A method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization

Abstract

The scheme provides a method for preparing high-quality polyamide 6 material by anion polymerization combined with fractional devolatilization. Caprolactam and a catalyst are added to a drying device A to remove water in the system, and then placed in a storage tank A. Caprolactam is added to a drying device B to remove water, and then placed in a storage tank B together with an initiator. Then, the caprolactam liquids in the storage tank A and the storage tank B are continuously injected into a screw extruder to perform an anionic ring-opening polymerization reaction to prepare a polyamide 6 base melt. The base melt is further conveyed to a series devolatilization reaction system to remove monomers and part of cyclic oligomers, and a polyamide 6 final polymer is obtained. Finally, spinning, injection molding or film blowing can be directly performed to obtain polyamide 6 fibers, engineering plastics or films.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of polyamide material preparation, and particularly relates to a method for preparing high-quality polyamide 6 material by combining anionic polymerization with staged devolatilization. BACKGROUND

[0002] Polyamide 6 (PA6) is an important engineering plastic and is widely used in the fields of textiles, automobiles, electronics, etc. Its traditional preparation process is mainly achieved by hydrolytic ring-opening polymerization of caprolactam. However, in actual industrial production, about 10% of residual caprolactam monomers and cyclic oligomers and other small molecules (also known as hot water extractables) need to be removed by a hot water continuous extraction process for tens of hours.

[0003] The monomer conversion rate of polyamide 6 prepared by anionic polymerization can reach about 95%, and about 5% of hot water extractables remain. Anionic polymerization has the advantages of fast and efficient reaction, low pollution and low energy consumption, but still has many problems, such as the need to remove residual monomers and oligomers to meet the application requirements in the fields of fibers, films, high-end engineering plastics, etc. Currently, caprolactam anionic polymerization polyamide 6 has not been used for the preparation of fibers, films, etc. in industry.

[0004] Vacuum devolatilization can remove part of the monomers and oligomers. 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 a screw extruder to directly melt-spinning. However, due to the presence of a large amount of oligomers, the fibers produced are millimeter-scale, which cannot meet the daily use requirements of fibers. By designing an efficient devolatilization method, it is expected to remove the residual monomers and oligomers in anionic polymerization polyamide 6, reduce the production energy consumption, and promote the more green and low-carbon development of the polyamide 6 material industry. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing high-quality polyamide 6 material by combining anionic polymerization with staged devolatilization. The method uses anionic reaction extrusion to prepare a polyamide 6 base melt and then combines two devolatilization reactors in series to efficiently remove monomers and cyclic oligomers, thereby achieving the preparation of high-quality polyamide 6 material.

[0006] The caprolactam monomer accounts for the majority of the small molecules in the residual polyamide 6, although the caprolactam has a low boiling point and is easy to remove by devolatilization, but it is difficult to remove the cyclic oligomers at the same time, and the accumulation of cyclic oligomers (especially cyclic dimers) will affect the processing stability of polyamide 6 and the quality of the product. According to the relationship between the physical properties of caprolactam monomers and cyclic oligomers in polyamide 6 and the temperature and pressure of the devolatilization reactor, a series devolatilization reaction system using a first devolatilization reactor and a second devolatilization reactor in series is proposed. Since the boiling point of caprolactam monomer is relatively low, the reaction temperature of the first devolatilization reactor of the series devolatilization reaction system is set to 240-280°C, and the reaction pressure is 200-4000 Pa. This condition can selectively remove more than 90% of the caprolactam monomers, while reducing the energy consumption required for vacuum power and effectively reducing the impact of high content monomers on the next devolatilization reaction. After a large amount of caprolactam monomers are removed, the second devolatilization reactor of the series devolatilization reaction system is set according to the physical parameters of the cyclic oligomers, with a reaction temperature of 240-280°C and a reaction pressure of 20-600 Pa, which can achieve enhanced removal of the remaining small amount of caprolactam monomers and cyclic oligomers, and achieve a monomer residue of less than 0.1wt% in the final polymer, a cyclic oligomer content of less than 1.5wt% (of which the cyclic dimer content in the cyclic oligomer is less than 0.1wt%), and a hot water extractable content of less than 0.5wt%. Compared with the traditional hot water extraction method, this method omits the steps of cooling, granulating, hot water extraction, drying and remelting, saving a lot of time and energy.

[0007] Based on the above series devolatilization reaction system, the technical scheme provides a method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, which comprises the following steps:

[0008] (1) Prepare basic active material A: mix catalyst and caprolactam to obtain a first mixture, and store the first mixture in a storage tank A after vacuum distillation, wherein the storage tank A is protected by inert atmosphere and the temperature is constant at 80-150°C;

[0009] (2) Prepare basic active material B: heat and melt the caprolactam monomer, then perform vacuum distillation, mix the caprolactam monomer and the initiator after removing the water to obtain a second mixture, and store the second mixture in a storage tank B, wherein the storage tank B is protected by inert atmosphere and the temperature is constant at 80-150°C;

[0010] (3) Inject the basic active material A and the basic active material B into the screw extruder in a volume ratio of 1-10:10 for anionic polymerization, and prepare a polyamide 6 basic melt by reaction extrusion;

[0011] (4) the polyamide 6 base melt is transported to a first devolatilization reactor to remove caprolactam monomers to obtain a polyamide 6 intermediate, and the polyamide 6 intermediate is input into a second devolatilization reactor to remove a small amount of caprolactam monomers, cyclic dimers, part of cyclic trimers and part of cyclic tetramers to obtain a polyamide 6 final polymer, wherein the reaction temperature of the first devolatilization reactor is set to 240-280°C, and the reaction pressure is 200-4000 Pa, and the reaction temperature of the second devolatilization reactor is 240-280°C, and the reaction pressure is 20-600 Pa.

[0012] In step (1), the catalyst is one or more of sodium caprolactamate, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH and KOH.

[0013] In step (1), the first mixture is subjected to vacuum distillation to sufficiently remove water, and the vacuum distillation conditions are a temperature of 80-150°C and a reaction absolute pressure of 5-95 kPa.

[0014] In step (1), the inert atmosphere is one or more of N2, CO2, He, Ne and Ar.

[0015] In step (1), 0.3-1.2 parts by mass of the catalyst and 10-100 parts by mass of caprolactam are mixed to obtain the first mixture.

[0016] In step (2), the initiator is one or more of N-acetyl caprolactam (AcCL), bisacylated lactam-1,6-hexanediamine, terephthaloyl bis-caprolactam (TBCL), isophthaloyl bis-caprolactam, toluene diisocyanate (TDI), methylene dianiline diisocyanate (MDI) and 1,6-hexane diisocyanate (HMDI).

[0017] In step (2), the caprolactam monomers are subjected to vacuum distillation, and the vacuum distillation conditions are a temperature of 80-150°C and a reaction absolute pressure of 5-95 kPa.

[0018] In step (2), the inert atmosphere is one or more of N2, CO2, He, Ne and Ar.

[0019] In step (2), 100 parts of the water-removed caprolactam monomers and 1.0-2.4 parts of the initiator are mixed to obtain the second mixture.

[0020] In step (3), the feeding temperature of the screw extruder is set to 90-160°C, the discharge port temperature is set to 220-240°C, the temperature in the middle section of the screw is set to gradually increase from the feeding temperature to the discharge port temperature, the heating section is not less than 1, and the rotation speed is 20-300 rpm.

[0021] In step (3), the polyamide 6 base melt has a relative viscosity of 2.0-4.5, a monomer content of less than 4.2 wt%, a cyclic oligomer content of less than 2.6 wt% (wherein the cyclic dimer content in the cyclic oligomer is less than 0.8 wt%), and a hot water extractable content of less than 5.5 wt%.

[0022] In step (4), the reaction temperature of the first devolatilization reactor and the second devolatilization reactor can be independently controlled, and both are connected to a vacuum system for controlling the reaction pressure of the first devolatilization reactor and the second devolatilization reactor. The first devolatilization reactor is selected from one of a horizontal squirrel cage reactor, a horizontal disc reactor, a falling bar devolatilizer, and a vertical falling film devolatilization reactor. The second devolatilization reactor is selected from a vertical falling film devolatilization reactor or a horizontal double-shaft devolatilization reactor. The reaction pressure of the first devolatilization reactor is controlled by the vacuum system to be 200-4000 Pa, and the reaction temperature is set to 240-280 °C. The reaction pressure of the second devolatilization reactor is controlled by the vacuum system to be 20-600 Pa, and the reaction temperature is set to 240-280 °C.

[0023] In step (4), the polyamide 6 final polymer has 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% (wherein the cyclic dimer content in the cyclic oligomer is less than 0.1 wt%), and a hot water extractable content of less than 0.5 wt%.

[0024] In some embodiments, the present technical solution provides a method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, comprising the following steps:

[0025] Further, the method for preparing polyamide 6 material by anionic polymerization of the present solution further comprises the following steps:

[0026] (5) Directly spinning the polyamide 6 final polymer to obtain polyamide 6 civilian or industrial yarns, or directly blowing the polyamide 6 final polymer to obtain a polyamide 6 film; or adding a fiber reinforcing material to the polyamide 6 final polymer for injection molding to obtain a polyamide 6 composite material.

[0027] When the polyamide 6 final polymer is directly spun to obtain polyamide 6 civilian or industrial yarns, the spinning temperature is 245-300 °C, and the spinning speed is 2500-6000 m / min.

[0028] When the polyamide 6 final polymer is added with a fiber reinforcing material 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 、 Figure 2 and Figure 3 Three anionic polymerization combined with fractional devolatilization to prepare high-quality polyamide 6 material framework schematic diagram is provided, as shown in Figure 1 、 Figure 2 and Figure 3 Caprolactam and catalyst are mixed and added to the drying device A for vacuum distillation and stored in the storage tank A; the caprolactam is heated and melted and placed in the drying device B for vacuum distillation, then the caprolactam removing water is mixed with the initiator to obtain the second mixture, and the second mixture is stored in the storage tank B; the base active material A and the base active material B are injected into the screw extruder at a volume ratio of 1-10:10 for anionic polymerization, and the polyamide 6 base melt is prepared by reaction extrusion; the polyamide 6 base melt is transported to the devolatilization reactor 1 to selectively remove more than 90% of the caprolactam monomer, and after the caprolactam monomer is largely removed, it enters the devolatilization reactor 2 to remove a small amount of residual caprolactam monomer and cyclic oligomers to obtain a polyamide 6 final polymer. The difference is that: Figure 1 The devolatilization reactor 1 in the above method adopts a vertical falling film devolatilization reactor, and the devolatilization reactor 2 also adopts a vertical falling film devolatilization reactor; Figure 2 The devolatilization reactor 1 in the above method adopts a horizontal devolatilization reactor, and the devolatilization reactor 2 adopts a vertical falling film devolatilization reactor, Figure 3 The devolatilization reactor 1 in the above method adopts a horizontal devolatilization reactor, and the devolatilization reactor 2 adopts a horizontal double-shaft devolatilization reactor.

[0030] The technical scheme of the present application can achieve the following beneficial effects:

[0031] The present application provides a method for preparing high-quality polyamide 6 by anionic polymerization combined with a series devolatilization reactor. Two devolatilization reactors can control the reaction temperature and pressure according to the physical property differences of monomers and cyclic oligomers. The first devolatilization reactor can selectively remove more than 90% of the caprolactam monomer, effectively reducing the influence of high content monomer on the next devolatilization reaction. After the monomer is largely removed, the reaction temperature and pressure of the second devolatilization reactor are set according to the physical properties of the cyclic oligomers, which can achieve the intensified removal of a small amount of residual caprolactam monomer and cyclic oligomers.

[0032] The series devolatilization reactor system provided by the present application is applied to the devolatilization of polyamide 6, and the monomer content in the obtained polyamide 6 final polymer is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt% (of which the cyclic dimer content is less than 0.1 wt%), and the hot water extractable content is less than 0.5 wt%. It can be directly used for spinning, injection molding or blowing film. Compared with the traditional hot water extraction process, the steps of cooling, granulating, hot water extraction, drying and remelting are omitted, a large amount of water and energy is saved, and the production efficiency is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 、 Figure 2 and Figure 3 is a schematic diagram of the preparation of high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization provided by the present application. DETAILED DESCRIPTION

[0034] The present application will be further described in conjunction with the specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not used to limit the scope of the present application. Furthermore, it should be understood that after reading the content taught by the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0035] In order to further illustrate the present application, a method for preparing high-quality polyamide 6 fiber by anionic polymerization provided by the present application is described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0036] The present application measures the content of monomers and cyclic oligomers in polyamide 6 base melt and final polymer by using ultra-high performance liquid chromatograph, and the specific condition parameters are as follows:

[0037] —chromatographic column: T3 column, 100 mm x 2.1 mm (inner diameter) x 1.7 μm, or equivalent;

[0038] —column temperature: 30°C;

[0039] —flow rate: 0.3 mL / min;

[0040] —detection wavelength: 200 nm;

[0041] —injection volume: 2 μL;

[0042] —elution program (as shown in the table below): mobile phase A is water, and mobile phase B is acetonitrile.

[0043]

[0044] Comparative Example

[0045] (1) Preparation of base active material A: 0.8 parts of NaOH is added to 100 parts of caprolactam by mass fraction, mixed uniformly, distilled to remove water at 100°C and 5 kPa under reduced pressure, and then stored in a storage tank A under N2 protection and at a constant temperature of 110°C;

[0046] (2) Preparation of the base active material B: 100 parts of monomer caprolactam were heated and melted, and water was removed by distillation under reduced pressure at 100°C and 5kPa, then 2.0 parts of N-acetyl caprolactam (AcCL) were added and mixed uniformly, and then stored in a storage tank B under N2 protection and at a constant temperature of 110°C;

[0047] (3) The base active materials A and B were injected into a screw extruder at a volume ratio of 1:1 for anionic polymerization, the feeding temperature of the screw extruder was set to 90°C, the discharge temperature of the screw extruder was set to 230°C, the intermediate segment temperature of the screw was set to gradually increase from 90°C to 230°C, the heating section was 3, the rotation speed was 30rpm, and a polyamide 6 base melt with a relative viscosity of 2.65, a monomer content of 4.09wt%, a cyclic oligomer content of 2.51wt% (including a cyclic dimer content of 0.78wt%), and a hot water extractable content of 5.32wt% was prepared by reaction extrusion;

[0048] (4) The polyamide 6 base melt was transported to a spinning machine for direct spinning, and a large amount of caprolactam gas was generated at the spinneret, which could not be spun.

[0049] Example 1

[0050] A method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, the specific steps are as follows:

[0051] (1) Preparation of the base active material A: 0.8 parts of NaOH were added to 100 parts of caprolactam and mixed uniformly, and then stored in a storage tank A under N2 protection and at a constant temperature of 110°C;

[0052] (2) Preparation of the base active material B: 100 parts of monomer caprolactam were heated and melted, and water was removed by distillation under reduced pressure at 100°C and 5kPa, then 2.0 parts of N-acetyl caprolactam (AcCL) were added and mixed uniformly, and then stored in a storage tank B under N2 protection and at a constant temperature of 110°C;

[0053] (3) The base active materials A and B were injected into a screw extruder at a volume ratio of 1:1 for anionic polymerization, the feeding temperature of the screw extruder was set to 90°C, the discharge temperature of the screw extruder was set to 230°C, the intermediate segment temperature of the screw was set to gradually increase from 90°C to 230°C, the heating section was 3, the rotation speed was 30rpm, and a polyamide 6 base melt with a relative viscosity of 2.63, a monomer content of 4.12wt%, a cyclic oligomer content of 2.55wt% (including a cyclic dimer content of 0.75wt%), and a hot water extractable content of 5.37wt% was prepared by reaction extrusion;

[0054] (4) The polyamide 6 base melt is transported to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a horizontal squirrel-cage reactor, and the second devolatilization reactor is a vertical falling-film devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum pump. The temperature of the first devolatilization reactor is 260 °C, and the reaction pressure is 1000 Pa. The temperature of the second devolatilization reactor is 270 °C, and the reaction pressure is 50 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 2.66, a monomer content of 0.02wt%, a cyclic oligomer content of 1.34wt% (of which the cyclic dimer content is 0.02wt%), and a hot water extractable content of 0.35wt% is prepared;

[0055] (5) The high-quality 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 high-quality polyamide 6 fiber is obtained, with a fiber breaking strength of 5.2 cN / dtex and an elongation of 23%.

[0056] Example 2

[0057] A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, the specific steps are as follows:

[0058] (1) Preparation of base active material A: 1.0 parts of NaOH is added to 10 parts of caprolactam and mixed uniformly, and then distilled under reduced pressure at 80 °C and 5 kPa to remove water, and then stored in a storage tank A under Ar protection and at a constant temperature of 150 °C;

[0059] (2) Preparation of base active material B: 100 parts of monomer caprolactam is heated and melted, distilled under reduced pressure at 80 °C and 5 kPa to remove water, and then 1.2 parts of m-terephthaloyl bis-caprolactam is added and mixed uniformly, and then stored in a storage tank B under Ar protection and at a constant temperature of 150 °C;

[0060] (3) The base active materials A and B are injected into a screw extruder at a volume ratio of 1:10 for anionic polymerization, the feeding temperature of the screw extruder is set to 110 °C, the discharging temperature of the screw extruder is set to 220 °C, the intermediate temperature of the screw is set to gradually increase from 110 °C to 220 °C, the heating section is 3, and the rotation speed is 30 rpm. A polyamide 6 base melt with a relative viscosity of 3.50, a monomer content of 4.05wt%, a cyclic oligomer content of 2.46wt% (of which the cyclic dimer content is 0.72wt%), and a hot water extractable content of 5.21wt% is prepared by reaction extrusion;

[0061] (4) The polyamide 6 base melt is transported to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a horizontal disc reactor, and the second devolatilization reactor is a vertical falling film devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum pump. The temperature of the first devolatilization reactor is 240 °C, and the reaction pressure is 1000 Pa. The temperature of the second devolatilization reactor is 250 °C, and the reaction pressure is 40 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 3.52, a monomer content of 0.04wt%, a cyclic oligomer content of 1.36wt% (of which the cyclic dimer content is 0.03wt%), and a hot water extractable content of 0.40wt% is prepared;

[0062] (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning, the spinning temperature is 290 °C, and the winding speed is 3100 m / min. A polyamide 6 industrial yarn is obtained, and the fiber breaking strength is 8.5 cN / dtex, and the elongation is 23%.

[0063] Example 3

[0064] A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, the specific steps are as follows:

[0065] (1) Preparation of base active material A: 1.1 parts of NaH is added to 100 parts of caprolactam and mixed uniformly, and then distilled to remove water at 130 °C and 95 kPa under reduced pressure, and then stored in a storage tank A under Ar protection and at a constant temperature of 130 °C;

[0066] (2) Preparation of base active material B: 100 parts of monomer caprolactam is heated and melted, distilled to remove water at 130 °C and 95 kPa under reduced pressure, and then 1.6 parts of terephthaloyl bis-caprolactam (TBCL) is added and mixed uniformly, and then stored in a storage tank B under Ar protection and at a constant temperature of 130 °C;

[0067] (3) The base 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 to 140 °C, the discharging temperature of the screw extruder is set to 240 °C, the intermediate temperature of the screw is set to gradually increase from 140 °C to 240 °C, there are three heating sections, and the rotation speed is 30 rpm. A polyamide 6 base melt with a relative viscosity of 3.2, a monomer content of 3.96wt%, a cyclic oligomer content of 2.49wt% (of which the cyclic dimer content is 0.71wt%), and a hot water extractable content of 5.29wt% is prepared by reaction extrusion;

[0068] (4) The polyamide 6 base melt is transported to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a falling bar devolatilizer, and the second devolatilization reactor is a horizontal double-shaft devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum pump. The temperature of the first devolatilization reactor is 250 °C, and the reaction pressure is 1500 Pa. The temperature of the second devolatilization reactor is 260 °C, and the reaction pressure is 60 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 3.2, a monomer content of 0.03wt%, a cyclic oligomer content of 1.25wt% (of which the cyclic dimer content is 0.04wt%), and a hot water extractable content of 0.35wt% is prepared;

[0069] (5) The high-quality polyamide 6 melt is mixed with 10% glass fiber reinforcing material, and a glass fiber reinforced polyamide 6 composite material is obtained by melt extrusion.

[0070] Example 4

[0071] A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, the specific steps are as follows:

[0072] (1) Preparation of base active material A: 0.5 parts of sodium ethoxide is added to 100 parts of caprolactam and mixed uniformly, and then distilled under reduced pressure at 120 °C and 50 kPa to remove water, and then stored in a storage tank A under Ar protection and at a constant temperature of 130 °C;

[0073] (2) Preparation of base active material B: 100 parts of monomer caprolactam is heated and melted, distilled under reduced pressure at 120 °C and 50 kPa to remove water, and then 1.5 parts of bisacylated lactam-1, 6-hexanediamine is added and mixed uniformly, and then stored in a storage tank B under Ar protection and at a constant temperature of 130 °C;

[0074] (3) The base active materials A and B are injected into a screw extruder in a volume ratio of 1:1 for anionic polymerization, the screw extruder feed temperature is set to 120 °C, the screw extruder discharge temperature is set to 240 °C, the screw intermediate section temperature is set to gradually increase from 120 °C to 240 °C, the heating section is 5, and the rotation speed is 30 rpm. A polyamide 6 base melt with a relative viscosity of 2.81, a monomer content of 3.84wt%, a cyclic oligomer content of 2.52wt% (of which the cyclic dimer content is 0.78wt%), and a hot water extractable content of 4.96wt% is prepared by reaction extrusion;

[0075] (4) The polyamide 6 base melt is transported to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a vertical falling film devolatilization reactor, and the second devolatilization reactor is a vertical falling film devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum pump. The temperature of the first devolatilization reactor is 265 °C, and the reaction pressure is 2000 Pa. The temperature of the second devolatilization reactor is 270 °C, and the reaction pressure is 50 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 2.83, a monomer content of 0.02wt%, a cyclic oligomer content of 1.39wt% (of which the cyclic dimer content is 0.07wt%), and a hot water extractable content of 0.37wt% is obtained;

[0076] (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning, the spinning temperature is 275 °C, and the winding speed is 4000 m / min. A high-quality polyamide 6 fiber is obtained, with a fiber breaking strength of 5.5 cN / dtex and an elongation of 20%.

[0077] Example 5

[0078] A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, the specific steps are as follows:

[0079] (1) Preparation of base active material A: 0.7 parts of NaOH is added to 100 parts of caprolactam and mixed uniformly, then distilled under reduced pressure at 120 °C and 90 kPa to remove water, and then stored in a storage tank A under Ar protection and at a constant temperature of 120 °C;

[0080] (2) Preparation of base active material B: 100 parts of monomer caprolactam is heated and melted, then distilled under reduced pressure at 120 °C and 90 kPa to remove water, then 1.1 parts of N-acetyl caprolactam (AcCL) is added and mixed uniformly, and then stored in a storage tank B under Ar protection and at a constant temperature of 120 °C;

[0081] (3) The base 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 to 150 °C, the discharging temperature of the screw extruder is set to 210 °C, the intermediate temperature of the screw is set to gradually increase from 150 °C to 210 °C, there are 5 heating sections, and the rotation speed is 30 rpm. A polyamide 6 base melt with a relative viscosity of 3.4, a monomer content of 3.87wt%, a cyclic oligomer content of 2.54wt% (of which the cyclic dimer content is 0.76wt%), and a hot water extractable content of 5.19wt% is prepared by reaction extrusion;

[0082] (4) The polyamide 6 base melt is transported to two series-connected devolatilization reactors, wherein the first devolatilization reactor is a vertical falling film devolatilization reactor, and the second devolatilization reactor is a vertical falling film devolatilization reactor, and each of the two devolatilization reactors is connected with a vacuum pump. The temperature of the first devolatilization reactor is 270 °C, and the reaction pressure is 900 Pa, the temperature of the second devolatilization reactor is 260 °C, and the reaction pressure is 60 Pa, and finally a high-quality polyamide 6 melt with a relative viscosity of 3.4, a monomer content of 0.02wt%, a cyclic oligomer content of 1.35wt% (of which the cyclic dimer content is 0.08wt%), and a hot water extractable content of 0.45wt% is prepared;

[0083] (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning, the spinning temperature is 290 °C, and the winding speed is 3000 m / min, and a high-quality polyamide 6 fiber is obtained, the fiber breaking strength is 8.4 cN / dtex, and the elongation is 22%.

[0084] Table 1 Performance characterization table of polyamide 6 base melt and polyamide 6 final polymer of comparative example and examples 1 to 5

[0085]

[0086] Those skilled in the art should understand that each technical feature of the above examples can be combined arbitrarily, and in order to make the description simple, each technical feature in the above examples is not described in all possible combinations, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0087] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the 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 producing high-quality polyamide 6 material by anionic polymerization in combination with fractional devolatilization, characterized by, The method comprises the following steps: (1) preparing a basic active material A: mixing a catalyst and caprolactam to obtain a first mixture, performing vacuum distillation on the first mixture, and storing the mixture in a storage tank A, wherein the storage tank A is protected by an inert atmosphere and kept at a constant temperature of 80-150°C; (2) preparing a basic active material B: heating and melting caprolactam monomers, performing vacuum distillation, mixing the caprolactam monomers and an initiator 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 kept at a constant temperature of 80-150°C; (3) injecting the basic active material A and the basic active material B into a screw extruder at a volume ratio of 1-10:10 to perform anionic polymerization, and obtaining a polyamide 6 basic melt through reaction extrusion; (4) conveying the polyamide 6 basic melt to a first devolatilization reactor to remove caprolactam monomers and obtain a polyamide 6 intermediate, and conveying the polyamide 6 intermediate to a second devolatilization reactor to remove a small amount of caprolactam monomers, cyclic dimers, part of cyclic trimers, and part of cyclic tetramers to obtain a polyamide 6 final polymer, wherein the reaction temperature of the first devolatilization reactor is set to 240-270°C, the reaction pressure is 900-2000 Pa, the reaction temperature of the second devolatilization reactor is 250-270°C, the reaction pressure is 40-60 Pa, the relative viscosity of the polyamide 6 final polymer is 2.0-4.5, the monomer content is less than 0.1wt%, and the cyclic oligomer content is less than 1.5wt%, wherein the cyclic dimer content in the cyclic oligomers is less than 0.1wt%, the hot water extractable content is less than 0.5wt%, and the first devolatilization reactor is selected from one of a horizontal squirrel cage reactor, a horizontal disc reactor, a falling strip devolatilizer, and a vertical falling film devolatilization reactor; the second devolatilization reactor is selected from a vertical falling film devolatilization reactor or a horizontal double-shaft devolatilization reactor; The polyamide 6 final polymer is directly used for spinning to obtain polyamide 6 consumer yarn or industrial yarn, or directly used for blown film to obtain a polyamide 6 film, or used for injection molding by adding fiber reinforcing materials to obtain a polyamide 6 composite material.

2. The method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, In step (1), the catalyst is one or more of sodium caprolactamate, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH, and KOH.

3. The method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, In steps (1) and (2), the vacuum distillation conditions are a temperature of 80-150°C and a reaction absolute pressure of 5-95kPa.

4. The method for preparing high quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that In step (2), the initiator is one or more of N-acetyl caprolactam, bisacylated lactam-1,6-hexanediamine, terephthalylidene bis-caprolactam, isophthalylidene bis-caprolactam, toluene diisocyanate, diphenylmethane diisocyanate, and 1,6-hexane diisocyanate.

5. The method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, In step (3), the feeding temperature of the screw extruder is set to 90-160°C, the discharge port temperature is set to 220-240°C, the intermediate segment temperature of the screw is set to gradually increase from the feeding temperature to the discharge port temperature, the heating section is not less than 1, and the rotation speed is 20-300rpm.

6. The process for preparing high quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, In step (3), the polyamide 6 base melt has a relative viscosity of 2.0-4.5, a monomer content of less than 4.2 wt%, a cyclic oligomer content of less than 2.6 wt%, wherein the cyclic dimer content in the cyclic oligomer is less than 0.8 wt%, and a hot water extractable content of less than 5.5 wt%.

7. The method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, In step (4), the reaction temperatures of the first devolatilization reactor and the second devolatilization reactor can be independently controlled, and both are connected to a vacuum system for controlling the reaction pressures of the first devolatilization reactor and the second devolatilization reactor.

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