JPH0617319A - Production of pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To easily provide the carbon fiber having a high tensile strength, high tensile modulus and high thermal conductivity, significantly reduced in the cost of the carbonizing process therefor. CONSTITUTION:Separation of the processes prior to continuous precarbonization from those after the continuous carbonization enables drawing intended to improve both the tensile strength and tensile modulus of precarbonized fiber bundles F in a graphitizing oven 50 in their graphitization, also enables their graphitization degree at lower temperature treatment with their prolonged residence time in the oven 50 to be improved. With this practice, both the tensile strength and tensile modulus of the graphite fibers obtained by drawing in the graphitization at lower temperatures can be improved at a reduced cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing pitch-based carbon fibers produced from carbonaceous pitch, and in particular, the cost of the carbonization step can be significantly reduced, and high tensile strength, high tensile elastic modulus and high heat resistance can be obtained. It is a method for producing a carbon fiber which makes it possible to easily obtain a conductive carbon fiber.

In the present specification, unless otherwise specified, "carbon fiber" is used to include not only carbon fiber but also graphite fiber.

[0003]

2. Description of the Related Art At present, rayon-based and PAN-based carbon fibers and pitch-based carbon fibers have come to be widely used in various technical fields, and in particular, they are manufactured from carbonaceous pitch such as petroleum-based pitch and coal-based pitch. The pitch-based carbon fiber has a higher carbonization yield than that of rayon-based or PAN-based carbon fiber, has excellent physical properties such as elastic modulus, and has the advantage that it can be manufactured at low cost. Because of this, it has been attracting attention in recent years.

Currently, pitch-based carbon fibers are prepared by (1) preparing a carbonaceous pitch suitable for carbon fibers from petroleum-based pitch, coal-based pitch, etc., heating and melting the carbonaceous pitch, and spinning with a spinning machine. Pitch fibers are produced by the above method, and the obtained fiber bundles of pitch fibers are further bundled, and then (2) the pitch fibers are infusibilized by heating to a temperature of 250 to 350 ° C. in an infusible furnace under an oxidizing atmosphere. Then, (3) subsequently, the infusible fiber is heated to a maximum temperature of 500 to 15 in a preliminary carbonization furnace under an inert atmosphere.
(4) Next, the pre-carbonized fiber is heated to 00 ° C. to pre-carbonize it, and the pre-carbonized fiber is heated to a temperature of 1500 to 2 in an inert atmosphere in a carbonization furnace.
It is manufactured by heating to 000 ° C. to carbonize, and further heating to 3000 ° C. to graphitize.

[0005]

By the way, the above-mentioned infusibilization of the pitch fiber, carbonization of the pre-carbonized fiber, and further graphitization are continuously carried out under tension.

According to such a continuous treatment, since the heat accumulation of the fiber bundle can be easily removed and uniform firing can be carried out, it is an excellent method for producing a large amount of carbon fibers of constant quality.

However, when the conditions before carbonization are kept constant, and only the graphitizing furnace, which requires a very high operating cost, is passed at a high speed to reduce the cost, the continuous treatment becomes an obstacle.

Further, when it is intended to increase the degree of graphitization at a low temperature treatment by improving the tensile strength and the tensile elastic modulus by the stretching treatment at the time of the graphitization treatment or by prolonging the residence time in the graphitization furnace. Was also limited.

Therefore, an object of the present invention is to reduce the cost of the carbonization process significantly and to easily obtain carbon fibers having high tensile strength, high tensile modulus and high thermal conductivity. It is to provide a manufacturing method.

[0010]

The above object can be achieved by the method for producing a pitch-based carbon fiber according to the present invention. In summary, the present invention is a method for producing a pitch-based carbon fiber in which pitch fibers are continuously infusibilized under tension, continuous pre-carbonization, continuous carbonization, and further continuous graphitization, if necessary.
A method for producing a pitch-based carbon fiber, characterized in that a step before continuous pre-carbonization and a step after continuous carbonization are separated.

In the present invention, by separating the process before the continuous pre-carbonization and the process after the continuous carbonization, it is possible to perform the stretching treatment for improving the tensile strength and the tensile elastic modulus during the carbonization (including graphitization) treatment. Also, it is possible to increase the degree of carbonization or graphitization by low temperature treatment by prolonging the residence time in the carbonization furnace or graphitization furnace, making it easy to obtain carbon fibers with high tensile strength, high tensile modulus and high thermal conductivity. The cost of the carbonization process can be significantly reduced.

[0012]

EXAMPLES An example of the method for producing pitch-based carbon fibers of the present invention will be described with reference to the production apparatus shown in FIGS.

As shown in FIG. 1 and FIG. 2, the carbon fiber manufacturing apparatus has at least a pitch fiber bundle F formed by converging the spun pitch fibers and adding a heat-resistant oil agent to the yarn.
An infusibilizing furnace 10 for infusibilizing the infusible material, a pre-carbonizing furnace 30 for pre-carbonizing the infusible fiber bundle from the infusibilizing furnace 10,
A graphitizing furnace 50 is provided for carbonizing the pre-carbonized fiber bundle from the pre-carbonizing furnace 30 and further graphitizing it as required. Usually, the infusibilization furnace 10, the preliminary carbonization furnace 30, and the graphitization furnace 50 are arranged in series for continuous treatment, but in the present invention, in order to separate the step before the preliminary carbonization and the step after the carbonization. In addition, the preliminary carbonization furnace 30 and the graphitization furnace 50 do not necessarily have to be arranged in series.

In this embodiment, the infusible furnace 10 has five private chambers R.
The chamber R1 having 1 to R5 and close to the entrance is, for example, 190
℃, room R2 to 220 ℃, room R3 to 250 ℃, room R
4 is heated to 280 ° C., and the chamber R5 is heated to and held at 310 ° C. Further, an oxygen-rich gas (for example, a mixed gas of oxygen and nitrogen with a mixing ratio of 50/50) is introduced into the infusibilizing furnace 10 and is forcibly stirred by a fan. An upstream of the infusibilizing furnace 10 is provided with a fiber bundle tensioning means 12 for applying a tension to a fiber bundle F continuously fed from the bobbin B ₁ to the infusibilizing furnace 10 and the preliminary carbonization furnace 30.

The preliminary carbonization furnace 30 is heated and held so that the temperature rises stepwise from the inlet to 400, 500, 600, 700, 1100 ° C., for example. In order to make the inside of the furnace 30 an atmosphere of an inert gas such as nitrogen gas or an atmosphere containing a small amount of oxygen, for example, nitrogen gas containing a small amount of oxygen is supplied into the furnace 30. The oxygen concentration in the atmosphere containing a small amount of oxygen is adjusted to 100 to 30,000 ppm.

Melt spinning, bundling and spinning from 1 to 5
Pitch fiber bundle F wound around a large number of 00 bobbins B ₁
Are released from the respective bobbins B ₁ and fed to the infusibilizing furnace 10 under tension by the fiber bundle tensioning means 12, and are infusibilized while being threaded in the furnace 10. Next, the infusibilized fiber bundle F continuously enters the pre-carbonization furnace 30, and while the pitch fiber bundle F is threaded in the furnace 30 while being tensioned by the tensioning means 12, the atmosphere containing a slight amount of oxygen is introduced. By being heated below, it is pre-carbonized and at the same time the gluing is released.

The pre-carbonized fiber bundles F obtained by pre-carbonizing the pitch fiber bundles in this manner are once wound on the respective bobbins B ₂ . The preliminary winding of the carbonized fiber bundle F, the outer diameter of the bobbin B ₂ is performed such that 50 to 1000 mm. As the winding bobbin B ₂ of the pre-carbonized fiber bundle F, a paper tube or a resin bobbin is usually used. A graphite bobbin can be used when graphitizing the wound bobbin as needed.

Next, the pre-carbonized fiber bundle F wound on the bobbin B ₂ is set in a bobbin holder of an unwinding mechanism (not shown) mounted on the upstream side of the graphitizing furnace 50 to be released, and tensioned by the tensioning means 52. While drawing, the yarn is passed through the furnace 50 to be graphitized.

The above graphitization furnace 50 is heated and maintained at a predetermined graphitization temperature, for example, 2000 to 3000 ° C. without a temperature gradient. In order to create an inert gas atmosphere in the furnace 50,
An inert gas such as argon, helium, or nitrogen is supplied into the furnace 50. When the carbonization is not performed and the carbonization is stopped, a carbonization furnace is installed in place of the graphitization furnace. At that time, the inside of the carbonization furnace is heated and maintained at 1500 to 2000 ° C.

According to this embodiment, the graphitization furnace 50 described above is used.
The unwinding mechanism of the bobbin B is pre-carbonized in the pre-carbonization furnace 30.
_The pre-carbonized fiber bundle F wound around ₂ is unwound so that the firing time in the graphitization furnace 50 can be set to 5 seconds to 30 minutes, and the winding speed change mechanism and the tension during firing become 50 to 10000 g. It has a tension changing function for changing the above. The above firing time means the time for the fibers to pass through the heating part (heating element part) of the furnace.

The bobbin holder of the unwinding mechanism has an electric type,
A creel type or the like is used. At the time of unwinding, in order to improve the focusing property of the fiber bundle after graphitization and reduce the feathers, the pre-carbonized fiber bundle F is twisted at about 0.1 to 50 times / m. .

In the graphitization treatment according to this embodiment, the residence time in the graphitization furnace 50 is lengthened, and the residence time is lengthened in order to graphitize the preliminary carbonized fiber bundle F in the low temperature treatment. The threading speed is set to 0.05 to 50 m / min (gear ratio of 0.1 to 100) in order to produce an identical property product at low cost. Further, in order to improve the tensile strength and the tensile elastic modulus of the obtained graphitized fiber, the pre-carbonized fiber bundle F has 50 to 5000 g.
Is applied to perform a stretching treatment with a stretching ratio of 0 to 50%.

The graphite fiber bundles F obtained by graphitizing as described above are wound on the respective bobbins B ₃ . Prior to the winding, the graphite fiber bundle F is subjected to surface treatment and sizing, if necessary.

According to the method for producing carbon fibers as described above, the steps before the continuous pre-carbonization and the steps after the continuous carbonization are separated, and the residence time of the pre-carbonized fibers in the graphitization furnace is increased to graphitize. Since the pre-carbonized fiber can be graphitized by the low temperature treatment, and the drawing treatment is performed during the graphitization, the tensile strength and the tensile elastic modulus of the obtained graphite fiber can be improved. . That is, carbon fibers having high tensile strength, high tensile modulus and high thermal conductivity can be easily obtained, and the cost of the carbonization step can be significantly reduced.

In the above examples, the pre-carbonized fiber bundle was graphitized in the graphitizing furnace 50 as it is, but the present invention is not limited to this, and a carbonizing furnace may be provided instead of the graphitizing furnace 50 if necessary. It can also be applied to the case where the carbonization treatment is performed and the same effect is obtained.

[0026]

EXAMPLES The method for producing pitch-based carbon fibers according to the present invention will be described below with reference to specific examples.

Example 1 In the production of pitch fibers used in the production of carbon fibers, an optical anisotropic phase is contained in an amount of about 55% and a softening point is 232.
The carbonaceous pitch at 0 ° C was used as the precursor pitch.
This precursor pitch was continuously separated into a pitch having a large amount of optically anisotropic phase and a pitch having a large amount of optically isotropic phase by centrifugal separation, and extracted.

The obtained pitch containing a large amount of the optically anisotropic phase contained 98% of the optically anisotropic phase and had a softening point of 265 ° C.
The quinoline insoluble content was 29.5%. The carbon fiber pitch was spun at 355 ° C. using a melt spinning machine (nozzle hole diameter: 0.3 mm) having a spinneret with 500 holes.

The 500 spun filaments were substantially bundled by an air sucker and guided to an oiling roller, and a focusing oil agent was supplied at a ratio of about 0.2% by weight with respect to the yarn.
A pitch fiber bundle consisting of 0 filaments was formed. Methylphenylpolysiloxane having a viscosity of 14 cst at 25 ° C. was used as an oil agent.

The pitch fiber bundle was wound on a bobbin having a diameter of 210 mm and a width of 200 mm, which was provided at the lower part of the nozzle and rotated at high speed, and was spun at a winding speed of about 500 m / min for 10 minutes. 1 traverse pitch per bobbin rotation
It was 0 mm / 1 rotation. No yarn breakage occurred during spinning.

Then, the six bobbins wound with the pitch fiber bundle are unwound, and combined with a heat-resistant oil agent using an oiling roller to form a pitch fiber bundle of 3000 filaments, and the like. It was wound on a stainless steel bobbin.

At the time of compounding, the oil agent is 40 cst at 25 ° C.
Methyl phenyl polysiloxane (phenyl group content 4
5 mol%) was used. The applied amount was 0.5% based on the yarn.

Pitch fiber bundle F produced as described above
Was continuously infusibilized and pre-carbonized by using the infusibilizing furnace 10 and the pre-carbonizing furnace 30 shown in FIG.

The infusible furnace 10 used in this embodiment has five individual chambers R1 to R5, and the chamber R1 adjacent to the inlet has 19 chambers.
The chamber R2 was heated to 220 ° C, the chamber R3 was heated to 250 ° C, the chamber R4 was heated to 280 ° C, and the chamber R5 was heated to 310 ° C. Further, an oxygen-rich gas (a mixed gas of oxygen and nitrogen: a mixing ratio of 50/50) was introduced into the infusible furnace 10 and was forcibly stirred by a fan. The wind speed at this time is 0.7 m / sec
Was taken. Then, the flow was replaced at a rate of 0.5 times per minute, and the old gas in the furnace was discharged.

The pitch fiber bundle F is 0.3 in the infusible furnace 10.
The fiber bundle F was moved at a speed of m / min, and a tension of 20 g was applied to the fiber bundle F by adjusting the fiber bundle tensioning means 12.

The time required for infusibilizing the pitch fiber bundle F with the above structure was 15 minutes. During the infusibilization, the unwinding of the pitch fiber bundle F from the bobbin B ₁ was carried out smoothly. The infusibilization process could be carried out smoothly without breaking the fiber bundle in the infusibilization furnace.

The pitch fiber bundle F infusibilized in this manner is continuously fed to the preliminary carbonization furnace 30 and the above-mentioned 20 g is fed.
Was pre-carbonized by threading to tension.

According to this embodiment, the preliminary carbonization furnace 30 is heated and held in a mode in which it rises stepwise from the inlet to 400, 500, 600, 700, 1100 ° C., and the inside of the furnace is within the scope of the present invention. 10 to create an atmosphere containing a trace amount of oxygen
Nitrogen gas was supplied containing 00 ppm oxygen. The time required for pre-carbonization was 7 minutes.

The infusibilized pitch fiber bundle F is used in the preliminary carbonization furnace 30.
While the yarn was being threaded, it was pre-carbonized and released from sticking by heating in an atmosphere containing a slight amount of oxygen.

The preliminary carbonized fiber bundle F has a strength of 1.5 GP.
The elastic modulus was 120 GPa. Further, the pre-carbonized fiber bundle F had gluing removed (de-glued), was fluffy like a cotton, and was supple. The degree of sticking of this preliminary carbonized fiber bundle F was 9%.

The above pre-carbonized fiber bundle was pre-carbonized and wound on a bobbin B ₂ having a diameter of 80 mm until the length became 20 km. The outer diameter of the bobbin B ₂ after winding the pre-carbonized fiber bundle was about 200 mm.

A preliminary carbonized fiber bundle F wound on this bobbin B _2.
2 is sent to the graphitization furnace 50 of FIG. 2, and the fiber bundle F is released and a predetermined tension is given by the unwinding and winding speed change mechanism and the tension changing function equipped therein, Then, the fiber bundle F was graphitized.

The temperature of the graphitizing furnace is 2500 ° C., the firing time is 12 seconds (threading speed 5 m / min), and the tension during firing is 1
It was set to 000 g.

The graphite fiber thus obtained was a fluffy and supple fiber with little sticking, like the pre-carbonized fiber before graphitization, and the sticking degree was 10%.

This graphite fiber was subsequently subjected to a surface treatment by a surface treatment device, and then a sizing agent was applied by a sizing agent applying device, dried and wound on a bobbin to a length of 500 m.
Subsequently, it was further wound on four bobbins 500 m each.

The strand tensile strength of this graphite fiber was measured by the resin-impregnated strand test method specified in JIS R7601, and the strand tensile strength was found to be 35.
0 kg / mm ² , tensile elastic modulus is 71 ton / mm
^{Was 2} .

According to this example, a graphite fiber having the same physical properties was obtained at a threading speed 20 times that of Comparative Example 1 described later.

Example 2 When releasing the pre-carbonized fiber bundle F from the bobbin B ₂ in the graphitizing furnace 50 of FIG. 2, the pre-carbonized fiber F was creeled and released, and the pre-carbonized fiber bundle F was turned into a fiber bundle at a rate of 4 times / m. Graphitization was performed in the same manner as in Example 1 except that twist was applied.

In this case, although the obtained graphite fiber is a fluffy fiber bundle having a degree of fusion of 10% and little fusion, the fiber bundle is bundled, and the surface treatment and the sizing treatment are continued. Was wound on the bobbin B ₃ by carrying out two of the above, and during the two steps, winding of the fiber bundle on the roller,
No yarn breakage was observed, less fluff was generated, and the wound shape after winding was good.

The strand strength of this graphite fiber is 370 k.
a g / mm ^2, a tensile modulus of 71ton / mm ^2.

Example 3 The same process as in Example 1 was carried out except that the firing time in the graphitization furnace 50 shown in FIG. 2 was 10 minutes and the tension was 1000 g.

In this case, the tensile strength of the obtained graphite fiber is 350 kg / mm ² , and the tensile elastic modulus is 71 ton.
/ Mm ² , electric resistance (volume resistivity) is 380 μΩ · cm
Thus, a fiber having low electric resistance and good electric conductivity was obtained.

Comparative Example 1 The infusibilizing furnace 10, the preliminary carbonizing furnace 30 and the graphitizing furnace 50 shown in FIGS. 1 and 2 were connected in series, and the fiber bundle F was continuously threaded and continuously treated. The firing time for graphitization is limited to 120 seconds because the graphitization furnace 50 is connected in series with the pre-carbonization furnace 30, and the tension during graphitization is as low as during infusibilization and pre-carbonization. 200
It was g. Other than that was processed like Example 1.

The graphite fiber thus obtained had a strand strength of 350 kg / mm ² and a tensile modulus of 70 ton / mm ² . The electric resistance (volume resistivity) was 510 μΩ · cm.

Example 4 A treatment was carried out in the same manner as in Example 1 except that the firing time during graphitization was 120 seconds, which was the same as in Comparative Example 1, and the tension during graphitization was 1000 g.

The graphite fiber thus obtained had a strand strength of 380 kg / mm ² and a tensile modulus of 7
It was 8 ton / mm ² . Also electrical resistance (volume resistivity)
Was 48 μΩ · cm.

By increasing the tension during firing,
The tensile strength and tensile modulus of the obtained graphite fiber increased obviously.

[0058]

As described above, in the method for producing carbon fiber of the present invention, the steps prior to the continuous pre-carbonization and the steps after the continuous carbonization are separated so that the tensile strength and the tensile elasticity during the carbonization or graphitization treatment are It is possible to perform stretching treatment to improve the rate, and to increase the carbonization degree or graphitization degree by low temperature treatment by increasing the residence time in the carbonization furnace or graphitization furnace, so that high tensile strength, high Carbon fibers having a tensile modulus and high thermal conductivity can be easily obtained, and the cost of the carbonization step can be significantly reduced.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an infusible furnace and a preliminary carbonization furnace of a manufacturing apparatus for carrying out a method for manufacturing a pitch-based carbon fiber according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a graphitization furnace of the same manufacturing apparatus.

[Explanation of symbols]

 10 Infusibilizing furnace 12 Tensioning means 30 Preliminary carbonization furnace 50 Graphitizing furnace 52 Tensioning means

Claims (1)

[Claims] 1. A method for producing a pitch-based carbon fiber, which comprises continuously infusibilizing pitch fibers under tension, continuously pre-carbonizing them, continuously carbonizing them, and, if necessary, further graphitizing them, prior to continuous pre-carbonization. And a step of continuous carbonization and subsequent steps are separated from each other.