A polyamide for preparing a textile material and a process for its preparation

Abstract

The application relates to the technical field of chemical synthesis, and discloses a polyamide for preparing textile materials and a preparation method thereof, the preparation method comprising the following steps: performing pre-polymerization on polyamide raw materials, water and an end-capping agent for 2h-8h; when the raw materials contain a lactam monomer, the pre-polymerization temperature (Tcp+100) <T1< (300-250 / p+20xlg(p)); after the pre-polymerization is completed, post-polycondensation is performed: first, polycondensation is performed for 0.5h-1h under the condition that 0kPa>P> (0.1xT1+0.2xT2-95) kPa, and then, polycondensation is performed for 0h-2h under the condition that-60kPa-90kPa, and the post-polycondensation temperature is controlled to satisfy (Tm+q)

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology, specifically relating to a polyamide for preparing textile materials and its preparation method. Background Technology

[0002] Polyamide fiber, also known as nylon fiber, holds an important historical position and practical value in the synthetic fiber industry. It is currently the world's second largest synthetic fiber variety and is widely used in clothing, home textiles, and industrial textile materials.

[0003] With the continuous expansion of nylon fiber applications, especially the increasing demand for high-performance and high-reliability industrial fibers, more stringent requirements have been placed on the spinnability and mechanical properties of the raw material polyamide resin.

[0004] However, in actual production, polyamide resins exhibit certain internal structural defects, with gel-like defects being particularly prominent. These gel-like defects are difficult to fully dissolve and uniformly disperse in the molten state, easily leading to localized viscosity abrupt changes and flow stagnation during spinning. This instability in the melt flow further results in frequent yarn breakage during spinning, significantly reducing continuous spinning capability. Simultaneously, fluctuations in melt flow disrupt the molecular chain orientation and crystallinity uniformity during fiber formation, ultimately manifesting as reduced mechanical strength and poor batch-to-batch performance consistency in the resulting nylon fibers. Therefore, the existence of internal defects in polyamide resins, especially gel-like defects, to some extent restricts the promotion and application of nylon fibers in high-end and high-reliability applications. Summary of the Invention

[0005] This invention provides a polyamide for preparing textile materials and its preparation method, in order to solve the problems of polyamide resin in the prior art, such as many optical defects, poor melt uniformity, high number of yarn breakages, insufficient monofilament strength, uneven yarn drying, and poor dyeing uniformity.

[0006] In a first aspect, the present invention provides a method for preparing polyamide for textile materials, comprising the following steps: (1) The polyamide raw material, water and end-capping agent are subjected to a prepolymerization reaction for 2h to 8h; preferably, the prepolymerization reaction time is 2h to 5h; preferably, the amount of the end-capping agent added is 0.05wt% to 5wt% of the total mass of the polyamide raw material, preferably 0.3wt% to 1wt%, more preferably 0.4wt% to 0.7wt%; the amount of water added is 5wt% to 15wt% of the total mass of the polyamide raw material, preferably 10wt%.

[0007] When the polyamide raw material contains lactam monomers, control the pre-polymerization temperature such that (Tcp + 100) < T1 < (300 - 250 / p + 20×lg(p)), where Tcp is the melting point of the lactam monomer and p is the number of carbon atoms of the lactam monomer; Alternatively, when the polyamide raw material is an aliphatic diamine and an aliphatic diacid, control the pre-polymerization temperature such that Ts < T1 < (Tc + 10×q), where Ts is the melting point of the polyamide, Tc is the crystallization temperature of the polyamide, and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material; preferably, when the polyamide raw material is an aliphatic diamine and an aliphatic diacid, the molar ratio of the aliphatic diamine to the aliphatic diacid is 1:1.

[0008] Alternatively, when the polyamide raw material is an amino acid, control the pre-polymerization temperature such that Ta < T1 < (Tca + 10×q), where Ta is the melting point of the amino acid, Tca is the crystallization temperature of the polyamide, and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material; After the pre-polymerization reaction is completed, carry out post-polycondensation; First, carry out polycondensation for 0.5 h to 1 h under a pressure condition of 0 kPa > P > (0.1×T1 + 0.2×T2 - 95) kPa; then carry out polycondensation for 0 h to 2 h, preferably 0.2 h to 2 h, under a pressure condition of -60 kPa to -90 kPa; control the post-polycondensation temperature such that (Tm + q) < T2 < (Tm + 5×q), where Tm is the melting point of the polyamide and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material.

[0009] It should be noted that q represents the ratio of the total molar number of carbon atoms to the total molar number of nitrogen atoms in the polyamide chain-forming monomers, which is used to characterize the influence of the monomer structure characteristics on the polymerization temperature window. Water and end-capping agents are not included in the calculation of q. When the polyamide raw material includes multiple chain-forming monomers, q is the total ratio of the total molar number of carbon atoms to the total molar number of nitrogen atoms in each chain-forming monomer.

[0010] In the present invention, both Ts and Tm are used to represent the melting point of the polyamide, and they are only symbols set for distinguishing in the temperature control formulas at different process stages. The measurement units of the temperature parameters T1, T2, Tcp, Ts, Tm, Ta, Tc, and Tca involved in the formulas of the present invention are all °C, and the measurement unit of the pressure parameter P is kPa. When substituting each parameter into the formula for calculation, the values are taken according to the above units. For the expressions of "(300 - 250 / p + 20×lg(p))", "(Tc + 10×q)", "(Tca + 10×q)", "(Tm + q)", and "(Tm + 5×q)" in the formula, the unit of the calculation result is °C; for the expression of "(0.1×T1 + 0.2×T2 - 95)" in the formula, the unit of the calculation result is kPa.

[0011] It should be further noted that when the polyamide raw material contains lactam monomers, regardless of whether the polyamide raw material further contains amino acids, aliphatic diamines and / or aliphatic diacids, the pre-polymerization temperature is controlled according to the temperature range corresponding to the lactam monomer system, that is, based on the melting point Tcp of the lactam monomer and the number p of carbon atoms, the pre-polymerization temperature is calculated and determined according to (Tcp + 100) < T1 < (300 - 250 / p + 20×lg(p)).

[0012] In the present invention, the polyamide raw material is selected from one or more of lactam monomers, amino acids, aliphatic diamines and aliphatic diacids. Lactam monomers refer to cyclic amide monomers that can undergo ring-opening polymerization to form polyamide segments. Amino acids refer to monomers that contain both amino groups and carboxyl groups and can self-condense to form polyamide segments. Aliphatic diamines and aliphatic diacids refer to monomers with linear aliphatic chain structures, containing two amino groups and two carboxyl groups respectively, and can form polyamide repeating units through polycondensation reactions.

[0013] In the present invention, the pre-polymerization reaction refers to pre-polymerizing or ring-opening pre-reacting monomers before polycondensation to form oligomers and provide a suitable molecular chain basis for subsequent melt polycondensation. The post-polycondensation refers to, after the pre-polymerization reaction is completed, further controlling the temperature and reducing the pressure to make the oligomers continue to polycondense and increase viscosity to obtain polyamide with the target molecular weight and target relative viscosity.

[0014] Unless otherwise specified, the pressure parameters involved in the present invention refer to gauge pressure, that is, the relative pressure measured based on the standard atmospheric pressure.

[0015] By controlling the pre-polymerization temperature for different raw material systems respectively and segmentally regulating the temperature, pressure and time in the post-polycondensation stage in the present invention, it is beneficial to reduce local overheating and side reactions during the polymerization process, reduce the generation of optical defects such as gels and crystal points, improve the uniformity of the polyamide melt and the spinning stability, thereby reducing the number of spinning breaks, increasing the single fiber strength, and improving the fiber strand evenness and levelness of dyeing.

[0016] In an optional embodiment, in step (2), after the pre-polymerization reaction is completed, first release the pressure of the reaction system to a low positive pressure state, and adjust the temperature of the reaction system to the post-polycondensation temperature T2 and keep it constant; then introduce an inert gas into the reaction kettle for purging, preferably purging for 0.5 h - 1.5 h; after the purging is completed, evacuate the reaction kettle to a pressure of P, so that the vacuum pressure satisfies 0 kPa > P > (0.1×T1 + 0.2×T2 - 95) kPa, and carry out polycondensation for 0.5 h to 1 h under this pressure condition; then continue to evacuate to a pressure condition of -60 kPa to -90 kPa and carry out polycondensation for 0 h to 2 h, preferably polycondensation for 0.2 h to 2 h. Preferably, the pressure range of the low positive pressure is 5 kPa to 20 kPa, preferably 8 kPa to 12 kPa.

[0017] In one alternative embodiment, after the post-polymerization is completed, an inert gas is introduced into the reactor to restore the system to atmospheric pressure. The polymerized product is then discharged and subjected to cooling, pelletizing, and drying processes in sequence to obtain the target polyamide product.

[0018] In one alternative embodiment, the polyamide is a homopolymer or a copolymer.

[0019] The polyamide involved in this invention is a known type of polyamide in the art. The improvement of this invention lies in optimizing the process parameters during the prepolymerization reaction and postpolymerization process to improve the polymerization process and spinning properties of known polyamides, rather than providing a new polyamide composition. For parameters such as melting point and crystallization temperature involved in this invention, those skilled in the art can directly obtain the information based on the target polyamide variety, combined with existing published literature, product manuals, supplier information, etc., or determine them using conventional testing methods in the art such as differential scanning calorimetry. Since the target polyamide variety and its monomer composition are already determined before feeding, the corresponding thermal performance parameters can be predetermined by those skilled in the art, thereby enabling the reasonable setting of the control range of the prepolymerization temperature T1 and the postpolymerization temperature T2, and implementing this invention accordingly.

[0020] In one alternative embodiment, in step (1), the lactam monomer comprises one or more lactam monomers with different carbon chain lengths; When the lactam monomer includes multiple lactam monomers with different carbon chain lengths, p is the number of carbon atoms in the lactam monomer with the longest carbon chain.

[0021] In one optional embodiment, when the lactam monomer comprises a variety of lactam monomers with different carbon chain lengths, the melting point Tcp of the lactam monomer is the melting point of the lactam monomer with the longest carbon chain.

[0022] In one alternative embodiment, the lactam monomer comprises one or more of C6 to C18 lactams.

[0023] In one alternative embodiment, the lactam monomer includes one or more of caprolactam, octyllactam, nonanolactam, decanolactam, undecyllactam, and dodecalactam.

[0024] In one alternative embodiment, the amino acid includes one or more of C6 to C18 amino acids.

[0025] In one alternative embodiment, the amino acid includes one or more of 6-aminohexanoic acid, 10-aminoundecanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid.

[0026] In one alternative embodiment, the aliphatic diamine includes one or more linear aliphatic diamines from C6 to C18; In one alternative embodiment, the aliphatic diacid includes one or more linear aliphatic dicarboxylic acids from C6 to C18.

[0027] In one optional embodiment, the aliphatic diamine includes one or more of hexanediamine, heptadecanediamine, octanediamine, nonanediamine, decanediamine, undecanediamine, dodecanediamine, tridecanediamine, tetradecanediamine, hexadecanediamine, and octadecanediamine; In one alternative embodiment, the aliphatic diacid includes one or more of adipic acid, sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid.

[0028] In one optional embodiment, the capping agent comprises one or more of linear aliphatic C2-C12 monocarboxylic acids, linear aliphatic C4-C12 monoamines, linear aliphatic C4-C18 dicarboxylic acids, and linear aliphatic C4-C18 diamines.

[0029] Further, the linear aliphatic C2-C12 monocarboxylic acid may be selected from one or more of acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, and dodecaic acid; the linear aliphatic C4-C12 monoamine may be selected from one or more of n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, n-decylamine, n-undecylamine, and n-dodecylamine; the linear aliphatic C4-C18 dicarboxylic acid may be selected from succinic acid, glutaric acid, etc. The linear aliphatic C4-C18 diamine may be selected from one or more of the following: adipic acid, heptapic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid; the linear aliphatic C4-C18 diamine may be selected from one or more of the following: butanediamine, pentanediamine, hexanediamine, heptapicamine, octanediamine, nonanediamine, decanediamine, undecanediamine, dodecanediamine, tridecanediamine, tetradecanediamine, hexadecanediamine, and octadecanediamine.

[0030] Secondly, the present invention provides a polyamide prepared by any of the preparation methods described in the above-described technical solutions, wherein the polyamide has at least one of the following characteristics: (1) After polyamide was used to prepare cast films with a thickness of 95 to 105 micrometers using a casting equipment, the number of optical defects per square meter of cast film sample was measured by an optical inspection system as follows: The number of optical defects with a size greater than 500 micrometers is 0; In one optional embodiment, the number of optical defects with a size greater than 300 micrometers and less than or equal to 500 micrometers is less than 50; preferably 9 to 43. In one optional embodiment, the number of optical defects with a size greater than 100 micrometers and less than or equal to 300 micrometers is less than 200, preferably 20 to 182; In one optional embodiment, the number of optical defects with a size greater than 50 micrometers and less than or equal to 100 micrometers is less than 300, preferably 105 to 267. In one optional embodiment, the number of optical defects with a size greater than 25 micrometers and less than or equal to 50 micrometers is less than 500, preferably 178 to 479. (2) When the polyamide is used to prepare 70D yarn, the number of spinning breaks is less than 5 times / 10 tons, and / or the monofilament strength is 5.1cN / dtex to 6.8cN / dtex, and / or the monofilament breaking elongation is 28% to 45%, and / or the yarn unevenness is 2.8% to 4.8%.

[0031] Optical defects such as gels and crystal points in polyamide resins can adversely affect the resin's spinnability and the monofilament strength, evenness, and dyeability of the fabric filaments. These optical defects can be detected using industrial material optical inspection systems. This invention effectively reduces the generation of optical defects such as gels and crystal points by lowering the temperature during polyamide production, shortening the residence time of polyamide at high temperatures, and controlling the uniformity of polyamide molecular chain growth. This results in aliphatic polyamides with low optical defects, suitable for preparing textile materials.

[0032] In one optional embodiment, the polyamide has a relative viscosity of 1.5 to 2.5, preferably 1.6 to 2.3, and more preferably 1.60 to 2.21.

[0033] In one optional embodiment, the polyamide has a melting point of 140°C-260°C, preferably 167°C-192°C.

[0034] In an optional embodiment, when the polyamide contains repeating units XY, X is a linear aliphatic diamine and Y is a linear aliphatic diacid; wherein X is selected from one or more of hexadiamine, heptanediamine, octanediamine, nonanediamine, decanedanediamine, undecanediamine, dodecanediamine, tridecanediamine, tetradecanediamine, hexadecanediamine, and octadecanediamine, and Y is selected from one or more of hexadiic acid, sebacic acid, undecanediic acid, dodecanediic acid, tridecanediic acid, tetradecanediic acid, hexadecanediic acid, and octadecanediic acid.

[0035] In one alternative embodiment, the polyamide includes one or more of PA11, PA12, PA610, PA612, PA1010, PA1012, PA12 / 610 copolymer, PA12 / 612 copolymer, PA12 / 1010 copolymer, PA12 / 1012 copolymer, and PA6 / 12 copolymer.

[0036] The technical solution of this invention has the following advantages: The polyamide of this invention exhibits excellent spinnability and high monofilament strength, resulting in a low number of yarn breakages during spinning. Optical defects in resins are typically caused by gels, crystal points, or impurities. The polyamide resin of this invention has a low number of optical defects and a low impurity content, resulting in good melt uniformity during spinning and ensuring stable and consistent output from each spinneret. This leads to uniform monofilament thickness after cooling and solidification, and a significant reduction in fiber evenness.

[0037] Furthermore, some optical defects can easily form localized weak points or protrusions on the fiber surface, which can easily generate fuzz when rubbed against the guide during high-speed winding. The polyamide described in this invention can effectively reduce the possibility of fuzz formation. Moreover, because the optical defect area differs from the normal fiber structure, its dye uptake behavior differs during dyeing, easily leading to dye spots or white spots. The polyamide described in this invention, especially the polyamide resin prepared by the polymerization method disclosed in this invention, produces yarns with excellent level dyeing properties, especially when dyeing dark or sensitive colors, making it suitable for the preparation and promotion of high-end textile fabrics. Detailed Implementation

[0038] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0039] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0040] Example 1 This embodiment provides a method for preparing nylon 12 resin, as detailed below: (1) Prepolymerization reaction; Add 5000 kg of laurolactam (purchased from Wanhua Chemical), 30 kg of chain terminator hexamethylenediamine (purchased from Shenma Industry Co., Ltd.), and 500 kg of deionized water into the reaction kettle in sequence, and conduct three nitrogen replacements on the reaction kettle to remove air. Subsequently, heat up to the prepolymerization temperature T1, where T1 is 270 °C, and the temperature satisfies: (Tcp + 100) °C < T1 < (300 - 250 / p + 20×lg(p)) °C, where p is the number of carbon atoms of the lactam monomer, i.e., p = 12, and Tcp is the melting point of the lactam monomer. In this example, the melting point of laurolactam is 153 °C. Maintain the reaction for 5 h at the prepolymerization temperature T1 to complete the ring-opening prepolymerization reaction of laurolactam.

[0041] (2)Post-polycondensation; After the prepolymerization reaction is completed, slowly relieve the pressure to 10 kPa at a rate of -2 kPa / s. At the same time, the temperature of the reaction system in the reaction kettle drops to the post-polycondensation temperature T2, where T2 is 220 °C, and maintain this temperature constant; the post-polycondensation temperature satisfies (Tm + q) °C < T2 < (Tm + 5×q) °C, where Tm is the melting point of nylon 12 resin. In this example, the melting point of nylon 12 is 178 °C, and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material. In this example, the molar ratio q of carbon atoms to nitrogen atoms in laurolactam is 12.

[0042] Under the condition of maintaining the temperature at 220 °C, introduce nitrogen into the reaction kettle for purging. The nitrogen flow rate is 3 m³ / h, and purge for 1 h. Subsequently, evacuate the reaction kettle to P, where P is -20 kPa, so that the vacuum pressure satisfies 0 kPa > P > (0.1×T1 + 0.2×T2 - 95) kPa, where T1 is the prepolymerization temperature of 270 °C and T2 is the post-polycondensation temperature of 220 °C, and react under this condition for 0.5 h; subsequently, continue to evacuate to -70 kPa and react under this vacuum degree for 0.5 h to complete the melt polycondensation reaction.

[0043] After the polycondensation is completed, replenish nitrogen into the reaction kettle to 100 kPa, then discharge the material, and successively conduct cooling, pelletizing, and drying treatments to obtain a nylon 12 resin product.

[0044] After testing, the relative viscosity of the obtained nylon 12 resin is 1.62, and the melting point Tm is 178 °C.

[0045] Example 2 This example provides a method for preparing nylon 11 resin, which is as follows: (1)Prepolymerization reaction; Add 5000 kg of 11-aminoundecanoic acid (purchased from Arkema), 35 kg of end-capping agent decanediamine (purchased from Wuxi Yinda), and 500 kg of deionized water into the reaction kettle in sequence, and conduct three nitrogen replacements on the reaction kettle. Then heat up to the pre-polymerization temperature T1, where T1 is 200 °C, and the temperature satisfies Ta °C < T1 < (Tca + 10×q) °C. Here, Ta is the melting point of 11-aminoundecanoic acid, which is 190 °C, Tca is the crystallization temperature of polyamide. In this example, the crystallization temperature of nylon 11 is 150 °C, and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material. In this example, q is the molar ratio of carbon atoms to nitrogen atoms in 11-aminoundecanoic acid, which is 11. Keep the reaction at the pre-polymerization temperature T1 for 2 h to complete the pre-polymerization reaction of amino acids.

[0046] (2) Post-polycondensation; After the pre-polymerization reaction is completed, slowly relieve the pressure to 10 kPa at a rate of -2 kPa / s. At the same time, the temperature of the reaction system in the reaction kettle rises to the post-polycondensation temperature T2, where T2 is 230 °C, and keep this temperature constant. The post-polycondensation temperature satisfies (Tm + q) °C < T2 < (Tm + 5×q) °C. Here, Tm is the melting point of nylon 11 resin. In this example, the melting point of nylon 11 is 187 °C, and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material. In this example, the molar ratio q of carbon atoms to nitrogen atoms in 11-aminoundecanoic acid is 11.

[0047] Under the condition of keeping the temperature at 230 °C, introduce nitrogen into the reaction kettle for purging. The nitrogen flow rate is 3 m³ / h, and purge for 1 h. Then evacuate the reaction kettle to P, where P is -10 kPa, so that the vacuum pressure satisfies 0 kPa > P > (0.1×T1 + 0.2×T2 - 95) kPa. Here, T1 is the pre-polymerization temperature of 200 °C, and T2 is the post-polycondensation temperature of 230 °C, and react under this condition for 1 h. Then continue to evacuate to -60 kPa and react for 1 h under this vacuum degree to complete the melt polycondensation reaction.

[0048] After the polycondensation is completed, replenish nitrogen into the reaction kettle to 100 kPa, then discharge the material, and conduct cooling, pelletizing, and drying treatments in sequence to obtain nylon 11 resin products.

[0049] After testing, the relative viscosity of the obtained nylon 11 resin is 1.90, and the melting point Tm is 187 °C.

[0050] Example 3 This example provides a preparation method of nylon 1012 resin, which is as follows: (1) Pre-polymerization reaction; 2175 kg of decanediamine (purchased from Wuxi Yinda), 2860 kg of dodecanedioic acid (purchased from Kaisai Biotech), and 500 kg of deionized water were successively added to the reaction kettle. Among them, 35 kg of decanediamine in the 2175 kg of decanediamine was used as a terminator. The reaction kettle was purged with nitrogen three times to remove air. Subsequently, the temperature was heated up to the pre-polymerization temperature T1, where T1 was 210 °C, and the temperature satisfied Ts °C < T1 < (Tc + 10×q) °C, where Ts was the melting point of nylon 1012 resin, 192 °C, Tc was the crystallization temperature of nylon 1012 resin, 156 °C, and q was the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material, 11. The reaction was maintained for 2 h at the pre-polymerization temperature T1 to complete the pre-polymerization reaction of the nylon salt system.

[0051] (2)Post-polycondensation; After the pre-polymerization reaction was completed, the pressure was slowly released to 10 kPa at a rate of -2 kPa / s. At the same time, the temperature of the reaction system in the reaction kettle rose to the post-polycondensation temperature T2, where T2 was 240 °C, and this temperature was kept constant; the temperature satisfied (Tm + q) °C < T2 < (Tm + 5×q) °C, where Tm was the melting point of nylon 1012 resin, 192 °C, and q was the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material, 11.

[0052] Under the condition of maintaining the temperature at 240 °C, nitrogen was introduced into the reaction kettle for purging, and the nitrogen flow rate was 3 m³ / h for 1 h. Subsequently, the reaction kettle was evacuated to -25 kPa, and the vacuum pressure satisfied 0 > P > (0.1×T1 + 0.2×T2 - 95) kPa, where T1 was the pre-polymerization temperature 210 °C and T2 was the post-polycondensation temperature 240 °C, and the reaction was carried out for 1 h under this condition; then it was continuously evacuated to -90 kPa, and the reaction was carried out for 0.5 h under this vacuum degree to complete the melt polycondensation reaction.

[0053] After the polycondensation was completed, nitrogen was replenished into the reaction kettle to 100 kPa, and then the material was discharged, followed by cooling, pelletizing, and drying treatments to obtain the nylon 1012 resin product.

[0054] After testing, the relative viscosity of the obtained nylon 1012 resin was 2.21, and the melting point Tm was 192 °C.

[0055] Example 4 This example provides a preparation method of nylon 12 / 1012 copolymer resin, which is as follows: (1)Pre-polymerization reaction; 4000 kg of laurolactam (purchased from Wanhua Chemical), 423 kg of decanediamine (purchased from Wuxi Yinda), 572 kg of dodecanedioic acid (purchased from Kaisai Biological), 20 kg of capping agent n-hexylamine (purchased from Shandong Xuchen Chemical Technology Co., Ltd.) and 500 kg of deionized water were successively added to the reaction kettle, and the reaction kettle was purged with nitrogen three times. Subsequently, the temperature was heated up to the prepolymerization temperature T1, T1 was 280 °C, and the temperature satisfied (Tcp + 100) °C < T1 < (300 - 250 / p + 20 × lg(p)) °C, where p was the number of carbon atoms of the lactam monomer, which was 12, and Tcp was the melting point of the lactam monomer, that is, the melting point of laurolactam, which was 153 °C. The reaction was maintained for 4 h at the prepolymerization temperature T1 to complete the ring-opening prepolymerization reaction of the lactam system.

[0056] (2) Post-polycondensation; After the prepolymerization reaction was completed, the pressure was slowly released to 10 kPa at a rate of -2 kPa / s. At the same time, the temperature of the reaction system in the reaction kettle dropped to the post-polycondensation temperature T2, T2 was 200 °C, and this temperature was kept constant. The temperature satisfied (Tm + q) °C < T2 < (Tm + 5 × q) °C, where Tm was the melting point of the nylon 12 / 1012 copolymer resin. In this embodiment, the melting point of the nylon 12 / 1012 copolymer resin was 167 °C, and q was the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw materials, that is, the molar ratio of carbon atoms to nitrogen atoms in laurolactam, decanediamine, and dodecanedioic acid, which was 11.8.

[0057] Subsequently, the reaction kettle was evacuated to -20 kPa, and the vacuum pressure satisfied 0 kPa > P > (0.1 × T1 + 0.2 × T2 - 95) kPa, where T1 was the prepolymerization temperature of 280 °C and T2 was the post-polycondensation temperature of 200 °C, and the reaction was carried out under this condition for 1 h to complete the melt polycondensation reaction.

[0058] After the polycondensation was completed, the vacuum evacuation was stopped, nitrogen was replenished to the reaction kettle to 100 kPa, and then the material was discharged, and cooling, pelletizing and drying treatments were carried out in sequence to obtain the nylon 12 / 1012 copolymer resin product.

[0059] After testing, the relative viscosity of the obtained nylon 12 / 1012 copolymer resin was 1.61, and the melting point Tm was 167 °C.

[0060] Example 5 This example provides a method for preparing a nylon 6 / 12 copolymer resin, which is as follows: (1) Prepolymerization reaction; 1000 kg of dodecanolactam (purchased from Wanhua Chemical), 4000 kg of caprolactam (purchased from Henan Shenma), 20 kg of end-capping agent n-hexylamine (purchased from Shandong Xuchen Chemical Technology Co., Ltd.), and 500 kg of deionized water were successively added to the reaction kettle. The reaction kettle was purged with nitrogen three times to remove air. Subsequently, the temperature was heated up to the prepolymerization temperature T1, where T1 was 280 °C, and the temperature satisfied (Tcp + 100) °C < T1 < (300 - 250 / p + 20×lg(p)) °C, where p was the number of carbon atoms in dodecanolactam, which was 12, and Tcp was the melting point of dodecanolactam, which was 153 °C. The reaction was maintained at this temperature for 4 h to complete the ring-opening prepolymerization reaction of the lactam system and form a copolymer structure.

[0061] (2) Post-polycondensation; After the prepolymerization reaction was completed, the pressure was slowly released to 10 kPa at a rate of -2 kPa / s. At the same time, the temperature of the reaction system in the reaction kettle dropped to the post-polycondensation temperature T2, where T2 was 220 °C, and this temperature was kept constant; the temperature satisfied (Tm + q) °C < T2 < (Tm + 5×q) °C, where Tm was the melting point of the obtained nylon 6 / 12 copolymer resin, which was Tm = 198 °C, and q was the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw materials, that is, the molar ratio of carbon atoms to nitrogen atoms in dodecanolactam and caprolactam, which was 6.75.

[0062] Under the condition of maintaining the temperature at 220 °C, nitrogen was introduced into the reaction kettle for purging, and the nitrogen flow rate was 3 m³ / h for 1 h. Subsequently, the reaction kettle was evacuated to -15 kPa, and the vacuum pressure satisfied 0 kPa > P > (0.1×T1 + 0.2×T2 - 95) kPa, where T1 was the prepolymerization temperature of 280 °C and T2 was the post-polycondensation temperature of 220 °C, and the reaction was carried out under this condition for 0.5 h; subsequently, it was continuously evacuated to -80 kPa, and the reaction was carried out at this vacuum degree for 0.2 h to complete the melt polycondensation reaction.

[0063] After the polycondensation was completed, the vacuum evacuation was stopped, nitrogen was replenished into the reaction kettle to 100 kPa, and then the material was discharged, followed by cooling, pelletizing, and drying treatments to obtain the nylon 6 / 12 copolymer resin product.

[0064] After testing, the relative viscosity of the obtained nylon 6 / 12 copolymer resin was 1.61, and the melting point Tm was 198 °C.

[0065] Example 6 This example provides a preparation method of nylon 12 / 11 copolymer resin, which is as follows: (1) Prepolymerization reaction; Add 4000 kg of laurolactam (purchased from Wanhua Chemical), 1000 kg of 11-aminoundecanoic acid (purchased from Arkema), 30 kg of chain terminator hexamethylenediamine (purchased from Henan Shenma), and 500 kg of deionized water into the reaction kettle in sequence, and conduct 3 nitrogen replacements on the reaction kettle to remove air. Subsequently, heat up to the prepolymerization temperature T1, where T1 is 270 °C, and the temperature satisfies (Tcp + 100) °C < T1 < (300 - 250 / p + 20×lg(p)) °C, where p is the number of carbon atoms of the lactam monomer in the raw material system, which is 12 for laurolactam, and Tcp is the melting point of this lactam monomer, that is, the melting point of laurolactam is 153 °C. Maintain the reaction at this temperature for 5 h to complete the ring-opening prepolymerization reaction of lactam and participate in the formation of a copolymer structure with 11-aminoundecanoic acid.

[0066] (2)Post-polycondensation; After the prepolymerization reaction is completed, slowly relieve the pressure to 10 kPa at a rate of -2 kPa / s, and at the same time, the temperature of the reaction system in the reaction kettle drops to the post-polycondensation temperature T2, where T2 is 220 °C, and maintain this temperature constant; the temperature satisfies (Tm + q) °C < T2 < (Tm + 5×q) °C, where Tm is the melting point of the obtained nylon 12 / 11 copolymer resin, which is 170 °C, and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw materials, that is, the molar ratio of carbon atoms to nitrogen atoms in laurolactam and 11-aminoundecanoic acid is 11.8.

[0067] Under the condition of maintaining the temperature at 220 °C, evacuate the reaction kettle to -20 kPa so that the vacuum pressure satisfies 0 kPa > P > (0.1×T1 + 0.2×T2 - 95) kPa, where T1 is the prepolymerization temperature of 270 °C and T2 is the post-polycondensation temperature of 220 °C, and react under this condition for 0.5 h; then continue to evacuate to -70 kPa and react under this vacuum degree for 0.5 h to complete the melt polycondensation reaction.

[0068] After the polycondensation is completed, stop evacuating, replenish nitrogen into the reaction kettle to 100 kPa, then discharge the material, and successively carry out cooling, pelletizing, and drying treatments to obtain the nylon 12 / 11 copolymer resin product.

[0069] After testing, the relative viscosity of the obtained nylon 12 / 11 copolymer resin is 1.63, and the melting point Tm is 170 °C.

[0070] Example 7 This example provides a preparation method of nylon 12 resin, specifically as follows: (1)Prepolymerization reaction; 5000 kg of dodecanolactam (purchased from Wanhua Chemical), 30 kg of chain terminator hexamethylenediamine (purchased from Shenma Industry Co., Ltd.), and 500 kg of deionized water were successively added to the reaction kettle. The reaction kettle was purged with nitrogen three times to remove air. Subsequently, the temperature was heated up to the prepolymerization temperature T1, where T1 was 270 °C, and the temperature satisfied: (Tcp + 100) °C < T1 < (300 - 250 / p + 20×lg(p)) °C, where p was the number of carbon atoms of the lactam monomer, which was 12 in this example, and Tcp was the melting point of the lactam monomer. The melting point of dodecanolactam in this example was 153 °C. The reaction was maintained at the prepolymerization temperature T1 for 5 h to complete the ring-opening prepolymerization reaction of dodecanolactam.

[0071] (2) Post-polycondensation; After the prepolymerization reaction was completed, the pressure was slowly relieved to 10 kPa at a rate of -2 kPa / s. At the same time, the temperature of the reaction system in the reaction kettle dropped to the post-polycondensation temperature T2, where T2 was 220 °C, and this temperature was kept constant; the post-polycondensation temperature satisfied (Tm + q) < T2 < (Tm + 5×q) °C, where Tm was the melting point of the nylon 12 resin. The melting point of nylon 12 in this example was 178 °C, and q was the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material. The molar ratio q of carbon atoms to nitrogen atoms in dodecanolactam in this example was 12.

[0072] Under the condition of maintaining the temperature at 220 °C, nitrogen was introduced into the reaction kettle for purging. The nitrogen flow rate was 3 m³ / h, and the purging time was 1 h. Subsequently, the reaction kettle was evacuated to P, where P was -20 kPa, so that the vacuum pressure satisfied 0 > P > (0.1×T1 + 0.2×T2 - 95) kPa, where T1 was the prepolymerization temperature of 270 °C and T2 was the post-polycondensation temperature of 220 °C, and the reaction was carried out under this condition for 0.75 h; subsequently, the vacuum was continued to be evacuated to -70 kPa, and the reaction was carried out for 2 h under this vacuum degree to complete the melt polycondensation reaction.

[0073] After the polycondensation was completed, nitrogen was replenished into the reaction kettle to 100 kPa, and then the material was discharged, followed by cooling, pelletizing, and drying treatments to obtain the nylon 12 resin product.

[0074] After testing, the relative viscosity of the obtained nylon 12 resin was 1.65, and the melting point Tm was 178 °C.

[0075] Example 8 This example provides a method for preparing nylon 12 resin, which is as follows: (1) Prepolymerization reaction; 5000 kg of dodecanolactam (purchased from Wanhua Chemical), 30 kg of chain terminator hexamethylenediamine (purchased from Shenma Industry Co., Ltd.), and 500 kg of deionized water were successively added to the reaction kettle. The reaction kettle was purged with nitrogen three times to remove air. Subsequently, the temperature was heated up to the prepolymerization temperature T1, where T1 was 270 °C, and the temperature satisfied: (Tcp + 100) °C < T1 < (300 - 250 / p + 20×lg(p)) °C, where p was the number of carbon atoms of the lactam monomer, which was 12 in this example, and Tcp was the melting point of the lactam monomer. The melting point of dodecanolactam in this example was 153 °C. The reaction was maintained for 5 h at the prepolymerization temperature T1 to complete the ring-opening prepolymerization reaction of dodecanolactam.

[0076] (2) Post-polycondensation; After the prepolymerization reaction was completed, the pressure was slowly released to 10 kPa at a rate of -2 kPa / s. At the same time, the temperature of the reaction system in the reaction kettle dropped to the post-polycondensation temperature T2, where T2 was 220 °C, and this temperature was kept constant; the post-polycondensation temperature satisfied (Tm + q) °C < T2 < (Tm + 5×q) °C, where Tm was the melting point of the nylon 12 resin. The melting point of nylon 12 in this example was 178 °C, and q was the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw material. The molar ratio q of carbon atoms to nitrogen atoms in dodecanolactam in this example was 12.

[0077] Under the condition of maintaining the temperature at 220 °C, nitrogen was introduced into the reaction kettle for purging. The nitrogen flow rate was 3 m³ / h, and the purging was carried out for 1 h. Subsequently, the reaction kettle was evacuated to P, where P was -20 kPa, so that the vacuum pressure satisfied 0 kPa > P > (0.1×T1 + 0.2×T2 - 95) kPa, where T1 was the prepolymerization temperature of 270 °C and T2 was the post-polycondensation temperature of 220 °C, and the reaction was carried out for 1 h under this condition; subsequently, the vacuum was continued to be pumped to -70 kPa, and the reaction was carried out for 0.5 h under this vacuum degree to complete the melt polycondensation reaction.

[0078] After the polycondensation was completed, nitrogen was replenished into the reaction kettle to 100 kPa, and then the material was discharged, and cooling, pelletizing, and drying treatments were carried out in sequence to obtain a nylon 12 resin product.

[0079] After testing, the relative viscosity of the obtained nylon 12 resin was 1.60, and the melting point Tm was 178 °C.

[0080] Comparative Example 1 The difference between this comparative example and Example 1 was only that: the prepolymerization temperature was increased from 270 °C to 320 °C, and the prepolymerization temperature exceeded the upper limit range defined by (Tcp + 100) °C < T1 < (300 - 250 / p + 20×lg(p)) °C, where p was 12 and Tcp was 153 °C, and nylon 12 resin was prepared with the remaining process conditions unchanged.

[0081] Comparative Example 2 The difference between this comparative example and Example 1 is only that: the pre-polymerization temperature is decreased from 270 °C to 240 °C, and the pre-polymerization temperature exceeds the lower limit range defined by (Tcp + 100) °C < T1 < (300 - 250 / p + 20×lg(p)) °C, where p is 12 and Tcp is 153 °C. Nylon 12 resin is prepared with the remaining process conditions unchanged.

[0082] Comparative Example 3 The difference between this comparative example and Example 1 is only that: the post-polycondensation temperature is increased from 220 °C to 260 °C, and the post-polycondensation temperature exceeds the upper limit range defined by (Tm + q) °C < T2 < (Tm + 5×q) °C, where Tm is 178 °C and q is 12; Nylon 12 resin is prepared with the remaining process conditions unchanged.

[0083] Comparative Example 4 The difference between this comparative example and Example 1 is only that: the pre-polymerization reaction time is extended from 5 h to 10 h, and the remaining process conditions remain unchanged.

[0084] Comparative Example 5 The difference between this comparative example and Example 1 is only that: in the post-polycondensation step, the reaction is carried out at a vacuum pressure of -20 kPa for 2 h; then the vacuum is continued to be pumped to -70 kPa, and the reaction is carried out at this vacuum degree for 0.5 h to complete the melt polycondensation reaction.

[0085] Comparative Example 6 The difference between this comparative example and Example 1 is only that: in the post-polycondensation step, the reaction is carried out at a vacuum pressure of -20 kPa for 0.5 h; then the vacuum is continued to be pumped to -70 kPa, and the reaction is carried out at this vacuum degree for 3 h to complete the melt polycondensation reaction.

[0086] Comparative Example 7 The difference between this comparative example and Example 1 is only that: in the post-polycondensation process, the vacuum is directly pumped to -70 kPa and the reaction is carried out for 1 h, and nylon 12 resin is prepared with the remaining process conditions unchanged.

[0087] Comparative Example 8 The difference between this comparative example and Example 2 is only that: the pre-polymerization temperature is increased from 200 °C to 280 °C, and the pre-polymerization temperature exceeds the upper limit range defined by Ta °C < T1 < (Tca + 10×q) °C, where Ta is the melting point of 11-aminoundecanoic acid, 190 °C, Tca is 150 °C, and q is 11.

[0088] Comparative Example 9 The difference between this comparative example and Example 3 is only that: the pre-polymerization temperature is increased from 210 °C to 280 °C, and the pre-polymerization temperature exceeds the upper limit range defined by Ts °C < T1 < (Tc + 10×q) °C, where Ts is 192 °C, Tc is 156 °C, and q is 11.

[0089] Test Example 1 The number of optical defects in different size ranges of the polyamide resins prepared in each embodiment and comparative example were tested and statistically analyzed, and the evaluation results are summarized in Table 2. At the same time, the polyamide resins were further evaluated for properties such as the number of spinning breaks, monofilament strength and elongation at break, yarn dryness unevenness (U%), yarn fuzz grade and yarn evenness, and the relevant evaluation results are summarized in Table 3.

[0090] The test methods involved in this test case are as follows: (1) Relative viscosity test: conducted according to ISO307 standard, using m-cresol as solvent, with a solution concentration of 0.5g / 100ml and a test temperature of 25℃.

[0091] (2) Melting point test: The melting point was determined by differential scanning calorimetry (DSC) in accordance with ISO11357-3 standard, under nitrogen atmosphere, at a heating and cooling rate of 10℃ / min.

[0092] (3) Test of the number of optical defects in polyamide: Polyamide resin was cast at 280°C using an extrusion casting equipment to prepare a film with a thickness of 95-105 micrometers. The optical defects in the film were detected and counted using an OCS optical detection system. (4) Spinning breakage test: Polyamide resin was spun at 280℃ using a spinning machine at 70D / 48F. After the spinning production line stabilized, the number of fiber breaks was recorded based on a continuous production of 10t of fiber products. If the fiber breaks at any stage of cooling, stretching, or winding after being extruded from the spinneret, and the number of broken fibers is greater than or equal to 1, it is counted as 1 breakage. Breakage caused by human error, such as improper splicing, or sudden equipment failure such as spinneret blockage, is not included in the statistics. (5) Monofilament strength and elongation at break: tested in accordance with GB / T14344-2022 standard; (6) Yarn unevenness (U%): Tested according to GB / T3292.1 standard; (7) Yarn fuzz grade: Polyamide resin is spun at 280℃ using a spinning machine to produce 70D / 48F yarn. The yarn fuzz size and number are tested using a YG172 fuzz detector, and the yarn is graded. The grading standards are shown in Table 1 below: Table 1: Grading Standards

[0093] The method for determining the level is as follows: First, determine the corresponding grade based on the number of short fibers and long fibers respectively; when the grades of short fibers and long fibers are inconsistent, the lower grade of the two shall be used as the final fiber grade of the yarn.

[0094] For example, if a yarn has 30 or fewer short fibers per 100m (corresponding to Grade A) and more than 4 but less than or equal to 8 long fibers per 100m (corresponding to Grade B), then the final yarn grade is determined to be Grade B. If the number of short fibers exceeds 300 per 100m or the number of long fibers exceeds 25 per 100m, it is determined to be Grade D or below, which does not meet the requirements.

[0095] (8) Yarn evenness: The tests were conducted using an X-Rite Ci7800 colorimeter under D65 light source and 10° observer conditions. The dyed yarn was tightly wound onto a dedicated yarn testing box, ensuring no gaps or overlaps to form a uniform testing surface.

[0096] For each yarn segment, five different locations were selected along its length for testing: the yarn head, middle, tail, and two intermediate locations near the head and tail. The CIELab color parameter values ​​at each test location were measured using a colorimeter and denoted as (Li, ai, bi), where i = 1, 2, 3, 4, 5.

[0097] Using the CIELab color parameters (L0, a0, b0) measured at the middle of the same yarn segment as reference values, the color difference value ΔEab is calculated between each of the other test positions and this reference value. The color difference calculation formula is as follows: ΔEab= ; The maximum value of ΔEab obtained from 5 test positions of the same yarn segment is taken as the longitudinal color difference value of the yarn segment.

[0098] For the same batch of yarn, 10 segments of yarn were randomly selected and tested according to the above method. The arithmetic mean of the 10 longitudinal color difference values ​​was taken as the evaluation index of the uniformity of the yarn in that batch.

[0099] The uniformity of dyeing is graded according to the longitudinal color difference value: when ΔEab≤0.5, it is judged as excellent (Grade A); when 0.5<ΔEab≤1.0, it is judged as good (Grade B); when ΔEab>1.0, it is judged as unqualified (Grade C).

[0100] Table 2. Number of optical defects in polyamide resins of the examples and comparative examples

[0101] Table 3. Performance evaluation results of polyamide resins in the examples and comparative examples.

[0102] Comparing Example 1 with Comparative Examples 1 and 2, it is evident that when the prepolymerization temperature deviates from the range defined in this invention, it leads to a significant increase in resin optical defects and a marked deterioration in spinning performance. When the prepolymerization temperature is too high, the system is prone to local overheating and side reactions, resulting in an increase in defects such as gelation and crystal points; when the prepolymerization temperature is too low, the prepolymerization reaction is incomplete, easily leaving behind more unreacted monomers and oligomers, causing an increase in impurities and structural inhomogeneity.

[0103] Comparing Example 1 and Comparative Example 3, it is evident that when the post-polymerization temperature deviates from the range defined in this invention, it also leads to a significant increase in resin optical defects and a marked deterioration in spinning performance. When the post-polymerization temperature is too high, the system is more prone to thermal degradation and side reactions at high temperatures, resulting in an increase in defects such as gelation and crystal points, and exacerbating structural inhomogeneity. This increases the number of resin optical defects, leading to an increase in the number of spinning breaks, a decrease in monofilament strength and elongation at break, an increase in yarn unevenness, and a deterioration in filament grade and dyeability. This demonstrates that controlling the post-polymerization temperature within the range defined in this invention is beneficial for balancing the polymerization reaction with the thermal stability of the system, thereby reducing resin defects and improving the spinnability and fiber properties of the polyamide.

[0104] Comparing Example 1 and Comparative Example 4, when the prepolymerization reaction time deviates from the range defined in this invention, it also leads to a significant increase in resin optical defects and a marked deterioration in spinning performance. When the prepolymerization reaction time is too long, the residence time of the polymerization system at high temperature is prolonged, which easily leads to thermal degradation, side reactions, and excessive growth of local structures, thereby increasing defects such as gels and crystal points, and exacerbating the non-uniformity of the resin structure.

[0105] A comparison of Example 1 with Comparative Examples 5 and 6 shows that longer reaction times in each stage of post-polymerization are not necessarily better. Whether the first or second step of polymerization is too long, the system remains at high temperatures for too long, leading to increased optical defects in the resin and deterioration of spinning performance. Table 2 shows that the number of optical defects in Comparative Examples 5 and 6 is higher than in Example 1; Table 3 shows a significant increase in the number of spinning ends, a decrease in monofilament strength and elongation at break, and an increase in yarn unevenness. This indicates that controlling the reaction times in each stage of post-polymerization within the limits defined in this invention is beneficial for reducing resin defects and improving the spinnability and fiber properties of polyamide.

[0106] Comparing Example 1 and Comparative Example 7, it is evident that directly skipping the stepwise polycondensation process in the post-polymerization process also leads to an increase in resin optical defects and a deterioration in spinning performance. Table 2 shows that the number of optical defects in all size ranges of Comparative Example 7 is higher than that in Example 1; Table 3 shows that the number of spinning breaks increases, monofilament strength and elongation at break decrease, and yarn unevenness increases. This indicates that using stepwise pressure reduction in the post-polymerization process is more conducive to stable polycondensation and removal of small molecules, thereby reducing resin defects and improving the spinnability and fiber properties of the polyamide.

[0107] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing polyamide for textile materials, characterized in that: It includes the following steps: (1) Carry out pre-polymerization of polyamide raw materials, water, and end-capping agent for 2 h to 8 h; When the polyamide raw materials contain lactam monomers, control the pre-polymerization temperature (Tcp + 100) < T1 < (300 - 250 / p + 20×lg(p)), where Tcp is the melting point of the lactam monomer and p is the number of carbon atoms of the lactam monomer; Or, when the polyamide raw materials are aliphatic diamine and aliphatic diacid, control the pre-polymerization temperature Ts < T1 < (Tc + 10×q), where Ts is the melting point of the polyamide, Tc is the crystallization temperature of the polyamide, and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw materials; Or, when the polyamide raw materials are amino acids, control the pre-polymerization temperature Ta < T1 < (Tca + 10×q), where Ta is the melting point of the amino acid, Tca is the crystallization temperature of the polyamide, and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw materials; (2) After the pre-polymerization reaction is completed, carry out post-polycondensation; First, carry out polycondensation for 0.5 h to 1 h under the pressure condition of 0 kPa > P > (0.1×T1 + 0.2×T2 - 95) kPa, and then carry out polycondensation for 0 h to 2 h under the pressure condition of -60 kPa to -90 kPa, control the post-polycondensation temperature (Tm + q) < T2 < (Tm + 5×q), where Tm is the melting point of the polyamide and q is the molar ratio of carbon atoms to nitrogen atoms in the polyamide raw materials.

2. The preparation method according to claim 1, characterized in that: In step (1), the lactam monomer includes one or more lactam monomers with different carbon chain lengths; When the lactam monomer includes multiple lactam monomers with different carbon chain lengths, p is the number of carbon atoms of the lactam monomer with the longest carbon chain.

3. The preparation method according to claim 1 or 2, characterized in that: The lactam monomer includes one or more of C6 to C18 lactams.

4. The preparation method according to claim 3, characterized in that: The lactam monomer includes one or more of caprolactam, octanolactam, nonanolactam, decanolactam, undecanolactam, and dodecanolactam.

5. The preparation method according to claim 1, 2 or 4, characterized in that: The amino acid includes one or more of C6 to C18 amino acids.

6. The preparation method according to claim 5, characterized in that: The amino acid includes one or more of 6-aminohexanoic acid, 10-aminoundecanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid.

7. The preparation method according to claim 1, 2, 4 or 6, characterized in that: The aliphatic diamine includes one or more of linear aliphatic diamines with C6 to C18; And / or, the aliphatic diacid includes one or more of linear aliphatic dicarboxylic acids with C6 to C18.

8. The preparation method according to claim 7, characterized in that: The aliphatic diamine includes one or more of hexanediamine, heptanediamine, octanediamine, nonanediamine, decanediamine, undecanediamine, dodecanediamine, tridecanediamine, tetradecanediamine, hexadecanediamine, and octadecanediamine; And / or, the aliphatic diacid includes one or more of adipic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, and octadecanedioic acid.

9. The preparation method according to claim 1, 2, 4, 6 or 8, characterized in that: The end-capping agent includes one or more of linear aliphatic C2-C12 monocarboxylic acids, linear aliphatic C4-C12 monoamines, linear aliphatic C4-C18 dicarboxylic acids, and linear aliphatic C4-C18 diamines.

10. A polyamide prepared by any one of the preparation methods described in claims 1-9, characterized in that, The polyamide has at least one of the following characteristics: (1) After polyamide is used to prepare a cast film with a thickness of 95-105 micrometers using a casting equipment, the number of optical defects per square meter of cast film sample is as follows, as measured by an optical detection system: The number of optical defects with a size greater than 500 micrometers is 0; And / or, the number of optical defects with a size greater than 300 micrometers and less than or equal to 500 micrometers is less than 50; And / or, the number of optical defects with a size greater than 100 micrometers and less than or equal to 300 micrometers is less than 200; And / or, the number of optical defects with a size greater than 50 micrometers and less than or equal to 100 micrometers is less than 300; And / or, the number of optical defects with a size greater than 25 micrometers and less than or equal to 50 micrometers is less than 500; (2) When the polyamide is used to prepare 70D yarn, the number of spinning breaks is less than 5 times / 10 tons, and / or the monofilament strength is 5.1cN / dtex to 6.8cN / dtex, and / or the monofilament breaking elongation is 28% to 45%, and / or the yarn unevenness is 2.8% to 4.8%.

Images