Preparation method of polyacrylonitrile carbon fiber precursor

Abstract

The invention provides a preparation method of a polyacrylonitrile carbon fiber precursor. The preparation method comprises the following steps: forming a series of nascent fibers in a transition solidification state in a coagulation bath; the series of nascent fibers in the transition solidification state are slowly solidified through a tow arrangement device, series of solidified fibers are formed, the tow arrangement device is located outside the solidification bath and comprises a positioning guide rod, and all fiber tows are guided and solidified under the limiting effect of all guide grooves of the positioning guide rod; and carrying out post-treatment on the series of solidified fibers to obtain the series of polyacrylonitrile carbon fiber precursors. According to the invention, the phenomena of fuzzing and yarn breaking caused by mutual adhesion of tows on adjacent spinning positions due to lack of necessary traction and guide at a coagulating bath outlet are effectively avoided, so that the original yarn density CV value is reduced; meanwhile, the size of the corresponding coagulating bath does not need to be designed to be too large, production operation is facilitated, and occupied production space is reduced to a certain extent.

Description

Technical Field

[0001] The invention belongs to the technical field of polyacrylonitrile carbon fiber precursor preparation, and specifically relates to a method for preparing polyacrylonitrile carbon fiber precursor. Background Art

[0002] Polyacrylonitrile carbon fiber is a main reinforcement for composite materials. It has excellent properties such as high specific strength, high specific modulus, low density, and corrosion resistance. It is widely used in various fields of the national economy, such as aerospace, aviation, wind power, high-pressure gas cylinders, building reinforcement, and sporting goods. Since the production and manufacturing costs of polyacrylonitrile carbon fiber have been at a high level for a long time, it is difficult to meet the growing industrial demand. As the application fields of high-performance fibers and their composite materials in my country continue to expand, the high performance, stable quality, and low-cost production of carbon fibers will be the mainstream direction of the development of domestic carbon fiber and its composite materials technology in the future.

[0003] The manufacturing cost of polyacrylonitrile carbon fiber is mainly related to factors such as raw material cost, process flow setting, energy consumption utilization rate and production capacity scale. At present, the main means to reduce the cost of polyacrylonitrile carbon fiber are: producing large tow carbon fiber, using low-cost precursors such as lignin, and expanding the scale of single-line production. Studies have shown that with the increase in production scale and output, the production cost of carbon fiber is on a downward trend.

[0004] In the process of developing large-scale complete sets of production technology for carbon fiber, problems such as unstable quality of carbon fiber products, many hairy fibers and clumps, and high defective rates are prone to occur. The designed production capacity has been delayed, resulting in poor process application performance of carbon fiber products. For carbon fiber precursor, the main means of expanding the production scale include increasing the spinneret speed, that is, increasing the spinning speed and increasing the number of spinning positions. With the increase of the spinneret speed, the residence time of the nascent fiber in the coagulation bath becomes shorter. The existing technology achieves the equivalent by lengthening the coagulation bath immersion length or adjusting the coagulation bath parameters, resulting in the coagulation bath tank being too large to be convenient for production operation, and the nascent fiber having poor density. With the increase of the number of spinning positions, the existing technology easily leads to problems such as the fibers in adjacent spinning positions sticking to each other, many hairy fibers and broken fibers, and a large CV value of the linear density of the obtained precursor. Summary of the invention

[0005] Therefore, the present invention provides a method for preparing polyacrylonitrile carbon fiber precursor, which can solve the technical problems in the prior art that adjacent spinning position fibers in multi-spinning position spinning equipment are stuck to each other in the coagulation bath, resulting in many broken fibers and a large CV value of the prepared precursor line density.

[0006] In order to solve the above problems, the present invention provides a method for preparing polyacrylonitrile carbon fiber precursor, comprising the following steps:

[0007] Spinning and coagulation process: the polyacrylonitrile spinning stock solution passes through a series of metering devices and then passes through a spinneret assembly to form a spinning fine flow, and the spinning fine flow passes through an air section and enters a coagulation bath to undergo phase separation, thereby forming a series of primary fibers in a transitional coagulation state, and the series of primary fibers are pulled and run in the coagulation bath for a first target time;

[0008] Tow finishing process: slowly solidify the series of primary fibers in the transitional solidification state through a tow finishing device to form a series of solidified fibers, the time for the fiber tows to be pulled and traveled in the tow finishing device is not less than a second target time, and the second target time is greater than the first target time, the tow finishing device is outside the coagulation bath, and the tow finishing device includes a positioning guide rod, and each strand of the fiber tow is guided and solidified under the limiting action of each guide groove of the positioning guide rod;

[0009] Post-processing step: post-processing the series of coagulated fibers to obtain a series of polyacrylonitrile carbon fiber precursors.

[0010] In some embodiments, the spinning speed of the spinning fine stream is not less than 10 m / min.

[0011] In some embodiments, the solvent concentration C1 of the liquid on the surface of the nascent fibers at the bundle inlet of the bundle finishing device and the solvent concentration C2 of the liquid on the surface of the coagulated fibers at the bundle outlet of the bundle finishing device are obtained, and the difference (C2-C1) between C2 and C1 is obtained. When the difference (C2-C1) is greater than the preset concentration difference A, the spinning flow jet speed is reduced.

[0012] In some embodiments, 0.5%≤A≤2%.

[0013] In some embodiments, the first target duration is 3.5s to 6.0s, the second target duration is 20s to 125s, and the number of spinning positions in the spinning and coagulation process is not less than 60.

[0014] In some embodiments, the filament bundle finishing device also includes deflection rollers arranged one by one corresponding to each spinning position, and each deflection roller guides each nascent fiber drawn out of the coagulation bath at each spinning position in parallel to the guide groove of the positioning guide rod after deflecting by a preset angle in the horizontal plane.

[0015] In some embodiments, the preset angle is 90°; and / or, the filament bundle sorting device further includes a stranding guide rod, which is located at the outlet end of the filament bundle sorting device, and has a stranding groove on the top surface, each stranding groove being able to merge a preset number of fiber bundles into one strand.

[0016] In some embodiments, the deviation angle of the center line of each fiber bundle twisted in each twisting groove is no more than 1°.

[0017] In some embodiments, the filament bundle arrangement device further includes a plurality of supporting guide rollers, and the positioning guide rods are multiple, and the supporting guide rollers and the positioning guide rods are alternately arranged along the traction direction of the fiber bundle.

[0018] In some embodiments, the filament bundle arrangement device further includes a plurality of liquid receiving pans, each of which is correspondingly disposed in an area below each of the supporting guide rollers, the positioning guide rod, and the stranding guide rod.

[0019] The method for preparing polyacrylonitrile carbon fiber precursor provided by the present invention has the following beneficial effects:

[0020] The spinning streams of each spinning position (corresponding to the number of spinning components) first enter the coagulation bath to undergo phase separation and coagulation to form a series of primary fibers in a transitional coagulation state, and the aforementioned series of primary fibers in a transitional coagulation state are further pulled into the tow finishing process outside the coagulation bath for stranding and guiding to achieve final coagulation into a series of coagulated fibers. That is, after the spinning streams undergo phase separation and achieve preliminary coagulation in the coagulation bath, they can be pulled into the tow finishing device to rely on longer slow coagulation, which can significantly reduce the residence time of the fiber tow in the coagulation bath, and effectively avoid the occurrence of fluffing and broken fibers caused by the adhesion of tows on adjacent spinning positions at the coagulation bath outlet due to the lack of necessary traction and guidance, thereby reducing the CV value of the original fiber line density; at the same time, the volume of the corresponding coagulation bath does not need to be designed to be too large, which facilitates production operations and reduces the occupation of production space and the amount of solution used to a certain extent;

[0021] The solvent concentration of the surface liquid of the fiber bundle at the bundle inlet and the bundle outlet of the bundle finishing device is obtained in real time, and it can be judged whether the solvent content in the fiber bundle meets the standard by the size relationship between the solvent concentration difference of the surface liquid of the fiber bundle before and after entering and exiting the bundle finishing device and the preset concentration difference. If it is less than the preset concentration difference A, it means that the solvent content meets the standard, and the density of the finally prepared carbon fiber precursor will also be within a better range. Otherwise, it means that the density of the finally prepared carbon fiber precursor is poor. At this time, the spinning fine flow jet speed is reduced, and the residence time of the primary fiber in the coagulation bath is increased to a certain extent. At the same time, the coagulation time of the fiber bundle in the bundle finishing device is further reduced, thereby ensuring the full diffusion and separation of the solvent in the fiber bundle;

[0022] By means of deflection rollers arranged one by one corresponding to each spinning position, each spun fiber drawn out of the coagulation bath is deflected 90° and then introduced into a tow finishing device. In this way, the distance between each parallel and spaced strand of spun fiber tow drawn out from the coagulation bath can be shortened after being deflected by a preset angle. That is, there is no need to be limited by the distance between each spinning position, but it is only necessary to ensure that the fiber tows in the transitional coagulation state or even in the coagulation state do not contact each other. The deflection of the traction path of the fiber tow can be used to reduce the space occupied by the tow, especially when there are many spinning positions, the demand for working space can be significantly reduced, which is conducive to meeting the needs of large-scale spinning operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0024] Figure 1 Schematic diagram of the steps of the method for preparing polyacrylonitrile carbon fiber precursor according to an embodiment of the present invention;

[0025] Figure 2 1 is a schematic diagram of a top view of a tow arrangement device used in a method for preparing polyacrylonitrile carbon fiber precursor according to an embodiment of the present invention, in which only part of the spun fibers and part of the deflection rollers are shown;

[0026] Figure 3 This is an electron microscope image of the axial structure of the polyacrylonitrile carbon fiber precursor (T800 grade carbon fiber precursor) prepared in Example 1 of the present invention;

[0027] Figure 4 This is an electron microscope image of the axial structure of the polyacrylonitrile carbon fiber precursor (T700 grade carbon fiber precursor) prepared in Example 2 of the present invention.

[0028] The accompanying drawings are marked as follows:

[0029] 11. Positioning guide rod; 12. Deflection roller; 13. Plying guide rod; 14. Support guide roller. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the devices or elements referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention. The directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0032] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90° or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0033] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0034] See also Figures 1 to 4 As shown, according to an embodiment of the present invention, a method for preparing polyacrylonitrile carbon fiber precursor is provided, comprising the following steps:

[0035] Spinning and coagulation process: the polyacrylonitrile spinning stock solution passes through a series of metering devices (not shown in the figure) and then passes through a spinning assembly (not shown in the figure) to form a spinning fine flow, and the spinning fine flow passes through the air section and enters the coagulation bath to undergo phase separation, forming a series of primary fibers in a transitional coagulation state, and the series of primary fibers are pulled and run in the coagulation bath for a first target time. The aforementioned transitional coagulation state is a state before the complete coagulation state, specifically refers to: the bidirectional diffusion of the solvent and the coagulant in the primary filaments (i.e., the primary fibers) is in a transitional state, and is at a level where diffusion equilibrium has not yet been reached. The filaments drawn out in this state can continue to undergo bidirectional diffusion at a lower rate, so as to achieve uniform coagulation and molding of the primary filaments, and ensure the density within the monofilaments and the consistency between the monofilaments;

[0036] Tow finishing step: the series of as-spun fibers in the transitional solidification state are passed through a tow finishing device (such as Figure 2 The fiber bundle is slowly coagulated in the fiber bundle finishing device (as shown) to form a series of coagulated fibers. The time for the fiber bundle to be pulled and walked in the fiber bundle finishing device is not less than the second target time, and the second target time is greater than the first target time. The fiber bundle finishing device is outside the coagulation bath. The fiber bundle finishing device includes a positioning guide rod 11. Each strand of the fiber bundle is guided and coagulated under the limiting action of each guide groove (not shown and not labeled) of the positioning guide rod 11. It can be understood that the number of the aforementioned guide grooves is the same as the number of spinning positions, that is, the same as the number of strands of the nascent fiber. Specifically, when the number of strands of the nascent fiber is 60, the number of guide grooves on one positioning guide rod 11 is also 60. The guide grooves are arranged at equal intervals along the length direction of the positioning guide rod 11, and are positioned with equal widths with the series of nascent fibers. In a specific embodiment, the equal width spacing of each guide groove is 15 mm to 25 mm, which can prevent the spacing from being too large, wasting space and increasing costs. If the spacing is too small, the fibers are prone to twisting and uneven force, which is not conducive to improving the uniformity of fiber structure and performance.

[0037] Post-processing step: post-processing the series of coagulated fibers to obtain a series of polyacrylonitrile carbon fiber precursors, specifically including: washing, oiling, drying and densification and steam drawing the series of coagulated fibers in sequence to obtain polyacrylonitrile carbon fiber precursors. It should be noted that the series in the aforementioned series of primary fibers and series of coagulated fibers refers to a fiber bundle with a large number of strands, generally not less than 60 strands, and at this time, the corresponding number of spinning positions in the spinning and coagulation process is not less than 60.

[0038] In this technical solution, the spinning streams of each spinning position (corresponding to the number of spinning assemblies) first enter the coagulation bath to undergo phase separation and coagulation to form a series of primary fibers in a transitional coagulation state, and the aforementioned series of primary fibers in a transitional coagulation state are further pulled into the strand finishing process outside the coagulation bath for stranding and guiding to achieve final coagulation into a series of coagulated fibers, that is, the spinning streams can be pulled into the strand finishing device after phase separation and initial coagulation in the coagulation bath, and can significantly reduce the residence time of the fiber bundles in the coagulation bath by relying on longer slow coagulation. Effectively avoid the occurrence of fluffing and broken wires caused by the mutual adhesion of the bundles on adjacent spinning positions at the outlet of the coagulation bath due to the lack of necessary traction and guidance, thereby reducing the CV value of the original fiber line density; at the same time, slow coagulation effectively improves the structural uniformity of the epidermis and core of the primary fiber, thereby reducing the CV value of the mechanical properties of the original fiber; at the same time, the volume of the corresponding coagulation bath does not need to be designed too large, which is convenient for production operation and reduces the occupation of production space and the amount of solution used to a certain extent, reducing production costs.

[0039] In some embodiments, the spinning fine stream spinning speed is not less than 10m / min, which prevents the primary fibers from being completely solidified during their stay in the coagulation bath, resulting in a large structural difference between the skin and the core of the primary fibers formed at a faster diffusion rate, thereby making the prepared carbon fiber precursor have poor density, poor uniformity of structure and performance. In addition, a slower spinning speed is not conducive to improving the spinning production efficiency and is not conducive to the industrial promotion of spinning. A faster spinning speed can reduce time costs while increasing production capacity.

[0040] In some embodiments, the solvent concentration C1 of the liquid on the surface of the nascent fibers at the bundle inlet of the bundle finishing device and the solvent concentration C2 of the liquid on the surface of the coagulated fibers at the bundle outlet of the bundle finishing device are obtained, and the difference (C2-C1) between C2 and C1 is obtained. When the difference (C2-C1) is greater than the preset concentration difference A, the spinning stream spinneret speed is reduced. It can be understood that the spinning stream spinneret speed here should also meet the requirement of not less than 10m / min after being reduced.

[0041] In this technical solution, by real-time detection of the solvent concentration of the surface liquid of the fiber bundle at the bundle inlet and the bundle outlet of the bundle finishing device, it can be judged whether the solvent content in the fiber bundle meets the standard by measuring the size relationship between the solvent concentration difference of the surface liquid of the fiber bundle before and after entering and exiting the bundle finishing device and the preset concentration difference. If it is less than the preset concentration difference A, it means that the solvent content meets the standard, and the density of the finally prepared carbon fiber precursor will also be within a better range. Otherwise, it means that the density of the finally prepared carbon fiber precursor is poor. At this time, the spinning fine stream jet speed is reduced, and the residence time of the primary fiber in the coagulation bath is increased to a certain extent. At the same time, the coagulation time of the fiber bundle in the bundle finishing device can be further reduced, thereby ensuring sufficient diffusion of the solvent in the fiber bundle.

[0042] In a specific embodiment, 0.5%≤A≤2%, that is, in this embodiment, in order to ensure the density of the finally prepared carbon fiber tow, when the difference 0.5%≤(C2-C1)≤2%, it means that the traction speed of the spun fiber is within a reasonable range, and when the difference (C2-C1)>2%, it means that the traction speed of the spun fiber is too fast, which leads to insufficient residence time in the coagulation bath and the tow finishing device, and the solvent diffusion and separation in the fiber tow is not thorough enough, and the density of the finally prepared carbon fiber tow will deviate, and when the difference (C2-C1)<0.5%, it means that the traction speed of the spun fiber is too slow or the residence time in the coagulation bath is too long, resulting in low production efficiency, which is not conducive to reducing production costs.

[0043] The specifications of the aforementioned spinneret assembly may be, for example, 3K, 4K, or 6K, which may be reasonably selected according to actual production requirements.

[0044] In a feasible embodiment, the first target time is 3.5s to 6.0s, and the second target time is 20s to 125s, that is, the fiber residence time in the tow finishing device is much longer than the fiber residence time in the coagulation bath. This can significantly reduce the volume of the coagulation bath, and can also reduce the amount of reagent solution in the coagulation bath, thereby facilitating production operations and reducing production costs.

[0045] See Figure 2 As shown, in some embodiments, the filament bundle finishing device also includes a deflection roller 12 arranged one by one corresponding to each spinning position, and each deflection roller 12 guides each nascent fiber drawn out from the coagulation bath at each spinning position in parallel to the guide groove of the positioning guide rod 11 after deflecting by a preset angle in the horizontal plane. The aforementioned preset angle is generally 90° to 93°, preferably 90°.

[0046] In this technical solution, each nascent fiber drawn out of the coagulation bath is deflected 90° by the deflection rollers 12 arranged one by one corresponding to each spinning position and then introduced into the tow finishing device, so that the distance between each strand of parallel and spaced nascent fiber tow drawn out of the coagulation bath can be shortened after being deflected by a preset angle, that is, it is not necessary to be limited by the distance between each spinning position, but only needs to ensure that the fiber tows in the transitional coagulation state or even the coagulation state do not contact each other, and the deflection of the fiber tow traction path can be used to reduce the space occupied by the tow, especially when there are many spinning positions, it can significantly reduce the demand for working space, so as to meet the needs of large-scale spinning operations. Especially when the deflection angle is 90°, the space occupied by the fiber tow can be minimized.

[0047] It should be noted that Figure 2 The orientation shown is for reference. The primary fibers formed by spinning at each spinning position are pulled from top to bottom. After passing through the corresponding deflection roller 12, the corresponding primary fibers are deflected 90° and then pulled from left to right. It can be understood that in order to ensure that the primary fibers are still in a parallel and spaced state after deflection, the arrangement position of each deflection roller 12 is also along Figure 2 The directions shown are different up and down.

[0048] In a preferred embodiment, the filament bundle sorting device also includes a stranding guide rod 13, which is located at the outlet end of the filament bundle sorting device. The top surface of the stranding guide rod 13 is provided with a stranding groove (not shown and not labeled in the figure), and each stranding groove can combine a preset number of fiber bundles into one strand, thereby meeting the requirements for different stranding quantities.

[0049] In a preferred embodiment, the aforementioned positioning guide rod 11 and the stranding guide rod 13 are specifically fixed with different structures, that is, the guide groove on the aforementioned positioning guide rod 11 and the stranding groove of the stranding guide rod 13 only need to be constructed on the top surface of the rod body, which can effectively reduce the installation space of the positioning guide rod 11 and the stranding guide rod 13. For example, when the aforementioned positioning guide rod 11 and the stranding guide rod 13 are both driven rotatable structures, it is necessary to set annular guide grooves and stranding grooves in the circumferential direction of the rod body, which will require increasing the diameter of the rod body and occupy the installation space.

[0050] In some embodiments, the centerline deviation angle of each fiber tow stranded in each stranding groove is no more than 1°, which can further reduce the overall width of the tow finishing device (i.e. Figure 2The upper and lower heights in the direction shown) are further reduced to occupy the working space; and / or, the stranding guide rods 13 have at least two, and each of the stranding guide rods 13 is arranged in sequence front and back along the traction direction of the fiber bundle. In a specific embodiment, the width of the stranding groove upstream in the traction direction is greater than the width of the stranding groove downstream, so that the fiber bundles in each stranding groove can be stranded step by step, ensuring that the deflection angle of each fiber bundle is small, which can further reduce the friction between the surface of the fiber bundle and the stranding groove. The occurrence of fuzzing and even broken wires can be reduced.

[0051] In some embodiments, the tow arrangement device further comprises a plurality of supporting guide rollers 14, and the positioning guide rods 11 have a plurality of supporting guide rollers 14 and the positioning guide rods 11 are alternately arranged along the traction direction of the fiber tow to form reliable support for the traction of the fiber tow in the tow arrangement device. In a specific embodiment, the supporting guide roller 14 is a passive roller or a stationary roller, preferably a stationary roller, with a diameter of φ40mm-80mm.

[0052] In a specific embodiment, the drafting ratio of the spun fiber in the tow finishing device is 0.99-1.05 to prevent the tow from being too loose and unable to run due to too small drafting, and being too large to cause the tow to be easily pulled to produce fuzz and breakage; the operating environment temperature of the tow finishing device is 10°C-30°C.

[0053] In some embodiments, the filament bundle finishing device also includes a plurality of liquid receiving trays (not shown in the figure), each of which is correspondingly arranged in the lower area of ​​each of the supporting guide rollers 14, the positioning guide rods 11 and the twisting guide rods 13, so as to be able to recover the liquid formed by the contact between the fiber bundle and the corresponding rod body or roller body. In a specific embodiment, each of the aforementioned liquid receiving trays is connected to the coagulation bath through a corresponding pipeline, so that the solution collected therein can be returned to the coagulation bath for reuse, thereby saving production costs.

[0054] Furthermore, the coagulated fiber formed in the aforementioned preparation method has a crystallinity of 20%-30%, a tensile strength of ≥100MPa, and an elongation of ≥230%; the polyacrylonitrile carbon fiber precursor prepared by the aforementioned preparation method of the present invention has a crystallinity of 60%-80%, a linear density CV value of ≤0.6%, and a bulk density of ≥1.18g / cm 3 , tensile strength ≥ 600MPa, tensile strength CV value ≤ 2.0%, elongation ≥ 7%, elongation CV value ≤ 2.0%.

[0055] The preparation method of the present invention is further described below in conjunction with several embodiments:

[0056] Example 1

[0057] In this embodiment, polyacrylonitrile carbon fiber precursor is prepared, and the number of spinning positions is 80. The specific steps are as follows:

[0058] 1. Spinning and coagulation process: The polyacrylonitrile spinning solution with a viscosity of 120Pa.s passes through 80 metering devices and then passes through a 3K spinning assembly to form a spinning fine flow, and the spinning speed is 10m / min. The spinning fine flow passes through a 6mm air section and enters a coagulation bath with a DMSO (dimethyl sulfoxide) concentration of 35% and a temperature of 5°C to undergo phase separation. The coagulation bath residence time is 5.7s, forming 80 bundles of nascent fibers in a transitional coagulation state.

[0059] 2. Tow finishing process: 80 bundles of spun fibers in a transitional solidification state are deflected 90° and passed through the tow finishing device. The supporting guide roller 14 is a stationary roller with a diameter of φ40mm. The spun fibers pass through the positioning guide rod 11 at an equal width interval of 20mm. The temperature of the tow finishing device is 20°C, the drafting ratio is 1.00, the residence time of the spun fibers is 40-119.8s, and the residence time of each adjacent bundle of spun fibers increases by 1.4s. The DMSO solvent concentration (C2) of the liquid surrounding the coagulated fibers at the outlet of the tow finishing process is 36.25%, and the solvent concentration (C1) of the liquid surrounding the spun fibers at the inlet is 35.63%. The difference between C2 and C1 is 0.62%.

[0060] 80 bundles of spun fibers are converted into 20 bundles of 12K coagulated fibers through the plying guide rod 13. The spun fibers deviate from the center line by an angle of 0.55° through the plying guide rod 13. The coagulated fibers have a crystallinity of 28.5%, a tensile strength of 141 MPa, and an elongation of 280%.

[0061] Post-treatment process: The obtained coagulated fiber was washed with water at a gradient temperature of 40 to 60°C, stretched with hot water at a gradient temperature of 85 to 90°C, oiled (oil concentration 2.5%), dried and densified (temperature 120 to 140°C), and steam stretched (pressure 0.6MPa) to obtain polyacrylonitrile carbon fiber precursor. The prepared polyacrylonitrile carbon fiber precursor had a crystallinity of 76.3%, a linear density CV value of 0.5%, and a bulk density of 1.183 g / cm 3 , tensile strength 780MPa, tensile strength CV value 1.56%; elongation 8.2%, elongation CV value 1.60%.

[0062] Example 2

[0063] In this embodiment, polyacrylonitrile carbon fiber precursor is prepared, and the number of spinning positions is 72. The specific steps are as follows:

[0064] 1. Spinning and coagulation process: The polyacrylonitrile spinning solution with a viscosity of 120Pa.s passes through 72 metering devices and then passes through a 4K spinneret assembly to form a spinning fine flow, and the spinning speed is 14.5m / min. The spinning fine flow passes through a 6mm air section and enters a coagulation bath with a DMSO concentration of 35% and a temperature of 5°C to undergo phase separation. The coagulation bath residence time is 4.1s, forming 72 bundles of nascent fibers in a transitional coagulation state.

[0065] 2. Tow finishing process: 72 bundles of spun fibers in a transitional solidification state are deflected 90° and passed through the tow finishing device. The supporting guide roller 14 is a stationary roller with a diameter of φ60mm. The spun fibers pass through the positioning guide rod 11 at an equal width interval of 25mm. The temperature of the tow finishing device is 20°C, the draft ratio is 1.02, the residence time of the spun fibers is 26.8-93.5s, and the residence time of each adjacent bundle of spun fibers increases by 0.967s. The DMSO solvent concentration (C2) of the liquid surrounding the coagulated fibers at the outlet of the tow finishing process is 36.62%, and the solvent concentration (C1) of the liquid surrounding the spun fibers at the inlet is 35.43%. The difference between C2 and C1 is 1.19%.

[0066] 72 bundles of spun fibers pass through the plying guide rod 13 to become 24 bundles of 12K coagulated fibers. The spun fibers pass through the plying guide rod 13 and deviate from the center line by an angle of 0.67°. The coagulated fibers have a crystallinity of 26.4%, a tensile strength of 120 MPa, and an elongation of 290%.

[0067] Post-processing process: the coagulated fiber is washed with water at a gradient temperature of 40 to 60°C, stretched with hot water at a gradient temperature of 85 to 90°C, oiled (oil concentration 2.5%), dried and densified (temperature 130 to 160°C), and steam stretched (pressure 0.6MPa) to obtain polyacrylonitrile carbon fiber precursor. The prepared polyacrylonitrile carbon fiber precursor has a crystallinity of 73.6%, a linear density CV value of 0.45%, a bulk density of 1.181g / cm3, a tensile strength of 630MPa, a tensile strength CV value of 1.68%, an elongation of 8.1%, and an elongation CV value of 1.70%.

[0068] It is easy for those skilled in the art to understand that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0069] The above description is only 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 principle of the present invention shall be included in the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention. These improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing polyacrylonitrile carbon fiber precursor, characterized in that: The steps include: Spinning and coagulation process: the polyacrylonitrile spinning stock solution passes through a series of metering devices and then passes through a spinneret assembly to form a spinning fine flow, and the spinning fine flow passes through an air section and enters a coagulation bath to undergo phase separation, thereby forming a series of primary fibers in a transitional coagulation state, and the series of primary fibers are pulled and run in the coagulation bath for a first target time; Tow finishing process: slowly solidify the series of primary fibers in the transitional solidification state through a tow finishing device to form a series of solidified fibers, the time for the fiber tows to be pulled and run in the tow finishing device is not less than a second target time, and the second target time is greater than the first target time, the tow finishing device is outside the coagulation bath, and the tow finishing device comprises a positioning guide rod (11), and each strand of the fiber tow is guided and solidified under the limiting action of each guide groove of the positioning guide rod (11); Post-processing step: post-processing the series of coagulated fibers to obtain a series of polyacrylonitrile carbon fiber precursors.

2. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 1, characterized in that: The spinning fine stream has a spinning speed of not less than 10 m / min.

3. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 2, characterized in that: The solvent concentration C1 of the liquid on the surface of the nascent fibers at the inlet of the tow finishing device and the solvent concentration C2 of the liquid on the surface of the coagulated fibers at the outlet of the tow finishing device are obtained, and the difference (C2-C1) between C2 and C1 is obtained. When the difference (C2-C1) is greater than the preset concentration difference A, the spinning flow jet speed is reduced.

4. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 3, characterized in that: 0.5％≤A≤2％。 5. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 1, characterized in that: The first target time is 3.5s to 6.0s, and the second target time is 20s to 125s; the number of spinning positions in the spinning and coagulation process is not less than 60.

6. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 1, characterized in that: The tow arrangement device also includes deflection rollers (12) arranged one by one in correspondence with each spinning position, and each deflection roller (12) guides each nascent fiber drawn out of the coagulation bath at each spinning position in parallel to a guide groove respectively provided on the positioning guide rod (11) after being deflected by a preset angle in a horizontal plane.

7. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 6, characterized in that: The preset angle is 90°; and / or, the filament bundle sorting device further comprises a stranding guide rod (13), the stranding guide rod (13) is located at the outlet end of the filament bundle sorting device, and a stranding groove is provided on the top surface of the stranding guide rod (13), each stranding groove can combine a preset number of fiber bundles into one strand.

8. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 7, characterized in that: The deviation angle of the center line of each fiber bundle twisted in each twisting groove is no more than 1°.

9. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 7, characterized in that: The fiber bundle arrangement device also includes a plurality of supporting guide rollers (14), and the positioning guide rods (11) are multiple, and the supporting guide rollers (14) and the positioning guide rods (11) are alternately arranged along the pulling direction of the fiber bundle.

10. The method for preparing polyacrylonitrile carbon fiber precursor according to claim 9, characterized in that: The yarn bundle arrangement device also includes a plurality of liquid receiving pans, each of which is correspondingly arranged in the area below each of the supporting guide rollers (14), the positioning guide rods (11) and the stranding guide rods (13).

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