KR20110134136A - Manufacturing method of carbon fiber - Google Patents

Abstract

PURPOSE: A method for fabricating carbon fiber is provided to properly control elongation condition and to minimize fineness deviation. CONSTITUTION: A method of fabricating carbon fiber with reduced fineness deviation comprises: a step of preparing polyacrylonitrile(PAN) precursor spinning solution containing 15-25 wt% of polyacrylonitrile polymers using DMSO as a solvent(100); a step of performing solidification bath of the PAN-based precursor spinning solution in a solidifying solution containing DMSO(110); a step of performing cool elongation of the precursor carbon fiber(120); and a performing primary and second heat elongation of the precursor carbon fiber(130).

Description

Manufacturing method of carbon fiber with reduced fineness deviation {Manufacturing method of carbon fiber}

The present invention relates to a method for producing carbon fibers, and more particularly, to a method for producing polyacrylonitrile-based carbon fibers that can reduce fineness deviation.

Carbon fiber manufactured using polyacrylonitrile-based fiber (hereinafter referred to as 'PAN-based fiber') as a precursor is a reinforcing fiber material of high-performance composite materials such as aerospace, sports, and leisure due to its excellent mechanical properties. As commercially produced and sold. In recent years, the demand for carbon fiber in general industrial fields such as automobiles, ships and building materials is increasing. In the market, high quality and low cost carbon fiber is required for high performance of such composite materials.

The manufacturing method of carbon fiber for such a high performance composite material is largely (1) manufacturing method of carbon fiber using a gas phase method, (2) manufacturing method from melt spinning of a resin composition, and (3) spinning solution There are methods for producing carbon fibers by spinning, dry spinning or wet spinning, but wet and wet spinning are the most widely used methods.

First, as a manufacturing method using a gas phase method, organic compounds, such as benzene, are used as a raw material, organic transition metal compounds, such as ferrocene, are introduced into a high temperature reactor with a carrier gas as a catalyst, and are produced on a base material. , A method of producing carbon fibers by a gas phase method in a suspended state, or a method of growing on a wall of a reactor. However, although the carbon fiber obtained by these methods has high strength and high elastic modulus, there are many branches and there is a problem that the performance for the reinforcing filler is very low. Moreover, in order to use a metal catalyst, the amount of metal contained is large, and when it mixes with resin etc., for example, it had a problem of deteriorating resin by the catalysis.

Next, as a method for producing carbon fibers from melt spinning of a resin composition, a method of producing ultrafine carbon fibers from a composite fiber of a phenol resin and polyethylene is disclosed. In the case of this method, carbon fibers having a small branching structure can be obtained, but since the phenol resin is completely amorphous, it is difficult to form an orientation and exhibits the strength and elastic modulus of the ultrafine carbon fibers that can be obtained because of poor graphitization. There was a problem such as cannot be expected.

On the other hand, in the case of manufacturing the PAN-based carbon fiber by wet or wet spinning method (1) to prepare a PAN-based precursor solution, (2) spinning the prepared precursor solution and solidify it to produce a carbon fiber precursor fiber (PC) And (3) flame-proofing (stabilizing) the prepared carbon fiber precursor fiber at a high temperature and finally carbonizing at a high temperature to produce a final carbon fiber. However, there was a problem that the defect rate of the final product is increased due to the fluctuation of fineness deviation in the carbon fiber finally produced through the above-described steps.

The present invention has been made to solve the above problems, the first problem to be solved of the present invention is to prepare a PAN-based carbon fiber that can reduce the fineness deviation by appropriately adjusting the stretching conditions, etc. during the production of PAN-based precursor fiber To provide a way.

In order to achieve the first object described above, the present invention provides a method for producing carbon fibers, comprising: (1) a polyacrylonitrile-based polymer having a concentration of 15 to 25% by weight of a polyacrylonitrile-based polymer using DMSO as a solvent; PAN-based) preparing a precursor spinning solution, (2) discharging the prepared PAN-based precursor spinning solution from the spinneret by dry-wet spinning method and performing a coagulation bath in a coagulation solution containing DMSO, (3) Cold stretching the precursor carbon fibers subjected to the coagulation bath, (4) performing primary and secondary thermal stretching processes on the precursor carbon fibers subjected to the cold stretching process, and (5) performing the hot stretching process. It provides a method for producing a carbon fiber comprising a step of drying the precursor carbon fiber carried out and the fineness deviation is reduced, characterized in that to satisfy all the following relations (a) ~ (c).

[Relationship]

(a) 0 ≤ [secondary hot drawing temperature (° C)-1st hot drawing temperature (° C)] ≤ 12 ° C

(b) 1.7 ≤ [primary hot draw ratio + secondary hot draw ratio] / [cold draw ratio] ≤ 2.0

(c) 3 ° C. ≦ cold drawing temperature ≦ 12 ° C.

According to a preferred embodiment of the present invention, the polyacrylonitrile-based polymer may be prepared by polymerizing acrylonitrile (AN), methyl acrylate (MA) and itaconic acid (IA).

According to another preferred embodiment of the present invention, the coagulation bath of step (2) preferably includes DMSO as a solvent and a coagulation promoting component. As the coagulation promoting component, those which are compatible with the solvent DMSO used for spinning without dissolving the polymer can be used. Specifically, deionized water is preferably used, and the concentration of DMSO aqueous solution may be 15 to 35% by weight. Higher concentrations of DMSO can complicate and lengthen the flushing process, resulting in lower productivity.

According to another preferred embodiment of the present invention, the precursor passing through the coagulation bath may be subjected to a cold drawing process, and the process may also be performed in a DMSO aqueous solution.

According to another preferred embodiment of the present invention, the cold drawn solvent may be performed in a DMSO aqueous solution.

According to another preferred embodiment of the present invention, the step (4) is; Iii) washing the cold-drawn precursor carbon fibers, ii) oiling the washed precursor carbon fibers, and iii) subjecting the carbon fibers subjected to the oiling process to primary and secondary heat stretching. May comprise a step.

According to another preferred embodiment of the present invention, the oil ring process may use a silicone-based oil.

According to another preferred embodiment of the present invention, the time for performing the coagulation bath in step (2) may be 10 seconds to 2 minutes.

According to another preferred embodiment of the present invention, the primary thermal stretching may be performed at 75 ~ 95 ℃.

According to another preferred embodiment of the present invention, the cold draw ratio may be 3.5 to 4.0.

According to another preferred embodiment of the present invention, the steam stretching step is further performed between the steps (4) and (5), the steam stretching process may be stretched at a draw ratio of 2.5 to 2.9 times.

According to another preferred embodiment of the present invention, the steam stretching step may be performed at 132 ~ 137 ℃.

According to another preferred embodiment of the present invention, after the step (5), it may further comprise the step of flame-resistant treatment and carbonization treatment of the produced carbon fiber precursor fiber.

According to another preferred embodiment of the present invention, there is provided a carbon fiber produced by the above-described manufacturing method, the carbon fiber may be a tensile strength of 4,500 MPa or more and a tensile modulus of 260 GPa or more.

According to another preferred embodiment of the present invention, the carbon fiber may have a fineness variation of less than 0.95%.

Satisfying the relationship of the present invention and the carbon fiber produced using DMSO as a spinning solvent and a coagulating solution can minimize the fineness deviation.

1 is a flow chart of a process according to one preferred embodiment of the present invention.
2 is a flow diagram of a process according to one preferred embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to FIGS. 1 and 2.

As described above, in the case of manufacturing the PAN-based carbon fiber by the conventional melt spinning method, (1) the PAN-based precursor solution is largely prepared, and (2) the prepared precursor solution is spun and solidified to form the carbon fiber precursor fiber ( PC), and (3) flame-resistant (stabilized) the carbon fiber precursor fiber prepared at a high temperature and finally carbonized at a high temperature to produce a final carbon fiber. However, there was a problem that the defect rate of the final product is increased due to the fluctuation of fineness deviation in the carbon fiber finally produced through the above-described steps.

In the present invention, in the method for producing carbon fibers, 1) to prepare a polyacrylonitrile (PAN-based) precursor spinning solution having a concentration of 15 to 25% by weight of polyacrylonitrile-based polymer using DMSO as a solvent (2) discharging the prepared PAN-based precursor spinning solution from the spinneret by dry-wetting spinning method and performing a coagulation bath in a coagulation solution containing DMSO, and (3) a precursor carbon fiber performing the coagulation bath. Cold stretching step, (4) performing the primary and secondary thermal stretching process for the precursor carbon fibers subjected to the cold stretching process, and (5) drying the precursor carbon fibers subjected to the hot stretching process It provides a method for producing a carbon fiber including the steps and satisfying all of the following relations (a) ~ (c) through this to achieve an effect of reducing below a certain level of fineness variation.

[Relationship]

(a) 0 ≤ [secondary thermal drawing temperature (° C)-primary thermal drawing temperature (° C)] ≤ 12 ° C

(b) 1.7 ≤ [primary hot draw ratio + secondary hot draw ratio] / [cold draw ratio] ≤ 2.0

(c) 3 ° C. ≦ cold drawing temperature ≦ 12 ° C.

The above-described content will be described in detail with reference to FIG. 1. First, as a step (1), a polyacrylonitrile-based (PAN-based) precursor spinning solution having a concentration of 15 to 25 wt% of a polyacrylonitrile-based polymer is prepared. (100). Specifically, in order to prepare a PAN polymer, a polymerization process may be performed by a known method by mixing a salt resistance promoting component and / or a sacrificial improvement component with acrylonitrile (AN) as a main component. In this case, the copolymerization process may be performed by using acrylate, methacrylate or methyl acrylate (MA) alone or mixed as a component for improving the sacrificial properties, but is not limited thereto. Any one capable of forming a ronitrile (PAN based) polymer can be used without limitation. The flameproofing promoting component may be specifically used alone or in combination of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide and methacrylamide, and most preferably The itaconic acid may be used, but is not limited thereto, and may be used without limitation as long as it can form a polyacrylonitrile (PAN-based) polymer in the manufacturing process of carbon fiber.

On the other hand, the acrylonitrile (AN) component, methyl acrylate (MA) and itaconic acid (IA) component is preferably 95 to 99.8 wt% of acrylonitrile (AN) component, methylacryl with respect to 100 wt% of the total polymer. 0.1 to 3% by weight of the rate (MA) component 0.1 to 2% by weight of itaconic acid may be mixed but not limited thereto. It is also well known to those skilled in the art to appropriately mix and polymerize the aforementioned sacrificial improving material.

As a polymerization method for producing the polyacrylonitrile-based polymer used in the present invention, known polymerization methods such as solution polymerization, suspension polymerization, and emulsion polymerization can be selected, and the purpose of improving productivity and uniformly polymerizing the copolymerization components is achieved. In order to do this, it is preferable to use solution polymerization.

In this case, as a solution usually used in solution polymerization, a solvent capable of dissolving polyacrylonitrile such as dimethyl sulfoxide (DMSO), dimethylformamide, and dimethylacetamide may be used. It is necessarily applied to carbon fibers prepared as spinning solutions using DMSO as solvent.

On the other hand, the concentration of the polyacrylonitrile-based polymer in the polyacrylonitrile-based (PAN-based) precursor spinning solution should satisfy the range of 15 to 25% by weight. Specifically if the polymer concentration is less than 15% by weight. Not only the intermolecular entanglement in the spinning solution is reduced, but also the compressive strength can be reduced. The higher the polymer concentration, the stronger the linkage between the molecules described above, but when it exceeds 25% by weight, gelation of the spinning stock solution becomes remarkable, and stable spinning becomes difficult. On the other hand, the polymer concentration is polyacrylonitrile-based

It can be controlled by the ratio of spinning solvent to coalescence.

Next, in step (2), the prepared PAN-based precursor spinning solution is discharged from the spinneret by a wet-and-dry spinning method, and a coagulation bath is performed in the coagulation solution containing DMSO (110). Specifically, the spinneret which can be used in the present invention can appropriately adjust the diameter and the number of the hole in accordance with the specifications of the desired carbon fiber. On the other hand, the spinning method of the present invention is limited to the wet and dry spinning method in order to increase the compactness of the polyacrylonitrile-based precursor fiber for producing carbon fibers, and to increase the mechanical properties of the carbon fiber obtained, the wet spinning method or dry spinning method It is difficult to achieve the object of the invention.

In the present invention, when using the wet-dry method, a plurality of precursor fiber bundles are first discharged into the air through a spinneret, and then passed through a space of approximately 1 to 20 mm, and then solidified in a coagulation bath containing a DMSO aqueous solution. You will perform swear words.

According to one feature of the present invention, the coagulation solution used in the coagulation bath must include DMSO, and in the case of using dimethylformamide, zinc chloride aqueous solution and dimethylacetamide solution, which are commonly used as coagulation solutions, It does not fall within the scope of the present invention. On the other hand, the concentration of the aqueous solution of DMSO coagulation in step (2) may be 15 to 35% by weight.

On the other hand, the conditions of the coagulation bath is sufficient to satisfy the conditions of the usual coagulation bath, preferably the time of the coagulation bath may be performed for 10 seconds to 2 minutes, but is not limited thereto, the temperature of the spinning solution is preferably 10 It may be ~ 50 ℃ but is not limited thereto. In addition, the solidification temperature may also be preferably 5 ~ 30 ℃ but is not limited thereto.

Next, as the step (3) and (4), the precursor carbon fibers subjected to the coagulation bath are cold drawn (S120), and the primary and secondary heat stretching processes are performed on the precursor carbon fibers subjected to the cold stretching process. (130). Specifically, the cold drawing process may be performed in a DMSO aqueous solution. Also preferably, the cold drawing step may be performed at 3 to 12 ° C. If the cold drawing temperature is less than 3 ℃ may cause problems in the openness, if the temperature exceeds 12 ℃ may be increased fiber variability. Cold drawing time can be 10 seconds to 1 minute and can be adjusted within the appropriate range. In this case, the precursor carbon fiber may form a precursor fiber bundle (fiber bundle) of several hundreds to tens of thousands of strands depending on the number of detained holes to be spun.

2 is a flowchart specifically showing a preferred embodiment of the step (4), which will be described with reference to FIG. Iii) washing the cold-drawn precursor carbon fibers, ii) oiling the washed precursor carbon fibers, and iii) subjecting the carbon fibers subjected to the oiling process to primary and secondary heat stretching. May be performed including a step, but is not limited thereto.

 Specifically, iii) the cold carbon may be subjected to a washing process of the precursor carbon fiber, and in this case, the washing may be repeated 1 to 3 times. Next, ii) oiling the washed precursor carbon fibers (Oiling), wherein the oiling process may use a silicone-based oil, but is not limited thereto, and is known in the present invention as an oil known in the art Anything that can be used can be used without limitation. Next, i) thermal stretching of the carbon fiber subjected to the oiling process may be performed, wherein the thermal stretching temperature and the stretching ratio should satisfy the conditions of the following equation. Specifically, in order to achieve the effect of reducing the fineness variation, which is an object of the present invention, all of the conditions of the following relations (a) to (c) must be satisfied.

[Relationship]

(a) 0 ≤ [secondary hot drawing temperature (° C)-1st hot drawing temperature (° C)] ≤ 12 ° C

(b) 1.7 ≤ [primary hot draw ratio + secondary hot draw ratio] / [cold draw ratio] ≤ 2.0

(c) 3 ° C. ≦ cold drawing temperature ≦ 12 ° C.

Specifically, even if the range of the b and c values are satisfied, the range of the a value is not satisfied, or conversely, even if the range of the a and b values is satisfied, the range of the value c is not satisfied or Even if the value is satisfied, the object of the present invention cannot be achieved unless the value of b is satisfied (Table 1).

More preferably, the primary thermal stretching temperature that satisfies (a) in the relational formula may be in the range of 75 to 95 ° C., and if the primary thermal stretching temperature is less than 75 ° C., the effect of stretching is well exhibited. There is a problem, and if it exceeds 95 ℃ there is a fear that the fineness variation increases. In addition, the cold draw ratio may preferably be 3.5 to 4.0 times, and if it is out of the range, the effect of reducing the fineness variation may not be properly exhibited.

According to one feature of the present invention, the step (5) may comprise the step of drying the precursor carbon fiber that has performed the thermal stretching process. Specifically, the second oiling process, the drying process, and the steam stretching process may be further included after the heat drawing process of step iii), and the oiling process, the drying process, and the like may follow process conditions that are commonly used. However, in the case of the steam stretching process can be carried out within the range normally used, preferably when drawn at a draw ratio of 2.5 to 2.9 times at 132 ~ 137 ℃ can maximize the effect of reducing the fiber variability (see Table 1). ).

According to a preferred aspect of the present invention, after the step (5), it may further comprise the step of carbonizing the carbon fiber precursor fiber prepared and the step of carbonization, in this case the flameproofing and carbonization step May be carried out through the conditions of conventional PAN-based carbon fiber. Specifically, the flameproofing step may be carried out a flameproofing process while stretching at a draw ratio of 0.75 to 1.25 in air at a temperature of 200 to 400 ℃ to the prepared precursor fiber. When the draw ratio is less than 0.75, the degree of orientation of the flame resistant fiber obtained is insufficient, and the strand tensile modulus of the carbon fiber obtained may decrease. Moreover, when draw ratio exceeds 1.25, workability may fall by fluff occurrence and thread break | fever generation.

The treatment time of flameproofing can be appropriately selected in the range of 10 to 120 minutes, but is not limited thereto.

The carbonized process may be performed on the oxidized PAN fiber having undergone the flameproofing process to obtain a final carbon fiber. Although carbonization is performed in an inert atmosphere, as an inert gas used, nitrogen, argon, xenon, etc. are used, for example. From an economic point of view, nitrogen is preferably used. Carbonization is preferably divided into pre-carbonization and carbonization process, the pre-carbonization temperature is preferably set to 300 to 900 ℃, the heating rate is 300 ℃ / hour or less, the carbonization temperature is 800 to 1500 ℃, the temperature rising rate 500 ℃ It is preferable to set it to / hour or less.

The draw ratio at the time of carbonization may be 0.9-1.2. If the draw ratio is less than 0.9, the degree of orientation and denseness of the carbon fiber obtained may become insufficient, and the strand tensile modulus may decrease. In addition, if the draw ratio exceeds 1.2, fluffing or yarn may occur.

Occasionally, workability may decrease due to breakage.

Meanwhile, according to one feature of the present invention, the carbon fiber produced through the carbonization process may be electrolytically treated to modify the surface thereof. As the electrolyte solution used for the electrolytic treatment, an acidic solution such as sulfuric acid, nitric acid and hydrochloric acid, or an aqueous solution of an alkali such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate and ammonium bicarbonate or salts thereof can be used. The electric current amount and voltage required for the electrolytic treatment are 10 to 30 A and 5 to 30 V, respectively, and can be appropriately selected according to the carbonization degree of the carbon fiber to be applied.

By such an electrolytic treatment, in the composite material obtained, the adhesiveness of carbon fiber and matrix resin can be optimized, the fracture brittleness of the composite material due to excessively strong adhesion, the problem that the tensile strength in the fiber direction falls, and the fiber Although the tensile strength in a direction is high, the adhesiveness with resin is inferior, the problem which the strength characteristic in a non-fiber direction does not express is solved, and the composite material obtained has balanced | balanced in both directions of a fiber direction and a non-fiber direction. Strength properties will be developed.

After such an electrolytic treatment, the sizing treatment can be performed in order to impart focusing properties to the obtained carbon fibers. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected depending on the kind of the matrix resin used for the composite material.

After all, the carbon fiber produced by the above-described manufacturing method of the present invention may have a tensile strength of 4,500 MPa or more and a tensile modulus of 260 GPa or more. In addition, the number of fluff is three or less per 50m carbon fiber, the fineness of the carbon fiber fluctuation rate can also satisfy the value of less than 0.95 (%). If the carbon fiber fluctuation rate is greater than 0.95%, not only the fluctuation of the tow weight per unit length increases, but also the defect causing the fracture increases, the tensile strength decreases, or between the tow and the tow during prepreg molding. There is a possibility of causing a problem such as a gap occurs. Here, the variation rate of the fineness is the variation rate when the toe fineness is measured continuously in the longitudinal direction.

Hereinafter, the present invention will be described in detail by Examples and Experimental Examples. The following Examples and Experimental Examples are only illustrative of the present invention, and the scope of the present invention is not limited to the following Examples and Experimental Examples.

≪ Example 1 >

(1) PAN based precursor solution step

Acrylonitrile (AN), methylacrylate (MA) and itaconic acid (IA) were mixed in a constant monomer composition weight ratio (AN / MA / IA = 98.5 / 1.1 / 0.4) and dissolved homogeneously in dimethyl sulfoxide. Thereafter, 0.3 parts by weight of 2,2'-azobisisobutyronitrile was added to the DMSO solution as a radical initiator and 0.3 parts by weight of octylmercaptan as a chain transfer agent, followed by polymerization to polymerize a concentration of 22% by weight. A spinning solution was prepared to be. The temperature of the reactor was raised from room temperature to 45 ° C. while maintaining the inside of the reactor under a nitrogen atmosphere.

(2) spinning the precursor solution to produce carbon fiber precursor fibers (PC)

The spinning solution (Dope) was quantitatively supplied using a gear pump (25 rpm (15 cc / rev)) and impurities were removed using a Dope Filter having a pore of 40 nm, and the temperature was maintained at 18 ° C. Spinning was performed using an air-gap process, and the nozzle used was 0.35 mm in hole diameter and the total number of holes in the nozzle was 5,000.

The spinning solution was spun into the air through the spinneret described above, passed through a space of about 10 mm, and then introduced into the coagulation bath. At this time, the concentration of the coagulation bath was 30% by weight of DMSO in Deionized Water (DW), and the temperature was 7 ° C. The PC undergoing a coagulation bath for 10 seconds was subjected to a cold stretching process in a DMSO aqueous solution having the same composition as the coagulation bath. 3.9 times stretching is performed through the cold drawing process, and the PC which has undergone the cold drawing process is subjected to an oiling process using silicone-based oil, followed by 2.4 times at 91 ° C. and 4.5 times at 101 ° C. for 2 times of continuous stretching. Was carried out. Thereafter, a drying process was performed at 90 ° C. and 2.7-fold steam stretching at 135 ° C. to prepare a PAN-based precursor fiber.

(3) Preparation of Carbon Fiber

After flameproofing the prepared PAN-based precursor fiber at 300 ° C. for 120 minutes, carbon fiber was prepared by pre-carbonization at 800 ° C. and carbonization at 1400 ° C. in a nitrogen atmosphere, and each draw ratio was 1.01 and 0.98. .

<Examples 2 to 3>

The carbon fiber was prepared in the same manner as in Example 1 except that the carbon fiber was prepared under the reaction conditions shown in Table 1 below.

<Comparative Examples 1 to 5>

The carbon fiber was prepared in the same manner as in Example 1 except that the carbon fiber was prepared under the reaction conditions shown in Table 1 below.

Experimental Example

The fiber fluctuation was measured for the carbon fibers prepared through Examples 1 to 4 and Comparative Examples 1 to 6, and the results are shown in Table 1.

1.Flatness rate of change

The tow of 1 m length was continuously cut exactly 100 times in the longitudinal direction of the carbon fiber tow, and after drying for 12 hours with a dryer at 85 ° C., respectively, the weight after drying was measured and the variation ratio was obtained by the following equation.

% Change = (s / E) × 100

s: standard deviation of the measured data, E: average value of the measured data

Primary heat drawing temperature (℃) Secondary heat drawing temperature (℃) (a) Cold rolling 1st Extension Second extension fee (b) Cold drawn temperature
(c)
(℃) Steam Stretching Ratio (d) Fineness percentage (%) Example 1 91 101 10 3.9 2.4 4.5 1.77 7 2.6 0.81 Example 2 87 98 11 3.6 3.4 3.6 1.94 8 3.1 0.92 Example 3 93 98 5 3.6 3.5 3.5 1.94 10 3.1 0.89 Example 4 82 91 9 3.8 2.9 4.2 1.87 12 2.3 0.86 Comparative Example 1 100 117 17 3.6 3.5 3.5 1.94 9 3.1 1.16 Comparative Example 2 93 90 -3 3.6 3.5 3.5 1.94 10 3.1 1.25 Comparative Example 3 91 101 10 3.9 2.4 3.8 1.59 8 3.1 1.31 Comparative Example 4 82 93 11 3.6 3.9 4.0 1.19 11 3.1 1.39 Comparative Example 5 85 91 6 3.3 3.2 3.2 1.94 15 3.1 0.98 Comparative Example 6 91 101 10 4.2 3.6 3.8 1.76 7 3.15 0.96

However, in Table 1, (a) is a secondary hot draw temperature (° C.)-primary hot draw temperature (° C.), and (b) is [primary hot draw ratio + secondary hot draw ratio] / [cold draw ratio].

As can be seen from Table 1, it can be seen that carbon fiber that satisfies the conditions (a) ~ (c) of the relationship of the present invention at the same time significantly reduced the fineness fluctuation rate compared to the carbon fibers of Comparative Examples 1 to 4 that do not satisfy this have.

Furthermore, in the case of Example 1 which satisfies all of the relational conditions (a) to (d), it can be seen that the decrease in the degree of fineness fluctuation rate is greater than in Examples 2 to 4 which satisfy only (a) to (c) under the same conditions. have. In addition, even when the relations (a) to (c) are all high, when the cold draw ratio is 3.5 to 4.0 times, the degree of decrease in the fineness variation is lower than that of the case.

Carbon fiber produced through the production method of the present invention is commercially produced and sold as a reinforcing fiber material of high-performance composite materials, such as aerospace applications, sports and leisure applications. In recent years, it can be widely used in general industrial fields such as automobile, ship use, building material use.

Claims (16)

In the method for producing carbon fiber,
(1) preparing a polyacrylonitrile-based (PAN-based) precursor spinning solution having a concentration of 15-25 wt% of a polyacrylonitrile-based polymer using DMSO as a solvent;
(2) discharging the prepared PAN-based precursor spinning solution from the spinneret by a wet and dry spinning method and performing a coagulation bath in a coagulating solution containing DMSO;
(3) cold stretching the precursor carbon fiber subjected to the coagulation bath
(4) performing primary and secondary hot stretching processes on the precursor carbon fibers subjected to the cold stretching process; And
(5) a method for producing carbon fibers including a step of drying the precursor carbon fibers subjected to the thermal stretching process and satisfying the following formulas (a) to (c):
[Relationship]
(a) 0 ° C. ≤ [secondary hot drawing temperature (° C.)-primary hot drawing temperature (° C.)] ≤ 12 ° C.
(b) 1.7 ≤ [primary hot draw ratio + secondary hot draw ratio] / [cold draw ratio] ≤ 2.0
(c) 3 ° C. ≦ cold drawing temperature ≦ 12 ° C. The method of claim 1,
The polyacrylonitrile-based polymer is a method for producing carbon fibers with reduced fineness deviation, characterized in that the polymer is produced by polymerizing acrylonitrile (AN), methyl acrylate (MA) and itaconic acid (IA). The method of claim 1,
The concentration of the fine water solution of DMSO coagulation step (2) is 15 to 35% by weight manufacturing method of the carbon fiber, the fineness deviation is reduced. The method of claim 1, wherein the cold drawing step is performed in a DMSO aqueous solution. 4. The method of claim 1, wherein step (4) comprises:
Iii) washing the cold drawn precursor carbon fiber;
Ii) oiling the washed precursor carbon fibers; And
Iii) a method for producing carbon fibers with reduced fineness deviation, comprising the steps of primary and secondary thermal stretching of the carbon fibers subjected to the oiling process. The method of claim 5,
The oiling process is a method of producing a carbon fiber is reduced fineness deviation, characterized in that using a silicone-based oil. The method of claim 1,
Method of producing a carbon fiber in which the fineness deviation is reduced, characterized in that the time for performing the coagulation bath of step (2) is 10 seconds to 2 minutes. The method of claim 1,
The primary thermal stretching is a method for producing a carbon fiber is reduced fineness deviation, characterized in that carried out at 75 ~ 95 ℃. The method of claim 1,
The cold draw ratio is a carbon fiber manufacturing method of reducing fineness deviation, characterized in that 3.5 to 4.0. The method of claim 1,
Further performing the steam stretching step between the steps (4) and (5), the steam stretching process is a method of producing a carbon fiber, the fineness deviation is reduced, characterized in that the stretching ratio of 2.5 to 2.9 times. The method of claim 10,
The steam stretching step is a method for producing a carbon fiber is reduced fineness deviation, characterized in that carried out at 132 ~ 137 ℃. The method of claim 1,
After the step (5), the method of producing a carbon fiber, the fineness deviation is reduced, further comprising the step of flameproofing and carbonizing the prepared carbon fiber precursor fiber. Carbon fiber produced through the method of any one of claims 1 to 12. The method of claim 13,
The carbon fiber is carbon fiber, characterized in that the tensile strength of more than 4,500 MPa. The method of claim 13,
The carbon fiber is a carbon fiber, characterized in that the tensile modulus of 260GPa or more. The method of claim 12,
The carbon fiber has a fineness variation of less than 0.95% carbon fiber.

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