Fibrous carbon nanostructures

Abstract

To provide a fibrous carbon nanostructure that facilitates surface modification treatment.SOLUTION: In a fibrous carbon nanostructure, a half width of a peak of a temperature differential curve that is a primary differential curve of a thermogravimetric curve obtained by a thermogravimetric analysis in a dry air atmosphere is 38°C or higher and below than 90°C, and a high temperature side temperature at a height of one tenth of a peak top height of the peak is 658°C or higher.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to fibrous carbon nanostructures, methods for producing fibrous carbon nanostructures, and methods for producing surface-modified fibrous carbon nanostructures. [Background technology]

[0002] In recent years, fibrous carbon nanostructures such as carbon nanotubes (hereinafter sometimes referred to as "CNTs") have attracted attention as materials with excellent conductivity, thermal conductivity, and mechanical properties.

[0003] However, fibrous carbon nanostructures such as CNTs tend to form bundle structures due to van der Waals forces and other factors, making them difficult to disperse in solvents or resins, thus hindering their ability to exhibit the desired high performance.

[0004] Therefore, a technique has been proposed to improve the dispersibility of fibrous carbon nanostructures such as CNTs by subjecting them to surface modification treatments, such as oxidation treatment (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2015 / 045418 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In this context, from the perspective of obtaining surface-modified fibrous carbon nanostructures with excellent dispersibility through surface modification treatment of fibrous carbon nanostructures, it is required that the fibrous carbon nanostructures used as raw materials be properly surface-modified.

[0007] However, conventional fibrous carbon nanostructures had room for improvement in terms of making them easier to modify.

[0008] Therefore, an object of the present invention is to provide a fibrous carbon nanostructure that is easy to surface-modify and a method for producing the same. Another object of the present invention is to provide a surface-modified fibrous carbon nanostructure that is well surface-modified.

Means for Solving the Problems

[0009] The present inventor has conducted intensive studies to achieve the above object. As a result, the present inventor has found that a fibrous carbon nanostructure having predetermined properties is easy to be surface-modified, and thus completed the present invention.

[0010] That is, the present invention aims to advantageously solve the above problems. The fibrous carbon nanostructure of the present invention has a temperature differential curve (hereinafter, the "temperature differential curve which is the first derivative curve of the thermogravimetric curve" is simply referred to as the "temperature differential curve") that is the first derivative curve of the thermogravimetric curve obtained by thermogravimetric analysis in a dry air atmosphere, and the half-value width of the peak of the temperature differential curve is 38 °C or more and less than 90 °C, and the high-temperature side temperature at a height of 1 / 10 of the peak top height of the peak is 658 °C or more. A fibrous carbon nanostructure having a half-value width of the peak of the temperature differential curve of 38 °C or more and less than 90 °C and a high-temperature side temperature at a height of 1 / 10 of the peak top height of the peak of 658 °C or more is easy to be surface-modified when subjected to a surface-modifying treatment such as an oxidation treatment. Here, in the present invention, the "peak" means, in the figure of the temperature differential curve (for example, FIG. 1), among the convex curve portions including the point where the absolute value of the weight change rate per °C becomes the maximum value, the point where the absolute value of the weight change rate per °C becomes the maximum value (for example, DTG in FIG. 1) max ) and the convex curve portion including the point where the absolute value of the weight change rate per °C becomes the minimum value (when there is one peak (maximum value) as in FIG. 1 and there is no minimum value, the minimum value), the low-temperature side temperature (for example, T in FIG. 1) iniIt means the curved portion between [[ID=]] and the high-temperature side temperature. However, the point at which the absolute value of the weight change rate per 1°C becomes the minimum value (when there is only one peak (maximum value) as shown in FIG. 1 and no minimum value, it is the minimum value) is below the height of 1 / 10 of the peak top height of the peak. Also, the "half-width of the peak" and the "high-temperature side temperature at the height of 1 / 10 of the peak top height of the peak" can be obtained using the method described in the examples of this specification.

[0011] In addition, it is preferable that the weight reduction rate at the low-temperature side temperature at the height of 7.5 / 10 of the peak top height of the peak of the fibrous carbon nanostructure of the present invention is 40 wt% or less. A fibrous carbon nanostructure having a weight reduction rate of 40 wt% or less at the low-temperature side temperature at the height of 7.5 / 10 of the peak top height of the peak is more easily surface-modified when subjected to a surface modification treatment such as an oxidation treatment. Here, in the present invention, the "weight reduction rate at the low-temperature side temperature at the height of 7.5 / 10 of the peak top height of the peak" can be obtained using the method described in the examples of this specification.

[0012] And, it is preferable that the peak top temperature of the peak of the fibrous carbon nanostructure of the present invention is 530°C or higher and lower than 730°C. A fibrous carbon nanostructure having a peak top temperature of less than 530°C is likely to burn out when subjected to a surface treatment modification such as an oxidation treatment, while a fibrous carbon nanostructure having a peak top temperature of 730°C or higher is difficult to be surface-modified when subjected to a surface treatment modification such as an oxidation treatment. Here, in the present invention, the "peak top temperature of the peak" can be obtained using the method described in the examples of this specification.

[0013] Moreover, this invention aims to advantageously solve the above problems, and the manufacturing method of the fibrous carbon nanostructure of the present invention is a manufacturing method of a fibrous carbon nanostructure for manufacturing any of the above-described fibrous carbon nanostructures, characterized by including a step of heating the fibrous carbon nanostructure to a temperature of 120°C or higher in a vacuum atmosphere.

[0014] Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the method for producing fibrous carbon nanostructures of the present invention is a method for producing any of the above-mentioned fibrous carbon nanostructures, characterized in that it includes a step of heating the fibrous carbon nanostructure to a temperature of 800°C or higher under an inert gas atmosphere.

[0015] Furthermore, the present invention provides a method for producing a surface-modified fibrous carbon nanostructure, characterized by comprising the step of applying a surface modification treatment to any of the above-described fibrous carbon nanostructures to obtain a surface-modified fibrous carbon nanostructure. Here, the surface modification treatment may be a wet oxidation treatment. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide fibrous carbon nanostructures that are easily subjected to surface modification treatment and a method for producing the same. Furthermore, according to the present invention, it is possible to provide a method for producing surface-modified fibrous carbon nanostructures that have undergone good surface modification treatment. [Brief explanation of the drawing]

[0017] [Figure 1] This graph schematically shows the shape of the peak in the temperature differential curve. [Modes for carrying out the invention]

[0018] Embodiments of the present invention will be described in detail below. Herein, the fibrous carbon nanostructure of the present invention is easily surface-modified when subjected to surface modification treatments such as oxidation treatment. Furthermore, the surface-modified fibrous carbon nanostructure obtained by surface-modifying the fibrous carbon nanostructure of the present invention is not particularly limited and can be suitably used, for example, when preparing a dispersion liquid obtained by dispersing the surface-modified fibrous carbon nanostructure in a dispersion medium.

[0019] (Fibrous carbon nanostructures) The fibrous carbon nanostructure of the present invention requires that the full width at half maximum (FWHM) of the peak of the temperature differential curve obtained by thermogravimetric analysis in a dry air atmosphere is 38°C or higher and less than 90°C, and that the high-temperature side temperature at 1 / 10th of the peak top height is 658°C or higher. Furthermore, since the fibrous carbon nanostructure of the present invention has a FWHM of 38°C or higher and less than 90°C, and the high-temperature side temperature at 1 / 10th of the peak top height is 658°C or higher, it undergoes good surface modification when subjected to surface modification treatments such as oxidation treatment.

[0020] Here, the fibrous carbon nanostructure is not particularly limited and includes, for example, cylindrical carbon nanostructures such as carbon nanotubes (CNTs), and non-cylindrical carbon nanostructures such as carbon nanostructures in which a network of six-membered carbon rings is formed in a flattened cylindrical shape. Furthermore, the fibrous carbon nanostructure of the present invention may contain one type of the above-described carbon nanostructure alone, or it may contain two or more types.

[0021] Among the above, fibrous carbon nanostructures containing CNTs are preferred. This is because fibrous carbon nanostructures containing CNTs can exhibit particularly excellent properties (e.g., electrical conductivity, thermal conductivity, strength, etc.) when their dispersibility is enhanced by surface modification treatment.

[0022] Furthermore, the fibrous carbon nanostructure containing CNTs may consist solely of CNTs, or it may be a mixture of CNTs and other fibrous carbon nanostructures. Furthermore, while single-walled carbon nanotubes and / or multi-walled carbon nanotubes can be used as CNTs in the fibrous carbon nanostructure, they are not particularly limited. However, the CNTs are preferably single-walled to five-walled carbon nanotubes, and more preferably single-walled carbon nanotubes. This is because the fewer the number of layers of carbon nanotubes, the better the properties that can be exhibited when the dispersibility is improved by surface modification treatment.

[0023] Here, the fibrous carbon nanostructure of the present invention is required to have a full width at half maximum (FWHM) of the peak of the temperature differential curve obtained by thermogravimetric analysis in a dry air atmosphere of 38°C or higher and less than 90°C, and preferably 40°C or higher, and more preferably 49°C or lower. Furthermore, preferably 85°C or lower, and more preferably 80°C or lower. If the FWHM of the peak of the temperature differential curve is above the lower limit of the preferred range, impurities that promote air oxidation can be removed, and if the FWHM of the peak of the temperature differential curve is below the upper limit of the preferred range, incineration during surface modification of the fibrous carbon nanostructure can be suppressed.

[0024] Furthermore, the fibrous carbon nanostructure of the present invention requires that the high-temperature side temperature at 1 / 10th the peak top height of the temperature differential curve obtained by thermogravimetric analysis in a dry air atmosphere be 658°C or higher, preferably 660°C or higher, more preferably 665°C or higher, even more preferably 673°C or higher, and even more preferably 689°C or higher, and is usually 760°C or lower. If the high-temperature side temperature at 1 / 10th the peak top height of the temperature differential curve is above the lower limit of the preferred range, the surface will be modified more effectively when surface modification treatments such as oxidation treatment are applied.

[0025] Furthermore, the fibrous carbon nanostructure of the present invention preferably has a weight loss rate of 40% by weight or less at low temperatures at a peak top height of 7.5 / 10 of the peak height of the temperature differential curve obtained by thermogravimetric analysis in a dry air atmosphere, more preferably 38% by weight or less, even more preferably 35% by weight or less, even more preferably 31% by weight or less, and even more preferably 29% by weight or less, and is usually 10% by weight or more. When the weight loss rate at low temperatures at a peak top height of 7.5 / 10 of the peak height of the temperature differential curve is below the above upper limit, the surface is modified more effectively when surface modification treatments such as oxidation treatment are applied.

[0026] Furthermore, the fibrous carbon nanostructure of the present invention preferably has a peak top temperature of 530°C or higher, more preferably 550°C or higher, even more preferably 570°C or higher, preferably less than 730°C, more preferably 710°C or lower, and even more preferably 690°C or lower. When the peak top temperature of the peak of the temperature differential curve is 530°C or higher and less than 730°C, the surface is more effectively modified when surface modification treatments such as oxidation treatment are applied.

[0027] The thermogravimetric curve is a curve where the vertical axis is mass and the horizontal axis is temperature, and the first differential curve of the thermogravimetric curve is a curve where the vertical axis is differential thermogravimetric (DTG) and the horizontal axis is temperature.

[0028] Furthermore, the (i) full width at half maximum (°C), (ii) the high-temperature side temperature at 1 / 10th of the peak top height (the "b value" in Table 1) (°C), (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10th of the peak top height, and (iv) the peak top temperature (°C) of the peak of the temperature differential curve of the fibrous carbon nanostructure can be adjusted by changing the pretreatment conditions of the fibrous carbon nanostructure (e.g., the atmosphere during pretreatment (vacuum atmosphere or inert gas atmosphere) and the treatment temperature).

[0029] Furthermore, the average diameter of the fibrous carbon nanostructure 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. Fibrous carbon nanostructures with an average diameter within the above range can exhibit particularly excellent properties when their dispersibility is improved by surface modification treatment. In this invention, the "average diameter of fibrous carbon nanostructures" can be determined by measuring the diameter (outer diameter) of, for example, 20 randomly selected fibrous carbon nanostructures on a transmission electron microscope (TEM) image and calculating the numerical average value.

[0030] Furthermore, as fibrous carbon nanostructures, it is preferable to use fibrous carbon nanostructures in which the ratio (3σ / Av) of the standard deviation of the diameter (σ: sample standard deviation) multiplied by 3 (3σ) to the average diameter (Av) is greater than 0.20 and less than 0.80, more preferably fibrous carbon nanostructures in which 3σ / Av is greater than 0.25, and even more preferably fibrous carbon nanostructures in which 3σ / Av is greater than 0.50. Fibrous carbon nanostructures in which 3σ / Av is greater than 0.20 and less than 0.80 can exhibit particularly excellent properties when their dispersibility is improved by surface modification treatment. The average diameter (Av) and standard deviation (σ) of the fibrous carbon nanostructure may be adjusted by changing the manufacturing method or manufacturing conditions of the fibrous carbon nanostructure, or by combining multiple types of fibrous carbon nanostructures obtained by different manufacturing methods.

[0031] Furthermore, the fibrous carbon nanostructures preferably have an average length of 10 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, preferably 600 μm or less, more preferably 550 μm or less, and even more preferably 500 μm or less. Fibrous carbon nanostructures with an average length within the above range can exhibit particularly excellent properties when their dispersibility is enhanced by surface modification treatment. In the present invention, the "average length of the fibrous carbon nanostructure" can be determined by measuring the lengths of, for example, 20 fibrous carbon nanostructures on a scanning electron microscope (SEM) image and calculating the number average value.

[0032] Here, the fibrous carbon nanostructure usually has an aspect ratio exceeding 10. The aspect ratio of the fibrous carbon nanostructure can be determined by measuring the diameters and lengths of 20 randomly selected fibrous carbon nanostructures using a scanning electron microscope or a transmission electron microscope and calculating the average value of the ratio of the length to the diameter (length / diameter).

[0033] Also, the fibrous carbon nanostructure preferably has a BET specific surface area of 600 m 2 / g or more, more preferably 800 m 2 / g or more, preferably 2000 m 2 / g or less, more preferably 1800 m 2 / g or less, and even more preferably 1600 m 2 / g or less. If the BET specific surface area of the fibrous carbon nanostructure is 600 m 2 / g or more, particularly excellent properties can be exhibited when the dispersibility is enhanced by surface modification treatment. Also, if the BET specific surface area of the fibrous carbon nanostructure is 2000 m 2 / g or less, the dispersibility can be sufficiently enhanced when surface modification treatment is performed. In the present invention, the "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET method.

[0034] Also, the fibrous carbon nanostructure is preferably not subjected to opening treatment and the t-plot obtained from the adsorption isotherm shows a convex upward shape. A fibrous carbon nanostructure with a convex upward t-plot can exhibit particularly excellent properties when the dispersibility is enhanced by surface modification treatment. The "t-plot" can be obtained by converting the relative pressure to the average thickness t (nm) of the nitrogen gas adsorption layer in the adsorption isotherm of a fibrous carbon nanostructure measured by the nitrogen gas adsorption method. That is, by plotting the average thickness t of the nitrogen gas adsorption layer against the relative pressure P / P0 from a known standard isotherm, the average thickness t of the nitrogen gas adsorption layer corresponding to the relative pressure is determined and the above conversion is performed to obtain the t-plot of the fibrous carbon nanostructure (t-plot method by de Boer et al.). In this specification, a "t-plot" can be obtained using the method described in the examples of this specification.

[0035] In materials with pores on their surface, the growth of the nitrogen gas adsorption layer can be classified into the following processes (1) to (3). These processes (1) to (3) result in a change in the slope of the t-plot. (1) Process of forming a single-molecule adsorbed layer of nitrogen molecules on the entire surface (2) Formation of a multimolecular adsorption layer and the accompanying capillary condensation and filling process within the pores (3) Process of forming a multimolecular adsorption layer on an apparent non-porous surface where pores are filled with nitrogen

[0036] Furthermore, in the 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, while as t increases, the plot shifts downward from that straight line. Fibrous carbon nanostructures with this t-plot shape have a large ratio of internal specific surface area to total specific surface area, indicating that numerous openings are formed in the carbon nanostructures constituting the fibrous carbon nanostructure.

[0037] Furthermore, the inflection point of the t-plot of the fibrous carbon nanostructure is preferably in the range of 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. If the inflection point of the t-plot of the fibrous carbon nanostructure is within this range, it can exhibit particularly excellent properties when its dispersibility is improved by surface modification treatment. The "position of the inflection point" is the intersection of the approximate line A from process (1) described above and the approximate line B from process (3) described above.

[0038] Furthermore, it is preferable that the ratio of the internal specific surface area S2 to the total specific surface area S1 obtained from the t-plot (S2 / S1) is between 0.05 and 0.30. If the S2 / S1 value of the fibrous carbon nanostructure is within this range, it can exhibit particularly excellent properties when its dispersibility is improved by surface modification treatment. Here, the total specific surface area S1 and internal specific surface area S2 of the fibrous carbon nanostructure can be determined from its t-plot. Specifically, first, the total specific surface area S1 can be determined from the slope of the approximate line in process (1), and the external specific surface area S3 can be determined from the slope of the approximate line in process (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.

[0039] Incidentally, the measurement of adsorption isotherms of fibrous carbon nanostructures, the creation of t-plots, and the calculation of the total specific surface area S1 and internal specific surface area S2 based on the analysis of the t-plots can be performed, for example, using a commercially available measuring device called "BELSORP(registered trademark)-mini" (manufactured by Nippon Bell Co., Ltd.).

[0040] Furthermore, fibrous carbon nanostructures containing carbon nanotubes (CNTs), which are suitable as fibrous carbon nanostructures, preferably exhibit a Radial Breathing Mode (RBM) peak when evaluated using Raman spectroscopy. Note that RBM is absent in the Raman spectrum of fibrous carbon nanostructures consisting solely of three or more multilayer carbon nanotubes.

[0041] Furthermore, fibrous carbon nanostructures containing CNTs preferably have a ratio of the G-band peak intensity to the D-band peak intensity (G / D ratio) in the Raman spectrum between 0.5 and 5.0. When the G / D ratio is between 0.5 and 5.0, particularly excellent properties can be exhibited when the dispersibility is improved by surface modification treatment. In addition, in this specification, the "G / D ratio" can be determined using the following method. <G / D ratio> Using a microscopic Raman system (Nicolet Almega XR, manufactured by Thermo Fisher Scientific Co., Ltd.), measurements are made on the fibrous carbon nanostructure near the center of the substrate.

[0042] The carbon purity of the fibrous carbon nanostructure is preferably 98% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more. In addition, in this specification, the "carbon purity" can be determined using the following method. <Carbon purity> Using a thermogravimetric analyzer (TG), the carbon purity (= (weight reduced by combustion until reaching 800°C / initial weight) × 100 (%)) is determined from the weight reduction when the fibrous carbon nanostructure is heated to 800°C in air.

[0043] <Pretreatment> The pretreatment may include (i) a step of heating the fibrous carbon nanostructure at a temperature of 120°C or higher, preferably 190°C or higher (usually 300°C or lower) in a vacuum atmosphere, or (ii) a step of heating the fibrous carbon nanostructure at a temperature of 800°C or higher, preferably 900°C or higher (usually 1,100°C or lower) in an inert gas atmosphere, but it is preferable to include a step of heating under vacuum. By setting the treatment temperature to a temperature not lower than the lower limit, it becomes easier to be surface-modified when a surface modification treatment such as an oxidation treatment is performed, and by setting the treatment temperature to a temperature not higher than the upper limit, the burnout of the fibrous carbon nanostructure can be suppressed. Examples of suitable inert gases include nitrogen, argon, helium, etc. Furthermore, after performing the above-mentioned step (i) of heating the fibrous carbon nanostructure to 120°C or higher under a vacuum atmosphere, the above-mentioned step (ii) of heating the fibrous carbon nanostructure to 800°C or higher under an inert gas atmosphere may be performed, or after performing the above-mentioned step (ii) of heating the fibrous carbon nanostructure to 800°C or higher under an inert gas atmosphere, the above-mentioned step (i) of heating the fibrous carbon nanostructure to 120°C or higher under a vacuum atmosphere may be performed.

[0044] The pretreatment processing time is preferably 10 minutes or more, more preferably 1 hour or more, even more preferably 3 hours or more, preferably 36 hours or less, more preferably 30 hours or less, and even more preferably 24 hours or less. By setting the processing time above the lower limit, impurities that promote air oxidation can be removed, and by setting the processing time below the upper limit, the burning of fibrous carbon nanostructures can be suppressed.

[0045] (Method for manufacturing surface-modified fibrous carbon nanostructures) In the method for producing surface-modified fibrous carbon nanostructures of the present invention, a surface modification treatment is applied to a fibrous carbon nanostructure having the predetermined properties described above to obtain a surface-modified fibrous carbon nanostructure.

[0046] <Surface modification treatment> The surface modification treatment is not particularly limited and can be carried out using surface modification agents such as nitric acid, sulfuric acid, a mixed acid of nitric acid and sulfuric acid, ozone, fluorine gas, or hydrogen peroxide. In particular, from the viewpoint of obtaining a surface-modified fibrous carbon nanostructure with excellent dispersibility, the surface modification treatment is preferably a wet oxidation treatment using nitric acid, sulfuric acid, or a mixed acid of nitric acid and sulfuric acid, and more preferably a wet oxidation treatment using a mixed acid of nitric acid and sulfuric acid. Furthermore, the surface modification treatment conditions can be set according to the type of surface modification agent used and the desired properties of the surface-modified fibrous carbon nanostructure.

[0047] <Surface-modified fibrous carbon nanostructures> Furthermore, the surface-modified fibrous carbon nanostructure obtained by surface-modifying the fibrous carbon nanostructure of the present invention can be dispersed well in a dispersion medium such as water without the use of a dispersant, without any particular limitations. The resulting dispersion of fibrous carbon nanostructure can be used in the manufacture of various molded products (for example, antistatic films and transparent conductive films). [Examples]

[0048] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following, "%" representing quantities refers to mass unless otherwise specified.

[0049] In the examples and comparative examples, the following characteristics of fibrous carbon nanostructures containing CNTs were measured or evaluated using the following methods: (I) the full width at half maximum (°C), (ii) the high-temperature side temperature (b-value) (°C) at 1 / 10 of the peak height of the temperature differential curve, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability.

[0050] <Temperature differential curve> Using a thermogravimetric differential thermal analyzer (manufactured by BrukerAXS, product name "TG-DTA2020SA"), a 2.00 mg sample was placed in the Pt pan (100 μL) of the thermogravimetric differential thermal analyzer, and the thermogravimetric curve of the fibrous carbon nanostructure was measured under conditions of a heating rate of 5°C / min and a dry air flow rate of 200 mL / min (data acquisition frequency: 0.5 seconds / point), and a temperature differential curve, which is a first differential curve (first differential curve creation conditions: differential width 10 points), was obtained. Here, the thermogravimetric curve has mass on the vertical axis and temperature on the horizontal axis, while the temperature differential curve, as shown in Figure 1 for example, has differential thermogravimetric (DTG) on the vertical axis and temperature on the horizontal axis. In Figure 1, the peaks shown by solid lines represent the results before pretreatment (e.g., Comparative Examples 1-4), and the peaks shown by dashed lines represent the results after pretreatment (e.g., Examples 1-4). Then, from the peaks of the temperature differential curve, we determined (i) the full width at half maximum (°C), (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C). (i) Full width at half maximum (°C): T b -T a (ii) High temperature (°C) at a height of 1 / 10 of the peak top height h (h / 10) ("b value" in Table 1): T c (iii) Low-temperature side temperature T at a peak top height h of 7.5 / 10 (7.5h / 10) d Weight loss rate (weight %) ("Weight loss rate" in Table 1): A (iv) Peak top temperature (°C): T max T max Peak top temperature (°C) DTG max :Temperature T max Differential thermogravimetric (% / °C) (peak top height h) T ini : Temperature at the start of the peak (°C) T a : The value of differential thermogravimetric analysis is DTG max The temperature at which the temperature becomes 1 / 2 (h / 2) (in °C) (low temperature side) T b : The value of differential thermogravimetric analysis is DTG max The temperature at which it becomes 1 / 2 (h / 2) (°C) (high temperature side, T b >T a ) T c : The value of differential thermogravimetric analysis is DTG max The temperature at which the temperature becomes 1 / 10 (h / 10) (°C) (high temperature side) T d : The value of differential thermogravimetric analysis is DTG max The temperature (°C) at which the temperature becomes 7.5 / 10 (7.5h / 10) (low temperature side) A:T ini From T d Peak area (peak integral value) in the temperature range up to [this point] <Surface modification treatment properties> In a 300 mL flask equipped with a condenser and stirring blades, 0.80 g of the obtained fibrous carbon nanostructure (Examples 1-4: after pretreatment, Comparative Examples 1-4: without pretreatment), 54.8 g of deionized water, and 83 mL of a mixed acid solution containing sulfuric acid (manufactured by Wako Pure Chemical Industries, Ltd., concentration 96-98%) and nitric acid (manufactured by Wako Pure Chemical Industries, Ltd., concentration 69-70%) in a 1:3 (volume ratio) ratio were added, and the mixture was heated at an internal temperature of 110°C for 8 hours while stirring. 3.0 g of the fibrous carbon nanostructure / mixed acid solution obtained after the mixed acid treatment (sometimes called "main treatment" or "wet oxidation treatment") was weighed into a 50 mL sample bottle and diluted with 27.0 g of deionized water. After removing the supernatant, deionized water was added to make a volume of 30 mL. After adjusting the pH to 7.0 by adding 0.1% aqueous ammonia, ultrasonic irradiation was performed at a frequency of 42 Hz for 50 minutes using an ultrasonic irradiation device (Branson, product name "BRANSON5510") to obtain a dispersion of fibrous carbon nanostructures. [Evaluation of dispersions] The obtained dispersion was then subjected to a centrifuge (Beckman Coulter, product name "OPTIMA XL100K"), where it was centrifuged at 20,000 G for 40 minutes, and the supernatant was collected. This cycle was repeated three times to obtain 20 mL of the fibrous carbon nanostructure dispersion after centrifugation. The obtained dispersion was visually inspected for the presence or absence of aggregates. Furthermore, using a spectrophotometer (JASCO Corporation, product name "V670"), the absorbance Ab1 (path length 1 cm, wavelength 550 nm) of the dispersion before centrifugation and the absorbance Ab2 (path length 1 cm, wavelength 550 nm) of the dispersion after centrifugation were measured. The dispersibility of the fibrous carbon nanostructure was evaluated by determining the rate of absorbance reduction due to centrifugation using the following formula. A smaller absorbance reduction rate (50% or less) indicates that the fibrous carbon nanostructure has been well surface-modified and has excellent dispersibility. Absorbance reduction rate (%)={1-(Ab2 / Ab1)}×100 [Evaluation of molded products (films)] Furthermore, the obtained dispersion was applied to a glass substrate using a bar coater #2, and then dried at 130°C for 10 minutes to form a film consisting of fibrous carbon nanostructures on the glass substrate. The obtained film was then observed using an optical microscope (100x magnification), and the dispersibility of the fibrous carbon nanostructures was evaluated by checking for the presence or absence of aggregates of fibrous carbon nanostructures (diameter 30 μm or larger) visible in the field of view of the microscope. A smaller number of aggregates of fibrous carbon nanostructures indicates that the fibrous carbon nanostructures have been well surface-modified and that their dispersibility is superior. 〔comprehensive evaluation〕 A sample was rated "Excellent" if the absorbance reduction rate was 50% or less, there were no aggregates in the dispersion, and there were no aggregate clumps in the membrane. Any other result was rated "Unacceptable."

[0051] (Example 1) As the oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs), we used ZEONANO SG101, a single-walled carbon nanotube manufactured by Zeon Nanotechnology Co., Ltd. This CNT-containing fibrous carbon nanostructure was pre-treated by heating it under vacuum at 190°C for 15 hours in an oven equipped with an oil-sealed rotary vacuum pump. Then, for the obtained fibrous carbon nanostructures, (I) the (i) full width at half maximum (°C) of the peak of the temperature differential curve, (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability were evaluated. The results are shown in Table 1.

[0052] (Example 2) In Example 1, an oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) was obtained in the same manner as in Example 1, except that instead of performing a pretreatment of heating at 190°C for 15 hours under vacuum, a pretreatment of heating at 120°C for 15 hours under vacuum was performed. Then, for the obtained fibrous carbon nanostructures, (I) the (i) full width at half maximum (°C) of the peak of the temperature differential curve, (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability were evaluated. The results are shown in Table 1.

[0053] (Example 3) In Example 1, instead of performing a pretreatment by heating at 190°C for 15 hours under vacuum, a pretreatment by heating at 900°C for 6 hours under a nitrogen atmosphere was performed. The same procedure as in Example 1 was used to obtain an oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs). Then, for the obtained fibrous carbon nanostructures, (I) the (i) full width at half maximum (°C) of the peak of the temperature differential curve, (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability were evaluated. The results are shown in Table 1.

[0054] (Example 4) In Example 1, an oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) was obtained in the same manner as in Example 1, except that instead of performing a pretreatment of heating at 190°C for 15 hours under vacuum, a pretreatment of heating at 800°C for 6 hours under a nitrogen atmosphere was performed. Then, for the obtained fibrous carbon nanostructures, (I) the (i) full width at half maximum (°C) of the peak of the temperature differential curve, (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability were evaluated. The results are shown in Table 1.

[0055] (Comparative Example 1) For ZEONANO SG101, a single-walled carbon nanotube manufactured by Zeon Nanotechnology Co., Ltd., which is an oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) that has not undergone pretreatment by heating under vacuum, the following were evaluated: (I) the (i) full width at half maximum (°C), (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability. The results are shown in Table 1.

[0056] (Comparative Example 2) In Comparative Example 1, except that Ocsial's "Tuball" single-walled carbon nanotubes were used as the oriented aggregate of fibrous carbon nanostructures, the oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) was evaluated in the same manner as in Comparative Example 1, as follows: (I) the (i) full width at half maximum (°C) of the peak of the temperature differential curve, (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability. The results are shown in Table 1.

[0057] (Comparative Example 3) In Comparative Example 1, except that Signis SG-65i, a single-walled carbon nanotube, was used as the oriented aggregate of fibrous carbon nanostructures, the oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) was evaluated in the same manner as in Comparative Example 1, as follows: (I) the (i) full width at half maximum (°C) of the peak of the temperature differential curve, (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability. The results are shown in Table 1.

[0058] (Comparative Example 4) In Comparative Example 1, except that MEIJO eDIPS EC1.5, manufactured by Meijo Nanocarbon Co., Ltd., was used as the oriented aggregate of fibrous carbon nanostructures, the oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures including CNTs) was evaluated in the same manner as in Comparative Example 1, as follows: (I) the (i) full width at half maximum (°C) of the peak of the temperature differential curve, (ii) the high-temperature side temperature (b value) (°C) at 1 / 10 of the peak top height, (iii) the weight loss rate (weight %) at the low-temperature side temperature at 7.5 / 10 of the peak top height, and (iv) the peak top temperature (°C), as well as (II) the surface modification treatability. The results are shown in Table 1.

[0059] [Table 1]

[0060] Table 1 shows that the fibrous carbon nanostructures of Examples 1-4 exhibit better surface modification and superior dispersibility (overall evaluation is "Excellent") compared to the fibrous carbon nanostructures of Comparative Examples 1-4. [Industrial applicability]

[0061] According to the present invention, it is possible to provide fibrous carbon nanostructures that are easily subjected to surface modification treatment and a method for producing the same. Furthermore, according to the present invention, it is possible to provide a method for producing surface-modified fibrous carbon nanostructures that have undergone good surface modification treatment. [Explanation of symbols]

[0062] T max Peak top temperature (°C) DTG max temperature T max Differential thermogravimetric (% / °C) (peak top height h) T ini Temperature at the start of the peak (°C) T a The value of differential thermogravimetric analysis is DTG max The temperature at which the temperature becomes 1 / 2 (h / 2) (in °C) (low temperature side) Tb The value of differential thermogravimetric analysis is DTG max The temperature at which it becomes 1 / 2 (h / 2) (°C) (high temperature side, T b >T a ) T c The value of differential thermogravimetric analysis is DTG max The temperature at which the temperature becomes 1 / 10 (h / 10) (°C) (high temperature side) T d The value of differential thermogravimetric analysis is DTG max The temperature (°C) at which the temperature becomes 7.5 / 10 (7.5h / 10) (low temperature side) AT ini From T d Peak area (peak integral value) in the temperature range up to [this point]

Claims

1. The full width at half maximum of the peak of the temperature differential curve, which is the first differential curve of the thermogravimetric curve obtained by thermogravimetric analysis in a dry air atmosphere, is between 38°C and 42°C. The high-temperature side temperature at 1 / 10th the height of the peak top of the aforementioned peak is 658°C or higher. A fibrous carbon nanostructure having a weight loss rate of 29% by weight or more and 40% by weight or less at the lower temperature side, at a height of 7.5 / 10 of the peak top height of the aforementioned peak.

2. The fibrous carbon nanostructure according to claim 1, wherein the peak top temperature of the aforementioned peak is 530°C or higher and less than 730°C.

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