Spinning method for preparing polyacrylonitrile precursor

Abstract

The invention relates to the technical field of spinning, in particular to a spinning method for preparing polyacrylonitrile protofilaments, which comprises the following steps of: spraying polyacrylonitrile stock solution into a solidification pool from a plurality of spinning nozzles on a spinning nozzle for solidification to obtain spinning protofilaments, and collecting contour images of the plurality of spinning protofilaments in the solidification pool; judging whether the spinning precursor has the risk of abnormal spraying form according to the contour image, constructing a spinning unit vector according to the spraying direction of the polyacrylonitrile stock solution, obtaining the environment airflow direction to construct an airflow characterization vector, and determining the type of the abnormal spraying form of the spinning precursor according to the vector included angle between the airflow characterization vector and the spinning unit vector. According to the method, the compensation mode for solidifying the polyacrylonitrile stock solution is selected, and the polyacrylonitrile stock solution is solidified according to the compensation mode to prepare the target spun yarn, so that in the wet spinning process, the compensation mode for solidifying the polyacrylonitrile stock solution is adjusted according to different adaptability of environment airflow, and the target spun yarn is prepared. And the quality uniformity of the polyacrylonitrile precursor is improved.

Description

Technical Field

[0001] The invention relates to the technical field of spinning, in particular to a spinning method for preparing polyacrylonitrile precursor. Background Art

[0002] Polyacrylonitrile precursor is an important precursor for the preparation of high-performance carbon fiber. Carbon fiber has a series of excellent properties such as high strength, high modulus, high temperature resistance, corrosion resistance, etc. It has extensive and critical applications in many fields such as aerospace, national defense, etc. The quality and performance of polyacrylonitrile precursor plays a decisive role in the quality of the final carbon fiber. Wet spinning is widely used because it can better control the structure and properties of polyacrylonitrile precursor and provide a good foundation for the subsequent preparation of carbon fiber. However, in the actual production process, the coagulation pool of wet spinning will be affected by environmental factors, and there will be airflows in different directions. In the process of spraying polyacrylonitrile stock solution into the coagulation pool for coagulation to obtain spinning precursor, the sprayed polyacrylonitrile stock solution will be affected by the direction of the airflow, thereby affecting the morphology of the sprayed polyacrylonitrile stock solution, and then affecting the morphological stability of the polyacrylonitrile precursor. Therefore, in the production process, timely discovering production abnormality risks and improving the quality uniformity of polyacrylonitrile precursor are technical problems that need to be solved urgently.

[0003] For example, the Chinese patent authorization announcement number is: CN105420855B. This invention discloses a continuous coagulation device for spinning solution and its control method. The coagulation process is carried out in the same section of the coagulation bath. The concentration gradient distribution of the coagulation bath in the tank is controlled by changing the flow rate of the inlet and outlet materials of the coagulation bath, the temperature of the temperature-controlled water pipe in the coagulation bath, and the stirring rate of the magnetic stirrer, and it can be quickly balanced. The coagulation bath solution in the tank can achieve dynamic equilibrium of concentration and realize the gradient distribution of the concentration of the coagulation bath solution through the replenishment of the new solution in the coagulation bath preparation tank and the free diffusion of the solution in the tank. This invention realizes the continuous coagulation of polyacrylonitrile solution, and the coagulation bath concentration presents a gradient distribution, realizing the refinement of the equipment.

[0004] The prior art still has the following problems: The prior art does not take into account that during the wet spinning process, the coagulation pool will be affected by environmental factors, there are airflows in different directions, and the sprayed polyacrylonitrile stock solution will be affected by the airflow, thereby affecting the coagulation morphology of the polyacrylonitrile stock solution. During the wet spinning process, the prior art cannot adjust the compensation method for the coagulation of the polyacrylonitrile stock solution according to the different adaptability of the environmental airflow, which affects the quality uniformity of the polyacrylonitrile precursor. Summary of the invention

[0005] To this end, the present invention provides a spinning method for preparing polyacrylonitrile precursor, which is used to overcome the problem that the prior art cannot compensate for the coagulation of the polyacrylonitrile stock solution according to the different adaptability of the ambient airflow during the wet spinning process, thus affecting the quality uniformity of the polyacrylonitrile precursor.

[0006] To achieve the above object, the present invention provides a spinning method for preparing polyacrylonitrile precursor, comprising: Obtain polyacrylonitrile stock solution according to spinning requirements; The polyacrylonitrile stock solution is sprayed from a plurality of spinnerets on a spinneret into a coagulation tank for coagulation to obtain spinning precursors, contour images of the spinning precursors in the coagulation tank at a plurality of moments within a preset monitoring period are collected, and contour characteristic parameters of the spinning precursors are determined according to the contour images to determine whether there is a risk of abnormal ejection morphology of the spinning precursors; Wherein, the contour feature parameter is determined according to a first span value and a second span value of the contour in the contour image; Based on the judgment result that there is a risk of abnormal ejection morphology, a spinneret unit vector is constructed according to the injection direction of the polyacrylonitrile stock solution, the ambient airflow direction is acquired in a preset airflow collection period to construct an airflow characterization vector, and the abnormal ejection morphology category of the spinning precursor is determined according to the vector angle between the airflow characterization vector and the spinneret unit vector at several characteristic moments; The compensation method for solidifying the polyacrylonitrile stock solution is selected according to the abnormal type of the ejection morphology, including: Adjusting the spinning direction of the spinneret according to the direction of the airflow concentration characterization vector; Or, the opening and closing state of the airflow opening arranged on the side wall of the coagulation pool is determined according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector; Wherein, the concentrated airflow characterization vector is determined according to the airflow characterization vectors at several characteristic moments; The polyacrylonitrile stock solution is coagulated according to the compensation method to obtain the target spinning.

[0007] Furthermore, the process of determining the profile feature parameters includes: Determine the profile of the spinning raw fiber within a preset distance from the spinneret in the profile image at several moments in a preset monitoring period as a characteristic profile; Obtaining a first maximum span value and a second maximum span value of the characteristic profile, calculating a ratio of the first maximum span value to the second maximum span value, and determining the ratio as a profile coefficient of the characteristic profile; The variance of the contour coefficient in the contour image at several moments is calculated, and the variance is determined as the contour feature parameter.

[0008] Further, the first span value is a value of a contour length along a length direction of the coagulation pool in the contour image, and the second span value is a value of a contour width along a width direction of the coagulation pool in the contour image.

[0009] Further, determining whether the spinning precursor has a risk of abnormal ejection morphology includes: If the profile characteristic parameters of the spinning precursor meet the normal profile judgment conditions, it is determined that the spinning precursor does not have the risk of abnormal ejection morphology; If the profile characteristic parameters of the spinning precursor do not meet the normal profile judgment conditions, it is determined that the spinning precursor has a risk of abnormal ejection morphology; The normality judgment condition of the contour is that the contour feature parameter does not exceed a preset contour feature reference value.

[0010] Furthermore, the methods of constructing the spinneret unit vector and the airflow characterization vector are: Taking the spinneret as the vector starting point and the ejection direction of the polyacrylonitrile stock solution as the vector direction, a spinneret unit subvector is constructed, and a vector obtained by adding a plurality of spinneret unit subvectors is determined as the spinneret unit vector; Taking the spinneret as the vector starting point and the ambient airflow direction at several characteristic moments as the vector direction, several airflow characterization vectors are constructed.

[0011] Further, the process of determining the abnormal category of the ejection morphology of the spinning precursor includes: Calculating the vector angle between the airflow characterization vector and the spinneret unit vector at each characteristic moment; If the vector angles at a number of characteristic moments meet the single airflow influence condition, then the abnormal ejection morphology category of the spinning precursor is determined to be the first abnormal ejection morphology category; If the vector angles at several characteristic moments do not meet the single airflow influence condition, the abnormal ejection morphology category of the spinning precursor is determined to be the second abnormal ejection morphology category.

[0012] Furthermore, the single airflow influencing condition is that the variance of the angles of a plurality of vectors does not exceed a preset variance threshold.

[0013] Further, the compensation method selected for solidifying the polyacrylonitrile stock solution includes: If the ejection morphology abnormality category is the first ejection morphology abnormality category, the opening and closing state of the airflow opening arranged on the side wall of the coagulation pool is determined according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector; If the ejection morphology abnormality category is the second ejection morphology abnormality category, the ejection direction of the spinneret is adjusted according to the direction of the airflow concentration characterization vector.

[0014] Further, determining the open and closed state of the air flow opening disposed on the side wall of the coagulation pool includes: Determine a vector determined by adding the airflow characterization vectors at a plurality of characteristic moments as the airflow concentrated characterization vector; The air flow openings on the side wall of the coagulation pool pointed to by the angle opening direction are set to an open state, and the air flow openings on the other side walls are set to a closed state.

[0015] Furthermore, the adjusted spinning direction of the spinneret is the same as the vector direction of the airflow concentration characterization vector.

[0016] Compared with the prior art, the beneficial effect of the present invention lies in that, the present invention sprays polyacrylonitrile stock solution from a plurality of spinnerets on a spinneret into a coagulation pool for coagulation to obtain spinning precursor, collects contour images of the spinning precursor in the coagulation pool at a plurality of moments within a preset monitoring period, determines contour characteristic parameters of the spinning precursor according to the contour images, so as to determine whether the spinning precursor has a risk of abnormal ejection morphology, and based on the determination result of the existence of the risk of abnormal ejection morphology, constructs a spinneret unit vector according to the injection direction of the polyacrylonitrile stock solution, obtains the ambient airflow direction in a preset airflow collection period to construct an airflow characterization vector, determines the abnormal ejection morphology category of the spinning precursor according to the vector angle between the airflow characterization vector and the spinneret unit vector at a plurality of characteristic moments, selects a compensation method for coagulating the polyacrylonitrile stock solution according to the abnormal ejection morphology category, coagulates the polyacrylonitrile stock solution according to the compensation method to obtain the target spinning, thereby realizing a compensation method for coagulating the polyacrylonitrile stock solution according to the different adaptability adjustments of the ambient airflow in the wet spinning process, and improving the quality uniformity of the polyacrylonitrile precursor.

[0017] In particular, the present invention determines the contour characteristic parameters of the spinning precursor through contour images at several moments to determine whether the spinning precursor has a risk of abnormal ejection morphology. It can be understood that the coagulation rate of the spinning precursor sprayed into the coagulation pool for coagulation is consistent during the coagulation process, and the shapes and sizes of the spinning precursors sprayed into the coagulation pool for coagulation at different moments should be relatively stable. Whether the shape and size of the spinning precursor are relatively stable is determined based on the contour of the spinning precursor within a preset distance from the spinneret in the contour image. The spinning precursor here has just been ejected from the spinneret and has not been affected by too many complex factors. It can more directly reflect the initial ejection morphology of spinning, which is convenient for timely discovering whether the spinning precursor has a risk of abnormal ejection morphology. In a common ejection morphology, the cross-sectional shape in the contour image of the spinning precursor should have good symmetry and uniformity, the growth and solidification rates in all directions during the solidification process should be relatively consistent, the dimensional changes in the length and width directions should be relatively stable, and through the change in the ratio of the maximum value of the contour length to the maximum value of the contour width, it is possible to intuitively understand whether the symmetry and uniformity of the precursor shape are destroyed. The present invention determines the contour characteristic parameters of the spinning precursor through contour images at several moments to determine whether the spinning precursor has a risk of abnormal ejection morphology, thereby achieving timely discovery of whether the spinning precursor has a risk of abnormal ejection morphology during the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0018] In particular, the present invention constructs a spinneret unit vector according to the injection direction of the polyacrylonitrile stock solution, obtains the ambient airflow direction in a preset airflow collection period to construct an airflow characterization vector. It can be understood that during the spinning process, the spinneret unit vector can accurately characterize the direction in which the polyacrylonitrile stock solution is ejected from the spinneret. The ambient airflow has an important influence on the coagulation process of spinning. The ambient airflow will interfere with the coagulation process of the spinning stock solution in the coagulation bath. By obtaining the ambient airflow direction in a preset airflow collection period and constructing an airflow characterization vector, the directional characteristics of the ambient airflow can be quantitatively described, and the directional deviation between the ambient airflow direction and the ejection direction of the polyacrylonitrile stock solution can be The ambient airflow will cause an unbalanced force on the ejected polyacrylonitrile stock solution. The airflow will cause the ejected polyacrylonitrile stock solution to be subjected to a greater impact force on one side, resulting in the coagulation speed of this side being accelerated, while the other side is relatively slow, thereby destroying the uniformity of spinning coagulation, resulting in quality problems such as uneven thickness and rough surface of the spinning precursor, and even causing the precursor to break, affecting the continuity of spinning and product quality. The present invention constructs a spinneret unit vector and an airflow characterization vector, thereby achieving timely discovery of the potential impact of the ambient airflow on the uniformity of spinning coagulation during the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0019] In particular, the present invention determines the abnormal category of the ejection morphology of the spinning precursor according to the vector angle between the airflow characterization vector and the spinneret unit vector at several characteristic moments. It can be understood that the vector angle between the airflow characterization vector and the spinneret unit vector can characterize the directional deviation between the ambient airflow direction and the ejection direction of the polyacrylonitrile stock solution. When the ambient airflow direction changes frequently, the airflow characterization vector will turn to a large extent, and the angle formed by it and the spinneret unit vector will also change frequently, that is, the change in the angle is large, which will cause the direction of the force of the ambient airflow on the spinning precursor to change frequently during the coagulation process. When the directions of the airflow characterization vectors are relatively consistent, the direction of the airflow characterization vectors is relatively stable, and the change in the angle between the airflow characterization vectors and the spinneret unit vector is small. The influence of the airflow is divided into two categories according to the change in the angle, which provides a clear and definite direction for the optimization and adjustment of the spinning process, so that the operator can take corresponding compensation measures. The present invention determines the abnormal category of the ejection morphology of the spinning precursor according to the vector angle between the airflow characterization vectors and the spinneret unit vector at several characteristic moments, and further, realizes the determination of the abnormal category of the ejection morphology of the spinning precursor according to the different ambient airflows in the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0020] In particular, under the first category of abnormal ejection morphology, the present invention determines the opening and closing state of the airflow outlet arranged on the side wall of the coagulation pool according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector. It can be understood that the first category of abnormal ejection morphology, that is, the ambient airflow direction does not change frequently, and the airflow concentration characterization vector is obtained by adding the airflow characterization vectors at each characteristic moment, which can characterize the overall direction of the current ambient airflow. The opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector characterizes the direction of action of the ambient airflow relative to the spinneret direction. By opening the airflow outlet on the side of the coagulation pool pointed by the angle opening direction, the influence of the ambient airflow on the spinning precursor during the coagulation process can be reduced, so that the airflow effect on the spinning precursor during the coagulation process is more uniform. Under the first category of abnormal ejection morphology, the present invention determines the opening and closing state of the airflow outlet arranged on the side wall of the coagulation pool according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector. Furthermore, a compensation method for coagulating the polyacrylonitrile stock solution according to the different adaptability adjustments of the ambient airflow is realized during the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0021] In particular, the present invention adjusts the spinning direction of the spinneret according to the direction of the airflow concentration characterization vector under the second ejection morphology abnormality category. It can be understood that the second ejection morphology abnormality category, i.e., the ambient airflow direction changes frequently. When the ambient airflow direction changes frequently, the airflow changes quickly. It takes a certain amount of time to adjust the opening and closing of the airflow port, and it is difficult to keep up with the airflow changes in real time. At the same time, the opening and closing of the airflow port will change the airflow distribution in the coagulation pool. The rapid and frequent opening and closing of the airflow port will further affect the spinning precursor, making the spinning quality more difficult to control. Adjusting the spinning direction of the spinneret to be the same as the vector direction of the airflow concentration characterization vector can minimize the angle between the ambient airflow and the spinneret. The airflow disturbance to the polyacrylonitrile stock solution during the ejection process is relatively uniform, and the surrounding airflow environment during the coagulation process is relatively consistent, which is beneficial to the volatilization of the solvent and the diffusion of the coagulant, and optimizes the coagulation conditions. The operator can adjust the direction of the spinneret in a targeted manner according to the airflow concentration characterization vector, so that the spinning process remains controllable in a changeable airflow environment, which is beneficial to achieving stable production. Under the second ejection morphology abnormality category, the present invention adjusts the spinning direction of the spinneret according to the direction of the airflow concentration characterization vector, thereby realizing a compensation method for coagulating the polyacrylonitrile stock solution according to the different adaptability of the environmental airflow during the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A step diagram of a spinning method for preparing polyacrylonitrile precursor according to an embodiment of the present invention; Figure 2 A logic flow chart for determining whether there is a risk of abnormal ejection morphology of spinning precursor according to an embodiment of the present invention; Figure 3 A logic flow chart for determining the abnormal category of the ejection morphology of the spinning precursor according to an embodiment of the present invention; Figure 4 A logic flow chart for selecting a compensation method for coagulating polyacrylonitrile stock solution according to an embodiment of the present invention; Figure 5 A schematic diagram of determining the open and closed states of the air flow ports disposed on the side wall of the coagulation pool according to an embodiment of the present invention; In the figure: 1-coagulation pool; 2-spinneret; 3-air flow outlet A; 4-air flow outlet B; 5-spinneret unit vector; 6-air flow concentration characterization vector; 7-coagulation pool side wall A; 8-coagulation pool side wall B. DETAILED DESCRIPTION

[0023] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0025] It should be noted that, in the description of the present invention, terms such as "upper", "lower", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0026] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] See also Figure 1 As shown, it is a step diagram of a spinning method for preparing polyacrylonitrile precursor according to an embodiment of the present invention. The spinning method for preparing polyacrylonitrile precursor according to the present invention comprises: Step S100, obtaining polyacrylonitrile stock solution according to spinning requirements; Specifically, in the actual production process of polyacrylonitrile precursor, the requirements for fiber mechanical properties and fiber functionality are different, and the composition of the polyacrylonitrile stock solution will also be different. For example, to produce high-strength, high-modulus polyacrylonitrile fibers, some components that help to improve the molecular chain orientation and crystallinity will be added to the stock solution, so that the polyacrylonitrile molecular chains can be better stretched and oriented in the solution, and a more regular structure can be formed during the spinning process, thereby improving the mechanical properties of the fiber. This is a prior art and will not be repeated here.

[0028] Step S200, spraying the polyacrylonitrile stock solution from a plurality of spinnerets on a spinneret into a coagulation tank for coagulation to obtain spinning precursors, collecting contour images of the spinning precursors in the coagulation tank at a plurality of moments within a preset monitoring period, and determining contour characteristic parameters of the spinning precursors according to the contour images to determine whether there is a risk of abnormal ejection morphology of the spinning precursors; Wherein, the contour feature parameter is determined according to a first span value and a second span value of the contour in the contour image; Specifically, the preset monitoring period can be set by technical personnel in this field according to the accuracy requirements of the preparation process of polyacrylonitrile precursor. The higher the accuracy requirements, the longer the preset monitoring period. The value range of the monitoring period can be [3, 10], and the interval unit is min. Preferably, the monitoring period can be 5 minutes, and the interval time of each moment in the monitoring period can be 10 seconds.

[0029] Step S300, based on the judgment result that there is a risk of abnormal ejection morphology, a spinneret unit vector is constructed according to the injection direction of the polyacrylonitrile stock solution, the ambient airflow direction is acquired in a preset airflow collection period to construct an airflow characterization vector, and the ejection morphology abnormality category of the spinning precursor is determined according to the vector angle between the airflow characterization vector and the spinneret unit vector at several characteristic moments; The characteristic moments are several moments of obtaining the direction of the ambient airflow during the airflow collection period; Specifically, the preset airflow collection period can be set by technical personnel in this field according to the precision requirements of the preparation process of polyacrylonitrile precursor. The higher the precision requirement, the longer the preset airflow collection period. The value range of the airflow collection period can be [3, 10], and the interval unit is min. Preferably, the airflow collection period can be 5 minutes, and the interval between characteristic moments can be 10 seconds.

[0030] Specifically, the present invention does not specifically limit the method for obtaining the direction of ambient airflow. Preferably, it can obtain the airflow direction through an ultrasonic sensor by utilizing the propagation characteristics of ultrasonic waves in a medium. This is widely used in airflow monitoring and will not be described in detail here.

[0031] Step S400, selecting a compensation method for solidifying the polyacrylonitrile stock solution according to the abnormal spraying morphology type, including: Adjusting the spinning direction of the spinneret according to the direction of the airflow concentration characterization vector; Or, the opening and closing state of the airflow opening arranged on the side wall of the coagulation pool is determined according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector; Wherein, the concentrated airflow characterization vector is determined according to the airflow characterization vectors at several characteristic moments; Step S500, coagulating the polyacrylonitrile stock solution according to the compensation method to obtain the target spinning.

[0032] Specifically, the process of determining the contour feature parameters includes: Determine the profile of the spinning raw fiber within a preset distance from the spinneret in the profile image at several moments in a preset monitoring period as a characteristic profile; Obtaining a first maximum span value and a second maximum span value of the characteristic profile, calculating a ratio of the first maximum span value to the second maximum span value, and determining the ratio as a profile coefficient of the characteristic profile; The variance of the contour coefficient in the contour images at several moments is calculated, and the variance is determined as the contour feature parameter.

[0033] Specifically, the preset distance from the spinneret can be set by a technician in this field according to the spinning speed. The faster the spinning speed, the longer the preset distance. The value range of the preset distance from the spinneret can be [10, 30], and the interval unit is cm. Preferably, the preset distance from the spinneret can be 15 cm.

[0034] Specifically, the contour image of the spinning precursor in the coagulation pool can be obtained through an industrial camera, and the first span value and the second span value of the contour in the contour image can be obtained using an edge algorithm in conjunction with an image processor to determine the contour coefficient and contour feature parameters, which will not be repeated here.

[0035] Specifically, the first span value is a contour length value along the length direction of the coagulation pool in the contour image, and the second span value is a contour width value along the width direction of the coagulation pool in the contour image.

[0036] Specifically, a specific embodiment of determining the contour feature parameters is given here, and the maximum values ​​of the first span value and the second span value at 5 moments are obtained, respectively, the maximum value of the first span value at moment 1 is 12 cm, and the maximum value of the second span value is 4 cm, the maximum value of the first span value at moment 2 is 10 cm, and the maximum value of the second span value is 5 cm, the maximum value of the first span value at moment 3 is 14 cm, and the maximum value of the second span value is 7 cm, the maximum value of the first span value at moment 4 is 1 cm, and the maximum value of the second span value is 3 cm, the maximum value of the first span value at moment 5 is 13 cm, and the maximum value of the second span value is 6 cm, and the maximum value of the first span value at 5 moments is 14 cm, and the maximum value of the second span value is 7 cm. The ratio of the maximum value of the first span value to the maximum value of the second span value at moment 1 is 3, the ratio of the maximum value of the first span value to the maximum value of the second span value at moment 2 is 2, the ratio of the maximum value of the first span value to the maximum value of the second span value at moment 3 is 2, the ratio of the maximum value of the first span value to the maximum value of the second span value at moment 4 is 3.67, and the ratio of the maximum value of the first span value to the maximum value of the second span value at moment 5 is 2.17. The contour coefficients are 3, 2, 2, 3.67, and 2.17, respectively. The variance of the contour coefficient in the contour image is 0.42. Therefore, the contour feature parameter is 0.42.

[0037] Specifically, see Figure 2As shown, it is a logic flow chart of determining whether the spinning precursor has a risk of abnormal ejection morphology according to an embodiment of the present invention. Determining whether the spinning precursor has a risk of abnormal ejection morphology includes: If the profile characteristic parameters of the spinning precursor meet the normal profile judgment conditions, it is determined that the spinning precursor does not have the risk of abnormal ejection morphology; If the profile characteristic parameters of the spinning precursor do not meet the normal profile judgment conditions, it is determined that the spinning precursor has a risk of abnormal ejection morphology; The normality judgment condition of the contour is that the contour feature parameter does not exceed a preset contour feature reference value.

[0038] Specifically, the preset profile feature reference value can be set by technical personnel in this field according to the accuracy requirements of the preparation process of polyacrylonitrile precursor. The higher the accuracy requirement, the smaller the preset profile feature reference value. The value range of the profile feature reference value can be [0.2, 0.8]. Preferably, the profile feature reference value can be 0.5.

[0039] Specifically, the present invention determines the contour characteristic parameters of the spinning precursor through contour images at several moments to determine whether the spinning precursor has a risk of abnormal ejection morphology. It can be understood that the coagulation rate of the spinning precursor sprayed into the coagulation pool for coagulation is consistent during the coagulation process, and the shapes and sizes of the spinning precursors sprayed into the coagulation pool for coagulation at different moments should be relatively stable. Whether the shape and size of the spinning precursor are relatively stable is determined based on the contour of the spinning precursor within a preset distance from the spinneret in the contour image. The spinning precursor here has just been ejected from the spinneret and has not been affected by too many complex factors. It can more directly reflect the initial ejection morphology of spinning, which is convenient for timely discovering whether the spinning precursor has a risk of abnormal ejection morphology. In a normal ejection morphology, the cross-sectional shape in the contour image of the spinning precursor should have good symmetry and uniformity, the growth and solidification rates in all directions during the solidification process should be relatively consistent, the dimensional changes in the length and width directions should be relatively stable, and through the change in the ratio of the maximum value of the contour length to the maximum value of the contour width, it is possible to intuitively understand whether the symmetry and uniformity of the precursor shape are destroyed. The present invention determines the contour characteristic parameters of the spinning precursor through contour images at several moments to determine whether the spinning precursor has a risk of abnormal ejection morphology, thereby achieving timely detection of whether the spinning precursor has a risk of abnormal ejection morphology during the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0040] Specifically, the methods of constructing the spinneret unit vector and the airflow characterization vector are: Taking the spinneret as the vector starting point and the ejection direction of the polyacrylonitrile stock solution as the vector direction, a spinneret unit subvector is constructed, and a vector obtained by adding a plurality of spinneret unit subvectors is determined as the spinneret unit vector; Taking the spinneret as the vector starting point and the ambient airflow direction at several characteristic moments as the vector direction, several airflow characterization vectors are constructed.

[0041] Specifically, a specific embodiment of determining the spinneret unit vector is given here. The spinneret unit sub-vectors of the five spinnerets are respectively (1, 0, 0), (0, 1, 0), (0, 0, 1), (-0.5, -0.5, -0.5), (0.3, 0.3, 0.3), and the five spinneret unit sub-vectors are added to (0.8, 0.8, 0.8). Therefore, the spinneret unit vector is (0.8, 0.8, 0.8).

[0042] Specifically, the microprocessor can construct a spinneret unit vector and an airflow characterization vector according to the obtained injection direction of the polyacrylonitrile stock solution and the ambient airflow direction, which will not be described in detail here.

[0043] Specifically, the present invention constructs a spinneret unit vector according to the injection direction of the polyacrylonitrile stock solution, obtains the ambient airflow direction in a preset airflow collection period to construct an airflow characterization vector. It can be understood that in the spinning process, the spinneret unit vector can accurately characterize the direction in which the polyacrylonitrile stock solution is ejected from the spinneret. The ambient airflow has an important influence on the coagulation process of spinning. The ambient airflow will interfere with the coagulation process of the spinning stock solution in the coagulation bath. By obtaining the ambient airflow direction in a preset airflow collection period and constructing an airflow characterization vector, the directional characteristics of the ambient airflow can be quantitatively described. The directional deviation of the ambient airflow direction from the ejection direction of the polyacrylonitrile stock solution is The difference will cause the ambient airflow to produce an unbalanced force on the ejected polyacrylonitrile stock solution. The airflow will cause the ejected polyacrylonitrile stock solution to receive a greater impact force on one side, resulting in the coagulation speed of this side to be accelerated, while the other side is relatively slow, thereby destroying the uniformity of spinning coagulation, resulting in quality problems such as uneven thickness and rough surface of the spinning precursor, and even causing the precursor to break, affecting the continuity of spinning and product quality. The present invention constructs a spinneret unit vector and an airflow characterization vector, thereby achieving timely discovery of the potential impact of the ambient airflow on the uniformity of spinning coagulation during the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0044] Specifically, see Figure 3 As shown, it is a logic flow chart for determining the abnormal category of the ejection morphology of the spinning precursor according to an embodiment of the present invention. The process of determining the abnormal category of the ejection morphology of the spinning precursor includes: Calculating the vector angle between the airflow characterization vector and the spinneret unit vector at each characteristic moment; If the vector angles at the characteristic moments meet the single airflow influence condition, the abnormal ejection morphology category of the spinning precursor is determined to be the first abnormal ejection morphology category; If a number of vector angles at a number of characteristic moments do not meet the single airflow influence condition, the ejection morphology abnormality category of the spinning precursor is determined to be the second ejection morphology abnormality category.

[0045] Specifically, the ambient airflow direction of five airflow collection cycles can be obtained at a position 5 cm away from the spinneret in the direction of the spinneret unit vector to construct five airflow characterization vectors.

[0046] Specifically, the single airflow influencing condition is that the variance of the angles of a plurality of vectors does not exceed a preset variance threshold.

[0047] Specifically, the preset variance threshold can be set by technical personnel in this field according to the accuracy requirements of the preparation process of polyacrylonitrile precursor. The higher the accuracy requirement, the smaller the preset variance threshold. The value range of the variance threshold can be [0.8, 1.5]. Preferably, the variance threshold can be 1.

[0048] Specifically, the present invention determines the abnormal category of the ejection morphology of the spinning precursor according to the vector angle between the airflow characterization vector and the spinneret unit vector at several characteristic moments. It can be understood that the vector angle between the airflow characterization vector and the spinneret unit vector can characterize the directional deviation between the ambient airflow direction and the ejection direction of the polyacrylonitrile stock solution. When the ambient airflow direction changes frequently, the airflow characterization vector will turn to a large extent, and the angle formed by it and the spinneret unit vector will also change frequently, that is, the change in the angle is large, which will cause the direction of the force of the ambient airflow on the spinning precursor to change frequently during the coagulation process. When the directions are relatively consistent, the direction of the airflow characterization vector is relatively stable, and the change in the angle between it and the spinneret unit vector is small. The influence of the airflow is divided into two categories according to the change in the angle, which provides a clear and definite direction for the optimization and adjustment of the spinning process, so that the operator can take corresponding compensation measures. The present invention determines the abnormal category of the ejection morphology of the spinning precursor according to the vector angle between the airflow characterization vector and the spinneret unit vector at several characteristic moments, and further, realizes the determination of the abnormal category of the ejection morphology of the spinning precursor according to the different ambient airflows in the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0049] Specifically, see Figure 4 As shown, it is a logic flow chart of selecting a compensation method for solidifying polyacrylonitrile stock solution in an embodiment of the present invention. The compensation method for solidifying polyacrylonitrile stock solution includes: If the ejection morphology abnormality category is the first ejection morphology abnormality category, the opening and closing state of the airflow opening arranged on the side wall of the coagulation pool is determined according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector; If the ejection morphology abnormality category is the second ejection morphology abnormality category, the ejection direction of the spinneret is adjusted according to the direction of the airflow concentration characterization vector.

[0050] Specifically, determining the open and closed state of the air flow opening disposed on the side wall of the coagulation pool includes: Determine a vector determined by adding the airflow characterization vectors at a plurality of characteristic moments as the airflow concentrated characterization vector; The air flow openings on the side wall of the coagulation pool pointed to by the angle opening direction are set to an open state, and the air flow openings on the other side walls are set to a closed state.

[0051] Specifically, see Figure 5 As shown, it is a schematic diagram of determining the opening and closing state of the air flow outlet arranged on the side wall of the coagulation pool according to an embodiment of the present invention. The opening direction of the angle between the air flow concentration characterization vector 6 and the spinneret unit vector 5 points to the coagulation pool side wall A7. Therefore, the air flow outlet A3 on the coagulation pool side wall A7 is set to an open state, and the air flow outlet B4 on the coagulation pool side wall B8 is set to a closed state.

[0052] Specifically, the air flow outlets are arranged on the two side walls in the length direction of the coagulation pool. It can be understood that after the polyacrylonitrile stock solution is ejected from the spinneret, it extends and distributes in the length direction of the coagulation pool. The air flow outlets are arranged on the two side walls in the length direction of the coagulation pool, so that the air flow can be evenly distributed in the entire spinning area. By controlling the opening and closing states of the air flow outlets on the two side walls, the air flow field in the coagulation pool can be flexibly adjusted. When the air flow direction needs to be changed to compensate for the abnormal ejection morphology of the spun precursor, the air flow outlets on both sides of the coagulation pool can be selectively opened or closed to regulate the direction of the air flow.

[0053] Specifically, the airflow volume of the airflow port is positively correlated with the vector size of the airflow concentration characterization vector. The larger the vector size of the airflow concentration characterization vector is, the greater the ambient airflow is, and the greater the airflow volume of the airflow port is.

[0054] Specifically, the present invention determines the opening and closing state of the airflow outlet arranged on the side wall of the coagulation pool according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector under the first category of abnormal ejection morphology. It can be understood that the first category of abnormal ejection morphology, that is, the direction of the ambient airflow does not change frequently, and the airflow concentration characterization vector is obtained by adding the airflow characterization vectors at each characteristic moment, which can characterize the overall direction of the current ambient airflow. The opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector characterizes the direction of action of the ambient airflow relative to the spinneret direction. By opening the airflow outlet on the side of the coagulation pool pointed by the angle opening direction, the influence of the ambient airflow on the spinning precursor during the coagulation process can be reduced, so that the airflow effect on the spinning precursor during the coagulation process is more uniform. The present invention determines the opening and closing state of the airflow outlet arranged on the side wall of the coagulation pool according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector under the first category of abnormal ejection morphology. Furthermore, a compensation method for coagulating the polyacrylonitrile stock solution according to the different adaptability of the ambient airflow is realized during the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0055] Specifically, the adjusted spinning direction of the spinneret is the same as the vector direction of the airflow concentration characterization vector.

[0056] Specifically, the present invention adjusts the spinning direction of the spinneret according to the direction of the airflow concentration characterization vector under the second ejection morphology abnormality category. It can be understood that the second ejection morphology abnormality category, namely, the ambient airflow direction changes frequently. When the ambient airflow direction changes frequently, the airflow changes rapidly. It takes a certain amount of time to adjust the opening and closing of the airflow port, and it is difficult to keep up with the airflow changes in real time. At the same time, the opening and closing of the airflow port will change the airflow distribution in the coagulation pool. The rapid and frequent opening and closing of the airflow port will further affect the spinning precursor, making the spinning quality more difficult to control. Adjusting the spinning direction of the spinneret to be the same as the vector direction of the airflow concentration characterization vector can minimize the angle between the ambient airflow and the spinneret. , so that the airflow interference to the polyacrylonitrile stock solution during the ejection process is relatively uniform, and the surrounding airflow environment during the coagulation process is relatively consistent, which is conducive to the volatilization of the solvent and the diffusion of the coagulant, and optimizes the coagulation conditions. The operator can adjust the direction of the spinneret in a targeted manner according to the airflow concentration characterization vector, so that the spinning process remains controllable in a changeable airflow environment, which is conducive to achieving stable production. Under the second ejection morphology abnormality category, the present invention adjusts the spinning direction of the spinneret according to the direction of the airflow concentration characterization vector, and further realizes a compensation method for coagulating the polyacrylonitrile stock solution according to the different adaptability of the environmental airflow during the wet spinning process, thereby improving the quality uniformity of the polyacrylonitrile precursor.

[0057] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A spinning method for preparing polyacrylonitrile precursor, characterized in that: include: Obtain polyacrylonitrile stock solution according to spinning requirements; The polyacrylonitrile stock solution is sprayed from a plurality of spinnerets on a spinneret into a coagulation tank for coagulation to obtain spinning precursors, contour images of the spinning precursors in the coagulation tank at a plurality of moments within a preset monitoring period are collected, and contour characteristic parameters of the spinning precursors are determined according to the contour images to determine whether there is a risk of abnormal ejection morphology of the spinning precursors; Wherein, the contour feature parameter is determined according to a first span value and a second span value of the contour in the contour image; Based on the judgment result that there is a risk of abnormal ejection morphology, a spinneret unit vector is constructed according to the injection direction of the polyacrylonitrile stock solution, the ambient airflow direction is acquired in a preset airflow collection period to construct an airflow characterization vector, and the abnormal ejection morphology category of the spinning precursor is determined according to the vector angle between the airflow characterization vector and the spinneret unit vector at several characteristic moments; The compensation method for solidifying the polyacrylonitrile stock solution is selected according to the abnormal type of the ejection morphology, including: Adjusting the spinning direction of the spinneret according to the direction of the airflow concentration characterization vector; Or, the opening and closing state of the airflow opening arranged on the side wall of the coagulation pool is determined according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector; Wherein, the concentrated airflow characterization vector is determined according to the airflow characterization vectors at several characteristic moments; The polyacrylonitrile stock solution is coagulated according to the compensation method to obtain the target spinning.

2. The spinning method for preparing polyacrylonitrile precursor according to claim 1, characterized in that: The process of determining the contour feature parameters includes: Determine the profile of the spinning raw fiber within a preset distance from the spinneret in the profile image at several moments in a preset monitoring period as a characteristic profile; Obtaining a first maximum span value and a second maximum span value of the characteristic profile, calculating a ratio of the first maximum span value to the second maximum span value, and determining the ratio as a profile coefficient of the characteristic profile; The variance of the contour coefficient in the contour images at several moments is calculated, and the variance is determined as the contour feature parameter.

3. The spinning method for preparing polyacrylonitrile precursor according to claim 2, characterized in that: The first span value is a value of the contour length along the length direction of the coagulation pool in the contour image, and the second span value is a value of the contour width along the width direction of the coagulation pool in the contour image.

4. The spinning method for preparing polyacrylonitrile precursor according to claim 2, characterized in that: Determining whether the spinning precursor has a risk of abnormal ejection morphology includes: If the profile characteristic parameters of the spinning precursor meet the normal profile judgment conditions, it is determined that the spinning precursor does not have the risk of abnormal ejection morphology; If the profile characteristic parameters of the spinning precursor do not meet the normal profile judgment conditions, it is determined that the spinning precursor has a risk of abnormal ejection morphology; The normality judgment condition of the contour is that the contour feature parameter does not exceed a preset contour feature reference value.

5. The spinning method for preparing polyacrylonitrile precursor according to claim 4, characterized in that: The methods of constructing the spinneret unit vector and the airflow characterization vector are: Taking the spinneret as the vector starting point and the ejection direction of the polyacrylonitrile stock solution as the vector direction, a spinneret unit subvector is constructed, and a vector obtained by adding a plurality of spinneret unit subvectors is determined as the spinneret unit vector; Taking the spinneret as the vector starting point and the ambient airflow direction at several characteristic moments as the vector direction, several airflow characterization vectors are constructed.

6. The spinning method for preparing polyacrylonitrile precursor according to claim 5, characterized in that: The process of determining the abnormal category of the ejection morphology of the spinning precursor includes: Calculating the vector angle between the airflow characterization vector and the spinneret unit vector at each characteristic moment; If the vector angles at a number of characteristic moments meet the single airflow influence condition, then the abnormal ejection morphology category of the spinning precursor is determined to be the first abnormal ejection morphology category; If the vector angles at several characteristic moments do not meet the single airflow influence condition, the abnormal ejection morphology category of the spinning precursor is determined to be the second abnormal ejection morphology category.

7. The spinning method for preparing polyacrylonitrile precursor according to claim 6, characterized in that: The single airflow influencing condition is that the variance of the angles of a plurality of vectors does not exceed a preset variance threshold.

8. The spinning method for preparing polyacrylonitrile precursor according to claim 7, characterized in that: The selected compensation methods for solidifying the polyacrylonitrile stock solution include: If the ejection morphology abnormality category is the first ejection morphology abnormality category, the opening and closing state of the airflow opening arranged on the side wall of the coagulation pool is determined according to the opening direction of the angle between the airflow concentration characterization vector and the spinneret unit vector; If the ejection morphology abnormality category is the second ejection morphology abnormality category, the ejection direction of the spinneret is adjusted according to the direction of the airflow concentration characterization vector.

9. The spinning method for preparing polyacrylonitrile precursor according to claim 8, characterized in that: Determining the open and closed state of the air flow opening disposed on the side wall of the coagulation pool includes: Determine a vector determined by adding the airflow characterization vectors at a plurality of characteristic moments as the airflow concentrated characterization vector; The air flow openings on the side wall of the coagulation pool pointed to by the angle opening direction are set to an open state, and the air flow openings on the other side walls are set to a closed state.

10. The spinning method for preparing polyacrylonitrile precursor according to claim 7, characterized in that: The adjusted spinning direction of the spinneret is the same as the vector direction of the airflow concentration characterization vector.

Images