Carbon nanotube dispersion and method for producing the same

Abstract

Provided is a carbon nanotube dispersion liquid in which the electrical characteristics of CNTs are excellent, and a method for producing the same. A gas flowing out from a CNT synthesis furnace (11) is circulated with respect to a liquid dispersant inside a diffuser (13). The dispersant used has a property of not foaming due to the circulation of the gas. CNTs in a dispersed state are contained in the gas flowing out from the CNT synthesis furnace (11). Thus, it is not necessary to impart ultrasonic waves to the CNTs using an ultrasonic wave crusher with a power of 150 W or more in order to disentangle the CNTs in a lump, and therefore it is possible to suppress the degree of damage to the CNTs due to defects being introduced. When the gas is circulated in the dispersant, it is possible to suppress the dispersant from becoming foamy and being discharged to the outside of the container, and the dispersant inside the container from drying out. Thus, it is possible to obtain a CNT dispersion liquid in which the electrical characteristics of CNTs are excellent.

Description

Technical Field

[0001] This invention relates to a CNT dispersion in which carbon nanotubes (i.e., CNTs) are dispersed in a liquid dispersant and a method for manufacturing the same. Background Technology

[0002] CNTs, especially single-layer and multi-layer CNTs, tend to solidify due to their own aggregation. Therefore, when used in transparent conductive films and composite materials, for example, a CNT dispersion is needed to break down the CNT blocks and disperse them, preventing them from re-aggregating. Conventionally, CNT blocks are placed in a dispersant containing a surfactant. A CNT dispersion is produced by applying ultrasound to the CNT blocks using an ultrasonic pulverizer with a power of 150W or higher. The ultrasound breaks down the CNT blocks, dispersing them in the dispersant. By including a surfactant in the dispersant, the CNTs are prevented from re-aggregating (see, for example, Japanese Patent Application Laid-Open No. 2005-89738).

[0003] In the aforementioned prior art, mechanical energy is applied to the CNTs using an ultrasonic crusher to break them apart, causing damage. This introduces defects into the CNTs and facilitates their reduction in size. Consequently, the electrical properties of the CNTs deteriorate.

[0004] To avoid this situation, the inventors of the present invention have investigated the circulation of a gas containing dispersed CNTs in a liquid dispersant. For example, a gas flowing from a CNT synthesis furnace can be used as the gas containing dispersed CNTs. The gas flowing from the CNT synthesis furnace contains CNTs synthesized in the CNT synthesis furnace. The CNTs can be dispersed by the CNT synthesis conditions. Alternatively, a gas in which CNTs are dispersed can also be used as the gas containing dispersed CNTs.

[0005] However, when using a dispersant containing surfactants as the liquid dispersant, when a gas containing CNTs is passed through the dispersant, foam forms on the surface of the dispersant due to bubbles generated by the gas flow. Bubbles are bubbles in the liquid. Foam is a bubble on the liquid surface, meaning the gas is covered by a liquid film. Due to the presence of the surfactant, the foam grows, becoming layered, stacked in two or more layers. This results in a multi-layered foam covering the surface of the dispersant. The gas introduced into the dispersant, after passing through the dispersant, is discharged to the outside of the container containing the dispersant. At this time, the foam formed on the surface of the dispersant is squeezed out by the gas flowing downstream of the container. That is, the dispersant is discharged to the outside of the container. During the passage of gas through the dispersant, the discharge of the dispersant continues as the foam growth continues. The inventors of this invention discovered that this is one of the reasons for the depletion of the dispersant inside the container, making it impossible to obtain a CNT dispersion. Summary of the Invention

[0006] The purpose of this invention is, in view of the above points, to provide a CNT dispersion with excellent electrical properties and a method for manufacturing the same.

[0007] To achieve the above objectives, according to one embodiment of the present invention,

[0008] Carbon nanotube dispersions possess the following characteristics:

[0009] A liquid dispersant that has the property of not foaming due to gas flow, or has the property of not growing foam formed on the surface of the dispersant by bubbles generated by gas flow; and

[0010] Carbon nanotubes, which are dispersed in a dispersant.

[0011] When the performance index of carbon nanotubes is set as αρ, the performance index is calculated by measuring the transmittance and film resistance at a wavelength of 550 nm for a transparent conductive film formed from a carbon nanotube dispersion, and by the following formula (1):

[0012] αρ=-ln(transmittance)×film resistance···Equation (1)

[0013] The performance index is less than 60 in the undoped state of carbon nanotubes.

[0014] This CNT dispersion is manufactured by passing a gas containing dispersed CNTs through a liquid dispersant. Therefore, it eliminates the need for an ultrasonic crusher with a power of 150W or higher to impart ultrasonic waves to the CNTs in order to break them apart. This also helps to reduce the extent to which defects are introduced into the CNTs and the shortening of their size.

[0015] Furthermore, as a dispersant, a dispersant is used that has the property of not foaming due to gas flow, or that the foam formed on the surface of the dispersant by bubbles generated by gas flow does not grow. "Foam not growing on the surface of the dispersant" means that the foam does not form two or more layers in a layered manner. Therefore, when a gas containing CNTs flows through the dispersant, the situation where the dispersant foams and escapes to the outside of the container, causing the dispersant inside the container to deplete, can be prevented. For this reason, a CNT dispersion can be obtained.

[0016] Therefore, it is possible to provide a CNT dispersion with a lower CNT performance index compared to conventional CNT dispersions, that is, a CNT dispersion with superior electrical properties.

[0017] Furthermore, according to other examples of the present invention, a method for manufacturing a carbon nanotube dispersion includes: passing a gas containing dispersed carbon nanotubes through a liquid dispersant, wherein the liquid dispersant has the property of not foaming due to the gas flow, or has the property of not growing foam formed on the surface of the dispersant by bubbles generated by the gas flow.

[0018] Therefore, it is unnecessary to use an ultrasonic crusher with a power of 150W or more to apply ultrasonic waves to the CNTs in order to break them apart. This reduces the extent to which defects are introduced into the CNTs and the shortening of their size can occur.

[0019] Furthermore, as a dispersant, a dispersant is used that has the property of not foaming due to gas flow, or that the foam formed on the surface of the dispersant by bubbles generated by gas flow does not grow. "Foam not growing on the surface of the dispersant" means that the foam does not form two or more layers in a layered manner. Therefore, when a gas containing CNTs is passed through the dispersant, the situation where the dispersant bubbles out of the container and causes the dispersant inside the container to deplete can be prevented. For this reason, a CNT dispersion can be obtained.

[0020] Therefore, a method for manufacturing CNT dispersions with superior electrical properties compared to conventional CNT dispersions is provided. Attached Figure Description

[0021] Figure 1 This is a schematic diagram showing the structure of the apparatus for manufacturing the CNT dispersion in the first embodiment.

[0022] Figure 2 This is a flowchart illustrating the manufacturing steps of the CNT dispersion manufacturing method in the first embodiment.

[0023] Figure 3AThis is a flowchart illustrating the manufacturing steps of the CNT dispersion manufacturing method in the second embodiment.

[0024] Figure 3B This is a flowchart illustrating the manufacturing steps of the CNT dispersion manufacturing method in the third embodiment.

[0025] Figure 4 The left side is a photograph showing the CNT dispersion prepared in Example 1. Figure 4 The image on the right is a comparison photo of NMP.

[0026] Figure 5 This is a photograph showing a transparent conductive film formed using the CNT dispersion obtained in Example 1.

[0027] Figure 6 This is a photograph of a transparent conductive film formed using the CNT dispersion obtained in Example 1.

[0028] Figure 7 The left side shows a photograph of the CNT dispersion obtained in Example 4. Figure 7 The image on the right is a comparison photo of NMP.

[0029] Figure 8 The left side shows a photograph of the liquid after the CNT dispersion obtained in Example 4 has been left to stand for 24 hours. Figure 8 The image on the right is a comparison photo of NMP.

[0030] Figure 9 The left side indicates that Figure 8 The image on the left shows the liquid after it has been stirred in an ultrasonic bath for 30 minutes. Figure 9 The image on the right is a comparison photo of NMP.

[0031] Figure 10 The first image from the left shows a photograph of a reference liquid after the CNT dispersion obtained in Example 4 has been left to stand for 24 hours. Figure 10 The second image from the left shows a sample of a reference solution diluted twice with NMP. Figure 10 The third image from the left shows a photograph of a reference liquid diluted four times with NMP. Figure 10 The fourth one from the left is a photograph of a base liquid diluted eight times with NMP.

[0032] Figure 11 This is a photograph showing the filter used in Example 7 and the CNTs captured by the filter.

[0033] Figure 12This is a photograph showing the CNT dispersion obtained in Example 7. Detailed Implementation

[0034] Hereinafter, embodiments of the present invention will be described with reference to the figures.

[0035] (First Implementation)

[0036] By using Figure 1 The CNT dispersion is manufactured using a method described in the apparatus 10 shown for manufacturing CNT dispersions. The CNT dispersion is a colloidal solution comprising a liquid dispersant and CNTs dispersed in the dispersant.

[0037] [Apparatus for manufacturing CNT dispersion]

[0038] like Figure 1 As shown, the CNT dispersion manufacturing apparatus 10 includes a CNT synthesis furnace 11, a raw material supply unit 12, a diffuser 13, a cooler 14, and a filter 15.

[0039] CNT synthesis furnace 11 is an electric furnace that synthesizes CNTs internally using a fluidized bed CVD (i.e., chemical vapor deposition) method. In the fluidized bed, the carbon source and catalyst are simultaneously supplied to the interior of the furnace. The synthesized CNTs can be any of the following: monolayer CNTs, bilayer CNTs, multilayer CNTs, or mixtures thereof.

[0040] The raw material supply unit 12 supplies carbon sources, along with catalysts, to the CNT synthesis furnace 11 as raw materials for CNT synthesis. The raw material supply unit 12 includes a first gas cylinder 21, a first supply flow path 22, a first MFC (mass flow controller) 23, a second gas cylinder 24, a second supply flow path 25, a second MFC 26, a third gas cylinder 27, a third supply flow path 28, a third MFC 29, a fourth supply flow path 30, a fourth MFC 31, a fifth supply flow path 32, a fifth MFC 33, a first container 34, and a second container 35.

[0041] The first gas cylinder 21 contains methane gas. The first supply flow path 22 is a gas flow path for supplying methane gas from the first gas cylinder 21 to the CNT synthesis furnace 11. One end of the first supply flow path 22 is connected to the outlet side of the first gas cylinder 21. The other end of the first supply flow path 22 is connected to the inlet side of the CNT synthesis furnace 11. A first MFC 23 is provided in the first supply flow path 22. The first MFC 23 is a flow adjustment unit that adjusts the flow rate of the methane gas flowing in the first supply flow path 22.

[0042] Hydrogen gas is contained in the second gas cylinder 24. The second supply flow path 25 is a gas flow path for supplying hydrogen gas from the second gas cylinder 24 to the CNT synthesis furnace 11. One end of the second supply flow path 25 is connected to the outlet side of the second gas cylinder 24. The other end of the second supply flow path 25 is connected to the middle of the first supply flow path 22. A second MFC 26 is provided in the second supply flow path 25. The second MFC 26 is a flow adjustment unit that adjusts the flow rate of hydrogen gas flowing in the second supply flow path 25.

[0043] Nitrogen gas is contained in the third gas cylinder 27. The third supply flow path 28 is a gas flow path for supplying nitrogen gas from the third gas cylinder 27 to the CNT synthesis furnace 11. One end of the third supply flow path 28 is connected to the outlet side of the third gas cylinder 27. The other end of the third supply flow path 28 is connected to the middle of the first supply flow path 22. A third MFC 29 is provided in the third supply flow path 28. The third MFC 29 is a flow adjustment unit that adjusts the flow rate of nitrogen gas flowing in the third supply flow path 28.

[0044] The fourth supply path 30 is a gas flow path for supplying ferrocene. One end of the fourth supply path 30 is connected to the outlet side of the third gas cylinder 27. The other end of the fourth supply path 30 is connected to the middle of the first supply path 22. A fourth MFC 31 is provided in the fourth supply path 30. The fourth MFC 31 is a flow adjustment unit that adjusts the flow rate of nitrogen flowing in the fourth supply path 30. A first container 34 is provided in the fourth supply path 30. Ferrocene is contained in the first container 34. Ferrocene is transported to the CNT synthesis furnace 11 by the nitrogen flowing in the fourth supply path 30.

[0045] The fifth supply flow path 32 is a gas flow path for supplying sulfur. One end of the fifth supply flow path 32 is connected to the outlet side of the third gas cylinder 27. The other end of the fifth supply flow path 32 is connected to the middle of the first supply flow path 22. A fifth MFC 33 is provided in the fifth supply flow path 32. The fifth MFC 33 is a flow adjustment unit that adjusts the flow rate of nitrogen flowing in the fifth supply flow path 32. A second container 35 is provided in the fifth supply flow path 32. Sulfur is contained in the second container 35. The sulfur is transported to the CNT synthesis furnace 11 by the nitrogen flowing in the fifth supply flow path 32.

[0046] The diffuser 13 is a device used to allow CNT-containing gas, which contains dispersed CNTs, to flow through a liquid dispersant. The CNT-containing gas used is the gas flowing out of the CNT synthesis furnace 11.

[0047] As a dispersant, a dispersant is used that has the property of not foaming due to gas flow, or the property of preventing foam formation on the surface of the dispersant caused by gas flow from growing, and also has the property of dispersing CNTs. "Non-foaming" means that no foam forms on the surface of the dispersant. "No foam formation on the surface of the dispersant caused by gas flow from growing" means that even if foam forms on the surface of the dispersant, the foam will not be layered in more than two layers. That is, even if foam forms on the surface of the dispersant where the upper side of the gas is covered by a film of liquid and the lower side of the gas faces the liquid, it will not become layered on top of other foams covering the surface of the dispersant; this is "no foam formation on the surface of the dispersant caused by gas flow from growing".

[0048] A dispersant possesses the property of "not foaming due to gas flow, or the property that foam formed by bubbles generated by gas flow on the surface of the dispersant does not grow." This is achieved by the dispersant not containing surfactants, containing a small amount of surfactants, or containing defoamers in a dispersant containing surfactants. Surfactants are a general term for substances whose molecules contain portions that are readily soluble in water and readily soluble in oil. Defoamers are substances that reduce the surface tension of a liquid film, causing bubbles to break, or that inhibit the formation of a liquid film, thus suppressing foam formation.

[0049] If a dispersant possesses such properties, either an organic solvent or an aqueous solution containing an inorganic dispersant can be used as a dispersant. Examples of organic solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), and dimethylacetamide (DMAc). Examples of inorganic dispersants include aluminum zinc oxide. Furthermore, when the dispersant contains an antifoamer, either a silicone-based or organic antifoamer is used. Silicone-based antifoamers are used for both organic solvents and aqueous solutions containing inorganic dispersants. Organic antifoamers are used for aqueous solutions containing inorganic dispersants.

[0050] The diffuser 13 has a container 41 that houses a dispersant inside, and an inlet flow path 42 that introduces CNT-containing gas into the dispersant. The inlet flow path 42 is constructed of a pipe. The gas inlet 42a of the inlet flow path 42 is connected to the outlet side of the CNT synthesis furnace 11. The gas outlet 42b of the inlet flow path 42 is located in the dispersant inside the container 41. The gas flowing out of the gas outlet 42b of the inlet flow path 42 circulates in the dispersant and flows out of the dispersant.

[0051] In this embodiment, the gas flowing out of the gas outlet 42b of the inlet flow path 42 becomes bubbles and travels in a straight line from bottom to top in the dispersant. Preferably, the bubbles travel in a meandering manner by placing obstacles or the like in the dispersant, or one bubble travels as multiple bubbles. This increases the probability of contact between the gas flowing out of the gas outlet 42b and the dispersant, making the CNTs more dispersed. Thus, the flow of CNT-containing gas in the dispersant includes various modes of movement of the CNT-containing gas. For example, the CNT-containing gas is not limited to traveling in a straight line in the dispersant, but also includes cases where the CNT-containing gas travels in a meandering manner.

[0052] The cooler 14 is a cooling unit that cools the dispersant inside the diffuser 13 using circulating coolant. The cooler 14 includes a container 51 that holds the coolant, an adjustment unit 52 that adjusts the temperature of the coolant, and coolant flow paths 53 and 54 for the coolant to flow between the container 51 and the adjustment unit 52. Part or all of the container 41 of the diffuser 13 is immersed in the coolant inside the container 51. The adjustment unit 52 cools the coolant and maintains its temperature at a constant level. The coolant cooled by the adjustment unit 52 flows through the coolant flow path 53 and is sent to the container 51. The coolant inside the container 51 flows through the coolant flow path 54 to the adjustment unit 52. The coolant inside the container 51 cools the dispersant inside the diffuser 13. Alternatively, components other than the cooler 14 can be used as the cooling unit.

[0053] Filter 15 is a trapping section that captures CNTs contained in the gas discharged from diffuser 13. The discharge path 43, which allows the gas, after flowing through the dispersant, to exit the diffuser 13, is connected to the upper part of the container 41 of diffuser 13. Filter 15 is located midway through the discharge path 43. Filter 15 is a mesh component.

[0054] [Preparation method of CNT dispersion]

[0055] like Figure 2 As shown, the method for manufacturing CNT dispersion includes a flow-through step S11 and a collection step S12.

[0056] In the flow process S11, CNT-containing gas is circulated in a liquid dispersant. Specifically, a carbon source and a catalyst are supplied to the CNT synthesis furnace 11 at a temperature suitable for CNT synthesis. For example, methane is supplied as the carbon source, and ferrocene as the catalyst. Furthermore, sulfur is supplied as an auxiliary catalyst, and nitrogen and hydrogen are supplied as the carrier gas and reducing gas, respectively. Thus, CNTs are synthesized inside the CNT synthesis furnace 11. The CNTs synthesized in the CNT synthesis furnace 11 flow out of the CNT synthesis furnace 11 along with the carrier gas, which is mainly composed of nitrogen. The gas flowing out of the CNT synthesis furnace 11 is a CNT-containing gas. Through the CNT synthesis conditions, CNTs can be dispersed in the gas flowing out of the CNT synthesis furnace 11.

[0057] The gas flowing from the CNT synthesis furnace 11 causes the diffuser 13 to flow from the gas inlet 42a to the gas outlet 42b via the inlet flow path 42. The gas exiting the gas outlet 42b flows through the dispersant, which has been cooled by the chiller 14, and then exits from the dispersant. In this way, the gas flowing from the CNT synthesis furnace 11 continuously flows from the CNT synthesis furnace 11 to the dispersant. As the gas exiting the gas outlet 42b becomes bubbles and passes through the dispersant, the CNTs are dispersed in the dispersant. The gas exiting the diffuser 13 flows through the outlet flow path 43 and is discharged to the outside.

[0058] In the capture process S12, the filter 15 captures the CNTs contained in the gas flowing in the discharge path 43.

[0059] After a specified time in the flow process S11, the CNT dispersion is recovered from the diffuser 13. This produces a CNT dispersion in which CNTs are dispersed in a dispersant.

[0060] The gas exiting the diffuser 13 contains a portion of the CNTs synthesized in the CNT synthesis furnace 11. Although not shown, multi-stage diffusers 13 can be provided to improve CNT recovery rate. That is, multiple diffusers 13 can also be provided in series.

[0061] [Evaluation of the electrical properties of CNTs]

[0062] The electrical properties of the CNTs contained in the CNT dispersion manufactured by the above method were evaluated as follows, using the performance index of the transparent conductive film. The performance index of the transparent conductive film is also the performance index of the CNTs.

[0063] First, the prepared CNT dispersion is filtered through a filter (not shown). A CNT film is then formed on the filter. The formed CNT film is transferred onto a substrate such as a quartz substrate. This forms a transparent conductive film. The transmittance and film resistance of the transparent conductive film are then measured.

[0064] Here, there is a trade-off between the transmittance and the film resistance of the transparent conductive film. Therefore, it is difficult to evaluate the electrical properties of the transparent conductive film by comparing only the measured values ​​of transmittance and film resistance. Thus, the performance index αρ is used as an indicator to easily evaluate the electrical properties of the transparent conductive film. αρ is represented by the following formula (1). The smaller the value of αρ, the better the electrical properties.

[0065] αρ=-ln(transmittance)×film resistance···Equation (1)

[0066] In equation (1), ln represents the natural logarithm. The transmittance in equation (1) is the measured transmittance of the transparent conductive film at a wavelength of 550 nm. The unit of transmittance is %. The film resistance in equation (1) is the measured film resistance of the transparent conductive film. The unit of film resistance is Ω / □. Film resistance is also called surface resistance.

[0067] Thus, the performance index αρ is calculated using the measured values ​​of the transmittance and film resistance of the transparent conductive film formed with CNT dispersion, and the formula (1).

[0068] Japanese Patent Application Publication No. 2016-126847, as an example of prior art, describes the transmittance and film resistance of a transparent conductive film formed using a CNT dispersion. In this prior art, the transmittance is measured to be 87% and the film resistance is measured to be 430 Ω / □ in the undoped state of CNTs, therefore αρ is 60.

[0069] In contrast, according to the CNT dispersion manufacturing method of this embodiment, a CNT dispersion with a performance index αp of less than 60 is obtained in the undoped state of CNTs. That is, a CNT dispersion with superior electrical properties is obtained. Furthermore, the undoped state refers to the state in which no dopant is applied to the CNTs. A dopant is a substance used to improve the conductivity of CNTs.

[0070] As explained above, the method for manufacturing a CNT dispersion according to this embodiment includes passing a gas containing dispersed CNTs through a liquid dispersant. By passing a gas containing CNTs through the dispersant, a CNT dispersion in which CNTs are dispersed is manufactured. Therefore, it is unnecessary to use an ultrasonic crusher with a power of 150W or more to impart ultrasonic waves to the CNTs in order to break them apart. This reduces the likelihood of damage to the CNTs caused by defects being introduced into them and the extent to which CNTs become shorter.

[0071] Furthermore, as a dispersant, a dispersant with the property of not foaming due to gas flow, or with the property of not growing foam formed on the surface of the dispersant by bubbles generated by gas flow, is used. This prevents the dispersant from foaming and discharging to the outside of the container 41 when CNT-containing gas flows through it, thus preventing the depletion of the dispersant inside the container 41. Therefore, a CNT dispersion can be obtained.

[0072] Therefore, the CNT dispersion manufacturing method of this embodiment can produce a CNT dispersion with excellent electrical properties.

[0073] The following effects can be obtained by the method for manufacturing CNT dispersion according to this embodiment.

[0074] (1) In the flow process S11, a dispersant that does not contain surfactants is used, which has the property of not foaming due to gas flow, or the property of not growing foam formed on the surface of the dispersant by bubbles generated by gas flow. Therefore, when the manufactured CNT dispersion is used to manufacture structures such as transparent conductive films, the deterioration of the electrical properties of CNTs due to residual surfactants can be avoided.

[0075] (2) In the flow process S11, the gas containing CNTs in a dispersed state is used, which is the gas flowing out of the CNT synthesis furnace 11 containing CNTs synthesized in the furnace. The gas flowing out of the CNT synthesis furnace 11 continuously flows from the CNT synthesis furnace 11 into the dispersant inside the diffuser 13. Thus, the synthesis and dispersion of CNTs are carried out in a continuous process. Therefore, compared with the case where the synthesis and dispersion of CNTs are carried out in separate, discontinuous processes, the manufacturing process of the NT dispersion can be simplified.

[0076] (3) In the flow process S11, when the gas containing CNT flows through the dispersant, the dispersant is cooled. As a result, compared with the dispersant temperature being at room temperature, the saturated vapor pressure of the dispersant can be reduced, and the evaporation of the dispersant can be suppressed. As a result, the situation where the dispersant evaporates and the dispersant inside the container 41 is depleted can also be suppressed.

[0077] Furthermore, the CNT dispersion of this embodiment includes a liquid dispersant having the property of not foaming due to gas flow or the property of not growing foam formed on the surface of the dispersant by bubbles generated by gas flow, and CNTs dispersed in this dispersant. Moreover, the performance index αρ of the CNTs contained in the CNT dispersion is less than 60 in the undoped state of the CNTs.

[0078] This CNT dispersion, as described in the above-described method for manufacturing a CNT dispersion, is produced by passing a gas containing dispersed CNTs through a liquid dispersant. Therefore, as mentioned above, it is possible to suppress damage to the CNTs caused by defects being introduced into them and the CNTs becoming shorter in size.

[0079] Furthermore, the dispersant contained in this CNT dispersion has the property of not foaming due to gas flow, or the property of not growing foam formed on the surface of the dispersant by bubbles generated by gas flow. Therefore, when gas containing CNTs flows through the dispersant, it is possible to prevent the dispersant from becoming foam and discharging to the outside of the container 41, thus preventing the dispersant inside the container 41 from drying up. For this reason, a CNT dispersion can be obtained.

[0080] Therefore, compared with previous CNT dispersions, it can provide a CNT dispersion with a low performance index αρ, that is, excellent electrical properties of CNTs.

[0081] Furthermore, the dispersant contained in this CNT dispersion, by not containing surfactants, possesses the property of not foaming due to gas flow, or of not allowing foam formed on the surface of the dispersant by bubbles generated by gas flow to grow. Therefore, when using this CNT dispersion to manufacture structures such as transparent conductive films, the degradation of the electrical properties of CNTs due to residual surfactants can be avoided.

[0082] Furthermore, to date, no one other than the inventors of this invention has discovered the method for manufacturing the CNT dispersion of this invention, nor the CNT dispersion itself. One reason for this is that using a surfactant as a dispersant was common technical knowledge at the time of the application. Therefore, it can be assumed that even if attempts were made to use a dispersant without surfactants and allow CNT-containing gas to circulate within the dispersant, the aforementioned problems prevented further investigation. Moreover, CNT synthesis and dispersant manufacturing are separate industries. An environment suitable for conducting research spanning the synthesis and dispersion of CNTs is lacking, which is another reason for this.

[0083] (Second Implementation)

[0084] like Figure 3AAs shown, the method for manufacturing the CNT dispersion in this embodiment includes a flow-through step S11, a collection step S12, and a concentration adjustment step S13. The flow-through step S11 and the collection step S12 are the same as in the first embodiment.

[0085] In the concentration adjustment step S13, the concentration of CNTs in the liquid obtained through the flow-through step S11 is adjusted in a way that suppresses the formation of CNT agglomerates. The concentration adjustment is performed by adding a dispersant to the liquid obtained through the flow-through step S11.

[0086] According to this embodiment, the same effect as the first embodiment can be obtained by using the same structure as the first embodiment. Furthermore, the CNT dispersion manufacturing method of this embodiment can achieve the following effects.

[0087] (1) By adjusting the concentration step S13, the formation of CNT aggregates when the CNT dispersion is left to stand for a long time can be suppressed. In addition, if the formation of aggregates is suppressed compared with the concentration of CNTs before adjustment, a small amount of CNT aggregates may still be formed after the concentration of CNTs is adjusted.

[0088] (Third Implementation)

[0089] like Figure 3B As shown, the method for manufacturing the CNT dispersion in this embodiment includes a flow-through step S11, a collection step S12, and a dispersion step S14. The flow-through step S11 and the collection step S12 are the same as in the first embodiment. The dispersant used in the flow-through step S11 is a first dispersant. The CNT dispersion manufactured through the flow-through step S11 is a first dispersion in which CNTs are dispersed in the first dispersant.

[0090] In the dispersion step S14, with the CNTs obtained in the collection step S12 added to a liquid second dispersant, a second dispersion of CNTs is created by vibrating the CNTs in the second dispersant. The second dispersant is the same type as the first dispersant. The second dispersant only needs to have the property of dispersing CNTs, and can also be a different type of dispersant from the first dispersant. The second dispersant is contained in a container other than the container 41 of the diffuser 13. The vibration applied to the CNTs is ultrasonic waves with a power of approximately 30-55W.

[0091] According to this embodiment, the structure is the same as that of the first embodiment, and therefore the same effects as those of the first embodiment can be obtained. Furthermore, the method for manufacturing the CNT dispersion according to this embodiment can achieve the following effects.

[0092] (1) Conventionally, for dispersants containing CNT blocks, a CNT dispersion could not be obtained by applying ultrasound with a power of 150W or higher. In contrast, according to this embodiment, a second dispersion can be obtained in the dispersion step S14 by applying ultrasound with a lower power than before. That is, a second dispersion can be produced by applying less mechanical energy to the CNTs in the second dispersant. The CNTs captured in the capture step S12 have passed through the first dispersant in the flow step S11. This can be considered the main reason why a CNT dispersion can be obtained by applying ultrasound with a lower power than before.

[0093] Therefore, it is possible to suppress the extent to which CNTs are damaged by defects introduced into them and the resulting reduction in their size. As a result, it is also possible to produce CNT dispersions with superior electrical properties compared to the past.

[0094] In this way, a first dispersion and a second dispersion can be produced. According to this embodiment, most of the CNTs synthesized in the CNT synthesis furnace 11 can be made into a CNT dispersion. Furthermore, when the CNT dispersion is used, the second dispersion can also be mixed with the first dispersion. Moreover, the first dispersion recovered in the circulation process S11 can also be used as the second dispersant in the dispersion step S14.

[0095] (Other implementation methods)

[0096] (1) In the above embodiments, a transparent conductive film is formed in order to evaluate the electrical properties of CNTs, but the use of CNT dispersion is not limited to transparent conductive film.

[0097] (2) In the above embodiments, the CNT synthesis method is the fluidized bed CVD method. However, the CNT synthesis method can be any method that allows the synthesized CNTs to be recovered using gas.

[0098] (3) In the above embodiment, the gas flowing out of the CNT synthesis furnace 11 is directly blown into the dispersant. However, the gas flowing out of the CNT synthesis furnace 11 may also be stored in a container and then blown into the dispersant from the container. In this case, the gas flow stops because the gas flowing out of the CNT synthesis furnace 11 is stored in the container. Therefore, the gas flowing out of the CNT synthesis furnace 11 does not flow continuously from the CNT synthesis furnace 11 to the dispersant.

[0099] (4) In the above embodiment, the gas containing CNTs in a dispersed state is the gas flowing out of the CNT synthesis furnace 11. However, it is not limited to this, and the gas containing CNTs that has been dispersed by any method may also be used as the gas containing CNTs in a dispersed state.

[0100] (5) In the above embodiment, the dispersant is cooled in the flow process S11 in order to suppress the evaporation of the dispersant. However, if the CNT dispersion can be recovered even if the dispersant evaporates, the dispersant may not be cooled in the flow process S11.

[0101] (6) When using the CNT dispersion prepared according to the above embodiments, doping of CNTs with dopants can also be performed. Furthermore, after the structure such as the transparent conductive film is formed, the structure can be subjected to atmospheric heat treatment.

[0102] (7) This invention is not limited to the embodiments described above, and can be appropriately modified within the scope of the claimed protection, including various variations and modifications within the same range. In the above embodiments, the elements constituting the embodiments are not necessarily essential, except where specifically stated to be necessary or where they are obviously necessary in principle. Furthermore, in the above embodiments, when referring to the number, quantity, quantity, range, etc., of the structural elements of the embodiments, the specific number is not limited to that number, except where specifically stated to be necessary or where they are obviously necessary in principle.

[0103] Example

[0104] (Example 1)

[0105] The inventor of this invention used Figure 1 The CNT dispersion was manufactured by the CNT dispersion manufacturing method of the first embodiment of the CNT dispersion manufacturing apparatus 10.

[0106] Specifically, CNTs are synthesized using a fluidized bed CVD method. The synthesis conditions are as follows: methane is used as the carbon source, ferrocene as the catalyst, and sulfur as the co-catalyst. The internal temperature of the CNT synthesis furnace 11 is 950°C, the methane concentration is 1.4 vol%, the hydrogen concentration is 1.4 vol%, the total flow rate is 1100 sccm, the ferrocene heating temperature is 30°C, the ferrocene flow rate is 120 sccm, the sulfur heating temperature is 60°C, and the sulfur flow rate is 50 sccm. The flow conditions for the CNT-containing gas are as follows: the dispersant inside the diffuser 13 is 50 mL of NMP. The temperature of the coolant supplied to container 51 is 10°C. The gas supply time from the CNT synthesis furnace 11 to the diffuser 13 is 4 hours.

[0107] Figure 4 The liquid in the container on the left is a CNT dispersion obtained in Example 1. Figure 4 The liquid in the container on the right is NMP in its state before the CNT gas was circulated. Figure 4The liquid in the container on the right side was compared with the color of the CNT dispersion obtained in Example 1, while... Figure 4 Indicates. For example... Figure 4 As shown, NMP is colorless, while the CNT dispersion obtained in Example 1 is colored. Thus, CNTs are dispersed in the obtained CNT dispersion, and no CNT aggregates are formed. Furthermore, the reduction in NMP after the experiment was less than 5%. This reduction is largely due to residues adhering to the diffuser 13.

[0108] The inventors of this invention used a carbon aerosol analyzer manufactured by Tokyo Dairek Co., Ltd. to determine the CNT concentration of the obtained CNT dispersion. The result was that the CNT concentration was 0.6 μg / mL.

[0109] Next, the inventors diluted the obtained CNT dispersion with NMP to a 1 / 2 ratio, and then used a PTTE membrane filter with a diameter of 47 mm to perform suction filtration on 3 mL of the solution. A SUS perforated mask with circular holes of 10 mm diameter was provided on the downstream side of the filter due to the filter area being a circle with a diameter of 10 mm. Then, the CNT film on the filter was transferred onto a quartz substrate. Thus, as... Figure 5 As shown, a transparent conductive film 62 is formed on the quartz substrate 61.

[0110] Furthermore, the inventors of this invention used a spectrophotometer manufactured by Optosilius Co., Ltd., under the trade name FLAME, to measure the transmittance of the transparent conductive film 62 at a wavelength of 550 nm. Moreover, the thin-film resistance of the transparent conductive film 62 was measured using a 4-probe detector manufactured by Heisol Co., Ltd., under the trade name SR-H1000C. The results showed a transmittance of 83%, a thin-film resistance of 172 Ω / □, and an αρ of 33.

[0111] Depend on Figure 6 It can be seen that in the transparent conductive film 62, the fine CNT wire bundles form a CNT network.

[0112] Furthermore, the inventors of this invention measured the infrared absorption spectrum of the transparent conductive film 62 in order to study the doping effect of the dispersant itself. As a result, the same absorption spectrum as that of the CNTs used for dispersion was obtained, confirming that there was no doping based on the dispersant.

[0113] The results above show that by using the CNT dispersion prepared in Example 1, a transparent conductive film with superior properties not previously available can be produced.

[0114] (Comparative Example 1)

[0115] The inventor of this invention, Figure 1 In the CNT dispersion manufacturing apparatus 10 shown, 50 mL of water with 1% sodium dodecylbenzene sulfate added as a surfactant was used as the dispersant. Furthermore, the chiller 14 was not used, and the dispersant was kept at room temperature. Other conditions were the same as in Example 1, and the CNT dispersion was attempted to be manufactured using the same method as in Example 1. As a result, foam continued to grow inside the diffuser 13, and the dispersant flowed out in a foamy state to the downstream side of the diffuser 13. Therefore, the CNT dispersion could not be recovered.

[0116] (Example 2)

[0117] The inventors of this invention used DMF as the dispersant inside the diffuser 13. Otherwise, a CNT dispersion was prepared in the same manner as in Example 1, forming a transparent conductive film. Furthermore, the transmittance and film resistance of the transparent conductive film were measured in the same manner as in Example 1. The results showed a transmittance of 86.9%, a film resistance of 310 Ω / □, and an αp of 43.

[0118] (Example 3)

[0119] The inventors of this invention used DMAc as the dispersant inside the diffuser 13. Otherwise, a CNT dispersion was prepared in the same manner as in Example 1, forming a transparent conductive film. Furthermore, the transmittance and film resistance of the transparent conductive film were measured in the same manner as in Example 1. The results showed a transmittance of 85.2%, a film resistance of 290 Ω / □, and an αp of 46.

[0120] (Example 4)

[0121] The inventors of this invention supplied the gas flowing from the CNT synthesis furnace 11 to the diffuser 13 for 8 hours, and otherwise produced a CNT dispersion in the same manner as in Example 1. In this embodiment, compared with Example 1, the CNT dispersion contains more CNTs due to the longer supply time.

[0122] Figure 7 The liquid in the container on the left is the CNT dispersion that has just been recovered from diffuser 13. Figure 7 The liquid in the container on the right is NMP in its state before the CNT gas was introduced. For example... Figure 7 As shown, the CNT dispersion just recovered from diffuser 13 is colored, indicating that the CNTs have been dispersed.

[0123] Figure 8 The liquid in the container on the left is the liquid after the CNT dispersion recovered from diffuser 13 has been left for 24 hours. Figure 8The liquid in the container on the right is NMP in its previous state before the flow of CNT gas. Figure 8 It can be seen that after the CNT dispersion recovered from diffuser 13 was left for 24 hours, CNT aggregates were produced.

[0124] The inventors of this invention applied ultrasound to a liquid that had been left to stand for 24 hours using an ultrasonic bath with an ultrasonic power of 55W, and stirred it for 30 minutes. The result was as follows: Figure 9 As shown, the CNT aggregates disappeared, and the CNTs dispersed again. Figure 9 The liquid in the container on the left is the liquid that has been left to stand for 24 hours and then stirred. Figure 9 The liquid in the container on the right is NMP in its state before the CNT-containing gas was circulated. Moreover, although not shown in the figure, the inventors of this invention have confirmed that even when shaking is performed only while the liquid that has formed agglomerates is in the bottle, instead of stirring by an ultrasonic bath, the CNT agglomerates disappear.

[0125] In conventional CNT dispersions, when aggregates form, stirring with an ultrasonic bath at approximately 55W or shaking while the CNTs are in the bottle fails to redisperse them. In contrast, with the CNT dispersion of this embodiment, even if CNT aggregates form, the CNTs can be redispersed by applying weak vibrations to a degree that conventional CNT dispersions could not achieve.

[0126] The dispersant contained in the CNT dispersion obtained in the flow process S11 has the property of dispersing CNTs. Therefore, it is believed that even if CNT aggregates are formed in the CNT dispersion, the cohesion is weak. It is therefore believed that even weak vibrations can redisperse CNTs.

[0127] (Example 5)

[0128] The inventors of this invention performed the concentration adjustment step S13 of the second embodiment to obtain a CNT dispersion. Specifically, the CNT dispersion obtained in Example 4 was prepared as a liquid that produced aggregates. The prepared liquid was diluted with NMP to 2, 4, and 8 times, producing multiple portions of liquid with different CNT concentrations. Furthermore, each portion of liquid was stirred by applying ultrasound to an ultrasonic bath with an ultrasonic power of 55W for 20 minutes.

[0129] Figure 10 The liquid in the container marked "×1" is the liquid before dilution, that is, the reference liquid. Figure 10 The containers labeled "×2", "×4", and "×8" contain liquids that have been diluted with NMP to a concentration of 2, 4, and 8 times, respectively. Figure 10As shown, the agglomerates disappeared in the liquid diluted 4 times and 8 times. Even after being left for more than a month, no agglomerates formed in the 4-fold and 8-fold diluted liquids. This indicates that the smaller the proportion of CNTs relative to the overall CNT dispersion, the more effectively the formation of agglomerates is suppressed.

[0130] In cases where aggregates form in conventional CNT dispersions, simply diluting the CNT dispersion is insufficient to disperse the CNTs. Specifically, when a conventional CNT dispersion containing a surfactant is diluted with water, the concentration of the surfactant decreases. Consequently, CNT aggregates are formed.

[0131] In contrast, even if CNT aggregates form in the CNT dispersion obtained in Example 4, the CNTs can be redispersed by diluting the CNT dispersion with a dispersant. Furthermore, by reducing the CNT concentration in the CNT dispersion, the formation of aggregates during prolonged storage of the CNT dispersion can be suppressed.

[0132] (Example 6)

[0133] The inventors of this invention used the same method as in Example 1 to form a transparent conductive film after manufacturing the CNT dispersion. Furthermore, the transmittance and film resistance of the transparent conductive film were measured in the same manner as in Example 1. The results showed a transmittance of 97.0%, a film resistance of 264 Ω / □, and αρ of 36. Furthermore, the inventors of this invention subjected the transparent conductive film to a heat treatment at 250°C for 30 minutes in air. Measurements of the transmittance and film resistance of the heat-treated transparent conductive film showed that αρ increased to 25.

[0134] (Example 7)

[0135] The inventor of this invention used Figure 1 The CNT dispersion was produced by performing the dispersion step S14 of the third embodiment in the CNT dispersion manufacturing apparatus 10. The synthesis conditions of CNTs and the flow conditions of CNT-containing gas were the same as in Example 1.

[0136] Specifically, the inventor of this invention will be... Figure 11 The CNTs captured by filter 15 were placed in 80 mL of NMP. The liquid was agitated for 60 minutes by applying ultrasound to it using an ultrasonic bath with a power of 55 W. The result was the acquisition of… Figure 12 The CNT dispersion shown is illustrated. The CNT concentration of the obtained CNT dispersion was determined in the same manner as in Example 1. The result was a CNT concentration of 2.0 μg / mL. No aggregates were formed after the CNT dispersion was allowed to stand for one week.

[0137] Furthermore, a transparent conductive film was formed using the obtained CNT dispersion in the same manner as in Example 1. The transmittance and film resistance of the transparent conductive film were then measured. The results showed a transmittance of 95%, a film resistance of 970 Ω / □, and an αp of 48.

[0138] A dispersant is attached to the surface of the CNTs captured by filter 15 downstream of the dispersant. This dispersant has the property of dispersing CNTs. Therefore, it is believed that even if the CNTs captured by filter 15 agglomerate, the agglomeration force is weak. Thus, it is believed that CNTs can be dispersed by subjecting them to a weaker vibration than before.

[0139] [Technical Feature 1]

[0140] A carbon nanotube dispersion, comprising:

[0141] A liquid dispersant that has the property of not foaming due to gas flow, or has the property of not growing foam formed on the surface of the dispersant by bubbles generated by gas flow; and

[0142] Carbon nanotubes, which are dispersed in the dispersant,

[0143] When the performance index of the carbon nanotubes is set as αρ, the performance index is calculated by the measured values ​​of the transmittance and film resistance of the transparent conductive film formed by the carbon nanotube dispersion at a wavelength of 550 nm, and the following formula (1):

[0144] αρ=-ln(transmittance)×film resistance···Equation (1)

[0145] The performance index is less than 60 in the undoped state of the carbon nanotubes.

[0146] [Technical Feature 2]

[0147] The carbon nanotube dispersion as described in technical feature 1, wherein the dispersant has the property of not foaming by not containing a surfactant, or has the property of not growing foam formed by the bubbles on the surface of the dispersant.

[0148] [Technical Feature 3]

[0149] A method for manufacturing a carbon nanotube dispersion, comprising:

[0150] A gas containing dispersed carbon nanotubes is passed through a liquid dispersant, which has the property of not foaming due to the passage of gas, or has the property of not growing foam formed on the surface of the dispersant by bubbles generated by the passage of gas.

[0151] [Technical Feature 4]

[0152] The method for manufacturing a carbon nanotube dispersion as described in technical feature 3, wherein, in the circulation, the dispersant has the property of not foaming by not containing a surfactant, or has the property of not growing foam formed by the bubbles on the surface of the dispersant.

[0153] [Technical Feature 5]

[0154] In the method for manufacturing a carbon nanotube dispersion as described in technical feature 3 or 4, during the flow, a gas flowing out of the synthesis furnace in a state containing carbon nanotubes in the dispersed state is used as the gas.

[0155] The gas exiting the synthesis furnace flows continuously from the synthesis furnace to the dispersant.

[0156] [Technical Feature 6]

[0157] In the method for manufacturing a carbon nanotube dispersion according to any one of claims 3 to 5, the dispersant is cooled during the flow.

[0158] [Technical Feature 7]

[0159] The method for manufacturing a carbon nanotube dispersion according to any one of claims 3 to 6, wherein the method for manufacturing the carbon nanotube dispersion comprises:

[0160] For the liquid obtained through the circulation, the concentration of the carbon nanotubes contained in the liquid is adjusted in a manner that inhibits the formation of carbon nanotube aggregates.

[0161] [Technical Feature 8]

[0162] The method for manufacturing a carbon nanotube dispersion according to any one of claims 3 to 7, wherein the dispersant used in the flow is a first dispersant, and a first dispersion in which the carbon nanotubes are dispersed in the first dispersant is manufactured through the flow.

[0163] The method for manufacturing the carbon nanotubes includes:

[0164] The carbon nanotubes contained in the gas exiting from the first dispersant; and

[0165] With the carbon nanotubes obtained by the capture added to a second dispersant in a liquid, a second dispersion in which the carbon nanotubes are dispersed in the second dispersant is produced by applying vibration to the carbon nanotubes in the second dispersant.

Claims

1. A carbon nanotube dispersion, characterized in that, have: A liquid dispersant that has the property of not foaming due to gas flow, or has the property of not growing foam formed on the surface of the dispersant by bubbles generated by gas flow; and Carbon nanotubes, which are dispersed in the dispersant, The liquid dispersant is obtained by passing a gas containing dispersed carbon nanotubes through a liquid dispersant, the liquid dispersant having the property of not foaming due to the gas flow, or having the property of not growing foam formed on the surface of the dispersant by bubbles generated by the gas flow. In the aforementioned flow, the gas containing the dispersed carbon nanotubes is the gas flowing out of the synthesis furnace in a state containing carbon nanotubes synthesized by the synthesis furnace. The gas exiting the synthesis furnace flows continuously from the synthesis furnace to the dispersant. When the performance index of the carbon nanotubes is set as αρ, the performance index is calculated by measuring the transmittance and film resistance at a wavelength of 550 nm for the transparent conductive film formed by the carbon nanotube dispersion and the following formula (1): αρ=-ln(transmittance)×film resistance···Equation (1) The performance index is below 46 in the undoped state of the carbon nanotubes.

2. The carbon nanotube dispersion as described in claim 1, characterized in that, The dispersant has the property of not foaming by not containing surfactants, or has the property of not growing foam formed by the bubbles on the surface of the dispersant.

3. A method for manufacturing a carbon nanotube dispersion, characterized in that, include: A gas containing dispersed carbon nanotubes is passed through a liquid dispersant, which has the property of not foaming due to the gas flow, or has the property of not growing foam formed by bubbles generated by the gas flow on the surface of the dispersant. In the aforementioned flow, the gas containing the dispersed carbon nanotubes is the gas flowing out of the synthesis furnace in a state containing carbon nanotubes synthesized by the synthesis furnace. The gas exiting the synthesis furnace flows continuously from the synthesis furnace to the dispersant.

4. The method for manufacturing the carbon nanotube dispersion as described in claim 3, characterized in that, In the circulation, the dispersant has the property of not foaming by not containing surfactants, or has the property of not growing foam formed by the bubbles on the surface of the dispersant.

5. The method for manufacturing the carbon nanotube dispersion as described in claim 3 or 4, characterized in that, During the flow, the dispersant is cooled.

6. The method for manufacturing the carbon nanotube dispersion as described in claim 3 or 4, characterized in that, The method for manufacturing the carbon nanotube dispersion includes: For the liquid obtained through the circulation, the concentration of the carbon nanotubes contained in the liquid is adjusted in a manner that inhibits the formation of carbon nanotube aggregates.

7. The method for manufacturing the carbon nanotube dispersion as described in claim 3 or 4, characterized in that, The dispersant used in the circulation is a first dispersant, and the carbon nanotubes are dispersed in the first dispersant through the circulation to produce a first dispersion. The method for manufacturing the carbon nanotubes includes: The carbon nanotubes contained in the gas exiting from the first dispersant; and With the carbon nanotubes obtained by the capture added to a second dispersant in a liquid, a second dispersion in which the carbon nanotubes are dispersed in the second dispersant is produced by applying vibration to the carbon nanotubes in the second dispersant.

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