JPH05214613A - Production of mesophase pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the subject mesophase pitch-based carbon fiber, useful for obtaining infusibilized fiber, having retained molecular orientation possessed by the pitch fiber itself and improved in physical properties by oxidatively polymerizing mesophase pitch fiber in the liquid phase at a low temperature. CONSTITUTION:The objective method for producing mesophase pitch-based carbon fiber is to (1) melt spin mesophase pitch according to a conventional method, provide pitch fiber, oxidatively polymerize the fiber in the liquid phase in a solvent in the presence of an acidic catalyst and a cross-linking agent and infusibilize the fiber. In the method, (2) an acidic solvent such as a carboxylic acid is used as the solvent and (3) the oxidatively polymerizing conditions are 90-150 deg.C and 0.1-10hr. The mixing ratios of the cross-linking agent and acidic catalyst to the pitch fiber are respectively 0.0001-0.05mol and 0.0001-0.05mol based on 1g pitch fiber.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an improved process for producing mesophase pitch carbon fibers. More specifically, the method of the present invention is to obtain infusible fibers by liquid-phase oxidation / polymerization of mesophase pitch fibers at a low temperature, the molecular orientation of the pitch fibers themselves is maintained, and To provide an improved mesophase pitch carbon fiber.

[0002]

2. Description of the Related Art Conventionally, mesophase pitch fibers are spun to produce mesophase pitch fibers, and the mesophase pitch fibers are produced in air for 200
By oxidizing and polymerizing at a high temperature of about 400 ° C., the infusible fiber obtained has oxygen penetrating into the inside of the fiber, and the orientation property of the pitch molecule is lowered by the oxidation.
It was difficult to obtain a carbon fiber having high physical properties because the crystal growth in the latter carbonization process is hindered and a structural defect occurs due to the desorption of the introduced oxygen atom.

[0003]

As described above, in the conventional method for producing infusibilized fiber by vapor phase oxidation, the orientation of pitch molecules is lowered, so that the crystal growth in the subsequent carbonization process is hindered. Therefore, it was difficult to grow a crystal structure sufficiently, and it was difficult to obtain a mesophase pitch carbon fiber having high physical properties.

As a result of various studies on the above-mentioned problems, the present inventors have conducted insolubilization by mesophase pitch fibers obtained from mesophase pitch being infusibilized by liquid phase oxidation / polymerization at a relatively low temperature. The disorder of the molecular orientation is suppressed, and the infusibilized fiber can be formed while maintaining the orientation during the formation of the mesophase pitch fiber. As a result, the mesophase pitch system with unexpectedly improved physical properties, especially tensile strength, can be formed. The inventors have found that carbon fibers can be obtained, and completed the present invention.

[0005]

Means for Solving the Problems The present invention is as follows: Melt-spinning mesophase pitch into pitch fibers by a conventional method, and then subjecting the pitch fibers to liquid-phase oxidation in a solvent in the presence of an acid catalyst and a crosslinking agent. A method for producing a mesophase pitch carbon fiber, which is characterized by being infusibilized by polymerizing,

It is also characterized in that an acidic solvent such as carboxylic acid is used as a solvent, and the oxidation / polymerization conditions are 90 to 150 ° C. for 0.1 to 10 hours, and the crosslinking agent and the acid for the pitch fiber are The mixing ratio of the catalyst is 0.0001 to 1 g of pitch fiber, respectively.
It is also characterized in that it is 0.05 mol and 0.0001 to 0.05 mol.

The present invention will be described in detail below. In the present invention, to produce mesophase pitch-based carbon fiber having high physical properties, (a) the mesophase pitch is spun according to a conventional method to produce pitch fiber, and (b) the pitch fiber is present in the presence of an acid catalyst and a crosslinking agent. It is necessary to oxidize and polymerize in a solvent at a relatively low temperature.

By adopting such a method, the disorder of the molecular orientation due to infusibilization is suppressed, and the surface layer of the pitch fiber is oxidized and polymerized to form the infusibilized fiber while maintaining the orientation at the time of pitch fiber formation. Therefore, the mesophase pitch carbon fiber having high physical properties can be produced.

The mesophase pitch used in the method of the present invention includes petroleum pitch and coal pitch, which are filtered by a conventional method.
It is produced by appropriately selecting treatment steps such as purification, distillation, hydrogenation and catalytic decomposition. From the viewpoint of fiber properties, it is preferable to use mesophase pitch having a mesophase content of about 70% or more.

The mesophase pitch fiber can be produced by a known spinning method as long as the mesophase pitch can be spun into a fibrous state.

The infusibilization treatment of liquid phase oxidation / polymerization of mesophase pitch fibers requires that liquid phase oxidation / polymerization be performed under controlled conditions at a relatively low temperature in a solvent in the presence of an acid catalyst and a crosslinking agent. is there.

The mechanism of the oxidation / polymerization reaction for infusibilizing the pitch fiber in the present invention is considered to be basically the same as in the case of synthesizing a phenol resin.

The cross-linking agent used in the present invention may be in any form as long as it forms a monomer formaldehyde in the reaction system, such as various commercially available concentrations of formalin, paraformaldehyde and trioxane. Aldehydes and compounds having a hydroxymethyl group can be used, but it is preferable to use paraformaldehyde, which does not lower the catalyst concentration and can be obtained at a low price. Also, gaseous formaldehyde can be charged into the reaction system.

The acid catalyst used in the present invention is not particularly limited as long as it is a solvent-soluble acid catalyst. For example, strong inorganic acid such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid; strong organic acid such as paratoluenesulfonic acid. Examples thereof include Lewis acids such as boron trifluoride and aluminum chloride.
Use of an organic strong acid such as p-toluenesulfonic acid is preferable in terms of catalytic activity, handleability and the like.

The solvent is preferably an acidic solvent in relation to the acid catalyst used, and particularly acetic acid, propionic acid,
Examples thereof include organic carboxylic acids such as lactic acid, and the use of acetic acid is preferable from the viewpoint of convenience of handling.

In the method of the present invention, the addition ratio of various components to mesophase pitch is not particularly limited as long as the reaction and reaction conditions are appropriately maintained, but generally, the amount of the crosslinking agent is 0.0001 to 1 g of pitch fiber. 0.0
5 mol, the amount of acid catalyst is 0.000 per 1 g of pitch fiber
It is preferably 1 to 0.05 mol, and the amount of the solvent is not particularly limited. The number of moles when formalin is used as the crosslinking agent is the number of moles in terms of formaldehyde.

When the amount of the cross-linking agent is less than 0.0001 mol, the content of oxygen atoms is lowered, and the oxidative polymerization is not sufficiently carried out, so that the intended infusible fiber cannot be obtained. Further, when the amount of the cross-linking agent exceeds 0.05 mol, the oxygen content becomes extremely high and the orientation of pitch molecules is deteriorated due to excessive oxidation, which makes it difficult to obtain carbon fibers having high physical properties. ..

The conditions of the oxidation / polymerization reaction for infusibilization of the present invention are not particularly limited as long as the surface layer of the mesophase pitch fiber can react predominantly, but generally 90
~ 150 ° C, preferably 110-130 ° C, 0.1
It is 10 hours, preferably 1 to 2 hours.

If the reaction temperature is lower than 90 ° C., sufficient oxidation / polymerization cannot be carried out. If the reaction temperature exceeds 150 ° C., the oxidation proceeds to the inside of the fiber and the orientation is disturbed to the inside of the fiber. , Carbon fibers having sufficiently high physical properties cannot be obtained.

The reaction time is 0.1 depending on the reaction temperature.
The reaction time is selected within the range of 10 hours, but if the reaction time is less than 0.1 hours, the reaction will not be carried out sufficiently, and a reaction time of more than 10 hours is meaningless in practice.

The apparatus used for the oxidation / polymerization of the present invention is not particularly limited in shape, but it can be continuously or separately performed after spinning the mesophase pitch fiber, and a usual batch type, flow type or the like is used. be able to.

The infusible fiber obtained by the method of the present invention is then carbonized according to a conventional method to produce carbon fiber or graphite fiber having high physical properties.

In the carbonization step, various reaction conditions can be selected according to the use of the carbon fiber, but generally, it is 400 at a temperature rising rate of 5 to 100 ° C./min under an inert gas such as nitrogen or argon.
Heat treatment is performed up to 3000C, preferably 900-2500C.

[0024]

[Function] In the infusibilizing treatment of the pitch fiber by the vapor phase oxidation of the conventional method, oxygen penetrates into the inside of the fiber and the orientation of the pitch molecule is lowered by the oxidation, so that the crystal growth in the subsequent carbonization process is hindered. Therefore, it is difficult to grow a crystal structure sufficiently, and structural defects occur due to desorption of introduced oxygen atoms, and it is difficult to obtain carbon fibers having high physical properties.

In this case, the infusible reaction temperature is 200 to 40.
Since it is as high as 0 ° C., if the reaction temperature is lowered to suppress the reaction, the reaction may become inhomogeneous or insufficient.

On the other hand, according to the method of the present invention,
Since it is infusibilized in a liquid phase under a low temperature reaction condition of 150 ° C., particularly in an acidic solvent, the reaction is rapid and the surface layer is mainly oxidized and polymerized without proceeding to the inner layer of the fiber. It Therefore, the disorder of the molecular orientation due to the infusibilization is suppressed, and the infusibilized fiber can be formed while maintaining the orientation when the pitch fiber is formed. As a result, a mesophase pitch carbon fiber having high physical properties, particularly improved tensile strength can be obtained.

[0027]

The present invention is illustrated by the following examples and comparative examples, which do not limit the scope of the present invention.

[0028]

Example 1 The softening point measured by a flow tester is 245.
Mesophase pitch at 90 ℃ (Mesophase content 90%)
Spindle spinneret temperature of 320 ℃ by melt spinning method
At a winding speed of 170 m / min, the fiber diameter is 13 μm.
The mesophase pitch fiber of was obtained. Next, a reaction solution was prepared by adding 0.075 mol of a paratoluenesulfonic acid catalyst and 0.075 mol of a formalin crosslinking agent (in terms of formaldehyde) to a propionic acid solvent.

The mesophase pitch fiber 3 is added to the reaction solution.
g was soaked and reacted at 120 ° C. for 7 hours, then the fiber was taken out and vacuum dried at 130 ° C. to obtain an infusible yarn. The infusibilization yield at this time was 96% by weight.

The infusibilized yarn was graphitized at 2500 ° C. to obtain a graphitized fiber having a yield of 81% by weight and a fiber diameter of 9.5 μm. The tensile strength of this graphitized fiber was 343 kgf / mm ² , and the elastic modulus was 54 tf / mm ² .

[0031]

Example 2 A reaction solution was prepared by adding 0.15 mol of a paratoluenesulfonic acid catalyst and 0.15 mol of a formalin crosslinking agent (formaldehyde conversion) to a propionic acid solvent.

3 g of the mesophase pitch fiber obtained in Example 1 was dipped in the reaction solution, reacted at 120 ° C. for 5 hours, taken out of the fiber, and vacuum dried at 130 ° C. to obtain an infusibilized yarn. The infusibilization yield at this time was 100% by weight.

The infusible yarn was graphitized at 2500 ° C. to obtain graphitized fiber having a yield of 81% by weight and a fiber diameter of 9.5 μm. The tensile strength of this graphitized fiber was 370 kgf / mm ² , and the elastic modulus was 64 tf / mm ² .

[0034]

Comparative Example 1 The mesophase pitch fiber used in Example 1 was heated to 300 ° C. in air at a temperature rising temperature of 1.8 ° C./min to obtain an infusible yarn having a yield of 106.7% by weight. It was

The infusible yarn was graphitized at 2500 ° C. to obtain a graphitized fiber having a yield of 88% by weight and a fiber diameter of 9.9 μm. The tensile strength of this graphitized fiber was 307 kgf / mm ² , and the elastic modulus was 56 tf / mm ² . These results are shown in Table 1 below.
Are summarized in.

[0036]

[Table 1]

[0037]

EFFECTS OF THE INVENTION By the method of the present invention, the mesophase pitch fibers are liquid-phase oxidized and polymerized at a low temperature, whereby the disorder of the molecular orientation due to infusibilization is suppressed, and the misalignment of the mesophase pitch fibers is prevented while maintaining the orientation during pitch fiber formation. Fused fibers can be formed. Therefore, there is an effect that a mesophase pitch carbon fiber having high physical properties can be obtained.

Claims (3)

[Claims] 1. Mesophase pitch is melt-spun according to a conventional method to give pitch fibers, and the pitch fibers are infusibilized by liquid-phase oxidation / polymerization in a solvent in the presence of an acid catalyst and a crosslinking agent. A method for producing a mesophase pitch carbon fiber, which is characterized. 2. The method for producing mesophase pitch carbon fiber according to claim 1, wherein an acidic solvent such as carboxylic acid is used as the solvent. 3. Oxidation / polymerization conditions of 90 to 150 ° C.
1 to 10 hours, and the mixing ratio of the cross-linking agent and the acid catalyst to the pitch fiber is 0.0 per 1 g of the pitch fiber, respectively.
The method for producing a mesophase pitch carbon fiber according to claim 1, wherein the amount is 001 to 0.05 mol and 0.0001 to 0.05 mol.