A bath-in-bath coagulation stretch forming method for aramid filaments
By using a bath-in-bath coagulation and stretching method, the flow rate of the coagulating liquid is controlled to achieve negative and positive stretching operations of the spinneret. Combined with multi-stage stretching and multi-station integrated layout, the problems of high cost and low efficiency in aramid filament production are solved, and efficient production and large-scale preparation of high-quality fibers are realized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA BLUESTAR CHENGRAND CO LTD
- Filing Date
- 2024-11-27
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies for aramid filament production suffer from high costs in producing fine fibers, low spinning speeds, and difficulties in integrating multi-station spinning machines, which limit market application and competitiveness.
The bath-in-bath coagulation stretching forming method is adopted. By controlling the flow rate of the coagulation liquid in the large coagulation bath and the U-shaped small coagulation bath, negative stretching of the spinneret and positive stretching of the gel-like nascent fiber are achieved in the coagulation bath. Combined with multi-stage stretching and multi-station integrated layout, production efficiency and fiber output are improved.
This technology enables multi-stage stretching of aramid filaments and integrated multi-station arrangement of spinning lines, improving production efficiency, reducing fiber manufacturing costs, and resulting in high fiber density and excellent appearance quality, making it suitable for the large-scale preparation of ultrafine linear density fibers.
Smart Images
Figure CN122105644A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of aramid spinning processing technology, specifically to a bath-in-bath solidification and stretching forming method for aramid filaments. Background Technology
[0002] Aramid is a high-performance specialty organic fiber, broadly classified into meta-aramid and para-aramid types. It possesses excellent properties such as high-temperature resistance, corrosion resistance, flame retardancy, and dimensional stability. Aramid production mainly involves two parts: polymerization and spinning. The polymerization process typically employs solution polycondensation, where organic monomers undergo a condensation polymerization reaction in a solvent system to generate a polymer solution. Spinning usually utilizes wet spinning technology, where the polymer solution is extruded through spinnerets to form a fine stream that enters a coagulation bath. The extruded stream then forms fibers under the influence of double diffusion and stretching.
[0003] Fiber wet spinning coagulation typically employs coagulation bath forming and tube forming methods. Various forms of coagulation baths have been developed, such as horizontal, vertical, and inclined types. Depending on the spinning function requirements, some coagulation baths are equipped with baffles to physically separate the polymer solution extruded from the spinneret from the coagulated liquid, thus guiding the flow. The flow velocity of the coagulated liquid within the bath varies greatly depending on the type of fiber. The tube forming method provides good symmetry in the coagulated liquid streamline distribution, which, under certain conditions, helps reduce the frictional resistance between the fiber and the coagulated liquid.
[0004] Regarding the coagulation forming method of aramid, the existing technology "202210452337.0, a preparation method for stretching and coagulating aramid slurry" uses a coagulation tank containing a coagulating liquid. A spinneret assembly is placed at the bottom of the coagulation tank, spinning the aramid fibers vertically upwards. A guide roller is located above the coagulation tank. The aramid slurry ejected from the spinneret solidifies in the coagulating liquid to form aramid fibers, which then wind around the guide roller. This method increases the density of the coagulating liquid by adding additives, causing the ejected aramid fibers to float on the surface of the coagulating liquid after formation, making them easier for workers to spot and handle. This patent describes a coagulation forming method in a vertical tank. Patent No. 201911015711.5, "Coagulation Bath for Wet Spinning and Coagulation Forming Method of Polyacrylonitrile Spinning Dosage," describes a coagulation bath for wet spinning, comprising a gooseneck tube, a rectifier plate, a spinneret, a rectifier A, a guide roller, a rectifier B, an overflow plate, and a main tank, for the wet spinning production of polyacrylonitrile-based carbon fiber precursor. This patent describes a method for coagulation formation in a horizontal tank. Patent No. 202011401154.3, "A Heterocyclic Aramid Fiber Coagulation Forming Device and its Process," discloses a heterocyclic aramid fiber coagulation forming device comprising an aramid III spinning polymerization solution tank, a take-up system, a first coagulation solution system, and a second coagulation solution system. The first coagulation solution system includes a first coagulation solution tank, a first coagulation solution inlet pipe, a spinneret, a U-shaped glass tube tank, and a first coagulation solution return pipe. This method can improve the wet spinning process of fibers. This patent describes a method for coagulation formation in a tube.
[0005] The above technical methods have several drawbacks: ① The manufacturing cost of producing fine fibers is relatively high. The finer the fiber, the lower the fiber output per unit time and the higher the manufacturing cost, which limits market application and promotion and reduces the product's market competitiveness; ② There is the problem of integrated layout of multi-station spinning machines. Wet spinning speed is relatively low. To produce fine fibers, the only way to improve production efficiency is to increase the number of production stations. Therefore, multi-station spinning machines need to be integrated to make the most of limited space and arrange as many production stations as possible to increase fiber output. Summary of the Invention
[0006] This invention aims to solve the problems existing in the prior art and provides a bath-in-bath coagulation and stretching forming method for aramid filaments. By controlling the flow rate of the coagulating liquid in the large coagulation bath and the U-shaped small coagulation bath, the negative stretching of the spinneret and the positive stretching of the gel-like nascent fiber in the wet spinning process can be achieved simultaneously in the coagulation bath. This method can effectively realize multi-stage stretching and multi-station integrated arrangement of the spinning line, thereby improving production efficiency and reducing fiber manufacturing costs.
[0007] The objective of this invention is achieved through the following technical solution: A method for solidifying and stretching aramid filaments in a bath includes the following steps: Step 1: The spinning coagulation solution first enters the inlet of the U-shaped small coagulation bath, flows out from its outlet, and then enters the large coagulation bath outside it. After the bath fills the large coagulation bath, it overflows from its end and returns to the coagulation solution circulation system. Step 2: The spinning solution is extruded through the spinneret to form a fine stream that enters the U-shaped coagulation bath. It undergoes double diffusion exchange with the coagulation liquid in the U-shaped coagulation bath, and then enters the outer large coagulation bath. There, it undergoes further double diffusion mass and heat transfer exchange with the coagulation liquid in the large coagulation bath to solidify and form the fiber. The fine stream extruded by the spinneret undergoes negative stretching in the U-shaped coagulation bath, and then undergoes the first stage of positive stretching after entering the outer large coagulation bath. Step 3: The fibers drawn from the large coagulation bath enter the drawing machine for a second-stage positive stretching operation, while further coagulating and forming. Then, through subsequent washing and drying processes, aramid yarn is obtained. The yarn is then heat-treated to obtain the finished yarn.
[0008] Preferably, the large coagulation bath is wider at the front and narrower at the back, and its depth is shallower at the front and deeper at the back; the U-shaped small coagulation bath is wider at the front and narrower at the back, and its depth is the same.
[0009] Preferably, the length of the U-shaped small coagulation bath is 1 / 3 to 2 / 3 of the length of the large coagulation bath.
[0010] Preferably, the solvent of the spinning solution is any one of N-methylpyrrolidone, N,N-dimethylacetamide, or N-methylformamide.
[0011] Preferably, the coagulation solution includes a solvent for the spinning solution and another liquid, wherein the other liquid is any one of water, ethanol, or ethylene glycol.
[0012] Preferably, the solvent content in the spinning solution is 35% to 65% in the coagulation solution.
[0013] Preferably, the flow rate of the coagulation bath in the U-shaped small coagulation bath is 0.2 to 1 m / min, and the flow rate of the coagulation bath in the large coagulation bath is 0.02 to 0.1 m / min.
[0014] Preferably, the temperature of the coagulated liquid is 20–40°C.
[0015] Preferably, during the first stage of positive stretching operation, the negative stretching rate is -55% to -25%.
[0016] Preferably, during the second-stage positive stretching operation, the fiber stretching rate is 50% to 90%.
[0017] The beneficial effects of this technical solution are as follows: I. The present invention provides a bath-in-bath coagulation and stretching forming method for aramid filaments. By controlling the flow rate of the coagulation liquid in the large coagulation bath and the U-shaped small coagulation bath, the negative stretching of the spinneret and the positive stretching of the gel-like nascent fiber in the wet spinning process can be achieved simultaneously in the coagulation bath. This method can effectively realize multi-stage stretching and multi-station integrated arrangement of the spinning line, thereby improving production efficiency and reducing fiber manufacturing costs.
[0018] II. The present invention provides a bath-in-bath coagulation and stretching forming method for aramid filaments, which improves the structural density of the fiber during coagulation; makes full use of the space inside the large coagulation bath, designs as many U-shaped small coagulation baths as possible inside it, increases the spinning station of the spinning line as much as possible, and increases the fiber output of the spinning line; it can achieve a fiber production scale of more than 32 stations on a spinning line.
[0019] III. The present invention provides a bath-in-bath coagulation and stretching method for aramid filaments. After the spinneret extrudes a fine stream into a large coagulation bath, the first stage of positive stretching is achieved under the resistance of the low-speed coagulation liquid and the traction of the subsequent drawing rollers. At the same time, further coagulation occurs in the large coagulation bath to form the primary structure of the fiber. The fiber drawn out from the large coagulation bath enters the drawing machine for a second stage of positive stretching to further form the secondary structure of the fiber. This two-stage stretching process not only achieves the stretching and orientation function of the fiber structure, but also produces less fiber fuzz and has a better fiber appearance quality.
[0020] IV. The present invention provides a bath-in-bath solidification and stretching forming method for aramid filaments, which is suitable for the large-scale preparation of ultrafine linear density fibers. The lower the fiber linear density, the lower the output per unit time and the lower the production efficiency. Increasing the number of spinning stations for integrated production is a good solution. It is conducive to the integrated arrangement of multiple spinning stations and provides a solution for the integrated large-scale preparation of ultrafine linear density fibers. The fiber produced by the present invention has fewer fuzzy fibers, which meets the high standard requirements of ultrafine linear density fibers for fuzzy fibers. Attached Figure Description
[0021] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a top view of the process flow of the present invention; The components include: 1. Coagulation bath rectifier plate; 2. Spinneret; 3. U-shaped small coagulation bath; 4. Large coagulation bath; 5. Fiber; 6. Drafting roller; 7. Small coagulation bath support plate. Detailed Implementation
[0022] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.
[0023] like Figure 1 , 2As shown, a bath-in-bath coagulation and stretching forming device for aramid filaments includes a large coagulation bath 4 of a specific shape, multiple U-shaped small coagulation baths 3 embedded in the large coagulation bath 4, and two sets of stretching rollers 6; the end of the U-shaped small coagulation bath 3 is provided with a small coagulation bath support plate 7.
[0024] The large coagulation bath 4 is wider at the front and narrower at the back, resembling a trapezoid in its top-view projection; its depth is also shallower at the front and deeper at the back, similarly resembling a trapezoid in its front-view projection. Multiple U-shaped smaller coagulation baths 3 are embedded within the large coagulation bath 4. The length of each U-shaped smaller coagulation bath 3 is approximately 1 / 3 to 2 / 3 of the length of the large coagulation bath 4. The width of each U-shaped smaller coagulation bath 3 is wider at the front and narrower at the back, resembling a trapezoid in its top-view projection. All parts of the U-shaped smaller coagulation bath 3 have the same depth, resembling a rectangle in its front-view projection.
[0025] When the large coagulation bath 4 is filled with coagulation liquid, the coagulation liquid enters the entire bath, and the U-shaped small coagulation bath 3 is partially submerged in the coagulation liquid, forming a "bath within a bath" coagulation forming device in which multiple U-shaped small coagulation baths 3 are contained within the large coagulation bath 4.
[0026] The coagulating liquid enters the large coagulation bath 4 from the front end, passes through the coagulation bath rectifier plate 1, and enters the location of the spinneret 2. Then, together with the fine stream extruded from the spinneret 2, it enters the U-shaped small coagulation bath 3, flows out from the U-shaped small coagulation bath 3, and then enters the large coagulation bath 4. Finally, it flows out from the tail end of the large coagulation bath 4.
[0027] The spinneret 2 extrudes a fine stream (fiber 5) which solidifies and forms in a U-shaped small coagulation bath 3 and undergoes a negative stretching operation. Then it enters a large coagulation bath 4 for further solidification and forms, undergoes a first positive stretching operation, and finally undergoes a second positive stretching operation through the stretching roller 6.
[0028] A method for solidifying and stretching aramid filaments in a bath includes the following steps: Step 1: The spinning coagulation solution first enters the inlet of the U-shaped small coagulation bath, flows out from its outlet, and then enters the large coagulation bath outside it. After the bath fills the large coagulation bath, it overflows from its end and returns to the coagulation solution circulation system. Step 2: The spinning solution is extruded through the spinneret to form a fine stream that enters the U-shaped coagulation bath. It undergoes double diffusion exchange with the coagulation liquid in the U-shaped coagulation bath, and then enters the outer large coagulation bath. There, it undergoes further double diffusion mass and heat transfer exchange with the coagulation liquid in the large coagulation bath to solidify and form the fiber. The fine stream extruded by the spinneret undergoes negative stretching in the U-shaped coagulation bath, and then undergoes the first stage of positive stretching after entering the outer large coagulation bath. Step 3: The fibers drawn from the large coagulation bath enter the drawing machine for a second-stage positive stretching operation, while further coagulating and forming. Then, through subsequent washing and drying processes, aramid yarn is obtained. The yarn is then heat-treated to obtain the finished yarn.
[0029] The large coagulation bath is wider at the front and narrower at the back, and its depth is shallower at the front and deeper at the back; the U-shaped small coagulation bath is wider at the front and narrower at the back, and its depth is the same.
[0030] The length of the U-shaped small coagulation bath is 1 / 3 to 2 / 3 of the length of the large coagulation bath.
[0031] The solvent of the spinning solution is any one of N-methylpyrrolidone, N,N-dimethylacetamide, or N-methylformamide.
[0032] The coagulation solution includes the solvent of the spinning solution and another liquid, which can be any one of water, ethanol, or ethylene glycol.
[0033] The solvent content in the spinning solution is 35% to 65% in the coagulation solution.
[0034] The coagulation bath flows at a velocity of 0.2–1 m / min in the small U-shaped coagulation bath and 0.02–0.1 m / min in the large coagulation bath. The flow rate of the coagulation bath is controlled by adjusting the cross-sectional area of the flow channel. A larger cross-sectional area in the large coagulation bath results in a lower flow velocity of the coagulation bath, which increases the resistance to the fiber spinning process and facilitates positive stretching under the traction of the subsequent drafting rollers.
[0035] The temperature of the coagulation liquid is 20–40°C. If the temperature is too low, the fiber coagulation rate is too slow; if the temperature is too high, the fiber coagulation rate is too fast. Both situations are unfavorable for subsequent fiber stretching operations.
[0036] During the first stage of positive stretching, the negative stretching rate is -55% to -25%. If the negative stretching is too large, the fine streams extruded from the spinneret will easily accumulate in the bath, preventing normal spinning; if the negative stretching is too small, the fine streams extruded from the spinneret will not solidify and shrink completely in the bath, affecting fiber properties.
[0037] After the spinneret extrudes a fine stream into the large coagulation bath, it achieves the first stage of positive stretching under the resistance of the low-speed coagulation liquid and the traction of the subsequent drawing rollers. At the same time, it further solidifies in the large coagulation bath to form the primary structure of the fiber.
[0038] During the second stage of positive stretching, the fiber stretch rate is 50% to 90%. If the stretch rate is too low, the fiber performance will be reduced and will not meet the application requirements; if the stretch rate is too high, the fiber fuzz will increase and the quality will decrease.
[0039] Example 1 A bath-in-bath coagulation and stretching method for aramid filaments involves dissolving para-heterocyclic aramid polymers in the solvent N-methylpyrrolidone to form a spinning solution. The spinning solution is extruded through a spinneret to form a fine stream, which then enters a U-shaped small coagulation bath and an external large coagulation bath for coagulation and stretching operations. It then enters a drawing roller for secondary stretching, followed by subsequent washing and drying processes to obtain aramid precursor fibers. The precursor fibers are then heat-treated to obtain the finished filaments.
[0040] The coagulation solution is composed of N-methylpyrrolidone and water, wherein the content of N-methylpyrrolidone in water is 35%.
[0041] The flow rate of the coagulating liquid in the U-shaped small coagulation bath is 1 m / min, and the flow rate in the large coagulation bath is 0.1 m / min.
[0042] The temperature of the coagulated liquid was the same in both the small U-shaped coagulation bath and the large coagulation bath, which was 20℃.
[0043] The spinneret extrudes a fine stream into a small U-shaped coagulation bath for negative stretching, with a negative stretching rate of -55%.
[0044] The fibers drawn from the large coagulation bath enter the drawing machine for a second-stage positive stretching operation, with a fiber stretching rate of 90%.
[0045] The fiber prepared by the bath-in-bath solidification stretching method of this embodiment has a tensile strength of 31.3 cN / dtex and a fiber filament grade of 1.
[0046] Example 2 A bath-in-bath coagulation and stretching method for aramid filaments involves dissolving para-heterocyclic aramid polymers in the solvent N-methylpyrrolidone to form a spinning solution. The spinning solution is extruded through a spinneret to form a fine stream, which then enters a U-shaped small coagulation bath and an external large coagulation bath for coagulation and stretching operations. It then enters a drawing roller for secondary stretching, followed by subsequent washing and drying processes to obtain aramid precursor fibers. The precursor fibers are then heat-treated to obtain the finished filaments.
[0047] The coagulation solution is composed of N-methylpyrrolidone and water, wherein the content of N-methylpyrrolidone in water is 65%.
[0048] The flow rate of the coagulating liquid in the U-shaped small coagulation bath is 0.2 m / min, and the flow rate in the large coagulation bath is 0.02 m / min.
[0049] The temperature of the coagulated liquid was the same in both the small U-shaped coagulation bath and the large coagulation bath, which was 40℃.
[0050] The spinneret extrudes a fine stream into a small U-shaped coagulation bath for negative stretching, with a negative stretching rate of -25%.
[0051] The fibers drawn from the large coagulation bath enter the drawing machine for a second-stage positive stretching operation, with a fiber stretching rate of 50%.
[0052] The fiber prepared by the bath-in-bath solidification stretching method of this embodiment has a tensile strength of 28.7 cN / dtex and a fiber filament grade of 1.
[0053] Example 3 A bath-in-bath coagulation and stretching method for aramid filaments involves dissolving para-heterocyclic aramid polymers in N-methylformamide to form a spinning solution. The spinning solution is extruded through a spinneret to form a fine stream, which then enters a U-shaped small coagulation bath and an external large coagulation bath for coagulation and stretching operations. It then enters a drawing roller for secondary stretching, followed by washing and drying processes to obtain aramid precursor fibers. The precursor fibers are then heat-treated to obtain the finished filaments.
[0054] The coagulation solution is composed of N-methylformamide and water, wherein the content of N-methylformamide in the water is 65%.
[0055] The flow rate of the coagulating liquid in the U-shaped small coagulation bath is 0.5 m / min, and the flow rate in the large coagulation bath is 0.05 m / min.
[0056] The temperature of the coagulated liquid was the same in both the small U-shaped coagulation bath and the large coagulation bath, which was 30℃.
[0057] The spinneret extrudes a fine stream into a small U-shaped coagulation bath for negative stretching, with a negative stretching rate of -45%.
[0058] The fibers drawn from the large coagulation bath enter the drawing machine for a second-stage positive stretching operation, with a fiber stretching rate of 79%.
[0059] The fiber prepared by the bath-in-bath solidification stretching method of this embodiment has a tensile strength of 30.2 cN / dtex and a fiber filament grade of 1.
[0060] Example 4 A bath-in-bath coagulation and stretching method for aramid filaments involves dissolving para-heterocyclic aramid polymers in the solvent N,N-dimethylacetamide to form a spinning solution. The spinning solution is extruded through a spinneret to form a fine stream, which then enters a U-shaped small coagulation bath and an external large coagulation bath for coagulation and stretching operations. The filament then enters a drawing roller for secondary stretching, followed by washing and drying processes to obtain aramid precursor fibers. The precursor fibers are then heat-treated to obtain the finished filament.
[0061] The coagulation solution is composed of N,N-dimethylacetamide and water, wherein the content of N,N-dimethylacetamide in water is 55%.
[0062] The flow rate of the coagulating liquid in the U-shaped small coagulation bath is 0.6 m / min, and the flow rate in the large coagulation bath is 0.06 m / min.
[0063] The temperature of the coagulated liquid was the same in both the small U-shaped coagulation bath and the large coagulation bath, which was 35℃.
[0064] The spinneret extrudes a fine stream into a small U-shaped coagulation bath for negative stretching, with a negative stretching rate of -40%.
[0065] The fibers drawn from the large coagulation bath enter the drawing machine for a second-stage positive stretching operation, with a fiber stretching rate of 68%.
[0066] The fiber prepared by the bath-in-bath solidification stretching method of this embodiment has a tensile strength of 29.6 cN / dtex and a fiber filament grade of 1.
[0067] Example 5 A bath-in-bath coagulation and stretching method for aramid filaments involves dissolving para-heterocyclic aramid polymers in the solvent N,N-dimethylacetamide to form a spinning solution. The spinning solution is extruded through a spinneret to form a fine stream, which then enters a U-shaped small coagulation bath and an external large coagulation bath for coagulation and stretching operations. The filament then enters a drawing roller for secondary stretching, followed by washing and drying processes to obtain aramid precursor fibers. The precursor fibers are then heat-treated to obtain the finished filament.
[0068] The coagulation solution is composed of N,N-dimethylacetamide and water, wherein the content of N,N-dimethylacetamide in water is 45%.
[0069] The flow rate of the coagulating liquid in the U-shaped small coagulation bath is 0.3 m / min, and the flow rate in the large coagulation bath is 0.03 m / min.
[0070] The temperature of the coagulated liquid was the same in both the small U-shaped coagulation bath and the large coagulation bath, which was 25°C.
[0071] The spinneret extrudes a fine stream into a small U-shaped coagulation bath for negative stretching, with a negative stretching rate of -50%.
[0072] The fibers drawn from the large coagulation bath enter the drawing machine for a second-stage positive stretching operation, with a fiber stretching rate of 85%.
[0073] The fiber prepared by the bath-in-bath solidification stretching method of this embodiment has a tensile strength of 30.8 cN / dtex and a fiber filament grade of 1.
[0074] Example 6 This embodiment is based on Example 5, with all other conditions being the same. The main difference is that the water in the coagulation solution is replaced with ethanol and ethylene glycol, respectively, to compare the mechanical properties and filament state of the prepared fibers.
[0075] The experimental conditions and results of Examples 5 and 6 are compared and listed in Table 1 below.
[0076] Table 1 As a comparative example, Example 6 is an adjustment based on Example 5, in which the water in the coagulation liquid is replaced with ethanol and ethylene glycol respectively, while the other process parameters remain unchanged.
[0077] Replacing water with ethanol in the coagulation solution did not change the fiber filaments to Grade 1, but the tensile strength of the fibers increased. This indicates that using ethanol instead of water as the coagulation solution is beneficial for improving fiber properties.
[0078] Replacing ethanol in the coagulation solution with ethylene glycol did not change the fiber filaments; instead, the tensile strength of the fibers remained at grade 1. This is because ethylene glycol is more polar than ethanol, making it easier to extract DMAC from the polymer stream extruded from the spinneret during coagulation. This results in a denser fiber structure and higher performance.
[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.
Claims
1. A method for solidifying and stretching aramid filaments in a bath, characterized in that, Includes the following steps: Step 1: The spinning coagulation solution first enters the inlet of the U-shaped small coagulation bath, flows out from its outlet, and then enters the large coagulation bath outside it. After the bath fills the large coagulation bath, it overflows from its end and returns to the coagulation solution circulation system. Step 2: The spinning solution is extruded through the spinneret to form a fine stream that enters the U-shaped coagulation bath. It undergoes double diffusion exchange with the coagulation liquid in the U-shaped coagulation bath and then enters the external large coagulation bath, where it undergoes further double diffusion mass and heat transfer exchange with the coagulation liquid to solidify and form the fiber. The spinneret extrudes a fine stream that undergoes negative stretching in a small U-shaped coagulation bath, and then undergoes the first stage of positive stretching after entering a large coagulation bath outside it. Step 3: The fibers drawn from the large coagulation bath enter the drawing machine for a second-stage positive stretching operation, while further coagulating and forming. Then, through subsequent washing and drying processes, aramid yarn is obtained. The yarn is then heat-treated to obtain the finished yarn.
2. The method for solidifying and stretching aramid filaments in a bath according to claim 1, characterized in that: The large coagulation bath is wider at the front and narrower at the back, and its depth is shallower at the front and deeper at the back; the U-shaped small coagulation bath is wider at the front and narrower at the back, and its depth is the same.
3. The bath-in-bath solidification and stretching method for aramid filaments according to claim 1, characterized in that: The length of the U-shaped small coagulation bath is 1 / 3 to 2 / 3 of the length of the large coagulation bath.
4. The bath-in-bath solidification and stretching method for aramid filaments according to claim 1, characterized in that: The solvent of the spinning solution is any one of N-methylpyrrolidone, N,N-dimethylacetamide, or N-methylformamide.
5. The method for solidifying and stretching aramid filaments in a bath according to claim 1, characterized in that: The coagulation solution includes the solvent of the spinning solution and another liquid, which can be any one of water, ethanol, or ethylene glycol.
6. The method for solidifying and stretching aramid filaments in a bath according to claim 1, characterized in that: The solvent content in the spinning solution is 35% to 65% in the coagulation solution.
7. The method for solidifying and stretching aramid filaments in a bath according to claim 1, characterized in that: The flow rate of the coagulation bath in the U-shaped small coagulation bath is 0.2 to 1 m / min, and the flow rate of the coagulation bath in the large coagulation bath is 0.02 to 0.1 m / min.
8. The method for solidifying and stretching aramid filaments in a bath according to claim 1, characterized in that: The temperature of the coagulated liquid is 20–40°C.
9. The method for solidifying and stretching aramid filaments in a bath according to claim 1, characterized in that: During the first stage of positive stretching operation, the negative stretching rate is -55% to -25%.
10. The method for solidifying and stretching aramid filaments in a bath according to claim 1, characterized in that: During the second stage of positive stretching, the fiber stretch rate is 50% to 90%.