JPS6121189A - Preparation of pitch for producing high elongation type carbon fiber - Google Patents

Abstract

PURPOSE:To obtain pitch for producing high elongation type carbon fiber having improved handleability, by bringing a pitch material before treatment with a hydrogen donor solvent and reduced pitch after the treatment into contact with an acid, polymerizing the pitch thermally while removing low-boiling substances. CONSTITUTION:A pitch material before it is treated with a hydrogen donor solvent such as tetrahydroquinone, etc. and/or reduced pitch after the treatment is brought into contact with an acid(preferable example; aqueous solution of organic carboxylic acid such as oxialic acid, etc., hydrochloric acid, nitric acid, sulfuric acid, etc.), and the pitch is thermally polymerized at 400-550 deg.C while removing low-boiling components, to give the aimed pitch. USE:Usable in a field of new cmposite material which was not suitable for existing carbon fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for preparing pitch for producing high elongation carbon fibers. More specifically, pitch-based carbon li, which has a high elongation comparable to that of PAN-based carbon fiber obtained from polyacrynitrile fiber,
The present invention relates to a method for industrially preparing pitch for producing fibers.

``Mei'' Self (Carbon!! Navy blue is being used in various fields because it has properties such as heat resistance, chemical resistance, and compression resistance that cannot be expected from organic fibers such as thermoplastic synthetic fibers.

Such carbon fibers are currently dominated by PAN-based carbon fibers made from polyacrylonitrile or pitch-based carbon fibers made from petroleum-based pitches.

By the way, carbon-11 fibers are known to have various mechanical properties, such as tensile strength and modulus, depending on their starting materials and manufacturing methods, but generally all carbon fibers have low elongation. High-performance grade carbon fibers, which have particularly excellent mechanical properties, have a problem in that they have particularly low I'J elongation.

In other words, pitch-based general-purpose grade carbon I! i-Navy blue has a strength of about 9/mA to 100 and an elongation of 2 to 2.5%, whereas pitch-based high-performance grade carbon fiber has a strength of about 2/mA.
Although the elongation is as high as 00 to 300 Kg/-, the elongation is usually 1% or less. On the other hand, PAN-based high-performance grade carbon fiber has recently been significantly improved and has a strength of 50ONg/
mtA, some with elongation reaching 2% have appeared,
It cannot be denied that the elongation is low.

In recent years, there has been increasing interest in the technology of producing high-performance grade carbon fibers using pitch as a raw material from an economic point of view, and Dormant Mesoface (Japanese Patent Application Laid-open No. 57-100186) and Burimesoface (Japanese Unexamined Patent Publication No. 1982-100186) and Brimesoface (1986-100186) have been developed as pitches for producing carbon fibers. New technologies such as JP-A-58-18421) are being developed, but the carbon obtained from these pitches! It is hard to say that navy blue is beyond the conventional range in terms of elongation. and,
Carbon I like this! The low elongation of carbon fiber leads to low impact resistance and difficulty in handling, narrowing the uses of carbon fiber. For this reason, the emergence of 111ft of high-performance grade carbon with high elongation is strongly desired.

An object of the present invention is to provide a method for preparing pitch capable of producing high performance grade carbon fibers having much higher elongation than conventional carbon 411It.

Structure of the Invention The inventors of the present invention have conducted extensive research to achieve the above object, and as a result, when preparing pitch for carbon fiber production, by adding special measures during pitch preparation, the inventors have unexpectedly achieved the above goal. From pitch, not only conventional pitch-based carbon fiber but also PA
It was discovered that a pitch-based carbon fiber having high elongation and excellent strength, which is not found in N-based carbon fibers, can be obtained, and based on this knowledge, the present invention was completed.

That is, the present invention processes a pitch-like substance obtained from coal or petroleum in a hydrogen-donating solvent to obtain reduced pitch, and then thermally polymerizes it while removing low-boiling components to obtain pitch for carbon II fiber production. The present invention is a method for preparing pitch for carbon fiber production, which comprises bringing the pitch-like substance and/or reduced pitch into contact with an acid.

The method of the present invention involves treating a pitch-like material (original pitch) obtained from coal or petroleum in a hydrogen-donating solvent to obtain reduced pitch, and then thermally polymerizing it while removing low-boiling components to produce carbon fiber. Applies to methods of preparing pitch. The method for preparing such a pitch is known in the art, for example, Japanese Patent Application Laid-open No. 58-18421 and Japanese Patent Application Laid-open No. 59-3.
It is described in detail in Publication No. 6726 and the like.

In this method, examples of the hydrogen-donating solvent used in preparing the reduced pitch include tetrahydroquinoline, hydrogenated anthuran oil, and tetoprine. The reduced pitch thus obtained forms developed mesophase by thermal polymerization while removing low boiling point components. In the thermal polymerization, as a method for removing low-boiling components, commonly used methods such as a reduced pressure method and an inert gas flow method are preferably used, and the thermal polymerization temperature is preferably 400 to 550°C.

In the method of the present invention, in step (1) of pitch preparation as described above, the pitch-like material before being treated in a hydrogen-donating solvent or the reduced pitch after being treated is brought into contact with an acid at least once.

Acids used for this sharpening include formic acid, propionic acid,
Monovalent organic carboxylic acids such as benzoic acid, divalent organic carboxylic acids such as oxalic acid, or inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid are preferred. The latter inorganic acid is usually used as an aqueous solution.

According to the research conducted by the present inventors, oxalic acid and nitric acid are particularly preferred among the various organic carboxylic acids and inorganic acids mentioned above.

In general, the method of treating pitch with an acid is sufficient as long as the pitch and the acid can come into sufficient contact with each other, and usually the pitch is made into fine particles or heated above its melting point to become a liquid, and the acid is made into an aqueous solution. , a method of mixing both is adopted. At this time, when liquid-liquid mixing is employed, the mixing temperature is often higher than the normal pressure boiling point of the system, and in this case, a mixing method under pressure is adopted.

After contacting with acid as described above, excess acid is easily removed by allowing the system to stand. Then, if necessary,
Wash the pitch thoroughly. As acids, hydrochloric acid, sulfuric acid, etc.
When an acid containing elements other than -1, 0, and N is used, it is necessary to perform a particularly thorough cleaning operation. The material of the equipment for acid treatment should be one that does not elute heavy metals; for example, glass-lined equipment is preferable.

The pitch may be treated with an acid before the thermal polymerization, and it may be before or after the pitch is treated with a hydrogen-donating solvent to prepare reduced pitch. The time for the acid treatment depends on the treatment temperature, but if the pitch is brought into contact with the acid at a temperature above its melting point, about one hour is sufficient.

The pitch after thermal polymerization prepared according to the method of the present invention has good spinnability and can be easily spun by a conventional method. The spun pitch [t is then heated in an oxidizing gas atmosphere at a temperature of 250 to 350°C to make it infusible, and then in an inert gas at a temperature of 1000 to 1500°C. It can be made into carbon fiber by firing with IalilIt.

Effects of the Invention Carbon fibers formed from acid-treated pitch according to the method of the present invention as described above by spinning, infusibility, and sintering have a 200%
It has excellent strength exceeding 9/InIR, and
It has a high elongation of as much as 3.5%. Therefore, the high elongation carbon fiber obtained from the pitch prepared by the method of the present invention has excellent handling properties and can be used in fields where conventional carbon fibers are not suitable, such as fields such as new composite monthly materials. It becomes possible to use it.

EXAMPLES Hereinafter, the present invention will be explained in more detail by giving Examples and Comparative Examples of the present invention.

Note that mp in the examples means the melting point of pitch measured by DSC.

Example 1 ]-Lutarvich (till) = 700C) 35
09 and 1 ρ of a 1N oxalic acid aqueous solution were charged into a glass three-lough flask with an internal volume of 5 cm equipped with a condenser, and the mixture was stirred at normal pressure boiling point for 1 hour to perform acid treatment. Thereafter, the pitch phase was recovered by thermal separation, followed by thorough washing with hot ion-exchanged water and drying. All of the acid-treated pitch obtained and 1050 g of tetrahydroquinoline were placed in an autoclave with an internal volume of 3ρ equipped with a stirrer, and heated at 450°C.
After that, a solvent mainly consisting of tetrahydroquinoline and quinoline was heated at 300℃ and 107 or
The reduced pitch was prepared by distillation under r. Next, the reduced pitch was heat-treated at 460° C. and 10 mm for 25 minutes to produce pitch for forming carbon fibers.

The pitch obtained in this way is heated at a spinneret temperature of 340°C.
After melt spinning at a spinning take-off speed of 800 m 2 /min, it was subjected to infusibility treatment at 300° C. in air for 30 minutes, and then fired at 1500° C. in nitrogen to obtain carbon fibers. The physical properties of the carbon fibers thus produced were as shown in Table 1, and all had excellent elongation and strength.

Table 1 Comparative Examples Carbon fibers were produced in the same manner as in Example 1 except that the oxalic acid treatment was not performed. The physical properties of the obtained carbon fibers are shown in Table 2 below, and pitch-based carbon l! Although it exhibited good physical properties as a dark blue color, it had clearly lower elongation than carbon fiber made from pitch produced by the method of the present invention.

Table 2 Example 2 Carbon fibers were produced in the same manner as in Example 1 except that hydrochloric acid or nitric acid was used instead of oxalic acid. The results are shown in Table 3 below.

Table 3

Claims (3)

[Claims] (1) In a method for preparing pitch for carbon fiber production by treating a pitch-like substance in a hydrogen-donating solvent to obtain reduced pitch, and then thermally polymerizing it while removing low-boiling components, the pitch-like substance and/or A method for preparing pitch for producing high elongation carbon fibers, which comprises bringing reduced pitch into contact with an acid. (2) The acid is an organic carboxylic acid (
Preparation method described in section 1). (3) The preparation method according to claim (1), wherein the acid is at least one inorganic acid selected from hydrochloric acid, nitric acid, and sulfuric acid.