JPS63145420A - Heat treatment of pitch carbon yarn - Google Patents

Abstract

PURPOSE:To efficiently obtain pitch carbon yarn without causing end breakage, crimping of yarn, etc., by winding pitch yarn round a heat-resistant bobbin having electrical conductivity, carbonizing or graphitizing. CONSTITUTION:Pitch yarn is wound round a heat-resistant bobbin (e.g. ceramic bobbin of silicon carbide type, etc.) having electrical conductivity, made infusible under heating, electric current is sent to the bobbin and the carbon yarn is carbonized or graphitized to give pitch carbon yarn.

Description

[Detailed Description of the Invention] [Industrial Application] The present invention relates to a method for heat treatment of pitch-based carbon fibers, and particularly to an infusible treatment step and a carbonization or graphitization step in producing pitch-based carbon fibers. The present invention relates to a simplified heat treatment method that has been improved and can produce pitch-based carbon fibers with excellent performance without causing yarn breakage or the like.

[Prior Art] Since carbon fiber has characteristics such as low volume, high strength, and high modulus of elasticity, it is being considered to manufacture it using various raw materials. Raw materials that have been used so far include rayon, polyacrylonitrile (PAN), lignin, and various pitches such as coal-based and petroleum-based pitches, and various manufacturing methods have been devised depending on the characteristics of the raw materials. Among these, the ones that have reached the point of being commercially available are mainly rayon-based carbon 1a fiber and PAN-based carbon 1am, especially in Japan.
AN-based carbon ia fibers are the mainstream and are widely used mainly in the field of reinforcing materials for composite materials. However, P A, N
Because the raw material for carbon fiber, PAN, is expensive, the carbon fiber is also extremely expensive, which is one of the factors that hinders its widespread use.
It is one. Also, in terms of the property of high elastic modulus (40
~50) It is said that g/mm' is the limit for xlO', and the current situation is that it has reached a plateau.

On the other hand, pitch-based carbon fiber, which is made from pitches, has high expectations for its low cost due to its low raw material cost, and also has a modulus of elasticity of 50×1.
There are hopes that it will be possible to spell out 0' Kg/mm.However, when pitches are used as raw materials, various problems remain in the manufacturing process, and practical application is delayed. The conventional manufacturing technology will be explained below.

The first conventional method is a method in which pitch is melt-spun, wound onto a bobbin, and then unwound to form a fiber bundle, which is then infusible and carbonized.
In this method, the spun yarn is not wound onto a bobbin, but is dropped onto a metal belt conveyor or into a container, stacked at random, and transported in that state into a heating furnace to be infusible and carbonized. However, pitch-based fibers as spun are extremely weak and require great care in handling until they are carbonized to achieve high strength.

In addition, in order to achieve the goal of lowering the price of carbon fiber, there is a need to increase the efficiency of use of equipment, especially heating furnaces, and the above-mentioned first and second conventional methods do not fully satisfy these demands. It's not like I'm getting it. For example, in the first conventional method, the pitch fibers are unwound from the bobbin, bundled, and run while infusible and carbonized, so the furnace length, that is, the furnace volume, becomes extremely large, and the volumetric efficiency of the furnace body decreases. The downside is that it has no choice but to be low. In other words, the infusibility process is a process for converting pitch fibers, which are originally thermoplastic, into thermosetting fibers by oxidizing them from the surface.
This is done by heating at 50 to 350°C for about an hour, so let's say you start at room temperature and raise it to 10°C.
Assuming that the temperature is raised at a rate of 1/min to 300°C, and then the infusibility treatment is performed for 1 hour (production fi: 10 to 8
7 hours), and with this conventional method, the straight line distance is approximately 133 m.
(However, single fiber diameter: 10 μm, density 1.2 g/cm', fiber bundle: 12 x 105).

Therefore, it has been considered to prevent the decrease in volumetric efficiency by making the fiber bundle reciprocate in the furnace, but there is a risk that increasing the number of U-turns for reciprocating will increase the number of yarn breakages. This not only leads to contamination inside the furnace, but also may lead to operational shutdown. Moreover, in the first method, the pitch fa
There is a drawback that thread breakage is likely to occur during the process of unwinding the 1ffl from the bobbin, and if the U-turn method as described above is adopted, the internal structure of the furnace will become complicated, resulting in high equipment and maintenance costs. Furthermore, it does not significantly improve the volumetric efficiency of the furnace body, nor can it significantly contribute to lowering production costs. A heating medium held between fibers in the infusibility process (
This is not a preferable method since air (generally air) may be brought into the next carbonization step and cause trouble.

On the other hand, the second conventional method is extremely advantageous in that there is less risk of yarn breakage, but since the fibers shrink unevenly during the carbonization process, causing wrinkles in the fibers, the product carbon The properties of the fibers were not as expected;
PAN-based carbon fibers cannot be rotated, and although this method has a higher volumetric efficiency of the furnace body than the first conventional method,
This cannot be considered sufficient and productivity is still low. Incidentally, troubles caused by the heating medium brought in from the infusibility process also occur in the final process.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a method for producing pitch-based carbon fibers, in particular to infusible spun fibers. By solving the problem of yarn breakage that occurs in each process of carbonization, carbonization, and graphitization, and by making it possible to perform the treatment without causing the fiber to unravel, the performance of carbon fiber can be improved, and furthermore, it can be easily heat treated. The present invention aims to provide a heat treatment method that can also improve the volumetric efficiency of the furnace body used.

[Means for Solving the Problems] The structure of the present invention that has achieved the above object is to wind pitch-based carbon fiber around a conductive heat-resistant bobbin and heat it in that state to make it infusible. After that, the bobbin is directly energized to carbonize or graphitize it.

[Function] The greatest feature of the present invention is that the spun yarn wound around the bobbin is made infusible and carbonized or graphitized as it is.
By adopting such a configuration, the following effects can be obtained.

Thread breakage when rewinding to 0 is suppressed (there is no need to worry about thread breakage when rewinding after carbonization).

- Since the bobbin is supported from the inside, the fibers do not shrink and become loose, resulting in carbon fibers with high properties.

■Pitch fibers are tightly wound on a bobbin, resulting in a small volume, which improves handling as an independent solid and allows for processing in aggregation, increasing the volumetric efficiency of the furnace body. Much improved.

(2) Since the bobbin used in the present invention is cylindrical and the heating element is the cylindrical bobbin itself, the pitch fibers are heated from within the bobbin, and the heating efficiency is also very high.

The present invention can be easily carried out by setting the aforementioned bobbin in place of the heating element in an electric furnace using a conventional cylindrical heating element. In this case, it is preferable to provide a slit or the like in the bobbin in order to match the electrical resistance with the heating element.

As is clear from the above description, the material of the bobbin is not particularly limited as long as it has electrical conductivity and appropriate resistance heating properties, but it is preferably one that has heat resistance of 900° C. or higher. This is because the carbonization treatment of the present invention is 850%
This is because it takes into consideration that the carbonization process is carried out at a temperature of 0.degree. Note that the carbonization temperature is 850℃
If it is less than that, the progress of carbonization will be insufficient and the desired properties as a pitch-based carbon fiber will not be obtained.

The most common material for the cylindrical bobbin used in the present invention is carbon fiber or graphite, but other materials such as ceramics such as silicon carbide, which have appropriate conductivity and appropriate electrical resistance, may also be used. Any heat-resistant material may be used as long as it can be heated with electricity. Additionally, it is recommended to provide slits, round holes, etc. in this bobbin as mentioned above, but since the purpose of this is to adjust the electrical resistance value as a heating element, it will not adversely affect shape retention. There are no limitations on the shape, direction, size, number, etc. However, in order to increase the heating efficiency by making sufficient contact between the inner surface of the pitch fiber wrapping and the heating medium, it is necessary to wrap the pitch fiber around the entire surface of the bobbin. It is desirable that the inner surface has an area ratio of 20% or more, and from the viewpoint of not adversely affecting the bobbin strength, it should be suppressed to 80% or less. Regarding the melt spinning conditions, pitch fiber thickness, infusibility treatment conditions, carbonization treatment conditions, etc., conventional methods and methods to be developed in the future may be followed, and there are no particular limitations in the present invention. . Further, as raw materials for pitch fibers, resinous pitch, coal tar pitch, petroleum pitch, etc. are used.

[Example] Example 1 Tetrahydroquinoline 100 was added to commercially available coal-based medium pitch.
Parts by weight were added, and the mixture was incubated at 450°C for 20 minutes. The resulting pitch was heated at 460 °C under a reduced pressure of 10 mm) Ig for 20
A spinning pitch with a softening point of 280t was obtained by processing for a minute. This spinning pitch was spun at 360'e, and a pitch fiber was obtained by winding it onto a cylindrical bobbin made of commercially available isotropic graphite and having an inner diameter of 107 mm, an outer diameter of 110 mm, and a length of 250 mm. This bobbin was provided with 34 slits having a length of 210 mm and a width of 5 cm at approximately equal intervals along the axial direction.The weight of the zero-wound pitch fiber was 210 g. The pitch fibers wound around a bobbin were fed as they were into an infusibility furnace to be infusible. The infusibility conditions are a heating rate of 10°C.
/win, 300t: for 1 hour. The obtained infusible fibers were wound around a bobbin and the bobbin was energized, and the bobbin was heated at 1900°C at a boundary temperature rate of 1°'e/ll1in in an N2 atmosphere.
The carbon fibers were obtained by holding for a minute. The mechanical properties of this carbon fiber were a tensile strength of 160 to 180 g/am and a tensile modulus of (15 to 17) x 103 kg/am.

In addition, the obtained carbon la fibers have a surface and a 2II
The fibers were completely continuous IA fibers, except for the fiber breakage at ivJ locations in the layer below Tl.

Example 2 The spinning pitch obtained in exactly the same manner as in Example 1 was melt-spun into a silicon carbide-based cylindrical ceramic bobbin (inner diameter 107 ma+, outer diameter 115 mm, length 250 mm).
A pitch fiber was obtained by winding. The ceramic bobbin used was provided with 150 holes with a diameter of 10 m+o. The weight of the wound pitch fiber was 195 g. This pitch fiber was fed into an infusibility furnace while being wound around a bobbin, and was held at 300° C. for 1 hour at a temperature increase rate of 10° C./win to infusible. Next, it is sent to a carbonization furnace in this state, and N
Carbon fibers were obtained by holding the carbon fibers at a heating rate of 10° C./win% of 1300° C. for 5 minutes under two atmospheres. When the mechanical strength of this carbon fiber was measured, the tensile strength was 230 to 250 g/m.
m', tensile modulus is (24-25) x 10'' g/mm
The fibers obtained had only two breaks on the surface, and the rest were completely continuous U fibers.

Comparative Example 1 Spun pitch obtained in exactly the same manner as in Example 1 was wound into a vinyl chloride cylindrical bobbin (inner diameter 107 mm, outer diameter 110 ma+, length 250 fflI11) by melt spinning to obtain pitch fibers. Cut this along the axial direction of the bobbin,
190 g of pitch fiber bundles having a length of about 350 mm (outer circumference of the bobbin) were obtained. This was sent to an infusibility furnace and Example 1
It was made infusible under exactly the same conditions. As a result, a part of the taii was disturbed and blown away by the air flow inside the infusibility furnace. This infusible fiber was placed in a carbonization furnace and held at 1300°C for 5 minutes at a temperature increase rate of 10°C/min under N2 atmosphere to obtain carbon fiber. When the mechanical strength of this carbon fiber was measured, the tensile strength was 150 to 180 g/mm2, and the tensile modulus was (18 to 20) x 10' g/mm. was clearly inferior to that of In addition, wrinkles were observed in the obtained carbon fiber.

[Effects of the Invention] The present invention is configured as described above, and its effects are summarized as follows.

(2) Since there is no unwinding after spinning and winding, there is no fear of yarn breakage, and the operation is extremely simplified.

- No more sagging due to fiber shrinkage during heat treatment, and the physical properties of carbon fiber products are further improved.

■Since this method handles the pitch fibers while still being wound around the bobbin, it is easy to handle, and the heat treatment equipment can also be downsized, greatly improving the volumetric efficiency of the furnace body.

■High thermal efficiency as the bobbin itself is a heating element.

Claims (1)

[Claims] A pitch-based carbon fiber characterized in that the pitch-based carbon fiber is wound around a conductive heat-resistant bobbin, heated as it is to make it infusible, and then carbonized or graphitized by directly applying electricity to the bobbin. heat treatment method.