A process for the production of dry-jet wet-spun nascent fibres and a coagulation bath fibre turning device and the resulting nascent fibres

Abstract

The application provides a preparation method of dry-jet wet-spun primary fiber and relates to the field of polyacrylonitrile-based carbon fiber precursor preparation, and mainly solves the problems of large single-fiber variation, more hair, broken filaments and more blocking. The technical scheme of the application is that the spinning dope containing solvent and acrylonitrile copolymer is extruded through a spinneret into an air bath and is jetted into a coagulation bath tank after being drawn, and the dope is coagulated, turned and led out in the coagulation bath tank with combined passive rollers, so that the above problems are solved. The application can be used in the field of carbon fiber dry-jet wet-spun precursor preparation.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber preparation, specifically relating to a method for preparing dry-jet wet-spinning nascent fibers and the obtained nascent fibers, as well as a coagulation bath fiber turning device used to prepare the nascent fibers. Background Technology

[0002] Carbon fiber is a special fiber material with extremely high tensile strength and Young's modulus, and it has a wide range of applications. In recent years, its usage has increased significantly in various applications requiring lightweighting. Based on different mechanical properties, carbon fiber can be divided into several categories, including general-purpose grade, high-strength carbon fiber, and high-modulus carbon fiber. Among them, polyacrylonitrile-based high-strength carbon fiber is currently the most widely used carbon fiber product.

[0003] Over the years, there have been two main processes for forming polyacrylonitrile-based carbon fiber precursor: wet spinning and dry-jet wet spinning. Compared to wet spinning, dry-jet wet spinning is relatively new, with only about forty years of reported applications. Although dry-jet wet spinning presents more technical challenges, its advantages are significant. It readily yields fiber products with fewer defects, which is crucial for carbon fiber production. Carbon fiber is a brittle material, highly sensitive to stress concentration caused by defects, and stress concentration is a major cause of carbon fiber breakage. Therefore, carbon fibers obtained through the dry-jet wet spinning process have better mechanical strength. Specifically, currently, commercially available carbon fiber products based on the dry-jet wet spinning process have a strength reaching 7.0 GPa, while the highest tensile strength of products obtained through wet spinning is approximately 5.5 GPa.

[0004] In practical applications, carbon fiber needs to be composited with various resins to prepare structural components. This requires that, in addition to high modulus and high strength, the carbon fiber must have low levels of defects such as fiber fineness variation, fuzz, broken fibers, fused fibers, and agglomerates. If there are many such defects in the precursor fiber, they will be inherited by the carbon fiber, resulting in a situation where, although the carbon fiber meets or even exceeds the nominal specifications in terms of mechanical properties, the structural components that meet the expected performance after being composited with the resin cannot be obtained. This requires that the process design not only consider the characteristics of the precursor fiber but also the stability of the spinning process. Overall, the coagulation process of dry-jet wet spinning is the most problematic stage, with many issues such as fuzz, broken fibers, fused fibers, and agglomerates most likely to occur in the first coagulation bath. Therefore, how to control the first coagulation bath to improve fiber quality is a major focus of current technological research and development in this field.

[0005] While there are numerous reports on improving the stability of the coagulation process, the problems of fiber fuzz, broken fibers, tangled fibers, and agglomeration have not been completely resolved. KR1020180087545A reports the use of a special surface treatment method to treat the internal components of the coagulation bath to mitigate liquid level fluctuations caused by the collapse of rising bubbles, thus making the coagulation process more stable. Although this method can prevent fluctuations in the coagulation bath liquid level caused by the collapse of rising bubbles, problems such as fuzz and roller wrapping still cannot be avoided due to defects in stress transmission.

[0006] KR101401148B1 discloses a design scheme for internal components of a coagulation bath, which involves setting multiple passive rollers inside the coagulation bath, with the angle of each passive roller limited to an obtuse angle to reduce tension loss caused by friction. However, while setting too many passive rollers can reduce the wrap angle when passing through each passive roller, the patent uses a maximum of nine passive rollers. Since the filament needs to pass through multiple passive rollers during movement, the possibility of it wrapping around the rollers without changing the shape of the passive rollers is also greatly increased.

[0007] KR101429378B1 discloses a method for controlling airflow in dry-jet wet spinning to improve spinning stability. However, since the air section is very short in conventional processes, it is difficult to fully diffuse the gas to solve the problem of runoff, even if the airflow field is adjusted.

[0008] JP2001049524A proposes controlling the contact time between the filament and the roller to produce high-quality carbon fiber. However, the proposed solution uses a small-diameter passive roller to achieve an acute-angle turn, making filament entanglement during the spinning process virtually unavoidable. CN206799803U proposes using a tubular coagulation bath to enhance the directionality of liquid flow, improve the quality of the raw filament, and avoid instability during the spinning process. However, due to the relatively small operating space of this solution, cleaning is inevitably difficult when the fiber entangles the roller, and production efficiency cannot be guaranteed.

[0009] A relatively simple and practical solution to address various instabilities in spinning remains adjusting the geometric arrangement and passive roller morphology. This approach means minimal impact on other production processes, requires no changes to existing techniques, and is relatively easy to implement. Summary of the Invention

[0010] To address the problems existing in the prior art, this invention provides a method for preparing dry-jet wet-spun nascent fibers, which can effectively improve the transmission efficiency of tensile stress and obtain fibers with small monofilament variability under low draw-out tension. At the same time, this invention can also significantly expand the operating space of air gap length and reduce abnormalities such as fuzz, broken fibers, and agglomeration.

[0011] One objective of this invention is to provide a method for preparing dry-jet wet-spun nascent fibers, comprising extruding the spinning solution through a spinneret into an air bath for drafting, followed by coagulation in a coagulation bath to obtain the nascent fibers, wherein the included angle formed between the spinneret, the passive roller in the coagulation bath, and the first roller is 120-150°. In this invention, the spinning solution is extruded through a spinneret into an air bath for drafting, and after the solution passes through a coagulation bath with special internal components and is drawn out, nascent fibers with fewer fuzz and lower monofilament variability can be obtained.

[0012] In the above preparation method, the coagulation bath includes at least one passive roller, preferably 2 to 4 passive rollers.

[0013] In the above preparation method:

[0014] The passive roller can be designed in the field of passive rollers. Preferably, the passive roller is at least one of elliptical, strip-shaped, and teardrop-shaped. The passive roller with a special shape design in this invention can prevent the elastic fibers from entering the filament bundle and prevent fuzz and filament wrapping.

[0015] The surface finish of the passive roller is Ra≤0.5, preferably Ra≤0.2;

[0016] The surface of the passive roller that contacts the fiber is arc-shaped, preferably with a radius of 2 to 10 mm.

[0017] In the above preparation method, the spinning solution includes a polyacrylonitrile copolymer and a solvent.

[0018] Specifically, the polyacrylonitrile copolymer is obtained by copolymerizing at least one of itaconic acid, acrylic acid, methyl acrylate, methacrylic acid, acrylamide, and styrene sulfonate with acrylonitrile;

[0019] The intrinsic viscosity of the polyacrylonitrile copolymer is 1.6 to 3.6.

[0020] The acrylonitrile monomer content in the polyacrylonitrile copolymer is not less than 97% by mass percentage;

[0021] The solvent of the spinning solution is selected from polar aprotic solvents, preferably selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide;

[0022] The polyacrylonitrile copolymer content in the spinning solution is 15-28% by mass percentage, preferably 18-24%.

[0023] In the above preparation method,

[0024] The spinneret has an orifice diameter of 0.075–0.3 mm;

[0025] The extrusion temperature of the spinning solution is 25–90°C.

[0026] In the above preparation method, the air bath stretching ratio is 1.2 to 4.8;

[0027] The height of the air bath is 5-30mm.

[0028] In the above preparation method,

[0029] The solvent of the coagulation bath is a mixture of water and a polar aprotic solvent, wherein the polar aprotic solvent in the coagulation bath solvent is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0030] The water content in the coagulation bath solvent is 25-85% by mass percentage, preferably 30-80%;

[0031] The temperature of the coagulation bath is -20 to 35°C.

[0032] The second objective of this invention is to provide a nascent polyacrylonitrile fiber, which is prepared by the above-described preparation method.

[0033] The third objective of this invention is to provide a coagulation bath fiber turning device for preparing the above-mentioned polyacrylonitrile nascent fibers. Preferably, the coagulation bath fiber turning device includes a spinneret, a passive roller, and a first roller.

[0034] Specifically, the aforementioned coagulation bath fiber turning device includes at least one passive roller, preferably 2 to 4 passive rollers; in the coagulation bath fiber turning device, the angle formed by the line connecting any three adjacent components among the spinneret, the coagulation bath passive roller, and the first roller is 120 to 150°; the surface finish of the passive roller is Ra≤0.5, preferably Ra≤0.2; the surface of the passive roller in contact with the fiber is arc-shaped, preferably with a radius of 2 to 10 mm.

[0035] This invention primarily achieves the aforementioned effects by adjusting the morphology and spatial arrangement of the passive rollers. Specifically, it utilizes a steering device composed of multiple passive rollers in the coagulation bath, with obtuse angles between the components. This reduces the passive friction force on the filaments, improves stress transmission efficiency during the spinning process, and enhances spinning stability. When fibers experience abnormal breakage, they spring back, and under various disturbances, these springback fibers are drawn into the filament bundle, ultimately resulting in roller wrapping. This invention alters the structure of the inherent steering roller, making roller wrapping more difficult and solving the problem of nascent fibers wrapping around the roller in dry-jet wet spinning.

[0036] Compared with the prior art, this application has the following beneficial effects:

[0037] This invention significantly reduces tensile stress loss due to friction without altering existing processes by employing a special coagulation bath steering internal component, thereby minimizing the possibility of fuzzy fibers, broken fibers, and roller wrapping. It can be used to prepare nascent fibers with fewer defects and lower monofilament variability. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the internal component arrangement of the coagulation bath fiber turning device in an embodiment of the present invention.

[0039] The diagram shows the following labels: 1 is the first passive roller, 2 is the second passive roller, 3 is the third passive roller, 4 is the first roller, and 5 is the spinneret.

[0040] Figure 1 visible:

[0041] The coagulation bath fiber turning device described in this embodiment of the invention comprises three passive rollers. In this device, the angles formed by the lines connecting any three adjacent components—the spinneret, the passive rollers, and the first roller—are, in sequence, the first included angle, the second included angle, and the third included angle. The surface finish Ra of the passive rollers is ≤0.2. The surface of the passive rollers in contact with the fibers is arc-shaped.

[0042] Figure 2 This is a schematic diagram of the elliptical passive roller in this invention.

[0043] Figure 3 This is a schematic diagram of the strip-shaped passive roller in this invention.

[0044] Figure 4 This is a schematic diagram of the teardrop-shaped passive roller in this invention. Detailed Implementation

[0045] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0046] The testing instruments and conditions used in this embodiment are as follows:

[0047] In the following cases, the fiber monofilament variability test was performed in accordance with the standard specified in GB / T 31290-2014 Determination of Tensile Properties of Carbon Fiber Monofilaments.

[0048] The mass of fibers removed from the rollers per hour is the total number of broken fibers in the coagulation bath at the end of spinning, divided by the spinning time.

[0049] All raw materials used in the examples are commercially available products.

[0050] Example 1

[0051] A 22% (w / w) dimethyl sulfoxide solution of polyacrylonitrile copolymer was used. The copolymer monomers were acrylonitrile and itaconic acid, with acrylonitrile comprising 97% (w / w) and itaconic acid comprising 3% (w / w). The intrinsic viscosity of the copolymer was 2.4.

[0052] The stock solution is extruded from a spinneret at 25°C, with an air bath stretch ratio of 2.1. The coagulation bath is a mixture of dimethyl sulfoxide and water, with a water content of 75% by mass. The coagulation bath contains a guide roller consisting of three passive rollers; the structure of the guide roller is shown in the attached diagram. Figure 2 The surface roughness Ra≤0.2, the surface of the passive roller in contact with the fiber is arc-shaped with a radius of 5mm; the three segments formed by the spinneret 5, the first passive roller 1, the second passive roller 2, the third passive roller 3, and the first roller 4 have included angles of 120°, 120°, and 120° respectively, with no winding around the roller, 0.5g of broken filaments are removed per hour, and the fiber fineness cv value is 2.2%.

[0053] Example 2

[0054] A 22% (w / w) dimethyl sulfoxide solution of polyacrylonitrile copolymer was used. The copolymer monomers were acrylonitrile and itaconic acid, with acrylonitrile comprising 97% (w / w) and itaconic acid comprising 3% (w / w). The intrinsic viscosity of the copolymer was 1.9.

[0055] The stock solution is extruded from a spinneret at 25°C, with an air bath stretch ratio of 2.4. The coagulation bath is a mixture of dimethyl sulfoxide and water, with a water content of 75% by mass. The coagulation bath contains a guide roller consisting of three passive rollers; the structure of the guide roller is shown in the attached diagram. Figure 4 The surface roughness Ra≤0.2, the contact surface between the passive roller and the fiber is arc-shaped with a radius of 5mm; the three segments formed by the spinneret 5, the first passive roller 1, the second passive roller 2, the third passive roller 3, and the first roller 4 have included angles of 135°, 120°, and 120° respectively, with no winding around the roller, and 0.7g of broken filaments are removed per hour, with a fiber fineness cv value of 2.4%.

[0056] Example 3

[0057] A 22% (w / w) dimethyl sulfoxide solution of polyacrylonitrile copolymer was used. The copolymer monomers were acrylonitrile and itaconic acid, with acrylonitrile comprising 97% (w / w) and itaconic acid comprising 3% (w / w). The intrinsic viscosity of the copolymer was 1.9.

[0058] The stock solution is extruded from a spinneret at 25°C, with an air bath stretch ratio of 2.4. The coagulation bath is a mixture of dimethyl sulfoxide and water, with a water content of 75% by mass. The coagulation bath contains a guide roller consisting of three passive rollers; the structure of the guide roller is shown in the attached diagram. Figure 2The surface roughness Ra≤0.2, the contact surface between the passive roller and the fiber is arc-shaped with a radius of 5mm; the three segments formed by the spinneret 5, the first passive roller 1, the second passive roller 2, the third passive roller 3, and the first roller 4 have included angles of 135°, 135°, and 120° respectively, with no winding around the roller, 0.2g of broken filaments are removed per hour, and the fiber fineness cv value is 2.5%.

[0059] Comparative Example 1

[0060] A 22% (w / w) dimethyl sulfoxide solution of polyacrylonitrile copolymer was used. The copolymer monomers were acrylonitrile and itaconic acid, with acrylonitrile comprising 97% (w / w) and itaconic acid comprising 3% (w / w). The intrinsic viscosity of the copolymer was 1.9.

[0061] The solution is extruded from a spinneret at 25°C, with an air bath stretch ratio of 2.4. The coagulation bath is a mixture of dimethyl sulfoxide and water, with a water content of 75% by mass. A single passive steering roller is used; the passive roller is cylindrical with a diameter of 5mm and a surface roughness Ra≤0.2. The angle formed by the spinneret, the passive roller, and the first roller is 75°. 5g of fiber is removed from the roller per hour, along with 0.8g of broken fibers, and the fiber fineness cv value is 3.5%.

[0062] Comparative Example 2

[0063] A 22% (w / w) dimethyl sulfoxide solution of polyacrylonitrile copolymer was used. The copolymer monomers were acrylonitrile and itaconic acid, with acrylonitrile comprising 97% (w / w) and itaconic acid comprising 3% (w / w). The intrinsic viscosity of the copolymer was 1.9.

[0064] The raw solution is extruded from the spinneret at 25°C, with an air bath stretch ratio of 2.4. The coagulation bath is a mixture of dimethyl sulfoxide and water, with a water content of 75% by mass. A single passive steering roller is used. The passive roller is cylindrical with a diameter of 15 mm and a surface roughness Ra≤0.2. The included angle between the spinneret, the passive roller, and the first roller is 75°. During the spinning process, coagulation and adsorption onto the plate surface frequently occur, causing filament breakage and making the spinning process impossible.

[0065] As can be seen from the above embodiments and comparative examples, using the combined guide roller described in this invention, nascent fibers with low monofilament variability can be stably obtained under low tensile stress conditions. Even under low stress and large air gaps, the monofilament variability can still be controlled at a low level, reducing the probability of spinning abnormalities such as clumping, breakage, and fuzz. Furthermore, it fundamentally solves the problem of roller wrapping, resulting in a more stable spinning process and better fiber quality.

Claims

1. A method for preparing dry-jet wet-spun nascent fibers, comprising extruding a spinning solution through a spinneret into an air bath for drafting, followed by coagulation in a coagulation bath to obtain the nascent fibers, wherein... The included angle formed between the fiber and the spinneret, the passive roller in the coagulation bath, and the first roller is 120-150°. The passive roller is shaped as at least one of elliptical, strip-shaped, or teardrop-shaped. The surface of the passive roller that contacts the fiber is arc-shaped with a radius of 2-10 mm.

2. The preparation method according to claim 1, characterized in that, The coagulation bath includes at least one passive roller.

3. The preparation method according to claim 2, characterized in that, The coagulation bath includes 2 to 4 passive rollers.

4. The preparation method according to claim 1, characterized in that, The surface finish of the passive roller is Ra≤0.

5.

5. The preparation method according to claim 4, characterized in that, The surface finish of the passive roller is Ra≤0.

2.

6. The preparation method according to claim 1, characterized in that, The spinning solution includes a polyacrylonitrile copolymer and a solvent.

7. The preparation method according to claim 6, characterized in that, The polyacrylonitrile copolymer is obtained by copolymerizing at least one of itaconic acid, acrylic acid, methyl acrylate, methacrylic acid, acrylamide, and styrene sulfonate with acrylonitrile; and / or, The intrinsic viscosity of the polyacrylonitrile copolymer is 1.6–3.6; and / or, The acrylonitrile monomer content in the polyacrylonitrile copolymer is not less than 97% by mass percentage; and / or, The solvent of the spinning solution is selected from polar aprotic solvents; and / or, The polyacrylonitrile copolymer content in the spinning solution is 15-28% by mass percentage.

8. The preparation method according to claim 7, characterized in that, The solvent of the spinning solution is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; and / or, The polyacrylonitrile copolymer content in the spinning solution is 18-24% by mass percentage.

9. The preparation method according to claim 1, characterized in that, The spinneret orifice diameter is 0.075–0.3 mm; and / or, The extrusion temperature of the spinning solution is 25–90°C.

10. The preparation method according to claim 1, characterized in that, The air bath draw ratio is 1.2 to 4.8; and / or, The height of the air bath is 5–30 mm.

11. The preparation method according to claim 1, characterized in that, The solvent in the coagulation bath is a mixture of water and a polar aprotic solvent; and / or, The temperature of the coagulation bath is -20 to 35°C.

12. The preparation method according to claim 11, characterized in that, The water content in the coagulation bath solvent is 25-85% by mass percentage; and / or, The polar aprotic solvent in the coagulation bath solvent is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

13. The preparation method according to claim 12, characterized in that, The water content in the coagulation bath solvent is 30-80% by mass percentage.

14. A type of nascent polyacrylonitrile fiber, prepared by the preparation method according to any one of claims 1 to 13.

15. A coagulation bath fiber turning device for preparing the polyacrylonitrile nascent fiber of claim 14, wherein the coagulation bath fiber turning device comprises a spinneret, a passive roller and a first roller, and the passive roller is shaped as at least one of elliptical, strip-shaped and teardrop-shaped.

16. The coagulation bath fiber turning device according to claim 15, characterized in that, The coagulation bath fiber turning device includes at least one passive roller; and / or, In the aforementioned coagulation bath fiber turning device, the angle formed by the lines connecting any three adjacent components—the spinneret, the coagulation bath passive roller, and the first roller—is 120–150°; and / or, The surface finish of the passive roller is Ra≤0.5; and / or, The surface of the passive roller that contacts the fiber is arc-shaped.

17. The coagulation bath fiber turning device according to claim 16, characterized in that, The coagulation bath fiber turning device includes 2 to 4 passive rollers; and / or, The surface finish of the passive roller is Ra≤0.2; and / or, The radius of the arc is 2 to 10 mm.

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