A method for preparing polyamide 6 material through anionic polymerization

Abstract

This solution provides a method for preparing polyamide 6 material by anionic polymerization. Caprolactam and a catalyst are added to a drying device A to remove moisture from the system and then placed in a storage tank A. Caprolactam is added to a drying device B to remove moisture and then placed in a storage tank B with an initiator and a cyclic oligomer inhibitor. The caprolactam liquid in storage tanks A and B is then continuously injected into a screw extruder through a conveying device to carry out an anionic ring-opening polymerization reaction to prepare a polyamide 6 base melt. The base melt is further conveyed to a devolatilization reactor to efficiently remove monomers and oligomers to obtain a polyamide 6 final polymer. The final polymer can be directly melt-spun, injection molded, or blown into a film to obtain high-quality polyamide 6 fiber, engineering plastic, or film.

Description

Technical Field

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

[0002] Polyamide 6 refers to a polymer with repeating structural units (-NH(CH2)5CO-) on its molecular chain. Polyamide 6 fiber has high mechanical strength and wear resistance and is widely used in automotive, industrial, aerospace, shipbuilding, textile and other fields.

[0003] Currently, the industrial production of polyamide 6 primarily utilizes hydrolysis-ring-opening polymerization, a process that takes dozens of hours. Approximately 10% of caprolactam monomers and oligomers (also known as hot water extractables) remain in the polymer, requiring dozens of hours of continuous hot water extraction to remove these monomers and oligomers. According to FZ / T 51004-2011, polyamide 6 chips with a hot water extractable content of ≤0.5 are considered superior, ≤0.6 are considered first-class, and ≤0.8 are considered qualified. Consequently, the production cycle for polyamide 6 through caprolactam hydrolysis polymerization, chip extraction and drying, and subsequent melt spinning is long and consumes significant amounts of water and energy. In contrast, the anionic polymerization of caprolactam to produce polyamide 6 is extremely rapid, leaving approximately 5% of hot water extractables. However, due to the extremely rapid polymerization reaction, control is difficult, and the small amount of residual oligomers still requires hot water extraction. Consequently, the anionic polymerization of caprolactam to produce polyamide 6 for fibers, films, and other applications has not yet been commercially realized.

[0004] A small amount 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 from anionic polyamide 6, and then added a spinneret at the outlet of the screw extruder for direct melt spinning. However, due to the large amount of oligomer residues, the fibers produced were millimeter-sized and could not meet the requirements for daily fiber use. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a polyamide 6 material by anionic polymerization, wherein a cyclic oligomer inhibitor is used to reduce the production of monomers and cyclic oligomers during the polymerization process, and a high-efficiency devolatilization reactor is used to remove monomers and oligomers. The resulting polyamide 6 final polymer can be directly spun to obtain polyamide 6 civilian yarn or industrial yarn, or can be directly blown into a polyamide 6 film, or can be added with fiber reinforcement material for injection molding to obtain a polyamide 6 composite material.

[0006] It should be noted that the present solution introduces a cyclic oligomer inhibitor during the anionic polymerization of polyamide 6, which has the following effects:

[0007] On the one hand, the metal ions in the cyclic oligomer inhibitor are coordinated with the amide bond of polyamide 6 to prevent the amide bond from being attacked and cyclized during the polymerization process, reduce the formation of cyclic oligomers, and thus reduce the content of cyclic oligomers in the polymer, especially the content of cyclic dimers that affect the processing performance of polyamide 6.

[0008] On the other hand, the anionic polymerization reaction rate of polyamide 6 is usually extremely fast, releasing a large amount of polymerization heat in a short period of 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 more gentle and controllable, thereby controlling the content of small molecules.

[0009] The polyamide 6 melt prepared in this way can be directly melt-spun to obtain polyamide 6 fiber after further devolatilization reaction system to remove unreacted monomers and some cyclic oligomers, or directly blown into film to obtain polyamide 6 film, or added with fiber reinforcement material for injection molding to obtain polyamide 6 composite material, omitting the processes of cooling and pelletizing, hot water extraction, drying and remelting.

[0010] To achieve the above objectives, the present technical solution provides a method for preparing polyamide 6 material by anionic polymerization, comprising the following steps:

[0011] (1) Preparing a basic active material A: uniformly mixing the catalyst with caprolactam to obtain a first mixture, performing reduced pressure distillation on the first mixture and storing it in a storage tank A, wherein the storage tank A is protected by an inert atmosphere and the temperature is kept constant at 80-150°C;

[0012] (2) Preparing the base active material B: heating and melting caprolactam and then distilling it under reduced pressure, then uniformly mixing the caprolactam with the initiator and the cyclic oligomer inhibitor after removing the water, and storing the second mixture in a storage tank B, wherein the storage tank B is protected by an inert atmosphere and the temperature is kept constant at 80-150°C;

[0013] (3) injecting the basic active material A and the basic active material B into a screw extruder at a volume ratio of 1 to 10:10 for anionic polymerization, and then reactively extruding to obtain a polyamide 6 basic melt;

[0014] (4) The polyamide 6 base melt is transported to a devolatilization reactor to remove monomers and cyclic oligomers to obtain a polyamide 6 final polymer.

[0015] In some embodiments, in (1), the catalyst is one or more of sodium caprolactam, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH, and KOH.

[0016] In step (1), the inert atmosphere is one or more of N2, CO2, He, Ne, and Ar.

[0017] In step (1), the first mixture is subjected to reduced pressure distillation to fully remove water, and the conditions for the reduced pressure distillation are a temperature of 80-150° C. and a reaction absolute pressure of 5-95 kPa.

[0018] In step (1), 0.3 to 1.2 parts of a catalyst and 10 to 100 parts of caprolactam are mixed, based on parts by mass, to obtain a first mixture.

[0019] 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).

[0020] Similarly, in step (2), the caprolactam is subjected to reduced pressure distillation to remove water, and the conditions for the reduced pressure distillation are a temperature of 80-150° C. and a reaction absolute pressure of 5-95 kPa.

[0021] In step (2), the inert atmosphere is one or more of N2, CO2, He, Ne, and Ar.

[0022] In step (2), 100 parts of caprolactam, 1.0-2.4 parts of initiator, and 0.01-2.0 parts of cyclic oligomer inhibitor are mixed according to the mass ratio to obtain a second mixture.

[0023] In step (2), 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.

[0024] 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 ions are 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 ions are Be 2+ Mg 2+ , Ca 2+ The metal cation M can also be Li + 、Al 3+ One of them.

[0025] 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, organic monobasic acid ion H(CH2) n COO - (n=0~12), benzoate ion, naphthoate ion, organic dibasic acid ion COO - (CH2) m COO - (m=0~12), terephthalate ion, phthalate ion, isophthalate ion or naphthalene dicarboxylate ion, saturated fatty acid root ion C x H 2x+1 COO - (x=13~20), unsaturated fatty acid ions, 6-aminocaproic acid ion NH2C5H 10 COO - , 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 an oleate root ion C 17 H 33 COO - , linoleate ion C 17 H 31 COO -, α-linolenic acid ion C 17 H 29 COO - , arachidonic acid 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 a glycine root ion, an alanine root ion, a valine root ion, a leucine root ion, an isoleucine root ion, a proline root ion, a phenylalanine root ion, a methionine root ion, a serine root ion, a threonine root ion, an asparagine root ion, a glutamine root ion, an aspartic acid root ion, a glutamate root ion, a cysteine ​​root ion, a tyrosine root ion, and a selenocysteine ​​root ion.

[0026] In some embodiments, the cyclic oligomer inhibitor is added in an amount of 0.01 wt % to 2.0 wt % of caprolactam.

[0027] In step (3), the feed temperature of the screw extruder is set to 90~160℃, the discharge port temperature is set to 220~240℃, the temperature of the middle section of the screw is set to gradually increase from the feed port temperature to the discharge port temperature, with no less than one heating section, and the rotation speed is 20~300rpm.

[0028] 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 cyclic dimer content in the cyclic oligomer is less than 0.5 wt%.

[0029] In step (4), the high-quality polyamide 6 melt has a relative viscosity of 2.0 to 4.5, a monomer content of less than 0.1 wt%, a cyclic oligomer content of less than 1.5 wt%, a cyclic dimer content of less than 0.1 wt%, and a hot water extractable content of less than 0.5 wt%.

[0030] In step (4), the devolatilization reactor may be one of a horizontal twin-shaft devolatilization reactor, a horizontal disc reactor, a horizontal disc reactor, a vertical devolatilization reactor, a scraper film devolatilizer, a falling strip devolatilizer, a falling film devolatilizer, and a flash evaporator, the reaction temperature is 240-280°C, and the reaction pressure is 20-200 Pa.

[0031] Furthermore, the method for preparing polyamide 6 material by anionic polymerization of this scheme further comprises the steps of:

[0032] (5) The polyamide 6 final polymer is directly spun to obtain polyamide 6 civilian yarn or industrial yarn, or directly blown into a film to obtain a polyamide 6 film; or fiber reinforcement material is added to the polyamide 6 final polymer and injection molded to obtain a polyamide 6 composite material.

[0033] When polyamide 6 final polymer is directly spun 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.

[0034] When fiber reinforcement material is added to polyamide 6 final polymer and injection molding is performed to obtain a polyamide 6 composite material, wherein the fiber reinforcement 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 reinforcement material is not more than 50wt%.

[0035] Figure 1 This is a schematic diagram of the system framework of the method for preparing polyamide 6 material by anionic polymerization provided in this scheme, such as Figure 1 As shown, caprolactam and a catalyst are mixed and added to a drying device A for vacuum distillation and then stored in a storage tank A. The caprolactam is heated and melted and then placed in a drying device B for vacuum distillation. The caprolactam from which water has been removed is uniformly mixed with an initiator and a cyclic oligomer inhibitor to obtain a second mixture, which is stored in a storage tank B. Basic active material A and basic active material B are injected into a screw extruder in a volume ratio of 1 to 10:10 for anionic polymerization, and a polyamide 6 basic melt is obtained by reactive extrusion. The polyamide 6 basic melt is transported to a devolatilization reactor to remove monomers and cyclic oligomers to obtain a polyamide 6 final polymer.

[0036] The technical solution of the present invention can achieve the following beneficial effects:

[0037] The present invention utilizes oligomer control during polymerization and subsequent devolatilization to remove monomers and some cyclic oligomers, resulting in a polyamide 6 endpolymer with a relative viscosity of 2.0 to 4.5, a monomer content of less than 0.1 wt%, a cyclic oligomer content of less than 1.5 wt% (including a cyclic dimer content of less than 0.1%), and a hot water extractable content of less than 0.5 wt%. The polyamide 6 endpolymer of the present invention can be used for melt spinning, injection molding, or film blowing, eliminating the need for cooling and pelletizing, hot water extraction, drying, and remelting, significantly saving energy and water consumption and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the system framework of the method for preparing polyamide 6 material by anionic polymerization provided in this scheme. DETAILED DESCRIPTION

[0039] In order to further illustrate the present invention, a method for preparing polyamide 6 material by anionic polymerization provided by the present invention is described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0040] The present invention uses ultra-high performance liquid chromatography to measure the content of monomers and cyclic oligomers in the polyamide 6 base melt and final polymer. The specific conditions and parameters are as follows:

[0041] --Chromatographic column: T3 column, 100 mm × 2.1 mm (inner diameter) × 1.7 μm, or equivalent;

[0042] ——Column temperature: 30℃;

[0043] Flow rate: 0.3 mL / min

[0044] ——Detection wavelength: 200 nm;

[0045] ——Injection volume: 2 μL;

[0046] ——Elution procedure (as shown in the table below): Mobile phase A is water, and mobile phase B is acetonitrile.

[0047]

[0048] Comparative Example

[0049] (1) Preparation of basic active material A: Add 0.8 parts of NaOH to 100 parts of caprolactam by mass and mix well. Remove water by vacuum distillation at 120°C and 5kPa. Then store in a storage tank A under N2 protection and a constant temperature of 120°C.

[0050] (2) Preparation of basic active material B: Heat and melt 100 parts of monomer caprolactam by mass, remove water by reduced pressure distillation at 130°C and 50 Pa, then add 2.0 parts of N-acetyl caprolactam and mix well, and then store in a storage tank B under N2 protection and a constant temperature of 120°C;

[0051] (3) The basic active material A and B components were injected into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feed temperature of the screw extruder was set to 100°C, the discharge temperature of the screw extruder was set to 240°C, the temperature of the middle section of the screw was set to gradually increase from 100°C to 240°C, the number of heating sections was 2, the rotation speed was 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% (of which the cyclic dimer content was 0.79 wt%), and a hot water extractable content of 5.32 wt% was obtained by reactive extrusion.

[0052] (4) The polyamide 6 melt was transported to the spinning machine for direct spinning. The spinning temperature was 270 °C and the winding speed was 4200 m / min. During the spinning of polyamide 6, a large amount of caprolactam volatile gas appeared and fibers could not be formed.

[0053] Example 1

[0054] A method for preparing polyamide 6 material by anionic polymerization, the specific steps are as follows:

[0055] (1) Preparation of basic active material A: Add 0.8 parts of NaOH to 100 parts of caprolactam by mass and mix well. Remove water by vacuum distillation at 120°C and 5kPa. Then store in a storage tank A under N2 protection and a constant temperature of 120°C.

[0056] (2) Preparation of basic active material B: Heat and melt 100 parts of monomer caprolactam by mass, remove water by reduced pressure distillation at 120°C and 5kPa, then add 2.0 parts of N-acetyl caprolactam and 1.5 parts of magnesium chloride and mix well, and then store in a storage tank B under N2 protection and a constant temperature of 120°C;

[0057] (3) The basic active material A and B components were injected into the screw extruder in a volume ratio of 1:1 for anionic polymerization. The feed temperature of the screw extruder was set to 100°C, the discharge temperature of the screw extruder was set to 240°C, the temperature of the middle section of the screw was set to gradually increase from 100°C to 240°C, there were two heating sections, the rotation speed was 30 rpm, and the reactive extrusion produced a 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% (of which the cyclic dimer content was 0.42 wt%), and a hot water extractable content of 3.91 wt%;

[0058] (4) The polyamide 6 base 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, a polyamide 6 final polymer with a relative viscosity of 2.58, a monomer content of 0.02 wt%, a cyclic oligomer content of 0.75 wt% (including a cyclic dimer content of 0.08 wt%), and a hot water extractable content of 0.35 wt% was obtained.

[0059] (5) The polyamide 6 final polymer was transported to a spinning machine for direct spinning at a spinning temperature of 270°C and a winding speed of 4200 m / min to obtain high-quality polyamide 6 fibers with a fiber breaking strength of 4.9 cN / dtex and an elongation of 23%.

[0060] Example 2

[0061] A method for preparing polyamide 6 material by anionic polymerization, the specific steps are as follows:

[0062] (1) Preparation of basic active material A: Add 0.45 parts of sodium ethoxide to 10 parts of caprolactam by mass, mix well, remove water by vacuum distillation at 80°C and 10 kPa, and then store in a storage tank A protected by He and kept at a constant temperature of 130°C;

[0063] (2) Preparation of basic active material B: 100 parts of monomer caprolactam were heated and melted by weight, and water was removed by vacuum distillation at 80°C and 12 kPa. Then 2.0 parts of bis-acylated lactam-1,6-caprolactam and 2.0 parts of lanthanum aminocaproate were added and mixed evenly, and then stored in a storage tank B protected by He at a constant temperature of 130°C;

[0064] (3) The basic active material A and B components were injected into the screw extruder in a volume ratio of 1:10 for anionic polymerization. The feed temperature of the screw extruder was set to 120°C, the discharge temperature of the screw extruder was set to 220°C, the temperature of the middle section of the screw was set to gradually increase from 120°C to 220°C, and there were 3 heating sections. The rotation speed was 40 rpm. The 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% (of which the cyclic dimer content was 0.36 wt%), and a hot water extractable content of 3.82 wt% was obtained by reactive extrusion.

[0065] (4) The polyamide 6 base melt was transported to a falling film devolatilizer to remove monomers and cyclic oligomers. The reaction temperature was 250 °C and the reaction pressure was 50 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 2.46, a monomer content of 0.01 wt%, a cyclic oligomer content of 0.59 wt% (including a cyclic dimer content of 0.06 wt%), and a hot water extractable content of 0.31 wt% was obtained.

[0066] (5) The polyamide 6 final polymer was transported to a spinning machine for direct spinning at a spinning temperature of 275°C and a winding speed of 4500 m / min to obtain high-quality polyamide 6 fibers with a fiber breaking strength of 4.5 cN / dtex and an elongation of 22%.

[0067] Example 3

[0068] A method for preparing polyamide 6 material by anionic polymerization, the specific steps are as follows:

[0069] (1) Preparation of basic active material A: Add 1.1 parts of NaH to 100 parts of caprolactam by mass and mix well. Remove water by vacuum distillation at 130°C and 95 kPa. Then store in a storage tank A under Ar protection and a constant temperature of 80°C.

[0070] (2) Preparation of basic active material B: 100 parts by mass of monomer caprolactam were heated and melted, and water was removed by vacuum distillation at 130°C and 95 kPa. Then 1.3 parts of terephthaloyl biscaprolactam (TBCL) and 0.02 parts of cerium acetate were added and mixed evenly. The mixture was then stored in a storage tank B under Ar protection and a constant temperature of 80°C.

[0071] (3) The basic active material A and B components were injected into the screw extruder in a volume ratio of 1:1 for anionic polymerization. The feed temperature of the screw extruder was set to 150°C, the discharge temperature of the screw extruder was set to 230°C, the temperature of the middle section of the screw was set to 150°C to 230°C and gradually increased, with 3 heating sections. The rotation speed was 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% (of which the cyclic dimer content was 0.46 wt%), and a hot water extractable content of 3.75 wt% was obtained by reactive extrusion.

[0072] (4) The polyamide 6 base melt was transported to a strip devolatilizer to remove monomers and cyclic oligomers. The reaction temperature was 260 ° C and the reaction pressure was 40 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 2.69, a monomer content of 0.03 wt%, a cyclic oligomer content of 0.91 wt% (including a cyclic dimer content of 0.02 wt%), and a hot water extractable content of 0.41 wt% was obtained.

[0073] (5) Add carbon fiber to the polyamide 6 final polymer, mix it evenly through a screw extruder, and then pelletize it. The amount of carbon fiber added is 10wt% of polyamide 6. Finally, high-quality carbon fiber reinforced polyamide 6 material for injection molding is obtained.

[0074] Example 4

[0075] A method for preparing polyamide 6 material by anionic polymerization, the specific steps are as follows:

[0076] (1) Preparation of basic active material A: Add 1.2 parts of sodium ethoxide to 100 parts of caprolactam by mass and mix well. Remove water by vacuum distillation at 120°C and 80 kPa. Then store in a storage tank A under N2 protection and a constant temperature of 130°C.

[0077] (2) Preparation of basic active material B: 100 parts by mass of monomer caprolactam were heated and melted, and water was removed by vacuum distillation at 120°C and 80 kPa. Then 1.2 parts of N-acetyl caprolactam and 0.9 parts of lanthanum acetate were added and mixed evenly, and then stored in a storage tank B under N2 protection and a constant temperature of 130°C;

[0078] (3) The basic active material A and B components were injected into the screw extruder in a volume ratio of 1:1 for anionic polymerization. The feed temperature of the screw extruder was set to 130°C, the discharge temperature of the screw extruder was set to 230°C, the temperature of the middle section of the screw was set to gradually increase from 130°C to 230°C, and there were 5 heating sections. The rotation speed was 50 rpm. The polyamide 6 basic melt with a relative viscosity of 2.96, a monomer content of 3.67 wt%, a cyclic oligomer content of 1.53 wt% (of which the cyclic dimer content was 0.40 wt%), and a hot water extractable content of 3.90 wt% was obtained by reactive extrusion.

[0079] (4) The polyamide 6 base melt was transported to a vertical devolatilizer to remove monomers and cyclic oligomers. The reaction temperature was 280 °C and the reaction pressure was 70 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 3.03, a monomer content of 0.03 wt%, a cyclic oligomer content of 0.97 wt% (including a cyclic dimer content of 0.07 wt%), and a hot water extractable content of 0.48 wt% was obtained.

[0080] (5) The polyamide 6 final polymer was transported to a spinning machine for direct spinning at a spinning temperature of 280°C and a winding speed of 3500 m / min to obtain polyamide 6 industrial yarn with a fiber breaking strength of 6.3 cN / dtex and an elongation of 20%.

[0081] Example 5 A method for preparing polyamide 6 material by anionic polymerization, the specific steps are as follows:

[0082] (1) Preparation of basic active material A: Add 0.6 parts of NaOH to 100 parts of caprolactam by mass and mix well. Remove water by vacuum distillation at 150°C and 90 kPa. Then store in a storage tank A under Ar protection and a constant temperature of 120°C.

[0083] (2) Preparation of basic active material B: Heat and melt 100 parts of monomer caprolactam by mass, remove water by reduced pressure distillation at 150°C and 90 kPa, then add 1.2 parts of N-acetyl caprolactam and 0.5 parts of zinc citrate and mix well, and then store in a storage tank B under Ar protection and a constant temperature of 120°C;

[0084] (3) The basic active material A and B components were injected into the screw extruder in a volume ratio of 1:1 for anionic polymerization. The feed temperature of the screw extruder was set to 160°C, the discharge temperature of the screw extruder was set to 240°C, the temperature of the middle section of the screw was set to 160°C to 210°C and gradually increased, with 5 heating sections and a rotation speed of 60 rpm. The polyamide 6 basic melt with a relative viscosity of 3.36, a monomer content of 3.81 wt%, a cyclic oligomer content of 1.73 wt% (of which the cyclic dimer content was 0.39 wt%), and a hot water extractable content of 4.09 wt% was obtained by reactive extrusion.

[0085] (4) The polyamide 6 base melt was transported to a strip devolatilizer to remove monomers and cyclic oligomers. The reaction temperature was 280 ° C and the reaction pressure was 40 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 3.42, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.03 wt% (including a cyclic dimer content of 0.07 wt%), and a hot water extractable content of 0.43 wt% was obtained.

[0086] (5) The polyamide 6 final polymer was transported to a spinning machine for direct spinning at a spinning temperature of 285°C and a winding speed of 3000 m / min to obtain high-quality polyamide 6 fibers with a fiber breaking strength of 8.2 cN / dtex and an elongation of 20%.

[0087] The performance of the polyamide 6 base melt and polyamide 6 final polymer of the comparative example and Examples 1 to 5 was characterized to obtain a performance characterization table as shown in Table 1 below:

[0088] Table 1 Performance characterization table of polyamide 6 base melt and polyamide 6 final polymer of comparative example and example 1 to example 5

[0089]

[0090] Those skilled in the art should understand that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, 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, they should be considered to be within the scope of this specification.

[0091] The above embodiments merely illustrate several embodiments of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A method for preparing polyamide 6 material by anionic polymerization, characterized in that: The following steps are involved: (1) Preparing a basic active material A: uniformly mixing the catalyst with caprolactam to obtain a first mixture, performing reduced pressure distillation on the first mixture and storing it in a storage tank A, wherein the storage tank A is protected by an inert atmosphere and the temperature is kept constant at 80-150°C; (2) Preparing a basic active material B: heating and melting caprolactam and then distilling it under reduced pressure, uniformly mixing the caprolactam after removing moisture with an initiator and a cyclic oligomer inhibitor to obtain a second mixture, and storing the second mixture in a storage tank B, wherein the storage tank B is protected by an inert atmosphere and the temperature is constant at 80-150° C., the initiator is one or more of N-acetyl caprolactam, bisacylated lactam-1,6-caprolactam, terephthaloyl biscaprolactam, isophthaloyl biscaprolactam, toluene diisocyanate, diphenylmethane diisocyanate, and 1,6-hexamethylene diisocyanate, and the cyclic oligomer inhibitor is one or more of magnesium chloride, lanthanum aminocaproate, cerium acetate, lanthanum acetate, and zinc citrate; (3) injecting the base active material A and the base active material B into a screw extruder in a volume ratio of 1 to 10:10 for anionic polymerization, and obtaining a polyamide 6 base melt by reactive extrusion. The polyamide 6 base melt has a relative viscosity of 2.0 to 4.5, a monomer content of less than 3.9 wt%, a cyclic oligomer content of less than 2.0 wt%, wherein the cyclic dimer content in the cyclic oligomer is less than 0.5 wt%, and a hot water extractable content of less than 4.6 wt%. (4) The polyamide 6 base melt is transported to a devolatilization reactor to remove monomers and cyclic oligomers to obtain a polyamide 6 final polymer. The polyamide 6 final polymer has a relative viscosity of 2.0 to 4.5, a monomer content of less than 0.1 wt%, and a cyclic oligomer content of less than 1.5 wt%, wherein the cyclic dimer content in the cyclic oligomer is less than 0.1 wt%, and the hot water extractable content is less than 0.5 wt%.

2. The method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that: The method comprises the following steps: directly spinning polyamide 6 final polymer to obtain polyamide 6 civilian yarn or industrial yarn, or directly blowing film to obtain polyamide 6 film; or adding fiber reinforcement material to polyamide 6 final polymer for injection molding to obtain polyamide 6 composite material.

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

4. The method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that: In step (1), the first mixture is subjected to reduced pressure distillation to fully remove water, and the conditions for the reduced pressure distillation are a temperature of 80-150° C. and a reaction absolute pressure of 5-95 kPa. In step (2), the caprolactam is subjected to reduced pressure distillation to remove water, and the conditions for the reduced pressure distillation are a temperature of 80-150° C. and a reaction absolute pressure of 5-95 kPa.

5. The method for preparing polyamide 6 material by anionic polymerization according to claim 1, characterized in that: In step (3), the feed temperature of the screw extruder is set to 90~160℃, the discharge port temperature is set to 220~240℃, the temperature of the middle section of the screw is set to gradually increase from the feed port temperature to the discharge port temperature, with no less than one heating section, and the rotation speed is 20~300rpm.

6. 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-shaft devolatilization reactor, a horizontal disc reactor, a vertical devolatilization reactor, a scraper film devolatilizer, a falling strip devolatilizer, a falling film devolatilizer, and a flash evaporator, the reaction temperature is 240-280°C, and the reaction pressure is 20-200 Pa.

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