Preparation method of high-strength nylon 6 fiber

Abstract

The application relates to the technical field of fiber material preparation, and provides a preparation method of high-strength nylon 6 fiber, which comprises the following steps: activating nylon 6 chips by using plasma; activating the reaction activity of amide bonds and increasing the density of the amide bonds; melt spinning the nylon 6 chips; multiple flow channels are arranged in a spinneret; the flow channels are in a spiral structure; the nylon 6 filaments in a molten state are subjected to low-temperature cooling and pre-drawing treatment to obtain low-crystallinity pre-oriented filaments; the low-crystallinity pre-oriented filaments are subjected to stretching and setting treatment to obtain the high-strength nylon 6 fiber. Therefore, the application improves the activity of amide bonds of the nylon 6 by plasma activation, induces the directional arrangement of molecular chains by the flow channels in the spiral structure, realizes the close packing of the molecular chains by multi-stage stretching, and provides a dense guarantee for the formation of hydrogen bonds. The three steps are progressive and synergistic, and the fiber structure is strengthened from the molecular level. The preparation process is free of fillers, the fiber structure is uniform, and the strength stability is significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of fiber material preparation technology, and particularly relates to a method for preparing high-strength nylon 6 fiber. Background Technology

[0002] Nylon 6 (polyamide 6), as a mainstream variety of polyamide fiber, is widely used in civilian and industrial applications such as industrial filter cloth, fishing lines, and high-end textile fabrics due to its mature synthesis process, controllable cost, lightweight and wear-resistant properties. However, nylon 6 fiber has insufficient mechanical strength, making it difficult to meet the core requirements of downstream industries for high strength and low deformation.

[0003] The current core method for improving the strength of nylon 6 is to add reinforcing fillers (such as glass fiber, montmorillonite, wollastonite, etc.). However, the fillers have poor compatibility with the nylon 6 matrix, are prone to agglomeration and uneven dispersion, leading to stress concentration within the fiber. This not only makes it difficult to effectively improve strength but also causes uneven strength distribution and excessive tensile strength variation coefficient.

[0004] In conclusion, the existing technology obviously has inconveniences and defects in practical use, so it is necessary to improve it. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention provides a method for preparing high-strength nylon 6 fiber, thereby solving the technical bottleneck problem of existing methods that improve the strength of nylon 6 by adding reinforcing fillers.

[0006] To address the above problems, this invention provides a method for preparing high-strength nylon 6 fiber, comprising the following steps: S1, Activation treatment of nylon 6 chips using plasma; Plasma is generated when a mixture of argon and oxygen is excited. The plasma activates the surface of the dried nylon 6 chips, thereby activating the reactivity of the amide bonds and increasing the density of amide bonds on the chip surface. The plasma generation power is 50-100W, the processing time for nylon 6 chips is 5-10min, and the processing pressure is 10-20Pa. S2, melt spinning the activated nylon 6 chips; The activated nylon 6 chips are fed into a screw extruder; The screw extruder has a spinneret, and the spinneret has multiple flow channels; the flow channels have a spiral structure, and inlets and outlets are formed on both sides of the spinneret respectively; Nylon 6 chips are heated to a molten state in a screw extruder, and the molten nylon 6 is extruded from the flow channel of the spinneret to obtain molten nylon 6 filament; screw extrusion temperature: 250-265℃, melt pressure: 13-16MPa; S3, for preparing low-crystallinity pre-oriented fibers; Molten nylon 6 yarn extruded from the spinneret channel is cooled at low temperature and pre-stretched to obtain low-crystallinity pre-oriented yarn. The low-temperature cooling method is spiral air blowing cooling, with a wind speed of 0.4~0.6m / s and a wind temperature of 25~30℃; the pre-stretch ratio is 1.2~1.5 times, and the orientation factor is 0.4~0.5; S4, low-crystallinity pre-oriented yarn is stretched and shaped to obtain high-strength nylon 6 fiber.

[0007] According to the method for preparing high-strength nylon 6 fiber of the present invention, the volume ratio of argon to oxygen in step S1 is 9:1.

[0008] The method for preparing high-strength nylon 6 fiber according to the present invention includes an activation treatment apparatus for performing the S1 step; The activation treatment device includes a reactor connected to a mixing tank for holding a mixture of argon and oxygen; the reactor is equipped with electrodes that generate plasma, and the electrodes are electrically connected to a radio frequency power supply; the reactor is also connected to a vacuum pump.

[0009] According to the preparation method of high-strength nylon 6 fiber of the present invention, before step S1, nylon 6 chips with a relative viscosity of 2.6-3.0 and a moisture content ≤600μg / g are placed in a vacuum drying oven and dried at 105℃ for 6 hours.

[0010] According to the preparation method of high-strength nylon 6 fiber of the present invention, the pitch of the flow channel is 5-8 mm, the helix angle is 30-45°, the inlet diameter of the flow channel is 1 mm, the outlet diameter is 0.3-0.4 mm, and the aspect ratio of the flow channel is 2.5-3.0.

[0011] According to the method for preparing high-strength nylon 6 fiber of the present invention, the surface of the flow channel has a silicon nitride coating.

[0012] According to the method for preparing high-strength nylon 6 fiber of the present invention, the spinning speed in step S3 is 1000-1200 m / min and the winding tension is 0.15-0.20 cN / dtex.

[0013] According to the method for preparing high-strength nylon 6 fiber of the present invention, the screw extrusion temperature includes: Zone 1: 250-255℃, Zone 2: 255-260℃, Zone 3: 260-265℃, and Zone 4: 260-265℃.

[0014] According to the method for preparing high-strength nylon 6 fiber of the present invention, the stretching treatment in step S4 is a three-stage stretching process, including... First-order tensile test, temperature: 100-120℃, draw ratio: 1.8-2.2 times, tensile rate: 50-80mm / min; Secondary tensile test: Temperature: 160-180℃, draw ratio: 2.5-3.0 times, tensile rate: 80-100mm / min; Three-stage tensile testing: Temperature: 190-210℃, draw ratio: 1.1-1.3 times.

[0015] According to the preparation method of high-strength nylon 6 fiber of the present invention, the shaping process includes winding, with a winding speed of 4500-4800 m / min and a winding tension of 0.25-0.30 cN / dtex.

[0016] In summary, this invention enhances the amide bond activity of nylon 6 through plasma activation, induces the directional alignment of molecular chains through a helical flow channel, and achieves tight molecular chain packing through multi-stage stretching, providing a "dense guarantee" for hydrogen bond formation. These three progressive and synergistic effects strengthen the fiber structure at the molecular level. The preparation process is filler-free, resulting in good fiber structure uniformity and significantly improved strength and stability. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the activation treatment device of the present invention; Figure 2 This is a schematic diagram of the spinneret structure of the present invention; Figure 3 yes Figure 2 Schematic diagram of the structure in the AA direction; Figure 4 This is a schematic diagram illustrating the principle of the nylon 6 chip activation treatment of the present invention; Figure 5 This is a three-dimensional structural diagram of the spinneret of the present invention; Figure 6 yes Figure 5 A schematic diagram of the cross-sectional structure; In the diagram: 1-reactor, 11-mixing tank, 12-electrode, 13-RF power supply, 14-oxygen cylinder, 15-argon cylinder, 16-vacuum pump; 2-spinneret, 21-flow channel, 22-inlet, 23-outlet. Detailed Implementation

[0018] See Figure 1 This invention provides a method for preparing high-strength nylon 6 fiber, comprising the following steps: S1, Activation treatment of nylon 6 chips using plasma; Plasma is generated when a mixture of argon and oxygen is excited. The plasma activates the surface of the dried nylon 6 chips, thereby activating the reactivity of amide bonds (-NH-CO-) and increasing the density of amide bonds on the chip surface. The plasma generation power is 50-100W, the processing time for nylon 6 chips is 5-10min, and the processing pressure is 10-20Pa. See Figure 4 Under the influence of an electric field, argon (Ar) and oxygen (O2) ionize to produce high-energy electrons (electrons). - Argon ions (Ar) + ), excited-state oxygen atoms (O ∗ )wait.

[0019] High-energy particles (energy range 1-10 eV) in plasma (energy range 1-10 eV), including high-energy electrons (e-), argon ions (Ar+), and excited-state oxygen atoms (O*), bombard the surface of nylon 6 chips, triggering the following reactions: Weak bond breakage: The physical adsorption layer (such as moisture and impurities) and some unstable intermolecular weak bonds (such as segments bound by van der Waals forces) on the surface of nylon 6 chips are broken, exposing new amide bonds (-NH-CO-). Amide bond activation: High-energy particles bombard the NH and CO bonds in the amide bond, reducing the bond energy and reconstructing the electron cloud distribution, significantly enhancing the reactivity of the imino (-NH-) and carbonyl (-CO-) groups.

[0020] Argon (Ar), as an inert gas, ionizes under an electric field to produce high-energy electrons (electrons). - Argon ions (Ar) + (This provides core bombardment energy and does not chemically react with the slice surface); Oxygen (O2) ionizes to produce excited-state oxygen atoms (O2). ∗ It assists in the oxidation of weak bonds on the surface and participates in the formation of active groups, thereby improving the activation efficiency of amide bonds.

[0021] After activation treatment, the nylon 6 chips of the present invention exhibit an increase in active sites and slight degradation of some surface molecular chains, forming more terminal amino (-NH2) and carboxyl (-COOH) groups. Simultaneously, excited oxygen atoms (O2) are also generated. ∗ It participates in the reaction, introducing auxiliary active sites such as hydroxyl groups (-OH) on the surface, ultimately increasing the amide bond density by 30-50%.

[0022] Preferably, the volume ratio of argon to oxygen in step S1 is 9:1.

[0023] See Figure 1 As one embodiment, it includes an activation processing apparatus for performing the S1 step; The activation treatment device includes a reactor 1, which is connected to a mixing tank 11 for holding a mixture of argon and oxygen; the reactor 1 is provided with an electrode 12 for generating plasma, which is electrically connected to a radio frequency power supply 13; the reactor 1 is also connected to a vacuum pump 16. Nylon 6 chips are placed in reactor 1, and reactor 1 is evacuated to a vacuum state using vacuum pump 16. Then, a mixture of argon and oxygen gas is introduced, and radio frequency power supply 13 (50-100W) is used to energize electrode 12 to generate plasma.

[0024] Furthermore, the mixing tank 11 is also connected to an oxygen cylinder 14 and an argon cylinder 15, and the volume ratio of argon to oxygen is adjusted by supplying gas to the mixing tank 11 through the oxygen cylinder 14 and the argon cylinder 15.

[0025] As an example, before step S1, nylon 6 chips with a relative viscosity of 2.6-3.0 and a moisture content of ≤600μg / g are placed in a vacuum drying oven and dried at 105℃ for 6 hours to remove moisture from the nylon 6 chips and avoid affecting the activation effect.

[0026] S2, melt spinning the activated nylon 6 chips; The activated nylon 6 chips are fed into a screw extruder; See Figure 2 and Figure 5 The screw extruder has a spinneret 2, and the spinneret 2 has multiple flow channels 21; combined with Figure 3 and Figure 6 The flow channel 21 has a spiral structure, and an inlet 22 and an outlet 23 are formed on both sides of the spinneret 2, respectively. Nylon 6 chips are heated to a molten state in a screw extruder, and the molten nylon 6 is extruded from the flow channel 21 of the spinneret 2 to obtain molten nylon 6 filaments; Screw extrusion temperature: 250-265℃, melt pressure: 13-16MPa; Extrusion temperature should not exceed 265℃ to avoid molecular chain degradation caused by high temperature.

[0027] Optionally, the screw extrusion temperature includes: Zone 1: 250-255℃, Zone 2: 255-260℃, Zone 3: 260-265℃, and Zone 4: 260-265℃.

[0028] During the extrusion of nylon 6 melt from flow channel 21, under the action of axial helical shear force, the nylon 6 molecular chains are oriented along the helical direction, so that the activated amide bonds (-NH-CO-) are aligned along the axial direction of the helical flow channel 21, forming hydrogen bonds with consistent orientation. Furthermore, the alignment of the amide bond (-NH-CO-) along the helical axis of the present invention is improved by more than 50%, creating conditions for directional crosslinking of hydrogen bonds.

[0029] The present invention induces the nylon 6 melt to form helically oriented molecular chains through the flow channel 21 of the spinneret 2, thereby forming oriented hydrogen bonds and strengthening the fiber structure at the molecular level.

[0030] As one embodiment, the pitch of the flow channel 21 is 5-8 mm, and the helix angle is 30-45°; the inlet diameter 22 of the flow channel 21 is 1 mm, and the outlet diameter 23 is 0.3-0.4 mm; Furthermore, the surface of the flow channel 21 has a silicon nitride coating, which reduces the coefficient of friction between the melt and the flow channel wall and ensures stable shear force.

[0031] Even better, the length-to-diameter ratio of the flow channel 21 is 2.5-3.0, and the hole spacing is 1.5-2.0 mm, to ensure uniform melt flow and consistent shear force.

[0032] Optionally, the spinneret 2 of the present invention is made of stainless steel and is formed using 3D printing technology.

[0033] S3, preparation of low-crystallinity pre-oriented yarn (POY); The molten nylon 6 yarn extruded from the flow channel 21 of the spinneret 2 is cooled at low temperature and pre-stretched to obtain a low-crystallinity pre-oriented yarn. The low-temperature cooling method is spiral air blowing cooling, with a wind speed of 0.4~0.6m / s and a wind temperature of 25~30℃; Optionally, a 10-20mm slow cooling zone can be set below the spinneret 2 for air cooling.

[0034] The pre-stretch ratio is 1.2 to 1.5 times, and the orientation factor is 0.4 to 0.5.

[0035] Even better, the air blowing direction is consistent with the flow channel 21 to control the crystallinity of the pre-oriented yarn to 8~12%; Optionally, the spinning speed in step S3 is 1000-1200 m / min, and the winding tension is 0.15-0.20 cN / dtex.

[0036] The pre-orientation process of this invention employs a low draw ratio (1.2-1.5 times) for initial drawing, which initially orients the molecular chains without forming a large amount of crystals, thus preserving space for rearrangement during subsequent stretching. The orientation factor of the pre-oriented yarn (POY) is controlled at 0.4-0.5. Compared with the stretching of highly crystalline pre-oriented yarns, the low-crystalline pre-oriented yarn of this application preserves space for molecular chain rearrangement, avoiding molecular chain slippage during stretching.

[0037] S4, low-crystallinity pre-oriented yarn (POY) is stretched and shaped to obtain high-strength nylon 6 fiber.

[0038] As one embodiment, the stretching treatment in step S4 is a three-stage stretching process, including... First-stage stretching, temperature: 100-120℃, using hot roller heating, hot roller surface temperature uniformity ±2℃; draw ratio: 1.8-2.2 times, stretching rate 50-80mm / min; guides molecular chains to further orient along the helical orientation direction, increasing crystallinity to 20%-25%.

[0039] Secondary stretching: Temperature: 160-180℃, heated roller insulation to ensure sufficient mobility of molecular chains. Draw ratio: 2.5-3.0 times, stretching rate: 80-100mm / min; forces molecular chains to be tightly aligned, increasing crystallinity to 35%-40%. At this point, the amide bonds between the helically oriented molecular chains are in full contact, forming a large number of directional hydrogen bonds.

[0040] Three-stage stretching: Temperature: 190-210℃, heated in a constant temperature oven, holding time 30-60s; stretching ratio: 1.1-1.3 times (micro-stretching); further eliminates internal stress of molecular chains, promotes close packing of molecular chains, stabilizes crystallinity at 45%-50%, and orientation factor ≥0.85.

[0041] By gradually strengthening the stretching in three stages, the orientation degree, crystallinity and hydrogen bond density of the molecular chains are simultaneously improved, so as to achieve the orderly stacking of molecular chains.

[0042] Optionally, the shaping process includes winding, with a winding speed of 4500-4800 m / min and a winding tension of 0.25-0.30 cN / dtex, to avoid fiber shrinkage leading to orientation relaxation.

[0043] The method for preparing high-strength nylon 6 fiber of the present invention enhances the amide bond activity of nylon 6 through plasma activation, providing an "active basis" for hydrogen bond formation. The helical flow channel 21 induces the directional alignment of molecular chains, providing "orientation conditions" for hydrogen bond formation. Multi-stage stretching achieves tight packing of molecular chains, providing a "dense guarantee" for hydrogen bond formation. These three progressive and synergistic effects strengthen the fiber structure at the molecular level. The nylon 6 fiber prepared by the present invention has a breaking strength ≥9.0 cN / dtex, significantly higher than that of nylon 6 fibers prepared by existing technologies (breaking strength <6.0 cN / dtex).

[0044] The preparation process relies on filler-free materials, avoiding problems such as uneven dispersion and spinneret clogging caused by adding reinforcing fillers; the fiber structure has good uniformity and the strength stability is significantly improved.

[0045] The process of this invention is highly controllable, with clear process parameters for each step and low difficulty in equipment modification (only requiring the customization of a spinneret with a spiral structure 21 and the addition of a plasma activation treatment device, etc.), making it suitable for industrial production.

[0046] To illustrate the technical effects in detail, this invention uses the aforementioned method, changing the parameters of certain steps, to prepare multiple example samples. Simultaneously, to facilitate comparison of the technical effects, comparative example samples were prepared using the same raw materials and the parameters of Example 1. Specifically: Comparative Example 1: The activation treatment in step S1 is not performed, and the spinneret for melt spinning in step S2 does not have the spiral flow channel 21 of the present invention; the parameters of the remaining steps are the same as those in Example 1.

[0047] Comparative Example 2: The activation treatment in step S1 was not performed, and the parameters for the remaining steps were the same as in Example 1.

[0048] The breaking strength of the fiber samples in each embodiment and comparative example was tested. Specific experimental parameters and test results are shown in Table 1. (Note: Table 1 only lists the varied parameters; the same parts and steps can be found above and will not be repeated here.) The testing process for the breaking strength of this invention follows the provisions of the national standard GB / T 14344 "Test Method for Tensile Properties of Chemical Fiber Filaments".

[0049] Table 1. Parameters and test results for each embodiment and comparative example. .

[0050] Comparing the tensile strength values ​​of the embodiments and comparative examples, it can be seen that the tensile strength of the nylon 6 fiber prepared by the method of the present invention is significantly improved. This demonstrates that the plasma activation, helical flow channel, and multi-stage stretching of the present invention work synergistically to strengthen the fiber structure at the molecular level.

[0051] Comparing the fracture strength values ​​of Comparative Example 1 and Comparative Example 2, it can be seen that although neither underwent plasma activation treatment, the fracture strength of Comparative Example 2 was improved to a certain extent. This demonstrates that the helical flow channel 21 of the spinneret 2 of the present invention induces the nylon 6 melt to form helically oriented molecular chains, thereby forming oriented hydrogen bonds and strengthening the fiber structure at the molecular level.

[0052] In summary, this invention provides a method for preparing high-strength nylon 6 fiber. Plasma activation enhances the amide bond activity of nylon 6, a helical flow channel induces the directional alignment of molecular chains, and multi-stage stretching achieves tight molecular chain packing, providing a "dense guarantee" for hydrogen bond formation. These three progressively synergistically strengthen the fiber structure at the molecular level. The preparation process is filler-free, resulting in good fiber structural uniformity and significantly improved strength and stability.

[0053] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A method for preparing high-strength nylon 6 fiber, characterized in that, Includes the following steps: S1, Activation treatment of nylon 6 chips using plasma; Plasma is generated when a mixture of argon and oxygen is excited. The plasma activates the surface of the dried nylon 6 chips, thereby activating the reactivity of the amide bonds and increasing the density of amide bonds on the chip surface. The plasma generation power is 50-100W, the processing time for nylon 6 chips is 5-10min, and the processing pressure is 10-20Pa. S2, melt spinning the activated nylon 6 chips; The activated nylon 6 chips are fed into a screw extruder; The screw extruder has a spinneret, and the spinneret has multiple flow channels; the flow channels have a spiral structure, and inlets and outlets are formed on both sides of the spinneret respectively; Nylon 6 chips are heated to a molten state in a screw extruder, and the molten nylon 6 is extruded from the flow channel of the spinneret to obtain molten nylon 6 filaments; Screw extrusion temperature: 250-265℃, melt pressure: 13-16MPa; S3, for preparing low-crystallinity pre-oriented fibers; Molten nylon 6 yarn extruded from the spinneret channel is cooled at low temperature and pre-stretched to obtain low-crystallinity pre-oriented yarn. The low-temperature cooling method is spiral air blowing cooling, with a wind speed of 0.4~0.6m / s and a wind temperature of 25~30℃; the pre-stretch ratio is 1.2~1.5 times, and the orientation factor is 0.4~0.5; S4, low-crystallinity pre-oriented yarn is stretched and shaped to obtain high-strength nylon 6 fiber.

2. The method for preparing high-strength nylon 6 fiber as described in claim 1, characterized in that, The volume ratio of argon to oxygen in step S1 is 9:

1.

3. The method for preparing high-strength nylon 6 fiber as described in claim 1, characterized in that, Includes an activation processing device for performing step S1; The activation treatment device includes a reactor connected to a mixing tank for holding a mixture of argon and oxygen; the reactor is equipped with electrodes that generate plasma, and the electrodes are electrically connected to a radio frequency power supply; the reactor is also connected to a vacuum pump.

4. The method for preparing high-strength nylon 6 fiber as described in claim 1, characterized in that, Before step S1, nylon 6 chips with a relative viscosity of 2.6-3.0 and a moisture content of ≤600μg / g are placed in a vacuum drying oven and dried at 105℃ for 6 hours.

5. The method for preparing high-strength nylon 6 fiber as described in claim 1, characterized in that, The flow channel has a pitch of 5-8 mm and a helix angle of 30-45°; the inlet diameter of the flow channel is 1 mm and the outlet diameter is 0.3-0.4 mm; the length-to-diameter ratio of the flow channel is 2.5-3.

0.

6. The method for preparing high-strength nylon 6 fiber as described in claim 1, characterized in that, The surface of the flow channel has a silicon nitride coating.

7. The method for preparing high-strength nylon 6 fiber as described in claim 1, characterized in that, The spinning speed in step S3 is 1000-1200 m / min, and the winding tension is 0.15-0.20 cN / dtex.

8. The method for preparing high-strength nylon 6 fiber as described in claim 1, characterized in that, The screw extrusion temperatures include: Zone 1: 250-255℃, Zone 2: 255-260℃, Zone 3: 260-265℃, and Zone 4: 260-265℃.

9. The method for preparing high-strength nylon 6 fiber according to any one of claims 1 to 8, characterized in that, The stretching process in step S4 is a three-stage stretching process, including... First-order tensile test, temperature: 100-120℃, draw ratio: 1.8-2.2 times, tensile rate: 50-80mm / min; Secondary tension: Temperature: 160-180℃, draw ratio: 2.5-3.0 times, stretching rate: 80-100mm / min; Three-stage tensile testing: Temperature: 190-210℃, draw ratio: 1.1-1.3 times.

10. The method for preparing high-strength nylon 6 fiber as described in claim 9, characterized in that, The shaping process includes winding, with a winding speed of 4500-4800 m / min and a winding tension of 0.25-0.30 cN / dtex.

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