Polyester fiber directional stretching production process for improving tensile strength

Abstract

The invention relates to the technical field of polyester fiber production, and discloses a polyester fiber directional stretching production process for improving tensile strength, which comprises the following steps: S1, raw material preparation: slicing polyester by an underwater pelletizing system, then adding an antioxidant and a heat stabilizer, and carrying out plasma grafting modification; s2, melt extrusion: mixing the raw materials by using an extruder, and monitoring melt parameters by using a melt rheometer; s3, cooling and forming: cooling the melt by using an air suspension cooling technology; s4, directional stretching: stretching the solidified melt by adopting a gradient temperature control technology, and monitoring the surface temperature of the fiber in real time in combination with infrared thermal imaging. According to the invention, the antioxidant and the heat stabilizer are added after the polyester is sliced through the underwater pelletizing system, so that the oxidation resistance and the heat degradation resistance of the polyester fiber can be enhanced, and the problem that the performance is reduced due to the fact that the traditional polyester fiber is easy to generate fatigue damage under the condition of repeated stress is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of polyester fiber production, specifically to a process for the oriented stretching production of polyester fiber with improved tensile strength. Background Art

[0002] Polyester fiber is a synthetic fiber obtained by chemically polycondensing organic dibasic acids and diols to form polyester and then subjecting it to spinning processing. Among them, polyethylene terephthalate (PET) fiber is the most common. Polyester fiber has many excellent properties. It has high strength. During the stretching process, the molecular chains are highly oriented, enabling it to withstand large external forces and not easily break. It is often used in manufacturing ropes, industrial fabrics, etc. It has good elasticity, similar to wool. After the fabric is kneaded multiple times, it can still quickly return to its original shape and has good shape retention. It is not easily deformed after washing, which makes it widely used in the clothing field. Polyester fiber also has good abrasion resistance, superior to natural fibers and some chemical fibers, and has strong durability. At the same time, it has low moisture absorption. Clothing is not easily mildewed and deteriorated due to moisture absorption, and it dries quickly after washing, providing a comfortable wearing experience. In addition, polyester fiber has high chemical stability, is resistant to acids and alkalis, and is resistant to light, and can maintain stable performance for a long time in different environments. Due to its excellent properties, polyester fiber has extremely wide applications. In the clothing industry, it is often blended with natural fibers to improve the quality of clothing; in the home textile field, it is used to make curtains, bedding, etc.; in industry, it can be used to manufacture tire cord, conveyor belts, etc.

[0003] Traditional polyester fiber is prone to fatigue damage under repeated stress, thus resulting in a problem of performance degradation. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a process for the oriented stretching production of polyester fiber with improved tensile strength, which solves the problem that traditional polyester fiber is prone to fatigue damage under repeated stress, thus resulting in performance degradation.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A process for the oriented stretching production of polyester fiber with improved tensile strength, comprising the following steps:

[0006] S1. Raw material preparation: The underwater pelletizing system slices the polyester, then adds antioxidants and heat stabilizers, and performs plasma grafting modification;

[0007] S2. Melting and extrusion: The extruder is used to knead the raw materials, and at the same time, a melt rheometer is used to monitor the melt parameters;

[0008] S3. Cooling and forming: The air suspension cooling technology is used to cool the melt;

[0009] S4. Oriented stretching: The solidified melt is stretched using gradient temperature control technology, while the surface temperature of the fiber is monitored in real time by infrared thermal imaging. A closed-loop feedback system is adopted, and the fiber fracture signal is monitored by an on-line acoustic emission sensor.

[0010] S5. Heat setting: The fiber is heat set using a hot air circulation oven, and at the same time, inert gas protection is used for heat setting.

[0011] S6. Winding: An advanced tension control system is adopted to automatically adjust the winding tension according to the real-time state of the fiber.

[0012] S7. Post-treatment: The physical properties of the fiber are tested, and after meeting the standards, it is stored in the warehouse.

[0013] Preferably, in the S1, the underwater pelletizing system uses a variable-frequency motor to drive the cutter, controls the cutter speed at 500 - 3000 rpm, controls the cutting temperature at 280 - 310 °C, controls the pelletizing speed at 500 - 2000 kg / h, and controls the particle size uniformity at ±0.2 mm.

[0014] Preferably, in the S2, the extruder uses a barrier screw with a pin mixing section, controls the temperature of the feeding section at 230 - 240 °C, the temperature of the compression section at 250 - 260 °C, the temperature of the metering section at 265 - 275 °C, and controls the screw speed at 30 - 80 r / min.

[0015] Preferably, in the S3, the fan air speed is controlled at 15 - 30 m / s, and the temperature of the cooling air is at 15 - 25 °C.

[0016] Preferably, in the S4, the gradient temperature control technology sets the initial stretching temperature at 100 - 110 °C, finally raises the temperature to 130 - 140 °C, and controls the heating rate at 1 - 3 °C per minute.

[0017] Preferably, in the S5, the final temperature of the hot air circulation oven is controlled at 170 - 190 °C, the heating rate of the hot air circulation oven is controlled at 5 - 10 °C per minute, the inert gas is nitrogen, the flow rate of nitrogen input is controlled at 5 - 10 cubic meters per minute, and it is kept at a constant temperature for 1 - 3 minutes after reaching the final temperature.

[0018] Preferably, in the S6, the winding tension is controlled at 5 - 15 cN, and the winding speed is controlled at 500 - 1000 m / min.

[0019] Preferably, in the S7, the physical properties include thermal stability, elongation at break, linear density, moisture regain, and crimp properties.

[0020] The present invention provides a polyester fiber oriented stretching production process for improving the tensile strength, having the following beneficial effects:

[0021] 1. In the present invention, by adding antioxidants and heat stabilizers to the polyester chips through an underwater pelletizing system, the ability of the polyester fiber to resist oxidation and thermal degradation can be enhanced, reducing the performance deterioration caused by oxidation and heat during use. At the same time, plasma grafting modification can introduce new functional groups or polymer chains on the surface of the polyester fiber, improving the surface properties and structure of the fiber, enhancing the overall performance of the fiber, and helping to reduce the generation of fatigue damage, thus solving the problem that traditional polyester fibers are prone to fatigue damage under repeated stress, resulting in performance degradation.

[0022] 2. In the present invention, by precisely controlling the temperature change during the stretching process through gradient temperature control technology, combined with infrared thermal imaging monitoring and a closed-loop feedback system, as well as the monitoring of fiber fracture signals by an on-line acoustic emission sensor, the fiber molecular chains can be highly oriented along the stretching direction, significantly improving the tensile strength and structural regularity of the fiber and reducing the fracture risk during the stretching process.

[0023] 3. In the present invention, by combining a hot air circulation oven with inert gas protection for heat setting and controlling the final temperature, heating rate, nitrogen flow rate, and constant temperature time, the internal stress in the fiber can be eliminated, the fiber morphology and structure can be stabilized, the dimensional stability and mechanical properties of the fiber can be further improved, and its performance stability under repeated stress can be enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flowchart of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0026] Please refer to the attached Figure 1 , the embodiment of the present invention provides a polyester fiber directional stretching production process for improving tensile strength, including the following steps:

[0027] S1. Raw material preparation: The underwater pelletizing system slices the polyester, then adds antioxidants and heat stabilizers, and uses plasma grafting modification;

[0028] S2. Melting and extrusion: The extruder is used to knead the raw materials, and at the same time, a melt rheometer is used to monitor the melt parameters;

[0029] S3. Cooling and forming: The air suspension cooling technology is used to cool the melt;

[0030] S4. Oriented stretching: The solidified melt is stretched using gradient temperature control technology. Meanwhile, the surface temperature of the fiber is monitored in real time by infrared thermal imaging. A closed-loop feedback system is adopted, and the fiber breakage signal is monitored through an on-line acoustic emission sensor.

[0031] S5. Heat setting: The fiber is heat set using a hot air circulation oven, and inert gas protection is adopted during heat setting.

[0032] S6. Winding: An advanced tension control system is adopted to automatically adjust the winding tension according to the real-time state of the fiber.

[0033] S7. Post-treatment: The physical properties of the fiber are tested, and after meeting the standards, it is stored in the warehouse.

[0034] Specifically, by adding antioxidants, the oxidation reaction of polyester during processing and use can be inhibited, the breakage and degradation of polyester molecular chains can be delayed, the material can be prevented from turning yellow and brittle due to oxidation, and the service life of polyester fiber can be extended; by adding heat stabilizers, the molecular structure of polyester can be stabilized under high-temperature conditions, and phenomena such as the intensification of molecular chain movement and depolymerization caused by heat can be reduced, so that polyester can maintain stable performance in high-temperature processing and use environments, and the performance such as tensile strength can be prevented from being reduced due to thermal degradation; by adopting plasma grafting modification, new functional groups or polymer chains can be introduced, such as hydrophilic groups, functional polymers, etc., which can improve the surface properties of polyester fiber, such as hydrophilicity, dyeability, biocompatibility, etc. By forming a grafting layer on the fiber surface, the interaction force between fibers can be increased, the integrity and stability of the fiber aggregate can be improved, the surface structure of the grafted modified polyester fiber is optimized, and it can better resist the action of environmental factors such as light, heat, and oxygen, slow down the aging process, and maintain the stable performance of the fiber.

[0035] In S1, the underwater pelletizing system uses a variable-frequency motor to drive the cutter, controls the cutter speed at 500 - 3000 rpm, controls the cutting temperature at 280 - 310 °C, controls the pelletizing speed at 500 - 2000 kg / h, and controls the particle size uniformity at ±0.2 mm.

[0036] Specifically, with a cutter speed of 500 - 3000 rpm, a relatively low speed such as around 500 rpm can make the action of the cutter on polyester milder. It is suitable for preliminary rough cutting or processing softer polyester materials, reducing material heating and molecular chain breakage caused by excessive shearing, and is beneficial to maintaining the basic properties of polyester. While a higher speed of 3000 rpm can provide sufficient shear force when processing polyester with higher hardness or viscosity, ensuring the cutting efficiency and quality, enabling polyester to be quickly and evenly cut into the required granular shape, and improving production efficiency; a cutting temperature of 280 - 310 °C. Within this temperature range, polyester is in a suitable softening state. At 280 °C, polyester has a certain softness, and the resistance received by the cutter during cutting is small, which can reduce cutter wear. At the same time, it can reduce the irregularity of particle shape caused by excessive cutting force. At 310 °C, the fluidity of polyester is better, which helps the cutter to cut more smoothly, making the cutting surface smoother, reducing burrs and defects on the particle surface, and improving the appearance quality of the particles. Moreover, this temperature range can ensure that polyester will not be difficult to cut due to too low temperature during the cutting process, nor will it undergo excessive degradation or color change due to too high temperature, maintaining the chemical stability of polyester; a pelletizing speed of 500 - 2000 kg / h. A lower pelletizing speed of 500 kg / h is suitable for situations with extremely high requirements for particle size uniformity and product quality, or when processing some special formulations and relatively difficult-to-cut polyesters. It can make the cutting process more delicate and stable, ensuring that each particle can be fully and evenly cut. A higher pelletizing speed of 2000 kg / h can meet the needs of large-scale production. On the premise of ensuring a certain product quality, it can significantly increase production output, reduce production costs, and improve production efficiency; the particle size uniformity is controlled within ±0.2 mm, which can ensure that the polyester particles are basically the same size. This is beneficial to the subsequent melting and mixing processes in the extruder, making the polyester particles heat evenly, with similar melting time and degree, thereby improving the uniformity and stability of the melt.

[0037] In S2, the extruder adopts a barrier screw with a pin mixing section, controlling the temperature of the feeding section at 230 - 240 °C, the temperature of the compression section at 250 - 260 °C, the temperature of the metering section at 265 - 275 °C, and controlling the screw speed at 30 - 80 r / min.

[0038] Specifically, through the barrier screw, the material can be efficiently sheared and divided between different flow channels under the rotation of the screw, promoting the mixing and dispersion of the material, fully mixing the polyester chips with additives such as antioxidants and heat stabilizers, and ensuring uniform distribution of each component; through the pin mixing section, the shearing and stirring effects on the material can be further enhanced. When the material passes through the pin area, it is subjected to stronger disturbances, which can break the agglomerates in the material, refine the material particles, improve the melting uniformity of the material, and enable the polyester chips to be more fully fused in the molten state, laying a foundation for the subsequent production of polyester fibers with stable quality; through the feeding section with a temperature of 230 - 240 °C, this temperature range can appropriately preheat the polyester particles in the initial stage of entering the extruder, making them start to soften but not completely melt, maintaining a certain solid form, which is conducive to the smooth forward transportation of the particles under the push of the screw, and avoiding the slippage phenomenon caused by premature melting of the material due to too high temperature; through the compression section with a temperature of 250 - 260 °C, as the material advances to the compression section, the temperature rises to 250 - 260 °C, and the polyester particles further soften and gradually start to melt. This temperature can provide sufficient energy for the material, enabling its volume to gradually decrease and density to increase under the compression of the screw, while promoting the mutual friction and shearing between the materials, accelerating the melting process, and improving the melting efficiency; through the metering section with a temperature of 265 - 275 °C, it can ensure that the material is completely melted, reaching a good flow state, facilitating the accurate metering and control of the extrusion volume of the material; by controlling the screw speed at 30 - 80 r / min, not only can the material have a longer residence time in the extruder, which is conducive to the full melting, mixing, and plasticization of the material, but also can improve the conveying efficiency of the material and increase the output of the extruder, meeting the requirements of large-scale production on the premise of ensuring a certain mixing and melting effect.

[0039] In S3, the fan wind speed is controlled at 15 - 30 m / s, and the temperature of the cooling air is 15 - 25 °C.

[0040] Specifically, by controlling the fan wind speed at 15 - 30 m / s, the heat on the surface of the melt can be quickly removed. For melts with high extrusion speeds or large diameters, sufficient wind speed can ensure the formation of a stable fiber structure in a short time. The cooling air can cover the entire surface of the melt, making the cooling rates of each part of the melt basically the same, thus ensuring the uniformity of the structure and properties of the fiber in the cross-section and reducing internal stress and quality defects caused by uneven cooling; by the temperature of the cooling air being 15 - 25 °C, during the cooling process of the melt, the molecular chains have enough time to carry out a certain degree of ordered arrangement to form a good crystalline structure, which can enable the fiber to maintain a relatively stable size and shape during the shrinkage process and improve the qualified rate of the product.

[0041] In S4, the gradient temperature control technology sets the initial stretching temperature to be controlled at 100 - 110 °C, and finally raises the temperature to 130 - 140 °C, with the heating rate controlled at 1 - 3 °C per minute.

[0042] Specifically, by controlling the initial stretching temperature at 100 - 110 °C, the molecular chains can undergo relative sliding and rearrangement under a relatively small external force, avoiding the stiffness of the molecular chains caused by too low temperature, which makes it difficult to achieve effective orientation, thus laying a foundation for improving the fiber stretching strength. It can also keep the fiber with a certain rigidity and strength at the beginning of stretching, reducing the risk of fiber breakage during the stretching process, helping to control the deformation speed of the fiber, making the stretching process smoother, and avoiding the destruction of the internal structure of the fiber due to instantaneous over-stretching; by finally raising the temperature to 130 - 140 °C, the activity of the molecular chains is further enhanced. Under the action of the stretching force, the molecular chains can be more fully oriented along the stretching direction, enabling the fiber to better transfer stress and resist deformation when stressed. This temperature range is conducive to the formation of a more perfect crystalline structure of the polyester molecular chains, and the increase in crystallinity helps to enhance the mechanical properties of the fiber, improving the hardness, wear resistance, and dimensional stability of the fiber; by controlling the heating rate at 1 - 3 °C per minute, the molecular chains have enough time to be oriented during the stretching process, and at the same time can promptly promote the formation of crystallization, making the temperature distribution inside the fiber more uniform, reducing the internal stress generated by the temperature gradient, and further enabling the fiber to maintain the structural stability during the stretching and heating processes, improving the quality and performance of the fiber.

[0043] In S5, the final temperature of the hot air circulation oven is controlled at 170 - 190 °C, the heating rate of the hot air circulation oven is controlled at 5 - 10 °C per minute, the inert gas is nitrogen, and the flow rate of nitrogen input is controlled at 5 - 10 cubic meters per minute. After reaching the final temperature, keep it at a constant temperature for 1 - 3 minutes.

[0044] Specifically, by controlling the final temperature of the hot air circulation oven at 170-190°C, the molecular chain segments inside the polyester fiber have sufficient energy to relax and adjust, which can effectively eliminate the internal stress generated by the fiber during directional stretching, making the internal structure of the fiber more stable, improving the dimensional stability of the fiber and the uniformity of the mechanical properties, and at the same time helping to further improve the crystallization of the polyester fiber, increase the crystallization area, and increase the crystallinity, thereby enhancing the fiber's strength, hardness, wear resistance and other properties, and improving the fiber's quality and performance; by heating at a rate of 5-10°C per minute, it can ensure that the heat in the hot air circulation oven is evenly transferred to the polyester fiber, so that all parts of the fiber are heated evenly, avoiding uneven fiber structure due to local overheating or overcooling, thereby ensuring the consistency and stability of the overall fiber performance, and can also make the movement and rearrangement of the molecular chain proceed in an orderly manner, so that the molecular chain will not move too violently due to excessive heating and fail to form a stable structure, nor will it be inefficient due to excessive heating, which is conducive to achieving the best arrangement of the molecular chain and crystallization during the heat setting process. The inert gas nitrogen can effectively isolate oxygen in the air, prevent oxidation reaction of polyester fiber during high-temperature heat setting, and avoid oxidation damage of fiber molecular chain, so as to maintain the original performance of fiber and improve the service life and stability of fiber. The flow of nitrogen can assist hot air circulation, make the temperature distribution in the oven more uniform, ensure that all parts of fiber can be in a stable and suitable temperature environment during heat setting, which is conducive to improving heat setting effect and consistency of fiber quality. During heat setting, polyester fiber may release some low molecular volatiles, and the flow of nitrogen can take these volatiles out of the oven in time to prevent them from accumulating on the fiber surface or inside, affecting the performance and appearance quality of fiber. After reaching the final temperature, the constant temperature can be maintained for 1-3 minutes, so that polyester fiber can fully complete the relaxation, rearrangement and crystallization of molecular chain in a stable high temperature environment, ensure the full realization of heat setting effect, make the structure and performance of fiber reach a stable state, and improve the dimensional stability, mechanical properties and heat resistance of fiber.

[0045] In S6, the winding tension is controlled at 5-15 cN, and the winding speed is controlled at 500-1000 m / min.

[0046] Specifically, by controlling the winding tension at 5-15cN, the fibers can maintain good arrangement and tightness during the winding process, preventing the fibers from being too loose and slipping or deforming, and maintaining the structure of the fibers formed in processes such as stretching and heat setting; by controlling the winding speed at 500-1000m / min, a higher winding output can be achieved while ensuring product quality, meeting the needs of large-scale production and improving overall production efficiency.

[0047] In S7, the physical properties include thermal stability, elongation at break, linear density, moisture regain, and crimp properties.

[0048] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyester fiber directional stretching production process for improving tensile strength, characterized by: The following steps are involved: S1. Raw material preparation: The underwater pelletizing system slices the polyester, then adds antioxidants and heat stabilizers, and uses plasma grafting modification; S2, melt extrusion: the raw materials are mixed by an extruder, and melt rheometer is used to monitor melt parameters; S3, cooling molding: using air suspension cooling technology to cool the melt; S4, directional stretching: Gradient temperature control technology is used to stretch the solidified melt, and infrared thermal imaging is combined to monitor the fiber surface temperature in real time. A closed-loop feedback system is used to monitor the fiber breakage signal through an online acoustic emission sensor; S5. Heat setting: Use hot air circulation oven to heat set the fiber, and use inert gas to protect the heat setting; S6, Winding: Using advanced tension control system, automatically adjust the winding tension according to the real-time status of the fiber; S7, post-processing: Test the physical properties of the fiber and store it in warehouse after it meets the standards.

2. The polyester fiber directional stretching production process for improving tensile strength according to claim 1, characterized in that: In S1, the underwater pelletizing system uses a variable frequency motor to drive the cutter, controls the cutter speed to 500-3000rpm, controls the cutting temperature to 280-310°C, controls the pelletizing speed to 500-2000kg / h, and controls the particle size uniformity to ±0.2mm.

3. The polyester fiber directional stretching production process for improving tensile strength according to claim 1, characterized in that: In the S2, the extruder adopts a barrier screw with a pin mixing section, the feeding section temperature is controlled at 230-240°C, the compression section temperature is controlled at 250-260°C, the metering section temperature is 265-275°C, and the screw speed is controlled at 30-80r / min.

4. The polyester fiber directional stretching production process for improving tensile strength according to claim 1, characterized in that: In S3, the wind speed of the fan is controlled at 15-30 m / s, and the temperature of the cooling air is controlled at 15-25°C.

5. The polyester fiber directional stretching production process for improving tensile strength according to claim 1, characterized in that: In S4, the gradient temperature control technology sets the initial stretching temperature to be controlled at 100-110°C, and finally the temperature is raised to 130-140°C, and the heating rate is controlled at 1-3°C per minute.

6. The polyester fiber directional stretching production process for improving tensile strength according to claim 1, characterized in that: In S5, the final temperature of the hot air circulation oven is controlled at 170-190°C, the heating rate of the hot air circulation oven is controlled at 5-10°C per minute, the inert gas is nitrogen, the flow rate of nitrogen input is controlled at 5-10 cubic meters per minute, and the constant temperature is maintained for 1-3 minutes after reaching the final temperature.

7. The polyester fiber directional stretching production process for improving tensile strength according to claim 1, characterized in that: In S6, the winding tension is controlled at 5-15 cN, and the winding speed is controlled at 500-1000 m / min.

8. The polyester fiber directional stretching production process for improving tensile strength according to claim 1, characterized in that: In S7, the physical properties include thermal stability, elongation at break, linear density, moisture regain and curling properties.

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