JPS6224522B2 - - 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 electronic materials such as composite materials with plastics, metals, and carbon materials, electrical conductors, resistors, and heating elements, but they are still not widely used due to the following drawbacks. Not commonly 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 less than m. (3) The reaction temperature is high, generally requiring a temperature of 1000°C 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 in order to eliminate the drawbacks of conventional vapor-grown carbon fibers, and the purpose is to create fibers with a thin thickness of 0.1 to 5 μm and a uniform thickness throughout the fiber. It is an object of the present invention to provide a method for producing carbonaceous fibers made of novel vapor-grown carbon fibers, which can produce fibers having the following properties even at low temperatures of 300 to 1000°C. 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 carbon fibers using reactions other than dehydrogenation reactions, and found that when aromatic dianhydride is used as a raw material and it is vaporized, The carbonyl group part is cleaved,
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 dianhydride, fibers can be grown at temperatures as low as 300°C. It is. The present invention was completed based on such new knowledge. The gist of the present invention is to prepare an aromatic diacid anhydride or a compound that produces an aromatic diacid anhydride by heating in a gas atmosphere selected from argon, nitrogen, helium, hydrogen, and a mixed gas thereof or in a vacuum. A method for producing carbonaceous fibers characterized by vapor phase growth through heating and vaporization. Representative compounds of aromatic diacid anhydrides include:
Examples include the following compounds. Pyromellitic acid dianhydride (abbreviated as BTCD);
1, 4, 5, 8, naphthalenetetracarboxylic acid 2
Anhydride (NTCD-1); 2, 3, 6, 7, naphthalenetetracarboxylic dianhydride (NTCD-2);
1, 2, 5, 6, naphthalenetetracarboxylic acid 2
Anhydride (NTCD-3); 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCD-1); 1.
12.6.7 Perylenetetracarboxylic dianhydride (PTCD-2); 3.4.8.9 Anthracenetetracarboxylic dianhydride (ATCD); 3.4.
8.9.Pyrenetetracarboxylic dianhydride; 3.
3', 4, 4' biphenyltetracarboxylic dianhydride; 2, 2', 3, 3' biphenyltetracarboxylic dianhydride; 2, 2-bis(3, 4-benzophenonetetracarboxylic acid) 2 anhydride; bis(3,4-dicarboxyphenyl) sulfone 2 anhydride; bis(3,4-dicarboxyphenyl) ether 2 acid anhydride; 2,3,4,5 thiophenetetracarboxylic acid 2 Anhydrides; There are also diacid anhydrides such as these diacid anhydride isomers, phenanthrene, acridine, pyrrole, quinoline, colomene, etc. However, the present invention is not limited to these exemplified compounds. As starting materials for invention,
Compounds that produce the aromatic diacid anhydride when heated, such as tetraaromatic carboxylic acids that produce aromatic diacid anhydrides when heated, can also be used. The mechanism for growing gas-phase growth carbon fibers using aromatic diacid anhydride as a raw material essentially does not require a catalyst for growth promotion. In fact, many aromatic dianhydrides can be made into fibrous products simply by heating. However, in the case of a compound with a relatively low melting point such as BTCDA (melting point 283-286°C), the presence of a catalyst is preferred since the presence of a catalyst promotes the cleavage reaction of the carbonyl group. Catalysts used in such cases include Fe, Co, Ni, V, Nb, Ta, or compounds such as their carbides and nitrides, which are commonly used in the production of vapor-grown carbon fibers. Catalysts can also be used. 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, as shown in Example 2,
A flat fiber with a square cross section is 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. The presence of a small amount of oxygen has the effect of promoting the growth reaction, but the presence of 10% or more of 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, a carbon fiber production mechanism will be described when PTCD-1, which is the most typical compound among aromatic tetracarboxylic dianhydrides, is used. The weight loss reaction of PTCD-1 starts at 516°C, and a rapid decrease in oxygen is observed from around this temperature. It is thought that this causes cleavage of the carbonyl substituent, which eliminates oxygen and generates perylene radicals. The FT-IR spectra of fibers produced at 600°C, 800°C, and 1000°C in argon are shown in a, b, c, and d in Figure 1. However, a is
In the spectrum of PTCD-1, b is 600℃ and c is 800℃.
°C and d are spectra at 1000 °C.
In spectrum a of PTCD-1, the absorption at 1774 cm ^-1 is based on νC = 0, and the absorptions at 1757, 1743, and 1730 cm ^-1 are aromatic δC-H (out-of-plane), 1595, and 1508 cm
The absorption at ^-1 is aromatic νC=C, the absorption at 1407 cm ^-1 is δC-H (in-plane) of unsaturated carbon, the absorption at 1299 and 1234 cm ^-1 is C-O-C, and the absorption at 1022 cm ^-1 is

[Formula] Each absorption at 859, 808, 792, and 733 cm ^-1 can be identified as δC-H (out-of-plane) of an aromatic compound. In the spectrum b of the fiber prepared at 600℃, C-O-C,

The absorption based on [Formula] almost disappears, but δC-H of aromatic compounds,
Each absorption based on νC=C remains without disappearing. On the other hand, in the spectra c and d of fibers prepared at 800°C and 1000°C, absorption of δC-H almost disappears, resulting in an overall broad spectrum and poor infrared light transmittance. On the other hand, the results of elemental analysis show that the fiber made at 600℃ has C=93.6% and H=2.4.
%, and the fiber at 800℃ is C = 94.5%, H = 0.9
%, fibers made at 1000℃ have C=98.5%, H=
It was 0.4%. Furthermore, XPS measurements showed that the amount of oxygen present in all samples was 1.5% or less. From these results, it is thought that fibers grow through the mechanism shown in Figure 2, in which perylene radicals generated by the decomposition of PTCD occur. Here, in the polyperylene structure, the amount of hydrogen present is 3.2%
and 1.6% in the structure where two molecules are bonded.
It is. Therefore, the fiber produced at 600℃ has an intermediate structure with hydrogen abundance ratio of 800℃.
The fibers produced at 1000°C and 1000°C are considered to have a more graphite structure than the structure of . The above has described the formation mechanism and basic fiber structure when using PTCD-1 as the raw material, but even 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. e Examples Example 1 Various aromatic dianhydrides pressed into pellets (pellet diameter 13 mm, thickness 1 mm) were set in a heating furnace and heated to a temperature between 200 and 1000°C at a rate of 10°C/min. The temperature was raised to the set temperature, held 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.
In BTCD, all the pellets were vaporized by heating, leaving no residue, and no fibrous product was obtained with this method. With other aromatic dianhydrides, fibrous products were obtained in all 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, PTCD-1 yielded the largest amount of fibrous product. FIG. 3 shows an electron micrograph of a fibrous product produced by heat treating PTCD-1 at 700°C.

【table】

[Table] As shown in Figure 3, the diameter of the obtained fibers is 0.2~
The thickness was 0.3 μm, the length was about 3 mm, and the thickness was very uniform. Comparative Example 1 Perylene without 2 carboxylic anhydride substituents,
Pellets of anthracene and pyrene 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 dicarboxylic anhydride is required. Example 2 PTCD-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
It can be seen that in case of -1, a fibrous product cannot be obtained at a temperature of less than 520°C, and a temperature of 520°C or higher is required for formation. Fiber growth occurs at a relatively low temperature of 520 to 600°C, and growth in the thickness direction occurs at higher temperatures (700 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 tetracarboxylic dianhydrides (BTCD, NTCD-1, PTCD-1, PyTCD-
1) was heated to 800°C at a rate of 10°C/min, and the vaporized components were delivered onto the substrate carrier heated to 800°C together 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 fiber produced is 0.4~5μ
The diameter was 0.1 to 10 mm, and almost no difference was observed depending on the starting material. Furthermore, the method of Example 1 did not yield a fibrous product.
The product was also obtained in BTCD. 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 diacid anhydride, which is a different raw material for conventional vapor-grown carbon fibers, a catalyst is not necessarily required, and the conventional method The carbon fibers are produced at a much lower temperature than the production temperature of vapor-grown carbon fibers, and the carbon fibers obtained are much thinner than the vapor-grown carbon fibers obtained by conventional methods, and have a uniform thickness. This provides excellent effects.

[Brief explanation of the drawing]

Figure 1 shows the FT-IR spectra of PTCD-1 and carbonaceous fibers made from PTCD-1, where a is
PTCD-1, b is fiber made at 600℃, c is 800℃
d is the spectrum of the fiber made at 1000°C, Figure 2 shows the mechanism of carbon fiber formation of PTCD-1, and Figure 3 shows the spectrum of PTCD-1 treated at 700°C in argon. This is an electron micrograph of carbonaceous fiber obtained by

Claims (1)

[Claims] 1 Aromatic 2 acid anhydride or aromatic 2 by heating
Compounds that produce acid anhydrides include argon, nitrogen,
A method for producing carbonaceous fibers, which is characterized by vapor phase growth by heating and vaporizing in a gas atmosphere selected from helium, hydrogen, and a mixed gas thereof or in a vacuum.