JP2010248660A - Method for surface treating fine carbon fiber and coated fine carbon fiber produced by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for surface treating fine carbon fiber, which is a treatment method not requiring washing of fiber after surface treatment of fine carbon fiber and easily performs the treatment in a short time in order to obtain a fine carbon fiber for providing a composite material having excellent adhesiveness to a resin matrix material and excellent mechanical characteristics when made into a composite material. <P>SOLUTION: The method for surface treating fine carbon fiber includes using an aromatic carboxylic acid such as trimellitic acid. The fine carbon fiber is obtained by using the method. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a surface treatment method for fine carbon fibers. Furthermore, the present invention relates to a surface treatment technology for fine carbon fibers for improving wettability with a resin matrix and a composite material containing carbon nanotubes.

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, it is estimated that the surface structure with few defects of carbon nanotubes works in the direction of worsening the wettability with the matrix resin etc. normally used for composite materials for structural materials. Since the interfacial adhesive force with a matrix material (for example, synthetic resin, rubber, ceramics, metal, etc.) is weak, a pull-out phenomenon occurs and sufficient physical property values cannot be obtained (Non-Patent Documents 1 to 3). 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 composed of graphene sheets with few defects of carbon nanotubes deteriorates the wettability with the matrix polymer and metal used in the composite material for structural materials. It is estimated that it works in the direction of In order to obtain a composite material with high expected strength, it is necessary to reinforce the interface bond between the carbon nanotube and the resin matrix.

For example, 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 such as oxygen plasma (see, for example, 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, a coating treatment on the surface of the carbon nanotube corresponding to the matrix material has been studied. 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. However, in order to facilitate polymer wrapping, an oxidation process of carbon nanotubes and a chemical reaction for introducing a functional group are required, so that an actual operation process becomes complicated and there is a problem that costs increase.

There are several reports on the surface treatment method using a chemical solution that chemically reacts with carbon nanotubes to introduce functional groups onto the tube surface.

A surface treatment method is described in which a carbon nanotube is heated in an acyl succinate peroxide to introduce a carboxyl group on the surface of the carbon nanotube (for example, Patent Document 9).

It has been reported that a carbon nanotube is once reacted with another compound (3,4-dihydroxybenzaldehyde) to form a scaffold, and trimellitic acid is chemically bonded thereto to perform surface treatment (for example, Non-Patent Document 6). .

Non-Patent Document 7 reports that the carbon fiber is oxidized, the hydroxyl group is once bonded to the carbon fiber, and the hydroxyl group is surface-treated with trimellitic acid.

However, since the chemicals used are either strong acids or a large-scale apparatus is required, there has been a problem of process costs for post-treatment and surface modification of waste liquid.

The dry processing method is based on heat treatment in an oxidizing atmosphere as a basic technique, and has a great advantage that there is no need to wash the fibers after the processing, and many improved methods have been proposed. As the method, a gas phase oxidation method using ozone or plasma is known. When performing air oxidation using ozone, usually, the carbon fiber is treated by introducing ozonized air into a chamber having a heater. Ozone is very easy to decompose, and the decomposition is particularly severe at higher temperatures, so it is generally performed at a low temperature. In this case, however, the oxidation reaction is extremely slow. In order to promote the reaction, it is necessary to increase the ozone concentration. To that end, excess ozone must be supplied, and ozone reaction efficiency deteriorates. In addition, ozone has a danger of being extremely harmful to the human body. In addition, since plasma treatment discharges under reduced pressure, continuous treatment cannot be performed and is not suitable for industrialization.

Due to the various problems described above, there is still room for improvement in the surface treatment of fine carbon fibers.

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 JP 2007-217194 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. J. et al. AM. CHEM. SOC. 2008, No130, 8733-8740 American Chemical Society, 1995, No. 585, 348-361

Fine carbon fibers are expected to be used in various applications such as conductive materials and metal reinforcing materials. However, the fine carbon fibers generally have poor wettability, and the mechanical strength of the fiber reinforced plastic that should be reinforced with the fine carbonaceous fibers, which is poorly compatible with the surface of the fine carbonaceous fibers and the resin or metal material, is expected. Various problems occurred, such as not reaching. Therefore, the present invention provides a method for improving the surface wettability of the fine carbon fiber at a low cost in order to enhance the adhesion between the fine carbon fiber and the resin material that is the matrix, and performs surface treatment using the method. An object of the present invention is to provide a coated fine carbon fiber.

The present invention provides a method for improving wettability when a surface treatment of fine carbon fibers is directly performed using an aromatic carboxylic acid such as trimellitic acid or benzoic acid and kneaded into a resin or the like, and the method is used. The present invention provides a coated fine carbon fiber characterized by the above.

The present invention is a coated fine carbon fiber obtained by treating the surface of a fine carbon fiber with an aromatic carboxylic acid.

The coated fine carbon fiber, wherein the aromatic carboxylic acid is treated by directly contacting the surface of the fine carbon fiber.

The aromatic carboxylic acid is benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid (2-hydroxybenzenecarboxylic acid), gallic acid (3,4,5-trihydroxybenzenecarboxylic acid), meritic acid (benzenehexahexan). The coated fine carbon, which is one or more selected from carboxylic acid), cinnamic acid (3-phenylprop-2-enoic acid), and derivatives of these aromatic carboxylic acids Fiber.

The merit acid is the coated fine carbon fiber, which is at least one selected from trimellitic acid, trimellitic anhydride, and hemimellitic acid.

A composite material comprising the coated fine carbon fiber and a resin material.

In this method, the aromatic carboxylic acid is directly brought into contact with the surface of the fine carbon fiber.

Benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid (2-hydroxybenzenecarboxylic acid), gallic acid (3,4,5-trihydroxybenzenecarboxylic acid), meritic acid (benzene) used in the surface treatment method The fine carbon, which is one or more selected from hexacarboxylic acid), cinnamic acid (3-phenylprop-2-enoic acid), and derivatives of these aromatic carboxylic acids This is a fiber surface treatment method.

The merit acid used in the surface treatment method is one or more selected from trimellitic acid, trimellitic anhydride, or hemimellitic acid.

The present invention has been completed by paying attention to the high affinity between fine carbon fibers and aromatic carboxylic acids. The aromatic carboxylic acid is a compound having a benzene ring and a carboxylic acid structure (R—COOH), and has a carboxylic acid structure (R—COOH) as an acid component and is hydrophilic. On the other hand, the carbon nanotube is in a form in which a sheet of carbon atoms arranged in a hexagonal network is wound in a cylindrical shape, and the diameter D is 1.0 nm (nanometer) to 150 nm. From the atomic level, it is formed of a regular six-membered ring network, so it has a high affinity for π-electron rich organic substances such as aromatic ring compounds. The present invention speculates that strong adsorption is caused by the strong van der Waals force and π-π interaction between the six-membered ring structure of carbon atoms in the fine carbon fiber and the benzene ring in the aromatic carboxylic acid, It has been completed. The carboxylic acid derived from the aromatic carboxylic acid can improve the wettability to the fine carbon fiber and the resin matrix. In addition, in the case of a straight chain carboxylic acid having no aromatic ring, efficient adhesion to the fine carbon fiber hardly occurs unless the fine carbon fiber is subjected to a pretreatment such as an oxidation treatment (see, for example, Polymer, 2007, Vol. 48, No. 14, 4034-4040).

Until now, when functional groups were introduced into fine carbon fibers, they were treated with alkali or acid to introduce hydroxyl groups or carboxyl groups. Alternatively, the surface treatment is performed by binding a functional group chemically bonded to the fine carbon fiber to a scaffold and further binding another compound. By using the present invention, it is possible to directly modify the surface with trimellitic acid or benzoic acid without acid treatment.

According to the present invention, fine carbon fibers can be directly surface-treated without the need for modification with hydrochloric acid or the introduction of functional groups, and the aromatic carboxylic acid solution only needs to be distributed throughout the fine carbon fibers. Surface treatment can be performed in a short time. Since the carbon fiber treated according to the present invention is excellent in adhesiveness with a matrix material when used in a composite material, a composite material having excellent mechanical properties can be obtained. After the surface treatment with the aromatic carboxylic acid, post-treatment steps such as filtration and washing are unnecessary, and therefore, there is an effect that the surface of the fine carbon fiber can be rapidly treated at a low cost.

Conceptual diagram of CNT surface treatment using merit acid, an aromatic carboxylic acid It is a SEM photograph of the 1st intermediate body of the carbon fiber structure concerning the present invention. It is a TEM photograph of the 1st intermediate body of the carbon fiber structure concerning the present invention. It is a SEM photograph of the carbon fiber structure concerning the present invention. It is a TEM photograph of the carbon fiber structure concerning the present invention. It is a SEM photograph of the carbon fiber structure concerning the present invention. Evaluation of wettability of fine carbon fiber A and various treated fine carbon fibers A according to the present invention with water Confirmation test of trimellitic acid adhesion amount of fine carbon fiber A by TG analysis Observation of surface condition of fine carbon fiber A after surface treatment (SEM photo, 70,000 times) Observation of cross-sectional state of epoxy resin composite kneaded with surface untreated fine carbon fiber A (SEM photo, 3,000 times) Observation of surface wet state in epoxy resin kneaded with fine carbon fiber A with no surface treatment (SEM photo, 100,000 times) Observation of cross-sectional state of epoxy resin composite kneaded with surface-treated fine carbon fiber A (SEM photo, 3,000 times) Observation of surface wet state in epoxy resin kneaded with surface-treated fine carbon fiber A (SEM photo, 100,000 times) Observation of surface wet state in epoxy resin kneaded with surface-treated fine carbon fiber A (SEM photo, 100,000 times)

The present invention provides a method for improving wettability when a surface treatment of fine carbon fibers is directly performed using an aromatic carboxylic acid such as trimellitic acid or benzoic acid and kneaded into a resin or the like, and the method is used. It consists of a coated fine carbon fiber characterized by being made.

When the fine carbon fiber is treated with the aromatic carboxylic acid, the aromatic carboxylic acid can be dissolved in water or an organic solvent and then sprayed as it is, or the solution may be impregnated with the fine carbon fiber. When the fine carbon fiber is passed through the granulation process with ethanol or the like, it is more efficient to spread the aromatic carboxylic acid to the surface. Therefore, it is not necessary to add a new process separately, and almost no processing time is required.

A preferred ratio of aromatic carboxylic acid to fine carbon fiber is 1: 4 to 1: 2. More preferably, it is 1: 4-3: 8.

Aromatic carboxylic acids used in the present invention are benzoic acid (benzenecarboxylic acid), phthalic acid (benzene-1,2-dicarboxylic acid), isophthalic acid (benzene-1,3-dicarboxylic acid), terephthalic acid (benzene-1). , 4-dicarboxylic acid), salicylic acid (2-hydroxybenzenecarboxylic acid), gallic acid (3,4,5-trihydroxybenzenecarboxylic acid), meritic acid (benzenehexacarboxylic acid), or cinnamic acid (3-phenyl) Propa-2-enoic acid) or derivatives thereof are preferred. Derivatives include anhydrides, hydrates or salts thereof bound.

A preferable aromatic carboxylic acid used in the present invention preferably has a larger number of carboxyl groups bonded to one benzene ring. Therefore, among aromatic carboxylic acids, merit acid, more preferably trimellitic acid CAS 528-44-9O or trimellitic anhydride CAS 552-30-7, or a derivative thereof is preferable.

If the fine carbon fiber surface-treated with the aromatic carboxylic acid of the present invention is used, the voids existing between the fine carbon fiber and the resin matrix when kneaded into the resin, compared to the fine carbon fiber not subjected to the surface treatment. Can be reduced or eliminated. Therefore, when a composite material with a resin is molded using fine carbon fibers that have been surface-treated according to the present invention, the adhesive properties between the fine carbon fibers and the resin matrix are good, so that mechanical properties such as bending strength and elastic modulus are obtained. Will improve.

When manufacturing a composite material, the preferable compounding quantity of a fine carbon fiber is the range of 0.1-20 weight part with respect to 100 weight part of various resin. Within this range, the mechanical properties and good conductivity can be confirmed without impairing the properties of the resin. More preferably, a compounding quantity is the range of 0.2-10 weight part with respect to 100 weight part of various resin.

Since the method of the present invention is an embodiment in which an aromatic carboxylic acid is brought into contact with fine carbon fibers, it is different from a conventional method in which a functional group is directly introduced into fine carbon fibers by a strong chemical bond. Therefore, even if the surface treatment is carried out by the method of the present invention, it does not become a separate compound. Therefore, if knowledge of the safety of fine carbon fibers has been obtained, it is safe to coat with the present invention. Is likely to be maintained.

The coated fine carbon fiber in the present invention means a fine carbon fiber obtained by coating a fine carbon fiber with an aromatic carboxylic acid.

As the fine carbon fiber of the present invention, for example, single-walled, double-walled, triple-walled, four-walled and multi-walled carbon nanotubes are shown and can be used according to the purpose. In the present invention, more preferably, multi-walled carbon nanotubes are used. Multi-walled carbon nanotubes are inexpensive in terms of manufacturing cost as long as they are the same weight as single-walled carbon nanotubes. Also, since it is easy to disperse when added to the resin, a multi-walled carbon nanotube is more desirable for the purpose of improving the mechanical properties. The carbon nanotube production method is not particularly limited, and any conventionally known production method such as a vapor phase growth method using a catalyst, an arc discharge method, a laser evaporation method and a HiPco method (High-pressure carbon monoxide process). The method may be used.

For example, a method for producing a single-walled carbon nanotube by laser vapor deposition is shown below. As a raw material, graphite powder and a mixed lot of nickel and cobalt fine powder were prepared. This mixed lot is heated to 1250 ° C. in an electric furnace under an argon atmosphere of 665 hPa (500 Torr), and irradiated with a second harmonic pulse of 350 mJ / Pulse Nd: YAG laser to evaporate carbon and metal fine particles. Thus, a single-walled carbon nanotube can be produced.

The above manufacturing method is merely a typical example, and the metal type, gas type, electric furnace temperature, laser wavelength, and the like may be changed. In addition, other than laser deposition methods, for example, HiPco method, vapor phase growth method, arc discharge method, carbon monoxide thermal decomposition method, template method in which organic molecules are inserted into fine pores, thermal decomposition, fullerene -You may use the single-walled carbon nanotube produced by other methods, such as a metal co-evaporation method.

For example, a method for producing a double-walled carbon nanotube by a constant temperature arc discharge method is shown below. The substrate was a surface-treated Si substrate, and the treatment method was a solution obtained by immersing alumina powder in a solution in which the catalyst metal and the catalyst auxiliary metal were dissolved for 30 minutes, and then dispersing by ultrasonic treatment for 3 hours. Was applied to a Si substrate and dried in air at 120 ° C. for maintenance. A substrate was installed in the reaction chamber of the carbon nanotube production apparatus, a mixed gas of hydrogen and methane was used as a reaction gas, the supply amount of gas was 500 sccm for hydrogen, 10 sccm for methane, and the pressure in the reaction chamber was 70 Torr. As the cathode part, a rod-like discharge part made of Ta was used. Next, a DC voltage was applied between the anode part and the cathode part, and between the anode part and the substrate, and the discharge voltage was controlled so that the discharge current was constant at 2.5A. When the temperature of the cathode part is 2300 ° C. due to discharge, the normal glow discharge state is changed to an abnormal glow discharge state, and the discharge current is 2.5 A, the discharge voltage is 700 V, and the reaction gas temperature is 3000 ° C. for 10 minutes. Single-walled and double-walled carbon nanotubes can be produced on the entire substrate.

The above manufacturing method is merely an example, and various conditions such as the type of metal and the type of gas may be changed. Moreover, you may use the single-walled carbon nanotube produced by production methods other than the arc discharge method.

For example, a method for producing a multi-walled carbon nanotube having a three-dimensional structure by vapor deposition is shown below. Basically, an organic compound such as a hydrocarbon is chemically pyrolyzed by a CVD method using ultrafine transition metal particles as a catalyst to obtain a fiber structure (hereinafter referred to as an intermediate). A multi-walled carbon nanotube having a high degree of graphitization can be produced by performing a high temperature annealing treatment at any temperature within the range.

The degree of graphitization of the multi-walled carbon nanotube obtained after the high-temperature annealing treatment is in the range of 1000 to 3000 ° C., and the higher the high-temperature annealing treatment temperature, the higher the degree of graphitization of the carbon nanotube.

As the raw material organic compound, hydrocarbons such as benzene, toluene and xylene, and alcohols such as carbon monoxide and ethanol are used, but it is preferable to use at least two or more carbon compounds having different decomposition temperatures as the carbon source. . Note that at least two or more carbon compounds do not necessarily use two or more types of raw material organic compounds, and even when one type of raw material organic compound is used, the fiber structure In the body synthesis process, for example, a reaction such as hydrogen dealkylation of toluene or xylene occurs, and in the subsequent thermal decomposition reaction system, it becomes two or more carbon compounds having different decomposition temperatures. Including embodiments. The atmosphere gas is an inert gas such as argon, helium, xenon or hydrogen, and the catalyst is a transition metal such as iron, cobalt or molybdenum, or a transition metal compound such as ferrocene or metal acetate, and sulfur or thiophene or iron sulfide. Use a mixture of sulfur compounds such as

The synthesis of the intermediate is carried out by using a CVD method such as hydrocarbon, which is usually performed, by evaporating the mixture 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. Thereby, from several centimeters in which a plurality of carbon nanotube structures (intermediates) having a sparse three-dimensional structure in which fibers having an outer diameter of 15 to 100 nm are bonded together by granular materials grown using the catalyst particles as nuclei. Synthesize an aggregate of several tens of centimeters.

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, by intentionally changing the balance between the thermal decomposition rate and the growth rate, for example, by using at least two or more carbon compounds having different decomposition temperatures as a carbon source as described above, the carbon material is only in a one-dimensional direction. The carbon material is grown three-dimensionally around the granular material without growing the material. Of course, the growth of such three-dimensional carbon nanotubes 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, and the furnace temperature. In general, if the growth rate is faster than the pyrolysis rate as described above, the carbon material grows in a fibrous form, while the pyrolysis rate is faster than the growth rate. The carbon material grows in the circumferential direction of the catalyst particles. Therefore, by intentionally changing the balance between the pyrolysis rate and the growth rate, it is possible to form a three-dimensional structure in the other direction under control without making the growth of the carbon material as described above constant. It is possible. In the intermediate to be produced, the composition of the catalyst, the residence time in the reaction furnace, the reaction temperature, and the gas temperature are used to easily form the three-dimensional structure as described above in which the fibers are bonded together by the granular material. Etc. are preferably optimized.

An intermediate obtained by heating and generating a mixed gas of catalyst and hydrocarbon at a constant temperature in the range of 800 to 1300 ° C. has a structure in which patch-like sheet pieces made of carbon atoms are bonded together, and Raman When spectroscopic analysis is performed, the D band is very large and there are many defects. Moreover, the produced | generated intermediate body contains the unreacted raw material, non-fibrous carbon material, a tar content, and a catalyst metal.

Therefore, in order to remove these residues from such an intermediate and obtain a carbon nanotube structure with few defects, heat treatment is performed at 900 to 3000 ° C. by an appropriate method.

That is, for example, this intermediate is heated at 800 to 1300 ° C. to remove volatile components such as unreacted raw materials and tars, and then annealed at 1500 to 3000 ° C. to prepare the desired structure. At the same time, the catalyst metal contained in the fibers is removed by evaporation. At this time, in order to protect the substance structure, a reducing gas or a small amount of carbon monoxide gas may be added to the inert gas atmosphere. Further, when the annealing temperature is 900 to 1500 ° C., the surface has a lot of diapers, constrictions, and metals, resulting in a rough shape and low crystallinity.

When the intermediate is annealed at a temperature in the range of 1500 to 3000 ° C., the patch-like sheet pieces made of carbon atoms are bonded to each other to form a plurality of graphene sheet-like layers.

When improving the mechanical properties of the resin, adjustment of the wettability of the fine carbon fibers is an important factor. In general, fine carbon fibers that have not been surface-treated have a rough shape with many irregularities, constrictions, impurities, and metals on the surface, if the crystallinity is low, or if the surface shape is not uniform in the fiber direction, the resin etc. The wettability is improved. These surface shape properties are different even in various manufacturing methods. In particular, it is likely to occur when the temperature at which the surface of the fine carbon fiber is annealed is lowered (about 900 to 1500 ° C.). The present invention is particularly excellent in terms of improving the wettability of fine carbon fibers having high crystallinity and poor wettability, and a synergistic effect for further improving the wettability although there are many irregularities can be confirmed.

Further, before or after such high-temperature heat treatment, a step of crushing the equivalent circle average diameter of the carbon nanotube structure to several centimeters, and a circle equivalent average diameter of the cleaved carbon nanotube structure of 50 to The carbon nanotube which has a desired equivalent circle | round | yen average diameter is produced through the process of grind | pulverizing to 100 micrometers.

As a method for evaluating the graphitization degree of a carbon material, there is a method of measuring an R value using a Raman spectroscopic analyzer. Therefore, the carbon nanotube, which is a fine carbon material, also uses the R value measured and calculated by Raman spectroscopic analysis as an index of the degree of graphitization.

In Raman spectroscopic analysis, large single crystal graphite has no disorder in the graphene structure, so that only G band (IG, 1580 cm-1) appears at 1500-1600 cm-1. However, when the crystal has a finite minute size and the graphene structure has a defect, a D band (ID, 1360 cm-1) appears at 1250 to 1400 cm-1.

The R value is the intensity ratio (ID / IG) of the D band of 1250 to 1400 cm −1 due to this disorder of the graphite structure and the G band appearing at 1500 to 1600 cm −1 due to the graphene structure.

In the present invention, the measurement was performed using a Raman spectroscopic analyzer LabRamHR-800 manufactured by Horiba Joban Yvon, Inc. using an argon ion laser (514 nm), a laser spot diameter of 2 to 3 μm, and an excitation wavelength of a laser power of 2 mW.

The above manufacturing method is merely an example, and various conditions such as the type of metal and the type of gas may be changed. Moreover, you may use the multi-layered carbon nanotube produced by production methods other than a vapor phase growth method.

The carbon nanotube referred to in the present invention is a kind of fine carbon fiber, and has a hollow structure inside.

The vapor-grown carbon fiber is not limited to those obtained by the above-described production method, and the carbon source compound can be made into a carbon fiber or carbon whisker in a floating state by the catalytic action of a transition metal. As long as it is a method, it may be obtained by any manufacturing method.

The graphite whisker can be produced by heating the vapor-grown carbon fiber to a high temperature of 2000 ° C. or higher, preferably 2800 ° C. or higher. The heat treatment is usually performed in an atmosphere of an inert gas such as nitrogen or argon. The time required for the heat treatment is sufficient if it is 5 minutes or longer, but usually it takes about 30 minutes.

The fine carbon fiber used in the present invention was synthesized as follows.

Carbon fibers were synthesized using toluene as a raw material by the CVD method.

A mixture of ferrocene and thiophene was used as the catalyst, the mass ratio of the catalyst to carbon in the raw material was 150: 1, the raw material gas introduction rate into the reactor was 1300 NL / min, and the pressure was 1.03 atm. The synthesis reaction was performed in a reducing atmosphere of hydrogen gas. Toluene and the catalyst were heated to 380 ° C. together with hydrogen gas, supplied to the production furnace, and pyrolyzed at 1250 ° C. to obtain a carbon fiber structure (first intermediate). The outer diameter distribution of the carbon fibers was a minimum of 40 nm, a maximum of 90 nm, and an average outer diameter of 70 nm. The synthesized intermediate was calcined at 900 ° C. in nitrogen to separate hydrocarbons such as tar to obtain a second intermediate. The R value of this second intermediate measured by Raman spectroscopy was 0.98. Moreover, the SEM and TEM photograph which disperse | distributed this 1st intermediate body in toluene and observed after preparing the sample for electron microscopes are shown in FIG.

Furthermore, this second intermediate was heat treated at 900 ° C. to 2600 ° C. in argon at high temperature, and aggregates of carbon fiber structures obtained at various temperatures were pulverized with an airflow pulverizer, and the carbon fiber structure according to the present invention was obtained. Got.

FIGS. 4 and 5 show SEM and TEM photographs of the obtained carbon fiber structure dispersed in toluene with ultrasonic waves and observed after preparing a sample for an electron microscope.

Further, FIG. 6 shows an SEM photograph in which the obtained carbon fiber structure was directly placed on an electron microscope sample holder and observed.

Further, before and after the high temperature heat treatment, the carbon fiber structure was subjected to X-ray diffraction and Raman spectroscopic analysis, and the change was examined.

The obtained high-temperature treated carbon fiber structure had an equivalent circle average diameter of 45.8 μm, a bulk density of 0.0057 g / cm 3, a Raman ID / IG ratio value of 0.094, a TG combustion temperature of 832 ° C., and a surface. The spacing was 3.384 Å, the powder resistance value was 0.0122 Ω · cm, and the density after restoration was 0.18 g / cm 3.

Various parameters relating to the carbon fiber structure were measured according to the following methods.

<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 LabRam800 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>
The carbon fiber structure after the annealing treatment was examined using a powder X-ray diffractometer (JDX3532, manufactured by JEOL Ltd.). 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.

[Fine carbon fiber A]
The method of synthesizing fine carbon fibers having an average diameter of 70 nm and an R value of 0.107 uses a CVD method, evaporates a mixture of hydrocarbon and catalyst as raw materials, and uses hydrogen gas or the like as a carrier gas in the reactor. It was introduced and thermally decomposed at a temperature of 800 to 1300 ° C. to synthesize an intermediate. The obtained intermediate was heated at 800 to 1300 ° C. to remove volatile components such as unreacted raw materials and tars, and then annealed at 2000 ° C. to obtain an average diameter of 70 nm and an R value of 0.41. A certain fine carbon fiber A was obtained.

[Fine carbon fiber B]
The method for synthesizing fine carbon fibers having an average diameter of 70 nm and an R value of 0.85 is different from the fine carbon fibers A except that the annealing temperature is treated at 1200 ° C., and the average diameter is 70 nm and the R value is Obtained a fine carbon fiber B of 0.85.

The fine carbon fiber A and the fine carbon fiber B obtained in Example 1 were each subjected to pulverization treatment for 60 minutes by VOLMILL (NITTO KAGKUKU CO. LTD, Ball Mill ANZ-50S).

[Surface treatment of fine carbon fiber using trimellitic anhydride]
1 g of trimellitic anhydride was dissolved in 200 ml of ethanol to obtain a solution. Thereafter, 2 g each of the fine carbon fiber A and fine carbon fiber B produced in Example 1 were put into the solution, and ethanol was distilled off at room temperature while stirring. Furthermore, the obtained fine carbon fiber was dried at 100 ° C. for 1 hour or longer to complete the surface treatment.

Each fine carbon fiber A that had not been subjected to surface treatment and then pulverized was added to the surface of distilled water, and stored for 3 hours. The fine carbon fiber not treated with the aromatic carboxylic acid was held in a floating state on the water surface (FIG. 7). The left end is one in which fine carbon fiber A is not pulverized by a bead mill, the center is pulverized by a bead mill, and the right end is crushed by a bead mill and then surface-treated with trimellitic acid. From this, it is inferred that the fine carbon fibers not subjected to the surface treatment did not become hydrophilic. In addition, the product treated with trimellitic acid at the right end almost settled. A small amount remains on the surface of distilled water without precipitating, but this is presumed to be due to fine carbon fibers in which trimellitic acid is not sufficiently distributed on the surface.

[Confirmation of adhesion of trimellitic anhydride to fine carbon fiber]
The surface treated fine carbon fiber A sample was heated up to 700 ° C. in an argon gas and hydrogen gas atmosphere using TG (manufactured by Mac Science Co., Ltd., thermal analyzer system WS002) to reduce the weight. Was measured. FIG. 8 shows the measurement results of weight loss of the fine carbon fiber A produced in Example 1 before and after the modification. Even if the temperature is raised to 700 ° C. in the (Ar + H2) atmosphere before the modification, there is almost no weight reduction. After the reforming treatment with a ratio of trimellitic anhydride and fine carbon fiber of 1: 2, the weight started to decrease from about 160 ° C., and the weight reduction almost ended at about 250 ° C. The rate of weight loss was 24%. Considering the melting point (161-163 ° C.) and boiling point (240-245 ° C., 1.87 kPa) of trimellitic acid, the 24% weight loss seems to be due to the evaporation of trimellitic acid.

Further, the surface-treated fine carbon fiber A was observed by SEM, and the surface adhesion state of trimellitic anhydride to the surface-treated fine carbon fiber was observed. The photographed SEM photograph is shown in FIG. Compared with the smooth surface of the untreated fine carbon fiber A, it was confirmed that something was attached to the surface of the treated fine carbon fiber.

[Adhesiveness between surface-treated fine carbon fiber and resin matrix]
The fine carbon fiber A and the fine carbon fiber B subjected to the surface treatment were 0.5% of the fine carbon fiber relative to the epoxy resin (manufactured by ADEKA, main agent: EP-4901E, curing agent: EH-3895), respectively. The mixture was added so as to have a wt mass, and kneading was performed for 8 minutes with Awatori Nertaro (manufactured by Shinky Co., Ltd., AR-250). Curing molding was performed at room temperature. The molded product was broken and SEM observation of the cross section of the fine carbon fiber A was performed (FIGS. 10 to 14). Compared to the gaps clearly present at the roots of the untreated fine carbon fibers, it was confirmed that there were no gaps at the roots of the treated fine carbon fibers and something was attached to the surface of the fine carbon fibers.

[Mechanical properties of resin moldings kneaded with fine carbon fibers with surface treatment]
The fine carbon fiber A1 wt% obtained in Example 1 was added to a bisphenol F type epoxy resin (manufactured by ADEKA, main agent: EP-4901E, curing agent: EH-3895), kneaded, defoamed, and room temperature Then, after heating and molding overnight at 80 ° C for 1 hour, a test piece was prepared, a three-point bending test was performed (SHIMADZU, AUTOGRAPH AG-I 20KNT), and bending strength and elastic modulus were measured. It is shown in Table 1.

The present invention provides a surface treatment method that can easily improve the wettability of fine carbon fibers to a resin. Since the fine carbon fiber treated according to the present invention is excellent in adhesiveness with a matrix material when used in a composite material, various composite materials having excellent mechanical properties can be obtained.

Even if the treatment with trimellitic acid is washed with water and ethanol, both precipitate. That is, the functional group remains. It is the same as the fine carbon fiber after silane treatment. Most are physical adsorption and a few are chemical adsorption. From Mr. Chen's monthly report

Claims (8)

A coated fine carbon fiber obtained by treating the surface of a fine carbon fiber with an aromatic carboxylic acid. The coated fine carbon fiber according to claim 1, wherein the aromatic carboxylic acid is treated by directly contacting the surface of the fine carbon fiber. The aromatic carboxylic acid is benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid (2-hydroxybenzenecarboxylic acid), gallic acid (3,4,5-trihydroxybenzenecarboxylic acid), meritic acid (benzenehexahexan). A carboxylic acid), cinnamic acid (3-phenylprop-2-enoic acid), and one or more selected from derivatives of these aromatic carboxylic acids. The coated fine carbon fiber described. 2. The coated fine carbon fiber according to claim 1, wherein the merit acid is at least one selected from trimellitic acid, trimellitic anhydride, and hemimellitic acid. A composite material comprising the coated fine carbon fiber and a resin material. A method in which an aromatic carboxylic acid is directly brought into contact with the surface of fine carbon fibers. Benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid (2-hydroxybenzenecarboxylic acid), gallic acid (3,4,5-trihydroxybenzenecarboxylic acid), meritic acid (benzene) used in the surface treatment method 6. A hexacarboxylic acid), cinnamic acid (3-phenylprop-2-enoic acid), and one or more selected from derivatives of these aromatic carboxylic acids. The surface treatment method of the fine carbon fiber as described in 2. A surface treatment method for fine carbon fibers, wherein the merit acid used in the surface treatment method is one or more selected from trimellitic acid, trimellitic anhydride, or hemimellitic acid.

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