JPS6360132B2 - - Google Patents

Description

[Detailed description of the invention]

a. Industrial Application Field The present invention relates to a method for producing carbonaceous or graphite fibers with excellent electrical conductivity. 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 elastic modulus, tensile strength, electrical conductivity, etc., compared to carbon fibers produced by the method (1) above. For example, the tensile strength of carbon fibers made from polyacrylonitrile,
The values of elastic modulus and room temperature electrical resistivity are 6 to 6, respectively.
12ton/cm ² , 600ton/cm ² , 5-10×10 ^-3 Ωcm, whereas vapor-generated carbonaceous fiber (benzene raw material,
The value of generation temperature (1100℃) is 10~
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 for electrical conductors, resistors, heating elements, etc., but they are not yet widely used because of the following drawbacks. (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, and it is difficult to stably obtain fibers with a diameter of 5 μm 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. (5) The value of electrical conductivity is 5×10 ^-2 Ωcm (when using benzene as a raw material and the gas phase growth temperature is 1100°C), which is insufficient for use as an electrical conductor. As a result of research to eliminate the drawbacks of conventional vapor-grown carbon fibers, the present inventors have found that, in place of benzene, aromatic diacid anhydrides, aromatic diimide compounds,
Alternatively, a compound that generates an aromatic dianhydride or an aromatic imide compound by heating may be heated with argon,
We have invented a method for producing carbonaceous fibers by heating and vaporizing them in a gas atmosphere selected from nitrogen, helium, hydrogen, and a mixture of these gases or in a vacuum (Japanese Patent Application No. 49167/1982). This method eliminates the drawbacks of conventional vapor phase growth methods, and allows fibers with a thickness of 0.1 to 5 μm to be grown at 300 to 1000℃.
It has become possible to easily produce and obtain it even at low temperatures.
Although the electrical conductivity of these fibers is superior to that of conventional vapor-grown carbon fibers (when compared at the same processing temperature), there are still some problems in which they are not sufficient. In addition, when these fibers are treated at high temperatures of 2000°C or higher, they become graphite (Japanese Patent Application No. 59-50850).
issue). As a result, the conductivity could not be improved to a satisfactory degree. c. Purpose of the Invention The present invention aims to improve the electrical conductivity of the vapor-grown fibers developed by the present inventors, and its purpose is to improve the electrical conductivity of the vapor-grown fibers developed by the present inventors. The present invention provides a method for producing fibers or graphite fibers. d Structure of the present invention In order to achieve the above-mentioned object, the present inventors added acceptor properties to the obtained vapor-grown carbon fibers and graphitic fibers that were graphitized by treating them at a high temperature of 2000°C or higher. Alternatively, an attempt was made to dope with a donor dopant. As a result, it was found that electrical conductivity can be improved, although it differs depending on the raw material of the fiber, the heat treatment temperature of the carbon fiber, and the type of dopant. The present invention was completed based on this knowledge. The gist of the present invention is to convert aromatic diacid anhydrides, aromatic diimide compounds, or compounds that produce aromatic diacid anhydrides or aromatic diimide compounds by heating into argon, nitrogen, helium, hydrogen, or mixed gases thereof. It is characterized by doping an acceptor or donor dopant into a carbonaceous fiber grown in a vapor phase by heating and vaporizing it in a gas atmosphere or in a vacuum selected from The present invention provides a method for producing carbonaceous or graphite fibers with excellent electrical conductivity. The method of the invention consists of two steps. In the first step, an aromatic diacid anhydride, an aromatic diimide compound, or a compound that produces an aromatic diacid anhydride or an aromatic diimide compound by heating,
Producing carbonaceous fibers by vaporizing and growing in a vapor phase by heating in a mixed gas atmosphere of one or more of argon, nitrogen, helium, and hydrogen or in a vacuum. Furthermore, it is possible to produce graphite fibers by subjecting this to high temperature treatment at 2000°C or higher. 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-11); 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 dianhydride); bis(3,4-dicarboxyphenyl)sulfone dianhydride; bis(3,4-dicarboxyphenyl)ether dianhydride; 2,3,4,5 thiophenetetracarboxylic dianhydride; also, these dianhydride isomers, phenanthrene, Examples include diacid anhydrides such as acridine, pyrrole, quinoline, and coronene.However, the compounds are not limited to these examples.Furthermore, starting materials in the present invention include:
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. 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) ;1,12,6,77,
Perylene diimide (abbreviated as PTDI-2); 3, 4,
8,9, anthracene diimide (abbreviated as ATDI); 3,4,8,9, pyrene diimide (P _y TDI
), 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 gas-phase growth carbon fibers using aromatic diacid anhydride or aromatic diimide as a raw material essentially does not require a catalyst for growth promotion. In fact, fibrous products can be produced from many aromatic diacid anhydrides and aromatic diimides simply by heating them. However, BTCDA
In the case of a compound having a relatively low melting point such as (melting point: 283 to 286°C), the presence of a catalyst is preferred because 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 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, it is preferable to have hydrogen present when the growth reaction is carried out in the presence of a catalyst. 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. The presence of large amounts of oxygen causes combustion to produce sooty carbon,
This is thought to inhibit the growth reaction. Next, we will describe the carbon fiber production mechanism when using PTCD-1, which is the most typical compound among aromatic tetracarboxylic dianhydrides. 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 as 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 ^-1
The absorption of is aromatic νC=C, the absorption of 1407 cm ^-1 is unsaturated carbon δC-H (in-plane), the absorption of 1299 and 1234 cm ^-1 is C-O-C, and the absorption of 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 created at 600℃, C-O-C,

The absorption based on [Formula] almost disappears, but the δC-H of aromatic compounds,
Each absorption based on υC=C remains without disappearing. On the other hand, in the spectra c and d of the 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 PTCD-1 is used 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. When the carbonaceous fiber thus obtained is heat-treated, its electrical conductivity increases, and when it is heat-treated at 2000° C. or higher, it becomes a graphite fiber, and its electrical conductivity further increases. For example, carbon fiber made from PTCD-1,
530℃, 600℃, 800℃, 1000℃, 1200℃, 2000℃,
The electrical conductivity of the fibers heat-treated at 2500℃ is
0.2, 10, 200, 570, 1100, 10000, 17000S/cm. The electrical conductivity of these carbon fibers is higher than that of conventional vapor-grown carbon fibers made from benzene. The second step is a chemical doping treatment to improve conductivity, ie, doping with acceptor or donor dopants. Examples of acceptor dopants include H ₂ SO ₄ , SO ₃ , I ₂ , HF, FeCl ₃ , FeCl ₂ ,
CuCl ₂ , ICl, Br ₂ , Cl ₂ , HNO ₃ , HCl,
Examples include Et ₂ O ⁺ BF ^- ₄ , NO ⁺ ₂ BF ^- ₄ , SbF ₅ and AsF ₅ . Examples of donor dopants include Na,
Examples include K, Li, and Cs. Among these dopants, H ₂ SO ₄ , SO ₃ ,
Doping with AsF ₅ gas has the greatest effect, increasing conductivity by up to 100 times.
Also, for FeCl ₃ , I ₂ , HF, HNO ₃ , K, Na, 10~
100 times, ICl, Br ₂ , Cl ₂ , HCl, Et ⁺ ₂ OBF ^- ₄ ,
Improvement in conductivity was also observed with FeCl ₂ , CuCl ₂ , NO ⁺ ₂ BF ^- ₄ , SbF ₅ , Li, Cs, etc. Furthermore, the heat treatment temperature of carbonaceous fibers also affects the doping effect. Generally, when the heat treatment temperature is 800℃ or less, the doping effect is relatively large, and the 800℃
The doping effect is small in the range above 1400°C, the doping effect increases again when the temperature exceeds 1400°C, and the doping effect becomes significant above 2000°C. e Examples Example 1 Various aromatic dianhydrides and aromatic diimide compounds pressed into pellets (pellet diameter 13
mm, thickness 1 mm) in a heating furnace, heated at a rate of 10°C/min to a preset temperature between 200 and 1000°C, and held at that temperature for 1 hour.
The temperature was lowered at a rate of °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.

【table】

【table】

【table】

【table】

[Table] The obtained fibers were doped as follows. a Set in a cell under reduced pressure, and remove sulfuric acid vapor or I ₂
A method of introducing gas into a cell. b Method of immersing _FeCl3 in nitromethane solution and Na in THF solution. c A method of introducing CuCl ₂ and FeCl ₂ in vacuum. The results of measuring the electrical conductivity before and after doping are shown in the second
It was as shown in the table. The conductivity was measured using silver paste, gold wire, and gold electrodes, and a four-terminal electrode was attached.

【table】

[Table] As shown in these results, doping can improve the electrical conductivity of the fibers. 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 3. PTCD
-1 shows that a fibrous product cannot be obtained at a temperature below 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, and N ₂ in vacuum occurred in the same way, with almost no difference observed.

[Table] The PTCD-1 fibers treated at the various temperatures described above were doped in the same manner as in Example 1, and the conductivity was measured. The results were as shown in Table 4.

【table】

【table】

[Table] As is clear from the above results, the doping effect is small in carbon fibers heated at a temperature of 1000 to 1200°C, but the doping effect is significant when treated at temperatures lower than this temperature or particularly at high temperatures. Example 3 Using the same method as Example 2, using PTCD-1 as a raw material,
Carbon fibers prepared at 600°C were doped with various dopants and their electrical conductivity was measured. The results were as shown in Table 5.

[Table] As is clear from the above results, dopants that improve conductivity include H ₂ SO ₄ , SbF ₅ ,
AsF ₅ and FeCl ₃ are excellent. Example 4 2500 carbon fibers obtained from PTCD-1 as raw material
Graphite fiber heat-treated at °C (conductivity
17000S/cm) using CuCl ₂ and FeCl ₂ as dopants. That is, the fibers and CuCl ₂ or FeCl ₂ were placed in a quartz glass container, the glass container was sealed under vacuum, and the container was placed in a 350° C. furnace and left for about 20 hours. Fibers with increased metallic luster were obtained. The electrical conductivity of the obtained fibers at room temperature is 170000S/cm for CuCl ₂ and 170000S/cm for FeCl ₂
It was 190000S/cm. Even when the fiber doped with CuCl ₂ was left at 150°C for 2 hours, the conductivity did not change and it showed high stability. Fibers doped with FeCl ₂ were less stable in moisture, but showed similar stability to CuCl ₂ in dry gas. The conductivity of these fibers is much higher than the increase in conductivity when doping conventional carbon fibers. f. Effects of the Invention As described above, according to the method of the present invention, carbonaceous material obtained by using aromatic diacid anhydride or aromatic diimide compound, which is different from the raw material of conventional vapor-grown carbon fibers, can be obtained. By subjecting the fibers and the graphite fibers obtained therefrom to a doping treatment, it is possible to obtain carbonaceous fibers having much better conductivity than conventional carbon fibers.

[Brief explanation of drawings]

Figure 1 shows carbon fiber made from PTCD-1.
FT-IR spectrum, a is PTCD-1, b
is the spectrum of the fiber produced at 600°C, c is the fiber produced at 800°C, d is the spectrum of the fiber produced at 1000°C, and Figure 2 is a diagram showing the mechanism of carbon fiber production of PTCD-1.

Claims (1)

[Scope of Claims] 1. Argon,
Carbon fibers grown in vapor phase by heating and vaporizing in a gas atmosphere selected from nitrogen, helium, hydrogen, and mixed gases thereof or in vacuum, or fibers made from graphite by heat treatment, have acceptor properties. Alternatively, a method for producing a carbonaceous or graphite fiber with excellent electrical conductivity, which is characterized by doping with a donor dopant. 2 The acceptor dopant is H ₂ SO ₄ ,
SO ₃ , I ₂ , HF, FeCl ₃ , FeCl ₂ , CuCl ₂ , ICl,
Br ₂ , Cl ₂ , HNO ₃ , HCl, Et ₂ O ⁺ BF ^- ₄ , NO ⁺ ₂ BF ^- ₄ ,
A method for producing a carbonaceous or graphite fiber with excellent electrical conductivity according to claim 1, which is made of a fiber selected from SbF ₅ and AsF ₅ . 3 Donor dopants include Na, K, Li and
A method for producing a carbonaceous or graphite fiber with excellent electrical conductivity according to claim 1, which is made of a fiber selected from Cs.