Carbon nanofiber-containing composition and molded article containing the carbon nanofiber-containing composition

Abstract

To provide a carbon nanofiber group having a large aspect ratio and with size and distribution specified, and a carbon nanofiber-containing composition in which the carbon nanofibers are contained in a base resin with good dispersibility, and provide a composition in which the carbon nanofibers are dispersed well in a base material at a higher concentration than conventional products, or a molded article or coating material having the composition.SOLUTION: Provided is a method for producing a carbon nanofiber-containing composition, wherein the base material contains a group of carbon nanofibers obtained by using pitch-based carbon fibers as a raw material, subjecting the raw material to dry grinding followed by wet grinding, the group of carbon nanofibers having a diameter in the range of 30 nm or more and 1000 nm or less, and a length in the range of 0.2 μm or more and 70 μm or less, with 50% or more of the total number distributed within said ranges, the method being characterized in that the content of a sizing agent in the group of carbon nanofibers is 0.1 mass% or less.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a composition in which a base material contains "a group of carbon nanofibers containing carbon nanofibers having a specific shape," and to a molded body or paint comprising the carbon nanofiber-containing composition. [Background technology]

[0002] Carbon fiber and carbon fiber reinforced plastics (CFRP) are lightweight and have both strength and flexibility, making them widely used in various molded products as a substitute for metals. The shortest carbon fibers are also called milled fibers, and generally have an average fiber length of 70 μm to 200 μm and an average fiber diameter of approximately 3 μm to 10 μm (3,000 nm to 10,000 nm). Because of their small size, they are often used as abrasives, reinforcing agents, and auxiliary materials.

[0003] Chopped fibers and long fibers, which have a longer average fiber length than milled fibers, are primarily used in molded products such as prepregs and forged products. In addition, fine CFRP made by further pulverizing milled fibers to shorten the fiber length is used as a reinforcement material for concrete, for example. However, the shorter the particle size, the more difficult it is to process, and the more likely it is to aggregate after being pulverized. Therefore, at present, there is little value in using such particles in fields where good dispersion is required.

[0004] If we define carbon fibers simply by their shape (size), without considering the actual dispersion of carbon fibers (the presence of individual fibers) or the utility value of the carbon fibers, the currently known general definitions are "carbon fibers defined as having a diameter of 3 μm to 10 μm and a length of 500 μm to 10,000 μm," "carbon nanofibers having a diameter of 50 nm to 1,000 nm and a length of 0.2 μm to 200 μm," and "carbon nanotubes having a diameter of 0.4 nm to 100 nm and a length of 50 nm to 20,000 nm."

[0005] Although there are documents that describe the diameter and aspect ratio of carbon fibers (for example, Patent Documents 1 and 2), currently, there are almost no carbon fiber groups of carbon nanofibers that have a small shape (size) like that of the present invention, have a particularly large aspect ratio, and are in a state where they can be isolated (separated) approximately one by one, or are in a state where they can be dispersed (dispersed) approximately one by one. Currently, there are almost no carbon nanofibers with a good shape (size) as defined above, and the utilization rate of carbon fibers of this carbon nanofiber size is extremely low due to poor dispersibility or redispersibility, etc.

[0006] Furthermore, nano-sized carbon fibers with large aspect ratios that are dispersed or in a dispersible state are not available on the market (at least commercially). The reason for this is thought to be that when the raw carbon fibers are crushed, they are specifically split cleanly vertically, in other words, the raw filaments cannot be suitably peeled off from the filaments. Therefore, there is no known dispersion in which "carbon fibers such as carbon nanofibers" having a large aspect ratio as in the present invention are stably dispersed.

[0007] Carbon nanofibers have a large aspect ratio and are dispersible and stable in dispersion. Although there are a wide variety of potential applications (applications), such as incorporating them into base materials such as resins, such as thermoplastic resins and thermosetting resins, and inorganic materials, such as glass, metals, and alloys, to produce carbon nanofiber-containing compositions or molded bodies, no satisfactory results have been achieved to date. In particular, it has not been possible to disperse carbon nanofibers in large amounts in a base material due to the poor dispersibility of the carbon nanofibers.

[0008] There is a strong demand for carbon nanofiber-containing compositions that are excellent in dynamic (mechanical) properties, thermal and electrical properties, etc., as well as molded articles and paints containing the same. However, at present, due to the poor dispersibility of carbon nanofiber groups themselves and the fact that they cannot be "incorporated into a base material at a high concentration" caused by this poor dispersibility, the above-mentioned compositions, molded bodies, paints, etc. have not yet been realized, and there is still room for development. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-188790 [Patent Document 2] Japanese Patent Application Publication No. 2017-066546 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made in view of the above-mentioned background art, and its object is to develop a group of carbon nanofibers that have a large aspect ratio and furthermore, a specified size and distribution, and to provide a carbon nanofiber-containing composition in which the carbon nanofibers are contained with good dispersibility in a base resin. Another object of the present invention is to provide a composition in which the carbon nanofibers are well dispersed in a base material at a higher concentration than in conventional products, or a molded article or paint containing the composition. [Means for solving the problem]

[0011] As a result of extensive research to solve the above-mentioned problems, the inventors have found that only by using specific carbon fibers as raw materials and performing dry grinding followed by wet grinding can carbon nanofibers with specified sizes and distribution be made into a state in which they can be isolated approximately individually, or a group of carbon nanofibers in a dispersed or dispersible state in which they are approximately individually dispersed can be obtained.

[0012] Furthermore, the present inventors have discovered that by using the carbon nanofiber group, it is possible to unexpectedly incorporate the carbon nanofiber group into a base material at a concentration that has never been achieved before, and that, at least due to this "high concentration inclusion," the various performance properties of the resulting carbon nanofiber-containing composition can be improved to a degree never before achieved, which has led to the completion of the present invention.

[0013] That is, the present invention provides a carbon nanofiber-containing composition characterized by comprising a base material containing "a group of carbon nanofibers having a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less, with 50% or more by number of the total carbon nanofibers being distributed" obtained by dry-pulverizing pitch-based carbon fibers and then wet-pulverizing the fibers.

[0014] The present invention also provides the carbon nanofiber-containing composition, wherein the number average aspect ratio of the carbon nanofibers contained in the carbon nanofiber group is 3 or more and 200 or less.

[0015] The present invention also provides the carbon nanofiber-containing composition, wherein the carbon nanofibers contained in the carbon nanofiber group have a number average diameter of 30 nm or more and 1000 nm or less and a number average length of 0.2 μm or more and 70 μm or less.

[0016] The present invention also provides the carbon nanofiber-containing composition, in which the number average thickness or number average thickness of the elementary filaments constituting the "filaments possessed by the pitch-based carbon fiber as the raw material" is 10 nm or more and 200 nm or less.

[0017] The present invention also provides the carbon nanofiber-containing composition, in which the carbon nanofibers of the carbon nanofiber group are constituted by an aggregation of 2 to 20 elementary filaments that constitute "the filaments possessed by the pitch-based carbon fiber that is the raw material."

[0018] The present invention also provides the carbon nanofiber-containing composition, wherein the pitch-based carbon fiber as a raw material is a mesophase pitch-based carbon fiber.

[0019] The present invention also provides the carbon nanofiber-containing composition, wherein the mesophase pitch-based carbon fibers used as raw materials are random mesophase pitch-based carbon fibers.

[0020] The present invention also provides the carbon nanofiber-containing composition, wherein the carbon nanofiber group containing "carbon nanofibers substantially free of mixed resins" is contained in a base material.

[0021] The present invention also provides the carbon nanofiber-containing composition, in which "a group of carbon nanofibers from which the mixed resin present in the raw material has been removed by carrying out a heat treatment between the dry grinding and the wet grinding" is contained in a base material.

[0022] The present invention also provides the carbon nanofiber-containing composition, in which the carbon nanofiber groups are contained in a dispersed state in an amount of 25 mass % or more of the total.

[0023] The present invention also provides the carbon nanofiber-containing composition, in which the carbon nanofiber groups are dispersed in an amount of 45 mass% or more of the total, and which has a thermal conductivity of 1.0 [W / (m·K)] or more.

[0024] The present invention also provides the carbon nanofiber-containing composition, wherein the base material is a polyalkylene or epoxy resin, the carbon nanofiber groups are contained in a dispersed state at 30 mass% or more of the total, and the flexural modulus is 7 GPa or more.

[0025] The present invention also provides the carbon nanofiber-containing composition, wherein the base material is a polyalkylene or epoxy resin, the carbon nanofiber groups are contained in a dispersed state at 30 mass% or more of the total, and the bending strength is 70 MPa or more.

[0026] The present invention also provides a carbon nanofiber composite material containing the carbon nanofiber group and having a surface resistivity of 1.0×10 3 The present invention provides the carbon nanofiber-containing composition having a surface roughness of [Ω / □] or less.

[0027] The present invention also provides the carbon nanofiber-containing composition described above, which contains the carbon nanofiber groups and has a volume resistivity of 1.0 [Ω·cm] or less.

[0028] The present invention also provides a molded article comprising the above-mentioned carbon nanofiber-containing composition.

[0029] The present invention also provides a paint comprising the above carbon nanofiber-containing composition. [Effects of the Invention]

[0030] The carbon nanofiber-containing composition of the present invention solves the above-mentioned problems and issues, and carbon nanofibers with a large aspect ratio, such as a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less, can be isolated approximately individually or can be dispersed or made dispersible approximately individually.

[0031] Carbon nanofibers are what we commonly know as carbon fibers in the broad sense, with multiple fibers tightly bound to their surroundings to form a single unit. Conventionally, it has not been possible to produce carbon nanofibers by separating or peeling them while maintaining a high aspect ratio. In other words, current technology has not been able to produce carbon nanofibers by pulverization or other methods while maintaining a high aspect ratio, and to make them reproducibly and stably isolable (separable) or (re)dispersible without causing aggregation.

[0032] The "carbon nanofiber-containing composition of the present invention in which the carbon nanofibers of the present invention are dispersed in a base material" of the present invention has various excellent properties due to the good dispersion state. For example, it can be dispersed at a high concentration in the base material while maintaining a good dispersion state.

[0033] In the present invention, "good dispersion" means that thermal properties such as thermal conductivity; mechanical properties such as flexural modulus and flexural strength; electrical properties such as surface resistivity and volume resistivity; etc., are shifted in the direction that occurs when dispersibility is good, and means that the above properties are improved. Furthermore, since it is impossible to define the dispersion state from its form (shape) or to directly define the dispersion state using parameters, it can only be specified by the "physical properties of the composition in which carbon nanofibers are dispersed in a base resin."

[0034] In the carbon nanofiber-containing composition of the present invention, the "carbon nanofiber group of the present invention" can be incorporated into the base resin with good dispersion and at a high concentration, thereby obtaining a novel carbon nanofiber-containing composition with a high concentration dispersion that has never been seen before. The fact that the "high content with good dispersion" of the present invention is novel is evident from the fact that the above physical properties are superior to anything ever seen before.

[0035] Molded bodies that simply contain high concentrations of carbon fibers, i.e., "carbon fibers that are not the carbon nanofibers of the present invention," in a base material do not achieve the excellent thermal properties of the present invention, such as high thermal conductivity [W / (m·K)] and high heat resistance; excellent mechanical properties, such as high flexural modulus [GPa]; and excellent electrical properties, such as low surface resistivity [Ω / □] and volume resistivity [Ω·cm].

[0036] In the present invention, specific carbon fibers are used as raw materials, and by dry-pulverizing and then wet-pulverizing, a group of carbon nanofibers with specific sizes and distributions can be obtained. Molded bodies and paints containing these dispersed carbon nanofibers can contain the dispersed carbon nanofibers at high concentrations, and the various excellent properties described above can be obtained.

[0037] Furthermore, by further limiting the type of carbon fiber used as the raw material, further limiting the dry grinding method and / or the wet grinding method, or further limiting the manufacturing method by adding a manufacturing step, the dispersibility of the carbon nanofiber group can be further increased, and the carbon nanofiber group can be dispersed in the base material at an even higher concentration, thereby improving the various properties described above.

[0038] The carbon nanofiber-containing composition of the present invention is also useful when incorporated into a base material such as a base resin and used as a matrix (resin) for fiber-reinforced plastics. [Brief explanation of the drawings]

[0039] [Figure 1] Scanning electron microscope (SEM) photographs of the cross section of pitch-based carbon fiber, the raw material before grinding. (Left) Radial mesophase pitch-based carbon fiber, (center) Random mesophase pitch-based carbon fiber, (right) Onion mesophase pitch-based carbon fiber [Figure 2]Schematic diagrams of cross sections of pitch-based carbon fibers. (a) (a') Random mesophase pitch-based carbon fiber (b) Radial mesophase pitch-based carbon fiber (c) Onion mesophase pitch-based carbon fiber [Figure 3] 1 is a scanning electron microscope (SEM) photograph of the cross section of a single random mesophase pitch-based carbon fiber that is preferably used as a raw material. [Figure 4] These are scanning electron microscope (SEM) photographs of random mesophase pitch-based carbon fibers (before grinding), which are preferably used as raw materials. (a) 400x magnification (b) 1300x magnification [Figure 5] 1A and 1B are scanning electron microscope (SEM) photographs of carbon fibers after dry grinding in the present invention. (a) 600x magnification (b) 1500x magnification [Figure 6] 1 is a 700x optical microscope (biological microscope) photograph showing the wet grinding process in the present invention (reference drawing). [Figure 7] 1A and 1B are scanning electron microscope (SEM) photographs of the present invention after wet grinding. (a) 1500x magnification (b) 6500x magnification [Figure 8] FIG. 1 is a schematic diagram showing a manufacturing process for filaments of (random type) mesophase pitch-based carbon fibers that are preferably used as a raw material. [Figure 9] FIG. 1 is a schematic diagram showing an example of an apparatus used for dry grinding in the present invention. [Figure 10] 1 is a graph showing the carbon nanofiber concentration dependency of the thermal conductivity [W / (m·K)] of a molded article in which carbon nanofiber groups are dispersed according to the present invention. [Figure 11] 1 is a graph showing the carbon material concentration dependency of the flexural modulus [GPa] of a molded body in which a total of four types of carbon materials (carbonaceous substances) including carbon nanofiber groups according to the present invention are dispersed. [Figure 12] 1 is a graph showing the carbon material concentration dependency of the bending strength [MPa] of a molded body in which a total of four types of carbon materials (carbonaceous substances) including carbon nanofiber groups according to the present invention are dispersed. [Figure 13]1 is a graph showing the carbon nanofiber concentration dependency of the surface resistivity [Ω / □] of a coating material in which carbon nanofiber groups are dispersed according to the present invention. [Figure 14] 1 is a graph showing the carbon nanofiber concentration dependency of the volume resistivity [Ω·cm] of a coating material in which carbon nanofiber groups are dispersed according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0040] The present invention will be described below, but the present invention is not limited to the specific embodiments below and can be modified as desired within the scope of the technical concept.

[0041] The carbon nanofiber-containing composition of the present invention is characterized in that it contains, in a base material, "a group of carbon nanofibers having a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less, with 50% or more by number of the total distributed within this range," which is obtained by dry-pulverizing pitch-based carbon fibers and then wet-pulverizing them.

[0042] <Carbon nanofiber(s)> In the present invention, the term "carbon fiber" refers to any long and thin carbonaceous material (carbon material) having a graphene structure, and includes carbon fiber, carbon nanofiber, and carbonaceous materials (carbon materials) of similar size, etc. Furthermore, the term "carbon fiber" also includes filaments of carbonaceous materials (carbon materials) having a graphene structure, elementary filaments constituting such filaments, and strands formed by vertically arranging such filaments.

[0043] The carbon nanofiber groups in the present invention have a diameter of 30 nm or more and 1000 nm or less, and 50% or more by number of the entire carbon nanofiber groups are distributed in the range of a length of 0.2 μm or more and 70 μm or less. It is essential that 50% or more of the total particles are distributed within the above range, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, particularly preferably 95% or more, and most preferably 98% or more. According to the present invention, particles with the above-mentioned percentage or more can be produced, and therefore, in consideration of dispersibility and the properties of the molded body and coating material containing the particles, the sharper the distribution, the better, but a broader distribution is acceptable in consideration of productivity, etc.

[0044] The diameter of the carbon nanofibers is 30 nm to 1000 nm, preferably 50 nm to 900 nm, more preferably 100 nm to 850 nm, and particularly preferably 300 nm to 800 nm. According to the present invention, carbon nanofibers with diameters in the above range can be produced with good yield. If the diameter is too small, it may be difficult to manufacture, or the length may be too short, resulting in a small aspect ratio, etc. On the other hand, if the diameter is too large, the performance may be poor in the intended use, or the applications of the carbon nanofiber group may be limited.

[0045] The length of the carbon nanofiber is 0.2 μm to 70 μm, more preferably 1 μm to 50 μm, even more preferably 2 μm to 30 μm, and particularly preferably 5 μm to 20 μm. According to the present invention, carbon nanofibers having a length within the above range can be produced with good yield. If the length is too short, the aspect ratio may become small, the performance may be poor in the application (for example, molded body, paint, etc.), the use of the carbon nanofiber group may be limited, it may be difficult to prevent aggregation, etc. On the other hand, if the length is too long, the use of the carbon nanofiber group may be limited, it may be difficult to manufacture while maintaining a large aspect ratio, etc.

[0046] The isolable and dispersible carbon nanofibers produced by the present invention have a diameter and length within the above ranges (the above ranges are preferred), and are therefore characterized by a large aspect ratio. The number average aspect ratio of the carbon nanofibers is preferably 3 or more and 200 or less, more preferably 5 or more and 160 or less, even more preferably 7 or more and 130 or less, particularly preferably 15 or more and 100 or less, and most preferably 20 or more and 70 or less. If the number-average aspect ratio is too small, the performance of the carbon nanofibers may be poor or their applications may be limited (e.g., molded products, paints, etc.), whereas if the (number-average) aspect ratio is too large, manufacturing may be difficult.

[0047] When pitch-based carbon fibers are used as the raw material and dry-milled and then wet-milled, the raw carbon fibers are specifically and neatly split vertically during milling, in other words, the raw filaments can be suitably peeled off from the filaments without shortening their length too much. In the present invention, this has resulted in carbon nanofibers with a suitable aspect ratio that has never been seen before, and it is believed that the large aspect ratio and suitable size and shape have improved the physical properties of molded bodies and paints in which the obtained carbon nanofiber groups are dispersed.

[0048] The diameter and length of the carbon nanofibers contained in the carbon nanofiber group produced by the present invention are determined by randomly selecting 100 fibers, measuring the diameter and length of each fiber, and calculating the arithmetic mean using an optical microscope or a scanning electron microscope (SEM). The optical microscope is preferably equipped with a size measurement gauge to improve measurement accuracy and reduce measurement time. When measurement is difficult without increasing the magnification, a scanning electron microscope (SEM) (photograph) is used instead of an optical microscope. Since the carbon nanofibers produced by the present invention have a large aspect ratio, the diameter and length of each fiber are measured using a microscope rather than using a particle size distribution analyzer. This method is unavoidable because an automatic particle size distribution analyzer cannot adequately measure the diameter and length. In the present invention, size values ​​such as diameter, length, number average aspect ratio, etc. are defined as those measured as described above.

[0049] When the carbon nanofibers are contained or dispersed in a base material such as a base resin, they may be contained in the form of a solid (powder) or may be contained in the form of a dispersion liquid. When present in a solid (powder) form, the carbon nanofibers are in a state where they can be isolated individually or dispersed individually, as shown in Figure 7. When present in a dispersion liquid, the carbon nanofibers are in a dispersed state where they can be isolated individually. Note that the carbon nanofibers described below are not necessarily separable individually, but they may be dispersed individually. The carbon nanofibers in the present invention can be dispersed or in a dispersed state as described above.

[0050] <Production of carbon nanofibers> In the present invention, the carbon nanofibers having the above-described shape (diameter and length) and the carbon nanofiber group having the above-described distribution are obtained by at least dry pulverization followed by wet pulverization. Furthermore, by specifying the raw carbon fibers, the (re)dispersible carbon nanofiber group having the above-described shape and distribution can be obtained. It is also preferable to add other treatments (operations) as necessary before the dry milling, between or during the two types of milling, or after the wet milling. Furthermore, the dry milling and the wet milling may each be carried out in one stage or in two or more stages.

[0051] "Carbon nanofibers obtained by dry-pulverizing and then wet-pulverizing pitch-based carbon fibers as a raw material" can be dispersed at a high concentration in a base material such as a base resin, and a molded body or paint dispersed at such a high concentration has excellent physical properties as will be described later. However, a "more preferred manufacturing process" in the present invention is shown below. Regarding the manufacturing process, when the following treatments are performed, it is particularly preferable to perform them in the following order. Preparation of raw carbon fiber, pre-grinding, dry grinding, heat treatment, moistening treatment, wet grinding, anti-agglomeration treatment, water removal treatment.

[0052] Of the above, at least the preparation of specific raw carbon fibers, dry grinding, and wet grinding are essential, and if these are the case, the carbon nanofiber-containing composition of the present invention, and molded bodies or paints containing the same, etc. can be produced. Of the above, pre-grinding, heat treatment, wetting treatment, aggregation prevention treatment, and water removal treatment are not essential, but for good production, it is preferable to perform some or all of them as necessary. In particular, heat treatment is preferable when the raw material contains a resin such as a sizing material, but it does not have to be performed when the raw material has not been subjected to sizing treatment or the like. Each processing step will be explained below in the order of processing.

[0053] <<Raw carbon fiber>> In the present invention, it is essential to use pitch-based carbon fibers as the carbon fibers before pulverization (raw carbon fibers), but it is preferable to use mesophase pitch-based carbon fibers, and it is particularly preferable to use random mesophase pitch-based carbon fibers. With PAN-based carbon fibers, no matter what grinding method is used, it is not possible to obtain a group of carbon nanofibers with a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less, which have the high number-average aspect ratio described above.

[0054] Furthermore, even if pitch-based carbon fibers are used, it may be difficult to obtain carbon nanofibers having the above size, shape, and distribution when using isotropic pitch-based carbon fibers.

[0055] On the other hand, mesophase pitch-based carbon fibers are classified into at least radial type (Figure 1 (left), Figure 2 (b)), random type (Figure 1 (center), Figure 2 (a) (a'), Figure 3), and onion type (Figure 1 (right), Figure 2 (c)) based on their cross-sectional shape (i.e., internal shape). "Random type" refers to fibers whose cross sections are random. This is why they are called random type.

[0056] In the present invention, even if mesophase pitch-based carbon fibers are used, it may be somewhat difficult to obtain carbon nanofibers having the above size, shape, and distribution when using radial mesophase pitch-based carbon fibers or onion mesophase pitch-based carbon fibers. When radial or onion type carbon fibers are used as raw materials, it may not be possible to obtain the above-mentioned shape, form, and distribution, and in particular, it may not be possible to obtain carbon nanofibers with a large number average aspect ratio (for example, only carbon nanofibers with a number average aspect ratio of less than 3 may be obtained).

[0057] The "filaments constituting the random mesophase pitch carbon fiber" are made up of rod-shaped or even smaller plate-shaped (sheet-shaped) filaments. For example, in Figure 3, plate-shaped (sheet-shaped) filaments are assembled vertically. In this specification, the "smaller rod-shaped or plate-shaped (sheet-shaped) objects" that make up the filaments are abbreviated as "elementary filaments." It is thought that within one elementary filament, graphene structures with condensed benzene rings are stacked together facing the same direction, or one or more carbon nanotubes are bundled together facing the same direction.

[0058] In the present invention, the carbon fiber used as the raw material has a number average thickness or number average thickness of the elementary filaments constituting the filament of preferably 10 nm or more and 200 nm or less, more preferably 15 nm or more and 150 nm or less, even more preferably 20 nm or more and 100 nm or less, and particularly preferably 30 nm or more and 70 nm or less. When the size of the raw carbon fiber filaments is equal to or greater than the lower limit, the thermal conductivity [W / (m·K)] of the filaments containing the raw carbon fiber filaments increases sharply, and therefore the "various thermal properties, including the thermal conductivity" of the carbon nanofibers containing the raw filaments (or molded articles, paints, etc. containing the carbon nanofibers) also improve. On the other hand, when the content is equal to or less than the upper limit, it is easy to prepare "filaments or carbon fibers" containing such elemental filaments as raw materials.

[0059] Figure 8 shows an outline of the manufacturing process for mesophase pitch-based carbon fiber filaments 10. Random mesophase pitch-based carbon fibers 1 can also be obtained by adjusting the spinning viscosity, nozzle shape, flow state of the raw material pitch, etc. in Figure 8. The manufacturing process for mesophase pitch-based carbon fiber does not include a drawing process. The microstructure controlled in the spinning process is almost directly transferred to the crystalline structure of the filament 10, creating boundaries where the orientation of the crystalline structure differs, resulting in the appearance (existence) of the raw filament 20.

[0060] In Figure 8, the thickness of the raw material filament 10 is usually 4000 nm to 10000 nm, and often 5000 nm to 7000 nm. On the other hand, the number average thickness or number average thickness of the element filaments 20 in the raw material carbon fiber filament 10 in the present invention is preferably 10 nm or more and 200 nm or less, more preferably 15 nm or more and 100 nm or less. Therefore, in the raw material carbon fiber, one filament 10 usually contains 40 to 700 element filaments 20, and in most cases 60 to 400 element filaments 20. When one elementary filament 20 is divided (defined) at a boundary where the orientation of the crystal structure is different, the above number of elementary filaments 20 are bundled together to form one filament 10. In Figure 8, for ease of viewing, the schematic diagram is drawn as if one filament is made up of three elementary filaments when viewed from the front.

[0061] In the present invention, when random mesophase pitch carbon fibers are used as the raw material, the above-mentioned embodiment is particularly preferred, although there are no limitations thereon. The shape, distribution, etc. of the carbon nanofiber clusters in the present invention, as well as whether or not such carbon nanofiber clusters can be formed in the first place, are largely dependent on the type of carbon fiber used as the raw material.

[0062] <<<Relationship between the carbon nanofiber of the present invention and the original filament>>> The carbon nanofibers produced by the present invention are preferably composed of an aggregate of 2 to 20 "element filaments constituting the raw material filament," more preferably 3 to 16, and particularly preferably 4 to 12. The number of element filaments is the average value for each carbon nanofiber in the carbon nanofiber group. When producing carbon nanofibers, the crystallinity and external shape of the filaments may be slightly distorted, but this is included in the "number" mentioned above. Also, even if the filaments are originally plate-shaped, they become elongated after being crushed, and so the "number" is mentioned above.

[0063] <<Pre-grinding>> The carbon fibers used as raw materials may be in the form of chopped fibers or milled fibers, but chopped fibers are preferred. Milled fibers contain many short fibers with lengths of about 1 μm, so chopped fibers are preferred in order to obtain carbon nanofibers with a high aspect ratio. Milled fibers may contain many short fibers with lengths of about 1 μm, even if they are said to have an average length of 70 μm.

[0064] Although not limited, the carbon fiber raw material is preferably pre-pulverized to an average size of 1 mm to 15 mm, more preferably 2 mm to 10 mm, and particularly preferably 5 mm to 8 mm. For example, in the case of a long fiber bobbin type, pre-pulverization may be necessary. If the size is within the above range from the beginning, it is preferable not to perform pre-pulverization.

[0065] The grinding method for pre-grinding is not particularly limited, and any commercially available dry grinder can be used, for example, a cutter mill or the like.

[0066] <<Dry grinding>> The dry milling in the present invention is preferably airflow milling, cutter milling, or "milling in which both airflow milling and cutter milling are performed simultaneously." "Milling in which both airflow milling and cutter milling are performed simultaneously" means "milling that has both an airflow milling mechanism and function and a cutter milling mechanism and function simultaneously."

[0067] <<<Airflow grinding>>> Examples of airflow pulverization include pulverization using an airflow pulverizer such as a cyclone mill, or a jet mill. Airflow pulverization using a cyclone mill generates an airflow by rotating an impeller (rotating blades) and dry-pulverizes the object thrown into the airflow to produce fine particles, while airflow pulverization using a jet mill produces fine particles by colliding the object with a collision plate. In order to obtain carbon nanofiber groups of a predetermined shape by wet grinding, an airflow grinder or a grinder described below in <<Grinding that simultaneously performs both airflow grinding and cutter grinding>> that has a rotating body such as an impeller, rotor, blade, or rotary blade (such as a jet mill) is preferable as the "dry grinding before wet grinding."

[0068] As the cyclone mill, commercially available devices can also be suitably used, such as the Cyclone Mill manufactured by Shizuoka Seiki Co., Ltd., the Super Powder Mill manufactured by Nishimura Machinery Works, Ltd., the Tornado Mill manufactured by Sansho Industry Co., Ltd., and the Dream Mill manufactured by Furukawa Industrial Machinery Systems Co., Ltd.

[0069] The structure of the cyclone mill is not particularly limited, but it is particularly preferred that the cyclone mill has one or more impellers and crushes the materials to be crushed by mainly causing them to collide with each other using a swirling airflow generated by the impeller, as this makes it easier to achieve the effects of using the airflow crusher, and results in very little metal contamination.

[0070] Commercially available jet mills can also be used suitably, and examples of commercially available jet mills include those manufactured by Seishin Enterprise Co., Ltd., Hosokawa Micron Corporation, Nippon Pneumatic Co., Ltd., and Nisshin Engineering Inc.

[0071] <<<Cutter-type crushing>>> Examples of cutter-type pulverization include pulverization using a crusher mill, pin mill, cutter mill, hammer mill, axial flow mill, etc.

[0072] <<<Simultaneous airflow crushing and cutter crushing>>> As the dry pulverization in the present invention, pulverization in which both airflow pulverization and cutter pulverization are carried out simultaneously is particularly preferred. In particular, the dry pulverization in the present invention is preferably carried out using a dry pulverizer having a blade and capable of applying shear and impact, or a dry pulverizer that applies "shear and impact by a blade." A schematic diagram of an example of such a dry grinder is shown in FIG.

[0073] In the case of "total airflow mills that do not use impellers for pulverization" such as jet mills, cyclone mills, tornado mills, and Dream Mill (registered trademark), depending on the raw material, the diameter may become too small during the dry pulverization stage, resulting in an aspect ratio that is too small (resulting in a round shape) during the subsequent wet pulverization. Therefore, although not limited thereto, they may not be very suitable for pulverization performed before wet pulverization.

[0074] The ambient temperature or set temperature for dry grinding is not particularly limited and may be in accordance with the method of use of the equipment used, but is preferably 0°C or higher and 50°C or lower, and particularly preferably 5°C or higher and 35°C or lower. The impeller rotation speed may also be determined in accordance with the method of use of the device used, but is preferably 4,000 rpm or more and 20,000 rpm or less, and particularly preferably 8,000 rpm or more and 15,000 rpm or less.

[0075] Using the above-mentioned apparatus and the above-mentioned grinding method, the powder is dry-ground until the number average length is 100 μm or less, and then the powder is subjected to the next step. By dry-pulverizing the carbon nanofibers to a particle size of 100 μm or less and then wet-pulverizing the particles, the diameter, length, (number average) aspect ratio, shape distribution, etc. of the carbon nanofibers tend to fall within the required or preferred ranges described above.

[0076] By dry grinding, the number average length is preferably 100 μm or less, more preferably 5 μm to 70 μm, even more preferably 7 μm to 50 μm, and particularly preferably 10 μm to 40 μm. If the number average length after dry pulverization is too long, it may be difficult to achieve a final diameter and length of the carbon nanofiber within the above-mentioned ranges in the subsequent wet pulverization step, even if the wet pulverization conditions are adjusted. On the other hand, if the length after dry pulverization is too short, the length of the carbon nanofibers after wet pulverization cannot be longer, and it may be difficult to achieve the final length and number average aspect ratio of the carbon nanofibers within the above-mentioned preferred ranges. In particular, the aspect ratio of the carbon nanofibers finally obtained may be too small.

[0077] Regarding the number average diameter after dry pulverization, it is difficult to reduce it by dry pulverization alone, that is, it is difficult to pulverize so as to increase the aspect ratio. Furthermore, if the diameter is forcibly reduced by dry pulverization, the length also becomes shorter, making it difficult for the final aspect ratio after wet pulverization to fall within a suitable range. The diameter after dry pulverization is preferably 3000 nm or more, more preferably 5000 nm to 15000 nm, and particularly preferably 7000 nm to 12000 nm. It is desirable to carry out dry pulverization so that the diameter falls within this range.

[0078] The number average aspect ratio after dry pulverization is not particularly limited, but is preferably 10 or less, more preferably 1.2 or more and 7 or less, and particularly preferably 1.5 or more and 5 or less. By dry pulverization, it is difficult to increase the number average aspect ratio above the upper limit, i.e., it is difficult to reduce the average fiber diameter to a degree that allows the number average aspect ratio to be increased above the upper limit. In the present invention, it has been found that, even if the number average length is set to preferably 100 μm or less and the diameter is set to a relatively large value and the number average aspect ratio is set to a relatively small value by dry pulverization, or by setting the number average length and the number average aspect ratio to a relatively large value, a group of carbon nanofibers having the above-mentioned suitable diameter, length and large number average aspect ratio can be finally obtained by subsequent wet pulverization.

[0079] <<Heat treatment>> The carbon nanofiber-containing composition of the present invention is preferably one in which the carbon nanofiber group containing "carbon nanofibers substantially free of mixed resins" is contained in a base material. Here, the mixed resin may be, for example, a case where a sizing agent or the like is contained in the carbon fiber as a raw material. That is, the mixed resin is not limited to, but may be, for example, a sizing agent or the like.

[0080] In the present invention, when a resin is mixed in the dry-pulverized product, it is preferable to remove the resin by carrying out a heat treatment. In other words, the carbon nanofiber-containing composition of the present invention is a base material containing "carbon nanofibers in a state in which the mixed resin mixed in the raw material has been removed by carrying out a heat treatment between the dry-pulverization and the wet-pulverization." If no resin such as a sizing agent is mixed in, the heat treatment can be omitted.

[0081] The heat treatment conditions are not limited, but for example, the material is heated at a furnace temperature of 320°C to 480°C for 5 to 15 minutes, and the resin content is reduced to preferably 0.1 mass % or less, particularly preferably 0.01 mass % or less. By carrying out the heat treatment, preferably after dry grinding and before wet grinding, the grinding and dispersion effects of the wetting agent or surfactant used in the subsequent wet treatment or wet grinding step (if wet treatment is performed) are improved.

[0082] <<Wet treatment>> Although not limited thereto, it is preferable to further carry out a wet treatment, and it is particularly preferable to carry out the wet treatment after dry grinding or heat treatment. The wet treatment is preferably carried out by immersing the product obtained above in an aqueous solution containing an anionic surfactant, a cationic surfactant, or an amphoteric surfactant, which can also be suitably used in the subsequent wet grinding.

[0083] The anionic surfactant is preferably a polymeric anionic surfactant ("polymer" also includes oligomers), and more preferably an alkali metal salt, ammonium salt, alkylammonium salt, alkylolammonium salt, or the like, of a (co)polymer having an acid group. The above-mentioned anionic surfactants may be used alone or in combination of two or more kinds.

[0084] The "acid group-containing (co)polymer" is particularly preferably at least one (co)polymer selected from the group consisting of (co)polymers of (meth)acrylic acid, (co)polymers of (phthalic anhydride), (co)polymers of vinylbenzenesulfonic acid, and (co)condensates of naphthalenesulfonic acid. Here, the terms "(co)", "(meth)", and "(anhydride)" refer to both the presence and absence of parentheses. The copolymerizable monomer in the copolymer is not particularly limited, but examples include (meth)acrylic acid alkyl esters, (meth)acrylic acid hydroxyalkyl esters, styrene, and vinyl acetate. Examples of the (co)condensation product of naphthalenesulfonic acid include those in which the rings are bonded with an aldehyde such as formaldehyde. In the case of the co-condensation product, examples of the co-condensation monomer include phenol, cresol, naphthol, etc.

[0085] The cationic surfactant is preferably a surfactant in which quaternary ammonium is a hydrophilic group, and the substituent on the "N+" of the quaternary ammonium is not particularly limited, but is preferably an alkyl group (which may have a substituent), such as a stearyl group, palmityl group, dodecyl group, methyl group, benzyl group, or butyl group. Furthermore, a long-chain alkyl group having preferably 6 or more carbon atoms, particularly preferably 12 or more carbon atoms, is desirable. The counter anion is not particularly limited, but halogen ions such as chloride ion and bromide ion are particularly preferred.

[0086] Examples of amphoteric surfactants include alkyl betaine type, fatty acid amidopropyl betaine type, alkyl imidazole type, amino acid type, and amine oxide type.

[0087] Among these, it is preferable to use an anionic surfactant or an amphoteric surfactant. The surfactant content and the carbon fiber content (after dry pulverization) in the aqueous dispersion medium are the same as the numerical ranges for <wet pulverization> described below.

[0088] The use of a surfactant, and in particular the use of the above-mentioned preferred anionic or amphoteric surfactant, has the effect of unraveling the carbon fibers vertically, allowing the diameter to be reduced while maintaining a long length, thereby producing carbon nanofiber(s) with a large average aspect ratio.

[0089] <<Wet grinding>> In the present invention, it is essential to carry out wet milling after dry milling. The wet milling is not particularly limited, but is preferably bead mill milling or ball mill milling. Bead mill milling or ball mill milling carried out in an aqueous medium in the presence of a surfactant is particularly preferred. Between the dry milling and the wet milling, the above-mentioned "other treatments" such as heat treatment and wet treatment may be performed. Examples of the "other treatments" include premixing and preliminarily preparing a liquid.

[0090] The surfactant may be any of those described in the <Wetting Treatment> section above, whether or not the wetting treatment has been performed. The same surfactants are also preferred. That is, the anionic surfactants, cationic surfactants, and amphoteric surfactants described in the section on <Wet Treatment> are preferred. The surfactant used in the wet treatment may be used as is in the wet grinding, or a new surfactant may be added or a different surfactant from that used in the wet treatment may be added during the wet grinding.

[0091] The amount of surfactant used is not particularly limited and may not be used, but is preferably 30 parts by mass or less (when two or more surfactants are used in combination, the total amount) relative to 100 parts by mass of the carbon fibers (carbon nanofibers in the process of being ground) to be ground and dispersed, more preferably 0.1 to 20 parts by mass, and particularly preferably 0.5 to 10 parts by mass. If too much surfactant is used, the carbon fibers may aggregate as they dissolve vertically, resulting in a dispersion of aggregated carbon nanofibers, which may affect the physical properties of the resulting product when applied to an object.

[0092] When wet treatment is carried out, a new surfactant may be added during wet pulverization, or the surfactant that was blended during wet treatment may be used as is. When a surfactant is newly added during wet grinding, it may be the same as or different from the surfactant used in the wet treatment.

[0093] <<<Wet grinding method, equipment and conditions>>> Only by carrying out wet pulverization can a group of carbon nanofibers having the specific shape (diameter, length, aspect ratio) and particle size distribution as described above be produced. The wet pulverization conditions are adjusted so as to obtain carbon nanofibers (groups) having the above-mentioned specific shape (diameter, length, aspect ratio) of the present invention.

[0094] Preferred materials for the grinding media used in wet grinding include glass, alumina, zircon (zirconia-silica ceramics), zirconia, metal (steel), and the like.

[0095] Taking a bead mill as an example, the diameter of the beads used is preferably 0.1 mm or more and 3 mm or less, more preferably 0.2 mm or more and 2 mm or less, and particularly preferably 0.3 mm or more and 1 mm or less. If the bead diameter is too large, the number of beads in the bead mill container will decrease, which will reduce the number of contact points, making it impossible to properly grind and disperse the material, or to grind the material to a sufficiently small diameter.On the other hand, if the bead diameter is too small, it may not be possible to properly grind and disperse the material, or grinding may take too long.

[0096] The bead filling rate used in the bead mill is preferably 45% or more and 90% or less, more preferably 55% or more and 87% or less, and particularly preferably 65% ​​or more and 85% or less. If the bead filling rate is too low, the carbon fibers are less likely to split longitudinally, making it difficult to produce carbon nanofibers with a large aspect ratio. On the other hand, if the bead filling rate is too high, it may become difficult for the stirring blades of the bead mill to rotate.

[0097] The carbon fiber content after dry milling is preferably 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, and particularly preferably 5% by mass or more and 10% by mass or less, based on the entire slurry to be bead milled.

[0098] The shape of the stirring blade used in the bead mill treatment is not particularly limited. The rotation speed of the agitator varies depending on the width of the agitator and the capacity of the bead mill, but is preferably 600 rpm or more and 4500 rpm or less, more preferably 800 rpm or more and 4000 rpm or less, and particularly preferably 1000 rpm or more and 3500 rpm or less, calculated for a 2 L capacity. The peripheral speed of the tip of the agitator blade depends on the span of the blade, but is preferably within the range that can be calculated from the rotation speed above, assuming a diameter of 20 cm. Specifically, it is preferably 5 m / s or more and 40 m / s or less, more preferably 7 m / s or more and 30 m / s or less, and particularly preferably 9 m / s or more and 20 m / s or less.

[0099] The operation method of the bead mill for pulverization and dispersion may be either a circulation type or a batch type, but the circulation type is preferred. In the circulation type, the material is not transferred to a container as in the batch type, so aggregation does not progress. When using a circulation system, the degree of micronization varies depending on the number of passes. For example, if the residence time per pass is increased, the particle size distribution becomes sharper because there is no short pass of the processed material, but the aspect ratio of the carbon nanofibers also becomes smaller. Therefore, for example, when converted to 4 L, the bead mill treatment is performed by circulation for preferably 70 minutes to 270 minutes, more preferably 80 minutes to 230 minutes, and particularly preferably 90 minutes to 180 minutes.

[0100] The temperature in the wet treatment is preferably 0° C. or higher and 50° C. or lower, particularly preferably 5° C. or higher and 35° C. The bead mill may be of either a vertical or horizontal type. Commercially available bead mills can also be used, such as the Dynomill manufactured by Willy & Bachofen (WAB) and the bead mill manufactured by Netsch (USA).

[0101] The time per pass (continuous operation time), the number of passes, and the total time may depend on the equipment structure, slurry concentration, grinding and dispersion conditions, the type of surfactant, etc., so it is preferable to withdraw the material after each pass or during wet grinding and observe it one by one using a particle size distribution analyzer, an optical microscope, a scanning electron microscope (SEM), etc., and adjust the time as appropriate.

[0102] By using the above-mentioned "production method requiring dry milling and wet milling" and adjusting the milling conditions, etc. appropriately within the above-mentioned ranges, it is possible to obtain carbon nanofibers (groups) with diameters of 30 nm to 1000 nm and lengths of 0.2 μm to 70 μm. A group of carbon nanofibers can be obtained in which the carbon nanofibers are in a state where they can be isolated individually, or in a dispersed or dispersible state where they are individually dispersed. It is also possible to obtain carbon nanofibers (groups) with a number-average aspect ratio of 5 to 200. The present invention also relates to a group of carbon nanofibers produced by the above-mentioned method for producing a group of carbon nanofibers.

[0103] <<Anti-aggregation treatment>> After wet grinding, it is particularly preferable to carry out an anti-aggregation treatment, although this is not a limitation. Examples of the anti-agglomeration agent used in the anti-agglomeration treatment include, but are not limited to, metal-containing anti-agglomeration agents such as (composite) metal chelate compounds, (composite) metal oxide fine particles, metal-containing wax, and (composite) metal ion water; coblock polymers having polyester, polyacrylate, polyurethane, or the like as units; comb-type coblock polymers having such polymers as units; surfactants, etc. The anti-agglomeration treatment is preferably carried out by blending the anti-agglomeration agent. The agglomeration prevention treatment may be carried out immediately after the wet pulverization described above, or after the water removal treatment described below, or may be carried out at both stages.

[0104] When a metal-containing anti-aggregation agent such as those described above is used as the anti-aggregation agent used in the anti-aggregation treatment, a (composite) metal chelate compound is more preferred, and metal salts such as HEDTA, EDTA, PDTA, NTA, ethylenediamine, bipyridine, phenanthroline, and porphyrin are even more preferred. Among these, metal salts (of acetic acid derivatives) such as HEDTA (hydroxyethyl ethylene diamine triacetic acid), EDTA (ethylenediaminetetraacetic acid), PDTA (1,3-propanediamine tetraacetic acid), and NTA (nitrilo triacetic acid) are particularly preferred.

[0105] The surfactant used in the anti-aggregation treatment is preferably an anionic surfactant, a cationic surfactant, or an amphoteric surfactant, more preferably an anionic surfactant or an amphoteric surfactant. Specific, particularly preferred surfactants include, but are not limited to, those described above in the sections <Wet treatment> and <Wet grinding>.

[0106] The type of anti-aggregation agent, such as a metal-containing anti-aggregation agent, a surfactant used in the anti-aggregation treatment, or a coblock polymer, is determined taking into consideration the surface condition of the object to be prevented from aggregating immediately before the anti-aggregation treatment. When the type of anti-aggregation agent, such as a metal-containing anti-aggregation agent, surfactant, or coblock polymer, is as described above, aggregation is less likely to occur during the dispersing medium (water) removal treatment step and over time thereafter, and storage stability is improved.

[0107] The amount of "anti-agglomerating agent, such as a metal-containing anti-agglomerating agent (e.g., a (composite) metal chelate compound); a surfactant used in the anti-agglomerating treatment; or a coblock polymer" used is not particularly limited, but is preferably added in an amount of 0.1 mass% or less, more preferably 0.0001 mass% to 0.06 mass%, and particularly preferably 0.0002 mass% to 0.03 mass%, relative to the total amount of the slurry after wet grinding (when two or more anti-agglomerating agents are used in combination, the total amount).

[0108] Furthermore, the amount of the anti-aggregation agent used is not particularly limited, but is preferably added in an amount of 1 mass % or less, more preferably 0.001 mass % to 0.5 mass % or less, even more preferably 0.002 mass % to 0.3 mass % or less, and particularly preferably 0.003 mass % to 0.1 mass % or less, relative to the total amount of the object to be prevented from aggregating, such as carbon nanofiber groups (the total amount when two or more anti-aggregation agents are used in combination).

[0109] When the blending amount of the anti-aggregation agent, such as "a metal-containing anti-aggregation agent, a surfactant used in the anti-aggregation treatment, a coblock polymer, etc." is within the above range, aggregation is less likely to occur during the dispersing medium (water) removal treatment step and over time thereafter, and storage stability is improved.

[0110] The stirring during the aggregation prevention treatment is not particularly limited, but examples thereof include stirring with a hand mixer, etc. The stirring speed is not particularly limited, but is preferably 300 to 1200 rpm, and particularly preferably 500 to 1000 rpm. The temperature for the aggregation prevention treatment is not particularly limited, but is preferably 20°C to 100°C, more preferably 40°C to 90°C, and particularly preferably 60°C to 80°C.

[0111] <<Water removal treatment>> The present invention also relates to a group of carbon nanofibers produced by the above-mentioned method for producing a group of carbon nanofibers. That is, it may be a group of carbon nanofibers contained in a slurry after wet pulverization, a group of carbon nanofibers contained in a slurry after the above-mentioned anti-aggregation treatment, or a group of powdered carbon nanofibers after water has been removed from the slurry. The carbon nanofiber group in any of the above states can be used as a product (finished product) for various purposes.

[0112] The method for the water removal treatment is not particularly limited, and can be carried out by reducing pressure and / or increasing temperature. It is particularly preferred to semi-dry the mixture by a cyclone separation and recovery method, and then remove (dry) the water by reducing pressure and / or increasing temperature in an oven. The temperature for the water removal treatment is not particularly limited, but is preferably 40°C to 160°C, more preferably 55°C to 150°C, and particularly preferably 70°C to 130°C.

[0113] Furthermore, in order to remove surfactants and the like, it is also preferable to perform baking at, for example, 250° C. or higher and 400° C. or lower. The carbon nanofibers constituting the carbon nanofiber group produced by the production method of the present invention are preferably those having no dispersant or surfactant attached to their surface, since the carbon nanofibers themselves have good dispersibility.

[0114] It is also preferable to carry out the above-mentioned anti-aggregation treatment after the above-mentioned water removal treatment, that is, it is also preferable to blend the above-mentioned anti-aggregation agent and surfactant into the concentrated slurry or powder after the above-mentioned water removal treatment.

[0115] The powdered carbon nanofibers produced by the production method of the present invention (even if solidified) are easily dispersed and diffused without agglomeration in resin emulsions or resins themselves at the destination. Examples of such resins include thermoplastic resins and thermosetting resins, and in the case of thermosetting resins, they are well dispersed in both the base resin and the curing agent. Resin emulsions for use are not limited, but examples thereof include (meth)acrylic resins, styrene-maleic anhydride resins, and urethane resins, which have particularly good dispersibility. Preferred examples of thermoplastic resins and thermosetting resins include those described below.

[0116] <Carbon nanofiber dispersion> The carbon nanofiber dispersion containing the carbon nanofiber-containing composition has good dispersibility and can be made highly concentrated if necessary. The carbon nanofiber dispersion may be the slurry itself after the above-mentioned wet grinding or after the above-mentioned anti-aggregation treatment, or may be obtained by adding a new dispersion medium to the slurry or by replacing the dispersion medium with a new dispersion medium, or may be obtained by re-dispersing the carbon nanofiber powder after the above-mentioned water removal treatment.

[0117] The carbon nanofiber dispersion can also be applied in a dispersed state to a resin or resin emulsion at the intended use without causing aggregation.

[0118] <Carbon nanofiber-containing composition> As described above, the present invention allows specific carbon nanofibers to be incorporated into a base material at a high concentration, and therefore the present invention is also a carbon nanofiber-containing composition in which the carbon nanofiber groups are contained in a dispersed state at 25% by mass or more of the total. The present invention is more preferably a carbon nanofiber-containing composition in which the carbon nanofiber groups are contained in a dispersed state at 30% by mass or more of the total, more preferably 35% by mass or more of the total, and particularly preferably 40% by mass or more of the total. The composition itself, in which carbon nanofiber groups having the above-mentioned shape, size, and distribution are contained in the above-mentioned high concentration range and in a well-dispersed state, is novel.

[0119] In the carbon nanofiber-containing composition of the present invention, the base material is not particularly limited, and examples thereof include organic materials such as resins; and inorganic materials such as glass, metals, and alloys. A particularly preferred base material is a base resin, and examples of the base resin include thermoplastic resins and thermosetting resins.

[0120] The thermoplastic resin is particularly preferably one or more thermoplastic resins selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, thermoplastic polyurethane, polytetrafluoroethylene, acrylonitrile butadiene styrene resin, acrylonitrile styrene resin, (meth)acrylic resin, polyamide, polyacetal, polycarbonate, (modified) polyphenylene ether, polyester, cyclic polyolefin, polyphenylene sulfide, polytetrafluoroethylene, polysulfone, polyether sulfone, polyarylate, polyether ether ketone, thermoplastic polyimide, and polyamide imide.

[0121] The carbon nanofiber(s) of the present invention are suitably dispersed (especially at a high concentration) in a thermoplastic resin, and as described above, exhibit superior thermal, mechanical, and electrical effects compared to other carbon nanofiber(s).

[0122] The thermosetting resin is particularly preferably one or more thermosetting resins selected from the group consisting of phenolic resins, epoxy resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, thermosetting polyurethanes, and thermosetting polyimides.

[0123] The carbon nanofiber(s) of the present invention are suitably dispersed (especially at a high concentration) in the base resin (containing unreacted resin having functional groups) of a thermosetting resin and / or the curing agent (which crosslinks, reacts, and polymerizes the functional groups), and exhibit the above-mentioned superior thermal, mechanical, and electrical effects compared to other carbon nanofiber(s).

[0124] <Other ingredients> The carbon nanofiber-containing composition of the present invention and a molded body or paint comprising the "carbon nanofiber-containing composition of the present invention" may contain "other components" as needed, as long as the effects of the present invention can be obtained. Examples of the "other components" include colorants such as inorganic pigments and organic dyes; antioxidants; crystallization modifiers such as nucleating agents; release agents such as wax; lubricants; antistatic agents; light stabilizers; ultraviolet absorbers; particles such as inorganic fillers and organic fillers; processing aids for each base material; flame retardants; plasticizers, etc. These "other components" may be used alone or in combination of two or more. The content thereof may be determined appropriately.

[0125] <Molded objects, paints, etc.> The carbon nanofiber-containing composition of the present invention is not limited, but is preferably the carbon nanofiber-containing resin of the present invention. Furthermore, molded articles comprising the carbon nanofiber-containing composition of the present invention are suitable for use in a variety of fields. The coating film (comprising the carbon nanofiber-containing composition of the present invention) is also conceptually included in the molded article (of the present invention). Furthermore, the carbon nanofibers obtained by the present invention and the carbon nanofiber-containing composition of the present invention can be impregnated or penetrated into the mesh of a fabric (sheet) woven or knitted from carbon fibers, glass fibers, organic fibers, etc., and used in the form of a molded product called fiber reinforced plastics (FRP).

[0126] The method for producing a molded body is not particularly limited, and examples thereof include injection molding, extrusion molding, blow (air) molding, vacuum molding, pressure molding, roll molding, cast molding, compression molding, coating and drying of a paint, impregnation, etc. If necessary, the composition can be kneaded using a kneader, mixer, etc. before molding.

[0127] Furthermore, the method for producing the paint is not particularly limited, but the paint can be obtained by placing a carbon nanofiber-containing composition (carbon nanofiber groups, a base material such as a base resin, and, if necessary, "other components") in a container and mixing, stirring, and dispersing the composition in a solvent (dispersion medium) using a stirrer or the like.

[0128] The following describes a particularly preferred embodiment of the carbon nanofiber-containing composition of the present invention and a molded article or coating material containing the same, in which the concentration and physical properties are specified, which particularly significantly exhibits the above-described effects of the present invention. This embodiment was first achieved in the present invention. In the case of a paint, the content of carbon nanofiber groups relative to the entire composition is not the content relative to the entire paint, but the content relative to the entire solid content in the paint, i.e., the content relative to the entire coating film (molded body) formed by the paint.

[0129] <<Carbon nanofiber-containing composition with excellent thermal properties>> A preferred embodiment of the composition of the present invention is the carbon nanofiber-containing composition, in which the carbon nanofiber groups are contained in a dispersed state in an amount of 45 mass% or more of the total, and which has a thermal conductivity of 1.0 [W / (m·K)] or more.

[0130] The carbon nanofiber groups are preferably dispersed in the base material at a content of 45% by mass or more relative to the entire carbon nanofiber-containing composition, more preferably 45% by mass or more and 90% by mass or less, even more preferably 50% by mass or more and 85% by mass or less, and particularly preferably 55% by mass or more and 80% by mass or less.

[0131] The base material to be dispersed is not particularly limited, but examples include resins such as the thermoplastic resins and thermosetting resins mentioned above. When the base material is a resin, the thermal conductivity does not depend much on the type of resin, so the physical property of "thermal conductivity of 1.0 [W / (m·K)] or more" does not particularly depend on the resin that is the base material.

[0132] The carbon nanofiber-containing composition of the present invention is a carbon nanofiber-containing composition with high thermal conductivity. The carbon nanofiber-containing composition of the present invention is preferably dispersed in the base resin at the above content and has a thermal conductivity of 1.0 [W / (m·K)] or more. The thermal conductivity is more preferably 3 [W / (m·K)] or more, even more preferably 10 [W / (m·K)] or more, particularly preferably 30 [W / (m·K)] or more, and most preferably 50 [W / (m·K)] or more.

[0133] When the base material is an organic material such as a resin, the thermal conductivity increases as the carbon nanofiber content increases. The carbon nanofibers in the present invention have good dispersibility in the base material, allowing the content to be increased, thereby increasing the thermal conductivity. If the dispersibility in the base material is poor, it is not said that the material is "contained in a dispersed state in the base material" as described above, but in that case the thermal conductivity will generally be low.

[0134] Furthermore, for example, when the base material is polyimide, "general carbon nanofibers defined as having a diameter of 50 nm to 1000 nm and a length of 0.2 μm to 200 μm" cannot be incorporated into polyimide at high concentrations while maintaining good dispersion (none have been incorporated). In the past, even if the carbon nanofiber content was 45 mass % or more, the above-mentioned high thermal conductivity could not be achieved. In particular, in the case of the "group of carbon nanofibers in which 50 number % or more of the total carbon nanofibers have a length of 70 μm or less" of the present invention and the "group of carbon nanofibers with a number average length of 70 μm or less," the thermal conductivity was even lower.

[0135] The catalog listing the physical properties of "Super Engineering Plastics AURUM (registered trademark)," a thermoplastic polyimide manufactured by Mitsui Chemicals, Inc., lists only one example of the thermal conductivity of a thermoplastic polyimide containing 30 mass% carbon fiber, which is 0.49 [W / (m·K)]. In the case of such a typical catalog value, the content is slightly low at 30 mass %, but the thermal conductivity is one order of magnitude smaller than that of the present invention.

[0136] Furthermore, Figure 4 of JP 2014-076750 A shows that the thermal conductivity of a composite material with a polyimide content of 80 mass % is 0.12 [W / (m·K)], but even at higher content rates, the thermal conductivity is about two orders of magnitude lower.

[0137] The carbon nanofiber-containing composition of the present invention has high thermal conductivity due to the good dispersibility of the contained carbon nanofibers. Furthermore, the good dispersibility of the carbon nanofibers allows them to be contained at a high concentration while maintaining good dispersion, which also increases thermal conductivity. As a result, the above-mentioned content and thermal conductivity have been achieved for the first time. The carbon nanofiber-containing composition with the above-mentioned content and thermal conductivity is a novel composition.

[0138] <<Carbon nanofiber-containing composition with excellent mechanical properties>> <<<Flexural modulus>>> A preferred embodiment of the composition of the present invention is the carbon nanofiber-containing composition in which the base material is a polyalkylene or epoxy resin, the carbon nanofiber groups are contained in a dispersed state at 30 mass% or more of the total, and the flexural modulus is 7 GPa or more.

[0139] That is, it is preferable that the carbon nanofiber group is dispersed in the base material at a content of 30% by mass or more relative to the entire carbon nanofiber-containing composition, more preferably 33% by mass or more and 75% by mass or less, even more preferably 36% by mass or more and 70% by mass or less, particularly preferably 40% by mass or more and 65% by mass or less, and most preferably 43% by mass or more and 60% by mass or less.

[0140] The flexural modulus depends on the type of base material, and in this case the base material is polyalkylene or epoxy resin. When the base material is polyalkylene, it is not possible to incorporate general carbon nanofibers into the base material at high concentrations while maintaining good dispersion (none have been incorporated). Conventionally, when the base material is polyalkylene, the carbon nanofibers have been contained in a dispersed state at less than 30 mass% of the entire composition. For example, according to Tables 6 and 8 of JP 2006-124454 A, although the average fiber length is longer than that of the carbon nanofibers of the present invention, only about 5% by mass of the carbon nanofibers can be blended into polypropylene (masterbatch concentration 30% by mass × masterbatch blending ratio 16.7% by mass = 5.0% by mass).

[0141] Furthermore, even when the base material is epoxy resin, it is not possible to disperse and incorporate general carbon nanofibers at high concentrations in a well-dispersed state, particularly at concentrations of 30 mass % or more. According to the present invention, the carbon nanofibers of the present invention are contained in the polyalkylene or epoxy resin at the above-mentioned high concentration while maintaining a well-dispersed state.

[0142] The polyalkylene used as the base material is not particularly limited, but examples thereof include polyethylene, polypropylene, polybutylene, etc. Copolymers thereof are also included. The molecular weight, stereoregularity, crystallinity, and 5 mol% or less of other copolymerized vinyl compounds of the polyalkylene are not particularly limited as long as they can contain 30 mass% or more of the carbon nanofiber group of the present invention in a dispersed state and have a flexural modulus of 7 GPa or more.

[0143] The epoxy resin used as the base material is not particularly limited, and examples thereof include a carbon nanofiber-containing composition (epoxy resin) made of a known main agent and curing agent, and a carbon nanofiber-containing composition (epoxy resin) obtained by curing the same.

[0144] The carbon nanofiber-containing composition of the present invention is a carbon nanofiber-containing composition having an extremely high flexural modulus. The carbon nanofiber-containing composition of the present invention is preferably dispersed in a polyalkylene or epoxy resin at the above-mentioned content, and has a flexural modulus of 7 GPa or more. The flexural modulus is more preferably 8.5 GPa or more, even more preferably 10 GPa or more, particularly preferably 11.5 GPa or more, and most preferably 13 GPa or more.

[0145] When the base material is a resin such as polyalkylene, the flexural modulus increases as the carbon nanofiber content increases. The carbon nanofibers in the present invention have good dispersibility in the base material, allowing the content to be increased, thereby increasing the flexural modulus. When the dispersibility in the base material is poor, it is not said that the material is "contained in a dispersed state in the base material" as described above, but in that case the flexural modulus will generally be low.

[0146] For example, according to Tables 7, 9, and 10 of JP 2006-124454 A, as mentioned above, only about 5% by mass of polypropylene can be blended (or not blended at all), and the flexural modulus is about 1.6 to 3.3 GPa (1600 to 3300 MPa), which is a fraction of the flexural modulus of the present invention.

[0147] The carbon nanofiber-containing composition of the present invention has a high flexural modulus due to the good dispersibility of the contained carbon nanofibers. Furthermore, the good dispersibility of the carbon nanofibers allows them to be contained at a high concentration while maintaining good dispersion, which also increases the flexural modulus. As a result, the above-mentioned content and flexural modulus have been achieved for the first time. A carbon nanofiber-containing composition with the above-mentioned content and flexural modulus, which uses a polyalkylene or epoxy resin as a base material, is a novel composition.

[0148] <<<Bending strength>>> A preferred embodiment of the composition of the present invention is the carbon nanofiber-containing composition, in which the base material is a polyalkylene or epoxy resin, the carbon nanofiber groups are contained in a dispersed state at 30 mass% or more of the total, and the bending strength is 70 MPa or more.

[0149] The content of the carbon nanofiber group relative to the entire carbon nanofiber-containing composition is the same as that of the flexural modulus, including the preferred range, particularly preferred range, etc. Conventionally, when the base material is a polyalkylene or epoxy resin, the carbon nanofibers have been contained in a dispersed state in an amount of less than 30 mass% relative to the entire composition.

[0150] The polyalkylene or epoxy resin used as the base material is similar to the flexural modulus described above. The molecular weight, stereoregularity, crystallinity, and 5 mol% or less of other copolymerized vinyl compounds of the polyalkylene are not particularly limited as long as they can contain 30 mass% or more of the carbon nanofibers of the present invention in a dispersed state and can achieve a flexural strength of 70 MPa or more.

[0151] The carbon nanofiber-containing composition of the present invention is a carbon nanofiber-containing composition with extremely high bending strength. The carbon nanofiber-containing composition of the present invention is preferably dispersed in a polyalkylene or epoxy resin at the above-mentioned content, and has a bending modulus of elasticity of 70 MPa or more. The flexural modulus is more preferably 75 MPa or more, further preferably 80 MPa or more, particularly preferably 85 MPa or more, and most preferably 90 MPa or more.

[0152] When the base material is a resin such as polyalkylene, the bending strength increases as the carbon nanofiber content increases. The carbon nanofiber groups in the present invention have good dispersibility in the base material, allowing the content to be increased, thereby increasing the bending strength. When the dispersibility in the base material is poor, it is not said that the material is "contained in a dispersed state in the base material" as described above, but in that case the bending strength will generally be low.

[0153] The carbon nanofiber-containing composition of the present invention has high flexural strength due to the good dispersibility of the contained carbon nanofibers. Furthermore, the good dispersibility of the carbon nanofibers allows them to be contained at a high concentration while maintaining good dispersion, which also increases flexural strength. As a result, the above-mentioned content and flexural strength have been achieved for the first time. A carbon nanofiber-containing composition with the above-mentioned content and flexural strength, which uses a polyalkylene or epoxy resin as a base material, is a novel composition.

[0154] <<Carbon nanofiber-containing composition with excellent electrical properties (surface resistivity)>> In a preferred embodiment of the composition of the present invention, the carbon nanofiber group is contained in an amount of 30 mass % or more of the total, and the surface resistivity is 1.0 × 10 3 The carbon nanofiber-containing composition has a surface roughness of [Ω / □] or less.

[0155] The carbon nanofiber groups are preferably dispersed in the base material at a content of 30% by mass or more relative to the entire carbon nanofiber-containing composition, more preferably 35% by mass or more and 90% by mass or less, even more preferably 40% by mass or more and 85% by mass or less, particularly preferably 45% by mass or more and 80% by mass or less, and most preferably 50% by mass or more and 75% by mass or less.

[0156] The base material to be dispersed is not particularly limited, but examples thereof include resins such as the thermoplastic resins and thermosetting resins described above. When the base material is a resin, the surface resistivity does not depend much on the type of resin, so the term "a surface resistivity of 1.0 x 10" is used. 3 The physical property of "[Ω / □] or less" does not particularly depend on the resin that is the base material.

[0157] The carbon nanofiber-containing composition of the present invention is a carbon nanofiber-containing composition having a low surface resistivity. The carbon nanofiber-containing composition of the present invention is dispersed in a base material such as a base resin at the above content, and has a surface resistivity of 1.0 × 10 3 It is preferable that the resistance is [Ω / □] or less. The surface resistivity is 4×10 2 [Ω / □] or less is more preferable, and 2×10 2 [Ω / □] or less is more preferable, and 3×10 1 [Ω / □] or less is particularly preferable, and 1.0 × 10 1 [Ω / □] or less is most preferable.

[0158] When the base material is an organic material such as a resin, the surface resistivity decreases as the carbon nanofiber content increases. The carbon nanofiber groups in the present invention have good dispersibility in the base material, allowing the content to be increased, thereby reducing the surface resistivity. When the dispersibility in the base material is poor, it is not said that the material is "contained in a dispersed state in the base material" as described above, but in that case the surface resistivity generally becomes large.

[0159] Furthermore, for example, when the base material is polyimide, "general carbon nanofibers defined as having a diameter of 50 nm to 1000 nm and a length of 0.2 μm to 200 μm" cannot be incorporated into polyimide at high concentrations while maintaining good dispersion (none have been incorporated). Alternatively, conventionally, even if the carbon nanofiber content is 30 mass % or more, the above-mentioned low surface resistivity could not be achieved. In particular, in the case of the "group of carbon nanofibers in which 50 number % or more of the total carbon nanofibers have a length of 70 μm or less" and the "group of carbon nanofibers with a number average length of 70 μm or less" of the present invention, the surface resistivity is even higher.

[0160] The catalogue for Super Engineering Plastics AURUM (registered trademark), a thermoplastic polyimide manufactured by Mitsui Chemicals, lists only one example of the surface resistivity of a thermoplastic polyimide containing 30% by mass of carbon fiber. 4 ~10 8 [Ω], i.e., 10 4 ~10 8 [Ω / □]. In the case of such typical catalog values, if the content is the same, the surface resistivity is one to five orders of magnitude larger than that of the present invention.

[0161] The carbon nanofiber-containing composition of the present invention has low surface resistivity due to the good dispersibility of the contained carbon nanofibers. Furthermore, the good dispersibility of the carbon nanofibers allows them to be contained at a high concentration while maintaining good dispersion, which also results in low surface resistivity. As a result, the above-mentioned content and surface resistivity have been achieved for the first time. The carbon nanofiber-containing composition with the above-mentioned content and surface resistivity is a novel composition.

[0162] <<Carbon nanofiber-containing composition with excellent electrical properties (volume resistivity)>> A preferred embodiment of the composition of the present invention is the carbon nanofiber-containing composition, in which the carbon nanofiber groups account for 30 mass % or more of the total, and the volume resistivity is 1.0 [Ω·cm] or less.

[0163] The carbon nanofiber groups are preferably dispersed in the base material at a content of 30% by mass or more relative to the entire carbon nanofiber-containing composition, more preferably 35% by mass or more and 90% by mass or less, even more preferably 40% by mass or more and 85% by mass or less, particularly preferably 45% by mass or more and 80% by mass or less, and most preferably 50% by mass or more and 75% by mass or less.

[0164] The base material to be dispersed is not particularly limited, but examples include resins such as the thermoplastic resins and thermosetting resins described above. When the base material is a resin, the volume resistivity does not depend much on the type of resin, so the physical property of "volume resistivity of 1.0 [Ω cm] or less" does not particularly depend on the resin that is the base material.

[0165] The carbon nanofiber-containing composition of the present invention is a carbon nanofiber-containing composition with low volume resistivity. The carbon nanofiber-containing composition of the present invention is preferably dispersed in a base material such as a base resin at the above-mentioned content, and has a volume resistivity of 1.0 Ω cm or less. The volume resistivity is more preferably less than 1.0 [Ω·cm], even more preferably 0.5 [Ω·cm] or less, and particularly preferably 0.3 [Ω·cm] or less.

[0166] When the base material is an organic material such as a resin, the volume resistivity decreases as the carbon nanofiber content increases. The carbon nanofiber groups in the present invention have good dispersibility in the base material, allowing the content to be increased, thereby reducing the volume resistivity. If the dispersibility in the base material is poor, it is not said that the material is "contained in a dispersed state in the base material" as described above, but in that case the volume resistivity generally becomes large.

[0167] Furthermore, for example, when the base material is polyimide, general carbon nanofibers cannot be incorporated into polyimide at high concentrations while maintaining good dispersion (none have been incorporated). Alternatively, in the past, even if the carbon nanofiber content was 30 mass % or more, the above-mentioned low volume resistivity could not be achieved. In particular, in the case of "a group of carbon nanofibers in which 50 number % or more of the total carbon nanofibers have a length of 70 μm or less" and "a group of carbon nanofibers with a number average length of 70 μm or less" of the present invention, the volume resistivity was even higher.

[0168] The carbon nanofiber-containing composition of the present invention has a low volume resistivity due to the good dispersibility of the contained carbon nanofibers. Furthermore, the good dispersibility of the carbon nanofibers allows them to be contained at a high concentration while maintaining good dispersion, which also results in a low volume resistivity. As a result, the above-mentioned content and volume resistivity have been achieved for the first time. The carbon nanofiber-containing composition with the above-mentioned content and volume resistivity is a novel composition.

[0169] <Action / Principle> Although the present invention is not limited to the scope in which the following actions and principles are established, it is believed that the various properties described above are improved in the present invention due to the shape and size (distribution), aspect ratio, and (chemical or physical) surface condition of the carbon nanofibers. Furthermore, it is believed that the shape and surface condition of the carbon nanofibers enable high dispersion in the base material. It is believed that the high dispersion made it possible to further improve various properties, thereby enabling the production of a composition with novel composition and physical properties. [Example]

[0170] The present invention will be explained in more detail below by way of examples and comparative examples, but the present invention is not limited to these examples as long as it does not depart from the gist of the invention.

[0171] Example 1 [Raw carbon fiber] <Dry grinding> "Chopped fibers of approximately 6 mm," which are random mesophase pitch-based carbon fibers that have not been subjected to sizing treatment, were dry-ground, without pre-grinding, using a "shear and impact grinder with blades" as shown in Figure 9, for 10 minutes at 30°C, so that 90% of the total particles were in the range of 10 μm in diameter and 10 μm to 40 μm in length.

[0172] <Wet treatment> A slurry was obtained by mixing and stirring 100 parts by mass of dry-milled carbon fiber (e.g., Figure 5(a)(b)) that had not been subjected to heat treatment, 1 part by mass of a wetting agent (surfactant), and 1,500 parts by mass of purified water. Here, the wetting agent (surfactant) was an ammonium salt of a compound having an acid group.

[0173] The above slurry was subjected to a wetting treatment by stirring at 30° C. for 10 minutes with a hand mixer at 800 rpm.

[0174] <Wet grinding> Using a bead mill with a volume of 0.6 L, beads with a diameter of 0.3 mm, a bead filling rate of 60%, a vessel motor rotation speed of 1500 rpm, and a tube-type circulation pump with a transfer rate of 500 mL per minute, 4 L of the slurry obtained above was circulated for more than 90 minutes.

[0175] <Anti-aggregation treatment> Only 3500 mL of the obtained slurry was transferred from the container of the bead mill to another container, and then 0.01% by mass of a coblock polymer was added as an anti-aggregation agent relative to the entire slurry (3500 mL). After the addition, the mixture was stirred at room temperature (15 to 25°C) at 800 rpm using a hand mixer for 5 minutes to carry out an anti-aggregation treatment.

[0176] <Water removal treatment> After applying heat and reducing the pressure, the semi-dried material was collected using a cyclone separation and collection method, and heated in an oven at 150°C for 240 minutes to remove water and prepare solid carbon nanofibers. After that, it was heated in an oven at 260°C for 1 hour to remove surfactants and other substances.

[0177] <Evaluation of the carbon nanofiber group obtained in Example 1> The obtained solid carbon nanofiber group and the carbon nanofiber group in the dispersion liquid (slurry) before the water removal treatment were observed with an optical microscope and a scanning electron microscope and measured as described above. As a result, it was found that the carbon nanofiber group had a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less, with 90% by number of the total carbon nanofibers distributed within the above range.

[0178] The obtained solid carbon nanofiber clusters were added to an aqueous emulsion of acrylic resin, an aqueous emulsion of styrene-maleic anhydride resin, and an aqueous emulsion of polyurethane resin, and by stirring normally, the carbon nanofiber clusters were dispersed in water approximately individually. The carbon nanofibers did not aggregate during dispersion, and did not aggregate over time.

[0179] Furthermore, when the obtained solid carbon nanofiber groups were dispersed in a base resin made of any general-purpose thermoplastic resin using a conventional kneader, the fibers were dispersed appropriately in the base resin, approximately one by one.

[0180] Furthermore, when the obtained solid carbon nanofibers were dispersed into the curing agent side of any general-purpose thermosetting resin using a conventional stirrer, the fibers were dispersed appropriately in the curing agent almost individually. When a curing agent containing dispersed carbon nanofibers was mixed with a base resin containing either an epoxy resin or a urethane resin, the dispersion was maintained and no aggregation occurred, making it suitable for use as a thermosetting resin.

[0181] Carbon nanofiber groups were prepared (or attempted to be prepared) in the same manner as in Example 1, except that isotropic pitch-based carbon fibers, radial mesophase pitch-based carbon fibers, and onion mesophase pitch-based carbon fibers were used as raw materials instead of random mesophase pitch-based carbon fibers.

[0182] The ease of production of "carbon nanofibers having a diameter of 30 nm or more and 1000 nm or less, a length of 0.2 μm or more and 70 μm or less, and preferably a number average aspect ratio of 3 or more" was as follows. Regarding ">>", ">" and ">≒", the higher (left) you go, the better it is. The degree of superiority is also indicated by ">>", ">" and ">≒. Random mesophase pitch carbon fiber >>Radial mesophase pitch carbon fiber ≒ Onion-type mesophase pitch carbon fiber >>Isotropic pitch-based carbon fiber (actually not prepared) ≒ PAN-based carbon fiber (Comparative Example 1 (described later), which could not actually be prepared)

[0183] The order of superiority was also roughly the same for dispersibility, dispersion stability, high-concentration dispersibility, thermal properties, mechanical properties, and electrical properties. The order of superiority also seemed to be the same as above, with the order being ">>", ">", and "≒".

[0184] Comparative Example 1 An attempt was made to prepare carbon nanofiber groups in the same manner as in Example 1, except that PAN-based carbon fibers were used as raw materials instead of the pitch-based carbon fibers of Example 1. However, no carbon nanofiber groups were obtained in which the number-average aspect ratio was less than 3, the diameter was 30 nm or more and 1000 nm or less, and the length was 0.2 μm or more and 70 μm or less, with 50% or more by number of the total carbon nanofibers distributed within the above ranges.

[0185] Example 2 A group of carbon nanofibers was obtained in the same manner as in Example 1, except that milled fibers having a diameter of 10 μm and a length of 70 μm were used as the raw material instead of chopped fibers. Because many short fibers, approximately 1 μm in length, were mixed in, the number-average aspect ratio tended to be small, but good carbon nanofiber groups were obtained and evaluations of dispersibility, etc. were also good.

[0186] Example 3 A long fiber bobbin type was used as the raw material instead of the "6 mm chopped fiber" in Example 1. Although pre-pulverization using a cutter mill was necessary, carbon nanofiber groups were successfully obtained in the same manner as in Example 1, and evaluations of dispersibility, etc. were also favorable.

[0187] Example 4 The same treatment as in Example 1 was carried out except that in the dry grinding step of Example 1, instead of the "mill using shear and impact with blades" a full airflow mill that does not grind with impellers, blades, etc. (or does not use impellers, etc.), such as a jet mill, cyclone mill, tornado mill, or dream mill, was used.

[0188] A group of carbon nanofibers was obtained satisfactorily, and evaluations of dispersibility and the like were also favorable. However, the number-average aspect ratio tended to become slightly smaller during the dry pulverization stage, and this tendency for the number-average aspect ratio to become smaller remained even after the subsequent wet pulverization.

[0189] Example 5 In Example 1, a group of carbon nanofibers was obtained in the same manner as in Example 1, except that sized random mesophase pitch carbon fibers were used as raw materials instead of the unsized random mesophase pitch carbon fibers, and further, heat treatment was performed after dry grinding. The heat treatment was carried out in an electric furnace at a temperature of 400° C. for 10 minutes.

[0190] The epoxy resin content of the raw materials was reduced to 0.01% by mass or less, which allowed the surfactant (wetting agent) to effectively penetrate into the filaments (into the gaps between the filaments), resulting in the creation of carbon nanofibers with a large number-average aspect ratio.

[0191] Example 6 In Example 1, the wetting treatment was not carried out, and instead, the same wetting agent (surfactant) as that used in the wetting treatment in Example 1 was blended as a surfactant in the wet grinding. Other than that, the same procedures as in Example 1 were carried out to obtain carbon nanofiber groups.

[0192] Although the effect of the wetting agent (surfactant) was slightly reduced compared to Example 1 and the number average aspect ratio tended to be smaller, good carbon nanofiber groups were obtained and the dispersibility and other properties were also evaluated as good.

[0193] Example 7 Several types of carbon nanofiber groups were obtained in the same manner as in Example 6, except that a carbobetaine-type, imidazoline-type, amidobetaine-type, amidosulfobetaine-type, or amidoamine oxide-type amphoteric surfactant was used instead of the surfactant used in Example 6 (the wetting agent (surfactant) used in the wetting treatment in Example 1). Those using amphoteric surfactants showed good high foaming properties in hard water and over a wide pH range. As the carbobetaine type amphoteric surfactant, Softazoline (manufactured by Kawaken Fine Chemicals Co., Ltd.) was used.

[0194] As in Examples 1 and 6, carbon nanofiber groups were obtained satisfactorily, and evaluations of dispersibility and the like were also favorable.

[0195] Example 8 Using the raw material of Example 5, groups of carbon nanofibers were obtained in the same manner as in Examples 1 and 5, except that the aggregation prevention treatment in Example 1 was not carried out.

[0196] In all cases, carbon nanofibers were obtained satisfactorily, and evaluations of dispersibility and the like were also favorable. However, the obtained carbon nanofiber dispersion tended to aggregate slightly over time compared to the dispersion obtained in Example 1, but this was not to a level that caused any problems.

[0197] Example 9 A carbon nanofiber dispersion was obtained without carrying out the water removal treatment in Example 1. The dispersion had excellent dispersibility and could be used for the next application as it was.

[0198] Example 10 In the aggregation prevention treatment of Example 1, instead of the composite metal chelate used in Example 1, highly condensed sodium naphthalene sulfonate, an anionic surfactant, was added in an amount of 5 mass % relative to the total slurry (3500 mL). That is, 50 mass parts were added relative to 100 mass parts of the target material. Carbon nanofiber groups were obtained in the same manner as in Example 1 except for this.

[0199] A good group of carbon nanofibers was obtained, and the evaluation of dispersibility and dispersion stability was also good.

[0200] Example 11 In Examples 1 and 10, the order of the anti-agglomeration treatment and the water removal treatment was reversed, and the target material that had been subjected to the water removal treatment and turned into a thick slurry or powder was mixed with the "surfactant that is an anionic surfactant" of Example 10 or the "composite metal chelate that is an anti-agglomeration agent" of Example 1. Carbon nanofiber groups were obtained in the same manner as in Examples 1 and 10, except that the order of the anti-agglomeration treatment and the water removal treatment was reversed, and the target material that had been subjected to the water removal treatment and turned into a thick slurry or powder was mixed with the "surfactant that is an anionic surfactant" of Example 10 or the "composite metal chelate that is an anti-agglomeration agent" of Example 1.

[0201] A good group of carbon nanofibers was obtained, and the evaluation of dispersibility and dispersion stability was also good.

[0202] Comparative Example 2 In Example 1, an attempt was made to obtain carbon nanofibers by dry pulverization alone without wet pulverization, but a group of carbon nanofibers having a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less, with 50% or more by number of the total carbon nanofibers distributed within the above range, was not obtained.

[0203] Comparative Example 3 In Example 1, an attempt was made to obtain carbon nanofibers by wet pulverization alone without dry pulverization, but pulverization did not progress, and a group of carbon nanofibers having a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less, with 50% or more by number of the total carbon nanofibers distributed within the above range, was not obtained.

[0204] Example 12 The carbon nanofiber groups obtained in Examples 1 and 8 were mixed with a thermoplastic resin, polycarbonate (Teijin Limited, Panlite L-1225Z100 (registered trademark)), so that the total amount was 5 mass % to obtain a carbon nanofiber-containing composition.

[0205] The mechanical properties of the obtained molded body of the carbon nanofiber-containing composition were measured using a dedicated measuring device. As a result, the molded bodies obtained using the carbon nanofiber groups obtained in Example 1 and the carbon nanofiber groups obtained in Example 8 showed physical properties that were improved by 20% or more compared to molded bodies made only of the above polycarbonate that did not contain carbon nanofiber groups.

[0206] Example 13 The carbon nanofiber groups obtained in Examples 1 and 8 were mixed with a base resin of a thermosetting epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER828 (registered trademark)) so that the total amount of the base resin and the "curing agent described below to be mixed later" (total resin) was 10 mass % to obtain a carbon nanofiber-containing composition. Next, a dedicated epoxy resin curing agent (manufactured by the same company, jER Cure ST14 (registered trademark)) was mixed thereto in the ratio described in the instructions to obtain a carbon nanofiber-containing composition for forming a molded body. After that, the mixture was left to stand to obtain a molded body.

[0207] The mechanical properties of the obtained molded body of the carbon nanofiber-containing composition were measured using a dedicated measuring device. As a result, both the carbon nanofibers obtained in Example 1 and the carbon nanofibers obtained in Example 8 showed not only improved electrical performance such as reduced resistivity, but also improved mechanical performance compared to the cured epoxy resin not containing carbon nanofibers. In particular, the flexural modulus [GPa] showed a significant improvement of more than 20%.

[0208] Example 14 The carbon nanofiber groups obtained in Examples 1 and 8 were mixed with the same epoxy resin base as in Example 13 at 20.0 mass%, 25.0 mass%, and 30.0 mass% relative to the total of the base and the "curing agent to be mixed later" (total resin) to obtain carbon nanofiber-containing compositions. Next, the same curing agent as in Example 13 was mixed therein in the ratio described in the instructions to obtain a carbon nanofiber-containing composition for forming a molded body.The mixture was then allowed to stand to obtain a molded body. That is, molded bodies were obtained in the same manner as in Example 13 except that the mixing ratio in Example 13 was increased from "14.5 mass %" to "20.0 mass %, 25.5 mass %, and 30.0 mass %, respectively.

[0209] The obtained molded body of the carbon nanofiber-containing composition was molded in accordance with JIS K6921-2, and the flexural modulus and flexural strength were measured in accordance with JIS K7171.

[0210] As a result, for both the carbon nanofiber group obtained in Example 1 and the carbon nanofiber group obtained in Example 8, the "30.0 mass% containing molded body" had a flexural modulus of 7.45 GPa and a flexural strength of 78.7 MPa. In particular, the flexural modulus [MPa] of the "molded body containing 30.0% by mass" was 2.5 times that of the cured epoxy resin not containing carbon nanofibers, and the improvement was remarkable.

[0211] Example 21 <Thermal conductivity of molded body> A carbon nanofiber-containing composition was prepared by mixing 15 parts by mass of the carbon nanofiber group obtained in Example 1 and 60 parts by mass of thermosetting polyimide (manufactured by Ube Industries, Ltd., UPIA (solid content 20% by mass) (registered trademark)) at room temperature using a planetary stirrer. Similarly, multiple carbon nanofiber-containing compositions were prepared by varying the mixing ratio of the carbon nanofiber groups and the thermoplastic polyimide to achieve the concentrations shown on the horizontal axis of Figure 10. All of the compositions were extremely excellent in terms of dispersibility.

[0212] The obtained carbon nanofiber-containing composition was applied onto an aluminum foil, cured and dried, and then peeled off to remove the film alone, which was used as a sample. The thermal diffusivity was measured by a xenon flash analyzer using a Netsch Japan LFA447 Nanoflash analyzer.

[0213] The results are shown in Figure 10. Carbon nanofiber-containing compositions containing 45 mass% or more of dispersed carbon nanofibers had higher thermal conductivity than conventional products. As the carbon nanofiber content increased, the thermal conductivity also increased, as shown in Figure 10.

[0214] Example 22 <Flexural modulus of molded body> (1) 30 parts by mass of the carbon nanofibers obtained in Example 5 and 70 parts by mass of homo-type polypropylene (J105G, manufactured by Prime Polymer Co., Ltd.) were mixed at 200°C using a batch mixer to prepare a carbon nanofiber-containing composition. Similarly, a number of carbon nanofiber-containing compositions with different concentrations were prepared by varying the mixing ratio of the carbon nanofiber groups to the polypropylene so as to achieve the concentrations shown on the horizontal axis of Figure 11. All of the compositions had extremely excellent dispersibility.

[0215] For comparison, compositions containing the carbon materials (carbonaceous materials) shown in (2), (3) and (4) below were prepared in the same manner as above. (2) Carbon nanofibers obtained by pulverizing PAN-based carbon fibers (T700, manufactured by Toray Industries, Inc.) as raw materials to a diameter of 7 μm, a number-average length of 80 μm to 100 μm, and a number-average aspect ratio of 10 to 15; (3) Pitch-based carbon microfibers having a diameter of 10 μm and a number-average length of 10 μm to 20 μm; and (4) Graphite flakes (graphene) with an average particle size of 20 μm to 30 μm A carbon-containing composition (carbon material-containing composition) was prepared or prepared in the same manner as in (1) above.

[0216] As in (1) above, multiple carbon-containing compositions (carbonaceous material-containing compositions) were prepared by varying the mixing ratio of the carbons (2) to (4) above and the polypropylene, so that the concentrations were as shown on the horizontal axis of Figure 11.

[0217] The obtained "composition containing carbon material (carbonaceous material) such as carbon nanofiber" was molded in accordance with JIS K6921-2 "Plastics - Polypropylene (PP) materials for molding and extrusion - Part 2: Methods for preparing test pieces and determining their properties." The flexural modulus was measured in accordance with JIS K7171. The results are shown in Figure 11. The (1) to (4) in the graph of Figure 11 respectively represent the above-mentioned carbon materials (carbonaceous substances).

[0218] While known (conventional) carbon materials (carbonaceous materials) such as carbon nanofibers ((2)(3)(4)) can be contained in a well-dispersed state at less than 30 mass %, the carbon nanofibers (1) of the present invention can be contained in a well-dispersed state at 30 mass % or more. The plots in Figure 11 also show that all of the compositions (1) of the present invention were well-dispersed.

[0219] The carbon nanofiber-containing composition of the present invention, which contains well-dispersed carbon nanofibers at 30 mass % or more of the total, had a higher flexural modulus than other carbon materials (carbonaceous substances) (see FIG. 11). As the carbon nanofiber content increased, the flexural modulus increased, as shown in Figure 11. As a result, a composition with a high flexural modulus that had not previously been achieved was obtained.

[0220] Example 23 <Bending strength of molded body> A carbon nanofiber-containing composition was prepared by mixing 30 parts by mass of the (1) carbon nanofiber group obtained in Example 5 and 70 parts by mass of homo-type polypropylene (J105G, manufactured by Prime Polymer Co., Ltd.) at 200°C using a batch mixer. Similarly, multiple carbon nanofiber-containing compositions were prepared by varying the mixing ratio of the carbon nanofiber groups and the polypropylene to achieve the concentrations shown on the horizontal axis of Figure 12. All of the compositions were extremely excellent in terms of dispersibility.

[0221] The carbon materials (1), (2), (3) and (4) are the same as those used in the measurement of the above-mentioned <flexural modulus of the molded body>. A plurality of sample compositions were prepared by varying the mixing ratio of the carbon material group and the polypropylene so as to achieve the concentrations shown on the horizontal axis of FIG.

[0222] The obtained "composition containing carbon material (carbonaceous material) such as carbon nanofiber" was molded in accordance with JIS K6921-2 "Plastics - Polypropylene (PP) materials for molding and extrusion - Part 2: Methods for preparing test pieces and determining their properties" for measuring bending strength. The bending strength was measured in accordance with JIS K7171. The results are shown in Figure 12. The symbols (1) to (4) in the graph of Figure 12 respectively represent the carbon materials (carbonaceous materials) described above.

[0223] While known (conventional) carbon materials (carbonaceous materials) such as carbon nanofibers (groups) could only be contained in a well-dispersed state at less than 30 mass %, the carbon nanofibers of the present invention could be contained in a well-dispersed state at 30 mass % or more. Note that the plots in Figure 12 also show that all of the compositions (1) of the present invention were well-dispersed.

[0224] The carbon nanofiber-containing composition of the present invention, which contains 30 mass % or more of the total carbon nanofibers in a dispersed state, had higher bending strength than other carbon materials (carbonaceous substances) (see FIG. 12). As the carbon nanofiber content increased, the bending strength increased as shown in Figure 12. As a result, a composition with unprecedented high bending strength was obtained.

[0225] Example 24 <Surface resistivity of coating film> A carbon nanofiber-containing composition was prepared by mixing 16.2 parts by mass of the carbon nanofibers obtained in Example 1, 30 parts by mass (solid content) of polyimide (U-Varnish-A (registered trademark), manufactured by Ube Industries, Ltd.), and NMP (N-methylpyrrolidone) as a solvent / dispersion medium at room temperature using a planetary stirrer ("CNF 35%" on the horizontal axis of Figure 13). Similarly, the mixing ratio of the carbon nanofiber groups and the polyimide was varied to achieve the concentration shown on the horizontal axis of Figure 13, and the mixture was added to NMP, which is a solvent and dispersion medium, and stirred at room temperature using a planetary stirrer to prepare a paint containing multiple carbon nanofiber-containing compositions. All of them were extremely excellent in terms of dispersibility.

[0226] The resulting coating material was applied to a glass substrate using a bar coater so that the dry film thickness was 50 μm for measuring the surface resistivity, and then the coating was dried by heating at 200° C. to form a coating film. The surface resistivity was measured in accordance with JIS K7194 "Test method for resistivity of conductive plastics by four-probe method."

[0227] The results are shown in Figure 13. It was found that the carbon nanofibers of the present invention can be incorporated into the polyimide base material, in this case the coating film, in a well-dispersed state at a higher concentration than ever before. In FIG. 13, "CNF" indicates carbon nanofibers in the present invention, and "CFRP" indicates carbon fiber reinforced plastics made from carbon fibers and epoxy resin.

[0228] The carbon nanofiber-containing composition of the present invention, in which the carbon nanofibers of the present invention are dispersed, i.e., the resulting coating film, had a lower surface resistivity than conventional products. As the carbon nanofiber content increased, the surface resistivity further decreased, as shown in Figure 13.

[0229] Example 25 <Volume resistivity of coating film> Using a method similar to that used in Example 24, a paint containing multiple carbon nanofiber-containing compositions was prepared by varying the mixing ratio of the carbon nanofiber groups and the thermoplastic polyimide to achieve the concentrations shown on the horizontal axis of Figure 14. All of them were extremely excellent in terms of dispersibility.

[0230] The resulting coating material was applied using a bar coater to a dry film thickness of 50 μm for volume resistivity measurement, and then dried to form a coating film. The volume resistivity was measured in accordance with JIS K7194.

[0231] The results are shown in Figure 14. It was found that the carbon nanofibers of the present invention can be incorporated at a high concentration into the base material (base resin), in this case the coating film, in a well-dispersed state. The carbon nanofiber-containing composition containing the carbon nanofibers of the present invention in a dispersed state had lower surface resistivity than the conventional composition containing carbon nanofibers. Furthermore, as the carbon nanofiber content increased, the surface resistivity further decreased, as shown in Figure 14. [Industrial Applicability]

[0232] The carbon nanofiber group of the present invention, which has a special shape, size, distribution, etc. and surface condition, is a collection of individual carbon nanofibers with excellent shapes, particularly those with a large aspect ratio and being fine; furthermore, it contains almost no impurities other than the carbon nanofibers themselves, and is highly dispersible in liquids (aqueous media, oil-based media, etc.) and (molten) solids (base resins, etc.), allowing for high dispersion and little aggregation. It can also be incorporated into resins and molded. Therefore, it can be widely used in a variety of fields requiring various performance properties, such as heat-resistant objects, high thermal conductivity objects, high mechanical strength objects, wear-resistant objects, radio wave shielding / absorbing objects, and high electrical conductivity objects, in the form of dispersions, paints, films, structures, layers (membranes), circuits, powders, etc.

[0233] Furthermore, the carbon nanofibers of the present invention can be dispersed in a matrix resin for FRP, which can then be impregnated into a fiber substrate to produce various fiber reinforced plastics (FRP). Therefore, the present invention can be widely used in the fields of manufacturing fiber reinforced plastics (FRP) and using FRP. [Explanation of symbols]

[0234] 10 filament 20... Plain filament

Claims

1. A method for producing a carbon nanofiber-containing composition in which a group of carbon nanofibers having a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less is contained in a base material by dry-pulverizing and then wet-pulverizing pitch-based carbon fibers as the raw material, and 50% or more of the total number of carbon nanofibers is distributed in the range of 30 nm or more and 1000 nm or less, and 0.2 μm or more and 70 μm or less in length, wherein the content of a sizing agent in the group of carbon nanofibers is 0.1% by mass or less.

2. The method for producing a carbon nanofiber-containing composition according to claim 1 , wherein the carbon nanofiber group does not contain a sizing agent.

3. The method for producing a carbon nanofiber-containing composition according to claim 1 or 2, wherein the pitch-based carbon fibers are not subjected to a sizing treatment.

4. A method for producing a carbon nanofiber-containing composition, in which a group of carbon nanofibers having a diameter of 30 nm or more and 1000 nm or less and a length of 0.2 μm or more and 70 μm or less is contained in a base material by dry-pulverizing pitch-based carbon fibers and then wet-pulverizing the same, comprising: The method for producing a carbon nanofiber-containing composition is characterized in that the content of mixed resin in the carbon nanofiber group is 0.1 mass % or less.

5. The method for producing a carbon nanofiber-containing composition according to claim 4 , wherein the carbon nanofiber group does not contain a mixed resin.

6. The method for producing a carbon nanofiber-containing composition according to claim 1 , wherein a heat treatment is carried out between the dry pulverization and the wet pulverization.

7. 7. The method for producing a carbon nanofiber-containing composition according to claim 1, wherein the number average aspect ratio of the carbon nanofibers contained in the carbon nanofiber group is 3 or more and 200 or less.

8. A method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 7, wherein the carbon nanofibers contained in the carbon nanofiber group have a number average diameter of 30 nm or more and 1000 nm or less and a number average length of 0.2 μm or more and 70 μm or less.

9. A method for producing a carbon nanofiber-containing composition described in any one of claims 1 to 8, wherein the carbon nanofibers contained in the carbon nanofiber group are in a state where they can be isolated individually, or are in a dispersed or dispersible state where they can be dispersed individually.

10. A method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 9, wherein the number average thickness or number average diameter of the elementary filaments constituting the "filaments possessed by the pitch-based carbon fiber as the raw material" is 10 nm or more and 200 nm or less.

11. A method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 10, wherein the carbon nanofibers of the carbon nanofiber group are constituted by an aggregation of 2 to 20 individual filaments that constitute "the filaments possessed by the pitch-based carbon fiber that is the raw material."

12. 12. The method for producing a carbon nanofiber-containing composition according to claim 1, wherein the pitch-based carbon fiber used as a raw material is a mesophase pitch-based carbon fiber.

13. 13. The method for producing a carbon nanofiber-containing composition according to claim 12, wherein the mesophase pitch carbon fibers used as raw materials are random mesophase pitch carbon fibers.

14. 14. The method for producing a carbon nanofiber-containing composition according to claim 1, wherein the carbon nanofiber-containing composition is obtained by dry-pulverizing the carbon nanofibers until the number average length is 100 μm or less, and then wet-pulverizing the carbon nanofibers to obtain a carbon nanofiber-containing composition in which the carbon nanofiber groups are contained in a base material.

15. A method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 14, wherein the wet grinding is performed by bead mill grinding or ball mill grinding in an aqueous medium in the presence of a surfactant.

16. 16. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 15, wherein the base material is a base resin, and the base resin is one or more thermoplastic resins selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, thermoplastic polyurethane, polytetrafluoroethylene, acrylonitrile butadiene styrene resin, acrylonitrile styrene resin, (meth)acrylic resin, polyamide, polyacetal, polycarbonate, (modified) polyphenylene ether, polyester, cyclic polyolefin, polyphenylene sulfide, polytetrafluoroethylene, polysulfone, polyethersulfone, polyarylate, polyetheretherketone, thermoplastic polyimide, and polyamideimide, or one or more thermosetting resins selected from the group consisting of phenolic resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, thermosetting polyurethane, and thermosetting polyimide.

17. A method for producing a molded body, comprising producing a carbon nanofiber-containing composition by the method for producing a carbon nanofiber-containing composition described in any one of claims 1 to 16, and producing a molded body comprising the carbon nanofiber-containing composition.

18. A method for producing a paint, comprising producing a carbon nanofiber-containing composition by the method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 16, and producing a paint containing the carbon nanofiber-containing composition.

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