JPH0341592B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for forming a coating on a substrate. [Prior Art] As a method for producing coated fibers using carbon fiber as a base material and graphite as a coating layer, there is a method described in JP-A-59-187622. This method heats the carbon fibers by passing an electric current directly through them, and also applies chemical vapor deposition (CVD) to the carbon fibers.
A coating layer of easily graphitizable carbon is formed by the method), and then the coated carbon fiber is heated to a temperature of 2800° C. or higher to graphitize the easily graphitizable carbon. [Problems to be Solved by the Invention] However, in this method, carbon fibers are heated using Joule heat generated by directly applying electricity to the carbon fibers. As the coated carbon fibers are formed, the heat capacity and resistance value of the coated carbon fibers change continuously. Therefore, a large temperature distribution occurs in the fiber axis direction, causing localized heating and causing the carbon fiber to break. In addition, attempts were made to graphitize the graphitizable carbon fiber obtained by the above method by heating it at a temperature of 2,800°C or higher in an inert gas atmosphere at normal pressure, but the fibers were cut and the feathers were damaged. It was impossible to obtain continuous coated graphite long fibers. In particular, the higher the temperature is around 3500° C., the more the carbon rises and the fibers are cut, making it impossible to obtain continuous coated graphite long fibers. Furthermore, in JP-A No. 62-6973, a coating layer of easily graphitable carbon is formed on carbon fibers by chemical vapor deposition, and then heated to a temperature of 2500°C or higher to form easily graphitable carbon. The technology to turn it into an item is described. However, even in this technique, since graphite is formed under low pressure, it has not been possible to obtain continuous coated graphite long fibers. The purpose of the present invention is to eliminate the drawbacks of the conventional methods as described above, and to form a highly graphitizable layer on a base material by CVD method without damaging the base material and the coating layer. The purpose is to provide a method that can handle this. [Means for Solving the Problems] The present invention has the following configuration to achieve the above object. “After forming an easily graphitizable layer on the carbon fiber base material by chemical vapor deposition using infrared heating,
A method for producing highly graphitized fibers by heat treatment at a temperature of 2800°C or higher, characterized in that the formation of the easily graphitized layer and the heat treatment are performed in a pressurized atmosphere. Method for producing synthetic fibers. ” The carbon fiber base material of the present invention has a carbon content of
A material whose main component is 95wt% or more of carbon,
It may be of any type, such as polyacrylonitrile type, pitch type, cellulose type, vinylon type, lignin/poval type, etc. Therefore, the carbon fiber used usually has a single yarn diameter of about 5 to 30 μm. Note that the shape may be a monofilament or a multifilament with a total denier of several thousand to tens of thousands of deniers. The CVD method in the present invention is a method in which compounds having various condensed rings, which become easily graphitized carbon, are deposited on a substrate by thermally decomposing hydrocarbons in a gaseous state. In the present invention, this
In the CVD method, a coating layer of graphitizable carbon is formed by using infrared heating. The hydrocarbons used as raw material gases are as follows:
_C6 to _C14 aromatic hydrocarbons, e.g. benzene,
naphthalene, anthracene and its derivatives, and
C ₃ to _{C 8} alicyclic hydrocarbons, such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclobutene, cyclopentene, cyclohexene and its derivatives, or C ₁ to _{C 8} aliphatic carbonization hydrogen,
Examples include methane, ethane, propane, butane, pentane, hexane, heptane, octane and derivatives thereof, and acetylene compounds such as acetylene and cyanoacetylene. Among them, benzene and cyanoacetylene are preferred, and cyanoacetylene is more preferred. Thermal decomposition of hydrocarbons is carried out by directly or indirectly heating the substrate under a pressurized atmosphere.
If there is a heat source or high-temperature part in the pressurized atmosphere during heating, apart from the base material, pyrolytic carbon will precipitate and become dirty in this part, making continuous CVD impossible for a long period of time. Furthermore, from the standpoint of effective use of raw material monomers, heating using concentrated light energy that can indirectly heat only the base material to a high temperature is most desirable. Examples of light energy sources include carbon dioxide lasers, which have a large capacity and a discontinuous spectrum in the infrared to near-infrared region, and infrared lamps, which have a discontinuous spectrum in the infrared to near-infrared region. A device with a continuous spectrum, a halogen lamp, a xenon arc lamp, etc. can be used. Further, as a means for condensing the light energy radiated from these light energy sources onto the base material, a spheroidal mirror, an optical lens, or the like can be used. Preferably, a spheroidal mirror is arranged to surround the base material so that, for example, light energy is focused on the carbon fiber from all directions within a plane perpendicular to the fiber axis direction. The thermal decomposition temperature is preferably about 700 to 1800°C, more preferably 1100 to 1500°C, although it depends on the type of hydrocarbon used. That is, below 700°C, the formation rate of the graphitizable carbon coating layer becomes slow. Furthermore, if the temperature exceeds 1800°C, the amount of non-graphitizable carbon produced increases, and the amount of the desired highly graphitized fiber produced becomes insufficient. The concentration of hydrocarbon, which is a CVD raw material, is preferably in the range of 0.05 to 10% by volume in the presence of an inert gas. More preferably, it is 0.1 to 5% by volume. That is, if the amount is less than 0.05% by volume, the formation rate of the graphitizable carbon coating layer becomes slow. Also, 10
If the volume % is exceeded, a large amount of non-graphitizable carbon (such as soot) will be generated, and a large amount of deposits (such as soot) will also be generated on the chamber other than carbon fibers, and this will cause the inner wall of the chamber (especially (transparent quartz reaction tube) becomes dirty, making it difficult to continuously produce the desired highly graphitized fiber. Moreover, it can also be carried out in the coexistence of several percent to several tens of percent of hydrogen, if necessary. In this case, the hydrocarbon concentration is 0.1-20% by volume
It can be done. CVD time varies depending on the type of hydrocarbon used, hydrocarbon concentration, thermal decomposition temperature, etc.
Usually, it takes from several minutes to several hours. In order to form a more homogeneous graphitizable carbon coating layer, it is preferable to lower the thermal decomposition temperature and hydrocarbon concentration and to lengthen the CVD time. The thickness of the graphitizable carbon coating layer can be adjusted by adjusting the hydrocarbon concentration, thermal decomposition temperature, CVD time, etc. For example, in the case of coated carbon fiber, the
The thickness is preferably about 200 μm. In addition, when carbonized fibers as a base material are provided in the form of a multifilament, the deposited graphitizable carbon binds the single fibers to each other, and the coated carbon fibers and ultimately the coated graphite fibers obtained are bonded together. Since flexibility tends to be lost, it is preferable to slow down the coating formation rate as much as possible and to not increase the thickness of the coating layer too much. In the present invention, the above-mentioned easily graphitizable carbon-coated substrate is then heat-treated in a pressurized atmosphere to graphitize the easily graphitizable carbon, thereby producing coated graphite having carbon as a substrate and graphite as an outer layer. obtain. In the present invention, graphite is a compound whose main component is carbon, which has developed a structure in which surfaces composed of six-membered ring carbons bonded by SP ₂ bonds are bonded by π bonds. Such compounds include Cu
It is characterized by the interplanar spacing determined from the 002 plane by X-ray diffraction using −Kα rays to be 3.363 Å or less. The heating method for graphitization is not particularly limited as long as it can be heated under a pressurized atmosphere.
For example, resistance heating, induction heating, light energy, etc. can be used. In that case, the graphitization temperature at which pressure treatment is particularly effective is 2800°C or higher, preferably 3400°C or higher.
℃ or higher, and the upper limit is not particularly limited, but is about 3700℃. The atmospheric pressure is preferably 3 kg/cm ² ·G or more, more preferably 5 kg/cm ² ·G or more, the better. Further, as the atmospheric gas in the present invention, an inert gas such as Ar, He, _N2 , etc. can be used. According to the present invention, it is possible to continuously perform the coating formation of the easily graphitizable layer and the graphitization treatment by the CVD method, which is a remarkable effect on the production process. Of course, you can do it in batches. In addition, the electrical conductivity (hereinafter referred to as electrical conductivity) of the highly graphitized long fiber obtained in this way is 1.5×10 ⁴
The conductivity is extremely high at ~2.1×10 ⁴ S/cm, close to that of single crystal graphite. Next, a preferred example of the present invention in which a coating is continuously formed on a carbon fiber base material under a pressurized atmosphere will be described in detail with reference to the drawings. In the figure, carbon fiber A is unwound from a package 7, passes through infrared heating means 2 for CVD, forms coating layer forming fiber B, and then passes through another heating means 3 for graphitization treatment. , a graphite-coated fiber C was obtained and wound onto a bobbin 11 driven by a motor 13 to form a package 18. In this example, reaction tubes 1, 1',
a chamber 21 that houses the carbon fiber supply means 8;
The graphite-coated fiber winding means 9 is controlled by a speed controller 14.
The chamber 22 and the intermediate chamber 34, which accommodate all but one part, constitute a pressurized atmosphere system having pressure resistance. The reaction tubes 1, 1' are made of a heat-resistant material and have a cylindrical shape as a whole. If the heating means 3 is induction heating, the reaction tubes 1 and 1' are preferably made of a non-metallic material, and if the heating means 3 is used for optical energy, it is preferably made of a translucent material, such as quartz glass or ceramic. Atmospheric gas is supplied from the inlet hole 4 via the valve 31, and exhausted from the outlet hole 5 via the valve 32.
The overall configuration was such that gas flows from the graphitization region to the CVD region. The raw material gas is supplied individually from the raw material gas introduction hole 30 provided in the intermediate chamber 34 via the valve 33.
Alternatively, it is supplied together with carrier gas Ar, He, _N2 , etc. [Example] Example 1 Pitch-based carbon fiber “Thornel” P75 (monofilament, diameter 10 μm) manufactured by Union Carbide Company, USA was used as the carbon fiber, and light energy condensed heating was performed using a halogen lamp as the heating means 2.
With the respective temperatures set to 1300°C and 3500°C by optical energy condensing heating using a xenon arc lamp as the heating means 3,
900 ml of Ar is supplied from the atmospheric gas introduction hole 4 through the valve 31.
At a flow rate of cc/min, benzene is supplied as a raw material gas from the raw material gas introduction hole 30 via the valve 33 at a gas conversion rate of 5 cc/min.
It is supplied at a flow rate of cc/min, and is evacuated from the atmosphere gas outlet hole 5 by adjusting the valve 32, and the processing atmosphere pressure is set to 5 cc/min.
An attempt was made to produce coated graphite long fibers while adjusting the amount of Kg/cm ² ·G. The thus obtained coated graphite long fibers had a length of 5 m and a diameter of 85 μm, and it was possible to continuously produce graphite long fibers without cutting the fibers at all. In addition, the interplanar spacing of the 002 planes was determined by X-ray diffraction of this coated graphite long fiber using an RU200 manufactured by Rigaku Corporation and an X-ray generator micro-defractometer MDG2193D. The results are shown in Table 1. Since the interplanar spacing of the 002 plane of graphite single crystal is 3.354 Å, it is very close to this, and it can be seen that highly graphitizable carbon is produced. Furthermore, when the electrical conductivity of the obtained fiber was measured using the four-probe method at room temperature, it was as high as 1.7×10 ⁴ S/cm, which is close to the electrical conductivity of single crystal graphite. Example 2 An attempt was made to produce coated graphite long fibers in exactly the same manner as in Example 1 except that the treatment atmosphere pressure in Example 1 was changed from 5 kg/cm ² ·G to 3 kg/cm ² ·G. Even at a treatment atmosphere pressure of 3 Kg/cm ² ·G, there was no fiber breakage, and graphite long fibers almost the same as in Example 1 were obtained. Table 1 also shows the spacing and conductivity of the 002 plane as determined by X-ray diffraction. Comparative Example 1, Comparative Example 2 For comparison, the processing atmosphere pressure in Example 1 was changed to normal pressure (Comparative Example 1) and 1 Kg/cm ² ·G (Comparative Example 2), and the other conditions were exactly the same as in Example 1. I tried to process it. The results are shown in Table 1. When the treatment atmosphere pressure was normal pressure or 1 kg/cm ² ·G, fiber breakage occurred and long fibers could not be obtained.

[Table] Example 3 A treatment was attempted in exactly the same manner as in Example 1 except that the CVD raw material gas in Example 1 was changed from benzene to cyanoacetylene. The results are shown in Table 2. Even when the raw material is replaced with cyanoacetylene, coated graphite long fibers with a length of 5 m and a diameter of 100 μm can be continuously produced without yarn breakage. by X-ray diffraction
The spacing of the 002 planes is also close to the theoretical value of graphite,
It can be seen that highly graphitic carbon is produced. Example 4 A treatment was attempted in exactly the same manner as in Example 3 except that the treatment atmosphere pressure in Example 3 was changed from 5 kg/cm ² ·G to 3 kg/cm ² ·G. Table 2 also shows the results of the spacing and conductivity of the 002 plane. Comparative Example 3, Comparative Example 4 For comparison, the processing atmosphere pressure in Example 3 was changed to normal pressure (Comparative Example 3) and 1 Kg/cm ² ·G (Comparative Example 4), but the other conditions were exactly the same as in Example 3. I tried to process it. The results are shown in Table 2. Processing pressure is normal pressure and 1
At Kg/cm ² ·G, fiber breakage occurred and long fibers could not be obtained.

【table】

[Table] [Effects of the Invention] The present invention forms a graphitizable layer by CVD using infrared heating in a pressurized atmosphere.
Furthermore, by heating at 2800℃ or higher and performing graphitization treatment, it is possible to form a coating with a high-density easily graphitized layer without pinholes. It has become possible to form coatings on substrates without fiber cutting or surface defects. In addition, when focused light energy is used as a heating means, only the base material is selectively heated, which prevents the walls of the heating furnace from becoming dirty and allows stable thermal decomposition of hydrocarbon monomers over a long period of time. At the same time, it is an efficient manufacturing method that allows coating and graphitization of the base carbon fiber. Further, according to the method of the present invention, it is possible to obtain highly conductive fibers that have high conductivity and are lightweight. Therefore, if this is used, for example, as a power transmission line, the load on the support can be reduced and the construction cost can be reduced. Moreover, because the outer skin layer has particularly high electrical conductivity, there is little energy loss even when used as an AC power transmission line that exhibits a skin effect. Moreover, the light weight makes it suitable for use as an aircraft electric wire, which has a large weight reduction effect. Furthermore, since the highly conductive fibers obtained by the method of the present invention are essentially composed of carbon, they can withstand high temperatures and have high corrosion resistance. Therefore,
For example, it is suitable as an electrode plate material for storage batteries and fuel cells.

[Brief explanation of drawings]

The drawing is a schematic cross-sectional view of one apparatus to which the processing method of the present invention is applied. 1, 1': Reaction tube, 2: CVD heating means, 3:
Heating means for graphitization, 4: Atmospheric gas introduction hole, 5:
Atmospheric gas outlet hole, 6, 10: Rotation guide, 7:
Carbon fiber package, 8: Carbon fiber supply means,
9: graphite-coated fiber winding means, 11: winding bobbin,
12: Reducer, 13: Motor, 14: Speed controller, 18: Graphite-coated fiber package, 2
1, 22: Chamber, 30: Raw material gas introduction hole,
31, 32, 33: valve, 34: intermediate chamber.

Claims (1)

[Claims] 1. After forming an easily graphitizable layer on a carbon fiber base material by chemical vapor deposition using infrared heating,
A method for producing highly graphitized fibers by heat treatment at a temperature of 2800°C or higher, characterized in that the formation of the easily graphitized layer and the heat treatment are performed in a pressurized atmosphere. Method for producing synthetic fibers. 2. The method for producing a highly graphitizable fiber according to claim 1, wherein the formation of the easily graphitizable layer and the heat treatment are performed continuously. 3. The method for producing highly graphitized fibers according to claim 1, wherein the pressure of the atmosphere is 3 kg/cm ² ·G or more. 4 The concentration of the raw material of the easily graphitizable layer is 0.1 to 5% by volume.
The method for producing a highly graphitized fiber according to claim 1, characterized in that: 5. The method for producing a highly graphitizable fiber according to claim 1, wherein the forming temperature of the easily graphitizable layer is 1100 to 1500°C. 6. The method for producing a highly graphitizable fiber according to claim 1, wherein the raw material for the easily graphitizable layer is benzene or cyanoacetylene.