Polyamide and preparation method thereof

Abstract

The invention provides polyamide and a preparation method thereof, and belongs to the technical field of compounds and preparation methods thereof. The amount-of-substance ratio of the amino-terminated group to the carboxyl-terminated group of the polyamide is 1: (0.77-1.5). The preparation method comprises the following steps that diamine, binary acid and water react under the nitrogen atmosphere and the set temperature condition, a polyamide salt solution is obtained, the molar ratio of diamine to binary acid is 1: 1, and the value range of the mass percentage content of solute in the polyamide salt solution is 50%-80%; the polyamide solution and an auxiliary agent are subjected to a polymerization reaction in a polymerization reaction kettle under the conditions of nitrogen atmosphere and micro-positive pressure to obtain polyamide, and the auxiliary agent is selected from one or more of a nucleating agent, a molecular weight regulator, an antioxidant, a delustering agent and a catalyst. According to the present invention, the requirements on equipment and pipelines are low, the cost can be effectively reduced, the safety can be effectively improved, the process flow is simple, the energy consumption is low, and one or more of the raw materials are derived from the biomass material so as to meet the low-carbon environmental protection requirements.

Description

Technical Field

[0001] This invention relates to the field of compounds and their preparation methods, and in particular to polyamides and their preparation methods. Background Technology

[0002] Polyamide (PA, commonly known as nylon) was industrialized in 1939. Injection-molded products were developed and produced starting in the 1950s to replace metals and meet the demands of downstream industries for lightweighting and cost reduction. It is widely used in the automotive, textile, electronics, and machinery industries. Polyamides can be produced from diamines and diacids, or synthesized from ω-amino acids or cyclic lactams. Depending on the number of carbon atoms in the diamine, diacid, or amino acid, various polyamides can be produced; currently, there are dozens of polyamide varieties, among which polyamide-6, polyamide-66, and polyamide-610 are the most widely used. However, existing polyamide preparation methods are complex, and the quality of the resulting polyamides is not ideal. Summary of the Invention

[0003] In view of this, the present invention provides a polyamide and a method for preparing the same. When polyamide is prepared by this method, the requirements for equipment and pipelines are low, which can effectively reduce costs and improve safety. At the same time, the process is simple and energy consumption is low. Moreover, one or more of the raw materials used in the present invention are derived from biomass materials, which meets the current requirements for low carbon and environmental protection, and is therefore more suitable for practical use.

[0004] To achieve the first objective mentioned above, the technical solution for preparing polyamide provided by this invention is as follows:

[0005] This invention provides a method for preparing a polyamide, wherein the molar ratio of terminal amino groups to terminal carboxyl groups in the polyamide is 1:(0.77-1.5), and the method for preparing the polyamide includes the following steps:

[0006] Diamine, diacid, and water react under a nitrogen atmosphere and a set temperature to obtain a polyamide salt solution, wherein the molar ratio of the diamine to the diacid is 1:1, and the mass percentage of the solute in the polyamide salt solution ranges from 50% to 80%.

[0007] The polyamide solution and additives are polymerized in a polymerization reactor under a nitrogen atmosphere to obtain the polyamide. The additives are selected from one or more of nucleating agents, molecular weight regulators, antioxidants, matting agents, and catalysts. The polymerization reaction sequentially includes a prepolymerization stage, a mid-polymerization stage, and a late-polymerization stage. During the prepolymerization stage, the reaction pressure is maintained at 0.1 MPa-0.2 MPa; during the mid-polymerization stage, the reaction pressure is maintained at 0.01 MPa-0.05 MPa; and during the late-polymerization stage, the pressure is vented until it drops below atmospheric pressure. Under these conditions, nitrogen purging is performed three times, stirring is initiated, and the polymerization temperature and pressure are adjusted under the protection of a nitrogen atmosphere to control the polymerization process and obtain the polyamide polymer. If the relative viscosity of the obtained polyamide polymer is lower than the expected viscosity, a vacuum can be drawn to negative pressure to continue the reaction, thereby obtaining the polyamide product with the target viscosity. After the reaction is complete, nitrogen is introduced to restore the pressure inside the reactor to atmospheric pressure, followed by cooling, discharge, pelletizing, and drying to obtain the polyamide polymer.

[0008] The polyamide preparation method provided by this invention can be further implemented using the following technical measures.

[0009] Preferably, the relative viscosity of the polyamide is in the range of 2.2-3.4.

[0010] Preferably, the polyamide can be polymerized using a conventional solid-state polymerization process, which can increase the relative viscosity to 4.0.

[0011] Preferably, in the step of reacting the diamine, diacid, and water under a nitrogen atmosphere and a set temperature to obtain a polyamide salt solution, the nitrogen atmosphere is a nitrogen atmosphere and the set temperature is 55℃-90℃.

[0012] Preferably, in the step of reacting the diamine, diacid, and water under a nitrogen atmosphere and a set temperature to obtain a polyamide salt solution...

[0013] The diamine is one or more of pentanediamine and hexanediamine;

[0014] The dicarboxylic acid is selected from one or more of sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, and octadecyl dicolic acid.

[0015] Preferably, the reaction parameters for the prepolymerization reaction stage include: heating from 55℃-75℃ to 140℃-160℃, and then reacting at a constant temperature of 140℃-160℃ for 1h-2h.

[0016] Preferably, the reaction parameters for the intermediate stage of polymerization include: heating rate of 1℃ / min to 170℃-190℃, and reaction time of 0.5h-2h.

[0017] Preferably, the reaction parameters for the later stage of polymerization include: raising the temperature to 220℃-240℃, continuously purging with nitrogen, and reacting at a constant temperature for 2-5 hours.

[0018] Preferably, between the step of reacting the diamine, diacid, and water under a nitrogen atmosphere and a set temperature to obtain a polyamide salt solution, and the step of polymerizing the polyamide solution and the additives in a polymerization reactor to obtain the polyamide, the following step is further included:

[0019] A pH adjuster is added to the polyamide salt solution so that the pH value of the polyamide salt solution is in the range of 7.8-9.0.

[0020] Preferably, the pH adjuster is selected from one or more of 2-methylpentanediamine, pentanediamine, hexamethylenediamine, p-phenylenediamine, and m-phenylenediamine. In this case, by adding an additional diamine to adjust the pH of the polyamide salt solution, the stoichiometric ratio of the diamine and diacid during polymerization is effectively maintained, which helps to ensure the mechanical properties and thermal stability of the prepared polyamide material.

[0021] To achieve the second objective mentioned above, the present invention provides the following technical solution for polyamide:

[0022] The polyamide provided by this invention is prepared by the polyamide preparation method provided by this invention.

[0023] The polyamide preparation method provided by this invention employs a low-pressure-atmospheric-pressure polymerization process. By controlling the temperature and pressure at different polymerization stages, a controllable prepolymerization reaction of the polyamide salt solution is achieved, ensuring a stable and controllable increase in polymer viscosity. This addresses the performance instability problem of polyamides produced by traditional high-temperature and high-pressure polymerization processes. Traditional poly(diacidic acid diamide) polymerization uses a high-temperature and high-pressure process, which is time-consuming, involves high polymerization temperatures and pressures, and requires precise control of heating, pressurization, and depressurization. This process is cumbersome and prone to problems such as poor color and unstable performance. This invention uses an atmospheric-pressure polymerization process. By controlling the temperature and pressure at different polymerization stages, the oligomer polymerization reaction is effectively controlled, and salt decomposition is inhibited. This achieves a controllable polymerization reaction of the polyamide salt solution, ensuring a stable and controllable increase in polymer viscosity, thus solving the performance instability problem of polyamides produced by traditional high-temperature and high-pressure polymerization processes. Compared to traditional high-temperature and high-pressure polymerization processes, this process has lower requirements for equipment and pipelines, effectively reducing costs and improving safety. Furthermore, the process is simple, energy-efficient, and one or more of the raw materials used in this invention are derived from biomass materials, meeting current low-carbon and environmental protection requirements. The polyamide prepared by the method provided in the embodiments of the present invention can be applied to engineering plastics, fibers, films and other fields. Detailed Implementation

[0024] In view of this, the present invention provides a polyamide and a method for preparing the same. When polyamide is prepared by this method, the requirements for equipment and pipelines are low, which can effectively reduce costs and improve safety. At the same time, the process is simple and energy consumption is low. Moreover, one or more of the raw materials used in the present invention are derived from biomass materials, which meets the current requirements for low carbon and environmental protection, and is therefore more suitable for practical use.

[0025] Through arduous and persistent efforts, the inventor discovered that

[0026] In existing technologies, polyamide preparation methods can be broadly classified into two categories: one, represented by polyamide 6 (PA6), is obtained through lactam condensation or ring-opening polymerization; the other, represented by polyamide 66 (PA66), is obtained through the condensation of diamines and diacids to form polydiacid diacids. PA6 and PA66 are the main varieties of nylon, still accounting for approximately 90% of the total PA market share, holding a dominant position. Currently, there are dozens of polyamide varieties, among which the polymerization process of polydiacid diacids largely follows the PA66 polymerization process. This process suffers from technical bottlenecks such as reliance on high temperature and pressure, complex procedures, and limited single-line production capacity and poor slice quality due to gelation.

[0027] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description, in conjunction with preferred embodiments, details the specific implementation, structure, features, and effects of a polyamide and its preparation method according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0028] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships, such as A and / or B. Specifically, it can mean that A and B can be included at the same time, A can exist alone, or B can exist alone, and any of the above three situations can be met.

[0029] In the following examples and comparative examples, the relative viscosity was tested using the GB / T 38138-2019 fiber-grade polycaprolactam (PA6) slice test method.

[0030] Example 1

[0031] In this embodiment, polyamide 510 is prepared using the following method.

[0032] a. Weigh 330 kg of pentanediamine, 640 kg of sebacic acid and 970 kg of deionized water, add them to the reaction vessel, start stirring, set the temperature to 70℃, and react at a constant temperature for 1.5 h. Then add pentanediamine to adjust the pH of the solution to 8.0, and obtain a clear and transparent polyamide salt solution with a solution concentration of 50 wt%.

[0033] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0034] c. Heat to 150℃, maintain the temperature for 1.5 hours, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0035] d. Heat to 180℃ and then react at 0.05MPa for 0.5h to carry out the intermediate stage of polymerization.

[0036] e. Heat to 230℃, reduce pressure to atmospheric pressure, maintain stable temperature and pressure, react for 2 hours, and proceed to the later stage of polymerization.

[0037] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 510 chips.

[0038] The relative viscosity of the slices in this example was 2.39, the terminal amino group was 90.2 mmol / kg, and the terminal carboxyl group was 70.1 mmol / kg.

[0039] Example 2

[0040] In this embodiment, polyamide 510 is prepared using the following method.

[0041] a. Weigh 323 kg of pentanediamine, 640 kg of sebacic acid, 5.5 kg of 2-methyl-pentanediamine and 970 kg of deionized water, add them to the reaction vessel, start stirring, set the temperature to 70℃, and react at a constant temperature for 1.5 h. Then add pentanediamine to adjust the pH of the solution to 7.8, and obtain a clear and transparent polyamide salt solution with a concentration of 50 wt%.

[0042] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0043] c. Heat to 150℃, maintain the temperature for 1.5 hours, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0044] d. Heat to 180℃ and then react at 0.05MPa for 0.5h to carry out the intermediate stage of polymerization.

[0045] e. Heat to 230℃, reduce pressure to atmospheric pressure, maintain stable temperature and pressure, react for 2 hours, and proceed to the later stage of polymerization.

[0046] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 510 chips.

[0047] The relative viscosity of the slices in this example was 2.32, the terminal amino group concentration was 80.5 mmol / kg, and the terminal carboxyl group concentration was 65.8 mmol / kg. Implementation Example 3

[0048] In this embodiment, polyamide 610 is prepared using the following method.

[0049] a. Weigh 368 kg hexamethylenediamine, 640 kg sebacic acid and 672 kg deionized water, add them to the reaction vessel, turn on the stirrer, set the temperature to 80℃, and react at a constant temperature for 1.2 h. Then add hexamethylenediamine to adjust the pH of the solution to 8.2, and obtain a clear and transparent polyamide salt solution with a solution concentration of 60 wt%.

[0050] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0051] c. Heat to 155℃, maintain the temperature for 1.5 hours, and keep the pressure at 0.2 MPa to allow the polyamide salt to fully prepolymerize;

[0052] d. Heat to 185℃ and then react at 0.05MPa for 1 hour to carry out the intermediate stage of polymerization.

[0053] e. Heat to 240℃, reduce pressure to atmospheric pressure, maintain stable temperature and pressure, react for 3 hours, and proceed to the later stage of polymerization.

[0054] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 610 chips.

[0055] The relative viscosity of the slices in this example was 2.52, the terminal amino group concentration was 72.8 mmol / kg, and the terminal carboxyl group concentration was 55.8 mmol / kg. Implementation Example 4

[0056] In this embodiment, polyamide 511 was prepared using the following method.

[0057] a. Weigh 323 kg of pentanediamine, 685 kg of undecanoic acid and 543 kg of deionized water, add them to the reaction vessel, start stirring, set the temperature to 80℃, and react at a constant temperature for 1 hour. Then add m-phenylenediamine to adjust the pH of the solution to 8.5, and obtain a clear and transparent polyamide salt solution with a solution concentration of 65 wt%.

[0058] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0059] c. Heat to 148℃, maintain the temperature for 2 hours, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0060] d. Heat to 175℃ and then react at 0.05MPa for 1 hour to carry out the intermediate stage of polymerization.

[0061] e. Increase the temperature to 240℃, reduce the pressure to atmospheric pressure, maintain stable temperature and pressure, and react for 1.5 hours to proceed to the later stage of polymerization;

[0062] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 511 chips.

[0063] The relative viscosity of the slices in this example was 2.29, the terminal amino group was 95.2 mmol / kg, and the terminal carboxyl group was 80.6 mmol / kg. Implementation Example 5

[0064] In this embodiment, polyamide 512 was prepared using the following method.

[0065] a. Weigh 330 kg of pentanediamine, 744 kg of dodecanoic acid and 460 kg of deionized water, add them to the reaction vessel, start stirring, set the temperature to 82℃, and react at a constant temperature for 1 h. Then add pentanediamine to adjust the pH of the solution to 9.0, and obtain a clear and transparent polyamide salt solution with a solution concentration of 70 wt%.

[0066] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0067] c. Heat to 160℃, maintain the temperature for 1.5 hours, and keep the pressure at 0.2MPa to allow the polyamide salt to fully prepolymerize;

[0068] d. Heat to 180℃ and then react at 0.05MPa for 0.5h to carry out the intermediate stage of polymerization.

[0069] e. Increase the temperature to 238℃, reduce the pressure to atmospheric pressure, maintain stable temperature and pressure, and react for 1.5 hours to proceed to the later stage of polymerization;

[0070] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 512 chips.

[0071] The relative viscosity of the slices in this example was 2.10, the terminal amino group was 100.5 mmol / kg, and the terminal carboxyl group was 50.3 mmol / kg.

[0072] Example 6

[0073] In this embodiment, polyamide 612 is prepared using the following method.

[0074] a. Weigh 301 kg hexamethylenediamine, 599 kg dodecanoic acid and 900 kg deionized water, add them to the reaction vessel, turn on the stirrer, set the temperature to 75℃, and react at a constant temperature for 2.5 h. Then add pentanediamine to adjust the pH of the solution to 7.8, and obtain a clear and transparent polyamide salt solution with a solution concentration of 50 wt%.

[0075] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0076] c. Heat to 140℃, maintain the temperature for 1 hour, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0077] d. Heat to 170℃, and then react at 0.05MPa for h to carry out the intermediate stage of polymerization.

[0078] e. Heat to 230℃, reduce pressure to atmospheric pressure, maintain stable temperature and pressure, react for 2 hours, and proceed to the later stage of polymerization.

[0079] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 612 chips.

[0080] The relative viscosity of the slices in this example was 2.2, the terminal amino group was 60.3 mmol / kg, and the terminal carboxyl group was 75.5 mmol / kg. Implementation Example 7

[0081] In this embodiment, polyamide 514 was prepared using the following method.

[0082] a. Weigh 330 kg of pentanediamine, 833 kg of tetradecanoic acid and 970 kg of deionized water, add them to the reaction vessel, turn on the stirrer, set the temperature to 85℃, and react at a constant temperature for 1.5 h. Then adjust the pH of the solution to 8.0 to obtain a clear and transparent polyamide salt solution with a concentration of 50 wt%.

[0083] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0084] c. Heat to 150℃, maintain the temperature for 1.5 hours, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0085] d. Heat to 180℃ and then react at 0.05MPa for 0.5h to carry out the intermediate stage of polymerization.

[0086] e. Heat to 230℃, reduce pressure to atmospheric pressure, maintain stable temperature and pressure, react for 2 hours, and proceed to the later stage of polymerization.

[0087] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 510 chips.

[0088] The relative viscosity of the slices in this example was 2.39, the terminal amino group was 90.22 mmol / kg, and the terminal carboxyl group was 70.15 mmol / kg.

[0089] Example 8

[0090] In this embodiment, polyamide 518 is prepared using the following method.

[0091] a. Weigh 330 kg of pentanediamine, 640 kg of octadecyl diacid and 970 kg of deionized water, add them to the reaction vessel, turn on the stirrer, set the temperature to 70℃, and react at a constant temperature for 1.5 h. Then adjust the pH of the solution to 8.0 to obtain a clear and transparent polyamide salt solution with a concentration of 50 wt%.

[0092] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0093] c. Heat to 150℃, maintain the temperature for 1.5 hours, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0094] d. Heat to 180℃ and then react at 0.05MPa for 0.5h to carry out the intermediate stage of polymerization.

[0095] e. Heat to 230℃, reduce pressure to atmospheric pressure, maintain stable temperature and pressure, react for 2 hours, and proceed to the later stage of polymerization.

[0096] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 510 chips.

[0097] The relative viscosity of the slices in this example was 2.39, the terminal amino group was 90.22 mmol / kg, and the terminal carboxyl group was 70.15 mmol / kg.

[0098] Example 9

[0099] In this embodiment, polyamide 510 is prepared using the following method.

[0100] a. Weigh 330 kg of pentanediamine, 640 kg of sebacic acid and 970 kg of deionized water, add them to the reaction vessel, start stirring, set the temperature to 70℃, and react at a constant temperature for 1.5 h. Then add pentanediamine to adjust the pH of the solution to 8.0, and obtain a clear and transparent polyamide salt solution with a solution concentration of 50 wt%.

[0101] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0102] c. Heat to 150℃, maintain the temperature for 1.5 hours, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0103] d. Heat to 180℃ and then react at 0.05MPa for 0.5h to carry out the intermediate stage of polymerization.

[0104] e. Heat to 230℃, reduce pressure to atmospheric pressure, maintain stable temperature and pressure, react for 2 hours, and proceed to the later stage of polymerization.

[0105] f. Close the exhaust valve and slowly evacuate at 230℃. After the vacuum reaches 0.09MPa, continue the reaction for 1 hour.

[0106] h. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 510 chips.

[0107] The relative viscosity of the slices in this example is 3.31, the terminal amino group is 50.2 mmol / kg, and the terminal carboxyl group is 40.1 mmol / kg.

[0108] Example 10

[0109] In this embodiment, copolyamide 510 / 610 was prepared using the following method.

[0110] a. Weigh 204 kg of pentanediamine, 143 kg of hexanediamine, 640 kg of sebacic acid and 970 kg of deionized water, add them to the reaction vessel, turn on the stirrer, set the temperature to 70℃, and react at a constant temperature for 1.5 h. Then add pentanediamine to adjust the pH of the solution to 8.0, and obtain a clear and transparent polyamide salt solution with a solution concentration of 50 wt%.

[0111] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0112] c. Heat to 150℃, maintain the temperature for 1.5 hours, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0113] d. Heat to 180℃ and then react at 0.05MPa for 0.5h to carry out the intermediate stage of polymerization.

[0114] e. Heat to 230℃, reduce pressure to atmospheric pressure, maintain stable temperature and pressure, react for 2 hours, and proceed to the later stage of polymerization.

[0115] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain copolyamide 510 / 610 chips.

[0116] The relative viscosity of the slices in this example was 2.29, the terminal amino group was 96.5 mmol / kg, and the terminal carboxyl group was 81.2 mmol / kg.

[0117] Comparative Example 1

[0118] In this embodiment, polyamide 510 is prepared using the following method.

[0119] a. Weigh 330 kg of pentanediamine, 640 kg of sebacic acid and 970 kg of deionized water, add them to the reaction vessel, turn on the stirrer, set the temperature to 70℃, and react at a constant temperature for 1.5 h. Then adjust the pH of the solution to 8.0 to obtain a clear and transparent polyamide salt solution with a concentration of 50 wt%.

[0120] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0121] c. Heat to 150℃, maintain the temperature for 0.5h, and keep the pressure at 0.1MPa to allow the polyamide salt to fully prepolymerize;

[0122] d. Increase the temperature to 210℃ and the pressure to 1.8MPa, and maintain the pressure and temperature stable for 1.5h.

[0123] e. Heat to 240℃, slowly reduce the pressure to atmospheric pressure within 1 hour, maintain stable temperature and pressure, and react for 2 hours.

[0124] f. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 510 chips.

[0125] The relative viscosity of the slices in this example was 2.41, the terminal amino group concentration was 50.72 mmol / kg, and the terminal carboxyl group concentration was 60.21 mmol / kg.

[0126] Comparative Example 2

[0127] In this embodiment, polyamide 510 is prepared using the following method.

[0128] a. Weigh 330 kg of pentanediamine, 640 kg of sebacic acid and 970 kg of deionized water, add them to the reaction vessel, turn on the stirrer, set the temperature to 70℃, and react at a constant temperature for 1.5 h. Then adjust the pH of the solution to 8.0 to obtain a clear and transparent polyamide salt solution with a concentration of 50 wt%.

[0129] b. Replace the air in the vessel with nitrogen three times, then fill the vessel with nitrogen to make the pressure 0.1 MPa, and start stirring.

[0130] c. Increase the temperature to 210℃ and the pressure to 1.8MPa, and maintain the pressure and temperature stable for 1.5h.

[0131] d. Heat to 240℃, slowly reduce the pressure to atmospheric pressure within 1 hour, maintain stable temperature and pressure, and react for 2 hours.

[0132] e. Nitrogen gas is introduced into the reactor, the material is discharged, cooled, granulated, and dried to obtain polyamide 510 chips.

[0133] The relative viscosity of the slices in this example was 2.79, the terminal amino group concentration was 56.88 mmol / kg, and the terminal carboxyl group concentration was 42.45 mmol / kg.

[0134] As can be seen from the above examples and comparative examples, while conventional high-pressure polymerization processes can produce polyamide chips, the viscosity of the polyamide increases too rapidly during the depressurization process, making it difficult to control and guarantee the quality of each batch of polyamide. Furthermore, the high-pressure, high-temperature process involves a slow heating process and places high demands on equipment, thus increasing production costs. The examples employing a micro-positive pressure process solve these problems. The polyamide products prepared using this process have controllable viscosity and adjustable end groups.

[0135] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0136] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing a polyamide, wherein the molar ratio of terminal amino groups to terminal carboxyl groups in the polyamide is 1:(0.77-1.5), characterized in that, The method for preparing the polyamide includes the following steps: Diamine, diacid, and water react under a nitrogen atmosphere and a set temperature to obtain a polyamide salt solution, wherein the molar ratio of the diamine to the diacid is 1:1, and the mass percentage of the solute in the polyamide salt solution ranges from 50% to 80%. The polyamide solution and additives are polymerized in a polymerization reactor under a nitrogen atmosphere to obtain the polyamide. The additives are selected from one or more of nucleating agents, molecular weight regulators, antioxidants, matting agents, and catalysts; The polymerization reaction sequentially includes a prepolymerization stage, a mid-polymerization stage, and a late-polymerization stage. The reaction pressure in the prepolymerization stage is maintained at 0.1 MPa-0.2 MPa, the reaction pressure in the mid-polymerization stage is maintained at 0.01 MPa-0.05 MPa, and the late-polymerization stage is vented until the pressure drops below atmospheric pressure.

2. The method for preparing polyamide according to claim 1, characterized in that, The relative viscosity of the polyamide ranges from 2.2 to 3.

4.

3. The method for preparing polyamide according to claim 1, characterized in that, The polyamide was subjected to a conventional solid-state polymerization process, which increased its relative viscosity to 4.

0.

4. The method for preparing polyamide according to claim 1, characterized in that, In the step of reacting diamine, diacid, and water under a nitrogen atmosphere and a set temperature to obtain a polyamide salt solution, the set temperature is 55℃-90℃.

5. The method for preparing polyamide according to claim 1, characterized in that, In the step of reacting the diamine, diacid, and water under a nitrogen atmosphere and at a set temperature to obtain a polyamide salt solution... The diamine is one or more of pentanediamine and hexanediamine; The dicarboxylic acid is selected from one or more of sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, and octadecyl dicolic acid.

6. The method for preparing polyamide according to claim 1, characterized in that, The reaction parameters for the prepolymerization reaction stage include: heating from 55℃-75℃ to 140℃-160℃, and then reacting at a constant temperature of 140℃-160℃ for 1h-2h.

7. The method for preparing polyamide according to claim 1, characterized in that, The reaction parameters for the intermediate stage of polymerization include: heating rate of 1℃ / min to 170℃-190℃, reaction time of 0.5h-2h.

8. The method for preparing polyamide according to claim 1, characterized in that, The reaction parameters for the later stage of polymerization include: raising the temperature to 220℃-240℃, continuously purging with nitrogen, and reacting at a constant temperature for 2-5 hours.

9. The method for preparing polyamide according to claim 1, characterized in that, Between the steps of reacting the diamine, diacid, and water under a nitrogen atmosphere and a set temperature to obtain a polyamide salt solution, and the steps of polymerizing the polyamide solution and additives in a polymerization reactor to obtain the polyamide, the following steps are also included: A pH adjuster is added to the polyamide salt solution so that the pH value of the polyamide salt solution is in the range of 7.8-9.0; Preferably, the pH adjuster is selected from one or more of 2-methyl-pentanediamine, pentanediamine, hexanediamine, p-phenylenediamine, and m-phenylenediamine.

10. A polyamide, characterized in that, It is prepared by any of the polyamide preparation methods described in claims 1-9.