JPH052640B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to whisker-like carbon fibers produced by a vapor phase growth method, and particularly to whisker-like carbon fibers that have a rough surface, are highly crystalline, and are easily graphitized. [Prior Art] Carbon fiber has excellent properties such as high strength and high modulus of elasticity, and is attracting attention as a variety of composite materials. Conventionally, carbon fibers were mainly made of PAN, Pitzchi,
It is manufactured by carbonizing organic fibers such as cellulose. When making fiber-reinforced composite materials using these carbon fibers, it is desired to increase the contact area with the base material, reduce the diameter, and increase the length to increase the reinforcing effect. Furthermore, surface treatments such as oxidation and coating are performed to improve adhesion to the base material. Graphitization treatment is also performed to improve crystallinity, electrical conductivity, etc. However, conventionally, when carbonized carbon fibers are made from organic fibers, it is difficult to spin them, so the diameter of the fibers is only about 5 to 10 μm at most. Therefore, a time-consuming and time-consuming oxidation treatment process is required under severe conditions. Further, even if graphitization treatment is performed, this carbon fiber is difficult to graphitize, and a sufficient graphite structure cannot be obtained. For example, PAN-based carbon fiber is
The interplanar spacing d ₀₀₂ of the carbon hexagonal network plane 002 according to the X-ray diffraction method of the yarn graphitized at 3000°C is about 3.42 Å,
The density is around 1.8g/cm ³ . Carbon fiber made from mesophase pitch, which has a higher degree of graphitization than PAN or pitch carbon fibers, is used.
Even when graphitized at 3000℃, the interplanar spacing d ₀₀₂
is approximately 3.38 Å, and the crystallite size Lc002 is approximately
180 Å, and the density is a little less than 2.0 g/cm ³ . On the other hand, it is also known to produce carbon fibers by thermally decomposing hydrocarbons and using a vapor phase growth method. This vapor grown carbon fiber has extremely few crystal defects and has excellent crystallite orientation. Therefore, it is a material with higher density and higher elastic modulus than organic fiber carbonized carbon fiber, and is expected to be used in many fields as a fiber-reinforced composite material. However, although conventionally known vapor-grown carbon fibers are easily graphitized, the density of the carbon fibers immediately after carbon fiber production is around 1.85 g/cm ³ at most, and they still do not have sufficient graphite structure. I haven't gotten around to taking it yet. Therefore, in order to have high orientation, graphitization treatment is required. Further, carbon fiber is disclosed in JP-A No. 61-225325, and this carbon fiber has a Raman scattering spectrum with a peak height ratio of I1360/I1580 between the peak height of the 1360 cm ^-1 band and the peak height of the 1580 cm ^-1 band. is less than 1.0, and the surface is smooth. Similarly, JP-A-61-
The carbon fiber disclosed in No. 70014 has a smooth surface. Therefore, these carbon fibers have poor chemical reactivity, and when used as a composite material, it is necessary to sufficiently oxidize the surface. [Problems to be Solved by the Invention] The present invention solves the above-mentioned problems of the prior art. The object of the present invention is to provide whisker-like carbon fibers with a rough surface and easy graphitization properties that can be processed easily. [Means for solving the problem] The carbon fiber of the present invention has a fiber diameter of 0.1 μm to
50 μm, preferably 0.5 μm to 5 μm. Fiber length/fiber diameter (aspect ratio) is 50 to 10,000,
Preferably, it is 100 to 10,000. Density is 1.9g/ ^cm3
The amount is preferably 2.0 g/cm ³ or more. Also X
Interplanar spacing of carbon hexagonal network plane 002 by line diffraction method
d ₀₀₂ is 3.36 Å to 3.49 Å, the crystallite size Lc002 in the c-axis direction is 50 Å or more, the ratio of the peak height of the 1360 cm ^-1 band to the peak height of the 1580 cm ^-1 band in the Raman scattering spectrum (R value) I1360 /I1580 is 1.05 or more, preferably 1.1 or more. It is a whisker-like carbon fiber that is easily graphitized and has a fuzzy appearance on the surface within about 300 Å from the fiber surface. The reason why the aspect ratio is limited to the above range in the present invention is that if it is less than 50, the strength reinforcement effect of the composite material will not be obtained when a composite material of carbon fiber, resin, metal, compact cement, ceramic, etc. is made. This is because there is no Moreover, if it is less than 50, there will be little bonding between fibers, making it difficult to make paper. In addition, the density, the interplanar spacing d ₀₀₂ of the carbon hexagonal network plane 002,
The reason why the crystallite size Lc002 in the c-axis direction is limited to the above range is that carbon fibers in this range are heated to 2000℃.
When graphitized at a temperature above, it easily becomes graphitized fiber with a density of 2.1 g/cm ³ or more and a d ₀₀₂ of
This is because Lc002 is 3.45 Å or less and Lc002 is 150 Å or more. Note that the upper limits of these values were set in consideration of economic efficiency during manufacturing. Since the carbon fiber of the present invention has a fluffy surface, the R value of the Raman scattering spectrum is
It is over 1.05, but the density of the fiber is high because the fiber has a highly crystalline graphite structure inside. Because of this surface structure, it is possible to mix easily without oxidation treatment or by applying mild oxidation treatment, for example, due to good wettability with resin, and sufficient reinforcement. effect can be obtained. As described above, the carbon fiber according to the present invention can be obtained as a whisker-like carbon fiber having excellent adhesiveness to a base material without undergoing any surface treatment or only by being subjected to a mild oxidation treatment. The whisker-like carbon fiber according to the present invention is produced by introducing a hydrocarbon (raw carbon source) and an organometallic compound into a reaction system, and converting the carbon obtained by pyrolysis of the hydrocarbon into the carbon produced by the pyrolysis of the organometallic compound. This can be achieved by using a gas containing predetermined amounts of carbon monoxide, carbon dioxide, and hydrogen as a carrier gas when growing on fine particles. Hydrocarbons used in the present invention include aliphatic hydrocarbons such as methane, ethane, propane, ethylene, propylene, and butadiene, monocyclic aromatic hydrocarbons such as benzene, toluene, and xylene, and naphthalene and anthracene. Polycyclic aromatic hydrocarbons or mixtures thereof can be applied, but crude light oils that are by-products from coke ovens, absorbed oils,
Carbol oil, anthracene oil, heavy oil, pitch, and mixtures thereof are inexpensive and can be supplied in large quantities, and sulfur-containing thiophenes, thiols, and thiophenols are particularly useful because they accelerate the production of carbon fibers. It is. Any known organometallic compound can be used as long as it has a carbon-metal bond, but if it is used by dissolving it in the raw material hydrocarbon, it should be soluble, and if it is used in a gaseous state, it should be sublimated. Something with gender is desirable. Specifically, organic transition metal compounds containing titanium, vanadium, chromium, manganese, iron, cobalt, nickel, rubidium, rhodium, tungsten, palladium, or platinum are suitable, particularly organic transition metal compounds containing iron. is the most suitable. In particular, metallocenes having a cyclopentadienyl group as a ligand are useful because they form dinuclear complexes with many high-valent metal salts and are inexpensive and active. The metal compound that is a decomposition catalyst for the organometallic compound is used in an amount of 0.01 to 1 mole of the organometallic compound used.
It is best to add about 50 moles. Moreover, any metal compound can be used as long as it has the same type of metal atom or a different type of metal atom with respect to the organometallic compound used. The metal is preferably titanium, vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, ruthenium, rhodium, osmium, or iridium, and particularly preferably manganese, iron, cobalt, or nickel. The form of the compound may be any, and examples include inorganic compounds such as sulfates, nitrates, acetates, chlorides, sulfides, oxides, carbides, nitrides, and acetylacetonate salts, and organic transition metal complexes such as carbonyl compounds. used. The carrier gas used to obtain the carbon fibers according to the present invention is a gas containing at least 50 to 80% carbon monoxide and 5 to 30% carbon dioxide. ~
30%, hydrogen 0.1 to 10%, and nitrogen 20% or less. Specifically, it is a mixed gas of converter gas, blast furnace gas, or a gas obtained by mixing these gases with a hydrogen-containing gas such as coke oven gas. In particular, converter gas
It is effective because it has this composition alone. [Effects of the Invention] Therefore, the carbon fiber of the present invention obtained by the above method has a large fiber diameter, a large fiber length/fiber diameter, a high density, and a highly crystalline graphite structure inside the fiber. However, the fiber surface is a whisker-like carbon fiber that is easily graphitized. Therefore, when a fiber-reinforced composite material is made using this carbon fiber,
Not only does it have a sufficient reinforcing effect as a reinforcing fiber, but it can also easily undergo time-consuming surface treatment. For this reason, the time and cost required for surface treatment,
It is effective in reducing the amount of labor required. The present invention will be explained below with reference to Examples. Example 1 Carbon fibers were manufactured using the apparatus shown in FIG. In the figure, reference numeral 11 is a gas cylinder filled with argon gas. 12 is a gas cylinder filled with converter gas, which has a composition of 70% by volume of carbon monoxide gas, 15% by volume of carbon dioxide gas, 1.1% by volume of hydrogen gas, and 15% by volume of nitrogen gas, This is introduced into the reaction system as an atmospheric gas. Each cylinder 11, 12 has a flow meter 13, 14.
are connected to each other, thereby controlling the gas flow rate. 15 is a raw material tank, into which benzene was put as raw material oil. This benzene has
Ferrocene, thiophene, and Mn(II) acetylacetonate salt, which is a decomposition catalyst for ferrocene, are dissolved, and the weight composition is as follows: ferrocene, thiophene, and Mn(II) acetylacetonate salt to 100 parts by weight of benzene. The ratios are 0.4, 0.2, and 0.1, respectively. . These cylinders 11 and 12 are connected to a reaction tube 20 via a stainless steel pipe 16, and the raw material tank 15 is connected to the reaction tube 20 via a stainless steel pipe 17. The reaction tube 20 is an alumina tube with an inner diameter of 90 mm and a length of 1000 mm.
3 is installed. The temperature of this electric furnace 23 is
The thermocouple 24 detects the temperature, and the temperature controller 25 controls the temperature to be constant. In this example, the temperature during operation of the electric furnace 23 was set at 1150°C. During operation, argon gas is first supplied from the cylinder 11 into the reaction tube to replace the inside of the reaction tube with argon gas. Subsequently, the converter gas contained in the cylinder 12 was flowed into the reaction tube 20 at a rate of 300 ml/min. Furthermore,
A raw material oil having the above composition was supplied into the reaction tube 20 at a rate of 2 ml/min using a chemical pump 22. As a result, thermal decomposition and catalytic reaction of the raw material oil occurred in the reaction tube, thereby continuously producing whisker-like carbon fibers, which were collected by the collector 21. The obtained carbon fibers have an average diameter of 1 μm and an average length of 2000 μm, and the yield is 68% based on benzene.
It was hot. In addition, the density is 2.05g/cm ³ , the interplanar spacing d ₀₀₂ of carbon hexagonal network plane 002 is 3.48 Å, and the size of crystallites is
Lc002 was 70 Å. Moreover, the R value of the Raman scattering spectrum is 1.10. Observation of the carbon fiber surface using a transmission electron microscope revealed that the fiber surface was rough and had a fluffy appearance at a depth of approximately 300 Å.
This micrograph is shown in FIG. Furthermore, this fiber was treated with epoxy resin (trade name: Epicote 828, curing agent BF ₃ MEA) at a ratio of 5 and 20% by volume without any oxidation treatment, and 30% by volume.
FRP was prepared by mixing with PP in the following proportions (sample numbers: 5, 6, and 2, respectively). In addition, fibers boiled with concentrated nitric acid for 0.5 hours are mixed with epoxy resin at a rate of 20% by volume and PP at a rate of 30% by volume for FRP.
were produced (sample numbers: 7 and 3, respectively). this
A three-point bending test was conducted using a specimen made of FRP with a width of 10 mm, thickness of 4 mm, and distance between fulcrums of 64 mm. The results are shown for epoxy resin base material alone (sample number: 1),
Table 1 shows the bending strength of the polypropylene base material alone (sample number: 4). In both cases, the carbon fibers of the present invention were found to have a reinforcement hardening of 1.3 to 2.1 times the strength of the base material. Also, in terms of wettability with resin, it was better than pitch-based carbon fiber whose surface was oxidized with nitric acid. Example 2 The whisker-like carbon fiber produced in Example 1 was
Graphitization treatment was performed at 2000℃. The density of this graphitized thread is 2.15 g/cm ³ , the interplanar spacing d ₀₀₂ of the carbon hexagonal network plane 002 is 3.43 Å, and the crystallite size Lc 002 is
It was 200Å. When this whisker-like carbon fiber was graphitized at 2800°C, the density of the graphitized yarn was 2.21 g/cm ³ , and the carbon hexagonal network plane was 002
The interplanar spacing d ₀₀₂ is 3.37 Å, and the crystallite size Lc 002
was 660 Å. Thus, it can be seen that this whisker-like carbon fiber is easily graphitized. Comparative Example 1 Whisker-like carbon fibers were produced using the same apparatus as in Example 1, using hydrogen as a carrier gas, and with the other conditions being the same as in Example 1. The obtained carbon fibers have an average diameter of 0.5 μm and an average length of 2000 μm.
, the density is 1.80g/cm ³ , carbon hexagonal mesh plane 00
The interplanar spacing d ₀₀₂ of 2 is 3.53 Å, and the crystallite size Lc00
2 was 35 Å. In addition, the value of the Raman scattering spectrum is 0.89, and as a result of observation with a transmission microscope,
The carbon fiber surface was smooth. A transmission micrograph of the surface of the carbon fiber is shown in FIG. When this whisker-like carbon fiber was graphitized at 2000°C, the density increased only to 1.90g/cm ³ . Using this fiber, FRP was produced in the same manner as shown in Example 1, and a bending strength test was conducted.
The results are shown in Table 2. Table 2 shows that the carbon fibers of the comparative example have inferior bending strength compared to those of the present invention. Example 3 The apparatus used in Example 1 was transformed into a horizontal type, a magnetic plate in which commercially available ultrafine iron powder (manufactured by Vacuum Metallurgy) was dispersed was placed in a furnace, and the inside of the furnace was replaced with argon. The electric furnace is heated up, and when it reaches 600℃, the converter gas is turned off.
300 sccm was flowed into the reaction tube for 30 minutes. Thereafter, the electric furnace was maintained at 1150°C, and benzene was supplied at a flow rate of 0.1 ml/min. The carbon fibers obtained after one hour of operation had an average diameter of 30 μm and an average length of 60 mm.
Each time is 2.03 g/cm ³ , the interplanar spacing d ₀₀₂ of carbon hexagonal network plane 002 is 3.49 Å, and the crystallite size Lc 002 is 55 Å.
It was hot. In addition, the R value of the Raman scattering spectrum is
1.05, and when observed with a transmission electron microscope,
The fiber surface had a fluffy appearance over approximately 500 Å.

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【table】 [Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the outline of an apparatus for implementing the method of the present invention, Fig. 2 is a micrograph showing the surface shape of carbon fibers obtained by the method of the present invention, and Fig. 3 is a photomicrograph showing the surface shape of carbon fibers obtained by the method of the present invention. 1 is a micrograph showing the surface shape of carbon fibers obtained by 11... Argon gas cylinder, 12... Carrier gas cylinder, 13, 14... Flow meter, 15...
... Raw material tank, 16, 17 ... Stainless steel pipe, 20 ... Reaction tube, 21 ... Collector, 22 ...
Chemical pump, 23... electric furnace, 24... thermocouple, 25... temperature controller.

Claims (1)

[Claims] 1. The fiber diameter is 0.1 μm to 50 μm, the fiber length/
Fiber diameter is 50 to 10,000, density is 1.9 g/cm ³ or more, spacing between carbon hexagonal network planes 002 by X-ray diffraction method d ₀₀₂
is 3.36 Å to 3.49 Å, crystallite size Lc002 is 50
Å or more, the ratio of the peak height of the 1360 cm ^-1 band and the peak height of the 1580 cm ^-1 band in the Raman scattering spectrum
I1360/I1580 is 1.05 or more, per fiber diameter 1
A whisker-like carbon fiber that is easily graphitized and has a fluffy appearance with a fiber surface depth of about 0.001 to 0.1. 2 The fiber diameter is 0.5 μm to 5 μm, the fiber length/fiber diameter is 100 to 10000, the density is 2.0 g/cm ³ or more, and the interplanar spacing d ₀₀₂ of carbon hexagonal network planes 002 by X-ray diffraction method is
3.36 Å to 3.49 Å, crystallite size Lc002 is 50 Å
The above is the ratio of the peak height of the 1360 cm ^-1 band and the peak height of the 1580 cm ^-1 band in the Raman scattering spectrum.
Easily graphitized whisker-like carbon fiber with I1360/I1580 of 1.1 or more and a fiber surface with a fluffy appearance at a depth of about 300 Å.