A spinning process for polyamide fibers

Abstract

The application provides a polyamide fiber spinning process to solve the problem that the impurity removal method of polyamide fiber in the prior art is too simple and rough, and the fiber impurities are difficult to remove, and to improve the insulation performance and aging resistance of the fiber and its products. The application scheme comprises the following steps: polyamide fiber spinning solution is coagulated and formed to obtain a formed fiber yarn, then the formed fiber yarn is subjected to plasticization stretching, washing and drying, and finally the dried fiber yarn is subjected to heat treatment to obtain a polyamide fiber; ultrasonic waves are added in the plasticization stretching process to wash the fiber yarn. The application promotes the diffusion of residual inorganic salts, solvents and other substances in the fiber out through the multistage plasticization stretching and countercurrent washing process, effectively reduces the content of metal elements and solvent impurities in the fiber. Through the combination of wet heat treatment and dry heat treatment, the insulation performance and aging resistance of the fiber and its products are improved.

Description

Technical Field

[0001] This invention belongs to the field of polyamide fiber material technology, and particularly relates to a spinning process for polyamide fibers. Background Technology

[0002] Polyamide fiber materials, due to their unique molecular structure, possess excellent insulation, heat resistance, and chemical stability, and are widely used in high-temperature insulation, filtration, and other fields. For example, meta-aramid fiber (also known as meta-aramid fiber or aramid 1313) has been widely used in the preparation of insulating paper and electrical insulation materials. However, impurities such as metal elements and solvents are introduced during the preparation of polyamide fiber dopes; the amount of these impurities significantly affects the insulation and aging resistance of the fibers. Therefore, removing impurities from polyamide fibers is a crucial problem that must be solved to improve fiber performance.

[0003] Chinese patent CN201310153950.3 discloses a method for preparing meta-aramid fibers. By not neutralizing the spinning solution, the hydrogen chloride generated during the reaction is retained in the spinning solution, resulting in a salt-free poly(m-phenylene isophthalamide) spinning solution. Furthermore, the entire fiber manufacturing process uses only deionized water and solvents, eliminating the need for salt. This leads to a final meta-aramid fiber product with extremely low ion content and ash content, and simplifies the solvent recovery process, saving significant energy. However, the presence of a large amount of hydrogen chloride in the spinning solution in this patent can cause the polymer to easily undergo degradation reactions, placing high demands on the equipment in contact with the spinning solution.

[0004] Chinese patent CN201610885181.X discloses a washing method for meta-aramid precipitated fibers. This method employs a six-stage continuous washing process, with acid added to the wash water from the fourth stage to the first stage. The acidic wash solution acidifies the fibers, loosening the surface crust and increasing the penetration rate of the wash water, thus accelerating the precipitation of Cl- from the fibers. - And the diffusion and dissolution of chloride salts in the washing water. The precipitated fiber product obtained by this washing method contains Cl... - Ion content ≤50ppm. This patent optimizes the washing method for meta-aramid precipitated fibers. There are significant differences in the morphology and manufacturing process between precipitated fibers and spun fibers. Therefore, the graded acid washing method cannot completely solve the impurity problem in meta-aramid spun fibers.

[0005] In existing technologies, methods to reduce impurities in fibers include optimizing the preparation process of polyamide fiber spinning solutions to reduce the content of impurity elements, thereby improving fiber performance and production costs; and washing the shaped fibers to remove impurities. However, since polyamide fiber spinning solutions require additives to achieve suitable spinning quality, controlling the production process of the polyamide fiber spinning solution to remove impurities is somewhat counterproductive. Therefore, removing impurities during the spinning process is a worthwhile direction to explore; however, the current method of simply washing with water is too simplistic and crude, far from achieving the desired impurity removal. Summary of the Invention

[0006] This invention addresses the technical deficiencies of existing technologies by providing a spinning process for polyamide fibers. This process solves the problem that the existing methods for cleaning polyamide fibers through washing are too simple and crude, making it difficult to remove fiber impurities. The goal is to improve the insulation and aging resistance of the fibers and their products.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows:

[0008] A polyamide fiber spinning process includes the following steps: solidifying the polyamide fiber spinning solution to obtain shaped fiber filaments, then plasticizing and stretching the shaped fiber filaments, washing and drying them, and finally heat-treating the dried fiber filaments to obtain polyamide fibers; ultrasonic waves are added during the plasticizing and stretching process to wash the fiber filaments.

[0009] The introduction of ultrasound can effectively promote the uniform diffusion of impurities (metal elements and solvents introduced during the preparation of polyamide fibers) from the fiber, avoid the generation of large defects inside the fiber, and obtain fibers with dense internal structure and low impurity content, which is beneficial for subsequent heat treatment such as wet heat stretching and dry heat stretching.

[0010] Preferably, the plasticizing and stretching process described above is carried out in a system containing amide solvents. Because the plasticizing and stretching bath contains amide solvents, the filaments, compared to those in pure water, are more likely to close the pores left after impurities diffuse out of the filaments, resulting in a denser internal structure and facilitating the production of high-performance fibers.

[0011] Further preferably, the above plasticizing and stretching process is carried out in stages, with ≥2 stages. By performing the plasticizing and stretching process in stages, the stretching ratio of a single stage of plasticizing and stretching can be effectively reduced, making the filaments more uniformly stressed during the stretching process and reducing the dispersion of fiber properties.

[0012] More preferably, the residence time of the fiber filaments in the single-stage plasticizing bath during the above-mentioned plasticizing and stretching process is 5 to 60 seconds. More preferably, the residence time is 8 to 40 seconds.

[0013] More preferably, the moisture content of the dried fiber is controlled between 50% and 500%. More preferably, the moisture content range of the fiber is 100% to 350%. By retaining appropriate moisture on the fiber, it is beneficial to carry out the subsequent wet heat stretching process.

[0014] More preferably, the heat treatment includes wet heat treatment and dry heat treatment, with wet heat treatment performed first and then dry heat treatment performed; the wet heat treatment refers to the process of rapidly heating the fiber to vaporize the moisture carried by the fiber filament during wet heat stretching, forming water vapor that surrounds the fiber filament.

[0015] Fiber orientation, crystallinity, and dimensional stability can be significantly improved through both wet and dry heat treatment. Compared to fibers that undergo only dry heat treatment, fibers treated with wet heat exhibit more stable performance in high humidity environments. In this invention, the moisture used in the wet heat treatment process is primarily the moisture contained within the fiber itself, which not only effectively reduces the complexity of the process but also allows the fiber to fully contact water vapor, thus enhancing the wet heat treatment effect.

[0016] Typically, fiber heat treatment primarily involves dry heat treatment, without any moist heat treatment. Studies have shown that fibers treated only with dry heat exhibit significantly lower aging resistance under moist heat conditions compared to those treated with dry heat. This is because the fibers, without moist heat treatment to form the necessary microstructure, cannot effectively maintain the stability of this microstructure under such conditions, resulting in insufficient resistance to moist heat aging. The moist heat treatment method of this invention does not require the addition of external steam. Instead, it achieves steam formation by allowing the moisture carried by the fiber itself to vaporize. This not only effectively saves energy and reduces the complexity of the process equipment but also achieves better treatment results (the vaporization of moisture inside the fiber achieves the same purpose of moist heat treatment, while externally introduced steam has difficulty penetrating the filament).

[0017] More preferably, the above-mentioned damp heat treatment temperature is 100–300°C, and the damp heat treatment time is 5–60 s. More preferably, the damp heat treatment temperature is 150–250°C, and the damp heat treatment time is 15–40 s.

[0018] The temperature of the above-mentioned dry heat treatment is 280–380°C, and the treatment time is 5–60 s. More preferably, the temperature of the dry heat treatment is 310–350°C, and the treatment time is 15–40 s.

[0019] More preferably, the above-mentioned water washing is a multi-stage water washing with ≥2 stages; and ultrasonic waves are added during the water washing process.

[0020] More preferably, the above-mentioned multi-stage water washing is in the form of a counter-current trough; each stage of the water washing process involves positive stretching with a stretching ratio of ≤1.1. More preferably, the stretching ratio of the water washing process is ≤1.05.

[0021] Ultrasonic waves are incorporated into the washing process to promote the diffusion of residual inorganic salts and solvents from the fibers into the water. A multi-stage, counter-current washing method ensures sufficient contact between the yarn and water, facilitating the diffusion of residual inorganic salts and solvents from the fibers.

[0022] Further preferably, before solidifying the polyamide fiber spinning solution, the polyamide fiber spinning solution needs to be filtered and then fed into a degassing kettle for degassing. The degassing process is vacuum degassing with a vacuum degree of ≤-0.01MPa. More preferably, the vacuum degree is ≤-0.08MPa. The lower the vacuum degree, the shorter the time for removing bubbles from the spinning solution can be, and the more effectively the extremely fine bubbles in the spinning solution can be removed, ensuring the stability of the spinning process and avoiding the occurrence of fiber breakage and fuzzing.

[0023] In a further preferred embodiment, the above-mentioned spinning solution is solidified and formed by a metering spinning method, and the metering is carried out by one or both of volumetric flow control and mass flow control.

[0024] More preferably, the spinneret used for the above-mentioned metering spinneret is a circular spinneret or a spinneret cap, and the distribution of the spinneret holes adopts one of the following: annular or fan-shaped, or both.

[0025] Compared with the prior art, the technical advantages of the present invention are as follows:

[0026] (1) This invention improves the polyamide spinning process by incorporating multi-stage plasticizing stretching and counter-current washing with ultrasound to promote the diffusion of residual inorganic salts and solvents from the fiber, effectively reducing the content of metal elements and solvents in the fiber. By combining wet heat treatment and dry heat treatment, the insulation and aging resistance of the fiber and its products are improved.

[0027] (2) In the spinning process of the present invention, ultrasonication is performed during plasticizing and stretching to advance the impurity removal process. Combined with stretching in amide solvent, this is beneficial for impurity removal and also ensures that the fiber morphology is intact after impurity removal, which is beneficial for improving fiber performance.

[0028] (3) The meta-aromatic polyamide fiber obtained by the process of this invention has a metal element content of <200ppm, a DMAc content of <200ppm, and a strength retention rate of about 90% at 300℃ / 100h. The insulation paper prepared has a breakdown strength of >35kV / mm, exhibiting excellent insulation performance and good aging resistance. It can be widely used in high-temperature insulation, filtration, and other applications. Attached Figure Description

[0029] Figure 1 The spinning process for preparing meta-aromatic polyamide fibers is described in Example 1 of this invention. Detailed Implementation

[0030] To facilitate understanding of the present invention, it will be described more fully and in detail below by way of embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used below are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments and equipment used in the present invention can be purchased commercially or prepared by existing methods.

[0031] Example 1:

[0032] A spinning process for preparing meta-aromatic polyamide fibers, such as... Figure 1 As shown, it includes the following steps:

[0033] (I) Preparation of spinning solution: In N,N-dimethylacetamide solvent, m-phenylenediamine and isophthaloyl chloride are added to obtain poly(m-phenylenediamine) and byproduct hydrogen chloride through polymerization reaction. Calcium hydroxide is added as a neutralizing agent to neutralize the mixed solution to obtain the spinning solution.

[0034] (II) Spinning treatment:

[0035] (1) After filtering the spinning solution, it is fed into a vacuum degassing kettle for degassing. The vacuum degree is controlled at -0.08MPa.

[0036] (2) The deaerated spinning solution is metered and spun using a volumetric flow rate control method. The spinneret used for metering and spinning is a circular spinneret, and the spinneret holes are distributed in a ring. The filaments are then solidified in a coagulation bath to obtain the shaped fibers.

[0037] (3) The formed fibers are plasticized and stretched in a system containing N,N-dimethylacetamide solvent. Ultrasonic waves are added during the plasticization and stretching process. The plasticization and stretching process is carried out in stages, with two stages. The fiber stays in the plasticizing bath for 8 seconds in each stage.

[0038] After plasticizing and stretching, the product undergoes a water wash. The water wash is a multi-stage wash with two stages; the washing method is a counter-current tank type; ultrasonic waves are incorporated during the washing process. The product is subjected to positive stretching during the water wash, with a stretch ratio of 1.05.

[0039] After washing, the fibers are dried, and the moisture content of the dried fibers is controlled at 100%.

[0040] (4) The dried fibers are introduced into a wet heat treatment device for wet heat stretching. Rapid heating causes the moisture carried by the fiber filaments to quickly vaporize, forming water vapor that surrounds the fiber filaments. The wet heat treatment temperature is 250℃, and the treatment time is 40 seconds. Then, the fibers are introduced into a dry heat treatment device for dry heat stretching. The dry heat treatment temperature is 350℃, and the treatment time is 40 seconds. After dry heat treatment, meta-aromatic polyamide fibers are obtained.

[0041] The properties of the prepared meta-aromatic polyamide fiber were tested, and the performance parameters were as follows: metal element content was 156 ppm, DMAc content was 173 ppm, strength retention rate at 300℃ / 100h was 90%, and the breakdown strength of the prepared insulating paper was 37.0 kV / mm.

[0042] Example 2:

[0043] A spinning process for preparing meta-aromatic polyamide fibers includes the following steps:

[0044] (I) Preparation of spinning solution: In N,N-dimethylacetamide solvent, m-phenylenediamine and isophthaloyl chloride are added to obtain poly(m-phenylenediamine) and byproduct hydrogen chloride through polymerization reaction. Calcium hydroxide is added as a neutralizing agent to neutralize the mixed solution to obtain the spinning solution.

[0045] (II) Spinning treatment:

[0046] (1) After filtering the spinning solution, it is fed into a vacuum degassing kettle for degassing. The vacuum degree is controlled at -0.09MPa.

[0047] (2) The deaerated spinning solution is metered and spun using a volumetric flow rate control method. The spinneret used for metering and spinning is a circular spinneret, and the spinneret holes are distributed in a ring. The filaments are then solidified in a coagulation bath to obtain the shaped fibers.

[0048] (3) The formed fibers were plasticized and stretched in a system containing N,N-dimethylacetamide solvent. Ultrasonic waves were added during the plasticizing and stretching process; the plasticizing and stretching process was carried out in stages, with three stages. The fiber filaments remained in the plasticizing bath for 8 seconds in each stage.

[0049] After plasticizing and stretching, the product undergoes a water wash. The water wash is a multi-stage wash with three stages; the washing method is a counter-current tank type; ultrasonic waves are incorporated during the washing process. The product is subjected to positive stretching during the water wash, with a stretching ratio of 1.03.

[0050] After washing, the fibers are dried, and the moisture content of the dried fibers is controlled at 260%.

[0051] (4) The dried fibers are introduced into a wet heat treatment device for wet heat stretching. Rapid heating causes the moisture carried by the fiber filaments to quickly vaporize, forming water vapor that surrounds the fiber filaments. The wet heat treatment temperature is 250℃, and the treatment time is 35s. Then, the fibers are introduced into a dry heat treatment device for dry heat stretching. The dry heat treatment temperature is 340℃, and the treatment time is 35s. After dry heat treatment, meta-aromatic polyamide fibers are obtained.

[0052] The properties of the prepared meta-aromatic polyamide fiber were tested, and the performance parameters were as follows: metal element content was 96 ppm, DMAc content was 83 ppm, strength retention rate at 300℃ / 100h was 93%, and the breakdown strength of the prepared insulating paper was 38.2 kV / mm.

[0053] Comparative Example 1:

[0054] A spinning process for preparing meta-aromatic polyamide fibers includes the following steps:

[0055] (I) Preparation of spinning solution: In N,N-dimethylacetamide solvent, m-phenylenediamine and isophthaloyl chloride are added to obtain poly(m-phenylenediamine) and byproduct hydrogen chloride through polymerization reaction. Calcium hydroxide is added as a neutralizing agent to neutralize the mixed solution to obtain the spinning solution.

[0056] (II) Spinning treatment:

[0057] (1) After filtering the spinning solution, it is fed into a vacuum degassing kettle for degassing. The vacuum degree is controlled at -0.08MPa.

[0058] (2) The deaerated spinning solution is metered and spun using a volumetric flow rate control method. The spinneret used for metering and spinning is a circular spinneret, and the spinneret holes are distributed in a ring. The filaments are then solidified in a coagulation bath to obtain the shaped fibers.

[0059] (3) The formed fibers were plasticized and stretched in a system containing N,N-dimethylacetamide solvent. The plasticizing and stretching process was carried out in stages, with two stages. The fiber filaments were held in the plasticizing bath for 8 seconds in each stage.

[0060] After plasticizing and stretching, the product is washed with water. The washing process is multi-stage, with two washing stages; the washing method is a counter-current tank type; the product is stretched in the washing bath with a stretch ratio of 1.05.

[0061] After washing, the fibers are dried, and the moisture content of the dried fibers is controlled at 100%.

[0062] (4) The dried fibers are introduced into a wet heat treatment device for wet heat stretching. Rapid heating causes the moisture carried by the fiber filaments to quickly vaporize, forming water vapor that surrounds the fiber filaments. The wet heat treatment temperature is 250℃, and the treatment time is 40 seconds. Then, the fibers are introduced into a dry heat treatment device for dry heat stretching. The dry heat treatment temperature is 350℃, and the treatment time is 40 seconds. After dry heat treatment, meta-aromatic polyamide fibers are obtained.

[0063] The properties of the prepared meta-aromatic polyamide fiber were tested, and the performance parameters were as follows: metal element content was 467 ppm, DMAc content was 398 ppm, strength retention rate at 300℃ / 100h was 79%, and the breakdown strength of the prepared insulating paper was 27.3 kV / mm.

[0064] Comparative Example 2:

[0065] A spinning process for preparing meta-aromatic polyamide fibers includes the following steps:

[0066] (I) Preparation of spinning solution: In N,N-dimethylacetamide solvent, m-phenylenediamine and isophthaloyl chloride are added to obtain poly(m-phenylenediamine) and byproduct hydrogen chloride through polymerization reaction. Calcium hydroxide is added as a neutralizing agent to neutralize the mixed solution to obtain the spinning solution.

[0067] (II) Spinning treatment:

[0068] (1) After filtering the spinning solution, it is fed into a vacuum degassing kettle for degassing. The vacuum degree is controlled at -0.08MPa.

[0069] (2) The deaerated spinning solution is metered and spun using a volumetric flow rate control method. The spinneret used for metering and spinning is a circular spinneret, and the spinneret holes are distributed in a ring. The filaments are then solidified in a coagulation bath to obtain the shaped fibers.

[0070] (3) The formed fibers were plasticized and stretched in a system containing N,N-dimethylacetamide solvent. Ultrasonic waves were added during the plasticizing and stretching process; the plasticizing and stretching process was carried out in stages, with two stages. The fiber filaments remained in the plasticizing bath for 8 seconds in each stage.

[0071] After plasticizing and stretching, the product undergoes a water wash. The water wash is a multi-stage wash with two stages; the washing method is a counter-current tank type; ultrasonic waves are incorporated during the washing process. The product is subjected to positive stretching during the water wash, with a stretch ratio of 1.05.

[0072] After washing, the fibers are dried, and the moisture content of the dried fibers is controlled at 10%.

[0073] (4) The fiber is introduced into a dry heat treatment device for dry heat stretching. The temperature of the dry heat treatment is 350℃ and the treatment time is 40s. After dry heat treatment, meta-aromatic polyamide fiber is obtained.

[0074] The properties of the prepared meta-aromatic polyamide fiber were tested, and the performance parameters were as follows: metal element content was 171 ppm, DMAc content was 186 ppm, strength retention rate at 300℃ / 100h was 72%, and the breakdown strength of the prepared insulating paper was 35.9 kV / mm.

[0075] The performance test comparison between Examples 1-2 and Comparative Examples 1-2 is shown in Table 1 below.

[0076] Table 1

[0077]

[0078] As shown in Table 1 above, the spinning process employed in this invention uses a graded approach during plasticizing, stretching, and washing, and introduces ultrasonic waves to promote the diffusion of inorganic salts and solvents from the filaments, reducing impurity content and improving fiber insulation performance. The heat treatment process combines wet and dry heat treatment to enhance fiber aging resistance. Through this combination, meta-aromatic polyamide fibers with excellent insulation and good aging resistance are obtained.

Claims

1. A spinning process for meta-aromatic polyamide fibers, characterized in that, Includes the following steps: Meta-aromatic polyamide fiber spinning solution is solidified to form shaped fiber filaments, which are then plasticized, stretched, washed, and dried. Finally, the dried fiber filaments are heat-treated to obtain meta-aromatic polyamide fibers. Ultrasonic waves are added during the plasticizing and stretching process to wash the fiber filaments. The plasticizing and stretching process is carried out in a system containing amide solvents; the plasticizing and stretching process is carried out in stages, with a stage number ≥ 2; the fiber filaments stay in the single-stage plasticizing bath for 8 seconds during the plasticizing and stretching process; The moisture content of the dried fiber filaments is controlled at 100%~260%; The heat treatment includes wet heat treatment and dry heat treatment, with wet heat treatment performed first and then dry heat treatment. The wet heat treatment refers to the process of rapidly heating the fiber to vaporize the moisture carried by the fiber during wet heat stretching, forming water vapor that surrounds the fiber. The wet heat treatment temperature is 250℃ and the wet heat treatment time is 35s~40s.

2. The spinning process as described in claim 1, characterized in that: The dry heat treatment temperature is 280~380℃, and the dry heat treatment time is 5~60s.

3. The spinning process as described in claim 1, characterized in that: The water washing is a multi-stage water washing process with a water washing stage of ≥2; and ultrasonic waves are added during the water washing process.

4. The spinning process as described in claim 3, characterized in that: The multi-stage water washing is in the form of a counter-current trough; each stage of the water washing process involves positive stretching with a stretching ratio of ≤1.

1.

5. The spinning process according to claim 1, characterized in that: Before the meta-aromatic polyamide fiber spinning solution is solidified and formed, it needs to be filtered and then fed into a degassing kettle for degassing. The degassing process is vacuum degassing with a vacuum degree of ≤-0.01Mpa.

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