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

Abstract

To provide a carbon nanofiber-containing composition by developing a carbon nanofiber group having a large aspect ratio, further specified in a size or distribution, and formed by containing the carbon nanofibers dispersed excellently in a base resin, a composition in which the carbon nanofibers are more excellently dispersed in a base material at a higher concentration more than ever, or a molded body or a coating material having the composition.SOLUTION: A carbon nanofiber-containing composition characterized in that "a carbon nanofiber group having a diameter of 30 nm or more and 1000 nm or less, and, in a length range of 0.2 μm or more and 70 μm or less, and having a distribution in which 50% or more of a total is present" obtained by wet pulverizing after dry pulverizing pitch-based carbon fibers as a raw material is contained in the base material, as well as, a molded body formed by having the composition, and a coating material.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a composition in which a “carbon nanofiber group containing carbon nanofibers having a specific shape” is contained in a base material, and a molded article or paint having the carbon nanofiber-containing composition.

Background Art

[0002] Carbon fibers and carbon fiber reinforced plastics (CFRP) are lightweight and have both toughness and flexibility, so they are widely used in various molded products as a substitute for metals. Among them, the shortest carbon fibers are also called mild fibers. Generally, the average fiber length is 70 μm to 200 μm, and the average fiber diameter is about 3 μm to 10 μm (3000 nm to 10000 nm). Due to their small shape (size), they are often used as abrasives, reinforcing agents, auxiliary agents, etc.

[0003] Chopped fibers and long fibers having an average fiber length longer than that of mild fibers are mainly used for molded products such as prepregs and forgings. In addition, as other sizes, fine particle CFRP obtained by further pulverizing mild fibers to shorten the fiber length is used, for example, as a reinforcing material for concrete. However, these become more difficult to process as they become shorter, and they tend to aggregate even after being pulverized. Therefore, in fields where good dispersion is required, their current utility value is low.

[0004] When defined simply by its shape (size), apart from the actual dispersibility (the existence of each individual fiber) of carbon fibers and their utility value, according to the current general definition, "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 with a diameter of 50 nm to 1000 nm and a length of 0.2 μm to 200 μm"; and "carbon nanotubes with a diameter of 0.4 nm to 100 nm and a length of 50 nm to 20,000 nm" are known.

[0005] There are documents that describe the diameter and aspect ratio of carbon fibers (for example, Patent Documents 1 and 2). Currently, however, there are few carbon fiber groups of carbon nanofibers that have a small shape (size) like that of the present invention, particularly a very large aspect ratio, and are in a state where they can be isolated (separated) or dispersed approximately one by one. Currently, in addition to the fact that there are few good carbon nanofiber groups with the shape (size) defined above, the utilization rate of carbon fibers of the carbon nanofiber size is extremely low at present because of poor dispersibility or redispersibility.

[0006] Also, those in which nano-sized carbon fibers with a large aspect ratio are dispersed or can be dispersed are not present in the market (commercially) at least. The reason is considered to be that during the pulverization of the raw carbon fibers, they do not specifically break neatly longitudinally, in other words, the filaments cannot be suitably peeled from the filaments. Therefore, a dispersion liquid in which "carbon fibers such as carbon nanofibers" with a large aspect ratio like that of the present invention are stably dispersed is not known either.

[0007] Carbon nanofiber groups with a large aspect ratio, which can be dispersed and have good dispersion stability, can be incorporated into base materials such as resins such as thermoplastic resins and thermosetting resins; inorganic substances such as glass, metals, and alloys; etc., to form carbon nanofiber-containing compositions or molded articles, etc. Although various broad demands (applications) are conceivable, hitherto, good ones have not been achievable. In particular, dispersing a large amount in the base material has hitherto not been achievable due to the poor dispersibility of the carbon nanofiber groups.

[0008] There is a strong demand for carbon nanofiber-containing compositions that are excellent in mechanical (mechanical) properties, thermal and electrical properties, etc., and molded articles and paints having the same. However, currently, due to the poor dispersibility of the carbon nanofiber groups themselves and the fact that they "cannot be incorporated into the base material at a high concentration" due to such poor dispersibility, etc., the above-described compositions, molded articles, paints, etc. have not been achievable, and there has been room for development.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention has been made in view of the above background art, and its problem is to develop a carbon nanofiber group having a large aspect ratio and further having a specified size and distribution, and to provide a carbon nanofiber-containing composition in which the carbon nanofibers are contained in a base resin with good dispersibility. It is also to provide a composition in which the carbon nanofibers are better dispersed in the base material at a higher concentration than conventional products, or a molded article or paint having the composition.

Means for Solving the Problems

[0011] As a result of intensive studies to solve the above problems, the present inventors have found that by using specific carbon fibers as raw materials, performing dry grinding and then wet grinding, carbon nanofibers with specific sizes and distributions can be made into a state where they can be isolated one by one, or a group of carbon nanofibers in a dispersed state or a dispersible state can be obtained, one by one.

[0012] In addition, unexpectedly, when using the group of carbon nanofibers, the group of carbon nanofibers can be contained in a base material at an unprecedentedly high concentration. At least due to the "high-concentration inclusion", various performances of the obtained carbon nanofiber-containing composition can be made extremely good, and the present invention has been completed based on this finding.

[0013] That is, the present invention provides a carbon nanofiber-containing composition characterized in that 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, and 50% or more of the total number is distributed in this range" obtained by using pitch-based carbon fibers as raw materials and performing wet grinding after dry grinding is contained in a base material.

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

[0015] In addition, the present invention provides the above carbon nanofiber-containing composition in which the number average diameter of the carbon nanofibers contained in the group of carbon nanofibers is 30 nm or more and 1000 nm or less, and the number average length is 0.2 μm or more and 70 μm or less.

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

[0017] Further, the present invention provides the above carbon nanofiber-containing composition in which the elementary filaments constituting the "filaments of the above pitch-based carbon fiber as a raw material" are aggregated in the range of 2 or more and 20 or less to form the carbon nanofibers of the above carbon nanofiber group.

[0018] Further, the present invention provides the above carbon nanofiber-containing composition in which the above pitch-based carbon fiber as a raw material is a mesophase pitch-based carbon fiber.

[0019] Further, the present invention provides the above carbon nanofiber-containing composition in which the above mesophase pitch-based carbon fiber as a raw material is a random-type mesophase pitch-based carbon fiber.

[0020] Further, the present invention provides the above carbon nanofiber-containing composition in which the above carbon nanofiber group containing "substantially resin-free carbon nanofibers" is contained in the base material.

[0021] Further, the present invention provides the above carbon nanofiber-containing composition in which the above carbon nanofiber group in a state where the mixed resin mixed in the above raw material is removed by performing heat treatment between the above dry pulverization and the above wet pulverization is contained in the base material.

[0022] Further, the present invention provides the above carbon nanofiber-containing composition in which the above carbon nanofiber group is contained in a dispersed state at 25% by mass or more of the whole.

[0023] The present invention also provides the above carbon nanofiber-containing composition, wherein the above carbon nanofiber group is contained in a dispersed state at 45% by mass or more of the whole, and has a thermal conductivity of 1.0 [W / (m·K)] or more.

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

[0025] The present invention also provides the above carbon nanofiber-containing composition, wherein the base material is a polyalkylene or an epoxy resin, the above carbon nanofiber group is contained in a dispersed state at 30% by mass or more of the whole, and has a flexural strength of 70 MPa or more.

[0026] The present invention also provides the above carbon nanofiber-containing composition, wherein the above carbon nanofiber group is contained and has a surface resistivity of 1.0×10 3 [Ω / □] or less.

[0027] The present invention also provides the above carbon nanofiber-containing composition, wherein the above carbon nanofiber group is contained and has a volume resistivity of 1.0 [Ω·cm] or less.

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

[0029] The present invention also provides a paint characterized by comprising the above carbon nanofiber-containing composition.

Advantages of the Invention

[0030] According to the carbon nanofiber-containing composition of the present invention, the above problems and issues are solved, and carbon nanofibers having a large aspect ratio, 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, can be isolated one by one substantially, or can be in a dispersed state or a dispersible state one by one substantially.

[0031] Carbon nanofibers are a plurality of carbon fibers firmly bonded to the surroundings and integrated into one body among carbon fibers in the commonly known broad sense. Conventionally, it has not been possible to produce carbon nanofibers by separation, peeling, etc. while maintaining a high aspect ratio. In other words, it has not been possible in the current technology to produce carbon nanofibers by pulverization or the like while maintaining a high aspect ratio, and to make them in a state where they can be stably isolated (separated) or (re)dispersed with good reproducibility without causing aggregation.

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

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

[0034] In the carbon nanofiber-containing composition of the present invention, since the "carbon nanofiber group in the present invention" is contained in the base resin with good dispersion and at a high concentration, a novel carbon nanofiber-containing composition with a high-concentration dispersion that has never existed before is obtained. It can be understood that the "well-dispersed and high-concentration contained" in the present invention is novel because the above physical properties are more excellent than ever before.

[0035] In a molded body in which a mere carbon fiber, that is, "a carbon fiber that is not the carbon nanofiber group in the present invention", is simply contained in a high concentration in a base material, excellent thermal properties such as a high thermal conductivity [W / (m·K)] and high heat resistance as in the present invention; excellent mechanical properties such as a high flexural modulus [GPa]; excellent electrical properties such as a low surface resistivity [Ω / □] and volume resistivity [Ω·cm] cannot be achieved.

[0036] In the present invention, by using a specific carbon fiber as a raw material, performing dry pulverization and then wet pulverization, a group of carbon nanofibers with specific sizes and distributions can be obtained. In a molded body or paint in which it is dispersed, carbon nanofibers can be dispersed and contained in a high concentration, and the above-described various excellent properties can be obtained.

[0037] Further, by further limiting the type of carbon fiber used as a raw material, further limiting the dry pulverization method and / or wet pulverization method, or further limiting the manufacturing method by adding a manufacturing process, the dispersibility of the carbon nanofiber group can be further increased, and it can be dispersed in a base material at a higher concentration, thereby increasing the above-described various properties.

[0038] Further, the carbon nanofiber-containing composition of the present invention is also useful when contained in a base material such as a base resin and used as a matrix (resin) for fiber-reinforced plastics.

Brief Description of the Drawings

[0039]

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Mode for Carrying Out the Invention

[0040] Hereinafter, the present invention will be described. However, the present invention is not limited to the following specific forms and can be arbitrarily modified within the scope of the technical idea.

[0041] The carbon nanofiber-containing composition of the present invention is characterized in that a "carbon nanofiber group 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, and in which 50% or more of the total number is distributed" is contained in the base material, which is obtained by using pitch-based carbon fiber as a raw material, performing dry pulverization, and then performing wet pulverization.

[0042] <(Carbon nanofiber (group))> In the present invention, the "carbon fiber" refers to an elongated one among all carbonaceous substances (carbon materials) having a graphene structure, and includes carbon fibers, carbon nanofibers, and carbonaceous substances (carbon materials) having a size approximate to them. Further, the "carbon fiber" includes filaments of carbonaceous substances (carbon materials) having a graphene structure, elementary filaments constituting the filaments, strands formed by arranging the filaments in parallel vertically, and the like.

[0043] The carbon nanofiber group in the present invention has a diameter of 30 nm or more and 1000 nm or less, and 50% or more of the total number of the carbon nanofiber group is 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 is distributed within the above range, preferably 70% or more, more preferably 80% or more, still more preferably 90% or more, particularly preferably 95% or more, and most preferably 98% or more. According to the present invention, those with the above percentage or more can be manufactured. Considering dispersibility and the properties of molded articles and paints containing the same, the sharper the distribution, the more preferable it is. However, considering productivity and the like, a broader distribution may also be acceptable.

[0044] The diameter of the above carbon nanofibers is 30 nm or more and 1000 nm or less, preferably 50 nm or more and 900 nm or less, more preferably 100 nm or more and 850 nm or less, and particularly preferably 300 nm or more and 800 nm or less. According to the present invention, those with a diameter within the above range can be manufactured with good yield. If the diameter is too small, there may be cases where manufacturing becomes difficult or, at the same time, the length also becomes short, resulting in a small aspect ratio. On the other hand, if the diameter is too large, the performance at the point of use may deteriorate, or the applications of the carbon nanofiber group may be limited.

[0045] The length of the carbon nanofibers is 0.2 μm or more and 70 μm or less, preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 30 μm or less, and particularly preferably 5 μm or more and 20 μm or less. According to the present invention, those with a length within the above range can be manufactured with good yield. If the length is too short, there may be cases where the aspect ratio becomes small, the performance at the point of use (e.g., molded articles, paints, etc.) deteriorates, the applications of the carbon nanofiber group are limited, or it becomes difficult to prevent aggregation. On the other hand, if the length is too long, there may be cases where the applications of the carbon nanofiber group are limited or it becomes difficult to manufacture while maintaining a large aspect ratio.

[0046] The isolated and dispersible carbon nanofibers produced by the present invention are characterized by having a large aspect ratio because their diameter and length are within the above range (the above range is preferred). 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, still 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 nanofiber group in the intended use (e.g., molded body, paint, etc.) may be inferior or the applications may be limited. On the other hand, if the (number average) aspect ratio is too large, manufacturing may become difficult.

[0047] Using pitch-based carbon fibers as raw materials and performing wet grinding after dry grinding allows for specific and clean longitudinal cracking during the grinding of the raw carbon fibers. In other words, the elementary filaments can be preferably peeled off from the filaments without significantly shortening the length. In the present invention, carbon nanofibers having a hitherto unobtained suitable aspect ratio were obtained in this way. It is considered that due to the large aspect ratio and suitable size / shape, the physical properties of the molded body or paint in which the obtained carbon nanofiber group is dispersed have been improved.

[0048] The diameter and length of the carbon nanofibers contained in the carbon nanofiber group produced in the present invention are determined by randomly selecting 100 fibers one by one with an optical microscope or a scanning electron microscope (SEM) and measuring the diameter and length of each fiber, and then taking the arithmetic mean. It is preferable that the optical microscope is equipped with a gauge for size measurement to improve the measurement accuracy and shorten the measurement time. When it is difficult to measure without increasing the magnification, a scanning electron microscope (SEM) (photograph) is used instead of the optical microscope. Since the carbon nanofibers produced in the present invention have a large aspect ratio, the diameter and length of each fiber are measured one by one using a microscope rather than by measurement with a particle size distribution analyzer. An automatic particle size distribution analyzer cannot preferably measure the diameter and length, so it is necessary to do as described above. In the present invention, the size values such as diameter, length, and number average aspect ratio are defined as those measured as described above.

[0049] When incorporating and dispersing a group of carbon nanofibers into a base material such as a base resin, it may be incorporated in a solid (powder) form or once incorporated as a dispersion liquid. When present in a solid (powder) form, for example, as shown in Fig. 7, the carbon nanofibers are in a state where each can be isolated, or in a state where each can be dispersed. When present in a dispersion liquid, the carbon nanofibers are in a dispersed state one by one. Note that although the raw filaments described later are not necessarily separable into individual ones, it is sufficient if each carbon nanofiber can be dispersed. The group of carbon nanofibers in the present invention can have the dispersibility and dispersion state as described above.

[0050] <Manufacture of Carbon Nanofiber(s) Group> The carbon nanofibers having the above-described shape (diameter and length) and the group of carbon nanofibers having the above-described distribution in the present invention are obtained by at least performing dry pulverization and then wet pulverization. Further, by using specific carbon fibers as raw materials, a group of (re)dispersible carbon nanofibers having the above shape and distribution can be obtained. It is also preferable to add other treatments (operations) as necessary before the dry pulverization, between or during the above two pulverizations, or after the wet pulverization. Further, the dry pulverization and the wet pulverization may each be performed in one step or in two or more steps.

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

[0052] Among the above, at least preparing specific raw material carbon fibers, dry grinding, and wet grinding are essential. If so, a carbon nanofiber-containing composition of the present invention, a molded body or paint having the same can be manufactured. Among the above, pre-grinding, heat treatment, wet treatment, anti-aggregation treatment, and water removal treatment are not essential, but in order to manufacture well, it is preferable to perform some or all of them as necessary. In particular, heat treatment is preferably performed when the raw material contains a resin such as a sizing material, and may not be performed when the raw material is not sized. Hereinafter, each treatment step will be described in the order of treatment.

[0053] <<Raw Material Carbon Fibers>> In the present invention, it is essential to use pitch-based carbon fibers as the carbon fibers (raw material carbon fibers) before grinding, but it is preferable to use mesophase pitch-based carbon fibers, and it is particularly preferable to use random-type mesophase pitch-based carbon fibers. In PAN-based carbon fibers, no matter what grinding method is used, a carbon nanofiber group 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, and having the high number average aspect ratio as described above cannot be obtained.

[0054] Also, even in the case of pitch-based carbon fibers, it may be difficult to obtain a carbon nanofiber group with the above size, shape, and distribution in isotropic pitch-based carbon fibers.

[0055] On the other hand, mesophase pitch-based carbon fibers are classified into at least a radial type (Fig. 1 (left), Fig. 2 (b)), a random type (Fig. 1 (middle), Fig. 2 (a)(a’), Fig. 3), and an onion type (Fig. 1 (right), Fig. 2 (c)) according to their cross-sectional shape (i.e., internal shape). The "random type" means that the fiber cross-section is random. Therefore, it is named the random type.

[0056] In the present invention, even in the case of mesophase pitch-based carbon fibers, such as radial mesophase pitch-based carbon fibers or onion-type mesophase pitch-based carbon fibers, it may be somewhat difficult to obtain the carbon nanofiber group having the above size, shape, and distribution. When using radial or onion-type carbon fibers as the raw material carbon fibers, those having the above shape, form, and distribution may not be preferably obtained, and in particular, a carbon nanofiber group having a large number-average aspect ratio may not be preferably obtained (for example, only those having a number-average aspect ratio of less than 3 may be obtained).

[0057] The "filaments constituting the above random-type mesophase pitch-based carbon fibers" are formed by aggregating smaller-sized rod-shaped or plate-shaped (sheet-shaped) ones. For example, in FIG. 3, plate-shaped (sheet-shaped) ones are vertically aggregated. In this specification, the "smaller-sized rod-shaped or plate-shaped (sheet-shaped) ones" constituting the filaments are abbreviated as "elementary filaments". Inside one elementary filament, it is considered that graphene structures with condensed benzene rings are stacked in the same direction to form one, or one or more carbon nanotubes are bundled in the same direction to form one, etc.

[0058] In the present invention, the carbon fibers as the raw material preferably have a number-average thickness or number-average thickness of the elementary filaments constituting the filaments of 10 nm or more and 200 nm or less. More preferably, it is 15 nm or more and 150 nm or less, still 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 elementary filaments of the raw material carbon fibers is equal to or greater than the above lower limit, the thermal conductivity [W / (m·K)] of the filaments containing the elementary filaments rapidly increases, so the "various thermal properties including thermal conductivity" of the carbon nanofibers (containing molded bodies, paints, etc.) containing the elementary filaments also improve. On the other hand, when it is equal to or less than the above upper limit, it is easy to prepare "filaments and carbon fibers" containing such elementary filaments as raw materials.

[0059] Figure 8 shows an overview of the manufacturing process of the filaments 10 of mesophase pitch-based carbon fibers. The random-type mesophase pitch-based carbon fibers 1 can also be obtained in Figure 8 by adjusting the spinning viscosity, nozzle shape, flow state of the raw material pitch, and the like. There is no drawing process in the manufacturing process of mesophase pitch-based carbon fibers. The microstructures controlled in the spinning process almost directly become the crystal structures of the filaments 10, and boundaries with different crystal structure orientations are formed, so that the elementary filaments 20 can be seen (exist).

[0060] In Figure 8, the thickness of the filament 10 as the raw material is usually 4000 nm to 10000 nm, and mostly 5000 nm to 7000 nm. On the other hand, in the present invention, the number average thickness or number average thickness of the elementary filaments 20 in the carbon fiber filament 10 as the raw material 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 carbon fiber as the raw material, usually 40 to 700 elementary filaments 20, and in most cases 60 to 400 elementary filaments 20 are present in one filament 10. When one elementary filament 20 is separated (defined) at the boundary with a different crystal structure orientation, the above-mentioned number of elementary filaments 20 are bundled to form one filament 10. In Figure 8, for easy viewing, it is schematically drawn as if one filament is formed by three elementary filaments when viewed from the front.

[0061] In the present invention, when using random-type mesophase pitch-based carbon fibers as the raw material, although there is no limitation, it is particularly preferable that they are in the above-described mode. The carbon nanofiber group in the present invention, including the shape, distribution, etc., and whether such a carbon nanofiber group can be formed in the first place, greatly depends on what kind of carbon fiber is the raw material.

[0062] <<<Relationship between the carbon nanofibers and elementary filaments of the present invention>>> The carbon nanofibers produced by the present invention preferably have the "elementary filaments constituting the above-mentioned filaments as raw materials" aggregated in a range of 2 or more and 20 or less. More preferably, it is 3 or more and 16 or less, and particularly preferably 4 or more and 12 or less. The number of the elementary filaments is a value obtained by taking an average for each carbon nanofiber in the carbon nanofiber group. When manufacturing carbon nanofibers, the crystallinity, outer shape, etc. of the elementary filaments may be slightly disrupted, but even including that, it is referred to as the "number" as described above. Also, even if the elementary filament is originally plate-shaped, it becomes slender after pulverization, so it is referred to as the "number" as described above.

[0063] <<Pre-pulverization>> The carbon fiber as a raw material may be in the form of chopped fibers or mild fibers, but it is preferably in the form of chopped fibers. In the case of mild fibers, since many short ones with a length of about 1 μm are mixed, in order to obtain carbon nanofibers with a large aspect ratio, it is preferably in the form of chopped fibers. In the case of mild fibers, for example, even if it is said to be "average length 70 μm", there may be many short ones with a length of about 1 μm mixed.

[0064] Although not limited, it is preferable to make the carbon fiber as a raw material 1 mm to 15 mm on average by pre-pulverization, 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 required. If it is within the above range from the beginning, it is preferable not to perform pre-pulverization.

[0065] The pulverization method of pre-pulverization is not particularly limited, and any commercially available dry pulverizer can be used. For example, a cutter mill etc. can be mentioned as the device.

[0066] <<Dry pulverization>> The dry grinding in the present invention is preferably air jet grinding, cutter grinding, or "grinding that simultaneously performs both air jet grinding and cutter grinding". "Grinding that simultaneously performs both air jet grinding and cutter grinding" means "grinding that simultaneously has both an air jet grinding mechanism / function and a cutter grinding mechanism / function".

[0067] <<<Air jet grinding>>> Examples of air jet grinding include grinding using an air jet mill such as a cyclone mill, or a jet mill. Air jet grinding using a cyclone mill generates an air flow by the rotation of an impeller (rotating blade), and dry-grinds an object introduced into the air flow to produce fine particles. Also, air jet grinding using a jet mill collides an object against a collision plate to dry-grind the object and produce fine particles. For obtaining a carbon nanofiber group with a predetermined shape by wet grinding, a grinding machine having a rotating body such as an impeller, rotating blade, blade, or rotating cutter (such as a jet mill), an air jet grinding machine having such a rotating body, or a grinding machine described later as <<grinding that simultaneously performs both air jet grinding and cutter grinding>> is preferable as the "dry grinding before wet grinding".

[0068] As the cyclone mill, commercially available devices can also be suitably used. Examples of commercially available products include cyclone mills manufactured by Shizuoka Seiki Co., Ltd., super powder mills manufactured by Nishimura Machinery Co., Ltd., Tornade mills manufactured by Sanjo Industries Co., Ltd., and Dream mills manufactured by Furukawa Sangyo Systems Co., Ltd.

[0069] The structure of the above cyclone mill is not particularly limited, but having one or more impellers and mainly causing the grinding objects to collide with each other by the swirling air flow generated by the impeller is particularly preferable from the viewpoints of easily achieving the above effects by using the air jet grinding machine; having very little metal contamination; etc.

[0070] As the jet mill, commercially available devices can also be suitably used. Examples of commercially available manufacturers include Seishin Enterprise Co., Ltd., Hosokawa Micron Corporation, Nippon Pneumatic Mfg. Co., Ltd., and Nisshin Engineering Co., Ltd.

[0071] <<<Cutter type grinding>>> Moreover, examples of cutter type grinding include grinding using a crusher mill, pin mill, cutter mill, hammer mill, axial flow mill, etc.

[0072] <<<Grinding that simultaneously performs both pneumatic grinding and cutter type grinding>>> As the dry grinding in the present invention, it is particularly preferable that it is grinding that simultaneously performs both pneumatic grinding and cutter type grinding. In particular, the dry grinding in the present invention is preferably performed using a dry grinder having blades that apply shear and impact. Or, it is preferably performed using a dry grinder that adds "shear and impact by blades". A schematic diagram of an example of such a dry grinder is shown in FIG. 9.

[0073] In the case of "all pneumatic grinders that are not ground by an impeller or the like" such as jet mills, cyclone mills, tornado mills, Dream Mill (registered trademark), etc., depending on the raw material, in the dry grinding stage, the diameter may become too small, etc., and in the subsequent wet grinding, the aspect ratio may become too small (become a round shape). Although not limited, as the grinding performed before wet grinding, there may be cases where it is not suitable.

[0074] The ambient temperature or set temperature in the case of dry grinding is not particularly limited and may follow the usage method of the device to be used. Preferably, it is 0°C or higher and 50°C or lower, and particularly preferably 5°C or higher and 35°C or lower. Also, the impeller rotation speed may follow the usage method of the device to be used. Preferably, it is 4000 rpm or higher and 20000 rpm or lower, and particularly preferably 8000 rpm or higher and 15000 rpm or lower.

[0075] Using the apparatus as described above, after dry grinding by the above-described grinding method until the number average length becomes 100 μm or less, it is subjected to the following step. By performing wet grinding after dry grinding until it becomes 100 μm or less, it becomes easier for the diameter, length, (number average) aspect ratio, shape distribution, etc. of the carbon nanofibers to fall within the above-described essential range or preferred range.

[0076] It is preferable to make the number average length 100 μm or less by dry grinding, more preferably 5 μm or more and 70 μm or less, still more preferably 7 μm or more and 50 μm or less, and particularly preferably 10 μm or more and 40 μm or less. If the number average length after dry grinding is too long, even if the conditions of the subsequent wet grinding are adjusted, it may be difficult for the diameter and length of the carbon nanofibers to finally fall within the above-described range. On the other hand, if the length after dry grinding is too short, the length of the carbon nanofibers cannot become longer after wet grinding, so there are cases where it is difficult for the length and number average aspect ratio of the carbon nanofibers to finally fall within the above-described preferred range. In particular, there are cases where the aspect ratio of the finally obtained carbon nanofibers becomes too small.

[0077] Regarding the number average diameter after dry grinding, it is difficult to reduce it only by dry grinding, that is, it is difficult to grind so that the aspect ratio becomes large. Also, if the diameter is forcibly reduced by dry grinding, the length will also become short, and it will be difficult for the final aspect ratio after wet grinding to fall within a suitable range. The diameter after dry grinding is preferably 3000 nm or more, more preferably 5000 nm or more and 15000 nm or less, and particularly preferably 7000 nm or more and 12000 nm or less. It is desirable to perform dry grinding so as to be within this range.

[0078] The number average aspect ratio after dry grinding 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. In dry grinding, it is difficult to increase the number average aspect ratio beyond the above upper limit in the first place. That is, it is difficult to reduce the average fiber diameter to such an extent that the number average aspect ratio can be made larger than the above upper limit. In the present invention, by dry grinding, the number average length is preferably set to 100 μm or less, and even if the diameter is relatively large or the number average aspect ratio is relatively small, or by doing so, it has been found that by subsequent wet grinding, a group of carbon nanofibers having the above-described suitable "diameter, length, and large number average aspect ratio" can finally be obtained.

[0079] <<Heat treatment>> The carbon nanofiber-containing composition of the present invention preferably comprises the above-described group of carbon nanofibers containing "substantially resin-free carbon nanofibers" contained in a base material. Here, examples of the mixed resin include cases where a sizing agent or the like is contained in the carbon fiber as a raw material. That is, the mixed resin includes, but is not limited to, for example, a sizing agent or the like.

[0080] In the present invention, when a resin is mixed in the dry-ground product, it is preferable to perform a heat treatment to remove the resin. In other words, the carbon nanofiber-containing composition of the present invention is composed of a "group of carbon nanofibers in a state where the mixed resin mixed in the above raw material has been removed by performing a heat treatment between the above dry grinding and the above wet grinding" contained in a base material. Note that, for example, when there is no mixing of a resin such as a sizing agent, the heat treatment can be omitted.

[0081] The conditions of the heat treatment are not limited, but for example, heating is performed at a furnace temperature of 320°C to 480°C for 5 to 15 minutes to reduce the resin content to preferably 0.1% by mass or less, particularly preferably 0.01% by mass or less. By performing this heat treatment, preferably after dry grinding and before wet grinding, the grinding and dispersion effects of wetting agents and surfactants used in subsequent processes (when wet treatment is performed) such as wet treatment and wet grinding are enhanced.

[0082] <<Wet treatment>> Although not limited, it is further preferable to perform wet treatment. It is particularly preferable to perform wet treatment after dry grinding or after heat treatment. It is also preferable to immerse the product obtained above in an aqueous solution containing an anionic surfactant, a cationic surfactant, or an amphoteric surfactant for the wet treatment. The surfactant can also be suitably used in subsequent wet grinding.

[0083] The above anionic surfactant is preferably a polymer anionic surfactant (the term "polymer" includes oligomers), and more preferably an alkali metal salt, ammonium salt, alkylammonium salt, alkylolammonium salt, etc. of a (co)polymer having an acid group. The above-described anionic surfactant may be used alone or in combination of multiple types.

[0084] The above "(co)polymer having an acid group" is particularly preferably at least one (co)polymer selected from the group consisting of (co)polymers of (meth)acrylic acid, (co)polymers of (anhydrous) phthalic acid, (co)polymers of vinylbenzenesulfonic acid, and (co)condensates of naphthalenesulfonic acid. Here, the notations "(co)", "(meth)", and "(anhydrous)" indicate that they include both cases with parentheses and without parentheses. The comonomers in the case of copolymers are not particularly limited, and examples include alkyl (meth)acrylate, hydroxyalkyl (meth)acrylate, styrene, vinyl acetate, etc. The (co)condensate of naphthalenesulfonic acid refers to those in which rings are bonded with aldehydes such as formaldehyde. Examples of the co-condensation monomers in the case of co-condensates include phenol, cresol, naphthol, etc.

[0085] Further, the cationic surfactant is preferably a surfactant in which a quaternary ammonium is a hydrophilic group, and the substituent on the "N" of the quaternary ammonium + is not particularly limited, but an alkyl group (which may have a substituent) such as a stearyl group, a palmityl group, a dodecyl group, a methyl group, a benzyl group, or a butyl group is preferable. Further, 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 ions and bromide ions are particularly preferable.

[0086] Examples of the amphoteric surfactant include alkyl betaine type, fatty acid amide propyl betaine type, alkyl imidazole type, amino acid type, amine oxide type, and the like.

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

[0088] By using a surfactant, and further by using the above-described preferable anionic surfactant or amphoteric surfactant, the effect of unraveling the carbon fiber longitudinally can be achieved, and the diameter can be made thinner while maintaining the length, and carbon nanofibers (group) having a large average aspect ratio can be obtained.

[0089] <<Wet grinding>> In the present invention, it is essential to perform wet grinding after dry grinding. The wet grinding is not particularly limited, but bead mill grinding or ball mill grinding is preferable. It is particularly preferable to perform bead mill grinding or ball mill grinding in an aqueous medium in which a surfactant is present. Note that between the dry grinding and the wet grinding, "other treatments" such as the above-described heat treatment and wet treatment may be interposed. Examples of "other treatments" further include premixing and preliminary liquid preparation.

[0090] As the surfactant, regardless of whether the wet treatment is performed or not, the surfactants described in the above <Wet treatment> section can be mentioned in any case. Preferred surfactants are also the same ones. That is, anionic surfactants, cationic surfactants, or amphoteric surfactants as described above in the <Wet treatment> section are mentioned as preferred ones. In addition, the surfactant used during the wet treatment may be used as it is in wet grinding, or a newly blended or added surfactant or a different type of surfactant from that used during wet treatment can be blended during wet grinding.

[0091] The amount of surfactant used is not particularly limited and may not be used. However, with respect to 100 parts by mass of carbon fiber (carbon nanofiber during grinding) which is the object of grinding and dispersion (when two or more surfactants are used in combination, it is the total amount), it is preferably 30 parts by mass or less, more preferably 0.1 part by mass or more and 20 parts by mass or less, and particularly preferably 0.5 part by mass or more and 10 parts by mass or less. If the amount of surfactant used is too large, the carbon fiber may aggregate during the process of unraveling longitudinally. As a result, a dispersion in a state where the carbon nanofibers are aggregated is obtained, and when applied to the object, the physical properties of the obtained product may be affected.

[0092] When the wet treatment is performed, during wet grinding, a new surfactant may be added, or the surfactant blended during the wet treatment may be used as it is. When a new surfactant is added during wet grinding, it may be the same as the surfactant for wet treatment or different.

[0093] <<<Method, apparatus, and conditions for wet grinding>>> Only by performing wet grinding, a group of carbon nanofibers having the specific shape (diameter, length, aspect ratio) and particle size distribution as described above can be produced. The conditions for wet grinding are adjusted so that carbon nanofibers (group) having the specific shape (diameter, length, aspect ratio) described above of the present invention can be obtained.

[0094] As the material of the grinding media used for wet grinding, glass, alumina, zircon (zirconia - silica - based ceramics), zirconia, metal (steel), etc. can be preferably cited.

[0095] Taking a bead mill as an example, the bead 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 and the contact points will decrease, resulting in cases where suitable grinding and dispersion cannot be achieved, cases where the diameter cannot be ground small enough, etc. On the other hand, if the bead diameter is too small, there may be cases where suitable grinding and dispersion cannot be achieved, cases where the grinding takes too much time, etc.

[0096] As the bead filling rate used for the bead mill, 45% or more and 90% or less is preferable, 55% or more and 87% or less is more preferable, and 65% or more and 85% or less is particularly preferable. If the bead filling rate is too small, it becomes difficult for the carbon fiber to crack longitudinally, and there may be cases where it is difficult to obtain carbon nanofibers with a large aspect ratio. On the other hand, if the bead filling rate is too large, there may be cases where the stirring blades of the bead mill are difficult to rotate.

[0097] With respect to the entire slurry to be treated by the bead mill, the carbon fiber after dry grinding 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.

[0098] The shape of the stirring blades used for the above bead mill treatment is not particularly limited. The rotational speed of the stirring blade (agitator) depends on the delivery length of the stirring blade and the capacity of the bead mill. When converted to a capacity of 2 L, it 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. The peripheral speed of the tip of the stirring blade (agitator) depends on the delivery length of the stirring blade. Assuming a diameter of 20 cm, the range calculated from the above rotational speed is preferable. 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 mode of the bead mill for grinding and dispersion can be either a circulation type or a batch type, but the circulation type is preferred. In the case of the circulation type, since there is no transfer to a container as in the batch type, aggregation does not progress during that time. When performing in the circulation type, the degree of refinement changes with the number of passes. For example, when the residence time per pass is lengthened, since there is no short path of the processed material, the particle size distribution becomes sharp, but the aspect ratio of the carbon nanofibers also becomes small. Therefore, for example, when converted to 4 L, it is preferably circulated for 70 minutes or more and 270 minutes or less, more preferably 80 minutes or more and 230 minutes or less, and particularly preferably 90 minutes or more and 180 minutes or less for bead mill treatment.

[0100] The temperature in the wet treatment is preferably 0°C or more and 50°C or less, and particularly preferably 5°C or more and 35°C or less. The bead mill can be either vertical or horizontal. Also, commercially available devices can be used as the bead mill. Examples of commercially available devices include the Dyno-Mill from Willy E. Bachofen (WAB) and the bead mill from Netzsch (USA), etc.

[0101] The time per pass (continuous operation time), the number of passes, and the total time may depend on the apparatus structure, slurry concentration, pulverization and dispersion conditions, type of surfactant, etc. Therefore, it is preferable to extract at each pass or during wet pulverization and observe one by one with a particle size distribution measuring device, optical microscope, scanning electron microscope (SEM), etc., and adjust appropriately.

[0102] By using the above-mentioned "manufacturing method that requires dry pulverization and wet pulverization" and appropriately adjusting the pulverization conditions, etc. within the above-mentioned range, carbon nanofibers (group) 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 can be obtained. Carbon nanofibers in a state where each can be isolated, or a group of carbon nanofibers in a dispersed state or a dispersible state can be obtained. Also, carbon nanofibers (group) with a number average aspect ratio of 5 or more and 200 or less can be obtained. The present invention is also a group of carbon nanofibers produced by the method for producing the above-mentioned group of carbon nanofibers.

[0103] <<Anti-aggregation treatment>> After wet pulverization, although not limited, it is particularly preferable to perform an anti-aggregation treatment. Examples of the anti-aggregation agent used for the anti-aggregation treatment include, but are not limited to, (composite) metal chelate compounds, fine particles of (composite) metal oxides, waxes containing metals, metal-containing anti-aggregation agents such as (composite) metal ion water; coblock polymers having units such as polyester, polyacrylate, polyurethane, etc.; comb-type coblock polymers having the polymer as a unit; surfactants, etc. The anti-aggregation treatment is preferably performed by blending the anti-aggregation agent. The anti-aggregation treatment may be performed immediately after the above-mentioned wet pulverization, may be performed after the water removal treatment described later, or may be performed at both stages.

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

[0105] Also, as the surfactant used in the anti - aggregation treatment, an anionic surfactant, a cationic surfactant, or an amphoteric surfactant is preferably mentioned, and an anionic surfactant or an amphoteric surfactant is more preferably mentioned. Although not limited, particularly preferable specific surfactants include the same ones as those described in the sections of <wetting treatment> and <wet grinding>.

[0106] Regarding anti - aggregating agents such as metal - containing anti - aggregating agents, surfactants used in the anti - aggregation treatment, and block copolymers, their types are determined in consideration of the surface state of the object to be anti - aggregated immediately before the anti - aggregation treatment. When the types of anti - aggregating agents such as metal - containing anti - aggregating agents, surfactants, and block copolymers are as described above, it becomes difficult to aggregate during the removal treatment process of the dispersion medium (water) and over time thereafter, and the storage stability is improved.

[0107] The usage amount of "metal-containing anti-aggregation agents such as (composite) metal chelate compounds; surfactants used in anti-aggregation treatment; coblock polymers; and other anti-aggregation agents" is not particularly limited, but it is preferably added in an amount of 0.1% by mass or less (when two or more anti-aggregation agents are used in combination, it is the total amount thereof) based on the total amount of the slurry after wet grinding, more preferably added in an amount of 0.0001% by mass or more and 0.06% by mass or less, and particularly preferably added in an amount of 0.0002% by mass or more and 0.03% by mass or less.

[0108] Also, the usage amount of the above anti-aggregation agent is not particularly limited, but it is preferably added in an amount of 1% by mass or less (when two or more anti-aggregation agents are used in combination, it is the total amount thereof) based on the total amount of the object to be anti-aggregated such as the carbon nanofiber group, more preferably added in an amount of 0.001% by mass or more and 0.5% by mass or less, still more preferably added in an amount of 0.002% by mass or more and 0.3% by mass or less, and particularly preferably added in an amount of 0.003% by mass or more and 0.1% by mass or less.

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

[0110] The stirring during the anti-aggregation treatment is not particularly limited, and examples thereof include stirring with a hand mixer or the like. The stirring speed is not particularly limited, but is preferably 300 to 1200 rpm, and particularly preferably 500 to 1000 rpm. The temperature of the anti-aggregation 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 is also a carbon nanofiber group produced by the method for producing the above carbon nanofiber group. That is, it may be a group of carbon nanofibers contained in the slurry after wet grinding, a group of carbon nanofibers contained in the slurry after the above anti-aggregation treatment, or a group of powdery carbon nanofibers after removing water from the slurry. Any of the above-mentioned carbon nanofiber groups can be used for various applications as a product (finished product).

[0112] The method in the water removal treatment is not particularly limited and can be carried out by reducing pressure and / or raising the temperature. After semi-drying by a cyclone separation and recovery method, it is particularly preferable to remove (dry) water by reducing pressure and / or raising the temperature in an oven. The temperature of 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 bake at 250°C or higher and 400°C or lower, for example. The carbon nanofibers constituting the group of carbon nanofibers produced by the production method of the present invention preferably have good dispersibility of the carbon nanofibers themselves and no dispersant or surfactant adhering to their surfaces.

[0114] It is also preferable to perform the above-mentioned anti-aggregation treatment after the above water removal treatment. That is, it is also preferable to mix the above-mentioned anti-aggregation agent or surfactant into the concentrated slurry or powder after the above water removal treatment.

[0115] The powdery group of carbon nanofibers produced by the production method of the present invention (even if solidified) can be easily dispersed, does not aggregate, and diffuses into the resin emulsion or the resin itself at the application destination. Examples of the resin include thermoplastic resins and thermosetting resins. For thermosetting resins, they disperse well in both the main agent and the curing agent. Examples of the resin emulsion for the intended use include, but are not limited to, for example, (meth)acrylic resins, styrene maleic anhydride resins, urethane resins, etc., which are particularly mentioned as having good dispersibility, and as thermoplastic resins and thermosetting resins, those described later are preferably mentioned.

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

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

[0118] <Carbon nanofiber-containing composition> As described above, in the present invention, since specific carbon nanofibers can be contained in the base material at a high concentration, the present invention is preferably also a carbon nanofiber-containing composition in which the carbon nanofiber group is contained in a dispersed state at 25% by mass or more of the whole. More preferably, it is a carbon nanofiber-containing composition in which it is 30% by mass or more of the whole, still more preferably 35% by mass or more of the whole, and particularly preferably 40% by mass or more of the whole, in a dispersed state. The composition itself in which the carbon nanofiber group having the above shape, size, and distribution is contained in the above 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 include organic substances such as resins; inorganic substances such as glass, metals, and alloys; and the like. Particularly preferred base materials are base resins, and examples of the base resins include thermoplastic resins and thermosetting resins.

[0120] The thermoplastic resin is preferably at least one thermoplastic resin 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.

[0121] The carbon nanofiber(s) described above in the present invention is preferably dispersed (particularly at a high concentration) in the thermoplastic resin and exhibits excellent thermal, mechanical, and electrical effects as described above compared to other carbon nanofiber(s).

[0122] The thermosetting resin is preferably at least one thermosetting resin selected from the group consisting of phenol resin, epoxy resin, melamine resin, urea resin (urethane resin), unsaturated polyester resin, alkyd resin, thermosetting polyurethane, and thermosetting polyimide.

[0123] The carbon nanofiber(s) described above in the present invention is preferably dispersed (particularly at a high concentration) in the main agent of the thermosetting resin (containing unreacted resin having a functional group) and / or the curing agent (crosslinking, reacting, or polymerizing the functional group) and exhibits excellent thermal, mechanical, and electrical effects as described above compared to other carbon nanofiber(s). The excellent effects described above are exhibited.

[0124] <Other components> The carbon nanofiber-containing composition of the present invention, a molded article or a paint comprising the "carbon nanofiber-containing composition of the present invention" can contain "other components" as necessary within the range where the effects of the present invention can be obtained. Examples of such "other components" include colorants such as inorganic pigments and organic dyes; antioxidants; crystallization regulators such as nucleating agents; mold release agents such as waxes; lubricants; antistatic agents; light stabilizers; ultraviolet absorbers; particles such as inorganic fillers and organic fillers; processing aids for each base material; flame retardants; plasticizers and the like. These "other components" may be used alone or in combination of two or more. Also, the content thereof can be determined as appropriate.

[0125] <Molded article, paint, etc.> The carbon nanofiber-containing composition of the present invention is preferably, although not limited to, a carbon nanofiber-containing resin of the present invention. Further, a molded article comprising the carbon nanofiber-containing composition of the present invention is suitably used in various fields. Note that a coating film (comprising the carbon nanofiber-containing composition of the present invention) is conceptually included in the molded article (of the present invention). Also, the carbon nanofiber group obtained in the present invention and the carbon nanofiber-containing composition of the present invention can be impregnated and infiltrated into the meshes of woven or knitted cloth (sheet) made of carbon fiber, glass fiber, organic fiber, etc., and used in the form of a molded article called fiber reinforced plastic (FRP).

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

[0127] Also, the method for manufacturing the paint is not particularly limited, but a carbon nanofiber-containing composition (a group of carbon nanofibers, a base material such as a base resin, and, if necessary, "other components", etc.) is placed in a container and mixed, stirred, and dispersed in a solvent (dispersion medium) using a stirrer or the like to obtain the paint.

[0128] Particularly, the "particularly preferred forms defining the concentration and physical properties" of the "carbon nanofiber-containing composition of the present invention" and the "molded article or paint having the same" that exhibit the above effects of the present invention remarkably are shown below. This form was obtained for the first time in the present invention. In the case of the paint, the content rate of the group of carbon nanofibers with respect to the whole composition is not the content rate with respect to the whole paint, but the content rate with respect to the whole solid content in the paint, that is, the content rate with respect to the whole coating film (molded article) formed by the paint.

[0129] <<Carbon Nanofiber-Containing Composition Excellent in Thermal Characteristics>> A preferred embodiment of the composition of the present invention is the above carbon nanofiber-containing composition in which the above group of carbon nanofibers is contained in a dispersed state at 45% by mass or more of the whole and has a thermal conductivity of 1.0 [W / (m·K)] or more.

[0130] It is preferable that the group of carbon nanofibers is contained in a dispersed state in the base material at a content rate of 45% by mass or more with respect to the whole carbon nanofiber-containing composition, more preferably in the content rate range of 45% by mass or more and 90% by mass or less, still 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, and examples thereof include resins such as the above-mentioned thermoplastic resins and thermosetting resins. When the base material is a resin, the thermal conductivity does not depend much on the type of the resin, so the physical property of "having a thermal conductivity of 1.0 [W / (m·K)] or more" does not particularly select the resin as the base material.

[0132] The carbon nanofiber-containing composition of the present invention is a carbon nanofiber-containing composition having a high thermal conductivity. The carbon nanofiber-containing composition of the present invention is preferably contained in a base resin in a dispersed state at the above content rate 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, still 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 substance such as a resin, the thermal conductivity increases as the content rate of the carbon nanofibers increases. The carbon nanofiber group in the present invention has good dispersibility in the base material and can have a high content rate, so the thermal conductivity can be increased. When the dispersibility in the base material is poor, it cannot be said that it is "contained in the base material in a dispersed state" as described above in the first place, and in that case, the thermal conductivity generally becomes low.

[0134] Also, 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 contained in polyimide at a high concentration while maintaining good dispersion (there is no such thing as being contained). Alternatively, conventionally, even if it is contained at 45% by mass or more, the above high thermal conductivity cannot be achieved. In particular, in the case of the "carbon nanofiber group in which carbon nanofibers having a length of 70 μm or less account for 50% or more of the total" or the "carbon nanofiber group having a number average length of 70 μm or less" of the present invention, the thermal conductivity was even lower.

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

[0136] In addition, FIG. 4 of JP-A-2014-076750 shows that the thermal conductivity of the composite material with a content rate of 80% by mass in polyimide is 0.12 [W / (m·K)]. However, even if the content rate is high, the thermal conductivity is about two orders of magnitude lower.

[0137] The carbon nanofiber-containing composition of the present invention has a high thermal conductivity because the dispersibility of the contained carbon nanofibers is good. In addition, because the dispersibility of the carbon nanofibers is good, they can be contained at a high concentration while remaining well dispersed, and this also increases the thermal conductivity. As a result, the above-described content rate and thermal conductivity could be achieved for the first time. The carbon nanofiber-containing composition having the above-described content rate and thermal conductivity is a novel composition.

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

[0139] That is, it is preferable that the above carbon nanofiber group is contained in a dispersed state in the base material at a content rate of 30% by mass or more with respect to the whole carbon nanofiber-containing composition, more preferably 33% by mass or more and 75% by mass or less, still 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] Since the flexural modulus depends on the type of the base material, the base material in this case is a polyalkylene or an epoxy resin. When the base material is polyalkylene, general carbon nanofibers cannot be contained in the base material at a high concentration while maintaining good dispersion (none have been contained). Conventionally, when the base material is polyalkylene, carbon nanofibers have been contained in a dispersed state at less than 30% by mass based on the whole composition. For example, according to Tables 6 and 8 of JP-A-2006-124454, although the average fiber length is longer than that of the carbon nanofibers of the present invention, only about 5% by mass can be blended with polypropylene (concentration of masterbatch 30% by mass × blending ratio of masterbatch 16.7% by mass = 5.0% by mass).

[0141] Also, when the base material is an epoxy resin, general carbon nanofibers could not be dispersed and contained at a high concentration in a well-dispersed state. In particular, it has not been possible to contain 30% by mass or more. According to the present invention, the above carbon nanofibers in the present invention can be contained in polyalkylene or an epoxy resin at the above high concentration while maintaining a well-dispersed state.

[0142] The polyalkylene as the base material is not particularly limited, and examples include polyethylene, polypropylene, polybutylene, etc. Copolymers thereof are also included. Regarding the molecular weight, stereoregularity, crystallinity of the polyalkylene, and other copolymerized vinyl compounds of 5 mol% or less, there is no particular limitation as long as the above carbon nanofiber group in the present invention can be contained in a dispersed state at 30% by mass or more and the flexural modulus can be 7 GPa or more.

[0143] The epoxy resin as the base material is not particularly limited, and examples include a carbon nanofiber-containing composition (epoxy resin) composed of a known main agent and a 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 contained in a polyalkylene or epoxy resin in a dispersed state at the above content rate and has a flexural modulus of 7 GPa or more. More preferably, the flexural modulus is 8.5 GPa or more, still 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 content rate of carbon nanofibers increases. Since the carbon nanofiber group in the present invention has good dispersibility in the base material and can have a high content rate, the flexural modulus can be increased. When the dispersibility in the base material is poor, it cannot be said that it is "contained in the base material in a dispersed state" as described above. In that case, the flexural modulus generally becomes low.

[0146] For example, according to Tables 7, 9, and 10 of JP-A-2006-124454, as described above, only about 5% by mass can be blended in polypropylene (although it cannot be blended), 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 because the dispersibility of the contained carbon nanofibers is good. In addition, because the dispersibility of the carbon nanofibers is good, it can be contained at a high concentration while remaining well-dispersed, which also increases the flexural modulus. As a result, the above-described content rate and flexural modulus could be achieved for the first time. The carbon nanofiber-containing composition having the above content rate and flexural modulus with polyalkylene or epoxy resin as the base material is a novel composition.

[0148] <<<Flexural strength>>> A preferred embodiment of the composition of the present invention is the above carbon nanofiber-containing composition in which the base material is a polyalkylene or an epoxy resin, the above carbon nanofiber group is contained in a dispersed state at 30% by mass or more of the whole, and the flexural strength is 70 MPa or more.

[0149] The content rate of the carbon nanofiber group with respect to the whole carbon nanofiber-containing composition is the same as in the case of the above-described flexural modulus, including a preferred range, a particularly preferred range, etc. Conventionally, when the base material is a polyalkylene or an epoxy resin, the carbon nanofiber has been contained in a dispersed state in an amount of less than 30% by mass with respect to the whole composition.

[0150] Regarding the polyalkylene or epoxy resin as the base material, it is the same as in the case of the above-described flexural modulus. The molecular weight, stereoregularity, crystallinity of the polyalkylene, other copolymerizable vinyl compounds of 5 mol% or less, etc. are not particularly limited as long as the above carbon nanofiber group can be contained in a dispersed state at 30% by mass or more and the flexural strength can be 70 MPa or more.

[0151] The carbon nanofiber-containing composition of the present invention is a carbon nanofiber-containing composition having an extremely high flexural strength. The carbon nanofiber-containing composition of the present invention is preferably contained in a dispersed state in a polyalkylene or an epoxy resin at the above content rate and has a flexural modulus of 70 MPa or more. The flexural modulus is more preferably 75 MPa or more, still more 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 flexural strength increases as the content rate of the carbon nanofiber increases. The carbon nanofiber group in the present invention has good dispersibility with respect to the base material and can have a high content rate, so the flexural strength can be increased. If the dispersibility in the base material is poor, it cannot be said that it is "contained in the base material in a dispersed state" as described above in the first place. In that case, the flexural strength generally becomes low.

[0153] The carbon nanofiber-containing composition of the present invention has a high flexural strength because the contained carbon nanofibers are well-dispersed. In addition, since the carbon nanofibers are well-dispersed, they can be contained at a high concentration while remaining well-dispersed, which also increases the flexural strength. As a result, the above-described content rate and flexural strength could be achieved for the first time. The carbon nanofiber-containing composition having the above-described content rate and flexural strength with polyalkylene or epoxy resin as the base material is a novel composition.

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

[0155] It is preferable that the carbon nanofiber group is contained in the base material in a dispersed state at a content rate of 30% by mass or more with respect to the whole carbon nanofiber-containing composition. More preferably, it is 35% by mass or more and 90% by mass or less, still 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, and examples include resins such as the above-described thermoplastic resins and thermosetting resins. When the base material is a resin, the surface resistivity does not depend much on the type of the resin. Therefore, the physical property of "surface resistivity of 1.0×10 3 [Ω / □] or less" does not particularly select the resin as 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 contained in a base material such as a base resin in a dispersed state at the above content rate, and has a surface resistivity of 1.0×10 3 [Ω / sq] or less, preferably. The surface resistivity is more preferably 4×10 2 [Ω / sq] or less, still more preferably 2×10 2 [Ω / sq] or less, particularly preferably 3×10 1 [Ω / sq] or less, and most preferably 1.0×10 1 [Ω / sq] or less.

[0158] When the base material is an organic substance such as a resin, the surface resistivity decreases as the content rate of the carbon nanofibers increases. The carbon nanofiber group in the present invention has good dispersibility in the base material and can have a high content rate, so the surface resistivity can be decreased. When the dispersibility in the base material is poor, it cannot be said to be "contained in the base material in a dispersed state" as described above in the first place, and in that case, the surface resistivity generally increases.

[0159] Also, 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 contained in polyimide at a high concentration while maintaining good dispersion (there is no such thing as being contained). Alternatively, conventionally, even if it is contained at 30 mass% or more, the above low surface resistivity cannot be achieved. In particular, in the case of the "carbon nanofiber group in which carbon nanofibers having a length of 70 μm or less account for 50% or more of the total" or the "carbon nanofiber group having a number average length of 70 μm or less" of the present application, the surface resistivity was even higher.

[0160] In the list of physical properties in the catalog of "Super-Enpla-AURUM (registered trademark)", a thermoplastic polyimide manufactured by Mitsui Chemicals, Inc., there is only one example of the surface resistivity of a thermoplastic polyimide containing 30% by mass of carbon fiber, but 10 4 ~10 8 [Ω], that is, 10 4 ~10 8 [Ω / □]. In the case of such typical catalog values, when the content rate is the same, the surface resistivity is a value about 1 to 5 digits larger than that of the present invention.

[0161] In the carbon nanofiber-containing composition of the present invention, the surface resistivity is lowered because the dispersibility of the contained carbon nanofibers is good. In addition, since the dispersibility of the carbon nanofibers is good, they can be contained at a high concentration while being well dispersed, and thereby the surface resistivity is also lowered. As a result, the above-described content rate and surface resistivity could be achieved for the first time. The carbon nanofiber-containing composition having the above-described content rate and surface resistivity is a novel composition.

[0162] <<Carbon nanofiber-containing composition excellent in electrical properties (volume resistivity)>> A preferred embodiment of the composition of the present invention is the above-described carbon nanofiber-containing composition in which the above carbon nanofiber group is contained in an amount of 30% by mass or more of the whole and the volume resistivity is 1.0 [Ω·cm] or less.

[0163] It is preferable that the above carbon nanofiber group is contained in a dispersed state in the base material at a content rate of 30% by mass or more with respect to the whole carbon nanofiber-containing composition, more preferably 35% by mass or more and 90% by mass or less, still 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, and examples thereof include resins such as the above-described thermoplastic resins and thermosetting resins. When the base material is a resin, the volume resistivity does not depend much on the type of the resin. Therefore, for the physical property of "volume resistivity of 1.0 [Ω·cm] or less", the resin as the base material is not particularly selected.

[0165] The carbon nanofiber-containing composition of the present invention is a carbon nanofiber-containing composition having a low volume resistivity. The carbon nanofiber-containing composition of the present invention is preferably contained in a base material such as a base resin in a dispersed state at the above content rate and has a volume resistivity of 1.0 [Ω·cm] or less. The volume resistivity is more preferably less than 1.0 [Ω·cm], still 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 substance such as a resin, the volume resistivity decreases as the content rate of the carbon nanofibers increases. The carbon nanofiber group in the present invention has good dispersibility in the base material and can have a high content rate, so that the volume resistivity can be reduced. When the dispersibility in the base material is poor, it cannot be said that it is "contained in a dispersed state in the base material" as described above in the first place. In that case, generally, the volume resistivity increases.

[0167] Further, for example, when the base material is polyimide, general carbon nanofibers cannot be contained in polyimide at a high concentration while maintaining good dispersion (there is no one that can be contained). Alternatively, conventionally, even if the content is 30% by mass or more, the low volume resistivity cannot be achieved. In particular, in the case of the "carbon nanofiber group in which carbon nanofibers having a length of 70 μm or less account for 50% or more of the total" or the "carbon nanofiber group having a number average length of 70 μm or less" of the present invention, the volume resistivity is even higher.

[0168] The carbon nanofiber-containing composition of the present invention has a low volume resistivity because the contained carbon nanofibers are well-dispersed. Also, because the carbon nanofibers are well-dispersed, they can be contained at a high concentration while remaining well-dispersed, which also results in a low volume resistivity. As a result, the above-described content rate and volume resistivity could be achieved for the first time. The carbon nanofiber-containing composition with the above-described content rate and volume resistivity is a novel composition.

[0169] <Function and Principle> Although the present invention is not limited to the range in which the following function and principle are established, in the present invention, it is considered that various properties have become good as described above depending on the shape and size (distribution) and aspect ratio of the carbon nanofibers; and the (chemical or physical) surface state of the carbon nanofibers. Also, it is considered that high dispersion in the base material has become possible due to the above-described shape, etc. and surface state of the carbon nanofibers. And because high dispersion has become possible, it is considered that by achieving high dispersion, various properties have become even better, and a composition having a novel composition and physical properties has been obtained.

Examples

[0170] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded.

[0171] Example 1 [Raw Material Carbon Fiber] <Dry Grinding> "Approximately 6 mm chopped fibers", which are random-type mesophase pitch-based carbon fibers without sizing treatment, were dry-ground at 30°C for 10 minutes using a "grinder with a blade for shearing and impact" as shown in Fig. 9 without pre-grinding, with a diameter of 10 μm and a length such that 90% of the total number falls within the range of 10 μm to 40 μm, with 1000 g.

[0172] <Wetting Treatment> 100 parts by mass of dry-crushed carbon fibers (e.g., FIGS. 5(a)(b)) that have not been heat-treated; 1 part by mass of a wetting agent (surfactant); and 1500 parts by mass of purified water were mixed and stirred to obtain a slurry. 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 with a hand mixer at 800 rpm for 10 minutes at 30°C.

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

[0175] <Anti-aggregation treatment> After transferring 3500 mL of the obtained slurry from the container of the above bead mill to another container, as an anti-aggregation agent, coblock polymer was added at 0.01% by mass based on the whole slurry (3500 mL). After the addition, stirring was performed at 800 rpm for 5 minutes using a hand mixer at room temperature (15 - 25°C) to conduct an anti-aggregation treatment.

[0176] <Water removal treatment> Heating and reduced pressure were applied, and a semi-dried-up product was recovered by a cyclone separation and recovery method, and heated in an oven at 150°C for 240 minutes to remove water, thereby preparing a solid carbon nanofiber group. Then, it was heated in an oven at 260°C for 1 hour to remove surfactants and the like.

[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 (slurry) before water removal treatment were observed with an optical microscope and a scanning electron microscope and measured as described above. As a result, a carbon nanofiber group was obtained in which 90% by number of the total was distributed in the range of 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.

[0178] The obtained solid carbon nanofiber group was put into an aqueous emulsion of an acrylic resin, an aqueous emulsion of a styrene-(anhydrous) maleic acid resin, and an aqueous emulsion of a polyurethane resin, respectively, and stirred normally. As a result, the carbon nanofibers were preferably dispersed one by one in water from the solid carbon nanofiber group. They did not aggregate during dispersion and did not aggregate over time.

[0179] In addition, when the obtained solid carbon nanofiber group was dispersed in a general-purpose thermoplastic resin as a base resin using a commonly used kneader (a kneader), it was preferably dispersed one by one in the base resin.

[0180] In addition, when the obtained solid carbon nanofiber group was dispersed in the curing agent side of a general-purpose thermosetting resin using a commonly used stirrer, it was preferably dispersed one by one in the curing agent. When the curing agent in which the carbon nanofibers were dispersed was mixed with a main agent containing an epoxy resin or a urethane resin, respectively, the dispersion was maintained in both cases and did not aggregate, and it could be preferably used as a thermosetting resin.

[0181] A carbon nanofiber group was prepared (or attempted to be prepared) in the same manner as in Example 1, except that an isotropic pitch-based carbon fiber, a radial mesophase pitch-based carbon fiber, or an onion-type mesophase pitch-based carbon fiber was used as a raw material instead of the random-type mesophase pitch-based carbon fiber.

[0182] The ease of manufacturing "carbon nanofibers with 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 "≒", going up (to the left) indicates better performance. The degree of superiority or inferiority is also indicated by ">>", ">", and "≒". Random type mesophase pitch-based carbon fiber >>Radial type mesophase pitch-based carbon fiber ≒Onion type mesophase pitch-based carbon fiber >>Isotropic pitch-based carbon fiber (actually not preparable) ≒PAN-based carbon fiber (Comparative Example 1 (described later), actually not preparable)

[0183] Also, regarding dispersibility, dispersion stability, high-concentration dispersibility, thermal properties, mechanical properties, and electrical properties, they were generally in the above order. The degree of superiority or inferiority was also like the above ">>", ">", "≒".

[0184] Comparative Example 1 An attempt was made to prepare a group of carbon nanofibers in the same manner as in Example 1, except that PAN-based carbon fiber was used as the raw material instead of the pitch-based carbon fiber of Example 1. However, in all cases, carbon nanofibers with a number average aspect ratio of less than 3, 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, and a group of carbon nanofibers in which 50% or more of the total was distributed within the above range could not be obtained.

[0185] Example 2 A group of carbon nanofibers was obtained in the same manner as in Example 1, except that the raw material was changed to milled fibers with a diameter of 10 μm and a length of 70 μm instead of chopped fibers. Since many short ones with a length of about 1 μm were mixed, the number average aspect ratio tended to be small. However, a group of carbon nanofibers was obtained satisfactorily, and the evaluations such as dispersibility were also good.

[0186] Example 3 Instead of the "6 mm chopped fiber" in Example 1, a long fiber bobbin type was used as the raw material. Although pre-grinding with a cutter mill was necessary, carbon nanofiber groups were obtained favorably in the same manner as in Example 1, and evaluations such as dispersibility were also good.

[0187] Example 4 In the dry grinding stage of Example 1, instead of the "grinder by shear and impact with blades", a jet mill, a cyclone mill, a tornado mill, a dream mill, etc., all air current type grinders that do not grind with an impeller, blades, etc. (or do not use an impeller, etc.) were used, and the treatment was carried out in the same manner as in Example 1.

[0188] Carbon nanofiber groups were obtained favorably, and evaluations such as dispersibility were also good. However, at the dry grinding stage, there was a tendency for the number average aspect ratio to become smaller, and even after the subsequent wet grinding, the tendency for the number average aspect ratio to become smaller remained.

[0189] Example 5 In Example 1, instead of the random type mesophase pitch based carbon fiber without sizing treatment, a random type mesophase pitch based carbon fiber with sizing treatment was used as the raw material, and carbon nanofiber groups were obtained in the same manner as in Example 1, except that heat treatment was carried out 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 contained in the raw material was reduced to 0.01 mass% or less. As a result, the surfactant (wetting agent) effectively entered the filaments (into the gaps between the bare filaments), and carbon nanofibers with a large number average aspect ratio were formed favorably.

[0191] Example 6 In Example 1, wetting treatment was not carried out. Instead, the same surfactant (wetting agent) as that used in the wetting treatment in Example 1 was blended as a surfactant in the wet grinding. Except for this, carbon nanofiber groups were obtained in the same manner as in Example 1.

[0192] Although the effect of the wetting agent (surfactant) was slightly reduced and the number average aspect ratio tended to be smaller than that in Example 1, carbon nanofiber groups were successfully obtained, and the evaluation of dispersibility and the like was also good.

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

[0194] Similar to Example 1 and Example 6, carbon nanofiber groups were successfully obtained, and the evaluation of dispersibility and the like was also good.

[0195] Example 8 Using the raw materials of Example 5, carbon nanofiber groups were obtained in the same manner as in Example 1 and Example 5, except that the anti-aggregation treatment was not performed in Example 1.

[0196] In all cases, carbon nanofiber groups were successfully obtained, and the evaluation of dispersibility and the like was also good. However, the obtained carbon nanofiber dispersion tended to agglomerate slightly over time compared to the dispersion obtained in Example 1, but it was at a level that did not cause problems.

[0197] Example 9 In Example 1, a carbon nanofiber dispersion was obtained without performing the water removal treatment. It had excellent dispersibility and could be provided for the next use as a dispersion.

[0198] Example 10 In the anti-aggregation treatment of Example 1, instead of the composite metal chelate used in Example 1, 5% by mass of sodium naphthalene sulfonate with high condensation, which is an anionic surfactant, was added to the entire slurry (3500 mL). That is, 50 parts by mass was added to 100 parts by mass of the object. Otherwise, in the same manner as in Example 1, a carbon nanofiber group was obtained.

[0199] A carbon nanofiber group was obtained satisfactorily, and both the evaluation of dispersibility and the evaluation of dispersion stability were good.

[0200] Example 11 In Examples 1 and 10, the order of the anti-aggregation treatment and the water removal treatment was reversed. For the object that was made into a thick slurry or powder by performing the water removal treatment, except that the "surfactant which is an anionic surfactant" of Example 10 or the "composite metal chelate which is an anti-aggregation agent" of Example 1 was blended, in the same manner as in Examples 1 and 10, a carbon nanofiber group was obtained.

[0201] A carbon nanofiber group was obtained satisfactorily, and both the evaluation of dispersibility and the evaluation of dispersion stability were good.

[0202] Comparative Example 2 In Example 1, an attempt was made to obtain carbon nanofibers by dry grinding only without performing wet grinding. However, a carbon nanofiber group in which 50% or more of the total was distributed in the range 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 could not be obtained.

[0203] Comparative Example 3 In Example 1, an attempt was made to obtain carbon nanofibers by wet grinding only without performing dry grinding. However, the grinding did not progress, and a carbon nanofiber group in which 50% or more of the total was distributed in the range 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 could not be obtained.

[0204] Example 12 The carbon nanofiber groups obtained in Example 1 and Example 8 were each mixed with polycarbonate (manufactured by Teijin Limited, Panlite L-1225Z100 (registered trademark)), which is a thermoplastic resin, so as to be 5% by mass based on the whole, to obtain a carbon nanofiber-containing composition.

[0205] Regarding the molded body of the obtained carbon nanofiber-containing composition, the mechanical properties were measured with a dedicated measuring device. As a result, in both the carbon nanofiber group obtained in Example 1 and the carbon nanofiber group obtained in Example 8, the obtained molded body showed an improvement in physical properties of 20% or more compared to the molded body of only the above polycarbonate not containing the carbon nanofiber group.

[0206] Example 13 The carbon nanofiber groups obtained in Example 1 and Example 8 were each mixed with the main agent of an epoxy resin, which is a thermosetting resin (manufactured by Mitsubishi Chemical Corporation, jER828 (registered trademark)), so as to be 10% by mass based on the total of the main agent and the following curing agent to be mixed later (the whole resin), to obtain a carbon nanofiber-containing composition. Next, a dedicated curing agent for epoxy resin (manufactured by the same company, jER Cure ST14 (registered trademark)) was mixed therein at the ratio described in the instruction manual to obtain a carbon nanofiber-containing composition for forming a molded body. Then, it was allowed to stand to obtain a molded body.

[0207] Regarding the molded body of the obtained carbon nanofiber-containing composition, the mechanical properties were measured with a dedicated measuring device. As a result, in both the carbon nanofiber group obtained in Example 1 and the carbon nanofiber group obtained in Example 8, compared to the above cured epoxy resin not containing the carbon nanofiber group, not only was there an improvement in electrical performance such as a decrease in resistivity, but also an improvement in mechanical performance was observed. Among them, in particular, the improvement in the flexural modulus [GPa] was remarkable, with an improvement of 20% or more being observed.

[0208] Example 14 The carbon nanofiber groups obtained in Example 1 and Example 8 were mixed with the main agent of the same epoxy resin as in Example 13 so as to be 20.0% by mass, 25.0% by mass, and 30.0% by mass based on the total of the main agent and the "hardener to be mixed later" (the whole resin), and a carbon nanofiber-containing composition was obtained. Next, the same hardener as in Example 13 was mixed therein at the ratio described in the instruction manual to obtain a carbon nanofiber-containing composition for forming a molded body. Then, it was allowed to stand to obtain a molded body. That is, a molded body was obtained in the same manner as in Example 13 except that the mixing ratio of Example 13, "14.5% by mass", was increased to "20.0% by mass", "25.5% by mass", and "30.0% by mass", respectively.

[0209] Regarding the molded body of the obtained carbon nanofiber-containing composition, molding was performed in accordance with JIS K6921-2, and the measurement of the flexural modulus and flexural strength was performed 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, for the "molded body containing 30.0% by mass", the flexural modulus was 7.45 GPa and the flexural strength was 78.7 MPa. Compared with the above-mentioned cured epoxy resin not containing a carbon nanofiber group, particularly, the flexural modulus [MPa] became 2.5 times that of the "molded body containing 30.0% by mass", and the improvement was remarkable.

[0211] Example 21 <Thermal conductivity of molded body> 15 parts by mass of the carbon nanofiber group obtained in Example 1 and 60 parts by mass of a thermosetting polyimide (manufactured by Ube Industries, Ltd., Upia (solid content 20% by mass) (registered trademark)) were mixed at room temperature using a self-revolving stirrer to prepare a carbon nanofiber-containing composition. Similarly, a plurality of carbon nanofiber-containing compositions were prepared by varying the mixing ratio of the carbon nanofiber group and the thermoplastic polyimide so as to achieve the concentration shown on the horizontal axis of FIG. 10. All of them were extremely excellent in terms of dispersibility.

[0212] The obtained carbon nanofiber-containing composition was applied onto an aluminum foil, and after curing and drying, it was peeled off to take out a single film as a sample. The measurement of the thermal diffusivity was carried out by the xenon flash analyzer method. The measuring equipment used was LFA447 Nanoflash manufactured by Netzsch Japan Co., Ltd. to measure the thermal diffusivity in the plane direction.

[0213] The results are shown in FIG. 10. The carbon nanofiber-containing composition in which 45 mass% or more of the total carbon nanofibers were contained in a dispersed state had a higher thermal conductivity than the conventional product. And as shown in FIG. 10, the thermal conductivity increased as the content of carbon nanofibers increased.

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

[0215] For comparison, in the same manner as above, compositions containing the carbon materials (carbonaceous substances) shown in the following (2), (3) and (4) were prepared. (2) As raw materials, PAN-based carbon fibers (T700 manufactured by Toray Industries, Inc.) were used, and carbon nanofibers ground 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 with a diameter of 10 μm and a number average length of 10 μm to 20 μm; and; (4) Flaky graphite (graphene) with an average particle size of 20 μm to 30 μm Regarding these, a carbon-containing composition (carbon material-containing composition) was prepared or prepared in the same manner as in the above (1).

[0216] Similar to the above (1), the mixing ratios of the carbons in the above (2) to (4) and the polypropylene were adjusted so that the concentrations shown on the horizontal axis of FIG. 11 were obtained, and a plurality of carbon-containing compositions (carbon material-containing compositions) were prepared respectively.

[0217] The obtained "composition containing a carbon material (carbonaceous material) such as carbon nanofibers" was molded in accordance with JIS K6921-2 "Plastics - Materials for molding and extrusion of polypropylene (PP) - Part 2: Methods for producing test pieces and methods for determining properties". The measurement of the flexural modulus was carried out in accordance with JIS K7171. The results are shown in FIG. 11. (1) to (4) attached to the graph in FIG. 11 respectively indicate the above-mentioned carbon materials (carbonaceous materials).

[0218] In known (conventional) carbon materials (carbonaceous materials) such as carbon nanofibers ((2)(3)(4)), only less than 30% by mass can be contained in a good dispersion state, whereas in the carbon nanofibers (1) of the present invention, it can be contained up to 30% by mass or more in a good dispersion state. In addition, the compositions of (1) of the present invention plotted in FIG. 11 also show that all of them could be well dispersed.

[0219] The carbon nanofiber-containing composition of the present invention in which 30% by mass or more of the total carbon nanofibers are contained in a good dispersion state had a higher flexural modulus than other carbon materials (carbonaceous materials) (see FIG. 11). And as the content of the carbon nanofibers increased, the flexural modulus increased as shown in FIG. 11. As a result, a composition having a high flexural modulus, which has never existed before, was obtained.

[0220] Example 23 <Flexural strength of the molded body> (1) 30 parts by mass of a carbon nanofiber group and 70 parts by mass of a homopolymer polypropylene (manufactured by Prime Polymer Co., Ltd., J105G) obtained in Example 5 were mixed at 200 °C using a batch kneader to prepare a carbon nanofiber-containing composition. Similarly, a plurality of carbon nanofiber-containing compositions were prepared by varying the mixing ratio of the carbon nanofiber group and the polypropylene so as to achieve the concentrations shown on the horizontal axis of FIG. 12. All of them were extremely excellent in terms of dispersibility.

[0221] The carbon materials (1), (2), (3), and (4) are the same as those used for the measurement of the flexural modulus of elasticity of the molded body described above. 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. 12, respectively.

[0222] The obtained "composition containing a carbon material (carbonaceous material) such as carbon nanofibers" was molded for flexural strength measurement in accordance with JIS K6921-2 "Plastics - Materials for polypropylene (PP) molding and extrusion - Part 2: Methods for preparing test pieces and determining properties". The measurement of the flexural strength was carried out in accordance with JIS K7171. The results are shown in FIG. 12. (1) to (4) attached to the graph in FIG. 12 indicate the above-mentioned carbon materials (carbonaceous materials), respectively.

[0223] In the case of carbon materials (carbonaceous materials) such as publicly known (conventional) carbon nanofiber (groups), they could be contained in a good dispersion state by less than 30% by mass, whereas in the case of the carbon nanofibers in the present invention, they could be contained up to 30% by mass or more in a good dispersion state. In addition, it also shows that all the compositions (1) of the present invention plotted in FIG. 12 could be well dispersed.

[0224] The carbon nanofiber-containing composition of the present invention, in which 30% by mass or more of carbon nanofibers in total are contained in a dispersed state, had a higher flexural strength than other carbon materials (carbonaceous substances) (see Fig. 12). As the content of carbon nanofibers increased, the flexural strength increased as shown in Fig. 12. As a result, a composition having a higher flexural strength than ever before was obtained.

[0225] Example 24 <Surface Resistivity of Coating Film> 16.2 parts by mass of the carbon nanofiber group obtained in Example 1, 30 parts by mass (solid content) of polyimide (manufactured by Ube Industries, Ltd., U-Varnish-A (registered trademark)), and NMP (N-methylpyrrolidone) as a solvent / dispersing medium were mixed at room temperature using a self-revolving stirrer to prepare a carbon nanofiber-containing composition (the "CNF35%" on the horizontal axis of Fig. 13). Similarly, the mixing ratio of the above carbon nanofiber group and the above polyimide was adjusted to the concentrations shown on the horizontal axis of Fig. 13, and the mixture was put into NMP as a solvent / dispersing medium and stirred at room temperature using a self-revolving stirrer to prepare a paint having a plurality of carbon nanofiber-containing compositions. All of them were extremely excellent in terms of dispersibility.

[0226] The obtained paint was applied onto a glass substrate for measuring the surface resistivity using a bar coater so as to have a dry film thickness of 50 μm, and then heated and dried at 200°C to form a coating film. The surface resistivity was measured in accordance with JI SK7 194 "Test Method for Resistivity of Conductive Plastics by Four-Probe Method".

[0227] The results are shown in Fig. 13. It was found that the carbon nanofibers in the present invention can be contained in a polyimide as a base material, in this case a coating film, in a well-dispersed state at a concentration never achieved before. In addition, "CNF" in Fig. 13 indicates the carbon nanofibers in the present invention, and "CFRP" indicates a carbon fiber reinforced plastic using carbon fibers and an epoxy resin.

[0228] The carbon nanofiber-containing composition in which the carbon nanofibers of the present invention are contained in a dispersed state, that is, the obtained coating film had a smaller surface resistivity than conventional products. And as the content of the carbon nanofibers increased, the surface resistivity became even smaller as shown in FIG. 13.

[0229] Example 25 <Volume resistivity of the coating film> In the same manner as in Example 24, paints having a plurality of carbon nanofiber-containing compositions were prepared by adjusting the mixing ratio of the carbon nanofiber group and the thermoplastic polyimide so as to have the concentrations shown on the horizontal axis of FIG. 14. All of them were extremely excellent in terms of dispersibility.

[0230] The obtained paint was applied using a bar coater so as to have a dry film thickness of 50 μm for measuring the volume resistivity, and then dried to form a coating film. The measurement of the volume resistivity was carried out in accordance with JIS K7194.

[0231] The results are shown in FIG. 14. It was found that the carbon nanofibers in the present invention can be contained in a base material (base resin), in this case a coating film, in a well-dispersed state at a high concentration. And the carbon nanofiber-containing composition in which the carbon nanofiber group of the present invention is contained in a dispersed state had a lower surface resistivity than the composition containing conventional carbon nanofibers. Also, as the content of the carbon nanofibers increased, the surface resistivity became even lower as shown in FIG. 14.

Industrial applicability

[0232] The carbon nanofiber group having special shapes, sizes, distributions, etc. and surface states in the present invention is a collection of individual carbon nanofibers each having an excellent shape such as a large aspect ratio and fineness. Furthermore, there are almost no impurities other than the carbon nanofibers themselves, and it has good dispersibility in liquids (aqueous media, oily media, etc.) and (melted) solids (base resins, etc.), can be highly dispersed, is difficult to agglomerate, and can be incorporated into resins for molding. Therefore, it can be widely used in various fields that require various performances, 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 forms of dispersion liquids, paints, films, structures, layers (films), circuits, powders, etc.

[0233] Furthermore, the carbon nanofiber group in the present invention can be dispersed and contained in a matrix resin for FRP, and the fiber base material can be impregnated with it to produce various fiber-reinforced plastics (FRP). Therefore, the present invention is also widely used in the field of manufacturing fiber-reinforced plastics (FRP) and the field of using FRP.

Explanation of Reference Signs

[0234] 10 ··· filament 20 ··· elementary filament

Claims

1. A method for producing a carbon nanofiber-containing composition, comprising: using pitch-based carbon fibers as raw materials, subjecting them to dry grinding and then wet grinding to obtain a carbon nanofiber-containing composition in which a carbon nanofiber group 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 is contained in a base material, and 50% or more of the total number is distributed therein, wherein the carbon nanofiber group is contained in a dispersed state at 25% by mass or more of the entire carbon nanofiber-containing composition.

2. 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.

3. The method for producing a carbon nanofiber-containing composition according to Claim 1 or Claim 2, wherein the number average diameter of the carbon nanofibers contained in the carbon nanofiber group is 30 nm or more and 1000 nm or less, and the number average length is 0.2 µm or more and 70 µm or less.

4. The method for producing a carbon nanofiber-containing composition according to any one of Claims 1 to 3, wherein the carbon nanofibers contained in the carbon nanofiber group are in a state where they can be isolated one by one, or in a dispersed state or a dispersible state one by one.

5. The method for producing a carbon nanofiber-containing composition according to any one of Claims 1 to 4, wherein the number average thickness or number average thickness of the elementary filaments constituting the "filaments of the pitch-based carbon fibers as the raw material" is 10 nm or more and 200 nm or less.

6. The method for producing a carbon nanofiber-containing composition according to any one of Claims 1 to 5, wherein the elementary filaments constituting the "filaments of the pitch-based carbon fibers as the raw material" are aggregated in a range of 2 or more and 20 or less to form the carbon nanofibers of the carbon nanofiber group.

7. The method for producing a carbon nanofiber-containing composition according to any one of Claims 1 to 6, wherein the pitch-based carbon fibers as the raw material are mesophase pitch-based carbon fibers.

8. The method for producing a carbon nanofiber-containing composition according to claim 7, wherein the mesophase pitch-based carbon fiber as the raw material is a random-type mesophase pitch-based carbon fiber.

9. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 8, wherein dry pulverization is performed until the number average length becomes 100 μm or less, and then wet pulverization is performed to obtain a carbon nanofiber-containing composition in which a carbon nanofiber group is contained in a base material.

10. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 9, wherein a heat treatment is performed between the dry pulverization and the wet pulverization to remove the mixed resin mixed in the raw material, and a carbon nanofiber-containing composition in which a carbon nanofiber group is contained in a base material is obtained.

11. The method for producing a carbon nanofiber-containing composition according to claim 10, wherein the content of the mixed resin is made 0.1% by mass or less by the heat treatment.

12. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 11, wherein bead mill pulverization or ball mill pulverization is performed in an aqueous medium in which a surfactant is present as the wet pulverization.

13. 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 phenol resin, epoxy resin, melamine resin, urea resin (urea resin), unsaturated polyester resin, alkyd resin, thermosetting polyurethane, and thermosetting polyimide. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 12.

14. The carbon nanofiber group is contained in a dispersed state at 45% by mass or more of the entire carbon nanofiber-containing composition, and the thermal conductivity of the molded body when the carbon nanofiber-containing composition is molded is 1.0 [W / (m·K)] or more. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 13.

15. The base material is a polyalkylene or an epoxy resin, the carbon nanofiber group is contained in a dispersed state at 30% by mass or more of the entire carbon nanofiber-containing composition, and the flexural modulus of the molded body measured in accordance with JIS K7171 when the carbon nanofiber-containing composition is molded is 7 GPa or more. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 14.

16. The base material is a polyalkylene or an epoxy resin, the carbon nanofiber group is contained in a dispersed state at 30% by mass or more of the entire carbon nanofiber-containing composition, and when the carbon nanofiber-containing composition is molded, the flexural strength of the molded body measured in accordance with JIS K7171 is 70 MPa or more. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 15.

17. The carbon nanofiber group is contained, and when the carbon nanofiber-containing composition is made into a coating film, the surface resistivity of the coating film measured in accordance with JIS K7194 is 1.0×10 ３ The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 16, wherein the surface resistivity is [Ω / square] or less.

18. The carbon nanofiber group is contained, and when the carbon nanofiber-containing composition is made into a coating film, the volume resistivity of the coating film measured in accordance with JIS K7194 is 1.0 [Ω·cm] or less. The method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 17.

19. A method for producing a molded body, characterized by producing a carbon nanofiber-containing composition by the method for producing a carbon nanofiber-containing composition according to any one of claims 1 to 18, and producing a molded body having the carbon nanofiber-containing composition.

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

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