JP2008308775A - Method for producing carbon fiber precursor fiber and carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing carbon fiber precursor fibers by which carbon fibers having good strength can be obtained by feeding an acrylonitrile-based polymer solution with little gel to spinning without being accompanied with deterioration in productivity and a cost increase, achieving stable spinning operation efficiency and subsequently carrying out flameproofing and carbonizing treatment. <P>SOLUTION: The method for producing the carbon fiber precursor fibers includes spinning the acrylonitrile-based polymer solution obtained by copolymerizing 0.01-2 mol% of at least one kind of carboxy group-containing vinylic compound. Furthermore, the method for producing the carbon fiber precursor fibers includes adding at least one kind of compound selected from the group comprising ammonia, an amine compound and a quaternary ammonium salt to a part between a storage tank of the polymer solution and a spinneret and then spinning the acrylonitrile-based polymer solution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a production method for stably supplying precursor fibers of acrylonitrile-based carbon fibers and a production method for carbon fibers having excellent mechanical properties.

  Carbon fiber obtained by flame-treating and carbonizing precursor fiber obtained by spinning acrylonitrile polymer is used for aerospace applications, sports and leisure applications due to its excellent mechanical properties. It is widely used as a reinforcing fiber for composite materials.

  In the acrylonitrile polymer used as the raw material for the carbon fiber, it is preferable to copolymerize a carboxyl group-containing vinyl compound in order to accelerate the flameproofing treatment. In addition, when wet spinning or dry-wet spinning is performed using a polymer solution in which such an acrylonitrile polymer is dissolved in a solvent, voids are generated in the spinning coagulation bath by increasing the hydrophilicity of the polymer solution. Various methods for ionizing the copolymerized carboxyl group have been proposed as a suppression technique, and methods for adding ammonia or ammonium salts have been proposed as one of them (Patent Documents 1, 2, and 3). .

  The precursor fiber obtained by spinning by the above-described method can be suitably used as a precursor of high-strength carbon fiber, but the acrylonitrile polymer after addition of ammonia or ammonium salt tends to generate a gel. May act as a foreign substance, and the operability of the spinning process may deteriorate.

  Although it is not clear why the gel generation is promoted by adding ammonia or ammonium salt, the nucleophilic addition of the amine compound to polyacrylonitrile promotes the cyclic reaction or crosslinking reaction of polyacrylonitrile ( Non-Patent Document 1) is considered to be insoluble in a gel, that is, a solvent, when such a cyclic reaction or crosslinking reaction proceeds.

  On the other hand, in recent years, environmentally-friendly technical studies have progressed, and as a typical example, polymerization unreacted monomers are recovered as much as possible at the polymer solution stage, and the next spinning process working environment or spinning process is transferred to the atmosphere or drainage. A method for preventing unreacted monomer from being discharged has been proposed. For example, in Patent Documents 4, 5, and 6, the acrylonitrile-based polymer solution is supplied from the upper part of the packed column that has been depressurized, and the vapor of the solvent of the polymer solution is supplied from the lower part of the packed column so as to make countercurrent contact with the polymer solution. And a high unreacted acrylonitrile removal rate is achieved.

  However, it has been found that the gel generation in the polymer solution becomes more remarkable as the amount of unreacted acrylonitrile remaining in the acrylonitrile-based polymer solution is reduced by these methods. The cause of this phenomenon was that the presence of unreacted acrylonitrile suppressed the cyclization reaction and cross-linking reaction with polyacrylonitrile described above, but by removing unreacted acrylonitrile, the cyclization reaction with polyacrylonitrile and This is probably because the cross-linking reaction has progressed and gel generation has become prominent.

As a technique for suppressing gel generation in an acrylonitrile-based polymer solution, a method of adding a radical polymerization inhibitor into the polymer solution as in Patent Document 7, or a method of adding acrylonitrile-based polymer solution as in Patent Document 8 There has been proposed a method in which a certain amount of a compound containing an ethylenic double bond is contained. Although these methods can certainly suppress gel generation, they lead to increased production costs, and radical polymerization inhibitors and compounds containing ethylenic double bonds act as foreign substances in the spinning and firing processes, thereby improving operability and mechanical properties. The characteristics may be deteriorated.
JP 59-82421 A Japanese Patent Laid-Open No. 11-12856 WO99 / 10572 Publication Japanese Patent Laid-Open No. 11-181019 JP 2001-89517 A JP 2002-363214 A JP-A-1-168750 JP 2002-249924 A Acrylic synthetic fiber (published by Nikkan Kogyo Shimbun, written by Masamichi Katayama) P217-218

  In view of the problems of the prior art, the present invention is to stably provide a precursor fiber as a raw material for acrylonitrile-based carbon fiber having excellent mechanical properties, and has excellent mechanical properties. It is intended to provide a method for producing a carbon fiber.

  The present invention employs the following means in order to solve such problems.

  A method for producing a carbon fiber precursor fiber by spinning an acrylonitrile polymer solution obtained by copolymerizing 0.01 to 2 mol% of at least one carboxyl group-containing vinyl compound, the polymer solution storage tank And at least one compound selected from the group consisting of ammonia, an amine compound and a quaternary ammonium salt is added between the base and the base, and then the acrylonitrile-based polymer solution is spun. .

  Moreover, it is the manufacturing method of the said carbon fiber precursor fiber which adds the at least 1 sort (s) of compound chosen from the group which consists of the said ammonia, an amine compound, and a quaternary ammonium salt in the piping part near a nozzle | cap | die.

  Furthermore, it is the manufacturing method of the said carbon fiber precursor fiber whose density | concentration of the acrylonitrile monomer in an acrylonitrile-type polymer solution is 0.001-0.1 weight%.

  This is a carbon fiber manufacturing method in which the precursor fiber obtained by the above manufacturing method is flameproofed at 180 to 300 ° C. in an oxidizing atmosphere and subsequently carbonized at 400 to 2000 ° C. in an inert atmosphere.

  ADVANTAGE OF THE INVENTION According to this invention, the stable supply by the operativity improvement by spinning becomes possible, and the carbon fiber which has a high mechanical characteristic can be provided.

  Hereinafter, the present invention will be described in detail. As a result of intensive studies on the above-described problem, ie, a method for suppressing gel generation in an acrylonitrile-based polymer solution to which ammonia, ammonium salt or the like has been added, the present inventors have found that ammonia and ammonium that have not been studied so far. Focusing on the place where salt or the like is added, the problem is solved by adding between the storage tank of the polymer solution and the base, particularly in the pipe portion closest to the base.

  In the present invention, the acrylonitrile-based polymer is a polymer obtained by polymerizing acrylonitrile and a vinyl monomer copolymerizable therewith and containing 95 to 99.99 mol% of an acrylonitrile-derived skeleton. The coalescence solution is a solution obtained by dissolving the acrylonitrile-based polymer in a solvent so as to be 15 to 25% by weight. In such an acrylonitrile-based polymer solution, the acrylonitrile-based polymer content is preferably 17 to 23% by weight, and more preferably 18 to 22% by weight. When the acrylonitrile-based polymer content is less than 15%, a solidified structure formed in a coagulation bath due to a small amount of polymer when producing a carbon fiber precursor fiber by wet spinning or dry-wet spinning of the polymer solution. Sparse, and the strength of the precursor fiber and the strength of the carbon fiber obtained by firing the precursor fiber may decrease. If the acrylonitrile polymer content exceeds 25% by weight, the viscosity of the acrylonitrile polymer solution becomes too high, resulting in a decrease in processability due to a decrease in stretchability in the spinning process. It is economically disadvantageous because it is necessary to increase the sex.

  The solvent for dissolving the acrylonitrile polymer is not specified, and dimethyl sulfoxide (hereinafter sometimes referred to as DMSO), dimethylformamide (hereinafter sometimes referred to as DMF), and dimethylacetamide (hereinafter also referred to as DMAc). ), Zinc chloride aqueous solution, sodium thiosulfate aqueous solution and the like can be used, but DMSO is preferred from the viewpoint of solubility.

  The acrylonitrile polymer solution of the present invention may be produced from solution polymerization in the solvent, or may be produced by dissolving the acrylonitrile polymer obtained by bulk polymerization and aqueous suspension polymerization in the solvent. However, in bulk polymerization and aqueous suspension polymerization, operations such as washing, drying, and re-dissolution are required when spinning after polymerization. From the viewpoint of productivity, solution polymerization that does not require such operations is used. Is preferred.

  In addition, the acrylonitrile polymer in the present invention contains a acrylonitrile-derived skeleton of 95 to 99.99 mol% and a copolymerizable vinyl monomer-derived skeleton of 0.01 to 2 mol%. It is necessary to contain a skeleton derived from a group-containing vinyl compound in an amount of 0.01 to 2 mol% of the entire polymer. The skeleton derived from acrylonitrile is preferably 98 mol% or more. However, when the skeleton is less than 95 mol%, the carbon fiber is produced by spinning and baking such a polymer, so that the strength is increased because more components are released. It may decrease or productivity may decrease. The content of the carboxyl group-containing vinyl compound is preferably 0.1 to 1 mol%. When the content is out of the range of 0.01 to 2 mol%, there is no effect of promoting the flame resistance, or the flame resistance is excessively promoted and the reaction may not be controlled. Preferred examples of the carboxyl group-containing vinyl compound include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, and mesaconic acid. A compound having a larger number of carboxyl groups has a flame resistance promoting effect. Itaconic acid is most preferred because of its high value.

  In addition, for the purpose of improving stretchability in spinning, monomers such as acrylate and methacrylate may be copolymerized.

  In the present invention, at least one compound selected from the group consisting of ammonia, an amine compound and a quaternary ammonium salt is added to ionize the carboxyl group portion derived from the carboxyl group-containing vinyl compound in the acrylonitrile polymer. To do. Thereby, the hydrophilicity of the acrylonitrile-based polymer can be improved, and the generation of voids during coagulation in the coagulation bath when producing the precursor fiber by wet spinning or dry wet spinning can be suppressed. Higher strength carbon fibers can be produced by firing the precursor fibers obtained by this method.

  Examples of the compound to be added include mono-tri-trialkylamines as ammonia and amine compounds, and mono-gee-tri-tetraalkylammonium hydroxides as quaternary ammonium salts, but they are inexpensive and versatile. Ammonia is particularly preferred. At least one of these compounds needs to be added, and two or more may be added.

  The addition amount of at least one compound selected from the group consisting of ammonia, an amine compound and a quaternary ammonium salt is 0.5 to 1.2 times the molar ratio of the copolymerized carboxyl group-containing vinyl compound. It is preferable that the molar ratio is 0.8 to 1.1 times. When the amount added is less than 0.5 times the molar ratio, the effect of improving the hydrophilicity of the acrylonitrile-based polymer solution may not be exhibited. When the added amount exceeds 1.2 times the molar ratio, at least one compound selected from the group consisting of ammonia, an amine compound, and a quaternary ammonium salt becomes excessive in the acrylonitrile-based polymer solution, and the spin coagulation step. It is not preferable because it will contaminate the acrylonitrile polymer solution and gelation of the acrylonitrile-based polymer solution is more facilitated.

  In the present invention, at least one compound selected from the group consisting of ammonia, an amine compound, and a quaternary ammonium salt is added between a storage tank of an acrylonitrile-based polymer solution and a base, and is used for wet spinning or dry wet spinning. To obtain precursor fibers.

  Here, the storage tank refers to a tank for storing an acrylonitrile polymer solution. That is, in the case of solution polymerization, to complete spinning of an acrylonitrile-based polymer solution in which the unreacted acrylonitrile residual ratio and the polymer concentration are in the desired ranges, after the completion of polymerization, through a step of removing unreacted acrylonitrile, a polymer concentration adjusting step, and the like. It is a tank for storing liquid. In the case of bulk polymerization and aqueous suspension polymerization, after the acrylonitrile polymer obtained by polymerization is dissolved in a solvent, the unreacted acrylonitrile residual ratio and the polymer concentration are desired through the unreacted acrylonitrile removal step, the polymer concentration adjustment step, etc. This is a tank for storing the acrylonitrile-based polymer solution in the range for spinning.

  If such a storage tank is not provided, if trouble occurs in the unreacted acrylonitrile removal step or the polymer concentration adjustment step, the supply of the acrylonitrile-based polymer solution to the spinning stops and spinning may not be possible. In order to stop spinning when trouble occurs in spinning, the process of removing unreacted acrylonitrile or the polymer concentration adjusting process must be stopped. Therefore, the storage tank 1 shown in FIG. 1 is usually provided as described in JP-A-60-209005.

  When the addition of at least one compound selected from the group consisting of ammonia, an amine compound, and a quaternary ammonium salt is made before or in the storage tank, it is added between the storage tank and the base, Compared with the case where it is added in part A, B or C in FIG. 2, the time after adding at least one compound selected from the group consisting of ammonia, an amine compound and a quaternary ammonium salt is increased. Gel generation becomes significant. The shorter the time from the addition of at least one compound selected from the group consisting of ammonia, an amine compound, and a quaternary ammonium salt to the spinning, the less gel is likely to occur. That is, it is preferable to carry out at the part C in FIG. Here, the immediate vicinity of the base means a place where there is no facility where a polymer solution such as a pump or a filter can stay between the base and the base is connected to the base by a pipe or a static mixer. Specifically, the portion indicated by reference numeral 8 in FIGS.

  In the present invention, a static mixer for mixing the acrylonitrile-based polymer solution immediately after the addition of at least one compound selected from the group consisting of ammonia, an amine compound, and a quaternary ammonium salt is provided by mixing. It is preferable for improving the state. This embodiment is shown in FIGS. Although it is not particularly defined as a mixer, a static mixer (registered trademark of Noritake Co., Ltd.) and a high mixer (registered trademark of Toray Engineering Co., Ltd.) are preferably exemplified because a good mixing state can be obtained. it can.

  In the present invention, the acrylonitrile monomer concentration in the acrylonitrile-based polymer solution is preferably 0.001 to 0.1% by weight, and more preferably 0.0015 to 0.08% by weight. Such a acrylonitrile concentration is less than 0.001%, which is difficult to achieve by a known method and difficult to implement industrially. When it is less than 0.001%, it remains in the acrylonitrile-based polymer solution. Since the amount of unreacted acrylonitrile is too small, there is a high possibility that gel generation will be remarkable. When the acrylonitrile concentration in the acrylonitrile polymer solution exceeds 0.1% by weight, unreacted acrylonitrile remaining in the acrylonitrile polymer solution is discharged during spinning, which may deteriorate the working environment.

  In addition, the method described in Patent Documents 4, 5, and 6 can be suitably used as the method for adjusting the acrylonitrile concentration in the acrylonitrile-based polymer solution to 0.001 to 0.1% by weight. This is performed before the acrylonitrile polymer solution is stored in the storage tank.

  In the spinning process of the present invention, carbon fiber precursor fibers are obtained by wet spinning or dry wet spinning, and each may be performed by a known method. In the present invention, since the influence of the gel can be greatly reduced, the frequency of occurrence of yarn breakage during the spinning process is reduced, that is, the carbon fiber precursor fiber can be stably obtained.

  The precursor fiber obtained by the above production method is flameproofed at 180 to 300 ° C. in an oxidizing atmosphere, and then carbonized at 400 to 2000 ° C. in an inert atmosphere to produce carbon fibers. A known method can be used for the flameproofing treatment and the carbon fiber production method, and the carbon fiber obtained in the present invention has no effect on the strength of the gel because the effect of the gel is greatly reduced. It has high strength characteristics in strength.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. The characteristics described in this example were determined by the following method.
(1) Number of yarn breaks in the yarn making process It was determined by dividing the number of yarn breaks in the yarn making process by the net raw yarn production (t).
(2) Tensile strength of carbon fibers Using carbon fiber bundles, the tensile strength of six strands was measured according to the Japanese Industrial Standard (JIS) -R-7601 (1986) “Resin-impregnated strand test method”, and the average value was calculated. It calculated | required as strand tensile strength.
[Example 1]
The monomer composition is acrylonitrile / itaconic acid = 99.5 / 0.5 (mol%), DMSO is used as a solvent so that the total monomer concentration is 22% by weight with respect to the total charged amount, and 2,2′- A reflux tube, agitation, so that azobisisobutylnitrile (hereinafter referred to as AIBN) is 0.004 mol / L with respect to the total charged amount, and monothioglycol as the polymerization degree adjusting agent is 0.2% by weight with respect to the total monomers. The reaction vessel equipped with wings was charged. A polymerization reaction was performed at 70 ° C. with stirring in a nitrogen atmosphere. After polymerization, an acrylonitrile polymer solution having an acrylonitrile polymer content of 20% was obtained. The monomer concentration of unreacted acrylonitrile in the polymer solution was 2% by weight.

  Next, the method described in Patent Document 6, that is, the method of removing the unreacted acrylonitrile monomer by supplying the obtained acrylonitrile-based polymer solution to a degassing tank with reduced pressure, An acrylonitrile polymer solution having a concentration of 0.03% by weight was obtained. The polymer solution is continuously stored in a storage tank, filtered through a liquid feed pump, filtered by a filter, then passed through a metering pump, and ammonia is 1 time the amount of itaconic acid in the pipe section (part C in FIG. 5). After mixing with a static mixer, precursor fibers were obtained by wet spinning.

The operability of wet spinning was stable, and the number of yarn breakage was 0.2 times / t.
The obtained precursor fiber is flame-resistant at 240 ° C. in an air atmosphere, followed by carbonization treatment at 400 to 1300 ° C. in a nitrogen atmosphere, and a surface treatment at an electric quantity of 10 coulomb per gram of carbon fiber using an aqueous sulfuric acid solution as an electrolyte After washing with water and washing with water, 1% by weight of a sizing agent mainly composed of bisphenol A type epoxy resin was attached to the carbon fiber and dried to obtain carbon fiber. The obtained carbon fiber had good tensile strength.
[Example 2]
Precursor fibers and carbon fibers were produced in the same manner as in Example 1 except that the mixing with a static mixer was not performed after the addition of ammonia (FIG. 2).

As for the operability of wet spinning, the number of yarn breaks was stable at 0.4 times / t, and the carbon fiber obtained had high tensile strength.
[Example 3]
Ammonia addition was performed after the storage tank and the liquid feed pump, that is, in front of the filter, and the precursor fiber and carbon fiber were mixed in the same manner as in Example 1 except that mixing was performed using a static mixer immediately after the ammonia addition (FIG. 3). Manufactured.

As for the operability of wet spinning, the number of yarn breaks was stable at 0.3 times / t, and the carbon fiber obtained had high tensile strength.
[Example 4]
Precursor fibers and carbon fibers were produced in the same manner as in Example 1 except that ammonia addition was performed after the filter, that is, before the metering pump, and mixing was performed using a static mixer immediately after ammonia addition (FIG. 4).

As for the operability of wet spinning, the number of yarn breaks was stable at 0.3 times / t, and the carbon fiber obtained had high tensile strength.
[Example 5]
After completion of the polymerization, precursor fibers and carbon fibers were produced in the same manner as in Example 1 except that the unreacted acrylonitrile monomer was not removed.

As for the operability of wet spinning, the number of breaks was stable at 0.1 times / t, but the acrylonitrile concentration in the atmosphere above the coagulation bath liquid surface of wet spinning was as high as 20 ppm. The obtained carbon fiber had high tensile strength.
[Comparative Example 1]
Precursor fibers and carbon fibers were produced in the same manner as in Example 1 except that ammonia addition and mixing with a static mixer were performed before storing in the storage tank.

The operability of wet spinning was unstable, and the number of yarn breaks was 1.5 times / t. The tensile strength of the obtained carbon fiber was also low.
[Comparative Example 2]
Precursor fibers and carbon fibers were produced in the same manner as in Example 2 except that ammonia was added in the storage tank.

  The operability of wet spinning was unstable, and the number of yarn breaks was 1.2 times / t. The tensile strength of the obtained carbon fiber was also low.

  According to the method for producing a carbon fiber precursor fiber of the present invention, an acrylonitrile-based polymer solution with a small amount of gel can be used for spinning, and stable spinning operability can be achieved. In addition, it can be suitably used for textile production for clothing and industrial applications.

  Further, according to the present invention, carbon fibers having good strength with few defects inside the fibers can be obtained.

It is a conceptual diagram from the storage tank to the coagulation bath in the conventional wet spinning. It is the schematic of the place where the at least 1 sort (s) of compound chosen from the group which consists of ammonia, an amine compound, and a quaternary ammonium salt is added. It is the schematic which shows an example of the preferable aspect of this invention. It is the schematic which shows another example of the preferable aspect of this invention. It is the schematic which shows another example of the preferable aspect of this invention.

Explanation of symbols

1: storage tank 2: liquid feed pump 3: filter 4: metering pump 5: base 6: coagulation bath 7: static mixer 8: portions A, B, C near the base: ammonia of the present invention, amine compound, quaternary ammonium Where to add at least one compound selected from the group consisting of salts

Claims (4)

A method for producing a carbon fiber precursor fiber by spinning an acrylonitrile polymer solution obtained by copolymerizing 0.01 to 2 mol% of at least one carboxyl group-containing vinyl compound, the polymer solution storage tank A method for producing a carbon fiber precursor fiber, wherein at least one compound selected from the group consisting of ammonia, an amine compound and a quaternary ammonium salt is added between the base and the base, and then the acrylonitrile polymer solution is spun. The method for producing a carbon fiber precursor fiber according to claim 1, wherein at least one compound selected from the group consisting of ammonia, an amine compound, and a quaternary ammonium salt is added at a pipe portion closest to the die. The method for producing a carbon fiber precursor fiber according to claim 1 or 2, wherein the concentration of the acrylonitrile monomer in the acrylonitrile-based polymer solution is 0.001 to 0.1% by weight. A precursor fiber obtained by the production method according to any one of claims 1 to 3 is subjected to flameproofing treatment at 180 to 300 ° C in an oxidizing atmosphere, and subsequently carbonized at 400 to 2000 ° C in an inert atmosphere. Production method

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