Fibrous carbon nanostructures, methods for evaluating fibrous carbon nanostructures, and methods for manufacturing surface-modified fibrous carbon nanostructures.

Abstract

To provide a fibrous carbon nanostructure that can be easily surface-modified.SOLUTION: A fibrous carbon nanostructure of the present invention has a symmetry factor of 3.70 or less for a peak of a first derivative curve of a thermogravimetric curve obtained by thermogravimetric analysis under a dry air atmosphere. The first derivative curve of the thermogravimetric curve can be a temperature derivative curve of the thermogravimetric curve or a time derivative curve of the thermogravimetric curve.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to fibrous carbon nanostructures, methods for evaluating 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 easily surface-modified. Another object of the present invention is to provide a surface-modified fibrous carbon nanostructure that has been well surface-modified.

Means for Solving the Problems

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

[0010] That is, the object of this invention is to advantageously solve the above problems. The fibrous carbon nanostructure of the present invention is characterized in that the symmetry coefficient of the peak of the first derivative curve of the thermogravimetric curve obtained by thermogravimetric analysis in a dry air atmosphere is 3.70 or less. A fibrous carbon nanostructure having a symmetry coefficient of the peak of the first derivative curve of the thermogravimetric curve of 3.70 or less is easily surface-modified when subjected to a surface-modifying treatment such as an oxidation treatment. Here, in the present invention, the "symmetry coefficient of the peak" can be determined using the method described in the examples of this specification.

[0011] Here, the first derivative curve can be the temperature derivative curve or the time derivative curve of the thermogravimetric curve.

[0012] Further, it is preferable that the t-plot obtained from the adsorption isotherm of the fibrous carbon nanostructure of the present invention shows a convex upward shape. This is because a fibrous carbon nanostructure having a convex upward t-plot can exhibit particularly excellent properties (such as conductivity, heat conductivity, strength, etc.) when its dispersibility is enhanced by a surface-modifying treatment.

[0013] Furthermore, it is preferable that the fibrous carbon nanostructure of the present invention has a t-plot inflection point in the range of 0.2 ≤ t(nm) ≤ 1.5. This is because fibrous carbon nanostructures with a t-plot inflection point within the above range can exhibit particularly excellent properties (e.g., electrical conductivity, thermal conductivity, strength, etc.) when their dispersibility is enhanced by surface modification treatment.

[0014] Furthermore, it is preferable that the fibrous carbon nanostructure of the present invention satisfies the relationship: 0.05 ≤ S2 / S1 ≤ 0.30 between the total specific surface area S1 and the internal specific surface area S2 obtained from the t-plot obtained from the adsorption isotherm. This is because fibrous carbon nanostructures with S2 / S1 within the above range can exhibit particularly excellent properties (e.g., conductivity, thermal conductivity, strength, etc.) when their dispersibility is enhanced by surface modification treatment.

[0015] Furthermore, the fibrous carbon nanostructure of the present invention preferably contains carbon nanotubes, and more preferably contains single-walled carbon nanotubes. This is because fibrous carbon nanostructures containing carbon nanotubes, and especially fibrous carbon nanostructures containing single-walled carbon nanotubes, can exhibit particularly excellent properties (e.g., electrical conductivity, thermal conductivity, strength, etc.) when their dispersibility is enhanced by surface modification treatment.

[0016] Furthermore, this invention aims to advantageously solve the above-mentioned problems, and the method for evaluating fibrous carbon nanostructures of the present invention is characterized by including the steps of: performing thermogravimetric analysis on the fibrous carbon nanostructure under a dry air atmosphere to obtain a first derivative curve of the thermogravimetric curve; determining the symmetry coefficient of the peak of the first derivative curve of the thermogravimetric curve; and determining that those with a symmetry coefficient of 3.70 or less are good products, and those with a symmetry coefficient greater than 3.70 are defective products. Furthermore, the present invention provides a method for producing surface-modified fibrous carbon nanostructures, comprising the steps of: evaluating fibrous carbon nanostructures using the above-described method for evaluating fibrous carbon nanostructures; and applying a surface modification treatment to the fibrous carbon nanostructures deemed to be of good quality to obtain surface-modified fibrous carbon nanostructures. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide fibrous carbon nanostructures that are easily subjected to surface modification treatment. Furthermore, according to the present invention, it is possible to provide a surface-modified fibrous carbon nanostructure that has undergone good surface modification treatment. [Brief explanation of the drawing]

[0018] [Figure 1] This graph schematically shows the shape of the peak of the first derivative curve of the thermogravimetric curve. (a) shows the case where the first derivative curve is a temperature derivative curve, and (b) shows the case where the first derivative curve is a time derivative curve. [Figure 2] This graph shows the first derivative curves of the thermogravimetric curves of the fibrous carbon nanostructures in the examples and comparative examples. [Modes for carrying out the invention]

[0019] 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.

[0020] (Fibrous carbon nanostructures) The fibrous carbon nanostructure of the present invention requires that the symmetry coefficient of the peak of the first derivative curve of the thermogravimetric curve obtained by thermogravimetric analysis in a dry air atmosphere be 3.70 or less. Furthermore, since the fibrous carbon nanostructure of the present invention has a symmetry coefficient of 3.70 or less of the peak of the first derivative curve of the thermogravimetric curve, it undergoes good surface modification when subjected to surface modification treatments such as oxidation treatment.

[0021] Here, the fibrous carbon nanostructure is not particularly limited, and examples include 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.

[0022] 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.

[0023] 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.

[0024] Here, the fibrous carbon nanostructure of the present invention must have a symmetry coefficient of 3.70 or less at the peak of the first derivative curve of the thermogravimetric curve obtained by thermogravimetric analysis in a dry air atmosphere. Preferably, the symmetry coefficient of 3.30 or less is preferred, more preferably 2.60 or less, and even more preferably 2.00 or less. Furthermore, the symmetry coefficient of 0.50 or more is preferred, more preferably 0.70 or more, and even more preferably 0.80 or more. This is because if the symmetry coefficient of the peak of the first derivative curve of the thermogravimetric curve of the fibrous carbon nanostructure is within the above range, the surface becomes more easily modified when surface modification treatments such as oxidation treatment are applied.

[0025] The thermogravimetric curve may have mass on the vertical axis and temperature on the horizontal axis, or it may have mass on the vertical axis and time on the horizontal axis. Furthermore, the first derivative of the thermogravimetric curve may have differential thermogravimetric (DTG) on the vertical axis and temperature on the horizontal axis, or it may have differential thermogravimetric (DTG) on the vertical axis and time on the horizontal axis. Here, if the first derivative curve is a temperature derivative curve, the peak of the first derivative curve is usually located within the range of 500 to 800°C. Also, if the first derivative curve is a time derivative curve, and the heating rate during thermogravimetric analysis is v [°C / min], the peak of the first derivative curve is usually located within the range of 20 × v to 36 × v minutes (for example, if the heating rate is 5 [°C / min], it will be within the range of 100 to 180 minutes).

[0026] Furthermore, the magnitude of the symmetry coefficient of the peak of the first derivative curve of the thermogravimetric curve of the fibrous carbon nanostructure is not particularly limited and can be adjusted by changing the synthesis conditions of the fibrous carbon nanostructure (for example, the composition of the raw material gas, the type of catalyst used in synthesis, etc.).

[0027] 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 fibrous carbon nanostructures on a transmission electron microscope (TEM) image and calculating the numerical average value.

[0028] 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 to the average diameter (Av) is greater than 0.20 and less than 0.60, 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 0.60 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.

[0029] 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 this invention, the "average length of fibrous carbon nanostructures" can be determined by measuring the length of, for example, 20 fibrous carbon nanostructures on a scanning electron microscope (SEM) image and calculating the numerical average value.

[0030] Here, fibrous carbon nanostructures typically have an aspect ratio greater than 10. The aspect ratio of fibrous carbon nanostructures can be determined by measuring the diameter and length of 20 randomly selected fibrous carbon nanostructures using a scanning electron microscope or transmission electron microscope, and calculating the average value of the diameter-to-length ratio (length / diameter).

[0031] Furthermore, the fibrous carbon nanostructure has a BET specific surface area of ​​600 m². 2 It is preferable that it be 1 / g or more, and 800m 2 It is more preferable that it be 2000m or more per gram. 2 It is preferable that it be less than or equal to / g, and 1800m 2 It is more preferable that it be less than or equal to / g, and 1600m 2 It is even more preferable that the BET specific surface area of ​​the fibrous carbon nanostructure is 600 m². 2 If the amount is greater than / g, it can exhibit particularly excellent properties when its dispersibility is improved by surface modification treatment. Also, if the BET specific surface area of ​​the fibrous carbon nanostructure is 2000 m² 2 If the amount is less than / g, the dispersibility can be sufficiently improved when surface modification treatment is performed.

[0032] Furthermore, it is preferable that the fibrous carbon nanostructures exhibit an upwardly convex shape in the t-plot obtained from the adsorption isotherm. Fibrous carbon nanostructures exhibiting an upwardly convex shape in the t-plot can exhibit particularly excellent properties when their 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.).

[0033] 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

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Incidentally, the measurement of adsorption isotherms of fibrous carbon nanostructures, the creation of t-plots, and the calculation of total specific surface area S1 and internal specific surface area S2 based on the analysis of t-plots can be performed, for example, using a commercially available measuring device called "BELSORP(registered trademark)-mini" (manufactured by Nippon Bell Co., Ltd.).

[0038] 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.

[0039] 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.

[0040] Furthermore, 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.

[0041] (Method for manufacturing fibrous carbon nanostructures) Furthermore, fibrous carbon nanostructures having the above-described properties can be efficiently produced, for example, by a method in which, when synthesizing fibrous carbon nanostructures by CVD by supplying raw material compounds and a carrier gas onto a substrate having a catalyst layer on its surface, the catalytic activity of the catalyst layer is dramatically improved by introducing a small amount of oxidizing agent (catalyst activating substance) into the system (see, for example, International Publication No. 2006 / 011655), by performing the formation of the catalyst layer on the substrate surface by a wet process and using a raw material gas containing ethylene (for example, a gas containing more than 10% by volume of ethylene).

[0042] Here, the formation of a catalyst layer on the substrate surface by a wet process can be carried out, for example, by applying a coating solution A containing an aluminum compound to the substrate, drying coating solution A to form an aluminum thin film (a catalyst-supporting layer that supports an iron thin film (catalyst layer)) on the substrate, and then applying a coating solution B containing an iron compound on the aluminum thin film, and drying coating solution B to form an iron thin film (catalyst layer) on the aluminum thin film. Note that "aluminum thin film" refers to a thin film containing aluminum as a metal component, and "iron thin film" refers to a thin film containing iron as a metal component.

[0043] Furthermore, the substrate can be made of metals such as iron, nickel, chromium, molybdenum, tungsten, titanium, aluminum, manganese, cobalt, copper, silver, gold, platinum, niobium, tantalum, lead, zinc, gallium, indium, germanium, and antimony; alloys or oxides of these metals; non-metals such as silicon, quartz, glass, mica, graphite, and diamond; or ceramics.

[0044] Furthermore, as coating solution A, a metal organic compound or metal salt capable of forming an alumina thin film as an aluminum thin film can be dissolved or dispersed in an organic solvent. Examples of metal-organic compounds that can form alumina thin films include aluminum alkoxides such as aluminum trimethoxide, aluminum triethoxide, aluminum tri-n-propoxide, aluminum tri-i-propoxide, aluminum tri-n-butoxide, aluminum tri-sec-butoxide, and aluminum tri-tert-butoxide. Other metal-organic compounds containing aluminum include complexes such as tris(acetylacetonato)aluminum(III). Examples of metal salts that can form alumina thin films include aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum bromide, aluminum iodide, aluminum lactate, basic aluminum chloride, and basic aluminum nitrate. Furthermore, various organic solvents such as alcohols, glycols, ketones, ethers, esters, and hydrocarbons can be used as organic solvents. These can be used individually or in mixtures. Furthermore, a stabilizer may be added to coating solution A to suppress the condensation polymerization reaction of metal organic compounds and metal salts. The stabilizer is preferably at least one selected from the group consisting of β-diketones and alkanolamines. Examples of β-diketones include acetylacetone, methyl acetoacetate, ethyl acetoacetate, benzoylacetone, dibenzoylmethane, benzoyltrifluoroacetone, fluoracetone, and trifluoroacetylacetone, but acetylacetone and ethyl acetoacetate are particularly preferred. Examples of alkanolamines include monoethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, N,N-dimethylaminoethanol, diisopropanolamine, and triisopropanolamine, but secondary or tertiary alkanolamines are preferred.

[0045] Furthermore, as coating solution B, a metal organic compound or metal salt capable of forming a thin iron film can be dissolved or dispersed in an organic solvent. Examples of metal-organic compounds that can form an iron thin film include iron pentacarbonyl, ferrocene, iron(II) acetylacetone, iron(III) acetylacetone, iron(II) trifluoroacetylacetone, and iron(III) trifluoroacetylacetone. Examples of metal salts that can form an iron thin film include inorganic iron acids such as iron sulfate, iron nitrate, iron phosphate, iron chloride, and iron bromide, and organic iron acids such as iron acetate, iron oxalate, iron citrate, and iron lactate. These can be used individually or in mixtures. The organic solvent contained in coating solution B is not particularly limited, and the same organic solvents that can be used in coating solution A described above can be used. In addition, coating solution B may contain the same stabilizers as those that can be incorporated into coating solution A described above.

[0046] Furthermore, the application and drying of coating liquids A and B described above can be carried out using known methods.

[0047] (Surface modification treatment) The fibrous carbon nanostructure of the present invention is easily surface-modified when subjected to surface modification treatments such as oxidation treatment. Herein, the surface modification treatment of the fibrous carbon nanostructure of the present invention is not particularly limited and can be carried out using, for example, a surface modification agent 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 of the fibrous carbon nanostructure of the present invention is preferably carried out using nitric acid, sulfuric acid, or a mixed acid of nitric acid and sulfuric acid, and more preferably 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.

[0048] 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).

[0049] Furthermore, if the properties of the fibrous carbon nanostructure to be surface-modified are unknown (i.e., if it is unclear whether or not it falls under the category of the fibrous carbon nanostructure of the present invention), it is preferable to evaluate the fibrous carbon nanostructure using the evaluation method for the fibrous carbon nanostructure of the present invention described below, and to produce a surface-modified fibrous carbon nanostructure by applying the surface modification treatment to the fibrous carbon nanostructure that is judged to be of good quality. By applying the surface modification treatment to a fibrous carbon nanostructure that is judged to be of good quality, a surface-modified fibrous carbon nanostructure with good surface modification treatment can be obtained.

[0050] (Evaluation methods for fibrous carbon nanostructures) The present invention provides a method for evaluating fibrous carbon nanostructures, comprising the steps of: (A) performing thermogravimetric analysis on the fibrous carbon nanostructure under a dry air atmosphere to obtain the first derivative of the thermogravimetric curve; (B) determining the symmetry coefficient of the peak of the first derivative of the thermogravimetric curve obtained in step (A); and determining that nanostructures with a symmetry coefficient of 3.70 or less obtained in step (B) are good products, and those with a symmetry coefficient greater than 3.70 are defective products. By determining that nanostructures with a symmetry coefficient of 3.70 or less are good products in this way, fibrous carbon nanostructures that are easily surface-modified can be appropriately evaluated and sorted. Note that the symmetry coefficient of the peak serving as the criterion for determining good products and defective products is preferably 3.30 or less, more preferably 2.60 or less, still more preferably 2.00 or less, preferably 0.50 or more, more preferably 0.70 or more, and still more preferably 0.80 or more. If the symmetry coefficient of the peak of the first derivative curve is within the above range, it becomes easier to be further surface-modified when a surface modification treatment such as an oxidation treatment is performed. The thermogravimetric curve may be a thermogravimetric curve with the vertical axis being mass and the horizontal axis being temperature, or a thermogravimetric curve with the vertical axis being mass and the horizontal axis being time. Further, the first derivative curve of the thermogravimetric curve may be a temperature derivative curve with the vertical axis being differential thermogravimetry (DTG) and the horizontal axis being temperature, or a time derivative curve with the vertical axis being differential thermogravimetry (DTG) and the horizontal axis being time.

Example

[0051] 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 an amount is based on mass unless otherwise specified.

[0052] In the examples and comparative examples, the G / D ratio, average diameter, t-plot, total specific surface area, internal specific surface area, carbon purity, symmetry coefficient of the peak of the first derivative curve of the thermogravimetric curve, and surface modification treatability of the fibrous carbon nanostructure containing CNT were measured or evaluated using the following methods, respectively.

[0053] <G / D ratio> Using a microscopic laser Raman system (manufactured by Thermo Fisher Scientific K.K., Nicolet Almega XR), measurement was performed on the fibrous carbon nanostructure near the center of the substrate. <Average diameter> The diameters (outer diameters) of 20 fibrous carbon nanostructures randomly selected from the images obtained using a transmission electron microscope were measured and determined as the number average value. <t-plot, total specific surface area, and internal specific surface area> The measurement was carried out using a BET specific surface area measurement device (manufactured by Nippon Bell Co., Ltd., BELSORP (registered trademark)-mini). <Carbon purity> Using a thermogravimetric analyzer (TG), the carbon purity (= (mass reduced by combustion until reaching 800 °C / initial mass) × 100 (%)) was determined from the mass reduction when the fibrous carbon nanostructure was heated up to 800 °C in air. <Symmetry coefficient> Using a thermogravimetric differential thermal simultaneous measurement device (manufactured by Bruker AXS, product name "TG-DTA2020SA"), the thermogravimetric curve of the fibrous carbon nanostructure was measured under the conditions of a heating rate of 5 °C / min and a dry air flow rate of 200 mL / min, and a first derivative curve was obtained. [In the case of the temperature derivative curve] Here, when the vertical axis of the thermogravimetric curve is mass and the horizontal axis is temperature, and the first derivative curve is a temperature derivative curve where the vertical axis is differential thermogravimetry (DTG) and the horizontal axis is temperature as shown in, for example, Fig. 1(a), from the peak of the temperature derivative curve, the symmetry coefficient W a / W b of the DTG peak of the fibrous carbon nanostructure was determined by the following formula (1). W a / W b =(T max -T a ) / (T b -T max ) ···(1) T max : Temperature at the peak top DTG max : Differential thermogravimetry at temperature T max T a : Temperature at which the value of differential thermogravimetry becomes 1 / 10 of DTG max (low temperature side) T b : Temperature at which the value of differential thermogravimetry becomes 1 / 10 of DTG max (high temperature side, T b >T a ) [In the case of the time derivative curve] ​Furthermore, if the thermogravimetric curve has mass on the vertical axis and time on the horizontal axis, and the first derivative curve is a time derivative curve with differential thermogravimetric (DTG) on the vertical axis and time on the horizontal axis, as shown in Figure 1(b), then the symmetry coefficient W of the DTG peak of the fibrous carbon nanostructure can be calculated from the peak of the time derivative curve using the following equation (2). a / W b They sought it. W a / W b =( t max -t a ) / (t b -t max ) ···(2) t max : Peak time DTG max :time t max Differential thermogravimetric t a : The value of differential thermogravimetric analysis is DTG max The time it takes to become 1 / 10 of that (short-time side) t b : The value of differential thermogravimetric analysis is DTG max The time it takes for it to become 1 / 10 of that (long time side, t b >t a ) <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, 54.8 g of deionized water, and 83 mL of a mixed acid solution containing sulfuric acid (Wako Pure Chemical Industries, concentration 96-98%) and nitric acid (Wako Pure Chemical Industries, 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 resulting fibrous carbon nanostructure / mixed acid solution after mixed acid 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 total volume of 30 mL. 0.1% aqueous ammonia was added to adjust the pH to 7.0, and then 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 decrease in absorbance due to centrifugation using the following formula. A smaller rate of decrease in absorbance indicates that the fibrous carbon nanostructure has been well surface-modified and that the dispersibility of the fibrous carbon nanostructure is excellent. 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.

[0054] (Example 1) <Manufacturing of catalyst substrates> 0.19 kg of aluminum tri-sec-butoxide was dissolved in 10 L (7.8 kg) of 2-propanol. Furthermore, 0.09 kg of triisopropanolamine as a stabilizer was added and dissolved to prepare coating solution A. Additionally, 174 mg of iron acetate was dissolved in 10 L (7.8 kg) of 2-propanol. Furthermore, 0.019 kg of triisopropanolamine as a stabilizer was added and dissolved to prepare coating solution B. The above-mentioned coating solution A was applied to the surface of a SUS430 substrate made of Fe-Cr alloy, which served as a flat substrate, to form an alumina thin film (catalyst support layer) with a thickness of 40 nm. Next, the above-mentioned coating solution B was applied onto the alumina thin film provided on the substrate to obtain a catalyst substrate having an iron thin film with a thickness of 3 nm. <Synthesis of fibrous carbon nanostructures> An oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) was synthesized by continuously performing a formation process (reduction process), a synthesis process, and a cooling process on the catalyst substrate described above. In the synthesis process, the raw material gas (composition (by volume): ethylene: 20%, H2O: 55-440 ppm, N2: remainder) was supplied to the catalyst substrate at a flow rate of 150 sLm. The resulting fibrous carbon nanostructures containing CNTs had a G / D ratio of 3.7, an average diameter of 4 nm, and a carbon purity of 99.9%. Raman spectrophotometer measurements showed a characteristic range of 100–300 cm for single-walled carbon nanotubes. -1 A peak of radial breathing mode (RBM) was observed in the low wavenumber region. Furthermore, the t-plot of the fibrous carbon nanostructure obtained from the adsorption isotherm showed an upwardly convex shape with inflection. The inflection point was located at t=0.7nm, and the total specific surface area S1 was 1270m². 2 The value is / g, and the internal specific surface area S2 is 290m². 2 The ratio was / g, and S2 / S1 was 0.23. The symmetry coefficient of the peak in the first derivative curve of the thermogravimetric curve and the surface modification properties of the obtained fibrous carbon nanostructures were evaluated. The results are shown in Table 1. The symmetry coefficient of the peak was determined from the temperature derivative curve of the thermogravimetric curve.

[0055] (Example 2) An oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) was synthesized in the same manner as in Example 1, except that the ethylene concentration in the synthesis process was set to 17%. The resulting fibrous carbon nanostructures containing CNTs had a G / D ratio of 2.9, an average diameter of 4 nm, and a carbon purity of 99.9%. Raman spectrophotometer measurements showed a characteristic range of 100–300 cm for single-walled carbon nanotubes. -1 A peak of radial breathing mode (RBM) was observed in the low wavenumber region. Furthermore, the t-plot of the fibrous carbon nanostructure obtained from the adsorption isotherm showed an upwardly convex shape with a bend. The position of the bend was at t=0.7nm, and the total specific surface area S1 was 1130m². 2 The value is / g, and the internal specific surface area S2 is 240m². 2 The ratio was / g, and S2 / S1 was 0.21. The symmetry coefficient of the peak in the first derivative curve of the thermogravimetric curve and the surface modification properties of the obtained fibrous carbon nanostructures were evaluated. The results are shown in Table 1. The symmetry coefficient of the peak was determined from the temperature derivative curve of the thermogravimetric curve.

[0056] (Example 3) An oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) was synthesized in the same manner as in Example 1, except that the ethylene concentration in the synthesis process was set to 14%. The resulting fibrous carbon nanostructures containing CNTs had a G / D ratio of 2.8, an average diameter of 4 nm, and a carbon purity of 99.9%. Raman spectrophotometer measurements showed a characteristic range of 100–300 cm for single-walled carbon nanotubes. -1 A peak of radial breathing mode (RBM) was observed in the low wavenumber region. Furthermore, the t-plot of the fibrous carbon nanostructure obtained from the adsorption isotherm showed an upwardly convex shape with inflection. The inflection point was located at t=0.7nm, and the total specific surface area S1 was 1240m². 2 The value is / g, and the internal specific surface area S2 is 230m². 2 The ratio was / g, and S2 / S1 was 0.19. The symmetry coefficient of the peak in the first derivative curve of the thermogravimetric curve and the surface modification properties of the obtained fibrous carbon nanostructures were evaluated. The results are shown in Table 1. The symmetry coefficient of the peak was determined from the temperature derivative curve of the thermogravimetric curve.

[0057] (Comparative Example 1) An oriented aggregate of fibrous carbon nanostructures (fibrous carbon nanostructures containing CNTs) was synthesized in the same manner as in Example 1, except that the ethylene concentration in the synthesis process was set to 10%. The resulting fibrous carbon nanostructures containing CNTs had a G / D ratio of 3.4, an average diameter of 4 nm, and a carbon purity of 99.9%. Raman spectrophotometer measurements showed a characteristic range of 100–300 cm for single-walled carbon nanotubes. -1 A peak of radial breathing mode (RBM) was observed in the low wavenumber region. Furthermore, the t-plot of the fibrous carbon nanostructure obtained from the adsorption isotherm showed an upwardly convex shape with inflection. The inflection point was located at t=0.7nm, and the total specific surface area S1 was 1320m². 2 The value is / g, and the internal specific surface area S2 is 55m². 2 The ratio was / g, and S2 / S1 was 0.04. The symmetry coefficient of the peak in the first derivative curve of the thermogravimetric curve and the surface modification properties of the obtained fibrous carbon nanostructures were evaluated. The results are shown in Table 1. The symmetry coefficient of the peak was determined from the temperature derivative curve of the thermogravimetric curve.

[0058] [Table 1]

[0059] Table 1 shows that the fibrous carbon nanostructures of Examples 1-3 are surface-modified and exhibit superior dispersibility compared to the fibrous carbon nanostructure of Comparative Example 1. [Industrial applicability]

[0060] According to the present invention, it is possible to provide fibrous carbon nanostructures that are easily subjected to surface modification treatment. Furthermore, according to the present invention, it is possible to provide a surface-modified fibrous carbon nanostructure that has undergone good surface modification treatment.

Claims

1. Contains carbon nanotubes, The symmetry coefficient of the peak of the first derivative curve of the thermogravimetric curve obtained by thermogravimetric analysis in a dry air atmosphere is 3.70 or less. A method for producing fibrous carbon nanostructures, wherein the ratio of the G-band peak intensity to the D-band peak intensity in the Raman spectrum is 0.5 or more and 5.0 or less, A manufacturing process for a catalyst substrate, in which a catalyst layer is formed on the surface of the substrate by a wet process, A synthesis step for fibrous carbon nanostructures, comprising supplying a raw material gas containing a raw material compound, a catalyst activator, and a carrier gas onto the substrate having the catalyst layer on its surface, and synthesizing fibrous carbon nanostructures by CVD, Includes, A method for producing fibrous carbon nanostructures, wherein the raw material gas in the synthesis step contains ethylene in an amount greater than 10% by volume and less than or equal to 20% by volume.

2. The method for producing fibrous carbon nanostructures according to claim 1, wherein the first differential curve is the temperature differential curve or the time differential curve of the thermogravimetric curve.

3. A method for producing fibrous carbon nanostructures according to claim 1 or 2, wherein the t-plot obtained from the adsorption isotherm shows an upwardly convex shape.

4. The method for producing a fibrous carbon nanostructure according to claim 3, wherein the inflection point of the t-plot is in the range of 0.2 ≤ t (nm) ≤ 1.

5.

5. A method for producing a fibrous carbon nanostructure according to any one of claims 1 to 4, wherein the total specific surface area S1 and the internal specific surface area S2 obtained from the t-plot obtained from the adsorption isotherm satisfy the relation: 0.05 ≤ S2 / S1 ≤ 0.

30.

6. A method for producing a fibrous carbon nanostructure according to any one of claims 1 to 5, wherein the carbon nanotube is a single-walled carbon nanotube.

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