KR20190019297A - Method for preparing carbon fiber - Google Patents

Abstract

The present invention relates to a method for producing a carbon fiber which reduces oxidation stabilization time. The method comprises the steps of: (S1) fiberizing a polyacrylonitrile-based polymer; (S2) oxidizing and stabilizing a fibrous polyacrylonitrile-based polymer to produce a polyacrylonitrile-based fiber; and (S3) carbonizing the polyacrylonitrile-based fiber to produce a carbon fiber. In addition, the oxidation stabilization comprises the steps of: plasma-treating the fibrous polyacrylonitrile-based polymer at 150 to 350 °C; and thermally treating the plasma-treated polyacrylonitrile-based polymer at 150 to 350 °C.

Description

METHOD FOR PREPARING CARBON FIBER [0002]

More specifically, the present invention relates to a method for producing a carbon fiber excellent in tensile strength, tensile elastic modulus, and elongation by oxidizing and stabilizing a fibrous polyacrylonitrile-based polymer while continuously performing a plasma treatment and a heat treatment The present invention relates to a method for producing carbon fibers.

Carbon fiber is one-fifth the weight of steel, but its strength is more than ten times stronger. Accordingly, carbon fiber is used as a high-strength structural material in various industrial fields such as aerospace, sports, automobiles, and bridges. Carbon fiber has begun to attract attention as a next-generation material due to the rapid development and upgrading of the automobile and aerospace industries, and demand is increasing as the automobile industry aims for environment-friendly, low-energy consumption futuristic automobile. In the field of automobiles, there is a growing demand for lighter automobiles as well as environmental regulations related to automobile exhaust gas, which will be a problem in the future. Therefore, the demand for carbon fiber reinforced composites that can maintain the structural mechanical strength while increasing the weight of automobiles has increased rapidly .

However, since the price of carbon fiber is too high to be used for the above purposes, it is necessary to use the carbon fiber suitable for the automobile industry and the construction infra. 1 or more should be lowered.

Generally, carbon fibers are prepared through an oxidation stabilization process that oxidizes and stabilizes by applying heat in an oxidizing atmosphere to infuse precursor fibers, and a carbonization process that carbonizes the oxidized stabilized fibers at a high temperature. And subsequently subjected to a graphitization process. At this time, the precursor fibers of the carbon fiber include polyacrylonitrile (PAN), pitch, rayon, lignin, and polyethylene. Of these, polyacrylonitrile fibers have an excellent carbon yield of 50% or higher and a high melting point, which is an optimum precursor for producing high-performance carbon fibers as compared with other precursors. Accordingly, most current carbon fibers are made from polyacrylonitrile fibers.

However, the process of oxidizing and stabilizing the polyacrylonitrile polymerized with fibers is slower than the carbonization process, and thus takes a long time and consumes a large amount of energy. Accordingly, in order to improve the production efficiency of carbon fibers, various attempts have been made to improve the properties of carbon fibers while shortening the oxidation stabilization time.

KR2011-0078246A

The present invention provides a method for producing carbon fibers which can remarkably improve the properties of carbon fibers while shortening the oxidation stabilization time.

In order to solve the above problems, the present invention provides a method for producing a polyacrylonitrile-based polymer, comprising: (S1) fiberizing a polyacrylonitrile-based polymer; Oxidizing and stabilizing the fibrous polyacrylonitrile-based polymer to prepare a polyacrylonitrile-based fiber (S2); And S3) carbonizing the polyacrylonitrile-based fiber to form a carbon fiber, wherein the oxidation stabilization comprises: plasma-treating the fibrous polyacrylonitrile-based polymer at 150 to 350 DEG C; And heat treating the plasma-treated polyacrylonitrile-based polymer at 150 to 350 占 폚.

The method for producing carbon fibers according to the present invention can accelerate the oxidation stabilization by sequentially performing the plasma treatment and the heat treatment on the fibrous polyacrylonitrile-based polymer, thereby remarkably reducing the production time of the carbon fibers . Further, it is possible to provide a carbon fiber having remarkably excellent tensile strength, tensile elastic modulus and elongation.

Fig. 1 shows an example of the oxidation stabilizing apparatus used in the present invention.
Fig. 2 shows a top view of the showerhead shown in Fig. 1. Fig.
3 is a graph showing tensile strength and tensile elastic modulus of carbon fibers of Examples 1 to 6 and Comparative Examples 1 to 3. FIG.
4 is a graph showing the diameter and elongation of carbon fibers of Examples 1 to 6 and Comparative Examples 1 to 3.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the description of the present invention and in the claims should not be construed to be limited to ordinary or dictionary terms and the inventor should appropriately interpret the concept of the term appropriately The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention.

One. Carbon fiber  Manufacturing method

According to one embodiment of the present invention, there is provided a method for producing a polyacrylonitrile-based polymer (hereinafter referred to as " PAN-based polymer " Oxidizing and stabilizing the fibrous PAN-based polymer to produce polyacrylonitrile-based fiber (hereinafter referred to as PAN-based fiber) (S2); And S3) carbonizing the PAN-based fiber to form a carbon fiber, wherein the oxidative stabilization comprises plasma-treating the fibrous PAN-based polymer at 150-350 占 폚; And heat treating the plasma-treated PAN-based polymer at 150 to 350 占 폚.

PAN system  The step of fiberizing the polymer (S1)

The PAN-based polymer used in the step of fiberizing the PAN-based polymer may be a homopolymer obtained by polymerizing acrylonitrile alone, and may be a homopolymer obtained by polymerizing an acrylonitrile-based monomer, a carboxylic acid-based monomer, and an alkyl (meth) And may be a PAN-based copolymer that is copolymerized with at least one comonomer selected.

The carboxylic acid monomer is not particularly limited, but may be at least one member selected from the group consisting of itaconic acid, acrylic acid and methacrylic acid, and it may specifically be itaconic acid. The alkyl (meth) acrylate monomer is not particularly limited, but may be at least one selected from the group consisting of methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate and propyl methacrylate And specifically may be methyl acrylate.

As the polymerization method of the PAN-based polymer, known polymerization methods such as solution polymerization, suspension polymerization and emulsion polymerization can be used, and solution polymerization is preferable in consideration of process convenience. Examples of the solvent used in the solution polymerization include dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide and the like. In consideration of the productivity, that is, the solidification rate, dimethylsulfoxide Lt; / RTI >

The step of fiberizing the PAN-based polymer may be a step of making the PAN-based polymer have a fiber shape by applying a spinning process or the like.

More specifically, the prepared PAN-based polymer can be added to a solvent capable of dissolving the PAN-based polymer such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, etc. and dissolved to prepare a spinning solution. If a solution polymerization method is used in the production of the PAN-based polymer, a step of dissolving the produced PAN-based polymer in a spinning solvent may be unnecessary if the same solvent and spinning solvent are used as the polymerization solvent.

The concentration of the PAN-based polymer in the spinning stock solution may be 10 to 40 wt%, preferably 15 to 35 wt%, more preferably 20 to 30 wt%. When the above-mentioned range is satisfied, the viscosity of the spinning stock solution can be maintained at a level at which the fiberization process can be easily carried out. Further, the stability of the spinning stock solution can be improved because the viscosity of the spinning stock solution is not changed with time.

In addition, it may be desirable to perform a process of filtering a filter having a pore size of about 1 탆 or less before spinning the spinning stock solution to remove the raw material of the polymerization reaction and the impurities mixed in each step. In this case, The strength of the product carbon fiber can be improved.

The spinning may be dry spinning, wet spinning or dry spinning, and it may be desirable to apply wet or dry spinning radiation. For the purpose of improving the compactness of PAN-based fibers and improving mechanical properties, it may be preferable to use dry-wet spinning.

The radiation may be performed while passing the spinning solution through a spinneret. The shape, diameter and number of holes in the spinneret can be adjusted to suit the end product carbon fiber. The material of the spinneret is not particularly limited, but examples thereof include stainless steel, gold, and platinum.

In the present invention, the fiberization of the PAN-based polymer in the present invention can be initiated by causing the spinning stock solution to coagulate after the spinning solution is discharged into the coagulation bath through the spinneret during wet or dry wet spinning. The coagulation bath may include a coagulation solution containing an organic solvent such as dimethylsulfoxide, dimethylformamide, dimethylacetamide and the like, which is used as a solvent for the spinning solution, and a coagulation promoter. As the coagulation promoter, those which are compatible with the solvent used in the spinning solution without dissolving the PAN-based polymer can be used, for example, water can be applied.

The discharge amount and the discharge speed of the spinning stock solution can be adjusted according to the concentration of the spinning solution. Specifically, when the diameter of the hole in the spinneret is 0.1 mm and the number of the holes is 100, the discharge amount is 1 to 10 cc / min, the discharge speed is 0.3 to 4 m / min, specifically 0.5 to 2 m / Lt; / RTI > Specifically, when the solvent contained in the spinning solution is dimethylsulfoxide, the temperature at the time of discharging may be 40 to 60 캜. When the above-mentioned temperature range is satisfied, the fluidity and viscosity of the spinning stock solution can be appropriately maintained.

The temperature of the solidifying solution can be determined in consideration of the solidification point of the solidifying solution, the boiling point, the density of the PAN-based fibers, and the balance of the strength of the carbon fiber as a final product. Specifically, the temperature of the solidifying solution may be 40 to 60 캜. More specifically, the temperature of the coagulation solution may be the same as the temperature of the spinning solution. This is because high-quality PAN-based fibers are produced only when the temperature and viscosity are kept constant or the temperature and viscosity gradient are minimized in the entire process until the spinning liquid becomes fibers.

After the coagulation step, a washing step and a stretching step may be applied. The two processes may be carried out in a reactor or reactors provided from 5 to 15 depending on the design, and the washing and stretching may be carried out sequentially or successively or in reverse order, and may be a plurality of processes, And the number of times each process is performed can be adjusted, and each process can be performed at least once.

The washing and stretching are classified according to the function to be carried out. The washing and stretching may be performed simultaneously in one reaction tank, and the washing and stretching may be performed several times, And there is no particular limitation on the order.

The stretching step may be performed preferably in a single or multiple stretching baths controlled at a temperature of 60 to 100 DEG C, preferably 70 to 100 DEG C, more preferably 80 to 100 DEG C, It may be 1.5 to 10 times, preferably 2 to 6 times, more preferably 3 to 5 times the entire length of the washed coagulated yarn.

In the spinning process, an emulsifier composed of silicone or the like may be added to prevent adhesion between fibers. The silicone emulsifier may use modified silicone and it may be preferable to add an amino-modified silicone emulsifier having high heat resistance.

In addition, further processes such as dry heat treatment or steam drawing can be further performed, and the spinning process can be carried out through such a process, thereby obtaining a fibrous PAN-based polymer.

PAN system  The step of fabricating the fibers (S2)

The step of producing a PAN-based fiber oxidizes and stabilizes the fibrous PAN-based polymer, wherein the oxidative stabilization comprises plasma-treating the fibrous PAN-based polymer at 150 to 350 캜; And heat treating the plasma-treated PAN-based polymer at 150 to 350 占 폚.

The oxidation stabilization is performed in order to prevent the PAN-based fiber, which is a polymer material, from dissolving in the carbonization process to be described later. It changes the molecular structure in the fibrous PAN-based polymer so that the PAN-based fiber has salt resistance, Which is an insolubilizing process.

The oxidation stabilization can be largely divided into a cyclization reaction, a dehydrogenation reaction and an oxidation reaction. The cyclization reaction is a cyclization of radicals in the fiber molecule due to external energy. The dehydrogenation reaction and the oxidation reaction are carried out in such a manner that the hydrogen atoms are separated from the molecules in the oxidizing atmosphere (dehydrogenation reaction) (Oxidation reaction). At this time, when the oxygen atoms are uniformly transferred to the inside of the fiber, a stable ladder structure is formed as a whole to have excellent salt resistance.

The oxidation stabilization can be performed by using the oxidation stabilization apparatus used in the technical field of the present invention without any particular limitation, but for the sake of understanding, one example will be explained with reference to FIG. 1 and FIG.

Referring to FIG. 1, the oxidation stabilization apparatus 100 includes a plasma generator (not shown), a showerhead 110, a chamber 120, and a heating source 130.

The plasma generating unit (not shown) is a region where a plasma containing oxygen-active species is generated. A cathode electrode and an anode electrode, to which high-frequency power is supplied, may be provided therein. . When a high frequency power is supplied to the cathode and anode electrodes and a reactive gas is supplied to the plasma generation unit, a plasma containing oxygen-active species may be generated in the plasma generation unit. The oxygen active species may be oxygen atom (O), superoxide (O ₂ ^- ), hydrogen peroxide (H ₂ O ₂ ), hydroxyl radical (OH)

Referring to Figure 2, the showerhead 110 is shown. The showerhead 110 is positioned below the plasma generator and includes a plurality of jetting ports 110a on the upper surface thereof. The number and arrangement of the jetting ports can be appropriately adjusted as necessary. The showerhead 110 can serve as an auxiliary electrode for generating plasma, and can also provide a path for movement of a plasma containing oxygen-active species.

The chamber 120 is positioned below the showerhead 110 so that the plasma can be supplied through the injection port of the showerhead 110. The fibrous PAN-based polymer is received and plasma and heat treatment are performed.

Further, the inside of the chamber 120 may be set in a vacuum atmosphere, an inert gas atmosphere, an atmospheric atmosphere, or an oxygen atmosphere. Also, a fixing device capable of fixing the fiberized PAN-based polymer with a predetermined tensile force can be accommodated in the chamber 120. The chamber 120 may be provided with a window 120a for observing the inside thereof.

A heating source 130 may be positioned below the chamber 120 to supply heat to the chamber 120. The type of the heating source 130 is not particularly limited as long as it can supply heat to the chamber 120, but it may be a heating air inlet or heater for supplying heated air into the chamber 120. Oxidation of the fibrousized PAN-based polymer to heat of the heated air or heater supplied through the air inlet may occur. The supply of heat energy can be controlled by the flow rate and temperature of the heated air or the temperature of the heater, and the oxidation stabilization can be controlled by adjusting the flow rate, the temperature and the power ratio of the heated air or the heat of the heater.

Meanwhile, the plasma treatment step oxidizes and stabilizes the PAN-based polymer that is simultaneously fibrillated using plasma and heat. The plasma treatment step may be performed at a temperature rise phase (P1) of 1 to 20 ° C / minute, An isothermal phase P2 that maintains a constant temperature for 1 to 20 占 폚 / min; And an isothermal phase (P3) to maintain the temperature elevated for 1 to 20 minutes. When both the temperature rise phase P1 and the isothermal phase P3 are included, the temperature rise phase P1 and the isothermal phase P3 may be repeated for at least one cycle and repeated for 1 to 5 cycles.

The temperature-raising phase P1 is preferably a temperature raising phase of 1 to 15 占 폚 / min, more preferably a temperature raising phase of 1 to 10 占 폚 / min. The starting temperature of the heating phase P1 may be 150 to 250 캜, preferably 160 to 240 캜, and more preferably 180 to 220 캜. Further, the temperature-raising phase (P1) can be performed for 1 to 20 minutes, preferably for 1 to 15 minutes, and more preferably for 1 to 12 minutes.

The isothermal phase P2 preferably maintains a constant temperature for 1 to 15 minutes and more preferably maintains the temperature for 1 to 12 minutes.

The isothermal phase (P3) preferably maintains the elevated temperature for 1 to 15 minutes, and more preferably maintains the elevated temperature for 1 to 12 minutes.

If the plasma processing step includes the heating phase P1 and the isothermal phase P3 and the heating phase P1 and the isothermal phase P3 are repeated for two or more cycles, (P3) is preferably performed for 1 to 10 minutes, and more preferably for 1 to 6 minutes.

If the plasma treatment is carried out under the above-mentioned conditions, the fibrous PAN-based polymer can be oxidized and stabilized without being damaged. In addition, in the heat treatment step described later, the oxidation stabilization of the plasma-treated PAN-based polymer can be accelerated and the oxidation stabilization time can be remarkably reduced. In addition, the physical properties of the carbon fiber as a final product, that is, the tensile strength, the tensile elastic modulus and the elongation can be improved.

However, if the plasma treatment is performed at a temperature lower than the above-mentioned temperature raising rate, the physical properties of the final product, i.e., tensile strength, tensile elastic modulus and elongation, may be lowered. If the plasma treatment is performed in excess of the above-mentioned heating rate, the fibrous PAN-based polymer may be damaged during the plasma treatment. When the plasma treatment is carried out at a temperature lower than the above-described initiation temperature, the fibrous PAN-based polymer can not be oxidized and stabilized in the early stage, so that oxidation stabilization can not be performed in a short time. When the plasma treatment is performed above the above- The polymer may be damaged and the physical properties of the carbon fiber as a final product may be deteriorated. If the plasma treatment is performed for less than the above-mentioned time, the fibrous PAN-based polymer can not be sufficiently oxidatively stabilized, and if the plasma treatment is performed for more than the above-mentioned time, the physical properties of the carbon fiber as the final product, The elastic modulus may be lowered.

The heat treatment step is a step of oxidizing and stabilizing the thermally treated PAN-based polymer. The step of heat-treating is a step of oxidizing and stabilizing the PAN-based polymer subjected to heat treatment, which includes a temperature rising period (H1) of 1 to 20 DEG C / minute, an isothermal period (H2) of maintaining a constant temperature for 1 to 20 minutes, A temperature rise period H1 of 20 DEG C / min and an isothermal period H3 of maintaining the temperature of the temperature increase for 1 to 20 minutes. If both the temperature rising period H1 and the isothermic period H3 are included, the temperature rising period H1 and the isothermal period H3 may be repeated for one or more cycles and repeated one to five cycles.

The temperature rising section H1 is preferably a temperature rising section at a rate of 1 to 15 DEG C / minute, and more preferably a temperature rising section at a rate of 1 to 10 DEG C / minute. Also, when one cycle of the temperature rising period H1 and the isothermal period H3 is performed, the starting temperature of the temperature rising period H1 may be the temperature at the end of plasma processing. If the temperature rise section H1 and the isothermal section H3 are repeated for two or more cycles, the temperature of the immediately preceding section may be the start temperature. Also, the temperature rising period (H1) may be performed for 1 to 20 minutes, preferably 1 to 15 minutes, and more preferably 1 to 12 minutes.

The isothermal section H2 preferably maintains a constant temperature for 1 to 15 minutes, and more preferably maintains a constant temperature for 1 to 12 minutes. The temperature of the isothermal section H2 may be the same as the temperature at the end of the plasma treatment.

The isothermal section H3 preferably maintains the temperature that has been raised for 1 to 15 minutes and more preferably maintains the temperature that has been raised for 1 to 12 minutes.

If the heating period H1 and the isothermic period H3 include the heating period H1 and the isothermal period H3 repeated for two or more cycles, the heating period H1 and the isothermal period H3 H3) is preferably performed for 1 to 10 minutes, and more preferably for 1 to 6 minutes.

If the heat treatment step is carried out under the above-described conditions, the oxidized stabilization can be accelerated without damaging the fibrous PAN-based polymer, and thereby the oxidation stabilization time can be remarkably reduced. In addition, the physical properties of the carbon fiber as a final product, that is, the tensile strength, the tensile elastic modulus and the elongation can be improved.

However, if the heat treatment is performed at a temperature lower than the above-mentioned temperature raising rate, the physical properties of the carbon fiber as a final product, that is, the tensile strength, the tensile elastic modulus and the elongation can be lowered. If the heat treatment is performed in excess of the above-mentioned heating rate, the fibrous PAN-based polymer may be damaged during the heat treatment. If the heat treatment is performed for less than the above-mentioned period of time, the fibrous PAN-based polymer can not be sufficiently oxidatively stabilized, and if the heat treatment is performed in excess of the above-mentioned time, not only the oxidation stabilization time can be shortened, There is no effect to further improve the physical properties of the resin.

PAN system  Carbonizing the fiber (S3)

The carbonization step may be performed generally in an inert atmosphere, and a gas such as nitrogen, argon or xenon may be applied to the substance forming the inert atmosphere. The carbonization temperature in the carbonization step may be about 1,000 ° C or higher, preferably 1,200 ° C or higher, and the upper limit may be 2,000 ° C or lower, preferably 1,800 ° C or lower.

The carbonization step may be a general carbonization process applied in the production of carbon fibers, and is not particularly limited to the above conditions.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

<Preparation of Oxidation Stabilization Apparatus>

A plasma generation unit generating a plasma including an oxygen active species; A showerhead positioned below the plasma generator and including a plurality of ejection openings to provide a path for movement of the plasma; A chamber positioned below the showerhead to allow the plasma to be provided through the injection port of the showerhead, wherein the fibrous PAN-based polymer is accommodated and subjected to plasma and heat treatment; And a heating source disposed at a lower portion of the chamber to supply heat to the chamber. The chamber is filled with 30,000 sccm of argon gas and 200 sccm of oxygen gas, and a power of 250 W is applied. Atmosphere.

A fibrous PAN-based polymer (manufacturer: Jilin, trade name: 12K) was placed in the chamber of the oxidation stabilizer.

< Carbon fiber  Manufacturing>

Example  One

The fibrous PAN polymer was subjected to plasma treatment while raising the temperature of the heating source at a rate of 4 DEG C / min from 200 DEG C for 3 minutes. Subsequently, the temperature was raised to 220 ° C at 212 ° C at a rate of 4 ° C / minute, maintained at 220 ° C for 5 minutes, raised to 240 ° C at 220 ° C at a rate of 4 ° C / minute, The temperature was raised to 260 ° C at a rate of 4 ° C / minute from 240 ° C, held at 260 ° C for 5 minutes, raised to 280 ° C at 260 ° C at a rate of 4 ° C / minute, maintained at 280 ° C for 5 minutes PAN-based polymer was heat-treated to produce PAN-based fiber.

Subsequently, the PAN fibers were carbonized while raising the temperature from 25 占 폚 to 1,200 占 폚 at 5 占 폚 / min and naturally cooled at room temperature to produce carbon fibers.

Example  2

The fibrous PAN polymer was subjected to plasma treatment while raising the temperature of the heating source to 220 DEG C at a rate of 4 DEG C / min at 200 DEG C for 5 minutes. Then, the temperature was maintained at 220 캜 for 5 minutes, the temperature was raised to 240 캜 at a rate of 4 캜 / minute from 220 캜, the temperature was maintained at 240 캜 for 5 minutes, the temperature was increased from 240 캜 to 260 캜 at a rate of 4 캜 / The PAN-based polymer was heat-treated at 260 ° C for 5 minutes, heated to 260 ° C at a rate of 4 ° C / minute to 280 ° C and maintained at 280 ° C for 5 minutes, The carbon fiber was prepared in the same manner as in Example 1 except for the following.

Example  3

The heating source was heated to 220 DEG C at 200 DEG C at a rate of 4 DEG C / min for 5 minutes, and the fibrous PAN polymer was plasma-treated while being maintained at 220 DEG C for 2 minutes. Subsequently, the temperature was maintained at 220 DEG C for 3 minutes, the temperature was increased from 220 DEG C to 240 DEG C at a rate of 4 DEG C / minute, the temperature was maintained at 240 DEG C for 5 minutes, The PAN-based polymer was heat-treated at 260 ° C for 5 minutes, heated to 260 ° C at a rate of 4 ° C / minute to 280 ° C and maintained at 280 ° C for 5 minutes, The carbon fiber was prepared in the same manner as in Example 1 except for the following.

Example  4

The heating source was heated to 200 ° C at a rate of 4 ° C / minute for 5 minutes to 220 ° C, and the fibrous PAN polymer was plasma treated while being maintained at 220 ° C for 5 minutes. Subsequently, the temperature was raised to 240 ° C at 220 ° C at a rate of 4 ° C / minute, held at 240 ° C for 5 minutes, raised to 260 ° C at 240 ° C at a rate of 4 ° C / minute, The same procedure as in Example 1 was carried out except that the PAN-based fiber was prepared by heating the plasma-treated PAN-based polymer at 260 ° C at a rate of 4 ° C / min to 280 ° C and holding it at 280 ° C for 5 minutes Carbon fibers were prepared.

Example  5

The heating source was heated to 220 DEG C at 200 DEG C at a rate of 4 DEG C / min for 5 minutes and maintained at 220 DEG C for 5 minutes to heat the fibrous PAN polymer. Then, the temperature was raised to 240 DEG C at 220 DEG C at a rate of 4 DEG C / minute, and the PAN-based polymer subjected to the heat treatment was plasma-treated while maintaining the temperature at 240 DEG C for 5 minutes. Then, the temperature was raised to 260 占 폚 at a rate of 4 占 폚 / min at 240 占 폚, held at 260 占 폚 for 5 minutes, raised to 280 占 폚 at 260 占 폚 at a rate of 4 占 폚 / min, Carbon fiber was produced in the same manner as in Example 1, except that the PAN-based fiber was prepared by heat-treating the plasma-treated PAN-based polymer.

Example  6

The heating source was heated from 220 DEG C to 220 DEG C for 5 minutes at a rate of 4 DEG C / min at 200 DEG C, held at 220 DEG C for 5 minutes, heated to 220 DEG C at 240 DEG C for 5 minutes at a rate of 4 DEG C / , And the fibrous PAN-based polymer was heat-treated at 240 DEG C for 5 minutes. Then, the temperature was raised to 260 ° C at 240 ° C at a rate of 4 ° C / minute, and the heat-treated PAN-based polymer was plasma-treated while maintaining the temperature at 260 ° C for 5 minutes. Subsequently, the same process as in Example 1 was carried out except that the PAN-based fiber was prepared by heating the plasma-treated PAN-based polymer at 260 ° C at a rate of 4 ° C / min to 280 ° C and holding the cell at 280 ° C for 5 minutes Carbon fibers were prepared.

Comparative Example  One

The heating source was heated from 220 DEG C to 220 DEG C for 5 minutes at a rate of 4 DEG C / min at 200 DEG C, held at 220 DEG C for 5 minutes, heated to 220 DEG C at 240 DEG C for 5 minutes at a rate of 4 DEG C / , Maintained at 240 DEG C for 5 minutes, heated at 240 DEG C at a rate of 4 DEG C / min for 5 minutes to 260 DEG C, and maintained at 260 DEG C for 5 minutes to heat-treat the fibrous PAN polymer. Next, the same procedure as in Example 1 was carried out except that the PAN-based fiber was prepared by plasma-treating the heat-treated PAN-based polymer at 280 ° C for 5 minutes while raising the temperature to 260 ° C at 260 ° C at a rate of 4 ° C / Carbon fibers were prepared.

Comparative Example  2

The heating source was heated from 220 DEG C to 220 DEG C for 5 minutes at a rate of 4 DEG C / min at 200 DEG C, held at 220 DEG C for 5 minutes, heated to 220 DEG C at 240 DEG C for 5 minutes at a rate of 4 DEG C / , Held at 240 DEG C for 5 minutes, heated at 240 DEG C at a rate of 4 DEG C / minute to 260 DEG C for 5 minutes, held at 260 DEG C for 5 minutes, held at 260 DEG C at a rate of 4 DEG C / Carbon fiber was prepared in the same manner as in Example 1, except that PAN-based fibers were prepared by plasma-treating the fibrous PAN-based polymer while maintaining the temperature at 280 DEG C for 5 minutes.

Comparative Example  3

The heating source was heated from 220 DEG C to 220 DEG C for 5 minutes at a rate of 4 DEG C / min at 200 DEG C, held at 220 DEG C for 5 minutes, heated to 220 DEG C at 240 DEG C for 5 minutes at a rate of 4 DEG C / , Held at 240 DEG C for 5 minutes, heated at 240 DEG C at a rate of 4 DEG C / minute to 260 DEG C for 5 minutes, held at 260 DEG C for 5 minutes, held at 260 DEG C at a rate of 4 DEG C / Carbon fiber was prepared in the same manner as in Example 1, except that the PAN-based fiber was prepared by heating the fibrous PAN-based polymer to 280 DEG C while maintaining the temperature at 280 DEG C for 5 minutes.

Comparative Example  4

The carbon fiber was prepared in the same manner as in Example 1, except that the PAN-based fiber was prepared by plasma-treating the fibrous PAN-based polymer while maintaining the heating source at 260 캜 for 30 minutes.

Experimental Example  One: Carbon fiber  Property evaluation

The properties of the carbon fibers of Examples 1 to 6 and Comparative Examples 1 to 4 were evaluated and shown in Fig. 3, Fig. 4, and Table 1.

1) Tensile strength and tensile elastic modulus (㎬): Measured using Single-Fiber Testers (manufactured by Textechno (trade name: Favimat +)).

A group of fibers having a fiber length of 40 to 50 mm was taken from the sample and single fibers were pulled out one by one and attached to the binding apparatus of the tensile tester. The length of the specimen was set to 25 mm and the tensile speed was 10 mm / min. Tensile strength and modulus of elasticity were measured on 20 specimens and their average values were indicated.

2) Elongation (%): Measured using Single-Fiber Testers (manufacturer: Textechno, trade name: Favimat +).

 In order to measure the tensile strength and the tensile elasticity, the selected fibers were stretched in the longitudinal direction, and the ratio of the elongation of the fibers until the fracture was measured using the difference between the length of the fibers and the length of the initial fibers at the moment when the fibers failed. The average value thereof is indicated.

3) Diameter of carbon fiber (㎛): Diameter of carbon fiber was calculated by dividing linear density by density.

Density was measured using Archimedes' principle.

p = W _a / (W _a -W _l ) x p _l

(p: density, W _a : weight of carbon fiber in air, W _l : weight of carbon fiber in liquid, p _l : density of liquid)

Linear density was calculated using Mersenne's law.

Where [f] is the resonance frequency of the vibration, L [km] is the length of the vibration string, T [N] is the tensile force applied to the carbon fiber, and μ [tex = g km ^-1 ]

division Tensile strength (㎬) Tensile modulus (㎬) Elongation (%) Diameter (탆) Example 1 2.87 207.76 1.50 7.35 Example 2 3.54 215.68 1.81 7.40 Example 3 3.23 217.58 1.61 7.25 Example 4 3.21 218.65 1.60 7.42 Example 5 2.53 174.32 1.56 7.50 Example 6 2.63 168.19 1.68 7.43 Comparative Example 1 2.50 200.21 1.36 7.20 Comparative Example 2 2.06 130.96 1.69 7.33 Comparative Example 3 2.54 198.84 1.38 7.43 Comparative Example 4 1.66 120.20 1.49 7.16

Referring to FIGS. 3, 4, and 1, as in the case of the carbon fibers of Examples 1 to 4, plasma treatment was performed while heating at 200 ° C. or plasma treatment was performed while maintaining the temperature at 200 ° C. and maintained at 220 ° C., It was confirmed that when the fibrous PAN copolymer was oxidized and stabilized, it was possible to produce a carbon fiber having a small diameter with excellent tensile strength, tensile elastic modulus and elongation. This is attributed to the acceleration of the oxidation stabilization due to the plasma treatment performed in the early stage, and the acceleration of the plasma treatment positively influenced the physical properties of the carbon fiber. When the plasma treatment time was 5 minutes or more, it was confirmed that the longer the heat treatment time in the continuous process, the better the physical properties of the carbon fiber.

It was confirmed that when the heat treatment was performed before and after the plasma treatment as in the carbon fibers of Example 5 and Example 6, the tensile strength and the elongation were excellent when the plasma treatment temperature was high, and the tensile elasticity was excellent when the plasma treatment temperature was low .

On the other hand, when oxidation stabilization was carried out for the same temperature condition and time as in the case of the carbon fibers of Comparative Examples 1 to 3 but the plasma treatment or the plasma treatment time was different, plasma treatment was not performed as in Comparative Example 3, It was found that the case of plasma treatment for only a short period of time was advantageous in terms of tensile strength and tensile elastic modulus and that it was advantageous in terms of elongation when plasma treatment alone as in Comparative Example 2 was carried out. In addition, in the case of the carbon fibers of Comparative Example 1 and Comparative Example 3, since the tensile strength, the tensile elastic modulus and the elongation are at the same level, the plasma treatment after the heat treatment, It was confirmed that the effect of improving the tensile strength, tensile elastic modulus and elongation was insufficient and only the diameter of the carbon fiber was affected.

When the plasma treatment was carried out while the temperature was raised and maintained repeatedly, as compared with Comparative Example 1 and Comparative Example 4, in which the plasma treatment was carried out but the temperature conditions were different, plasma treatment was carried out at a constant temperature to oxidize and stabilize. And that it is advantageous in terms of elongation.

However, when the oxidation stabilization was carried out only by the plasma treatment or the heat treatment as in the carbon fibers of Comparative Examples 1 to 4, the tensile strength, tensile elastic modulus and elongation were not more excellent than those of the carbon fibers of Examples 1 to 4, It was confirmed that the elongation was not superior to that of the carbon fibers of Examples 5 to 7. [

Claims (13)

Fiberizing the polyacrylonitrile-based polymer (S1);
Oxidizing and stabilizing the fibrous polyacrylonitrile-based polymer to prepare a polyacrylonitrile-based fiber (S2); And
(S3) carbonizing the polyacrylonitrile-based fiber to produce a carbon fiber,
The oxidation stabilization
Subjecting the fibrous polyacrylonitrile-based polymer to plasma treatment at 150 to 350 占 폚; And heat treating the plasma-treated polyacrylonitrile-based polymer at 150 to 350 占 폚.
The method according to claim 1,
The oxidation stabilization
A plasma generation unit generating a plasma including an oxygen active species;
A showerhead positioned below the plasma generator and including a plurality of ejection openings to provide a path for movement of the plasma;
A chamber positioned below the showerhead to allow the plasma to be provided through the injection port of the showerhead, wherein the fibrous polyacrylonitrile-based polymer is accommodated and subjected to plasma and heat treatment; And
And a heating source located in the lower portion of the chamber to supply heat to the chamber.
The method according to claim 1,
Wherein the plasma treatment step comprises an elevation phase (P1) at 1 to 20 占 폚 / min.
The method according to claim 1,
Wherein the step of plasma treatment comprises an isothermal phase (P2) maintaining a constant temperature for 1 to 20 minutes.
The method according to claim 1,
The plasma processing step
A heating phase (P1) of 1 to 20 DEG C / min; And
An isothermal phase (P3) that maintains the elevated temperature for 1 to 20 minutes,
Wherein the temperature increase phase (P1) and the isothermal phase (P3) are repeated one cycle or more.
The method according to claim 3 or 5,
Wherein the heating phase (P1) is performed for 1 to 20 minutes.
The method according to claim 1,
Wherein the heat treatment step includes a temperature rising period (H1) of 1 to 20 DEG C / min.
The method according to claim 1,
Wherein the heat treatment step includes an isothermal section (H2) maintaining a constant temperature for 1 to 20 minutes.
The method according to claim 1,
The step of heat-
A temperature rise period (H1) of 1 to 20 DEG C / minute; And
And an isothermal section (H3) maintaining the temperature elevated for 1 to 20 minutes,
Wherein the temperature rising section (H1) and the isothermal section (H3) are repeated one cycle or more.
The method according to claim 7 or 9,
And the temperature rising period (H1) is performed for 1 to 20 minutes.
The method according to claim 7 or 9,
Wherein the heat treatment further comprises maintaining the temperature at the end of the plasma treatment for 1 to 20 minutes before the temperature rise period (H1).
The method according to claim 1,
Further comprising preliminary heat treatment at a temperature lower than the temperature during the plasma treatment before the step of plasma treatment.
The method of claim 12,
Wherein the preliminary heat treatment includes a preliminary temperature rise period of 1 to 20 DEG C / min and a preliminary temperature increase period of 1 to 20 minutes to maintain the temperature of the preliminary heat treatment period, and wherein the preliminary temperature rise period and the preliminary temperature rise period are repeated one cycle or more Method of making fiber.

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