JPH0320432B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing substantially 100% mesophase pitch and the pitch-based carbon fiber, and more specifically, a method for producing high-quality pitch through a simple process, and a method for producing high-quality pitch using a simple process, and a method for producing high-quality pitch using a simple process. The present invention relates to a method for producing carbon fiber with excellent elastic modulus.

It has been well known that composite materials with carbon fiber can be used to strengthen plastics, metals, etc. The carbon fibers used in this case are preferably those made from acrylonitrile fibers in terms of their performance, but this carbon fiber is expensive and has various limitations in its use.

Therefore, in recent years, various types of inexpensive carbon fibers using pitch as a raw material have been proposed. However, this pitch-based carbon fiber has a drawback in spinnability. On the other hand, pitch-based carbon fibers with improved spinnability do not have sufficient physical properties such as strength, and various proposals have been made to use pitch containing a meso phase in order to improve these properties. For example, there is a method of using pitch with a meso phase content of 40 to 90% obtained by heat treatment, and a method of using pitch of essentially 100% meso phase obtained by a similar heat treatment.

However, although the above method uses a mixture of mesophase pitch and isotropic pitch, there is a drawback that uniform fibers cannot be obtained because the two pitches are not compatible. In addition, if the entire pitch is changed to a mesophase as in the method described above, coking will occur partially and the pitch will no longer be usable as a fiber raw material, so it is necessary to set various processing conditions to suppress coking. This is a method that is extremely difficult to implement industrially. Therefore, as an improvement to the above method, after producing a product containing a predetermined proportion of mesophase pitches, the isotropic pitches are eluted using various solvents at temperatures below 300°C to separate the mesophase pitches. , a method using this has been proposed (Special Publications
No. 50-39633, JP-A-56-125210, etc.). However, since this improved method uses a solvent, the process is complicated, and there is also the problem of recovering and reusing the solvent, so it is not an energy-saving method. Moreover, the resulting pitch has a high softening point and has poor spinnability.

The object of the present invention is to provide a method for manufacturing pitch that eliminates the above-mentioned drawbacks, and a method for manufacturing carbon fiber using the obtained pitch.

That is, the present invention heat-treats pitches at a temperature of 350 to 450°C to obtain pitches containing 10 to 80% by weight of mesophase, and then heat-processes pitches containing mesophase at a temperature equal to or higher than the softening point of the pitches containing mesophase. A method for producing a substantially 100% mesophase pitch characterized by separating a substantially 100% mesophase pitch by centrifugation, and a substantially 100% mesophase pitch obtained by this method.
The present invention provides a method for producing pitch-based carbon fiber, which comprises spinning 100% mesophase pitch, subjecting it to infusibility treatment, and then firing it.

The pitches used in the present invention are not particularly limited, and include, for example, petroleum pitches derived from petroleum refining (asphalt, fluid catalytic cracking residue, etc.) or petrochemicals (naphtha cracking residue, etc.), coal tar, coal liquefied oil, etc. There are synthetic pitches obtained by polycondensation from coal-based pitches, naphthalene, aromatic compounds, etc.

The heat treatment of pitts is carried out at a temperature of 350 to 450°C, but the pressure conditions may be normal pressure, reduced pressure, or increased pressure. Further, this treatment can be performed under an inert gas atmosphere or in the presence of hydrogen gas. If the processing temperature is below 350°C, it will take an extremely long time to produce the mesophase-containing pitch, which is impractical, and if it is above 450°C, coke formation will occur, making it difficult to obtain the desired mesophase-containing pitch. is difficult.

The mesophase-containing pitch obtained by heat treatment is
The mesophase is contained in a proportion of 10 to 80% by weight, preferably 20 to 70% by weight, and the content can be adjusted by appropriately setting processing conditions.

The mesophase-containing pitch is then centrifuged at a temperature above the softening point of the mesophase-containing pitch, typically 250 DEG to 380 DEG C., to separate substantially 100% mesophase pitch from the mixed pitch. If the temperature exceeds the upper limit of 350°C, there is a risk that the pitch will deteriorate, so care should be taken. Note that the separated isotropic pitch may contain a small amount of mesophase, and this pitch can be returned and heated together with the raw material pitches to be converted into mesophase pitch.

The pitch obtained by the present invention has substantially 100% mesophase (optical anisotropy) and is of extremely good quality. Therefore, it is suitable for manufacturing high-strength carbon products such as carbon fiber. In addition, it has high uniformity and has a lower softening point than conventional essentially 100% mesophase pitches, resulting in good spinnability. on the other hand,
From a production standpoint, the process is simple, there is no risk of coke formation, and operation control is easy.Also, unlike conventional methods, it does not use solvents, so there is no need for equipment or power for solvent recovery and reuse. Without,
You can get high quality pitch. Another feature of the present invention is that the by-produced isotropic pitch can be reused.

In any case, the method for producing pitchi of the present invention is as follows:
A conventionally known method, that is, to obtain substantially 100% mesophase pitch from raw material pitch, the pitch system is changed to a mesophase, and the remaining isotropic pitch is distilled off by heating or eluted with a solvent. On the other hand, it was completed based on a completely opposite new concept of removing the mesophase pitch from the system and leaving the isotropic pitch within the system.

The second aspect of the present invention is a method for producing pitch-based carbon fiber from substantially 100% mesophase pitch obtained as described above.
% mesophase pitch. This spinning step is usually carried out by a melt spinning method in which pitch is extruded in a molten state through a nozzle or the like, and the operating temperature is generally desirably 10 to 40°C higher than the softening point of the raw pitch.

Next, the spun pitch (pitch fiber) is subjected to an infusible treatment. This treatment is carried out, for example, by heating the pitch fibers from room temperature to 300°C at a rate of 1 to 5°C/min.
This is done by raising the temperature over a period of time and holding it in air for about 0.5 to 1 hour.

After the infusibility treatment, the pitch fiber is heated to 900 to 1200°C at a rate of 2 to 10°C/minute and then held at that temperature for about 0 to 30 minutes to perform firing. This firing is preferably performed under a nitrogen gas atmosphere. This firing yields carbonized, high-performance carbon fibers.
If necessary, this carbon fiber can be graphitized by heat treatment at a high temperature of 1500° C. or higher to obtain carbon fiber with even better strength and elastic modulus.

As described above, according to the present invention, it is possible to effectively utilize residual oil and the like, and to add high value to inexpensive pitch.

Next, examples of the present invention will be shown.

Example 1 Distillation of fluidized catalytic cracking residue oil under reduced pressure (bottom temperature
380°C) to obtain a distillation residue pitch.

Next, the distillation residue pitch was heat-treated at 400° C. for 5.5 hours under a reduced pressure of 10 mmHg to obtain pitch with a yield of 9% by weight from the residue oil.
The softening point of this pitch is 250℃, and the quinoline insoluble content is 23
It contained approximately 30% mesophase by weight.

This mesophase-containing pitch was centrifuged using a centrifugal separator heated to 320° C. for a residence time of 20 minutes and a centrifugal force of 3000 G. Substantially 100% mesophase pitch was obtained from the lower part of the centrifuge tube. The softening point of the mesophase pitch obtained was 300°C.

The mesophase was measured by embedding the obtained pitch in a resin, polishing the cross section, and observing it under crossed Nicols.

Example 2 The substantially 100% mesophase pitch obtained in Example 1 was melt-spun at 318° C. through a spinneret with a diameter of 0.5 mm to continuously obtain pitch fibers with a uniform diameter.

Next, the temperature was raised to 300°C at a rate of 1°C/min in air, held at this temperature for 1 hour to perform infusibility treatment, and then heated at a rate of 5°C/min in a nitrogen gas atmosphere. After raising the temperature to 1000℃ at a rate of ., hold it at this temperature for 20 minutes, and then
A carbon fiber of 10.5μ was obtained.

The obtained carbon fiber had a tensile strength of 230 Kg/mm ² , a tensile modulus of 18 t/mm ² and an elongation of 1.3%.

Comparative Example 1 Spinning was carried out using the pitch of Example 1 containing about 30% mesophase, but uniform pitch fibers could not be obtained even when the spinning temperature was varied.

Comparative Example 2 The pitch of Example 1 containing about 30% meso phase was pulverized, the soluble matter was extracted and removed with boiling benzene, and the infusible matter was obtained by filtration. The infusible portion did not melt even when heated and could not be spun.

Comparative Example 3 The pitch of Example 1 containing about 30% mesophase was pulverized and then treated with hot quinoline to obtain an infusible fraction, which did not melt even when heated and could not be spun. Ta.

Claims (1)

[Claims] 1. Pitches are heat-treated at a temperature of 350 to 450°C.
A pitch containing 10-80% by weight of mesophase was obtained, and then
At a temperature above the softening point of the mesophase-containing pitch,
The mesophase-containing pitches were centrifuged to give a substantially 100%
1. A method for producing a substantially 100% mesophase pitch, characterized by separating a % mesophase pitch. 2. Heat-treat the pituti at a temperature of 350 to 400℃.
A pitch containing 10-80% by weight of mesophase was obtained, and then
At a temperature above the softening point of the mesophase-containing pitch,
The mesophase-containing pitches were centrifuged to give a substantially 100%
% mesophase pitch was separated and obtained substantially 100
1. A method for producing pitch-based carbon fiber, which comprises spinning % mesophase pitch, subjecting it to infusibility treatment, and then firing it.