Chlorine-resistant polyacrylonitrile-based fiber, carbon fiber, and method for producing same

Abstract

The present invention provides a carbon fiber, even if the single fiber diameter is 6.0 μm or more, has excellent tensile strength due to less internal defects, and can provide the effect of reducing cost while increasing the production to improve the productivity of the carbon fiber.

Description

Technical Field

[0001] The present invention relates to polyacrylonitrile-based chlorine-resistant fiber, carbon fiber and a preparation method thereof, and more particularly to polyacrylonitrile-based chlorine-resistant fiber, carbon fiber and a preparation method thereof having high strength and no reduction in productivity. Background Art

[0002] Carbon fiber has excellent properties such as light weight, high strength, and high elasticity. Therefore, it is used in sporting goods such as fishing rods, golf clubs, and skis; in molding materials such as compressed natural gas (CNG) tanks, flywheels, wind turbine blades, and turbine blades; and in reinforcing materials for structures such as roads and bridge piers. Furthermore, it is used as a material for aircraft and space, and its uses are further expanding. In particular, carbon fiber can be used in high-pressure hydrogen fuel tanks for vehicles, aerospace fuel tanks, and aerospace centrifuges, which require high tensile strength. As the use of such carbon fiber continues to expand, there is a need to develop carbon fiber with higher tensile strength.

[0003] To improve the tensile strength of carbon fibers, Japanese Patent Publication No. 59-82420 and Japanese Patent Publication No. 6-15722 disclose technologies for densifying micro-drawn yarns by optimizing the coagulation bath. However, these technologies for improving the density of micro-drawn yarns reduce the oxygen permeability of the fibers during the oxidation process, thereby reducing the tensile strength of the resin-impregnated carbon fiber strands.

[0004] As another method, Japanese Patent Publication No. 7-37685 discloses that the average single fiber diameter of carbon fiber is reduced to 5.5 μm or less to increase the average single fiber tensile strength to 530 kg / mm. 2 The above technology is effective only in improving tensile strength for fine carbon fibers with a single fiber diameter of less than 5.5 μm. However, this technology is limited in improving tensile strength for coarse carbon fibers with a single fiber diameter greater than 6.0 μm. In other words, achieving high tensile strength is difficult without fine fiber diameters, and increasing fiber diameters leads to decreased productivity. Summary of the Invention

[0005] In order to overcome the above-mentioned problems of the prior art, an object of the present invention is to provide a polyacrylonitrile-based chlorine-resistant fiber that can produce a carbon fiber having high tensile strength even at a coarse fineness and excellent productivity.

[0006] Another object of the present invention is to provide a carbon fiber that can be used in pressure vessels and the like, and that can achieve low cost and high productivity while having high strength and high elongation, and a high-pressure pressure vessel using the same.

[0007] To solve the above-mentioned problems, one embodiment of the present invention relates to a polyacrylonitrile-based chlorine-resistant fiber having a single fiber diameter of 10.0 μm or greater and satisfying the following equations 1 and 2.

[0008] Formula 1

[0009] Log(ρ)≥(α / β) / 100

[0010] Formula 2

[0011] 0.120≤(α / β) / 100≤0.135

[0012] Where, ρ: density of chlorine-resistant fiber (g / cm 3 ), α: reaction cyclization degree of chlorination-resistant fiber, EOR (%), β: oxygen content in chlorination-resistant fiber (%).

[0013] Another embodiment of the present invention relates to a carbon fiber prepared by carbonizing the above-mentioned polyacrylonitrile-based chlorine-resistant fiber, wherein the single carbon fiber has a diameter of 6.0 μm or more, the number of fiber filaments in the fiber bundle is 24,000 to 36,000, the tensile strength of the resin-impregnated strand is 5.8 GPa to 6.4 GPa, and the elongation is 2.2% to 2.6%.

[0014] Another embodiment of the present invention relates to a method for preparing carbon fiber, characterized in that a polymer solution with a polymer concentration of 20 weight percent to 24 weight percent is formed into coagulated fibers by dry-wet spinning in a coagulation bath containing the same solvent as the solvent used in polymerization and 30 weight percent to 40 weight percent of water, and then a carbon fiber precursor fiber is obtained by multiple water washing and stretching. After being imparted with an emulsion, the carbon fiber precursor fiber is dried and stretched to obtain a surface densification degree of 65% to 70% at a wavelength of 380 nm and 82% to 95% at a wavelength of 430 nm, and then carbonized at a temperature of 1000°C to 1400°C to make the carbon fiber diameter reach 6.0 μm or more.

[0015] In the method of the present invention, the weight average molecular weight (Mw) of the polymer may be approximately 120,000 to 180,000, and a polymer having a weight average molecular weight to number average molecular weight ratio (Mw / Mn) in the range of 1.6 to 1.8 may be used.

[0016] During spinning, the temperature difference between the spinning solution and the coagulation bath was kept within 30° C., and the air cap was kept within 10.0 mm.

[0017] Yet another embodiment of the present invention relates to a high-pressure pressure vessel, comprising: a pressure vessel body; and a fiber-reinforced resin layer composed of a fiber-reinforced resin formed on a surface of the pressure vessel body. The fibers constituting the fiber-reinforced resin layer are carbon fibers prepared by carbonizing the aforementioned polyacrylonitrile-based, chloride-resistant fibers. The carbon fibers have a single fiber diameter of 6.0 μm or greater, a fiber bundle containing 24,000 to 36,000 fibers, and a tensile strength of 5.8 to 6.4 GPa and an elongation of 2.2 to 2.6% for the resin-impregnated strands.

[0018] Conventional methods have increased the tensile strength of carbon fibers by reducing their single fiber fineness. This reduces the diameter of the carbon fibers to less than 6.0 μm, narrowing the elastic modulus distribution within each single fiber to improve carbon fiber strength. However, this also results in an increase in the tensile modulus. In contrast, the present invention increases tensile strength without reducing the single fiber diameter as in conventional methods. This not only improves carbon fiber productivity by increasing production volume, but also minimizes increases in equipment costs, resulting in cost reductions.

[0019] The present invention provides a molding material utilizing high-strength, high-tensile carbon fibers. The carbon fibers of the present invention exhibit excellent resin impregnation and strand diffusion during molding. Furthermore, the molding material utilizing the carbon fibers exhibits high carbon fiber strength expression and excellent mechanical properties. This molding material is suitable for applications in fiber-reinforced composite materials, such as pressure vessels. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a microscope photograph of a cross section of a carbon fiber according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] Hereinafter, the present invention will be described in more detail.

[0022] In this specification, the term "fiber" includes the meaning of a single fiber filament or a plurality of fiber filaments bundled into a bundle (also called a "tow").

[0023] In this specification, the term "carbon fiber precursor fiber" refers to a fiber comprising a polymer material that can be converted into a carbon fiber having a carbon content of approximately 90 weight percent or greater, specifically, approximately 95 weight percent or greater, upon application of sufficient heat. The precursor fiber can include polymers and copolymers of acrylonitrile (AN), and can also include copolymers such as methyl acrylate (MA), methacrylic acid (MAA), sodium methanesulfonate (SMAS), itaconic acid (ITA), vinyl bromide (VB), isobutyl methacrylate (IBMA), and combinations thereof.

[0024] One embodiment of the present invention relates to a polyacrylonitrile-based chlorine-resistant fiber having a single fiber diameter of 10.0 μm or greater and satisfying the following conditions of Formula 1 and Formula 2.

[0025] Formula 1

[0026] Log(ρ)≥(α / β) / 100

[0027] Formula 2

[0028] 0.120≤(α / β) / 100≤0.135

[0029] Where, ρ: density of chlorine-resistant fiber (g / cm 3 ), α: reaction cyclization degree of chlorination-resistant fiber, EOR (%), β: oxygen content in chlorination-resistant fiber (%).

[0030] In the present invention, if Log(ρ) is less than 0.01α / β, the fiber cross-section internal structure becomes a double structure, which may cause the carbon fiber to fail to exhibit high tensile strength. If the Log(ρ) 0.01α / β value is less than 0.120, while it is beneficial for forming a uniform internal and external structure, the fiber bundle may be unstable and may cause fusion and fiber breakage during carbonization. Conversely, if the 0.01α / β value is greater than 0.135, the fiber cross-section internal structure becomes a double structure, which may cause the carbon fiber to fail to exhibit high tensile strength.

[0031] To obtain carbon fibers with high physical properties, the formation of a duplex structure within the fiber cross-section should be avoided during flame retardancy. The structure of such chlorine-resistant fibers is controlled by factors such as the fiber precursor fineness, the temperature, tension, residence time, and air flow rate within the oxidation furnace, resulting in a heat-resistant molecular structure. In the present invention, the oxidized fibers can be oxidized to achieve an EOR (Excess Ordination Rate) of 80% to 95% and an oxygen content of 5% to 8%.

[0032] If the degree of cyclization is less than 80%, the heat resistance is insufficient, resulting in poor physical properties during carbonization and increased fiber breakage. Conversely, if the degree of cyclization exceeds 95%, the ladder structure and the molecular structure formed by carbon are overly developed, forming a rigid structure, which degrades physical properties during carbonization.

[0033] The oxygen content within chlorine-resistant fibers refers to the oxygen content relative to the entire fiber interior and exterior. While a higher oxygen content improves heat resistance, a more uniform fiber cross-section achieves superior physical properties. Therefore, by controlling and avoiding abrupt structural changes to ensure smooth oxygen diffusion within the fiber, the oxygen content within the oxidized fiber of chlorine-resistant fibers can be kept within the range of 5% to 8%.

[0034] Yet another embodiment of the present invention relates to a carbon fiber bundle, characterized in that it is prepared by carbonizing the above-mentioned chlorine-resistant fiber, the carbon fiber single fiber diameter is greater than 6.0 μm, the number of fiber filaments in the fiber bundle is 24,000 to 36,000, the tensile strength of the resin-impregnated strand is 5.8 GPa to 6.4 GPa, and the elongation is 2.2% to 2.6%.

[0035] Moreover, in a preferred embodiment of the present invention, the single fiber diameter of the carbon fiber precursor fiber can be greater than 9.0 μm, the single fiber tensile strength can be 9 g / d to 11 g / d, and the single fiber elongation can be in the range of 10% to 12%.

[0036] In the carbon fiber bundle of the present invention, the single fiber diameter of the carbon fiber is 6.0 μm or more (refer to Figure 1 The average single fiber diameter can be calculated from the mass, density, and number of fiber strands per unit length of the carbon fiber bundle, and can be measured by polishing a carbon fiber resin tensile test specimen using an optical microscope or scanning electron microscope (SEM).

[0037] While smaller carbon fiber diameters minimize differences in internal and external structure, resulting in higher strength, they are complex and expensive to produce. This makes impregnation with high matrix resin viscosity difficult when preparing composite materials, leading to reduced tensile strength due to insufficient impregnation. Carbon fiber diameters between 6.5 μm and 8.0 μm are preferred, offering advantages in terms of process efficiency and cost, reducing the likelihood of fiber breakage and improving resin impregnation when preparing composite materials.

[0038] The average single fiber diameter of the carbon fiber bundle can be increased by enlarging the average single fiber diameter of the carbon fiber precursor bundle, or by controlling the flame retardant conditions to improve the carbonization yield in the carbonization process, or by reducing the draw ratio in low-temperature carbonization.

[0039] When using carbon fiber bundles with a small number of filaments, a large number of carbon fiber bundles are required. When using carbon fiber bundles with a large number of filaments, a small number of carbon fiber bundles are required, but the number of filaments is increased. Therefore, in either case, the voids between the fibers are small, and the resin flow during the molding process is poor, resulting in poor impregnation or requiring a long impregnation time.

[0040] In the present invention, the carbon fiber precursor fiber is a fiber filament. And, preferably, the number of fiber filaments (single fibers) constituting the fiber bundle group is 24,000 to 36,000. Although from the purpose of improving productivity, the more single fibers in each filament group, the better, but if there are too many, it will be impossible to evenly flame retard the inside of the bundle. The fineness of the single fiber and the number of single fibers can be appropriately adjusted according to the purpose. Only when the number of the above-mentioned fiber filaments reaches 24,000 or more can the number of carbon fiber rolls be reduced when making a high-pressure vessel, thereby facilitating operation. If the number of fiber filaments is greater than 36,000, it may not be possible to exhibit the sufficient tensile strength required in the field of high-pressure vessels.

[0041] The carbon fiber precursor fiber bundle of the present invention has a tensile strength of 5.4 GPa or greater, preferably 5.4 GPa to 6.4 GPa. If the tensile strength is less than 5.4 GPa, a pressure vessel manufactured using a fiber-reinforced composite material formed from such a carbon fiber bundle will not have the sufficient tensile strength required for a pressure vessel requiring a high pressure of 700 bar or greater.

[0042] The carbon fiber precursor fiber bundle of the present invention preferably has a tensile elongation of 2.2% to 2.6%. If the tensile elongation is less than 2.2%, the tensile strength of the carbon fiber reinforced composite material using the bundle is insufficient. The upper limit of the tensile elongation of the strand is not particularly limited, but for the purposes of the present invention, 2.6% is appropriate.

[0043] Another embodiment of the present invention relates to a method for preparing carbon fiber, characterized in that a polymer solution with a polymer concentration of 20 weight percent to 24 weight percent is formed into coagulated fibers by dry-wet spinning in a coagulation bath containing the same solvent as the solvent used in polymerization and 30 weight percent to 40 weight percent of water, and then a carbon fiber precursor fiber is obtained by multiple water washing and stretching. After being imparted with an emulsion, the carbon fiber precursor fiber is dried and stretched to obtain a surface densification degree of 65% to 70% at a wavelength of 380 nm and 82% to 95% at a wavelength of 430 nm, and then carbonized at a temperature of 1000°C to 1400°C to make the carbon fiber diameter reach 6.0 μm or more.

[0044] The present invention enables the production of a carbon fiber precursor bundle having a single carbon fiber diameter of 6.0 μm or greater, enhanced tensile strength, and no reduction in productivity. To produce carbon fiber precursor fibers with excellent tensile strength, a spinning solution with low impurities and uniform molecular weight distribution is prepared by solution polymerization using dimethyl sulfoxide (DMSO) as a solvent. Dry-wet spinning is then performed to optimize the coagulation bath to reduce voids and densify the surface layer, ensuring both extrusion stability and coagulation stretchability.

[0045] The polyacrylonitrile (PAN)-based polymer used in the present invention has an intrinsic viscosity of 1.5 to 2.0 and a weight-average molecular weight (Mw) of 120,000 to 180,000. A higher molecular weight allows for the production of stronger polyacrylonitrile-based precursor fibers. Generally, high-molecular-weight polyacrylonitrile-based precursor fibers with a molecular weight higher than that of low-molecular-weight polyacrylonitrile-based precursor fibers yield relatively strong carbon fibers. This indicates that a polyacrylonitrile polymer with a molecular weight above a specified level is required to produce polyacrylonitrile-based precursor fibers.

[0046] In the present invention, a polyacrylonitrile-based polymer having a molecular weight distribution (PD) (Mw / Mn) within the range of 1.6 to 1.8 is preferred because it contains less low-molecular-weight components that can easily cause structural defects in the carbon fibers. A narrower molecular weight distribution (PD) of the polyacrylonitrile-based polymer improves the stretchability during spinning and contributes to increased carbon fiber strength.

[0047] In the present invention, if the molecular weight distribution PD (Mw / Mn) of the polyacrylonitrile-based polymer is less than 1.6, the polymerization process becomes complicated due to the large number of steps and long time, thereby reducing the economic efficiency. On the contrary, if the PD is greater than 1.8, the frequency of gel formation in the polymer increases, and broken fibers such as dripping from the nozzle often occur, the uniformity of the discharge decreases, and the frequency of broken fibers increases during water washing and stretching or steam stretching, which increases the possibility of uneven physical properties of the precursor fiber, thereby inducing a decrease in the physical properties and quality of the carbon fiber.

[0048] In the present invention, the polymerization method used to prepare the polyacrylonitrile-based polymer can be selected from solution polymerization, suspension polymerization, and emulsion polymerization. However, solution polymerization is preferred for uniformly polymerizing acrylonitrile (AN) or the polymer components. When using solution polymerization, the polyacrylonitrile-based polymer is dissolved in a solvent capable of dissolving the polyacrylonitrile-based polymer, such as dimethyl sulfoxide, dimethylformamide, or dimethylacetamide, to prepare a spinning solution. When using solution polymerization, if the solvent used for polymerization is the same as the spinning solvent, there is no need to separate the obtained polyacrylonitrile-based polymer and then dissolve it in the spinning solvent.

[0049] Preferably, the polymer concentration of the polyacrylonitrile-based polymer solution is in the range of 20 to 24 weight percent. A polymer concentration less than 20 weight percent is uneconomical due to the increased amount of solvent used. Furthermore, the coagulation rate in the coagulation bath is reduced, resulting in internal voids and an inability to achieve a dense structure. On the other hand, a polymer concentration greater than 24 weight percent increases the viscosity, making spinning difficult. The polymer concentration of the spinning solution can be adjusted by adjusting the amount of solvent used.

[0050] In the present invention, polymer concentration refers to the weight percentage of the polyacrylonitrile-based polymer contained in the polyacrylonitrile-based polymer solution. Specifically, after measuring the polyacrylonitrile-based polymer solution, the polyacrylonitrile-based polymer is measured after desolventizing the polyacrylonitrile-based polymer solution, which is measured with a solvent compatible with the solvent used for the polyacrylonitrile-based polymer solution, in which the polyacrylonitrile-based polymer is not dissolved. The polymer concentration is calculated by dividing the weight of the polyacrylonitrile-based polymer after desolventization by the weight of the polyacrylonitrile-based polymer solution before desolventization.

[0051] In order to obtain high-strength carbon fibers before spinning the polyacrylonitrile-based polymer solution, for example, the polyacrylonitrile-based polymer solution is preferably filtered through a filter with a filtration precision of 1 μm or less to remove impurities mixed in from the polymer raw materials and in various steps.

[0052] In the present invention, a spinning solution with few impurities, uniform molecular weight distribution and high viscosity is used to carry out dry-wet spinning through a nozzle hole with a diameter of 0.12mm to 0.18mm. Preferably, the diameter of the average spinning hole of the spinning die used in the present invention is 0.12mm to 0.18mm. If the diameter of the average spinning hole of the spinning die is less than 0.12mm, it is necessary to spit out the polymer solution as the spinning solution from the spinning die at high pressure, which will reduce the durability of the spinning device and may be difficult to spit out from the nozzle. On the other hand, if the diameter of the spinning hole of the spinning die is greater than 0.18mm, it may be difficult to obtain a coagulated filament with the desired single fiber fineness.

[0053] In wet-dry spinning, the spinning dope discharged from the nozzle is stretched in air and then coagulated in a coagulation bath. In the present invention, the temperature difference between the spinning dope and the coagulation bath is adjusted to within 30°C. The air cap distance from the front of the spinning nozzle to the surface of the coagulation bath can be 10 mm or less, preferably between about 2 mm and about 8 mm.

[0054] The lower the temperature of the spinning solution, the higher the viscosity. When it is discharged from the nozzle hole, the discharge pressure is sufficiently high, which can be beneficial to the stability of spinning, but may be detrimental to coagulation and stretching. If the temperature is high, it may be detrimental to maintaining the air cap due to the decrease in viscosity.

[0055] The coagulation bath used in the present invention comprises a mixture of coagulation-promoting components, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, an aqueous zinc chloride solution, and an aqueous sodium thiosulfate solution, which are used as solvents in the polyacrylonitrile-based polymer solution. Preferably, the coagulation-promoting components do not dissolve the polyacrylonitrile-based polymer and are compatible with the solvent used in the polyacrylonitrile-based polymer solution. Specifically, the coagulation-promoting components include water, methanol, ethanol, and acetone, with water being the most preferred.

[0056] The coagulation bath temperature affects the rate at which the solvent diffuses into the coagulation bath and the rate at which the coagulation-promoting component diffuses into the spinning solution. Consequently, lower coagulation bath temperatures produce denser coagulated fibers, leading to higher-strength carbon fibers. A temperature difference of more than 30°C between the spinning solution and the coagulation bath can increase the size of the coagulated phase separation units and the resulting voids. However, if the temperature difference between the spinning solution and the coagulation bath is too low, the coagulation phase separation becomes too small, resulting in a soft surface and a tendency for small fibers to form due to friction, which can lead to fiber breakage.

[0057] In the present invention, a polyacrylonitrile-based polymer solution is introduced into a coagulation bath for coagulation to form coagulated fibers, and then undergoes a water washing step, an in-bath stretching step, an emulsion application step, and a drying step to obtain a carbon fiber precursor fiber. The in-bath stretching step can typically be performed in a single or multiple stretching baths maintained at a temperature of 30°C to 98°C. Preferably, the in-bath stretching ratio is 1x to 5x.

[0058] After the bath stretching step, an emulsion composed of silicone or the like is preferably applied to the stretched yarns to prevent adhesion between the individual fibers. The silicone emulsion preferably contains silicone modified to a highly heat-resistant amino-modified silicone or the like. The subsequent drying step can be performed using a known method. For example, drying can be performed at a temperature of 70°C to 200°C for 10 to 200 seconds.

[0059] After the drying and heat treatment step, a steam stretching step is performed in which the fiber precursor is stretched 2 to 6 times in pressurized steam to produce a single fiber fineness of 0.95 dtex or more.

[0060] The carbon fiber precursor fiber prepared by the above method is subjected to a tension in the range of 7 cN / dtex to 12 cN / dtex in an oxidation furnace under an air atmosphere at 200°C to 300°C to make the degree of reaction cyclization (EOR) and oxygen content in the chlorination-resistant fiber reach the specified range, so that the single fiber diameter of the chlorination-resistant fiber is 10.0 μm to 11.5 μm.

[0061] The surface densification degree of the carbon fiber precursor fiber bundle at a wavelength of 380nm to 480nm is in the range of 87.5% to 93%. If the above-mentioned surface densification degree is less than 87.5%, pores will be generated during the firing process, resulting in defects in the carbon fiber that reduce the physical properties, thereby reducing the tensile strength of the composite material. The upper limit of the surface densification degree is as large as possible and is not particularly limited, but from the perspective of the purpose of the present invention, 87.5% or more is sufficient. Preferably, the surface densification degree of the above-mentioned carbon fiber precursor fiber bundle is 65% to 70% at a wavelength of 380nm and 82% to 95% at a wavelength of 430nm.

[0062] Preferably, the carbon fiber bundle is obtained by carbonizing the chlorine-resistant fiber or the low-temperature carbonized fiber bundle at a temperature of 1000°C to 1400°C in an inert gas atmosphere. If the high-temperature carbonization temperature is less than 1000°C, the nitrogen content in the carbon fiber bundle increases, and thus the strand strength may not be stably exhibited. If the carbonization temperature exceeds 1400°C, it may be difficult to achieve a satisfactory carbonization yield.

[0063] In the present invention, both low-temperature and high-temperature carbonization are performed in an inert gas atmosphere. Carbonization is performed so that the carbon fibers have a diameter of 6.0 μm or greater. Gases used in the inert gas atmosphere include nitrogen, argon, and xenon. Nitrogen is preferred for economic reasons.

[0064] Sizing treatment is performed to impart bundling properties to carbon fibers.

[0065] The sizing agent can be selected based on the type of the matrix resin used and has good compatibility with the matrix resin.

[0066] Yet another embodiment of the present invention relates to a pressure vessel comprising a vessel body and a fiber-reinforced resin layer formed on a surface of the vessel body. The fiber-reinforced resin layer of the pressure vessel of the present invention comprises a fiber-reinforced resin layer comprising reinforcing fibers impregnated with a resin. The reinforcing fibers are prepared by carbonizing polyacrylonitrile-based, chlorine-resistant fibers having a single fiber diameter of 10.0 μm or greater and satisfying the conditions of Equations 1 and 2. The fibers comprise carbon fibers having a single fiber diameter of 6.0 μm or greater, a fiber bundle having a fiber count of 24,000 to 36,000 fibers, and a tensile strength of the resin-impregnated strand of 5.8 GPa to 6.4 GPa and an elongation of 2.2% to 2.6%.

[0067] The carbon fibers obtained in the present invention can be used as prepregs in autoclave molding, pre-processed products such as fabrics, and various molding methods, including resin transfer molding and filament winding, for applications in aircraft components, pressure vessels, automotive products, and sporting goods. In particular, the present invention improves tensile strength, making the pressure vessels of the present invention suitable for use in fuel tanks for various transportation vehicles, including automobiles.

[0068] The present invention will be described in more detail below by way of examples, which are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0069] Example

[0070] Comparative Example 1

[0071] 99 weight percent (wt%) acrylonitrile, 1 weight percent itaconic acid, and 0.01 weight percent chain transfer agent are placed in a dimethyl sulfoxide (DMSO) solvent to a monomer concentration of 20-22 weight percent. A 0.5 weight percent initiator (azobisisobutyronitrile (AIBN)) is added to the nitrogen phase and a polymerization reaction is carried out. In an inert gas atmosphere, the mixture is mixed at 65°C for 4 hours, then the temperature is raised to 80°C at regular intervals over 3 hours and maintained for 6 hours. After the reaction is completed, the mixture is defoamed and the carboxyl groups of the itaconic acid in the polymer are neutralized with ammonia to prepare a 22 weight percent spinning solution. The spinning solution temperature is set 20°C above the coagulation bath temperature. Dry-wet spinning is performed using a 6K to 8K nozzle, with the fibers ejected into a coagulation bath containing 30-40 weight percent dimethyl sulfoxide aqueous solution. The coagulated yarn that has passed through the coagulation bath is step-washed and then stretched in hot water to impart an amino-modified silicone emulsion. The resulting stretched fiber bundle is then run in contact with step-heated rollers and then subjected to a drying heat treatment. Subsequently, the fiber is stretched in pressurized steam at a temperature of 140°C to 185°C at a maximum draw ratio of 80% to produce a polyacrylonitrile-based precursor fiber bundle. The precursor fiber is placed in an oxidation furnace, and the temperature and shrinkage are controlled to achieve an oxidation tension in air of less than 20 cN / tex and an oxidized fiber density of less than 1.35. Subsequently, low-temperature carbonization is performed in a nitrogen atmosphere at 300°C to 700°C, and high-temperature carbonization is performed at a temperature of 1100°C to 1400°C in a nitrogen atmosphere to achieve a carbonization tension of less than 15 cN / tex, thereby producing a carbon fiber bundle.

[0072] The single fiber diameter of the carbon fiber bundle is changed by adjusting the single fiber diameter of the precursor fiber and the calcining conditions, and the single fiber diameter of the precursor fiber bundle is changed by adjusting the discharge amount of the spinning solution.

[0073] Comparative Example 2

[0074] Polyacrylonitrile-based precursor fiber bundles were prepared by polymerization and spinning in the same manner as in Comparative Example 1, except that the spinning solution discharge rate was changed to 70% of that in Comparative Example 1 and the spinning conditions were different as shown in Table 1 below.

[0075] Example 1

[0076] Polymerization and spinning were carried out in the same manner as in Comparative Example 1, with the spinning dope discharge rate being 90% of that in Comparative Example 1 to produce a precursor fiber bundle. Subsequently, oxidation and carbonization were performed to produce a carbon fiber bundle.

[0077] Comparative Example 3

[0078] Except for changing the amount of the dope discharged to 90% of the level of Comparative Example 1, the polyacrylonitrile-based precursor fiber bundle was prepared by polymerizing and spinning in the same manner as in Comparative Example 1 except for the different conditions of spinning shown in Table 1 below.

[0079] Example 2 to Example 3

[0080] Except for changing the difference (ΔT) between the temperature of the dope and the temperature of the coagulating bath as shown in Table 2 below, the carbon fiber precursor fiber bundle and the carbon fiber bundle were prepared by conducting in the same manner as in Example 1.

[0081] Examples 4 to 6 and Comparative Example 4

[0082] Except for preparing the polymer with a molecular weight distribution of 2.0 at the time of polymerization, the carbon fiber precursor fiber bundle and the carbon fiber bundle were prepared by conducting in the same manner as in Example 1 except for the different difference (ΔT) between the temperature of the dope and the temperature of the coagulating bath as shown in Table 1 below.

[0083] Comparative Examples 5 and 6

[0084] Except for preparing the polymer with a molecular weight distribution of 2.0 at the time of polymerization, the carbon fiber precursor fiber bundle and the carbon fiber bundle were prepared by conducting in the same manner as in Example 1 except for the different difference (ΔT) between the temperature of the dope and the temperature of the coagulating bath as shown in Table 1 below.

[0085] Examples 7 to 9 and Comparative Example 7

[0086] Except for preparing the polymer with a molecular weight distribution of 2.0 at the time of polymerization, the carbon fiber precursor fiber bundle and the carbon fiber bundle were prepared by conducting in the same manner as in Example 1 except for the different difference (ΔT) between the temperature of the dope and the temperature of the coagulating bath as shown in Table 1 below.

[0087] Comparative Example 8

[0088] Except for adjusting the amount of the dope discharged to the level of 70% of Comparative Example 1, the polyacrylonitrile-based precursor fiber bundle was prepared by polymerizing and spinning in the same manner as in Comparative Example 7.

[0089] Test example

[0090] The various molecular weights of the polyacrylonitrile-based polymers, the spinning conditions, and the tensile properties of the carbon fiber precursor fiber bundles obtained in Examples 1 to 9 and Comparative Examples 1 to 8 above were measured by the following methods, and the results are shown in Tables 1 and 2 below.

[0091] <Measurement of Polymer Molecular Weight and Molecular Weight Distribution>

[0092] The liquid polymer was cast thinly to prepare a film and, after being washed with water for one day in flowing water to prepare a dry sample, was dissolved in dimethylformamide at a concentration of 0.1 weight percent, and the molecular weight of the obtained liquid sample was measured using a GPC device. The molecular weight distribution curve was obtained from the GPC curve measured to calculate the weight average molecular weight (Mw) and the number average molecular weight (Mn).

[0093] <Measurement of Density>

[0094] A chlorine-resistant fiber bundle of 1.0 g to 3.0 g was completely dried at a temperature of 120°C for 2 hours. Then, after measuring the completely dried mass (A) (g), the bundle was sufficiently defoamed in an ethanol solvent bath, and then the density was obtained by "Density = (A x p) / (AB)", where p is the specific gravity of ethanol at the measurement temperature.

[0095] <Surface densification degree of precursor fiber>

[0096] The surface densification degree (%) was represented by measuring the ultraviolet transmittance in the range of 380 nm to 480 nm in the ultraviolet spectrophotometer with methoxybenzene as a reference solution. The precursor fiber bundle was a bundle prepared by drying after removing the emulsion, and 10 samples each having a width of 9 mm were prepared by thinly spreading the bundle using a bundle screen, and the average value of the 10 samples was represented as the surface densification degree (%). The higher the value, the more dense it was.

[0097] <Reaction cyclization degree of chlorine-resistant fiber (EOR%, the extent of oxidation)>

[0098] The chlorine-resistant fiber undergoes polymer cyclization as the temperature increases in an air atmosphere. In this case, the cyclization degree of the molecular structure was obtained by irradiating FR-IR to the surface of the oxidized fiber through the wave peak corresponding to the functional group (C=N, C≡N), and the cyclization degree could be calculated by the following formula.

[0099] EOR (%) [the extent of oxidation] = I(C=N) / [I(C≡N) + I(C=N)]

[0100] <Internal oxygen content (%) of chlorine-resistant fiber>

[0101] The oxygen content of the chlorine-resistant fiber was measured using an elemental analysis instrument.

[0102] <Average single fiber diameter of carbon fiber bundle>

[0103] For the measured carbon fiber bundle formed of a plurality of carbon fiber filaments, the mass A f (g / m) and the density B f(g / cm 3 The average single fiber diameter (μm) of the carbon fiber can also be observed by optical microscopy after preparing the resin tensile test specimen and polishing.

[0104] <Measurement of tensile properties of carbon fiber resin impregnated strands>

[0105] The bundles of carbon fibers prepared in the examples and comparative examples were disentangled to measure the tensile properties of the carbon fiber precursor fiber bundles as strands. The tensile properties of the carbon fibers were evaluated by tensile testing of carbon fiber strands impregnated in epoxy resin and cured according to ISO 10618. In this case, 10 carbon fiber precursor fiber bundles were measured, the minimum and maximum values were removed and the average value was taken to represent the tensile strength as strands and the strand elongation.

[0106] Table 1

[0107]

[0108] Table 2

[0109]

[0110] As shown in Table 1 and Table 2 above, it can be confirmed that the carbon fiber bundles of Examples 7 to 9 still show a tensile strength of 5.8 GPa or more and a tensile elongation of 2.2% or more even in the case where the carbon fiber single fiber diameter is 6.0 μm or more, in contrast to which the tensile strength or the tensile elongation of the carbon fiber bundles of Comparative Examples 7 to 8 decreases and is not suitable for use in pressure vessels and the like that require high pressure.

[0111] The present application has been described in detail with reference to the preferred embodiments thereof. However, it should be understood by those having ordinary skill in the art that various changes or modifications can be made to the present application. Therefore, the present application should not be limited to the specific embodiments but should include all the examples falling within the scope of the appended claims and equivalents thereof.

Claims

1. A carbon fiber prepared by carbonizing polyacrylonitrile-based chlorine-resistant fiber, characterized in that: The single fiber diameter of the polyacrylonitrile-based chlorine-resistant fiber is 10.0 μm to 11.5 μm and satisfies the following equations 1 and 2: Formula 1: Log(ρ)≥(α / β) / 100 Formula 2: 0.120≤(α / β) / 100≤0.135 Where ρ is the density of chlorine-resistant fiber, in g / cm 3 , α is the reaction cyclization degree EOR of chlorination-resistant fiber, expressed in %, β is the oxygen content in chlorination-resistant fiber, expressed in %, The carbonization includes low-temperature carbonization in a nitrogen atmosphere at 300° C. to 700° C. and high-temperature carbonization in a nitrogen atmosphere at a temperature of 1100° C. to 1400° C. to achieve a carbonization tension of 15 cN / tex or less, thereby obtaining a carbon fiber bundle in which the resin-impregnated strand has a tensile strength of 5.8 GPa to 6.4 GPa and an elongation of 2.2% to 2.6%. The single fiber diameter of the carbon fiber is 6.0 μm or more, and The spinning was performed while keeping the temperature difference between the spinning solution and the coagulation bath within 30°C.

2. A method for preparing the carbon fiber according to claim 1, characterized in that: After forming a coagulated fiber by dry-wet spinning in a coagulation bath containing the same solvent as that used in polymerizing the polymer solution and water at a concentration of 30% to 40% by weight, the obtained carbon fiber precursor fiber is stretched by multiple water washing baths, and after applying an emulsion, the fiber precursor fiber is dried and stretched to obtain a carbon fiber precursor fiber having a surface densification degree of 65% to 70% at a wavelength of 380nm and 82% to 95% at a wavelength of 430nm, and then carbonized at a temperature of 1000°C to 1400°C to reduce the diameter of the carbon fiber to 6.0μm or more. The weight average molecular weight Mw of the polymer is 120,000 to 180,000, and the ratio of the weight average molecular weight to the number average molecular weight Mw / Mn is in the range of 1.6 to 1.

8. The spinning was performed with the temperature difference between the spinning solution and the coagulation bath within 30°C, and the air cap interval within 10.0 mm. The above method involves spinning the spinning solution through a nozzle hole having a diameter of 0.12 mm to 0.18 mm.

3. A high-pressure pressure vessel, characterized in that: include: the pressure vessel body; and The fiber-reinforced resin layer is composed of a fiber-reinforced resin formed on the surface of the pressure vessel body, and the fibers constituting the fiber-reinforced resin layer are the carbon fibers according to claim 1 .

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