阅读说明：本技术 消除凝固浴气泡丝的方法 (Method for eliminating bubble filaments in coagulating bath ) 是由 王贺团 沈志刚 张静 赵微微 于 2018-07-06 设计创作，主要内容包括：本发明涉及一种消除凝固浴气泡丝的方法,主要解决现有技术存在的湿法纺丝喷丝板周围气泡丝多和凝固浴断丝多的技术问题。通过采用聚丙烯腈初生纤维的湿法纺丝方法,包括以下步骤：1)纺丝原液制备：将溶剂、丙烯腈、共聚单体、引发剂聚合得到纺丝原液；2)凝固成型：将经过过滤、计量的纺丝原液,通过喷丝头挤出,经凝固成型；其中,所述的纺丝原液经过两台计量泵计量输送,以表压计,两台泵计量泵之间纺丝原液的压差为0.30～0.80MPa,完成初生纤维成型的技术方案,较好地解决了该问题,可用于聚丙烯腈基碳纤维原丝的工业生产中。(The invention relates to a method for eliminating bubble filaments in a coagulation bath, which mainly solves the technical problems of more bubble filaments around a wet spinning spinneret plate and more broken filaments in the coagulation bath in the prior art. The wet spinning method adopting the polyacrylonitrile as-spun fiber comprises the following steps of: 1) preparing a spinning solution: polymerizing a solvent, acrylonitrile, a comonomer and an initiator to obtain a spinning solution; 2) solidification and forming: extruding the filtered and metered spinning solution through a spinning nozzle, and performing solidification molding; the spinning solution is metered and conveyed by the two metering pumps, and the differential pressure of the spinning solution between the two metering pumps is 0.30-0.80 MPa by gauge pressure, so that the technical scheme of primary fiber forming is completed, the problem is well solved, and the method can be used in industrial production of polyacrylonitrile-based carbon fiber precursors.)

1. A method for eliminating bubble filaments in a coagulation bath adopts wet spinning and comprises the following steps:

(1) preparing a spinning solution: polymerizing a solvent, acrylonitrile, a comonomer and an initiator to obtain a spinning solution;

(2) solidification and forming: extruding the filtered and metered spinning solution through a spinning nozzle, and carrying out solidification forming to obtain nascent fiber;

the spinning solution is metered and conveyed by two metering pumps, and the differential pressure of the spinning solution between the two metering pumps is 0.30-0.80 MPa by gauge pressure.

2. The method for eliminating bubble filaments in the coagulation bath according to claim 1, wherein the viscosity-average molecular weight of polyacrylonitrile in the spinning solution is 5 to 10 ten thousand.

3. The method for eliminating bubble filaments in a coagulation bath according to claim 1, wherein the viscosity of the spinning dope is 30 to 80 Pa-s.

4. The method for eliminating coagulation bath bubble yarns as claimed in claim 1, wherein the spinning solution is subjected to two filtration steps, and the spinning solution enters from the bottom of the filter and is discharged from the highest point of the top of the filter.

5. The method for eliminating coagulation bath bubble yarns as claimed in claim 1, wherein the spinning solution pipeline, the inner wall of the filter and the inside of the spinning assembly are in streamline structures, and an inner polishing treatment is adopted.

6. The method for eliminating filaments with coagulation bath bubbles according to claim 1, wherein the spinneret uses a spinneret plate having a number of holes of 6000 to 12000 and an outer diameter of not more than 13 cm.

7. The method for eliminating filaments in coagulation bath according to claim 1, wherein the coagulation bath crimping roller is located above the coagulation liquid surface, and the distance from the lowermost roller to the coagulation liquid surface is not more than 4 cm.

8. The method for eliminating bubble filaments in a coagulation bath according to claim 1, wherein the extrusion amount of the spinning dope is 30 to 150 mL/min.

9. The method for eliminating bubble filaments in a coagulation bath according to claim 1, wherein the metered spinning solution is discharged in a gooseneck for not less than 30 minutes, and the spinning is started after 2-5 minutes of continuous discharge without bubbles.

10. The method for eliminating bubble filaments in coagulation bath according to claim 1, wherein the temperature difference between the spinning dope entering the coagulation liquid and the coagulation liquid temperature in the step (2) is not more than 10 ℃.

Technical Field

The invention belongs to a preparation method of polyacrylonitrile protofilament for carbon fiber, and particularly relates to a method for eliminating coagulating bath bubble filament.

Background

From the last 50 century, developed countries are in urgent need of new structural materials and corrosion-resistant materials for developing large rockets and artificial satellites and improving the performance of airplanes in a comprehensive manner, so that carbon fibers reappear on a stage made of the new materials, and three raw material systems of PAN-based carbon fibers, viscose-based carbon fibers and asphalt-based carbon fibers are gradually formed. Compared with other methods, the PAN-based carbon fiber production process is simple, and the mechanical property of the product is good, so that the PAN-based carbon fiber is rapidly developed and becomes the mainstream of the current carbon fiber production.

PAN-based carbon fiber has excellent properties of high strength, high modulus, high temperature resistance, corrosion resistance and the like, and is widely applied to the fields of aerospace, national defense, military and the like. In addition, the composite material also has wide application prospect in the fields of airplane industry, automobile industry, ship manufacturing, medical appliances, sports equipment, novel building materials and the like. The preparation of the PAN-based carbon fiber mainly comprises the following steps: polymeric spinning, thermal stabilization of the PAN filaments, and carbonization or further graphitization of the PAN stabilized fibers. The polymerization spinning process mainly comprises monomer polymerization, monomer removal and separation and spinning. The spinning process comprises a wet method, a dry-wet method and a melting method, and the wet spinning is the most widely applied process at present. The quality of the precursor is easy to control in wet spinning, the obtained precursor has small fineness dispersion and less solvent residue, and the process is relatively mature.

The high-quality PAN precursor is the first necessary condition for manufacturing the high-performance carbon fiber and is one of the most critical factors influencing the quality of the carbon fiber. The prepared protofilament is required to realize high purification, high strengthening, fine denier and densification; the division linearity between the monofilaments is good, and the surface of the protofilament cannot have obvious defects. The precondition for preparing the high-quality carbon fiber is that high-quality polyacrylonitrile precursor fiber must be used, which is the summary of experience for many years, and the high-quality polyacrylonitrile precursor fiber can be spun only by good spinning solution. The good spinning dope, besides requiring regular polyacrylonitrile molecular chain structure, no branching and no crosslinking, and uniform distribution of the comonomer on the main chain, must also have moderate viscosity, high molecular weight and proper molecular weight distribution.

Wet spinning is an important spinning method for preparing polyacrylonitrile fibers, and high-quality polyacrylonitrile stock solution enters a coagulating bath after being filtered and metered, and is subjected to double diffusion to form nascent fibers. The quality of the formed primary fiber directly affects the quality of the polyacrylonitrile-based precursor and determines the properties of the final carbon fiber. Therefore, the formation of the nascent fiber is crucial to the production of polyacrylonitrile filaments, and is an important step in the production process of polyacrylonitrile filaments. The method is characterized in that a small amount of polyacrylonitrile stock solution trickle cannot normally form polyacrylonitrile nascent fiber after being extruded through spinneret holes under the influence of the processing precision, stock solution quality and a spinning process of spinning components and other equipment, and exists in a form of bubble filaments. The bubble filaments were finally collected at the overflow of the coagulation bath for analysis of the stability of the wet spinning process and the quality of the spinning dope.

Disclosure of Invention

The invention aims to solve the technical problems of more bubble filaments around a spinneret plate and more broken filaments in a coagulation bath in the prior art, and provides a method for eliminating the bubble filaments in the coagulation bath.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a method for eliminating bubble filaments in a coagulation bath adopts wet spinning and comprises the following steps:

(1) preparing a spinning solution: polymerizing a solvent, acrylonitrile, a comonomer and an initiator to obtain a spinning solution;

(2) solidification and forming: extruding the filtered and metered spinning solution through a spinning nozzle, and carrying out solidification forming to obtain nascent fiber;

the spinning solution is metered and conveyed by two metering pumps, and the differential pressure of the spinning solution between the two metering pumps is 0.30-0.80 MPa by gauge pressure.

In the technical scheme, the viscosity-average molecular weight of polyacrylonitrile in the spinning solution is preferably 5-10 ten thousand.

In the technical scheme, the viscosity of the spinning solution is preferably 30-80 Pa.s.

In the above technical scheme, the spinning solution is preferably subjected to two-stage filtration, and the spinning solution enters from the bottom of the filter and is discharged from the highest point of the top of the filter.

In the technical scheme, the spinning solution pipeline, the inner wall of the filter and the spinning assembly are optimized to be internally provided with a streamline structure and internally polished.

In the technical scheme, the number of holes of the spinneret plate used by the spinneret plate is optimized to be 6000-12000, and the outer diameter of the spinneret plate is optimized to be not more than 13 cm.

In the technical scheme, the coagulating bath crimping roller is optimized to be positioned above the coagulating liquid level, and the distance from the lowest part of the roller to the coagulating liquid level is not more than 4 cm.

In the technical scheme, the extrusion amount of the spinning solution is optimized to be 30-150 mL/min.

In the technical scheme, the discharge time of the metered spinning solution in the gooseneck is optimized to be not less than 30 minutes, and the spinning is started after 2-5 minutes of continuous discharge optimization and no air bubbles exist.

In the above technical solution, the temperature difference between the spinning dope entering the coagulation liquid and the coagulation liquid in the step (2) is optimized to be not more than 10 ℃.

According to the invention, by controlling the pressure difference of the spinning solution between the two pump metering pumps to be 0.30-0.80 MPa, the generation of bubble filaments around the spinneret plate is reduced, the quality of broken filaments in the coagulation bath is reduced, and by controlling the solution structure, the spinning process and the equipment characteristics, the bubble filaments around the spinneret plate can be further effectively reduced, and the number of broken filaments in the coagulation bath is obviously reduced.

By adopting the technical scheme of the invention, the bubble filaments around the spinneret plate are effectively reduced, the filament breakage quantity of the coagulating bath is obviously reduced, the polyacrylonitrile nascent fiber is obtained by wet spinning, the CV value of the polyacrylonitrile protofilament is reduced, and a better technical effect is obtained.

The following is a specific embodiment of the present invention and is described in detail with reference to comparative examples.

Detailed Description

[ example 1 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 7.8 ten thousand and viscosity of 75 Pa.s, discharging the stock solution from a gooseneck for 35 minutes, continuously discharging for 5 minutes, starting spinning after no bubbles exist, installing a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.65 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 108 mL/min; the spinning solution enters from the bottom of the polymerization and spinning filter and is discharged from the highest point of the filter; the stock solution pipeline, the inner wall of the filter and the interior of the spinning assembly have no dead angle and are subjected to internal polishing treatment; the number of holes of the spinneret plate is 12000, the outer dimension of the surface diameter of the spinneret plate is 11.5cm, the curling roller of the coagulating bath is positioned above the coagulating liquid level, the distance between the lowest part of the roller and the coagulating liquid level is 3cm, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 60 ℃, the temperature of the coagulating liquid is 55 ℃, the spinning time is 50 hours, no bubble filaments are observed on the surface of the spinneret plate all the time, and the mass of broken filaments at an overflow port of the coagulating bath is 0..

[ example 2 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 5.2 ten thousand and viscosity of 33 Pa.s, discharging the stock solution from a gooseneck tube for 40 minutes, continuously discharging for 3 minutes, starting spinning after no bubbles exist, installing a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.35 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 144 mL/min; the spinning solution enters from the bottom of the polymerization and spinning filter and is discharged from the highest point of the filter; the stock solution pipeline, the inner wall of the filter and the interior of the spinning assembly have no dead angle and are subjected to internal polishing treatment; the number of holes of the spinneret plate is 6000, the outer size of the surface diameter of the spinneret plate is 9cm, the curling roller of the coagulating bath is positioned above the coagulating liquid level, the distance between the lowest part of the roller and the coagulating liquid level is 3.5cm, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 63 ℃, the temperature of the coagulating liquid is 60 ℃, the spinning time is 50 hours, no bubble filaments are observed on the surface of the spinneret plate all the time, and the mass of broken filaments at an overflow port of the coagulating bath is 0.18.

[ example 3 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 7 ten thousand and viscosity of 68 Pa.s, discharging the stock solution from a gooseneck for 35 minutes, continuously discharging for 5 minutes, starting spinning after no bubbles exist, installing a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.50 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 72 mL/min; the spinning solution enters from the bottom of the polymerization and spinning filter and is discharged from the highest point of the filter; the stock solution pipeline, the inner wall of the filter and the interior of the spinning assembly have no dead angle and are subjected to internal polishing treatment; the number of holes of the spinneret plate is 12000, the outer dimension of the surface diameter of the spinneret plate is 11.5cm, the curling roller of the coagulating bath is positioned above the coagulating liquid level, the distance between the lowest part of the roller and the coagulating liquid level is 2cm, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 62 ℃, the temperature of the coagulating liquid is 58 ℃, the spinning time is 50 hours, no bubble filaments are observed on the surface of the spinneret plate all the time, and the mass of broken filaments at an overflow port of the coagulating bath is 0.32.

[ example 4 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 5.8 ten thousand and viscosity of 45 Pa.s, discharging the stock solution from a gooseneck for 35 minutes, continuously discharging for 5 minutes, starting spinning after no bubbles exist, installing a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.60 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 108 mL/min; the spinning solution enters from the bottom of the polymerization and spinning filter and is discharged from the highest point of the filter; the stock solution pipeline, the inner wall of the filter and the interior of the spinning assembly have no dead angle and are subjected to internal polishing treatment; the number of holes of the spinneret plate is 12000, the outer dimension of the surface diameter of the spinneret plate is 11.5cm, the curling roller of the coagulating bath is positioned above the coagulating liquid level, the distance between the lowest part of the roller and the coagulating liquid level is 3cm, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 60 ℃, the temperature of the coagulating liquid is 55 ℃, the spinning time is 50 hours, no bubble filaments are observed on the surface of the spinneret plate all the time, and the mass of broken filaments at an overflow port of the coagulating bath is 0..

[ example 5 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 8.5 ten thousand and viscosity of 80 Pa.s, discharging the stock solution from a gooseneck for 35 minutes, continuously discharging for 5 minutes, starting spinning after no bubbles exist, installing a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.78 +/-0.01 MPa; the extrusion amount of a metering pump is controlled to be 36 mL/min; the spinning solution enters from the bottom of the polymerization and spinning filter and is discharged from the highest point of the filter; the stock solution pipeline, the inner wall of the filter and the interior of the spinning assembly have no dead angle and are subjected to internal polishing treatment; the number of holes of the spinneret plate is 12000, the outer dimension of the surface diameter of the spinneret plate is 11.5cm, the curling roller of the coagulating bath is positioned above the coagulating liquid level, the distance between the lowest part of the roller and the coagulating liquid level is 3cm, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 65 ℃, the temperature of the coagulating liquid is 60 ℃, the spinning time is 50 hours, no bubble filaments are observed on the surface of the spinneret plate all the time, and the mass of broken filaments at an overflow port of the coagulating bath is 0.47.

[ example 6 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 7.8 ten thousand and viscosity of 75 Pa.s, discharging the stock solution from a gooseneck tube for 10 minutes, continuously discharging for 1 minute without bubbles, starting spinning, mounting a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.65 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 200 mL/min; the spinning solution enters from the lower side of the polymerization and spinning filter and is discharged from the upper side of the filter; dead angles exist in the stock solution pipeline, the inner wall of the filter and the spinning assembly, and internal polishing treatment is not adopted; the number of holes of the spinneret plate is 24000, the outer size of the surface diameter of the spinneret plate is 17.0cm, the curling roller of the coagulating bath is immersed below the coagulating liquid level, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 60 ℃, the temperature of the coagulating liquid is 30 ℃, the spinning time is 50 hours, a small amount of bubble filaments can be observed on the surface of the spinneret plate after 5 hours of spinning is started, and the mass of broken filaments at an overflow port of the coagulating bath is 1.2 g.

[ COMPARATIVE EXAMPLE 1 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 7.8 ten thousand and viscosity of 75 Pa.s, discharging the stock solution from a gooseneck for 35 minutes, continuously discharging for 5 minutes, starting spinning after no bubbles exist, installing a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.20 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 108 mL/min; the spinning solution enters from the bottom of the polymerization and spinning filter and is discharged from the highest point of the filter; the stock solution pipeline, the inner wall of the filter and the interior of the spinning assembly have no dead angle and are subjected to internal polishing treatment; the number of holes of a spinneret plate is 12000, the outer size of the surface diameter of the spinneret plate is 11.5cm, a curling roller of a coagulation bath is positioned above the coagulation liquid level, the distance between the lowest part of the roller and the coagulation liquid level is 3cm, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 60 ℃, the temperature of the coagulation liquid is 55 ℃, the spinning time is 50 hours, a certain amount of bubble filaments can be observed on the surface of the spinneret plate after 3 hours of spinning, and the mass of broken filaments at an overflow port of the coagulation bath is 2.7 g.

[ COMPARATIVE EXAMPLE 2 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 7.8 ten thousand and viscosity of 75 Pa.s, discharging the stock solution from a gooseneck for 35 minutes, continuously discharging for 5 minutes, starting spinning after no bubbles exist, installing a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.90 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 108 mL/min; the spinning solution enters from the bottom of the polymerization and spinning filter and is discharged from the highest point of the filter; the stock solution pipeline, the inner wall of the filter and the interior of the spinning assembly have no dead angle and are subjected to internal polishing treatment; the number of holes of a spinneret plate is 12000, the outer size of the surface diameter of the spinneret plate is 11.5cm, a curling roller of a coagulation bath is positioned above the coagulation liquid level, the distance between the lowest part of the roller and the coagulation liquid level is 3cm, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 60 ℃, the temperature of the coagulation liquid is 55 ℃, the spinning time is 50 hours, a certain amount of bubble filaments can be observed on the surface of the spinneret plate after 3 hours of spinning, and the mass of broken filaments at an overflow port of the coagulation bath is 1.5 g.

[ COMPARATIVE EXAMPLE 3 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 7.8 ten thousand and viscosity of 75 Pa.s, discharging the stock solution from a gooseneck tube for 10 minutes, continuously discharging for 1 minute without bubbles, starting spinning, mounting a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.20 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 200 mL/min; the spinning solution enters from the lower side of the polymerization and spinning filter and is discharged from the upper side of the filter; dead angles exist in the stock solution pipeline, the inner wall of the filter and the spinning assembly, and internal polishing treatment is not adopted; the number of holes of the spinneret plate is 24000, the outer size of the surface diameter of the spinneret plate is 17.0cm, the curling roller of the coagulating bath is immersed below the coagulating liquid level, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 60 ℃, the temperature of the coagulating liquid is 30 ℃, the spinning time is 50 hours, a large amount of bubble filaments can be observed on the surface of the spinneret plate after 2 hours of spinning is started, and the mass of broken filaments at an overflow port of the coagulating bath is 6.5 g.

[ COMPARATIVE EXAMPLE 4 ]

Filtering and metering polyacrylonitrile/dimethyl sulfoxide spinning stock solution with viscosity average molecular weight of 7.8 ten thousand and viscosity of 75 Pa.s, discharging the stock solution from a gooseneck tube for 10 minutes, continuously discharging for 1 minute without bubbles, starting spinning, mounting a spinneret plate, extruding through a spinneret plate, and carrying out solidification molding to obtain the nascent fiber. The spinning solution is conveyed by two metering pumps, and the pressure difference (gauge pressure) of the spinning solution between the two pumps is controlled to be 0.90 +/-0.01 MPa; the extrusion amount of a metering pump is controlled at 200 mL/min; the spinning solution enters from the lower side of the polymerization and spinning filter and is discharged from the upper side of the filter; dead angles exist in the stock solution pipeline, the inner wall of the filter and the spinning assembly, and internal polishing treatment is not adopted; the number of holes of the spinneret plate is 24000, the outer size of the surface diameter of the spinneret plate is 17.0cm, the curling roller of the coagulating bath is immersed below the coagulating liquid level, the heat preservation temperature of a spinning pipeline, a filter and a gooseneck is 60 ℃, the temperature of the coagulating liquid is 30 ℃, the spinning time is 50 hours, a large amount of bubble filaments can be observed on the surface of the spinneret plate after 2 hours of spinning is started, and the mass of broken filaments at an overflow port of the coagulating bath is 4.5 g.

As can be seen from examples 1 and 6 and comparative examples 1, 2, 3 and 4, by controlling the differential pressure of the spinning solution between the two pump metering pumps to be 0.30-0.80 MPa, the bubble filaments are obviously reduced, and the filament breakage quality at the overflow port of the coagulation bath is reduced by multiple times; and further discharging the stock solution from the highest point of the filter, wherein no dead angle exists among a stock solution pipeline, the inner wall of the filter and the spinning assembly, the optimization of internal polishing treatment and the like is adopted, the number of holes of a spinneret plate is optimized to be 6000-12000, the outer diameter of the spinneret plate is optimized to be not more than 13cm, and the like, so that the bubble filaments can be further reduced, and the filament breakage quality of an overflow port of a coagulation bath is further reduced.