JPH0148204B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a carbon material having high electrical conductivity and a method for producing a composition thereof. More specifically, the present invention relates to a method for producing a highly conductive carbon material and a composition thereof, which comprises firing a biaxially stretched conjugated polymer molded body. In recent years, it has been discovered that complex compounds of natural or artificial high-purity graphite and electron acceptors or electron donors (hereinafter referred to as dopants) exhibit high electrical conductivity exceeding that of metals, and have attracted attention as highly conductive materials. It's starting to feel like this. As this type of highly conductive carbon material, pyrolytic graphite is known, which is obtained by subjecting a hydrocarbon compound to gas phase pyrolysis at high temperature to produce pyrolytic carbon, which is then heat-treated at an ultra-high temperature. This carbon material had a highly developed graphite structure, and exhibited even higher conductivity through the formation of a complex compound with a dopant. On the other hand, attempts have also been made to obtain carbonized and even graphitized carbon materials by firing polymers. For example, there is a method of firing organic fibers such as polyacrylonitrile or rayon to make carbon fibers. However, the electrical conductivity of the obtained carbon fibers is low, and even after firing at 3000°C, the electrical conductivity is 10 ⁸ S/
cm or less, and the effect of improving conductivity due to the formation of a dopant complex compound is only slight, making it impossible to obtain a material that is sufficiently graphitized. Furthermore, for the purpose of improving the strength of polyacrylonitrile-based carbon fibers, it has been proposed to uniaxially stretch the polyacrylonitrile fibers and then sinter them, but the graphite formation has not been sufficient. In this way, the carbon material obtained by firing a polymer does not necessarily have a graphite structure even if it is fired at a high temperature or subjected to stretching treatment before firing. One of the few examples of graphite formation by firing is a method in which pitch mesophase is oriented, made insolubilized by oxidative crosslinking, and then fired. However, this method is limited to fibrous molded bodies and is not sufficient in terms of high conductivity. The present inventors extensively studied the firing of conjugated polymers, and as a result, discovered a new fact and arrived at the present invention. That is, a biaxially stretched poly-p-phenylene vinylene film was heated at 400° C. in an inert atmosphere.
When fired at a temperature exceeding °C, it not only becomes carbonized while retaining its shape without melting, but also turns into graphite at high temperatures, becoming a material with even higher conductivity than a similarly fired undrawn material. Furthermore, it was discovered that it exhibits high electrical conductivity. It has also been found that by adding biaxial stretching treatment, a highly conductive carbon material can be stably obtained. In this way, by firing the biaxially stretched poly-p-phenylene vinylene, melting,
It was unexpected that a carbon-based molded article could be made without softening, and that the carbon material would have higher conductivity than an unstretched carbon material. In addition, highly conductive carbon materials whose conductivity has been increased by biaxial stretching are not limited to firing poly-p-phenylene vinylene, but are broadly based on repeating units of vinylene groups and aromatic hydrocarbon groups conjugated to them. The present invention was completed based on the discovery that the present invention can also be obtained by biaxially stretching a conjugated polymer and then firing it. That is, the present invention provides (1) a compound having the general formula (-R-CH=CH) _-o (R: an aromatic hydrocarbon group forming a continuous carbon-carbon conjugated system with a vinylene group) that has been subjected to a biaxial stretching process; , n: an integer of 2 or more,) A method for producing a highly conductive carbon material, characterized by firing a conjugated polymer molded body having the following properties in an inert atmosphere at a temperature exceeding 400°C, and (2) biaxial carbon material. A conjugated polymer molded product having the general formula () that has been subjected to stretching treatment is heated at 400°C under an inert atmosphere.
It is an object of the present invention to provide a method for producing a highly conductive composition, characterized in that a dopant is made to interact with a carbon material obtained by firing at a temperature exceeding . There are no particular limitations on the method for synthesizing the conjugated polymer () used in the present invention, and various methods that can produce a film-like conjugated polymer () can be used. For example, J. Polymer Sci., A-1, 6 , 1058
(1968) is exemplified by the sulfonium salt decomposition method described by
In particular, the conjugated polymer obtained by the sulfonium salt decomposition method can be formed into a homogeneous film-like molded product and can be suitably used for the purpose of the present invention. The R group of the conjugated polymer () used in the present invention is an aromatic hydrocarbon group having a structure conjugated with a vinylene group or a derivative group thereof, particularly an aromatic hydrocarbon group having 6 to 20 carbon atoms or Derivatives thereof are preferred. These groups include o-phenylene group, p-phenylene group, 4,4'-biphenylene group, 2,5-
Examples include dimethyl-p-phenylene group, 2-5 dimethoxy-p-phenylene group, 3,4-dimethyl-o-phenylene group, and 3,4-dimethoxy-o-phenylene group. Among them, p with good symmetry
-phenylene group, 2,5-dimethyl-p-phenylene group, 4,4'-biphenylene group, and 2,5-dimethoxy-p-phenylene group are more preferable because they have good shape retention during the firing process. Especially p-
Particularly preferred is a phenylene group. The conjugated polymer used in the present invention preferably has a sufficiently large molecular weight, with n being 2 or more, preferably 5 or more and 50,000. used effectively. In the present invention, the biaxial stretching treatment of a conjugated polymer molded article refers to stretching treatment in one direction and in a direction that is not parallel to the said direction. At this time, the angle formed by the two directions is not particularly limited as long as it exceeds 0° and extends to 90°, but it is preferably 45° or more and 90° or less, and more preferably 90°. There are no particular restrictions on the stretching method used in the present invention, but methods include stretching in one direction and then stretching in a direction that is not parallel to that direction, a method that stretches in two directions that are not parallel at the same time, a roll rolling method, a sulfonium salt salt method, etc. For the conjugated polymer molded product obtained by the solution method, stretching methods using self-shrinkage during decomposition of the sulfonium salt are exemplified, but methods in which stretching is performed simultaneously in two non-parallel directions and stretching methods using self-shrinkage are particularly preferred. This stretching treatment may be performed on the conjugated polymer molded article, but it may also be performed during the process of modifying the precursor polymer or precursor into the conjugated polymer as in the sulfonium salt decomposition method. For the purpose of the invention:
It is effective and preferable to stretch the precursor into a conjugated polymer during the modification process. In the present invention, there are no restrictions on the atmosphere during stretching, but an inert atmosphere that does not react with the conjugated polymer or precursor is preferred. Particularly preferred is nitrogen gas or argon gas. The stretching temperature in the present invention varies depending on the conjugated polymer used, but is generally 30°C to 400°C,
Preferably 50°C to 300°C, more preferably 80°C
~200℃. In the present invention, the firing temperature is preferably higher than 400°C, and the upper temperature limit is limited by the evaporation temperature of carbon. Although it is possible to achieve a higher temperature by firing in a pressurized system, it is not economical. In order to obtain a highly conductive material, the higher the firing temperature, the better. Practically speaking, the temperature is preferably higher than 400°C and lower than 3500°C, and more preferably higher than 800°C and lower than 3300°C. Furthermore, when firing at a high temperature of 1000°C or higher, temporary firing may be performed at 1000°C or lower, followed by firing at 1000°C or higher. In the present invention, effective inert atmospheres are nitrogen gas, argon gas, vacuum, etc., and argon gas is more preferable at 2000° C. or higher. There are no particular restrictions on the heating method during firing, but the heating method differs depending on the firing temperature. That is,
At temperatures below 1500℃, use resistance wire furnaces, siliconite furnaces, etc.
At temperatures above 1500℃, graphite heating element Tammann furnaces and high-frequency induction heating furnaces are effectively used. The fired product of the conjugated polymer () obtained in this manner often exhibits an electrical conductivity of 1×10 ² to 2×10 ⁴ S/cm. More importantly, by doping the fired product with an electron acceptor or electron donor, the electrical conductivity is further improved, reaching 10 ³ to ^{10 5} S/cm or more. The dopant is not particularly limited, but compounds that have been found to have high conductivity in conjugated polymers such as graphite or polyacetylene can be effectively used. The doping method can be carried out by a known method, ie, a method of direct contact with a dopant in a gas phase or liquid phase, an electrochemical method, an ion implantation method, or the like. Specifically, electron acceptors include halogen compounds: bromine, etc., Lewis acids: iron trichloride, arsenic pentafluoride, antimony pentafluoride, boron trifluoride, sulfur trioxide, aluminum trichloride, antimony pentachloride, etc. , protonic acids: nitric acid, sulfuric acid, chlorosulfonic acid, etc.
Examples of electron donors include alkali metals: lithium, potassium, rubidium, cesium, etc., alkaline earth metals: calcium, strontium, barium, etc., and other rare earth metals: (Sm, Eu, Yb),
Metal amides: potassium amide, calcium amide, etc. are exemplified. There is no particular restriction on the amount of doping, but the preferred content is 0.1 per weight of the heat-treated product.
% to 150%, especially 10% to 100%. The feature of the present invention is that the fired product of a conjugated polymer () molded product subjected to biaxial stretching treatment is carbonized and graphitized than the fired product of a conjugated polymer () molded product that is unstretched or stretched in only one direction. As a result, carbon materials with higher conductivity can be provided. The reason for this is not clear, but by stretching in two directions, the aromatic ring planes in the molecules tend to take on a structure in which the planes are oriented parallel to the film surface, which makes it easier for intermolecular condensation to occur during firing. It is thought that this makes it easier for graphite structures to occur. The present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto. Example 1 An aqueous solution of a polymeric sulfonium salt having a sulfonium salt in its side chain was obtained by allowing p-xylylene bis(diethylsulfonium bromide) to react with an aqueous solution of caustic soda. Subsequently, after dialysis, it was cast and formed into a film. The obtained polymeric sulfonium salt film was blown 50x.
Cut to 50mm and stretch at 100℃ in a nitrogen atmosphere using a stretching machine that can simultaneously stretch in orthogonal directions.
The film dimensions before stretching in both directions at 120℃ from
Stretched to 2.5 times. Further, the temperature was raised to 250°C while still applying a weak stretching tension, and heat treatment was performed at 250°C for 30 minutes. The IR spectrum of the obtained film is given in the literature (J. Polymer Sci., A-1, 6 , 1058
(1968)), confirming the poly-p-phenylene vinylene structure. The electrical conductivity of this film was 10 ^-10 S/cm or less. Insert a quartz glass furnace core tube (30 mmφ x 700 mm L) into a resistance wire heating type horizontal tubular electric furnace (450 mm L),
The apparatus was assembled so that inert gas could be introduced.
A 20 x 30 mm cut piece of the above biaxially stretched film was placed in the furnace core tube at the center of the electric furnace, and nitrogen gas was passed through at 100 ml per minute to raise the temperature in the electric furnace to 950°C.
After firing at 950°C for 2 hours, the fired product was cooled to room temperature and taken out. The fired product maintained its film shape. This film exhibited an electrical conductivity of 100 S/cm at room temperature. Furthermore, when this film was doped from the gas phase at room temperature using an ordinary method using sulfuric anhydride as an electron acceptor compound, it was found that 24 hours
It showed an electrical conductivity of 140S/cm. The obtained film fired at 950°C was further fired at 3000°C. Firing was performed for 20 minutes in an argon stream using a graphite tube heating element. The fired product maintained its film shape. This film exhibited an electrical conductivity of 1.7×10 ⁴ S/cm at room temperature.
Further doping with sulfuric anhydride resulted in 1.2×
It showed an electrical conductivity of 10 ⁵ S/cm. The electrical conductivity was measured using a four-terminal method or a two-terminal method. Example 2 The polymer sulfonium salt film obtained in Example 1 was cut to a size of 50 x 50 mm, the four sides of the film were fixed to a mold, and then heat treated at 300°C for 30 minutes. This film had been stretched due to self-shrinkage. The obtained film was preliminarily fired at 950°C for 2 hours and then fired at 3000°C. The fired product maintained a film shape, and the obtained fired film showed an electrical conductivity of 1.4×10 ⁴ S/cm. or,
Doping with sulfuric anhydride showed an electrical conductivity of 1.1×10 ⁵ S/cm. Comparative Example The polymer sulfonium salt film obtained in Example 1 was cut out to a size of 50 x 50 mm, and heat treated at 300° C. for 30 minutes without fixing the film. The obtained film was preliminarily fired at 950°C for 2 hours and then fired at 3000°C. 2.1 for fired film
It showed an electrical conductivity of ×10 ³ S/cm. Furthermore, it showed an electrical conductivity of 1.1×10 ⁴ when doped with sulfuric anhydride. Example 3 The electrical conductivity of the stretched films fired at 3000°C obtained in Examples 1 and 2 and the unstretched films fired at 3000°C obtained in Comparative Example were measured at room temperature and liquid nitrogen temperature. The results are shown in Table 1.

[Table] In the fired films obtained in Examples 1 and 2, the ratio of electrical conductivity at room temperature and liquid nitrogen temperature was around 1,
Graphitization has progressed considerably, but in the comparative example, it was considerably smaller than 1, indicating that graphitization has not progressed very much. Example 4 Polymerization and film molding were carried out in the same manner as in Example 1 except that 2,5-dimethyl-p-xylylene bis(diethylsulfonium bromide) was used. The film was then simultaneously stretched 1.1 times in two orthogonal directions and converted into poly-2,5-dimethyl-p-phenylene vinylene at 300°C, followed by preliminary firing at 950°C and firing at 3000°C. The obtained fired film had a temperature of 7.3×10 ³ S/cm at room temperature,
When doped with nitric acid, the conductivity was 9.6×10 ³ S/cm. When not stretched in two directions, the conductivity is 5.2×
10 ³ S/cm, and 8.6×10 ³ S/cm when doped with nitric acid. Example 5 Polymerization, film forming, and orthogonal 2
Stretch 1.05 times simultaneously in the direction, poly-2,5 at 200℃
-Dimethoxy-p-phenylene vinylene was formed, followed by preliminary firing at 950°C and firing at 3000°C. The obtained fired film has a temperature of 6.4×10 ⁸ S/cm at room temperature,
When doped with nitric acid, the conductivity was 7.9×10 ⁸ S/cm. When not stretched in two directions, the conductivity is 5.5×
10 ⁸ S/cm, and 7.2×10 ⁸ S/cm when doped with nitric acid.

Claims (1)

[Claims] 1 Biaxially stretched general formula (-R-CH=CH) _-o (R: aromatic hydrocarbon group forming a continuous carbon-carbon conjugated system with a vinylene group, n: A conjugated polymer molded body having an integer of 2 or more) under an inert atmosphere,
A method for producing a highly conductive carbon material characterized by firing at a temperature exceeding 400°C. 2 General formula subjected to biaxial stretching treatment (-R-CH=CH)- _o (R: aromatic hydrocarbon group forming a continuous carbon-carbon conjugated system with a vinylene group, n: an integer of 2 or more) Under an inert atmosphere, a conjugated polymer molded body having
A method for producing a highly conductive composition, which comprises interacting a dopant with a carbon material obtained by firing at a temperature exceeding 400°C.