JPS639044B2 - - Google Patents

Description

[Detailed description of the invention]

a. Field of Industrial Application The present invention relates to a method for producing carbonaceous fibers that are widely used as materials for conductors, resistors, heating elements, electrodes, or as reinforcing materials for composite materials such as FRP and FRM. b. Prior Art Conventionally, as a method for producing carbonaceous fibers, the following methods have been widely used: (1) making fibers from polyacrylonitrile, cellulose, pitch, etc., making them infusible, and then firing them. Apart from this method, (2) benzene,
A method of directly producing fibers by thermally decomposing hydrocarbon gases such as methane and ethane and performing a gas phase reaction is also known. Fibers produced by this method are called vapor-grown carbon fibers, and have superior properties in terms of modulus of elasticity, tensile strength, electrical conductivity, etc., compared to carbon fibers produced by the method (1) above. For example, the tensile strength, elastic modulus, and room temperature electrical resistivity of carbon fibers made from polyacrylonitrile are as follows:
6~12ton/ ^cm2 , 600ton/ ^cm2 , 5~10× ^10-3 Ωcm
On the other hand, the values of vapor phase-generated carbonaceous fiber (benzene raw material, generation temperature 1100℃) are 10 to 1, respectively.
30ton/cm ² , 2000 to 4000ton/cm ² , and 1×10 ⁻³ Ωcm, and have excellent properties. Therefore, vapor-generated carbon fibers are expected to be used as composite materials with plastics, metals, and carbon materials, as well as electronic materials such as electrical conductors, resistors, and heating elements. However, they still have the following drawbacks. Not widely used. (1) Vapor-grown carbon fibers are difficult to obtain as continuous long fibers; they are short fibers and often have defects, making it difficult to obtain uniform fibers. (2) The thickness of the fibers is approximately 5 to 50 μm, which is highly variable and non-uniform. Thin fibers are preferred when used as reinforcing materials because they generally have higher strength and modulus of elasticity. However, 5μ
It is difficult to stably obtain fibers with a diameter of m or less. (3) The reaction temperature is high, generally requiring a temperature of 1000℃ or higher. (4) To promote the growth reaction, catalysts, e.g.
Requires ultrafine powder of Fe, Ni, Co, etc. When a catalyst is not used, it is difficult to control the reaction and fibers may not be obtained. c. Purpose of the Invention The present invention was made to eliminate the drawbacks of conventional vapor-grown carbon fibers, and its purpose is to
The object of the present invention is to provide a method for producing vapor-grown carbonaceous fibers that can be produced even at a low temperature of 1000°C and have a unique shape. d Structure of the Invention As a result of research to achieve the above object, the present inventors found that hydrocarbons such as benzene, toluene, methane, ethane, and octane, or low-boiling monomers are used as raw materials for conventional vapor-grown carbon fibers. This is used to produce carbon fibers while causing a dehydrogenation reaction on the catalyst surface. Such dehydrogenation reactions generally occur at temperatures of 1,000°C or higher, so a high temperature of 1,000°C or higher is required. The present inventors extensively studied raw materials that can grow carbonaceous fibers using reactions other than dehydrogenation reactions, and found that aromatic diimide compounds were used as raw materials,
When this is vaporized, the imide group part cleaves,
It was found that the aromatic hydrocarbon radicals generated by this process associate in the gas phase and grow to form a fibrous product. This growth mechanism is completely different from that of conventional gas-phase grown carbon fibers, and depending on the type of aromatic diimide, fibers can be grown even at temperatures as low as 400°C. The present invention was completed based on such new knowledge. The gist of the present invention is to heat and vaporize an aromatic diimide compound or a compound that generates an aromatic diimide compound by heating in a gas atmosphere selected from argon, nitrogen, helium, hydrogen, and a mixed gas thereof or in vacuum. A method for producing carbonaceous fibers characterized by vapor phase growth. Typical aromatic diimide compounds include the following compounds. Pyromellit diimide (abbreviated as PMDI); 1,
4,5,8 naphthalene diimide (abbreviated as NTDI-1); 2,3,6,7, naphthalene diimide (abbreviated as NTDI-2); 3,4,9,10, perylene diimide (abbreviated as PTDI-1) ;1, 12, 6, 7,
Perylene diimide (abbreviated as PTDI-2); 3, 4,
8,9, anthracene diimide (abbreviated as ATDI); 3,4,8,9, pyrene diimide (PyTDI)
), and the organic pigment CI
Pigment Red 123, Vat Red 23, Vat Red 29, etc. However, the invention is not limited to these exemplified compounds. Furthermore, starting materials in the present invention include:
Compounds that produce the aromatic diimide when heated, such as aromatic amic acids that produce aromatic diimides when heated, can also be used. The mechanism for growing vapor phase grown carbon fibers using aromatic diimide as a raw material essentially does not require a catalyst for growth promotion. In fact, many aromatic diimide compounds can be made into fibrous products simply by heating. However, in the case of a compound with a relatively low melting point such as BTDI (melting point about 350° C.), the presence of a catalyst is preferred since the presence of a catalyst promotes the cleavage reaction of the imide group.
Catalysts used in such cases include Fe,
Co, Ni, V, Nb, Ta, or their carbides,
Catalysts used in conventional vapor grown carbon fiber production can also be used, including compounds such as nitrides. These catalysts are placed in the heating zone where the carbonaceous fibers are precipitated, and are particularly effective when they are in the form of ultrafine powders. The growth reaction is carried out in a gas atmosphere selected from argon, nitrogen, helium, hydrogen, and mixed gases thereof, or in vacuum. Particularly when using raw materials whose vaporization temperature is high, it is effective to carry out the process in a vacuum. On the other hand, when using a raw material with a low vaporization temperature, it is effective to use an autoclave and pressurize the gas. Although the presence of hydrogen generally tends to slow down the growth reaction, in some cases fibers with unusual shapes may be obtained. Furthermore, when the growth reaction is carried out in the presence of a catalyst, it is preferable to have hydrogen present. In this case, hydrogen is considered to work effectively to maintain the activity of the catalyst. Although the presence of small amounts of oxygen has the effect of promoting growth reactions,
The presence of more than 10% oxygen inhibits the growth reaction. It is thought that the presence of a large amount of oxygen causes combustion and generates soot-like carbon, which inhibits the growth reaction. Next, the mechanism of carbon fiber formation when using DTDI-1, which is the most typical aromatic diimide compound, will be described. The weight loss reaction of PTDI-1 starts at 650°C, and a rapid decrease in oxygen and nitrogen is observed from around this temperature. It is thought that this causes cleavage of the diimide substituent, which eliminates oxygen and generates perylene radicals. Actually 800℃, 1000℃ in argon
In the FT-IR spectrum of the fiber produced with C=
O,

The absorption based on [Formula] almost disappears, but the absorption based on δC-H and νC=C of aromatic compounds still exists. From these results, it is thought that fibers grow due to the polymerization of perylene radicals generated by the decomposition of PTDI. The above has described the formation mechanism and basic fiber structure when PTDI-1 is used as the raw material, but when other raw materials are used, the same generation mechanism and corresponding fiber structure will apply depending on the raw material. You can get something. As will be described later (see Figure 1), the most significant feature of the fibers obtained in this manner is that they have a complex shape, such as entangled or branched fibers. This kind of fiber shape is FRM, FRP
It is particularly effective as a reinforcing material for composite materials such as, and as electrodes for batteries that require a large area. e Examples Example 1 Various aromatic diimide compounds pressed into pellets (pellet diameter 13 mm, thickness 1 mm) were set in a heating furnace and heated at a preset temperature between 300 and 1000°C at a rate of 10°C/min. The temperature was raised to that temperature, maintained at that temperature for 1 hour, and then lowered at a rate of 40°C/min. All reactions were carried out in an argon atmosphere, and after the reaction was completed, the pellet surface was observed to confirm the presence or absence of products. The lowest temperature at which the presence of the product was recognized was defined as the formation temperature, and the general shape (diameter and length) of the fibers formed between this formation temperature and 1000°C was measured using an electron microscope. The results are shown in Table 1.
A fibrous product was obtained in both cases. The formation temperature approximately corresponds to the temperature at which the vaporization reaction of the raw materials occurs, indicating that these reactions are gas phase reactions. Among the various raw materials shown in Table 1, PTDI-1 yielded the largest amount of fibrous product. FIG. 1 shows an electron micrograph of a fibrous product produced by heat treatment of PTDI-1 at 800°C.

【table】

【table】

[Table] As shown in Figure 1, the diameter of the obtained fibers is 0.1~
Fibers with a diameter of 0.4 μm and a length of approximately 3 mm and a very complex shape were obtained. Comparative Example 1 Pellets of perylene, anthracene, and pyrene having no diimide substituent were heat-treated in the same manner as in Example 1, but no fibrous product was obtained. Therefore, it can be seen that an aromatic diimide compound is required. Example 2 PTDI-1, which had been pressed into a pellet shape in the same manner as in Example 1, was heat-treated by changing the treatment temperature, treatment time, and atmosphere. The results are shown in Table 2. PTCD
-1 shows that a fibrous product cannot be obtained at a temperature of less than 650°C, and that a temperature of 650°C or higher is required for production. Fiber growth occurs at a relatively low temperature of 650 to 750°C, and growth in the thickness direction occurs at higher temperatures (800 to 1000°C). Although the long-term treatment causes growth in the length and thickness directions, it is not very large. Furthermore, the growth in Ar, He, N ₂ , and vacuum is the same, with almost no difference observed.
When treated in the presence of hydrogen, unique fibers with a flat plate shape are produced. The presence of a small amount (5%) of oxygen has the effect of promoting fiber growth rather than hindering it.

[Table] Example 3 Heating of raw materials (first furnace) and substrate heating (second furnace)
Using a furnace that can perform these processes independently, we conducted an experiment to see if a fibrous product could be obtained by decomposing the raw material vaporized in the first furnace on a substrate in the second furnace containing a catalyst. Ultrafine Fe powder was used as a catalyst, and the ultrafine Fe powder dispersed in methanol was sprayed onto a ceramic substrate and heat treated to form a substrate carrier. Aromatic diimide compounds (BTDI,
NTDI-1, PTDI-1, Vat. Red23) to 10
It was heated to 800°C at a rate of 0°C/min and the vaporized components were channeled onto the substrate carrier heated to 800°C with argon or a mixed carrier gas of argon and hydrogen. After keeping the temperature at 800°C for 1 hour, the furnace was cooled and it was examined whether fibrous products were formed on the substrate. When the carrier gas was only argon, no fibrous product was obtained and a black film was formed. This is considered to be due to a decrease in catalyst activity. On the other hand, when a mixed gas of argon and hydrogen was used as a carrier gas, a fibrous product was produced. The produced fibers have a diameter of 0.1 to 5 μm.
The length ranged from 0.1 to 20 mm, and almost no difference was observed depending on the raw material. Comparative Example 2 An attempt was made to produce carbon fiber using benzene as a raw material in the same manner as in Example 3, but no product was obtained at 800°C. f. Effects of the Invention As described above, according to the method of the present invention, by using aromatic diimide, which is a different raw material for conventional vapor-grown carbon fibers, a catalyst is not necessarily required, and the vapor-phase grown carbon fiber is not necessarily required. The carbonaceous fibers are produced at a much lower temperature than the production temperature of grown carbon fibers, and the resulting carbon fibers are much thinner than the vapor-grown carbon fibers obtained by conventional methods, and have a unique shape, making them composite fibers. Excellent effects can be achieved that are suitable for reinforcing materials and battery electrodes.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph of carbonaceous fibers produced by the method of the present invention.

Claims (1)

[Claims] 1. Argon,
A method for producing carbonaceous fibers, which comprises heating and vaporizing them in a gas atmosphere selected from nitrogen, helium, hydrogen, and a mixed gas thereof or in a vacuum to grow them in a vapor phase.