KR101536780B1 - Method of preparing for polyacrylonitrile based carbon fiber - Google Patents

Abstract

The present invention relates to a method for producing a PAN-based carbon fiber which removes or reduces a foreign substance which can exist in a large amount in a precursor fiber through a water washing and ultrasonic treatment in a washing process before the PAN precursor fiber is subjected to chlorination treatment, and a polyacrylonitrile polymer A dope producing step of preparing a dope using the dope; A precursor fiber preparation step in which the dope is wet-laid or dry-wet-spinned to produce a PAN-based precursor fiber; A dechlorination step of dechlorinating the precursor fiber; And a carbonization step of carbonizing the dechlorinated fiber, wherein the polyacrylonitrile polymer comprises 95 wt% or more of acrylonitrile and 5 wt% or less of comonomer, and the nose The monomer includes two or more monomers selected from the group consisting of methyl acrylate, acrylic acid, methacrylic acid, and itaconic acid, and the precursor fibers are washed with a washing tank equipped with an ultrasonic generator before the chlorination step. And a water-washing step of washing with water.

According to the present invention, the PAN-based carbon fiber precursor fibers are washed with ultrasonic waves before the chlorination treatment, whereby high-strength / high-elasticity carbon fibers can be produced without high-quality chlorinated fibers, furthermore, surface defects and macroscopic and micro voids have.

Precursor fiber for carbon fiber, carbon fiber, PAN, ultrasonic, foreign matter, water washing device

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a polyacrylonitrile-

The present invention relates to a method for producing polyacrylonitrile (PAN) carbon fibers, and more particularly, to a method for producing polyacrylonitrile (PAN) carbon fibers, which comprises subjecting polyacrylonitrile-based precursor fibers to abundance in precursor fibers through water- The present invention relates to a method for producing a PAN-based carbon fiber which removes or reduces foreign matters.

BACKGROUND ART Carbon fibers, so-called PAN (polyacrylonitrile) -based carbon fibers, produced from acrylonitrile-based polymers are very strong and widely used as raw materials for carbon fibers. More recently, more than 90% of the total carbon fibers are PAN-based carbon fibers. In addition, since PAN-based carbon fibers are also applicable to carbon electrode materials for secondary batteries and carbon films, research and development thereof have also been actively conducted.

In the case of producing a carbon fiber from an acrylonitrile-based polymer, acrylic fiber obtained by spinning an acrylonitrile-based polymer, that is, a precursor for a carbon fiber is subjected to chlorination treatment at 200 to 400 ° C in an oxidizing atmosphere. Is called chlorinated fiber.

The chlorinated fibers thus obtained are carbonized at 800 to 2000 占 폚 in an inert gas atmosphere to produce carbon fibers. The carbon fiber thus obtained may be treated in an inert gas at a higher temperature. The thus obtained fiber is referred to as graphite fiber.

As the application of carbon fibers has expanded, the demand for high tensile strength carbon fibers has also increased. In the past, a resin impregnation technique was used to increase the tensile strength of carbon fibers.

In this connection, in order to reduce the foreign matter and voids present in the fibers of each single fiber constituting the carbon fiber, a technique of strengthening the filtration of the monomer or polymer stock solution is disclosed in Japanese Patent Application No. 59-88924, -12882.

Further, in order to suppress the generation of surface defects, a technique for controlling the shape of the fiber guide used in the manufacturing process of the precursor fiber or the tension of the fiber in contact with the guide is disclosed in Japanese Patent Publication No. 3-41561.

Further, a technique of modifying the precursor fibers by densifying the precursor fibers to suppress the generation of voids or fine defects has also been proposed. A technique for compacting the undrawn yarn by optimizing the coagulation bath condition is disclosed in Japanese Patent Laid-Open Publication No. 59-82420, and a technique for making the drawn yarn compact by increasing the drawing temperature of the coagulation bath is disclosed in Japanese Patent Publication 15722.

However, such a densification improving technique tends to lower the oxygen permeability to the fibers in the chloride-reducing process, so that there is a problem that the tensile strength of the finally obtained carbon fiber is lowered.

The chlorination process is a preliminary process for carbonizing the precursor fibers, that is, the acrylic fibers. If the chlorination process is carried out with the precursor fibers that have not sufficiently removed the foreign substances, the quality of the carbon fibers produced deteriorates.

Specifically, the precursor fibers in which the foreign matters are not sufficiently removed may form voids in the chloride-decomposing process or cause the filaments to contact each other, and as a result, the strength of the carbon fibers may be deteriorated.

DISCLOSURE Technical Problem The present invention has been conceived to solve the problems described above, and it is an object of the present invention to provide a precursor fiber in which foreign substances are completely removed in the chloride- And a method for producing carbon fibers.

In order to solve the above-mentioned problems, the present invention provides a dope preparation method comprising: a dope preparation step of preparing a dope using a polyacrylonitrile polymer; A precursor fiber preparation step in which the dope is wet-laid or dry-wet-spinned to produce a PAN-based precursor fiber; A dechlorination step of dechlorinating the precursor fiber; And a carbonization step of carbonizing the dechlorinated fiber, wherein the polyacrylonitrile polymer comprises 95 wt% or more of acrylonitrile and 5 wt% or less of comonomer, and the nose The monomer includes two or more monomers selected from the group consisting of methyl acrylate, acrylic acid, methacrylic acid, and itaconic acid, and the precursor fibers are washed with a washing tank equipped with an ultrasonic generator before the chlorination step. And a water-washing step of washing with water.

The carbonization step may be performed at a temperature of 200 to 400 ° C. in an oxygen atmosphere and the carbonization step may be performed at a temperature of 800 to 2000 ° C. in an inert atmosphere And the carbon fiber is treated.

According to the present invention, the PAN-based carbon fiber precursor fibers are washed with ultrasonic waves before the chlorination treatment to remove foreign substances present in the fibers, thereby obtaining a high-strength / high-strength chlorinated fiber with no surface defects and macroscopic and micro voids, A high-elasticity carbon fiber can be produced.

Hereinafter, the features and advantages of the present invention will be described in detail with reference to the accompanying drawings.

The present invention relates to a method of producing carbon fibers, and is characterized in that the precursor fibers are ultrasonically cleaned to remove impurities of the precursor fibers before the chlorination of the precursor fibers.

The carbon fiber produced according to the present invention is obtained from an acrylonitrile-based polymer. The properties of the carbon fiber basically vary depending on the composition of the acrylonitrile-based polymer. The main component of the acrylonitrile-based polymer used in the present invention is an acrylonitrile unit, and the content of the acrylonitrile unit is 90% by weight or more, preferably 95% by weight or more, based on the total acrylonitrile-based polymer. If the content of the acrylonitrile unit is too small, the strength of the carbon fiber obtained by the firing process may be lowered, and the mechanical properties of the carbon fiber may be deteriorated.

The acrylonitrile-based polymer may contain, if necessary, one or more copolymerizable components (other auxiliary components other than acrylonitrile), a unit including a densification accelerating component and a stretching accelerating component in the spinning process; A unit containing an anti-chloride-promoting component in an anti-chloride process; A unit including an oxygen permeation promoting component, and the like. The content of the additional copolymerizable component is 10% by weight or less, preferably 5% by weight or less, based on the total acrylonitrile-based polymer.

The structural unit which becomes the densification promoting component is produced by copolymerization of a vinyl compound monomer having a hydrophilic functional group such as a carboxyl group, a sulfonic group or an amide group. Examples of the densification accelerating component-containing monomer having a carboxyl group include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, maleic acid, and alkyl esters thereof (such as methyl acrylate) Of these, acrylic acid, methacrylic acid, itaconic acid and the like are preferably used. Specific examples of the sulfone group-containing densification accelerating component include aryl sulfonic acid, metharylsulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid 2-acrylamido-2-methyl propane sulfonic acid, vinyl sulfonic acid, and sulfopropyl methacrylate. Specific examples of the structural unit of the densification accelerating component having an amide group include acrylamide, methacrylamide, and dimethylmetacrylamide.

Also, in order to improve the oxygen permeability of the fiber end in the chlorination furnace, alkyl amines such as octyl amine, dodecyl amine and lauryl amine; Dialkylamines such as dioctyl amine; Trialkylamines such as trioctylamine; A diamine component such as ethylene diamine or hexamethylene diamine may be used. Among them, in order to improve the uniformity of the polymerization, it is preferable to use a component having solubility in a polymerization solvent, a medium, a spinning solvent and the like.

In addition, the unit including the oxygen permeation accelerating component may be introduced by copolymerization of one alkyl ester of an unsaturated carboxylic acid structure, for example, ethyl methacrylate. When such an auxiliary component (comonomer) and the main component are subjected to aqueous suspension polymerization using an inorganic redox catalyst according to a conventional method, an acrylonitrile-based copolymer can be obtained.

The precursor fibers used in the process for producing carbon fibers according to the present invention are obtained from a polyacrylonitrile polymer comprising 95 wt% or more of acrylonitrile and 5 wt% or less of comonomer. The comonomer preferably includes two or more kinds of monomers selected from the group consisting of methyl acrylate, acrylic acid, methacrylic acid and itaconic acid.

As described above, the chlorination treatment is a step for stabilizing the precursor fibers before carbonizing the precursor fibers. When the precursor fibers that have not sufficiently removed the foreign materials are subjected to the chlorination treatment, voids are formed in the chloride- It is important to completely remove impurities of the precursor fibers in the previous stage of the chloride attack.

The present invention is characterized in that a washing process is performed to remove foreign substances present inside the precursor fibers before the chlorination step, and ultrasonic treatment is performed in order to increase the removal efficiency of foreign substances during the washing process.

Therefore, an ultrasonic wave generating device is provided in a lower portion of the water washing apparatus used in the present invention. Any type of the ultrasonic wave generator may be used, but it is preferable to use one capable of controlling the intensity of the ultrasonic wave generated.

Further, the flushing apparatus used in the present invention has a flushing bath of one stage to four stages, preferably one stage or two stages. The number of wash rollers at each stage is 2 to 6, preferably 2 to 4.

Hereinafter, the present invention will be described in more detail by way of examples. The following examples illustrate the present invention, and the scope of the present invention is not limited by the following examples.

Preparation of precursor fibers

A polymer obtained by copolymerizing acrylonitrile (96 wt%), methyl acrylate (3 wt%) and itaconic acid (1 wt%) was dissolved in dimethyl sulfoxide (DMSO) to a concentration of 20 wt% and defoamed to prepare a dope stock solution Respectively. The stored dope stock solution was wet-spinned using 3000 nozzles of 0.06 mm diameter and solidified in a coagulation bath consisting of a 50 wt% aqueous DMSO solution adjusted to 50 ° C to form coagulation.

After the multi-layered water was washed with water, the layer was firstly drawn in hot water to give an amino-modified silicone-based silicone emulsion. The thus obtained fibers were dried in a roller heated at 120 占 폚 and then drawn in a pressure steam at 140 to 185 占 폚 to obtain PAN-based precursor fibers having a single fiber fineness of 0.98 denier and a filament number of 6,000.

< Example  1>

The precursor fibers obtained as described above were washed with water in a water bath at a temperature of 220 to 270 DEG C in an aqueous bath before being subjected to dechlorination. Next, the carbonization process was carried out in a nitrogen atmosphere at 300 to 1500 ° C to obtain carbon fibers. The strand tensile strength and the CV% of the tensile strength of the carbon fibers thus obtained were measured, and the results are shown in Table 1.

< Example  2>

The precursor fibers thus obtained were subjected to two-stage flushing in a water bath before the chlorination step, and then subjected to chlorination treatment in air at 220 to 270 ° C. Next, the carbonization process was carried out in a nitrogen atmosphere at 300 to 1500 ° C to obtain carbon fibers. The strand tensile strength and the CV% of the tensile strength of the carbon fibers thus obtained were measured, and the results are shown in Table 1.

< Example  3>

The precursor fibers obtained as described above were subjected to two-stage washing and ultrasonic treatment in a water bath equipped with an ultrasonic device before the chlorination process, and then subjected to chlorination treatment in the air at 220 to 270 캜. Next, the carbonization process was carried out in a nitrogen atmosphere at 300 to 1500 ° C to obtain carbon fibers. The strand tensile strength and the CV% of the tensile strength of the carbon fibers thus obtained were measured, and the results are shown in Table 1.

< Comparative Example >

The precursor fibers thus obtained were immediately chlorinated in the air at 220 to 270 ° C without washing with water, and carbonization was carried out in a nitrogen atmosphere at 300 to 1500 ° C to obtain carbon fibers. The strand tensile strength and the CV% of the tensile strength of the carbon fibers thus obtained were measured, and the results are shown in Table 1.

division Example 1 Example 2 Example 3 Comparative Example 1
polymer
The polymerization composition and
Properties AN / MA / IA = 96/3/1
Intrinsic viscosity: 1.65
Yield: 85%
radiation
Precursor fiber 0.98 denier
6000 filament
Washing condition Whether it is waterproof O O O X Suesse singles One 2 2 - Ultrasonic treatment X X O X
Properties
The tensile strength
(GPa)
3.92
3.99
4.13
3.71 Tensile strength change rate
(CV%)
5.2
4.5
4.0
6.0

Comparing Examples 1 to 3 and Comparative Example with reference to Table 1, it can be seen that the strength of the final carbon fiber increases as the water washing step is performed before the chlorination of the precursor fibers. Further, even if the same water washing step is performed, the strength of the final carbon fiber is further increased in the case of ultrasonic treatment.

Therefore, according to the present invention, high strength / high quality carbon fibers can be produced.

Claims (2)

A dope is prepared using a polyacrylonitrile polymer composed of not less than 95 wt% of acrylonitrile and not more than 5 wt% of a comonomer containing two or more monomers selected from methyl acrylate, acrylic acid, methacrylic acid and itaconic acid A dope producing step; A precursor fiber preparation step in which the dope is wet-laid or dry-wet-spinned to produce a PAN-based precursor fiber; A dechlorination step of dechlorinating the precursor fiber; And a carbonization step of carbonizing the chlorinated fiber, the method comprising the steps of: In order to remove impurities and micro / macro defect existing in a precursor fiber or in a precursor fiber in large quantities before the chlorination step, there is provided an ultrasonic wave generator having a first to fourth water bath, And washing the precursor fibers with a washing tank having two to six wash rollers at a stage of washing the precursor fibers. delete