Method for preparing high-quality polyamide 6 fiber in short process

Abstract

The invention provides a method for preparing high-quality polyamide 6 fiber in a short process, which comprises the following steps: mixing basic components such as caprolactam, water, a molecular weight regulator and a cyclic oligomer inhibitor according to a ratio, preheating, conveying to a VK tube reactor, and carrying out polymerization reaction to obtain a polyamide 6 basic melt; the basic melt is further conveyed to a devolatilization reaction system to remove monomers and part of cyclic oligomers, a polyamide 6 final polymer is finally prepared, the polyamide 6 final polymer is spun to obtain polyamide 6 fibers, the breaking strength of the fibers is larger than or equal to 4.0 cN / dtex, and the elongation is 15-25%. Compared with chip spinning, a large amount of energy and time are saved, and the production efficiency is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of polyamide materials, and particularly to a method for preparing high-quality polyamide 6 fibers with a short process, especially a method for preparing high-quality polyamide 6 fibers by introducing a cyclic oligomer inhibitor during the hydrolysis polymerization process of polyamide 6 and combining a devolatilization technique. Background Art

[0002] Polyamide 6 is a semi-transparent or opaque crystalline polymer formed by the polycondensation of caprolactam. It is one of the most important varieties in the polyamide industry and has good colorability, toughness, wear resistance, self-lubricity, molding processability, thermoplasticity, and chemical resistance, and is widely used in fields such as fibers, engineering plastics, and films.

[0003] Currently, the production of polyamide 6 in China mainly adopts the hydrolysis polymerization method, and the prepared polyamide 6 melt contains about 8-10% of caprolactam monomers and cyclic oligomers. Caprolactam monomers are prone to gasification and generate bubbles at high temperatures, resulting in the failure of the fibers to be formed smoothly. The accumulation of cyclic oligomers is likely to block the spinneret and cause filament breakage and a decrease in the mechanical properties of the fibers. Therefore, in order to ensure the stability of spinning and forming, the polyamide 6 melt needs to go through steps such as cooling, casting, pelletizing, hot water extraction of monomers and cyclic oligomers, drying, and then melt spinning. These cumbersome processes will cause a large waste of energy and time, resulting in a significant reduction in production efficiency.

[0004] In addition to the hot water extraction method, the melt direct devolatilization method can reduce the content of monomers and oligomers in polyamide 6, realize the direct melt spinning to prepare polyamide 6 fibers, shorten the production process, improve production efficiency, and reduce production energy consumption. The patent "A production system and production method for high-quality polycaprolactam" (CN202210657759.1) effectively connects a VK tube reactor and an external tube falling film devolatilization reactor, and designs a total control unit to adjust and match the process parameters of each part, and performs real-time optimization control on the production system to obtain polyamide 6 chips with a hot water extractable content of less than 1.5 wt%. According to FZ / T 51004-2011, the hot water extractable content of polyamide 6 chips ≤ 0.5 wt% is of excellent quality, and it is still necessary to realize the direct melt spinning to prepare high-quality polyamide 6 fibers through the optimization of the polymerization process and the improvement of the devolatilization technique. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing high-quality polyamide 6 fibers with a short process, reducing the formation of monomers and cyclic oligomers during polymerization, and combining a devolatilization technique to further remove residual monomers and oligomers to prepare high-quality polyamide 6 fibers.

[0006] The method for preparing high-quality polyamide 6 fibers with a short process proposed by the present invention is to introduce a metal ion compound as a cyclic oligomer inhibitor during the hydrolysis polymerization of polyamide 6 to reduce the formation of cyclic oligomers. The cyclic oligomer inhibitor is a metal ion compound MY or a mixture of multiple metal ion compounds MY, where M is a metal cation and Y is an inorganic anion or an organic anion (M: transition metal ions (Sc 3+ 、Ni 2+ 、Zn 2+ 、Y 3+ 、Zr 4+ 、Ru 4+ 、Rh 3 + ), lanthanide metal ions (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+ ), group IIA metal ions (Be 2+ 、Mg 2+ 、Ca 2+ ), Li + 、Al 3+ ); Y: F - 、Cl - 、NO3 - 、SO4 2- 、PO4 3- 、citrate ion, salicylate ion, 3-hydroxybutyrate ion, L-aspartate ion, lactate ion, malate ion, 2-hydroxypropionate ion, an organic monocarboxylate ion H(CH2) n COO - (n = 0~12), benzoate ion, naphthoate ion, an organic dicarboxylate ion COO - (CH2) m COO - (m = 0~12), terephthalate ion, phthalate ion, isophthalate ion or naphthalenedicarboxylate ion, a saturated fatty acid root ion C x H 2x+1 COO - (x = 13~20), an unsaturated fatty acid root ion (oleate ion C 17 H33 COO - 、 Linoleate ion C 17 H 31 COO - 、 α-Linolenate ion C 17 H 29 COO - 、 Arachidonate ion C 19 H 31 COO - 、 Palmitoleate ion C 15 H 29 COO - ), 6-Aminocaproate ion NH2C5H 10 COO - 、 Amino acid ions (glycinate ion, alaninate ion, valinate ion, leucinate ion, isoleucinate ion, prolinate ion, phenylalaninate ion, methioninate ion, serine ion, threonine ion, asparagine ion, glutamine ion, aspartate ion, glutamate ion, cysteinate ion, tyrosine ion, selenocysteinate ion). The introduction of the cyclic oligomer inhibitor in the present invention utilizes the coordination of metal ions with amide bonds to inhibit the backbiting attack of the amino group at the chain end of polyamide 6 molecules on the amide bond during polymerization, so as to reduce the formation of cyclic oligomers. After the polyamide 6 melt passes through a further devolatilization reaction system to remove unreacted monomers and some cyclic oligomers, it can be directly melt-spun to obtain polyamide 6 fibers. This method saves steps such as pelletizing, hot water extraction, drying, and re-melting, saves a large amount of energy and time, and the monomers and cyclic oligomers obtained by devolatilization can be directly recycled without further purification.

[0007] Regarding the devolatilization reaction system used in this solution, it can be a vertical devolatilization reactor or a series devolatilization system composed of two vertical devolatilization reactors. After the polyamide 6 base melt is subjected to the removal of monomers and cyclic oligomers through the devolatilization reaction system, the relative viscosity of the finally prepared polyamide 6 end polymer is 2.3 - 4.2, the monomer content is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt% (where the cyclic dimer content is less than 0.1 wt%), and the hot water extractable content is less than 0.5 wt%.

[0008] To achieve the above objectives, the present technical solution provides a method for preparing high-quality polyamide 6 fibers with a short process, including the following steps: (1) Mix caprolactam, water, a molecular weight regulator, and a cyclic oligomer inhibitor in proportion, preheat them, and then add them to a VK tube for polymerization reaction to prepare a polyamide 6 base melt, where the cyclic oligomer inhibitor is a metal ion compound; (2)Transport the polyamide 6 base melt through a pipeline to a devolatilization reaction system to remove monomers and some cyclic oligomers to prepare the polyamide 6 end-polymer; (3)Directly spin the polyamide 6 end-polymer to obtain high-quality polyamide 6 fibers.

[0009] In some embodiments, the polyamide 6 end-polymer is directly spun, or directly processed into products such as engineering plastics and films. Additives can also be added to the base components for modification or other components can be added for copolymerization according to specific application ranges. In other words, caprolactam, water, a molecular weight regulator, a cyclic oligomer inhibitor, and additives are mixed in proportion according to functional requirements.

[0010] Correspondingly, the additive is selected from one or more of a matting agent, an antioxidant, a colorant, a flame retardant, an antibacterial agent, an antistatic agent, an ultraviolet inhibitor, a fluorescent agent, and a far-infrared agent, and the addition amount of the additive is not more than 5 wt%. Among them, the matting agent is one or more of titanium dioxide, diatomite, and silicon dioxide; the antioxidant is one or more of a phenolic antioxidant, a hindered phenolic antioxidant, a semi-hindered phenolic antioxidant, a phosphite antioxidant, a benzofuranone antioxidant, a hydroxylamine antioxidant, a tertiary amine oxide antioxidant, a bisphenol monoacrylate antioxidant, a bis(salicylidene)diamine antioxidant, and a thio propionate antioxidant; the colorant is one or more of carbon black, phthalocyanine pigments, quinacridone pigments, triarylmethane pigments, benzimidazolone pigments, azo pigments, dioxazines, isoindolinones, anthraquinones, and perinones; the flame retardant is one or more of a phosphorus-based flame retardant, a phosphorus-nitrogen-based flame retardant, a nitrogen-based flame retardant, magnesium hydroxide, aluminum hydroxide, a silicon-based flame retardant, zinc borate, and ammonium polyphosphate; the antibacterial agent is one or more of silver nanoparticles, copper nanoparticles, zinc oxide, cuprous oxide, copper oxide, acyl aniline compounds, imidazole compounds, thiazole compounds, isothiazolone derivatives, quaternary ammonium salt compounds, biguanide compounds, chitin, and chitosan; the antistatic agent is one or more of carbon black, graphene, carbon nanotubes, metal powders, alkali metal alkyl sulfonates, alkali metal alkyl phosphates, alkali metal dithiocarbamates, alkyl quaternary ammonium salts, alkyl phosphates, alkyl phosphonium salts, and ethoxylated aliphatic alkylamine antistatic agents; the ultraviolet inhibitor is one or more of carbon black, iron oxide red, zinc oxide, salicylate ultraviolet absorbers, benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, substituted acrylonitrile ultraviolet absorbers, triazine ultraviolet absorbers, and hindered amine ultraviolet absorbers; the fluorescent agent is one or more of oxadiazole and its derivatives, triazole and its derivatives, rhodamine and its derivatives, coumarin and its derivatives, naphthalimide and its derivatives, pyrazolines, triphenylamines, porphyrins, carbazoles, pyrazines, thiazoles, perylenes, benzoxazines, and phthalimides, or a fluorescent agent using alkaline earth metal sulfides or aluminates as a luminescent matrix and rare earth lanthanide elements as an activator; the far-infrared agent is one or more of far-infrared ceramics, tourmaline, silicon carbide, carbon fiber, biochar, aluminum oxide, copper oxide, and silver oxide.

[0011] When the polyamide 6 end polymer is directly spun into polyamide 6 fibers, the spinning temperature is 245 to 300 °C, the spinning speed is 2500 to 6000 m / min, and the obtained polyamide 6 fibers have a breaking strength of ≥4.5 cN / dtex and an elongation at break of 15 to 25%.

[0012] In some embodiments, the content of the molecular weight regulator is 1.5 wt% or less; the molecular weight regulator is one or a combination of more of an organic monocarboxylic acid, an organic dicarboxylic acid, an organic monoamine, and an organic diamine. The organic monocarboxylic acid is H(CH2) n COOH (n = 1 to 10), benzoic acid, or naphthoic acid; the organic dicarboxylic acid is COOH(CH2) m COOH (m = 1 to 10), terephthalic acid, phthalic acid, isophthalic acid, or naphthalenedicarboxylic acid; the organic monoamine is H(CH2) x NH2 (x = 1 to 10), aniline, or naphthylamine; the organic diamine is, H2N(CH2) y NH2 (y = 1 to 10), p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, or naphthalenediamine.

[0013] In some embodiments, the relative viscosity of the polyamide 6 base melt is 1.5 to 3.5, the monomer content is less than 9.5 wt%, the cyclic oligomer content is less than 2.5 wt%, and the hot water extractable content is less than 10.5 wt%.

[0014] In some embodiments, the relative viscosity of the polyamide 6 end polymer is 2.3 to 4.2, the monomer content is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt%, and the hot water extractable content is less than 0.5 wt%.

[0015] In some embodiments, the cyclic oligomer inhibitor is a metal ion compound MY or a mixture of multiple metal ion compounds MY, where M is a metal cation and Y is an inorganic anion or an organic anion, and M is selected from transition metal ions (Sc 3+ 、Ni 2+ 、Zn 2+ 、Y 3+ 、Zr 4+ 、Ru 4+ 、Rh 3+ ), lanthanide metal ions (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+ ), group IIA metal ions (Be 2+ 、Mg 2+, Ca 2+ ), Li + , Al 3+ ; 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 monocarboxylate ion H(CH2) n COO - (n = 0~12), benzoate ion, naphthoate ion, organic dicarboxylate ion COO - (CH2) m COO - (m = 0~12), terephthalate ion, phthalate ion, isophthalate ion or naphthalenedicarboxylate ion, saturated fatty acid root ion C x H 2x+1 COO - (x = 13~20), unsaturated fatty acid root ion (oleate ion C 17 H 33 COO - , linoleate ion C 17 H 31 COO - , α-linolenate ion C 17 H 29 COO - , arachidonate ion C 19 H 31 COO - , palmitoleate ion C 15 H 29 COO - ), aminohexanoate ion NH2C5H 10 COO - , amino acid root ion (glycinate ion, alaninate ion, valinate ion, leucinate ion, isoleucinate ion, prolinate ion, phenylalaninate ion, methioninate ion, serine ion, threonine ion, asparagine ion, glutamine ion, aspartate ion, glutamate ion, cysteinate ion, tyrosine ion, selenocysteinate ion). The addition amount of the cyclic oligomer inhibitor is 0.01 wt%~1.0 wt% of caprolactam.

[0016] In some embodiments, the devolatilization reaction system consists of a vertical devolatilization reactor connected to a vacuum system, or is composed of two vertical devolatilization reactors connected to independent vacuum systems in series. As Figure 1 Figure Figure 1 is a system diagram of the method for preparing high-quality polyamide 6 fibers with a short process when the devolatilization reaction system consists of a vertical devolatilization reactor connected to a vacuum system; Figure 2 Figure Figure 2 is a system diagram of the method for preparing high-quality polyamide 6 fibers with a short process when the devolatilization reaction system is composed of two vertical devolatilization reactors connected to independent vacuum systems in series.

[0017] When the devolatilization reaction system consists of a vertical devolatilization reactor connected to a vacuum system, the system diagram of the method for preparing high-quality polyamide 6 fibers with a short process is as shown in Figure 1 Figure Figure 1 . The reaction temperature is 240 - 280 °C, the reaction pressure is 20 - 200 Pa. The vacuum system includes a vacuum pump and a condensation collector with a buffer tank added in front of the pump. The condensation collector can also be a caprolactam spray pump or a caprolactam injection pump with a buffer tank added in front of the pump.

[0018] When the devolatilization reaction system is composed of two vertical devolatilization reactors connected to independent vacuum systems in series, the system diagram of the method for preparing high-quality polyamide 6 fibers with a short process is as shown in Figure 2 Figure Figure 2 . The reaction temperature of devolatilization reactor 1 is 240 - 280 °C, the reaction pressure is 200 - 4000 Pa. The vacuum system 1 includes a vacuum pump and a condensation collector 1. The condensation collector 1 is connected to devolatilization reactor 1 to collect the steam in devolatilization reactor 1, and the vacuum pump is connected to the condensation collector 1 to provide vacuum power. The condensation collector 1 can also be a caprolactam spray pump or an injection pump with or without a buffer tank added in front of the pump; the reaction temperature of devolatilization reactor 2 is 240 - 280 °C, the reaction pressure is 20 - 400 Pa. The vacuum system 2 includes a vacuum pump and a condensation collector 2 with or without a buffer tank added in front of the pump. The condensation collector 2 is connected to devolatilization reactor 2 to collect the steam in devolatilization reactor 2, and the vacuum pump is connected to the condensation collector 2 to provide vacuum power. The condensation collector 2 can also be a caprolactam spray pump or an injection pump with or without a buffer tank added in front of the pump. The vacuum pump can be one or more of a rotary vane vacuum pump, a liquid ring vacuum pump, a roots vacuum pump, a reciprocating vacuum pump, a screw vacuum pump, and a steam jet pump in series or parallel combination.

[0019] In some embodiments, the VK tube reactor can be a one-stage reactor or a two-stage reactor; when the VK tube reactor is a one-stage reactor, the reaction temperature is 200~270 °C, the reaction pressure is 0.1 MPa~0.8 MPa, and the viscosity of the polyamide 6 base melt obtained is 1.5~3.0; when the VK tube reactor is a two-stage reactor, the reaction temperature of the prepolymerization reactor is 200~270 °C, the reaction pressure is 0.1 MPa~1.0 MPa, the reaction temperature of the post-polymerization reactor is 240~280 °C, the reaction pressure is 0.01 MPa~0.2 MPa, and the viscosity of the polyamide 6 base melt obtained is 1.8~3.5.

[0020] Compared with the prior art, the technical solution has the following characteristics and beneficial effects: (1) The introduction of the cyclic oligomer inhibitor makes the content of cyclic oligomers in the polyamide 6 base melt lower than 2.2 wt%, which is 0.5~1.0 wt% lower than that of the slice without the cyclic oligomer inhibitor; the content of hot water extractables is lower than 9.5 wt%, which is 0.6~1.2 wt% lower than that of the slice without the cyclic oligomer inhibitor. The content of hot water extractables in the polyamide 6 end polymer after devolatilization is lower than 0.5 wt%, having the quality of superior-grade polyamide 6.

[0021] (2) The polyamide 6 base melt prepared by introducing the cyclic oligomer inhibitor can be directly spun after devolatilization, eliminating steps such as pelletizing, hot water extraction, drying, and re-melting in the traditional hot water extraction process, saving a large amount of energy and time, greatly shortening the process flow, and significantly improving production efficiency. Description of the Drawings

[0022] Figure 1 It is a system diagram realized by the method for preparing high-quality polyamide 6 fibers with a short process when the devolatilization reaction system consists of a vertical devolatilization reactor connected to a vacuum system.

[0023] Figure 2 It is a system diagram realized by the method for preparing high-quality polyamide 6 fibers with a short process when the devolatilization reaction system consists of two vertical devolatilization reactors connected in series to independent vacuum systems. Detailed Embodiments

[0024] To further illustrate the present invention, the following describes in detail a method for preparing high-quality polyamide 6 fibers with a short process and its application provided by the present invention in combination with embodiments, but they cannot be construed as limiting the protection scope of the present invention.

[0025] The present invention uses an ultra-high performance liquid chromatograph to measure the contents of monomers and cyclic oligomers in the polyamide 6 base melt and end polymer, and the specific condition parameters are as follows: ——Chromatographic column: T3 column, 100 mm × 2.1 mm (inner diameter) × 1.7 μm, or equivalent; ——Column temperature: 30 °C; ——Flow rate: 0.3 mL / min; ——Detection wavelength: 200 nm; ——Injection volume: 2 μL; ——Elution program (as shown in the following table): Mobile phase A is water, and mobile phase B is acetonitrile.

[0026]

[0027] Control Example (1) Fresh caprolactam, water, and terephthalic acid were mixed in a ratio of 100:2:0.375, preheated, and then added to a one-stage VK tube for polymerization reaction for 8 h. The reaction temperature was 250 °C, and the reaction pressure was 0.4 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.5, a monomer content of 7.92 wt%, a cyclic oligomer content of 2.87 wt% (where the cyclic dimer content was 0.65 wt%), and a hot water extractable content of 8.95 wt% was prepared; (2) The base melt was transported through a pipeline to a first-stage vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature was 260 °C, and the reaction pressure was 80 Pa. Finally, a polyamide 6 end product with a relative viscosity of 2.9, a monomer content of 0.06 wt%, a cyclic oligomer content of 2.05 wt% (where the cyclic dimer content was 0.32 wt%), and a hot water extractable content of 0.65 wt% was obtained.

[0028] (3) The polyamide 6 end product can be extracted with hot water, dried, and remelted to prepare civil silk. The spinning temperature was 270 °C, the spinning speed was 3800 m / min, the fiber breaking strength was 5.5 cN / dtex, and the elongation at break was 23%.

[0029] Example 1 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1) Fresh caprolactam, water, terephthalic acid, and lanthanum citrate were mixed in a ratio of 100:2:0.375:0.8, preheated, and then continuously injected into a one-stage VK tube for polymerization reaction for 11 h. The reaction temperature was 250 °C, and the reaction pressure was 0.4 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.5, a monomer content of 7.95 wt%, a cyclic oligomer content of 2.20 wt% (where the cyclic dimer content was 0.41 wt%), and a hot water extractable content of 8.54 wt% was prepared; (2)The base melt is transported through a pipeline to a first-stage vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature is 260 °C and the reaction pressure is 80 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 2.8, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.42 wt% (where the cyclic dimer content is 0.06 wt%), and a hot water extractable content of 0.43 wt% is obtained.

[0030] (3)The polyamide 6 end-polymer can be directly spun into polyamide 6 civil yarn. The spinning temperature is 270 °C, the spinning speed is 4000 m / min, the fiber breaking strength is 5.4 cN / dtex, and the elongation at break is 22%.

[0031] Example 2 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1)Fresh caprolactam, water, terephthalic acid, titanium dioxide, and cerium formate are mixed in a ratio of 100:2:0.375:0.2:0.4, and after preheating, they are continuously injected into a one-stage VK tube for polymerization reaction for 13 h. The reaction temperature is 220 °C and the reaction pressure is 0.25 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.2, a monomer content of 8.12 wt%, a cyclic oligomer content of 2.32 wt% (where the cyclic dimer content is 0.46 wt%), and a hot water extractable content of 8.67 wt% is prepared; (2)The base melt is transported through a pipeline to a first-stage vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature is 260 °C and the reaction pressure is 50 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 2.7, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.25 wt% (where the cyclic dimer content is 0.04 wt%), and a hot water extractable content of 0.37 wt% is obtained.

[0032] (3)The polyamide 6 end-polymer can be directly spun into semi-dull polyamide 6 civil yarn. The spinning temperature is 265 °C, the spinning speed is 4000 m / min, the fiber breaking strength is 5.2 cN / dtex, and the elongation at break is 24%.

[0033] Example 3 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1) Mix fresh caprolactam, water, decanediamine, and cerium acetate in a ratio of 100:2:0.5:0.6. After preheating, continuously inject the mixture into a one-stage VK tube for a polymerization reaction for 10 h. The reaction temperature is 230 °C, and the reaction pressure is 0.36 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.0, a monomer content of 8.25 wt%, a cyclic oligomer content of 1.98 wt% (where the cyclic dimer content is 0.31 wt%), and a hot water extractable content of 8.65 wt% is prepared. (2) Transport the base melt through a pipeline to a first-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature is 270 °C, and the reaction pressure is 100 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 2.5, a monomer content of 0.08 wt%, a cyclic oligomer content of 1.20 wt% (where the cyclic dimer content is 0.05 wt%), and a hot water extractable content of 0.32 wt% is obtained.

[0034] (3) The polyamide 6 end polymer can be directly spun into polyamide 6 civil yarn. The spinning temperature is 265 °C, the spinning speed is 4200 m / min, the fiber breaking strength is 4.5 cN / dtex, and the elongation at break is 24%.

[0035] Example 4 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, and zinc citrate in a ratio of 100:2:0.375:0.8. After preheating, continuously inject the mixture into the pre-polymerization reactor of a two-stage VK tube for a polymerization reaction. The reaction temperature of the pre-polymerization reactor is 220 °C, the reaction pressure is 0.20 MPa, and the reaction time is 8 h; the reaction temperature of the post-polymerization reactor is 250 °C, the reaction pressure is 0.08 MPa, and the reaction time is 6 h. Finally, a polyamide 6 base melt with a relative viscosity of 2.8, a monomer content of 7.85 wt%, a cyclic oligomer content of 2.14 wt% (where the cyclic dimer content is 0.38 wt%), and a hot water extractable content of 8.42 wt% is prepared. (2) Transport the base melt through a pipeline to a second-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature of devolatilization reactor 1 is 250 °C, the reaction pressure is 1500 Pa, the reaction temperature of devolatilization reactor 2 is 260 °C, and the reaction pressure is 80 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 3.5, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.18 wt% (where the cyclic dimer content is 0.04 wt%), and a hot water extractable content of 0.30 wt% is obtained.

[0036] (3) The polyamide 6 end-polymer can be directly spun into polyamide 6 industrial yarn. The spinning temperature is 290 °C, the spinning speed is 3200 m / min, the fiber breaking strength is 8.4 cN / dtex, and the elongation at break is 18%.

[0037] Example 5 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1) Mix fresh caprolactam, water, decanediamine, and magnesium nitrate in a ratio of 100:2:0.15:1.0, and continuously inject it into a one-stage VK tube after preheating for a polymerization reaction for 8 h, the reaction temperature is 250 °C, and the reaction pressure is 0.40 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.4, a monomer content of 8.07 wt%, a cyclic oligomer content of 2.04 wt% (where the cyclic dimer content is 0.33 wt%), and a hot water extractable content of 8.54 wt% is prepared; (2) Transport the base melt through a pipeline to a secondary vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature of devolatilization reactor 1 is 260 °C, the reaction pressure is 300 Pa, the reaction temperature of devolatilization reactor 2 is 260 °C, and the reaction pressure is 90 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 3.0, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.12 wt% (where the cyclic dimer content is 0.03 wt%), and a hot water extractable content of 0.25 wt% is prepared.

[0038] (3) The polyamide 6 end-polymer can be directly spun into polyamide 6 industrial yarn. The spinning temperature is 275 °C, the spinning speed is 3200 m / min, the fiber breaking strength is 6.0 cN / dtex, and the elongation at break is 23%.

[0039] Example 6 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, and yttrium benzoate in a ratio of 100:2:0.375:0.6, and continuously inject it into a one-stage VK tube for a polymerization reaction for 11 h, the reaction temperature is 250 °C, and the reaction pressure is 0.4 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.6, a monomer content of 7.82 wt%, a cyclic oligomer content of 2.35 wt% (where the cyclic dimer content is 0.45 wt%), and a hot water extractable content of 8.75 wt% is prepared; (2)The basic melt is transported through a pipeline to a first-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature is 260 °C, and the reaction pressure is 50 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 3.0, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.32 wt% (where the cyclic dimer content is 0.05 wt%), and a hot water extractable content of 0.35 wt% is obtained.

[0040] (3)The polyamide 6 end-polymer can be directly spun into polyamide 6 civil yarn. The spinning temperature is 275 °C, the spinning speed is 3800 m / min, the fiber breaking strength is 6.2 cN / dtex, and the elongation at break is 22%.

[0041] Example 7 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1)Fresh caprolactam, water, terephthalic acid, zinc formate, and lanthanum propionate are mixed in a ratio of 100:2:0.375:0.4:0.4, and after preheating, they are continuously injected into the pre-polymerization reactor in a two-stage VK tube for polymerization. The reaction temperature of the pre-polymerization reactor is 220 °C, the reaction pressure is 0.20 MPa, and the reaction time is 8 h; the reaction temperature of the post-polymerization reactor is 250 °C, the reaction pressure is 0.08 MPa, and the reaction time is 6 h. Finally, a polyamide 6 basic melt with a relative viscosity of 2.5, a monomer content of 7.98 wt%, a cyclic oligomer content of 2.24 wt% (where the cyclic dimer content is 0.42 wt%), and a hot water extractable content of 8.45 wt% is prepared; (2)The basic melt is transported through a pipeline to a second-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature of devolatilization reactor 1 is 250 °C, the reaction pressure is 1800 Pa, the reaction temperature of devolatilization reactor 2 is 260 °C, and the reaction pressure is 100 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 3.2, a monomer content of 0.08 wt%, a cyclic oligomer content of 1.26 wt% (where the cyclic dimer content is 0.06 wt%), and a hot water extractable content of 0.33 wt% is obtained.

[0042] (3)The polyamide 6 end-polymer can be directly spun into polyamide 6 civil yarn. The spinning temperature is 280 °C, the spinning speed is 3600 m / min, the fiber breaking strength is 6.8 cN / dtex, and the elongation at break is 20%.

[0043] Example 8 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, titanium dioxide, scandium terephthalate, and lithium nitrate in a ratio of 100:2:0.375:0.2:0.2:0.2. After preheating, continuously inject the mixture into a one-stage VK tube for a polymerization reaction for 13 h at a reaction temperature of 220 °C and a reaction pressure of 0.25 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.3, a monomer content of 8.04 wt%, a cyclic oligomer content of 2.36 wt% (where the cyclic dimer content is 0.47 wt%), and a hot water extractable content of 8.55 wt% is prepared; (2) Transport the base melt through a pipeline to a first-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature is 260 °C and the reaction pressure is 50 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 2.8, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.28 wt% (where the cyclic dimer content is 0.06 wt%), and a hot water extractable content of 0.33 wt% is prepared.

[0044] (3) The polyamide 6 end polymer can be directly spun into semi-dull polyamide 6 civil yarn. The spinning temperature is 265 °C, the spinning speed is 4000 m / min, the fiber breaking strength is 5.5 cN / dtex, and the elongation at break is 24%.

[0045] Example 9 A method for preparing high-quality polyamide 6 fibers in a short process, the specific steps are as follows: (1) Mix fresh caprolactam, water, decanediamine, terephthalic acid, and lanthanum aminohexanoate in a ratio of 100:2:0.2:0.4:1.0. After preheating, continuously inject the mixture into a one-stage VK tube for a polymerization reaction for 8 h at a reaction temperature of 250 °C and a reaction pressure of 0.40 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.0, a monomer content of 8.27 wt%, a cyclic oligomer content of 1.95 wt% (where the cyclic dimer content is 0.30 wt%), and a hot water extractable content of 8.62 wt% is prepared; (2) Transport the base melt through a pipeline to a second-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature of devolatilization reactor 1 is 260 °C and the reaction pressure is 250 Pa. The reaction temperature of devolatilization reactor 2 is 270 °C and the reaction pressure is 120 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 2.7, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.15 wt% (where the cyclic dimer content is 0.04 wt%), and a hot water extractable content of 0.23 wt% is prepared.

[0046] (3)The polyamide 6 end-polymer can be directly spun into fine-denier polyamide 6 civil yarn. The spinning temperature is 265 °C, the spinning speed is 4000 m / min, the fiber specification is 50D / 96F, the breaking strength is 6.5 cN / dtex, and the elongation at break is 22%.

[0047] Example 10 A method for preparing high-quality polyamide 6 fibers with a short process, the specific steps are as follows: (1)Mix fresh caprolactam, water, decanediamine, nickel adipate, and dysprosium isophthalate in a ratio of 100:2:0.1:0.2:0.2, and continuously inject it into a one-stage VK tube for polymerization reaction for 10 h after preheating. The reaction temperature is 260 °C, and the reaction pressure is 0.55 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.8, a monomer content of 7.82 wt%, a cyclic oligomer content of 2.38 wt% (where the cyclic dimer content is 0.46 wt%), and a hot water extractable content of 8.58 wt% is prepared; (2)Transport the base melt through a pipeline to a first-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature is 270 °C and the reaction pressure is 80 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 3.4, a monomer content of 0.06 wt%, a cyclic oligomer content of 1.35 wt% (where the cyclic dimer content is 0.07 wt%), and a hot water extractable content of 0.40 wt% is prepared.

[0048] (3)The polyamide 6 end-polymer can be directly spun into polyamide 6 industrial yarn. The spinning temperature is 280 °C, the spinning speed is 2800 m / min, the fiber breaking strength is 8.2 cN / dtex, and the elongation at break is 20%.

[0049] Perform performance characterization on the polyamide 6 base melt and polyamide 6 end-polymer of the comparative example and Examples 1 to 10, and the performance characterization table is shown in Table 1 below: Table 1 Performance characterization table of the polyamide 6 base melt and polyamide 6 end-polymer of the comparative example and Examples 1 to 10 .

[0050] The above examples only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing high-quality polyamide 6 fibers by a short process, characterized in that, It includes the following steps: (1) Caprolactam, water, a molecular weight regulator, and a cyclic oligomer inhibitor are mixed in proportion, preheated, and then added to a VK tube for polymerization reaction to prepare a polyamide 6 basic melt, where the cyclic oligomer inhibitor is a metal ion compound; (2) The polyamide 6 basic melt is transported through a pipeline to a devolatilization reaction system to remove monomers and some cyclic oligomers to prepare a polyamide 6 end polymer; (3) The polyamide 6 end polymer is directly spun to obtain high-quality polyamide 6 fibers.

2. The method for preparing high-quality polyamide 6 fibers by a short process according to claim 1, characterized in that, The cyclic oligomer inhibitor is a metal ion compound MY or a mixture of multiple metal ion compounds MY, where M is a metal cation and Y is an inorganic anion or an organic anion. M is selected from transition metal ions, lanthanide metal ions, Group IIA metal ions, and Li + , Al 3+ ; Y is selected from F - , Cl - , NO3 - , SO4 2- , PO4 3- , citrate ion, salicylate ion, 3-hydroxybutyrate ion, L-aspartate ion, lactate ion, malate ion, 2-hydroxypropionate ion, an organic monocarboxylate ion H(CH2) n COO - , benzoate ion, naphthoate ion, an organic dicarboxylate ion COO - (CH2) m COO - , terephthalate ion, phthalate ion, isophthalate ion, or naphthalenedicarboxylate ion, a saturated fatty acid root ion C x H 2x+1 COO - , an unsaturated fatty acid root ion, an aminohexanoate ion NH2C5H 10 COO - , or an amino acid root ion.

3. The method for preparing high-quality polyamide 6 fibers with a short process according to claim 1, characterized in that, The addition amount of the cyclic oligomer inhibitor is 0.01wt% - 1.0wt% of caprolactam.

4. The method for preparing high-quality polyamide 6 fibers with a short process according to claim 2, characterized in that Among them, the transition ion is Sc 3+ , Ni 2+ , Zn 2+ , Y 3+ , Zr 4+ , Ru 4+ , Rh 3+ , any one of which, the lanthanide metal ion is La 3+ , Ce 3+ , Pr 3+ , Nd 3+ , Sm 3+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Ho 3+ , Er 3+ , Tm 3+ , Lu 3+ , Yb 3+ , any one of which, the Group IIA metal ion is Be 2+ , Mg 2+ , Ca 2+ , any one of which, among which the unsaturated fatty acid ion is oleate ion C 17 H 33 COO - , linoleate ion C 17 H 31 COO - , α-linolenate ion C 17 H 29 COO - , arachidonate ion C 19 H 31 COO - , palmitoleate ion C 15 H 29 COO - , any one of which, the amino acid ion is any one of glycinate ion, alaninate ion, valinate ion, leucinate ion, isoleucinate ion, prolinate ion, phenylalaninate ion, methioninate ion, serine ion, threonine ion, asparagine ion, glutamine ion, aspartate ion, glutamate ion, cysteinate ion, tyrosine ion, selenocysteinate ion.

5. The method for preparing high-quality polyamide 6 fibers by a short process according to claim 1, characterized in that, When the polyamide 6 end polymer is directly spun to obtain polyamide 6 fibers, the spinning temperature is 245 - 300 °C, the spinning speed is 2500 - 6000 m / min, and the breaking strength of the obtained polyamide 6 fibers is ≥4.0 cN / dtex, and the elongation at break is 15 - 25%.

6. The method for preparing high-quality polyamide 6 fibers by a short process according to claim 1, characterized in that, The relative viscosity of the polyamide 6 basic melt is 1.5 - 3.5, the monomer content is less than 9.5wt%, the cyclic oligomer content is less than 2.5wt%, and the hot water extractable content is less than 10.5wt%; the relative viscosity of the polyamide 6 end polymer is 2.3 - 4.2, the monomer content is less than 0.1wt%, the cyclic oligomer content is less than 1.5wt%, and the hot water extractable content is less than 0.5wt%.

7. The method for preparing high-quality polyamide 6 fibers by a short process according to claim 1, characterized in that, The devolatilization reaction system consists of a vertical devolatilization reactor connected to a vacuum system, or is composed of two vertical devolatilization reactors connected to independent vacuum systems in series.

8. The method for preparing high-quality polyamide 6 fibers by a short process according to claim 1, characterized in that, The VK tube reactor is a one-stage reactor or a two-stage reactor.

9. The method for preparing high-quality polyamide 6 fibers by a short process according to claim 1, characterized in that, According to functional requirements, caprolactam, water, a molecular weight regulator, a cyclic oligomer inhibitor, and an additive are mixed in proportion. The additive is selected from one or more of a delustering agent, an antioxidant, a colorant, a flame retardant, an antibacterial agent, an antistatic agent, an ultraviolet protection agent, a fluorescent agent, and a far-infrared agent. The addition amount of the additive is not more than 5wt%.

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