JP7421789B2 - Functional hollow carbon fiber and its manufacturing method - Google Patents

Description

The present invention relates to a functional hollow carbon fiber and a method for producing the same.

Carbon fibers are generally classified into PAN (polyacrylonitrile) type and pitch (PITCH: made from by-products such as petroleum, coal, or coal tar) type.
PAN-based carbon fibers are generally produced by subjecting polyacrylonitrile fibers to flameproofing treatment (infusibility, stabilization) in air at a temperature of 200 to 300°C for several hours, and then applying an inert gas such as nitrogen or rare gas. It is manufactured by carbonization treatment in which it is heated at 600 to 1500°C in an atmosphere. High-strength carbon fibers can be obtained by this carbonization treatment, and if necessary, highly elastic carbon fibers can be obtained by graphitization treatment by heating to 2000 to 3000° C. in an inert gas atmosphere. Pitch-based carbon fibers are produced by forming pitch fibers by melt spinning, subjecting the pitch fibers to infusibility treatment, and then carbonizing them at high temperatures. The temperature conditions for carbonization treatment and graphitization treatment are determined depending on the properties of the carbon fiber to be obtained.

Such carbon fibers are used for various purposes.
Furthermore, since carbon, which is the main component of carbon fiber, is easily flammable in the air, composite materials of carbon fiber and inorganic flame-retardant substances such as ceramics are being developed (for example, see Non-Patent Document 1). .
Furthermore, carbon fibers, which have electrically conductive paths and have a large specific surface area, are widely used for electrodes of lithium ion batteries and fuel cells. In this application, a catalyst metal or the like is introduced onto the surface of the carbon fiber (see, for example, Patent Document 2).
Techniques for purifying water and air by supporting a substance with a catalytic action on the surface of carbon fibers have also been put to practical use (for example, see Patent Document 3).
In this way, functional materials are being developed by combining carbon fibers and functional inorganic compounds.

Japanese Patent Application Publication No. 2015-195193 Japanese Patent Application Publication No. 2002-86178

Motohiro Tagaya, Satoshi Honzuka, Yuji Hotta, Zhefeng Xu, Junzo Tanaka, "Evaluation of matrix resin in composite materials and effects associated with thermal conductivity of resin", Materials Integration, Vol. 26, No. 2, p. 16-22, (2013)

Composite materials made of carbon fibers and inorganic flame-retardant substances such as ceramics are required to have improved heat resistance. In addition, as described in Patent Document 2, when metal, etc. is supported on the outer surface of the carbon fiber used as the electrode material of the battery, performance deterioration due to metal falling off can be prevented during repeated use of the battery. This has become an issue. In addition, in water purification and air purification technologies, substances with catalytic action are supported on the surface of carbon fibers. Therefore, the bonding ability (supporting power) with inorganic functional substances (substances with catalytic action, etc.) on the surface of carbon fibers is important, but depending on the type of introduction (for example, kneading), the function and activity may decrease. There is sex. Therefore, regardless of the bonding form between carbon and inorganic functional substances, it is desired to prevent performance deterioration and extend life.
Therefore, there is a need for a technology that can further stabilize the composite state of carbon fibers and inorganic functional substances, and can also more stably exhibit functionality.

The present invention aims to provide a functional hollow carbon fiber that can further stabilize the composite state of a hollow carbon fiber and an inorganic functional substance, and that can more stably express its functions, and a method for producing the same. Take it as a challenge.

The above-mentioned problems of the present invention are solved by the following means.
[1]
A functional hollow carbon fiber having an internal hollow portion and retaining an inorganic functional substance in the hollow portion of the carbon fiber.
[2]
The functional hollow carbon fiber according to [1], wherein the inorganic functional substance contains at least one of metals, oxides, carbides, and nitrides.
[3]
The functional hollow carbon fiber according to [1] or [2], wherein the inorganic functional substance is in the form of particles with a particle size of 1 nm or more.
[4]
A step of infiltrating a reaction raw material solution into the hollow part of the carbon-containing hollow fiber material,
The carbon-containing hollow fiber material impregnated with the reaction raw material solution is immersed in a solvent that is immiscible with the reaction raw material solution, and the reaction raw material solution is applied to the inside of the hollow part of the carbon-containing hollow fiber material. or a step of transferring it into the fibrous tissue;
producing an inorganic functional substance through a chemical reaction of the reaction raw material solution transferred into the hollow portion of the carbon-containing hollow fiber material or into the fiber structure;
A method for producing functional hollow carbon fibers, comprising a carbonization step of heating the carbon-containing hollow fiber material that has produced the inorganic functional substance in an inert atmosphere to produce carbon fibers.
[5]
The method for producing functional hollow carbon fibers according to [4], wherein the chemical reaction is caused by heating.
[6]
The method for producing a functional hollow carbon fiber according to [5], wherein the heating is heating by microwave irradiation.
[7]
The method for producing functional hollow carbon fibers according to [6], wherein the microwave irradiation is single mode microwave irradiation.
[8]
The reaction raw material solution contains a metal precursor,
The method for producing a functional hollow carbon fiber according to any one of [4] to [7], wherein the chemical reaction is a reaction that precipitates a metal from the metal precursor.
[9]
The method for producing functional hollow carbon fibers according to any one of [4] to [7], wherein the chemical reaction is crystallization or precipitation of a chemical substance in the reaction raw material solution.
[10]
The reaction raw material solution contains a silica source, an aluminum source, an alkali source and water,
Or, in addition to the silica source, the aluminum source, the alkali source, and the water, it includes a metal source capable of replacing silicon,
The method for producing functional hollow carbon fibers according to any one of [4] to [7], wherein the chemical reaction is a reaction that produces zeolite.
[11]
The function according to any one of [4] to [10], wherein the carbon-containing hollow fiber material is composed of a vegetable fiber, an animal fiber, or a chemical fiber, or a composite material consisting of two or more of these. A method for manufacturing hollow carbon fiber.
[12]
The method for producing functional hollow carbon fibers according to any one of [4] to [10], wherein the carbon-containing hollow fiber material is cotton or linen.

According to the functional hollow carbon fiber and the method for producing the same of the present invention, it becomes possible to further stabilize the composite state of the carbon fiber and the inorganic functional substance, and to more stably exhibit the function.

Figure (A) is a photograph, taken in place of a drawing, of a cross-section of a cotton fabric on which silver has been deposited, taken with a scanning electron microscope, and the position where the composition was analyzed is indicated by a square box A. (B) The figure is a drawing substitute showing the component mapping of the carbon component of the functional hollow carbon fiber and the silver component of the inorganic functional substance in part A of Figure 1 (A) taken with a scanning electron microscope. In the photograph, white dots indicate silver components and gray dots indicate carbon components. This is cotton fiber used in a preferred embodiment of the method for producing functional hollow carbon fibers of the present invention, and is a composite photograph in place of a drawing showing a state in which each layer of cotton fiber is partially peeled off in a perspective view. FIG. 3 is a partially cross-sectional perspective view schematically showing cotton fibers (two cotton fibers shown in FIG. 2) used in a preferred embodiment of the method for producing functional hollow carbon fibers of the present invention. FIG. 4 is a partial cross-sectional perspective view schematically showing a permeation step in which a reaction raw material solution permeates the cotton fibers shown in FIG. 3 in a preferred embodiment of the method for producing functional hollow carbon fibers of the present invention. A partial cross-sectional perspective view schematically showing a transition step in which the reaction raw material solution further migrates into the cotton fiber shown in FIG. 4 in a preferred embodiment of the method for producing functional hollow carbon fibers of the present invention. It is. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially sectional perspective view schematically showing heating and chemical reaction steps in a preferred embodiment of the method for producing functional hollow carbon fibers of the present invention. This is a composite photograph in place of a drawing showing the cotton fibers used in a preferred embodiment of the method for producing functional hollow carbon fibers of the present invention, in which each layer of the cotton fibers is partially peeled off in a perspective view. (A) is a photograph substituted for a drawing taken by a scanning electron microscope (SEM) of a cross section of a cotton cloth of a sample in which silver was precipitated in Example 1. Figure (B) is a graph showing the results of compositional analysis of a cross section of cotton cloth in the direction of the arrow in figure (A) using energy dispersive X-ray spectroscopy, and the vertical axis shows the spectra of silver and carbon components. Intensity is shown, and the horizontal axis shows position. This is a photograph substituted for a drawing taken using a scanning electron microscope of a cross section of a cotton cloth of a sample on which silver was deposited in Example 1, and the position where the composition was analyzed is shown in a square box A. (A) is a photograph substituted for a drawing showing the component mapping of the carbon component in section A of FIG. 9 taken with a scanning electron microscope. White dots indicate carbon components. (B) is a photograph substituted for a drawing showing the component mapping of the silver component in part A of FIG. 9 taken with a scanning electron microscope. White dots indicate silver components.

[Functional hollow carbon fiber]
A preferred embodiment of the functional hollow carbon fiber of the present invention will be described below with reference to the drawings.

The functional hollow carbon fiber of the present invention is a carbon fiber that has a hollow part inside, and holds an inorganic functional substance in the hollow part. An example will be described below with reference to FIG.
As shown in FIG. 1, the functional hollow carbon fiber 11 has a hollow part 12 inside in the longitudinal direction of the fiber, and holds an inorganic functional substance 21 in the hollow part 12. The hollow portion 12 may be disposed in the longitudinal direction of the functional hollow carbon fiber 11 and may penetrate the functional hollow carbon fiber 11 at one end or both ends in the longitudinal direction. The hollow portion 12 has a length (for example, an inner diameter) that allows the inorganic functional substance to be generated therein, and the inner diameter is preferably 1 nm or more, more preferably 10 nm or more, and even more preferably It is 100 nm or more. The inner diameter is preferably 5 mm or less, more preferably 100 μm or less, even more preferably 10 μm or less. The above-mentioned inner diameter is, for example, when the cross section of the hollow portion 12 is circular or nearly circular, and is, for example, the diameter of an inscribed circle. Moreover, when the cross section of the hollow part 12 is rectangular, oval, etc., the maximum length of the cross section is taken as the maximum length.

Preferably, the inorganic functional substance 21 contains at least one of metals, oxides, carbides, and nitrides. Preferred oxides include metal oxides, preferred carbides include metal carbides, and preferred nitrides include metal nitrides. Specifically, metals such as silver, copper, platinum, nickel, iron, cobalt, palladium, and rhodium, oxides such as aluminosilicate, mesoporous silica, barium titanate, aluminum oxide (alumina), and zirconia, silicon carbide, Examples include carbides such as tungsten carbide and boron carbide, and nitrides such as silicon nitride, aluminum nitride, and boron nitride.
In addition, the inorganic functional substance 21 has a catalytic function, a heat resistance function, an antibacterial function, a humidity control function, a conductive function, a photocatalytic function, an antifungal function, an electromagnetic wave absorption function, an electromagnetic wave reflection function, a chemical substance capture function, and a chemical substance controlled release function. It is preferable to have at least one of the following functions. For example, from the viewpoint of catalytic function, it is preferable that the particles be in the form of particles containing at least one of metals, oxides, carbides, and nitrides having a particle size of 1 nm or more. Further, from the viewpoint of humidity control function, chemical substance capture function, and chemical substance sustained release function, it is preferable that the particles are in the form of particles containing a mesoporous material having a particle size of 10 nm or more. Alternatively, from the viewpoint of electromagnetic wave absorption function and electromagnetic wave reflection function, it must be a fibrous material containing at least one of metals, oxides, carbides, and nitrides with a length of 100 nm or more and a thickness of 1 nm or more. is preferred.
The particle size of the inorganic functional substance 21 is appropriately selected depending on the use of the inorganic functional substance 21, and from the viewpoint of a catalyst, the particle size is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less. preferable. The particle size is preferably 10 nm or more, more preferably 50 nm or more, and even more preferably 100 nm or more from the viewpoint of capturing and sustained release of the chemical substance.
The above particle size can be calculated by randomly selecting 30 fine particles of the inorganic functional substance 21 in an imaging range of 13 μm x 10 μm on a SEM photograph (magnification: 10,000 times), and measuring the maximum diameter of each particle for length measurement. It is preferable to measure it with a ruler.
In the above-mentioned functional hollow carbon fiber 11, since the inorganic functional substance 21 is precipitated in the hollow part 12, it is possible to avoid contact between the inorganic functional substance 21 and other substances during use, and the inorganic functional substance 21 can be prevented from falling off due to contact. Therefore, the above-described functions of the inorganic functional substance 21 can be fully expressed. As a result, functional hollow carbon fibers combine the general functions of carbon fibers such as high strength, high thermal conductivity, electrical conductivity, and heat resistance, as well as at least one of the above functions of inorganic functional substances. By having it, you can get multiple effects.

[Method for manufacturing functional hollow carbon fiber]
EMBODIMENT OF THE INVENTION Below, one preferable embodiment of the manufacturing method of the functional hollow carbon fiber of this invention is demonstrated with reference to drawings.
FIG. 2 shows a cotton fiber 111 as a carbon-containing hollow fiber material 110 that is used as a raw material for the functional hollow carbon fiber 11 (see FIG. 1). The cotton fiber 111 has a lumen 117 that becomes the hollow portion 12 (see FIG. 1) in the longitudinal direction of the material. Note that the carbon-containing hollow fiber material 110 may be a porous material having porosity as a whole. The cotton fibers 111 are made of elongated (for example, about 30 mm in length) cotton cells that contain a large amount of cellulose (for example, 95% by mass or more). The cotton fiber 111 has, from the outside, a primary cell wall 115 having a cuticle layer 112, a network layer 113 and a winding layer 114, a secondary cell wall 116 and a lumen 117. A multilayer structure is formed in which the primary cell wall 115 covers the secondary cell wall 116. The primary cell wall 115 and the secondary cell wall 116 are aggregates of microfibrils. Microfibrils are made up of multiple nanofibers (cellulose molecules) bundled together. In the cotton fiber 111, pores are formed by the gaps between the microfibrils, and the cotton fiber 111 also functions as a porous material.

As the carbon-containing hollow fiber material, in addition to the above-mentioned cotton fibers, natural fibers such as various plant fibers and animal fibers can be used. Further, it is possible to use chemical fibers such as purified fibers, regenerated fibers, semi-synthetic fibers, and synthetic fibers. When these fibers are single fibers, a fiber bundle (for example, thread) made by bundling the single fibers can be used as the carbon-containing hollow fiber material. In this case, the gaps between the single fibers become pores.
Plant fibers include fibers derived from various plants. Examples include cotton, linen, etc. Animal fibers include fibers derived from various animals. Examples include animal hair such as cashmere, angora, and alpaca, and feathers. Examples of hollow chemical fibers include regenerated cellulose fibers, semi-synthetic fibers, synthetic fibers, and high-performance fibers. Examples of regenerated cellulose fibers include rayon, cupra, and lyocell. Examples of semi-synthetic fibers include acetate, triacetate, and the like. Examples of synthetic fibers include polyamide fibers and polyester fibers. Examples of high-performance fibers include aramid fibers and polyimide fibers.

Next, a preferred example of the method for producing functional hollow carbon fibers of the present invention will be explained. 3 to 6 schematically show the case where the cotton fiber 111 shown in FIG. 2 is used as the carbon-containing hollow fiber material 110. Note that FIGS. 3 and 4 schematically show two cotton fibers, and FIGS. 5 and 6 schematically show one cotton fiber. In the present invention, the "carbon-containing hollow fiber material" has carbon as a main component. The "main component" preferably contains 20% by mass or more of carbon, more preferably 30% by mass or more, and even more preferably 50% by mass or more.

First, as shown in FIG. 3, a reaction raw material solution is infiltrated into the cotton fibers 111 (infiltration step). Specifically, the cotton fibers 111 are immersed in a reaction raw material solution (not shown) placed in a container (not shown), so that the reaction raw material solution permeates into the cotton fibers 111. This infiltration step can be performed, for example, at a liquid temperature of 15° C. to 30° C. and atmospheric pressure (for example, 1 atmosphere). As a result, as shown in FIG. 4, the reaction raw material solution is formed on the surface of the cotton fiber 111 and/or inside the cotton fiber 111 near the surface (for example, in the pores of the cotton fiber 111 and/or in the cotton fiber structure) by capillary action. Penetrate. The surface refers to the outermost outer surface 111S of the cotton fiber 111. The inside of the pores refers to the spaces between the microfibrils of the cotton fibers 111 (not shown). In the drawing, the darker colored portion of the cross section of the cotton fiber 111 indicates the permeation region 121 of the reaction raw material solution. The permeation region 121 is distributed from the outer surface 111S of the cotton fiber 111 toward the inside. In this state, more of the reaction raw material solution permeates into the surface side (cuticle layer 112 side) of the cotton fibers 111 than on the radial lumen 117 side. In order to promote permeation of the reaction raw material solution, the permeation step may be performed under reduced pressure. For example, if the reaction is carried out at a pressure of 0.01 to 1 atm, the air retained in/between the cotton fibers will be expelled, and the amount of reaction raw material solution retained in that area can be increased.
Here, since cotton fibers have polarity and are easily compatible with polar solvents, it is preferable to use water, a water-soluble organic solvent, or a mixture thereof as a medium for the reaction raw material solution. When the carbon-containing hollow fiber material has relatively low polarity such as a synthetic fiber and has physical properties that are difficult to mix with water, it is preferable to use a more hydrophobic solvent as the medium for the reaction raw material solution.

For example, a metal precursor (metal salt, etc.) can be included in the reaction raw material solution. In this case, the reaction product can be the precipitated metal.
For example, when the metal precursor is a silver salt, a solution obtained by dissolving silver nitrate in a solvent that exhibits a reducing action on metals (for example, alcohol or a mixed solvent of alcohol and water) can be used as the reaction raw material solution. . Examples of the alcohol include methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, tetraethylene glycol, glycerol, benzyl alcohol, dipropylene glycol, and the like. Furthermore, the metal precursor is not limited to silver salts, and various metal salts such as copper, platinum, palladium, ruthenium, nickel, cobalt, iron, aluminum, titanium, gold, chromium, and zinc can be used.
In addition to the above-mentioned metal precursors and precipitated metals, combinations of reaction raw material solutions and reaction products include, for example, combinations of metal hydroxides and oxides, combinations of metal alkoxides and metal oxides, and combinations of ligands ( Examples include a combination of a metal complex and a metal complex.

If necessary, excess reaction raw material solution exceeding the amount of reaction raw material solution that the cotton fibers 111 can hold is removed from the cotton fibers 111 into which the reaction raw material solution has permeated. For example, excess reaction raw material solution can be removed by gently squeezing. Next, as shown in FIG. 5, the cotton fibers 111 are immersed in a solvent 132 that is incompatible with the reaction raw material solution placed in a container 131. Then, it is preferable to cover the container 131 with a lid 133 so as to seal the inside thereof. Lightly squeezing means squeezing the liquid to the extent that it does not drip.
The fact that the solvent 132 is incompatible with the reaction raw material solution means that the solvent 132 is not substantially compatible with the solvent of the reaction raw material solution. That is, it means a relationship in which both solvents do not mix and exist as independent phases at 25°C. In this case, as long as the effects of the present invention are not impaired, there may be a relationship in which the two solvents are not completely phase-separated near the interface, but a region where they are mixed with each other. The relationship of substantially no compatibility is such that the solubility of the solvent of the reaction raw material solution in the solvent 132 at 25° C. is preferably 10 g/100 g or less, more preferably 5 g/100 g or less, and even more preferably 1 g/100 g or less.
For example, when cotton fiber is used as the carbon-containing hollow fiber material and water, a water-soluble organic solvent, or a mixture thereof (i.e., a polar solvent (hydrophilic solvent)) is used as the reaction raw material solution, the solvent 132 is Use a non-polar solvent (hydrophobic solvent). For example, as the solvent 132, dodecane, decane, hexane, toluene, benzene, naphthalene, Fluorinert (trade name), hydrofluoroolefin, silicone oil, linear alkanes, cyclic alkanes, linear unsaturated hydrocarbons, cyclic Unsaturated hydrocarbons, aromatics, fluorocarbons, mineral oil, vegetable oil, etc. can be used. The temperature of the solvent 132 is not particularly limited, and is appropriately set depending on the purpose. For example, the temperature can be -100°C to 300°C.

In the form of FIG. 5, the reaction raw material solution that is incompatible with the solvent 132 impregnated into the cotton fiber 111 is passed from the outer surface 111S side of the cotton fiber 111 through the gaps (inside the pores) between the microfibrils by the hydraulic pressure of the solvent 132. Furthermore, it migrates in the inner direction of the cotton fibers 111 and into the cotton fiber (material) structure, that is, into the inner direction of the cotton fibers 111 and/or into the cotton fiber (material) structure (transfer step). Note that when the capillary force acts further, the reaction raw material solution that has permeated into the inside of the cotton fibers 111 moves further into the inside through the gaps between the microfibrils. Therefore, the permeation region 121 of the reaction raw material solution moves from the outer surface 111S of the cotton fiber 111 toward the inside of the cotton fiber 111. As a result, a large amount of the reaction raw material solution exists from the outer surface 111S side of the cotton fiber 111 toward the inside of the cotton fiber 111.

In the embodiment shown in FIG. 5, pressure P is applied to the solvent 132 in which the cotton fibers 111 are soaked. For the pressure P, gas pressure or liquid pressure may be applied from outside the container. It is also possible to equip the container itself with a pressure cylinder and pressurize it by applying power to the cylinder. Alternatively, the pressure may be increased by sealing the container and heating the solution to expand its volume or generate vapor pressure. Alternatively, it is also possible to add a solvent having a boiling point lower than that of the main solvent to the main solvent, vaporize it by heating, and pressurize it. By applying a pressure higher than atmospheric pressure to the surface of the solvent 132 in this manner, the reaction raw material solution passes through the gaps (inside the pores) between the microfibrils of the cotton fibers 111 and is forced further into the interior. As a result, the reaction raw material solution is transferred from the surface to the inside of the cotton fiber 111 under stronger pressure, and it is also possible to transfer the reaction raw material solution to the inner surface of the inner cavity 117 of the cotton fiber 111 or the vicinity thereof. . In the manufacturing method of the present invention, the chemical reaction may be started after applying pressure before starting the chemical reaction, or the pressure may be applied while the chemical reaction is occurring. Further, the magnitude of this pressure can be appropriately set depending on the type of carbon-containing hollow fiber material, etc. For example, the pressure may be approximately 1.05 to 20 atmospheres, or approximately 1.1 to 10 atmospheres.

Next, as shown in FIG. 6, the permeation region 121 of the reaction raw material solution impregnated into the cotton fibers 111 is heated to a predetermined reaction temperature to cause a chemical reaction in the reaction raw material solution therein. When the reaction raw material solution contains the above-mentioned metal salt and reducing agent, the metal salt can be reduced by heating and the metal can be precipitated.

As an example of the above heating method, the cotton fibers 111 in the solvent 132 placed in the container 131 are irradiated with microwave MW. Then, the permeation region 121 of the reaction raw material solution impregnated into the cotton fiber 111 is heated and controlled to a predetermined reaction temperature, and the reaction raw material (for example, a precursor (not shown)) therein is heated. Can be done. The predetermined reaction temperature is appropriately set depending on the type of desired reaction. That is, it is preferable that the temperature is higher than the temperature at which the desired reaction occurs and lower than the boiling point of the solvent 132. The container 131 is made of a material that is difficult to absorb microwave MW, such as polytetrafluoroethylene (e.g., Teflon (registered trademark)), quartz, ceramic, aluminum oxide (alumina), or polyetheretherketone (PEEK). ), acrylic (trade name) resin, etc. are preferably used. The microwave MW can generally use an S band microwave frequency of 2 to 4 GHz. Alternatively, 900 to 930 MHz or 5.725 to 5.875 GHz can also be used. Further, microwaves having frequencies other than these may be used.
The above-mentioned microwave MW irradiation is preferable because silver nitrate in the reaction raw material solution directly generates heat, so it can be heated in a short time, and temperature unevenness caused by heat conduction can be reduced. Furthermore, it is preferable because it can be heated without contact and can selectively heat silver nitrate, which has good absorption of microwave MW.
Microwave irradiation may be in either multi-mode or single mode, and single-mode microwave irradiation is preferably employed from the viewpoint of efficiently and uniformly heating the target region.

The above heating is not limited to microwave heating. For example, optical heating may be used. Heating may also be performed using other heating means. Further, heating may be performed selectively on the reaction raw material solution, or the reaction raw material solution may be heated indirectly by heating cotton fibers or a solvent.
Furthermore, reaction promotion by means other than heating means can also be used. For example, in photopolymerization, irradiation with ultraviolet rays or visible light may be used. Further, reaction acceleration by irradiation with ultrasonic waves can also be used. Alternatively, pressure such as shock waves can be used to initiate the reaction. Alternatively, in the case of a slow reaction, simply leaving it standing is also an effective reaction control method. In addition, for reactions that are promoted at low temperatures, such as crystallization and precipitation, maintaining the reaction in a low temperature environment is an effective reaction control method.

The heating selectively causes a chemical reaction in the permeation region 121 within the cotton fiber 111 to produce a chemical substance. For example, metals are deposited from metal precursors.

Thereafter, the cotton fibers 111 are taken out from the solvent 132, washed by immersion in a desired solvent if necessary, and then dried to obtain the desired carbon-containing hollow fiber material. For cleaning, it is preferable to immerse it in ethanol and use an ultrasonic cleaner. Further, drying can be carried out by natural drying in the atmosphere or heating drying using an electric furnace. Alternatively, drying by contacting with air, nitrogen, etc. is also effective. Further, the above-mentioned cleaning may be performed by immersing in a liquid such as water or alcohol, or by contacting with running water or a liquid in a fluid state.

The cotton fiber 111 produced as described above has a functional chemical substance (metal, etc.) between the microfibrils 118 of the secondary cell wall 116, as shown in FIG.

Next, the carbon-containing hollow fiber material in which the inorganic functional substance has been formed is heated in an inert (oxygen-free) atmosphere (inert gas atmosphere) to perform a carbonization process.
In the carbonization step, a carbon-containing hollow fiber material in which an inorganic functional substance has been produced is placed in a heating furnace, and the atmosphere in the heating furnace is made into an inert gas atmosphere. For example, an electric furnace can be used as the heating furnace. This inert gas atmosphere is an oxygen-free atmosphere (reducing atmosphere), and is preferably a nitrogen gas atmosphere or a rare gas atmosphere, for example. Ideally, the atmosphere should not contain oxygen, and in practice, to prevent the carbon-containing hollow fiber material from burning, the oxygen concentration is desirably 1000 ppm or less, preferably 100 ppm or less, and more preferably 100 ppm or less. Preferably it is 10 ppm or less. After the inside of the heating furnace is converted to an inert gas atmosphere, the temperature inside the heating furnace is raised to 600° C. to 1500° C. from the viewpoint of carbonization. It is preferable that the temperature reached is appropriately selected depending on the material to be carbonized. In particular, it is important to determine the temperature reached so as not to lose the structure of the functional substance.
When the temperature of the functional hollow carbon fibers produced by carbonization reaches room temperature, the atmosphere inside the heating furnace is returned to the atmospheric atmosphere, and the functional hollow carbon fibers containing an inorganic functional substance are taken out from inside the heating furnace.
In addition, from the viewpoint of suppressing shape changes during carbonization treatment, it is also possible to add a flame-retardant process to convert the fibers into flame-retardant fibers by performing heat treatment at 200 to 300°C in an air atmosphere before carbonization treatment. good.
Furthermore, in order to develop the function of the functional substance, heat treatment may be performed at a desired temperature after replacing the atmospheric gas with a component necessary for the functional development.

When the melting point of the inorganic functional substance is higher than the carbonization temperature in the carbonization step, heat treatment for increasing strength can be performed at a higher temperature. For example, high-strength carbon fibers are produced by carbonization treatment, which involves heating at 600 to 1500° C. in an inert gas atmosphere such as nitrogen or rare gas.
Further, it is also possible to generate a reaction product between the inorganic functional substance and the carbon fibers by high-temperature heat treatment during or after the carbonization treatment.

In the above embodiment, the case where hydrophilic cotton fibers 111 were mainly used as the carbon-containing hollow fiber material was explained as an example, but the carbon-containing hollow fiber material is not limited to cotton fibers, as described above.
That is, a hydrophobic reaction raw material solution is used as the reaction raw material solution, the reaction raw material solution is infiltrated into the pores of the hydrophobic carbon-containing hollow fiber material, and then the carbon-containing hollow fiber material is introduced into the reaction raw material solution. On the other hand, by immersing it in an incompatible hydrophilic solvent, the reaction raw material solution can also be moved deeper into the pores of the carbon-containing hollow fiber material. Then, by causing a chemical reaction in the reaction raw material solution that has migrated into the interior of the carbon-containing hollow fiber material, similar to cotton fibers, more chemicals (such as metals) are contained inside the carbon-containing hollow fiber material than on the surface. can be generated.

In addition, chemical reactions can be carried out by heating as described above, but are not limited to heating. Depending on the type of reaction raw materials, chemical reactions may be carried out by light (radiation) irradiation, ultrasonic irradiation, shock wave irradiation, standing still, cooling, etc. It is also possible to use the following means.
In the present invention, the term chemical reaction is used in a broad sense. That is, in addition to the reaction of a chemical substance to change into another chemical substance, a change in the state of a chemical substance is also included in the chemical reaction in the present invention. For example, crystallization or precipitation that does not cause a change in the chemical substance itself is also included in the chemical reaction in the present invention. Preferred examples of chemical reactions to which the method for producing functional hollow carbon fibers of the present invention is applied include oxidation reactions, reduction reactions, polymerization reactions, condensation reactions, substitution reactions, crystallization, and precipitation.

As a specific example, as described above, the reaction raw material solution includes a metal precursor, and the chemical reaction is a reaction that precipitates a metal from the metal precursor.
Further, an embodiment may be mentioned in which the reaction raw material solution contains an alkoxysilane compound (preferably tetraalkoxysilane), and the chemical reaction is a reaction that produces silica through hydrolysis of the alkoxysilane compound and subsequent polycondensation. .
Another example is a form in which the chemical reaction is crystallization or precipitation of a chemical substance in the reaction raw material solution.
In addition, the reaction raw material solution contains a silica source, an aluminum source, an alkali source, and water, or contains a metal source capable of replacing silicon in addition to a silica source, an aluminum source, an alkali source, and water, and the chemical reaction is performed on zeolite. One example is a reaction that results in the following. Examples of the silica source include colloidal silica and tetraethoxysilane (TEOS). Examples of the aluminum source include aluminum hydroxide, aluminum nitrate, aluminum alkoxide, and the like. Examples of the alkali source include alkaline earth metal cations and alkylammonium cations. Examples of metal sources that can replace silicon include alumina, titanium, and the like.

[Functional hollow carbon fiber]
The functional hollow carbon fiber of the present invention is the above-described carbon-containing hollow fiber material that encapsulates an inorganic functional substance. Encapsulation means that more inorganic functional substances exist in the pores on the inner side than on the outer surface of the carbon fiber. The functional hollow carbon fiber of the present invention encapsulates an inorganic functional substance in its pores, so that the inorganic functional substance is protected by the functional hollow carbon fiber, and its functionality can be expressed over a long period of time. can do.
Specific examples of the inorganic functional substance include various metals such as silver, copper, platinum, palladium, tin, nickel, cobalt, and gold, or compounds containing these metals. Further examples include zeolite, inorganic crystals, amorphous particles, semiconductor materials, dielectric materials, magnetic materials, piezoelectric materials, thermoelectric materials, photocatalysts (eg, titanium oxide), and the like.

The functional hollow carbon fiber of the present invention can be used for various purposes.
[Application to flame-retardant carbon fiber]
Since flame-retardant inorganic crystals can be introduced into the hollow portions of the functional hollow carbon fibers of the present invention, it is possible to further make the carbon fibers flame-retardant.

[Application to electrode materials]
Carbon materials and carbon fibers, which have electrically conductive paths and have a large specific surface area, are widely used for electrodes of lithium ion batteries and fuel cells. In the functional hollow carbon fiber of the present invention, by growing metal nanoparticle crystals in the hollow portion, it can be expected to have the effect of suppressing loss from the inside of the carbon material due to falling off even if the battery is used repeatedly. This makes it possible to extend the life of the battery.

[Application to catalyst support material]
The functional hollow carbon fiber of the present invention can be applied to techniques for water purification and air purification by supporting a substance having a catalytic action in its hollow portion. This prevents the catalytic substance from falling off the carbon fiber even if there is no strong bond between the carbon and the catalytic substance, and prevents the catalytic component from flowing out of the functional hollow carbon fiber. disappears. Therefore, it is possible to maintain catalyst performance and extend the life of the catalyst.

[Application to sensors]
Since the functional hollow carbon fiber of the present invention has electrical conductivity, molecules or crystals that interact with a specific chemical substance can be introduced into the nanostructured surface of the carbon fiber in the hollow part. It can be expected to be used as a sensor that extracts the interaction response as an electrical signal.
Furthermore, by incorporating crystals used in piezoelectric elements, such as barium titanate, it can be expected to be used as a pressure sensor. Furthermore, if a photoresponsive element such as a cadmium sulfide (CdS) crystal is introduced, it can be expected to be used as a photosensor.

[Application to carbon fiber that can be bonded to other materials]
Carbon fiber has a small coefficient of thermal expansion and is characterized by little dimensional variation in products due to temperature changes. This feature causes strain at the bonded portion when carbon fiber is used as a composite with other materials. In the functional hollow carbon fiber of the present invention, it is expected that the coefficient of thermal expansion of the carbon fiber can be adjusted by introducing materials with different coefficients of thermal expansion into the hollow portion. This makes it possible to reduce strain and extend the life of the composite material.

EXAMPLES The present invention will be described in more detail below based on Examples, but the present invention is not to be construed as being limited to these.

Functional hollow carbon fibers containing silver in the hollow portions were manufactured using the above-described manufacturing method, and the details thereof will be explained below.

[Example 1]
In Example 1, a sample was prepared as follows. A standard fabric (cotton) for antibacterial testing (3.5 cm (length) x 20 cm (width), weight 0.8 g, distributed by the Fiber Evaluation Technology Council, a general incorporated association) was used as a sample.
The sample was immersed for 15 minutes in an ethylene glycol solution (1.2 g) in which 0.4 mol/L (400 mM) of silver nitrate, a reaction raw material solution, was dissolved to absorb the entire amount.
A mixed solvent of dodecane (30 ml) and hexane (5 ml) was placed in a Teflon (registered trademark) container (capacity: 100 ml), and a cotton cloth was placed in the mixed solvent and immersed for 5 minutes. Then, the reaction raw material solution existing on or near the surface of the cotton fibers was transferred into the pores of the cotton fibers of the cotton cloth and into the cotton fiber structure. Thereafter, the container was sealed with a Teflon (registered trademark) lid, and microwave heating was performed. MicroSYNTH (trade name) (manufactured by Milestone General Co., Ltd.) was used as the microwave heating device. Microwave heating was performed for 5 minutes with the heating set temperature of the solvent set at 140° C. and the pressure inside the container at the start of heating set at 1 atm (101 kPa). Note that the pressure inside the container when the temperature reached 140°C was 3.5 atm. This increase in the pressure inside the container is presumed to be due to part of the hexane (boiling point 69° C.) becoming a gas. The temperature of the mixed solvent of dodecane and hexane was measured using an optical fiber thermometer. The pressure inside the container was measured using a pressure sensor attached to MicroSYNTH.
After heating, the container was naturally cooled to 50° C., and the cotton cloth was taken out from the container. Then, it was washed and dried. For cleaning, the cotton cloth was soaked in ethanol and washed in an ultrasonic cleaner for 5 minutes. For drying, the cotton cloth was naturally dried in the air at room temperature (25° C.) for 24 hours.

Subsequently, the cotton fabric was carbonized in a tube furnace. A cotton cloth (86 mg) was placed on a quartz boat and placed in a tube furnace. As the tube furnace, TMF-500N manufactured by As One was used. The inside of the tube furnace was replaced with nitrogen at room temperature (25° C.) for 2 hours. Nitrogen substitution was performed by flowing 99.99995% by volume of high purity nitrogen at a flow rate of 100 ml/min. After replacing the tube with nitrogen, the temperature inside the tube furnace was raised from room temperature to 600° C. over 2 hours while continuously passing the high-purity nitrogen, and the temperature was maintained at 600° C. for 30 minutes. Thereafter, the inside of the tube furnace was cooled to 50° C. at a cooling rate of about 200° C./h. The mass of the cotton fabric after cooling was 11 mg.

Thereafter, carbonization was performed using a scanning electron microscope (SEM) (S-4800 (trade name) manufactured by Hitachi High-Technologies) and energy dispersive X-ray spectroscopy (EDX) (QUANTAX400 (trade name) manufactured by BRUKER). After treatment, the cross section of the cotton fabric was observed and its composition analyzed.
The cotton fabric was cut using a cutter, and the cross section was observed using SEM. As shown in Figure 8(A), in the SEM cross-sectional image of cotton cloth, the composition analysis of the cross-section of the cotton fiber was performed along the direction of the arrow shown near the center of the figure. The intensity distribution of the silver component and carbon component in the diametrical direction was investigated. As shown in FIG. 8(B), from the intensity distribution of the components, the distribution positions of the carbon component and the silver component almost overlapped, so it was confirmed that the silver component was distributed within the fiber. Furthermore, when we analyzed the composition of the area A surrounded by the square where the cross section of the cotton cloth in Figure 9 is shown, we found that the carbon component shown in Figure 10 (A) was different from that shown in Figure 10 (B). The silver component shown showed a tendency to be easily distributed on the inner wall of the fiber. Further, by SEM observation of the inner wall of the fiber, it was confirmed that fine silver particles with a particle size of 50 to 100 nm were present. The particle size was determined by randomly selecting 30 microparticles in a photographing range of 13 μm x 10 μm on a SEM photograph taken at a magnification of 10,000 times, and measuring the maximum diameter of each with a length measuring ruler.
From the above, it was found that functional hollow carbon fibers with silver fine particles retained in the hollow portions of the carbon fibers could be obtained.

11 Functional hollow carbon fiber 12 Hollow part 21 Inorganic functional substance 110 Carbon-containing hollow fiber material 111 Cotton fiber 111S Outer surface 112 Cuticle layer 113 Network layer 114 Winding layer 115 Primary cell wall 116 Secondary cell wall 117 Inner cavity (hollow part 12)
118 Microfibril 121 Permeation area of reaction raw material solution 131 Container 132 Solvent 133 Lid MW Microwave

Claims (9)

A step of infiltrating a reaction raw material solution into the hollow part of the carbon-containing hollow fiber material,
The carbon-containing hollow fiber material impregnated with the reaction raw material solution is immersed in a solvent that is immiscible with the reaction raw material solution, and the reaction raw material solution is applied to the inside of the hollow part of the carbon-containing hollow fiber material. or a step of transferring it into the fibrous tissue;
producing an inorganic functional substance through a chemical reaction of the reaction raw material solution transferred into the hollow portion of the carbon-containing hollow fiber material or into the fiber structure;
heating the carbon-containing hollow fiber material that has produced the inorganic functional substance in an inert atmosphere to produce carbon fibers;
A method for producing functional hollow carbon fiber, including: The method for producing functional hollow carbon fibers according to claim 1 , wherein the chemical reaction is caused by heating. The method for producing functional hollow carbon fibers according to claim 2 , wherein the heating is heating by microwave irradiation. The method for producing functional hollow carbon fibers according to claim 3 , wherein the microwave irradiation is single mode microwave irradiation. The reaction raw material solution contains a metal precursor,
The method for producing a functional hollow carbon fiber according to any one of claims 1 to 4 , wherein the chemical reaction is a reaction that precipitates a metal from the metal precursor. The method for producing functional hollow carbon fibers according to any one of claims 1 to 4 , wherein the chemical reaction is crystallization or precipitation of a chemical substance in the reaction raw material solution. The reaction raw material solution contains a silica source, an aluminum source, an alkali source and water,
Or, in addition to the silica source, the aluminum source, the alkali source, and the water, it includes a metal source capable of replacing silicon,
The method for producing functional hollow carbon fibers according to any one of claims 1 to 4 , wherein the chemical reaction is a reaction that produces zeolite. The function according to any one of claims 1 to 7 , wherein the carbon-containing hollow fiber material is composed of vegetable fiber, animal fiber, or chemical fiber, or a composite material consisting of two or more of these. A method for manufacturing hollow carbon fiber. The method for producing functional hollow carbon fibers according to claim 8 , wherein the carbon-containing hollow fiber material is cotton or linen.