JPH11124742A - Production of carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain carbon fiber that has excellent strength and modulus and is useful as a reinforcing material for a variety of composite materials by dissolving a prescribed amount of modified pitch in a solution of acrylic polymer in a solvent, spinning the solution to fiber, and firing the fiber. SOLUTION: To a solution of an acrylic polymer as polyacrylonitrile in a solvent, is added a modified pitch that is readily soluble in at least one polar organic solvents selected from dimethyl sulfoxide, dimethylformamide and dimethyl-acetamide in a concentration of 0.1-30 wt.%. Then, mixture is spun into filaments and fired to give the objective carbon fiber. In a preferred embodiment, the modified pitch has an anisotropic texture and is carbonized without deformation, when it is heated in an inert atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-performance carbon fiber having excellent strength and elastic modulus.

[0002]

2. Description of the Related Art Conventionally, carbon fibers have a high specific strength.
Due to its specific elastic modulus, it is industrially used as a reinforcing material for various composite materials in a wide range of fields such as the aerospace / sports and leisure industries. Currently, there are two major types of carbon fibers produced on an industrial scale: PAN-based carbon fibers made from synthetic fibers mainly composed of polyacrylonitrile and pitch-based carbon fibers made from petroleum, coal, synthetic pitch and the like. Divided.

[0003] PAN-based carbon fibers are mainly excellent in high strength and high elongation, but have a drawback that they have a low elastic modulus because they are derived from raw materials and are hardly graphitizable. 2 to improve elastic modulus
Baking at a high temperature exceeding 000 ° C. is effective, but at the same time causes a decrease in strength. Factors that lead to cost increases, such as shortening of furnace life due to high-temperature firing, are disadvantageous on an industrial scale.

[0004] Pitch-based carbon fibers can be roughly divided into those derived from isotropic pitch and those derived from anisotropic pitch. Anisotropic pitch is generally used to exhibit high performance. . Carbon fiber from anisotropic pitch raw material has high elasticity and high strength due to the property of easy graphitization of raw material, but has low elongation, and industrially, carbon fiber productivity and handling property at the time of compounding There is a disadvantage that it is inferior.

[0005] In view of the above, in order to compensate for the disadvantages of both the PAN-based carbon fiber and the pitch-based carbon fiber, various studies have been made on the compounding of both. For example, a carbon fiber production method in which pitch is mixed with an acrylic polymer, and then spun and fired (Japanese Patent Laid-Open No.
-47311) has been proposed. However, since this method is basically just mixing, it is disadvantageous for use on an industrial scale, for example, it is necessary to pulverize the mixing pitch very finely. Furthermore, since the pitch to be mixed has a softening point, if the infusibilization of the pitch is not performed simultaneously and optimally at the time of flame resistance during the carbon fiber production process, the pitch may be softened and melted, leading to a complicated process, and the carbon fiber It may cause an increase in manufacturing cost.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an industrially advantageous method for producing carbon fiber having excellent strength and elastic modulus in view of the above-mentioned current situation of producing high-performance carbon fiber. is there.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on a method for producing carbon fibers having the above-mentioned problems, and as a result, when producing polyacrylonitrile-based carbon fibers, they have been modified into an acrylic polymer solvent solution. It has been found that by mixing and dissolving 0.1 to 30% by weight of the prepared pitch and spinning and baking it, the elastic modulus can be improved while maintaining the strength without substantially changing the conventional manufacturing process. Reached the present invention. That is, the present invention is a method for producing carbon fibers, which comprises dissolving and mixing 0.1 to 30% by weight of a modified pitch in an acrylic polymer solvent solution and spinning and firing.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The acrylonitrile polymer used in the present invention is not particularly limited.
Considering the mechanical properties of carbon fibers, at least 90 mol% or more of acrylonitrile and 10 mol% or less of vinyl monomers copolymerizable with acrylonitrile, for example, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid; Examples thereof include acrylonitrile-based polymers comprising salts thereof, methyl acrylate, butyl acrylate, acrylamide, allylsulfonic acid and salts thereof.

The method of polymerizing acrylonitrile and vinyl monomer is not particularly limited, and a conventionally known method such as solution, suspension and emulsion polymerization can be applied. These acrylonitrile-based polymers are dimethylsulfoxide (DM), which is a solvent used for spinning of a general polyacrylonitrile-based polymer for spinning.
SO), dimethylformamide and dimethylacetamide.

The raw material of the modified pitch used in the present invention is:
Any pitch of coal, petroleum and synthetic system can be used. Such a pitch is an optical structure under a polarizing microscope,
Although the isotropic property and the anisotropy are not limited, the anisotropic property is preferably used in the production of the high performance carbon fiber which is the object of the present invention.

The pitch used in the present invention, particularly the anisotropic pitch, has low solubility in a polar organic solvent such as DMSO and has a softening point, so that the pitch has a solubility in a polar solvent and a softening point. It is necessary to modify the material so as not to have a point and a melting point and to be carbonized without being deformed by heating even in an inert atmosphere such as nitrogen. Modification is achieved, for example, by dispersing the finely ground raw material pitch in an aqueous acid solution such as sulfuric acid or acetic acid, and reacting by adding an oxidizing agent such as hydrogen peroxide at a temperature condition of about 50 ° C., after the reaction, A modified pitch is obtained by filtration, washing and drying. Well-modified pitch readily dissolves in polar organic solvents such as DMSO. Further, it is infused with heat and is carbonized while maintaining its form even when further heated. When the raw material pitch is optically anisotropic, the treated pitch also retains an anisotropic structure.

No special operation is required for mixing the acrylic polymer with the modified pitch. When a spinning stock solution is obtained from solution polymerization, acrylonitrile and a copolymer component are polymerized by a conventional procedure, a modified pitch is added thereto, and the mixture is dissolved and mixed at room temperature. Suspension, when the obtained polymer is re-dissolved in an organic solvent to obtain a spinning dope as in emulsion polymerization, the polymer may be dissolved after dissolving the modified pitch in the organic solvent, The reverse is also acceptable.

The mixing ratio between the acrylic polymer and the modified pitch is 0.1 to 30% by weight, preferably 2 to 15% by weight.
% By weight. If the amount is less than 0.1% by weight, the effect of the addition becomes unclear, and if the amount is more than 30% by weight, stretching in the spinning step becomes difficult, and yarn breakage or the like occurs.

As the spinning method in the present invention, a conventionally known method used in the production of acrylic carbon fibers can be applied, and a carbon fiber precursor can be obtained by subsequent drawing or dry densification. The flame retardation and calcination of the obtained precursor can be carried out under the conventional conditions, since the dissolved pitch is carbonized without being deformed by heat.

[0015]

Next, the present invention will be described in detail with reference to examples. However, the present invention is not limited by these examples.

Example 1 95 mol% of acrylonitrile, methyl acrylate
A monomer composition of 5 mol% and 0.5 mol% of itaconic acid was charged into dimethyl sulfoxide so that the concentration of the polymer after polymerization was about 20%, and azobiswisthbutylnitrile (AIBN) was used as an initiator and dodecyl. Solution polymerization was carried out at 65 ° C. using mercaptan as a chain transfer agent to obtain an acrylic polymer. On the other hand, a synthetic pitch of 100% mesophase obtained by polymerizing naphthalene using HF / BF ₃ catalyst was used as a raw material pitch for preparing a modified pitch. This raw material pitch was pulverized by a coffee mill and dispersed in a sulfuric acid aqueous solution heated to 50 ° C. with stirring. Hydrogen peroxide was added little by little to start the reaction. After adding 5 times the total amount of hydrogen peroxide to the bitch, perform the reaction overnight,
After completion of the reaction, the mixture was filtered through a glass filter, washed with ion-exchanged water until the filtrate no longer showed acidity, and dried under reduced pressure to obtain a modified pitch. It was confirmed that the obtained modified pitch easily dissolved in dimethylsulfoxide and dimethylformamide at room temperature. The modified pitch in a powder state was fired in a nitrogen atmosphere in an annular furnace up to 1000 ° C., but no fusion or deformation of the fired particles was observed and carbonization was confirmed. After the baked powder was filled with a resin and polished, optical structure observation was performed, and it was observed that the mesophase was 100% similarly to the raw material. 10% of the modified pitch thus prepared was added to the polymer and dissolved and mixed with stirring. After confirming dissolution, defoaming was performed under reduced pressure to obtain a spinning stock solution. The undiluted spinning solution is discharged through a spinneret of 0.08 mmφ · 100H into an aqueous coagulation bath composed of 65% DMSO, and then stretched three times in hot water.
The film was stretched twice in a glycerin bath at 35 ° C. Thereafter, it was sufficiently washed with water and dried under a tension at 150 ° C. and a heat treatment at 180 ° C. to obtain a carbon fiber precursor. The carbon fiber precursor was subjected to a heat treatment under tension at 220 ° C. for 30 minutes and at 250 ° C. for 30 minutes in air to obtain an oxidized yarn. The flame-resistant yarn was heated to 1000 ° C. at 10 ° C./min in high-purity nitrogen under tension to obtain carbon fibers. The performance of the obtained carbon fiber was a tensile strength of 189 kg / mm ² and an elastic modulus of 18 t / mm ² .

Comparative Example 1 In Example 1, a carbon fiber consisting only of polyacrylonitrile was produced in the same manner without mixing modified pitch. The performance of the obtained carbon fiber was a tensile strength of 180 kg /
mm ² , and the elastic modulus was 14 t / mm ² .

Example 2 A polyacrylonitrile copolymer was synthesized from monomers having the same composition as in Example 1 by suspension polymerization. 10% of the modified pitch was added and dissolved in the suspension polymer which was later dissolved in the DMSO solvent. The DMSO solution of the modified pitch was kept at 50 ° C., and the polymer was dissolved little by little so that the polymer concentration became about 20%. After dissolving the whole amount, defoaming was performed under reduced pressure to prepare a spinning stock solution. This spinning stock solution was spun in the same manner as in Example 1 to prepare a carbon fiber. The properties of the obtained carbon fiber were as follows: a tensile strength of 205 kg / mm ² and an elastic modulus of 20 kg / mm ² .
t / mm ² .

Comparative Example 2 In Example 2, a carbon fiber consisting of only polyacrylonitrile was produced in the same manner without mixing modified pitch. The performance of the obtained carbon fiber was 191 kg / tensile strength.
mm ² and an elastic modulus of 16 t / mm ² .

[0020]

As is clear from the above examples, in the method for producing carbon fiber of the present invention, the conventional method for polymerizing a polymer for polyacrylonitrile-based carbon fiber and the method for preparing carbon fiber are changed. Can be adopted without
The elastic modulus can be improved without lowering the strength of the polyacrylonitrile-based carbon fiber. Therefore, according to the present invention, a high-performance carbon fiber excellent in both strength and elastic modulus can be industrially advantageously produced, and the present invention has great industrial significance.

Claims (3)

[Claims] 1. A method for producing carbon fibers, comprising dissolving and mixing 0.1 to 30% by weight of a modified pitch in an acrylic polymer solvent solution and spinning and firing. 2. The method according to claim 1, wherein the modified pitch is easily dissolved in one or more polar organic solvents selected from dimethylsulfoxide, dimethylformamide and dimethylacetamide. 3. The modified pitch has an anisotropic structure,
The carbon fiber production method according to claim 1, wherein the carbonization is performed without deformation by heating in an inert atmosphere.