Method for preparing polyamide 6 material through anionic polymerization

Abstract

The invention provides a method for preparing a polyamide 6 material by anionic polymerization, which comprises the following steps: adding caprolactam and a catalyst into a drying device A to remove system moisture, putting into a storage tank A, adding caprolactam into a drying device B to remove moisture, putting into a storage tank B together with an initiator and a cyclic oligomer inhibitor, and carrying out anionic polymerization to obtain the polyamide 6 material. Then continuously injecting the caprolactam liquid in the storage tank A and the storage tank B into a screw extruder through a conveying device, carrying out anionic ring-opening polymerization reaction to prepare a polyamide 6 basic melt, further conveying the basic melt into a devolatilization reactor, and efficiently removing monomers and oligomers to obtain a polyamide 6 final polymer; the final polymer can be directly subjected to melt direct spinning, injection molding or film blowing to obtain high-quality polyamide 6 fibers, engineering plastics or films.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of polyamide 6 materials, and particularly relates to a method for preparing polyamide 6 materials by anionic polymerization. Background Art

[0002] Polyamide 6 refers to a polymer with a repeating structural unit of (-NH(CH2)5CO-) on the molecular chain. Polyamide 6 fibers have high mechanical strength and wear resistance and are widely used in fields such as automobiles, industry, aerospace, ships, and textiles.

[0003] Currently, in the industrial production of polyamide 6, hydrolysis ring-opening polymerization is mainly used for preparation. Its production cycle is as long as dozens of hours, and about 10% of caprolactam monomers and oligomers (also called hot water extractables) remain in the polymer. It requires a continuous hot water extraction process of dozens of hours to remove the monomers and oligomers in polyamide 6. According to FZ / T 51004-2011, the content of hot water extractables in polyamide 6 chips ≤ 0.5 is first-class product, ≤ 0.6 is first-class product, and ≤ 0.8 is qualified product. It can be seen that the process of preparing polyamide 6 by caprolactam hydrolysis polymerization, slicing extraction and drying, and then melt spinning has a long production cycle and requires a large amount of water and energy. In contrast, the anionic polymerization of caprolactam to prepare polyamide 6 has an extremely fast reaction rate and about 5% of hot water extractables remain. However, due to the extremely fast polymerization reaction rate and difficult to control, and still a small amount of oligomers need to be extracted by hot water and other problems, the anionic polymerization of caprolactam to polyamide 6 has not been realized for the preparation of fibers, films, etc. in industry.

[0004] A small part of monomers and oligomers can be removed by vacuum devolatilization. Hyoungsan Kye et al. (Journal of Applied Polymer Science 1994, 52(9), 1249-1262) used vacuum devolatilization to remove monomers and oligomers in anionic polyamide 6, and then added a spinneret at the outlet of the screw extruder to directly carry out melt spinning. However, due to a large amount of oligomers remaining, the fibers produced by it are on the millimeter scale and do not meet the use requirements of daily fibers. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing polyamide 6 materials by anionic polymerization, using a cyclic oligomer inhibitor to reduce the generation of monomers and cyclic oligomers during the polymerization process, and combining with a high-efficiency devolatilization reactor to remove monomers and oligomers. Furthermore, the obtained polyamide 6 end polymer can be directly spun to obtain polyamide 6 civil yarns or industrial yarns, or can be directly blown into films to obtain polyamide 6 films, or fiber-reinforced materials can be added for injection molding to obtain polyamide 6 composite materials.

[0006] It should be noted that in the anionic polymerization process of polyamide 6, a cyclic oligomer inhibitor is introduced, which has the following effects: On the one hand, the metal ions in the cyclic oligomer inhibitor coordinate with the amide bonds of polyamide 6 to prevent the amide bonds from being attacked and cyclized during the polymerization process, reducing the formation of cyclic oligomers, thereby reducing the content of cyclic oligomers in the polymer, especially reducing the content of cyclic dimers that affect the processing performance of polyamide 6.

[0007] On the other hand, usually the anionic polymerization reaction rate of polyamide 6 is extremely fast, releasing a large amount of polymerization heat in a short time, resulting in an increase in the system temperature and an increase in the content of small molecules such as monomers and cyclic oligomers. The cyclic oligomer inhibitor added in the present invention will appropriately reduce the reaction rate, making the entire anionic polymerization system milder and more controllable, and then controlling the content of small molecules.

[0008] After the polyamide 6 melt prepared in this way passes through a further devolatilization reaction system to remove unreacted monomers and some cyclic oligomers, it can be directly melt-spun to obtain polyamide 6 fibers, or directly blown into films to obtain polyamide 6 films, or fiber-reinforced materials can be added for injection molding to obtain polyamide 6 composite materials, omitting processes such as cooling and pelletizing, hot water extraction, drying and remelting.

[0009] To achieve the above objectives, the present technical solution provides a method for preparing polyamide 6 materials by anionic polymerization, including the following steps: (1) Prepare the basic active material A: Mix the catalyst and caprolactam evenly to obtain a first mixture, subject the first mixture to vacuum distillation and then store it in the storage tank A, where the inside of the storage tank A is protected by an inert atmosphere and the temperature is kept constant at 80-150°C; (2) Prepare the basic active material B: Heat and melt caprolactam and then perform vacuum distillation. After removing the moisture, mix the caprolactam with the initiator and the cyclic oligomer inhibitor evenly to obtain a second mixture, and store the second mixture in the storage tank B, where the inside of the storage tank B is protected by an inert atmosphere and the temperature is kept constant at 80-150°C; (3) Inject the basic active material A and the basic active material B into the screw extruder according to a volume ratio of 1-10:10 for anionic polymerization, and extrude and react to obtain a polyamide 6 basic melt; (4) Transport the polyamide 6 basic melt to a devolatilization reactor to remove monomers and cyclic oligomers to obtain a polyamide 6 final polymer.

[0010] In some embodiments, in (1), the catalyst is one or more of sodium caprolactamate, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH, and KOH.

[0011] In step (1), the inert atmosphere is one or more of N2, CO2, He, Ne, and Ar.

[0012] In step (1), the first mixture is subjected to vacuum distillation to fully remove moisture. The conditions for vacuum distillation are a temperature of 80 - 150 °C and an absolute reaction pressure of 5 - 95 kPa.

[0013] In step (1), 0.3 - 1.2 parts by mass of a catalyst and 10 - 100 parts by mass of caprolactam are mixed to obtain the first mixture.

[0014] In step (2), the initiator is one or more of N-acetylcaprolactam (AcCL), bisacylated lactam-1,6-caprolactam, terephthaloyl biscaprolactam (TBCL), isophthaloyl biscaprolactam, toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and 1,6-hexamethylene diisocyanate (HMDI).

[0015] Similarly, in step (2), caprolactam is subjected to vacuum distillation to remove moisture. The conditions for vacuum distillation are a temperature of 80 - 150 °C and an absolute reaction pressure of 5 - 95 kPa.

[0016] In step (2), the inert atmosphere is one or more of N2, CO2, He, Ne, and Ar.

[0017] In step (2), 100 parts by mass of caprolactam, 1.0 - 2.4 parts by mass of an initiator, and 0.01 - 2.0 parts by mass of a cyclic oligomer inhibitor are mixed to obtain the second mixture.

[0018] In step (2), the cyclic oligomer inhibitor is a metal ion compound MY or a mixture of two or more metal ion compounds MY, where M is a metal cation and Y is an inorganic anion or an organic anion.

[0019] Specifically, the metal cation M is selected from one of transition metal ions, lanthanide metal ions, and Group IIA metal ions. When the metal cation M is selected from transition metal ions, the metal cation M is Sc 3+ , Ni 2+ , Zn 2+ , Y 3+ , Zr 4+ , Ru 4+ , Rh 3+ ; when the metal cation M is selected from lanthanide metal ions, the lanthanide metal ion is La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Lu 3+ , Yb 3+ ; when the metal cation M is selected from Group IIA metal ions, the Group IIA metal ions are Be 2+ , Mg 2+ , Ca 2+ ; the metal cation M can also be one of Li + , Al 3+ .

[0020] The inorganic anion or organic anion Y is selected from F - , Cl - , NO3 - , SO4 2- , PO4 3- , citrate ion, salicylate ion, 3-hydroxybutyrate ion, L-aspartate ion, lactate ion, malate ion, 2-hydroxypropionate ion, an organic monocarboxylate ion H(CH2) n COO - (n = 0~12), benzoate ion, naphthoate ion, an organic dicarboxylate ion COO - (CH2) m COO - (m = 0~12), terephthalate ion, phthalate ion, isophthalate ion or naphthalenedicarboxylate ion, a saturated fatty acid root ion C x H 2x+1 COO - (x = 13~20), an unsaturated fatty acid root ion, 6-aminohexanoate ion NH2C5H 10 COO - , an amino acid root ion. When the inorganic anion or organic anion is an unsaturated fatty acid root ion, the unsaturated fatty acid root ion is oleate ion C 17 H 33 COO - , linoleate ion C 17 H 31 COO - , α-linolenate ion C 17 H 29 COO - , arachidonate ion C 19 H 31 COO - , palmitoleate ion C15 H 29 COO - ; When the inorganic anion or organic anion is an amino acid ion, the amino acid ion is any one of glycinate ion, alaninate ion, valinate ion, leucinate ion, isoleucinate ion, prolinate ion, phenylalaninate ion, methioninate ion, serine ion, threonine ion, asparagine ion, glutamine ion, aspartate ion, glutamate ion, cysteinate ion, tyrosine ion, selenocysteinate ion.

[0021] In some embodiments, the addition amount of the cyclic oligomer inhibitor is 0.01 wt% - 2.0 wt% of caprolactam.

[0022] In step (3), the feeding temperature of the screw extruder is set at 90 - 160 °C, the discharging temperature of the outlet is set at 220 - 240 °C, the temperature of the middle section of the screw is set to gradually increase from the feeding temperature to the discharging temperature, the number of heating sections is not less than 1, and the rotation speed is 20 - 300 rpm.

[0023] In step (3), the relative viscosity of the polyamide 6 base melt is 2.0 - 4.5, the monomer content is less than 3.9 wt%, the cyclic oligomer content is less than 2.0 wt%, the hot water extractable content is less than 4.6 wt%, and the content of the cyclic dimer in the cyclic oligomer is less than 0.5 wt%.

[0024] In step (4), the relative viscosity of the high-quality polyamide 6 melt is 2.0 - 4.5, the monomer content is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt%, the content of the cyclic dimer in the cyclic oligomer is less than 0.1 wt%, and the hot water extractable content is less than 0.5 wt%.

[0025] In step (4), the devolatilization reactor can be one of a horizontal twin-screw devolatilization reactor, a horizontal disk reactor, a horizontal disk reactor, a vertical devolatilization reactor, a scraping film devolatilization device, a falling strip devolatilization device, a falling film devolatilization device, a flash evaporator, the reaction temperature is 240 - 280 °C, and the reaction pressure is 20 - 200 Pa.

[0026] Furthermore, the method for preparing a polyamide 6 material by anionic polymerization in this solution further includes the steps: (5) Directly spinning the polyamide 6 end polymer to obtain polyamide 6 civil yarn or industrial yarn, or directly blowing a film to obtain a polyamide 6 film; or adding a fiber reinforcing material to the polyamide 6 end polymer and performing injection molding to obtain a polyamide 6 composite material.

[0027] When using the polyamide 6 end-polymer directly for spinning to obtain polyamide 6 civil yarn or industrial yarn, the spinning temperature is 245 - 300 °C and the spinning speed is 2500 - 6000 m / min.

[0028] When adding a fiber reinforcing material to the polyamide 6 end-polymer for injection molding to obtain a polyamide 6 composite material, the fiber reinforcing material is one or more of glass fiber, carbon fiber, aramid fiber, silicon carbide fiber, natural fiber, and basalt fiber, and the addition amount of the fiber reinforcing material is not more than 50 wt%.

[0029] Figure 1 It is a schematic diagram of the system framework of the method for preparing polyamide 6 material by anionic polymerization provided by this solution. As Figure 1 shown, after caprolactam and a catalyst are mixed, they are added to drying device A for vacuum distillation and then stored in storage tank A. After the caprolactam is heated and melted, it is placed in drying device B for vacuum distillation. Then, the water-removed caprolactam is mixed evenly with an initiator and a cyclic oligomer inhibitor to obtain a second mixture, and the second mixture is stored in storage tank B; basic reactive material A and basic reactive material B are injected into a screw extruder at a volume ratio of 1 - 10:10 for anionic polymerization, and the polyamide 6 basic melt is prepared by reactive extrusion; the polyamide 6 basic melt is transported to a devolatilization reactor to remove monomers and cyclic oligomers, and a polyamide 6 end-polymer is prepared.

[0030] Adopting the technical solution of the present invention can achieve the following beneficial effects: By controlling oligomers during the polymerization process and removing monomers and some cyclic oligomers by devolatilization in the later stage, the present invention prepares a polyamide 6 end-polymer with a relative viscosity of 2.0 - 4.5, a monomer content of less than 0.1 wt%, a cyclic oligomer content of less than 1.5 wt% (where the content of cyclic dimer is lower than 0.1%), and a hot water extractable content of less than 0.5 wt%. The polyamide 6 end-polymer of the present invention can be used for melt direct spinning, injection molding, or blown film, omitting processes such as cooling and pelletizing, hot water extraction, drying, and remelting, greatly saving the consumption of energy, water, etc., and improving production efficiency. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the system framework of the method for preparing polyamide 6 material by anionic polymerization provided by this solution. Detailed Embodiments

[0032] To further illustrate the present invention, the following describes in detail a method for preparing polyamide 6 material by anionic polymerization provided by the present invention with reference to embodiments, but they cannot be construed as limiting the protection scope of the present invention.

[0033] The present invention measures the contents of monomers and cyclic oligomers in polyamide 6 base melt and end polymer by using an ultra-high performance liquid chromatograph, and the specific condition parameters are as follows: —— Chromatographic column: T3 column, 100 mm × 2.1 mm (inner diameter) × 1.7 μm, or equivalent; —— Column temperature: 30°C; —— Flow rate: 0.3 mL / min; —— Detection wavelength: 200 nm; —— Injection volume: 2 μL; —— Elution program (as shown in the following table): Mobile phase A is water, and mobile phase B is acetonitrile.

[0034]

[0035] Comparative example (1) Preparation of basic active material A: By mass, 0.8 parts of NaOH is added to 100 parts of caprolactam and mixed evenly. Water is removed by vacuum distillation at 120°C and 5 kPa, and then it is stored in storage tank A protected by N2 and kept at a constant temperature of 120°C; (2) Preparation of basic active material B: By mass, 100 parts of monomer caprolactam is heated and melted. Water is removed by vacuum distillation at 130°C and 50 Pa, and then 2.0 parts of N-acetylcaprolactam is added and mixed evenly. Then it is stored in storage tank B protected by N2 and kept at a constant temperature of 120°C; (3) Inject components A and B of the basic active material into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 100°C, the discharging temperature of the screw extruder is set at 240°C, the temperature in the middle section of the screw is set to gradually increase from 100°C to 240°C, there are 2 heating sections, the rotation speed is 30 rpm, and a polyamide 6 melt with a relative viscosity of 2.42, a monomer content of 4.18 wt%, a cyclic oligomer content of 2.56 wt% (where the cyclic dimer content is 0.79 wt%), and a hot water extractable content of 5.32 wt% is prepared by reactive extrusion; (4) The polyamide 6 melt is transported to a spinning machine for direct spinning. The spinning temperature is 270°C, and the winding speed is 4200 m / min. A large amount of caprolactam volatilization gas appears during the spinning of polyamide 6, and fibers cannot be formed.

[0036] Example 1 A method for preparing polyamide 6 material by anionic polymerization, and the specific steps are as follows: (1) Preparation of basic active material A: By mass, 0.8 parts of NaOH was added to 100 parts of caprolactam and mixed evenly. Water was removed by vacuum distillation at 120 °C and 5 kPa, and then it was stored in storage tank A under N2 protection at a constant temperature of 120 °C; (2) Preparation of basic active material B: By mass, 100 parts of monomer caprolactam was heated and melted. Water was removed by vacuum distillation at 120 °C and 5 kPa, then 2.0 parts of N-acetylcaprolactam and 1.5 parts of magnesium chloride were added and mixed evenly, and then it was stored in storage tank B under N2 protection at a constant temperature of 120 °C; (3) The A and B components of the basic active materials were injected into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder was set at 100 °C, the discharging temperature of the screw extruder was set at 240 °C, the temperature of the middle section of the screw was set to gradually increase from 100 °C to 240 °C with 2 heating sections, the rotation speed was 30 rpm, and polyamide 6 basic melt with a relative viscosity of 2.56, a monomer content of 3.16 wt%, a cyclic oligomer content of 1.35 wt% (where the cyclic dimer content was 0.42 wt %), and a hot water extractable content of 3.91 wt% was prepared by reactive extrusion; (4) The polyamide 6 basic melt was transported to a vertical devolatilization reactor to remove monomers and cyclic oligomers. The reaction temperature was 260 °C and the reaction pressure was 50 Pa. Finally, polyamide 6 end polymer with a relative viscosity of 2.58, a monomer content of 0.02 wt%, a cyclic oligomer content of 0.75 wt% (where the cyclic dimer content was 0.08 wt %), and a hot water extractable content of 0.35 wt% was prepared; (5) The polyamide 6 end polymer was transported to a spinning machine for direct spinning. The spinning temperature was 270 °C and the winding speed was 4200 m / min to obtain high-quality polyamide 6 fibers with a fiber breaking strength of 4.9 cN / dtex and an elongation at break of 23%.

[0037] Example 2 A method for preparing polyamide 6 material by anionic polymerization, the specific steps are as follows: (1) Preparation of basic active material A: By mass, 0.45 parts of sodium ethoxide was added to 10 parts of caprolactam and mixed evenly. Water was removed by vacuum distillation at 80 °C and 10 kPa, and then it was stored in storage tank A under He protection at a constant temperature of 130 °C; (2) Preparation of basic active material B: By mass, 100 parts of monomer caprolactam was heated and melted. Water was removed by vacuum distillation at 80 °C and 12 kPa, then 2.0 parts of bisacylated lactam-1,6-caprolactam and 2.0 parts of lanthanum aminocaproate were added and mixed evenly, and then it was stored in storage tank B under He protection at a constant temperature of 130 °C; (3) Inject the basic reactive materials A and B into a screw extruder in a volume ratio of 1:10 for anionic polymerization. The feeding temperature of the screw extruder is set at 120 °C, the discharging temperature of the screw extruder is set at 220 °C, the temperature in the middle section of the screw is set to gradually increase from 120 °C to 220 °C with 3 heating zones, the rotational speed is 40 rpm, and a polyamide 6 basic melt with a relative viscosity of 2.43, a monomer content of 3.23 wt%, a cyclic oligomer content of 1.19 wt% (where the cyclic dimer content is 0.36 wt %), and a hot water extractable content of 3.82 wt% is prepared by reactive extrusion; (4) Transport the polyamide 6 basic melt to a falling film degassing device to remove monomers and cyclic oligomers. The reaction temperature is 250 °C and the reaction pressure is 50 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 2.46, a monomer content of 0.01 wt%, a cyclic oligomer content of 0.59 wt% (where the cyclic dimer content is 0.06 wt %), and a hot water extractable content of 0.31 wt% is obtained; (5) Transport the polyamide 6 end polymer to a spinning machine for direct spinning. The spinning temperature is 275 °C and the winding speed is 4500 m / min to obtain high-quality polyamide 6 fibers with a fiber breaking strength of 4.5 cN / dtex and an elongation at break of 22%.

[0038] Example 3 A method for preparing polyamide 6 materials by anionic polymerization, the specific steps are as follows: (1) Preparation of basic reactive material A: By mass, add 1.1 parts of NaH to 100 parts of caprolactam and mix evenly. Remove moisture by vacuum distillation at 130 °C and 95 kPa, and then store it in storage tank A protected by Ar and maintained at a constant temperature of 80 °C; (2) Preparation of basic reactive material B: By mass, heat 100 parts of monomer caprolactam to melt, remove moisture by vacuum distillation at 130 °C and 95 kPa, then add 1.3 parts of terephthaloyl biscaprolactam (TBCL) and 0.02 parts of cerium acetate and mix evenly, and then store it in storage tank B protected by Ar and maintained at a constant temperature of 80 °C; (3) Inject the basic reactive materials A and B into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 150 °C, the discharging temperature of the screw extruder is set at 230 °C, the temperature in the middle section of the screw is set to gradually increase from 150 °C to 230 °C with 3 heating zones, the rotational speed is 40 rpm, and a polyamide 6 basic melt with a relative viscosity of 2.65, a monomer content of 3.34 wt%, a cyclic oligomer content of 1.45 wt% (where the cyclic dimer content is 0.46 wt %), and a hot water extractable content of 3.75 wt% is prepared by reactive extrusion; (4) The polyamide 6 base melt is transported to a falling strand devolatilizer to remove monomers and cyclic oligomers. The reaction temperature is 260 °C and the reaction pressure is 40 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 2.69, a monomer content of 0.03 wt%, a cyclic oligomer content of 0.91 wt% (where the cyclic dimer content is 0.02 wt%), and a hot water extractable content of 0.41 wt% is obtained; (5) Carbon fibers are added to the polyamide 6 end polymer and mixed evenly by a screw extruder, and then pelletized. The addition amount of carbon fibers is 10 wt% of polyamide 6. Finally, a high-quality carbon fiber reinforced polyamide 6 material for injection molding is obtained.

[0039] Example 4 A method for preparing a polyamide 6 material by anionic polymerization, the specific steps are as follows: (1) Preparation of basic active material A: By mass, 1.2 parts of sodium ethoxide are added to 100 parts of caprolactam and mixed evenly. Water is removed by vacuum distillation at 120 °C and 80 kPa, and then stored in a storage tank A protected by N2 and kept at a constant temperature of 130 °C; (2) Preparation of basic active material B: By mass, 100 parts of monomer caprolactam are heated and melted. Water is removed by vacuum distillation at 120 °C and 80 kPa, and then 1.2 parts of N-acetylcaprolactam and 0.9 part of lanthanum acetate are added and mixed evenly. Then it is stored in a storage tank B protected by N2 and kept at a constant temperature of 130 °C; (3) The basic active materials A and B are injected into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 130 °C, the discharging temperature of the screw extruder is set at 230 °C, the temperature of the middle section of the screw is set to gradually increase from 130 °C to 230 °C, there are 5 heating sections, the rotation speed is 50 rpm, and a polyamide 6 base melt with a relative viscosity of 2.96, a monomer content of 3.67 wt%, a cyclic oligomer content of 1.53 wt% (where the cyclic dimer content is 0.40 wt%), and a hot water extractable content of 3.90 wt% is obtained by reactive extrusion; (4) The polyamide 6 base melt is transported to a vertical devolatilizer to remove monomers and cyclic oligomers. The reaction temperature is 280 °C and the reaction pressure is 70 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 3.03, a monomer content of 0.03 wt%, a cyclic oligomer content of 0.97 wt% (where the cyclic dimer content is 0.07 wt%), and a hot water extractable content of 0.48 wt% is obtained; (5) The polyamide 6 end polymer is transported to a spinning machine for direct spinning. The spinning temperature is 280 °C and the winding speed is 3500 m / min to obtain polyamide 6 industrial yarns with a fiber breaking strength of 6.3 cN / dtex and an elongation at break of 20%.

[0040] Example 5 A method for preparing polyamide 6 material by anionic polymerization, the specific steps are as follows: (1) Preparation of basic active material A: By mass, 0.6 parts of NaOH are added to 100 parts of caprolactam and mixed evenly. Water is removed by vacuum distillation at 150 °C and 90 kPa, and then stored in a storage tank A protected by Ar and maintained at a constant temperature of 120 °C; (2) Preparation of basic active material B: By mass, 100 parts of monomer caprolactam are heated and melted. Water is removed by vacuum distillation at 150 °C and 90 kPa, and then 1.2 parts of N-acetylcaprolactam and 0.5 parts of zinc citrate are added and mixed evenly, and then stored in a storage tank B protected by Ar and maintained at a constant temperature of 120 °C; (3) Inject the basic active materials A and B into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 160 °C, the discharging temperature of the screw extruder is set at 240 °C, the temperature in the middle section of the screw is set to gradually increase from 160 °C to 210 °C, there are 5 heating sections, the rotation speed is 60 rpm, and a polyamide 6 base melt with a relative viscosity of 3.36, a monomer content of 3.81 wt%, a cyclic oligomer content of 1.73 wt% (where the cyclic dimer content is 0.39 wt %), and a hot water extractable content of 4.09 wt% is prepared by reactive extrusion; (4) The polyamide 6 base melt is transported to a falling-strip devolatilizer to remove monomers and cyclic oligomers. The reaction temperature is 280 °C and the reaction pressure is 40 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 3.42, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.03 wt% (where the cyclic dimer content is 0.07 wt %), and a hot water extractable content of 0.43 wt% is prepared; (5) The polyamide 6 end polymer is transported to a spinning machine for direct spinning. The spinning temperature is 285 °C and the winding speed is 3000 m / min to obtain high-quality polyamide 6 fibers with a fiber breaking strength of 8.2 cN / dtex and an elongation at break of 20%.

[0041] The performance characterizations of the polyamide 6 base melts and polyamide 6 end polymers of the comparative examples and Examples 1 to 5 are shown in Table 1 below: Table 1 Performance characterization table of polyamide 6 base melts and polyamide 6 end polymers of comparative examples and Examples 1 to 5

[0042] Those skilled in the art should understand that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0043] The above embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing polyamide 6 material by anionic polymerization, characterized in that, It includes the following steps: (1) Prepare the basic active material A: Mix the catalyst and caprolactam evenly to obtain the first mixture, carry out vacuum distillation on the first mixture and store it in the storage tank A, wherein the inside of the storage tank A is protected by an inert atmosphere and the temperature is kept constant at 80~150°C; (2) Prepare the basic active material B: Heat and melt caprolactam and then carry out vacuum distillation, mix the dehydrated caprolactam with the initiator and the cyclic oligomer inhibitor evenly to obtain the second mixture, and store the second mixture in the storage tank B, wherein the inside of the storage tank B is protected by an inert atmosphere and the temperature is kept constant at 80~150°C; (3) Inject the basic active material A and the basic active material B into the screw extruder according to the volume ratio of 1~10:10 for anionic polymerization, and react and extrude to obtain the polyamide 6 basic melt; (4) Transport the polyamide 6 basic melt to the devolatilization reactor to remove monomers and cyclic oligomers, and obtain the polyamide 6 final polymer.

2. The method for preparing polyamide 6 material by anionic polymerization according to claim 1, wherein It includes the steps: directly carry out spinning on the polyamide 6 final polymer to obtain polyamide 6 civil yarn or industrial yarn, or directly carry out blown film to obtain polyamide 6 film; or add fiber reinforcing materials to the polyamide 6 final polymer for injection molding to obtain polyamide 6 composite materials.

3. The method for preparing polyamide 6 material by anionic polymerization according to claim 1, wherein, In step (1), the catalyst is one or more of sodium caprolactam, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH, KOH.

4. A method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that, In step (1), vacuum distillation is carried out on the first mixture to fully remove moisture. The conditions for vacuum distillation are a temperature of 80~150°C and an absolute reaction pressure of 5~95 kPa; in step (2), vacuum distillation is carried out on caprolactam to remove moisture. The conditions for vacuum distillation are a temperature of 80~150°C and an absolute reaction pressure of 5~95 kPa.

5. A method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that, In step (2), the initiator is one or more of N-acetyl caprolactam, bisacylated lactam-1,6-caprolactam, terephthaloyl biscaprolactam, isophthaloyl biscaprolactam, toluene diisocyanate, diphenylmethane diisocyanate, 1,6-hexane diisocyanate.

6. The method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that, The cyclic oligomer inhibitor is a metal ion compound MY or a mixture of two or more metal ion compounds MY, wherein M is a metal cation and Y is an inorganic anion or an organic anion.

7. A method for preparing polyamide 6 material by anionic polymerization according to claim 6, characterized in that, The metal cation M is selected from one of transition metal ions, lanthanide metal ions, and Group IIA metal ions. When the metal cation M is selected from transition metal ions, the metal cation M is Sc 3+ , Ni 2+ , Zn 2+ , Y 3+ , Zr 4+ , Ru 4+ , Rh 3+ ; when the metal cation M is selected from lanthanide metal ions, the lanthanide metal ion is La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Lu 3+ , Yb 3+ ; when the metal cation M is selected from Group IIA metal ions, the Group IIA metal ion is one of Be 2+ , Mg 2+ , Ca 2+ ; the metal cation M can also be one of Li + , Al 3+ ; the inorganic anion or organic anion Y is selected from F - , Cl - , NO3 - , SO4 2- , PO4 3- , citrate ion, salicylate ion, 3-hydroxybutyrate ion, L-aspartate ion, lactate ion, malate ion, 2-hydroxypropionate ion, an organic monocarboxylate ion H(CH2) n COO - , benzoate ion, naphthoate ion, an organic dicarboxylate ion COO - (CH2) m COO - , terephthalate ion, phthalate ion, isophthalate ion or naphthalenedicarboxylate ion, a saturated fatty acid root ion C x H 2x+1 COO - (x = 13 - 20), an unsaturated fatty acid root ion, 6-aminohexanoate ion NH2C5H 10 COO - , one of amino acid root ions; when the inorganic anion or organic anion is an unsaturated fatty acid root ion, the unsaturated fatty acid root ion is oleate ion C 17 H 33 COO - , linoleate ion C 17 H 31 COO - , α-linolenate ion C 17 H 29 COO - , arachidonate ion C 19 H 31 COO - , palmitoleate ion C 15 H 29 COO - ; when the inorganic anion or organic anion is an amino acid ion, the amino acid ion is any one of glycinate ion, alaninate ion, valinate ion, leucinate ion, isoleucinate ion, prolinate ion, phenylalaninate ion, methioninate ion, serineate ion, threoninate ion, asparaginateroot ion, glutaminateroot ion, aspartate ion, glutamate ion, cysteinate ion, tyrosineate ion, selenocysteinate ion; the addition amount of the cyclic oligomer inhibitor is 0.01 wt% - 2.0 wt% of caprolactam.

8. A method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that, In step (3), the feeding temperature of the screw extruder is set at 90~160°C, the discharging port temperature is set at 220~240°C, the temperature in the middle section of the screw is set to gradually increase from the feeding port temperature to the discharging port temperature, and the number of heating sections is not less than 1, and the rotation speed is 20~300 rpm.

9. A method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that, In step (3), the relative viscosity of the polyamide 6 base melt is 2.0 to 4.5, the monomer content is less than 3.9 wt%, the cyclic oligomer content is less than 2.0 wt%, wherein the content of cyclic dimer in the cyclic oligomer is less than 0.5 wt%, and the hot water extractable content is less than 4.6 wt%; in step (4), the relative viscosity of the high-quality polyamide 6 melt is 2.0 to 4.5, the monomer content is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt%, wherein the content of cyclic dimer in the cyclic oligomer is less than 0.1 wt%, and the hot water extractable content is less than 0.5 wt%.

10. The method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that In step (4), the devolatilization reactor is selected from one of a horizontal twin-screw devolatilization reactor, a horizontal disk reactor, a vertical devolatilization reactor, a scraping film devolatilizer, a falling strip devolatilizer, a falling film devolatilizer, and a flash evaporator, the reaction temperature is 240 to 280 °C, and the reaction pressure is 20 to 200 Pa.

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