KR101490529B1 - Preparation method of polyacrylonitrile precursor based carbon Fiber - Google Patents

Abstract

The present invention relates to a process for producing polyacrylonitrile precursor fibers for the production of high-performance carbon fibers by stably supplying a spinning dope to a spinning process to improve process stability, operability and productivity .

The polyacrylonitrile-based carbon fiber precursor fiber according to the present invention controls the frequency of the gel polymer that can be generated in the spinning solution to a predetermined standard, thereby minimizing the amount of fuzzy fibers generated in the spinning process Thereby improving the stability and operability of the precursor fiber production process.

The carbon fiber using the polyacrylonitrile-based precursor fiber of the present invention has a lower generation amount than the carbon fiber which does not manage the gel polymer, thereby improving the process stability, workability and productivity in manufacturing various composite materials, And mechanical properties such as tensile modulus, and can be preferably used for structural materials and reinforcing materials in various aerospace applications, sports leisure applications, and industrial applications.

Carbon fiber, polyacrylonitrile, fiber stock solution, gel polymer, frequency measurement, management standard

Description

Preparation method of polyacrylonitrile precursor based carbon fiber [0002]

The present invention relates to a method for producing polyacrylonitrile-based precursor fibers for carbon fibers, and more particularly, to a method for producing polyacrylonitrile-based precursor fibers for carbon fibers by controlling the frequency of gel polymers, The production of carbon fiber precursor fibers that minimizes the number of moths that can occur in the precursor fiber production process, and the production of polyacrylonitrile precursor fibers and the strength and tensile strength of the precursor fiber spinning process with improved process stability, The present invention relates to a method for producing a polyacrylonitrile-based precursor fiber for carbon fibers, which is improved in mechanical properties such as tensile modulus, modulus and elastic modulus.

Carbon fibers made from polyacrylonitrile-based precursor fibers have better productivity and mechanical properties than carbon fibers made from rayon-based and pitch-based precursors. Carbon fibers obtained by carbonizing polychloronitrile precursor fibers at 850 to 1800 ° C in an inert gas atmosphere stabilized at 200 to 350 ° C in an oxidizing gas atmosphere have a weight of less than one quarter of that of steel However, the mechanical strength is 6 to 10 times higher than that of steel. Therefore, it is used for various aerospace applications, sports leisure and industrial use, and its structural and reinforcing materials are expected to be used more widely.

The polyacrylonitrile-based polymer is a method of copolymerizing a small amount of a vinyl monomer including a carboxylic acid group together with acrylonitrile in order to accelerate the chlorination treatment of the precursor fiber to secure stability It is widely used. A method of ionizing the above carboxyl group with ammonia or ammonium salt in order to increase the hydrophilicity of the spinning solution and inhibit micro or macrovoids in wet or dry wet spinning by making a spinning solution with the polyacrylonitrile copolymer produced as described above Japanese Unexamined Patent Publication No. 59-82421 and Japanese Unexamined Patent Application, First Publication No. Hei 11-12856. However, the ammonia or ammonium salt injected for ionizing a carboxyl group easily generates a gel polymer in the spinning solution, Polymers tend to deteriorate production stability and operability because they act as impurities in the precursor fiber spinning process.

A method of adding a certain amount of a compound containing an ethylene-based double bond into a spinning stock solution to suppress the formation of a gel polymer in a polyacrylonitrile-based spinning stock solution has been proposed in Japanese Patent Application Laid-Open No. 2002-249924 . Unlike this, a method of minimizing the generation of gel polymer by positioning the position where ammonia is injected just before the spinning nozzle is disclosed in Japanese Patent Application Laid-Open No. 2008-308775. However, at present, precise quantification methods and management standards for gel polymers are not yet clearly proposed, and it is difficult for Goseong to secure process stability, productivity, and productivity in producing polyacrylonitrile precursor fibers for carbon fibers.

Among the processes for producing polyacrylonitrile-based precursor fibers for high-performance carbon fibers, the gel polymer present in the spinning solution causes deterioration of productivity, deterioration of workability and deterioration of stability in the spinning process. Therefore, by controlling the frequency of the gel polymer present in the spinning liquid to a certain level, it is possible to secure productivity, operability and stability in the spinning process, to produce stable precursors by reducing the number of droplets, and by treating them with chlorination and carbonization, It is an object of the present invention to provide a method for producing polyacrylonitrile-based precursor fibers for fibers.

In order to achieve the above object, the present invention relates to a method for producing a copolymer by copolymerizing an acrylonitrile monomer and a vinyl copolymerizable monomer including a carboxyl group, A method for producing a polyacrylonitrile precursor fiber for carbon fiber by using a stock solution is characterized in that the gel polymer frequency in the spinning stock solution is controlled to be 20 pieces / mm 2 or less.

By controlling the frequency of the gel polymer in the spinning stock solution on the basis of a certain standard, the quality of the precursor fibers is uniform, and the threading can be prevented in the process, thereby improving the productivity. Further, in the succeeding firing step, it is possible to reduce the defects of the carbon fibers and to easily manufacture the high strength / high elasticity carbon fibers.

In order to produce polyacrylonitrile precursor fibers for high performance carbon fibers, a copolymer is prepared by copolymerizing 95 to 99.8 wt% of an acrylonitrile monomer and 0.2 to 5 wt% of a vinyl copolymerizable monomer containing a carboxyl group, , The ammonia or ammonia water is injected, and defoaming and unreacted acrylonitrile monomer are recovered, and the gel polymer frequency in the spinning stock solution stored in the storage tank is controlled to be 20 / mm 2 or less to emit the precursor for high performance carbon fiber It is an object of the present invention to obtain fibers.

A detailed description of the present invention follows.

In order to promote and stabilize the chlorination process of the precursor fibers, 0.2 to 5 wt% of a vinyl copolymerizable monomer containing a carboxyl group is added to 95 to 99.8 wt% of an acrylonitrile monomer, and water suspension polymerization or solution polymerization is carried out to obtain polyacrylonitrile Based copolymer.

The content of acrylonitrile should be 95 ~ 99.8 wt%. When the content of acrylonitrile is less than 95 wt%, the components decomposed in the spinning or firing process are increased, so that the physical properties of the carbon fiber are lowered and the yield is lowered and the productivity is lowered. If the content of acrylonitrile is 99.8 wt% or more, oxidation reaction of the precursor fibers may not accelerate chloride attack and may cause a runaway reaction. At this time, the content of the acrylonitrile monomer is more preferably 97 to 99.5 wt%.

Examples of vinyl monomers containing carboxyl groups contained in the polyacrylonitrile copolymer include acrylic acid, itaconic acid, methacrylic acid and the like, and itaconic acid having a large number of carboxyl groups is the most preferable.

As the polymerization method of the polyacrylonitrile-based copolymer, the aqueous suspension polymerization method and the solution polymerization method can be used, and the solution polymerization method is preferable for convenience of processing and convenience of operation. Organic solvents such as dimethyl formamide, dimethyl sulfoxide, and dimethyl acetamide are widely used as solvents for solution polymerization. At this time, dimethylsulfoxide having good solubility, low toxicity and small chain transfer constant is most preferable as a solvent for solution polymerization.

Ammonia or ammonia water or an ammonium salt is added to the copolymer to ionize the carboxyl group portion of the vinyl compound of the polyacrylonitrile copolymer to improve the hydrophilicity and to suppress void formation during solidification in the coagulating bath. Ammonia or ammonia water, which is cheap and easy to handle, is preferable. Amount of ammonia or ammonia water to be added is preferably 0.6 to 1.5 times, and more preferably 0.9 to 1.1 times, in terms of a mole ratio with respect to the vinyl compound containing a carboxyl group in the copolymer.

For the preparation of the spinning solution, the aqueous suspension polymer may be dissolved in a solvent, or a solution obtained by removing unreacted monomer of the solution polymer may be used as it is. At this time, the concentration of the polyacrylonitrile-based copolymer constituting the spinning solution is suitably 15 to 25 wt%, particularly preferably 18 to 22 wt%. If the concentration of the copolymer in the spinning liquid is lower than 15 wt%, the structure of the coagulated yarn becomes coarse during the solidification process of the wet or dry wet spinning process, and the voids are formed. If the concentration is higher than 25 wt%, the viscosity of the spinning solution becomes excessively high, so that the spinning machine can become unstable and the stretchability is deteriorated and the productivity is deteriorated.

The frequency of the gel polymer in the spinning stock solution is preferably 20 / mm 2 or less, and more preferably 10 / mm 2 or less. If the frequency of the gel polymer is more than 20 / mm 2, the stability of the spinning process is deteriorated due to an increase in the number of milling cycles in the spinning process, and thereafter, the milling is increased in the firing process, resulting in obtaining low-quality carbon fibers. A method and a method for measuring the frequency of the gel polymer in the spinning stock solution are as follows.

After placing 10 μl of the spinning solution on a hemocytometer with a grid spacing of 1 mm, the spinning stock solution was spread evenly and the thickness of the spinning solution coated on the slide was 0.1 mm. When observed at a ratio, the appearance as shown in Fig. 1 can be found.

The number of gel polymers per grid (1 mm²) observed is counted regardless of shape and size. The number of times of measurement was determined by preparing three slide glasses, observing 10 lattices per slide glass, and averaging them to determine the frequency of the gel polymer in the spinning stock solution.

The spinning liquid is spinned by a wet or dry spinning process and then spun into a coagulating bath where it is subjected to a process such as water washing, hot water drawing, emulsion application, primary drying, steam drawing, secondary drying and heat fixing, relaxation, Nitrile-based carbon fiber precursor fibers are produced and then carbonized at low temperature, carbonized at high temperature, carbonized, surface treated, sizing treated, and wound to produce final carbon fiber.

Hereinafter, the present invention will be described in more detail with reference to specific examples. The following examples illustrate the present invention and are not intended to limit the scope of the present invention.

< Example  1>

A reactor having a capacity of 200 liters was charged with 79.7 wt% of dimethyl sulfoxide, 20 wt% of acrylonitrile, 0.2 wt% of itaconic acid, 0.1 wt% of initiator (AIBN) and a molecular weight regulator (DDM) To obtain a copolymer solution having a concentration of 20 wt%. After that, ammonia water was added by the molar ratio of itaconic acid and further stirred at 60 ° C for 2 hours to recover the final spinning solution. The frequency of the gel polymer in the spinning solution was 8.3 / mm 2.

Then, the spinning stock solution stored at 50 ° C was wet-radiated. The temperature of the coagulation bath was 55 ° C and the concentration of dimethylsulfoxide was 40wt%. The number of spinning nozzles was 6, and diameter of 0.1mm, 2000 hole nozzle was used. Thereafter, fibers for carbon fiber precursor were obtained through washing, stretching, emulsion application, drying, steam drawing, heat fixing, relaxation and winding. The tensile strength and the modulus of the fiber were measured. The results are shown in Table 1.

< Example  2>

The same procedure as in Example 1 was carried out except that the number of moles of ammonia water injected in Example 1 was set to 1.1 times the number of moles of itaconic acid to obtain fibers for a carbon fiber precursor. The frequency of the gel polymer in the spinning solution was measured to be 9.7 pieces / mm 2, and the physical properties of the fibers were measured for tensile strength and wetness. The results are shown in Table 1.

< Example  3>

The same procedure as in Example 1 was carried out except that the number of moles of ammonia water injected in Example 1 was 0.9 times the number of moles of itaconic acid. Thus, fibers for carbon fiber precursor were obtained. The frequency of the gel polymer in the spinning solution was measured to be 7.9 fibers / mm 2, and the physical properties of the fibers were measured. The results are shown in Table 1.

< Comparative Example  1>

The same procedure as in Example 1 was carried out except that the number of moles of ammonia water injected in Example 1 was twice the number of moles of itaconic acid. Thus, fibers for carbon fiber precursor were obtained. The frequency of the gel polymer in the spinning solution was measured to be 23.6 pieces / mm 2, and the physical properties of the fibers were measured with respect to tensile strength and moistness. The results are shown in Table 1.

< Comparative Example  2>

The same procedure as in Example 1 was carried out except that the molar number of injected ammonia water of Example 1 was injected as the number of moles of itaconic acid and stirring was carried out at 30 ° C for one hour to obtain fibers for carbon fiber precursor. The frequency of the gel polymer in the spinning solution was measured to be 32.8 / mm 2, and the physical properties of the fiber were measured with respect to tensile strength and moistness. The results are shown in Table 1.

Table 1. Examples Comparative Example

division Ammonia / itaconic acid molar ratio and stirring temperature Among the spinning solution
Gel polymer frequency Moisture of precursor fiber Tensile strength of precursor fibers Stability of spinning process Example 1 1: 1 (60 [deg.] C.) 8.3 pieces / mm² 0.4 pieces / m 7.8 g / d Stable Example 2 1.1: 1 (60 DEG C.) 9.7 pieces / mm² 0.5 pieces / m 7.8 g / d Stable Example 3 0.9: 1 (60 [deg.] C.) 7.9 / mm² 0.4 pieces / m 8.0 g / d Stable Comparative Example 1 2: 1 (60 [deg.] C) 23.6 pieces / mm² 1.2 pieces / m 7.6 g / d Unstable Comparative Example 2 1: 1 (30 [deg.] C) 32.8 / mm² 7.6 pieces / m 7.1 g / d Unstable

Brief Description of the Drawings Fig. 1 is a view showing a gel polymer in a spinning stock solution observed under an optical microscope (100 times). Fig.

Claims (3)

A copolymer is prepared by copolymerizing an acrylonitrile monomer and a vinyl copolymerizable monomer including a carboxyl group, and a copolymerization product is prepared by using a spinning stock solution stored in a storage tank through a process of defoaming and unreacted acrylonitrile monomer recovery. Polyacrylonitrile Based precursor fiber for carbon fibers, wherein the gel polymer frequency in the spinning stock solution is controlled to be 20 / mm &lt; 2 &gt; or less to produce polyacronitrile precursor fibers for carbon fibers. The method according to claim 1, wherein the copolymerization is performed by copolymerizing 95 to 99.8 wt% of an acrylonitrile monomer with 0.2 to 5 wt% of a carboxyl group of the polyacrylonitrile based precursor fiber. The method according to claim 1, wherein ammonia or ammonia water is added to the spinning solution to a molar ratio of the vinyl compound containing a carboxyl group in the copolymer to 0.6 to 1.5 times the amount of the polyacrylonitrile Method of manufacturing precursor precursor fibers.

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