JPS6221882B2 - - Google Patents

Description

[Detailed description of the invention]

a. Field of Industrial Application The present invention relates to a method for producing graphite fibers 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. However, the conventional method for producing vapor-grown carbon fibers using a hydrocarbon gas such as benzene as a raw material has 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. 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 1100°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. The present inventors conducted research to resolve the drawbacks of conventional vapor-grown carbon fibers, and found that when benzene is used as a raw material, carbon fibers are produced through a dehydrogenation reaction on the catalyst surface, so Requires high temperatures. Therefore, we conducted research to generate carbon fiber using reactions other than this reaction. As a result, when aromatic dianhydride is used as a raw material, the carbonyl group part cleaves, and the resulting aromatic hydrocarbon radicals associate in the gas phase and grow, forming a fibrous product. In other words, he discovered that aromatic diacid anhydride or a compound that produces aromatic diacid anhydride by heating is combined with argon, nitrogen, helium, hydrogen, and the like to produce carbonaceous fibers. We have invented a method for producing carbonaceous fibers, which is characterized by vapor phase growth by heating and vaporizing in a gas atmosphere selected from a mixed gas or in a vacuum. (Special application 1984-
No.) The carbonaceous fibers obtained in this way are shown in the table below.
As shown in Figure 1, compared to carbon fibers obtained from conventional polyacrylonitrile-based (abbreviated as PAN-based) and gas-grown carbon fibers made from benzene, the tensile strength, elastic modulus, and electrical resistivity are significantly lower. is also excellent.

[Table] Water Furthermore, the present inventors further used a hydrocarbon gas such as benzene or propane on the carbonaceous fiber grown in the vapor phase using aromatic dianhydride as a raw material to precipitate carbon and the diameter of the carbon fiber. I invented a way to make it thicker.
(Special issue No. 1981). The carbonaceous fiber thus obtained also has excellent physical properties. For example, PTCD fibers were prepared with a thickness of 5 cm at a benzene supply rate of 5 c.c./min, a reaction time of 30 minutes, and a temperature of 1100°C.
The tensile strength of carbon fiber grown to μmφ is 32
(ton/cm ² ), elastic modulus was 4100 (ton/cm ² ), and electrical resistivity was 1.50×10 ⁻³ (Ωcm). c. Purpose of the Invention The purpose of the present invention is to produce a carbonaceous fiber grown in a gas phase using the above-mentioned aromatic diacid anhydride or a compound that produces an aromatic diacid anhydride by heating, or a carbonaceous fiber grown in the vapor phase as a core. The purpose of the present invention is to provide a method for improving carbonaceous fibers grown as carbon fibers and further improving their tensile strength and electrical resistivity. d Structure of the Invention The present inventors heat-treated PTCD carbon fibers, conventional gas-grown carbon fibers made from benzene, and PAN-based carbon fibers, and investigated the relationship between heat treatment temperature, lattice constant, and electrical resistivity. As a result, it was found that the heat treatment temperature, the electrical resistance heat treatment temperature, and the lattice constant changed as shown in FIGS. 1 and 2, respectively. As these figures show, heat treatment starts from 1000℃
As a result of testing at 3000℃, the electrical resistivity and lattice constant of both PTCD carbon fiber and PAN-based carbon fiber suddenly changed at 2000℃, unlike PAN-based carbon fiber.
The graphitization reaction progresses from around this temperature,
It was found that the electrical resistivity was improved. Furthermore, as shown in Figure 3, the relationship between heat treatment temperature and tensile strength shows that the tensile strength suddenly increases from around 2000°C. The present inventors completed the present invention based on these findings. 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. The carbonaceous fibers are twisted, vaporized, and grown in the vapor phase.
In a chemically inert gas atmosphere or in vacuum
A method for producing graphite fibers characterized by heat treatment at a temperature of 2000 to 3000°C. And the graphite fiber created by this method is
It has electrical resistivity, elastic modulus, and tensile strength that are superior to graphite fibers obtained from PAN-based carbon fibers and graphite fibers obtained from vapor-grown carbon fibers made from benzene, etc. . 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 (ATCO); 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 isomers of these dianhydrides and dianhydrides such as phenanthrene, acridine, pyrrole, quinoline, and colomene.However, the compound is not limited to these exemplified compounds.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. The mechanism of growing vapor-grown 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 BTCD (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. The presence of hydrogen generally tends to slow down growth reactions. 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 sooty carbon, which inhibits the growth reaction. Examples of the catalyst include Fe, Ni, and Co. Examples of producing carbonaceous fibers using aromatic diacid anhydrides as raw materials are as follows. Various aromatic dianhydrides pressed into pellets (pellet diameter 13 mm, thickness 1 mm) are set in a heating furnace and heated to a preset temperature between 200 and 1000 °C at a rate of 10 °C/min. After holding at that temperature for 1 hour, the temperature was 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 were as shown in Table-2.

【table】

[Table] The carbonaceous fibers obtained in this way were heated to 2,000 to
When heated at a temperature of 3000°C, graphite fibers are obtained. If the treatment temperature is less than 2000°C, it is difficult to completely convert the material into graphite, so the degree of improvement in its physical properties and electrical resistivity is small. On the other hand, since the graphitization reaction is almost completed at about 3000°C, a temperature higher than 3000°C is unnecessary. In fact, no significant improvement in physical properties is observed even when heated to 3000°C or higher. Therefore, the heat treatment temperature needs to be 2000 to 3000°C. Although the treatment time varies depending on the heat treatment temperature, it is generally preferable to carry out the treatment for about 10 minutes to 8 hours. The properties of the graphite fibers obtained in this way vary depending on the type of starting dianhydride and heat treatment temperature conditions, but the average value is tensile strength.
It has values of 70 to 110 ton/cm ² , elastic modulus of 4000 to 8000 ton/cm ² , and electrical conductivity of 8 to 6×10 ⁻⁵ Ωcm. Fibers with such excellent properties can be used, for example, as composite materials, and when fibers with an elastic modulus of 6000 ton/cm ² or more are used, composites (FRP) with an elastic modulus of 100 GPa or more can be designed. e Examples Example 1 Graphite fibers were produced by heat-treating vapor-grown carbon fibers made from PTCD at 2800° C. for 30 minutes in argon gas. Tensile strength of the resulting fiber
The elasticity was 80 to 100 ton/cm ² , the elastic modulus was 4500 to 7000 ton/cm ² , and the electrical resistivity at room temperature was 8 to 6.5×Ωcm. Example 2 In place of PTCD in Example 1, NTCD-1 and PyTCD among the aromatic dianhydrides shown in Table 3 were used, and carbonaceous fibers grown in the vapor phase were heat-treated in the same manner as in Example 1. The physical properties of the graphite fiber obtained using NTCD-1 as a starting material were tensile strength of 80 ton/cm ² , elastic modulus of 4500 ton/cm ² , and electrical resistivity at room temperature of 8×10 ^-5 Ωcm. . Also
When using PyTCD as a starting material, tensile strength
85ton/cm ² , elastic modulus 5500ton/cm ² , electrical resistivity 7×
It was 10 ^-5 Ωcm. Example 2 is an example in which NTCD-1 and PyTCD were used, but graphite fibers with similar excellent properties can be obtained with fibers made from other dianhydrides. Example 3 PTCD fiber was heated to 5 μm in thickness at 1100°C in benzene gas.
Using carbonaceous fibers lengthened to mφ, Example 1
It was heat treated in the same way. The physical properties of the obtained graphite fiber are tensile strength of 75ton/cm ² and elastic modulus.
5000ton/cm ² , electrical resistivity at room temperature 8×10 ^-5
It was Ωcm. Comparative Example 1 In the same manner as in Example 1, vapor-grown carbonaceous fibers using benzene as a raw material were heat-treated to produce graphite fibers. Its physical properties are tensile strength of 50 tons/
cm ² , elastic modulus 2500ton/cm ² , room temperature electrical resistance 10×10 ^-5
It was Ωcm. f. Effects of the Invention According to the present invention, the tensile strength and electrical resistivity of vapor-grown carbon fibers made from aromatic dianhydrides can be significantly improved, and the tensile strength is superior to that of conventional carbon fibers. It has excellent effects that can be achieved with fibers of elastic modulus and low electrical resistivity.

[Brief explanation of the drawing]

FIG. 1 is a relationship diagram between heat treatment temperature and room temperature electrical resistivity, FIG. 2 is a relationship diagram between heat treatment temperature and lattice constant, and FIG. 3 is a relationship diagram between heat treatment temperature and tensile strength.

Claims (1)

[Claims] 1 Aromatic 2 acid anhydride or aromatic 2 by heating
Carbonaceous fibers or carbonaceous fibers grown in a vapor phase by heating and vaporizing a compound that generates an acid anhydride in a gas atmosphere selected from argon, nitrogen, helium, hydrogen, and a mixed gas thereof or in a vacuum. Carbonaceous fibers grown with a core of
A method for producing graphite fiber, characterized by heat treatment at a temperature of 3000°C.