Composite material manufacturing method

Abstract

To provide a composite material in which a fibrous carbon nanostructure is well dispersed.SOLUTION: There is provided a composite material containing a polymer and a fibrous carbon nanostructure, wherein in a sheet having a thickness 150 μm formed using the composite material, a polymer-removed body is obtained by removing a polymer component in the sheet at 600°C in an inert gas atmosphere and then, when the change with time in the mass of the polymer-removed body was measured by switching the atmosphere from inert gas to air, a time required for a mass M1 of the polymer-removed body in an elapsed time T1 at which the differential thermogravimetric curve obtained from the change in mass of the polymer-removed body and the elapsed time reaches a minimum value just before the final peak to decrease to M1×0.10 is 250 seconds or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a composite material, a method for evaluating a composite material, and a method for producing a composite material, and more particularly to a composite material containing a polymer and a fibrous carbon nanostructure, as well as a method for evaluating and a method for producing the same. [Background technology]

[0002] Conventionally, composite materials obtained by blending a carbon material with a polymer such as a resin or rubber have been used as materials that are excellent in electrical conductivity, thermal conductivity, mechanical properties, etc. In recent years, fibrous carbon materials, particularly fibrous carbon nanostructures such as carbon nanotubes, have been attracting attention as carbon materials that are highly effective in improving electrical conductivity, thermal conductivity, and mechanical properties.

[0003] Here, although fibrous carbon nanostructures such as carbon nanotubes have excellent individual properties, their small outer diameters mean that when used as bulk materials, they tend to bundle (tend to form bundles) due to van der Waals forces, and the effect of improving performance as a bulk material is not significant. Therefore, in the production of composite materials containing polymers and fibrous carbon nanostructures, it is necessary to unravel (defibrate) the bundled structures of fibrous carbon nanostructures and to disperse the fibrous carbon nanostructures well in the polymer matrix.

[0004] As a method for defibrating a bundle structure of fibrous carbon nanostructures, a method is known in which a dispersing machine such as a bead mill, disperser, homogenizer, or ultrasonic disperser is used to apply shear force to a dispersion liquid in which fibrous carbon nanostructures are dispersed in a dispersion medium, or to a polymer composition containing a polymer and fibrous carbon nanostructures, thereby carrying out a defibration process (see, for example, Patent Document 1).

[0005] Furthermore, as described in Patent Document 1, for example, in a composite material containing a polymer and a fibrous carbon nanostructure, the degree of defibration of the fibrous carbon nanostructure is evaluated by measuring the physical properties (e.g., electrical conductivity) of the composite material itself. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-274060 Summary of the Invention [Problem to be solved by the invention]

[0007] Here, if the desired performance is not achieved in a composite material containing fibrous carbon nanostructures that have been defibrated, the causes are thought to be insufficient defibration or damage to the fibrous carbon nanostructures due to excessive defibration. However, the above-mentioned conventional method of evaluating the degree of defibration of fibrous carbon nanostructures by measuring the physical properties of the composite material itself does not accurately grasp the defibration state of the fibrous carbon nanostructures in the composite material, and it is not possible to determine whether the desired performance is not achieved due to insufficient defibration or damage to the fibrous carbon nanostructures due to excessive defibration. Therefore, the above-mentioned conventional technology has problems such as the complicated adjustment of defibration treatment conditions for fibrous carbon nanostructures in the production of composite materials.

[0008] In addition, one possible solution to this problem is to use, for example, an electron microscope to observe the state of fibrous carbon nanostructures in the composite material.However, methods using electron microscopes have the problem that they are complicated to perform and do not allow for quantitative evaluation of the defibrillation state of the fibrous carbon nanostructures.

[0009] Therefore, there was a need for a technology that could quantitatively evaluate the defibrillation state of fibrous carbon nanostructures in composite materials in a simple manner. There has also been a demand for a technique for efficiently producing a composite material in which fibrous carbon nanostructures are well dispersed, and for a composite material in which fibrous carbon nanostructures are well dispersed. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems, and have found that the combustion time of a composite material containing a polymer and a fibrous carbon nanostructure, when the fibrous carbon nanostructure remaining after removing the polymer component, is combusted, is correlated with the degree of defibration of the fibrous carbon nanostructure in the composite material, thereby completing the present invention.

[0011] The present invention has an object to advantageously solve the above-mentioned problems, and provides a method for evaluating a composite material containing a polymer and fibrous carbon nanostructures, comprising the steps of: (A) heating the composite material in an inert gas atmosphere to remove the polymer component from the composite material to obtain a polymer-removed body; (B) performing thermogravimetric analysis of the polymer-removed body in an oxygen-containing atmosphere to measure the change in mass of the polymer-removed body over time; and (C) evaluating the defibrillation state of the fibrous carbon nanostructures in the composite material from the relationship between the mass change of the polymer-removed body obtained in step (B) and the elapsed time. In this way, by removing the polymer component from the composite material to obtain a polymer-removed body, and then performing thermogravimetric analysis of the polymer-removed body in an oxygen-containing atmosphere to evaluate the defibrillation state of the fibrous carbon nanostructures in the composite material from the relationship between the mass change of the polymer-removed body and the elapsed time, the defibrillation state of the fibrous carbon nanostructures in the composite material can be quantitatively evaluated by a simple method.

[0012] Here, in the composite material evaluation method of the present invention, the step (C) preferably includes a step (c1) of obtaining a differential thermogravimetric curve from the change in mass of the polymer-removed body obtained in the step (B) and the elapsed time, a step (c2) of determining the elapsed time T1 at which the differential thermogravimetric curve reaches a minimum value immediately before the final peak of the differential thermogravimetric curve, and a step (c3) of determining the time required for the mass M1 of the polymer-removed body at the elapsed time T1 to decrease to a predetermined proportion, and the defibration state of the fibrous carbon nanostructures in the composite material can be evaluated from the required time. By determining the time required for the mass M1 of the polymer-removed body at the elapsed time T1 to decrease to a predetermined proportion and evaluating the defibration state of the fibrous carbon nanostructures in the composite material from the required time, the defibration state of the fibrous carbon nanostructures can be evaluated more accurately.

[0013] In the composite material evaluation method of the present invention, it is preferable to determine the time required for the mass of the polymer-removed body to decrease to M1 × 0.10 in step (c3). In step (c3), by using the time required for the mass of the polymer-removed body to decrease to M1 × 0.10, the defibration state of the fibrous carbon nanostructure can be evaluated more accurately. In the composite material evaluation method of the present invention, the time required for the mass of the polymer-removed body to decrease to M1×0.50 may be determined in the step (c3).

[0014] The present invention also aims to advantageously solve the above-mentioned problems, and provides a composite material manufacturing method of the present invention, which is a method for manufacturing a composite material containing a polymer and fibrous carbon nanostructures via a step of subjecting fibrous carbon nanostructures to a defibration treatment, and is characterized by comprising the steps of: (a) evaluating the defibration state of the fibrous carbon nanostructures of the manufactured composite material using any of the composite material evaluation methods described above; and (b) changing the conditions of the defibration treatment so that the defibration state of the fibrous carbon nanostructures falls within a desired range based on the evaluation results obtained in step (a) If the defibration state of the fibrous carbon nanostructures falls outside a desired range, based on the evaluation results obtained in step (a), a composite material in which fibrous carbon nanostructures are well dispersed can be efficiently manufactured.

[0015] The composite material of the present invention is a composite material containing a polymer and fibrous carbon nanostructures, and is characterized in that when a 150 μm-thick sheet formed using the composite material is subjected to an inert gas atmosphere at 600°C to remove the polymer component from the sheet to obtain a polymer-removed body, the atmosphere is switched from the inert gas to air, and the change in mass of the polymer-removed body is measured over time, the time required for the mass M1 of the polymer-removed body to decrease to M1 × 0.10 at elapsed time T1, at which a differential thermogravimetric curve obtained from the change in mass of the polymer-removed body versus elapsed time reaches a minimum value just before the final peak, is 250 seconds or less. Thus, when thermogravimetric analysis is performed on a 150 μm-thick sheet, a composite material in which the time required for the mass M1 of the polymer-removed body to decrease to M1 × 0.10 is 250 seconds or less has well-dispersed fibrous carbon nanostructures and can exhibit excellent physical properties.

[0016] Here, in the composite material of the present invention, a fluorine-containing polymer can be used as the polymer.

[0017] In the composite material of the present invention, the fibrous carbon nanostructure preferably contains a single-walled carbon nanotube, which can exhibit even more excellent physical properties.

[0018] Furthermore, in the composite material of the present invention, the G / D ratio of the single-walled carbon nanotubes is preferably 1 or more and 4 or less. When the G / D ratio of the single-walled carbon nanotubes is 1 or more and 4 or less, even more excellent physical properties can be exhibited.

[0019] In the composite material of the present invention, the average diameter of the single-walled carbon nanotubes is preferably 1.5 nm or more and 5 nm or less, and more preferably 2 nm or more and 4 nm or less. If the average diameter of the single-walled carbon nanotubes is within the above numerical range, even more excellent physical properties can be exhibited. [Effects of the Invention]

[0020] According to the composite material evaluation method of the present invention, the defibrillation state of fibrous carbon nanostructures in a composite material can be quantitatively evaluated in a simple manner. Furthermore, according to the method for producing a composite material of the present invention, a composite material in which fibrous carbon nanostructures are well dispersed can be produced efficiently. Furthermore, according to the present invention, a composite material in which fibrous carbon nanostructures are well dispersed can be obtained. [Brief explanation of the drawings]

[0021] [Figure 1] Graphs (a) to (c) show the results of thermogravimetric analysis of the polymer-removed bodies of composite materials 1 to 3, respectively. [Figure 2] Graphs (a) and (b) show the relationship between the time required for the mass of the polymer-removed body of composite materials 1 to 3 to decrease to M1×0.10 and the time required for the mass to decrease to M1×0.50, respectively, and the physical properties of the composite materials. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail. Here, the composite material evaluation method of the present invention is used to evaluate the defibration state of fibrous carbon nanostructures in a composite material containing fibrous carbon nanostructures and a polymer. The composite material production method of the present invention is used to produce a composite material containing fibrous carbon nanostructures and a polymer. The composite material of the present invention can be used to produce various molded articles, such as belts, hoses, gaskets, packings, and oil seals, without any particular limitations.

[0023] (Method for evaluating composite materials) The composite material evaluation method of the present invention is a method for evaluating a composite material containing a polymer and a fibrous carbon nanostructure, and is characterized by comprising the steps of: (A) removing the polymer component from the composite material to obtain a polymer-removed body; (B) performing thermogravimetric analysis of the polymer-removed body to measure the change in mass over time of the polymer-removed body; and (C) evaluating the defibration state of the fibrous carbon nanostructure from the relationship between the change in mass of the polymer-removed body and the elapsed time. In this way, by evaluating the defibration state of fibrous carbon nanostructures in a composite material from the relationship between the change in mass of the polymer-removed body and the elapsed time, the defibration state of fibrous carbon nanostructures in a composite material can be quantitatively evaluated in a simple manner.

[0024] Although it is not clear why the defibration state of fibrous carbon nanostructures can be evaluated from the relationship between the change in mass of the polymer-removed body and the elapsed time, it is presumed that this is because the surface area of ​​the fibrous carbon nanostructures increases as they become more defibrated, making them more likely to burn when subjected to thermogravimetric analysis in an oxygen-containing atmosphere (i.e., the rate of mass loss increases).

[0025] <Composite materials> The composite material to be evaluated contains a polymer and a fibrous carbon nanostructure, and may optionally further contain various additives depending on the intended use of the composite material. The composite material is not particularly limited, and can be prepared, for example, by mixing the above-mentioned components by a known method.

[0026] [polymer] The polymer is not particularly limited, and any rubber, resin, or mixture thereof can be used.

[0027] Specifically, the rubber is not particularly limited, and examples thereof include natural rubber; fluororubbers such as vinylidene fluoride rubber (FKM), tetrafluoroethylene-propylene rubber (FEPM), and tetrafluoroethylene-purple vinyl ether rubber (FFKM); diene rubbers such as butadiene rubber (BR), isoprene rubber (IR), styrene-butadiene rubber (SBR), hydrogenated styrene-butadiene rubber (H-SBR), nitrile rubber (NBR), and hydrogenated nitrile rubber (H-NBR); and silicone rubber. The resin is not particularly limited, and examples thereof include fluororesins such as polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE); acrylic resins such as polymethyl methacrylate (PMMA); polystyrene (PS); polycarbonate (PC); cycloolefin polymer (COP); and the like. The above-mentioned polymers can be used alone or in combination of two or more.

[0028] [Fibrous carbon nanostructures] The fibrous carbon nanostructure is not particularly limited, and examples thereof include cylindrical carbon nanostructures such as carbon nanotubes (hereinafter sometimes referred to as "CNTs") and non-cylindrical carbon nanostructures such as carbon nanostructures in which a six-membered carbon ring network is formed into a flattened cylinder. These may be used alone or in combination of two or more.

[0029] Among the above, it is more preferable to use a fibrous carbon nanostructure containing CNT as the fibrous carbon nanostructure, because the use of a fibrous carbon nanostructure containing CNT can improve the properties (e.g., electrical conductivity, thermal conductivity, strength, etc.) of the composite material even when the blending amount is small.

[0030] Here, the fibrous carbon nanostructure containing CNT may be composed of only CNT, or may be a mixture of CNT and a fibrous carbon nanostructure other than CNT. The CNTs in the fibrous carbon nanostructure are not particularly limited and may be single-walled carbon nanotubes and / or multi-walled carbon nanotubes, but the CNTs are preferably single-walled to five-walled carbon nanotubes, and more preferably single-walled carbon nanotubes, because the fewer the number of walls of the carbon nanotubes, the more improved the properties (e.g., electrical conductivity, thermal conductivity, strength, etc.) of the composite material will be, even if the blending amount is small.

[0031] The average diameter of the fibrous carbon nanostructures is preferably 1 nm or more, more preferably 1.5 nm or more, even more preferably 2 nm or more, and is preferably 30 nm or less, more preferably 10 nm or less, even more preferably 5 nm or less, and particularly preferably 4 nm or less. If the average diameter of the fibrous carbon nanostructures is within the above range, the properties of the composite material (e.g., electrical conductivity, thermal conductivity, strength, etc.) can be sufficiently improved. Here, in the present 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 number average value.

[0032] Furthermore, it is preferable to use fibrous carbon nanostructures having a ratio (3σ / Av) of the standard deviation of diameter (σ: sample standard deviation) multiplied by 3 (3σ) to the average diameter (Av) of more than 0.20 and less than 0.80, more preferably a fibrous carbon nanostructure having a 3σ / Av of more than 0.25, and even more preferably a fibrous carbon nanostructure having a 3σ / Av of more than 0.50. Furthermore, it is also possible to use fibrous carbon nanostructures having the ratio (3σ / Av) of more than 0.20 and less than 0.60. The use of fibrous carbon nanostructures having a 3σ / Av of more than 0.20 and less than 0.80 can further improve the performance of composite materials. The average diameter (Av) and standard deviation (σ) of the fibrous carbon nanostructures may be adjusted by changing the manufacturing method or manufacturing conditions of the fibrous carbon nanostructures, or by combining multiple types of fibrous carbon nanostructures obtained by different manufacturing methods.

[0033] The fibrous carbon nanostructures that are usually used are those that show a normal distribution when the diameter measured as described above is plotted on the horizontal axis and the frequency on the vertical axis and approximated by a Gaussian.

[0034] Furthermore, the average length of the fibrous carbon nanostructures 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 550 μm or less, and even more preferably 500 μm or less. If the average length of the fibrous carbon nanostructures is within the above range, the properties of the composite material (e.g., electrical conductivity, thermal conductivity, strength, etc.) can be sufficiently improved. 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.

[0035] Furthermore, the fibrous carbon nanostructures usually have an aspect ratio of more than 10. The aspect ratio of the 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 a transmission electron microscope and calculating the average value of the ratio of the diameter to the length (length / diameter).

[0036] In addition, the fibrous carbon nanostructure has a BET specific surface area of ​​600m 2 / g or more is preferable, and 800m 2 / g or more is more preferable, and 2000m 2 / g or less, and 2 / g or less is more preferable, and 1600m 2 It is more preferable that the BET specific surface area of ​​the fibrous carbon nanostructure is 600 m / g or less. 2 / g or more, the properties (e.g., electrical conductivity, thermal conductivity, strength, etc.) of the composite material can be sufficiently improved with a small blending amount. 2 If the pore size is 1 / g or less, the fibrous carbon nanostructures can be dispersed well.

[0037] Furthermore, it is preferable that the t-plot obtained from the adsorption isotherm of the fibrous carbon nanostructure exhibits an upwardly convex shape, and it is more preferable that the fibrous carbon nanostructure is not subjected to an aperture treatment. The "t-plot" can be obtained by converting the relative pressure into the average thickness t (nm) of the nitrogen gas adsorption layer in the adsorption isotherm of the fibrous carbon nanostructure measured by the nitrogen gas adsorption method. That is, the average thickness t of the nitrogen gas adsorption layer corresponding to the relative pressure is calculated from a known standard isotherm in which the average thickness t of the nitrogen gas adsorption layer is plotted against the relative pressure P / P0, and the above conversion is performed to obtain the t-plot of the fibrous carbon nanostructure (the t-plot method by de Boer et al.).

[0038] 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

[0039] In the t-plot showing an upward convex shape, the plot is located 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. Fibrous carbon nanostructures having such a t-plot shape have a large ratio of the internal specific surface area to the total specific surface area of ​​the fibrous carbon nanostructure, indicating that a large number of openings are formed in the carbon nanostructures that make up the fibrous carbon nanostructure.

[0040] The bending point of the t-plot of the fibrous carbon nanostructure is preferably in a 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. If the bending point of the t-plot of the fibrous carbon nanostructure is in this range, the properties of the composite material (e.g., electrical conductivity, thermal conductivity, strength, etc.) can be improved with a small blending amount. The "position of the bending point" is the intersection of the approximate straight line A in the process (1) and the approximate straight line B in the process (3).

[0041] Furthermore, the fibrous carbon nanostructure preferably has a ratio (S2 / S1) of the internal specific surface area S2 to the total specific surface area S1 obtained from a t-plot of 0.05 to 0.30. If the S2 / S1 value of the fibrous carbon nanostructure is within this range, the properties of the composite material (e.g., electrical conductivity, thermal conductivity, strength, etc.) can be improved with a small blending amount. Here, the total specific surface area S1 and the internal specific surface area S2 of the fibrous carbon nanostructure 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.

[0042] Incidentally, the measurement of the adsorption isotherm of the fibrous carbon nanostructure, the creation of a t-plot, and the calculation of the total specific surface area S1 and the internal specific surface area S2 based on the analysis of the t-plot can be performed using, for example, a commercially available measuring device, "BELSORP (registered trademark)-mini" (manufactured by BEL Japan Co., Ltd.).

[0043] Furthermore, it is preferable that the fibrous carbon nanostructure containing CNTs suitable as the fibrous carbon nanostructure has a radial breathing mode (RBM) peak when evaluated by Raman spectroscopy. Note that the Raman spectrum of a fibrous carbon nanostructure consisting only of multi-walled carbon nanotubes with three or more walls does not have an RBM.

[0044] Furthermore, the fibrous carbon nanostructure containing CNTs preferably has a ratio of the G band peak intensity to the D band peak intensity in the Raman spectrum (G / D ratio) of 1 to 4. If the G / D ratio is 1 to 4, the performance of the composite material can be further improved.

[0045] Fibrous carbon nanostructures containing CNTs can be produced using known CNT synthesis methods, such as arc discharge, laser ablation, and chemical vapor deposition (CVD). Specifically, fibrous carbon nanostructures containing 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, synthesizing CNTs by chemical vapor deposition (CVD), and adding a trace amount of oxidant (catalytic activator) to the system to dramatically improve the catalytic activity of the catalyst layer (the super-growth method; see International Publication No. 2006 / 011655). The fibrous carbon nanostructures grown on the substrate can be peeled off from the substrate and used as-grown. Hereinafter, carbon nanotubes obtained by the super-growth method may be referred to as "SGCNTs." The fibrous carbon nanostructures produced by the super-growth method may be composed only of SGCNTs, or may contain, in addition to SGCNTs, other carbon nanostructures such as non-cylindrical carbon nanostructures.

[0046] The amount of fibrous carbon nanostructures contained in the composite material is not particularly limited, and is, for example, preferably 0.01 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of polymer. When the amount of fibrous carbon nanostructures is equal to or greater than the above lower limit, the properties of the composite material (e.g., electrical conductivity, thermal conductivity, strength, etc.) can be sufficiently improved. When the amount of fibrous carbon nanostructures is equal to or less than the above upper limit, the fibrous carbon nanostructures can be well dispersed.

[0047] [Additives] The additives are not particularly limited, and examples thereof include dispersants, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, crosslinking agents, pigments, colorants, foaming agents, antistatic agents, flame retardants, lubricants, softeners, tackifiers, plasticizers, release agents, deodorizers, and fragrances.

[0048] <Process (A)> In step (A), the composite material is heated in an inert gas atmosphere to remove the polymer component from the composite material, thereby obtaining a polymer-free body. By heating the composite material in an inert gas atmosphere in this way, the polymer component can be decomposed and removed while maintaining the defibrillated state of the fibrous carbon nanostructures.

[0049] [Inert gas] The inert gas is not particularly limited, and examples thereof include nitrogen gas, argon gas, neon gas, helium gas, carbon dioxide gas, etc. Among these, it is preferable to use nitrogen gas as the inert gas.

[0050] [heating] The heating of the composite material in an inert gas atmosphere can be carried out using any device without any particular limitation, but is preferably carried out using a thermogravimetric analyzer, because the use of a thermogravimetric analyzer makes it possible to carry out step (A) and step (B) consecutively in a single thermogravimetric analyzer, and also makes it possible to grasp the state of removal of the polymer component from data on the change in weight.

[0051] The temperature and time for heating the composite material are not particularly limited as long as they are capable of decomposing the polymer components in an inert gas atmosphere and do not denature or decompose the fibrous carbon nanostructure in an inert gas atmosphere, and can be any temperature and time depending on the type of polymer. Specifically, the temperature to which the composite material is heated is, for example, preferably 500°C or higher, more preferably 600°C or higher, and preferably 700°C or lower.

[0052] [Polymer removal body] The polymer-removed body obtained in step (A) usually contains the fibrous carbon nanostructures in almost the same state as in the composite material. The polymer-removed body may also contain polymers carbonized by heating and additives that may be optionally contained in the composite material.

[0053] <Process (B)> In step (B), the polymer-removed body is subjected to thermogravimetric analysis in an oxygen-containing atmosphere such as an air atmosphere, and the change in mass of the polymer-removed body over time is measured. Specifically, in step (B), the polymer-removed body is subjected to thermogravimetric analysis in an oxygen-containing atmosphere at a constant temperature, and the change in mass of the polymer-removed body over time is measured.

[0054] Here, step (B) is preferably carried out after step (A) is carried out using a thermogravimetric analyzer, and then the inert gas atmosphere used in step (A) is replaced with an oxygen-containing atmosphere.

[0055] Furthermore, the temperature at which the thermogravimetric analysis of the polymer-removed body is performed is not particularly limited as long as it is a temperature at which the fibrous carbon nanostructure can be burned in an oxygen-containing atmosphere, but is preferably 500°C or higher, more preferably 600°C or higher, and preferably 700°C or lower. If the temperature is below 500°C, the measurement takes a long time. If the temperature exceeds 700°C, the combustion rate becomes too fast, which may reduce the accuracy of evaluating the defibration state of the fibrous carbon nanostructure.

[0056] <Process (C)> In step (C), the defibrillation state of the fibrous carbon nanostructure in the composite material is evaluated from the relationship between the change in mass of the polymer-removed body and the elapsed time obtained in step (B). In step (C), a thermogravimetric curve may be created from the values ​​of the mass of the polymer-removed body and the elapsed time obtained by thermogravimetric analysis in step (B), and the defibrillation state of the fibrous carbon nanostructure may be evaluated using the thermogravimetric curve, or the defibrillation state of the fibrous carbon nanostructure may be evaluated from the values ​​of the mass of the polymer-removed body and the elapsed time without creating a thermogravimetric curve.

[0057] Specifically, in step (C), the fibrous carbon nanostructure has a larger surface area as it becomes more defibrillated, making it easier to burn (i.e., the rate of mass reduction during combustion increases), and the defibration state of the fibrous carbon nanostructure is evaluated based on the amount of mass reduction of the polymer-removed body and the time required for said mass reduction. More specifically, the longer the time required for mass reduction, the less defibration of the fibrous carbon nanostructure can be evaluated, and the shorter the time required for mass reduction, the more defibration of the fibrous carbon nanostructure can be evaluated.

[0058] Here, the polymer-removed body may contain components other than the fibrous carbon nanostructures, such as the polymer carbonized in step (A) and additives. If the polymer-removed body contains components other than the fibrous carbon nanostructures, the change in mass of the polymer-removed body over time when the polymer-removed body is subjected to thermogravimetric analysis in step (B) will also include changes in the mass of the components other than the fibrous carbon nanostructures. Therefore, from the perspective of evaluating the defibration state of the fibrous carbon nanostructures with higher accuracy in step (C), it is preferable that step (C) include the following steps (c1) to (c3).

[0059] Specifically, step (C) includes step (c1) of obtaining a differential thermogravimetric curve from the mass change of the polymer-removed body obtained in step (B) and the elapsed time; step (c2) of determining the elapsed time T1 at which the differential thermogravimetric curve reaches a minimum value just before the peak corresponding to the combustion of the fibrous carbon nanostructure; and step (c3) of determining the time required for the mass M1 of the polymer-removed body at elapsed time T1 to decrease to a predetermined proportion, and it is preferable to evaluate the defibration state of the fibrous carbon nanostructure in the composite material from the required time.

[0060] In the differential thermogravimetric curve, the change in mass of the polymer-removed body after elapsed time T1 corresponds to the change in mass of the fibrous carbon nanostructures only. Therefore, by determining the time required for the mass M1 of the polymer-removed body at elapsed time T1 to decrease to a predetermined proportion and evaluating the defibration state of the fibrous carbon nanostructures in the composite material from the required time, the influence of components other than the fibrous carbon nanostructures contained in the polymer-removed body can be reduced, and the defibration state of the fibrous carbon nanostructures can be evaluated with higher accuracy. Generally, in the differential thermogravimetric curve, the final peak of the differential thermogravimetric curve corresponds to the combustion of the fibrous carbon nanostructure.

[0061] Here, the differential thermogravimetric curve can be obtained, for example, by time-differentiating the thermogravimetric curve of the polymer-removed body obtained by fitting the mass change of the polymer-removed body to the elapsed time obtained in step (B). Specifically, the differential thermogravimetric curve is not particularly limited, and can be obtained, for example, by fitting the mass change of the polymer-removed body obtained in step (B) to the elapsed time using the double Boltzmann function shown below, and then time-differentiating the obtained thermogravimetric curve of the polymer-removed body.

number

[0062] Furthermore, the predetermined ratio is not particularly limited and can be, for example, M1 × 0.10 or M1 × 0.50. That is, the time required for the mass M1 of the polymer-removed body to decrease to the predetermined ratio at the elapsed time T1 can be, for example, the time required for the mass M1 of the polymer-removed body to decrease by 90% or the time required for the mass M1 of the polymer-removed body to decrease by 50%. In particular, the predetermined ratio is preferably M1 × 0.10. By using the time required for the mass of the polymer-removed body to decrease to M1 × 0.10, the defibration state of the fibrous carbon nanostructure can be evaluated more accurately.

[0063] In addition, from the viewpoint of reducing the influence of components other than the fibrous carbon nanostructures contained in the polymer-removed body and evaluating the defibration state of the fibrous carbon nanostructures with higher accuracy, in the composite material evaluation method of the present invention, a reference sample (a sample consisting only of components other than the fibrous carbon nanostructures) obtained by excluding the fibrous carbon nanostructures from the composite material may be subjected to thermogravimetric analysis under the same conditions as in step (B), and in step (C), the defibration state of the fibrous carbon nanostructures may be evaluated using the value obtained by subtracting the mass of the reference sample from the mass of the polymer-removed body.

[0064] (Manufacturing method for composite materials) The composite material manufacturing method of the present invention efficiently produces a composite material in which fibrous carbon nanostructures are well dispersed by evaluating the defibration state of the fibrous carbon nanostructures in the produced composite material using the composite material evaluation method of the present invention and optimizing the defibration treatment conditions for the fibrous carbon nanostructures during composite material manufacturing based on the evaluation results.The composite material manufacturing method of the present invention is a method for producing a composite material containing a polymer and fibrous carbon nanostructures via a step of defibration treating the fibrous carbon nanostructures, and is characterized by comprising: a step (α) of evaluating the defibration state of the fibrous carbon nanostructures in the produced composite material using the composite material evaluation method of the present invention described above; and a step (β) of changing the defibration treatment conditions so that the defibration state of the fibrous carbon nanostructures is within the desired range based on the evaluation results obtained in step (α) if the defibration state of the fibrous carbon nanostructures is outside the desired range.

[0065] <Preparation of composite material> Here, the composite material is not particularly limited as long as it involves a step of subjecting fibrous carbon nanostructures to defibrillation treatment, and can be prepared by any method. Specifically, the composite material can be prepared, for example, by (1) a method in which a polymer, fibrous carbon nanostructures, and optional additives are kneaded in the presence or absence of an organic solvent to prepare a composite material while defibrating the fibrous carbon nanostructures, or (2) a method in which a fibrous carbon nanostructure is defibrated in a liquid that may contain a polymer and / or additives, and if the resulting dispersion does not contain a polymer, a polymer is added and then the liquid (dispersion medium) is removed from the dispersion to prepare a composite material.

[0066] The polymer, fibrous carbon nanostructure, and additives may be the same as those described in the above "(Evaluation method for composite materials)," and therefore will not be described further below. The organic solvent is not particularly limited, and examples include polar organic solvents such as isopropyl alcohol, tetrahydrofuran, and methyl ethyl ketone, and nonpolar organic solvents such as cyclohexane and toluene. Furthermore, the dispersion medium may be water, the organic solvents listed above, or a mixture thereof.

[0067] The kneading can be carried out using, for example, a twin-screw kneader, an open roll, a Banbury mixer, a pressure kneader, or the like, without any particular limitation. Furthermore, the defibration of the fibrous carbon nanostructure in a liquid is not particularly limited, and can be carried out using, for example, an ultrasonic disperser, a homogenizer, a thin film rotary high-speed mixer, a bead mill, a wet jet mill, or the like.

[0068] <Process (α)> In step (α), the defibration state of the fibrous carbon nanostructures in the prepared composite material is evaluated using the composite material evaluation method of the present invention described above. In this way, by sampling and evaluating the prepared composite material using the composite material evaluation method of the present invention, the conditions for the defibration treatment in step (β) can be optimized.

[0069] <Process (β)> In step (β), if the defibration state of the fibrous carbon nanostructure is outside the desired range based on the evaluation results obtained in step (α), the conditions of the defibration process are changed so that the defibration state of the fibrous carbon nanostructure is within the desired range.

[0070] Specifically, for example, when evaluating the composite material in step (α), if the time required for the mass of the polymer-removed body to decrease is longer than when a composite material in a defibrated state within the desired range is evaluated using the composite material evaluation method of the present invention, it is determined that defibration is insufficient, and the conditions of the defibration treatment are changed so that the defibrated state of the fibrous carbon nanostructures falls within the desired range. Specifically, the defibration treatment time is extended or the intensity of the defibration treatment is increased. Furthermore, for example, when evaluating a composite material in step (α), if the time required for the mass of the polymer-removed body to decrease is shorter than when a composite material in a defibrated state within the desired range is evaluated using the composite material evaluation method of the present invention, it is determined that defibration is excessive, and the conditions of the defibration treatment are changed so that the defibrated state of the fibrous carbon nanostructures falls within the desired range. Specifically, the defibration treatment time is shortened or the intensity of the defibration treatment is weakened. Here, the desired range of defibrated state is not particularly limited, and can be set to a range in which the composite material can exhibit the desired physical properties.

[0071] Furthermore, if the evaluation of the composite material in step (α) reveals that the defibrated state of the fibrous carbon nanostructures is within the desired range, the production of the composite material may be continued without changing the conditions of the defibration process, or the conditions of the defibration process may be changed within a range that brings the defibrated state of the fibrous carbon nanostructures within the desired range.

[0072] (composite material) The composite material of the present invention contains a polymer and a fibrous carbon nanostructure, and may optionally further contain various additives depending on the intended use of the composite material. Note that the polymer, fibrous carbon nanostructure, and additives may be the same as those described above in "(Method for evaluating composite materials)," and therefore, further explanation will be omitted below.

[0073] The composite material of the present invention is characterized in that when the composite material is formed into a sheet having a thickness of 150 μm and evaluated under predetermined conditions using the evaluation method for the composite material of the present invention, predetermined evaluation results are obtained. Specifically, the composite material of the present invention is formed into a sheet having a thickness of 150 μm, and the polymer component in the sheet is removed under an inert gas atmosphere at 600° C. to obtain a polymer-removed body. After the atmosphere is switched from the inert gas to air, the change over time in the mass of the polymer-removed body is measured, and the following evaluation results are obtained: When the mass of the polymer-removed body at the elapsed time T1 at which the differential thermogravimetric curve obtained from the change in mass of the polymer-removed body versus elapsed time reaches a minimum value immediately before the final peak is defined as M1, the time required for the mass of the polymer-removed body to decrease from M1 to M1 × 0.10 is 250 seconds or less. The required time can also be 60 seconds or more. As the inert gas, the same gases as those described in the above "(Method for evaluating composite materials)" can be used, and therefore a description thereof will be omitted below.

[0074] Thus, when evaluated using a predetermined method and conditions, a composite material in which the time required for the mass of the polymer remover to decrease from M1 to M1 x 0.10 is 250 seconds or less has well-dispersed fibrous carbon nanostructures and can exhibit excellent physical properties. Also, a composite material in which the time required for the mass of the polymer remover to decrease from M1 to M1 x 0.10 is equal to or greater than the above lower limit has adequately defibrated fibrous carbon nanostructures and can exhibit excellent physical properties.

[0075] The above-mentioned composite material is not particularly limited, and can be prepared, for example, by removing the dispersion medium from a dispersion liquid containing a dispersion medium, a polymer dissolved in the dispersion medium, and bundles of fibrous carbon nanostructures, and in which the average diameter (DB) of the bundles is 20 nm or more and 600 nm or less. The dispersion medium may be the same as that described above in "(Method for producing a composite material)." The dispersion medium can be removed by a known drying method such as drying, vacuum drying, reduced pressure drying, or drying by passing an inert gas through the dispersion medium.

[0076] Here, the dispersion can be prepared by dispersing a polymer, a dispersion medium, and fibrous carbon nanostructures using a dispersion medium. In particular, the dispersion is preferably prepared by dissolving a polymer in a dispersion medium to obtain a polymer solution, and then dispersing the polymer solution and fibrous carbon nanostructures using a dispersion medium.

[0077] Dispersion using a dispersion medium can be suitably carried out using a known wet media dispersion device such as a bead mill. The material constituting the dispersion medium is not particularly limited and can be, for example, glass, alumina, zircon (zirconia-silica ceramics), zirconia, steel, etc.

[0078] The dispersion media has a Vickers hardness of 600 kgf / mm 2 It is preferable that the resistance is 800 kgf / mm or more. 2 More preferably, it is 1000 kgf / mm or more. 2 More preferably, it is 1500 kgf / mm or more. 2 It is preferable that the resistance is 1300 kgf / mm or less. 2 More preferably, it is:

[0079] Furthermore, the filling rate of the dispersion media is preferably 40% by volume or more, more preferably 50% by volume or more, and is preferably 80% by volume or less, more preferably 70% by volume or less, and even more preferably 60% by volume or less.

[0080] The average diameter of the dispersion media is preferably 0.1 mm or more, more preferably 0.3 mm or more, and is preferably 1.5 mm or less, more preferably 1 mm or less, and even more preferably 0.8 mm or less. [Example]

[0081] The present invention will be described below using specific 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.

[0082] (Preparation and Evaluation of Composite Material 1) To 900 g of methyl ethyl ketone as a dispersion medium, 100 g of FKM (vinylidene fluoride rubber, manufactured by Chemours Inc., product name "Viton GBL-600S") as a polymer was added, and the mixture was stirred at a temperature of 20°C for 12 hours to dissolve the polymer, thereby obtaining a polymer dissolved solution. Next, SGCNTs (manufactured by Zeon Nano Technology Co., Ltd., product name "ZEONANO SG101", average diameter (DS): 4 nm, BET specific surface area: 1391 m) were added to the polymer solution as fibrous carbon nanostructures containing single-walled CNTs. 2 4 g of the sieve was added to the mixture (4 g of sieve, 1000 mg / g, G / D ratio: 3.2, no opening treatment, t-plot is upwardly convex) and stirred at 20°C for 30 minutes using a mixer (manufactured by PRIMIX, Labo-Lusion (registered trademark), stirring part: Homo Disper). Further, a bead mill (manufactured by Asada Iron Works, trade name "Nano Mill NM-G1.4L"), dispersion media: glass beads (Vickers hardness of dispersion media: 550 kgf / mm 2Using a filling rate of the dispersion medium: 80% and an average diameter of the dispersion medium: 2 mm, the polymer solution added with SGCNT was subjected to a two-pass dispersion treatment at a temperature of 44 °C (dispersion treatment conditions: peripheral speed 8 m / s, discharge rate 180 g / min). Thereafter, the obtained dispersion was dropped into 4000 g of methanol to be coagulated, obtaining a black solid. Then, the obtained black solid was dried under reduced pressure at 60 °C for 12 hours, obtaining Composite Material 1. Using the obtained Composite Material 1, the elongation at break was evaluated as follows.

[0083] Next, four 300-mg lumps were weighed out from the obtained Composite Material 1, sandwiched with a polyimide film, and placed on the press plate of a hot press machine. Then, hot pressing was performed under the conditions of a pressing pressure: 4 MPa, a pressing time: 20 minutes, and a pressing temperature: 200 °C to obtain a sheet (molded body) with a thickness of 0.15 mm (150 μm). Using the obtained sheet, the defibrillation state of SGCNT was evaluated as follows.

[0084] <Defibrillation state of SGCNT> Thermogravimetric analysis of the sheet was performed using a thermogravimetric analyzer (manufactured by TA Instruments Japan, product name "Discovery TGA5500"). Specifically, after installing the sheet as the measurement sample, the temperature was raised to 600 °C at a heating rate of 20 °C / min in a nitrogen gas atmosphere and held at 600 °C for 10 minutes. Next, while maintaining the temperature at 600 °C, the atmosphere was switched from a nitrogen gas atmosphere to an air atmosphere and held at 600 °C for 20 minutes. Then, after switching to the air atmosphere, a thermogravimetric curve (thermogravimetric reduction curve) and a differential thermogravimetric curve were created from the mass change and the elapsed time. Each created curve is shown in Fig. 1(a). The thermogravimetric reduction curve was created by fitting the mass change and the elapsed time using a Double Boltzmann function, and the differential thermogravimetric curve was created by differentiating the thermogravimetric reduction curve with respect to time. The time T1 at which the differential thermogravimetric curve reaches a minimum value immediately before the final peak was determined from the differential thermogravimetric curve, and the mass M1 of the measurement sample at the time T1 was calculated from the thermogravimetric curve. The time required for M1 to decrease to M1 x 0.10 (90% decrease time) and the time required for M1 to decrease to M1 x 0.50 (50% decrease time) were then calculated. The results are shown in Table 1.

[0085] <Elongation at break> 208 g of the resulting composite material 1, 6 g of zinc oxide type 2, 9.84 g of TAIC M-60 (Mitsubishi Chemical Corporation), and 4 g of Perhexa 25B40 (NOF Corporation) were weighed and uniformly mixed using a 6-inch roll to produce an uncrosslinked compound. This uncrosslinked compound was placed in a preheated 150 mm x 150 mm x 2 mm sheet molding die, and bumping was performed twice at 3 MPa and once at 10 MPa. After that, compression crosslinking was performed under 10 MPa to produce a primarily crosslinked sheet. The primarily crosslinked sheet was then removed from the die and placed in a gear oven preheated to 232°C and heat-treated for 2 hours to produce a secondary crosslinked sheet. This secondarily crosslinked sheet was punched into a No. 3 dumbbell shape to obtain a test piece. The resulting test piece was then measured for elongation at break at 23°C in accordance with JIS K6251. The elongation at break is a value relative to the initial value (i.e., before the sheet was stretched) taken as 100%. Furthermore, the sheet was kept in an air atmosphere at 230° C. for 70 hours, and then the elongation at break at 23° C. (after heat aging test) was measured in the same manner as above. The results are shown in Table 1 and Figures 2(a) and (b).

[0086] (Preparation and Evaluation of Composite Material 2) When dispersing the polymer solution to which SGCNTs were added, the dispersion media was zirconia beads (Vickers hardness of dispersion media: 1250 kgf / mm 2Composite Material 2 was prepared and evaluated in the same manner as Composite Material 1, except that the dispersion media were changed to a 3-pass dispersion process at a peripheral speed of 12.5 m / s (dispersion media filling rate: 80%, average diameter of dispersion media: 1.5 mm). The results are shown in Table 1, Figure 1(b), and Figures 2(a) and (b).

[0087] (Preparation and Evaluation of Composite Material 3) When dispersing the polymer solution to which SGCNTs were added, the dispersion media was zirconia beads (Vickers hardness of dispersion media: 1250 kgf / mm 2 Composite material 3 was prepared and evaluated in the same manner as composite material 1, except that the dispersion media were changed to a 6-pass dispersion treatment at a peripheral speed of 12.5 m / s (dispersion media filling rate: 80%, average diameter of dispersion media: 0.3 mm). The results are shown in Table 1, Figure 1(c), and Figures 2(a) and (b).

[0088] [Table 1]

[0089] Table 1 and Figure 2 show that composite materials 2 and 3, which were subjected to increased dispersion treatment intensity and high shear force, had shorter 90% reduction times and 50% reduction times than composite material 1, indicating that the defibrillation state of SGCNTs can be quantitatively evaluated using the evaluation method of the present invention. Furthermore, when comparing Composite Materials 2 and 3 with Composite Material 1, Composite Materials 2 and 3 exhibit excellent elongation immediately after being formed into a sheet, as well as excellent elongation after heating, indicating that the SGCNTs are well dispersed. [Industrial Applicability]

[0090] According to the composite material evaluation method of the present invention, the defibrillation state of fibrous carbon nanostructures in a composite material can be quantitatively evaluated in a simple manner. Furthermore, according to the method for producing a composite material of the present invention, a composite material in which fibrous carbon nanostructures are well dispersed can be produced efficiently. Furthermore, according to the present invention, a composite material in which fibrous carbon nanostructures are well dispersed can be obtained.

Claims

1. A method for producing a composite material containing a polymer and a fibrous carbon nanostructure, comprising: a step of dissolving the polymer in a dispersion medium to obtain a polymer-dissolved solution, and then dispersing the polymer-dissolved solution and the fibrous carbon nanostructures using a dispersion medium to prepare a dispersion, and then removing the dispersion medium from the dispersion to obtain the composite material; the dispersion media have a Vickers hardness of 1000 kgf / mm 2 or more and an average diameter of 0.8 mm or less; A 150 μm thick sheet formed using the composite material was heated at 600° C. in an inert gas atmosphere to remove polymer components from the sheet to obtain a polymer-removed body. The atmosphere was then switched from the inert gas to air, and the change in mass of the polymer-removed body over time was measured. The differential thermogravimetric curve obtained from the change in mass of the polymer-removed body and the elapsed time was the minimum value immediately before the final peak at the elapsed time T １ The mass M of the polymer removed body １ M １ The method for producing a composite material, wherein the time required for the refractive index to decrease to 0.10 is 250 seconds or less.

2. The method for producing a composite material according to claim 1 , wherein the polymer is a fluorine-containing polymer.

3. The method for producing a composite material according to claim 1 or 2, wherein the fibrous carbon nanostructure comprises a single-walled carbon nanotube.

4. The method for producing a composite material according to claim 3 , wherein the G / D ratio of the single-walled carbon nanotubes is 1 or more and 4 or less.

5. The method for producing a composite material according to claim 3 or 4, wherein the single-walled carbon nanotubes have an average diameter of 1.5 nm or more and 5 nm or less.

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