithmetic mean roughness of the main surface was determined. In Comparative Example 2, the arithmetic mean roughness of the main surface was 1.5 μm, whereas in the carbon nanotube composite film of Example 1, the arithmetic mean roughness of the main surface was 0.17 μm, which was high flatness. Became clear. Although not shown, similar results were obtained in other examples.

From the above examples, it was clarified that the flatness of the main surface of the carbon nanotube composite film according to the present invention was significantly higher than that of the conventional one.

1 substrate, 7 substrate, 9 adhesion prevention layer, 10 carbon nanotubes, 30 elastomer, 100 carbon nanotube composite film

Claims (3)

It is a composite film composed of carbon nanotubes and elastomer.
With a film thickness of 1 μm or more and 15 μm or less,
The blending amount of the carbon nanotubes is 0.1% by weight or more and 15% by weight or less.
The residual water content of the composite film is 0.1% by weight or less.
A carbon nanotube composite film having an arithmetic mean roughness of the main surface of 10% or less of the film thickness. The carbon nanotubes, is not less 1μm or more in length, the average diameter is at 1nm or 30nm or less, a maximum in the range 1560 cm ^-1 or 1600 cm ^-1 The following spectrum obtained by measurement of the resonance Raman scattering measurement method When the peak intensity is G and ^{the maximum peak intensity in the range of 1310 cm -1} or more and 1350 cm ^-1 or less is D, the G / D ratio is 3 or more and the conductivity is 1 S / cm or more. The carbon nanotube composite film according to claim 1. The method for producing a carbon nanotube composite film according to claim 1 or 2.
After drying the carbon nanotubes under vacuum and / or heating
A paste containing carbon nanotubes is prepared under an argon atmosphere, a film is formed on the substrate with the paste, and a flattening treatment is further performed to produce a carbon nanotube composite film.
The paste further comprises an elastomer and
The method for producing a carbon nanotube composite film according to claim 1 or 2, wherein the carbon nanotube has a blending amount of 0.001% by weight or more and 15% by weight or less with respect to the paste.

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