Dried carbon nanotubes and method for producing the same

Abstract

To provide dried carbon nanotubes that are excellent both in dispersibility and handleability.SOLUTION: Provided are dried carbon nanotubes. More specifically, provided are dried carbon nanotubes where the value of a viscosity ratio B1 / A1, obtained by dividing B1, the viscosity when the dried carbon nanotubes are dispersed in a solvent for viscosity measurement of the dried product in a concentration of 0.1 mass%, by A1, the viscosity of the solvent for viscosity measurement of the dried product, is 2.0 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dried carbon nanotube product and a method for producing the same. [Background technology]

[0002] BACKGROUND ART Carbon nanotubes (hereinafter sometimes abbreviated as "CNTs") have been attracting attention as a material that has excellent properties such as electrical conductivity, thermal conductivity, and strength.

[0003] CNTs are generally used to impart desired properties to base materials such as resins by blending them with them. However, CNTs have a low density and tend to scatter easily, making them difficult to handle. Therefore, various attempts have been made to produce CNT granules that are easy to handle (see, for example, Patent Documents 1 to 3).

[0004] Patent Document 1 discloses a method for granulating carbon with different bulk densities, comprising a carbon nanotube dispersion step of dispersing carbon nanotubes with particle sizes of 100 nm or less in water, a granulation step of mixing the carbon nanotube dispersion obtained in the carbon nanotube dispersion step with carbon black powder in a granulator to granulate, and a drying step of drying the carbon granules obtained in the granulation step. Patent Document 2 also discloses a method for producing a carbon nanotube-blended aggregate by preparing an aqueous solution of a water-soluble polymer having a predetermined concentration, impregnating a predetermined amount of the aqueous solution of the water-soluble polymer into carbon nanotubes to prepare a wet aggregate, shearing and crushing the obtained wet aggregate to obtain a crushed aggregate, and drying the crushed aggregate. Patent Document 3 discloses a method for producing a carbon nanotube-blended aggregate having a bulk density of 200 kg / m 3 The above-mentioned granular agglomerates of carbonaceous fine fibrous materials are disclosed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-201006 [Patent Document 2] Patent Publication No. 2021-31514 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-18290 Summary of the Invention [Problem to be solved by the invention]

[0006] In addition to the above-mentioned issues regarding handleability, CNTs have a small outer diameter, which means they are easily bundled by van der Waals forces, and there is also room for improvement in terms of increasing their dispersibility in the substrate.

[0007] Therefore, an object of the present invention is to provide a dried carbon nanotube product that is excellent in both dispersibility and handleability. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and have newly discovered that a dried carbon nanotube product (hereinafter sometimes abbreviated as "dried CNT product") has excellent dispersibility and ease of handling when the viscosity ratio B1 / A1, calculated using the viscosity B1 of a dispersion obtained by dispersing the dried CNT product in a predetermined measurement solvent and the viscosity A1 of the measurement solvent, is 2.0 or greater, and have completed the present invention.

[0009] That is, the present invention aims to advantageously solve the above-mentioned problems, and provides the following dried CNT products [1] to [4] and the following methods for producing dried CNT products [5] to [7].

[0010] [1] A dried carbon nanotube product, wherein the viscosity ratio B1 / A1, obtained by dividing the viscosity B1 of the dried carbon nanotube product dispersed in the solvent for viscosity measurement of a dry product at a concentration of 0.1% by mass under the following conditions, by the viscosity A1 of the solvent for viscosity measurement of the dried carbon nanotube product, is 2.0 or more. <Condition> 0.01 g of the dried carbon nanotube product and 10.0 g of the solvent for measuring the viscosity of the dried product were placed in a vial (volume 30 mL, body diameter 33.0 mm, height 63.0 mm, inner diameter of the opening 12.5 mm), and then stirred at 1000 rpm for 60 minutes using a stirrer (20 mm x φ7 mm) and a stirrer. If the viscosity ratio B1 / A1 calculated by performing a dispersion treatment on the dried CNT material under predetermined conditions is 2.0 or more, the dried CNT material is excellent in both dispersibility and handleability. In the present invention, the "viscosity A1" and the "viscosity B1" can be measured using the method described in the examples of this specification.

[0011] [2] The dried carbon nanotube material according to [1] above, which contains only carbon nanotubes as the carbon material.

[0012] [3] Specific surface area is 400m 2 / g or more. The specific surface area of ​​the "carbon nanotubes" can be measured according to the BET (Brunauer-Emmett-Teller) method.

[0013] [4] A dried carbon nanotube product, characterized in that the dried carbon nanotube product is a carbon nanotube dispersion liquid containing carbon nanotubes as materials and a solvent for producing a dispersion liquid, and the viscosity ratio B2 / A2, obtained by dividing the viscosity B2 of the carbon nanotube dispersion liquid by the viscosity A2 of the solvent for producing the dispersion liquid, is 2.0 or more. If the dried carbon nanotube product is a dried carbon nanotube dispersion having the above-mentioned predetermined viscosity ratio B2 / A2 of 2.0 or more, both dispersibility and handleability will be even better. In the present invention, "viscosity A1" and "viscosity B2" can be measured using the methods described in the Examples of this specification. Viscosity B2 is the viscosity of a carbon nanotube dispersion obtained by adding carbon nanotubes as a material to a dispersion preparation solvent to a concentration of 0.2 mass % and dispersing the mixture in a bead mill disperser at a peripheral speed of 8 m / s for 20 minutes.

[0014] [5] A method for producing dried carbon nanotubes, comprising: a dispersion preparation step of preparing a carbon nanotube dispersion containing carbon nanotubes as materials and a dispersion preparation solvent, such that a viscosity ratio B2 / A2, obtained by dividing the viscosity B2 of the carbon nanotube dispersion by the viscosity A2 of the dispersion preparation solvent, is 2.0 or more; and a drying step of removing the dispersion preparation solvent from the carbon nanotube dispersion to obtain dried carbon nanotubes, wherein the dried carbon nanotubes have a viscosity ratio B1 / A1, obtained by dividing the viscosity B1 of the dried carbon nanotubes when the dried carbon nanotubes are dispersed in the solvent for measuring the viscosity of the dried carbon nanotubes at a concentration of 0.1% by mass under the following conditions, with a viscosity A1 of the solvent for measuring the viscosity of the dried carbon nanotubes, of 2.0 or more. <Condition> 0.01 g of the dried carbon nanotube product and 10.0 g of the solvent for measuring the viscosity of the dried product were placed in a vial (volume 30 mL, body diameter 33.0 mm, height 63.0 mm, inner diameter of the opening 12.5 mm), and then stirred at 1000 rpm for 60 minutes using a stirrer (20 mm x φ7 mm) and a stirrer. When producing dried carbon nanotubes having a viscosity ratio B1 / A1 of 2.0 or more, a carbon nanotube dispersion liquid having the above-mentioned predetermined viscosity ratio B2 / A2 of 2.0 or more is prepared and then dried, thereby enabling the efficient production of dried carbon nanotubes having excellent dispersibility and ease of handling.

[0015] [6] The method for producing dried carbon nanotubes according to [5] above, wherein the carbon nanotube dispersion contains a foaming agent.

[0016] [7] The method for producing a dried carbon nanotube product according to [5] above, wherein the solvent used for producing the dispersion liquid is removed by freeze-drying in the drying step. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a dried carbon nanotube product that is excellent in both dispersibility and handleability. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of a CNT re-dispersion liquid contained in a vial when evaluating dispersibility (sedimentation height). DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in detail. Here, the dried CNT material of the present invention is not particularly limited and can be suitably incorporated into, for example, secondary battery components, semiconductor wafer transport containers (FOUP: Front-Opening Unified Pod, etc.), semiconductor manufacturing components, and the like.

[0020] (Dried carbon nanotubes) The dried CNT material of the present invention is characterized in that the viscosity ratio B1 / A1, obtained by dividing the viscosity B1 when the dried carbon nanotubes are dispersed in the solvent for viscosity measurement of the dry material at a concentration of 0.1% by mass under the following conditions, by the viscosity A1 of the solvent for viscosity measurement of the dry material, is 2.0 or more. <Condition> 0.01 g of the dried carbon nanotube product and 10.0 g of the solvent for measuring the viscosity of the dried product were placed in a vial (volume 30 mL, body diameter 33.0 mm, height 63.0 mm, inner diameter of the opening 12.5 mm), and then stirred at 1000 rpm for 60 minutes using a stirrer (20 mm x φ7 mm) and a stirrer. Thus, if the viscosity ratio B1 / A1 calculated by subjecting the dried CNT material to a predetermined dispersion treatment is 2.0 or more, the dried CNT material is excellent in both dispersibility and handleability.

[0021] Here, the amount of residual solvent in the dried CNT material is at least 0.5% by mass or less. Examples of the residual solvent include the solvent used when dispersing the CNTs as a material in producing the dried CNT material. Specific examples include the various solvents listed as "solvents for producing dispersion liquid" in the section on the method for producing the dried CNT material described below. The amount of residual solvent can be measured by a thermal weight loss method.

[0022] Furthermore, t-butyl alcohol can be used as a solvent for measuring the dry viscosity. Here, the solvent for measuring the dry viscosity can contain 3% by mass of water in order to suppress solidification of the t-butyl alcohol. That is, a solvent consisting of 97% by mass of t-butyl alcohol and 3% by mass of water can be used as a solvent for measuring the dry viscosity.

[0023] The value of the viscosity ratio B1 / A1 is preferably 2.5 or more, more preferably 3.0 or more, and is usually not more than 100. When the value of the viscosity ratio B1 / A1 is equal to or more than the above lower limit, the dried CNT material is more excellent in both dispersibility and handleability.

[0024] The dried CNT material preferably contains only CNTs as the carbon material. That is, the dried CNT material preferably does not contain other carbon materials, such as carbon black and carbon nanohorns, in addition to CNTs. If the dried CNT material contains only CNTs as the carbon material, it can effectively exhibit the notable attributes of CNTs, such as a balance of light weight, mechanical strength, and toughness.

[0025] <cnt> The dried CNT material contains multiple CNTs. The multiple CNTs may include multiple multi-walled CNTs and multiple single-walled CNTs, but preferably contain multiple single-walled carbon nanotubes (single-walled CNTs) as the main component. Here, the ratio of single-walled CNTs to the total mass of the CNTs is preferably more than 50% by mass, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass. Note that when the CNTs contain multi-walled CNTs, the number of walls of the multi-walled CNTs is preferably 5 or less.

[0026] <<Properties>> [Specific surface area] The specific surface area of ​​the dried CNT is 400m 2 / g or more is preferable, and 600m 2 / g or more is more preferable, and 1800m 2 / g or less, and 1600m 2 When the specific surface area of ​​the dried CNT material is within the above range, the dried CNT material has excellent dispersibility.

[0027] The dried carbon nanotube product of the present invention is preferably produced by the production method of the present invention described below. In other words, it is preferably a dried carbon nanotube dispersion containing carbon nanotubes as materials and a dispersion-producing solvent, in which the viscosity ratio B2 / A2, obtained by dividing the viscosity B2 of the carbon nanotube dispersion by the viscosity A2 of the dispersion-producing solvent, is 2.0 or more.

[0028] (Method of producing dried carbon nanotubes) The method for producing dried carbon nanotubes of the present invention includes a dispersion preparation step of preparing a carbon nanotube dispersion containing carbon nanotubes as materials and a dispersion preparation solvent such that the viscosity ratio B2 / A2, obtained by dividing the viscosity B2 of the carbon nanotube dispersion by the viscosity A2 of the dispersion preparation solvent, is 2.0 or more, and a drying step of removing the dispersion preparation solvent from the carbon nanotube dispersion to obtain dried carbon nanotubes. This production method of the present invention allows for efficient production of the above-mentioned dried CNTs of the present invention.

[0029] <Dispersion liquid preparation process> In the dispersion preparation step, a carbon nanotube dispersion containing carbon nanotubes as a material and a solvent for producing the dispersion is prepared. If necessary, in the dispersion preparation step, the carbon nanotubes as a material and the solvent for producing the dispersion may be mixed to obtain a crude dispersion, and then the crude dispersion may be subjected to a dispersion treatment. The method and conditions for preparing the dispersion and the method and conditions for dispersing the dispersion may be appropriately selected depending on the desired dispersion strength. For example, a mixer such as a wet jet mill, a bead mill, a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, or a Filmix may be used.

[0030] <<CNT as a material>> The CNT material contains multiple CNTs, similar to the dried CNT material described above. The types of CNTs contained in the CNT material and their content ratios are as described above for the dried CNT material. In addition, it is preferable that the specific surface area of ​​the CNT material satisfies the preferred range described above for the dried CNT material.

[0031] [Effective Length] The effective length of the CNT is preferably 40 nm or more, more preferably 50 nm or more, and preferably 1000 nm or less, more preferably 300 nm or less. In the present invention, the effective length of the CNT refers to the distance between adjacent bent portions, in cases where the CNT is not completely straight and may have multiple bent portions (bent portions) along the length.

[0032] [Average diameter and average length] The average diameter of the CNTs is preferably 1 nm or more, preferably 60 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. The average length of the CNTs is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 80 μm or more, and is preferably 600 μm or less, more preferably 500 μm or less, and even more preferably 450 μm or less.

[0033] [purity] The purity of the CNTs is preferably 98% by mass or more, and more preferably 99% by mass or more. Such CNT aggregates contain almost no impurities, allowing the inherent properties of the CNTs to be fully exhibited. There is no particular upper limit to the purity of the CNTs. Furthermore, the purity of the CNTs can be determined by elemental analysis using fluorescent X-rays, thermogravimetric analysis (TGA), or the like.

[0034] Aspect Ratio Furthermore, CNTs typically have an aspect ratio (length / diameter) of more than 10. Such aspect ratio values ​​also apply to dried CNTs. The average diameter, average length and aspect ratio of CNTs can be determined by measuring the diameter and length of 100 randomly selected CNTs using a scanning electron microscope or a transmission electron microscope.

[0035] Furthermore, it is preferable that the t-plot obtained from the adsorption isotherm of the CNTs exhibits an upwardly convex shape.

[0036] In a material with pores on its surface, the growth of a nitrogen gas adsorption layer can be classified into the following three processes (1) to (3). The slope of the t-plot changes depending on the following processes (1) to (3). (1) The process of forming a monolayer of nitrogen molecules on the entire surface (2) Formation of multi-layer adsorption and the accompanying capillary condensation filling process in the pores (3) The process of multilayer adsorption on an apparently non-porous surface whose pores are filled with nitrogen

[0037] In the case of a t-plot showing an upward convex shape, the plot lies on a straight line passing through the origin in the region where the average thickness t of the nitrogen gas adsorption layer is small, but as t increases, the plot shifts downward from the straight line. CNTs with such a t-plot shape have a large ratio of internal specific surface area to total specific surface area of ​​the CNTs, indicating that many openings are formed in the CNTs. As a result, when a dispersion is prepared using such CNTs, the CNTs are less likely to aggregate in the dispersion, improving dispersibility.

[0038] The bending point of the t-plot of the CNTs is preferably in the range satisfying 0.2≦t (nm)≦1.5, more preferably in the range of 0.45≦t (nm)≦1.5, and even more preferably in the range of 0.55≦t (nm)≦1.0. When a dispersion is prepared using CNTs with a bending point in the t-plot within this range, the CNTs are less likely to aggregate in the dispersion and have excellent dispersibility. Here, the "position of the bending point" is the intersection of the approximate line A in the process (1) described above and the approximate line B in the process (3) described above.

[0039] Furthermore, the ratio of the internal specific surface area S2 to the total specific surface area S1 (S2 / S1) obtained from the t-plot is preferably 0.05 or more and 0.30 or less. When a dispersion is prepared using CNTs with an S2 / S1 value within this range, the CNTs are even less likely to aggregate in the dispersion.

[0040] Here, the total specific surface area S1 and internal specific surface area S2 of the CNT can be determined from the t-plot. Specifically, first, the total specific surface area S1 can be determined from the slope of the approximation line in step (1), and the external specific surface area S3 can be determined from the slope of the approximation line in step (3). Then, the internal specific surface area S2 can be calculated by subtracting the external specific surface area S3 from the total specific surface area S1.

[0041] Measurement of the adsorption isotherm of CNT, creation of t-plots, and calculation of the total specific surface area S1 and the internal specific surface area S2 based on analysis of the t-plots can be performed using, for example, a commercially available measuring device, "BELSORP (registered trademark)-mini" (manufactured by BEL Japan Co., Ltd.).

[0042] CNTs can be produced using known CNT synthesis methods, such as arc discharge, laser ablation, and chemical vapor deposition (CVD), without any particular limitation. Specifically, CNTs can be efficiently produced, for example, by supplying raw material compounds and a carrier gas onto a substrate having a catalyst layer for carbon nanotube production on its surface, and synthesizing CNTs by chemical vapor deposition (CVD) using a method known as the super-growth method (see International Publication No. 2006 / 011655), in which the catalytic activity of the catalyst layer is dramatically improved by the presence of a trace amount of oxidant (catalytic activator) in the system. Note that, hereinafter, carbon nanotubes obtained by the super-growth method may be referred to as "SGCNTs."

[0043] Furthermore, the CNTs contained in the electromagnetic wave absorbing member may be derived from a CNT aggregate (see, for example, WO 2022 / 114237) that satisfies at least one of the following conditions (1) to (3): (1) A carbon nanotube dispersion obtained by dispersing carbon nanotube aggregates so that the bundle length is 10 μm or more is subjected to Fourier transform infrared spectroscopy. In the spectrum obtained, a peak due to the plasmon resonance of the carbon nanotube dispersion is observed at a wave number of 300 cm. -1 Super 2000cm -1 At least one of the following is present: (2) For carbon nanotube aggregates, the maximum peak in the pore distribution curve showing the relationship between pore diameter and log differential pore volume, obtained based on the Barrett-Joyner-Halenda method from the adsorption isotherm of liquid nitrogen at 77 K, is in the pore diameter range of more than 100 nm and less than 400 nm. (3) The peak of the two-dimensional spatial frequency spectrum of the electron microscope image of the carbon nanotube aggregate is 1 μm -1 More than 100μm -1 At least one of the following ranges exists:

[0044] A CNT aggregate that satisfies the above-mentioned predetermined attributes can be produced according to the production method described in WO 2022 / 114237.

[0045] [Content ratio] The CNT content in the CNT dispersion is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and preferably 2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, based on 100% by mass of the total amount of the CNT dispersion. If the CNT content in the CNT dispersion is equal to or greater than the lower limit, the productivity of the dried CNT product can be improved. On the other hand, if the CNT content in the CNT dispersion is 2% by mass or less, the dispersion state of the CNT dispersion can be improved, thereby further increasing the dispersibility of the resulting dried CNT product.

[0046] [Viscosity ratio B2 / A2] The viscosity ratio B2 / A2, which is the value obtained by dividing the viscosity B2 of the CNT dispersion by the viscosity A2 of the dispersion-producing solvent, is preferably 5.0 or more, more preferably 10.0 or more, more preferably 20.0 or more, and even more preferably 30.0 or more, and is usually not more than 100. If the viscosity ratio B2 / A2 value is equal to or greater than the above-mentioned lower limit, the dispersibility and handleability of the obtained CNT dried product can be further improved.

[0047] [Solvent for manufacturing dispersion liquid] The solvent for producing the dispersion liquid is preferably an organic solvent containing at least one selected from isopropanol, 1-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, toluene, tetrahydrofuran, ethyl acetate, acetonitrile, ethylene glycol, methyl isobutyl ketone, t-butyl alcohol, etc. Furthermore, the solvent for producing the dispersion liquid may contain water as needed. When the solvent contains water, the water content is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, based on 100% by mass of the entire solvent.

[0048] <<Additives>> Optionally, the CNT dispersion may contain an additive. The additive is not particularly limited, and for example, a compound that can function as a foaming agent can be used. Adding a foaming agent and foaming it during the solvent removal in the drying step described below can improve the dispersibility of the resulting dried CNT product. Examples of foaming agents that can be used include carbonates such as ammonium carbonate, iodine, carbon dioxide (dry ice), naphthalene, oxalic acid, dinitrogen pentoxide, ammonium bromide, ammonium iodide, ammonium chloride, benzoic acid, p(para)-dichlorobenzene, and camphor. The amount of additive can be appropriately adjusted as needed. For example, when a foaming agent is added as an additive, the amount can be 0.5 to 2.0 times the mass of CNTs in the CNT dispersion.

[0049] <Drying process> In the drying process, the solvent for dispersion liquid production is removed from the carbon nanotube dispersion liquid to obtain a dried carbon nanotube product. In the drying process, it is preferable to remove most of the solvent for dispersion liquid production by means such as filtration and then further remove the solvent for dispersion liquid production that could not be completely removed. As the drying method at this time, a foaming drying method and a freeze-drying method can be preferably adopted. Among them, it is particularly preferable to adopt the freeze-drying method. By removing the solvent by the freeze-drying method, a CNT dried product with even better dispersibility can be efficiently produced. In addition, when the foaming drying method is adopted in the drying process, that is, when a foaming agent is added to the CNT dispersion liquid, it is preferable to set the drying conditions (for example, drying temperature) in the drying process so that the foaming agent sublimes and no foaming agent remains in the obtained CNT dried product.

Examples

[0050] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified. In the examples and comparative examples, various evaluations and measurements were carried out as follows.

[0051] <Redispersion method of CNT dried product> Regarding the CNT dried products obtained in the examples and comparative examples, a redispersion liquid was prepared as follows. 0.01 g of the CNT dried product, 9.7 g of t-butyl alcohol (manufactured by Fujifilm Wako Pure Chemical Corporation), and 0.3 g of ion-exchanged water were put into a Mighty Vial (manufactured by Maruemu Co., Ltd., No. 6, capacity 30 mL, body diameter 33.0 mm, height 63.0 mm, mouth inner diameter 12.5 mm). After that, a stirrer (manufactured by AS ONE Corporation, rotor (made of PTFE resin) 20 × diameter 7 mm) and a stirrer (manufactured by AS ONE Corporation) were used to stir at 1000 rpm for 60 minutes to obtain a CNT redispersion liquid.

[0052] <Dispersibility (sedimentation height)> Using a ruler, measure the liquid level height X of the redispersion liquid in the vial obtained above, and the height Y of the CNT sediment. By dividing Y by X, the sediment height was calculated. Figure 1 shows a schematic diagram of the CNT redispersion liquid contained in the vial. In the redispersion liquid contained in vial 1, the higher the dispersibility of CNT in the redispersion liquid, the closer the height Y of the CNT sediment is to the liquid level height X. Therefore, the closer the value obtained by dividing Y by X is to 1, the better the dispersibility of the CNT dry matter.

[0053] <Viscosity> In the examples and comparative examples, the viscosity B2 of the carbon nanotube dispersion liquid prepared during the production of the CNT dry matter, the viscosity A2 of the solvent for producing the dispersion liquid, and the viscosity A1 of the solvent for producing the dispersion liquid and the viscosity B1 of the redispersion liquid used when preparing the redispersion liquid of the obtained CNT dry matter were measured as follows. An LV adapter was attached to a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., TVB10), 22 ml of the sample (each solvent and dispersion liquid) was introduced, and the viscosity at 23 °C was evaluated. Regarding the rotation speed, the fastest rotation speed within the measurable range on the device was used according to the viscosity of the sample.

[0054] <Viscosity ratio> Using the viscosities A1, A2, B1, and B2 obtained above, the values of B1 / A1 and B2 / A2 were calculated respectively.

[0055] <Bulk density> A Mighty vial (manufactured by Maruemu Co., Ltd., No. 8) was filled with CNT dry matter up to about half of the container volume. Another vial of the same type was prepared and filled with ion-exchanged water up to the same height as the filling of the CNT dry matter. From the difference in the mass of each container, the filled CNT dry matter and ion-exchanged water were weighed, and the bulk density was calculated by dividing the mass of the CNT dry matter by the mass of the ion-exchanged water. If the bulk density is moderately high, the CNT dry matter has excellent handling properties.

[0056] (Example 1) <Preparation of CNT aggregate> The CNTs used as the material in Example 1 (hereinafter also referred to as "CNT1") were produced according to the method disclosed in Example 4 of WO 2022 / 114237.

[0057] The properties of the produced CNT aggregate are single-walled CNTs, and the typical value is tapped bulk density: 0.01 g / cm 3 , CNT average length: 120 μm, BET specific surface area: 718 m 2 / g, average diameter: 4.0 nm, and carbon purity: 99%.

[0058] <Dispersion liquid preparation process> A 0.2 mass% CNT dispersion was prepared by adding 0.028 kg of CNT1, the CNT material obtained above, 13.58 kg of t-butyl alcohol (Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade), and 0.42 kg of ion-exchanged water to a bead mill disperser and dispersing at a peripheral speed of 8 m / s for a residence time of 20 minutes. Various attributes of the prepared CNT dispersion were measured as described above. The results are shown in Table 1.

[0059] <Drying process> The drying process was carried out by freeze-drying. 100 g of the CNT dispersion was weighed into a 300 ml beaker and then filtered under reduced pressure using a Buchner funnel to obtain a CNT solid from which the solvent had been roughly removed. The obtained CNT solid was immersed in liquid nitrogen to solidify, and then dried overnight under reduced pressure at 20°C in a vacuum dryer to sublimate and remove the residual solvent, yielding a dried CNT product. The amount of residual solvent in the obtained dried CNT product was 0.5 mass% or less. Furthermore, various attributes of the obtained dried CNT product were measured as described above. The results are shown in Table 1.

[0060] Example 2 Various operations and measurements were carried out in the same manner as in Example 1, except that the <dispersion liquid preparation step> was carried out using a Hiflex homogenizer as described below. The results are shown in Table 1. <Dispersion liquid preparation process> 0.2 g of CNT, 97.0 g of t-butyl alcohol, and 3.0 g of ion-exchanged water were placed in a high-flex homogenizer (SMT Corporation, SMT Mixer HF93) and dispersed at 15,000 rpm for 20 minutes to prepare a 0.2 mass % CNT dispersion.

[0061] Example 3 The same dispersion preparation step as in Example 2 was carried out, and foam drying was carried out in the drying step as described below. Except for this, various operations and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. <Drying process> 100g of 0.2 mass% CNT dispersion was added to a 300ml beaker, and 0.2g of ammonium carbonate (Fujifilm Wako Pure Chemical Industries, Ltd., Wako Special Grade) was added as a foaming agent. The mixture was stirred gently with a spoon and then filtered to obtain a CNT solid containing ammonium carbonate as a foaming agent. The resulting CNT solid was heated at 100°C for 3 hours to remove residual solvent and ammonium carbonate, yielding a dried CNT product. The residual solvent content of the resulting dried CNT product was 0.5 mass% or less.

[0062] Example 4 The CNTs used as the material were single-walled CNTs different from those used in Examples 1 to 3 (manufactured by Zeon Corporation, product name "ZEONANO SG101", specific gravity 1.7, carbon purity: 99.5%, average diameter 3.5 nm, 3σ / Av: 0.60, average length: 450 μm, specific surface area: 1042 m). 2 / g, t-plot: upward convex). Except for this, various operations and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0063] (Comparative Example 1) In the dispersion preparation process, dispersion treatment using a bead mill was not performed. Instead, 0.028 kg of CNT1 similar to that in Example 1 and a dispersion solvent for production similar to that in Example 1 (a mixture of 13.58 kg of t-butyl alcohol and 0.42 kg of ion-exchanged water) were added to a mixing container to obtain a mixture of CNT1 and the dispersion solvent for production. For this obtained mixture, the aforementioned <viscosity> and <viscosity ratio (value of B2 / A2)> were measured. Also, using CNT1 as the CNT dried product, a CNT redispersion liquid was obtained based on the aforementioned <method for redispersing CNT dried product>, and <dispersion (settling height)> and <viscosity ratio (B1 / A1)> were measured respectively. The results are shown in Table 1.

[0064] (Comparative Example 2) Solvent drying was carried out as follows in the drying process. Except for this point, various operations and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. <Drying Process> After weighing 100 g of the CNT dispersion liquid in a 300 ml beaker, the solvent was roughly removed by vacuum filtration with a Buchner funnel to obtain a CNT solid. The obtained CNT solid was subjected to vacuum heat treatment at 80°C overnight in a vacuum dryer to remove the residual solvent and perform solvent drying, obtaining a CNT dried product. The residual solvent amount of the obtained CNT dried product was 0.5 mass% or less.

[0065] (Comparative Example 3) The dispersion preparation process was not carried out, and a CNT dried product was obtained as follows. Except for this point, various operations and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. After adding 0.2 g of CNT1, 97.0 g of t-butyl alcohol, and 3.0 g of ion-exchanged water to a 300 ml beaker to obtain a mixture, the solvent was roughly removed by vacuum filtration with a Buchner funnel to obtain a CNT solid. The obtained CNT solid was subjected to vacuum heat treatment at 80°C overnight in a vacuum dryer to remove the residual solvent and perform solvent drying, obtaining a CNT dried product. The residual solvent amount of the obtained CNT dried product was 0.5 mass% or less. Also, for the mixture obtained above, the aforementioned <viscosity> and <viscosity ratio (value of B2 / A2)> were measured.

[0066] [Table 1]

[0067] Table 1 shows that the dried CNT material has excellent dispersibility and ease of handling when the viscosity ratio B1 / A1, calculated using the viscosity B1 of the dispersion obtained by dispersing the dried CNT material in a specified measurement solvent at a concentration of 0.1 mass% under specified conditions and the viscosity A1 of the measurement solvent, is 2.0 or higher. On the other hand, in Comparative Examples 1 to 3 in which the viscosity ratio B1 / A1 was less than 2.0, it was found that the dispersibility and handleability of the dried CNT material could not be achieved at the same time. [Industrial Applicability]

[0068] According to the present invention, it is possible to provide a dried carbon nanotube product that is excellent in both dispersibility and handleability. [Explanation of symbols]

[0069] 1 vial X Liquid level Y CNT sediment height< / cnt>

Claims

1. A dried carbon nanotube product, a viscosity ratio B1 / A1 obtained by dividing the viscosity B1 of the solvent for measuring viscosity of a dry product by the viscosity A1 of the solvent for measuring viscosity of a dry product, when the dry product of the carbon nanotubes is dispersed in the solvent for measuring viscosity of a dry product at a concentration of 0.1% by mass under the following conditions, is 2.0 or more; Dried carbon nanotubes. <Conditions> 0.01 g of the dried carbon nanotube product and 10.0 g of the solvent for measuring the viscosity of the dried product were placed in a vial (volume 30 mL, body diameter 33.0 mm, height 63.0 mm, inner diameter of the opening 12.5 mm), and then stirred at 1000 rpm for 60 minutes using a stirrer (20 mm x φ7 mm) and a stirrer.

2. The dried carbon nanotube material according to claim 1 , which contains only carbon nanotubes as the carbon material.

3. Specific surface area is 400m ２ The dried carbon nanotube product according to claim 1, wherein the dry carbon nanotube content is 1 / g or more.

4. A dried carbon nanotube product, a dried carbon nanotube dispersion containing carbon nanotubes as a material and a dispersion production solvent, wherein a viscosity ratio B2 / A2 obtained by dividing a viscosity B2 of the carbon nanotube dispersion by a viscosity A2 of the dispersion production solvent is 2.0 or more; Dried carbon nanotubes.

5. A method for producing dried carbon nanotubes, comprising: a dispersion preparation step of preparing a carbon nanotube dispersion containing carbon nanotubes as a material and a dispersion preparation solvent, so that a viscosity ratio B2 / A2 obtained by dividing a viscosity B2 of the carbon nanotube dispersion by a viscosity A2 of the dispersion preparation solvent is 2.0 or more; a drying step of removing the solvent for producing the dispersion from the carbon nanotube dispersion to obtain a dried carbon nanotube product; Including, The dried carbon nanotube product has a viscosity ratio B1 / A1 of 2.0 or more, obtained by dividing the viscosity B1 of the dried carbon nanotube product dispersed in the solvent for viscosity measurement of a dry product at a concentration of 0.1% by mass under the following conditions by the viscosity A1 of the solvent for viscosity measurement of a dry product: A method for producing dried carbon nanotubes. <Conditions> 0.01 g of the dried carbon nanotube product and 10.0 g of the solvent for measuring the viscosity of the dried product were placed in a vial (volume 30 mL, body diameter 33.0 mm, height 63.0 mm, inner diameter of the opening 12.5 mm), and then stirred at 1000 rpm for 60 minutes using a stirrer (20 mm x φ7 mm) and a stirrer.

6. The method for producing dried carbon nanotubes according to claim 5 , wherein the carbon nanotube dispersion contains a foaming agent.

7. The method for producing a dried carbon nanotube product according to claim 5 , wherein the solvent used for producing the dispersion liquid is removed by freeze-drying in the drying step.

Images