A method for producing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control

Abstract

This invention provides a method for preparing polyacrylonitrile-based carbon fiber precursors using multi-stage tension control, belonging to the field of polyacrylonitrile-based carbon fibers. The method includes spinning, washing, and steam drawing. This method can reduce internal structural defects in the precursor and improve its orientation, thereby enhancing its mechanical properties. This method can address the problems of insufficient denier and high filament frequency in the large-scale production of polyacrylonitrile-based carbon fiber precursors, improving the quality stability of the obtained precursors, increasing production efficiency, and achieving stable large-scale production of polyacrylonitrile-based carbon fiber precursors.

Description

Technical Field

[0001] This invention relates to the field of polyacrylonitrile-based carbon fiber, and in particular to a method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control. Background Technology

[0002] Carbon fiber is a high-strength, high-specific-modulus reinforced and functional fiber material, known as the "black gold" of the 21st century. Carbon fiber and its composites have wide applications in aerospace, transportation, medical devices, sports equipment and other fields.

[0003] High-quality polyacrylonitrile (PAN) precursor is crucial for producing high-performance carbon fibers, and PAN carbon fiber is currently the mainstream process in carbon fiber production. Existing PAN-based carbon fiber precursor production processes employ a two-step method using dimethyl sulfoxide (DMSO) aqueous suspension polymerization. This involves dissolving PAN powder in DMSO under specific conditions to obtain a spinning solution, followed by dry-jet wet-spinning. The resulting fiber bundle undergoes drawing, washing, and other processes to produce PAN-based carbon fiber precursor.

[0004] However, in the existing production process of polyacrylonitrile-based carbon fiber precursor, the solvent residue in the precursor is relatively high, and there are also many defects in the internal structure of the precursor, low orientation degree, and poor mechanical properties. Furthermore, in the large-scale batch production of polyacrylonitrile-based carbon fiber precursor, the nascent precursor bundles cannot meet the requirements for fine denier and have a high fuzz frequency, resulting in poor quality stability of the produced polyacrylonitrile-based carbon fiber precursor, making it impossible to achieve large-scale stable production of polyacrylonitrile-based carbon fiber precursor and high-quality carbon fiber.

[0005] Chinese patent CN104805533A discloses a method for washing carbon fiber precursor fibers. It involves installing a porous coil at the bottom of the washing tank to spray hot demineralized water, thus forcing the water to flow within the tank. Simultaneously, it combines V-shaped, S-shaped, and wavy feeding methods with vibration from a patting roller to improve the washing effect and reduce dimethyl sulfoxide residue in the fiber bundle. However, in actual operation, due to the feeding method and multiple vibrations, this patent is prone to causing structural defects, low orientation, and poor mechanical properties in the precursor fibers. Furthermore, it easily leads to fiber breakage and fuzzing, which is detrimental to the control of precursor fiber quality stability. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a method for preparing polyacrylonitrile-based carbon fiber precursors through multi-stage tension control. This method reduces the solvent residue in the prepared polyacrylonitrile-based carbon fiber precursors, decreases internal structural defects, improves the orientation degree of the precursors, and enhances the mechanical properties of the precursors without altering the fiber path of the original equipment. Furthermore, it addresses the issues of insufficient denier and high fuzz frequency in the initial precursor bundles during large-scale batch production of polyacrylonitrile-based carbon fiber precursors, thereby improving the quality stability of the prepared polyacrylonitrile-based carbon fiber precursors, increasing production efficiency, and achieving stable large-scale production of polyacrylonitrile-based carbon fiber precursors.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control, the preparation method comprising: spinning, washing, oiling, and steam drawing;

[0009] The spinning method is as follows: a spinning solution is used to spin the filaments, which are then formed in the air and enter a coagulation bath. After the filaments are solidified in the coagulation bath, the stretching tension of the filaments exiting the coagulation bath is controlled within the range of 200-800 cN / dtex for coagulation bath stretching.

[0010] The spinning solution contains 18.5-21 wt% polyacrylonitrile solids, and the solvent used in the spinning solution is dimethyl sulfoxide.

[0011] The washing method involves performing nine stages of washing on the filament bundle after coagulation bath stretching, controlling the washing temperature within the range of 35-95℃, with the washing temperature increasing progressively at each stage; controlling the stretching tension after each stage of washing within the range of 800-1500 cN / dtex, with the stretching tension increasing progressively at each stage.

[0012] The steam drawing process controls the steam drawing tension within the range of 1500-2000 cN / dtex.

[0013] Furthermore, during the water washing process, the filament bundle is bubbled and vibrated during each stage of the water washing process, and desalinated water is continuously sprayed onto the filament bundle.

[0014] Preferably, during the water washing, the total draw ratio is controlled to be 2.0-2.5 times.

[0015] Preferably, in the steam stretching process, the steam pressure is controlled at 3.0-7.0 bar, and the steam stretching ratio is 2.3-5.0 times.

[0016] Furthermore, the bubbling oscillation is performed by a bubbling device, and the bubbling medium is compressed air with a pressure of not less than 3 bar.

[0017] Furthermore, the bubbling device includes a bubbler, a mounting frame, and an air supply pipe;

[0018] The bubbler is positioned below the surface of the washing liquid in each stage of the wash cycle;

[0019] The bubbler is connected to the air supply pipe, which is connected to an external compressed air source to supply compressed air to the bubbler; the top of the bubbler is equipped with an exhaust port to facilitate the passage of compressed air.

[0020] The bubbler has a drain outlet on its side bottom for draining water from inside the bubbler;

[0021] The bubbler is fixedly connected to the mounting bracket and is used to fix the bubbler below the liquid surface in the washing tank.

[0022] Furthermore, the exhaust ports are arranged along the long side of the bubbler and are configured as two rows symmetrically arranged with respect to the short side central axis of the bubbler; or the exhaust ports are arranged along the short side of the bubbler and are configured as multiple rows evenly arranged along the long side of the bubbler.

[0023] Preferably, the exhaust port is a perforated type or a straight strip type.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1) The method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control of the present invention involves obtaining a fiber bundle after the spinning solution is ejected from the spinneret, followed by solidification in a coagulation bath, stretching, multi-stage washing and stretching, oiling, and steam stretching. During the coagulation bath stretching, washing stretching, and steam stretching stages, the fiber bundle is fully stretched under controllable tension. This method can reduce the solvent residue in the obtained polyacrylonitrile-based carbon fiber precursor without changing the original equipment's fiber path, reduce internal structural defects in the precursor, improve the orientation degree of the precursor, improve the mechanical properties of the precursor, and further improve the problems of the initial precursor fiber bundle not meeting the requirements for fine denier and high fuzz frequency in the large-scale batch production of polyacrylonitrile-based carbon fiber precursor. This improves the quality stability of the obtained polyacrylonitrile-based carbon fiber precursor, increases production efficiency, and realizes the large-scale stable production of polyacrylonitrile-based carbon fiber precursor.

[0026] 2) The method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control of the present invention controls the stretching tension at each stage within a predetermined range and applies tension step by step, which can maximize the effect of uniaxial stretching force. During the process of forming precursor from the dope, the fiber bundle continuously and uniformly elongates axially and contracts radially, gradually refining the fiber. This effectively reduces or even eliminates precursor defects (such as core-sheath structure and porous structure) caused by insufficient or excessive stretching in existing processes, and finally obtains a uniform precursor cross section. This method can both stretch the precursor and achieve uniform denier refining along the fiber axis, and avoid damaging the nascent precursor.

[0027] In addition, by setting up spray and bubble devices during the washing process to oscillate the fiber bundle, thorough washing is achieved, reducing solvent residue inside the precursor fiber and improving the fiber bundle's drawability. Furthermore, in large-scale batch production, the resulting polyacrylonitrile-based carbon fiber precursor fiber exhibits good quality stability and high production efficiency, effectively realizing the large-scale and stable production of polyacrylonitrile-based carbon fiber precursor fiber, thereby improving the mechanical properties of polyacrylonitrile-based carbon fiber.

[0028] 3) The multi-stage tension control method for preparing polyacrylonitrile-based carbon fiber precursor of the present invention involves progressively increasing fiber bundle stretching and tension during the washing process. Combined with a thorough washing process, this ensures fiber orientation along the axial direction while eliminating internal defects caused by solvent residue. Simultaneously, during the stretching process in each stage of the washing tank, spraying and bubbling devices are added to maintain water and the precursor fiber bundle in a dynamic displacement state, increasing the solvent replacement rate and reducing solvent residue within the fiber bundle. Furthermore, the spray volume of the spraying device can be flexibly adjusted according to different precursor fiber specifications. The bubbling device has multiple exhaust port arrangements, allowing for flexible selection of a bubbler with appropriate exhaust ports based on the fiber bundle dispersion.

[0029] 4) The method of preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control of the present invention produces polyacrylonitrile-based carbon fiber precursor with uniform cross-section, no core-sheath structure or pore structure defects, and high orientation; the 3K precursor strength of polyacrylonitrile-based carbon fiber precursor can reach 80.0-88.5 cN / dtex, and the fineness of a single filament can reach 0.99-1.2 dtex. Attached Figure Description

[0030] Figure 1 A schematic diagram of the water washing device used in the multi-stage tension control method for preparing polyacrylonitrile-based carbon fiber precursor of the present invention;

[0031] In the diagram, 1-first washing tank; 2-second washing tank; 3-third washing tank; 4-fourth washing tank; 5-fifth washing tank; 6-sixth washing tank; 7-seventh washing tank; 8-eighth washing tank; 9-ninth washing tank; 10-filament bundle; 11-bubbling device; 12-spraying device.

[0032] Figure 2 A schematic diagram of the bubbling device used in the washing tank in the multi-stage tension control method for preparing polyacrylonitrile-based carbon fiber precursor of the present invention.

[0033] Figure 3 A top view of the bubbling device used in the washing tank in the multi-stage tension control method for preparing polyacrylonitrile-based carbon fiber precursor of the present invention.

[0034] Figure 4A side view of the bubbling device used in the washing tank in the multi-stage tension control method for preparing polyacrylonitrile-based carbon fiber precursor of the present invention.

[0035] Figure 5 A schematic diagram of the exhaust port of the bubbler in the bubbling device in the multi-stage tension control method for preparing polyacrylonitrile-based carbon fiber precursor of the present invention.

[0036] In the diagram, 21-bubbler; 22-fixed frame; 23-air supply pipe; 24-exhaust port; 25-drain port.

[0037] Figure 6 This is a SEM image of the polyacrylonitrile-based carbon fiber prepared in Example 1. Detailed Implementation

[0038] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0039] The inventors discovered in their production practice that during the production of polyacrylonitrile-based carbon fiber precursor, the stretching of the fiber bundle can continuously drive the transformation of the internal structure of the fiber, gradually deforming it from the initial spherulites into precursor. Precise control of the stretching tension allows for sufficient stretching and washing of the fiber bundle without fiber breakage, thereby obtaining a precursor with dense arrangement and fewer pore defects.

[0040] In one implementation of this invention, tension controllers are specifically installed at the outlet of the coagulation bath, the outlets of each stage of the washing tank, and the inlet and outlet of the steam drawing box. Bubbling devices and spraying devices are added during the washing process. This not only enables step-by-step drawing but also ensures thorough washing during the drawing process. This significantly reduces solvent residue inside the raw yarn while achieving a high degree of orientation of the internal structure of the raw yarn, thereby improving the quality of the raw yarn.

[0041] In one implementation of this invention, during the coagulation bath stretching process, a first tension controller is set to maintain the tension of the filament bundle exiting the coagulation bath within the range of 200-800 cN / dtex; within this tension range, the nascent fibers are moderately stretched along the axial direction.

[0042] In one implementation of this invention, during the washing and drawing process, the tension of each stage of washing and drawing is maintained within the range of 800-1500 cN / dtex. Simultaneously, a bubbling device and a spraying device are added to each washing tank. Under the aforementioned conditions, during the washing process, the fiber bundle drawing increases progressively, and the tension gradually increases. Combined with a thorough washing process, this ensures the fibers are oriented along the axis while eliminating internal defects caused by solvent residue. Furthermore, during the washing and drawing process in each stage of the washing tank, the addition of spraying and bubbling devices maintains the water and the raw fiber bundle in a dynamic displacement state, increasing the solvent replacement rate and reducing solvent residue within the fiber bundle. Further, the spray volume of the spraying device can be flexibly adjusted according to different raw fiber specifications. Moreover, the vents of the bubbling device can be arranged in various ways, allowing for flexible selection of a bubbler with suitable vents based on the fiber bundle dispersion.

[0043] Furthermore, by combining various technical means, this invention controls the stretching tension within a predetermined range in each stage of coagulation bath stretching, water washing stretching, and steam stretching, enabling the uniaxial stretching force to play its maximum role. In the process from spinning solution to the formation of filament, the filament bundle continuously and uniformly elongates axially and contracts radially, effectively reducing or even eliminating filament defects caused by insufficient or excessive stretching in existing processes, and finally obtaining a uniform filament cross-section.

[0044] Furthermore, by combining various technical means, this invention can reduce the solvent residue in the produced polyacrylonitrile carbon fiber precursor, reduce internal structural defects in the precursor, improve the orientation degree of the precursor, and enhance the mechanical properties of the precursor. Simultaneously, it addresses the problems of insufficient denier and high fuzz frequency in the initial precursor bundles during large-scale batch production of polyacrylonitrile carbon fiber precursor. This improves the quality stability of the produced polyacrylonitrile carbon fiber precursor, increases production efficiency, and enables stable large-scale production of polyacrylonitrile carbon fiber precursor. Consequently, it provides high-quality raw materials (i.e., polyacrylonitrile carbon fiber precursor) for subsequent carbon fiber production, ensuring the high strength and high modulus of the produced carbon fiber.

[0045] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0046] Example 1

[0047] This embodiment provides a method for preparing polyacrylonitrile-based carbon fiber precursors through multi-stage tension control, specifically as follows:

[0048] 1. Preparation of spinning solution

[0049] Polyacrylonitrile powder was dissolved in dimethyl sulfoxide (DMSO) to prepare a slurry with a solid content of 19.5 wt%. The slurry was passed through a heat exchanger at 80°C to form a raw solution. After thorough stirring and settling, the spinning solution was obtained. After two-stage filtration, the spinning solution was spun using a dry-jet wet spinning process.

[0050] 2. Spinning

[0051] The yarn is spun using a dry-jet wet-spinning process. After forming a yarn bundle in the air, it passes through an air layer with a height of 4 mm (i.e., the distance between the spinneret surface and the coagulation bath liquid surface is 4 mm) and enters the coagulation bath. After the yarn bundle is solidified in the coagulation bath, the stretching tension of the yarn bundle exiting the coagulation bath is controlled within the range of 400-600 cN / dtex for coagulation bath stretching. A first tension controller is used to control the speed of the coagulation bath stretching guide rollers to maintain the tension of the yarn bundle exiting the coagulation bath within the range of 400-600 cN / dtex.

[0052] 3. Wash with water

[0053] After the filament bundles are drawn in the coagulation bath, they are washed with water for nine stages and then oiled.

[0054] During the washing process, the washing temperature is controlled within the range of 35-95℃, and the washing temperature is gradually increased; the stretching tension after each washing stage is controlled within the range of 800-1500 cN / dtex, and the stretching tension is gradually increased.

[0055] The various stages of water washing stretching during the water washing process are hot water stretching, and the total water washing stretching ratio is controlled at 2.2 times.

[0056] During each stage of washing, the filament bundle is bubbled and vibrated, and desalinated water is continuously sprayed onto the filament bundle.

[0057] The bubbling oscillation is performed by the bubbling device 11, and the bubbling medium is compressed air with a pressure of not less than 3 bar.

[0058] 4. Steam traction

[0059] The oiled fiber bundle is steam drawn, and the steam drawing tension is maintained in the range of 1700-1900 cN / dtex. During the steam drawing process, the steam pressure is controlled at 5.0 bar and the steam drawing ratio is 3.6 times. After the steam drawing is completed, the fiber is dried and wound to obtain polyacrylonitrile-based carbon fiber precursor.

[0060] like Figure 1As shown, in the multi-stage tension control method for preparing polyacrylonitrile-based carbon fiber precursor in this embodiment, a washing device is used, including a first washing tank 1, a second washing tank 2, a third washing tank 3, a fourth washing tank 4, a fifth washing tank 5, a sixth washing tank 6, a seventh washing tank 7, an eighth washing tank 8, and a ninth washing tank 9 arranged sequentially. Each washing tank is equipped with a bubbling device 11, which is used to introduce compressed air to bubble during the washing process of the fiber bundle 10, so that the fiber bundle 10 vibrates with the water bath and does not scatter or break.

[0061] Each washing tank is also equipped with a spray device 12, which is used to spray desalinated water during the washing process of the filament bundle 10.

[0062] like Figure 2-4 As shown, the bubbling device 11 installed in each washing tank includes a bubbler 21, an air supply pipe 23, and a fixing frame 22. The bubbler 21 is connected to the air supply pipe 23, which is connected to an external compressed air source to supply compressed air to the bubbler 21. An exhaust port 24 is provided at the top of the bubbler 21, through which the compressed air is discharged, thus achieving bubbling of the washing water in the washing tank. A drain port 25 is provided at the bottom side of the bubbler 21 to drain the water inside the bubbler 21.

[0063] The bubbler 21 is fixedly connected to the fixing frame 22, and the fixing frame 22 is bolted to the inner wall of the washing tank. This is used to fix the bubbler 21 in a predetermined position in the washing tank and prevent the bubbler 21 from shifting.

[0064] During the bubbling process, the bubbling device 11 can adjust the air supply of compressed air to adjust the air volume of the bubbling device 11, so that the water flow and the filament bundle 10 in each washing tank are in a dynamic displacement state, so as to enhance the washing effect, but without causing the filament bundle 10 to spread too much and cause filament breakage, fuzz, and filament entanglement on the guide roller.

[0065] like Figure 5 As shown, depending on the process requirements, different bubble devices 11 in different water baths can be equipped with bubblers 21 of different exhaust port 24 forms. The exhaust port 24 of the bubbler 21 is hole-shaped or straight-strip-shaped; the exhaust port 24 can be arranged along the long side or short side of the bubbler 21; preferably, the exhaust port 24 is arranged along the long side of the bubbler 21 and is set in two rows symmetrically arranged with respect to the short side central axis of the bubbler 21; or the exhaust port 24 is arranged along the short side of the bubbler 21 and is set in multiple rows evenly arranged along the long side of the bubbler 21.

[0066] In this embodiment, the vent of the bubbler 21 used in the first to sixth water washing tanks is orifice-shaped, specifically the vent form is as follows: Figure 5 In the C-type model, the bubbler 21 used in the seventh to ninth washing tanks has a perforated exhaust port, specifically the exhaust port form is as follows: Figure 5 The e-type in the text.

[0067] like Figure 6 As shown, the polyacrylonitrile-based carbon fiber precursor obtained in this embodiment has a uniform cross-section, no core-sheath structure or porous structure defects, and a high degree of orientation. According to the test, the 3K precursor strength of the polyacrylonitrile-based carbon fiber precursor obtained in this embodiment is 80.6 cN / dtex, and the single filament fineness is 1.2 dtex.

[0068] Example 2

[0069] This embodiment provides a method for preparing polyacrylonitrile-based carbon fiber precursors through multi-stage tension control, specifically as follows:

[0070] 1. Preparation of spinning solution

[0071] Polyacrylonitrile powder was dissolved in dimethyl sulfoxide (DMSO) to prepare a slurry with a solid content of 18.5 wt%. The slurry was passed through a heat exchanger at 80°C to form a raw solution. After thorough stirring and settling, a spinning solution was obtained. The spinning solution was filtered in two stages and then spun using a dry-jet wet spinning process.

[0072] 2. Spinning

[0073] The yarn is spun using a dry-jet wet-spinning process. After forming a yarn bundle in the air, it passes through an air layer with a height of 3 mm (i.e., the distance between the spinneret surface and the coagulation bath liquid surface is 3 mm) and enters the coagulation bath. After the yarn bundle is solidified in the coagulation bath, the stretching tension of the yarn bundle exiting the coagulation bath is controlled within the range of 200-400 cN / dtex for coagulation bath stretching. A first tension controller is used to control the speed of the coagulation bath stretching guide rollers to maintain the tension of the yarn bundle exiting the coagulation bath within the range of 200-400 cN / dtex.

[0074] 3. Wash with water

[0075] After the filament bundles are drawn in the coagulation bath, they are washed with water for nine stages and then oiled.

[0076] During the washing process, the washing temperature is controlled within the range of 35-95℃, and the washing temperature is gradually increased; the stretching tension after each washing stage is controlled within the range of 800-1500 cN / dtex, and the stretching tension is gradually increased.

[0077] The various stages of water washing stretching during the water washing process are hot water stretching, and the total water washing stretching ratio is controlled at 2.35 times.

[0078] During each stage of washing, the filament bundle is bubbled and vibrated, and desalinated water is continuously sprayed onto the filament bundle.

[0079] The bubbling oscillation is performed by the bubbling device 11, and the bubbling medium is compressed air with a pressure of not less than 3 bar.

[0080] 4. Steam traction

[0081] The oiled fiber bundle is steam drawn, and the steam drawing tension is maintained in the range of 1500-1700 cN / dtex. During the steam drawing process, the steam pressure is controlled at 4.0 bar and the steam drawing ratio is 4.0 times. After the steam drawing is completed, the fiber is dried and wound to obtain polyacrylonitrile-based carbon fiber precursor.

[0082] In the method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control in this embodiment, the water washing device, bubbling device, and spraying device used are the same as in Example 1.

[0083] The polyacrylonitrile-based carbon fiber precursor obtained in this embodiment has a uniform cross-section, no core-sheath structure or porous structure defects, and high orientation. According to the test, the 3K precursor of the polyacrylonitrile-based carbon fiber precursor obtained in this embodiment has a strength of 88.5 cN / dtex and a single filament fineness of 1.05 dtex.

[0084] Example 3

[0085] This embodiment provides a method for preparing polyacrylonitrile-based carbon fiber precursors through multi-stage tension control, specifically as follows:

[0086] 1. Preparation of spinning solution

[0087] Polyacrylonitrile powder was dissolved in dimethyl sulfoxide (DMSO) to prepare a slurry with a solid content of 21 wt%. The slurry was passed through a heat exchanger at 80°C to form a raw solution, which was then thoroughly stirred and allowed to stand to obtain a spinning solution. After two-stage filtration, the spinning solution was spun using a dry-jet wet spinning process.

[0088] 2. Spinning

[0089] The yarn is spun using a dry-jet wet-spinning process. After forming a yarn bundle in the air, it passes through an air layer with a height of 5 mm (i.e., the distance between the spinneret surface and the coagulation bath liquid surface is 5 mm) and enters the coagulation bath. After the yarn bundle is solidified in the coagulation bath, the stretching tension of the yarn bundle exiting the coagulation bath is controlled within the range of 600-800 cN / dtex for coagulation bath stretching. A first tension controller is used to control the speed of the coagulation bath stretching guide rollers to maintain the tension of the yarn bundle exiting the coagulation bath within the range of 600-800 cN / dtex.

[0090] 3. Wash with water

[0091] After the filament bundles are drawn in the coagulation bath, they are washed with water for nine stages and then oiled.

[0092] During the washing process, the washing temperature is controlled within the range of 35-95℃, and the washing temperature is gradually increased; the stretching tension after each washing stage is controlled within the range of 800-1500 cN / dtex, and the stretching tension is gradually increased.

[0093] The various stages of water washing stretching during the water washing process are hot water stretching, and the total water washing stretching ratio is controlled at 2.5 times.

[0094] During each stage of washing, the filament bundle is bubbled and vibrated, and desalinated water is continuously sprayed onto the filament bundle.

[0095] The bubbling oscillation is performed by the bubbling device 11, and the bubbling medium is compressed air with a pressure of not less than 3 bar.

[0096] 4. Steam traction

[0097] The oiled fiber bundle is steam drawn, and the steam drawing tension is maintained in the range of 1800-2000 cN / dtex. During the steam drawing process, the steam pressure is controlled at 4.5 bar and the steam drawing ratio is 5.0 times. After the steam drawing is completed, the fiber is dried and wound to obtain polyacrylonitrile-based carbon fiber precursor.

[0098] In the method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control in this embodiment, the water washing device, bubbling device, and spraying device used are the same as in Example 1.

[0099] The polyacrylonitrile-based carbon fiber precursor obtained in this embodiment has a uniform cross-section, no core-sheath structure or porous structure defects, and high orientation. According to the test, the 3K precursor of the polyacrylonitrile-based carbon fiber precursor obtained in this embodiment has a strength of 86.8 cN / dtex and a single filament fineness of 0.99 dtex.

[0100] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0101] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control, characterized in that, The preparation method includes: spinning, washing, and steam drawing; The spinning method is as follows: a spinning solution is used to spin the filaments, which are then formed in the air and enter a coagulation bath. After the filaments are solidified in the coagulation bath, the stretching tension of the filaments exiting the coagulation bath is controlled within the range of 200-800 cN / dtex for coagulation bath stretching. The spinning solution contains 18.5-21 wt% polyacrylonitrile solids, and the solvent used in the spinning solution is dimethyl sulfoxide. The washing method involves performing nine stages of washing on the filament bundle after coagulation bath stretching, controlling the washing temperature within the range of 35-95℃, with the washing temperature increasing progressively at each stage; controlling the stretching tension after each stage of washing within the range of 800-1500 cN / dtex, with the stretching tension increasing progressively at each stage. During the washing process, the total draw ratio is controlled to be 2.0-2.5 times; During the washing process, the filament bundle is bubbled and vibrated during each stage of washing, and desalinated water is continuously sprayed onto the filament bundle. The steam drawing process controls the steam drawing tension within the range of 1500-2000 cN / dtex. In the steam stretching process, the steam pressure is controlled at 3.0-7.0 bar, and the steam stretching ratio is 2.3-5.0 times.

2. The method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control according to claim 1, characterized in that, The bubbling oscillation is carried out by a bubbling device (11), and the bubbling medium is compressed air with a pressure of not less than 3 bar.

3. The method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control according to claim 2, characterized in that, The bubbling device (11) includes: a bubbler (21) and an air supply pipe (23); The bubbler (21) is positioned below the surface of the washing liquid in each stage of the washing process; The bubbler (21) is connected to the air supply pipe (23), which is connected to an external compressed air source to supply compressed air to the bubbler (21); the top of the bubbler (21) is provided with an exhaust port (24) to facilitate the passage of compressed air. The bottom side of the bubbler (21) is provided with a drain outlet (25) for draining the water inside the bubbler (21).

4. The method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control according to claim 3, characterized in that, The bubbling device (11) also includes a fixing frame (22). The bubbler (21) is fixedly connected to the bracket (22) to fix the bubbler (21) below the liquid surface in the washing tank.

5. The method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control according to claim 3, characterized in that, The exhaust ports (24) are arranged along the long side of the bubbler (21) and are configured as two rows symmetrically arranged with respect to the short side central axis of the bubbler (21); or the exhaust ports (24) are arranged along the short side of the bubbler (21) and are configured as multiple rows evenly arranged along the long side of the bubbler (21).

6. The method for preparing polyacrylonitrile-based carbon fiber precursor by multi-stage tension control according to claim 3, characterized in that, The exhaust port (24) is a hole type or a straight bar type.

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