JP2021134125A - Production method of carbon nanotube dispersion - Google Patents

Abstract

To provide a production method of a carbon nanotube dispersion, with which a carbon nanotube dispersion with a desired characteristic can be produced with high accuracy.SOLUTION: A production method of a carbon nanotube dispersion includes an oxidation treatment step to heat a liquid to be treated containing an oxidizing agent and carbon nanotubes by using a heater. In the production method of the carbon nanotube dispersion, time to turn off the heater is determined based on a value of a product M*ΔT*tr, in which a mass or volume value of the liquid to be treated is set to be M, a rate of temperature rise of the liquid to be treated from time to turn on the heater to arrival time of temperature of the liquid to be treated to treatment temperature is set to be ΔT, and a treatment time period from arrival time of temperature of the liquid to be treated to treatment temperature to time to turn off of the heater is set to be tr.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for producing a carbon nanotube dispersion liquid.

Since carbon nanotubes (hereinafter, sometimes referred to as "CNT") have higher current density resistance and electrical conduction characteristics than copper, they are used in electronic devices such as semiconductor devices, displays, LEDs, lithium ion batteries, and solar cells. It is preferably used as a material. As a material for an electronic device, for example, a CNT dispersion liquid obtained by dispersing CNTs in a solvent is uniformly applied onto a silicon wafer by a coating method such as spin coating or inkjet, and then dried and high-temperature annealed. The formed CNT thin film is used.

In order to produce a high-quality electronic device that is uniform and has excellent reproducibility, it is necessary to form a CNT thin film using a CNT dispersion liquid having desired characteristics. The characteristics of the CNT dispersion liquid used for forming the CNT thin film include CNT crystallinity, functional groups, diameter, length, agglutination rate, carbon impurity content and the like. In particular, in order to manufacture an electronic device having excellent uniformity and reproducibility, it is important to accurately control the length of CNTs to about 100 nm or less. If the CNT length is not uniform, the characteristics of the manufactured electronic device will vary. Further, when long CNTs are mixed, they become nuclei and short carbon nanotubes gather to cause agglutination in the CNT dispersion liquid, so that the uniformity of the manufactured electronic device deteriorates. On the contrary, when the length of CNT is shortened to about 10 nm or less, the characteristics of amorphous carbon appear strongly, and the characteristics of a desired electronic device cannot be obtained.

The length of the CNT powder used as the raw material of the CNT dispersion liquid depends on the method for producing the CNT, and usually has a large range of 1 μm to 1 mm. Therefore, in order to reduce the length of CNTs in the produced CNT dispersion liquid to about 100 nm or less, it is necessary to cut the CNT powder accurately to about 1/100 to 1 / 100,000. As a method for cutting CNT powder, for example, mechanical cutting methods such as jet milling and ball milling are used, but it is difficult to cut to 1 μm or less by these methods.

As a method capable of decomposing and / or cutting CNT powder to a length of about 100 nm or less, liquid phase oxidation treatment with a mixed acid of sulfuric acid and nitric acid or an oxidizing agent such as nitric acid is known.
For example, in Patent Document 1, by performing liquid phase oxidation in which the pre-purification CNT-containing composition is heated and refluxed using nitric acid having a predetermined concentration, no catalyst remains, the heat resistance is high, and carbon sub-carbon is added. It has been reported that a CNT-containing composition with a small amount of product can be obtained in a high yield.
Further, Patent Document 2 discloses a method of selecting semiconducting CNTs in a large amount and with high purity by treating CNTs with a mixed acid of sulfuric acid and nitric acid.

International Publication No. 2018/043487 Japanese Unexamined Patent Publication No. 2005-194180

However, in the above-mentioned conventional oxidation treatment method, it is difficult to accurately produce a CNT dispersion liquid having desired characteristics.
Therefore, an object of the present invention is to provide a method for producing a carbon nanotube dispersion liquid, which can accurately produce a carbon nanotube dispersion liquid having desired characteristics.

It is considered that the reason why it is difficult to accurately produce the CNT dispersion liquid having desired characteristics in the above-mentioned conventional oxidation treatment method is that it is difficult to accurately control the end point of the oxidation treatment. .. For example, in order to cut a CNT having a length of about 1 mm into a length of about 100 nm, it usually takes about 10 hours depending on the type and concentration of the oxidizing agent used, but the end point is 30. If it is set as early as minutes, a large amount of long CNTs will remain, and the dispersion characteristics of the produced CNT dispersion will deteriorate. On the contrary, if it is set as late as 30 minutes, the CNTs are excessively cut and a large amount of carbon impurities such as amorphous carbon are generated. Further, it is difficult to predict the end point because the end point may differ depending on the shape and heat insulation efficiency of the apparatus used for the oxidation treatment, the process conditions of the oxidation treatment, the type of CNT used as a raw material, and the like.

Further, for example, even if an attempt is made to detect the end point by an online monitor using a spectroscopic method, it is difficult to detect the end point because the liquid to be treated for oxidation treatment is completely black. Further, in the offline measurement in which the liquid to be treated is sampled to check the desired characteristics, 30 minutes or more is required for sample preparation and measurement, and it is difficult to immediately detect and control the end point of the oxidation treatment. .. In other industrial fields such as molten steel refining, a method of detecting the reaction end point by monitoring the temperature in solution is used, but in the above-mentioned oxidation treatment, the temperature of the liquid to be treated becomes an azeotropic temperature. Therefore, it is difficult to apply the monitor temperature to the end point management because it changes almost constantly.

The present inventors have conducted diligent studies to achieve the above object. Then, the present inventors, in a method for producing a carbon nanotube dispersion liquid including an oxidation treatment step of heating a liquid to be treated containing an oxidizing agent and carbon nanotubes using a heater, a value M of the mass or volume of the liquid to be treated. The heating rate ΔT of the liquid to be treated from the time when the heater is turned on to the time when the temperature of the liquid to be treated reaches the treatment temperature, and the heater is turned off when the temperature of the liquid to be treated reaches the treatment temperature. We have found that if the time point at which the heater is turned off is determined based on the value M · ΔT · tr, which is the product of the processing time up to the time point, it is possible to accurately produce a carbon nanotube dispersion liquid having desired characteristics. The invention was completed.

That is, the present invention aims to advantageously solve the above problems, and the method for producing a carbon nanotube dispersion liquid of the present invention uses a heater to prepare a liquid to be treated containing an oxidizing agent and carbon nanotubes. A method for producing a carbon nanotube dispersion liquid including a heating oxidation treatment step, wherein the value of the mass or volume of the liquid to be treated is M, and the temperature of the liquid to be treated is the treatment temperature from the time when the heater is turned on. When the rate of temperature rise of the liquid to be treated up to the time when the temperature reaches is ΔT, and the treatment time from the time when the temperature of the liquid to be treated reaches the treatment temperature to the time when the heater is turned off is tr. It is characterized in that the time point at which the heater is turned off is determined based on the value of the product M · ΔT · tr. According to the method for producing a carbon nanotube dispersion liquid of the present invention, a CNT dispersion liquid having desired characteristics can be produced with high accuracy.

Here, in the method for producing a carbon nanotube dispersion liquid of the present invention, it is preferable to turn off the heater when the value of the product M · ΔT · tr reaches a predetermined range. If the heater is turned off when the value of the product M · ΔT · tr reaches within a predetermined range, a CNT dispersion liquid having desired characteristics can be produced with higher accuracy.

Further, in the method for producing a carbon nanotube dispersion liquid of the present invention, it is preferable that the concentration of carbon nanotubes in the liquid to be treated is 5% by mass or less. When the concentration of carbon nanotubes in the liquid to be treated is not more than the above-mentioned predetermined value, a CNT dispersion liquid having desired characteristics can be produced with higher accuracy.

Further, in the method for producing a carbon nanotube dispersion liquid of the present invention, it is preferable to use a cooling device in the oxidation treatment step and adjust the cooling conditions of the cooling device. If a cooling device is used in the oxidation treatment step and the cooling conditions of the cooling device are adjusted, a CNT dispersion liquid having desired characteristics can be produced with higher accuracy.

Further, in the method for producing a carbon nanotube dispersion liquid of the present invention, it is preferable to use a heat insulating material in the oxidation treatment step and adjust the heat insulating material. If a heat insulating material is used in the oxidation treatment step and the heat insulating material is adjusted, a CNT dispersion liquid having desired characteristics can be produced with higher accuracy.

Further, in the method for producing a carbon nanotube dispersion liquid of the present invention, it is preferable to adjust the calorific value of the heater. By adjusting the calorific value of the heater, a CNT dispersion liquid having desired characteristics can be produced with higher accuracy.

According to the present invention, it is possible to provide a method for producing a carbon nanotube dispersion liquid, which can accurately produce a carbon nanotube dispersion liquid having desired characteristics.

It is a schematic block diagram which shows an example of the oxidation treatment apparatus used in the oxidation treatment step of the manufacturing method of the carbon nanotube dispersion liquid of this invention. It is a graph which shows an example of the time-dependent change of the temperature of the liquid to be treated and the output work amount (relative amount) of a heater at the time of heating a liquid to be treated. It is a flow chart of an example of the control method of the oxidation treatment which concerns on this invention. It is a figure which shows the energy balance in the oxidation treatment which concerns on this invention. 6 is a graph showing the relationship between the treatment time and the agglutination rate of carbon nanotubes for the untreated liquid and Reference Examples 1 to 5. 6 is a graph showing the relationship between the treatment time and the carbon impurity content of carbon nanotubes for the untreated liquid and Reference Examples 1 to 5. 6 is a graph showing the relationship between the treatment time and the yield of effective carbon nanotubes for the untreated liquid and Reference Examples 1 to 5. It is a graph which shows the effective carbon nanotube yield for Comparative Example 2 (lots 101-106) and Example 2 (lots 201-208).

Hereinafter, embodiments of the present invention will be described in detail.

(Manufacturing method of carbon nanotube dispersion liquid)
The method for producing a CNT dispersion liquid of the present invention includes an oxidation treatment step of heating a liquid to be treated containing an oxidizing agent and carbon nanotubes using a heater. The method for producing a CNT dispersion liquid of the present invention is characterized in that the time point at which the heater is turned off is determined based on the value of a predetermined product. The method for producing the CNT dispersion liquid of the present invention may optionally include steps other than the above-mentioned oxidation treatment step.
According to the method for producing a CNT dispersion liquid of the present invention, a CNT dispersion liquid having desired characteristics can be produced with high accuracy. The CNT thin film formed by using the produced CNT dispersion liquid can be suitably used as a material for electronic devices such as semiconductor elements, displays, LEDs, lithium ion batteries, and solar cells.

Here, the desired "characteristics" of the produced CNT dispersion liquid vary depending on the application, and are, for example, CNT crystallinity, functional group, diameter, length, agglutination rate, carbon impurity content, yield and the like. Can be mentioned. In addition, a preferable range of numerical values and the like related to these characteristics can be appropriately set according to the intended use.

Further, "the CNT dispersion liquid having the desired characteristics can be produced with high accuracy" means that the CNT dispersion liquid has the desired characteristics even when the apparatus used for the oxidation treatment and the conditions of the oxidation treatment are changed. It means that the CNT dispersion liquid can be produced.
The apparatus and treatment conditions used for the oxidation treatment may be intentionally changed, but may be unintentionally changed due to some factor.
Then, according to the method for producing a CNT dispersion liquid of the present invention, the apparatus and treatment conditions used for the oxidation treatment are desired not only when they are intentionally changed but also when they are unintentionally changed. A CNT dispersion liquid having the above characteristics can be produced with high accuracy.

<Oxidation process>
In the oxidation treatment step, a heater is used to heat the liquid to be treated containing the oxidizing agent and carbon nanotubes. Then, the value M of the mass or volume of the liquid to be treated, the temperature rise rate ΔT of the liquid to be treated from the time when the heater is turned on to the time when the temperature of the liquid to be treated reaches the treatment temperature, and the temperature of the liquid to be treated. The time point at which the heater is turned off is determined based on the value M · ΔT · tr of the product of the treatment time tr from the time when the temperature reaches the treatment temperature to the time when the heater is turned off.

<< Liquid to be treated >>
Here, the liquid to be treated used in the oxidation treatment step contains an oxidizing agent and CNT. In addition, the liquid to be treated may further contain components other than the oxidizing agent and CNT within the range in which the desired effect of the present invention can be obtained. The liquid to be treated is usually a liquid obtained by mixing the above components in a solvent such as water. As the solvent, for example, a solvent such as water contained in nitric acid as an oxidizing agent can be used as it is.

[Oxidant]
As the oxidizing agent, nitric acid, sulfuric acid, hydrogen peroxide solution and the like can be used. One of these oxidizing agents may be used alone, or two or more of these oxidizing agents may be mixed and used in an arbitrary ratio.

The concentration of the oxidizing agent in the liquid to be treated is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 20% by mass or more, and 90% by mass or less. It is preferably 70% by mass or less, and further preferably 50% by mass or less. When the concentration of the oxidizing agent in the liquid to be treated is at least the above lower limit, the oxidation reaction can be satisfactorily promoted. On the other hand, when the concentration of the oxidizing agent in the liquid to be treated is not more than the above upper limit, it is possible to suppress the excessive progress of the oxidation reaction and the formation of carbon impurities.

[carbon nanotube]
The CNT contained in the liquid to be treated is a CNT that is a raw material of the CNT dispersion liquid, and is subjected to an oxidation treatment by being heated together with an oxidizing agent in the oxidation treatment step.

The CNTs in the liquid to be treated are not particularly limited, and single-walled carbon nanotubes and / or multi-walled carbon nanotubes can be used, but the CNTs are carbon nanotubes from a single layer to five layers. It is preferable, and it is more preferable that it is a single-walled carbon nanotube.
The average diameter (Av) of CNTs is preferably 0.5 nm or more, more preferably 1 nm or more, preferably 15 nm or less, and further preferably 10 nm or less. When the average diameter (Av) of CNTs is 0.5 nm or more, aggregation of CNTs can be suppressed and the dispersibility of CNTs can be enhanced.
The average diameter (Av) and average length of the CNTs can be determined by measuring the diameter (outer diameter) and length of 100 carbon nanotubes randomly selected using a transmission electron microscope, respectively. ..
The average diameter (Av) and average length of CNTs may be adjusted by changing the manufacturing method and manufacturing conditions of CNTs, or by combining a plurality of types of CNTs obtained by different manufacturing methods. May be good.
Further, the BET specific surface area of CNT ^{is preferably 600 m 2} / g or more, more preferably 700 m ² / g or more, ^{further preferably 800 m 2} / g or more, and 2000 m ² / g or less. It is preferably 1800 m ² / g or less, and more preferably 1500 m ² / g or less. Further, in the case where the CNT is mainly opened, the BET specific surface area ^{is preferably 1300 m 2} / g or more. When the BET specific surface area of CNT is 600 m ² / g or more, the surface uniformity of the obtained thin film can be sufficiently enhanced. Further, when the BET specific surface area of CNTs is 2000 m ² / g or less, aggregation of CNTs can be suppressed and the dispersibility of CNTs can be enhanced.

Further, the average length, aspect ratio, etc. of CNTs in the liquid to be treated are not particularly limited as long as the desired effects of the present invention can be obtained.

The CNT concentration in the liquid to be treated is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and further preferably 0.1% by mass or more. It is preferably 1% by mass or less, more preferably 1% by mass or less, and further preferably 0.5% by mass or less. When the CNT concentration in the liquid to be treated is 5% by mass or less, a CNT dispersion liquid having desired characteristics can be produced with higher accuracy.

[Mass or volume value M of the liquid to be treated]
The mass or volume value M of the liquid to be treated can be appropriately set according to the scale of the oxidation treatment apparatus to be used.
The mass of the liquid to be treated is preferably 100 g or more, more preferably 500 g or more, further preferably 1 kg or more, preferably 100 kg or less, and more preferably 20 kg or less. It is preferably 10 kg or less, and more preferably 10 kg or less.
The volume of the liquid to be treated is preferably 100 mL or more, more preferably 500 mL or more, further preferably 1 L or more, preferably 100 L or less, and more preferably 20 L or less. It is preferably 10 L or less, and more preferably 10 L or less.

<< Oxidation treatment equipment >>
The above-mentioned liquid to be treated is heated by using a heater. Here, usually, the heating of the liquid to be treated in the oxidation treatment step is performed by using an oxidation treatment device provided with a heater.

FIG. 1 is a schematic configuration diagram showing an example of an oxidation treatment apparatus used in the oxidation treatment step of the method for producing a CNT dispersion liquid of the present invention. In FIG. 1, the arrow indicates the heat transfer.

The oxidation treatment device 100 includes a heater 3, a container 8 containing the liquid to be treated 4, a heat insulating material 1 covering the lower surface and side surfaces of the container 8, a heat insulating material 9 covering the upper surface of the container 8, and the temperature of the liquid 4 to be treated. A thermometer 6 for measuring the temperature and a reflux cooling device 2 for cooling the gas phase portion in the container 8 are provided. The liquid to be treated 4 is filled in the container 8 after the mass or volume value M is measured in advance. Further, in order to make the temperature of the liquid to be treated 4 uniform and promote the oxidation reaction, a stirring device 5 is installed in the container 8.

As the material of the container 8, quartz which does not contain metal and has high nitric acid resistance is used. The shape of the container 8 is cylindrical in order to facilitate the attachment of equipment such as the reflux cooling device 2, the stirring device 5, and the thermometer 6. Further, the upper surface of the container 8 is covered with the heat insulating material 9. As the container 8, a spherical flask may be used from the viewpoint of improving the heat insulating property.

As the heater 3, an electric heater having a heating wire is used. Then, in order to heat the liquid to be treated 4 as uniformly as possible, heaters 3 (heating wires) are installed on both the lower surface portion and the side surface portion of the container 8. The heater 3 is provided with a power supply 7 for switching on / off. Further, as the heater 3, for example, another type such as induction heating can be used.

Further, as for the heat insulating material 1 that covers the lower surface portion and the side surface portion of the container 8, those that match the shapes of the container 8 and the heater 3 are prepared in advance and installed. Further, the heat insulating material 9 that covers the upper surface of the container 8 is also prepared and installed in advance so as to match the shape of the upper part of the container 8. As the material of the heat insulating material 1 and the heat insulating material 9, for example, non-combustible cotton such as glass wool can be used.

The PID method is used as a method for controlling the temperature of the liquid to be treated 4 in the oxidation treatment apparatus 100. As a method for controlling the temperature of the liquid to be treated, on / off control such as bimetal may be used.

The reflux cooling device 2 is installed in the upper gas phase space in the container 8. Thereby, for example, when nitric acid is used as the oxidation treatment agent, the concentrations of nitrogen dioxide and dinitrogen tetroxide generated by decomposition at high temperature can be controlled, and heat energy can be released from the liquid to be treated. As the refrigerant, for example, pure water that does not react with nitric acid or "Fluorinert (registered trademark)" manufactured by 3M Japan Ltd. can be used. Further, from the flow rate of the refrigerant measured by the flow meter 12 installed in the reflux cooling device 2, the thermometer 11 installed at the inlet of the reflux cooling device 2 and the thermometer 10 installed at the outlet, the reflux cooling device 2 The heat energy escaped from the liquid to be treated can be calculated.

Although an example of the oxidation treatment apparatus has been described above, the method for producing the CNT dispersion liquid of the present invention is not limited to this, and an apparatus other than the above-mentioned oxidation treatment apparatus 100 can also be used.

<< Heating >>
As an example of the oxidation treatment step in the method for producing the CNT dispersion liquid of the present invention, a case where the liquid to be treated is heated by using the oxidation treatment apparatus 100 shown in FIG. 1 will be described below.
Here, FIG. 2 is a graph showing an example of changes over time in the temperature of the liquid to be treated 4 and the output work amount (relative amount) of the heater 3 when the liquid to be treated 4 is heated by using the oxidation treatment apparatus 100. ..

First, the heater 3 is turned on, heating of the liquid to be treated 4 is started, and the temperature is raised until the temperature of the liquid to be treated 4 reaches the treatment temperature Tr. The time when the liquid to be treated 4 reaches the treatment temperature Tr is defined as ts. Next, after ts when the temperature of the liquid to be treated 4 reaches the treatment temperature Tr, the temperature of the liquid to be treated 4 fluctuates from the treatment temperature Tr as much as possible by adjusting the power (calorific value) of the heater 3. Control not to. After that, the heater 3 is turned off to finish heating the liquid to be treated 4. The time when the heater 3 is turned off is defined as te. After the time point te when the heater 3 is turned off, the temperature of the liquid to be treated 4 is lowered to around room temperature (25 ° C.). Then, the liquid to be treated after the above treatment is recovered as a CNT dispersion liquid.

The stirring device 5 is used before the heater 3 is turned on (before the start of heating), while the heater 3 is turned on (during heating), and after the heater 3 is turned off (after the heating is completed). It can be used to appropriately stir the liquid to be treated 4. By stirring the liquid to be treated 4, the temperature of the liquid to be treated 4 can be made uniform and the oxidation reaction can be promoted.
Similarly, reflux is performed before the heater 3 is turned on (before the start of heating), while the heater 3 is turned on (during heating), and after the heater 3 is turned off (after the end of heating). Cooling can be appropriately performed using the cooling device 2. For example, the temperature of the liquid to be treated can be quickly lowered to room temperature by operating the reflux cooling device 2 to perform cooling even after the time when the heater 3 is turned off.

Here, the treatment temperature Tr is usually a temperature near the boiling point of the liquid to be treated 4, and varies depending on the composition of the liquid to be treated 4 and the like, but can be set, for example, in the range of 100 ° C. or higher and 150 ° C. or lower. ..

Then, the rate of temperature rise of the liquid to be treated 4 from the time when the heater 3 is turned on to the time ts when the temperature of the liquid to be treated 4 reaches the treatment temperature Tr is defined as ΔT.
Here, the temperature rising rate ΔT is the rate of temperature rise of the liquid to be treated 4 at an arbitrary time point from the time when the heater 3 is turned on to the time when the temperature of the liquid to be treated 4 reaches the treatment temperature Tr. Can be done. Then, usually, the heating rate at an arbitrary time point in the time zone in which the heating rate of the liquid to be treated 4 is stable is set as ΔT. For example, the temperature rising rate ΔT of the liquid to be treated 4 can be the rate of temperature rise of the liquid to be treated 4 at the time point of the temperature Ta which is 1/2 the temperature of the processing temperature Tr.

The heating rate ΔT is preferably 0.2 ° C./min or more, more preferably 0.5 ° C./min or more, further preferably 1.0 ° C./min or more, and 50 ° C./min. Minutes or less is preferable, 20 ° C./min or less is more preferable, and 10 ° C./min or less is further preferable.
The heating rate ΔT is the cooling condition of the cooling device (for example, the flow rate of the refrigerant), the heat insulating material (for example, the material of the heat insulating material, the filling condition, and the installation condition), and the operating condition of the heater (for example, the heat generation of the heater). It can be controlled by adjusting the amount) and the like.

In the oxidation treatment in the oxidation treatment step, the start point is ts when the temperature of the liquid to be treated 4 reaches the treatment temperature Tr, and the end point is te when the heater 3 is turned off.
Then, the time from the time ts when the temperature of the liquid to be treated 4 reaches the treatment temperature Tr to the time te when the heater 3 is turned off is defined as the treatment time tr.
Here, the processing time tr is preferably 0.5 hours or more, more preferably 2 hours or more, more preferably 5 hours or more, preferably 100 hours or less, and preferably 50 hours. It is more preferably less than or equal to, and even more preferably 20 hours or less.

Then, in the oxidation treatment step, the heater 3 is turned off based on the value M of the mass or volume of the liquid to be treated 4 described above, the temperature rising rate ΔT, and the product M · ΔT · tr of the treatment time tr. Determine the time point te to be set.
More specifically, it is preferable to turn off the heater 3 when the value of the product M · ΔT · tr described above reaches a predetermined range.
In addition, "turning off the heater when the value of the product M, ΔT, tr reaches within a predetermined range" means that the value of the product matches the lower limit value or the upper limit value of the predetermined range. This means that the heater may be turned off while the value of the product is within a predetermined range, not limited to the time when the product is used.

[Predetermined range]
The above-mentioned "predetermined range" is, for example, different from the method for producing the CNT dispersion liquid of the present invention, and a preliminary experiment for determining _{the reference value Q 0 of the value of the product M · ΔT · tr is carried out.} It can be set based on the obtained reference value Q _0.

Here, in the preliminary experiment, a reference example of the oxidation treatment for heating the liquid to be treated containing the oxidizing agent and the carbon nanotubes using a heater was repeated a plurality of times, and the reference value Q ₀ was determined based on the result. do. An outline of an example of the preliminary experiment will be described below.
(1) Reference example 1
Reference example 1 is performed in the following procedure. First, the heater is turned on, and the temperature is raised until the temperature of the liquid to be treated (having a mass or volume value of M'is M') containing the oxidizing agent and carbon nanotubes reaches the treatment temperature Tr'. Here, the rate of temperature rise of the liquid to be treated from the time when the heater is turned on to the time when the temperature of the liquid to be treated reaches the treatment temperature Tr ′ is defined as ΔT ′. After the time when the temperature of the liquid to be treated reaches the treatment temperature Tr ′, the temperature of the liquid to be treated is controlled so as not to fluctuate from the treatment temperature Tr ′ as much as possible. Then, the heater is turned off when the treatment time tr'elapses from the time when the temperature of the liquid to be treated reaches the treatment temperature Tr'. Then, the liquid to be treated whose temperature has been lowered to around room temperature is acquired as a CNT dispersion liquid.
(2) Reference Example 2 and subsequent Reference Example 2 is obtained by performing an oxidation treatment in the same manner as in Reference Example 1 above, except that the treatment time tr'is changed, to obtain a CNT dispersion liquid.
By repeating the same operation as above and performing up to Reference Example N (N is an integer of 2 or more), finally, Reference Examples 1 to N (N is an integer of 2 or more) having different processing times tr'from each other). The CNT dispersion liquid produced by the oxidation treatment of is obtained.
(3) Comparison between Reference Examples The characteristics of the CNT dispersions obtained in Reference Examples 1 to N (for example, CNT aggregation rate, CNT carbon impurity content, effective CNT yield, etc.) are compared for reference. From Examples 1 to N, one reference example in which a CNT dispersion liquid having the most desired characteristics is obtained is selected as Reference Example X.
(4) _{Determination of reference value Q 0} The mass or volume value M ′ of the liquid to be treated in Reference Example X in which the CNT dispersion liquid having the most desired characteristics was obtained is M ₀ , and the temperature rising rate ΔT ′ is ΔT. _The reference value is the value of _{the product M 0} , ΔT ₀ , tr ₀ when the processing time tr ′ from the time when the liquid to be processed reaches the processing temperature Tr ′ to the time when the heater is turned off is tr _{0. Set} to 0.

In one example of the above preliminary experiment, a plurality of reference examples in which the processing time tr'is intentionally changed are carried out, but the preliminary experiment for determining the _{reference value Q 0 is limited to this.} However, for example, a plurality of reference examples may be carried out in which the treatment time is constant and the value M'of the mass or volume of the liquid to be treated and / or the rate of temperature rise ΔT'is intentionally changed. do.

The type and concentration of the oxidizing agent are the same between the liquid to be treated used in the preliminary experiment described above and the liquid to be treated used in the method for producing the CNT dispersion liquid of the present invention.
Further, the liquid to be treated used in the preliminary experiment and the liquid to be treated used in the method for producing the CNT dispersion liquid of the present invention use CNTs having the same number of layers, average length, average diameter, aspect ratio and the like.
The CNT concentration in the liquid to be treated may be the same or different between the preliminary experiment and the method for producing the CNT dispersion liquid of the present invention. Then, from the viewpoint of more accurately producing the CNT dispersion liquid having desired characteristics by the method for producing the CNT dispersion liquid of the present invention, the preliminary experiment and the method for producing the CNT dispersion liquid of the present invention are carried out in the liquid to be treated. It is preferable that the CNT concentrations are the same.
Further, the mass or volume value M'of the liquid to be treated used in the preliminary experiment may be the same as the mass or volume value M of the liquid to be treated used in the method for producing the CNT dispersion liquid of the present invention. It may be different.

Further, the same heater may be used or different heaters may be used in the preliminary experiment and the method for producing the CNT dispersion liquid of the present invention.
When an oxidation treatment device provided with a heater is used in the preliminary experiment, the same device as the oxidation treatment device used in the method for producing the CNT dispersion liquid of the present invention may be used, or a different device may be used. For example, in the oxidation treatment device used in the preliminary experiment and the oxidation treatment device used in the method for producing the CNT dispersion liquid of the present invention, the scale, material, performance of the container, heater, cooling device, heat insulating material, etc. The installation conditions may be different.
Further, in the preliminary experiment and the method for producing the CNT dispersion liquid of the present invention, the operating conditions (for example, calorific value) of the heater during the oxidation treatment and the cooling conditions (for example, the flow rate of the refrigerant) of the cooling device are the same. It may be, or it may be different.

It is assumed that the processing temperature Tr ′ in the preliminary experiment and the processing temperature Tr in the method for producing the CNT dispersion liquid of the present invention are the same temperature.
Further, the temperature rise rate ΔT ′ of the liquid to be treated in the preliminary experiment and the temperature rise rate ΔT in the method for producing the CNT dispersion liquid of the present invention may be the same or different.
However, the temperature rise rate ΔT'of the liquid to be treated in the preliminary experiment and the temperature rise rate ΔT in the method for producing the CNT dispersion liquid of the present invention are both set as the temperature rise rate of the liquid to be treated at the same temperature. There is a need. For example, in the method for producing a CNT dispersion liquid of the present invention, when the temperature rising rate of the liquid to be treated at a temperature Ta of 1/2 of the treatment temperature Tr is set as ΔT, the treatment temperature Tr ′ (=) is also set in the preliminary experiment. The rate of temperature rise of the liquid to be treated at a temperature Ta of 1/2 of Tr) is set as ΔT ′.

The treatment time tr'in Reference Examples 1 to N of the preliminary experiment may include the same time as the treatment time tr in the oxidation treatment step of the method for producing the CNT dispersion liquid of the present invention. It does not have to be.

Then, the predetermined range described above can be set based on the _{reference value Q 0} determined by the preliminary experiment.
For example, the predetermined range is represented by "k ₁ Q ₀ or more" _{using the reference value Q 0} and the values of k ₁ and k ₂ satisfying the relational expression: 0 <k ₁ ≤ 1 ≤ k _2. It may be a range having only the lower limit value to be specified, a range having only the upper limit value represented by _{"k 2} Q _{0 or less", or "k 1} Q ₀ or more and k ₂ Q ₀ or less". It may be a range having both a lower limit value and an upper limit value represented by.

The _{closer the values of k 1} and k ₂ are to 1 (that is, the closer the lower limit value and the upper limit value are to the reference value Q ₀ ), the more accurately the CNT dispersion liquid having the desired characteristics can be produced. For example, the _{closer the value of k 1} is to 1 (that is, the closer the lower limit value is to the reference value Q ₀ ), the more the CNTs are cut and dispersed well by the moderate progress of the oxidation reaction, which is effective. A CNT dispersion liquid having a high CNT yield can be obtained. Further, for example, the _{closer the value of k 2} is to 1 (that is, the closer the upper limit value is to the reference value Q ₀ ), the more effective it is because the oxidation reaction can be suppressed from progressing excessively and the generation of carbon impurities can be reduced. A CNT dispersion liquid having a high CNT yield can be obtained.

Then, set the range of predetermined only one point of reference values Q _0, if the heater off when the value of the product M · ΔT · tr described above matches the reference value Q _0, in particular precisely desired A CNT dispersion having the above characteristics can be produced.

Here, FIG. 3 shows a flow chart of an example of the method for controlling the oxidation treatment according to the present invention. In an example of the method for controlling the oxidation treatment shown in FIG. 3, in the oxidation treatment for heating the liquid to be treated containing the oxidizing agent and CNT, the mass or volume value of the liquid to be treated is set to M, and the heater is turned on. Let ΔT be the rate of temperature rise of the liquid to be treated until the temperature of the liquid to be treated reaches the treatment temperature, and set the treatment time from the time when the temperature of the liquid to be treated reaches the treatment temperature to the time when the heater is turned off. While the value of the product M, ΔT, tr when set to tr _{is less than the reference value Q 0} , the heater is turned on to continue the oxidation treatment, and the value of the product M, ΔT, tr is the reference value Q _0. When the above is reached, the heater is turned off to end the oxidation treatment. By controlling the oxidation treatment in this way, it is possible to accurately produce a CNT dispersion liquid having desired characteristics.
In the above example, the predetermined range is set to "reference value Q ₀ or more", but is not particularly limited as long as the desired effect of the present invention can be obtained. For example, the reference value Q _{0 described above is used.} It can be set arbitrarily based on the value of.

(Discussion)
The present invention will be considered below.
As shown in FIG. 4, a part of the heat energy generated by the heater is lost by heat dissipation and cooling, and the remaining energy is consumed as reaction energy in the CNT oxidation reaction. Since these heat dissipation amounts and cooling heat amounts vary depending on the heat insulating material and cooling conditions, as a result, the amount of reaction energy that can be substantially used varies. The heating rate ΔT of the liquid to be treated represents the heat energy applied to the liquid to be treated per unit time by subtracting the amount of heat lost by heat dissipation and cooling. Therefore, the product of the temperature rising rate ΔT, the mass or volume value M of the liquid to be treated, and the treatment time tr is M · ΔT · tr, which is a good parameter representing the effective energy substantially used for the oxidation treatment. .. Strictly speaking, the thermal energy from the heater during the temperature rise (from the time the heater is turned on to the time when the liquid to be treated reaches the treatment temperature) and the heat energy during the oxidation treatment (from the time when the liquid to be treated reaches the treatment temperature) The relative value of the effective energy to the energy loss due to heat dissipation and cooling is not so different between the temperature rise and the oxidation treatment, although it is different from the heat energy generated by the heater (until the time when the temperature is turned off). Therefore, for example, in the oxidation treatment step of the method for producing a CNT dispersion liquid, if the heater is turned off when the value of the product M · ΔT · tr reaches within the predetermined range described above, the CNT oxidation reaction will occur. It is desirable because the effective energy used can be the same as the effective energy used for the oxidation reaction of CNTs in Reference Example X of the preliminary experiment, which proved that a CNT dispersion with desired characteristics can be obtained. It is possible to accurately produce a CNT dispersion liquid having the above characteristics.
As a method for controlling the value of the product M, ΔT, tr, the processing time tr is adjusted, the mass or volume value M of the liquid to be treated is adjusted, the wattage (calorific value) of the heater, the heat insulating material, and the like. The temperature rising rate ΔT can be adjusted by changing the cooling conditions (for example, the flow rate of the refrigerant) of the cooling device, but the processing time tr can be adjusted most easily.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following, "%" representing the amount is based on mass unless otherwise specified.

The agglutination rate of CNTs, the carbon impurity content of CNTs, and the effective CNT yield were measured according to the following methods.

<Agglutination rate of CNT>
The obtained CNT dispersion liquid or untreated liquid was diluted 100-fold with water, and then a small amount of ammonia was added to adjust the pH to 7.0, and the light transmittance (A) of the obtained liquid was measured. Further, the light transmittance (B) of the liquid obtained by passing this liquid through a syringe filter having a pore size of 200 nm was measured. Here, the agglutination rate of CNTs was calculated by the formula: {1- (B / A)} × 100 [%]. If CNTs are completely dispersed in the CNT dispersion liquid, B and A have the same value, and the agglutination rate of CNTs is 0%.

<Carbon impurity content of CNT>
The obtained CNT dispersion liquid or untreated liquid was diluted 100-fold with water, and then a small amount of ammonia was added to adjust the pH to 7.0, and the light transmittance (A) of the obtained liquid was measured. Further, a salt was added to this solution to salt out only amorphous carbon, which is a carbon impurity, and the light transmittance (C) of the supernatant was measured. The carbon impurity content (relative value) of CNT was calculated by the formula: {1- (C / A)} × 100 [%]. When the CNT does not contain carbon impurities, C and A have the same value, and the carbon impurity content (relative value) is 0%.

<Effective CNT yield>
Using the agglutination rate and carbon impurity content of the CNTs obtained above, the effective CNT yield was calculated by the following formula. The higher the effective CNT yield in the CNT dispersion liquid, the better the CNTs are dispersed and the smaller the content of carbon impurities. Therefore, it is shown that the CNTs can be satisfactorily used in the production of electronic devices having excellent uniformity and reproducibility. ..
Effective CNT yield = {1- (CNT agglutination rate / 100)} x {1- (CNT carbon impurity content / 100)} x 100 [%]

(Preliminary experiment)
As a preliminary experiment, the following reference examples 1 to 5 were subjected to the oxidation treatment, the obtained CNT dispersions were compared, and the reference value Q was based on the reference example in which the CNT dispersion having the most desired characteristics was obtained. The value of _{0 was determined.}

<Reference example 1>
A liquid to be treated was prepared by adding 100 g of carbon nanotubes to 20 L of a 50% aqueous nitric acid solution. The mass value of the liquid to be treated was M'(= 20.1 kg), and the CNT concentration in the liquid to be treated was 0.5%. Using the liquid to be treated (untreated liquid) before the oxidation treatment, the agglutination rate of CNTs, the carbon impurity content of CNTs, and the effective CNT yield were measured by the above-mentioned method. The results are shown in FIGS. 5-7.
Next, the liquid to be treated prepared above was placed in the container 8 of the oxidation treatment apparatus 100 shown in FIG.
The heater 3 was turned on to start heating the liquid to be treated, and the temperature was raised to 115 ° C.
After the time when the liquid to be treated reached the treatment temperature of 115 ° C., the power of the heater 3 was controlled so that the temperature of the liquid to be treated did not fluctuate from 115 ° C. as much as possible. Specifically, the temperature of the liquid to be treated was maintained at 115 ° C. or higher and 120 ° C. or lower.
Then, when 11 hours have passed from the time when the liquid to be treated reaches the treatment temperature of 115 ° C. (that is, when the treatment time tr'is 480 minutes), the heater 3 is turned off to stop the heating, and the treatment is to be performed. The liquid was allowed to stand until it reached room temperature (25 ° C.), and the liquid to be treated after the oxidation treatment was recovered as a CNT dispersion liquid.
The above-mentioned operation was carried out while the reflux cooling device 2 was operated and cooled.
Using the obtained CNT dispersion liquid, the agglutination rate of CNTs, the carbon impurity content of CNTs, and the effective CNT yield were measured. The results are shown in FIGS. 5-7.

<Reference Examples 2-5>
Oxidation treatment was performed in the same manner as above except that the treatment time tr'was changed from 480 minutes to 540 minutes, 600 minutes, 660 minutes, and 720 minutes, respectively, and various types of CNT dispersions were used. Measurements were made. The results are shown in FIGS. 5-7.

As shown in FIG. 7, it can be seen that in Reference Example 4 (processing time tr'= 660 [minutes] = 11 [hours]), the effective CNT yield in the obtained CNT dispersion liquid is maximized. Therefore, the condition of the oxidation treatment in Reference Example 4 was set as the standard condition.
Then, for Reference Example 4 in which the CNT dispersion liquid having the most desired characteristics was obtained, the mass value M'(= 20.1 kg) of the liquid to be treated was set to M ₀ , and the treatment temperature was 1/2 of 115 ° C. the heating rate ΔT' the liquid to be treated and [Delta] T ₀ at the time of a certain temperature 57.5 ° C., the treatment time tr' (= 11 [times]) the product value M ₀ · _{ΔT 0} · of when a tr ₀ tr ₀ was obtained as the reference value Q _0.

(This experiment 1)
Assuming that the characteristics of the CNT dispersion liquid obtained in Reference Example 4 of the preliminary experiment described above are the desired characteristics, the following Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-2 Oxidation treatment was performed.

<Comparative Example 1-1>
The same oxidation treatment device as the oxidation treatment device 100 used in Reference Example 4 of the preliminary experiment described above was prepared except that the amount of the heat insulating material 9 (upper heat insulating material) covering the upper surface of the container 8 was reduced by 10%.
Next, the liquid to be treated (mass value M = M ₀ , CNT concentration 0.5%) prepared in the same manner as in Reference Example 4 was placed in the container 8.
The heater 3 was turned on to start heating the liquid to be treated, and the temperature was raised to 115 ° C. By reducing the upper heat insulating material by 10%, the temperature rise rate ΔT of the liquid to be treated at the time point of 57.5 ° C., which is 1/2 of the treatment temperature of 115 ° C., is the temperature rise rate in Reference Example 4 described above. It _{decreased by 45% from ΔT 0} (that is, the heating rate ΔT in Comparative Example 1-1 was 0.55 ΔT ₀ ).
After the time when the liquid to be treated reached the treatment temperature of 115 ° C., the power of the heater 3 was controlled so that the temperature of the liquid to be treated did not fluctuate from 115 ° C. as much as possible. Specifically, the temperature of the liquid to be treated was maintained at 115 ° C. or higher and 120 ° C. or lower.
Then, when 11 hours have passed from the time when the liquid to be treated reaches the treatment temperature of 115 ° C. (that is, when the treatment time tr reaches 11 hours), the heater 3 is turned off to stop the heating, and the liquid to be treated is stopped. Was allowed to stand until the temperature reached room temperature (25 ° C.), and the liquid to be treated after the oxidation treatment was recovered as a CNT dispersion liquid.
Using the obtained CNT dispersion liquid, the agglutination rate of CNT and the carbon impurity content of CNT were measured, and the effective CNT yield was determined based on the results. The results are shown in Table 1.

<Example 1-1>
The same oxidation treatment device as the oxidation treatment device 100 used in Reference Example 4 of the preliminary experiment described above was prepared except that the amount of the upper heat insulating material was reduced by 10%.
Next, the liquid to be treated (mass value M = M ₀ , CNT concentration 0.5%) prepared in the same manner as in Reference Example 4 was placed in the container 8.
The heater 3 was turned on to start heating the liquid to be treated, and the temperature was raised to 115 ° C. By reducing the upper heat insulating material by 10%, the temperature rise rate ΔT of the liquid to be treated at the time point of 57.5 ° C., which is 1/2 of the treatment temperature of 115 ° C., is the temperature rise rate in Reference Example 4 described above. It _{decreased by 45% from ΔT 0} (that is, the heating rate ΔT in Example 1-1 was 0.55 ΔT ₀ ).
After the time when the liquid to be treated reached the treatment temperature of 115 ° C., the power of the heater 3 was controlled so that the temperature of the liquid to be treated did not fluctuate as much as possible from 115 ° C. Specifically, the temperature of the liquid to be treated was maintained at 115 ° C. or higher and 120 ° C. or lower.
Then, the value M · ΔT · tr of the product of the mass value M (= M ₀ ) of the liquid to be treated, the heating rate ΔT (= 0.55ΔT _{0) of the liquid to be treated, and the treatment time tr is described above.} When the treatment time tr reaches 20 hours, the heater 3 is turned off, heating is stopped, and the mixture is allowed to stand until the liquid to be treated reaches room temperature (25 ° C.) so as to match the reference value Q _0. The liquid to be treated after the oxidation treatment was recovered as a CNT dispersion liquid.
Using the obtained CNT dispersion liquid, the agglutination rate of CNT and the carbon impurity content of CNT were measured, and the effective CNT yield was determined based on the results. The results are shown in Table 1.

<Comparative Example 1-2>
_{The liquid to be treated (mass value M = M 0} , CNT concentration 0.5%) was placed in the container 8 of the oxidation treatment apparatus 100 in the same operation as in Reference Example 4 of the preliminary experiment described above.
The heater 3 was turned on to start heating the liquid to be treated, and the temperature was raised to 115 ° C. At this time, the flow rate of the refrigerant in the reflux cooling device 2 was increased by 30% from the flow rate of the refrigerant in Reference Example 4. Due to the increase in the flow rate of the refrigerant, the temperature rise rate ΔT of the liquid to be treated at the time point of 57.5 ° C., which is 1/2 of the treatment temperature of 115 ° C., decreases by 18% from the _{temperature rise rate ΔT 0 in Reference Example 4 described above.} (That is, the heating rate ΔT in Comparative Example 1-2 was 0.82ΔT ₀ ).
After the time when the liquid to be treated reached the treatment temperature of 115 ° C., the power of the heater 3 was controlled so that the temperature of the liquid to be treated did not fluctuate from 115 ° C. as much as possible. Specifically, the temperature of the liquid to be treated was maintained at 115 ° C. or higher and 120 ° C. or lower.
Then, when 11 hours have passed from the time when the liquid to be treated reaches the treatment temperature of 115 ° C. (that is, when the treatment time tr reaches 11 hours), the heater 3 is turned off to stop the heating, and the liquid to be treated is stopped. Was allowed to stand until the temperature reached room temperature (25 ° C.), and the liquid to be treated after the oxidation treatment was recovered as a CNT dispersion liquid.
Using the obtained CNT dispersion liquid, the agglutination rate of CNT and the carbon impurity content of CNT were measured, and the effective CNT yield was determined based on the results. The results are shown in Table 1.

<Example 1-2>
_{The liquid to be treated (mass value M = M 0} , CNT concentration 0.5%) was placed in the container 8 of the oxidation treatment apparatus 100 in the same operation as in Reference Example 4 of the preliminary experiment described above.
The heater 3 was turned on to start heating the liquid to be treated, and the temperature was raised to 115 ° C. At this time, the flow rate of the refrigerant in the reflux cooling device 2 was increased by 30% from the flow rate of the refrigerant in Reference Example 4. Due to the increase in the flow rate of the refrigerant, the temperature rise rate ΔT of the liquid to be treated at the time point of 57.5 ° C., which is 1/2 of the treatment temperature of 115 ° C., decreases by 18% from the _{temperature rise rate ΔT 0 in Reference Example 4 described above.} (That is, the heating rate ΔT in Example 1-2 was 0.82ΔT ₀ ).
After the time when the liquid to be treated reached the treatment temperature of 115 ° C., the power of the heater 3 was controlled so that the temperature of the liquid to be treated did not fluctuate from 115 ° C. as much as possible. Specifically, the temperature of the liquid to be treated was maintained at 115 ° C. or higher and 120 ° C. or lower.
Then, the value M · ΔT · tr of the product of the mass value M (= M ₀ ) of the liquid to be treated, the heating rate ΔT (= 0.82ΔT _{0) of the liquid to be treated, and the treatment time tr is described above.} When the processing time tr reaches 13.4 hours, the heater 3 is turned off, heating is stopped, and the solution is allowed to stand until it reaches room temperature (25 ° C.) so as to match the reference value Q _0. Then, the liquid to be treated after the oxidation treatment was recovered as a CNT dispersion liquid.
Using the obtained CNT dispersion liquid, the agglutination rate of CNT and the carbon impurity content of CNT were measured, and the effective CNT yield was determined based on the results. The results are shown in Table 1.

From Table 1, the CNT dispersions produced by Examples 1-1 and 1-2 had a higher effective CNT yield value than the CNT dispersions produced by Comparative Examples 1-1 and 1-2 in the preliminary experiment. It can be seen that the CNT dispersion liquid produced in Reference Example 4 of the above is close to the effective CNT yield value and has desired characteristics. From this, the time point at which the heater was turned off was determined based on the value M of the mass or volume of the liquid to be treated, the value M · ΔT · tr of the product of the temperature rising rate ΔT and the treatment time tr. In 1-1 and 1-2, the accuracy of the carbon nanotube dispersion liquid having the desired characteristics was compared with Comparative Examples 1-1 and 1-2 in which the time point for turning off the heater was determined based only on the processing time tr. It turns out that it can be manufactured well.

(This experiment 2)
<Comparative Example 2 (lots 101-106)>
Oxidation treatment is performed in the same operation as in Reference Example 4 of the preliminary experiment described above (that is, the treatment time tr = 11 [hours] from the time when the liquid to be treated reaches the treatment temperature of 115 ° C. to the time when the heater 3 is turned off). , Lots 101-106 were repeated 6 times in total to produce a CNT dispersion liquid.
Although the same operation as in Reference Example 4 of the preliminary experiment described above was performed, the rate of temperature rise of the liquid to be treated ΔT at the time point of 57.5 ° C., which is 1/2 of the processing temperature of 115 ° C. for each lot 101-106. And the value of the temperature rising rate ΔT ₀ in Reference Example 4 did not match. In addition, the values of the temperature rising rates ΔT in each of the lots 101 to 106 did not match and were different from each other.
Using the CNT dispersions obtained in each lot 101-106, the agglutination rate of CNTs and the carbon impurity content of CNTs were measured, and the effective CNT yield was determined based on the results. The results are shown in FIG.

<Example 2 (lots 201-208)>
The value M of the mass of the liquid to be treated is not turned off so that the treatment time tr from the time when the liquid to be treated reaches the treatment temperature of 115 ° C. to the time when the heater 3 is turned off is 11 hours. The value M · ΔT · tr of the product of the heating rate ΔT of the liquid to be treated at the time point of 57.5 ° C., which is 1/2 of the treatment temperature 115 ° C., and the treatment time tr is the above-mentioned reference value Q _0. The oxidation treatment in the same operation as in Reference Example 4 of the preliminary experiment described above was performed in lots 201 to 1, except that the time point at which the heater 3 was turned off was determined and the treatment time tr was adjusted so as to match the value of. A total of 208 was repeated 8 times to produce a CNT dispersion.
Although the same operation as in Reference Example 4 of the preliminary experiment described above was performed, the value of the temperature rising rate ΔT in each lot 201-208 did not match the value of the _{temperature rising rate ΔT 0 in Reference Example 4.} .. Further, the values of the temperature rising rate ΔT in each lot 201 to 208 did not match, and were different from each other. Therefore, in order to match the product values M, ΔT, and tr with the reference values Q ₀ , the processing time tr values in each lot 201 to 208 did not match, and were different from each other.
Using the CNT dispersions obtained in each lot 201-208, the agglutination rate of CNTs and the carbon impurity content of CNTs were measured, and the effective CNT yield was determined based on the results. The results are shown in FIG.

From FIG. 8, the CNT dispersion liquid produced in Example 2 (lots 201-208) has a higher effective CNT yield value than the CNT dispersion liquid produced in Comparative Example 2 (lots 101-106) in the preliminary experiment. It can be seen that the CNT dispersion liquid produced in Reference Example 4 of the above is close to the effective CNT yield value, stable at a high level, and has desired characteristics. From this, the time point at which the heater was turned off was determined based on the value M of the mass or volume of the liquid to be treated, the value M · ΔT · tr of the product of the temperature rising rate ΔT and the treatment time tr. In 2 (lots 201-208), the accuracy of the carbon nanotube dispersion liquid having desired characteristics is compared with that of Comparative Example 2 (lots 101-106) in which the time point at which the heater is turned off is determined based only on the processing time tr. It turns out that it can be manufactured well.

According to the present invention, it is possible to provide a method for producing a carbon nanotube dispersion liquid, which can accurately produce a carbon nanotube dispersion liquid having desired characteristics.

1,9 Insulation material 2 Reflux cooling device 3 Heater 4 Liquid to be treated 5 Stirrer 6,10,11 Thermometer 7 Power supply 8 Container 12 Flowmeter 100 Oxidation treatment device

Claims (6)

A method for producing a carbon nanotube dispersion liquid, which comprises an oxidation treatment step of heating a liquid to be treated containing an oxidizing agent and carbon nanotubes using a heater.
Let M be the mass or volume value of the liquid to be treated.
Let ΔT be the rate of temperature rise of the liquid to be treated from the time when the heater is turned on to the time when the temperature of the liquid to be treated reaches the treatment temperature.
The heater is turned off based on the value of the product M · ΔT · tr when the treatment time from the time when the temperature of the liquid to be treated reaches the treatment temperature to the time when the heater is turned off is tr. A method for producing a carbon nanotube dispersion, which determines a time point. The method for producing a carbon nanotube dispersion liquid according to claim 1, wherein the heater is turned off when the value of the product M · ΔT · tr reaches a predetermined range. The method for producing a carbon nanotube dispersion liquid according to claim 1 or 2, wherein the concentration of carbon nanotubes in the liquid to be treated is 5% by mass or less. The method for producing a carbon nanotube dispersion liquid according to any one of claims 1 to 3, wherein a cooling device is used in the oxidation treatment step to adjust the cooling conditions of the cooling device. The method for producing a carbon nanotube dispersion liquid according to any one of claims 1 to 4, wherein a heat insulating material is used in the oxidation treatment step, and the heat insulating material is adjusted. The method for producing a carbon nanotube dispersion liquid according to any one of claims 1 to 5, wherein the calorific value of the heater is adjusted.

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