Polyacrylonitrile-based carbon fiber, its stock solution, and method for preparing the same.

Abstract

Polyacrylonitrile-based carbon fibers, polyacrylonitrile stock solution, and methods for producing them, primarily address the problem of prior art in which the presence of gel particles in polyacrylonitrile solution degrades the mechanical properties of carbon fibers. P The aspect ratio of the micropore is 2.0 nm or less. P The diameter C is 50 or greater and 100 or less. V The value is 3% or less. In the polyacrylonitrile spinning solution, the total number of gel particles with a particle size greater than 0.15 μm is 1 × 10⁻⁶. 5 The particle count is less than or equal to 0.3% or less of gel particles with a particle size greater than 5 μm relative to the total number of gel particles, and the equilibrium swelling degree of the gel particles is 250 to 5000%. Methods for preparing polyacrylonitrile stock solution and polyacrylonitrile-based carbon fibers are also provided accordingly.

Description

Detailed description of the invention

[0001] (Technical field) The present invention relates to polyacrylonitrile-based carbon fibers, their stock solution, and a method for preparing them.

[0002] (Background technology) Polyacrylonitrile carbon fibers possess excellent properties such as high specific strength and high specific modulus. Composite materials using polyacrylonitrile carbon fibers as reinforcing fibers are widely used in aerospace, new energy, and other fields. As the application fields of carbon fibers expand, the demands on the performance of polyacrylonitrile carbon fibers are increasing even further.

[0003] Primary fibers form the basis of the structure of polyacrylonitrile fibers (precursor fibers). Polyacrylonitrile fibers are prepared by solidifying and shaping a spinning stream to obtain primary fibers, which are then subjected to post-processing and other processes. More specifically, primary fibers are obtained by gradually shaping the fiber form by the spinning stream in a solidification bath. The fiber shaping process of the spinning stream in the solidification bath directly determines the structure of the primary fibers. Therefore, the state of solidification and shaping of the primary fibers has a decisive effect on the properties of the polyacrylonitrile precursor fibers and the carbon fibers. Whether using a wet spinning method or a dry-jet wet spinning method for polyacrylonitrile precursor fibers, the solidification and shaping of the raw material after it is extruded from the spinning nozzle is particularly important. The smoothness of the raw material extrusion affects the stability of the extrusion solidification process, the quality of the primary fibers, and the spinneret replacement cycle.

[0004] The most significant factor affecting the quality of polyacrylonitrile-based carbon fibers is the quality of the precursor fibers. Defects in the precursor fibers are inherited by the carbon fibers and can even be amplified during the pre-oxidation and carbonization stages. The primary requirement for producing high-quality polyacrylonitrile precursor fibers is the preparation of a high-quality polyacrylonitrile solution. A high-quality polyacrylonitrile solution possesses stable molecular weight characteristics, solids content, viscosity, and copolymer composition over long periods, as well as a sufficiently low impurity content. Impurities in the polyacrylonitrile solution generally include mechanical impurities introduced from the external environment, non-solvent impurities, and gel particles generated during equipment operation. These impurities adversely affect the filtration of the polyacrylonitrile solution and the extrusion process of the raw material. In severe cases, clogging of the spinneret can cause a series of spinning defects, such as fuzzing of the primary fibers and filament breakage, forcing the machine to be stopped and cleaned, seriously impacting production efficiency and the quality of the precursor fibers. Furthermore, if impurities such as gel particles in the polyacrylonitrile solution permeate the filter and enter the spinneret, it can cause poor extrusion of the spinneret. Additionally, the reduction in diameter due to multi-stage stretching of the primary fibers leads to a decrease in the mechanical properties of the polyacrylonitrile precursor fibers and carbon fibers, as well as an increase in the coefficient of dispersion. Moreover, the stretchability of microgel particles that have entered the interior of the precursor fibers differs significantly from that of the fiber itself. After the primary fibers are dried, densified, and multi-stage stretched, the microgel particles remain as defects inside the fibers, degrading the micro-oriented structure and mechanical properties of the polyacrylonitrile precursor fibers. Furthermore, among the gel particles present inside the precursor fibers, those with low swelling and difficulty in stretching tend to dissipate heat locally during the thermal stabilization process and are more prone to collapse compared to the polyacrylonitrile fiber itself. This forms micropores that result in large defects in the radial direction, further degrading the properties of the polyacrylonitrile nitrile carbon fibers. Therefore, the preparation of high-quality polyacrylonitrile solutions is particularly important for improving the properties and homogeneity of polyacrylonitrile-based precursor fibers and carbon fibers.

[0005] JP2017128838A, JP2018141251A, WO2019012999A1, JP2019112730A, and CN110832127A disclose that a carbon fiber thread bundle with fewer defects in the fiber cross-section can be obtained by oxidizing and carbonizing a fiber bundle, which is a carbon fiber precursor, obtained by spunting a spinning solution obtained by dissolving a polyacrylonitrile copolymer (Mz / Mw of 1.5 to 6.0) in a solvent, and filtering it under conditions that satisfy predetermined filtration rate, filtration accuracy (≧3μm), and filter media thickness, and then spinning the filtered spinning solution.

[0006] JP2008248219A5 contains 1-10% of components with a molecular weight exceeding 3 million, or higher (10 million), as measured by gel permeation chromatography (GPC), and has a polydispersity (M Z / M W Polyacrylonitrile (PAN) polymers with a weight-average molecular weight of 3.0 to 10.0 have been proposed, which can improve spinning speed and enhance the spinning draw ratio. Furthermore, JP2008248219A5 proposes a method for producing high-quality carbon fiber precursor fibers with minimal fuzz without compromising productivity. However, such high weight-average molecular weights raise concerns about the high pressure required for the precision filtration of polyacrylonitrile solutions, thus increasing the pressure resistance and replacement cycle of filters and spinnerets.

[0007] JP4924484B2 has a polyacrylonitrile polymer with a weight-average molecular weight of 300,000 to 500,000, a molecular weight distribution (Mz / Mw) of 2.5 to 10.0, and a filtration rate or processing volume per unit area of ​​1 to 150 L / m². 2·h, when the filtration residence time V / W (min) (where V is the effective volume of the filter L and W is the polymer flow rate L / min) is between 0.01 and 10, if the filtration rate exceeds the limit or the filtration residence time is too long, the strength of the carbon fibers will be significantly reduced due to the retention of high molecular weight components in the polymer or the extrusion of gel impurities. JP5141598B2 specifies the weight A per unit area of ​​the filtration layer before spinning the spinning solution, the density B of the material (where 0.01 ≤ A / B × 1000 ≤ 0.06), and the filtration resistance coefficient (5 × 10⁻¹⁰). 5 ~30×10 5 cm -1 It is noted that when the thickness of the filtration-securing layer (0.033 to 0.25 mm) meets predetermined conditions, not only can foreign substances such as gel-like substances be accurately removed from the spinning solution before filtration, but clogging of the filtration medium can also be eliminated.

[0008] CN1417393A proposes a microfiltration method in which the spinning solution is filtered using a filter material of 0.5 to 5 μm, preferably 0.5 to 3 μm, to effectively reduce the amount of gel particles in the spinning solution, reduce the number of particles larger than 0.2 μm from 1000 particles / L before filtration to 50 particles / L after filtration, and increase the strength of fibers spun from the filtered solution from 5.2 g / d to 7.5 g / d compared to the unfiltered solution. It should be noted that the document does not mention a method for measuring the number of gel particles. Furthermore, achieving a spinning solution with such a low gel particle content requires either extremely precise filtration or an extremely low controlled filtration pressure difference. However, this would inevitably lead to a significant increase in production costs and a significant decrease in production efficiency.

[0009] The above-mentioned literature aimed to achieve stable production of polyacrylonitrile-based carbon precursor fibers by establishing a rational operating range for filtration accuracy, filtration rate, filtration residence time, and polyacrylonitrile molecular weight, based on the molecular weight of polyacrylonitrile and the filtration of the solution. However, high-precision filters are not only expensive but also have a short service life. Furthermore, large filtration pressure differences increase the pressure resistance requirements of the spinneret during the raw material extrusion process.

[0010] In view of the above problems, the present invention provides a polyacrylonitrile solution that overcomes at least one of the problems in the prior art and can satisfy the requirement for stable production over a long period of time. The polyacrylonitrile solution of the present invention can be spun to prepare precursor fibers of polyacrylonitrile-based carbon fibers. Polyacrylonitrile-based carbon fibers can be prepared by subjecting the precursor fibers to processes such as pre-oxidation and carbonization.

[0011] (Summary of the invention) The inventors conducted detailed research and found that polyacrylonitrile gel particles are almost unavoidable in the manufacturing process. Further research revealed that the properties of polyacrylonitrile gel particles are closely related to the temperature during the molding process and the oxygen concentration in the atmosphere during the polymerization process. When a polyacrylonitrile solution is left in a medium-to-high temperature oxygen-containing atmosphere for a long period of time, gel particles are formed very easily. The chemical structure of the gel particles is dramatically different from that of polyacrylonitrile. In particular, both oxygen and high temperature promote the formation of a large amount of crosslinking between the chains of the polyacrylonitrile polymer. When the molecular chains between crosslinking points are short, the gel particles have a low equilibrium swelling degree, high rigidity, and poor tensile properties. Furthermore, because the gel particle morphology is maintained during the fiber stretching process, it leads to an increase in internal defects in the fiber and a significant decrease in mechanical properties. On the other hand, gel particles with a high equilibrium swelling degree have long molecular chains between crosslinking points and exhibit excellent tensile properties. Even if gel particles enter the interior of the fibers under a high filtration pressure difference, gel particles with a high equilibrium swelling degree will deform axially in tensile tension, following the fiber body, thereby forming elongated micropores along the axial direction within the final carbon fiber. This reduces the adverse effects on mechanical properties and improves the mechanical properties of the carbon fiber.

[0012] Therefore, the first object of the present invention is to provide a polyacrylonitrile-based carbon fiber having elongated micropores along the axial direction.

[0013] A second object of the present invention is to provide a polyacrylonitrile spinning stock solution containing gel particles having a high equilibrium swelling degree, for example, 250 to 5000%. The polyacrylonitrile spinning stock solution can be used to prepare the polyacrylonitrile-based carbon fibers.

[0014] A third object of the present invention is to provide a method for preparing a polyacrylonitrile spinning stock solution containing gel particles having a high equilibrium swelling degree, for example, 250 to 5000%.

[0015] A fourth object of the present invention is to provide a method for preparing polyacrylonitrile-based carbon fibers, for example, polyacrylonitrile-based carbon fibers having elongated micropores along the axial direction.

[0016] One aspect of the present invention relates to polyacrylonitrile-based carbon fibers containing micropores, wherein the average radial size L P of the micropores is 2.0 nm or less, the aspect ratio L / L P of the micropores is 50 or more and 100 or less, and the ratio of the volume of micropores having a radial size greater than 15 nm to the total volume of the micropores exceeds 0 and is less than 10%.

[0017] In some embodiments, the average radial size L P of the micropores is 1.5 nm or less, the aspect ratio L / L P of the micropores is 60 or more and 100 or less, and the ratio of the volume of micropores having a radial size greater than 15 nm to the total volume of the micropores exceeds 0 and is less than 5%.

[0018] In some embodiments, the C V value of the diameter of the carbon fibers is 3% or less.

[0019] In some embodiments, the number of the polyacrylonitrile-based carbon fibers is 3000 to 24000.

[0020] In some embodiments, the polyacrylonitrile-based carbon fibers have a diameter of 5 to 7 μm, a tensile strength of 4.9 to 5.8 GPa, and the C V value of the tensile strength is less than 5%, and / or a tensile modulus of 282 to 323 GPa and the C V value of the tensile modulus is less than 5%.

[0021] Another aspect of the present invention relates to a gel particle-containing material, wherein the total number of gel particles having a particle diameter greater than 0.15 μm is 1×10 5This invention relates to a polyacrylonitrile spinning stock solution having a particle count of less than or equal to 0.3% or less of gel particles with a particle diameter greater than 5 μm relative to the total number of gel particles, and an equilibrium swelling degree of 250 to 5000% of the gel particles.

[0022] In some embodiments, the polyacrylonitrile spinning stock comprises a polyacrylonitrile polymer and a solvent, wherein the weight ratio of the polyacrylonitrile polymer to the solvent is (15-30):(85-70), preferably (18-22):(82-78).

[0023] In some embodiments, the solvent is at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and mixtures thereof.

[0024] In some embodiments, the polyacrylonitrile spinning solution has a zero-shear viscosity of 50 to 150 Pa·s at a viscosity measurement temperature of 50°C.

[0025] In some embodiments, the polyacrylonitrile spinning solution is used to prepare the polyacrylonitrile-based carbon fibers of the present invention.

[0026] A further aspect of the present invention relates to a method for preparing a polyacrylonitrile spinning stock, which includes solution polymerization employing a three-stage temperature control system in which the temperature of the first stage, which is the initial starting stage, is T1°C, the temperature of the second stage, which is the isothermal polymerization stage, is T2°C, and the temperature of the third stage, which is the cooling polymerization stage, is T3°C, and T1, T2, and T3 satisfy the following relationship. T1 = (0.5 ~ 1.4) × T2, and 35 ≤ T1 ≤ 80; and T3 = T2 - (5 to 50), and 50 ≥ T3 ≥ 25.

[0027] In some embodiments, a method for preparing a polyacrylonitrile spinning stock solution is used for preparing the polyacrylonitrile spinning stock solution of the present invention.

[0028] In some embodiments, the temperature range is 35°C ≤ T1 ≤ 80°C, preferably 40°C ≤ T1 ≤ 70°C, 40°C ≤ T2 ≤ 90°C, preferably 50°C ≤ T2 ≤ 80°C, and 25°C ≤ T3 ≤ 50°C, preferably 25°C ≤ T3 ≤ 45°C, more preferably 30°C ≤ T3 ≤ 45°C.

[0029] In some embodiments, the temperatures are 50°C ≤ T2 ≤ 80°C, 40°C ≤ T1 ≤ 70°C, and 30°C ≤ T3 ≤ 45°C.

[0030] In some embodiments, T3 = T2 - (15 to 50), preferably T3 = T2 - (15 to 40), and more preferably T3 = T2 - (20 to 35).

[0031] In some embodiments, the polymerization time for the first stage, which is the initial initiation stage, is 20 to 150 minutes, preferably 30 to 120 minutes, more preferably 30 to 80 minutes; the polymerization time for the second stage, which is the isothermal polymerization stage, is 300 to 900 minutes, preferably 400 to 800 minutes, preferably 400 to 700 minutes, more preferably 500 to 600 minutes; and the polymerization time for the third stage, which is the cooling polymerization stage, is 80 to 300 minutes, preferably 80 to 250 minutes, preferably 100 to 250 minutes, more preferably 120 to 200 minutes.

[0032] In some embodiments, the monomer conversion rate of the second stage, which is a isothermal polymerization stage, is X; the monomer conversion rate of the first stage, which is an initial initiation stage, is (0.125~0.215)×X; the monomer conversion rate of the third stage, which is a cold polymerization stage, is (0.007~0.0715)×X; the monomer conversion rate X of the second stage, which is a isothermal polymerization stage, is 60%~85%, preferably 65%~85%, more preferably 70%~80% or 70%~79%; in the present invention, the monomer conversion rates of the first, second, and third stages are the ratio of the weight of monomers undergoing polymerization in each stage to the total weight of monomers.

[0033] In some embodiments, the solution polymerization is carried out under the protection of an inert gas. In some embodiments, it is preferable that the solution polymerization is carried out under the protection of an inert gas and under conditions where the oxygen content is less than 1000 ppm. In some embodiments, the solution polymerization is carried out in a polymerization vessel.

[0034] Another aspect of the present invention relates to a method for preparing polyacrylonitrile carbon fibers, preferably polyacrylonitrile carbon fibers of the present invention, comprising the steps of: preparing precursor fibers from a polyacrylonitrile spinning solution; and pre-oxidizing and carbonizing the precursor fibers to obtain the polyacrylonitrile carbon fibers, wherein the polyacrylonitrile spinning solution is the polyacrylonitrile spinning solution of the present invention, or a polyacrylonitrile spinning solution prepared by the method for preparing the polyacrylonitrile spinning solution of the present invention.

[0035] In some embodiments, the preparation step of the precursor fibers includes (1) coagulation of primary fibers, (2) stretching in hot water, (3) washing in hot water, (4) oiling, (5) drying and densification, (6) stretching under steam, (7) heat setting, and (8) winding.

[0036] In some embodiments, the pre-oxidation temperature is 180-300°C, preferably divided into 4-6 temperature zones, and the carbonization includes low-temperature carbonization and high-temperature carbonization, preferably with a low-temperature carbonization temperature of 300-700°C and a high-temperature carbonization temperature of 1000-1500°C.

[0037] In some embodiments, the preparation method further includes the steps of surface treatment and gluing.

[0038] (Detailed explanation) For the first purpose of the present invention, the present invention includes a micropore, wherein the average radial size L of the micropore P The aspect ratio of the micropore is 2.0 nm or less. PThe present invention provides a polyacrylonitrile-based carbon fiber in which the ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores is greater than 0 and less than 10%.

[0039] In this invention, L is the average value of the size (length) of micropores along the axial direction of the fiber (i.e., the length direction of the fiber). P This refers to the average radial size of micropores in the transverse direction of the fiber (i.e., the direction perpendicular to the length of the fiber).

[0040] In the present invention, L and L P This was determined using small-angle X-ray scattering (SAXS) testing and the double-model Debye-Bueche analysis method shown in the following equation.

[0041]

number

[0042] In this invention, the obtained L and L P Based on this, the aspect ratio of the micropore L / L P It is possible to calculate this.

[0043] In this invention, the scattering curves of two types of micropores (i.e., micropores with a radial size greater than 15 nm and all micropores) were approximated by the Debye-Bueche method, and the volume ratio of the two types of micropores was determined by calculating the relative volume of the two types of micropores according to the following equation.

[0044]

number

[0045] L, L P The specific methods for measuring and analyzing micropore volume are described in detail below.

[0046] In the present invention, the average radial size L of the micropore P This may be 0 nm or less and 2.0 nm or less, for example, 0.1 nm or more and 2.0 nm or less, 0.5 nm or more and 2.0 nm or less, or 1.0 nm or more and 2.0 nm or less.

[0047] In the present invention, the aspect ratio of the micropore is L / L P It may be between 50 and 100, for example, between 50 and 90, or between 50 and 80, or between 50 and 70.

[0048] In this invention, the ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores may be greater than 0 and less than 10%, for example, greater than 0.1% and less than 10%, or greater than 3% and less than 10%. In this invention, the volume of micropores with a radial size greater than 15 nm is the sum of the volumes of all micropores with a radial size greater than 15 nm. Also, in this invention, the total volume of micropores is the sum of the volumes of all micropores.

[0049] In some embodiments, preferably, the average radial size L of the micropore. P The aspect ratio of the micropore may be 1.5 nm or less. P L may be between 60 and 100, and the ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores may be greater than 0 and less than 5%. In the present invention, the average radial size L of the micropores P The aspect ratio of the micropore is L / L. PIt may be 60 or more and 100 or less, for example, 60 or more and 90 or less, or 60 or more and 80 or less, or 60 or more and 70 or less. In the present invention, the ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores may be greater than 0 and less than 5%, for example, greater than 0.1% and less than 5%, greater than 3% and less than 5%, or greater than 4% and less than 5%.

[0050] In some embodiments, the diameter of the carbon fiber is C V The value is less than 3%. In the present invention, C V The method for calculating the value is detailed below.

[0051] In the present invention, the number of fibers in the carbon fiber is not particularly limited, but for example, a number that is generally known in the field of carbon fiber may be adopted. Preferably, in some embodiments, the number of fibers in the polyacrylonitrile-based carbon fiber is 3,000 to 24,000.

[0052] In the present invention, the diameter of the carbon fiber is not particularly limited, but the carbon fiber may have a diameter of carbon fiber commonly used in the art. In some embodiments, the diameter of the polyacrylonitrile carbon fiber may be 1 to 10 μm, for example, 2 to 10 μm. In some embodiments, the diameter of the polyacrylonitrile carbon fiber may be 5 to 7 μm.

[0053] In the present invention, the tensile strength of the polyacrylonitrile carbon fiber may be 4.5 to 6.1 GPa, for example, 4.7 to 6.0 GPa, or 4.9 to 5.8 GPa. V The value is less than 10%, and may be, for example, less than 7% or less than 5%.

[0054] In the present invention, the tensile modulus of the polyacrylonitrile carbon fiber is 260 to 340 GPa, and may be, for example, 270 to 330 GPa or 282 to 323 GPa. V The value is less than 10%, and may be, for example, less than 7% or less than 5%.

[0055] In some embodiments, preferably, the polyacrylonitrile carbon fiber has a diameter of 5 to 7 μm, a tensile strength of 4.9 to 5.8 GPa, and a tensile strength of C V Value less than 5%, tensile modulus 282-323 GPa, tensile modulus C V The value is less than 5%.

[0056] In this invention, the number and diameter of the polyacrylonitrile precursor fibers and carbon fibers were measured using microscopy in accordance with GB / T3364-2008.

[0057] Furthermore, in this invention, the tensile strength and tensile modulus of the carbon fiber were measured using the mechanical tensile method in accordance with GB / T3362-2005.

[0058] To achieve the second objective of the present invention, the present invention provides a polyacrylonitrile spinning stock solution containing gel particles, wherein the total number of gel particles contained in the polyacrylonitrile spinning stock solution is 1 × 10¹⁶, with a particle size greater than 0.15 μm. 5 The present invention provides a polyacrylonitrile spinning stock solution having a particle count of 0.3% or less, a ratio of the number of gel particles with a particle diameter greater than 5 μm to the total number of gel particles (i.e., the ratio of the number of gel particles with a particle diameter greater than 5 μm to the total number of gel particles) of 0.3% or less, and an equilibrium swelling degree of the gel particles of 250 to 5000%.

[0059] In this invention, the particle size and number of gel particles are measured by a single-particle optical sensing technique. In this technique, a portion of the incident light is blocked when a single particle passes through a narrow photosensitive area, and the intensity of the incident light reaching the detector is instantaneously reduced. The attenuation of the intensity signal is theoretically proportional to the cross-sectional area of ​​the particle, i.e., the square of the particle diameter. A calibration curve is created using standard particles to determine the particle size and the size of the intensity signal. Based on this calibration curve, the particle size of the particles is calculated, and the number of particles is counted. The specific method for measuring the particle size and number of gel particles will be described later.

[0060] As those skilled in the art will understand, equilibrium swelling degree is the ratio of the weight of the gel particles at swelling equilibrium to the weight of the gel particles after the solvent has been removed. The specific method for measuring equilibrium swelling degree is described in detail below.

[0061] The total number of gel particles with a particle size larger than 0.15 μm contained in the polyacrylonitrile spinning stock solution of the present invention is 1 × 10⁻⁶ 5 The number of particles / mL or less. In some embodiments, the total number of gel particles with a particle size larger than 0.15 μm is 9.8 × 10⁶ 4 Less than 10 cells / mL, 9.7 × 10 4 Less than 10 cells / mL, 9.5 × 10 4 Less than 10 cells / mL, 9.3 × 10 4 Less than 10 cells / mL, 9.1 × 10 4 Less than 10 cells / mL, 9.0 × 10 4 Less than 10 cells / mL, 8.8 × 10 4 Less than 10 cells / mL, 8.6 × 10 4 Less than 10 cells / mL, 8.4 × 10 4 Less than 10 cells / mL, 8.2 × 10 4 Less than 10 cells / mL, 8.0 × 10 4 Less than 10 cells / mL, 7.8 × 10 4 Less than 10 cells / mL, 7.6 × 10 4 Less than 10 cells / mL, 7.4 × 10 4 Less than 10 cells / mL, 7.2 × 10 4 Less than 10 cells / mL, or 7.0 × 10 4 The number may be less than 10 particles / mL. The total number of gel particles with a particle size greater than 0.15 μm contained in the polyacrylonitrile spinning stock solution of the present invention is 1 × 10⁻¹⁶5 The number of particles / mL is less than and 0 or more. In some embodiments, the total number of gel particles with a particle size greater than 0.15 μm contained in the polyacrylonitrile spinning stock solution of the present invention is 1 × 10⁻¹⁶ 5 Less than or equal to 10 particles / mL, or 1 × 10 5 Less than or equal to 100 particles / mL, or 1 × 10⁶ 5 Less than or equal to 1000 particles / mL, or 1 × 10⁶ 5 Less than or equal to 10,000 particles / mL and more than 10,000 particles, or 1 × 10⁻⁶ 5 Less than or equal to 20,000 pieces / mL, or 1 × 10⁻⁶ 5 Less than or equal to 30,000 particles / mL, or 1 × 10⁻⁶ 5 Less than or equal to 40,000 particles / mL, or 1 × 10⁻⁶ 5 The number of particles / mL is less than or equal to 50,000 or more.

[0062] In the present invention, the equilibrium swelling degree of the gel particles may be 250 to 5000%, for example, 260 to 5000%, 270 to 5000%, 280 to 5000%, 290 to 5000%, 300 to 5000%, 310 to 5000%, 320 to 5000%, 330 to 5000%, 340 to 5000%, 350 to 5000%, 360 to 5000%, 370 to 5000%, 380 to 5000%, 390 to 5000%, or 400 to 5000%. In some embodiments, the equilibrium swelling degree of the gel particles in the spinning solution is 250-4000%, 250-3000%, 250-2000%, 250-1500%, 260-4000%, 260-3000%, 260-2000%, 260-1500%, 270-4000%, 270-300% 0%, 270-2000%, 270-1500%, 280-4000%, 280-3000%, 280-2000%, 280-1500%, 290-4000%, 290-3000%, 290-2000%, 290-1500%, 300-4000%, 300-3000%, 300-2000 %.300~1500%, 310~4000%, 310~3000%, 310~2000%, 310~1500%, 320~4000%, 320~3000%, 320~2000%, 320~1500%, 330~4000%, 330~3000%, 330~2000%, 330~1500% , 340-4000%, 340-3000%, 340-2000%, 340-1500%, 350-4000%, 350-3000%, 350-2000%, 350-1500%, 400-4000%, 400-3000%, 400-2000%, or 400-1500% may also be used.

[0063] In the polyacrylonitrile spinning solution of the present invention, the ratio of the number of gel particles with a particle diameter greater than 5 μm to the total number of gel particles may be 0.3% or less, preferably 0.25% or less, more preferably 0.20% or less, and even more preferably 0.15% or less. In some embodiments, the ratio of the number of gel particles with a particle diameter greater than 5 μm to the total number of gel particles in the polyacrylonitrile spinning solution may be less than 0.3%, less than 0.29%, less than 0.28%, less than 0.27%, less than 0.26%, less than 0.25%, less than 0.24%, less than 0.23%, less than 0.22%, less than 0.21%, less than 0.20%, less than 0.29%, less than 0.19%, less than 0.18%, less than 0.17%, less than 0.16%, less than 0.15%, or less than 0.14%.

[0064] In the polyacrylonitrile spinning stock solution of the present invention, the ratio of the number of gel particles with a particle diameter greater than 5 μm to the total number of gel particles may be less than 0.3% and 0 or more. In some embodiments, in the polyacrylonitrile spinning stock solution of the present invention, the ratio of the number of gel particles with a particle diameter greater than 5 μm to the total number of gel particles may be less than 0.3% and 0.01% or more, or less than 0.3% and 0.05% or more.

[0065] In some embodiments, preferably, in the polyacrylonitrile spinning stock solution of the present invention, the total number of gel particles with a particle size greater than 0.15 μm is 9.8 × 10 4 Less than 10 cells / mL, preferably 7.8 × 10 4 Less than 10 cells / mL, more preferably 7.0 × 10 4 The number of gel particles per mL is less than 0.25%, preferably less than 0.21%, more preferably less than 0.15%, and the proportion of gel particles with an average particle diameter greater than 5 μm to the total number of gel particles is less than 0.25%, preferably less than 0.21%, and more preferably less than 0.15%. The equilibrium swelling degree of the gel particles is 300-4000%, 300-2000%, 400-2000%, preferably 500-2000%, or 500-1000%.

[0066] The polyacrylonitrile spinning solution comprises a polyacrylonitrile polymer and a solvent.

[0067] As the polyacrylonitrile polymer, polyacrylonitrile homopolymers, polyacrylonitrile copolymers, or mixtures thereof can be used. Specifically, the polyacrylonitrile polymer may contain 90 to 100% by mass of monomer units derived from acrylonitrile and 0 to 10% by mass of structural units derived from monomers copolymerizable with acrylonitrile. As monomers copolymerizable with acrylonitrile, various copolymerizable monomers commonly known in the art may be used, such as acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts, ammonium salts, and lower alkyl esters; acrylamide and its derivatives; allyl sulfonic acid, methallyl sulfonic acid, and their salts or alkyl esters; and the like.

[0068] The concentration of the polyacrylonitrile polymer in the polyacrylonitrile spinning solution is not particularly limited, and an appropriate concentration generally known in the art for polyacrylonitrile spinning solutions may be adopted. In the present invention, for example, the concentration of the polyacrylonitrile polymer in the polyacrylonitrile spinning solution may be 15 to 30% by weight. In some embodiments, preferably, the weight ratio of the polyacrylonitrile polymer to the solvent in the polyacrylonitrile spinning solution may be (18 to 22):(82 to 78).

[0069] The solvent in the polyacrylonitrile spinning solution is not particularly limited, and any suitable solvent commonly known in the art for polyacrylonitrile spinning solutions may be used. The solvent may be at least one selected from the group consisting of dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAC), and mixtures thereof.

[0070] In the present invention, the zero-shear viscosity of the polyacrylonitrile spinning stock solution is 30 to 200 Pa·s, preferably 50 to 150 Pa·s. The viscosity is measured at 50°C. In this invention, the zero-shear viscosity is measured using a rotary rheometer at a measurement temperature of 50 ± 0.01°C, with a rotor diameter of 25 mm and a spacing of 1 mm, and the zero-shear viscosity of the polyacrylonitrile polymer solution is determined by extrapolation. The specific method for measuring the zero-shear viscosity is described below.

[0071] For the third purpose of the present invention, the present invention provides a method for preparing a polyacrylonitrile stock solution. This preparation method is preferably used to prepare the polyacrylonitrile stock solution described in the second purpose of the present invention. The method for preparing the polyacrylonitrile stock solution of the present invention includes solution polymerization. The solution polymerization employs a three-stage temperature control, with the temperature in the first stage (i.e., the initial starting stage) being T1°C, the temperature in the second stage (i.e., the constant-temperature polymerization stage) being T2°C, and the temperature in the third stage (i.e., the cooling polymerization stage) being T3°C. T1, T2, and T3 satisfy the following relationship.

[0072] T1 = (0.5 ~ 1.4) × T2, and 35 ≤ T1 ≤ 80; and T3 = T2 - (5 to 50), and 50 ≥ T3 ≥ 25.

[0073] In the method for preparing a polyacrylonitrile stock solution of the present invention, the polymerization process of solution polymerization is divided into a first stage (i.e., initial initiation stage), a second stage (constant temperature polymerization stage), and a third stage (cooling polymerization stage) according to the polymerization temperature, as described above, and the temperatures of these three stages are denoted as T1, T2, and T3, respectively.

[0074] The desired temperatures T1, T2, and T3 can be achieved by means of temperature detection and control commonly known in the art. For example, temperature detection devices such as thermometers and thermocouples may be provided to detect the temperature. For example, heating and cooling devices commonly used in the art may be used to provide the desired polymerization temperature. For example, a control device may be provided that heats or cools based on the detected temperature to provide the desired temperature. In some embodiments, temperature control may be achieved using a jacketed reactor.

[0075] In the present invention, the range of T2 may be 40°C ≤ T2 ≤ 90°C, preferably 50°C ≤ T2 ≤ 80°C. In some embodiments, T2 is preferably in the range of 50 to 80°C, for example, T2 may be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or a range consisting of any two of these values.

[0076] In the present invention, the range of T1 may be 35°C ≤ T1 ≤ 80°C, preferably 40°C ≤ T1 ≤ 70°C. In some embodiments, T1 is preferably in the range of 40 to 70°C, for example, T1 may be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or a range consisting of any two of these values.

[0077] In the present invention, the range of T3 may be 25°C ≤ T3 ≤ 50°C, preferably 25°C ≤ T3 ≤ 45°C, and more preferably 30°C ≤ T3 ≤ 45°C. In some embodiments, T3 is preferably in the range of 30 to 45°C, for example, T3 may be 30°C, 35°C, 40°C, 45°C, or a range consisting of any two of these values.

[0078] In some embodiments, the preferred temperatures are 50°C ≤ T2 ≤ 80°C, 40°C ≤ T1 ≤ 70°C, and 30°C ≤ T3 ≤ 45°C.

[0079] In some embodiments, T3 = T2 - (15~50), preferably T3 = T2 - (15~40), and more preferably T3 = T2 - (20~35) and 50°C ≥ T3 ≥ 25°C.

[0080] In the method of the present invention, a polyacrylonitrile spinning stock is obtained by preparing a polyacrylonitrile polymer using solution polymerization. In this art, it is known to prepare polyacrylonitrile polymers using solution polymerization. For example, in the method for preparing the polyacrylonitrile stock of the present invention, the spinning stock may be obtained using a solution polymerization process known in this art, but it is a condition that the three-stage programmed temperature control of the present invention is used in the solution polymerization.

[0081] Solution polymerization in the present invention may use initiators commonly used in the art. In some embodiments, the initiator may be a free radical initiator such as a peroxide initiator, an azo initiator, or a redox initiator.

[0082] The monomers and solvents used in solution polymerization may be those described above for the polyacrylonitrile spinning stock solution.

[0083] In some embodiments, in the solution polymerization, if the monomer conversion rate in the second stage is X, the monomer conversion rate in the first stage is (0.125~0.215) × X, and the monomer conversion rate in the third stage is (0.007~0.0715) × X. Here, the monomer conversion rate X in the second stage (isothermal polymerization stage) is 60%~85%, preferably 65%~85%, more preferably 70%~80% or 70%~79%.

[0084] In the present invention, the polymerization time for the first stage, which is the initial initiation stage, may be 20 to 150 minutes, preferably 30 to 120 minutes, more preferably 30 to 80 minutes; the polymerization time for the second stage, which is the isothermal polymerization stage, may be 300 to 900 minutes, preferably 400 to 800 minutes, preferably 400 to 700 minutes, more preferably 500 to 600 minutes; and the polymerization time for the third stage, which is the cooling polymerization stage, may be 80 to 300 minutes, preferably 80 to 250 minutes, preferably 100 to 250 minutes, more preferably 120 to 200 minutes. In some embodiments, preferably, the polymerization time for the first stage (initial initiation stage) is 30 to 80 minutes, the time for the second stage (isothermal polymerization stage) is 500 to 600 minutes, and the time for the third stage (cooling polymerization stage) is 120 to 200 minutes.

[0085] In the present invention, the monomer conversion rate in the first stage, which is the initial initiation stage, may be 8 to 25%, preferably 8 to 20%, more preferably 10 to 18%; the monomer conversion rate in the second stage, which is the isothermal polymerization stage, may be 60 to 85%, preferably 65 to 85%, more preferably 70 to 80% or 70 to 79%; and the monomer conversion rate in the third stage, which is the cooling polymerization stage, may be 0.2 to 8%, preferably 0.4 to 7%, more preferably 0.5 to 5% or 1 to 5%.

[0086] In some embodiments, preferably, the monomer conversion rate in the first stage may be 10 to 18%, and the monomer conversion rate in the third stage may be 0.5 to 5%, for example, 1 to 5%.

[0087] Solution polymerization in the present invention is preferably carried out in the presence of an inert gas. The inert gas may be, for example, nitrogen, helium, argon, xenon, etc.

[0088] In this invention, an inert gas is used such that the oxygen content (by volume) in the inert atmosphere is reduced to less than 3000 ppm, less than 2500 ppm, less than 2000 ppm, or less than 1000 ppm.

[0089] In some embodiments, the solution polymerization is preferably carried out under protection with an inert gas, where the oxygen content is less than 1000 ppm.

[0090] In the present invention, the solution polymerization may be carried out in any suitable polymerization reactor. In some embodiments, the solution polymerization is carried out in a polymerization vessel.

[0091] As is known in this field, the crude stock solution obtained after polymerization may be treated. For example, the crude stock solution may be subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile spinning stock solution.

[0092] In some advantageous embodiments, the polyacrylonitrile spinning stock of the present invention is prepared by the method for preparing the polyacrylonitrile spinning stock of the present invention.

[0093] To achieve the fourth object of the present invention, the present invention provides a method for preparing polyacrylonitrile carbon fibers, as described in one of the above objects of the invention. The method comprises the steps of preparing a precursor fiber from a polyacrylonitrile spinning solution and pre-oxidizing and carbonizing the precursor fiber to obtain the polyacrylonitrile carbon fiber, wherein the polyacrylonitrile spinning solution is the polyacrylonitrile spinning solution described in the second object of the present invention, or a polyacrylonitrile spinning solution prepared by the preparation method described in the third object of the present invention.

[0094] The preparation of precursor fibers from polyacrylonitrile spinning stock and the preparation of polyacrylonitrile-based carbon fibers from these precursor fibers are generally known in this field.

[0095] The precursor fibers may be prepared by wet spinning or dry-jet wet spinning, both of which are known in the art. In the present invention, it is preferable to prepare the precursor fibers using wet spinning.

[0096] When preparing precursor fibers from a polyacrylonitrile spinning solution, the preparation process may include steps such as coagulation, stretching, washing, oiling, drying and densification, stretching under steam, heat setting, and winding. These steps are known in the art and can be appropriately selected and used by those skilled in the art.

[0097] In the solidification process, after exiting the spinneret, the primary fibers enter a first solidification bath to solidify them. Those skilled in the art can easily select the composition and temperature of the first solidification bath. In some embodiments, the temperature of the first solidification bath is 35°C, and the first solidification bath is an 80% aqueous solution of dimethyl sulfoxide. After leaving the first solidification bath, the filaments may optionally be subjected to one or more subsequent solidification baths, for example, a second and a third solidification bath. After leaving the final solidification bath, the solidified filaments may be stretched. The stretching is carried out, for example, in steam or hot water. Those skilled in the art can appropriately select the stretching ratio. After stretching, the filaments may be washed, for example, by washing with water, to remove residual solvent. After washing, the filaments may be oiled and / or dried and densified. Oiling may be carried out using oils commonly used in the art, and drying and densification may be carried out using drying and densification operations commonly used in the art. The oiling and drying densification may be performed once or multiple times, and the same or different oiling agents and drying densification conditions may be used. After drying densification, the obtained filament may be subjected to further stretching, for example, stretching under steam. Those skilled in the art can appropriately select the stretching ratio and stretching conditions. After stretching, the obtained filament may be heat-fixed. For example, heat fixing may be performed by passing the filament between multiple heat rollers. After heat fixing, a precursor fiber may be obtained and wound up for later use.

[0098] As those skilled in the art will recognize, one or more of the aforementioned steps may be omitted or added, or the order of these steps may be changed.

[0099] In some embodiments, the precursor fibers are preferably prepared by a wet spinning process which includes (1) coagulation of primary fibers, (2) stretching in hot water, (3) washing in hot water, (4) oiling, (5) drying and densification, (6) stretching under steam, (7) heat setting, and (8) winding.

[0100] After obtaining precursor fibers, polyacrylonitrile-based carbon fibers may be prepared from these precursor fibers. Processes for preparing polyacrylonitrile-based carbon fibers from polyacrylonitrile-based precursor fibers are known in the art. The method of the present invention may also be used to prepare polyacrylonitrile-based carbon fibers using processes known in the art.

[0101] The process of preparing polyacrylonitrile-based carbon fibers from precursor fibers may include a pre-oxidation step and a carbonization step. For the pre-oxidation step, pre-oxidation may be carried out using a gradient heating method in multiple temperature zones, for example, two to six temperature zones, under an air atmosphere. The starting temperature for pre-oxidation may be 170°C to 200°C, and the ending temperature may be 260°C to 300°C. During pre-oxidation, the fibers may be stretched by a certain amount, for example, with an elongation ratio of 1 to 5%. The pre-oxidation period may be 30 to 120 minutes.

[0102] The obtained pre-oxidized fibers are subjected to a carbonization treatment to obtain polyacrylonitrile-based carbon fibers. The carbonization treatment may include low-temperature carbonization and high-temperature carbonization. The temperature of the low-temperature carbonization treatment may be 300°C to 900°C, and the treatment time may be 1 to 8 minutes. The temperature of the high-temperature carbonization treatment may be 1000°C to 1500°C, and the treatment time may be 1 to 8 minutes. In some embodiments, the temperature of the low-temperature carbonization treatment is 300 to 700°C, and the temperature of the high-temperature carbonization treatment is 1000 to 1500°C. As is known in the art, the carbonization treatment is carried out in the presence of an inert gas. The inert gas may be, for example, nitrogen, helium, argon, xenon, etc.

[0103] In some embodiments, the pre-oxidation temperature is preferably 180-300°C, and more preferably divided into 4-6 temperature zones. In some embodiments, the carbonization preferably includes low-temperature carbonization and high-temperature carbonization, with the low-temperature carbonization temperature being 300-700°C and the high-temperature carbonization temperature being 1000-1500°C.

[0104] In some embodiments, a graphitization treatment may be optionally performed after carbonization. Graphitization treatments are known in the art, and graphitization treatments generally known in the art may be employed.

[0105] In some embodiments, the preparation method may further include a surface treatment step and a gluing step.

[0106] As those skilled in the art will recognize, the carbon fibers (bundles) of the present invention may be subjected to a surface treatment before the gluing process. For example, an oxidation treatment may be performed to improve the affinity and adhesion between the carbon fibers in the composite material and the matrix resin.

[0107] The gluing treatment may be carried out using various gluing methods known in the art. In the method of the present invention, there are no particular limitations on the gluing method, gluing agent, or gluing conditions, as long as the desired gluing agent can be applied to the carbon fibers. After the gluing treatment, a drying treatment may be performed to remove the solvent or dispersion medium used during the gluing treatment.

[0108] In this invention, a polymerization process of an acrylonitrile solution is employed to prepare a polyacrylonitrile spinning stock solution. This polymerization process employs three-stage temperature control to optionally, but preferably, control the oxygen content in the polymerization vessel so that the gel particles present in the resulting polyacrylonitrile spinning stock solution satisfy the requirements of this application and have the high equilibrium swelling degree specified in this application. In subsequent processing steps, the gel particles deform axially in a tensile manner, following the fiber body, thereby forming axially elongated micropores within the final carbon fiber. This reduces adverse effects on the mechanical properties of the carbon fiber and ensures good mechanical properties of the carbon fiber. Therefore, the carbon fiber of this invention, which contains micropores and possesses high performance, can be obtained.

[0109] In the present invention, the carbon fiber obtained has an average radial size L P 2.0nm or less, aspect ratio L / L P The material has 50 or more micropores, and the ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores is less than 10%. When the micropores satisfy the requirements of this application, the adverse effect of the presence of micropores on the mechanical properties of the carbon fiber is reduced, and carbon fibers with good mechanical properties can be obtained.

[0110] This invention relates to the following measurement method.

[0111] Zero shear viscosity of polyacrylonitrile polymer solution A rotary rheometer was used, with a measurement temperature of 50 ± 0.01 °C, a rotor diameter of 25 mm, and a spacing of 1 mm. To prevent the influence of water absorption by the sample and volatilization of the solvent on the measurement results, a uniform layer of methyl silicone oil was applied to the free surface of the sample that was in contact with the air. The viscosity change of the sample with respect to the shear rate was measured, and the zero shear viscosity of the polyacrylonitrile polymer solution was determined by extrapolation.

[0112] Conversion rate The monomer conversion rate during the polymerization process was measured by gravimetric method. The initial monomer concentration during polymerization was A. 2.0000 g of the polymer solution was placed on a glass plate during or after the polymerization process. The polymer solution was flattened using the glass plate and washed with water to form a film. The polymer film was washed in boiling water for 1 hour to remove residual solvent. The polymer film was dried in a vacuum drying oven (pressure 2 kPa A, drying temperature 80°C, and drying time 8 hours) until its mass became constant. The mass was recorded as m (unit: g). The conversion rate is [m / (A×2)]×100%.

[0113] Counting of gel particles and analysis of particle size The number and particle size of gel particles in a polyacrylonitrile polymer solution were measured using an AccuSizer A7000 SIS count particle size analyzer. The ambient temperature during measurement was 25±1°C, and the humidity was 20-80%. To reduce the influence of dust and impurities in the environment on the measurement results, the count particle size analyzer was installed in a cleanroom. The AccuSizer A7000 SIS employs single-particle optical sensing technology to achieve particle counting and analysis. In this technology, a portion of the incident light is blocked as a single particle passes through a narrow photosensitive area, and the intensity of the incident light reaching the detector is instantaneously reduced. The attenuation of the intensity signal is theoretically proportional to the cross-sectional area of ​​the particle, i.e., the square of the particle diameter. A calibration curve was created using standard particles to show the relationship between particle diameter and the magnitude of the intensity signal. Based on this calibration curve, the particle diameter was calculated, and the number of particles was counted. As the detector, an LE400-05 with a particle size detection range of 0.15 to 400 μm and a maximum detection concentration of 10,000 particles / ml was used. The sample volume was set to 5 mL and the flow rate to 30.0 mL / min. Before measurement, the polyacrylonitrile polymer solution was diluted 20-fold with a clean solvent to ensure that the number of particles per milliliter in the diluted solution was less than 10,000. The clean solvent was obtained by filtering the solvent using a 0.45 μm PTFE filtration membrane so that the number of particles in the filtered solvent was less than 100 per milliliter.

[0114] Equilibrium swelling degree In this invention, the equilibrium swelling degree of the gel particles is measured by the following method.

[0115] An appropriate amount of gel sample was weighed and extracted using a Soxhlet extractor (solvent: DMF, extraction temperature: 145°C, pressure: atmospheric pressure). Soluble polymers adhering to the surface of the gel sample were removed by extraction, and the gel sample was swollen in the Soxhlet extractor until equilibrium was reached. The entire extraction process was continued for at least 24 hours. Subsequently, the equilibrium-swollen gel sample was removed, and the residual solvent on the surface was absorbed with absorbent paper. The mass (m³) of the sample was then measured. eq The mass (denoted as m0) was accurately measured. Finally, the swollen and equilibrated gel sample was washed with water and dried under vacuum heating (pressure of 2 kPa A, temperature of 80°C, time of 8 hours). After the gel sample was completely dry, it was removed and placed in a drying oven, where it was allowed to cool naturally to room temperature to obtain a dried gel sample. The cooled and dried gel sample was removed, and its mass (denoted as m0) was accurately measured. The degree of equilibrium swelling was calculated using the following formula.

[0116]

number

[0117] The gel sample was taken from insoluble polymer adhering to the outer surface of the filter element of the filter. The filter was a 316L stainless steel metal fiber sintered felt filter with a filtration accuracy of 1 μm. The polyacrylonitrile solution (spinning solution) flowed from the outer surface of the filter element to the center of the filter element, and the filtered polyacrylonitrile solution flowed out from the center. The gel particles were trapped on the outer surface of the filter element and within the pore structure inside the stainless steel metal fiber sintered felt. When the pressure difference across the filter exceeded 4 MPa, a spare filter was used, the used filter element was removed, and the insoluble polymer adhering to the outer surface of the filter element was collected and used to measure the equilibrium swelling degree of the gel particles.

[0118] Number and diameter of polyacrylonitrile precursor fibers and carbon fibers Measurements were performed using microscopy in accordance with GB / T3364-2008. A portion of a multifilament approximately 200 mm in length was randomly sampled from the polyacrylonitrile precursor fiber or carbon fiber multifilament, which was the sample to be measured. Using a sharp knife, a small fiber bundle of 0.2-0.3 mm in length was taken from the fiber multifilament to be measured, and the collected fiber bundle was placed on a microscope slide. A drop of optical clear resin diluted with xylene was added, and the fibers were loosened using a clean, sharp needle, and the slide was covered with a microscope cover slip. The transmission microscope has a mechanical stage that can move the microscope slide in two mutually orthogonal directions. Assuming that an observation magnification of at least 500x is met, the resolution of the transmission microscope needs to be reduced to about 2 μm.

[0119] Tensile strength and tensile modulus of carbon fiber The mechanical tensile method was performed according to GB / T3362-2005. Measurements were taken by applying a tensile load to resin-impregnated and cured fibers until fracture occurred. Tensile strength was determined by dividing the fracture load by the cross-sectional area of ​​the carbon fiber multifilament. Tensile modulus was measured based on a predetermined strain limit. Ten samples were measured per test group, but the number of valid samples had to be at least six. The multifilaments were prepared by manual resin impregnation, with the weight ratio of the impregnation solution being TDE-85 epoxy resin:diaminodiphenylmethane (DDM):acetone = 100:45:150. After impregnation, the samples had to be free of droplet adhesion and the multifilaments were not bonded to each other. Curing was performed in three stages of increasing temperature: 45 minutes at 60°C, 45 minutes at 90°C, and 45 minutes at 150°C. After curing, a reinforcing sheet was attached to the sample, and it was placed in an 80°C oven for 1 hour to cure, obtaining the final sample for measurement.

[0120] Variance coefficient In accordance with GB / T1446-2005, the arithmetic mean of the measured characteristics is calculated using the following formula.

[0121]

number

[0122] And the standard deviation S is calculated, and finally, the coefficient of variance C for the characteristic is calculated. V It can be calculated.

[0123]

number

[0124]

number

[0125]

number

[0126] Micropore properties in precursor fibers and carbon fibers The characteristics were evaluated using small-angle X-ray scattering (SAXS) according to the following reference [1]. The test was conducted at the BL16B1 small-angle scattering beamline of the Shanghai Synchrotron Radiation Source. The incident X-ray wavelength was 0.124 nm, and a Pilatus 2M detector was used. The detector had 1475 × 1679 pixels and a pixel size of 172 × 172 μm. The distance from the bundled fiber sample to the detector was 2092 mm. The measurement data was processed by identifying the center of the scattered signal, transforming the scattered data, normalizing the light intensity, and subtracting the background to eliminate the influence of external conditions such as the sample, light intensity, and background during measurement.

[0127] For micropore systems with two different sizes, the double-model Debye-Bueche analysis method shown in the following equation is employed.

[0128]

number

[0129] Here, q is the scattering vector, I(q) is the scattering intensity, and I0 is the intensity scaling factor, L c This is the Debye correlation length, and I f This is the background for electron density fluctuations. f It is obtained by the following process: "q 4 -I(q)×q 4 The curve is plotted and linearly fitted, and the slope represents the background of electron density fluctuations at this point. I0 and Lc can be determined by linear fitting. Based on this, the correlation distance L c1 and L c2 This can be determined by fitting the above formula. In the case of a sparse micropore system, the magnitude of the correlation distance is close to the size of the micropore. Therefore, by performing Debye-Bueche analysis on the SAXS signals in the meridian and equatorial directions, the micropore size L along the fiber axis and the micropore size L along the radial direction of the fiber can be determined. P This can be obtained. The axial size L and radial size L of the micropore. P Based on this, the aspect ratio of the micropore L / L P It is possible to calculate this.

[0130] The following invariants exist in scattering by micropores.

[0131]

number

[0132] V is the volume of the micropore. Based on the scattering curves of two types of micropores fitted by the Debye-Bueche method, the relative volumes of the two types of micropores can be calculated using this equation.

[0133] Reference [1]:Analysing the nanoporous structure of aramid fibers,Brian R. Pauw et al., J. Appl. Cryst. (2010). 43, 837-849 Evaluation of the amount of filament fluff in primary fibers During the normal spinning process, the amount of filament fluff accumulated on the bath roller of the first coagulation bath was collected every 24 hours. After thorough drying (pressure 2 kPa A, temperature 80°C, time 8 hours), the weight of the filament fluff was measured and this was taken as the amount of filament fluff of the primary fiber.

[0134] Cutting of primary fiber filaments The frequency of downtime due to filament breakage was tallied to determine the extent of filament breakage. For example, if the machine stopped due to filament breakage after 20 consecutive days of spinning, the downtime due to filament breakage would be counted as 20 days / time.

[0135] The present invention will be described in more detail below with reference to examples.

[0136] The raw materials and reagents used in the examples and comparative examples can be purchased directly or prepared based on preparation methods disclosed in the prior art. The raw materials or reagents may be treated before use by methods known in the art, as necessary, to meet the conditions required for the reaction. For example, in the case of acrylonitrile, polymerization inhibitors may be removed by distillation before use.

[0137] The oil used in the examples and comparative examples was ADVALON® CF3295, obtained from Wacker Chemicals (China).

[0138] [Example 1] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was performed using DMSO as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, the amount of initiator used was 0.34 wt% of the total monomer mass, and itaconic acid was used as the copolymer monomer, accounting for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature to set the oxygen content in the polymerization vessel to 980 ppm. The initial stage started at a temperature of 40°C and continued for 60 minutes. In the intermediate stage of constant-temperature polymerization, the temperature was set to 80°C and continued for 600 minutes. In the final stage of cold polymerization, the temperature was set to 45°C and continued for 120 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample introduction temperature was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample introduction temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solids content of the polyacrylonitrile solution was 19.0 wt%, and the zero shear viscosity of the solution measured at 50°C was 86 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 96,579 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.12% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 300%.

[0139] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), and then extruded through a spinneret and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 12,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers were passed through a godet roller into the second and third coagulation baths. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, the fibers were stretched three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with a 1.2% oil concentration was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with a 2.0% oil concentration was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, there was almost no fuzzing or breakage of the filaments, and the frequency of downtime due to filament fuzzing and breakage was 37 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.7%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.7%. P The wavelength is 1.85 nm, and the aspect ratio of the micropore is L / L. P The answer was 62.

[0140] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a heat stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the total elongation was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 1.65 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 8.5%. The average diameter of the carbon fibers was 5 μm, and the coefficient of dispersion of the diameter was (C V The value is 2.5%, the tensile strength is 5.5 GPa, and the tensile strength is C V The value is 4.5%, the tensile modulus is 303 GPa, and the tensile modulus is C V The value was 4.0%.

[0141] [Example 2] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was performed using DMF as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 760 ppm. The initial starting temperature for the first stage was 55°C, and the duration was 80 minutes. The temperature for the intermediate stage of constant-temperature polymerization was 65°C, and the duration was 500 minutes. The temperature for the final stage of cold polymerization was 40°C, and the duration was 200 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample introduction temperature was 72°C, and the residence time was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample introduction temperature was 65°C, and the residence time was 120 minutes. The solids content of the polyacrylonitrile solution was 18.0 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 50 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 75744 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.11% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 500%.

[0142] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 24,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, the fibers were stretched three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with a 1.2% oil concentration was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with a 2.0% oil concentration was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, there was almost no fuzzing or breakage of the filaments, and the frequency of downtime due to fuzzing and breakage of the filaments was 35 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.5%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.5%. P The wavelength is 1.85 nm, and the aspect ratio of the micropore is L / L. P The number was 58.

[0143] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a heat stabilization treatment by passing through five atmospheric heating furnaces in the range of 180 to 280 °C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181 °C, 222 °C, 234 °C, 252 °C, and 273 °C, respectively. The total heating time was 62 minutes, and the overall draw ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The temperature of low-temperature carbonization was 300 to 700 °C, the heat treatment time was 3.8 minutes, and the draw ratio was 2.8%. The temperature of high-temperature carbonization was 1000 to 1500 °C, the heat treatment time was 1.8 minutes, and the draw ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L P of the micropores perpendicular to the fiber axis was 1.76 nm, and the aspect ratio L / L P of the micropores was 53. The ratio of the volume of micropores with a radial size larger than 15 nm to the total volume of micropores was 9.5%. The average diameter of the carbon fibers was 7 μm, the dispersion coefficient (C V value) of the diameter was 2.6%, the tensile strength was 4.9 GPa, the C V value of the tensile strength was 4.5%, the tensile modulus was 282 GPa, and the C V value of the tensile modulus was 4.9%.

[0144] [Example 3] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMAC as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 340 ppm. The initial starting temperature for the first stage was 70°C, and the duration was 30 minutes. The temperature for the intermediate constant-temperature polymerization stage was 50°C, and the duration was 600 minutes. The temperature for the final cold polymerization stage was 30°C, and the duration was 150 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solid content of the polyacrylonitrile solution was 22.0 wt%, and the zero shear viscosity of the solution, measured at 50°C, was 150 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 67768 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.10% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 1000%.

[0145] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 3000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with a 1.2% oil concentration was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with a 2.0% oil concentration was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, there was almost no fuzzing or breakage of the filaments, and the frequency of downtime due to fuzzing and breakage of the filaments was 48 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.6%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.6%. P The wavelength is 1.62 nm, and the aspect ratio of the micropore is L / L. P The answer was 62.

[0146] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing through five air heating furnaces in the range of 180 to 280 °C to obtain pre-oxidized fibers. The temperatures of these five air heating furnaces were 181 °C, 222 °C, 234 °C, 252 °C, and 273 °C, respectively. The total heating time was 62 minutes, and the overall draw ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The temperature of low-temperature carbonization was 300 to 700 °C, the heat treatment time was 3.8 minutes, and the draw ratio was 2.8%. The temperature of high-temperature carbonization was 1000 to 1500 °C, the heat treatment time was 1.8 minutes, and the draw ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L P of the micropores perpendicular to the fiber axis was 1.57 nm, and the aspect ratio L / L P of the micropores was 59. The ratio of the volume of micropores with a radial size larger than 15 nm to the total volume of micropores was 6.3%. The average diameter of the carbon fibers was 6 μm, the coefficient of variation (C V value) of the diameter was 2.4%, the tensile strength was 5.8 GPa, the C V value of the tensile strength was 3.5%, the tensile modulus was 323 GPa, and the C V value of the tensile modulus was 4.3%.

[0147] 〔Example 4〕 (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMSO as the solvent and azobisisobutyronitrile as the initiator. The monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 600 ppm. The initial starting temperature for the first stage was 40°C, and the duration was 60 minutes. The temperature for the intermediate constant-temperature polymerization stage was 80°C, and the duration was 600 minutes. The temperature for the final cold polymerization stage was 45°C, and the duration was 120 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solids content of the polyacrylonitrile solution was 19.8 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 88 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 91456 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.11% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 800%.

[0148] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 12,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with a 1.2% oil concentration was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with a 2.0% oil concentration was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, there was almost no fuzzing or breakage of the filaments, and the frequency of downtime due to filament fuzzing and breakage was 37 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.5%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.5%. P The wavelength is 1.65 nm, and the aspect ratio of the micropore is L / L. P The answer was 61.

[0149] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 1.45 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 4.5%. The average diameter of the carbon fibers was 5 μm, and the coefficient of dispersion of the diameter was (C V The value is 2.5%, the tensile strength is 5.7 GPa, and the tensile strength C V The value is 4.4%, the tensile modulus is 312 GPa, and the tensile modulus is C V The value was 4.0%.

[0150] [Example 5] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMF as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 500 ppm. The initial starting temperature for the first stage was 55°C, and the duration was 80 minutes. The temperature for the intermediate stage of constant-temperature polymerization was 65°C, and the duration was 500 minutes. The temperature for the final stage of cold polymerization was 40°C, and the duration was 200 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solid content of the polyacrylonitrile solution was 18.0 wt%, and the zero shear viscosity of the solution, measured at 50°C, was 55 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 72324 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.10% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 900%.

[0151] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 24,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, there was almost no fuzzing or breakage of the filaments, and the frequency of downtime due to fuzzing and breakage of the filaments was 35 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.5%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.5%. P The wavelength is 1.55 nm, and the aspect ratio of the micropore is L / L. P It was 60.

[0152] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 1.46 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 4.6%. The average diameter of the carbon fibers was 7 μm, and the coefficient of dispersion of the diameter was (C V The value is 2.6%, the tensile strength is 5.2 GPa, and the tensile strength is C V The value is 4.7%, the tensile modulus is 289 GPa, and the tensile modulus is C V The value was 4.6%.

[0153] [Example 6] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMAC as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 100 ppm. The initial starting temperature for the first stage was 70°C, and the duration was 30 minutes. The temperature for the intermediate stage of constant-temperature polymerization was 50°C, and the duration was 600 minutes. The temperature for the final stage of cold polymerization was 30°C, and the duration was 150 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature was 72°C, and the residence time was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature was 65°C, and the residence time was 120 minutes. The solids content of the polyacrylonitrile solution was 22.0 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 162 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 60128 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.08% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 2000%.

[0154] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 3000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with a 1.2% oil concentration was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with a 2.0% oil concentration was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, there was almost no fuzzing or breakage of the filaments, and the frequency of downtime due to fuzzing and breakage of the filaments was 48 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.1%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.1%. P The wavelength is 1.42 nm, and the aspect ratio of the micropore is L / L. P The number was 65.

[0155] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 1.37 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 4.7%. The average diameter of the carbon fibers was 6 μm, and the coefficient of dispersion of the diameter was (C V The value is 2.4%, the tensile strength is 5.8 GPa, and the tensile strength C V The value is 2.5%, the tensile modulus is 323 GPa, and the tensile modulus is C V The value was 2.3%.

[0156] [Example 7] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMF as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 1500 ppm. The initial starting temperature for the first stage was 55°C, and the duration was 80 minutes. The temperature for the intermediate stage of constant-temperature polymerization was 65°C, and the duration was 500 minutes. The temperature for the final stage of cold polymerization was 30°C, and the duration was 200 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solid content of the polyacrylonitrile solution was 18.0 wt%, and the zero shear viscosity of the solution, measured at 50°C, was 48 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 78,630 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.13% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 480%.

[0157] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 24,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, the fibers were stretched three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with a 1.2% oil concentration was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with a 2.0% oil concentration was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, there was almost no fuzzing or breakage of the filaments, and the frequency of downtime due to fuzzing and breakage of the filaments was 35 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.8%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be... P It is 1.98 nm, and the micropore aspect ratio L / L P The number was 48.

[0158] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P It is 1.83 nm, and the aspect ratio of the micropore is L / L P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 9.3%. The average diameter of the carbon fibers was 7 μm, and the coefficient of dispersion of the diameter was (C V The value is 2.8%, the tensile strength is 4.98 GPa, and the tensile strength is C V The value is 4.9%, the tensile modulus is 292 GPa, and the tensile modulus is C V The value was 4.7%.

[0159] [Example 8] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMSO as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 2500 ppm. The initial starting temperature for the first stage was 55°C, and the duration was 120 minutes. The temperature for the intermediate stage of constant-temperature polymerization was 65°C, and the duration was 550 minutes. The temperature for the final stage of cold polymerization was 45°C, and the duration was 100 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature was 72°C, and the residence time was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature was 65°C, and the residence time was 120 minutes. The solids content of the polyacrylonitrile solution was 19.8 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 96 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 87,339 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.21% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 390%.

[0160] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 24,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, the fibers were stretched three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with a 1.2% oil concentration was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with a 2.0% oil concentration was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, there was almost no fuzzing or breakage of the filaments, and the frequency of downtime due to fuzzing and breakage of the filaments was 33 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.9%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.9%. P It is 1.99 nm, and the aspect ratio of the micropore is L / L P The number was 46.

[0161] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 1.96 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 9.5%. The average diameter of the carbon fibers was 7 μm, and the coefficient of dispersion of the diameter was (C V The value is 2.8%, the tensile strength is 4.93 GPa, and the tensile strength is C V The value is 4.9%, the tensile modulus is 289 GPa, and the tensile modulus is C V The value was 4.8%.

[0162] [Comparative Example 1] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMF as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in two stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 1500 ppm. The starting temperature for the initial stage was 30°C, and the duration was 30 minutes. The temperature for the isothermal polymerization stage was 65°C, and the duration was 750 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solids content of the polyacrylonitrile solution was 18.2 wt%, and the zero shear viscosity of the solution, measured at 50°C, was 65 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 112,822 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.65% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 180%.

[0163] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 24,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, fuzzing and breakage of the filaments occurred, and the frequency of downtime due to filament fuzzing and breakage was 20 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 3.8%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 3.8%. P The wavelength is 3.29 nm, and the aspect ratio of the micropore is L / L. P The number was 43.

[0164] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 3.18 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 12.4%. The average diameter of the carbon fibers was 7 μm, and the coefficient of dispersion of the diameter was (C V The value is 3.6%, the tensile strength is 4.2 GPa, and the tensile strength is C V The value is 6.5%, the tensile modulus is 257 GPa, and the tensile modulus is C V The value was 7.2%.

[0165] [Comparative Example 2] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMSO as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in two stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 680 ppm. The starting temperature for the initial stage was 20°C, and the duration was 60 minutes. The temperature for the isothermal polymerization stage was 80°C, and the duration was 720 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample introduction temperature was 72°C, and the residence time was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample introduction temperature was 65°C, and the residence time was 120 minutes. The solids content of the polyacrylonitrile solution was 19.0 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 92 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 134,925 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.87% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 120%.

[0166] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 12,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, fuzzing and breakage of the filaments occurred, and the frequency of downtime due to filament fuzzing and breakage was 23 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 6.7%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be... P The wavelength is 3.92 nm, and the aspect ratio of the micropore is L / L. P The number was 38.

[0167] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 3.73 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 16.3%. The average diameter of the carbon fibers was 5 μm, and the coefficient of dispersion of the diameter was (C V The value is 7.5%, the tensile strength is 3.8 GPa, and the tensile strength C V The value is 6.5%, the tensile modulus is 233 GPa, and the tensile modulus is C V The value was 7.0%.

[0168] [Comparative Example 3] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMAC as the solvent and azobisisobutyronitrile as the initiator. The total monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in two stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 340 ppm. The starting temperature for the initial stage was 20°C, and the duration was 100 minutes. The temperature for the isothermal polymerization stage was 85°C, and the duration was 680 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solid content of the polyacrylonitrile solution was 22.0 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 146 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 170,738 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 1.2% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 100%.

[0169] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 3000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, fuzzing and breakage of the filaments occurred, and the frequency of downtime due to filament fuzzing and breakage was 18 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 7.6%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be... P The wavelength is 4.62 nm, and the aspect ratio of the micropore is L / L. P It was 35.

[0170] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 3.92 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 15.5%. The average diameter of the carbon fibers was 6 μm, and the coefficient of dispersion of the diameter was (C V The value is 6.4%, the tensile strength is 3.8 GPa, and the tensile strength is C V The value is 6.5%, the tensile modulus is 256 GPa, and the tensile modulus is C V The value was 6.3%.

[0171] [Comparative Example 4] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMSO as the solvent and azobisisobutyronitrile as the initiator. The monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 2500 ppm. The initial starting temperature for the first stage was 25°C, and the duration was 120 minutes. The temperature for the intermediate constant-temperature polymerization stage was 80°C, and the duration was 640 minutes. The temperature for the final polymerization stage was 65°C, and the duration was 120 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solids content of the polyacrylonitrile solution was 18.6 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 78 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 125,990 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.96% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 150%.

[0172] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 12,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, fuzzing and breakage of the filaments occurred, and the frequency of downtime due to filament fuzzing and breakage was 19 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.7%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.7%. P The wavelength is 3.35 nm, and the aspect ratio of the micropore is L / L. P The number was 38.

[0173] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 3.65 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 12.1%. The average diameter of the carbon fibers was 5 μm, and the coefficient of dispersion of the diameter was (C V The value is 6.5%, the tensile strength is 4.06 GPa, and the tensile strength C V The value is 7.5%, the tensile modulus is 233 GPa, and the tensile modulus is C V The value was 6.0%.

[0174] [Comparative Example 5] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMSO as the solvent and azobisisobutyronitrile as the initiator. The monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 600 ppm. The initial starting temperature for the first stage was 40°C, and the duration was 60 minutes. The temperature for the intermediate constant-temperature polymerization stage was 75°C, and the duration was 600 minutes. The temperature for the final polymerization stage was 65°C, and the duration was 120 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solids content of the polyacrylonitrile solution was 19.8 wt%, and the zero shear viscosity of the solution, measured at 50°C, was 97 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 121,440 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.85% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 200%.

[0175] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 12,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, fuzzing and breakage of the filaments occurred, and the frequency of downtime due to filament fuzzing and breakage was 23 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.6%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.6%. P The wavelength is 3.25 nm, and the aspect ratio of the micropore is L / L. P The answer was 41.

[0176] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (1) above were subjected to a heat stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 2.79 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 12.3%. The average diameter of the carbon fibers was 5 μm, and the coefficient of dispersion of the diameter was (C V The value is 6.9%, the tensile strength is 4.10 GPa, and the tensile strength is C V The value is 7.3%, the tensile modulus is 238 GPa, and the tensile modulus is C V The value was 6.0%.

[0177] [Comparative Example 6] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMSO as the solvent and azobisisobutyronitrile as the initiator. The monomer concentration was 21.5 wt%, and the amount of initiator used was 0.45 wt% of the total monomer mass. Itaconic acid was used as the copolymer monomer, accounting for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 340 ppm. The starting temperature for the initial stage was 20°C, and the duration was 100 minutes. The temperature for the intermediate stage of constant-temperature polymerization was 85°C, and the duration was 550 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solids content of the polyacrylonitrile solution was 22.0 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 146 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 119,380 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.83% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 260%.

[0178] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 12,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, fuzzing and breakage of the filaments occurred, and the frequency of downtime due to filament fuzzing and breakage was 21 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.9%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.9%. P The wavelength is 3.16 nm, and the aspect ratio of the micropore is L / L. P It was 44.

[0179] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 2.56 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 11.5%. The average diameter of the carbon fibers was 5 μm, and the coefficient of dispersion of the diameter was (C V The value is 6.9%, the tensile strength is 4.32 GPa, and the tensile strength is C V The value is 6.8%, the tensile modulus is 248 GPa, and the tensile modulus is C V The value was 5.5%.

[0180] [Comparative Example 7] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMSO as the solvent and azobisisobutyronitrile as the initiator. The monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 600 ppm. The initial starting temperature for the first stage was 50°C, and the duration was 60 minutes. The temperature for the intermediate constant-temperature polymerization stage was 45°C, and the duration was 200 minutes. The temperature for the final polymerization stage was 75°C, and the duration was 550 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature was 72°C, and the residence time was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature was 65°C, and the residence time was 120 minutes. The solids content of the polyacrylonitrile solution was 19.8 wt%, and the zero-shear viscosity of the solution, measured at 50°C, was 112 Pa·s. In the polyacrylonitrile solution, the total number of gel particles Np with a particle diameter greater than 0.15 μm was 123,650 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.89% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 190%.

[0181] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 12,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, fuzzing and breakage of the filaments occurred, and the frequency of downtime due to filament fuzzing and breakage was 21 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.9%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.9%. P The wavelength is 3.35 nm, and the aspect ratio of the micropore is L / L. P The number was 39.

[0182] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 3.26 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 12.6%. The average diameter of the carbon fibers was 5 μm, and the coefficient of dispersion of the diameter was (C V The value is 7.0%, the tensile strength is 4.12 GPa, and the tensile strength C V The value is 6.6%, the tensile modulus is 237 GPa, and the tensile modulus is C V The value was 6.5%. [Comparative Example 8] (1) Preparation of the stock solution Solution polymerization of acrylonitrile was carried out using DMSO as the solvent and azobisisobutyronitrile as the initiator. The monomer concentration was 20.5 wt%, and the amount of initiator used was 0.34 wt% of the total monomer mass. The copolymer monomer was itaconic acid, which accounted for 1 mol% of the total monomer amount. The polymerization temperature was controlled in three stages. Nitrogen purging was performed before raising the polymerization temperature, and the oxygen content in the polymerization vessel was 600 ppm. The initial starting temperature for the first stage was 40°C, and the duration was 60 minutes. The temperature for the intermediate constant-temperature polymerization stage was 65°C, and the duration was 450 minutes. The temperature for the final polymerization stage was 75°C, and the duration was 250 minutes. After polymerization, the crude stock solution was subjected to demonomerization and defoaming treatment to obtain a polyacrylonitrile solution (stock solution). The demonomerization pressure was 1.0 kPa A, the sample input temperature for demonomerization was 72°C, and the residence time for demonomerization was 60 minutes. The defoaming pressure was 2.0 kPa A, the sample input temperature for defoaming was 65°C, and the residence time for defoaming was 120 minutes. The solid content of the polyacrylonitrile solution was 19.8 wt%, and the zero shear viscosity of the solution measured at 50°C was 134 Pa·s. In the polyacrylonitrile solution, the total number Np of gel particles with a particle diameter greater than 0.15 μm was 123,920 particles / mL, the number of gel particles with a particle diameter greater than 5 μm accounted for 0.92% of the total number of gel particles, and the equilibrium swelling degree of the gel particles was 180%.

[0183] (2) Preparation of precursor fibers The polyacrylonitrile solution prepared in (1) above was quantified using a metering pump, filtered through a sintered metal filter (filtration accuracy of 5 μm), extruded through a spinneret, and introduced into the first coagulation bath. The pore size of the spinneret was 55 μm, and the number of pores in the spinneret was 12,000. The temperature of the first coagulation bath was 35°C, the first coagulation bath was an 80% aqueous dimethyl sulfoxide solution, and the draw ratio was -30%. After coagulation, the primary fibers entered the second and third coagulation baths via a godet roller. The coagulation bath concentrations were 60% and 30%, respectively, the temperatures were 40°C and 60°C, respectively, and the draw ratios were 1.0 and 1.05, respectively. Subsequently, drawing was performed three times with hot water at temperatures of 90°C, 92°C, and 95°C, respectively, with draw ratios of 1.20, 1.41, and 2.0, respectively. Next, the water washing was performed nine times, with the temperature gradually increasing: 50°C for the first three washes, 60°C for the fourth to sixth washes, and 70°C for the seventh to ninth washes. No stretching was performed during the washing stage. Subsequently, the first oiling with an oil concentration of 1.2% was performed, followed by the first drying and densification at a drying temperature of 95°C. Next, the second oiling with an oil concentration of 2.0% was performed, followed by the second drying and densification at a drying temperature of 130°C. Subsequently, the fibers were stretched under steam at a steam pressure of 0.35 MPa and a steam stretching ratio of 3.2. After that, the fibers were heat-fixed at a heat-fixing steam pressure of 0.1 MPa. Finally, the fibers were wound up to obtain carbon precursor fibers. During the solidification process of the primary fibers, fuzzing and breakage of the filaments occurred, and the frequency of downtime due to filament fuzzing and breakage was 20 days / time. The coefficient of dispersion of the diameter of the precursor fibers (C V The value was 2.6%. When the precursor fibers were evaluated by small-angle X-ray scattering (SAXS), the average radial size L of the micropores was found to be 2.6%. P The wavelength is 3.25 nm, and the aspect ratio of the micropore is L / L. P The number was 38.

[0184] (3) Preparation of carbon fibers The polyacrylonitrile precursor fibers prepared in (2) above were subjected to a thermal stabilization treatment by passing them through five atmospheric heating furnaces in the range of 180-280°C to obtain pre-oxidized fibers. The temperatures of these five atmospheric heating furnaces were 181°C, 222°C, 234°C, 252°C, and 273°C, respectively. The total heating time was 62 minutes, and the overall elongation ratio was 2.2%. The obtained pre-oxidized fibers were subjected to low-temperature carbonization treatment and high-temperature carbonization treatment in nitrogen to obtain carbon fibers. The low-temperature carbonization temperature was 300-700°C, the heat treatment time was 3.8 minutes, and the elongation ratio was 2.8%. The high-temperature carbonization temperature was 1000-1500°C, the heat treatment time was 1.8 minutes, and the elongation ratio was -2.8%. The micropores of the obtained carbon fibers were evaluated by small-angle X-ray scattering (SAXS). The average radial size L of the micropores perpendicular to the axial direction of the fiber. P The wavelength is 3.19 nm, and the aspect ratio of the micropore is L / L. P The ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores was 13.3%. The average diameter of the carbon fibers was 5 μm, and the coefficient of dispersion of the diameter was (C V The value is 6.8%, the tensile strength is 4.16 GPa, and the tensile strength is C V The value is 6.5%, the tensile modulus is 239 GPa, and the tensile modulus is C V The value was 6.3%.

[0185] The data for each of the above examples and comparative examples are summarized in the table below.

[0186] [Table 1]

Claims

1. A polyacrylonitrile carbon fiber containing micropores, The average radius size L of the aforementioned micropore Ｐ It is 2.0 nm or less, Aspect ratio L / L of the aforementioned micropore Ｐ The number is 50 or more and 100 or less. A polyacrylonitrile-based carbon fiber characterized in that the ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores is greater than 0 and less than 10%.

2. The average radius size L of the aforementioned micropore Ｐ It is 1.5 nm or less, Aspect ratio L / L of the aforementioned micropore Ｐ The value is 60 or more and 100 or less. The polyacrylonitrile-based carbon fiber according to claim 1, characterized in that the ratio of the volume of micropores with a radial size greater than 15 nm to the total volume of micropores is greater than 0 and less than 5%.

3. The diameter of the carbon fiber C Ｖ The polyacrylonitrile-based carbon fiber according to claim 1, characterized in that the value is 3% or less.

4. The polyacrylonitrile-based carbon fiber according to claim 1, characterized in that the number of fibers in the polyacrylonitrile-based carbon fiber is 3,000 to 24,000.

5. The aforementioned polyacrylonitrile-based carbon fiber is The diameter is 5 to 7 μm; The tensile strength is 4.9 to 5.8 GPa, and the tensile strength is C Ｖ The value is less than 5%; and / or, The tensile modulus is 282 to 323 GPa, and the tensile modulus is C Ｖ The polyacrylonitrile-based carbon fiber according to claim 1, characterized in that the value is less than 5%.

6. A polyacrylonitrile spinning stock solution containing gel particles, The gel particles contained in the aforementioned polyacrylonitrile spinning solution have a total number of gel particles with a particle size larger than 0.15 μm, which is 1 × 10⁻¹⁶. ５ The number of particles / mL or less, and the ratio of gel particles with a particle diameter larger than 5 μm to the total number of gel particles is 0.3% or less. A polyacrylonitrile spinning solution in which the equilibrium swelling degree of the gel particles is 250 to 5000%.

7. The polyacrylonitrile spinning solution comprises a polyacrylonitrile polymer and a solvent. The polyacrylonitrile spinning stock solution according to claim 6, characterized in that the weight ratio of the polyacrylonitrile polymer to the solvent is (15-30):(85-70), preferably (18-22):(82-78).

8. The solvent is at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and mixtures thereof. and / or, The polyacrylonitrile spinning stock according to claim 7, characterized in that the polyacrylonitrile polymer is a polyacrylonitrile homopolymer, a polyacrylonitrile copolymer, or a mixture thereof.

9. The polyacrylonitrile spinning stock solution according to claim 6, characterized in that the zero shear viscosity at a viscosity measurement temperature of 50°C is 30 to 200 Pa·s, preferably 50 to 150 Pa·s.

10. A polyacrylonitrile spinning stock solution, preferably a method for preparing the polyacrylonitrile spinning stock solution according to claim 6, The temperature of the first stage, which is the initial start stage, is T １ °C, and the temperature of the second stage, which is the stage of isothermal polymerization, is T ２ °C, and the temperature of the third stage, which is the stage of cooling polymerization, is T ３ °C, and includes solution polymerization adopting a three-stage temperature control T １ , T ２ and T ３ A method for preparing a polyacrylonitrile spinning stock solution that satisfies the following relationship. T １ = (0.5 to 1.4) × T ２ , and 35 ≤ T １ ≤80; and T ３ = T ２ - (5 to 50), and 50 ≥ T ３ ≥25.

11. 35℃≦T １ ≤80°C, preferably 40°C ≤T １ ≤70℃, 40℃≦T ２ ≤90°C, preferably 50°C ≤T ２ ≤80℃, and, 25℃≦T ３ ≤50°C, preferably 25°C ≤T ３ ≤45℃, more preferably 30℃ ≤T ３ A method for preparing a polyacrylonitrile spinning stock solution according to claim 10, characterized in that the temperature is ≤45°C.

12. 50℃ ≤ T ２ ≤80℃, 40℃ ≤T １ ≤70°C and ≤30°C ３ The temperature is ≤45℃, and / or, T ３ = T ２ - (15 to 50), preferably T ３ = T ２ - (15 to 40), more preferably T ３ = T ２ A method for preparing a polyacrylonitrile spinning stock solution according to claim 10, characterized in that the value is -(20 to 35).

13. The polymerization time for the first stage, which is the initial starting stage, is 20 to 150 minutes, preferably 30 to 120 minutes, more preferably 30 to 80 minutes; the polymerization time for the second stage, which is the isothermal polymerization stage, is 300 to 900 minutes, preferably 400 to 800 minutes, preferably 400 to 700 minutes, more preferably 500 to 600 minutes; and the polymerization time for the third stage, which is the cooling polymerization stage, is 80 to 300 minutes, preferably 80 to 250 minutes, preferably 100 to 250 minutes, more preferably 120 to 200 minutes. and / or, A method for preparing a polyacrylonitrile spinning stock according to claim 10, characterized in that the monomer conversion rate in the second stage, which is a isothermal polymerization stage, is X, the monomer conversion rate in the first stage, which is an initial initiation stage, is (0.125 to 0.215) × X, and the monomer conversion rate in the third stage, which is a cold polymerization stage, is (0.007 to 0.0715) × X, where the monomer conversion rate X in the second stage, which is a isothermal polymerization stage, is 60% to 85%, preferably 65% ​​to 85%, more preferably 70% to 80% or 70% to 79%.

14. The solution polymerization is carried out under protection with an inert gas, preferably under protection with an inert gas and under conditions where the oxygen content is less than 1000 ppm. and / or, The method for preparing a polyacrylonitrile spinning stock according to claim 10, characterized in that the solution polymerization is carried out in a polymerization vessel.

15. A method for preparing polyacrylonitrile-based carbon fibers according to claim 1, A process for preparing precursor fibers from polyacrylonitrile spinning solution, The process includes pre-oxidation and carbonization of the precursor fiber to obtain the polyacrylonitrile-based carbon fiber, A method for preparing polyacrylonitrile carbon fibers, wherein the polyacrylonitrile spinning stock is the polyacrylonitrile spinning stock described in any one of claims 6 to 9, or a polyacrylonitrile spinning stock prepared by the preparation method described in any one of claims 10 to 14.

16. The method for preparing polyacrylonitrile-based carbon fibers according to claim 15, characterized in that the steps for preparing the precursor fibers include (1) coagulation of primary fibers, (2) stretching in hot water, (3) washing in hot water, (4) oiling, (5) drying and densification, (6) stretching under steam, (7) heat setting, and (8) winding.

17. The pre-oxidation temperature is 180 to 300°C, and is preferably divided into 4 to 6 temperature zones. and / or, The method for preparing polyacrylonitrile-based carbon fibers according to claim 15, characterized in that the carbonization includes low-temperature carbonization and high-temperature carbonization, preferably with a low-temperature carbonization temperature of 300 to 700°C and a high-temperature carbonization temperature of 1000 to 1500°C.

18. A method for preparing polyacrylonitrile-based carbon fibers according to claim 15, further comprising a surface treatment and gluing step.