Dry densified polyacrylonitrile fiber as well as drying densification method and application thereof

Abstract

The invention discloses a dried and densified polyacrylonitrile fiber as well as a drying and densification method and application thereof, and solves the problems that in the prior art, the polyacrylonitrile fiber is easy to wind a roller due to static electricity in the cooling process after being dried and densified, and the strength of the carbon fiber is poor when the polyacrylonitrile fiber is applied to the carbon fiber. The surface voltage and temperature of the dried and densified polyacrylonitrile fiber meet the formula (1): S = aT + b, wherein a is equal to 6-70, b is equal to-500 to-5660, and T is equal to 50-90 DEG C. According to the scheme, the roller winding frequency caused by static electricity in the precursor preparation process is 10 times / month or below, when the dried and densified fiber is applied to the carbon fiber, the tensile strength of the carbon fiber can reach 6.20 GPa, and a good technical effect is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of polyacrylonitrile fibers, and particularly relates to the drying densification process of polyacrylonitrile fibers. Specifically, it relates to a dried and densified polyacrylonitrile fiber, a method for drying and densifying the same, and an application thereof. Background Art

[0002] Polyacrylonitrile precursor is the basis for preparing polyacrylonitrile-based carbon fibers and is the key to preparing high-performance carbon fibers. High-quality carbon fiber precursor is the basis for preparing high-performance carbon fibers. How to prepare high-quality carbon fiber precursor has always been the focus and difficulty in the process of carbon fiber preparation. The preparation process of carbon fiber precursor can be divided into wet spinning and dry-jet wet spinning according to different spinning processes. Wet spinning has the advantages of less residual fiber solvent, easy process control, deep surface grooves of the prepared carbon fiber and good bonding performance with composites, and is one of the important methods for preparing carbon fiber precursor.

[0003] The preparation process of polyacrylonitrile-based carbon fiber precursor usually includes processes such as coagulation and fiber formation (wet spinning or dry-jet wet spinning method), water washing, hot water drawing, oiling, drying densification, and winding. The preparation of high-performance carbon fiber precursor also requires processes such as steam drawing and heat setting after drying densification. Polyacrylonitrile is an insulating material with a volume resistivity of 10 13 -10 14 Ω·cm, which is prone to generating static electricity. The fiber has poor bundle property and is easy to adhere to the roller and entangle, resulting in poor production stability. At the same time, static electricity is also likely to cause the fiber to adsorb dust in the air or dirt on the roller, resulting in an increase in surface defects of the fiber, which is not conducive to improving the mechanical properties of the fiber. Therefore, the control of static electricity during the fiber running process is crucial for the preparation process of carbon fiber precursor.

[0004] The drying densification process is a key process in the preparation process of carbon fiber precursor. In this process, the water in the fiber with a porous gel network gradually is removed, and under the action of shrinkage force and capillary attraction, the pores between the fibrils are merged or eliminated. Hot air drying and hot roller drying are two commonly used drying densification methods in the industrial production of polyacrylonitrile precursor. In the hot air drying process, the fiber continuously passes through a hot air device for heat transfer through hot air; in the hot roller drying densification process, the fiber continuously passes through multiple hot rollers with the same rotation speed for heat transfer through contact.

[0005] During the hot air drying process, there is friction between the tows. During the hot roller drying process, there is friction between the fibers and the hot roller. Especially after the moisture is removed, the conductivity of the fibers deteriorates further, generating strong static electricity (water is an excellent antistatic agent. After the moisture is removed, the conductive effect of water weakens). After the fibers are dried and densified, they can be directly wound up after cooling in the air for use as carbon fiber precursor filaments; they can also be further drawn finer through processes such as steam drawing after cooling in the air to prepare high-performance carbon fiber precursor filaments. The static electricity characteristics of the fibers during the cooling process are crucial for the amount of impurities adsorbed from the air, which in turn affects the mechanical properties of the carbon fibers. In severe cases, it can even cause the tow to wind around the roller and affect fiber production. For polyacrylonitrile fibers prepared by wet spinning, the significantly grooved surface structure is more likely to generate strong static electricity during processing. Therefore, it is particularly important to select and control the static electricity characteristics during the cooling process of wet-spun polyacrylonitrile fibers.

[0006] The control of static electricity in polyacrylonitrile fibers usually adopts methods such as surface coating with sizing agents or antistatic agents (Synthetic Fibers, Vol. 02, No. 02, 2002, pp. 34 - 36), adding conductive materials (Synthetic Fibers, Vol. 43, No. 04, 2014, pp. 21 - 24), and installing antistatic elimination devices (China Building Materials Science & Technology, Vol. 28, No. 03, 2019, pp. 5 - 6) to improve. However, some of the above methods will introduce additional impurities that cannot be oxidized and carbonized in the polyacrylonitrile fibers, resulting in a decrease in the performance of the carbon fibers or the inability to prepare carbon fibers, and are not suitable for the production of polyacrylonitrile-based carbon fiber precursor filaments. Patent JP6520787B2 proposes to control the absolute humidity of the environment at 12 g / m 3 or more in a high humidity environment to reduce or prevent the occurrence of reduced bundling and fuzzing. Static electricity generation can be reduced by moisture, but it additionally increases energy consumption, and long-term use of the equipment in a high humidity environment will accelerate equipment corrosion, resulting in an increase in equipment failure rate; when the tow travels in a high humidity environment, the moisture content of the fibers increases significantly, which will cause additional defects during the oxidation process; and it is difficult to ensure the humidity at the outlet of the fibers due to exhaust air or temperature at the outlet of the drying and densification process. The above existing technologies all ignore the inevitability of static electricity generation during the process and only start from eliminating static electricity. Either they are not applicable to the preparation process of carbon fiber precursor filaments, or they add additional facilities, increasing production costs and subsequent maintenance costs.

[0007] In view of this, the present invention is specifically proposed. Summary of the Invention

[0008] In order to overcome the problems existing in the prior art, namely, the fibers are prone to winding around the rollers due to static electricity during the cooling process after the drying densification of polyacrylonitrile fibers, and the poor strength of carbon fibers when applied to carbon fibers, the present invention provides a dried and densified polyacrylonitrile fiber, its drying densification method and application. By adopting the solution of the present invention, the winding frequency caused by static electricity during the preparation of the raw yarn is below 10 times per month. When the dried and densified fibers are applied to carbon fibers, the tensile strength of the carbon fibers can reach 6.20 GPa, achieving good technical effects.

[0009] One of the purposes of the present invention is to provide a dried and densified polyacrylonitrile fiber. By using in-situ testing of the static voltage, the surface voltage and temperature of the polyacrylonitrile fiber satisfy formula (1):

[0010] S = aT + b, formula (1); where a = 6 - 70, b = -500 - -5660, where T = 50 - 90 °C (preferably 55 - 80 °C), and S is the surface voltage.

[0011] For example, a = 6, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or 70, b = -500, -1000, -1500, -2000, -2500, -3000, -3500, -4000, -4500, -5000, -5500 or -5650, T = 50 °C, 55 °C, 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C or 90 °C.

[0012] The static electricity of polyacrylonitrile fibers is mainly formed by the re - arrangement of electrons due to the interfacial polarization phenomenon generated by the friction between fibers and between fibers and other substances (roller surface, air). The high volume resistance of polyacrylonitrile fibers themselves makes the generation of static electricity inevitable. During the cooling process of polyacrylonitrile fibers, radial shrinkage of the fibers occurs, resulting in molecular friction inside the fibers, and thus generating static electricity. The fiber cooling process is an inevitable process during the preparation of polyacrylonitrile fibers and their pre - oxidized fibers. In actual production, it is impossible to achieve continuous winding of fibers at the same temperature. The static electricity caused by fiber cooling can cause the fibers to adsorb impurities in the environment, increasing the surface defects of the fibers themselves, and thus reducing the fiber strength; at the same time, the fibers are more likely to adsorb onto the rollers during the processing, causing the fibers to wind around the rollers and break, affecting the stability of production.

[0013] During the cooling process of the fiber, static electricity is inevitable. However, if the absolute value of the surface voltage is too high, it is more likely to adsorb impurities in the environment. In the present invention, the relationship between the surface voltage and temperature of the polyacrylonitrile fiber during the cooling process and the static electricity range during the cooling process enable the fiber to achieve high strength even if it adsorbs impurities in the air, and at the same time, it is not easy for the tow to wind around the roll; the reason is that for the fiber with this property, the molecular friction inside the fiber is small, and static electricity is not likely to accumulate. Since the absolute value of the overall voltage is controlled, obvious winding around the roll will not occur.

[0014] In a preferred embodiment, the fineness of the single filament of the polyacrylonitrile fiber is 0.5 to 3.0 dtex, preferably 1.0 to 3.0 dtex, such as 0.5 dtex, 1 dtex, 1.5 dtex, 2 dtex, 2.5 dtex or 3 dtex.

[0015] The fineness of the fiber is closely related to the specific surface area of the fiber. A higher fineness can reduce the specific surface area of the fiber, reducing the amount of environmental impurities adsorbed per unit volume, but it will cause a greater difference in the skin-core structure of the polyacrylonitrile fiber during subsequent oxidation and carbonization processes, resulting in a decrease in the strength of the fiber. The fineness of the polyacrylonitrile fiber in the present invention can simultaneously achieve a better balance between the static electricity due to its impurity adsorption amount and the skin-core structure of the fiber.

[0016] In a preferred embodiment, the oil content of the polyacrylonitrile fiber is 0.1 to 4 wt%, preferably 0.4 to 2.5 wt%, such as 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt% or 4 wt%.

[0017] The fiber oil contains components such as lubricants and antistatic agents, which are beneficial to alleviating the generation of static electricity. An excessively high oil content of the fiber will increase the production cost on the one hand, and at the same time, the excessive oil agent will penetrate into the fiber interior, resulting in a large number of defects during the removal of the oil agent during oxidation and carbonization. An excessively low oil content of the fiber cannot effectively alleviate the generation of static electricity. The present invention controls the oil content of the polyacrylonitrile fiber within a more appropriate range, which can simultaneously alleviate static electricity and avoid a decrease in fiber strength.

[0018] In a preferred embodiment, the surface voltage of the polyacrylonitrile fiber is -10 to -2500, preferably -10 to -2000, such as -10, -50, -100, -200, -500, -800, -1000, -1200, -1500, -1800 or -2000.

[0019] A second object of the present invention is to provide a method for drying and densifying polyacrylonitrile fibers, preferably for preparing the polyacrylonitrile fibers described in the first object of the present invention. The preparation method includes: drying and densifying the polyacrylonitrile raw filaments in one or more temperature zones. The first temperature zone includes at least 3 hot rollers, and each of the optional remaining temperature zones (except the first temperature zone) independently includes at least 1 hot roller. Among them, the width of the fiber bundle on the roller surfaces of the first 3 hot rollers in the first temperature zone is controlled to gradually decrease. Among them, the width of the fiber bundle on the roller surface of the first hot roller in the first temperature zone is not controlled, but the width of the fiber bundle on the roller surfaces of the 2nd to 3rd hot rollers in the first temperature zone is controlled.

[0020] During the drying and densifying process, the diffusion processes of heat and moisture occur simultaneously, which is a key process in the preparation of carbon fiber precursor filaments. In the initial stage of drying, the moisture content of the fiber is relatively high, and water diffuses out from the inside of the filament bundle, which can form a protective substance between the fiber surface and the roller surface. Through the scheme of gradually shrinking the width of the filament bundle on the first three rollers, the fiber dehydrates faster in the initial stage with a high moisture content. As the moisture is removed, the protective effect of water gradually becomes smaller. At this time, the width of the fiber is reduced to reduce the friction between the filament bundle and the roller surface, reduce the generation of static electricity on the fiber surface, and lower the initial surface voltage of the fiber, so as to obtain polyacrylonitrile fibers with the characteristics of cooling static electricity.

[0021] In a preferred embodiment, the drying and densifying is carried out in 1 to 5 (for example, one or 2 to 5) temperature zones, for example, in 1, 2, 3, 4 or 5 temperature zones.

[0022] In a preferred embodiment, the first temperature zone includes 3 to 8, preferably 3 to 5 hot rollers, for example, 3, 4 or 5.

[0023] In a preferred embodiment, each of the remaining temperature zones except the first temperature zone independently includes 1 to 8, preferably 2 to 5 hot rollers, for example, 2, 3, 4 or 5.

[0024] In a preferred embodiment, the temperature of each temperature zone is independently controlled to be 90 to 160 °C, for example, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C or 160 °C.

[0025] In a further preferred embodiment, when there are multiple temperature zones, in the drying order, the temperature of each temperature zone gradually increases, for example, gradient heating.

[0026] Among them, when there are multiple temperature zones, the temperature of the first temperature zone is not lower than 90 °C, and the temperature of the last temperature zone is not higher than 160 °C.

[0027] In a preferred embodiment, on the surface of each hot roller in each temperature zone, the width of the fiber tow is independently 25 - 50 mm, preferably 30 - 40 mm, such as 25 mm, 30 mm, 35 mm, 40 mm, 45 mm or 50 mm.

[0028] In a preferred embodiment, the width of the fiber tow on the second hot roller surface in the first temperature zone is controlled as follows: the width of the fiber tow on the second hot roller surface is not less than 0.95 times the width on the first hot roller surface.

[0029] In a further preferred embodiment, the width of the fiber tow on the second hot roller surface in the first temperature zone is controlled as follows: the width of the fiber tow on the second hot roller surface is 0.95 - 1.0 times the width on the first hot roller surface and preferably does not include 1.0 times, for example, 0.95 times, 0.96 times, 0.97 times, 0.98 times or 0.99 times.

[0030] In a preferred embodiment, the width of the fiber tow on the third hot roller surface in the first temperature zone is controlled as follows: the width of the fiber tow on the third hot roller surface is not less than 0.8 times the width on the first hot roller surface.

[0031] In a further preferred embodiment, the width of the fiber tow on the first three hot roller surfaces in the first temperature zone is controlled as follows: the width of the fiber tow on the third hot roller surface is 0.8 - 0.98 times the width on the first hot roller surface, such as 0.8 times, 0.82 times, 0.84 times, 0.86 times, 0.88 times, 0.90 times, 0.92 times, 0.94 times, 0.96 times or 0.98 times.

[0032] No special control is performed on the roller surfaces after the fourth one in the first temperature zone, and it is preferably substantially the same as the width of the fiber tow on the third roller surface in the first temperature zone.

[0033] In a preferred embodiment, the width of the fiber tow on the hot roller surface is controlled by at least one of the following methods: using a wire blocking rod, a wire guiding wheel, or high-pressure air blowing.

[0034] In the present invention, the width of the fiber tow on the first hot roller surface in the first temperature zone is not controlled. However, the width of the fiber tow on the second and third hot roller surfaces in the first temperature zone is controlled within the above-defined range; meanwhile, the width of the fiber tow on the remaining hot rollers (starting from the fourth one) in the first temperature zone is not controlled, and the width of the fiber tow on the hot roller surfaces in the remaining temperature zones (except the first temperature zone) is not controlled.

[0035] In a preferred embodiment, the polyacrylonitrile precursor fiber has a fineness of 0.5 to 3.0 dtex, preferably 1.0 to 3.0 dtex, based on its dry basis.

[0036] The third object of the present invention is to provide a dried and densified polyacrylonitrile fiber obtained by the method for drying and densifying polyacrylonitrile fiber described in the second object of the present invention.

[0037] The fourth object of the present invention is to provide the application of the method for drying and densifying described in the second object of the present invention in the preparation of polyacrylonitrile fiber.

[0038] The fifth object of the present invention is to provide a method for preparing polyacrylonitrile fiber, comprising: (1) obtaining coagulated fiber, (2) hot water drawing treatment, (3) washing with water, (4) oiling, (5) drying and densifying; wherein, the drying and densifying is carried out by the method for drying and densifying described in the second object of the present invention.

[0039] In a preferred embodiment, the coagulated fiber can be obtained by any method disclosed in the prior art, preferably but not limited to being obtained by wet spinning.

[0040] In a further preferred embodiment, the wet spinning is carried out by any wet spinning method disclosed in the prior art, preferably but not limited to the wet spinning including the delivery of polyacrylonitrile spinning dope, precision filtration and multi-stage coagulation drawing.

[0041] In a preferred embodiment, the conditions of the hot water drawing treatment are carried out according to the conditions disclosed in the prior art, preferably but not limited to including: the hot water temperature is 90 - 99 °C, 1 - 6 stages of hot water drawing, and the total drawing ratio is 2 - 5.

[0042] For example, the conditions of the hot water drawing treatment include: the hot water temperature is 90 °C, 91 °C, 92 °C, 93 °C, 94 °C, 95 °C, 96 °C, 97 °C, 98 °C or 99 °C, 1 stage, 2 stages, 3 stages, 4 stages, 5 stages or 6 stages of hot water drawing, and the total drawing ratio is 2, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.6, 4.8 or 5.0.

[0043] In a further preferred embodiment, the conditions of the hot water drawing treatment are carried out according to the conditions disclosed in the prior art, preferably but not limited to including: the hot water temperature is 93 - 97 °C, 1 - 6 stages of hot water drawing.

[0044] In a preferred embodiment, the conditions of the washing with water are carried out according to the conditions disclosed in the prior art, preferably but not limited to including: the washing temperature is 50 - 90 °C, preferably 60 - 80 °C, such as 50 °C, 60 °C, 70 °C, 80 °C or 90 °C.

[0045] Among them, there is no drafting in the water washing process.

[0046] In a preferred embodiment, the oiling is carried out under the conditions disclosed in the prior art, preferably but not limited to including: carried out at 20-40°C, and the effective oil agent content in the oil agent tank is 1-5 wt%.

[0047] For example, carried out at 20°C, 25°C, 30°C, 35°C or 40°C, and the effective oil agent content in the oil agent tank is 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt% or 5 wt%.

[0048] In a further preferred embodiment, the excess oil agent is extruded after oiling, preferably extruded under a pressure of 0.3-0.4 MPa (such as 0.3, 0.32, 0.34, 0.36, 0.38 or 0.4 MPa).

[0049] The sixth object of the present invention is to provide a polyacrylonitrile fiber obtained by directly winding the silk after using the preparation method described in the fifth object of the present invention. Preferably, the fiber tension of the polyacrylonitrile fiber is 0.05-0.5 cN / dtex, preferably 0.1-0.2 cN / dtex.

[0050] The seventh object of the present invention is to provide an application of the polyacrylonitrile fiber obtained by using the preparation method described in the fifth object of the present invention in carbon fiber, wherein the polyacrylonitrile fiber is used for the polyacrylonitrile-based carbon fiber precursor after optionally steam drafting.

[0051] Among them, the polyacrylonitrile fiber is directly wound or wound after optionally steam drafting and used for the polyacrylonitrile-based carbon fiber precursor, and then the polyacrylonitrile-based carbon fiber is made by processes such as wire feeding, pre-oxidation, low-temperature carbonization, high-temperature carbonization, chemical treatment, water washing, sizing, drying and carbon fiber winding.

[0052] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. In the following text, in principle, the various technical solutions can be combined with each other to obtain new technical solutions, which should also be regarded as specifically disclosed herein.

[0053] Compared with the prior art, the present invention has the following beneficial effects: By adopting the solution of the present invention, the winding roll frequency caused by static electricity during the precursor preparation process is below 10 times per month. When the dried and densified fibers are applied to carbon fibers, the tensile strength of the carbon fibers can reach 6.20 GPa, achieving good technical effects. Detailed Embodiments

[0054] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0055] In addition, it should be noted that, in the following detailed embodiments, the various specific technical features described can be combined in any appropriate manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0056] Furthermore, any combination can be made between various different embodiments of the present invention as long as it does not violate the idea of the present invention. The technical solutions formed thereby belong to a part of the original public content of this specification and also fall within the protection scope of the present invention.

[0057] If there is no special limitation on the raw materials used in the examples and comparative examples, they are all disclosed in the prior art. For example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0058] The test method for the static electricity value on the fiber surface during the cooling process is as follows:

[0059] The in-situ measurement of the static electricity voltage during the running of the tow is carried out using a KEYENCE SK-H050 type handheld static electricity measuring instrument in high-precision mode to measure the surface static electricity voltage at the center value of the fiber.

[0060] The test method for the fiber surface temperature during the cooling process is as follows:

[0061] The change in the tow temperature during the cooling process is measured by a FLUKE Ti9 type thermal infrared imager.

[0062] The test method for the fiber oil content is as follows:

[0063] The Soxhlet extraction method was used to test the oil content of the fiber: Weigh about 3 g of the dried and densified fiber. After drying at 110 °C for 2 h, record the mass as m1. Put the fiber into a Soxhlet extractor with cyclohexane as the solvent. Adjust the temperature of the constant temperature water bath to 100 °C, the reflux rate to 6 - 8 times per hour, and the reflux time to 2 h. After reflux, let the fiber dry naturally, then dry it at 110 °C for 2 h and record the mass as m2. The calculation formula for the oil content (w) is as follows:

[0064]

[0065] The mechanical properties of carbon fiber multifilaments were measured according to the national standard GB-T3362-2017.

[0066]

Example 1

[0067] Preparation of polyacrylonitrile precursor filaments before drying and densification: Wet spinning was used to prepare the primary fibers. The intrinsic viscosity of the spinning dope used was 1.75, the solid content of the spinning dope was 22 wt%, and after the spinning dope was accurately metered by a metering pump and filtered again, wet spinning was carried out. The pore diameter of the spinneret plate was 70 μm, the number of spinneret holes was 12,000, the coagulation temperature was 30 °C, the concentration of the coagulation bath was 50 wt%, and two-stage coagulation drawing was carried out subsequently with draw ratios of 1.0 and 1.1 respectively to obtain coagulated fibers; The coagulated fibers were subjected to three-stage hot water drawing in hot water at 95 - 98 °C with a total draw ratio of 3 times to obtain hot water drawn fibers; The hot water drawn fibers were washed at 65 °C without drawing during the washing process to obtain washed fibers; The washed fibers were oiled at 35 °C, the effective oil content in the oil bath was 4 wt%, and the excess oil was extruded under a pressure of 0.3 MPa to obtain oiled fibers. The width of the fiber before drying and densification was 40 mm.

[0068] Preparation of polyacrylonitrile precursor filaments: Drying and densification were carried out by hot roll drying. A four-temperature zone gradient heating method was used to control the temperatures of each temperature zone to be 95 °C, 105 °C, 115 °C, and 130 °C respectively. There were 5 hot rolls with the same temperature in the first temperature zone. The width of the first roll surface of the fiber was 40 mm. A wire guide rod (controlling the distance between the wire guide rods) was used to control the widths of the second and third roll surfaces of the fiber to be 38 mm and 32 mm respectively. The widths of the fourth and fifth roll surfaces of the fiber in the first temperature zone were not controlled by the wire guide rod; After drying in the subsequent 3 temperature zones and cooling to room temperature (the widths of each roll surface of the fiber in the latter 3 temperature zones were not controlled by the wire guide rod), the fiber fineness was 3 dtex, the fiber oil content was 2 wt%, when the fiber was cooled from 80 °C to 55 °C, the surface voltage value (i.e., the surface static voltage) of the fiber was negative, and the absolute value of its voltage S (V) increased with the decrease in temperature and satisfied S = 6T - 500; The above fibers were drawn 3 times under saturated steam at 0.6 MPa to obtain carbon fiber precursor filaments; The winding frequency of the fiber due to static electricity during the precursor filament preparation process was 9 times per month.

[0069] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C. The total draft ratio of pre-oxidation is 1.05 times to obtain pre-oxidized fiber. The pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C with a draft ratio of 1.02 times. Subsequently, it is subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C with a draft ratio of 0.97 times. Then, electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 5.8 GPa.

[0070]

Example 2

[0071] Preparation of polyacrylonitrile (PAN) precursor before drying densification: Wet spinning is used to prepare the nascent fiber. The intrinsic viscosity of the spinning dope is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 70 μm, the number of spinneret holes is 12,000, the coagulation temperature is 30°C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drafting is carried out subsequently with draft ratios of 1.0 and 1.1 respectively to obtain coagulated fiber. The coagulated fiber is subjected to three-stage hot water drafting in hot water at 95 - 98°C with a total draft ratio of 3 times to obtain hot water drafted fiber. The hot water drafted fiber is washed in water at 65°C without drafting during the washing process to obtain washed fiber. The washed fiber is oiled at 35°C, and the effective oil content in the oil bath is 4 wt%. Excess oil is extruded under a pressure of 0.3 MPa to obtain oiled fiber. The width of the fiber before drying densification is 40 mm.

[0072] Preparation of PAN precursor: Drying densification is carried out by hot roll drying in a way of gradient temperature increase in 4 temperature zones, and the temperatures of each temperature zone are controlled to be 95°C, 105°C, 115°C, and 130°C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, and the width of the first roll surface of the fiber is 40 mm. A stop wire rod (to control the distance between the stop wire rods) is used to control the widths of the second and third roll surfaces of the fiber to be 38 mm and 36 mm respectively, and the widths of the fourth and fifth roll surfaces of the fiber in the first temperature zone are not controlled by the stop wire rod. After drying in the subsequent 3 temperature zones and cooling to room temperature (the widths of each roll surface of the fiber in the latter 3 temperature zones are not controlled by the stop wire rod), the fiber fineness is 3 dtex, the oil content of the fiber is 2 wt%, when the fiber is cooled from 80°C to 55°C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S (V) increases with the decrease of temperature and satisfies S = 40T - 4000. The above-mentioned fiber is drafted 3 times under saturated steam at 0.6 MPa to obtain carbon fiber precursor. The winding frequency of the fiber caused by static electricity during the preparation of the precursor is 9 times per month.

[0073] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180 °C, 200 °C, 220 °C, 240 °C, and 260 °C. The total draw ratio of pre-oxidation is 1.05 times to obtain pre-oxidized fiber; the pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300 °C, 500 °C, and 750 °C with a draw ratio of 1.02 times; subsequently, it is subjected to four-stage high-temperature carbonization at 800 °C, 1100 °C, 1300 °C, and 1500 °C with a draw ratio of 0.97 times; then, electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 6.0 GPa.

[0074]

Example 3

[0075] Preparation of polyacrylonitrile (PAN) precursor before drying densification: Wet spinning is used to prepare the primary fiber. The intrinsic viscosity of the spinning dope is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 70 μm, the number of spinneret holes is 12,000, the coagulation temperature is 30 °C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drawing is carried out subsequently with draw ratios of 1.0 and 1.1 respectively to obtain coagulated fiber; the coagulated fiber is subjected to three-stage hot water drawing in hot water at 95 - 98 °C with a total draw ratio of 3 times to obtain hot water drawn fiber; the hot water drawn fiber is washed in water at 65 °C without drawing during the washing process to obtain washed fiber; the washed fiber is oiled at 35 °C, the effective oil content in the oil bath is 4 wt%, and the excess oil is extruded under a pressure of 0.3 MPa to obtain oiled fiber. The width of the fiber before drying densification is 40 mm.

[0076] Preparation of PAN precursor: Drying densification is carried out by hot roll drying, and a four-temperature zone gradient heating method is adopted. The temperatures of each temperature zone are controlled to be 95 °C, 105 °C, 115 °C, and 130 °C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, the width of the first roll surface of the fiber is 40 mm, and a stop rod (controlling the distance between the stop rods) is used to control the widths of the second and third roll surfaces of the fiber to be 38.8 mm and 38 mm respectively. The widths of the fourth and fifth roll surfaces of the fiber in the first temperature zone are not controlled by the stop rod; after drying in the subsequent 3 temperature zones and cooling to room temperature (the widths of each roll surface of the fiber in the latter 3 temperature zones are not controlled by the stop rod), the fiber fineness is 3 dtex and the oil content of the fiber is 2.2 wt%; when the fiber is cooled from 80 °C to 55 °C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S (V) increases with the decrease of temperature and satisfies S = 70T - 5660; the above fiber is drawn 3 times under saturated steam at 0.6 MPa to obtain carbon fiber precursor. The winding frequency of the fiber caused by static electricity during the precursor preparation process is 9 times per month.

[0077] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C with a total pre-oxidation draw ratio of 1.05 times to obtain pre-oxidized fiber; the pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C with a draw ratio of 1.02 times; subsequently, it is subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C with a draw ratio of 0.97 times; then electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 6.1 GPa.

[0078]

Example 4

[0079] Preparation of polyacrylonitrile precursor before drying densification: Wet spinning is used to prepare primary fibers. The intrinsic viscosity of the spinning dope is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 60 μm, the number of spinneret holes is 12000, the coagulation temperature is 30°C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drawing is carried out subsequently with draw ratios of 1.0 and 1.1 respectively to obtain coagulated fiber; the coagulated fiber is subjected to three-stage hot water drawing in hot water at 95 - 98°C with a total drawing ratio of 3 times to obtain hot water drawn fiber; the hot water drawn fiber is washed with water at 65°C without drawing during the washing process to obtain washed fiber; the washed fiber is oiled at 35°C, the effective oil content in the oil bath is 3 wt%, and the excess oil is extruded under a pressure of 0.3 MPa to obtain oiled fiber. The width of the fiber before drying densification is 30 mm.

[0080] Preparation of polyacrylonitrile precursor: Drying densification is carried out by hot roll drying in a four-temperature zone gradient heating manner, and the temperature of each temperature zone is controlled to be 95°C, 105°C, 115°C, and 130°C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, the width of the first roll surface of the fiber is 30 mm, and a stop rod (controlling the distance between the stop rods) is used to control the widths of the second and third roll surfaces of the fiber to be 29.4 mm and 29.1 mm respectively. The widths of the fourth and fifth roll surfaces of the fiber in the first temperature zone are not controlled by the stop rod; after drying in the subsequent 3 temperature zones and cooling to room temperature (the widths of each roll surface of the fiber in the latter 3 temperature zones are not controlled by the stop rod), the fiber fineness is 1.0 dtex and the fiber oil content is 2.5 wt%; when the fiber is cooled from 80°C to 55°C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S (V) increases with the decrease of temperature and satisfies S = 10T - 1000; the above fiber is drawn 1.42 times under saturated steam at 0.3 MPa to obtain carbon fiber precursor; the winding frequency of the fiber due to static electricity during the precursor preparation process is 8 times per month.

[0081] Carbon fiber preparation: The fiber obtained in step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C with a total pre-oxidation draw ratio of 1.05 times to obtain pre-oxidized fibers; the pre-oxidized fibers are subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C with a draw ratio of 1.02 times; subsequently, they are subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C with a draw ratio of 0.97 times; then, electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fibers. The tensile strength of the obtained carbon fibers is 6.12 GPa.

[0082]

Example 5

[0083] Preparation of polyacrylonitrile precursor filaments before drying densification: Wet spinning is used to prepare primary fibers. The intrinsic viscosity of the spinning dope is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 60 μm, the number of spinneret holes is 12000, the coagulation temperature is 30°C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drawing is carried out subsequently with draw ratios of 1.0 and 1.1 respectively to obtain coagulated fibers; the coagulated fibers are subjected to three-stage hot water drawing in hot water at 95 - 98°C with a total draw ratio of 3 times to obtain hot water drawn fibers; the hot water drawn fibers are washed at 65°C without drawing during the washing process to obtain washed fibers; the washed fibers are oiled at 35°C, the effective oil content in the oil bath is 2 wt%, and the excess oil is extruded under a pressure of 0.3 MPa to obtain oiled fibers. The width of the fibers before drying densification is 30 mm.

[0084] Preparation of polyacrylonitrile precursor filaments: Drying densification is carried out by hot roll drying. A four-temperature zone gradient heating method is adopted, and the temperatures of each temperature zone are controlled to be 95°C, 105°C, 115°C, and 130°C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, the width of the first roll surface of the fiber is 30 mm, and a stop rod (controlling the distance between the stop rods) is used to control the widths of the second and third roll surfaces of the fiber to be 30.0 mm and 29.4 mm respectively. The widths of the fourth and fifth roll surfaces of the fiber in the first temperature zone are not controlled by the stop rod; after drying in the subsequent 3 temperature zones and cooling to room temperature (the widths of each roll surface of the fiber in the latter 3 temperature zones are not controlled by the stop rod), the fiber fineness is 1.5 dtex and the fiber oil content is 1.2 wt%; when the fiber is cooled from 80°C to 55°C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S (V) increases with the decrease of temperature and satisfies S = 8T - 800; the above fibers are drawn 1.42 times under saturated steam at 0.3 MPa to obtain carbon fiber precursor filaments; the winding frequency of the fiber due to static electricity during the precursor filament preparation process is 8 times per month.

[0085] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C with a total pre-oxidation draw ratio of 1.05 times to obtain pre-oxidized fiber; the pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C with a draw ratio of 1.02 times; subsequently, it is subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C with a draw ratio of 0.97 times; then, electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 6.2 GPa.

[0086]

Example 6

[0087] Preparation of polyacrylonitrile (PAN) precursor before drying densification: Wet spinning is used to prepare the nascent fiber. The intrinsic viscosity of the spinning dope used is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 60 μm, the number of spinneret holes is 12,000, the coagulation temperature is 30°C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drawing is carried out subsequently with draw ratios of 1.0 and 1.1 respectively to obtain coagulated fiber; the coagulated fiber is subjected to three-stage hot water drawing in hot water at 95 - 98°C with a total drawing ratio of 3 times to obtain hot water drawn fiber; the hot water drawn fiber is washed at 65°C without drawing during the washing process to obtain washed fiber; the washed fiber is oiled at 35°C, the effective oil content in the oil bath is 1 wt%, and the excess oil is extruded under a pressure of 0.3 MPa to obtain oiled fiber, and the width of the fiber before drying densification is 30 mm.

[0088] Preparation of PAN precursor: Drying densification is carried out by hot roll drying, and a four-temperature zone gradient heating method is adopted to control the temperatures of each temperature zone to be 95°C, 105°C, 115°C, and 130°C respectively. There are 5 hot rolls with the same temperature in the first temperature zone. A stop wire rod (controlling the distance between the stop wire rods) is used to control the widths of the second and third roller surfaces of the fiber to be 30.0 mm and 29.4 mm respectively, and the widths of the fourth and fifth roller surfaces of the fiber in the first temperature zone are not controlled by the stop wire rod; after drying in the subsequent 3 temperature zones and cooling to room temperature (the widths of each roller surface of the fiber in the latter 3 temperature zones are not controlled by the stop wire rod), the fiber fineness is 1.5 dtex and the fiber oil content is 0.4 wt%; when the fiber is cooled from 80°C to 55°C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S (V) increases with the decrease in temperature and satisfies S = 8T - 2000; the above fiber is drawn 1.42 times under saturated steam at 0.3 MPa to obtain carbon fiber precursor; the winding frequency of the fiber due to static electricity during the precursor preparation process is 9 times per month.

[0089] Carbon fiber preparation: The fiber obtained in step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C. The total draft ratio of pre-oxidation is 1.05 times to obtain pre-oxidized fiber; the pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C, and the draft ratio is 1.02 times; subsequently, it is subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C, and the draft ratio is 0.97 times; then electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 6.1 GPa.

[0090]

Example 7

[0091] Preparation of polyacrylonitrile raw fiber before drying densification: Wet spinning is used to prepare the nascent fiber. The intrinsic viscosity of the spinning dope used is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 60 μm, the number of spinneret holes is 12,000, the coagulation temperature is 30°C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drafting is carried out subsequently, with draft ratios of 1.0 and 1.1 respectively to obtain coagulated fiber; the coagulated fiber is subjected to three-stage hot water drafting in hot water at 95 - 98°C, and the total draft ratio is 3 times to obtain hot water drafted fiber; the hot water drafted fiber is washed with water at 65°C without drafting during the washing process to obtain washed fiber; the washed fiber is oiled at 35°C, and the effective oil content in the oil bath is 4 wt%, and the excess oil is extruded under a pressure of 0.2 MPa to obtain oiled fiber. The width of the fiber before drying densification is 30 mm.

[0092] Preparation of polyacrylonitrile raw fiber: Drying densification is carried out by hot roll drying, and a four-temperature zone gradient heating method is adopted to control the temperatures of each temperature zone to be 95°C, 105°C, 115°C, and 130°C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, the width of the first roll surface of the fiber is 30 mm, and a wire blocking rod (controlling the distance between the wire blocking rods) is used to control the widths of the second and third roll surfaces of the fiber to be 29.7 mm and 25.5 mm respectively. The widths of the fourth and fifth roll surfaces of the fiber in the first temperature zone are not controlled by the wire blocking rod; after drying in the subsequent 3 temperature zones and cooling to room temperature (the widths of each roll surface of the fiber in the latter 3 temperature zones are not controlled by the wire blocking rod), the fineness of the fiber is 1.5 dtex, and the oil content of the fiber is 2.5 wt%; when the fiber is cooled from 80°C to 55°C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S (V) increases with the decrease of temperature and satisfies S = 10T - 810; the above fiber is drawn 1.42 times under saturated steam at 0.4 MPa to obtain carbon fiber raw fiber; the winding frequency of the fiber caused by static electricity during the raw fiber preparation process is 10 times per month.

[0093] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180 °C, 200 °C, 220 °C, 240 °C, and 260 °C. The total draw ratio of pre-oxidation is 1.05 times to obtain pre-oxidized fiber; the pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300 °C, 500 °C, and 750 °C with a draw ratio of 1.02 times; subsequently, it is subjected to four-stage high-temperature carbonization at 800 °C, 1100 °C, 1300 °C, and 1500 °C with a draw ratio of 0.97 times; then, electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 5.8 GPa.

[0094]

Example 8

[0095] Preparation of polyacrylonitrile (PAN) precursor before drying densification: Wet spinning is used to prepare the primary fiber. The intrinsic viscosity of the spinning dope is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 60 μm, the number of spinneret holes is 12000, the coagulation temperature is 30 °C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drawing is carried out subsequently with draw ratios of 1.0 and 1.1 respectively to obtain coagulated fiber; the coagulated fiber is subjected to three-stage hot water drawing in hot water at 95 - 98 °C with a total draw ratio of 3 times to obtain hot water drawn fiber; the hot water drawn fiber is washed in water at 65 °C without drawing during the washing process to obtain washed fiber; the washed fiber is oiled at 35 °C, the effective oil content in the oil bath is 2 wt%, and the excess oil is extruded under a pressure of 0.35 MPa to obtain oiled fiber. The width of the fiber before drying densification is 30 mm.

[0096] Preparation of PAN precursor: Drying densification is carried out by hot roll drying, and a four-temperature zone gradient heating method is adopted. The temperatures of each temperature zone are controlled to be 95 °C, 105 °C, 115 °C, and 130 °C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, the width of the first roll surface of the fiber is 30 mm, and a stop wire rod (controlling the distance between the stop wire rods) is used to control the widths of the second and third roll surfaces of the fiber to be 28.8 mm and 25.5 mm respectively. The widths of the fourth and fifth roll surfaces of the fiber in the first temperature zone are not controlled by the stop wire rod; after drying in the subsequent 3 temperature zones and cooling to room temperature (the widths of each roll surface of the fiber in the latter 3 temperature zones are not controlled by the stop wire rod), the fiber fineness is 1.1 dtex and the fiber oil content is 1.2 wt%; when the fiber is cooled from 80 °C to 55 °C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S (V) increases with the decrease of temperature and satisfies S = 12T - 1000; each of the above fibers is under a tension of 0.165 cN; the winding frequency of the fiber caused by static electricity during the precursor preparation process is 9 times per month.

[0097] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C with a total pre-oxidation draw ratio of 1.05 times to obtain pre-oxidized fiber; the pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C with a draw ratio of 1.02 times; subsequently, it is subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C with a draw ratio of 0.97 times; then, electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 5.6 GPa.

[0098]

Comparative Example 1

[0099] Preparation of polyacrylonitrile raw fiber before drying densification: Wet spinning is used to prepare the primary fiber. The intrinsic viscosity of the spinning dope used is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 60 μm, the number of spinneret holes is 12,000, the coagulation temperature is 30°C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drawing is carried out subsequently with draw ratios of 1.0 and 1.1 respectively to obtain coagulated fiber; the coagulated fiber is subjected to three-stage hot water drawing in hot water at 95 - 98°C with a total drawing ratio of 3 times to obtain hot water drawn fiber; the hot water drawn fiber is washed in water at 65°C without drawing during the washing process to obtain washed fiber; the washed fiber is sized at 35°C with an effective sizing agent content of 4 wt% in the sizing agent tank, and the excess sizing agent is extruded under a pressure of 0.3 MPa to obtain sized fiber. The width of the fiber before drying densification is 40 mm.

[0100] Preparation of polyacrylonitrile raw fiber: Drying densification is carried out by hot roll drying, and a four-temperature zone gradient heating method is adopted to control the temperatures of each temperature zone to be 95°C, 105°C, 115°C, and 130°C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, the width of the first roll surface of the fiber is 40 mm, and a wire blocking rod is used to control the widths of the second and third roll surfaces of the fiber to be 24 mm and 27 mm respectively. The widths of the fourth and fifth roll surfaces of the fiber in the first temperature zone are not controlled; after drying in the subsequent 3 temperature zones and cooling to room temperature, the fiber fineness is 3 dtex, the oil content of the fiber is 2 wt%, when the fiber is cooled from 80°C to 55°C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S(V) decreases with the decrease of temperature. The above fiber is drawn 3 times under saturated steam at 0.7 MPa to obtain carbon fiber raw fiber; the winding frequency of the fiber due to static electricity during the raw fiber preparation process is 16 times per month.

[0101] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C. The total draw ratio of pre-oxidation is 1.05 times to obtain pre-oxidized fiber. The pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C with a draw ratio of 1.02 times. Subsequently, it is subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C with a draw ratio of 0.97 times. Then, electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 5.0 GPa.

[0102]

Comparative Example 2

[0103] Preparation of polyacrylonitrile (PAN) precursor before drying densification: Wet spinning is used to prepare the primary fiber. The intrinsic viscosity of the spinning dope is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 70 μm, the number of spinneret holes is 12,000, the coagulation temperature is 30°C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drawing is carried out subsequently, with draw ratios of 1.0 and 1.1 respectively, to obtain coagulated fiber. The coagulated fiber is subjected to three-stage hot water drawing in hot water at 95 - 98°C with a total draw ratio of 3 times to obtain hot water drawn fiber. The hot water drawn fiber is washed in water at 65°C without drawing during the washing process to obtain washed fiber. The washed fiber is oiled at 35°C, the effective oil content in the oil bath is 4 wt%, and the excess oil is extruded under a pressure of 0.3 MPa to obtain oiled fiber. The width of the fiber before drying densification is 40 mm.

[0104] Preparation of PAN precursor: Drying densification is carried out by hot roll drying, and a four-temperature zone gradient heating method is adopted. The temperatures of each temperature zone are controlled to be 95°C, 105°C, 115°C, and 130°C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, the width of the fiber on the first roll surface is 40 mm, and a stop rod is used to control the widths of the fiber on the second and third roll surfaces to be 36 mm and 28 mm respectively. The widths of the fiber on the fourth and fifth roll surfaces in the first temperature zone are not controlled. After drying in the subsequent 3 temperature zones and cooling to room temperature, the fiber fineness is 3 dtex, the oil content of the fiber is 2 wt%, when the fiber is cooled from 80°C to 55°C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S(V) increases with the decrease of temperature, but does not satisfy the linear decrease relationship. The above-mentioned fiber is drawn 3 times under saturated steam at 0.7 MPa to obtain carbon fiber precursor. The winding frequency of the fiber due to static electricity during the precursor preparation process is 14 times per month.

[0105] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C. The total draw ratio of pre-oxidation is 1.05 times to obtain pre-oxidized fiber; the pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C with a draw ratio of 1.02 times; subsequently, it is subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C with a draw ratio of 0.97 times; then electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 5.2 GPa.

[0106]

Comparative Example 3

[0107] Preparation of polyacrylonitrile (PAN) precursor before drying densification: Wet spinning is used to prepare the nascent fiber. The intrinsic viscosity of the spinning dope is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret is 60 μm, the number of spinneret holes is 12,000, the coagulation temperature is 30°C, the concentration of the coagulation bath is 50 wt%, and two-stage coagulation drawing is carried out subsequently with draw ratios of 1.1 and 1.1 respectively to obtain coagulated fiber; the coagulated fiber is subjected to three-stage hot water drawing in hot water at 95 - 98°C with a total draw ratio of 3 times to obtain hot water drawn fiber; the hot water drawn fiber is washed in water at 65°C without drawing during the washing process to obtain washed fiber; the washed fiber is oiled at 35°C, the effective oil content in the oil bath is 3 wt%, and the excess oil is extruded under a pressure of 0.3 MPa to obtain oiled fiber. The width of the fiber before drying densification is 30 mm.

[0108] Preparation of PAN precursor: Drying densification is carried out by hot roll drying, and a four-zone gradient temperature increase method is adopted. The temperatures of each zone are controlled at 95°C, 105°C, 115°C, and 130°C respectively. There are 5 hot rolls with the same temperature in the first zone, the width of the first roll surface of the fiber is 30 mm, and a wire blocking rod is used to control the widths of the second and third roll surfaces of the fiber to be 29.4 mm and 29.1 mm respectively. The widths of the fourth and fifth roll surfaces of the fiber in the first zone are not controlled; after drying in the subsequent 3 zones, it is cooled to room temperature. The fineness of the fiber is 3 dtex, the oil content of the fiber is 2.2 wt%, when the fiber is cooled from 80°C to 55°C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S(V) increases with the decrease of temperature and satisfies S = 65T - 6000; the above fiber is drawn 3 times under saturated steam at 0.4 MPa to obtain carbon fiber precursor; the winding frequency of the fiber due to static electricity during the precursor preparation process is 13 times per month.

[0109] Preparation of carbon fiber: The fiber obtained in Step 2 is subjected to five-stage pre-oxidation at 180 °C, 200 °C, 220 °C, 240 °C, and 260 °C. The total draw ratio of pre-oxidation is 1.05 times to obtain pre-oxidized fiber. The pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300 °C, 500 °C, and 750 °C with a draw ratio of 1.02 times. Subsequently, it is subjected to four-stage high-temperature carbonization at 800 °C, 1100 °C, 1300 °C, and 1500 °C with a draw ratio of 0.97 times. Then, electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 5.4 GPa.

[0110]

Comparative Example 4

[0111] Preparation of polyacrylonitrile raw fiber before drying densification: Wet spinning is used to prepare the primary fiber. The intrinsic viscosity of the spinning dope used is 1.75, the solid content of the spinning dope is 22 wt%, and after the spinning dope is accurately metered by a metering pump and filtered again, wet spinning is carried out. The pore diameter of the spinneret plate is 70 μm, the number of spinneret holes is 12,000, the coagulation temperature is 30 °C, the concentration of the coagulation bath is 50 wt%, and subsequent two-stage non-drawing coagulation is carried out to obtain coagulated fiber. The coagulated fiber is subjected to three-stage hot water drawing in hot water at 95-98 °C, and the total draw ratio is 3 times to obtain hot water drawn fiber. The hot water drawn fiber is washed with water at 65 °C without drawing during the washing process to obtain washed fiber. The washed fiber is oiled at 35 °C, the effective oil content in the oil bath is 4 wt%, and the excess oil is extruded under a pressure of 0.3 MPa to obtain oiled fiber. The width of the fiber before drying densification is 40 mm.

[0112] Preparation of polyacrylonitrile raw fiber: Drying densification is carried out by hot roll drying, and a four-temperature zone gradient heating method is adopted. The temperature of each temperature zone is controlled to be 95 °C, 105 °C, 115 °C, and 130 °C respectively. There are 5 hot rolls with the same temperature in the first temperature zone, the width of the first roll surface of the fiber is 40 mm, and a wire blocking rod is used to control the widths of the second and third roll surfaces of the fiber to be 38 mm and 32 mm respectively. After drying in the subsequent 3 temperature zones and cooling to room temperature, the fiber fineness is 3.3 dtex, the oil content of the fiber is 1.9 wt%, when the fiber is cooled from 80 °C to 55 °C, the surface voltage value of the fiber is negative, and the absolute value of its voltage S(V) increases with the decrease of temperature and satisfies S = 7T - 800. The above fiber is drawn 3 times under saturated steam at 0.6 MPa to obtain carbon fiber raw fiber. The winding frequency of the fiber caused by static electricity during the raw fiber preparation process is 13 times per month.

[0113] Preparation of carbon fiber: The fiber obtained in step 2 is subjected to five-stage pre-oxidation at 180°C, 200°C, 220°C, 240°C, and 260°C, with a total pre-oxidation draw ratio of 1.05 times, to obtain pre-oxidized fiber; the pre-oxidized fiber is subjected to three-stage low-temperature carbonization at 300°C, 500°C, and 750°C, with a draw ratio of 1.02 times; subsequently, it is subjected to four-stage high-temperature carbonization at 800°C, 1100°C, 1300°C, and 1500°C, with a draw ratio of 0.97 times; then electrochemical treatment, sizing, drying, and carbon fiber winding are carried out to obtain carbon fiber. The tensile strength of the obtained carbon fiber is 5.3 GPa.

[0114] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions of the present invention and their implementation manners, and these all fall within the scope of the present invention. The protection scope of the present invention shall be subject to the appended claims.

Claims

1. A dried and densified polyacrylonitrile fiber, wherein its surface voltage and temperature satisfy formula (1): S = aT + b, Equation (1); where, a = 6 - 70, b = -500 - -5660, where T = 50 - 90 °C and S is the surface voltage.

2. The polyacrylonitrile fiber according to claim 1, characterized in that the fineness of the monofilament of the polyacrylonitrile fiber is 0.5 - 3.0 dtex, preferably 1.0 - 3.0 dtex; and / or, the oil content of the polyacrylonitrile fiber is 0.1 - 4 wt%, preferably 0.4 - 2.5 wt%.

3. A method for drying and densifying polyacrylonitrile fibers, preferably used for preparing the polyacrylonitrile fibers described in claim 1 or 2, the preparation method comprising: The polyacrylonitrile precursor is dried and densified in one or more temperature zones. The first temperature zone includes at least 3 hot rolls, and each of the optional remaining temperature zones independently includes at least 1 hot roll. Among them, the width of the fiber bundle on the first 3 hot roll surfaces in the first temperature zone is controlled to gradually decrease.

4. The drying densification method according to claim 3, wherein The drying and densification is carried out in 1 - 5 temperature zones; Preferably, the first temperature zone includes 3 - 8, preferably 3 - 5 hot rolls; and / or, each of the remaining temperature zones except the first temperature zone independently includes 1 - 8, preferably 2 - 5 hot rolls; More preferably, the temperature of each temperature zone is independently controlled to be 90 - 160 °C.

5. The drying densification method according to claim 3, wherein On the surface of each hot roll in each temperature zone, the width of the fiber bundle is independently 25 - 50 mm, preferably 30 - 40 mm.

6. The drying densification method according to any one of claims 3 to 5, characterized in that The width of the fiber bundle on the second hot roll surface in the first temperature zone is controlled as follows: the width of the fiber bundle on the second hot roll surface is not less than 0.95 times the width on the first hot roll surface; preferably, the width of the fiber bundle on the second hot roll surface is 0.95 - 1.0 times the width on the first hot roll surface.

7. The drying densification method according to claim 1, characterized in that The width of the fiber bundle on the third hot roll surface in the first temperature zone is controlled as follows: the width of the fiber bundle on the third hot roll surface is not less than 0.8 times the width on the first hot roll surface; preferably, the width of the fiber bundle on the third hot roll surface is 0.8 - 0.98 times the width on the first hot roll surface.

8. A dried and densified polyacrylonitrile fiber obtained by the drying and densification method of the polyacrylonitrile fiber according to any one of claims 3 - 7.

9. The application of the drying and densification method according to any one of claims 3 - 7 in the preparation of polyacrylonitrile fibers.

10. A method for preparing polyacrylonitrile fibers, comprising: (1) Obtaining coagulated fibers, (2) hot water drawing treatment, (3) water washing, (4) oiling, (5) drying and densification; wherein, the drying and densification is carried out by the drying and densification method according to any one of claims 3 - 7; Preferably: the coagulated fibers are obtained by wet spinning; and / or, the conditions of the hot water drawing treatment include: the hot water temperature is 90 - 99 °C, 1 - 6 stages of hot water drawing, and the total drawing ratio is 2 - 5; and / or, the conditions of the water washing include: the water washing temperature is 50 - 90 °C, preferably 60 - 80 °C; and / or, the conditions of the oiling include: carried out at 20 - 40 °C, and the effective oil agent content in the oil agent tank is 1 - 5 wt%.

11. The polyacrylonitrile fiber obtained by directly collecting filaments using the preparation method described in claim 10. Preferably, the fiber tension of the polyacrylonitrile fiber is 0.05 to 0.5 cN / dtex, preferably 0.1 to 0.2 cN / dtex.

12. The application of the polyacrylonitrile fiber obtained by the preparation method described in claim 10 in carbon fibers.

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