Carbon nanotube dispersion, fluororesin composition, molded body, and method for producing fluororesin composition

Abstract

This carbon nanotube dispersion contains carbon nanotubes, a fluororesin and a dispersion medium. A coating film formed by removing the dispersion medium from the carbon nanotube dispersion has a color difference (ΔE＊ab), as calculated using formula (1), of 16.0 or more.　Formula (1): ΔE＊ab=[(ΔL＊)2+(Δa＊)2+(Δb＊)2]1 / 2. (Here, ΔL＊, Δa＊ and Δb＊ are all values measured in accordance with JIS K 5600-4.)

Description

Carbon nanotube dispersion, fluororesin composition, molded body, and method for producing fluororesin composition

[0001] The present invention relates to a carbon nanotube dispersion, a fluororesin composition, a molded article, and a method for producing a fluororesin composition.

[0002] Carbon nanotubes (hereinafter sometimes referred to as "CNTs") are excellent in electrical conductivity, thermal conductivity, sliding properties, mechanical properties, etc., and therefore their application to a wide range of uses is being considered. In recent years, therefore, progress has been made in developing a technology that takes advantage of the excellent properties of CNTs and combines them with resins to provide resin materials that combine the properties of resins, such as processability and strength, with the properties of CNTs, such as electrical conductivity.

[0003] For example, Patent Document 1 discloses composite particles containing a resin, a particulate carbon material, and a fibrous carbon nanostructure, in which the fibrous carbon nanostructure is unevenly distributed in the surface layer portion.

[0004] In addition, Patent Document 2 describes at least L ＊ The present invention discloses a laminate having a first layer having a certain value or less, and a second layer having an uneven structure on the surface and containing a certain amount of CNTs and resin, wherein the surface roughness parameters of the second layer in the height and lateral directions and the ratio thereof are within a certain range.

[0005] Furthermore, Patent Document 3 describes a method for producing an aqueous slurry for a secondary battery negative electrode, which includes providing a first composition containing at least a non-conductive negative electrode active material and an aqueous dispersion of CNTs, subjecting the first composition to a dispersion treatment, providing a second composition containing the first composition that has been subjected to the dispersion treatment and a polymer, and kneading the second composition.

[0006] Japanese Patent Application Publication No. 2017-088792 Japanese Patent Application Publication No. 2021-112843 Japanese Patent Application Publication No. 2023-084471

[0007] However, the above-mentioned conventional resin materials have room for improvement in terms of further increasing the electrical conductivity.

[0008] Therefore, an object of the present invention is to provide a CNT dispersion liquid that can give a fluororesin composition having excellent electrical conductivity, and the fluororesin composition.

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems, and have discovered that a coating film obtained by removing the dispersion medium from a CNT dispersion liquid containing CNTs, a fluororesin, and a dispersion medium has a color difference ΔE calculated according to a predetermined formula. ＊ The present inventors have newly found that a fluororesin composition with excellent electrical conductivity can be obtained by using a CNT dispersion liquid having an ab of 16.0 or more, and have completed the present invention.

[0010] That is, an object of the present invention is to advantageously solve the above-mentioned problems, and according to the present invention, there are provided the following carbon nanotube dispersions [1] to [6], the following fluororesin composition [7], the following molded article [8], and the following production method [9].

[0011] [1] A carbon nanotube dispersion containing carbon nanotubes, a fluororesin, and a dispersion medium, wherein a coating film obtained by removing the dispersion medium from the carbon nanotube dispersion has a color difference ΔE calculated according to the following formula (1): ＊ A carbon nanotube dispersion liquid having ab of 16.0 or more. ＊ ab = [(ΔL ＊ ) ２ + (Δa ＊ ) ２ + (Δb ＊ ) ２ ] １／２ ... (1) (where ΔL ＊ , Δa ＊ , and Δb ＊ are values ​​measured in accordance with JIS K 5600-4.) If the color difference is 16.0 or more, the conductivity of the fluororesin composition obtained by using the carbon nanotube dispersion can be further increased. The color difference of the coating film obtained by removing the dispersion medium from the carbon nanotube dispersion can be measured by the method described in the examples.

[0012] [2] Here, the carbon nanotube dispersion liquid of the above [1] preferably has a linearity of 9.0 or less as calculated according to the following formula (2): Linearity = Absolute maximum length ２ / area×π / 4 (2) When the linearity is equal to or less than the upper limit, the carbon nanotubes are sufficiently dispersed, and the conductivity of the fluororesin composition obtained using the carbon nanotube dispersion can be further increased. The linearity of the carbon nanotube dispersion can be measured by the method described in the Examples.

[0013] [3] In addition, the carbon nanotube dispersion liquid of [1] or [2] above preferably has a concentration of the carbon nanotubes in the solid content of 0.020 mass % or more and 0.250 mass % or less. When the concentration of the carbon nanotubes in the solid content is within the above range, the carbon nanotubes can be well dispersed, and the conductivity of the fluororesin composition obtained using the carbon nanotube dispersion liquid can be further improved.

[0014] [4] In the carbon nanotube dispersion liquid of any one of [1] to [3] above, the carbon nanotubes are preferably single-walled carbon nanotubes. Use of single-walled carbon nanotubes can further increase the electrical conductivity of the fluororesin composition obtained using the carbon nanotube dispersion liquid.

[0015] [5] In the carbon nanotube dispersion liquid of any one of [1] to [4] above, the fluororesin is preferably at least one selected from the group consisting of polytetrafluoroethylene, polychlorotrifluoroethylene, and a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene. Use of these resins can improve chemical resistance.

[0016] [6] The carbon nanotube dispersion according to any one of [1] to [5] above can be suitably used for antistatic members. A fluororesin composition obtained using the carbon nanotube dispersion described above has excellent electrical conductivity and high antistatic properties.

[0017] [7] A fluororesin composition obtained by removing the dispersion medium from the carbon nanotube dispersion liquid according to any one of [1] to [6] above.

[0018] [8] A molded article obtained by molding the fluororesin composition according to [7] above.

[0019] [9] A method for producing a fluororesin composition, comprising: a step of confirming a color difference in a carbon nanotube dispersion liquid containing carbon nanotubes, a fluororesin, and a dispersion medium, to confirm the dispersion state of the carbon nanotubes; forming a coating film by removing the dispersion medium from the carbon nanotube dispersion liquid; and measuring a color difference ΔE according to the following formula (1): ＊ ab is calculated, and the obtained color difference ΔE ＊ The method for producing a fluororesin composition includes a color difference confirmation step of determining that the dispersion state of the carbon nanotube dispersion is good when the value of ab is 16.0 or more, and when the determination result in the color difference confirmation step is "good", a fluororesin composition production step is carried out in which the dispersion medium is removed from the carbon nanotube dispersion and a fluororesin composition is produced. ＊ ab = [(ΔL ＊ ) ２ + (Δa ＊ ) ２ + (Δb ＊ ) ２ ] １／２ ... (1) (where ΔL ＊ , Δa ＊ , and Δb ＊ and are values ​​measured in accordance with JIS K 5600-4.) According to the above production method, a fluororesin composition or the like having a desired electrical conductivity can be efficiently produced.

[0020] According to the present invention, it is possible to provide a CNT dispersion liquid that can give a fluororesin composition having excellent electrical conductivity, and the fluororesin composition.

[0021] Hereinafter, embodiments of the present invention will be described in detail. The CNT dispersion of the present invention can be used to produce a fluororesin composition containing CNTs and a fluororesin. The fluororesin composition of the present invention can be suitably used as a molding material for the molded article of the present invention, particularly as a material for antistatic members. The molded article of the present invention can be suitably used, without particular limitation, for parts used in semiconductor manufacturing, such as semiconductor manufacturing equipment parts, chemical nozzles, tubes, chemical tanks, wafer cleaning containers, cleaning nozzles, antistatic sheets, integrated circuit trays, wafer carriers, chemical hoses, piping joints, diaphragms, and sealants, particularly as antistatic members used in semiconductor manufacturing.

[0022] (CNT Dispersion) <Composition of CNT Dispersion> The CNT dispersion of the present invention is required to contain CNTs, a fluororesin, and a dispersion medium. The CNT dispersion of the present invention may also optionally contain one or more other components selected from the group consisting of resins other than fluororesins, and additives such as antioxidants and plasticizers. However, the content of other components in the CNT dispersion of the present invention is preferably 5% by mass or less, more preferably 1% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0% by mass (i.e., the CNT dispersion consists only of CNTs, a fluororesin, a dispersion medium, and impurities that are inevitably mixed in during the preparation of the CNT dispersion).

[0023] <<CNT>> The CNT contained in the CNT dispersion of the present invention can be single-walled CNT and / or multi-walled CNT, but the CNT is preferably single-walled to five-walled CNT, and more preferably single-walled CNT. The use of single-walled CNT can further increase the conductivity of the fluororesin composition obtained using the CNT dispersion.

[0024] The specific surface area of ​​the CNT is not particularly limited, but is, for example, 800 m ２ / g or more, and 1000m ２ / g or more, and ２ / g or more, and 1500m ２ / g or less, and２ / g or less is more preferable. If the specific surface area of ​​the CNT is equal to or greater than the above lower limit, the conductivity of the fluororesin composition obtained using the CNT dispersion can be further increased. Furthermore, if the specific surface area of ​​the CNT is equal to or less than the above upper limit, the strength of a molded article using the fluororesin composition can be increased. In the present invention, the "specific surface area" refers to the nitrogen adsorption specific surface area measured according to the BET (Brunauer-Emmett-Teller) method.

[0025] Here, the carbon purity of the CNT is preferably 97.5% by mass or more, more preferably 99.0% by mass or more, and even more preferably 99.5% by mass or more. If the carbon purity of the CNT is equal to or greater than the above lower limit, the electrical resistance of the resulting fluororesin composition and molded article can be further reduced.

[0026] Furthermore, the average diameter of the CNTs is preferably 1 nm or more, preferably 60 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. If the average diameter of the CNTs is 1 nm or more, the dispersibility of the CNTs can be improved, and properties such as conductivity can be stably imparted to the fluororesin composition and molded article. If the average diameter of the CNTs is 60 nm or less, properties such as conductivity can be efficiently imparted to the fluororesin composition and molded article even when the blending amount is small. In the present invention, the "average diameter of the CNTs" can be determined by measuring the diameter (outer diameter) of, for example, 20 CNTs on a transmission electron microscope (TEM) image and calculating the number average value.

[0027] Furthermore, it is preferable to use CNTs 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 greater than 0.20, more preferably greater than 0.25, and even more preferably greater than 0.40. It is also preferable to use CNTs having a 3σ / Av of 0.80 or less, more preferably greater than 0.60. The use of CNTs having a 3σ / Av of greater than 0.20 and less than 0.80 can further improve the performance of the fluororesin composition and molded article. The average diameter (Av) and standard deviation (σ) of the CNTs may be adjusted by changing the CNT production method or conditions, or by combining multiple types of CNTs obtained by different production methods.

[0028] The CNTs that are usually used are those that exhibit 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 Gaussian.

[0029] Furthermore, the average length of the CNTs is preferably 10 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, and preferably 600 μm or less, more preferably 550 μm or less, and even more preferably 500 μm or less. When the average length is 10 μm or more, conductive paths can be well formed in the fluororesin composition and molded article, and dispersibility can be improved. When the average length is 600 μm or less, the conductivity of the fluororesin composition and molded article can be stabilized. Therefore, by setting the average length of the CNTs within the above range, the volume resistivity of the molded article can be sufficiently reduced. In the present invention, the average length of the CNTs can be determined by measuring the lengths of, for example, 20 CNTs on a scanning electron microscope (SEM) image and calculating the number average value.

[0030] Furthermore, CNTs typically have an aspect ratio of more than 10. The aspect ratio of CNTs can be determined by measuring the diameter and length of 100 randomly selected CNTs using a scanning electron microscope or a transmission electron microscope and calculating the average value of the ratio of the diameter to the length (length / diameter).

[0031] Furthermore, it is preferable that the t-plot obtained from the adsorption isotherm of CNTs shows an upwardly convex shape. 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 CNTs measured by the nitrogen gas adsorption method. That is, the average thickness t of the nitrogen gas adsorption layer is calculated by converting the relative pressure P / P ０ The t-plot of CNTs can be obtained by calculating the average thickness t of the nitrogen gas adsorption layer corresponding to the relative pressure from a known standard isotherm plotted against the relative pressure and performing the above conversion (t-plot method by de Boer et al.).

[0032] Here, in materials with pores on the surface, the growth of a nitrogen gas adsorption layer can be classified into the following 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 monomolecular adsorption layer of nitrogen molecules on the entire surface; (2) The process of forming a multimolecular adsorption layer and the accompanying capillary condensation filling process within the pores; and (3) The process of forming a multimolecular adsorption layer on an apparently non-porous surface where the pores are filled with nitrogen.

[0033] In the case of a 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. CNTs with such a t-plot shape have a large ratio of the internal specific surface area to the total specific surface area of ​​the CNT, indicating that many openings are formed in the CNT.

[0034] The inflection point of the CNT t-plot preferably falls within a range satisfying 0.2≦t (nm)≦1.5, more preferably within a range of 0.45≦t (nm)≦1.5, and even more preferably within a range of 0.55≦t (nm)≦1.0. If the inflection point of the CNT t-plot falls within this range, the dispersibility of the CNT can be improved, and properties such as the conductivity of the fluororesin composition and the molded article can be improved. Specifically, if the inflection point value is less than 0.2, the CNTs are likely to aggregate and the dispersibility may decrease. If the inflection point value is greater than 1.5, the CNTs may be likely to entangle with each other, resulting in a decrease in dispersibility. The "position of the inflection point" is the intersection of the approximate line A in the above-mentioned process (1) and the approximate line B in the above-mentioned process (3).

[0035] Furthermore, the ratio of the internal specific surface area S2 to the total specific surface area S1 (S2 / S1) of the CNT obtained from the t-plot is preferably 0.05 or more and 0.30 or less. When the S2 / S1 value of the CNT falls within this range, the dispersibility of the CNT is enhanced, and the properties of the fluororesin composition and molded article, such as the conductivity, can be improved with a small blend amount. The total specific surface area S1 and the internal specific surface area S2 of the CNT can be determined from the t-plot. Specifically, first, the total specific surface area S1 can be determined from the slope of the approximation line in step (1), and the external specific surface area S3 can be determined from the slope of the approximation line in step (3). The internal specific surface area S2 can then be calculated by subtracting the external specific surface area S3 from the total specific surface area S1.

[0036] Incidentally, the measurement of the adsorption isotherm of CNT, the creation of t-plots, and the calculation of the total specific surface area S1 and the internal specific surface area S2 based on the analysis of the t-plots can be performed using, for example, a commercially available measuring device, "BELSORP (registered trademark)-mini" (manufactured by Microtrac BEL).

[0037] Furthermore, when evaluated using Raman spectroscopy, the CNT preferably has a radial breathing mode (RBM) peak. Note that the Raman spectrum of multi-walled CNTs with three or more walls does not have an RBM.

[0038] Furthermore, the CNTs preferably have a ratio of the G band peak intensity to the D band peak intensity in a Raman spectrum (G / D ratio) of 0.5 or more, more preferably 2.0 or more, and even more preferably 3.0 or more, and preferably 150 or less, more preferably 50 or less, and even more preferably 5.0 or less. If the G / D ratio is 0.5 or more and 5.0 or less, the performance of the produced fluororesin composition and molded article can be further improved.

[0039] CNTs can be produced using known CNT synthesis methods, such as arc discharge, laser ablation, and chemical vapor deposition (CVD). Specifically, CNTs can be efficiently produced, for example, by supplying raw material compounds and a carrier gas onto a substrate having a catalyst layer for CNT production on its surface, and synthesizing CNTs by chemical vapor deposition (CVD) using a trace amount of oxidizing agent (catalytic activator) in the system, thereby dramatically improving the catalytic activity of the catalyst layer (the super-growth method; see International Publication No. 2006 / 011655). Hereinafter, CNTs obtained by the super-growth method may be referred to as "SGCNTs." CNTs produced by the super-growth method may consist solely of SGCNTs, or may contain, in addition to SGCNTs, other carbon components, such as non-cylindrical carbon nanostructures.

[0040] The CNT dispersion may contain, as a carbon component other than CNTs, a fibrous carbon material having an aspect ratio of more than 10. However, from the viewpoint of preventing the generation of aggregates when producing a molded article of the fluororesin composition obtained using the CNT dispersion, it is preferable that the CNT dispersion does not contain particulate carbon having an aspect ratio of 10 or less.

[0041] The CNT content in the CNT dispersion is preferably 0.003% by mass or more, more preferably 0.005% by mass or more, and even more preferably 0.007% by mass or more, and is preferably 0.050% by mass or less, more preferably 0.040% by mass or less, and even more preferably 0.030% by mass or less.

[0042] The CNT content in the solids (CNT, fluororesin, and other optional solids) contained in the CNT dispersion is preferably 0.020% by mass or more, more preferably 0.030% by mass or more, and preferably 0.250% by mass or less, more preferably 0.100% by mass or less, and even more preferably 0.075% by mass or less. When the CNT content in the solids contained in the dispersion is equal to or greater than the above-mentioned lower limit, the electrical conductivity of the resulting fluororesin composition can be further improved. When the CNT content in the solids contained in the dispersion is equal to or less than the above-mentioned upper limit, aggregation of CNTs in the resulting CNT dispersion can be suppressed, thereby further improving the electrical conductivity of the resulting fluororesin composition.

[0043] <<Fluororesin>> The fluororesin contained in the CNT dispersion of the present invention is not particularly limited, and examples thereof include polytetrafluoroethylene (PTFE), a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene (PFA), a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP), a copolymer of tetrafluoroethylene and ethylene (ETFE), polychlorotrifluoroethylene (PCTFE), a copolymer of chlorotrifluoroethylene and ethylene (ECTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF). These can be used alone or in combination of two or more. From the viewpoint of chemical resistance, the fluororesin is preferably at least one selected from the group consisting of polytetrafluoroethylene, polychlorotrifluoroethylene, and a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene, and more preferably polytetrafluoroethylene. The above fluororesins may be used alone or in combination of two or more.

[0044] Here, the fluororesin used in the CNT dispersion mixing step described below is preferably fluororesin particles. Fluororesin particles have excellent dispersibility in dispersions. Therefore, by using fluororesin particles, CNTs can be well dispersed in the resulting CNT dispersion, and the electrical conductivity of the resulting fluororesin composition can be further improved.

[0045] Furthermore, the average particle size of the fluororesin particles is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, and is preferably 700 μm or less, more preferably 250 μm or less, and even more preferably 150 μm or less. If the average particle size of the fluororesin particles is equal to or greater than the above-mentioned lower limit, the dispersibility of CNTs in the CNT dispersion can be further improved. In addition, if the average particle size of the fluororesin particles is equal to or less than the above-mentioned upper limit, the productivity of the CNT dispersion can be improved.

[0046] In the present invention, the "average particle size" of the fluororesin particles can be determined by measuring the particle size distribution (volume basis) by laser diffraction and calculating the particle size at which the cumulative volume frequency reaches 50%.

[0047] The content of the fluororesin in the CNT dispersion is preferably 19.5 mass% or more, more preferably 19.9 mass% or more, and is preferably 20.5 mass% or less, and more preferably 20.0 mass% or less. If the content of the fluororesin is within the above range, the CNTs can be well dispersed in the resulting CNT dispersion, and the electrical conductivity of the resulting fluororesin composition can be further improved.

[0048] <<Dispersion Medium>> The dispersion medium contained in the CNT dispersion liquid is not particularly limited, and examples thereof include polar solvents such as water, ketones such as methyl ethyl ketone (MEK), and alcohols such as ethanol and isopropyl alcohol, as well as nonpolar solvents such as hydrocarbon solvents such as cyclohexane, toluene, and xylene. One of these solvents may be used alone, or two or more may be used in combination at any ratio. Among these, from the viewpoint of improving the dispersibility of the components in the CNT dispersion liquid, a nonaqueous dispersion medium is preferred, and it is more preferable to use at least one selected from the group consisting of cyclohexane, xylene, methyl ethyl ketone, and toluene, with cyclohexane being particularly preferred.

[0049] <<Other Components>> Additives that can be optionally blended into the mixed liquid are not particularly limited, and examples thereof include known additives such as dispersants. Here, the dispersant can be a known dispersant that can assist in dispersing CNTs. Specific examples of the dispersant include surfactants, polysaccharides, π-conjugated polymers, and polymers with an ethylene chain as the main chain. Among these, surfactants are more preferred. Note that, from the viewpoint of suppressing a decrease in the conductivity of the fluororesin composition and the molded article, the blending amount of the additive is preferably 1 part by mass or less per 100 parts by mass of the above-mentioned fluororesin, and more preferably 0 part by mass (i.e., the CNT dispersion does not contain any additive).

[0050] <Properties of CNT Dispersion> <<Color Difference>> The CNT dispersion of the present invention has a color difference ΔE calculated according to the following formula (1) for a coating film obtained by removing the dispersion medium from the CNT dispersion. ＊ It is necessary that ab is 16.0 or more. ＊ ab = [(ΔL ＊ ) ２ + (Δa ＊ ) ２ + (Δb ＊ ) ２ ] １／２ ... (1) (where ΔL ＊ , Δa ＊ , and Δb ＊was measured in accordance with JIS K 5600-4-5 using a dry fluororesin that does not contain CNT as a standard, and ΔE ＊ ab are values ​​calculated in accordance with JIS K 5600-4-6.) The CNT dispersion of the present invention has a color difference of 16.0 or more when the coating film obtained after removing the dispersion medium is used, making it possible to obtain a fluororesin composition having excellent conductivity. The coating film of the CNT dispersion can be obtained by removing the dispersion medium using any drying method that can be used in the drying step of the CNT dispersion described below.

[0051] In the present invention, the color difference of the coating film obtained by removing the dispersion medium from the CNT dispersion is not particularly limited, and can be measured using a commercially available color difference meter by the method specified in JIS K 5600-4, for example, the method described in the examples.

[0052] The color difference is preferably 18.0 or more, more preferably 20.0 or more. The lower limit of the color difference is not particularly limited, but is generally 50.0 or less, preferably 30.0 or less. When the color difference is equal to or greater than the above lower limit, the CNT concentration in the CNT dispersion is sufficiently high, and the conductivity of the fluororesin composition obtained using the CNT dispersion can be further increased. Furthermore, by ensuring that the color difference is equal to or less than the above upper limit, the CNT concentration in the CNT dispersion can be prevented from becoming excessively high, and CNT aggregation can be suppressed in the fluororesin composition obtained using the CNT dispersion. The color difference can be controlled by adjusting the amount of CNT added to the CNT dispersion and adjusting the dispersion treatment conditions.

[0053] The present inventors have developed a new, specialized method for determining the dispersion state of CNTs in a CNT dispersion, replacing various conventional analytical methods. This method was developed after extensive research by the inventors. Rather than relying on various parameters obtainable by conventional methods, the inventors focused on the color difference, an indicator measured after forming a CNT dispersion into a film. The inventors discovered a new phenomenon in which a high correlation is observed between this color difference and the volume resistivity of a fluororesin composition obtained by removing the dispersion medium from the CNT dispersion. The concept of the present invention, which determines the CNT dispersion state based on color difference, is also extremely useful as a production control method for producing a CNT dispersion that can provide a fluororesin composition having a desired volume resistivity. In other words, it is highly effective to include a step of determining the color difference as a step for confirming the dispersion state of CNTs in a CNT dispersion during the production of a CNT dispersion or a fluororesin composition.

[0054] <<Linearity>> In the CNT dispersion of the present invention, the linearity of the CNTs calculated according to the following formula (2) is preferably 9.0 or less, more preferably 8.0 or less, and even more preferably 7.0 or less. The lower limit of the linearity is not particularly limited, but is generally 1.0 or more, and preferably 3.0 or more. Linearity = absolute maximum length ２ / area×π / 4 (2) When the linearity is equal to or less than the above upper limit, the CNTs are sufficiently dispersed in the CNT dispersion, and the conductivity of the fluororesin composition obtained using the CNT dispersion can be further increased.

[0055] In the present invention, the linearity is not particularly limited and can be measured by a method using image analysis of the dispersion, for example, the method described in the Examples. The linearity can be reduced by adjusting the time of the dispersion treatment in the mixing step of the CNT dispersion, which will be described later.

[0056] (Fluororesin Composition) The fluororesin composition of the present invention can be obtained by removing the dispersion medium from the above-mentioned CNT dispersion by any drying method that can be used in the drying step of the CNT dispersion described below. The fluororesin composition of the present invention can be suitably used to form a molded article having excellent electrical conductivity and low volume resistivity, and ultimately an antistatic material. The fluororesin composition of the present invention may contain any of the above-mentioned additives.

[0057] The color difference of the fluororesin composition can be calculated using the same method as described above for the coating film obtained by removing the dispersion medium from the CNT dispersion. The color difference of the fluororesin composition is preferably 16.0 or more, more preferably 18.0 or more, and even more preferably 20.0 or more. The upper limit of the color difference is not particularly limited, but is generally 50.0 or less, preferably 40.0 or less, and more preferably 30.0 or less. If the color difference is equal to or greater than the lower limit, the conductivity of the fluororesin composition and the molded article obtained by molding the fluororesin composition can be further improved. Furthermore, if the color difference is equal to or less than the upper limit, CNT aggregation can be suppressed in the fluororesin composition and the molded article. The color difference can be increased by adjusting the amount of CNT added to the CNT dispersion.

[0058] (Method for producing fluororesin composition) The fluororesin composition of the present invention is not particularly limited and can be obtained, for example, by carrying out a mixing step in which the CNTs, fluororesin, dispersion medium, and optional additives are mixed to obtain a CNT dispersion, and a drying step in which the dispersion medium is removed from the CNT dispersion obtained in the mixing step to obtain a fluororesin composition. Furthermore, optionally, a color difference confirmation step may be carried out prior to the production of the fluororesin composition, in which a coating film is formed by removing the dispersion medium from the CNT dispersion, a color difference is calculated, and the quality of the CNT dispersion is judged based on the obtained color difference value. A pulverization step in which the obtained fluororesin composition is pulverized may also be carried out.

[0059] <Mixing Step> The mixing of CNT, fluororesin, and dispersion medium in the mixing step is not particularly limited and can be carried out using a known mixing method. For example, the fluororesin and CNT can be dispersed using an in-line mixer, homogenizer, ultrasonic disperser, jet mill, ball mill, etc. Among these, from the viewpoint of suppressing damage to the CNT and dispersing the CNT well, it is preferable to use a wet media-less disperser that performs wet dispersion treatment without using a dispersion medium, such as a homogenizer or in-line mixer.

[0060] <Drying Step> The dispersion medium can be removed from the CNT dispersion liquid by pressure filtration, ventilation drying using a draft chamber or the like, hot air drying, vacuum drying, etc. The drying conditions, such as the drying time and drying temperature, can be set as appropriate.

[0061] <Color Difference Confirmation Step> In the color difference confirmation step, which can be optionally performed, prior to the production of the fluororesin composition, a coating film is formed by removing the dispersion from the CNT dispersion, the color difference is calculated, and the quality of the CNT dispersion is judged based on the obtained color difference value. Here, the method for measuring the color difference is not particularly limited, and it can be measured using a commercially available color difference meter according to the method specified in JIS K 5600-4. Note that the reference value for color difference can be a value obtained by drying a fluororesin that does not contain CNTs. In addition, the quality of the CNT dispersion can be judged, for example, based on the color difference ΔE calculated according to the following formula (1): ＊ When the value of ab is 16.0 or more, the CNT dispersion is judged to be good. A good CNT dispersion means that the dispersibility of CNTs in the CNT dispersion is good. When the dispersibility of CNTs in the CNT dispersion is good, it is decided to carry out the fluororesin composition production process. By carrying out the color difference confirmation process, it is possible to grasp the dispersion state of the CNT dispersion and predict the volume resistivity of the fluororesin composition obtained using the CNT dispersion. Therefore, it is possible to efficiently produce a fluororesin composition having a desired volume resistivity. ΔE ＊ ab = [(ΔL ＊ ) ２ + (Δa＊ ) ２ + (Δb ＊ ) ２ ] １／２ ... (1) (where ΔL ＊ , Δa ＊ , and Δb ＊ are values ​​measured in accordance with JIS K 5600-4.)

[0062] <Pulverization step> In the pulverization step, which can be optionally performed, the fluororesin composition containing CNTs and a fluororesin obtained through the mixing step and the drying step is pulverized. Here, the pulverization method is not particularly limited, and any pulverization method can be used. Among them, in the pulverization step, it is preferable to pulverize the fluororesin composition by, for example, rotation of a rotor.

[0063] (Molded Article) The molded article of the present invention can be obtained by molding the above-mentioned fluororesin composition using a molding machine, such as an extruder, an injection molding machine, a compressor, a roller, or the like, that is suited to the desired shape of the molded article. The molded article may optionally be subjected to a baking treatment. The molded article of the present invention has excellent electrical conductivity because it contains the fluororesin composition of the present invention.

[0064] Here, the compact has a volume resistivity of 1.0×10 ８ It is preferable that the resistance is less than 1.0×10 ７ More preferably, it is 5.0×10 Ω cm or less. ５ It is more preferable that the resistance is Ω cm or less, and 1.0 × 10 ５ The lower limit of the volume resistivity is not particularly limited, but is generally preferably 1.0 Ω cm or more, and more preferably 1.0×10 ３ It is more preferable that the volume resistivity is Ω cm or more. If the volume resistivity is not more than the above upper limit, the conductivity of the molded article and, therefore, the antistatic performance can be further improved. In the present invention, the volume resistivity can be measured by the method described in the examples.

[0065] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" representing amounts is based on mass unless otherwise specified. In the examples and comparative examples, various measurements were carried out by the following methods.

[0066] (Physical Property Measurement) <CNT Specific Surface Area> The BET specific surface area (m ) of the CNT was measured using a BET specific surface area measuring device (manufactured by Microtrac-Bell, product name "BELSORP (registered trademark)-mini") in accordance with JIS Z8830. ２ / g) was measured.

[0067] <Linearity> 0.09 ml (2 cm diameter x 0.3 mm thickness) of the CNT dispersion liquid was dropped onto a grooved glass sample plate, and a microscope image was obtained at 100x magnification using an optical microscope. The obtained microscope image (8-bit image) was imported into WinROOF (2021, Mitani Corporation), converted to a 256-level grayscale from 0 to 255, and then (i) binarized using a threshold of 85, and (ii) binarized the linear material (CNT) using a threshold of 159. (i) Areas falling below the threshold of 85 were extracted, or (ii) a threshold of 159 was set as the correction reference value for histogram average brightness correction, and areas falling below the threshold of 150 were extracted to extract and separate low-brightness areas corresponding to CNT. For the obtained low-brightness areas, the distance between the farthest pixels in each area was calculated to obtain the absolute maximum length. In addition, the area of ​​each area was also calculated and linearity was obtained according to the following formula (2): Linearity = Absolute Maximum Length ２ / Area×π / 4...(2)

[0068] <Color difference> A filter paper with a hole in the center was placed on a glass plate, and 2 ml of the obtained dispersion was poured into the center and dried at 150°C for 5 minutes. After being removed from the dryer, the sample was allowed to cool for 3 minutes, and the filter paper was peeled off from the glass plate. The color difference ΔE was measured using a color difference meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SE 6000"). ＊ ab is defined by the following formula (1): ＊ a ＊ b ＊ is measured according to JIS K 5600-4-5 (see 9. Procedure), and ΔE ＊ab was calculated according to JIS K 5600-4-6 (see 3.2 Color difference between two colors using the CIELAB color difference formula). ＊ ab = [(ΔL ＊ ) ２ + (Δa ＊ ) ２ + (Δb ＊ ) ２ ] １／２ ... (1) Note that, to determine the reference value of color difference, PTFE was wetted with cyclohexane at a solid content of 20% to produce pure PTFE that did not contain CNTs, and 2 ml of this pure PTFE was dropped into a round glass cuvette with a diameter of 30 mm and dried, and then measurement was performed.

[0069] <Volume Resistivity> The surface of the produced molded body was polished with waterproof abrasive paper (No. 3000), and then the surface was polished to a low resistance (10 ８ Ω cm or less) was measured using a resistivity meter Loresta (manufactured by Mitsubishi Chemical Analytech Co., Ltd., product name "MCP-T610", probe LSP), and high resistance (10 ８ The volume resistivity (Ω cm or more) was measured using a resistivity meter Hiresta (manufactured by Mitsubishi Chemical Analytech Co., Ltd., product name "MCP-HT800", probe URSS). The smaller the volume resistivity value, the better the conductivity and the higher the antistatic performance.

[0070] (Example 1) <Mixing step> In a 5 L SUS can, 2720 g (80.000 mass % in the dispersion) of cyclohexane as a dispersion medium, 679.83 g (19.995 mass % in the dispersion) of fluororesin particles (manufactured by AGC Corporation, product name "Fluon PTFE G163", average particle diameter 30 μm, specific gravity 2.15), and single-walled CNTs (manufactured by Zeon Corporation, product name "ZEONAN SG101", specific gravity 1.7, carbon purity: 99.5%, average diameter 3.5 nm, 3σ / Av: 0.60, average length: 450 nm, BET specific surface area: 1378 m) were mixed. ２ / g; t-plot: convex upward) was added to and mixed with 0.17 g (0.005 mass % in the dispersion) of fluororesin particles (the proportion of CNT in the solids (CNT and fluororesin) was 0.025 mass %), and a dispersion treatment was carried out for 30 minutes at a temperature of 20°C and a rotation speed of 6000 rpm using an in-line mixer Cavitron (manufactured by Pacific Machinery Works, Ltd., product name "CD1000", rotor / stator: slit type, minimum clearance 0.25 mm), to obtain a slurry-like dispersion containing fluororesin particles and single-walled CNT.

[0071] <Color Difference Confirmation Step> The color difference of the dispersion obtained in the above mixing step was measured by the above method. The results are shown in Table 1.

[0072] <Drying Step> Next, the dispersion liquid prepared above was pressure filtered using a multipurpose tank holder (KST-142-UH, manufactured by ADVANTEC CORPORATION) to remove the dispersion medium, and then dried at 125°C for 2 hours in a large vacuum dryer (DP610, manufactured by Yamato Scientific Co., Ltd.), to obtain a fluororesin composition containing fluororesin and single-walled CNTs.

[0073] <Pulverization Step> The fluororesin composition obtained through the drying step was pulverized at 2700 rpm using a Quick Mill (QMY-30, manufactured by Seishin Enterprise Co., Ltd.) as a pulverizer with an agitator blade to obtain fluororesin composition particles. The obtained fluororesin composition particles were placed in a mold and preformed using a compression molding machine (manufactured by Dumbbell Co., Ltd., model number "SDOP-1032IV-2HC-AT") at room temperature under a pressure of 9 MPa for a pressure holding time of 5 minutes to obtain a sheet-like preform measuring 130 mm wide x 80 mm long and 2 mm thick. The preform was demolded and then baked in a free state in a hot air circulating oven at 370°C for 6 hours to obtain a molded product. The volume resistivity of the obtained molded product was measured using the method described above. The results are shown in Table 1.

[0074] (Example 2) Various operations and measurements were performed in the same manner as in Example 1, except that in the mixing step, the amount of fluororesin added was changed to 679.66 g (19.990 mass % in the dispersion) and the amount of CNT added was changed to 0.34 g (0.010 mass % in the dispersion) (the proportion of CNT in the solid content (CNT and fluororesin) was 0.050 mass %). The results are shown in Table 1.

[0075] (Example 3) Various operations and measurements were performed in the same manner as in Example 1, except that in the mixing step, the amount of fluororesin added was changed to 679.32 g (19.980 mass % in the dispersion) and the amount of CNT added was changed to 0.68 g (0.020 mass % in the dispersion) (the proportion of CNT in the solid content (CNT and fluororesin) was 0.100 mass %). The results are shown in Table 1.

[0076] (Example 4) Various operations and measurements were performed in the same manner as in Example 1, except that in the mixing step, the amount of fluororesin added was changed to 678.64 g (19.960 mass % in the dispersion) and the amount of CNT added was changed to 1.36 g (0.040 mass % in the dispersion) (the proportion of CNT in the solid content (CNT and fluororesin) was 0.200 mass %). The results are shown in Table 1.

[0077] (Example 5) In the mixing step, the type of CNT was changed to single-walled CNT (specific surface area 1010 m) prepared by the super-growth method according to the description in WO 2006 / 011655. ２ / g) (referred to as CNT1), the amount of fluororesin added was changed to 679.66 g (19.990 mass % in the dispersion), and the amount of CNT added was changed to 0.34 g (0.010 mass % in the dispersion) (the proportion of CNT in the solid content (CNT and fluororesin) was 0.050 mass %). Various operations and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0078] Example 6 In the mixing step, the type of CNT was changed to single-walled CNT (specific surface area: 1454 m) prepared by the super-growth method according to the description in WO 2006 / 011655. ２ / g) (referred to as CNT2), the amount of fluororesin added was changed to 679.66 g (19.990 mass % in the dispersion), and the amount of CNT added was changed to 0.34 g (0.010 mass % in the dispersion) (the proportion of CNT in the solid content (CNT and fluororesin) was 0.050 mass %). Various operations and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0079] (Comparative Example 1) Various operations and measurements were performed in the same manner as in Example 1, except that in the mixing step, the amount of fluororesin added was changed to 679.93 g (19.998 mass % in the dispersion) and the amount of CNT added was changed to 0.07 g (0.002 mass % in the dispersion) (the proportion of CNT in the solid content (CNT and fluororesin) was 0.010 mass %). The results are shown in Table 1.

[0080] (Comparative Example 2) In the mixing step, the type of CNT was changed to the above-mentioned CNT1 (specific surface area 1010 m ２ The various operations and measurements were carried out in the same manner as in Example 1, except that the dispersion time was changed to 5 minutes and the weight of the dispersion was changed to 100g / g. The results are shown in Table 1.

[0081]

[0082] Table 1 shows that in Examples 1-6, which are CNT dispersions containing CNTs, a fluororesin, and a dispersion medium, and in which the color difference of the coating film obtained by removing the dispersion medium from the CNT dispersion is 16.0 or more, molded articles with excellent electrical conductivity could be produced, compared to Comparative Examples 1 and 2, in which the color difference of the coating films produced in the same manner was less than 16.0.

[0083] According to the present invention, it is possible to provide a CNT dispersion liquid that can give a fluororesin composition having excellent electrical conductivity, and the fluororesin composition.

Claims

1. A carbon nanotube dispersion containing carbon nanotubes, a fluororesin, and a dispersion medium, wherein the color difference ΔE is calculated according to the following formula (1) for a coating film obtained by removing the dispersion medium from the carbon nanotube dispersion. ＊ A carbon nanotube dispersion liquid having ab of 16.0 or more. ＊ ab = [(ΔL ＊ ) ２ + (Δa ＊ ) ２ + (Δb ＊ ) ２ ] １／２ ... (1) (where ΔL ＊ , Δa ＊ , and Δb ＊ are values measured in accordance with JIS K 5600-4.) 2. The carbon nanotube dispersion liquid according to claim 1, wherein the carbon nanotubes have a linearity of 9.0 or less as calculated according to the following formula (2): Linearity = Absolute Maximum Length ２ / Area×π / 4...(2) 3. The carbon nanotube dispersion liquid according to claim 1, wherein the concentration of the carbon nanotubes in the solid content of the carbon nanotube dispersion liquid is 0.020% by mass or more and 0.250% by mass or less.

4. The carbon nanotube dispersion according to claim 1, wherein the carbon nanotubes are single-walled carbon nanotubes.

5. The carbon nanotube dispersion liquid according to claim 1, wherein the fluororesin is at least one selected from the group consisting of polytetrafluoroethylene, polychlorotrifluoroethylene, and a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene.

6. The carbon nanotube dispersion liquid according to claim 1, which is used for antistatic members.

7. A fluororesin composition obtained by removing the dispersion medium from the carbon nanotube dispersion liquid according to any one of claims 1 to 6.

8. A molded article obtained by molding the fluororesin composition according to claim 7.

9. A method for producing a fluororesin composition, comprising: forming a coating film by removing the dispersion medium from a carbon nanotube dispersion liquid containing carbon nanotubes, a fluororesin, and a dispersion medium; and determining a color difference ΔE according to the following formula (1). ＊ ab is calculated, and the obtained color difference ΔE ＊ The method for producing a fluororesin composition includes a color difference confirmation step of determining that the carbon nanotube dispersion is good when the value of ab is 16.0 or more, and if the result of the determination in the color difference confirmation step is "good", a fluororesin composition production step is carried out in which the dispersion medium is removed from the carbon nanotube dispersion and a fluororesin composition is produced. ＊ ab = [(ΔL ＊ ) ２ + (Δa ＊ ) ２ + (Δb ＊ ) ２ ] １／２ ... (1) (where ΔL ＊ , Δa ＊ , and Δb ＊ are values measured in accordance with JIS K 5600-4.)

Images