Multi-field synergistic PBO high-speed liquid crystal spinning method

Abstract

The invention belongs to the technical field of high-performance fiber manufacturing, particularly provides a multi-field collaborative PBO high-speed liquid crystal spinning method, aims to solve the technical problems of large fiber diameter dispersion coefficient, poor strength consistency in batches and high yarn breaking rate in high-speed spinning, and can realize high orientation of molecular chains and surface homogenization regulation and control. The method is characterized in that a uniform composite drafting flow field, a uniform temperature gradient temperature field, a uniform flow gradient gas cutting field and a uniform pre-diffusion concentration field are applied in a spinning channel from an outlet of a spinneret orifice to an inlet of a coagulating bath; the diameter dispersion coefficient (CV value) of the fiber is less than or equal to 3.5%, the strength dispersion coefficient in a batch is less than or equal to 7.0%, the end breakage rate is less than or equal to 5 times / 100kg, the method is suitable for industrial continuous production, and the stability of subsequent composite material forming of the fiber is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of high-performance fiber manufacturing technology, specifically to a multi-field synergistic PBO high-speed liquid crystal spinning method, which can achieve high molecular chain orientation and surface uniformity control. Background Technology

[0002] PBO fiber, as a high-performance organic fiber, possesses excellent properties such as ultra-high strength, high modulus, and high temperature resistance, and is widely used in aerospace, defense, and high-end composite materials. In the high-speed liquid crystal spinning process of PBO, the spinning channel from the spinneret outlet to the coagulation bath inlet is a critical period for molecular chain orientation, fiber size formation, and strength development. However, existing technologies have the following problems: Traditional solutions lack a control mechanism for the "dispersion coefficient". A single stretching flow field is prone to causing local stress concentration. Uneven control of temperature field and air shear field leads to fiber diameter dispersion coefficient (CV value) generally ≥5% and batch strength dispersion coefficient ≥10%, which seriously affects the performance consistency of composite products. Large fiber bundle oscillation amplitude (≥±2mm), uneven curing rate and stress fluctuation lead to a breakage rate of ≥9 times / 100 kg during production, which reduces industrial production efficiency and increases production costs. Existing technologies lack a multi-field synergistic mechanism that focuses on "diameter consistency, strength stability, and production continuity," making it impossible to simultaneously balance the relationship among these three factors within the fiber exit window. This makes it difficult to meet the stringent requirements of high-end composite materials for core fiber indicators. Therefore, whether or not these problems can be solved is the focus of the inventor's research. Summary of the Invention

[0003] This invention provides a multi-field synergistic PBO high-speed liquid crystal spinning method, which can achieve high molecular chain orientation and surface homogenization control. This method does not employ electric field, ultrasonic, magnetic field, or micro-nano confinement control methods, and aims to solve the technical problems of large fiber diameter dispersion coefficient, poor batch strength consistency, and high fiber breakage rate in high-speed spinning (above 200 m / min). Within the spinning channel from the spinneret outlet to the coagulation bath inlet, a homogenized composite drawing flow field, a uniform temperature gradient field, a uniform flow gradient air shear field, and a homogenized pre-diffusion concentration field are applied. Through segmented matching of field strength and closed-loop control of the dispersion coefficient, the fiber diameter dispersion coefficient (CV value) is ≤3.5%, the batch strength dispersion coefficient is ≤7.0%, and the breakage rate is ≤5 times / 100 kg. This method is suitable for industrial continuous production and significantly improves the stability of subsequent fiber composite molding.

[0004] The specific technical solution of the present invention is as follows: A multi-field synergistic PBO high-speed liquid crystal spinning method, the specific steps of which are as follows: (1) Pretreatment of spinning solution Raw material selection: PBO polyphosphoric acid liquid crystal solution with an intrinsic viscosity of 27-28 dl / g is used, and the solid content is controlled at 14-16% to ensure the stability of the liquid crystal phase; Temperature and viscosity control: The material temperature in front of the spinneret is precisely controlled at 180-200℃ (fluctuation ≤ ±2℃) to avoid dimensional fluctuations caused by sudden changes in viscosity; Spinneret design: The spinneret uses a diameter of 0.25-0.35mm and an aspect ratio of 4-6. The outlet is designed with a 15° cone angle, which means that the outlet of the spinneret is a flared mouth to avoid stress abrupt changes caused by sharp edges. Pretreatment of the spinning solution provides a preliminary guarantee for the uniformity of subsequent spinning. (2) Multi-field coordinated control system In the spinning channel from the spinneret outlet to the coagulation bath inlet, a homogenized composite stretching flow field, a uniform temperature gradient field, a uniform flow gradient air shear field, and a homogenized pre-diffusion concentration field are applied. Through field strength segment matching and discrete coefficient closed-loop control, the diameter dispersion coefficient, batch strength dispersion coefficient, and fiber breakage rate are reduced. (3) Post-processing steps After undergoing multi-field coordinated control, the fiber bundle enters the coagulation bath from the spinning tunnel, and then proceeds through the following post-processing steps to obtain the finished PBO fiber: Coagulation bath: Enter the deionized water coagulation bath to achieve uniform coagulation; Multi-stage washing: Two-stage countercurrent washing removes residual polyphosphoric acid; Segmented drying: Dry in segments at 120-300℃ to avoid internal stress concentration and remove excess moisture; Winding: The winding rate is synchronized with the spinning rate.

[0005] Furthermore, the mechanism of the homogenized composite stretching flow field in step (2) is: to integrate the two-stage mechanism of "slow contraction stretching + constant stretching ratio stretching", control the stretching stress fluctuation ≤10%, and the spinneret outlet contraction angle 15°. The segmentation allocation is as follows: 0-25cm (spinneret outlet section): The 15° cone angle open design creates a uniform contraction and stretching field. Through a slow, linear, axisymmetric flow channel diameter expansion structure, the filament changes from "sudden contraction" to controllable slow contraction, and from "local concentrated stretching" to uniform stretching throughout the entire area, avoiding diameter unevenness caused by local stress concentration. Adapting to the viscoelastic properties and flow law of PBO polyphosphate liquid crystal solution, the 15° half-cone angle linear smooth open design allows the solution to flow through a continuous, stepless linear diameter expansion transition when it is extruded from the straight cylinder diameter section of the spinneret to the air section, thereby forming a uniform contraction and stretching field and completely avoiding the problem of local shear stress concentration from the source. In existing technologies, the spinning solution expands momentarily upon extrusion from the spinneret, which is a release of the elastic potential energy of the viscoelastic fluid and a process in which the polymer chains recover from a forced extended state to a naturally coiled state. At this time, under stretching force, it will contract rapidly. However, in this application, the linear expansion transition of the spinneret allows the spinning solution to gradually expand and stretch simultaneously, forming a uniform contraction and stretching field.

[0006] 25-100cm (Orientation Uniformity Stage): Through high-precision synchronous control, the traction roller speed fluctuation is ≤0.3%, maintaining a constant ratio between the traction roller linear speed and the melt extrusion linear speed at the spinneret, thus establishing a constant draw ratio. The purpose is to eliminate molecular chain disorientation caused by stretching fluctuations, ensuring uniform fiber axial strength, which is key to reducing the strength dispersion coefficient within a batch.

[0007] The draw ratio of this invention is not a fixed value, but is dynamically matched according to the target fiber fineness, spinning rate, and dosing characteristics. Draw ratio = traction roller linear speed / spinneret extrusion linear speed, wherein the spinneret extrusion linear speed is determined by the metering pump supply, spinneret diameter, and number of holes, which will not be elaborated further in this invention.

[0008] The homogenized composite drawing flow field provided by this invention integrates a two-stage mechanism of slow shrinkage drawing and constant draw ratio drawing. From 0-25cm, linear and smooth shrinkage drawing is formed through a 15° cone angle opening, which suppresses the extrusion swelling of the spinning fine stream and local stress concentration. From 25-100cm, a constant draw ratio is maintained through high-precision synchronous control, eliminating stretching fluctuations and molecular chain disorientation, achieving uniform and high orientation of molecular chains along the fiber axis, stabilizing the filament bundle morphology, reducing the diameter and strength dispersion coefficients, and ensuring smooth and continuous high-speed spinning.

[0009] Furthermore, the temperature gradient design of the uniform temperature gradient field in step (2) involves setting four temperature segments along the spinning path: a high-temperature uniform temperature field, a medium-temperature uniform temperature field, a medium-low-temperature uniform temperature field, and a low-temperature uniform temperature field; the corresponding temperatures are 185-195℃, 160-170℃, 130-140℃, and 100-110℃, respectively. The uniform temperature gradient field adopts a four-level gradient temperature control along the spinning path. Compared with a conventional single constant temperature field, it can gradually and steadily cool down along the spinning path, and the circumferential temperature is uniform and stable. This avoids the internal stress concentration caused by sudden cooling and heating of the filament bundle at a single temperature, reduces the breakage rate and the diameter / strength dispersion coefficient, and ensures continuous and stable high-speed spinning.

[0010] More specifically, to achieve the aforementioned temperature control, the tunnel is divided into four sections, corresponding to a high-temperature uniform temperature field, a medium-temperature uniform temperature field, a medium-low-temperature uniform temperature field, and a low-temperature uniform temperature field, respectively. A partition is installed on the inner side of the tunnel between each region, with through holes on the partition allowing the spinning stream to pass through. Air / steam outlets are evenly distributed on the tunnel wall above the partition. A separate tunnel interlayer is installed on the outer side of the tunnel above each air / steam outlet. Four sets of tunnel interlayers are installed on the outer sides of the tunnels corresponding to the high-temperature, medium-temperature, medium-low-temperature, and low-temperature uniform temperature fields, respectively. This ensures that the tunnel interlayers do not affect the airflow effect of the air / steam outlets.

[0011] Each tunnel interlayer is equipped with a separate air inlet. At distances of 5cm, 30cm, 55cm, and 80cm from the spinneret outlet, there are separate annular flow equalization air knives. These annular flow equalization air knives are actually a set of annular mesh holes set on the tunnel wall. On both the upper and lower sides of the mesh holes inside the tunnel, there are air guide plates. The angle between the air guide plates and the tunnel is ≤8°. With this design, the four sets of coaxial annular flow equalization air knives correspond to low-velocity air cutting fields, medium-velocity air cutting fields, medium-high-velocity air cutting fields, and high-velocity air cutting fields, respectively. The high-temperature gas in the corresponding temperature field enters the corresponding tunnel interlayer and fills the tunnel interlayer. Then, it enters the inner side of the tunnel through the coaxial annular flow equalization air knives. Since the angle between the air guide plates and the tunnel is ≤8°, the angle between the airflow direction and the spinning axis is also ≤8°, achieving a circumferentially uniform distribution of airflow.

[0012] Simultaneously, by controlling the inlet air velocity of different channel interlayers, the flow velocities of the low-velocity air-cutting field, medium-velocity air-cutting field, medium-high-velocity air-cutting field, and high-velocity air-cutting field along the filament exit path are controlled to be 4-6 m / s, 7-10 m / s, 12-16 m / s, and 18-22 m / s, respectively. The aforementioned uniform flow gradient air knife is set with a progressively increasing wind speed gradient along the spinning path, which can accurately match the strength and morphological changes of PBO spinning filaments from the soft state, orientation state to the solidified state. The low wind speed avoids the initial filaments from being blown off and deformed, while the medium-high wind speed progressively strengthens the filament attitude constraint and achieves uniform cooling in conjunction with the temperature field. This, combined with the molecular chain orientation, morphological locking, and stable solidification process, eliminates airflow disturbances and stress abrupt changes, reduces the diameter and strength dispersion coefficients, and ensures continuous and stable high-speed spinning. The function of the uniform flow gradient air-cutting field is to stabilize the filament attitude, reduce the oscillation amplitude, and avoid diameter fluctuations and filament breakage caused by environmental airflow interference; and to assist the temperature field in achieving uniform cooling and improving strength consistency.

[0013] Furthermore, the homogenization pre-diffusion concentration field device described in step (2) is designed as follows: a circumferentially symmetrical steam injection device is uniformly set on the tunnel wall corresponding to the medium-low temperature uniform field and the low temperature uniform field in the section 50-100cm from the spinneret outlet. Preferably, four injection holes are opened at the corresponding positions in the spinning tunnel to release phosphoric acid aqueous solution vapor and ensure uniform diffusion of the vapor. The injection holes pass through the corresponding tunnel interlayer and directly enter the tunnel, directly sending the phosphoric acid aqueous solution vapor into the tunnel to form a pre-diffusion field in the tunnel.

[0014] The aforementioned phosphoric acid aqueous solution vapor and the hot air used to maintain the uniform temperature field are both discharged from the tunnel through the air / steam outlets on the tunnel wall. Although the partitions are provided with through holes through which the spinning fine stream can pass, when the lower-level wind speed is higher than the upper-level wind speed, it can ensure that the spatial flow between the partitions is small, thereby minimizing the influence between the homogenized composite stretching flow field, the uniform temperature gradient field, the uniform flow gradient air shear field, and the homogenized pre-diffusion concentration field, and providing a more stable environment.

[0015] More specific concentration control: A high-concentration pre-diffusion field is set at 50-75cm (morphology locking stage), corresponding to a concentration range of 60-70wt% phosphoric acid aqueous solution, with a phosphoric acid aqueous solution spraying rate of 3000-5000mL / h in this section; a low-concentration pre-diffusion field is set at 75-100cm (stabilization and curing stage), corresponding to a concentration range of 20-30wt% phosphoric acid aqueous solution, with a phosphoric acid aqueous solution spraying rate of 3000-5000mL / h in this section.

[0016] The function of the above-mentioned homogenized pre-diffusion concentration field is to maintain the viscosity difference between the surface and core layers of the filament bundle, avoid dimensional deviations and uneven strength caused by excessively rapid local curing, and suppress relaxation of the molecular chain surface layer to reduce the risk of filament breakage.

[0017] Based on the above design concept, the segmented coordination under the optimal collaborative control mechanism (core indicator optimization logic) of this application is as follows: 0-25cm (Initial Uniform Stage): Slow-shrinkage stretching + high-temperature uniform field + low-flow-rate air-cutting field, initiate uniform initial orientation, stabilize the initial shape of the filament bundle, and lay the foundation for dimensional consistency. 25-50cm (uniform orientation stage): constant stretch ratio + medium temperature uniform field + medium flow rate air shearing field to ensure uniform arrangement of molecular chains and improve strength stability; 50-75cm (morphological locking stage): constant stretching ratio + medium and low temperature uniform temperature field + medium and high flow rate air shearing field + high concentration pre-diffusion field, slowly increase viscosity, lock size and strength structure, and reduce dispersion risk; 75-100cm (stabilized curing stage): constant stretch ratio + low temperature uniform field + high flow rate air cutting field + low concentration pre-diffusion field, uniform curing structure, avoiding filament deformation and filament breakage.

[0018] By employing the above-mentioned technical means, the present invention achieves the following beneficial effects compared with the prior art: (1) Significantly improved diameter consistency: The diameter dispersion coefficient (CV value) was reduced from ≥5% in the traditional scheme to ≤3.5%, providing a stable dimensional basis for composite material molding; (2) Significantly optimized strength stability: The strength dispersion coefficient within a batch is reduced from ≥10% in the traditional scheme to ≤7%, ensuring the uniformity of product performance; (3) Production continuity is significantly enhanced: the breakage rate is reduced from ≥9 times / 100 kg in the traditional scheme to ≤5 times / 100 kg, improving industrial production efficiency and reducing production costs. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the segmented collaborative structure of the multi-field collaborative control system of the present invention; Figure 2 This is a schematic cross-sectional view of the injection hole arrangement of the circumferentially symmetrical steam injection device in the homogenized pre-diffusion concentration field of the present invention, which has 4 injection holes. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to specific embodiments and data. These embodiments are merely illustrative and are not intended to limit the scope of the invention in any way.

[0021] The structure of the multi-field coordinated control system used in this application is as follows: Figure 1 As shown in the simplified diagram, the parts not shown in the diagram are conventional designs in the field, and the inventor will not elaborate further.

[0022] According to conventional processes, the spinning solution enters the spinneret assembly via a metering pump, is extruded from the spinneret into the spinning channel, forming a fine spinning stream. The fine spinning stream is then connected to the traction roller by manual traction and finally enters the coagulation bath to solidify and form the final product.

[0023] The feature of this application is that the tunnel is divided into four sections, corresponding to a high-temperature uniform temperature field, a medium-temperature uniform temperature field, a medium-low-temperature uniform temperature field, and a low-temperature uniform temperature field, respectively. A partition is provided on the inner side of the tunnel between each region, and the partition has through holes through which the spinning fine stream can pass. Air / steam outlets are evenly arranged on the tunnel wall above the partition. A separate tunnel interlayer is provided on the outer side of the tunnel above each air / steam outlet. There are four sets of tunnel interlayers, which are respectively arranged on the outer side of the tunnel corresponding to the high-temperature uniform temperature field, the medium-temperature uniform temperature field, the medium-low-temperature uniform temperature field, and the low-temperature uniform temperature field. In this way, the tunnel interlayer will not affect the air outlet effect of the air / steam outlet.

[0024] Each tunnel interlayer is equipped with a separate air inlet. At distances of 5cm, 30cm, 55cm, and 80cm from the spinneret outlet, there are individual annular flow equalization air knives. These annular flow equalization air knives are actually a set of annular mesh holes set on the tunnel wall. Guide plates are set on both the upper and lower sides of the mesh holes inside the tunnel. The angle between the guide plates and the tunnel is ≤8°. With this design, the four sets of coaxial annular flow equalization air knives correspond to low-velocity air cutting fields, medium-velocity air cutting fields, medium-high-velocity air cutting fields, and high-velocity air cutting fields, respectively. The high-temperature gas in the corresponding temperature field enters the corresponding tunnel interlayer and fills the tunnel interlayer. Then, it enters the inner side of the tunnel through the aforementioned coaxial annular flow equalization air knives. Since the angle between the guide plates and the tunnel is ≤8°, the angle between the airflow direction and the spinning axis is also ≤8°, achieving circumferential uniform distribution of airflow.

[0025] Simultaneously, by controlling the inlet air velocity of different channel interlayers, the flow velocities of the low-velocity air-cutting field, medium-velocity air-cutting field, medium-high-velocity air-cutting field, and high-velocity air-cutting field along the filament exit path are controlled to be 4-6 m / s, 7-10 m / s, 12-16 m / s, and 18-22 m / s, respectively. The aforementioned uniform flow gradient air knife is set with a progressively increasing wind speed gradient along the spinning path, which can accurately match the strength and morphological changes of PBO spinning filaments from the soft state, orientation state to the solidified state. The low wind speed avoids the initial filaments from being blown off and deformed, while the medium-high wind speed progressively strengthens the filament attitude constraint and achieves uniform cooling in conjunction with the temperature field. This, combined with the molecular chain orientation, morphological locking, and stable solidification process, eliminates airflow disturbances and stress abrupt changes, reduces the diameter and strength dispersion coefficients, and ensures continuous and stable high-speed spinning. The function of the uniform flow gradient air-cutting field is to stabilize the filament attitude, reduce the oscillation amplitude, and avoid diameter fluctuations and filament breakage caused by environmental airflow interference; and to assist the temperature field in achieving uniform cooling and improving strength consistency.

[0026] The homogenization pre-diffusion concentration field device is designed as follows: Circumferentially symmetrical steam injection devices are uniformly installed on the tunnel walls in the section 50-100cm from the spinneret outlet, corresponding to the medium-low temperature homogenization field and the low-temperature homogenization field. Figure 2 As shown, four injection holes are opened at corresponding positions in the spinning channel to release phosphoric acid aqueous solution vapor, ensuring uniform vapor diffusion. The injection holes pass through the corresponding channel interlayer and directly into the channel, sending the phosphoric acid aqueous solution vapor directly into the channel to form a pre-diffusion field within the channel.

[0027] The aforementioned phosphoric acid aqueous solution vapor and the hot air used to maintain the uniform temperature field are both discharged from the tunnel through the air / steam outlets on the tunnel wall. Although the partitions are provided with through holes through which the spinning fine stream can pass, when the lower-level wind speed is higher than the upper-level wind speed, it can ensure that the spatial flow between the partitions is small, thereby minimizing the influence between the homogenized composite stretching flow field, the uniform temperature gradient field, the uniform flow gradient air shear field, and the homogenized pre-diffusion concentration field, and providing a more stable environment.

[0028] Example 1: A multi-field synergistic PBO high-speed liquid crystal spinning method, the specific steps of which are as follows: (1) Pretreatment of spinning solution: Spinning solution: PBO polyphosphoric acid solution (solid content 15%, intrinsic viscosity 27.5 dl / g), spinneret temperature 180℃; spinneret parameters: orifice diameter 0.30 mm, aspect ratio 4:1, orifice shrinkage angle 15°; spinning rate 200 m / min; (2) Multi-field coordinated control system: Within the 0-100cm wire exit window from the spinneret outlet to the coagulation bath inlet, a homogenized composite drawing flow field, a uniform temperature gradient field, a uniform flow gradient air shear field, and a homogenized pre-diffusion concentration field are applied. The specifics of segmented collaboration are as follows: 0-25cm (Initial Uniform Stage): Slow-shrinkage stretching + high-temperature uniform field + low-flow-rate air-cutting field, initiate uniform initial orientation, stabilize the initial shape of the filament bundle, and lay the foundation for dimensional consistency. 25-50cm (uniform orientation stage): constant stretch ratio + medium temperature uniform field + medium flow rate air shearing field to ensure uniform arrangement of molecular chains and improve strength stability; 50-75cm (morphological locking stage): constant stretching ratio + medium and low temperature uniform temperature field + medium and high flow rate air shearing field + high concentration pre-diffusion field, slowly increase viscosity, lock size and strength structure, and reduce dispersion risk; 75-100cm (stabilized curing stage): constant stretch ratio + low temperature uniform temperature field + high flow rate air cutting field + low concentration pre-diffusion field, uniform curing structure, avoiding filament deformation and filament breakage. The specific parameters for each field are as follows: Homogenized composite drawing flow field: A linear, smooth, open design with a 15° semi-cone spinneret angle is used to achieve slow-shrinkage drawing in the 0-25cm stage; in the 25-100cm stage, a constant drawing ratio is constructed through high-precision synchronous control (speed fluctuation ≤0.3%). In this embodiment, by controlling the traction roller speed to 203.5 m / min and matching it with the metering pump speed, the drawing ratio is kept constant (speed fluctuation ≤0.3%), achieving uniform molecular chain orientation; Temperature gradient field: high temperature field, medium temperature field, medium-low temperature field, low temperature field, corresponding temperatures of 190℃, 165℃, 135℃, and 105℃ respectively. Uniform flow gradient air cutting field: The four sets of air knives correspond to the low flow rate air cutting field, medium flow rate air cutting field, medium-high flow rate air cutting field, and high flow rate air cutting field, respectively. That is, the flow rates along the yarn exit path are 5m / s, 8m / s, 14m / s, and 20m / s, respectively. The angle between the airflow direction and the spinning axis is ≤8°, and the airflow is uniformly distributed in the circumferential direction. Homogenize the pre-diffusion concentration field: The high-concentration pre-diffusion field corresponds to a 60wt% phosphoric acid aqueous solution with a spray rate of 3000mL / h; the low-concentration pre-diffusion field corresponds to a 20wt% phosphoric acid aqueous solution with a spray rate of 3000mL / h; a ring-shaped 4-point circumferentially symmetrical steam injection device is set up, that is, 4 injection holes are opened at the corresponding positions in the spinning channel to release phosphoric acid aqueous solution vapor and ensure uniform steam diffusion. (3) Post-processing steps After undergoing multi-field coordinated regulation, the fiber bundle enters the coagulation bath and sequentially performs the following post-processing steps to obtain the finished PBO fiber: Coagulation bath: Enter the deionized water coagulation bath to achieve uniform coagulation; Multi-stage washing: Two-stage countercurrent washing removes residual polyphosphoric acid; Segmented drying: Dry in segments at 120-300℃ to avoid internal stress concentration and remove excess moisture; Winding: The winding rate is synchronized with the spinning rate.

[0029] The diameter dispersion factor, batch strength dispersion factor, and breakage rate of the finished PBO fibers were tested. The specific test methods are as follows: Diameter dispersion coefficient test method: Randomly select 10 abnormal single filaments from the same batch of filament bundles, take 5 measuring points with a spacing of ≥2cm for each filament, measure the diameter using a laser diameter gauge, remove abnormal data using the Grubbs method (95% confidence level), and calculate the dispersion coefficient according to the coefficient of variation formula (diameter standard deviation / diameter arithmetic mean × 100%).

[0030] Test method for strength dispersion coefficient within batch: The linear density of the stable batch of fiber is assessed, and 3 rolls of fiber are randomly selected. High-strength PBO fiber filaments are randomly selected from the rolls for testing. Each sample is tested 5 times. The tensile strength of the fiber within the batch is tested according to GB / T 19975-2005. The breaking strength is recorded and invalid data at the clamping end are removed. The dispersion coefficient is calculated according to the formula of coefficient of variation (strength standard deviation / strength arithmetic mean × 100%).

[0031] Breakage rate test method: On-site operators count the number of fiber bundle breaks in real time during the production process (excluding non-process-related breaks such as human operation and sudden equipment failure), and simultaneously and accurately measure the actual net weight of PBO fibers produced in this cycle, and test the number of breaks per 100kg of fiber produced.

[0032] Test results: Diameter dispersion coefficient CV = 3.2%, intra-batch strength dispersion coefficient = 6.5%, breakage rate = 4 times / 100 kg.

[0033] Example 2: A multi-field synergistic PBO high-speed liquid crystal spinning method, the specific steps of which are as follows: (1) Pretreatment of spinning solution: Spinning solution: PBO polyphosphoric acid solution (solid content 16%, intrinsic viscosity 28 dl / g), spinneret temperature 183℃; Spinneret parameters: orifice diameter 0.32mm, length-to-diameter ratio 4:1, orifice contraction angle 15°; Spinning rate 220 m / min; (2) Pretreatment of spinning solution: Within the 0-100cm wire exit window from the spinneret outlet to the coagulation bath inlet, a homogenized composite drawing flow field, a uniform temperature gradient field, a uniform flow gradient air shear field, and a homogenized pre-diffusion concentration field are applied. In Segmented Coordination Example 1, the specific parameters for multiple fields are as follows: Homogenized composite drafting flow field: A linear, smooth, open design with a 15° semi-cone spinneret angle is used to achieve slow-shrink drafting, combined with constant draw ratio control. In this embodiment, the traction roller speed is 203.5 m / min, and the draw ratio is kept constant through synchronous control to achieve uniform orientation; Temperature gradient field: high temperature field, medium temperature field, medium-low temperature field, low temperature field, and low temperature field, with corresponding temperatures of 195℃, 170℃, 140℃, and 110℃ respectively. Uniform flow gradient air cutting field: The four sets of air knives correspond to the low flow rate air cutting field, medium flow rate air cutting field, medium-high flow rate air cutting field, and high flow rate air cutting field, respectively. That is, the flow rates along the yarn exit path are 6m / s, 10m / s, 16m / s, and 22m / s, respectively. The angle between the airflow direction and the spinning axis is ≤8°, and the airflow is uniformly distributed in the circumferential direction. Homogenize the pre-diffusion concentration field: The high-concentration pre-diffusion field corresponds to a 70wt% phosphoric acid aqueous solution with a spray rate of 4000mL / h; the low-concentration pre-diffusion field corresponds to a 30wt% phosphoric acid aqueous solution with a spray rate of 4000mL / h; set up a ring-shaped 4-point circumferentially symmetrical steam injection device, that is, open 4 injection holes at the corresponding positions in the spinning channel to release phosphoric acid aqueous solution vapor and ensure uniform steam diffusion. (3) The post-processing procedures and testing methods are the same as in Example 1. Test results: Diameter dispersion coefficient CV = 3.4%, intra-batch strength dispersion coefficient = 6.7%, breakage rate = 4 times / 100 kg.

[0034] Comparative example (traditional single-stretch flow field scheme) Spinning parameters: spinning rate 200m / min, PBO dosing solid content 15%, spinneret orifice diameter 0.30mm, using only a single stretching flow field, without uniform temperature gradient, uniform flow air shearing and pre-diffusion concentration field; the rest are conventional selections in this field.

[0035] Test results: Diameter dispersion coefficient CV = 5.3%, batch strength dispersion coefficient = 10.5%, breakage rate = 9 times / 100 kg, which is significantly different from the results of the example.

[0036] Therefore, it can be seen that the present invention adopts a synergistic system of "drawing-temperature-air shearing-concentration" of the entire physical field, which can specifically solve the three core problems of diameter dispersion, strength dispersion and wire breakage rate.

[0037] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art can utilize the above technical content to make changes or modifications to create equivalent embodiments. Any simple modifications, equivalent changes, and modifications made to the above embodiments without departing from the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A multi-field synergistic PBO high-speed liquid crystal spinning method, characterized in that, The specific steps are as follows: (1) Pretreatment of spinning solution Raw material selection: PBO polyphosphate liquid crystal solution with an intrinsic viscosity of 27-28 dl / g is used, and the solid content is controlled at 14-16%; Temperature and viscosity control: The material temperature in front of the spinneret is controlled at 180-200℃; Spinneret design: The spinneret has a diameter of 0.25-0.35mm and an aspect ratio of 4-6, and the outlet is set with a 15° cone angle open. (2) Multi-field coordinated control system In the spinning channel from the spinneret outlet to the coagulation bath inlet, a homogenized composite stretching flow field, a uniform temperature gradient field, a uniform flow gradient air shear field, and a homogenized pre-diffusion concentration field are applied. Through field strength segment matching and discrete coefficient closed-loop control, the diameter dispersion coefficient, batch strength dispersion coefficient, and fiber breakage rate are reduced. (3) Post-processing steps After undergoing multi-field coordinated regulation, the fiber bundle enters the coagulation bath and sequentially performs the following post-processing steps to obtain the finished PBO fiber: Coagulation bath: Enter the deionized water coagulation bath to achieve uniform coagulation; Multi-stage washing: Two-stage countercurrent washing removes residual polyphosphoric acid; Segmented drying: Dry in segments at 120-300℃ to avoid internal stress concentration and remove excess moisture; Winding: The winding rate is synchronized with the spinning rate.

2. The multi-field synergistic PBO high-speed liquid crystal spinning method according to claim 1, characterized in that, The mechanism of the homogenized composite stretching flow field described in step (2) is to integrate the two-stage mechanism of "slow contraction stretching + constant stretch ratio stretching", control the stretching stress fluctuation to ≤10%, and the spinneret outlet contraction angle to 15°; the segmented distribution is as follows: 0-25cm: A 15° cone angle opening forms a uniform contraction and stretching field, allowing the original liquid to be squeezed from the straight cylinder sizing section of the spinneret to the air section. The flow path is a continuous, stepless linear expansion transition, thus forming a uniform contraction and stretching field. 25-100cm: By controlling the rotational speed fluctuation to ≤0.3%, the ratio of the traction roller linear speed to the spinneret melt extrusion linear speed is kept constant, thus establishing a constant draw ratio.

3. The multi-field synergistic PBO high-speed liquid crystal spinning method according to claim 1, characterized in that, The temperature gradient design of the uniform temperature gradient field in step (2) is as follows: set up 4 temperature segments along the wire exit path, namely high temperature uniform temperature field, medium temperature uniform temperature field, medium and low temperature uniform temperature field and low temperature uniform temperature field; the corresponding temperatures of the four are 185-195℃, 160-170℃, 130-140℃ and 100-110℃ respectively.

4. The multi-field synergistic PBO high-speed liquid crystal spinning method according to claim 1 or 3, characterized in that, The spinning tunnel in step (2) is divided into four sections, corresponding to the high temperature uniform temperature field, the medium temperature uniform temperature field, the medium-low temperature uniform temperature field, and the low temperature uniform temperature field, respectively. A partition is provided on the inner side of the tunnel between each region. The partition is provided with through holes through which the spinning fine stream can pass. Air / steam outlets are evenly arranged on the tunnel wall above the partition. A separate tunnel interlayer is provided on the outer side of the tunnel above each air / steam outlet. There are four sets of tunnel interlayers, which are respectively arranged on the outer side of the tunnel corresponding to the high temperature uniform temperature field, the medium temperature uniform temperature field, the medium-low temperature uniform temperature field, and the low temperature uniform temperature field.

5. The multi-field synergistic PBO high-speed liquid crystal spinning method according to claim 4, characterized in that, In step (2), each tunnel interlayer is provided with a separate air inlet. At 5cm, 30cm, 55cm and 80cm from the spinneret outlet, a separate annular flow equalization air knife is provided. The above-mentioned annular flow equalization air knife is a set of annular mesh holes set on the tunnel wall. Air guide plates are provided on both the upper and lower sides of the mesh holes inside the tunnel. The included angle between the air guide plate and the tunnel is ≤8°.

6. The multi-field synergistic PBO high-speed liquid crystal spinning method according to claim 4, characterized in that, By controlling the inlet air velocity of different tunnel interlayers, the flow velocities of the low-velocity air shearing field, medium-velocity air shearing field, medium-high-velocity air shearing field, and high-velocity air shearing field are controlled to be 4-6 m / s, 7-10 m / s, 12-16 m / s, and 18-22 m / s respectively along the filament exit path.

7. The multi-field synergistic PBO high-speed liquid crystal spinning method according to claim 1, characterized in that, The homogenization pre-diffusion concentration field device in step (2) is designed as follows: a circumferentially symmetrical steam injection device is uniformly set on the channel wall corresponding to the medium-low temperature uniform field and the low temperature uniform field in the section 50-100cm from the spinneret outlet to release phosphoric acid aqueous solution vapor.

8. The multi-field synergistic PBO high-speed liquid crystal spinning method according to claim 7, characterized in that, A high-concentration pre-diffusion field was set up at 50-75cm, corresponding to a concentration range of 60-70wt% phosphoric acid aqueous solution, with a phosphoric acid aqueous solution spray rate of 3000-5000mL / h in this section; a low-concentration pre-diffusion field was set up at 75-100cm, corresponding to a concentration range of 20-30wt% phosphoric acid aqueous solution, with a phosphoric acid aqueous solution spray rate of 3000-5000mL / h in this section.

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