KR20230174418A - Polyimide precusor fibers, carbon fibers and graphite fibers with fine denier and manufacturing methods thereof - Google Patents

Abstract

The present invention uses an ethanol solution as a coagulating liquid during the production of polyimide precursor fibers, thereby enabling the production of fine-fine carbon fibers and graphite fibers with dense structures without the formation of large voids inside the structure of the polyimide-based precursor fibers. It is possible, and accordingly, it relates to a fine-fine polyimide-based precursor fiber with excellent physical properties without loss of physical properties such as tensile strength and elastic modulus, carbon fiber and graphite fiber manufactured using the same, and a method for producing the same.

Description

Polyimide precursor fibers, carbon fibers and graphite fibers manufactured using the same, and manufacturing methods thereof { Polyimide precusor fibers, carbon fibers and graphite fibers with fine denier and manufacturing methods thereof }

The present invention relates to a polyimide-based precursor fiber that has excellent mechanical properties such as elastic modulus, has a dense internal structure by slowing down the solidification rate during wet spinning, and can be manufactured with particularly fine fineness, and carbon fibers and graphite fibers manufactured using the same. It's about the manufacturing method.

Carbon fiber was first used in the filament of light bulbs by carbonizing bamboo fiber, and began to be manufactured industrially in 1959 based on cellulose fibers.

Carbon fiber was first defined in the literature in 1969 by R. Bacon and W. A. Schlamon in the United States. Carbon fiber is a fiber composed only of carbon through thermal decomposition of organic materials at a carbonization temperature of 800 to 1,500 ℃, and graphite. Fiber refers to carbon fiber that has been graphitized by heat treatment at a temperature of 2,000 ℃ or higher.

Generally, carbon fibers are classified into rayon-based, polyacrylonitrile (PAN)-based, and pitch-based carbon fibers depending on the type of precursor. The PAN-based carbon fiber has a carbon content of 93 to 98%, and the graphite fiber has a carbon content of 99% or more.

These carbon fibers and graphite fibers have specific strength, elastic modulus, heat resistance, chemical stability, electrical conductivity, thermal conductivity, dimensional stability due to low thermal expansion, low density, friction and wear characteristics, X-ray transparency, electromagnetic wave shielding, biocompatibility, flexibility, etc. It has excellent characteristics, and through the heat treatment process, molecules such as oxygen, hydrogen, and nitrogen, excluding carbon, escape, showing the structural and textural characteristics of a carbon material as well as high strength and high elastic modulus, which are characteristics of the fiber form. Because of this, it is 1/5 the weight of iron and is more than 10 times stronger. Due to these characteristics, it is widely used as an industrial material in various fields such as sporting goods, aviation industry, automobile, civil engineering, electrical and electronics, communication, and environmental industry.

As a prior art, in Korean Patent Publication No. 10-2018-0087545, an acrylonitrile-based polymer dope stock solution is prepared and the dope stock solution is prepared by wet spinning in a coagulating solution made of dimethyl sulfoxide aqueous solution and adjusted to 35 ° C. A precursor fiber for carbon fiber and a method for manufacturing the same are disclosed, and in Korean Patent Publication No. 10-1021881, an acrylonitrile-based polymer dope solution is prepared, the dope solution is made of a 35% by weight dimethyl sulfoxide aqueous solution, and is heated at 45 ° C. A precursor fiber for carbon fiber manufactured by coagulating in a coagulating solution adjusted to is disclosed.

That is, according to the above-described prior art, the coagulating liquid used in the production of precursor fibers for producing carbon fibers is mostly dimethylsulfoxide (DMSO), dimethylformamide (hereinafter DMF), or dimethylacetamide (N,N'-dimethylacetamide). Aqueous solutions of organic solvents such as , hereinafter DMAc) are used. However, the coagulation solution using the above organic solvent has excellent affinity with the precursor fiber for carbon fiber production and has a very fast coagulation speed. Therefore, the discharge rate and solidification rate of the solvent from the wet-spun carbon fiber precursor fiber are very fast, and as a result, large pores are formed inside the wet-spun carbon fiber precursor fiber. Along with this, the mechanical properties such as elastic modulus of the precursor fiber for producing carbon fiber are lowered, and as the mechanical properties are lowered as described above, there is a problem in that it becomes impossible to manufacture fine carbon fiber and graphite fiber using the same.

The purpose of the present invention is to provide a polyimide-based precursor fiber that has excellent mechanical properties such as elastic modulus by slowing down the solidification rate during wet spinning and is capable of fineness, carbon fiber and graphite fiber manufactured using the same, and a method for producing the same. Do it as However, the technical problem to be achieved by the present invention is not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

To solve the above problems, the method for producing polyimide-based precursor fibers of the present invention includes: i) a first step of producing polyamic acid by condensation polymerization of diamine and dianhydride in a polymerization solvent; ii) a second step of producing polyamic acid fibers by wet spinning the polyamic acid polymerized in the first step into a coagulating liquid; and iii) a third step of imidizing the wet-spun polyamic acid fiber, wherein the diamine is 4,4-oxydianiline, the dianhydride is pyromellitic dianhydride, and the polymerization solvent is N,N'-dimethylacetamide. (DMAc), and the coagulating liquid is an ethanol solution prepared with 45 to 100% by weight of ethanol and the balance in water, and the third step can be performed at a temperature of 350 ° C. or higher for 10 to 30 seconds using near infrared rays.

In addition, the fineness of the polyimide-based precursor fiber manufactured as described above is 1.5 denier or less, and carbon fiber and graphite fiber can be manufactured by continuously carbonizing and graphitizing the polyimide precursor fiber, and the carbonization is carried out using nitrogen, etc. It is performed in an inert gas atmosphere and includes a low-temperature carbonization process and a high-temperature carbonization process, wherein the low-temperature carbonization process is performed at 400 to 800 ° C. for 1 to 3 minutes, and the high temperature carbonization process is performed at 800 to 1,500 ° C. for 1 to 3 minutes. During the low-temperature carbonization process and the high-temperature carbonization process, a tension of 0.2 to 1.5 gf/tex may be added, and the graphitization is performed at 1,800 to 2,800 ° C. for 1 to 3 minutes in an argon atmosphere, The graphitization is performed under a tension of 0.2 to 1.5 gf/tex, the diameter of the graphite fiber is 8 ㎛ or less, the tensile strength is 2.0 GPa or more, the elastic modulus is 300 GPa or more, and the thermal conductivity is 100 W/mK or more. It is desirable.

The polyimide-based carbon fiber and graphite fiber according to the present invention have excellent physical properties such as thermal conductivity, and are especially manufactured with a fine fineness, so they have excellent mechanical properties such as elastic modulus. In addition, there is no formation of large voids inside the structure of the polyimide-based precursor fiber, so the internal structure is dense, there is no loss of physical properties such as elastic modulus, and thermal conductivity and density are increased. Accordingly, it has the effect of providing polyimide-based carbon fiber and graphite fiber that can be used as core materials in various application fields such as wearable electronic devices, sensors, and composite materials as well as space and aviation fields.

1 is a manufacturing process diagram of polyimide-based precursor fiber according to the present invention,
Figure 2 is a schematic diagram of a wet spinning device for producing polyimide-based precursor fiber according to the present invention;
Figure 3 is a micrograph of the cross section and side of the graphite fiber manufactured according to the present invention.

In this application, terms such as “comprise,” “have,” or “equipped with” are intended to designate the presence of features, numbers, steps, components, parts, or combinations thereof described in the specification, and are not intended to indicate the presence of one or more other features, numbers, steps, components, parts, or combinations thereof. It should be understood that this does not exclude in advance the possibility of the presence or addition of features, numbers, steps, operations, components, parts, or combinations thereof.

Additionally, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and unless clearly defined in the present application, should not be interpreted in an ideal or excessively formal sense. No.

Below, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings. In order to facilitate overall understanding when describing the present invention, the same reference numerals are used for the same components in the drawings, and duplicate descriptions for the same components are omitted.

Hereinafter, the polyimide-based precursor fiber, carbon fiber and graphite fiber using the same, and the manufacturing method thereof according to the present invention will be described in detail with reference to the accompanying drawings. Figure 1 attached to the present invention is a manufacturing process diagram of the polyimide-based precursor fiber according to the present invention, Figure 2 is a schematic diagram of a wet spinning device for manufacturing the polyimide-based precursor fiber according to the present invention, and Figure 3 is a schematic diagram of the present invention This is a micrograph of the cross section and side of the graphite fiber manufactured according to.

As shown in FIG. 1, the method for producing the polyimide precursor fiber 100 according to the present invention includes i) the first step of producing polyamic acid by condensation polymerization of diamine and dianhydride in a polymerization solvent. (S100); ii) a second step (S200) of producing polyamic acid fibers by wet spinning the polyamic acid polymerized in the first step (S100) into the coagulating liquid (30); and iii) a third step (S300) of imidizing the wet-spun polyamic acid fibers.

In general, polyimide is manufactured by condensation polymerization of aromatic diamine and aromatic dianhydride and then imidization.

The polyimide produced as described above is an infusible, insoluble, ultra-high heat-resistant resin and exhibits chemical stability, high heat resistance, excellent mechanical properties, low thermal expansion coefficient, and electrical insulation properties.

Polyimide that has been imidized has an oxygen functional group and an aromatic imide ring in the main chain, and has the characteristics of a wide structural range per molecular unit and excellent orientation.

In addition, polyimide has excellent thermal stability due to its high melting point, so unlike the existing carbon fiber precursor, Polyacrylonitrile (PAN) precursor, carbonization and graphitization processes are possible without going through a flameproofing process. Since the molecular structure is mostly aromatic, carbonization is possible. After carbonization, it shows a high yield.

Polyimide prepared as described above may have various molecular structures depending on the type of monomer used.

According to the present invention, the diamine as the monomer used to condensate the polyamic acid in the first step (S100) is 4,4-oxydianiline as shown in [Formula 1] below, and the dianhydride is shown in [Formula 2 below] ] is preferably a pyromellitic dianhydride.

The 4,4-oxydianiline and pyromellitic dianhydride can be condensation-polymerized using DMAc as a polymerization solvent, and the polyamic acid condensed as described above preferably has a number average molecular weight of 5,000 to 300,000. If the number average molecular weight of the condensation polymerized polyamic acid is outside the above range, it may be difficult to manufacture a polyimide precursor fiber having the desired strength and elastic modulus, and the variation in the physical properties of the produced polyimide precursor fiber 100 increases. This may result in a decrease in quality.

In addition, since the polyamic acid synthesized by condensation polymerization of 4,4-oxydianiline and pyromellitic dianhydride as described above is mixed and dissolved in DMAc, the polymerization solvent, the polyamic acid mixed and dissolved in DMAc is used as the spin dope (10). It can be wet-spun.

That is, the second step (S200) for producing the polyimide precursor fiber 100 according to the present invention uses the polyamic acid polymerized in the first step (S100) as the spinning dope (10) together with DMAc as a polymerization solvent. This refers to the step of producing polyamic acid fibers by wet spinning in the coagulating liquid (30).

As described above, the spinning dope 10 for wet spinning preferably has a mixing ratio of polyamic acid and DMAc of 15 to 30:70 to 85% by weight. If the mixing ratio of the polyamic acid in the spinning dope 10 is less than 15% by weight, the viscosity becomes too low, resulting in poor fiber formation. Additionally, if the mixing ratio of the polyamic acid exceeds 30% by weight, the viscosity may be high, making it unsuitable for spinning.

In addition, according to the present invention, the viscosity of the spinning dope 10 is preferably 50,000 to 250,000 cps. That is, the spin dope 10, in which polyamic acid, a precursor of polyimide, is dissolved in DMAc, preferably has a viscosity in the range of 50,000 to 250,000 cps by appropriately controlling the content of DMAc. In the case of having the above viscosity, it is possible to prevent a decrease in spinnability such as thread breakage in the subsequent spinning process, thereby improving spinning performance and increasing spinning speed.

The spinning dope 10 having the above viscosity range is subjected to a second step (S200) of producing polyamic acid fibers by wet spinning in the coagulating liquid 30.

Figure 2 is a schematic diagram of a wet spinning device for manufacturing polyimide precursor fiber 100 according to the present invention.

In the present invention, polyamic acid fiber bundles 40 are manufactured by spinning the spinning dope 10 into the coagulating liquid 30 using a wet spinning device as shown in FIG. 2.

That is, referring to FIG. 2, the wet spinning device for manufacturing the polyimide precursor fiber 100 according to the present invention includes a gear pump 15 for supplying the spinning dope 10 at a constant pressure, and the gear pump 15 ), a spinneret (20) for spinning the spinning dope (10) supplied from the spinneret (20) in the form of a fiber, a coagulation bath (50) to coagulate the uncoagulated polyamic acid fiber bundle (40) discharged from the spinneret (20) ) is provided with a coagulating liquid (30) supported therein.

In addition, in the present invention, for smooth spinning operation, the spinning dope 10 is extruded through the spinneret 20 under a pressure of 400 to 1,500 psi during wet spinning to prevent phenomena such as thread breakage in the polyamic acid fiber bundle 40. Radioactivity can be improved by preventing radioactivity.

The coagulating liquid 30 provided in the coagulating bath 50 is well compatible with DMAc, which is a solvent mixed in the spin dope 10 as a non-solvent. Any solvent that can solidify the polymer polyamic acid without dissolving it can be used without limitation.

Wet spinning manufactures a fiber that manufactures a spinning dope (10) of fiber polymer and extrudes it through a spinneret (20) into a coagulating liquid (30), where the fiber polymer is regenerated and coagulated to solidify into a fibrous shape. It's a method.

As shown in Figure 2, the spinning dope 10 extruded from the spinneret 20 is solidified in the coagulating liquid 30, and at this time, the solvent contained in the spinning dope 10 and the coagulating liquid ( Coagulation is achieved through exchange between non-solvents included in 30).

That is, an exchange occurs between the solvent contained within the spun fiber polymer and the non-solvent that does not dissolve the fiber polymer present in the coagulating liquid 30, and at this time, the coagulating liquid 30 diffuses into the spun fiber polymer. Fibers can be produced by coagulating while removing the solvent inside the spun fiber polymer by the non-solvent contained in,

Therefore, if the non-solvent present in the coagulating liquid 30 has excellent affinity with the fiber polymer, the coagulation speed of the fiber polymer becomes fast. When the coagulation speed of the spun fiber polymer becomes fast as described above, the solvent escapes from the inside of the fiber polymer at a high speed, forming large voids, thereby lowering the mechanical properties of the manufactured fiber. .

In general, in order to manufacture high-strength and high-elasticity carbon fibers and graphite fibers, it is essential to manufacture precursor fibers with a dense internal structure and no defects, and the internal structure of the precursor fibers is primarily formed through coagulation performed in the coagulating liquid 30. It is decided depending on the state. Therefore, the physical properties of carbon fiber and graphite fiber manufactured by uniformly coagulating the fiber and minimizing the occurrence of voids during the coagulation process are greatly affected.

Therefore, it is required to minimize the occurrence of voids while increasing the homogeneity of polyamic acid fibers when coagulated in the coagulating liquid 30 after wet spinning.

The present invention is characterized by using an ethanol solution mixed with water as a non-solvent contained in the coagulating liquid (30) to produce polyimide precursor fibers (100) with a dense internal structure and low occurrence of voids. .

The coagulating liquid 30 can be appropriately selected depending on the intended carbon fiber or graphite fiber. Therefore, when manufacturing carbon fiber, a solvent such as DMF, DMAc, or DMSO is usually used as the coagulating liquid 30.

According to the present invention, a polyimide precursor fiber (100) can be manufactured that can resolve the internal non-uniformity of the polyimide precursor fiber (100) and produce high-strength and high-elasticity carbon fiber and graphite fiber with little variation in coagulation speed. For this purpose, an ethanol solution can be used as the coagulating liquid 30, and the ethanol solution used as the coagulating liquid 30 is preferably prepared from 45 to 100% by weight of ethanol and the balance water.

The ethanol solution used as the coagulating liquid 30 prepared as described above is a solvent that does not dissolve polyamic acid, which is a polymer, and appropriately controls the coagulation speed of the polyamic acid discharged into the coagulating liquid 30 and discharges accordingly. By appropriately controlling the discharge rate of DMAc, a solvent contained within the polyamic acid fiber, the formation of voids within the fiber can be prevented, thereby producing a polyimide precursor fiber 100 having a dense structure.

As described above, polyamic acid fibers have no internal voids and have a dense structure, and can be manufactured with fine fineness. In addition, there is no formation of large voids inside the structure, so there is no loss in elastic modulus and tensile strength, and thermal conductivity, etc. It has the effect of enabling the production of carbon fiber and graphite fiber with excellent physical properties.

The ethanol solution used as the coagulating liquid 30 slows the coagulation rate of the wet-spun polyamic acid fibers and appropriately controls the discharge rate of the solvent, thereby suppressing the creation of voids inside the fiber structure and forming a dense internal structure. For this purpose, it is particularly preferable to prepare it with 45 to 100% by weight of ethanol and the balance with water.

In addition, when wet spinning polyamic acid, the temperature of the coagulating liquid 30 is preferably adjusted to the range of 10 to 60 ° C. If the temperature of the coagulating liquid 30 is outside the above range, the spinning dope 10 is not smoothly discharged from the spinneret 20, thereby reducing the efficiency of the spinning process, and the solvent may not be properly removed. You can.

As shown in FIG. 2, the polyamic acid fiber bundle 40 that has passed through the coagulating liquid 30 is then washed with water in the water washing tank 60 to wash the coagulating liquid contained in the polyamic acid fiber bundle 40. 30) and solvents are removed. Subsequently, the polyamic acid fiber bundle 40 that has passed through the water washing tank 60 is then stretched in the stretching tank 70. The stretching is preferably carried out at a rate of 5 to 25% at a temperature of 80 to 95 °C.

The polyamic acid fiber bundle 40 stretched as described above is then introduced into the IR heating chamber 80 and heated to perform imidization in the third step (S300). According to the present invention, the imidization performed in the third step (S300) is preferably performed using near infrared rays, and is particularly preferably performed at a temperature of 350° C. or higher for 10 to 30 seconds.

Typically, polycondensation polymerized polyamic acid is imidized by dehydration and ring closure through chemical or thermal methods to produce polyimide.

The chemical method for producing polyimide is performed by adding a chemical dehydrating agent, such as an acid anhydride such as acetic anhydride, and an imidization catalyst, such as tertiary amines such as pyridine, to a solution of polyamic acid, which is a precursor, and heating it at 160°C or higher. You can.

In addition, the thermal method for producing polyimide is a method of heating the precursor polyamic acid to evaporate the solvent and then imidizing it by heating without a chemical dehydrating agent or catalyst.

According to the present invention, polyamic acid synthesized by condensation of 4,4-oxydianiline, a diamine, and pyromellitic dianhydride, a dianhydride, is converted to polyimide by forming an imide ring through a thermal method. It is desirable to do so.

According to the present invention, it is particularly preferable that the third step (S300) of imidizing the polyamic acid fiber bundle 40 is performed at a temperature of 350° C. or higher for 10 to 30 seconds.

Through the third step (S300), the polyamic acid fiber bundle 40 is imidized to produce polyimide precursor fiber 100, and the polyimide precursor fiber 100 is wound by a winding device as shown in FIG. 2. By being wound around (90), the production of the polyimide precursor fiber 100 according to the present invention can be completed.

The polyimide precursor fiber 100 according to the present invention manufactured as described above can be manufactured to have a dense structure while minimizing the occurrence of voids inside the fiber structure by using an ethanol solution as the coagulating liquid 30. In addition, the polyimide precursor fiber 100 can be manufactured with fine fineness by minimizing the occurrence of voids as described above. Accordingly, the polyimide precursor fiber 100 according to the present invention has the feature of being able to be manufactured with a denier of 1.5 or less.

That is, carbon fiber and graphite fiber require physical properties such as excellent tensile strength and tensile modulus, and the tensile strength and tensile modulus are related to the diameter of the fiber. That is, as the diameter of the fiber increases, the tensile strength and tensile modulus decrease, and as the fiber becomes finer, the elastic modulus can be improved.

The polyimide precursor fiber 100 according to the present invention uses an ethanol solution as the coagulating liquid 30 during manufacture, thereby slowing down the coagulation speed of the wet-spun polyamic acid fiber and suppressing the generation of internal voids, thereby maintaining a dense internal structure. It has the feature of being able to manufacture Seomdoro.

As described above, the polyimide precursor fiber 100 manufactured through the third step (S300) can then be continuously carbonized to produce carbon fiber, and can also be continuously graphitized to produce graphite fiber.

Looking at the fourth step (S400), which is a carbonization step of carbonizing the polyimide precursor fiber 100 according to the present invention, the fourth step (S400) may be performed under a nitrogen atmosphere, which is an inert gas. Step 4 (S400) can be performed through a low-temperature carbonization process and a high-temperature carbonization process.

At this time, the low-temperature carbonization process may be carried out at 400 to 800 ° C. for 1 minute to 3 minutes, and the high temperature carbonization process may be carried out at 800 to 1,500 ° C. for 1 minute to 3 minutes.

Additionally, according to the present invention, a tension of 0.2 to 1.5 gf/tex may be added to the polyimide precursor fiber 100 during the low-temperature carbonization process and the high-temperature carbonization process. As described above, when the tension is added less than the above range during the low-temperature carbonization process and the high-temperature carbonization process, the physical properties such as tensile strength, tensile modulus, and thermal conductivity of the produced carbon fiber and graphite fiber decrease, and exceeding the above range In this case, yarn breakage occurs during the carbonization process, deteriorating spinning properties. Therefore, it is preferable that tension is added to the polyimide precursor fiber 100 in the above range during the low-temperature carbonization process and the high-temperature carbonization process.

When the fourth step (S400) is completed as described above, the polyimide-based carbon fiber according to the present invention can be manufactured.

The carbon fiber manufactured as described above can then be manufactured into graphite fiber through the graphitization step, which is the fifth step (S500). According to the present invention, the fifth step (S500) may be performed at 1,800 to 2,800 °C for 1 to 3 minutes.

Additionally, according to the present invention, when performing the fifth step (S500), a tension of 0.2 to 1.5 gf/tex may be added to the carbon fiber.

As described above, in the fifth step (S500), which is the graphitization step, when the tension is added less than the above range, the physical properties such as tensile strength, tensile modulus, and thermal conductivity of the produced graphite fiber decrease, and the above range is reduced. If it exceeds it, cutting may occur during the graphitization process and the spinning performance may deteriorate. Therefore, it is preferable that tension in the above range is added in the graphitization step.

When the fifth step (S500), which is the graphitization step, is completed as described above, the production of the polyimide-based graphite fiber according to the present invention is completed.

Hereinafter, the present invention will be examined in more detail through comparative examples and examples. However, the present invention is not limited to the following examples.

[Comparative Example 1-1]

After condensation polymerization of 4,4-oxydianiline with diamine and pyromellitic dianhydride with dianhydride, polyamic acid fiber was manufactured by wet spinning using a 45% by weight aqueous solution of DMAc as a coagulant (30). Afterwards, polyimide precursor fiber 100 was manufactured by imidization treatment at 350° C. for 30 seconds using an IR heating chamber 80. The polyimide precursor fiber 100 was put into a heat treatment furnace and carbonized at a low temperature for 1 minute at 800°C while applying a tension of 0.6 gf/tex, and carbonized at a high temperature at 2,800°C for 1 minute while applying a tension of 0.9 gf/tex. Thus, carbon fiber was manufactured. Afterwards, the carbon fiber was treated at 2,800°C for 3 minutes in an argon atmosphere to produce graphite fibers with a diameter of 6 ㎛, which were used as test pieces.

[Comparative Example 1-2]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 75% by weight DMAc aqueous solution was used as the coagulating liquid 30, and the diameter of the produced graphite fiber was 8 ㎛.

[Comparative Example 2-1]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 45% by weight DMSO aqueous solution was used as the coagulating liquid 30, and the diameter of the produced graphite fiber was 6 ㎛.

[Comparative Example 2-2]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 75% by weight DMSO aqueous solution was used as the coagulating liquid 30, and the diameter of the produced graphite fiber was 8 ㎛.

[Comparative Example 3-1]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 45% by weight DMF aqueous solution was used as the coagulating liquid 30, and the diameter of the produced graphite fiber was 6 ㎛.

[Comparative Example 3-2]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 75% by weight DMF aqueous solution was used as the coagulating liquid 30, and the diameter of the produced graphite fiber was 8 ㎛.

[Example 1-1]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 45% by weight ethanol solution was used as the coagulating liquid (30), and the diameter of the produced graphite fiber was 6 ㎛.

[Example 1-2]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 55% by weight ethanol solution was used as the coagulating liquid (30), and the diameter of the produced graphite fiber was 8 ㎛.

[Example 1-3]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 75% by weight ethanol solution was used as the coagulating liquid (30), and the diameter of the produced graphite fiber was 6 ㎛.

[Example 1-4]

A test piece was prepared in the same manner as in Comparative Example 1-1, except that a 100% by weight ethanol solution was used as the coagulating liquid (30), and the diameter of the produced graphite fiber was 8 ㎛.

Tensile strength, tensile strength, uniformity, thermal conductivity, and density were measured for the test pieces of Comparative Examples 1-1 to 3-2 and Examples 1-1 to 1-4, and the results are shown in Table 1. At this time, the tensile strength, tensile modulus, uniformity, thermal conductivity, and density were measured as follows.

1) Tensile strength and tensile modulus

The tensile strength and tensile modulus were measured according to KS L 2515 (carbon fiber test method), and the results are shown in Table 1.

2) Uniformity CV (%)

The uniformity (CV%) is the rate of change in weight per unit length of the filament yarn, and was measured based on (Equation 1) below, and the results are shown in Table 1.

2) Thermal conductivity

The thermal conductivity was measured using the vertical thermal conductivity method in accordance with ASTM D5470 (Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials) under temperature range conditions from room temperature to 60°C and is shown in Table 1.

4) Density

The density of the test piece was measured using a xylene/carbon tetrachloride density gradient tube at a temperature of 23°C, and the results are shown in Table 1. .

tensile strength
(GPa) modulus of elasticity
(GPa) density thermal conductivity
(W/mK) balance
(CV%) Comparative Example 1-1 1.13 189.47 0.64 70.6 11.87 Comparative Example 1-2 1.47 252.14 0.66 76.3 10.39 Comparative Example 2-1 1.02 166.22 0.67 86.7 12.23 Comparative Example 2-2 1.49 250.02 0.68 89.6 11.68 Comparative Example 3-1 1.22 210.12 0.76 76.3 11.66 Comparative Example 3-2 1.61 253.32 0.82 82.1 11.28 Example 1-1 2.43 342.42 1.70 104.8 12.33 Example 1-2 3.06 366.27 1.89 114.9 11.32 Example 1-3 3.32 385.58 1.92 126.8 13.76 Example 1-4 3.67 402.26 2.03 147.1 12.64

As shown in Table 1, the diameter of the graphite fibers, which are the test specimens of Examples 1-1 to 1-4 according to the present invention, is 8 ㎛ or less, enabling fineness, the tensile strength is 2.0 GPa or more, and the elastic modulus and heat conduction It can also be seen that the measured values are above 300 GPa and 100 W/mK, respectively. In particular, in the case of the test specimens of Examples 1-1 to 1-4, it can be seen that the tensile properties, elastic modulus, density, and thermal conductivity are improved as the concentration of ethanol increases when preparing the coagulation bath.

Figure 3(b) is a micrograph of the cross section of the test piece of Example 1-1. As shown in (b) of FIG. 3, it can be confirmed that the graphite fiber according to the present invention has a dense structure without any voids inside, and also has a smooth surface.

In addition, in the case of the graphite fiber according to the present invention, the graphite fibers manufactured with a diameter of 6 ㎛, that is, the test specimens of Examples 1-2 and 1-3, were the graphite fibers manufactured with a diameter of 8 ㎛, that is, the test pieces of Examples 1-2 and 1-3. It can be seen that it exhibits superior tensile strength and elastic modulus compared to the test specimen of Example 2-2. That is, it can be seen that the graphite fiber according to the present invention has better physical properties such as tensile strength and elastic modulus when manufactured with fineness.

On the other hand, in the case of the comparative example, the measured values of tensile strength and elastic modulus were less than 2.0 GPa and 300 GPa, respectively, the density also showed a measured value of 1.0 or less, and in particular, the measured value of thermal conductivity showed a measured value of 100 W/mK or less. You can check that.

In particular, in the case of the test specimens of Comparative Examples 1-1 and 2-1, the measured tensile strength was 1.13 GPa and 1.02 GPa, respectively, and the elastic modulus was 189.47 GPa and 166.22 GPa, respectively. That is, in the case of the comparative example, DMF, DMAc, or DMSO aqueous solution was used as the coagulating solution 30, and a number of voids were formed therein as shown in (a) of FIG. 3, and the structure was not dense, so density and heat conduction were low. It can be seen that the physical properties such as strength are very weak.

In addition, Figure 3 (a) is a micrograph of the cross section and side of the test piece of Comparative Example 1-2, and as shown in Figure 3 (s), a 75% by weight DMAc aqueous solution was used as the coagulating solution 30. In this case, the exchange rate of the solvent is very fast, and accordingly, it can be seen that the internal structure is relatively less dense compared to the micrograph shown in (b) of FIG. 3, that is, the test specimen of Example 1-1. It can be seen that as voids are created in the internal structure of the graphite fiber as described above, fineness becomes impossible and physical properties such as elastic modulus rapidly decrease.

In the case of uniformity, the comparative example and example test pieces were all found to be good in the range of 10.39 to 13.76 CV%.

In particular, looking at the test specimens prepared with 45% by weight of each non-solvent in the coagulation bath, that is, Comparative Examples 1-1, 2-1, 3-1, and Example 1-2, the tensile strength was Comparative Example 1-1, In the case of the 2-1 and 3-1 test specimens, the values were 1.13, 1.02, and 1.22 GPa, respectively, but in the case of the Example 1-1 test specimen, it was 2.43 GPa, showing excellent tensile properties. In addition, in terms of elastic modulus, density, and thermal conductivity, it can be seen that the physical properties of the test piece of Example 1-1 are much superior to those of the test pieces of Comparative Examples 1-1, 2-1, and 3-1.

As a result of the above review, by using an ethanol solution as the coagulating liquid 30 when manufacturing the polyimide precursor fiber 100 according to the present invention, there is no formation of large voids, etc. inside the structure of the polyimide-based precursor fiber, and the structure is It is possible to manufacture carbon fiber and graphite fiber with this dense fineness. In addition, it can be seen that it is possible to manufacture carbon fiber and graphite fiber with excellent thermal conductivity, etc. without loss of physical properties such as tensile strength and elastic modulus.

The present invention has been described with reference to the experimental examples shown in the drawings, but these are merely exemplary, and those skilled in the art will understand that various modifications and other equivalent experimental examples are possible therefrom. Additionally, a person skilled in the art to which the present invention pertains will understand that the present invention can be easily modified into another specific form without changing its technical idea or essential features. Therefore, the embodiments described above should be understood in all respects as illustrative and not restrictive, and the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

10: Radidope
20: Radiant detention
30: coagulation liquid
40: polyamic acid fiber bundle

Claims (7)

i) A first step of producing polyamic acid by condensation polymerization of diamine and dianhydride in a polymerization solvent;
ii) a second step of producing polyamic acid fibers by wet spinning the polyamic acid polymerized in the first step into a coagulating liquid; and
iii) a third step of imidizing the wet-spun polyamic acid fiber; a method of producing a polyimide precursor fiber comprising
In claim 1,
Method for producing polyimide precursor fiber, characterized in that the polymerization solvent is N,N'-dimethylacetamide.
In claim 1,
Method for producing polyimide precursor fiber, characterized in that the coagulating liquid is an ethanol solution
Polyimide precursor fiber produced by the method for producing the polyimide precursor fiber of any one of claims 1 to 3.
Carbon fiber manufactured by continuously carbonizing the polyimide precursor fiber of claim 4.
In claim 5,
The carbonization is performed in an inert gas atmosphere and includes a low-temperature carbonization process and a high-temperature carbonization process.
Graphite fiber manufactured continuously through the graphitization step of the carbon fiber of claim 5.