Nylon 6 slice continuous polymerization preparation method

Abstract

The invention relates to the technical field of high polymer material synthesis, and discloses a preparation method of a nylon 6 slice through continuous polymerization, the service life of the material is prolonged, the application range of the material is widened by carrying out anti-ultraviolet grafting on a caprolactam monomer, meanwhile, a catalyst for continuous polymerization reaction is improved, the catalytic efficiency and the oxidation resistance are improved, and the service life of the material is prolonged. The application range of the material is expanded, and benefits are increased.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, specifically relating to a method for preparing nylon 6 chips through continuous polymerization. Background Technology

[0002] Nylon 6, or polycaprolactam, is a synthetic fiber and thermoplastic resin widely used in textiles, engineering plastics, and other fields. Its preparation mainly involves the ring-opening polymerization of caprolactam, and nylon 6 chips are a common form of this material, used for subsequent processing into fibers or molded products. With increasing market demand and technological advancements, the production process of nylon 6 has been continuously optimized, with continuous polymerization technology becoming the mainstream due to its high efficiency and stability.

[0003] Traditional nylon 6 production often employs batch processes, which, while simple to operate, suffer from inconsistent product quality and low production efficiency. In contrast, continuous polymerization technology enables continuous input of raw materials and continuous output of products, significantly improving production efficiency while ensuring product consistency. For example, Chinese patent CN104387580A discloses a method for producing nylon 6 chips to improve polymerization conversion rate. This method describes a continuous polymerization process that typically includes multiple stages such as prepolymerization and final polymerization, each conducted under strictly controlled conditions to ensure the final product has ideal molecular weight and distribution, physical and mechanical properties. Currently, some domestic companies have mastered the technology for producing matte nylon 6 chips; however, the production of fully matte fibers still faces the problem of titanium dioxide agglomeration in the polymer. Furthermore, domestically produced nylon 6 chips have a high content of cyclic caprolactam dimers, making them unsuitable for high-speed textile applications. Additionally, there is a significant demand for nylon 6 with improved UV resistance and extended service life. Summary of the Invention

[0004] To address the existing technical problems mentioned in the background section regarding the increasing demand for UV resistance in nylon 6 materials, the tendency of titanium dioxide to agglomerate in nylon 6, and the high content of cyclic caprolactam dimers in the produced nylon 6 chips, this invention provides a method for the continuous polymerization of nylon 6 chips. This method involves grafting UV-absorbing groups onto caprolactam monomers to increase the material's UV resistance and lifespan. Pretreatment of titanium dioxide increases the steric hindrance of titanium dioxide particles, reducing interparticle attraction and preventing agglomeration. Simultaneously, the catalyst system for the ring-opening synthesis of nylon 6 is improved to increase polymerization conversion and reduce side reactions.

[0005] The technical solution adopted in this invention is as follows: A method for preparing nylon 6 chips by continuous polymerization includes the following steps: 1) After pulverizing and melting caprolactam that can absorb ultraviolet light, add 0.1wt%~0.3wt% of pretreated nano-sized titanium dioxide and stir at high speed to obtain the pretreated raw material; 2) Add 0.1wt%~0.3wt% of composite catalyst to the pretreated raw material prepared in step 1), heat and reduce pressure to carry out prepolymerization reaction to obtain prepolymerization intermediate; 3) The prepolymer intermediate obtained in step 2) is heated further to carry out the final polymerization reaction, and then benzoic acid is added to obtain a high-viscosity melt; 4) After rapidly cooling and solidifying the high-viscosity melt obtained in step 3), multi-stage extraction and drying were performed to obtain nylon 6 chips.

[0006] This invention directly grafts ultraviolet absorbers onto the nylon 6 molecular chain, avoiding the migration problems caused by traditional physical mixing, ensuring stability during long-term use, greatly improving the material's UV resistance, increasing the material's service life, and improving the catalyst to increase catalytic efficiency while reducing side reactions, thus significantly improving the overall performance of the product.

[0007] Furthermore, the preparation of caprolactam that absorbs ultraviolet light in step 1) includes the following steps: S1. Dissolve 2-(2'-hydroxy-5'-methylphenyl)benzotriazole in N,N-dimethylformamide to obtain a UV absorber solution with a concentration of 5~10wt%; S2. Mix the caprolactam monomer with the UV absorption solution obtained in S1 at a mass ratio of (50~100):1, add 0.1~0.5% of the mass of caprolactam monomer as an initiator, heat up, and react under a protective gas for 4~8 hours. After cooling, wash to obtain the caprolactam monomer that can absorb UV light.

[0008] Furthermore, the initiator in s2 is one or more of AIBN or BPO.

[0009] Furthermore, the preparation method of pretreated nano-sized titanium dioxide is as follows: after surface treatment of nano-sized titanium dioxide with silane coupling agent KH550, it is premixed with 3~5wt% of nylon 6 to prepare matting masterbatch, wherein the amount of silane coupling agent KH550 added is 1~2wt% of nano-sized titanium dioxide.

[0010] Further, the composite catalyst in step 1) is a composite of tetrabutyl titanate and triphenyl phosphite in a mass ratio of (5~10):1.

[0011] Furthermore, in step 2), the temperature of the prepolymerization reaction is 220~240℃, the pressure is 0.5~1MPa, and the reaction time is 1~2h.

[0012] Furthermore, in step 3), the final polymerization reaction temperature is 250~270℃, and the reaction time is 3~5h.

[0013] Furthermore, the amount of benzoic acid added is 0.1wt%~1wt%.

[0014] Furthermore, in step 4), ultrasonic-assisted extraction is used during multi-stage extraction.

[0015] Furthermore, step 1) is carried out under the protection of an inert gas.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1) By directly grafting the UV absorber onto the nylon 6 molecular chain, the migration problems caused by traditional physical mixing are avoided, ensuring stability during long-term use, greatly improving the material's UV resistance and increasing its service life.

[0017] 2) Surface treatment of the matting agent titanium dioxide effectively solves the problem of easy agglomeration of titanium dioxide and improves the mechanical properties and appearance of the material.

[0018] 3) The synergistic effect among the components in the composite catalyst greatly improves the catalytic efficiency. Tetrabutyl titanate provides high-efficiency catalytic activity, while triphenyl phosphite further optimizes the polymerization effect by suppressing side reactions. This combination can significantly improve the overall performance of the product.

[0019] 4) Use ultrasonic-assisted extraction during multi-stage extraction to increase the contact area between small molecule byproducts and the extractant, thereby improving extraction efficiency. Attached Figure Description

[0020] The present invention will be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 This is a flowchart of the operation of the present invention. Detailed Implementation

[0021] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0022] The present invention will be further described below with reference to embodiments.

[0023] Example 1 A method for preparing UV-resistant nylon 6 chips through continuous polymerization, such as... Figure 1 As shown, the specific steps are as follows: 1) Preparation of caprolactam monomers that can absorb ultraviolet light 1 g of 2-(2'-hydroxy-5'-methylphenyl)benzotriazole was dissolved in 10 ml of DMF and added to a reaction vessel along with 100 g of caprolactam monomer. After thorough mixing, 0.1 g of AIBN was added, nitrogen gas was introduced, the reaction vessel was sealed, and the mixture was heated to 80 °C and stirred for 6 h. After cooling to room temperature, the product was washed three times with distilled water, filtered, and dried to obtain caprolactam monomer that can absorb ultraviolet light.

[0024] 2) Pretreatment of titanium dioxide 100g of titanium dioxide and 5g of KH550 were dissolved in 100ml of anhydrous ethanol, stirred at 85℃ for 30min, dried in an oven at 105℃ for 2h, and then combined with 5g of nylon 6 to form pretreated titanium dioxide through a twin-screw extruder.

[0025] 3) Prepolymerization reaction The caprolactam monomer that absorbs ultraviolet light obtained in step 1) was pulverized and heated to 230°C. A composite catalyst (0.16g tetrabutyl titanate and 0.04g triphenyl phosphite) was added, and the mixture was stirred for 1 hour under a nitrogen atmosphere with a pressure of 0.6MPa. Then, 0.2g of the pretreated titanium dioxide prepared in step 2) was added and stirred for 45 minutes.

[0026] 4) Final polymerization reaction The temperature was increased to 265℃ and the reaction was allowed to proceed for 3 hours. Then, 0.2g of benzoic acid was added to obtain a high-viscosity melt.

[0027] 5) Follow-up processing After cooling the high-viscosity melt to room temperature, multi-stage extraction was performed using distilled water with ultrasonic-assisted extraction. After drying for 6 hours, nylon 6 slices were obtained.

[0028] 6) Performance Testing The nylon 6 slices obtained in step 5) were subjected to performance tests for ultraviolet absorption, mechanical properties and gloss.

[0029] Comparative Example 1 The only difference between this comparative example and Example 1 is that the caprolactam monomer was not grafted with absorbable ultraviolet light in this comparative example (i.e., step 1 of Example 1 was not performed), and the rest of the process is the same as in Example 1.

[0030] The material was subjected to 500 hours of simulated UV irradiation in a xenon lamp aging chamber. The long-term stability was determined by comparing the decrease in tensile strength and fracture growth rate before and after the simulation. The final material was subjected to UV-Vis spectroscopy testing, and the absorption in the wavelength range of 290~400nm was detected.

[0031] Table 1. Effect of caprolactam grafting with absorbable ultraviolet light on the long-term stability of the material. Should caprolactam monomer be grafted? Tensile strength reduction rate % The rate of decrease in elongation at break (%) Example 1 yes 5 10 Comparative Example 1 no 20 30 By comparing the data in Table 1, it can be concluded that without grafting caprolactam monomer with absorbable ultraviolet light, the decrease rate of tensile strength and the decrease rate of fracture growth rate both increased significantly during long-term stability testing, indicating insufficient long-term stability.

[0032] Table 2. Effect of caprolactam grafting with absorbable ultraviolet light on the optical properties of the materials. absorbance at 350nm Example 1 1.2AU Comparative Example 1 0.8AU The data in Table 2 show that after grafting caprolactam monomer with absorbable UV, the absorption capacity of UV is stronger and more uniform, and a better UV protection performance can be achieved.

[0033] Comparative Example 2 The only difference between this comparative example and Example 1 is that in this comparative example, the composite catalyst added in step 2) is 0.2g of tetrabutyl titanate; the rest of the process is the same as in Example 1.

[0034] Comparative Example 3 The only difference between this comparative example and Example 1 is that in this comparative example, the composite catalyst added in step 2) is 0.2g of triphenyl phosphite; the rest of the process is the same as in Example 1.

[0035] Table 2. Effects of composite catalysts on materials Catalyst types Molecular weight distribution thermal stability Color / Yellowing Index Mechanical properties Antioxidant capacity Example 1 0.16g tetrabutyl titanate, 0.04g triphenyl phosphite Narrower high Stablize Tensile strength 72MPa powerful Comparative Example 2 0.2g tetrabutyl titanate Wider Low Easily turns yellow Tensile strength 52MPa weak Comparative Example 3 0.2g triphenyl phosphite No effect No effect No effect No effect Strong Comparing the data in Table 2, it can be concluded that when tetrabutyl titanate is used alone as a catalyst to catalyze the polymerization reaction, it is difficult to effectively control the chain growth rate and it is prone to side reactions at high temperatures, which leads to a decrease in the processing performance, mechanical properties, and thermal stability of the generated material, failing to meet the needs of daily production. Triphenyl phosphite, when used alone as a catalyst, cannot effectively promote the polymerization reaction and is unable to achieve its inherent antioxidant properties. When tetrabutyl titanate and triphenyl phosphite are used together as a composite catalyst to catalyze the polymerization reaction, the synergistic effect of the two not only improves the catalytic efficiency but also enhances the thermal stability, color stability, mechanical properties, and antioxidant capacity of the material to a certain extent.

[0036] Comparative Example 4 The only difference between this comparative example and Example 1 is that no pretreatment of titanium dioxide was performed in this comparative example; all other processes are the same as in Example 1.

[0037] Comparative Example 5 The only difference between this comparative example and Example 1 is that no matting agent (titanium dioxide) is added in this comparative example; all other processes are the same as in Example 1.

[0038] Table 3 shows the effect of titanium dioxide pretreatment on material properties. Types of matting agents Gloss (60°) Example 1 Nanoscale titanium dioxide treated with silane coupling agent 22UG Comparative Example 4 Nanoscale titanium dioxide 47UG Comparative Example 5 No addition 85UG The data in Table 3 show that the addition of the matting agent titanium dioxide greatly reduces the gloss of the material. At the same time, untreated titanium dioxide tends to agglomerate, resulting in uneven gloss and making it difficult to achieve a high-quality matte effect. Surface treatment of silica can effectively improve its dispersibility and achieve a uniform and stable matte effect.

[0039] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0040] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A method for preparing nylon 6 chips through continuous polymerization, characterized in that, Includes the following steps: 1) After crushing and melting the caprolactam monomer that can absorb ultraviolet light, add 0.1wt%~0.3wt% of pretreated nano-sized titanium dioxide and stir at high speed to obtain the pretreated raw material; 2) Add 0.1wt%~0.3wt% of composite catalyst to the pretreated raw material prepared in step 1), heat and reduce pressure to carry out prepolymerization reaction to obtain prepolymerization intermediate; 3) The prepolymer intermediate obtained in step 2) is heated further to carry out the final polymerization reaction, and then benzoic acid is added to obtain a high-viscosity melt; 4) After rapidly cooling and solidifying the high-viscosity melt obtained in step 3), multi-stage extraction and drying were performed to obtain nylon 6 chips.

2. The method for preparing nylon 6 chips by continuous polymerization according to claim 1, characterized in that, The preparation of the ultraviolet-absorbing caprolactam monomer in step 1) includes the following steps: S1. Dissolve 2-(2'-hydroxy-5'-methylphenyl)benzotriazole in N,N-dimethylformamide to obtain a UV absorber solution with a concentration of 5~10wt%; S2. After mixing the solid caprolactam with the UV absorption solution obtained in S1 at a mass ratio of (50~100):1, add 0.1~0.5% of the mass of the solid caprolactam as an initiator, heat up, and react under a protective gas for 4~8 hours. After cooling and washing, the caprolactam monomer that can absorb UV light is obtained.

3. The method for preparing nylon 6 chips by continuous polymerization according to claim 2, characterized in that, The initiator in s2 is one or more of AIBN or BPO.

4. The method for preparing nylon 6 chips by continuous polymerization according to claim 1, characterized in that, The preparation method of pretreated nano-sized titanium dioxide is as follows: after surface treatment of nano-sized titanium dioxide with silane coupling agent KH550, it is premixed with 3~5wt% nylon 6 to prepare matting masterbatch, wherein the amount of silane coupling agent KH550 added is 1~2wt% of nano-sized titanium dioxide.

5. The method for preparing nylon 6 chips by continuous polymerization according to claim 1, characterized in that, The composite catalyst in step 2) is a composite of tetrabutyl titanate and triphenyl phosphite in a mass ratio of (5~10):

1.

6. The method for preparing nylon 6 chips by continuous polymerization according to claim 1, characterized in that, In step 2), the temperature of the prepolymerization reaction is 220~240℃, the pressure is 0.5~1MPa, and the reaction time is 1~2h.

7. The method for preparing nylon 6 chips by continuous polymerization according to claim 1, characterized in that, In step 3), the final polymerization reaction temperature is 250~270℃, and the reaction time is 3~5h.

8. The method for preparing nylon 6 chips by continuous polymerization according to claim 1, characterized in that, In step 3), the amount of benzoic acid added is 0.1wt%~1wt%.

9. The method for preparing nylon 6 chips by continuous polymerization according to claim 1, characterized in that, In step 4), ultrasonic-assisted extraction is used during multi-stage extraction.

10. A method for preparing nylon 6 chips by continuous polymerization according to any one of claims 1 to 9, characterized in that, Step 1) is carried out under the protection of an inert gas.

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