JPS6245725A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To carry out the heating of fragile pitch fiber, rapidl and uniformly in high efficiency, by the combined action of the heat-insulating vessel to retain the heat in the vessel and containing said pitch fiber used as a raw material of a carbon fiber and the microwave-reflecting enclosure of the vessel. CONSTITUTION:A fragile coal-based pitch fiber is heated and carbonized with microwave radiation in an insert atmosphere. The vessel 31 holding said pitch fiber is made of a heat-insulating refractory material having microwave- transmissibility and gas permeability. The vessel is placed in enclosures 12-16 made of microwave-reflecting material. The microwave is reflected by the inner surface of the enclosure to suppress the dissipation of generated heat.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for industrially producing coal-based pitch fibers from raw material fibers subjected to hand-dancing treatment by microwave irradiation.

<Prior art> Conventionally, in the production of pitch-based carbon fibers, fibers made infusible by low-temperature oxidation are heated to 1000 to 150% in an inert atmosphere.
Carbonization is carried out at a temperature of 00°C.

In this case, since the strength of the infusible fibers before carbonization is low, the method described in Japanese Patent Publication No. 47-24786, in which synthetic fibers are used as a pivot body and subjected to microwave irradiation while being stretched, cannot be applied. Therefore, in the production of pitch-based carbon, the fiber bundles are suspended, stacked on a conveyor, or housed in a container, and are heated by 18-irradiation heat transfer from an electric heating element or by , contact with hot inert gases:

Separately, as a method for producing pitch-based carbon fiber, JP-A-53
There is one described in JP-147822. This document describes the method of irradiating fibers that have been subjected to low-temperature oxidation treatment with microwaves by placing them in an inert refractory material support made of silicon tubes, but there is a method for producing them in large quantities industrially. is not shown.

<Problems to be Solved by the Invention> When heating means that do not use microwaves in the conventional method for manufacturing pitch-based carbon fibers are used, radiation heat transfer is performed using an external 77 I] heating method, so internal heating within the fiber assembly is used. Since we are heating something that contains an air layer, the heat transfer rate is low, and it is important to heat the whole thing evenly.
There are problems such as the heating time required because the temperature increase rate is limited by the heat transfer rate, and when contact with high temperature inert gas, a high temperature heat exchanger or circulating gas blower is required. However, not only is the cost high, but there are also restrictions on the heating temperature, and in practical terms, there are problems such as carbonization being difficult at temperatures of 800''C or higher.

In addition, the tensile strength of pitch-based carbon fiber is
It is well known that the temperature increases with the processing temperature up to about 00°C, and it is clearly disadvantageous that the processing temperature is limited to a low temperature.

Further, in the conventional manufacturing method of pitch-based carbon fiber using microwaves, there is a problem in that it cannot be efficiently manufactured in large quantities.

Means for Solving the Problems> The present invention uses microwaves to uniformly and quickly carbonize brittle pitch-based raw material fibers, thereby making it possible to efficiently produce large quantities of high-quality carbon fibers. The purpose is to provide a method.

The means of the present invention provides a method for producing carbon fibers, in which a group of raw material fibers obtained by non-emitting treatment of coal-based pitch fibers is irradiated with microwaves in an inert atmosphere to carbonize due to the generation of internal heat. is placed in a container with ventilation holes made of a material that transmits microwaves and has fireproof insulation properties, and the container is placed in an envelope made of a material that reflects microwaves, and an inert gas The method is characterized in that each time microwave is irradiated while aerating the raw material fibers in the container.

Effect〉 The microwaves irradiated to the raw material fibers inside the container pass through the container wall but are reflected on the inner surface of the envelope, so the repeated reflections cause the raw material fibers to be heated evenly and rapidly. Ru. The insulation of the container retains the generated heat within the container.
In other words, the 1'XI heat described above is extremely efficient because there is little heat dissipation. The best material for the container is one made of ceramic wool.

Embodiment An example of the carbon fiber manufacturing apparatus used is shown in FIGS. 1 to 4. This device is composed of a furnace body 1, a transport device 2, a microwave irradiation device 3, an inert gas distribution device 4, a temperature control device 5, and a cooling device 6.

As shown in FIGS. 1 to 4, the furnace body 1 is formed into a horizontally long rectangular tube shape having an inlet 10 at one end and an outlet 11 at a curved end, and the outer shell 12 is made of a material that reflects microwaves. It is made of heat-resistant steel plate. Inside the furnace body 1 is a partition wall 13
．． A jet zone 18, a second heating zone 20, a soaking zone 21, a cooling zone 22, and a jet zone 23 are formed, which are divided by 14, 15, 16, and 17.

Each of the partition walls 13 to 17 is made of the same heat-resistant steel plate as the outer shell 12, and has a through hole 13a for transporting the container 31, which will be described later.
~17a are provided. The outer shell 12 is divided into the above-mentioned zones, and the zones are connected to each other by interposing a partition wall between flanges that connect the zones. Entrance 1
o and the exit 11 are each provided with large sliding doors 24 and 25 made of steel plates that can be opened and closed. all heating zones 26,
That is, the inner surfaces of the furnace shell of the heating zone 19.20 and the soaking zone 21 and the inner surface of the cooling zone 22 are lined with ceramic fiber-based heat insulating material 27, which is a fireproof heat insulating material through which microwaves can pass. It is. Jet zone 18.
A number of nozzles each made of punched metal 28 are opened in the inside of the 23, and an inert gas such as nitrogen gas is supplied through the nozzles. It is designed to prevent air from entering. The entire furnace body 1 is mounted on a pedestal 30 via rollers 29.
The material is supported by a material that allows it to expand and contract due to heat.

The conveying device 2 conveys a container 31 containing raw materials and fibers from the inlet 10 to the outlet 11 within the furnace body 1, and is a belt conveyor mainly composed of a mesh belt 32 made of heat-resistant steel. The mesh belt 32 has a mesh size such that microwaves are not reflected, and has a mesh size of 7"-U 33.
34, a belt guide 35 inside the furnace, and a belt guide 36 outside the furnace. The in-furnace belt guide 35 is provided continuously along the entire length of the in-furnace, and in the jet zone 18.23, an outer shell (third
(see figure), and in the heating zone 26 and cooling zone 22, the outer shell 1 supports both end edges of the belt 32.
2, protruding inward from the inner surface of the
The interior of the furnace body 1 communicates vertically only between the guides 35 on both sides. Reference numeral 37 in FIG. 2 is a drive section for the mesh belt 32.

The container 31 is made of a microwave-transmissive fire-resistant material, such as ceramic wool, and is box-shaped with a width of 500 mm, a length of 1000 mm, and a height of 150 mm, with a bottom wall having a diameter of approximately 5 mm. It has many ventilation holes.

This container 31 has a lid 38, which is also made of the same material, has many similar ventilation holes, and further has a slit with a width of about l Q MlN for detecting the internal temperature. container 3
1 is placed on the belt 32 on the inlet 10 side, is conveyed within the furnace body 1 by the conveying device 2, and exits on the outlet 11 side.

The microwave irradiation device 3 has one end of microwave waveguides 39 and 40 opened from the upper and lower surfaces of each of the first heating/heating zone 19, the second heating zone 20, and the soaking zone 21. , the other is connected to a microwave generator. In addition,
An isolator is provided between each waveguide and the magnetron for the microwaves reflected within the furnace body 1 and returned to the furnace, and water is supplied into the isolator to be absorbed and discharged as heat. .

The inert gas flow a device 4 is connected to the first heating zone 19 in the furnace body 1.
, a nozzle 41 made of a tube having a large number of small holes arranged at the bottom of both sides of the second heating zone 20 and soaking zone 21, and an exhaust hole 42 provided at the top of each zone 19, 20, 21. , a damper 43 provided in the exhaust path, and a nozzle 4
1 and a pipe for supplying inert gas to the pipe. The total amount of inert gas is supplied from the nozzle 41,
By adjusting the damper 43, the internal pressure of the furnace body 1 is maintained at a positive pressure slightly higher than atmospheric pressure. In addition, the inert gas flows from the bottom to the top, but in the meantime, i
When the tg31 is on the mesh belt 32, most of the air passes through the vent holes in the container 31 and lid 38 due to the presence of the furnace pelt gas and lid 35.

The temperature control device 5 has a zone 19.20 as shown in FIG.
．． The fiber temperature is detected by a radiation type thermometer 44 installed in the ceiling of the container 21 and directed toward the raw material fiber inside through the M2S slit of the container 31, which is positioned on the mesh belt 32, and the fiber temperature is detected by another controller. It is designed to adjust the microwave output in the band. For example, the temperature control is such that the temperature is raised at about 700° Cvct in the first heating zone 19, the temperature is raised to a predetermined 1.300'C in the second heating zone 20, and 1300"C is maintained in the soaking zone. be.

The cooling device 6 is for cooling the heat-treated carbon fibers and then taking them out of the furnace, and has nozzles 41a1 and exhaust holes 42a1 at the bottom of both sides, similar to the inert gas distribution device 4 in the first heating zone 19, etc. It is composed of piping attached to the damper 43a1 and the nozzle 41a. However, since its purpose is cooling, a larger amount of inert gas can be passed through it than in the heating zone.

45 in FIG. 2 is a viewing window.

This carbon fiber manufacturing apparatus includes a container 3 from an inlet 10 of a furnace body 1.
When one vehicle's weight of fibers is stored in the furnace and the lid 38 is placed on the furnace, the processed carbon fibers come out from the outlet 11. The transport device 2 operates intermittently. The container 31 that is first sent into the furnace body stops in the first heating zone 19, and only the raw material fibers inside are heated by microwaves while being supplied with nitrogen gas.

The volume of nitrogen gas supplied is: ? It passes through the i31 and is discharged to the outside, displacing most of the air that was trapped between the raw material fibers at the initial stage of heating, and then continuing to circulate. The temperature of the raw material fiber is a predetermined temperature for a predetermined period of time, for example, 700°
C, and the container 31 is transported to the second heating zone 20.

Here too, it is heated by microwaves while being supplied with nitrogen gas, and the temperature of the raw material fiber reaches a predetermined treatment temperature, for example 130° C., in the same predetermined time t as above, and the container 31 is conveyed to the soaking zone 21. Here too, the container 31 is heated by microwaves while being supplied with nitrogen gas, and after the temperature of the raw fiber is maintained at the processing temperature of 1300° C. for the processing time, the container 31 is conveyed to the cooling zone 22. Here, a relatively large amount of nitrogen gas is supplied to cool the fibers in the container to about 300° C., and after a certain period of time has elapsed, the fibers are transported outside. The above is a description of the container 31 that is first sent into the furnace body 1, but the subsequent containers 31 are sequentially subjected to the same processing and then transported outside.

In the J-double system, inert gas is supplied and discharged for each zone, which is connected to the partition walls 13, 14, 15, .
16.17 is working effectively, and a favorable state is maintained by adjusting the inert gas supply. Thereby, the oxygen concentration in each zone can be controlled to be below the specified value. In addition, in the flow of inert gas, if the lower half of the furnace body is filled with
The behavior of the fibers passing through the air holes 1, 7, between the fibers, and reaching the upper space is due to the partitioning action of the guides 35. Therefore, when there is a gap between the containers that are successively fed into the furnace body 1, a protrusion extending along the bottom surface of the container 31 may be provided in the sense of the 1-lower section in the furnace body 1.

Further, the presence of the partition walls 13 to 17 effectively works to create a temperature increase pattern that defines the U & fiber temperature inside the container in each zone. That is, not only the rectifying action of the inert gas but also each zone 19, 20 .
Microwaves also have a rectifying effect so that the microwaves irradiated every 21 hours do not greatly affect the oil band.

An example using the above-mentioned apparatus will be shown below. The raw material fibers are coal-based pitch fibers that have been subjected to a heat treatment, and the fibers are made into tows with a thickness of 10 mm.
0 srs in a container 31 with a packing density of 5oKg/
It can be accommodated in about m3. A large number of such containers 31 are prepared and sequentially inserted into the IF 4. The obtained carbon fiber is
The strength and yield were unchanged compared to those produced by conventional radiant heating.

<Effects of the Invention> According to the present invention, uniform heating is efficiently performed at high speed due to the heat retention effect due to the heat insulation properties of the container that accommodates the group of fibers for one car and the microwave-reflecting envelope. Therefore, carbon fiber of constant quality can be provided at low cost and can be produced in large quantities.

Incidentally, according to the device used in the example, compared to the conventional radiation heating formula, the heating time can be shortened to I~4, and the temperature increase rate is 5°C/min with the conventional magnetic heater type. compared to 3
It was possible to heat from 0 to 45"C/min.

Furthermore, the temperature distribution at the stage of exiting the second auxiliary zone was within ±20'C.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional plan view showing the general configuration of the device used to carry out the present invention, and FIG. 2 is a vertical cross-section of the device shown in FIG. 1.
FIG. 3 is an enlarged cross-sectional view taken along line AA in FIG. 2, and FIG. 4 is an enlarged cross-sectional view taken along line B-B in FIG. 2. 12... Outer shell (envelope), 13.14.15.16.
...Division wall (envelope), 26...77I tropical zone, 31
... Container, 38... Lid, 39.4o... Microwave waveguide, 41... Nozzle (for inert gas), 42.
・Exhaust hole. Patent applicant Hiroshi Chikudo Co., Ltd. New Japan Radio Co., Ltd. Representative Tetsu Shimizu and 2 others Third mouth↓

Claims (1)

[Claims] (1) A method for producing carbon fiber in which a group of raw material fibers obtained by infusibility treatment of coal-based pitch fibers is irradiated with microwaves in an inert atmosphere and carbonized by the generation of internal heat,
The raw material fiber group is housed in a container having a ventilation hole and made of a material that transmits microwaves and has fire-resistant and heat-insulating properties,
The container is placed in an envelope made of a material that reflects microwaves, and the microwaves are irradiated while an inert gas is passed through the group of raw material fibers in the container. Production method.