JPH04119124A - Production of pitch-based carbon fiber and graphite fiber - Google Patents

Abstract

PURPOSE:To prevent fluffing and yarn breakage of fiber on the inside and outside of a carbonization furnace and obtain the subject fiber of high quality by forming the flow of an inert gas directing from the upstream to the downstream sides in a precarbonizing furnace for precarbonizing infusibilized fiber. CONSTITUTION:The flow of an inert gas from the upstream to the downstream sides is initially formed in the interior of a precarbonizing furnace 30. Infusibilized fiber prepared by infusibilizing carbonaceous pitch fiber is then continuously threaded through the inert gas atmosphere of the precarbonizing furnace at a prescribed temperature, heat-treated and precarbonized. The aforementioned fiber is carbonized and further, as necessary, graphitized to afford the objective fiber. Furthermore, the inert gas is preferably fed from gas feed ports (32b) to (32d) provided at plural places in the longitudinal direction, directing from the upstream to the downstream sides of the precarbonizing furnace 30, a gas feed port (32a) provided in an inlet part (30a) of the furnace and a gas feed port (32e) formed in an outlet part (30b) of the furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. The present invention relates to a method for producing pitch-based carbon fibers and graphite fibers produced from carbonaceous pitch, and particularly to methods for producing pitch-based carbon fibers and graphite fibers that are produced by infusible pitch fibers. The present invention relates to a manufacturing method characterized by a preliminary carbonization method that prevents.

In this specification, the term "carbon fiber" includes not only carbon fiber but also graphite fiber, unless otherwise specified.

Rayon-based and PAN-based carbon fibers, as well as pitch-based carbon fibers, have come to be widely used in various technical fields, especially for petroleum-based pitch, coal-based pitch, and aromatic hydrocarbons. Pitch-based carbon fibers manufactured from carbonaceous pitch such as pitch made from rayon-based and PAN-based carbon fibers have a higher carbonization yield and superior physical properties such as elastic modulus compared to rayon-based and PAN-based carbon fibers. Furthermore, it has attracted attention in recent years because it has the advantage of being able to be manufactured at low cost.

Currently, pitch-based carbon fibers are manufactured using the following methods: (1) Carbon pitch suitable for carbon fiber is prepared from petroleum pitch, coal pitch, pitch made from aromatic hydrocarbons, etc., and the carbon pitch is heated and melted. (2) heating the pitch fiber bundle to a temperature of 150 to 400° C. in an oxidizing atmosphere in an infusible furnace to infusible it; (3) Subsequently, the infusible fiber bundle obtained by the infusibility is heated in a pre-carbonization furnace at a maximum temperature of 50°C under an inert gas atmosphere.
(4) Next, the pre-carbonized fiber bundle is heated to a temperature of 3200°C or less in a carbonization furnace under an inert gas atmosphere to carbonize or graphitize it. Manufactured by .

In the above preliminary carbonization step, the infusible fibers undergo a significant weight loss (usually 10 to 30%) during the heating process, and a large amount of thermal decomposition products are contained in the inert gas atmosphere. As a result of this thermal decomposition, the decomposed gas containing oxygen-containing substances such as water vapor and tar-like substances are brought into the downstream region of the pre-carbonization furnace where the temperature is higher and react with the fibers, resulting in the quality of the carbon fibers that are the goal. decrease.

Therefore, it is considered necessary to keep the downstream area of the pre-carbonization furnace as clean as possible during pre-carbonization, and the flow of inert gas within the pre-carbonization furnace is basically from downstream to upstream of the furnace. It has been formed to flow (ie, in a countercurrent direction to the direction in which the fibers travel).

Formation of such an inert gas flow is also found in a method for manufacturing carbon fiber using polyacrylonitrile as a raw material (Japanese Patent Application Laid-open Nos. 57-25419 and 1983-1989).
115119 and JP-A-59-106519).

However, as mentioned above, in the method of flowing inert gas from downstream to upstream in the pre-carbonization furnace, the infusible fibers have a tensile strength of about 0.01 GPa, which is extremely weak. There were disadvantages such as tar-like substances adhering to the fibers in the low-temperature part of the furnace, especially near the entrance, resulting in frequent thread breakage and fuzzing, and the infusible fiber bundle itself being cut during threading.

In addition, as the infusible fiber bundles with tar-like substances attached to them in the low-temperature part of the furnace progress to the downstream region of the furnace where the temperature is higher, the fibers become fused and stuck to each other, which causes thread breakage of the pre-carbonized fibers, Fuzzing has been induced, and yarn breakage has also been induced in downstream processes after the preliminary carbonization step due to damage caused by fusion and agglutination during contact with guide rollers and the like.

Furthermore, it has been found that when a composite material is manufactured using carbon fibers manufactured from these fibers, problems such as deterioration of the physical properties of the composite material occur.

Therefore, it is an object of the present invention to improve the method for pre-carbonizing an infusible fiber bundle obtained by infusible pitch fiber bundles, and to prevent tar-like substances generated by heating the infusible fibers in a pre-carbonization furnace into fibers. It prevents the fibers from adhering and fusing together, and prevents fiber breakage and fluffing in the pre-carbonization furnace, as well as fiber breakage inside and outside the carbonization furnace during the subsequent carbonization process, resulting in high quality. An object of the present invention is to provide a method for producing pitch-based carbon fibers and graphite fibers, which makes it possible to obtain carbon fibers and graphite fibers.

The above objects are achieved by the method for producing pitch-based carbon fibers and graphite fibers according to the present invention. In summary, the present invention provides a pre-carbonization furnace at a predetermined temperature maintained in an inert gas atmosphere.
A pitch-based carbon fiber obtained by infusible fiber obtained by infusible carbonaceous pitch fiber, which is pre-carbonized by continuous threading and heat treatment, then carbonized, and optionally graphitized. and a method for producing pitch-based carbon fibers and graphite fibers, characterized in that a flow of inert gas is formed in the preliminary carbonization furnace from upstream to downstream.

In the present invention, by supplying inert gas from gas supply ports provided at multiple locations in the longitudinal direction from upstream to downstream of the preliminary carbonization furnace and at the inlet and outlet of the furnace,
Preferably, the inert gas atmosphere is formed within the furnace.

According to a preferred aspect of the present invention, the amount of inert gas supplied from the gas supply port into the pre-carbonization furnace is set to be smaller at the outlet than at each of the gas supply ports at a plurality of locations in the longitudinal direction of the furnace. A flow of the inert gas is formed in the furnace by making the gas supply port at the inlet section larger and the gas supply port at the inlet section larger than the gas supply port at the outlet section. According to another preferred aspect of the present invention, the slit opening at the outlet of the pre-carbonization furnace is made larger than the slit opening at the inlet. A gas discharge port is provided at a position opposite to the gas supply ports at multiple locations in the longitudinal direction and at a position closer to the downstream side,
By partially discharging the inert gas in the furnace through the gas outlet, a flow of inert gas is formed in the respective furnace.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory diagram showing one embodiment of the method for producing carbon fibers of the present invention.

In FIG. 1, 30 is a pre-carbonization furnace, and the present invention pre-carbonizes the infusible fiber bundle F by forming an inert gas flow 36 in a predetermined direction in the pre-carbonization furnace 30. It is characterized by improvements.

The pitch fiber bundle obtained by spinning and doubling pitch fibers is infusible in an infusible furnace (not shown), and the infusible fiber bundle F obtained by this infusibility is continuously passed through a preliminary carbonization furnace 30. The carbon fiber is preliminarily carbonized, then carbonized in a carbonization furnace (not shown), and graphitized if necessary to obtain carbon fiber.

The preliminary carbonization furnace 30 includes a pair of upper and lower heaters 31.
For example, along the longitudinal direction from upstream to downstream within
The temperature in the group 30 is maintained so as to increase stepwise from upstream to downstream, for example, to 450°C, 600°C, and 1100°C.

Further, gas supply ports 32b, 32c, and 32d are provided in the lower part of the preliminary carbonization furnace 30 along the longitudinal direction from upstream to downstream at the positions of the lower heaters 31, and the inside of the furnace 30 is filled with an inert gas atmosphere. In order to
Inert gas is supplied from Also, the inlet part 3 of the furnace 30
Gas supply ports 32a and 3 are also provided at the lower part of the outlet part 30b and the outlet part 30b.
2e are provided, and gas supply ports 32a and 3 are provided to prevent outside air from leaking from the inlet portion 30a and the outlet portion 30b.
An air curtain is formed at the inlet part 30a and the outlet part 30b by the inert gas supplied from the inert gas 2e, and the slit 3 provided at the end of the inlet part 30a and the outlet part 30b
The opening degrees of 4a and 34b are adjusted to a predetermined amount. As a result, the inside of the casing 30 is maintained in an inert gas atmosphere.

Now, in the present invention, the infusible fiber bundle F in the preliminary carbonization furnace 30 is
In order to prevent tar-like substances generated by the heat treatment of the fibers constituting the fiber bundle from flowing toward the inlet portion 30a, an inert gas flow 36 is directed from upstream to downstream in the same direction as the threading direction of the fiber bundle F. It is formed in a parallel flow mode.

In this embodiment, gas supply ports 328 to 32 into class 30
The amount of inert gas supplied from e is set to be smaller than the amount of inert gas supplied at the gas supply port 32e of the outlet portion 30b than the amount of supply Ib to Id at each of the gas supply ports 32b to 32d at multiple locations in the longitudinal direction of the furnace 30. Ie is made larger, and the inlet portion 30 is larger than the supply amount e.
By further increasing the supply amount Ia at the gas supply port 32a, that is, by setting Ia>Ie>Ib, Ic, and Id, the above-mentioned inert gas flow 36 was formed in the group 30.

Generally, if the gas supply amount Ia at the inlet portion 30a is made sufficiently larger than each of the gas supply amounts Ib to Ie at other locations, the inert gas flow 36 from upstream to downstream can be created in the group 30. Although it is possible to prevent the leakage of outside air from the inlet portion 30a by forming the hole, it is not possible to reliably prevent the leakage of outside air from the outlet portion 30b. Therefore, in order to reliably prevent outside air from leaking from the outlet portion 30b, as described above, the gas supply amount Ie at the outlet portion 30b is
is assumed to be the second largest after the gas supply amount Ia at the inlet portion 30a.

Gas supply amount Ib other than the inlet part 30a and the outlet part 30b,
As long as Ia>Ie>Ib, Ic, Id, the magnitude of Ic, Id can be selected as appropriate based on the gas supply amount. From the viewpoint of making the inert gas flow 36 more orderly, it is preferable that Ib>Ic>Id and the upstream side be larger.

These gas supply amounts Ia, Ib, Ic, Id, and Ie are:
Slits 34a, 34 in the inlet section 30a and outlet section 30b
Ia>Ie, taking into account the opening degree of b, whether or not gas is discharged from there when gas discharge ports 35a and 35e are provided at the inlet part 30a and the outlet part 30b, and the damper opening degree.
>Ib, IC1Id may be specifically determined as the amount necessary to form an inert gas flow 36 from upstream to downstream within class 30.

Flow 36 of inert gas from upstream to downstream within class 30
To confirm that is formed, the gas generated from the fibers of the infusible fiber bundle F in class 30 turns into white smoke, so
This can be confirmed by providing a location in the furnace 30 where the inside can be observed and visually observing the flow of the white smoke. Or the slits 34a, 3 of the inlet part 30a and the outlet part 30b
It is also possible to measure by installing a current meter such as an anemometer at the location 4b.

In this embodiment, as described above, the inert gas supply amounts Ia to Ire into the preliminary carbonization furnace 30 are set as Ia>Ie>
By setting I b, I c, and I d, a parallel inert gas flow 36 from upstream to downstream is formed within class 30, so that infusible fiber bundle F is configured within class 30. The tar-like substances generated by the heating of the fibers are carried away downstream by the inert gas flow 36, and as in the past, the tar-like substances adhere to the fibers toward the upstream region of the furnace 30 where the temperature is lower. Therefore, there is no breakage of the fragile infusible fibers, and there is no melting and sticking between the fibers. Although it may decompose in the downstream region of the furnace 30 and solidify and adhere to the fibers, the tar-like substance itself is not attached, so the fibers will not fuse together.
Just a weak adhesion state does not mean that the fibers are strongly bonded to each other. Surprisingly, when the infusible fiber bundle F is pre-carbonized using the method of the present invention, the carbon fibers obtained from it It was found that there was almost no decrease in physical properties such as tensile strength due to the reaction between the cracked gas and the fibers.

Therefore, it is possible to prevent thread breakage of the infusible fibers, which was caused by the fusion and aggregation of fibers in the pre-carbonization furnace 30, and damage caused by contact with guide rollers, etc. during the subsequent carbonization process inside and outside the carbonization furnace. This also prevents the occurrence of yarn breakage, making it possible to produce carbon fibers that exhibit sufficient strength, etc. with less yarn breakage.

In the embodiment described above, the gas supply ports 32b to 32d are provided at multiple locations in the longitudinal direction at the bottom of the preliminary carbonization furnace 30, and the gas supply ports 3 are provided at the bottom of the inlet section 30a and the outlet section 30b.
Although the inert gas flow 36 from upstream to downstream is formed within the group 30 by controlling the amount of inert gas supplied from 2a and 32e, the present invention is not limited thereto.

That is, the opening degree of the slit 34b of the outlet portion 30b is
The opening degree of the slit 34a of 0a is larger than that of the exit part 3.
By increasing the amount of inert gas discharged from 0b, the flow of inert gas from upstream to downstream within class 3o is increased.
6 may be formed.

In this case, the inert gas supply amounts Ia to Id do not necessarily have to satisfy Ia>Ie>Ib, Ic, and Id, and may be the same.

In the present invention, as shown in FIG.
Gas exhaust ports 35b to 35d are located downstream from this.
These gas exhaust ports 32b to 35d are provided with
By partially discharging the inert gas in the
An inert gas flow 36 may be formed within the chamber from upstream to downstream.

The amount of inert gas extracted from the gas discharge ports 35b to 35d of the furnace 30 is larger on the downstream side of the furnace.

Further, gas exhaust ports 35a and 35e may be provided at the inlet portion 30a and the outlet portion 30b, and the inert gas may be extracted from there. In this case, the inlet portion 30a and the outlet portion 3
This is preferable because an air curtain is well formed at 0b, and leakage of outside air can be prevented and inert gas can be discharged at the same time.

Discharge ports 35a, 35b, 35c, 35d
, 35e may be determined by changing the suction amount of these gas discharge pumps, or by providing a damper at the discharge port and changing the opening degree of the damper.

In all of the above, when performing preliminary carbonization of the infusible fiber bundle F in the preliminary carbonization furnace 30 in an inert gas atmosphere,
A flow of inert gas 36 from upstream to downstream within the furnace 30
Recently, the applicant filed a patent application for
As proposed in No. 137233, it is also possible to carry out preliminary carbonization by making the inert gas contain oxygen in a trace amount of 30,000 ppm or less.

The raw material carbonaceous pitch used in the present invention is made from known raw materials such as various petroleum-based heavy oils, pyrolysis tar, catalytic cracking tar, heavy oil and tar obtained by carbonization of coal, etc. Mesophase pitch (optically anisotropic pitch) obtained by decomposition polycondensation, mesophase pitch made from aromatic hydrocarbons, pitch or optical pitch containing an optically anisotropic phase and an optically isotropic phase It may be an isotropic pitch. For example, when producing ultrahigh-strength, high-performance carbon fiber from mesoface pitch obtained by pyrolysis polycondensation, the mesoface content is 70 to 100%.
% membrane pitch is preferred, especially substantially 10
Most preferred is a memface pitch containing 0% memface.

Next, the method for manufacturing carbon fiber according to the present invention will be further explained based on specific examples.

K plate j A melt spinning machine with a 500-hole spinneret (nozzle Hole size: 0.3 mm in diameter) and heated to 200 mmH at 355°C.
The fibers were extruded and spun at a nitrogen gas pressure of 1.5 g.

The 500 spun filaments are roughly converged by an air sucker and guided to an oiling roller, and a sizing agent is supplied at a ratio of approximately 0.2% by weight to the yarn to converge them to form a pitch fiber bundle consisting of 500 filaments. did.

Next, the six bobbins wound with pitch fiber bundles are unwound, and the yarns are doubled using an oiling roller while applying a heat-resistant doubling agent to form a pitch fiber bundle consisting of 3000 filaments. Wind it onto a bobbin.

At the time of yarn doubling, 400st methylphenylpolysiloxane (phenyl group content: 45 mol %) was used at 25° C. as an oil agent. The amount applied was 0.5% based on the yarn.

While unwinding the thus obtained bobbin-wound pitch fiber bundle from the bobbin, the furnace entrance temperature was 180°C, and the maximum temperature was 2.
Oxygen-rich atmosphere with a temperature gradient of 95°C (oxygen/nitrogen = 6
0/40) was continuously introduced in a linear manner into a continuous infusibility furnace.

The temperature increase rate was 6° C./min, and the infusibility time was 19 minutes. The tension applied to the fiber bundle is 0.0 per filament.
07g (20g for a fiber bundle of 3000 filaments)
)Met. The oxygen concentration of the infusible fibers was 90.5% by weight.

The thus obtained infusible fiber bundle F was continuously fed to the preliminary carbonization furnace 30.

According to this embodiment, the preliminary carbonization furnace 30 is heated at 400° C. and 60° C. from upstream to downstream by the heater 31.
The furnace 30 is heated and maintained so as to increase in stages from 0°C to 1100°C, and the gas supply ports 32b to 32d and the inlet section 30a at the bottom of the furnace 30, the gas supply port 32a at the bottom of the outlet section 30b,
Furnace 3 is supplied with nitrogen gas as an inert gas from 32e.
0 was maintained in an inert gas atmosphere.

In accordance with the invention, a flow of inert gas 3 is provided within the pre-carbonization furnace 30.
6 was formed in parallel flow from upstream to downstream, the infusible fiber bundle F was passed through the furnace 30, and pre-carbonized by heating under an inert gas atmosphere.

The inert gas flow 36 within the furnace 30 is connected to the gas supply port 32b.
~32d and the inert gas supply amount Ib-Id from the gas supply ports 32a and 32e of the inlet part 30a and outlet part 30b, Ia, and Ie, Ia=200, Ib=15, Ic=6
, Id=3, Ie=30 (these are relative values), and Ia>Ie>Ib, Ic, and Id were formed within the range of the conditions of the present invention.

During pre-carbonization, a tension of 0.007 g per 1 filament was applied to the infusible fiber bundle F. Pre-carbonization time was 5 minutes.

When the number of fluffs that were broken and fluffed during preliminary carbonization at the exit of the preliminary carbonization furnace 30 was visually measured, the number of fluffs was as follows.
The number of fiber bundles was extremely small at one per meter of fiber bundle.

Further, the pre-carbonized fiber bundle obtained by the above pre-carbonization was passed through a graphitization furnace at a temperature of 2500° C. in an argon gas atmosphere to graphitize and obtain graphite fibers.

When the number of fluffs on the fibers was visually measured at the exit of the graphitization furnace, two fluffs were observed per 1 m of the fiber bundle.

The obtained graphite fiber had a thread diameter of about 9.8 μm, a tensile strength of 3.6 GPa, and a tensile modulus of 705 GPa. The fusing degree of graphite fiber was 40%.

The degree of fusion and adhesion (%) was determined by cutting a fiber bundle consisting of 3000 filaments to a width of 3 mm, immersing it in ethanol, wiping it with air for 30 seconds, and then fusion and adhesion under a microscope at 20x magnification. By counting the total number of filaments (N), it was determined using the following formula.

Degree of fusion adhesion = (N/3000) x 100 (%) Man-hour 1 The conditions for the inert gas supply amount 1ayIe were set outside the scope of the present invention, Ia = 30, I b = 5, Ic = 10, Id = 20
, Ie=180 (the above relative values), the infusible fiber bundle F is pre-carbonized under the condition that an inert gas flow is formed in the furnace 30 in a counter-current manner from downstream to upstream. The number of fuzz was visually measured at the exit of the furnace 30. The number of fluffs per fiber bundle was as large as 50.

Further, the above-mentioned pre-carbonized fiber was threaded under the same conditions as in the example with the graphite tilting downward to obtain a graphite fiber. When the number of fluffs on the fibers was visually measured at the exit of the pre-carbonization furnace, a very large number of fluffs were observed, 80 per fiber bundle.

The graphite fibers obtained had a thread diameter of 9.8 μm and a tensile strength of 3.
．． 5 GPa, and the tensile modulus was 705 GPa. The degree of fusion adhesion of graphite fiber was 36%, which was slightly low.

As explained above, according to the manufacturing method of the present invention, inert gas is supplied from the gas supply ports at multiple locations in the longitudinal direction of the pre-carbonization furnace and from the gas supply ports at the inlet and outlet of the furnace. By controlling the gas supply amount, etc., a flow of inert gas is formed in the furnace in a parallel flow from upstream to downstream, and the infusible pitch fiber bundle is pre-carbonized. Therefore, it is possible to prevent tar-like substances generated by heating the fibers in the furnace from adhering to the fibers toward the upstream region of the furnace and causing the fibers to fuse and stick to each other. It is possible to prevent fiber bundles from breaking inside and outside the carbonization furnace, and to produce high-strength carbon fibers that exhibit sufficient strength.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the manufacturing method of the present invention. 0a 0b 32a~32e 34a, 34b 35a~35e Two preliminary carbonization furnace: Inlet part: Outlet part: Gas supply port: Slit: Gas discharge port: Fiber bundle subagent

Claims (1)

[Claims] 1) Infusible fibers obtained by infusible carbonaceous pitch fibers are continuously passed through a pre-carbonization furnace at a predetermined temperature maintained in an inert gas atmosphere and subjected to heat treatment. Pre-carbonized by
In the method for producing pitch-based carbon fibers and graphite fibers, which comprises carbonizing the fibers and graphitizing the fibers if necessary, a flow of inert gas is formed from upstream to downstream in the preliminary carbonization furnace. A method for producing pitch-based carbon fiber and graphite fiber. 2) By supplying inert gas from gas supply ports provided at multiple locations in the longitudinal direction from upstream to downstream of the preliminary carbonization furnace and at the inlet and outlet of the furnace, the 2. The method of claim 1, further comprising forming an inert gas atmosphere. 3) The amount of inert gas supplied from the gas supply port into the pre-carbonization furnace is set larger at the gas supply port at the outlet than at each of the gas supply ports at a plurality of locations in the longitudinal direction of the furnace; 3. The method according to claim 1, wherein the flow of the inert gas is formed in the furnace by making the gas supply port at the inlet part larger than the gas supply port at the outlet part. 4) The method according to claim 1 or 2, wherein the flow of the inert gas is formed in the furnace by making the slit opening at the outlet of the preliminary carbonization furnace larger than the slit opening at the inlet. 5) A gas exhaust port is provided at a position opposite to the gas supply ports at a plurality of locations in the longitudinal direction of the preliminary carbonization furnace and at a position closer to the downstream side thereof, and the gas inside the furnace is discharged through the gas exhaust port. 3. A method as claimed in claim 1 or 2, characterized in that the flow of inert gas is formed in the furnace by partially venting the inert gas.