JPH07150419A - Production of carbon fiber according to vapor process - Google Patents

Abstract

PURPOSE:To provide a method for producing carbon fiber excellent in characteristics such as electric conductivity by increasing the growth and yield of the carbon fiber in a method for producing the carbon fiber according to a vapor process. CONSTITUTION:This method for producing carbon fiber according to a vapor process comprises the steps of making a liquid of an organic compound contain a transition metal or a compound thereof, forming the resultant liquid into fine droplets, thermally decomposing the droplets while spraying the droplets on the wall surface of a heating furnace, producing the carbon fiber having branches on the wall surface and scraping off the produced carbon fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carbon fiber, and more particularly to a method for producing carbon fiber by vapor phase growth method by thermal decomposition of organic compounds.

[0002]

2. Description of the Related Art A method for producing carbon fibers by vapor phase growth is an excellent method for pyrolyzing an organic compound in a heating furnace to obtain carbon fibers in one step. There is a problem with the sex and improvements have been made. For example, the first method was to deposit ultrafine particles of a transition metal on a ceramic substrate, then supply an organic compound to decompose it and grow it for a long time to produce a relatively thick and long vapor grown carbon fiber. Although carbon fibers having good physical properties can be obtained by this method, the reaction rate becomes slower as the fiber becomes thicker, which is insufficient for industrial production. In order to improve this productivity, for example, Japanese Patent Application Laid-Open No. 58-180615 proposes a flow method in which an ultrafine powder of a transition metal or its compound is made to exist so as to be suspended in a thermal decomposition zone of an organic compound. . Further, as a flow method, in JP-A-63-92726, the metal particles were adjusted to have a particle size of 2 to 30 nm,
It is described that this is dispersed in a liquid of an organic compound and is made into liquid droplets and supplied into the furnace. At that time, it is preferable to adjust the diameter of the liquid droplets. Further, similarly, Japanese Patent Application Laid-Open No. 62-53419 describes that the diameter of the liquid droplets should be 30 μm or less. In these cases, the droplets are usually supplied so as to spread over the entire reaction zone as shown in FIG. In addition,
In 320, an organic compound of a transition metal such as ferrocene is converted into a vapor phase and introduced into a carbon fiber deposition zone, where it is thermally decomposed, and ultrafine particles of the produced metal are deposited on a substrate, where the carbon fiber is grown. It is disclosed.

[0003]

In the flow method, an organic compound (raw material) containing a transition metal or its compound is supplied in parallel with the length direction of the furnace, and carbon fibers are produced in a floating state, and most of them are left outside the furnace as they are. Since it was taken out, the reaction time was short because the reaction time was short, and the crystal growth was insufficient, and the thickness and length of the carbon fiber were small, and good carbon fiber could not be obtained. In the method of Japanese Patent Publication No. 4-24320, since ferrocene or the like is not sprayed so as to concentrate on the substrate, the concentration and utilization rate of the metal fine particles on the substrate are low, and the raw material is gasified and introduced into the furnace, so that the gas concentration is high. Becomes uniform within
In particular, the concentration of fine particles on the substrate and the raw material concentration around the fine particles cannot be increased, and as a result, the yield of carbon fibers on the substrate cannot be increased.

When the raw material is supplied in droplets to the reaction region, the energy required for the reaction is absorbed by radiant heat or flow heat transfer of the carrier gas. At that time, in order for the temperature of the droplet to rise to the reaction region, first, the amount of heat and the heat of vaporization required up to the vaporization temperature of the liquid are required, and if the heat supply is insufficient, the temperature will partially drop. As a result, the carbonization rate is lowered, the reaction rate and the fiber growth rate are lowered, and a fiber having a sufficient length cannot be obtained. Therefore, in order to solve these problems, in order to increase the residence time of the fiber and increase the reaction temperature transfer rate, not only flow heat transfer and radiant heat transfer but also heat transfer from the furnace wall is used. It is desirable to adopt the method of combined use. The present invention aims to increase the growth and yield of carbon fiber by a predetermined residence time, heat transfer from the furnace wall and high concentration of the raw material in the carbon fiber production zone, and carbon fiber having excellent characteristics such as heat conduction. The purpose is to provide.

[0005]

In order to solve the above problems, the present invention employs a method of improving the heat transfer instead of the substrate and generating and holding carbon fibers on the furnace wall so that a predetermined residence time can be obtained. In addition, the raw material is supplied in the form of droplets and sprayed toward the furnace wall to increase the concentration of the raw material near the furnace wall. That is, the present invention uses a transition metal ultrafine particle as a seed and produces carbon fibers by thermal decomposition of an organic compound. In the method, fine droplets of a transition metal or an organic compound containing the compound are continuously directed toward a wall surface of a heating furnace. Characterized by vaporization by intermittent or intermittent spraying to generate carbon fibers on the furnace wall surface, and then branched carbon fibers on the carbon fibers, which are intermittently scraped off It is a method for producing fibers. Further, the carbon fiber obtained here can be heat-treated at 1000 ° C. or higher, and it is desirable that the carbon fiber is further crushed after the heat treatment.

The present invention will be described in detail below. The transition metal or its compound that serves as a seed and a catalyst is
IVa, Va, VIa, VIIa, VIII elements and their alloys and mixtures and their inorganic and organic compounds are suitable. Among them, as the transition metal and its compound which become the ultrafine particle seed of the transition metal element, ultrafine powder (30 nm or less) such as Fe, Ni, Co, or organic compound such as ferrocene or nickelcene is preferable. Although ultrafine powders of Fe, Ni, Co and the like have problems in manufacturing method and aggregation, organic compounds such as ferrocene are particularly preferable because ultrafine particles of Fe and the like are generated by thermal decomposition. The content of the transition metal as a catalyst is preferably 0.03 to 10.0 wt% with respect to the carbon amount of the organic compound (in the case of using ferrocene or the like, the total amount including the carbon).
0.1 to 5.0% by weight is good.

Organic compounds used as raw materials for carbon fibers include benzene, toluene, xylene, methanol, ethanol,
It is also possible to use naphthalene, phenanthrene, cyclopropane, cyclopentene, cyclohexane and other organic compounds and mixtures thereof, volatile oil, kerosene and the like. Among them, aromatic compounds such as benzene, toluene and xylene are particularly preferable. Ultrafine particles of the transition metal or a compound such as ferrocene is dispersed or dissolved in this organic compound and supplied in the form of droplets. The whole amount of the organic compound may be in the form of droplets as described above, but it is also possible to use one part as droplets and supply the rest separately in liquid or gas form.

In order to increase the crystal growth rate, it is necessary to increase the concentration of the organic compound near the surface of the catalyst (seed). In the case of vaporizing the raw material liquid and supplying it as a gas, the raw material concentration in the reactor including the surface of the catalyst becomes an average concentration.
However, if the liquid is supplied in the form of liquid droplets, fine particles are generated from the liquid and the liquid is evaporated at the same time, so that the concentration of the raw material organic compound in the vicinity of the catalyst becomes considerably high, resulting in an increase in crystal growth rate. The method of supplying droplets is also one of the features of the present invention, and in the present invention, the droplets are supplied toward the furnace wall continuously or intermittently. Since the furnace is usually of the external heat type, the heat in the furnace is supplied from the wall of the furnace by heat transfer of radiation or gas. Therefore, it is advantageous for heating that the droplets are at or near the furnace wall. After carbon fibers are generated on the furnace wall and cover the furnace wall, the droplets are sprayed onto this fiber, but this carbon fiber has a very high thermal conductivity, so there is no disadvantage in heating the droplets. .

The improvement of the thermal conductivity accelerates the growth of the fibers, and after the fibers are formed on the furnace wall, the droplets are sprayed on the furnace wall to form the fibers including the branch, and further the droplets are sprayed continuously. However, since the fine particles are generated between or on the accumulated fibers, the utilization rate of the fine particles is increased, which is considered to be one of the reasons for the increased yield. As a method of supplying droplets, a method of spraying an organic compound containing a transition metal or its compound using a spray nozzle is suitable. The droplets may be sprayed as they are, but since hydrogen gas is usually used as a carrier gas, it is preferable to use a spray nozzle capable of spraying this hydrogen gas together. In order to spray the spray on the furnace wall, the structure is inclined so that the fluid passage at the tip of the nozzle is radially expanded.

FIG. 1 shows a schematic diagram of an apparatus used for carrying out the present invention. In the figure, 1 is a heating furnace, which is not impossible even with a horizontal type, but as shown in the figure, the vertical type is used because of the ease of scraping the fibers deposited on the furnace wall and the same conditions around the furnace wall. preferable. Reference numeral 2 is a pressure-type dispersion spray nozzle, and the lower portion 21 of the fluid passage is inclined so that the fluid spreads radially. The passage lower portion 21 has a structure in which, for example, several small holes are provided. The liquid in which ferrocene and the like are dissolved is supplied to the nozzle together with the carrier gas and atomized at the pressure of the carrier gas. In the figure, 3 is a sprayed fluid, and its apex angle is preferably 30 to 120 °.

The carrier gas is preferably a reducing gas such as hydrogen (H ₂ ) gas, and is used when the raw material and the catalyst are supplied to the thermal decomposition zone in order to exhibit and maintain the activity of the transition metal as a catalyst. The amount of the carrier gas is appropriately 1 to 70 parts by mol with respect to 1.0 part by mol of the organic compound which is the carbon source. The size of the droplet introduced into the reaction region is related to the size of the nucleus of the catalyst, and affects the thickness and length of the fiber and the reaction rate. If the size of the core of the catalyst is large, the fiber becomes thick, and if the length is short, on the contrary, if it is small, the fiber becomes thin and weak. Further, if the particle diameter of the droplet is large, a large amount of evaporation energy is required, resulting in a partial temperature drop, leading to a decrease in the reaction rate and a decrease in the carbon fiber deposition rate. On the other hand, if it is too small, the rate of evaporation immediately after introduction and vaporization before reaching the wall surface becomes high. Considering the above points, it is appropriate that the diameter of the sprayed microdroplets is 70 to 200 microns.

The droplets are sprayed continuously or intermittently. Therefore, since carbon fibers are first formed on the furnace wall surface and are further sprayed on the fibers, most of the fibers formed there are branched. In this way, fibers grow and grow on the furnace wall, and deposit on the inner wall of the furnace. This is scraped off intermittently. The scraping interval is determined by looking at the deposition condition, but a range of 10 seconds to 15 minutes is appropriate. For the scraping method, a jig with a ring attached to the tip of the rod can be used (Shokaisho 62-93379). The temperature of the inner wall of the furnace is about 800 to 1300 ° C, which is the same as in the usual case. Most of the carbon fibers obtained by the present invention have a thickness of 0.05 to 0.5 μm and a length of 1 to 100 μm.

[0013]

When the raw material is supplied to the entire decomposition zone in the furnace in order to improve the space productivity, temperature distribution is likely to occur in the thermal decomposition zone in the radial direction of the furnace and further in the longitudinal direction thereof, which causes non-uniformity. Becomes It is desirable to supply the raw material to a temperature zone as uniform as possible, but it is difficult to maintain a wider temperature zone even if external heating is controlled by an endothermic or exothermic reaction during the reaction. In the present invention, by producing carbon fibers on the wall surface of the furnace, not only the heat transfer method but also the conduction method from the furnace wall can be introduced. The thermal conductivity of carbon fiber is remarkably large, and by introducing conduction in addition to radiation, the heat transfer is better and more uniform than in the case where carbon fiber is generated throughout the furnace as in the flow method. And the reactivity and fiber growth are improved.

Further, by supplying the raw material in the form of droplets, the concentration of the carbon compound around the metal fine particles is increased and the yield is also improved. The raw material containing the catalyst is sprayed onto the substrate or the surface of the carbon fiber growing on the substrate, promoting the growth of the fiber in the process of evaporative reaction and forming new crystal nuclei on the surface of the carbon fiber. As a starting point, new growth is promoted. By repeating this, a branched vapor grown carbon fiber is obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings by way of examples and comparative examples of the present invention. Example As shown in FIG. 1, a vertical heating furnace (inner diameter 17.0 cm, length 150 c
m) Install spray nozzle 2 on top of 1. The temperature of the inner wall of the heating furnace 1 was raised to 1200 ° C and maintained, and 20 g / min of the liquid raw material of benzene containing 4% by weight of ferrocene was sprayed directly from the spray nozzle 2 to the furnace wall at a flow rate of 100 L / min of hydrogen gas. Supply as a spray. The shape of the spray 2 at this time is a conical side surface shape (trumpet shape or umbrella shape), and the apex angle θ of the nozzle is 60 °. Under these conditions, ferrocene is pyrolyzed to make fine iron particles,
This served as a seed, and carbon fibers were produced and grown from the carbon by the thermal decomposition of benzene. The vapor grown carbon fiber grown by this method was continuously produced for 1 hour while scraping it off at intervals of 5 minutes. A micrograph (× 5000) of this carbon fiber is shown in FIG. About 3 of the carbon fibers obtained
0 g was heat-treated at 2400 ° C., and this was mixed with PP resin (Showa Denko KK: SMA410) to produce a fiber reinforced plastic containing 50 wt% carbon fiber. The volume resistivity of this fiber reinforced plastic was measured and found to be 0.14 Ωcm.

Comparative Example A spray nozzle used was a type as shown in FIG. 2 for spraying the entire surface just below the furnace, and the other manufacturing conditions were the same as those of the above-mentioned embodiment, and the vapor grown carbon fiber was used. Was manufactured. Micrograph of the carbon fiber (× 500
0) is shown in FIG. About 20 g of the obtained carbon fiber is 2400 ° C
Was heat treated, and this was mixed with the above-mentioned PP resin to produce a fiber reinforced plastic containing 50 wt% of carbon fiber in the same manner, and the volume resistivity was measured and found to be 0.40 Ωcm.
As can be seen from the micrograph of the carbon fiber, the carbon fiber (FIG. 3) obtained by the production method according to the present invention has more branches than the carbon fiber of the comparative example (FIG. 4). Although it is a carbon fiber reinforced plastic, the carbon fiber of the present invention has better conductivity (smaller specific resistance).

[0017]

As described above, the carbon fiber obtained by the manufacturing method according to the present invention has a more uniform shape than the conventional one, has a large number of branches, and has a large number of fibers connected to each other. And the dispersibility (mixing) with the resin is also improved. In particular, it is possible to provide a carbon fiber effective as a micromaterial that functions as a raw material for imparting conductivity in a composite material.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a vapor grown carbon fiber production apparatus used in the present invention.

FIG. 2 is a schematic sectional view of a conventional vapor grown carbon fiber manufacturing apparatus.

FIG. 3 is a micrograph showing the shape of carbon fibers produced by the production method according to the present invention.

FIG. 4 is a micrograph showing the shape of carbon fibers produced by a manufacturing method of a comparative example.

[Explanation of symbols]

 1 Heating Furnace 2 Pressure Dispersion Type Spray Nozzle 3 Atomizing State According to the Present Invention 4 Conventional Spray Nozzle 5 Conventional Atomizing State 21 Inclined Nozzle Small Hole θ Spraying Angle

Claims (3)

[Claims] 1. An ultrafine particle of a transition metal element is used as a seed,
In a method for producing carbon fiber by thermal decomposition of an organic compound, fine particles of a transition metal or an organic compound containing the compound are reacted while being sprayed toward the wall surface of a heating furnace to generate carbon fiber on the wall surface of the furnace. A method for producing a vapor grown carbon fiber, characterized in that branched carbon fibers are produced on the carbon fibers and the carbon fibers are scraped off intermittently. 2. The vapor grown carbon fiber obtained in claim 1
A method for producing a vapor grown carbon fiber, which comprises heat treatment at 000 ° C. or higher. 3. A method for producing a vapor grown carbon fiber, which comprises pulverizing the vapor grown carbon fiber obtained in claim 1 or 2.