A polyacrylonitrile fiber and a method for producing the same

Abstract

This invention provides polyacrylonitrile fiber and its preparation method, relating to the field of polyacrylonitrile-based carbon fiber production technology. The method includes the following steps: conveying a polyacrylonitrile solution through a conveying pipe to a spinning device for spinning; followed by spinning to obtain polyacrylonitrile fiber; wherein the conveying pipe includes an inner tube, a first sleeve, and a second sleeve; the first sleeve is fitted outside the inner tube; the second sleeve is fitted outside the first sleeve; wherein the first sleeve is used to convey the polyacrylonitrile solution; the inner tube and the second sleeve are respectively used to store insulation media. The conveying pipe of this invention can reduce the temperature difference between the core and the outside of the polyacrylonitrile solution during conveying, thereby ensuring the uniform viscosity of the polyacrylonitrile solution.

Description

Technical Field

[0001] This invention belongs to the field of polyacrylonitrile-based carbon fiber production technology, specifically relating to a polyacrylonitrile fiber and its preparation method. Background Technology

[0002] Polyacrylonitrile (PAC) fiber is a prerequisite for producing high-performance carbon fiber. PAC fiber is produced by conveying a PAC solution through a pipeline to a metering pump, where it is metered, filtered, and then extruded from a spinneret into a coagulation bath. Under double diffusion, it solidifies into nascent fibers. These fibers then undergo washing, hot water drawing, oiling, drying and densification, and steam drawing before finally being wound into shape to produce PAC fiber. The viscosity of the PAC solution directly affects the filtration pressure, spinning pressure, spinnability, the formation of the dope stream, the tensile properties of the nascent fibers, and the quality of the finished fiber (carbon fiber).

[0003] However, in the existing polyacrylonitrile fiber preparation process, the conveying pipeline used is a single-sleeve pipe, which leads to a large temperature difference between the core and outer layer of the polyacrylonitrile solution during the conveying process. The viscosity of the polyacrylonitrile solution is uneven, which easily produces jelly-like or flocculent gel lumps. The filtration accuracy of the filtration equipment is generally 1-10μm, and the spinneret orifice is generally 0.10-0.15mm, which are both small. During the conveying process of polyacrylonitrile solution, the filtration equipment is easily blocked when filtering before spinning, and the spinneret is easily blocked during the spinning process, resulting in material lumps and broken ends, leading to roller wrapping and fiber breakage. As a result, the prepared polyacrylonitrile fiber has poor production stability, high appearance hairiness, and large fluctuations in performance indicators. Summary of the Invention

[0004] Therefore, the present invention provides a polyacrylonitrile fiber and its preparation method, which can solve the technical problem of uneven viscosity in the transportation process of polyacrylonitrile solution in the prior art.

[0005] To address the aforementioned problems, this invention provides a method for preparing polyacrylonitrile fibers, comprising the following steps:

[0006] The polyacrylonitrile solution is transported to the spinning device through a conveying pipeline for spinning. After spinning, it is spun into polyacrylonitrile fibers.

[0007] The conveying pipeline includes an inner pipe, a first sleeve, and a second sleeve; the first sleeve is fitted over the outer side of the inner pipe; and the second sleeve is fitted over the outer side of the first sleeve.

[0008] The first sleeve is used to transport the polyacrylonitrile solution; the inner tube and the second sleeve are used to store the insulation medium, respectively.

[0009] Furthermore, the temperature of the insulation medium in the inner tube is 20-70℃; the temperature of the insulation medium in the second sleeve is 20-70℃.

[0010] Preferably, the temperature difference between the insulation medium in the inner tube and the second sleeve is less than 5°C.

[0011] Furthermore, the polyacrylonitrile solution is transported to the metering pump via a pipeline by a booster pump to obtain the spinning solution, and then the spinning solution is transported to the spinneret.

[0012] The conveying pipeline includes a first pipeline and a second pipeline;

[0013] The first end of the first pipe is connected to a booster pump, and the second end of the first pipe is connected to a metering pump.

[0014] The first end of the second pipe is connected to the metering pump, and the second end of the second pipe is connected to the spinneret.

[0015] The temperature Q1 of the insulation medium in the inner pipe and the second sleeve of the first pipeline is 40-70℃; the temperature Q2 of the insulation medium in the inner pipe and the second sleeve of the second pipeline is 20-60℃.

[0016] Furthermore, wet spinning or dry-jet wet spinning processes are used for spinning;

[0017] The wet spinning and dry-jet wet spinning processes both include the following sequential processes: solidification forming treatment, water washing treatment, hot water drawing treatment, oiling treatment, drying densification treatment, and steam drawing treatment.

[0018] Preferably, during the solidification forming process, the stretching ratio applied to the fiber is K1; during the hot water stretching process, the stretching ratio applied to the fiber is K2; and during the steam stretching process, the stretching ratio applied to the fiber is K3; wherein, K1:K2:K3 = 1:0.6-1.0:1.0-2.0.

[0019] Furthermore, when wet spinning is used, Q2 is 40-60℃, and Q1≤Q2≤the temperature of the coagulation bath during solidification.

[0020] When using the dry-jet wet spinning method, Q2 is 20-40℃, and Q2≤Q1.

[0021] Furthermore, when using wet spinning, Q2-Q1≤35℃;

[0022] When using the dry-jet wet spinning method, Q1-Q2≤35℃.

[0023] Furthermore, the first pipe is inclined, and the end of the first pipe is inclined upward at 1-10°.

[0024] Furthermore, the solid content of the polyacrylonitrile solution is 18-25 wt%; and / or

[0025] The falling ball viscosity H1 of the polyacrylonitrile solution at 40°C is 60-110 Pa·s; and / or

[0026] The falling ball viscosity H2 of the spinning solution is 70-120 Pa·s, and the CV value is ≤0.5%.

[0027] Preferably, the H2-H1 or H1-H2 ≤ 10 Pa·s.

[0028] Furthermore, the inner wall surface of the first sleeve is polished, and its roughness is ≤ Ra0.1; and / or

[0029] The first sleeve is made of stainless steel; and / or

[0030] The insulation medium is water, preferably desalinated water.

[0031] On the other hand, the present invention provides a polyacrylonitrile fiber, wherein the monofilament diameter of the polyacrylonitrile fiber is 8-12 μm; the batch-to-batch and intra-batch dispersion coefficients of the linear density of the polyacrylonitrile fiber are both ≤0.5%; the batch-to-batch and intra-batch dispersion coefficients of the oiling rate of the polyacrylonitrile fiber are both ≤1.0%; and the batch-to-batch and intra-batch dispersion coefficients of the tensile strength, elastic modulus, and elongation of the polyacrylonitrile fiber are all ≤1.5%.

[0032] Preferably, the polyacrylonitrile fiber is obtained by any of the preparation methods described above.

[0033] The polyacrylonitrile fiber and its preparation method provided by this invention have the following beneficial effects:

[0034] 1. This invention transmits a polyacrylonitrile solution to a spinning device via a conveying pipe for spinning, followed by spinning to obtain polyacrylonitrile fibers. The conveying pipe includes an inner pipe, a first sleeve, and a second sleeve. The first sleeve is fitted over the inner pipe, and the second sleeve is fitted over the first sleeve. The first sleeve is used to convey the polyacrylonitrile solution. The inner pipe and the second sleeve are used to store insulation media. This design reduces the temperature difference between the core and the outside of the polyacrylonitrile solution (i.e., the polyacrylonitrile solution near the inner wall of the conveying pipe and the polyacrylonitrile solution near the core of the conveying pipe), thereby ensuring uniform viscosity of the polyacrylonitrile solution.

[0035] 2. Furthermore, the present invention sets two-stage conveying temperatures to match the spinning process, which is beneficial for continuous and stable spinning. Specifically, the temperature Q1 (i.e., the first-stage conveying temperature) of the insulation medium from the booster pump to the metering pump is set to 40-70℃ to improve the fluidity of the polyacrylonitrile solution and ensure that there is no clumping or gelling during the conveying process; the temperature Q2 (i.e., the second-stage conveying temperature) of the insulation medium from the metering pump to the spinning process is set to 20-60℃ to improve the spinnability of the spinning solution and ensure a stable and continuous spinning process.

[0036] 3. Furthermore, this invention improves the spinnability of the spinning solution and its compatibility with the spinning process by controlling the feeding temperature (i.e., conveying temperatures Q1 and Q2) to perform secondary concentration adjustment (i.e., adjusting the viscosity of the polyacrylonitrile solution), thereby preparing high-quality polyacrylonitrile fibers and polyacrylonitrile-based carbon fibers. Specifically, the polymerized polyacrylonitrile solution has a certain viscosity. It is then concentrated to achieve a spinnable viscosity or the required viscosity H1 for producing a certain specification of precursor fiber (polyacrylonitrile fiber). The viscosity is then finely adjusted again by controlling the feeding temperature so that the resulting spinning solution viscosity H2 satisfies H2-H1 or H1-H2≤10Pa.s, thereby improving spinnability and compatibility with the spinning process, and preparing high-quality polyacrylonitrile fibers and polyacrylonitrile-based carbon fibers. Attached Figure Description

[0037] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the conveying pipeline in this application;

[0039] Figure 2 This is an end face view of the polyacrylonitrile fiber prepared in Example 1 of the present invention;

[0040] Figure 3 This describes the tube blockage situation of the polyacrylonitrile solution in Comparative Example 1 of this invention;

[0041] Figure 4 This is an end view of the polyacrylonitrile fiber prepared in Comparative Example 2 of the present invention;

[0042] The attached diagram is labeled as follows: 1-inner tube, 2-first sleeve, 3-second sleeve. Detailed Implementation

[0043] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0044] This invention improves the uniformity of the spinning solution throughout the feeding process using a double-pipe conveying pipeline, and further concentrates the viscosity of the polyacrylonitrile solution by regulating the feeding temperature, thereby enhancing the spinnability, continuity, and stability of the polyacrylonitrile solution. Ultimately, this results in the production of polyacrylonitrile fibers with excellent performance and high stability in production and quality control. The specific scheme is as follows:

[0045] On one hand, the present invention provides a method for preparing polyacrylonitrile fibers, comprising the following steps:

[0046] The polyacrylonitrile solution is transported to the spinning device through a conveying pipeline for spinning. After spinning, it is spun into polyacrylonitrile fibers.

[0047] The conveying pipeline includes an inner pipe, a first sleeve, and a second sleeve; the first sleeve is fitted outside the inner pipe; and the second sleeve is fitted outside the first sleeve.

[0048] The first sleeve is used to transport the polyacrylonitrile solution; the inner sleeve and the second sleeve are used to store the insulation medium respectively; the temperature of the insulation medium in the inner sleeve is 20-70℃; the temperature of the insulation medium in the second sleeve is 20-70℃; preferably, the temperature difference between the insulation medium in the inner sleeve and the second sleeve is less than 5℃, preferably the same; the insulation medium can be tap water or demineralized water.

[0049] Based on the aforementioned delivery pipe, the temperature difference between the polyacrylonitrile solution near the inner wall of the delivery pipe and the solution near the core of the delivery pipe can be reduced, thereby ensuring the uniform viscosity of the polyacrylonitrile solution.

[0050] In some embodiments, a polyacrylonitrile solution is transported to a metering pump via a delivery pipeline by a booster pump to obtain a spinning solution, which is then transported to a spinning device. The delivery pipeline includes a first pipeline and a second pipeline. The first pipeline is connected to the booster pump at its beginning and to the metering pump at its end. The second pipeline is connected to the metering pump at its beginning and to the spinning device at its end.

[0051] The inner wall surface of the first sleeve is polished and has a roughness ≤ Ra0.1; the material of the first sleeve is stainless steel.

[0052] After polymerization, demonolysis, and degassing, the polyacrylonitrile solution becomes viscous upon natural standing. By setting the temperature of the insulation medium in the inner tube of the first pipeline and the second sleeve (i.e., the temperature of the insulation medium from the booster pump to the metering pump) Q1 to 40-70℃, the fluidity of the polyacrylonitrile solution can be improved, ensuring no clumping or gelling during transportation. Setting the temperature of the insulation medium in the inner tube of the second pipeline and the second sleeve (i.e., the temperature of the insulation medium from the metering pump to the spinning process) Q2 to 20-60℃ improves the spinnability of the spinning solution and ensures a stable and continuous spinning process. In other words, if the temperature during transportation is too low, the polyacrylonitrile solution is prone to clumping and gelling; if the temperature is too high, the polyacrylonitrile solution is prone to accelerated cross-linking and thickening, and its spinnability will also deteriorate.

[0053] If Q1 is too low, the polyacrylonitrile solution will have high viscosity and poor flowability; if it is too high, it will easily lead to the decomposition of residual initiator, and the polyacrylonitrile solution will easily generate bubbles and cause fiber breakage.

[0054] Furthermore, this invention adjusts the viscosity of the polyacrylonitrile solution by controlling the feeding temperature (i.e., conveying temperatures Q1 and Q2), thereby improving the spinnability of the spinning solution and its compatibility with the spinning process, and preparing high-quality polyacrylonitrile fibers and polyacrylonitrile-based carbon fibers. Specifically, the polymerized polyacrylonitrile solution has a certain viscosity, which is then reduced and concentrated to achieve a spinnable viscosity or the required viscosity H1 for producing a certain specification of precursor fiber (polyacrylonitrile fiber). The viscosity is then finely adjusted a second time by controlling the feeding temperature, so that the viscosity H2 of the resulting spinning solution satisfies H2-H1 or H1-H2≤10Pa.s, thereby improving spinnability and compatibility with the spinning process, and preparing high-quality polyacrylonitrile fibers and polyacrylonitrile-based carbon fibers.

[0055] In some embodiments, the solid content of the polyacrylonitrile solution after polymerization, demonolysis, and degassing is 18-25 wt%, and the falling ball viscosity H1 of the polyacrylonitrile solution is 60-110 Pa·s at 40°C.

[0056] An online viscometer is installed between the metering pump and the spinneret to regulate the feed temperatures Q1 and Q2, thereby adjusting the viscosity of the spinning solution. Specifically, when the detected viscosity H2 of the spinning solution is high, the feed temperatures Q1 and Q2 are increased; when the detected viscosity H2 of the spinning solution is low, the feed temperatures Q1 and Q2 are decreased.

[0057] In some embodiments, wet spinning or dry-jet wet spinning is used for spinning.

[0058] Both wet spinning and dry-jet wet spinning include sequential solidification forming treatment, water washing treatment, hot water drawing treatment, oiling treatment, drying densification treatment and steam drawing treatment.

[0059] Preferably, during the solidification forming process, the stretching ratio applied to the fiber is K1; during the hot water stretching process, the stretching ratio applied to the fiber is K2; and during the steam stretching process, the stretching ratio applied to the fiber is K3; wherein, K1:K2:K3 = 1:0.6-1.0:1.0-2.0;

[0060] The spinning device in the above method includes a spinneret with a spinneret orifice diameter of 0.05-0.12 mm. The viscosity of the polyacrylonitrile solution, the spinneret orifice diameter, and the stretching ratio applied to the fiber during solidification, hot water stretching treatment, and steam stretching treatment all affect the monofilament diameter of the polyacrylonitrile fiber.

[0061] In some embodiments, when wet spinning is used, Q2 is 40-60°C, and Q1≤Q2≤the temperature of the coagulation bath during solidification.

[0062] When using the dry-jet wet spinning method, Q2 is 20-40℃, and Q2≤Q1.

[0063] Furthermore, when using wet spinning, Q2-Q1≤35℃;

[0064] When using dry-jet wet spinning, Q1-Q2 ≤ 35℃. A large temperature difference between Q1 and Q2 during spinning can easily lead to gelation or uneven material temperature. In wet spinning, setting Q1 ≤ Q2 ≤ the gradient temperature of the coagulation bath during solidification is to ensure heating uniformity and reduce differences in solidification between the fiber surface and core. Dry-jet wet spinning generally involves high viscosity polyacrylonitrile solutions and long feed lines; if Q1 < Q2, gel lumps are easily formed during transport. A higher Q1 setting improves the fluidity of the polyacrylonitrile solution and avoids gel lumps, while a lower Q2 setting improves spinnability. Dry-jet wet spinning typically involves fast spinning speeds and a 2-5mm air gap; a lower Q2 temperature is beneficial for continuous spinning stability, but too low a temperature can easily lead to flow interruptions or lumps during spinning.

[0065] In some embodiments, the first pipe is inclined, and the end of the first pipe is inclined upward at 1-10°. Inclining the first pipe can prevent the polyacrylonitrile solution from generating bubbles in the conveying pipe, further ensuring spinning stability and producing high-performance polyacrylonitrile fibers.

[0066] On the other hand, the present invention provides a polyacrylonitrile fiber with a monofilament diameter of 8-12 μm; the batch-to-batch and intra-batch coefficients of variation of the linear density of the polyacrylonitrile fiber are both ≤0.5%; the batch-to-batch and intra-batch coefficients of variation of the oiling rate of the polyacrylonitrile fiber are both ≤1.0%; the batch-to-batch and intra-batch coefficients of variation of the tensile strength, elastic modulus, and elongation of the polyacrylonitrile fiber are both ≤1.5%; wherein, the coefficient of variation is the CV value, which is the ratio of the standard deviation to the mean; batch-to-batch refers to the difference between different production batches, and intra-batch refers to the difference between different spinning positions or the same long distance within the same spinning position during the production process of the same batch;

[0067] Preferably, the polyacrylonitrile fiber is obtained by any of the above preparation methods.

[0068] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0069] It should be noted that the following examples and comparative examples are based on dry-jet wet spinning.

[0070] Example 1

[0071] This embodiment provides a method for preparing T800S-12K polyacrylonitrile fiber, specifically including the following steps:

[0072] Under the action of a booster pump, the polyacrylonitrile solution after polymerization, demonolysis, and degassing is filtered and metered by a metering pump through a conveying pipeline to obtain spinning solution. The spinning solution is then conveyed to a spinneret, where it is sprayed out through a spinneret to form a fine stream of solution. The fine stream of solution is then subjected to solidification, washing, hot water stretching, oiling, drying and densification, and steam stretching in sequence. Finally, it is wound up to form polyacrylonitrile fiber.

[0073] The conveying pipeline includes an inner pipe 1, a first sleeve 2, and a second sleeve 3, see [link / reference]. Figure 1 The first sleeve is fitted outside the inner sleeve; the second sleeve is fitted outside the first sleeve; the first sleeve is used to transport the polyacrylonitrile solution; the inner sleeve and the second sleeve are used to store heat-insulating water, respectively.

[0074] The conveying pipeline includes a first pipeline and a second pipeline; the first pipeline is connected to a booster pump at its beginning and to a metering pump at its end; the second pipeline is connected to a metering pump at its beginning and to the spinneret at its end.

[0075] The solid content of the polyacrylonitrile solution after polymerization, demonolysis, and degassing is 20 wt%. At 40°C, the falling ball viscosity H1 of the polyacrylonitrile solution is 110 Pa·s; the falling ball viscosity H2 of the spinning solution is 118 Pa·s, and the CV value is 0.2%; the roughness of the inner wall of the first sleeve in the conveying pipeline is Ra0.1, and the first pipeline is inclined upward at 5° from the beginning to the end.

[0076] The temperature of the heat-insulating water from the booster pump to the metering pump, Q1, is 55℃, and the temperature of the heat-insulating water from the metering pump to the spinneret, Q2, is 20℃. During coagulation, the temperature of the coagulation bath area is 20℃, and the humidity of the coagulation bath area is 60%. The orifice diameter of the spinneret is 0.12mm, and the stretching ratios applied to the fiber during coagulation, hot water stretching, and steam stretching are 3.0, 2.5, and 4.5, respectively.

[0077] The end face view of the polyacrylonitrile fiber prepared in this embodiment is shown below. Figure 1 As shown, the end face is smooth; the prepared polyacrylonitrile fiber has a single filament diameter of 10 μm, a linear density CV value of 0.5%, a tensile strength CV value of 1%, an elastic modulus CV value of 1.2%, and an elongation CV value of 1%.

[0078] Example 2

[0079] This embodiment provides a method for preparing T800S-12K polyacrylonitrile fiber, specifically including the following steps:

[0080] Under the action of a booster pump, the polyacrylonitrile solution after polymerization, demonolysis, and degassing is filtered and metered by a metering pump through a conveying pipeline to obtain spinning solution. The spinning solution is then conveyed to a spinneret, where it is sprayed out through a spinneret to form a fine stream of solution. The fine stream of solution is then subjected to solidification, washing, hot water stretching, oiling, drying and densification, and steam stretching in sequence. Finally, it is wound up to form polyacrylonitrile fiber.

[0081] The conveying pipeline includes an inner pipe, a first sleeve, and a second sleeve, see [link / reference]. Figure 1 The first sleeve is fitted outside the inner sleeve; the second sleeve is fitted outside the first sleeve; the first sleeve is used to transport the polyacrylonitrile solution; the inner sleeve and the second sleeve are used to store heat-insulating water, respectively.

[0082] The conveying pipeline includes a first pipeline and a second pipeline; the first pipeline is connected to a booster pump at its beginning and to a metering pump at its end; the second pipeline is connected to a metering pump at its beginning and to the spinneret at its end.

[0083] The solid content of the polyacrylonitrile solution after polymerization, demonolysis, and degassing is 23 wt%. At 40°C, the falling ball viscosity H1 of the polyacrylonitrile solution is 110 Pa·s. The falling ball viscosity H2 of the spinning solution is 110 Pa·s, and the CV value is 0.2%. The roughness of the inner wall of the first sleeve in the conveying pipeline is Ra0.1, and the first pipeline is inclined upward at 10° from the beginning to the end.

[0084] The temperature of the heat-insulating water from the booster pump to the metering pump, Q1, is 40℃, and the temperature of the heat-insulating water from the metering pump to the spinneret, Q2, is 40℃. During coagulation, the temperature of the coagulation bath area is 25℃, and the humidity of the coagulation bath area is 60%. The orifice diameter of the spinneret is 0.12mm, and the stretching ratios applied to the fiber during coagulation, hot water stretching, and steam stretching are 3.0, 2.5, and 4.5, respectively.

[0085] The polyacrylonitrile fiber prepared in this embodiment has a single filament diameter of 9 μm, a linear density CV value of 0.3%, and a tensile strength CV value of 0.8%.

[0086] Comparative Example 1

[0087] This comparative example provides a method for preparing T800S-12K polyacrylonitrile fiber, specifically including the following steps:

[0088] Under the action of a booster pump, the polyacrylonitrile solution after polymerization, demonolysis, and degassing is filtered and metered by a metering pump through a conveying pipeline to obtain spinning solution. The spinning solution is then conveyed to a spinneret, where it is sprayed out through a spinneret to form a fine stream of solution. The fine stream of solution is then subjected to solidification, washing, hot water stretching, oiling, drying and densification, and steam stretching in sequence. Finally, it is wound up to form polyacrylonitrile fiber.

[0089] The conveying pipeline includes an inner pipe, a first sleeve, and a second sleeve, see [link / reference]. Figure 1 The first sleeve is fitted outside the inner sleeve; the second sleeve is fitted outside the first sleeve; the first sleeve is used to transport the polyacrylonitrile solution; the inner sleeve and the second sleeve are used to store heat-insulating water, respectively.

[0090] The conveying pipeline includes a first pipeline and a second pipeline; the first pipeline is connected to a booster pump at its beginning and to a metering pump at its end; the second pipeline is connected to a metering pump at its beginning and to the spinneret at its end.

[0091] The solid content of the polyacrylonitrile solution after polymerization, demonolysis, and degassing is 20wt%. At 40℃, the falling ball viscosity H1 of the polyacrylonitrile solution is 110 Pa·s; the falling ball viscosity H2 of the spinning solution is 118 Pa·s, and the CV value is 0.8%. The roughness of the inner wall of the first sleeve in the conveying pipeline is Ra0.8, and the first pipeline is set horizontally.

[0092] The temperature of the heat-insulating water from the booster pump to the metering pump, Q1, is 55℃, and the temperature of the heat-insulating water from the metering pump to the spinneret, Q2, is 20℃. During coagulation, the temperature of the coagulation bath area is 20℃, and the humidity of the coagulation bath area is 60%. The orifice diameter of the spinneret is 0.12mm, and the stretching ratios applied to the fiber during coagulation, hot water stretching, and steam stretching are 3.0, 2.5, and 4.5, respectively.

[0093] The polyacrylonitrile fibers prepared in this comparative example have a linear density CV value of 1.0% and a tensile strength CV value of 1.5%. Due to the high roughness of the inner wall of the first sleeve in the conveying pipeline, material easily accumulates inside the pipeline during feeding, leading to flow interruption, strand breakage, and gelation during the spinning process. Figure 3 As shown, a large amount of gel was formed; the first pipe was laid horizontally, and air bubbles were likely to exist in the first pipe, which led to flow interruption and strand breakage during the spinning process, resulting in unstable production operation at the spinning station and intermittent fiber breakage and roller entanglement problems. As a result, the linear density CV value and tensile strength CV value of the polyacrylonitrile fiber prepared in this comparative example were relatively high.

[0094] Comparative Example 2

[0095] This comparative example provides a method for preparing T800S-12K polyacrylonitrile fiber, specifically including the following steps:

[0096] Under the action of a booster pump, the polyacrylonitrile solution after polymerization, demonolysis, and degassing is filtered and metered by a metering pump through a conveying pipeline to obtain spinning solution. The spinning solution is then conveyed to a spinneret, where it is sprayed out through a spinneret to form a fine stream of solution. The fine stream of solution is then subjected to solidification, washing, hot water stretching, oiling, drying and densification, and steam stretching in sequence. Finally, it is wound up to form polyacrylonitrile fiber.

[0097] The conveying pipeline includes an inner pipe, a first sleeve, and a second sleeve, see [link / reference]. Figure 1 The first sleeve is fitted outside the inner sleeve; the second sleeve is fitted outside the first sleeve; the first sleeve is used to transport the polyacrylonitrile solution; the inner sleeve and the second sleeve are used to store heat-insulating water, respectively.

[0098] The conveying pipeline includes a first pipeline and a second pipeline; the first pipeline is connected to a booster pump at its beginning and to a metering pump at its end; the second pipeline is connected to a metering pump at its beginning and to the spinneret at its end.

[0099] The solid content of the polyacrylonitrile solution after polymerization, demonolysis, and degassing is 20wt%. At 40℃, the falling ball viscosity H1 of the polyacrylonitrile solution is 110 Pa·s; the falling ball viscosity H2 of the spinning solution is 125 Pa·s, and the CV value is 0.2%. The roughness of the inner wall of the first sleeve in the conveying pipeline is Ra0.1, and it is inclined upward at 5° from the beginning to the end.

[0100] The temperature of the heat-insulating water from the booster pump to the metering pump, Q1, is 30℃, and the temperature of the heat-insulating water from the metering pump to the spinneret, Q2, is 30℃. During coagulation, the temperature of the coagulation bath area is 20℃, and the humidity of the coagulation bath area is 60%. The orifice diameter of the spinneret is 0.12mm, and the stretching ratios applied to the fiber during coagulation, hot water stretching, and steam stretching are 3.0, 2.5, and 4.5, respectively.

[0101] The linear density CV value of the polyacrylonitrile fiber prepared in this comparative example is 3.5%, and the tensile strength CV value is 5%. Due to the excessively low feed temperature Q1, the viscosity of the polyacrylonitrile solution increases, resulting in poor fluidity during transportation and easy gel formation in the transportation pipeline. This leads to more material lumps during spinning, causing unstable spinning production, easy fiber breakage and roller entanglement, and thus resulting in higher linear density CV values ​​and tensile strength CV values ​​of the polyacrylonitrile fiber prepared in this comparative example.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing T800S-12K polyacrylonitrile fiber, specifically including the following steps:

[0104] Under the action of a booster pump, the polyacrylonitrile solution after polymerization, demonolysis, and degassing is filtered and metered by a metering pump through a conveying pipeline to obtain spinning solution. The spinning solution is then conveyed to a spinneret, where it is sprayed out through a spinneret to form a fine stream of solution. The fine stream of solution is then subjected to solidification, washing, hot water stretching, oiling, drying and densification, and steam stretching in sequence. Finally, it is wound up to form polyacrylonitrile fiber.

[0105] The conveying pipeline includes an inner pipe, a first sleeve, and a second sleeve, see [link / reference]. Figure 1 The first sleeve is fitted outside the inner sleeve; the second sleeve is fitted outside the first sleeve; the first sleeve is used to transport the polyacrylonitrile solution; the inner sleeve and the second sleeve are used to store heat-insulating water, respectively.

[0106] The conveying pipeline includes a first pipeline and a second pipeline; the first pipeline is connected to a booster pump at its beginning and to a metering pump at its end; the second pipeline is connected to a metering pump at its beginning and to the spinneret at its end.

[0107] The solid content of the polyacrylonitrile solution after polymerization, demonolysis, and degassing is 20 wt%. At 40℃, the falling ball viscosity H1 of the polyacrylonitrile solution is 110 Pa·s; the falling ball viscosity H2 of the spinning solution is 118 Pa·s, and the CV value is 0.2%. The roughness of the inner wall of the first sleeve in the conveying pipeline is Ra0.1, and it is inclined upward at 5° from the beginning to the end.

[0108] The temperature of the heat-insulating water from the booster pump to the metering pump, Q1, is 55℃, and the temperature of the heat-insulating water from the metering pump to the spinneret, Q2, is 20℃. During coagulation, the temperature of the coagulation bath area is 20℃, and the humidity of the coagulation bath area is 60%. The orifice diameter of the spinneret is 0.12mm, and the stretching ratios applied to the fiber during coagulation, hot water stretching, and steam stretching are 3.0, 4.0, and 2.8, respectively.

[0109] The polyacrylonitrile fiber prepared in this comparative example has a single filament diameter of 10 μm, a linear density CV value of 3.5%, and a tensile strength CV value of 4.2%. The comparative example has the same viscosity, spinneret diameter, and product of draw ratios (i.e., total draw ratio, which is the product of the draw ratios applied to the fibers in the steps of solidification, washing, hot water drawing, oiling, drying and densification, and steam drawing) as Example 1. Therefore, the monofilament diameter of the obtained polyacrylonitrile fibers is 10 μm. However, the ratio of the draw ratios applied to the fibers in the solidification, hot water drawing, and steam drawing processes does not match the viscosity of the polyacrylonitrile solution. That is, the ratio of the draw ratios applied to the fibers in the solidification, hot water drawing, and steam drawing processes, K1:K2:K3, does not meet the requirement of 1:0.6-1.0:1.0-2.0. The draw ratio applied to the fibers in the hot water drawing process is too large, which makes it easy to tear and fuzz the filament bundle during spinning. Figure 4 As shown, the polyacrylonitrile fiber has many fuzzy ends, which leads to unstable production operation and frequent roll wrapping at the hot water drawing point. The polyacrylonitrile fiber has many broken strands of fuzzy ends, resulting in higher linear density CV value and tensile strength CV value of the polyacrylonitrile fiber prepared in this comparative example.

[0110] The specific performance comparison of the polyacrylonitrile fibers prepared in the embodiments and comparative examples of the present invention is shown in the table below:

[0111]

[0112] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A method for preparing polyacrylonitrile fibers, characterized in that, Includes the following steps: The polyacrylonitrile solution is transported to the spinning device through a conveying pipeline for spinning. After spinning, it is spun into polyacrylonitrile fibers. The conveying pipeline includes an inner pipe, a first sleeve, and a second sleeve; the first sleeve is fitted over the outer side of the inner pipe; and the second sleeve is fitted over the outer side of the first sleeve. The first sleeve is used to transport the polyacrylonitrile solution; the inner tube and the second sleeve are used to store the heat-insulating medium, respectively. A polyacrylonitrile solution is pumped through a booster pump and then metered by a metering pump to obtain a spinning solution. This spinning solution is then transferred to a spinning device. The conveying pipeline includes a first pipeline and a second pipeline. The first pipeline is connected to the booster pump at one end and to the metering pump at the other. The second pipeline is connected to the metering pump at one end and to the spinning device at the other. The temperature Q1 of the insulating medium in the inner tube and the second sleeve of the first pipeline is 40-70°C. The temperature Q2 of the insulating medium in the inner tube and the second sleeve of the second pipeline is 20-60°C.

2. The method for preparing polyacrylonitrile fibers according to claim 1, characterized in that, The temperature difference between the insulation medium in the inner tube and the second sleeve is less than 5℃.

3. The method for preparing polyacrylonitrile fibers according to claim 1, characterized in that, Spinning is carried out using either wet spinning or dry-jet wet spinning processes; The wet spinning and dry-jet wet spinning processes both include the following sequential processes: solidification forming, water washing, hot water drawing, oiling, drying densification, and steam drawing.

4. The method for preparing polyacrylonitrile fibers according to claim 3, characterized in that, During the solidification forming process, the stretching ratio applied to the fiber is K1; during the hot water stretching process, the stretching ratio applied to the fiber is K2; during the steam stretching process, the stretching ratio applied to the fiber is K3; wherein, K1:K2:K3=1:0.6-1.0:1.0-2.

0.

5. The method for preparing polyacrylonitrile fibers according to claim 3, characterized in that, When wet spinning is used, Q2 is 40-60℃, and Q1≤Q2≤the temperature of the coagulation bath during solidification. When using the dry-jet wet spinning method, Q2 is 20-40℃, and Q2≤Q1.

6. The method for preparing polyacrylonitrile fibers according to claim 5, characterized in that, When using wet spinning, Q2-Q1≤35℃; When using the dry-jet wet spinning method, Q1-Q2≤35℃.

7. The method for preparing polyacrylonitrile fibers according to any one of claims 1-6, characterized in that, The first pipe is inclined, and the end of the first pipe is inclined upward at 1-10°.

8. The method for preparing polyacrylonitrile fibers according to claim 1, characterized in that, The solid content of the polyacrylonitrile solution is 18-25 wt%; and / or The falling ball viscosity H1 of the polyacrylonitrile solution at 40°C is 60-110 Pa·s; and / or The falling ball viscosity H2 of the spinning solution is 70-120 Pa·s, and the CV value is ≤0.5%; H2-H1 or H1-H2 ≤10 Pa·s.

9. The method for preparing polyacrylonitrile fibers according to claim 1, characterized in that, The inner wall surface of the first sleeve is polished, and the roughness is ≤ Ra0.1; and / or The first sleeve is made of stainless steel.

10. The method for preparing polyacrylonitrile fibers according to claim 1, characterized in that, The insulation medium is water.

11. The method for preparing polyacrylonitrile fibers according to claim 10, characterized in that, The insulation medium is demineralized water.

12. A polyacrylonitrile fiber, characterized in that, The polyacrylonitrile fiber is obtained by the preparation method according to any one of claims 1-11; the monofilament diameter of the polyacrylonitrile fiber is 8-12 μm; the inter-batch and intra-batch dispersion coefficients of the linear density of the polyacrylonitrile fiber are both ≤0.5%; the inter-batch and intra-batch dispersion coefficients of the oiling rate of the polyacrylonitrile fiber are both ≤1.0%; the inter-batch and intra-batch dispersion coefficients of the tensile strength, elastic modulus, and elongation of the polyacrylonitrile fiber are all ≤1.5%.

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