JP2009096694A - Fine carbon fiber and composite material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide fine carbon fibers improving physical properties such as electric characteristics, mechanical characteristics and thermal conductivity characteristics of a composite material with a small amount of addition by improving adhesiveness without degrading characteristics of the matrix in manufacturing a composite material without requiring a step of surface modification on the carbon fibers, and in particular, to provide carbon fibers in a three-dimensional network state and a method for manufacturing the fibers. <P>SOLUTION: The carbon fibers constituting a three-dimensional network carbon fiber structure composed of carbon fibers having outer diameters of 15 to 100 nm, are characterized in that: the carbon fiber structure includes granular portions having a grain diameter larger than the outer diameter of the carbon fibers and including the carbon fibers mutually bonded, with a plurality of carbon fibers extended from the granular portions; the granular portions are formed in a growing process of the carbon fibers; the carbon fibers have a rough surface by heat treatment in a range from 900 to 2,200°C; and the carbon fibers contain a catalytic iron as a structural component. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a fine carbon fiber, a method for producing the same, and a composite material. More specifically, when a composite material is produced, a process for surface modification treatment of the fine carbon fiber is not required and a rough surface is obtained by heat treatment. And, the reaction catalyst-derived iron is contained in the fine carbon fiber in an amount of 0.5 to 5.0% by mass, and 5 to 100% of the iron is in a state in which it can be eluted with dilute hydrochloric acid. The present invention relates to a fine carbon fiber capable of improving physical properties.

Fine carbon fibers typified by carbon nanotubes have excellent mechanical properties and properties such as high electrical conductivity and thermal conductivity. For example, they can be used as filler materials in various materials such as synthetic resins, rubber, ceramics, and metals. It is expected to improve the physical properties of composite materials such as mechanical properties, electrical conductivity, and thermal conductivity. However, as can be seen from many research results, carbon nanotubes with few defects on the surface have a weak interfacial adhesive force with a matrix material (for example, synthetic resin, rubber, ceramics, metal, etc.), so pull-out A phenomenon occurs, and sufficient physical property values cannot be obtained (see Non-Patent Documents 1 and 2).

  The following has been pointed out regarding composite materials containing carbon nanotubes in which a sheet of carbon atoms bonded in a network is cylindrical (see Non-Patent Documents 2 to 3). That is, what is important in developing the mechanical strength is the adhesive strength between the carbon nanotube and the matrix material. In addition, it is generally known that the interface structure in the carbon fiber composite material has a significant influence on the bonding force with the matrix material, and that the control of the interface structure of the carbon fiber is important (see Non-Patent Document 4). ). The matrix material may be metal, ceramic, polymer, carbon, etc., but the surface structure made of graphene sheet with few defects of carbon nanotubes deteriorates the wettability with the matrix polymer or metal used in the composite material for structural materials In order to obtain a composite material that is presumed to work in the direction and has the expected high strength, it is necessary to strengthen the interface bond between the carbon nanotube and the matrix. Usually, the carbon nanotube surface is modified or a composite material adjustment method is devised.

From the above viewpoint, the surface strength of the carbon nanotube is increased to improve the adhesive strength with the matrix material. For example, chemical surface modification such as introduction of a functional group on the surface of the carbon nanotube, or oxygen plasma (Oxygen plasma) There is a report of improving the interfacial adhesion strength with the matrix material by increasing the surface defects of the carbon nanotubes by a method such as oxidation treatment (for example, see Patent Documents 1 to 3). However, such a modification method is not desirable from the viewpoint of improving the physical properties of the composite material because the physical properties of the carbon nanotubes themselves are reduced due to the increase in surface defects of the carbon nanotubes.

In addition, the coating treatment of the carbon nanotube surface according to the matrix material is a well-considered method. For example, a method of covering a carbon nanotube surface with a metal coating layer for a metal composite material (see, for example, Patent Documents 4 to 6), and a ceramic-based composite material by a sol-gel method, a CVD method, or a conversion method using SiO gas, A method for forming a film (see, for example, Patent Documents 7 and 8) and a method such as polymer wrapping in the case of a resin matrix composite (for example, see Non-Patent Document 5) have been proposed.

In the above example, the coating effect of the carbon nanotubes still has various problems. For example, in Patent Documents 4 and 5, no post-treatment is performed at a particularly high temperature. The metal coating on the surface remains uneasy in terms of strength. In Patent Document 6, the types of coating metal and matrix metal are limited, and not carbon nanotubes but aggregates of carbon nanotubes are coated. In Patent Documents 7 and 8, the delamination phenomenon occurs based on the difference in thermal expansion between the carbon nanotube and the coated SiC. Furthermore, the carbon nanotube itself is consumed as a carbon source for the generation of SiC.

In addition to the carbon nanotube production process, purification process, and composite material manufacturing process, the surface modification process increases the surface modification process, and the surface modification process includes at least a mixture of the coating material and carbon nanotube, Processes such as chemical reaction treatment, heating reaction, and drying treatment are required, and the operation has not reached the practical level because it is complicated and economically undesirable.

On the other hand, there is a report that carbon nanotubes having a non-smooth surface can be obtained by controlling process conditions when performing a reaction generation process or a heat treatment process. For example, when carbon fibers are produced by a gas phase reaction, the layered carbon structure is divided in the longitudinal direction by controlling the conditions such as the decomposition temperature and introduction route of the reaction gas and heat treatment at 900 to 3,000 ° C., and the surface is smooth. Carbon fiber can be produced (for example, see Patent Document 9). Further, a carbon nanotube having a non-smooth surface and a defective crystal structure was obtained by controlling the reaction gas or catalyst particles (see, for example, Non-Patent Document 6). In addition, since the density of carbon nanotubes decreases rapidly when the transition metal reaction catalyst is removed by heat treatment after reaction generation, stress is generated inside the structure of carbon nanotubes, so the surface structure becomes rough by deforming the internal structure (For example, see Non-Patent Document 7).

In the above example, carbon nanotubes with a non-smooth surface structure can be produced without using surface modification treatment. However, since the crystal structure of the carbon nanotubes is also defective, there is a risk of adversely affecting the physical properties of the carbon nanotubes themselves. However, it remains doubtful whether a sufficient effect can be obtained for improving the physical properties of the composite material if added to the matrix material as a filler. Furthermore, it is predicted that these carbon nanotubes can improve the adhesion to the matrix, but no report has been made on the improvement effect. The other is a transition metal reaction catalyst such as Fe, Ni, Co, etc., which usually remains in the carbon nanotubes after the gas phase formation reaction and is removed as an impurity after the heat treatment, particularly after a temperature region heat treatment of 1800 ° C. or higher. There is no example that has been reported to be useful for improving the interfacial adhesion between the carbon nanotube and the matrix.

On the other hand, it has been reported that the mechanical strength, electrical conductivity and thermal conductivity are improved by making the carbon fiber aggregate into a three-dimensional structure. For example, carbon fiber aggregates, in which carbon fibers are heat-treated at 600 ° C. or higher and the contact points of the intertwined fibers are bonded and fixed by carbides such as tar and pitch, are added to the matrix to improve conductivity and thermal conductivity. An improved composite material has been obtained (see, for example, Patent Document 10). In addition, a composition containing a fibrous carbonaceous material, a thermosetting resin, and an easily graphitizable material is heated to a temperature lower than the temperature at which the easily graphitizable material graphitizes to form a molded body, and the molded body is further fired. A sintered body with improved mechanical strength is obtained. In this case, when the graphitizable material is graphitized by the firing step, the fibrous carbonaceous materials are joined to each other (see, for example, Patent Document 11).

Furthermore, as for the three-dimensional structure of the carbon fiber aggregate, synthetic resin, rubber, metal, and carbon-based materials can be selected as impregnation materials, and nano-carbon composite materials with a wide application range have been reported. Carbon nanotubes and thermosetting resin are kneaded, dried, and molded at a predetermined pressure and a predetermined temperature. This molded body is heated to carbonize the resin, and the nanocarbon is three-dimensionally connected with carbon. A porous material is obtained. A nanocarbon composite material is obtained by impregnating various impregnated materials after the carbonization step (see, for example, Patent Document 12).

In the above example, by giving a three-dimensional structure to the carbon fiber, the thermal conductivity, conductivity, and mechanical strength of the finally obtained composite material are improved. However, the three-dimensional structure of the carbon fiber can be obtained later and is not a reaction-generated three-dimensional network-like carbon fiber structure. In these reports, for example, the importance of adhesion between synthetic resin, rubber, ceramics, metal, and carbon nanotube, which are impregnated materials, is not mentioned.

On the other hand, a report on a three-dimensional network-like carbon fiber structure has also been made (for example, see Patent Document 13). It is a three-dimensional network-like carbon fiber structure composed of carbon fibers having an outer diameter of 15 to 100 nm, and the carbon fiber structure is a mode in which a plurality of carbon fibers extend, and the carbon fiber structure is more than the outer diameter of the carbon fiber. A carbon fiber structure having a large particle size and a granular part for bonding the carbon fibers to each other, and the granular part is formed in the growth process of the carbon fiber, There has been no report on the adhesion between the surface condition of the carbon fiber and the matrix when the material is produced.

Fine carbon fibers having an iron content of 3.2% by mass, an average diameter of 15 nm, a d002 determined by X-ray diffraction method of 0.345 nm, and an aspect ratio of 100 or more are described ( For example, see Patent Document 14). However, this fine carbon fiber has no description of the presence form or position of iron.
JP 2003-300716 A JP-T-2004-535349 Special table 2003-505332 gazette Japanese Patent No. 2953996 Japanese Patent Publication No. 63-60152 Special table 2004-10978 gazette JP 2005-75720 A JP 05-229886 A Japanese Patent No. 3841684 JP 2004-119386 A JP 2005-178151 A JP 2004-315297 A Japanese Patent No. 3776111 JP 2003-138432 A Pulickel M.M. Ajayan, Linda S .; Schadler, Cindy Giannaris, Angel Rubio, Adv. Mater. 2000, 12, no. 10, 750-753 Rupesh Khare, Suryasarathi Bose, Journal of Minerals & Materials Charactarization & Engineering, 2005, vol. 4, no. 1, 31-46 “Carbon Nanotube” Chemistry, 2001, p. 115 “Composite Materials and Interfaces—High Functionalization and Control of Materials” Materials Technology Research Association, 1988, p. 251 A. Star, J.A. F. Staudart, D.C. Steuerman, M.M. Diehl, A.D. Boukai, E .; W. Wong, X. Yang, S.M. -W. Chung, H.C. Choi, J. et al. R. Heath, Angew. Chem. Int. Ed. 2001, 40, 1721-1725. M.M. Jose-Yacaman, H.M. Terrones, L.M. Rendon, Carbon, vol. 33,669-678, 1995 J. et al. Chen, J.A. Y. Shan, T .; Tsukada, F.A. Munekane, A.M. Kuno et al. , Carbon, vol. 45, 274-280, 2007

As described above, in order to improve the mechanical strength, thermal conductivity, and conductivity of the finally obtained composite material, it is required to impart a three-dimensional structure to the carbon fiber. When a process for imparting a three-dimensional structure to the carbon fiber later is required at the stage of manufacturing the carbon fiber, various restrictions are imposed on the production of the composite material, and the three-dimensional structure is imparted. It becomes necessary to add a process. On the other hand, in the case of coating such as metal, ceramic (SiC) or polymer on the surface of carbon nanotubes, since it depends only on the physical bond strength, the coating remains uneasy in terms of strength, and has low heat resistance especially for applications at high temperatures. There is a possibility that the surface modification effect may be lost due to peeling of the coating layer or carbonization reaction caused by the difference in thermal expansion or thermal expansion. In addition, a method of chemically reacting with carbon nanotubes to introduce functional groups on the tube surface and increasing defects on the surface of carbon nanotubes by chemical surface modification and low-temperature heat treatment may cause a bad influence on the structure of carbon nanotubes. Therefore, the effect of finally improving the performance of the composite material cannot be obtained sufficiently. By pressing and sintering a plurality of carbon nanotubes, carbide forming metal and matrix metal at a temperature equal to or higher than the melting point of the matrix metal, metal carbide is formed on the surface of the plurality of carbon nanotubes, and between the matrix metal and the carbon nanotube. In a method for obtaining good adhesion, a metal matrix and a different metal from a metal carbide source must be charged at the same time, and the matrix material is limited to some metals. Further, in covering the aggregate of carbon nanotubes, the surface structure of the carbon nanotubes is not modified, the wettability with the matrix metal is not improved, and a device is required for adhesion to the matrix material. Moreover, since the dispersion in the matrix material becomes a problem by covering the aggregates of carbon nanotubes, it is difficult to expand to application ranges other than metals such as synthetic resins, rubber, ceramics, and carbon-based materials. Furthermore, the surface modification treatment of carbon nanotubes requires an increase in the number of surface modification treatment steps in addition to the carbon nanotube production process, purification process and composite material production process, and the operation of the surface modification process is complicated and economical. Is also undesirable. Carbon nanotubes with a non-smooth surface due to control of reaction generation process and heat treatment process conditions may cause defects in the crystal structure, which may adversely affect the physical properties of the carbon nanotubes themselves, improving the physical properties of the composite material The question remains whether there will be a sufficient effect.

The present invention does not require a step for imparting a three-dimensional structure to a fine carbon fiber and a step for surface modification treatment when producing a composite material, and the fine carbon capable of improving the adhesion to a matrix material. It is an object of the present invention to provide a fiber, particularly a three-dimensional network-like carbon fiber and a method for producing the same.

As a result of continual investigations on the above problems, the present inventors have found that the surface of the carbon nanotube is confined by treatment under heat treatment conditions of 900 to 2200 ° C., and iron derived from the catalyst is at least a constituent element. As a result, it was found that some of the iron was in a state where it could be eluted with dilute hydrochloric acid, and the present invention was completed.

That is, the present invention is a fine carbon fiber containing iron derived from a reaction catalyst as a constituent component, and the iron component is bonded to the fine carbon fiber, and the total iron content measured by the fluorescent X-ray method is fine. The fine carbon fiber is characterized in that it is 0.5 to 5.0% by mass in the carbon fiber, and 5 to 100% of the iron component is in a state capable of being eluted with dilute hydrochloric acid.

Further, the present invention is a fine carbon fiber characterized in that the form of the iron component is carbide, sulfide or pure iron.

Furthermore, the present invention is a three-dimensional network-like carbon fiber structure in which the fine carbon fiber is composed of carbon fibers having an outer diameter of 15 to 100 nm, and the carbon fiber structure is a mode in which a plurality of carbon fibers extend. The carbon fiber has a granular part larger than the outer diameter of the carbon fiber and bonds the carbon fiber to each other, and the granular part is formed during the growth process of the carbon fiber. It is a fine carbon fiber characterized by.

The present invention has the above-described fine carbon fibers are carbon fibers, wherein I _{D /} I _G which is determined by Raman spectroscopy is 0.2 or more.

The fine carbon fiber according to the present invention is a fine carbon fiber characterized in that d ₀₀₂ showing crystallinity as graphite obtained by an X-ray diffraction method is in a range of 3.42 mm or more.

In the present invention, the fine carbon fiber is characterized in that a part of the fiber surface is constricted and the fiber surface is rough.

  Furthermore, this invention is a fine carbon fiber characterized by the above-mentioned fine carbon fiber containing 0.001-30 mass% boron compound in conversion of boron with respect to carbon fiber.

Further, the present invention is the fine carbon fiber comprising iron derived from a reaction catalyst as a constituent component, wherein the iron component is bonded to the fine carbon fiber, and the total iron content measured by a fluorescent X-ray method is The fine carbon fiber is 0.5 to 5.0% by mass in the fine carbon fiber, and 5 to 100% of the iron component is in a state in which it can be eluted with dilute hydrochloric acid. A preform of a fine carbon fiber characterized by being molded.

Moreover, the present invention is a three-dimensional network-like carbon fiber structure in which the fine carbon fiber is preformed through a hot press in the course of its production and is composed of carbon fibers having an outer diameter of 15 to 100 nm, The carbon fiber structure is a mode in which a plurality of carbon fibers extend, and has a granular portion that has a larger particle diameter than the outer diameter of the carbon fiber and binds the carbon fibers together, and the granular portion is the A preform of a fine carbon fiber, which is formed during the growth process of the fine carbon fiber.

In the present invention, a mixed gas of a catalyst and a hydrocarbon is heated at a constant temperature of 800 ° C. to 1300 ° C. to grow a carbon substance into a fibrous form to obtain an intermediate of fine carbon fiber. Characterized in that it comprises a step of heat-treating the body at a temperature in the range of 900 to 2200 ° C., comprising a rough surface and containing an iron component derived from a reaction catalyst, said iron component being bonded to fine carbon fibers, The total iron content measured by the fluorescent X-ray method is 0.5 to 5.0% by mass in the fine carbon fiber, and 5 to 100% of the iron is in a state where it can be eluted with dilute hydrochloric acid. It is a manufacturing method of carbon fiber.

That is, according to the present invention, the catalyst gas is composed of sulfur or a sulfur compound and iron or an iron compound, and the molar ratio of sulfur atom in the sulfur source / iron atom in the iron source is 0.01 to 10. It is the manufacturing method of the fine carbon fiber characterized by the above-mentioned.

The present invention also provides a carbon substance by using at least two or more carbon compounds having different decomposition temperatures as a carbon source when the mixed gas of catalyst and hydrocarbon is heated at a constant temperature of 800 ° C. to 1300 ° C. While growing in the form of fibers, the intermediates of the obtained carbon fiber structure are obtained by growing in the circumferential direction of the catalyst particles used to obtain a three-dimensional network-like carbon fiber structure intermediate. A three-dimensional network-like carbon fiber structure composed of carbon fibers having an outer diameter of 15 to 100 nm, formed by heat treatment at a temperature in the range of 2200 ° C., wherein the carbon fiber structure has a plurality of carbon fibers extending. The carbon fiber has a particle part larger than the outer diameter of the carbon fiber and bonded to each other, and the particle part is formed in the growth process of the carbon fiber. The carbon fiber structure is rough, the surface thereof is rough and contains iron derived from the reaction catalyst, and the total iron content measured by the fluorescent X-ray method is 0.5 to 5.0 mass in the fine carbon fiber. %, And 5 to 100% of the iron is in a state where it can be eluted with dilute hydrochloric acid.

In the method for heat-treating the intermediate of the fine carbon fiber, the furnace comprises a furnace body that constitutes a flow path that allows the flow of the fine carbon fiber due to its own weight, and the fine carbon fiber is heat-treated by heating the carbon fiber in the flow path. A method for producing fine carbon fibers, characterized by using a heat treatment apparatus.

Furthermore, the present invention provides an organic solvent solution or an aqueous solution of a boron compound or a fine solid powder before the heat treatment after obtaining the fine carbon fiber intermediate described above, thereby converting the fine carbon fiber into a boron equivalent. In which 0.001 to 30% by mass of a boron compound is contained.

Further, the present invention is a method for producing a fine carbon fiber, wherein the fine carbon fiber is preliminarily molded through hot pressing in the course of the production process and contains catalytic iron as a constituent component, and is measured by a fluorescent X-ray method. The total iron content is 0.5 to 5.0% by mass in the fine carbon fiber, and 5 to 100% of the iron is in a state in which it can be eluted with dilute hydrochloric acid. A method for producing a preform of a fiber.

That is, the present invention is a three-dimensional network-like carbon fiber structure which is preformed through a hot press in the course of the production process and is composed of carbon fibers having an outer diameter of 15 to 100 nm. The carbon fiber structure is a mode in which a plurality of carbon fibers extend, has a granular portion that has a larger particle diameter than the outer diameter of the carbon fibers and bonds the carbon fibers to each other, and the granular structure Part is formed in the carbon fiber growth process, the carbon fiber structure has a rough surface and contains 0.5 to 5.0% by mass of reaction catalyst-derived iron in the fine carbon fiber, of which 5 to 100% of iron is in a state where it can be eluted with dilute hydrochloric acid.

Furthermore, the present invention is a composite material characterized in that the fine carbon fibers described above are blended in a matrix at a ratio of 0.1 to 30% by mass.

Furthermore, the present invention is a composite material characterized in that the above-mentioned preform is blended in a matrix at a ratio of 0.1 to 30% by mass of the whole.

The present invention is a composite material in which the matrix includes at least an organic polymer.

Moreover, this invention is a composite material in which the said matrix contains an inorganic material at least.

Moreover, this invention is a composite material in which the said matrix contains a metal at least.

Further, the present invention is a composite characterized in that the matrix further contains at least one filler selected from the group consisting of metal fine particles, silica, calcium carbonate, magnesium carbonate, carbon black, glass fiber, and carbon fiber. Material.

The fine carbon fiber of the present invention has a rough surface and contains 0.5 to 5.0% by mass of iron derived from the reaction catalyst in the fine carbon fiber, of which 5 to 100% of iron can be eluted with dilute hydrochloric acid. Therefore, the catalytic iron component is present on the surface of the fine carbon fiber, so that a process such as surface modification is not required when producing a composite material, and the surface has a rough surface structure and the reaction catalytic iron component is in the tube. By being present in the table, it can be expected to further enhance the adhesion to the matrix material. In addition, the reaction catalyst iron component is not present in the surface portion of the carbon nanotube in the form of grains or layers, but is present in a state where it is difficult to observe the shape, for example, on the surface of the tube in the form of atoms. Since the bond is strong and cannot be peeled off by physical external force, it can be expected to improve the adhesion with a better matrix material, particularly the wettability with a metal matrix. Further, in the fine carbon fiber of the present invention, the basic carbon fiber is a three-dimensional network-like carbon fiber structure composed of carbon fibers having an outer diameter of 15 to 100 nm, and the carbon fiber structure is a carbon fiber. In the form of a plurality of extending, the carbon fiber has a granular portion that has a particle size larger than the outer diameter and couples the carbon fibers to each other, and the granular portion is formed in the growth process of the carbon fiber Since the fine carbon fiber of the present invention is formed in a three-dimensional network, the adhesion with the matrix material is further improved by the surface roughness and the catalytic iron component present on the surface. When the composite material is finally produced, its thermal conductivity, conductivity, and mechanical strength are good. Moreover, the process for providing a three-dimensional structure later is unnecessary. In the fine carbon fiber of the present invention, metals, ceramics other than metals, rubber, synthetic resins, carbon-based materials, and the like can be used as matrix materials.

Hereinafter, the present invention will be described in detail based on embodiments.

First, the fine carbon fiber according to the present invention will be described.
The fine carbon fiber according to the present invention is a fine carbon fiber containing iron derived from a reaction catalyst as a constituent component, and the iron component is bonded to the fine carbon fiber, and the total iron measured by a fluorescent X-ray method. Fine carbon fiber characterized in that the content is 0.5 to 5.0% by mass in the fine carbon fiber, and 5 to 100% of the iron component is in a state in which it can be eluted with dilute hydrochloric acid. It is.

The fine carbon fiber of the present invention is not particularly limited, and can take various forms.
Specifically, as the fine carbon fiber, for example, a single-walled carbon nanotube having a diameter of about several nanometers formed by a single graphene sheet being rolled into a cylindrical shape, or a multi-layer carbon in which a cylindrical graphene sheet is stacked in a direction perpendicular to the axis Various types of carbon nanohorns such as nanotubes (multi-walled carbon nanotubes) and single-walled carbon nanotubes with a conical closed end are included. Further, these fine carbon fibers are not limited to single-fibrous ones, but are branched. Or a three-dimensional structure. In the present invention, these fine carbon fibers can be used alone or in a mixture of two or more.

Furthermore, the fiber characteristics such as the fiber diameter, fiber length, and aspect ratio of the fine carbon fiber are not particularly limited. However, the fine carbon fiber according to the present invention is uniformly formed in the matrix in constituting the composite material. It is desirable to have properties that can be dispersed. Although not particularly limited, for example, the fiber diameter is about (0.5 to 120) nm, and the aspect ratio of the fine carbon fiber is about (5 to 5,000). Can do.
Furthermore, it is desirable that the I _D / I _G ratio measured by Raman spectroscopy of fine carbon fibers is 0.2 or more, more preferably 1.0 to 0.40. Here, in the Raman spectroscopic analysis, only a peak (G band) near 1580 cm ⁻¹ appears in large single crystal graphite. A peak (D band) appears in the vicinity of 1360 cm ⁻¹ due to the crystal having a finite minute size or lattice defects. For this reason, the smaller the intensity ratio (R = I ₁₃₆₀ / I ₁₅₈₀ = I _D / I _G ) between the D band and the G band, the smaller the amount of defects in the graphene sheet constituting the carbon fiber, and I _D This is because the fine carbon fiber according to the present invention can exhibit higher adhesive strength with the matrix material when the / _IG ratio is the above-mentioned predetermined value.

Further, the fine carbon fiber is preferably a three-dimensional network-like carbon fiber structure having a predetermined structure as described in detail below.
That is, in a preferred embodiment of the present invention, the fine carbon fiber is a three-dimensional network-like carbon fiber structure composed of fine carbon fibers having an outer diameter of 15 to 100 nm, and the carbon fiber structure is a fine carbon. In a mode in which a plurality of fibers are extended, the fine carbon fibers have a particle size larger than an outer diameter of the fine carbon fibers, and the fine carbon fibers are bonded to each other. In the process, the fine carbon fiber constituting the carbon fiber structure is a fine carbon fiber containing iron derived from the reaction catalyst as a constituent element, and is the total of those measured by the fluorescent X-ray method. Fine carbon fiber, characterized in that the iron content is 0.5 to 5.0% by mass in the fine carbon fiber, and 10 to 100% of the iron is in a state in which it can be eluted with dilute hydrochloric acid. It is.

In a preferred embodiment of the fine carbon fiber according to the present invention, the outer diameter of the fine carbon fiber constituting the basic three-dimensional network-like carbon fiber structure is in the range of 15 to 100 nm. More desirably within the range of 70 nm. In this outer diameter range, a cylindrical graphene sheet laminated in a direction perpendicular to the axis, that is, a multilayer, is not easily bent, and is elastic, that is, has the property of returning to its original shape even after deformation. Therefore, a composite material having higher mechanical properties is obtained after being arranged in a matrix such as a resin.

In addition, it is desirable that the fine carbon fiber has an outer diameter that changes along the axial direction. If the outer diameter of the fine carbon fibers is not constant along the axial direction and changes, the carbon fiber is considered to have an anchor effect in the matrix such as a resin, and the movement in the matrix It is difficult to occur and the dispersion stability is increased.

Further, in this fine carbon fiber, fine carbon fibers having such a predetermined outer diameter are present in a three-dimensional network, and these fine carbon fibers are mutually connected in granular parts formed in the growth process of the fine carbon fibers. It is bonded and has a shape in which a plurality of the fine carbon fibers extend from the granular part. In this way, the fine carbon fibers are not simply entangled with each other, but are firmly bonded to each other in the granular portion, so that when the structure is disposed in a matrix such as a resin, the structure is Without being dispersed as a single fine carbon fiber, the bulky structure can be dispersed and blended in the matrix. Further, in the fine carbon fiber structure according to the present invention, since the fine carbon fibers are bonded to each other by the granular portion formed in the growth process of the fine carbon fiber, the electrical characteristics of the structure itself, etc. For example, the electrical resistance value measured at a constant compression density is a mere entanglement of fine carbon fibers, or a junction between fine carbon fibers at a carbonaceous material or a carbide thereof after synthesizing the carbon fiber. Compared with the value of a structure or the like formed by adhesion, a very low value is exhibited, and when dispersed in a matrix, a good conductive path can be formed.

Since the granular part is formed in the growth process of the carbon fiber as described above, the carbon-carbon bond in the granular part is sufficiently developed and includes a mixed state of sp ² bond and sp ³ bond. I think that the. And after the generation (intermediate and first intermediate described later), the granular part and the fiber part are continuous with a structure in which patch-like sheet pieces made of carbon atoms are bonded together, and thereafter After the heat treatment, at least a part of the graphene layer constituting the granular part is continuous with the graphene layer constituting the fine carbon fiber extending from the granular part. In the carbon fiber structure, between the granular portion and the fine carbon fiber, it is symbolized that the graphene layer constituting the granular portion as described above is continuous with the graphene layer constituting the fine carbon fiber. These are connected by carbon crystal structural bonds (at least a part thereof), whereby a strong bond between the granular portion and the fine carbon fiber is formed.

In the present specification, the term “extending” the carbon fiber from the granular part simply means that the granular part and the carbon fiber are apparently connected by other binder (including carbonaceous material). It does not indicate such a state, but mainly means a state in which they are connected by carbon crystal structural bonds as described above.

The particle size of the granular part is desirably larger than the outer diameter of the fine carbon fiber. Specifically, for example, the outer diameter of the fine carbon fiber is 1.3 to 250 times, more preferably 1.5 to 100 times, and still more preferably 2.0 to 25 times. In addition, the said value is an average value. Thus, if the particle size of the granular part, which is a bonding point between the fine carbon fibers, is sufficiently large as 1.3 times or more of the outer diameter of the fine carbon fiber, with respect to the fine carbon fiber extending from the granular part When the carbon fiber structure is disposed in a matrix such as a resin, even when a certain amount of shearing force is applied, the three-dimensional network structure is maintained in the matrix. Can be dispersed. On the other hand, if the size of the granular part is extremely large exceeding 250 times the outer diameter of the fine carbon fiber, the fibrous properties of the carbon fiber structure may be impaired. For example, addition to various matrices This is not desirable because it may not be suitable as an agent or a compounding agent. The “particle size of the granular part” in the present specification is a value measured by regarding the granular part, which is a bonding point between carbon fibers, as one particle.

The specific particle size of the granular part depends on the size of the carbon fiber structure and the outer diameter of the fine carbon fiber in the carbon fiber structure, but for example, an average value of 20 to 5000 nm, more preferably It is about 25 to 2000 nm, more preferably about 30 to 500 nm.

Furthermore, since this granular part is formed in the growth process of the fine carbon fiber as described above, it has a relatively nearly spherical shape, and the circularity is 0.2 to < 1, preferably 0.5 to 0.99, more preferably about 0.7 to 0.98.

In addition, the granular portion is formed in the process of growing fine carbon fibers as described above. For example, the joints between the fine carbon fibers are formed by the carbonaceous material or carbide thereof after the synthesis of the fine carbon fibers. Compared to a structure or the like that is attached, the bonding between the fine carbon fibers in the granular part is very strong, and even under conditions that cause breakage of the fine carbon fibers in the carbon fiber structure. The granular part (joint part) is held stably.

The carbon fiber structure desirably has an area-based circle-equivalent mean diameter of 50 to 1000 μm, preferably 50 to 500 μm, more preferably about 60 to 250 μm. Here, the area-based circle-equivalent mean diameter is obtained by photographing the outer shape of the carbon fiber structure using an electron microscope or the like, and in this photographed image, the contour of each carbon fiber structure is represented by an appropriate image analysis software such as WinRoof. (Trade name, manufactured by Mitani Shoji Co., Ltd.) is used to determine the area within the contour, calculate the equivalent circle diameter of each fiber structure, and average it.

Since it depends on the type of matrix material such as resin to be compounded, it is not applied in all cases, but when applied to a preform, the one with a larger equivalent circle average diameter is more conductive, This is preferable for mechanical properties and thermal properties, but if it exceeds 1000 μm, the distribution of the carbon fiber structure in the preform becomes inhomogeneous, and the above properties cannot be obtained. When blended in a matrix such as the above, it becomes a factor for determining the longest length of the carbon fiber structure. In general, if the average equivalent circle diameter is less than 50 μm, the mechanical properties and conductivity are sufficiently exhibited. There is a fear that it will not be.

The carbon fiber structure has a shape in which fine carbon fibers existing in a three-dimensional network are bonded to each other in a granular portion, and a plurality of the fine carbon fibers extend from the granular portion. In the structure, when there are a plurality of granular parts connecting fine carbon fibers to form a three-dimensional network, the average distance between adjacent granular parts is, for example, 0.5 μm to 300 μm, more preferably 0. .5 to 100 μm, more preferably about 1 to 50 μm. In addition, the distance between this adjacent granule part measures the distance from the center part of one granular material to the center part of the granule part adjacent to this. When the average distance between the granular materials is less than 0.5 μm, the fine carbon fiber does not sufficiently develop into a three-dimensional network, so that, for example, a good conductive path is obtained when dispersed in a matrix. On the other hand, if the average distance exceeds 300 μm, the dispersion of the carbon fiber structure into the matrix becomes a factor in increasing the viscosity when dispersed in the matrix. This is because there is a risk of decrease.
Furthermore, as described above, the carbon fiber structure has a shape in which fine carbon fibers existing in a three-dimensional network are bonded to each other in the granular portion, and a plurality of the fine carbon fibers extend from the granular portion. For this reason, the structure has a bulky structure in which fine carbon fibers are sparsely present. Specifically, for example, the bulk density is 0.0001 to 0.05 g / cm ³ , more preferably 0.001. It is desirable that it is ˜0.02 g / cm ³ . If the bulk density exceeds 0.05 g / cm ³ , the dispersibility of the filler deteriorates and it tends to aggregate in the matrix material. Therefore, the addition of a small amount can improve the physical properties of the matrix such as a resin. This is because it becomes difficult.

Further, the carbon fiber structures, _I D / _{I G} ratio determined by Raman spectroscopy is, it is preferable 0.2 or more, more preferably 1.0 to 0.4. Here, in the Raman spectroscopic analysis, only a peak (G band) near 1580 cm ⁻¹ appears in large single crystal graphite. A peak (D band) appears in the vicinity of 1360 cm ⁻¹ due to the crystal having a finite minute size or lattice defects. For this reason, the smaller the intensity ratio (R = I ₁₃₆₀ / I ₁₅₈₀ = I _D / I _G ) between the D band and the G band, the smaller the amount of defects in the graphene sheet constituting the carbon fiber structure, When the I _D / I _G ratio is the above predetermined value, the fine carbon fiber according to the present invention has an appropriate crystal structure and a non-smooth surface state, and has a higher adhesive strength with the matrix. It is because it can be demonstrated.

0.2 or higher when evaluated using the I _{D /} I _G ratio of defect in graphene sheets is measured by Raman spectroscopy constituting the fine carbon fibers described above, more preferably 1.0 to 0. 4 is desirable. Compared with the surface of the fine carbon fiber whose _ID / _IG ratio is 0.2 or less, it means that the surface of the fine carbon fiber is not smooth.

In the fine carbon fiber of the present invention, in particular, the carbon fiber structure having the three-dimensional network structure as described above contains iron derived from the reaction catalyst, and the total iron content measured by the fluorescent X-ray method is fine. Since the amount of iron in the carbon fiber is 0.5 to 5.0% by mass, and 5 to 100% of the iron is in a state that can be eluted with dilute hydrochloric acid, the catalyst iron component is present in the surface of the fine carbon fiber. It can be expected that the manufacturing process of the composite material does not require a process such as surface modification and enhances the adhesion with the matrix material. In addition, the reaction catalyst iron component is not present in the surface portion of the carbon nanotube in the form of grains or layers, but is present in a state where it is difficult to observe the shape, for example, on the surface of the tube in the form of atoms. Since the bond is strong and cannot be peeled off by physical external force, it can be expected to improve the adhesion with a better matrix material, particularly the wettability with a metal matrix.

The catalytic iron component present in the surface of the fine carbon fiber is present in the middle space of the fine carbon fiber in the form of catalyst particles after the CVD reaction in the reaction step, as will be described later. The iron catalyst component in the hollow is diffused by the heating effect and reaches the surface portion of the fine carbon fiber.

In the present invention, the chemical form of iron derived from the catalyst in the fine carbon fiber is mainly Fe ₃ C (compound composed of iron and carbon), Fe1-xS (compound composed of iron and sulfur), α iron and γ iron. . In addition, the presence form of iron of this invention is not limited to the above-mentioned thing, Other chemical forms, such as iron sulfide and iron oxide, may be sufficient. Further, a plurality of iron compounds may be present in combination.

The catalytic iron component present on the surface of the fine carbon fiber is not particularly limited in shape and size, and is not observable by an observation method such as TEM or SEM. 5 wt% or more of iron is detected, and XPS spectroscopy detects the presence of iron element on the surface of the fine carbon fiber. Furthermore, it does not dissolve in dilute hydrochloric acid from the fine carbon fiber obtained immediately after the CVD reaction in the reaction step described above. The catalytic iron component that will melt after the heat treatment in the heat treatment step described above.

Furthermore, the ratio of the catalytic iron component present on the surface of the fine carbon fiber described above to the catalytic iron component present in the whole fine carbon fiber can be measured by the following method. In the above-described heat treatment step, the fine carbon fiber after heat treatment is immersed in 1-5% hydrochloric acid for 25 hours, and the amount of catalytic iron remaining in the fine carbon fiber before and after the treatment soaked in this acid is measured by fluorescent X-ray analysis. From the above formula, the ratio of the catalytic iron component present on the surface of the fine carbon fiber can be obtained.
Catalytic iron components present on the surface (%)
= (1-iron remaining amount after soaking in acid / iron remaining amount before soaking in acid) x 100%

In the fine carbon fiber of the present invention, the position of the catalyst-derived iron may be present on the surface portion of the fine carbon fiber or may be present on the surface layer portion. By performing the annealing treatment in the temperature range of 900 to 2200 ° C., it is desirable that the amount of the catalytic iron component is hardly reduced as compared with that before the treatment, and the iron component has a higher degree of diffusion outside the carbon fiber.

Furthermore, the ratio of the catalytic iron present on the surface with respect to the catalytic iron present in the entire fine carbon fiber is not particularly limited, but exhibits sufficient mechanical strength and the expected ratio is For example, 5 to 100%, preferably 5 to 90%, more preferably about 5 to 70% is a composite material that is particularly excellent in terms of mechanical properties and imparts a higher adhesive effect with a matrix. It is desirable from the viewpoint of obtaining.

Further, although not particularly limited, the acid used in the above-mentioned pickling treatment is an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, and it is desirable that the acid concentration be as low as possible. It is suitable that it is 1 to 5%. If hydrochloric acid with a concentration of 5% or more is used, the physical properties of the fine carbon fiber itself may be reduced by increasing the surface defects of the fine carbon fiber due to the oxidation effect, which is undesirable from the viewpoint of improving the physical properties of the composite material. . When hydrochloric acid of 1% or less is used, the catalytic iron component present on the surface of the fine carbon fiber is not sufficiently dissolved, so that a correct measurement result cannot be obtained.

In the fine carbon fiber of the present invention, the catalytic iron component present on the surface is not present in the form of grains or layers, but the form is present in a state that is difficult to observe by an observation method such as TEM or SEM. The connection with the fine carbon fiber is strong. For example, as shown in the examples described later, the fine carbon fibers are dispersed in a liquid medium, and ultrasonic waves of a predetermined frequency are applied to the fine carbon fibers to examine the dropping rate of the catalytic iron. The dropping rate of the catalytic iron component at 0 is 0%, and it can be seen that the catalytic iron component is stably bonded to the fine carbon fibers.

In addition, in the composite material finally produced using the fine carbon fiber according to the present invention, the catalytic iron component is present on the surface of the fine carbon fiber, and the surface of the fine carbon fiber is not smooth. The adhesion between the fine carbon fibers and the matrix is improved, and it becomes stronger due to the anchor effect. When general fine carbon fibers are blended in the matrix as a filler, the surface of the filler is relatively smooth, so when strain stress is applied in the interface direction with the matrix, it is relatively easy between the matrix and the filler. A pull out problem occurs that causes a shift. On the other hand, when the fine carbon fiber according to the present invention is used, as described above, since the filler surface is not smooth and the catalytic iron component is present on the surface, the wettability at the interface with the matrix, in particular, the matrix of metals. Is improved, and even when strain stress is applied in the direction of the interface with the matrix, the matrix and the filler are less likely to be displaced.

In addition, the catalytic iron component which the fine carbon fiber of this invention has on the surface does not have a bad influence on the structure of a fine carbon fiber, and there is no possibility of deteriorating the physical property of carbon fiber.

If it is 1800 degrees C or less which is an evaporation start temperature of iron, the catalyst iron component in the surface of the above-mentioned fine carbon fiber will be stabilized, and it has fixed heat resistance.

As described above, the fine carbon fiber of the present invention is such that the surface of the basic fine carbon fiber is not smooth but has a catalytic iron component. In particular, the fine carbon fiber has a three-dimensional network structure as described above. And the network structure is not simply entangled between the fine carbon fibers, but finally has a granular part that firmly bonds the fine carbon fibers. When a composite material is manufactured, the thermal conductivity, conductivity, and mechanical strength of the composite material are good. Further, there is no need to add a process for imparting surface modification or a three-dimensional structure.

In the specification of the present application, “bundling” existing in the fine carbon fiber means that the thickness of the graphene layer varies in the outer layer portion of the fine carbon fiber, and a portion having a dent or a portion of the outer layer portion. This mainly means that the part is missing.

In the present specification, the term “coarse” of the fine carbon fiber mainly means a state in which the outer layer portion has undulations and the fiber surface is not smooth.

The fine carbon fiber according to the present invention also desirably has a combustion start temperature in air of 600 ° C. or higher, preferably 650 ° C. or higher, more preferably 680 to 700 ° C.

Furthermore, in preferable one Embodiment of the fine carbon fiber of this invention, 0.001-30 mass% in conversion of a boron with respect to a fine carbon fiber, Preferably it contains 0.01-3.0 mass% boron compound. You can also. In this case, the site where the boron compound is present in the fine carbon fiber and the compound type of the boron compound are not particularly limited. By the presence of the boron compound in the fine carbon fibers, high conductivity can be obtained even when the structure contains some defects.

(Method for producing fine carbon fiber)
Next, the method for producing fine carbon fibers according to the present invention as described above will be described.

Although the fine carbon fiber according to the present invention is not particularly limited, basically, a carbon gas is grown into a fiber by heating a mixed gas of catalyst and hydrocarbon at a constant temperature of 800 to 1300 ° C. And a heat treatment step of heating the obtained fine carbon fiber intermediate at 900 to 2200 ° C.
The basic fine carbon fiber is a three-dimensional network-like carbon fiber structure composed of fine carbon fibers having an outer diameter of 15 to 100 nm as described above, and the carbon fiber structure is composed of fine carbon fibers. In a form extending a plurality, the fine carbon fibers have a particle size larger than the outer diameter of the fine carbon fibers, and the fine carbon fibers are bonded to each other, and the granular portions are in the process of growing the fine carbon fibers In the embodiment which is formed, at the time of heating the mixed gas of the catalyst and the hydrocarbon at a constant temperature of 800 ° C. to 1300 ° C., at least two or more carbon compounds having different decomposition temperatures are used as a carbon source. Thus, while the carbon material is grown in a fibrous form, it is grown in the circumferential direction of the catalyst particles to be used to obtain an intermediate body of a three-dimensional network-like carbon fiber structure. Reaction step, by passing through a heat treatment step of heating the intermediate of obtained carbon fibrous structures at 900-2200 ° C., can be manufactured.

First, the reaction process for obtaining an intermediate of fine carbon fibers will be described. In this reaction step, basically, an organic compound such as hydrocarbon is chemically pyrolyzed by a CVD method using ultrafine transition metal particles as a catalyst to form fine carbon fibers (intermediates).

As the raw material organic compound, hydrocarbons such as benzene, toluene and xylene, alcohols such as carbon monoxide and ethanol can be used. Although not particularly limited, in order to obtain an intermediate of a carbon fiber structure having a three-dimensional network structure as described above, at least two or more carbon compounds having different decomposition temperatures may be used as a carbon source. preferable. The “at least two or more carbon compounds” described in the present specification does not necessarily mean that two or more kinds of raw material organic compounds are used, and one kind of raw material organic compound is used. However, in the process of synthesizing the fiber structure, for example, a reaction such as hydrogen dealkylation of toluene or xylene occurs, and in the subsequent thermal decomposition reaction system, there are two different decomposition temperatures. The aspect which becomes the above carbon compound is also included.

In addition, when two or more types of carbon compounds are present as carbon sources in the thermal decomposition reaction system, the decomposition temperature of each carbon compound is not limited to the type of the carbon compound, but the carbon compound in the raw material gas. Since it varies depending on the gas partial pressure or molar ratio, a relatively large number of combinations can be used as carbon compounds by adjusting the composition ratio of two or more carbon compounds in the raw material gas.

For example, alkanes or cycloalkanes such as methane, ethane, propanes, butanes, pentanes, hexanes, heptanes, cyclopropane, cyclohexane, etc., particularly alkanes having about 1 to 7 carbon atoms; ethylene, propylene, butylenes, Alkenes or cycloolefins such as pentenes, heptenes, cyclopentenes, especially alkenes having about 1 to 7 carbon atoms; alkynes such as acetylene and propyne, especially alkynes having about 1 to 7 carbon atoms; benzene, toluene, styrene, xylene, naphthalene , Aromatic or heteroaromatic hydrocarbons such as methylnaphthalene, indene and phenanthrene, especially aromatic or heteroaromatic hydrocarbons having about 6 to 18 carbon atoms, alcohols such as methanol and ethanol, especially about 1 to 7 carbon atoms Of alcohol; its Combine two or more carbon compounds selected from carbon monoxide, ketones, ethers, etc., by adjusting the gas partial pressure so that different decomposition temperatures can be exhibited in the desired thermal decomposition reaction temperature range. The carbon fiber structure according to the present invention can be efficiently produced by using the material and / or adjusting the residence time in a predetermined temperature range and optimizing the mixing ratio.

Among such combinations of two or more carbon compounds, for example, in the combination of methane and benzene, the molar ratio of methane / benzene is> 1 to 600, more preferably 1.1 to 200, still more preferably. It is desirable to set it as 3-100. This value is the gas composition ratio at the entrance of the reactor. For example, when toluene is used as one of the carbon sources, toluene is decomposed 100% in the reactor, and methane and benzene are 1 In consideration of the occurrence of: 1, a shortage of methane may be supplied separately. For example, when the methane / benzene molar ratio is 3, 2 moles of methane may be added to 1 mole of toluene. In addition, as methane added to such toluene, not only a method of preparing fresh methane separately, but also the unreacted methane contained in the exhaust gas discharged from the reactor is circulated and used. It is also possible to use it.

By setting the composition ratio within such a range, it is possible to obtain a carbon fiber structure having a structure in which both the carbon fiber part and the granular part are sufficiently developed.

Note that an inert gas such as argon, helium, or xenon, or hydrogen can be used as the atmospheric gas.

As the catalyst, a transition metal such as iron, cobalt or molybdenum, or a mixture of a transition metal compound such as ferrocene or metal acetate and sulfur or a sulfur compound such as thiophene or iron sulfide is used. The present invention mainly uses an iron catalyst.

The synthesis of the intermediate is carried out by using a CVD method such as hydrocarbon which is usually performed, evaporating a mixed liquid of hydrocarbon and catalyst as raw materials, introducing hydrogen gas or the like into the reaction furnace as a carrier gas, Pyrolysis at a temperature of 1300 ° C. As a result, a plurality of carbon fiber structures (intermediates) having a sparse three-dimensional structure in which fibers having an outer diameter of 15 to 100 nm are bonded together by a granular material grown using the catalyst particles as nuclei are several cm to An assembly of several tens of centimeters is synthesized.

The thermal cracking reaction of the hydrocarbon as a raw material mainly occurs on the surface of the granular particles grown using the catalyst particles or the core, and the recrystallization of carbon generated by the decomposition proceeds in a certain direction from the catalytic particles or granular materials. Grows in a fibrous form. However, in obtaining the carbon fiber structure according to the present invention, the balance between the thermal decomposition rate and the growth rate is intentionally changed. For example, as described above, at least two carbon sources having different decomposition temperatures are used. By using the above carbon compound, the carbon material is grown three-dimensionally around the granular material without growing the carbon material only in a one-dimensional direction. Such three-dimensional carbon fiber growth does not depend only on the balance between the thermal decomposition rate and the growth rate, but the crystal surface selectivity of the catalyst particles, the residence time in the reactor, the temperature distribution in the furnace, etc. In addition, the balance between the thermal decomposition reaction and the growth rate is influenced not only by the type of carbon source as described above but also by the reaction temperature and gas temperature. In general, when the growth rate is faster than the pyrolysis rate as described above, the carbon material grows in a fibrous form, whereas when the pyrolysis rate is faster than the growth rate, the carbon material is surrounded by catalyst particles. Grows in the plane direction. Therefore, by intentionally changing and controlling the balance between the thermal decomposition rate and the growth rate, the growth direction of the carbon material can be set to multiple directions instead of a fixed direction, and the three-dimensional structure according to the present invention can be formed. In this intermediate, the composition of the catalyst, residence time in the reactor, reaction temperature, gas temperature, etc. can be optimized in order to easily form a three-dimensional structure in which the fibers are bonded together by granular materials. desirable.

The intermediate obtained as described above has an incomplete structure in which patch-like sheet pieces made of carbon atoms are bonded together, and has many defects. This intermediate contains unreacted raw material, non-fibrous carbide, tar content and catalytic metal. In addition, 10 to 90% of the relative amount which exists as iron sulfide among catalyst iron is preferable, More preferably, it can be 30 to 80%.

In order to produce fine carbon fibers that have a rough surface, contain catalytic iron in an amount of 0.5 to 5.0% by mass, and some of the catalytic iron can be eluted with dilute hydrochloric acid, fine carbon fibers are used. It is preferable to control the catalyst component for reaction generation of the fiber intermediate. In order to easily generate the above-mentioned fine carbon fiber intermediate, it is desirable to optimize the composition of the catalyst, the residence time in the reaction furnace, the reaction temperature, the gas temperature, and the like. For example, when sulfur or a sulfur compound and iron or an iron compound are used as the catalyst, the molar ratio of sulfur atom in the sulfur source / iron atom in the iron source is preferably 0.01 to 10, more preferably 0.05. To 5, more preferably 0.1 to 2.

The “intermediate of fine carbon fiber” as used in the present invention is a product obtained by heating a mixed gas of a catalyst and a hydrocarbon at a predetermined temperature to grow a carbon material into a fibrous form, and before heat treatment. Means fine carbon fiber.

In the method for producing a carbon fiber structure of the present invention, a preliminary annealing process can be added as necessary. Specifically, the carbon fiber structure intermediate obtained in the reaction step is heated at 800 ° C. to 1200 ° C. for 5 to 20 minutes. By this preliminary annealing treatment step, the unreacted raw material, non-fibrous carbide, tar content and part or all of the catalytic metal contained in the intermediate obtained in the reaction step are removed.

Thereafter, as a heat treatment step, heat treatment is performed on the fine carbon fiber intermediate or the carbon fiber structure intermediate after the reaction step. As the heat treatment process, the fine carbon fiber intermediate or the graphene structure of the carbon fiber structure intermediate is appropriately developed, and as described above, the surface of the fine carbon fiber contains the catalytic iron component and forms a non-smooth surface. It will not specifically limit if it can be performed, For example, it can carry out by performing heat processing in 900-2200 degreeC.
As an example of a preferable heat treatment, first, the reaction step is completed, and the intermediate of the fine carbon fiber or the intermediate of the carbon fiber structure is annealed at 900 to 2200 ° C., more preferably 1500 to 1800 ° C. be able to.
Thus, when the annealing treatment is performed at a temperature in the range of 1500 to 1800 ° C., the crystallinity of the obtained fine carbon fibers is increased to some extent, and the catalytic iron component is diffused to the surface of the fine carbon fibers by the heating effect. Only when the composite material is produced by the presence of catalytic iron component on the surface of fine carbon fiber with non-smooth surface without evaporating, electrical conductivity, thermal conductivity, mechanical strength, etc. Sufficient performance.

The intermediate obtained by heating and generating the mixed gas of the catalyst and hydrocarbon in the generation furnace at a temperature in the range of 800 to 1300 ° C. is lowered in the heating furnace held at a temperature in the range of 900 to 2200 ° C. It may be obtained by heat purification.

In the production furnace, the mixed gas of catalyst and hydrocarbon is heated at a temperature in the range of 800 to 1300 ° C. to produce a first intermediate, and the first intermediate is heated to a temperature in the range of 800 to 1200 ° C. In the second heating furnace in which the second intermediate is produced by heating while passing through the first heating furnace, and the second intermediate is heated and held at a temperature in the range of 900 to 2200 ° C. It may be obtained by heating and purifying while lowering.

The intermediate of fine carbon fiber contains various iron components such as iron sulfide, iron carbide, and pure iron. A vertical heat treatment apparatus that includes a furnace body that constitutes a flow path that allows the flow of fine carbon fibers due to its own weight and heat-treats the carbon fibers in the flow path when heat treating the intermediate of the fine carbon fibers. Can be used to produce a fine carbon fiber in which the iron component easily dissolves in dilute hydrochloric acid and contains a large amount of the iron component in the surface layer portion. When the fine carbon fibers naturally fall into the heat treatment furnace, a part of the iron component derived from the catalyst existing in the fine carbon fibers can be evaporated, and the iron component can be vaporized in the heat treatment furnace. . By convection of the vaporized iron component in a vertically long heat treatment apparatus, it is possible to enhance the contact of the iron component with the fine carbon fiber surface. Further, the diffusion of iron from the inside of the fine carbon fiber to the outside may be promoted by heat treatment.

The heat treatment time is not particularly limited, but can be about 5 to 120 minutes, more preferably about 20 to 60 minutes.

At this time, a reducing gas or a small amount of carbon monoxide gas may be added to the inert gas atmosphere in order to protect the material structure.

Note that the fine carbon fiber obtained by annealing at 1500 ° C. to 2200 ° C. in the heat treatment step has high durability against high temperatures. In addition, since the defects in the fine carbon fibers are reduced to some extent by the annealing treatment, the thermal stability is high at 660 ° C. or higher even in the air.

In the embodiment for obtaining the fine carbon fiber containing the boron compound as described above as the fine carbon fiber of the present invention, for example, the reaction step as described above is performed as a step for containing the boron compound. It can be performed by adding the following steps to the manufacturing process.

That is, after the above-described reaction step, fine carbon fibers are mixed with an organic solvent solution or an aqueous solution of a boron compound.

As the boron compound used here, simple boron, B ₂ O ₃ , H ₃ BO ₄ , and B ₄ that have physical properties that do not evaporate due to decomposition or the like before reaching the temperature used in the heat treatment step. C, BN, etc. are mentioned. Content of a boron compound is 0.001-30 mass% in conversion of boron with respect to fine carbon fiber, Preferably it is 0.01-3.0 mass%. The portion where the boron compound is present in the fine carbon fiber is a state where a part of carbon atoms constituting the fine carbon fiber is substituted with boron, a state where boron is attached to the surface of the fine carbon fiber, a surface of the fine carbon fiber There is a state in which the catalyst iron component diffused in the vicinity is taken in. At this time, the boron compound can adopt various compound species. As described above, the presence of the boron compound in the fine carbon fiber makes it possible to obtain high conductivity even when the structure contains some defects.

(Pre-form of fine carbon fiber)
Next, the preform of the fine carbon fiber according to the present invention will be described.

As described above, the preform of the fine carbon fiber of the present invention is a fine carbon fiber, preferably a carbon fiber structure having a specific three-dimensional network structure as described above is hot-pressed during the production process. The surface is preliminarily molded through an annealing process, and the surface thereof is characterized by having a non-smooth surface having a catalytic iron component.

The shape and size of the preform of the fine carbon fiber according to the present invention are determined based on the shape and size of the composite material finally formed using the preform. The preform of the fine carbon fiber thus obtained has the characteristics of the fine carbon fiber according to the present invention as described above, has improved handling properties, and further produced a composite molded body at the previous stage. In this case, the contact with the matrix used is improved. As a result, it is possible to facilitate the molding process of the finally produced composite material and to make the obtained molded body strong.

(Method for producing a preform of fine carbon fiber)
The fine carbon fiber preform as described above is subjected to the reaction step as described in relation to the above-mentioned “method for producing fine carbon fiber”, and is applied to the surface of the intermediate of the fine carbon fiber or the intermediate of the carbon fiber structure. The carbon fiber intermediate or carbon fiber structure intermediate is hot-pressed at 100 ° C. to 200 ° C. with the binder attached, and then subjected to the heat treatment in the same heat treatment step as described above. Can be prepared.

It is the same as described above, and it is of course possible to add additional steps such as the preliminary annealing treatment as described above and a step for incorporating a boron compound.

For forming by hot pressing, a method of pressing from above and below using a mold, a method of pressing isotropically with hydrostatic pressure using a rubber die, and the like are preferable. The molding pressure during pressing is 1 × 10 ⁵ to 2 × 10 ⁸ P.

When a thermosetting resin is used as a binder, the thermosetting resin can be cured simultaneously with molding by heating to a curing temperature of the thermosetting resin, for example, 100 to 200 ° C. during pressing.

After forming by hot pressing, heat treatment is performed by a heat treatment step. The heat treatment process is also the same as described above, and a description thereof will be omitted to avoid duplication. Through these series of steps, a preform of fine carbon fiber can be produced.

The shape and size of the fine carbon fiber preform are determined based on the shape and size of the composite material finally formed using the preform. The preform of the fine carbon fiber thus obtained has a void inside, and in the further stage, the void is impregnated with a matrix material to produce a composite molded body. In the impregnation, the contact between the preform of the fine carbon fiber and the matrix becomes good, and the adhesion between the fine carbon fiber and the matrix becomes strong due to the anchor effect. As a result, the composite material finally produced can be made stronger.

(Use of fine carbon fiber and preform of fine carbon fiber)
Obtained by the fine carbon fiber and the fine carbon fiber preform according to the present invention as described above, or the fine carbon fiber production method and the fine carbon fiber preform according to the present invention as described above. As described above, the fine carbon fiber and the preform of the fine carbon fiber have properties such as mechanical properties, electrical conductivity, thermal conductivity, good dispersibility with respect to the matrix, and the like. It can be suitably used in a wide range as a filler for composite materials for solid materials such as ceramics and metals.

Next, in the composite material using the fine carbon fiber and the preform of the fine carbon fiber according to the present invention, an organic polymer, an inorganic material, a metal, or the like is preferably used as the matrix for dispersing the fine carbon fiber as described above. be able to.

Examples of organic polymers include polypropylene, polyethylene, polystyrene, polyvinyl chloride, polyacetal, polyethylene terephthalate, polycarbonate, polyvinyl acetate, polyamide, polyamideimide, polyetherimide, polyetheretherketone, polyvinyl alcohol, polyphenylene ether, and poly (meth) acrylate. And various thermoplastic resins such as liquid crystal polymers, epoxy resins, vinyl ester resins, phenol resins, unsaturated polyester resins, furan resins, imide resins, urethane resins, melamine resins, silicone resins and urea resins, Natural rubber, styrene / butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), ethylene / propylene rubber (EPDM), Various elastomers such as tolyl rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), urethane rubber, silicone rubber, fluorine rubber, acrylic rubber (ACM), epichlorohydrin rubber, ethylene acrylic rubber, norbornene rubber and thermoplastic elastomer Is mentioned.

The organic polymer may be in the form of various compositions such as adhesives, fibers, paints, and inks.

That is, the matrix is, for example, epoxy adhesive, acrylic adhesive, urethane adhesive, phenol adhesive, polyester adhesive, vinyl chloride adhesive, urea adhesive, melamine adhesive, olefin adhesive Adhesives, vinyl acetate adhesives, hot melt adhesives, cyanoacrylate adhesives, rubber adhesives and cellulose adhesives, acrylic fibers, acetate fibers, aramid fibers, nylon fibers, novoloid fibers, Cellulose fiber, viscose rayon fiber, vinylidene fiber, vinylon fiber, fluorine fiber, polyacetal fiber, polyurethane fiber, polyester fiber, polyethylene fiber, polyvinyl chloride fiber, polypropylene fiber, etc., phenol resin paint, alkyd resin paint Epoxy resin paint, Acrylic resin paint, unsaturated polyester paint, polyurethane paint, silicone paint, fluorine resin paint may be a paint such as a synthetic resin emulsion based paint.

Examples of the inorganic material include a ceramic material, an inorganic oxide polymer, and a carbon-based material. Specifically, for example, carbon materials such as carbon carbon composites, glass, glass fibers, sheet glass and other molded glass, silicate ceramics and other refractory ceramics such as aluminum oxide, silicon carbide, magnesium oxide, silicon nitride And boron nitride.

Moreover, when a matrix is a metal, metals, such as aluminum, magnesium, titanium, zinc, chromium, copper, silver, lead, copper, or 2 or more types of these metals, and a mixture are mentioned, for example.

Further, the composite material may contain other fillers in addition to the fine carbon fibers described above. Examples of such fillers include metal fine particles, silica, calcium carbonate, magnesium carbonate, carbon black, and glass fibers. , Carbon fibers, and the like, and these may be used alone or in combination of two or more.

The composite material includes an effective amount of the fine carbon fiber or the carbon fiber preform according to the present invention in the matrix as described above. The amount varies depending on the use of the composite material and the matrix, but can be, for example, about 0.1% to 98%. If it is less than 0.1%, the reinforcing effect of strength as a structural material is small, and the electrical conductivity is not sufficient. If it exceeds 98%, the characteristics of the matrix material cannot be exhibited sufficiently. In the composite material using the fine carbon fiber or the preform of the fine carbon fiber of the present invention, the fine carbon fiber can be arranged with a uniform spread in the matrix, and the surface is not smooth and the catalyst is on the surface. Since it has an iron component, it is a composite material useful as a functional material excellent in electrical conductivity, thermal conductivity, radio wave shielding, etc., a structural material having high strength, and the like.

Hereinafter, the present invention will be described more specifically based on examples. In the following, each physical property value was measured as follows.

<Area-based circle equivalent average diameter>
First, a photograph of the carbon fiber structure is taken with an SEM. In the obtained SEM photograph, only the carbon fiber structure with a clear outline was targeted, and the carbon fiber structure with a broken outline was not targeted because the outline was unclear. All carbon fiber structures (about 60 to 80) that can be targeted in one field of view were used, and about 200 carbon fiber structures were targeted in three fields of view. Trace the contour of each carbon fiber structure targeted using image analysis software WinRoof (trade name, manufactured by Mitani Corp.), obtain the area within the contour, and calculate the equivalent circle diameter of each fiber structure This was averaged.

<Measurement of bulk density>
A transparent cylinder with an inner diameter of 70 mm is filled with 1 g of powder, and air with a pressure of 0.1 Mpa and a capacity of 1.3 liters is sent from the lower part of the dispersion plate to blow out the powder and let it settle naturally. At the time of blowing out 5 times, the height of the powder layer after settling is measured. At this time, the number of measurement points was six, and after calculating the average of the six points, the bulk density was calculated.

<Raman spectroscopy>
Using a Yin Lab LabRam HR-800-Horiba manufactured by Horiba Jobin Yvon, measurement was performed using a wavelength of 514 nm of an argon laser.

<TG combustion temperature>
Using TG-DTA manufactured by Mac Science, the temperature was increased at a rate of 10 ° C./min while circulating air at a flow rate of 0.1 liter / min, and the combustion behavior was measured. During combustion, TG indicates a decrease in weight, and DTA indicates an exothermic peak. Therefore, the top position of the exothermic peak was defined as the combustion start temperature.

<X-ray diffraction analysis>
Using a powder X-ray diffractometer (JEOL-JDX-3532, manufactured by JEOL Ltd.), the fine carbon fiber or carbon fiber structure after the annealing treatment was examined. The Kα ray generated at 40 kV and 30 mA in a Cu tube is used, and the surface spacing is measured according to the Gakushin method (the latest carbon material experiment technology (analysis and analysis), edited by the Carbon Materials Society of Japan). Used as internal standard.

<Average particle size of granular part, circularity, ratio with fine carbon fiber>
Similar to the measurement of the area-based circle-equivalent mean diameter, first, a photograph of the carbon fiber structure is taken with an SEM. In the obtained SEM photograph, only the carbon fiber structure with a clear outline was targeted, and the carbon fiber structure with a broken outline was not targeted because the outline was unclear. All carbon fiber structures (about 60 to 80) that can be targeted in one field of view were used, and about 200 carbon fiber structures were targeted in three fields of view.

In each of the targeted carbon fiber structures, a granular portion that is a bonding point between carbon fibers is regarded as one particle, and its outline is defined by using image analysis software WinRoof (trade name, manufactured by Mitani Corporation). By tracing, the area in the contour was obtained, the equivalent circle diameter of each granular part was calculated, and this was averaged to obtain the average particle diameter of the granular part. Further, the circularity (R) is calculated based on the following equation from the area (A) in the contour measured using the image analysis software and the measured contour length (L) of each granular portion. Was averaged.

[Formula 1]
R = A * 4π / L ²

Furthermore, the outer diameter of fine carbon fibers in each targeted carbon fiber structure is obtained, and the size of the granular portion in each carbon fiber structure is determined from this and the equivalent circle diameter of the granular portion in each carbon fiber structure. It calculated | required as a ratio with a fine carbon fiber, and averaged this.

<Content of catalytic iron component in fine carbon fiber>
Metal elements were analyzed using a fluorescent X-ray measurement apparatus (Rigaku ZSXmini, manufactured by Rigaku Corporation). For confirmation, a catalytic iron component was separately detected using an X-ray diffraction measurement apparatus JEOL-JDX-3532 (manufactured by JEOL Ltd.).

<Composition and composition ratio of catalytic iron component in fine carbon fiber>
The composition and composition ratio of the catalytic iron component in the fine carbon fibers were analyzed using ⁵⁷ Fe Mossbauer spectroscopy (Austin Science S-600 Mossbauer spectrometer).

<Surface existence rate of fine carbon fiber of catalyst iron component>
In the heat treatment step, the fine carbon fiber after heat treatment is immersed in 1-5% hydrochloric acid for 25 hours, and the amount of iron derived from the catalyst remaining in the fine carbon fiber before and after the treatment immersed in this acid is measured by fluorescent X-ray analysis. Then, the abundance ratio can be obtained on the surface of the fine carbon fiber of the catalytic iron component from the following calculation formula.
Catalytic iron components present on the surface (%)
= (1-iron remaining amount after soaking in acid / iron remaining amount before soaking in acid) x 100%

<Dropping test of catalytic iron component present on the surface of fine carbon fiber>
Fine carbon fibers were added to 100 ml of toluene in a vial with a lid at a rate of 10 to 100 μg / ml to prepare a dispersion sample of fine carbon fibers.
The thus obtained fine carbon fiber dispersion liquid sample was subjected to ultrasonic waves using an ultrasonic cleaner having a transmission frequency of 38 kHz and an output of 150 w (trade name: USK-3, manufactured by SND Corporation). After 60 minutes from the application of the ultrasonic wave, the dispersion sample was dried, and the dried fine carbon fiber was detected for the elemental iron component by fluorescent X-ray analysis. The amount of iron element before and after the drop-off test was compared, and the drop-out property of the iron catalyst present on the surface of the fine carbon fiber was examined.

[Example 1] Production of intermediate of fine carbon fiber (reaction process)
It was synthesized by a CVD method using toluene as a raw material. A mixture of ferrocene and thiophene was used as a catalyst, and the reaction was carried out under a reducing atmosphere of hydrogen gas. The composition ratio in the circulating gas used was CH ₄ 7.5%, C ₆ H ₆ 0.3%, C ₂ H ₂ 0.7%, C ₂ H ₆ 0.1%, CO _{2 in} terms of a molar ratio based on volume. 0.3%, N ₂ 3.5%, H ₂ 87.6%, and the mixing molar ratio CH ₄ of methane and benzene in the raw material gas supplied to the production furnace by mixing with fresh raw material gas / C ₆ H ₆ (Toluene in fresh raw material gas was considered to have been 100% decomposed into CH ₄ : C ₆ H ₆ = 1: 1 by heating in a preheating furnace) 3.44. The mixing flow rate was adjusted so that The final raw material gas contains C ₂ H ₂ , C ₂ H _6, CO, and carbon compounds contained in the circulating gas to be mixed. The amount was extremely small, and was practically negligible as a carbon source. And in the production | generation furnace, it thermally decomposed at 1250 degreeC and the three-dimensional network-like fiber structure (intermediate body) was obtained. A TEM photograph of this intermediate is shown in FIG. The obtained intermediate was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Corporation). The three-dimensional network-like carbon fiber structure obtained after the reaction contained 1.7 wt% of iron. In addition, ⁵⁷ Fe Mossbauer spectrum was measured using ⁵⁷ Fe Mossbauer spectroscopy (shown in FIG. 2). The ⁵⁷ Fe Mossbauer spectrum was analyzed, and the composition and composition ratio of the catalytic iron component included in the three-dimensional network-like carbon fiber structure obtained after the reaction were carbide (24.74%), sulfide (58. 00%) and pure iron (17.26%).

[Example 2] Preliminary annealing treatment The intermediate of the three-dimensional network-like carbon fiber structure obtained in Example 1 was calcined in nitrogen at 900 ° C for 20 minutes to separate hydrocarbons such as tar. Then, a preliminary annealing treatment was performed. The obtained carbon fiber structure was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Corporation). The three-dimensional network-like carbon fiber structure obtained after the preliminary annealing treatment contained 1.7 wt% of iron. Also, a ⁵⁷ Fe Mossbauer spectrum was measured and analyzed using ⁵⁷ Fe Mossbauer spectroscopy, and a three-dimensional network-like carbon fiber structure obtained after preliminary annealing treatment was analyzed. The composition and composition ratio of the catalytic iron component included in the above are carbide (57.44%), sulfide (21.16%) and pure iron (21.41%).

Moreover, the R value (I _D / I _G ) of the Raman spectroscopic measurement was 0.98 by Raman spectroscopic analysis (manufactured by Jobin Yvon LabRam HR-800-Horiba).

Moreover, the surface presence rate of the catalyst iron contained in the obtained carbon fiber structure was obtained by the above-described procedure. 85 mg of the iron component was detected by fluorescent X-ray in 5.0 g of the carbon fiber structure obtained in Example 2, immersed in 1.8% hydrochloric acid for 25 hours, washed with distilled water to a pH value of 7.0, and dried. After that, 79.6 mg of iron component was detected. From these results, the surface presence rate of the catalyst iron contained in the carbon fiber structure obtained in Example 2 was 6.3%.

[Example 3]
Annealing (heat treatment process)
The intermediate of the three-dimensional network-like carbon fiber structure obtained in Example 2 was annealed at 1200 ° C. for 20 minutes in nitrogen. The finally obtained three-dimensional network-like carbon fiber structure after annealing was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Denki Kogyo Co., Ltd.). The finally obtained three-dimensional network-like carbon fiber structure after the annealing treatment contained 1.6 wt% of iron. It was ^also measured ⁵⁷ Fe Mössbauer spectra using 57 Fe Mossbauer spectroscopy (Austin Science S-600 Mossbauer spectrometer ). The ⁵⁷ Fe Mossbauer spectrum was analyzed, and the composition and composition ratio of the catalytic iron component included in the obtained three-dimensional network-like carbon fiber structure after the annealing treatment were carbide (27.01%), sulfide ( 43.31%) and pure iron (29.68%).

Further, the R value (I _D / I _G ) measured by Raman spectroscopy (manufactured by Jobin Yvon LabRam HR-800-Horiba) was 0.85.

Moreover, the surface presence rate of the catalyst iron contained in the obtained carbon fiber structure was obtained by the above-described procedure. 80 mg of the iron component was detected by fluorescent X-ray in 5.0 g of the carbon fiber structure obtained in Example 3, immersed in 1.8% hydrochloric acid for 25 hours, washed with distilled water to a pH value of 7.0, and dried. After that, about 74 mg of iron component was detected. From these results, the surface presence rate of the catalyst iron contained in the carbon fiber structure obtained in Example 3 was 7.5%.

[Example 4]
Annealing (heat treatment process)
The intermediate body of the three-dimensional network-like carbon fiber structure obtained in Example 2 was annealed at 1500 ° C. for 20 minutes. A TEM photograph of this annealed carbon fiber structure is shown in FIG. The fine carbon fiber was constricted on a part of the fiber surface, and the fiber surface was rough.
The finally obtained three-dimensional network-like carbon fiber structure after annealing was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Denki Kogyo Co., Ltd.). The finally obtained three-dimensional network-like carbon fiber structure after the annealing treatment contained 1.6 wt% of iron. In addition, ⁵⁷ Fe Mossbauer spectrum was measured using ⁵⁷ Fe Mossbauer spectroscopy (shown in FIG. 4). The ⁵⁷ Fe Mossbauer spectrum was analyzed, and the composition and composition ratio of the catalytic iron component included in the obtained three-dimensional network-like carbon fiber structure after the annealing treatment were carbide (30.13%), sulfide ( 31.43%) and pure iron (38.45%).

Further, the R value (I _D / I _G ) measured by Raman spectroscopy (manufactured by Jobin Yvon LabRam HR-800-Horiba) was 0.85.

Further, the obtained carbon fiber structure had a circle-equivalent average diameter of 180 μm, a bulk density of 0.0031 g / cm ³ , a TG combustion temperature of 665 ° C., and an interplanar spacing of 3.46 Å.

Further, the average particle size of the granular portion in the carbon fiber structure was 350 nm (SD 180 nm), which was 5.8 times the outer diameter of the fine carbon fiber in the carbon fiber structure. The circularity of the granular part was 0.69 (SD 0.15) on average.

Moreover, the surface presence rate of the catalyst iron contained in the obtained carbon fiber structure was obtained by the above-described procedure. In 5.0 g of the carbon fiber structure obtained in Example 4, 80 mg of an iron component was detected by fluorescent X-ray, immersed in 1.8% hydrochloric acid for 25 hours, washed with distilled water to a pH value of 7.0, and dried. After the treatment, about 47 mg of iron component was detected. From these results, the surface presence rate of the catalyst iron contained in the carbon fiber structure obtained in Example 4 was 41%.

In addition, when the catalyst iron existing on the surface of the fine carbon fiber was dropped by the above procedure, the content of the catalytic iron component of the fine carbon fiber was not changed before and after the dropout experiment. It became clear that it was stably bonded to the surface.

[Example 5]
Annealing (heat treatment process)
The intermediate body of the three-dimensional network-like carbon fiber structure obtained in Example 2 was annealed at 1800 ° C. for 20 minutes. The obtained three-dimensional network-like carbon fiber structure after the annealing treatment was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Denki Kogyo Co., Ltd.). The finally obtained three-dimensional network-like carbon fiber structure after the annealing treatment contained 1.2 wt% of iron.

In addition, the R value (I _D / I _G ) measured by Raman spectroscopy (manufactured by Jobin Yvon LabRam HR-800-Horiba) was 0.80.

Moreover, the surface presence rate of the catalyst iron contained in the obtained carbon fiber structure was obtained by the above-described procedure. In 5.0 g of the carbon fiber structure obtained in Example 5, 60 mg of an iron component was detected by fluorescent X-ray, immersed in 1.8% hydrochloric acid for 25 hours, washed with distilled water to a pH value of 7.0, and dried. About 15 mg of iron component was detected after the treatment. From these results, the surface presence rate of the catalyst iron contained in the carbon fiber structure obtained in Example 5 was 75%.

[Example 6]
Annealing (heat treatment process)
The intermediate body of the three-dimensional network-like carbon fiber structure obtained in Example 2 was annealed at 2000 ° C. for 20 minutes. The obtained three-dimensional network-like carbon fiber structure after the annealing treatment was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Denki Kogyo Co., Ltd.). The finally obtained three-dimensional network-like carbon fiber structure after the annealing treatment contained 0.87 wt% of iron. In addition, ⁵⁷ Fe Mossbauer spectrum was measured and analyzed using ⁵⁷ Fe Mossbauer spectroscopy, and the obtained three-dimensional network-like carbon fiber structure after annealing was analyzed. The composition and composition ratio of the catalyst iron component included are carbide (13.11%) and pure iron (86.89%).

Further, the R value (I _D / I _G ) measured by Raman spectroscopy (manufactured by Jobin Yvon LabRam HR-800-Horiba) was 0.40.

Moreover, the surface presence rate of the catalyst iron contained in the obtained carbon fiber structure was obtained by the above-described procedure. 44 mg of the iron component was detected by fluorescent X-rays in 5.0 g of the carbon fiber structure obtained in Example 6, immersed in 1.8% hydrochloric acid for 25 hours, washed with distilled water to a pH value of 7.0, and dried. After the treatment, about 4 mg of iron component was detected. From these results, the surface presence rate of the catalyst iron contained in the carbon fiber structure obtained in Example 6 was 91%.

[Example 7]
Annealing (heat treatment process)
The intermediate body of the three-dimensional network-like carbon fiber structure obtained in Example 2 was annealed at 2200 ° C. for 20 minutes. The obtained three-dimensional network-like carbon fiber structure after the annealing treatment was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Denki Kogyo Co., Ltd.). The finally obtained three-dimensional network-like carbon fiber structure after the annealing treatment contained 0.23 wt% of iron.

Further, the R value (I _D / I _G ) measured by Raman spectroscopy (manufactured by Jobin Yvon LabRam HR-800-Horiba) was 0.30.

Moreover, the surface presence rate of the catalyst iron contained in the obtained carbon fiber structure was obtained by the above-described procedure. 12 g of the iron component was detected by fluorescent X-rays in 5.0 g of the carbon fiber structure obtained in Example 7, immersed in 1.8% hydrochloric acid for 25 hours, washed with distilled water to a pH value of 7.0, and dried. After the treatment, no iron component was detected. From these results, the surface abundance of the catalyst iron contained in the carbon fiber structure obtained in Example 7 was 100%.

[Comparative Example 1] As a comparative example of the surface abundance ratio of catalyst iron contained in a carbon fiber structure, 85 mg of an iron component was detected by fluorescent X-ray in 5.0 g of the carbon fiber structure obtained in Example 1, and 1.8 After being soaked in 25% hydrochloric acid for 25 hours, washed with distilled water to a pH value of 7.0 and dried, 85 mg of an iron component was detected. From these results, the surface abundance of the catalyst iron contained in the carbon fiber structure obtained in Example 1 was 0%. Although there are many iron components present in the carbon fiber structure obtained in Example 1, they were not present on the surface of the carbon fiber structure.

[Comparative Example 2] As a comparative example of the surface abundance ratio of catalyst iron contained in the carbon fiber structure, the intermediate of the three-dimensional network-like carbon fiber structure obtained in Example 2 was annealed at 2500 ° C for 20 minutes. . The surface abundance ratio of the obtained carbon fiber structure-containing catalyst iron was measured by the procedure described above. In 5.0 g of carbon fiber structure annealed at 2500 ° C. for 20 minutes, 1.5 mg of iron component was detected by fluorescent X-ray, immersed in 1.8% hydrochloric acid for 25 hours, and then with distilled water to a pH value of 7.0. After washing and drying until no iron component was detected. From these results, the surface presence rate of the catalyst iron contained in the carbon fiber structure obtained in Comparative Example 2 was 100%, but the amount of the iron component present in the carbon fiber structure as a whole by evaporation of the iron component. Has decreased.

The results of the surface abundance ratio of the catalyst iron contained in the carbon fiber structures obtained in Examples 2 to 7 and Comparative Examples 1 and 2 are summarized in Table 1.

[Example 8] Three-dimensional network-like carbon fiber structure obtained in Example 1 after dissolving 5.0 g of boron-added B ₂ O ₃ (manufactured by High Purity Chemical Laboratory Co., Ltd.) in 400 ml of ethanol 10 g of the intermediate body was immersed in an immersion liquid at room temperature for 30 minutes and then dried at 100 ° C. for 12 hours.

Annealing treatment 10 g of the three-dimensional network-like carbon fiber structure obtained after immersion and drying obtained in Example 8 was heated to 900 ° C. for 20 minutes, and then annealed at 1800 ° C. for 20 minutes. The finally obtained three-dimensional network-like carbon fiber structure after annealing was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Denki Kogyo Co., Ltd.). As a result of analysis, the carbon fiber structure contained 0.7 wt% of iron. Separately, the R value (I _D / I _G ) measured by Raman spectroscopy (manufactured by Jobin Yvon LabRam HR-800-Horiba) was 0.80.

[Example 9] Molded article production example 8.0 g of the three-dimensional network-like carbon fiber structure obtained in Example 8 after immersion and drying, and 4.0 g of a 60% phenol resin solution separately with 200 ml of methanol. After adding to the solution prepared by diluting and immersing for 30 minutes, the organic solvent was dried at 100 ° C. for 12 hours. Then, it hot-pressed for 30 minutes at 150 degreeC using the hot press machine, and the molded object was obtained. The obtained molded body had a mass of 7.7 g, a diameter of 40 mm, a height of 7.5 mm, and a density of 0.81 g / cm ³ .

Annealing after forming the molded body The molded body of the three-dimensional network-like carbon fiber structure obtained in Example 9 was heated at 900 ° C. for 20 minutes, and then annealed at 1800 ° C. for 20 minutes. The finally obtained three-dimensional network-like carbon fiber structure preform after the annealing treatment had a mass of 5.33 g, a diameter of 40 mm, a height of 14 mm, and a density of 0.30 g / cm ³ . The obtained three-dimensional network-like carbon fiber structure preform was analyzed for iron elements using a fluorescent X-ray measurement apparatus Rigaku ZSXmini (manufactured by Rigaku Denki Kogyo Co., Ltd.). As a result of the analysis, the preform of the carbon fiber structure contained 0.7 wt% of iron.

[Example 10] Example of preparation of epoxy composite added with fine carbon fiber 1 wt% of the carbon fiber structure obtained in Example 4 was added to bisphenol A type epoxy resin (curing agent: dicyandiamide), kneaded, defoamed Thereafter, after curing and molding at 120 ° C. for 30 minutes, a test piece was prepared, a three-point bending test was performed, and bending strength and elastic modulus were measured. The results are shown in Table 2.

[Comparative Example 3] Preparation Example of Epoxy Neat Material As a comparative example, a bisphenol A type epoxy resin (curing agent: dicyandiamide) was used and molded under the same kneading and curing conditions as in Example 10, and a three-point bending test was performed. The bending strength and elastic modulus were measured and the results are shown in Table 2.

Comparative Example 4 Production Example of Epoxy Composite Material with Fine Carbon Fiber Added As a comparative example, 1 wt% of the three-dimensional network-like carbon fiber structure obtained in Comparative Example 2 was replaced with bisphenol A type epoxy resin (curing agent: dicyandiamide). ), Kneading and curing under the same kneading and curing conditions as in Example 10, a three-point bending test was performed, and the bending strength and elastic modulus were measured. The results are shown in Table 2.

In the fine carbon fiber of the present invention, in particular, the carbon fiber structure having the three-dimensional network structure as described above contains 0.5 to 5.0% by mass of catalyst-derived iron in the fine carbon fiber, of which 5% Since ~ 100% of iron is in a state that can be eluted with dilute hydrochloric acid, the catalytic iron component is present on the surface of the fine carbon fiber, so that a process such as surface modification is not required when producing a composite material, It can be expected to enhance the adhesion to the matrix material. In addition, the reaction catalyst iron component is not present in the surface portion of the carbon nanotube in the form of grains or layers, but is present in a state where it is difficult to observe the shape, for example, on the surface of the tube in the form of atoms. The bond is strong and cannot be peeled off by a physical external force. Therefore, better adhesion to a matrix material, particularly improvement of wettability to a metal matrix can be expected.

Although it does not specifically limit as a specific example of the utilization use of the carbon fiber composite_body | complex of this invention, For example, the following can be mentioned. (1) As a structural material utilizing mechanical strength. (2) Conductive resin, conductive molded body, thermally conductive resin, thermally conductive resin molded body, packaging material, gasket, container, resistor, electric wire, etc. as those utilizing conductivity and thermal conductivity. (3) Electromagnetic wave shielding materials, (4) Body materials such as home appliances, vehicles, and aircraft, machine housings, battery pole materials, etc. that utilize physical characteristics.

It is the TEM photograph of the intermediate body of the carbon fiber structure of a three-dimensional network shape obtained in the Example of this invention. It is a ⁵⁷ Fe Mossbauer spectrum of catalytic iron included in the carbon fiber structure after reaction, obtained in an example of the present invention. 3 is a TEM photograph of a three-dimensional network-like carbon fiber structure that has been annealed and obtained in an example of the present invention. It is a ⁵⁷ Fe Mossbauer spectrum of catalytic iron included in a carbon fiber structure after annealing, obtained in an example of the present invention.

Claims (22)

A fine carbon fiber comprising iron derived from a reaction catalyst as a constituent component, wherein the iron component is bonded to the fine carbon fiber, and the total iron content measured by a fluorescent X-ray method is 0. The fine carbon fiber is 5 to 5.0% by mass, and 5 to 100% of the iron component is in a state in which it can be eluted with dilute hydrochloric acid. The fine carbon fiber according to claim 1, wherein the form of the iron component is carbide, sulfide or pure iron. The fine carbon fiber is a three-dimensional network-like carbon fiber structure composed of carbon fibers having an outer diameter of 15 to 100 nm, and the carbon fiber structure is a mode in which a plurality of carbon fibers extend, And having a granular part that binds the carbon fibers to each other larger than the outer diameter of the carbon fiber, and the granular part is formed during the growth process of the carbon fiber. Item 3. The fine carbon fiber according to Item 1 or 2. The fine carbon fiber according to any one of claims 1 to 3, wherein the fine carbon fiber has an I _D / I _G measured by Raman spectroscopy of 0.2 or more. The above-mentioned fine carbon fiber has d ₀₀₂ showing crystallinity as graphite obtained by X-ray diffraction method in a range of 3.42 mm or more. Fine carbon fiber. The fine carbon fiber according to any one of claims 1 to 5, wherein the fine carbon fiber has a part of the fiber surface and the fiber surface is rough. Said fine carbon fiber contains 0.001-30 mass% boron compound in conversion of boron with respect to carbon fiber, The fine carbon fiber of any one of Claims 1-6 characterized by the above-mentioned. A fine carbon fiber comprising iron derived from a reaction catalyst as a constituent component, wherein the iron component is bonded to the fine carbon fiber, and the total iron content measured by a fluorescent X-ray method is 0. The fine carbon fiber which is 5 to 5.0% by mass and 5 to 100% of the iron component is in a state in which it can be eluted with dilute hydrochloric acid is preformed through hot pressing. A preform of fine carbon fiber. The fine carbon fiber is a three-dimensional network-like carbon fiber structure that is preformed through a hot press in the course of its production and is composed of carbon fibers having an outer diameter of 15 to 100 nm, the carbon fiber structure Is a mode in which a plurality of carbon fibers extend, and has a granular portion that has a particle size larger than the outer diameter of the carbon fiber and bonds the carbon fibers to each other, and the granular portion grows the fine carbon fiber. The preform of fine carbon fibers according to claim 8, wherein the preform is formed in the process. A mixed gas of catalyst and hydrocarbon is heated at a constant temperature of 800 ° C. to 1300 ° C. to grow a carbon substance into a fiber to obtain a fine carbon fiber intermediate. The method comprises a step of heat treatment at a temperature in the range of 2200 ° C., having a rough surface and containing an iron component derived from a reaction catalyst, the iron component being bonded to fine carbon fibers, Production of fine carbon fibers in which the total iron content measured in step 1 is 0.5 to 5.0% by mass in the fine carbon fibers, and 5 to 100% of the iron content is in a state that can be eluted with dilute hydrochloric acid. Method. The catalyst gas is composed of sulfur or a sulfur compound and iron or an iron compound, and a molar ratio of sulfur atom in the sulfur source / iron atom in the iron source is 0.01 to 10. The manufacturing method of the fine carbon fiber of Claim 10. When the mixed gas of catalyst and hydrocarbon is heated at a constant temperature of 800 ° C. to 1300 ° C., the carbon material is grown in a fibrous form by using at least two carbon compounds having different decomposition temperatures as the carbon source. On the other hand, the carbon fiber structure intermediate obtained in the range of 900 to 2200 ° C. is obtained by growing in the circumferential direction of the catalyst particles to be used to obtain a three-dimensional network-like carbon fiber structure intermediate. A three-dimensional network-like carbon fiber structure composed of carbon fibers having an outer diameter of 15 to 100 nm, formed by heat treatment at a temperature, wherein the carbon fiber structure is a mode in which a plurality of carbon fibers extend, and the carbon fibers Having a granular portion that has a particle size larger than the outer diameter of the carbon fiber and bonds the carbon fibers to each other, and the granular portion is formed in the process of growing the carbon fibers. The elementary fiber structure has a rough surface and contains iron derived from a reaction catalyst, and the total iron content measured by a fluorescent X-ray method is 0.5 to 5.0 mass% in the fine carbon fiber, The method for producing fine carbon fibers according to claim 10 or 11, wherein 5 to 100% of iron is in a state in which it can be eluted with dilute hydrochloric acid. In the method for heat-treating the intermediate of the fine carbon fiber, the furnace comprises a furnace body that constitutes a flow path that allows the flow of the fine carbon fiber due to its own weight, and the fine carbon fiber is heated and heat-treated in the flow path. The method for producing fine carbon fibers according to claim 10, wherein a heat treatment apparatus is used. Before the heat treatment after obtaining the intermediate of the fine carbon fiber described above, by mixing an organic solvent solution or an aqueous solution of boron compound or fine solid powder, 0.001 to 0.001 in terms of boron with respect to the fine carbon fiber described above. The method for producing fine carbon fibers according to any one of claims 10 to 13, wherein 30% by mass of a boron compound is contained. The method for producing fine carbon fiber according to claim 10, wherein the fine carbon fiber is preformed through hot pressing in the course of the production process and contains catalytic iron as a constituent component, and is measured by a fluorescent X-ray method. The total iron content is 0.5 to 5.0% by mass in the fine carbon fiber, and 5 to 100% of the iron is in a state where it can be eluted with dilute hydrochloric acid. The manufacturing method of the preform. The method for producing fine carbon fibers according to claims 12 to 14, wherein the three-dimensional network-like carbon fiber structure is formed from carbon fibers having an outer diameter of 15 to 100 nm, which is preformed through a hot press during the production process. The carbon fiber structure is a form in which a plurality of carbon fibers extend, and has a granular portion that has a larger particle diameter than the outer diameter of the carbon fibers and binds the carbon fibers together, and The granular part is formed in the carbon fiber growth process, and the carbon fiber structure has a rough surface and contains 0.5 to 5.0% by mass of reaction catalyst-derived iron in the fine carbon fiber. The method for producing a preform of a fine carbon fiber according to claim 8 or 9, wherein 5 to 100% of the iron is in a state that can be eluted with dilute hydrochloric acid. A composite material comprising the fine carbon fiber according to any one of claims 1 to 7 blended in a matrix at a ratio of 0.1 to 30% by mass of the whole. A composite material, wherein the preform according to any one of claims 8 to 9 is blended in a matrix at a ratio of 0.1 to 30% by mass of the whole. The composite material according to claim 17 or 18, wherein the matrix contains at least an organic polymer. The composite material according to claim 17 or 18, wherein the matrix includes at least an inorganic material. The composite material according to claim 17 or 18, wherein the matrix contains at least a metal. The at least one filler selected from the group consisting of metal fine particles, silica, calcium carbonate, magnesium carbonate, carbon black, glass fiber, and carbon fiber is further contained in the matrix. The composite material according to any one of the above.

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