Preparation process of low-melting-point polyester FDY (fully drawn yarn)

Abstract

The invention relates to the technical field of chemical fibers, in particular to a low-melting-point polyester FDY (fully drawn yarn) preparation process which comprises the following steps: preparing raw materials, selecting polyester chips and a low-molecular-weight polyester copolymer, mixing the polyester chips and the low-molecular-weight polyester copolymer according to a ratio, melting and blending the polyester chips and the low-molecular-weight polyester copolymer with the additive amount of 5-8wt% and the intrinsic viscosity of 0.65-0.70 dL / g, and performing extrusion molding to obtain the low-melting-point polyester FDY. And putting the mixed raw materials into a screw extruder, and carrying out melt blending and spinning treatment at 250-260 DEG C. According to the low-melting-point polyester FDY and the preparation method thereof disclosed by the invention, a component regulation end is arranged, so that a synergistic effect mechanism of a polyester matrix and a low-melting-point copolymer is accurately matched in a preparation process of the low-melting-point polyester FDY, and the uniformity of melt components is ensured; meanwhile, the copolymerization structure design directivity acts on molecular chain regularity regulation and control, thermal stability fluctuation in the spinning process is inhibited in real time, it is guaranteed that the continuous forming capacity of fibers is maintained under the high-speed spinning condition, and the stability of a production line is improved.

Description

Technical Field

[0001] This invention relates to the field of chemical fiber technology, and in particular to a process for preparing low-melting-point polyester FDY. Background Technology

[0002] Chemical fibers are fibers with textile properties made from natural and artificially synthesized polymers as raw materials, through processes such as preparing spinning solutions, spinning, and post-treatment.

[0003] The preparation process of low-melting-point polyester FDY is one of the key technologies in the field of chemical fiber production. It aims to achieve precise control of the fiber melting point by optimizing the raw material formula and processing conditions. This is one of the core indicators to meet the needs of high-end applications such as thermal bonding and composite textiles.

[0004] Currently, conventional polyester FDY production uses homopolymer polyester chips, which are then processed through high-temperature melt spinning and multi-stage drawing processes to produce highly oriented fibers, ensuring that the fibers possess high strength and high modulus properties. In existing technologies, due to the high regularity of the homopolymer polyester molecular chain structure, its melting point is usually higher than 260℃, which cannot meet the processing requirements of low-melting-point fibers. When low-melting-point copolymers are directly added for modification, the compatibility difference between the copolymer and the polyester matrix will cause fluctuations in melt viscosity, resulting in an increased breakage rate during the spinning process and a decrease in fiber strength. At the same time, during the cooling and molding stage, the traditional constant-temperature side-blowing method is difficult to suppress the abnormal crystallization rate caused by the introduction of copolymers, which will cause uneven fiber core-sheath structure and further aggravate the risk of breakage.

[0005] Therefore, a low-melting-point polyester FDY preparation process is proposed to solve the above problems. Summary of the Invention

[0006] The main objective of this invention is to provide a process for preparing low-melting-point polyester FDY to solve the problems mentioned in the background above.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a process for preparing low-melting-point polyester FDY, comprising the following steps: Step 1: Raw material preparation. Select polyester chips and low molecular weight polyester copolymer, and mix them in a certain proportion. The amount of low molecular weight polyester copolymer added is 5-8 wt%, and the intrinsic viscosity of the mixture is 0.65-0.70 dL / g. Step 2: Melt blending. Place the mixed raw materials in a screw extruder and melt blend at 250-260℃. Step 3: Spinning process. The melt after molten blending is transported to the spinning box, and the temperature of the box is controlled at 265℃. The nascent fibers are extruded through the spinneret. Step 4: Gradient cooling. The extruded nascent fibers are cooled by gradient side blowing, with the air temperature decreasing from 25℃ to 20℃, the air velocity being 0.4m / s, and the relative humidity being 65%. Step 5: Oiling. The cooled fibers are oiled with an oil concentration of 12% and an oiling rate of 0.8%. Step 6: Drafting treatment. The oiled fibers are fed into the drafting zone, which includes a first hot roller and a second hot roller. The temperature of the first hot roller is 70-75℃ and the speed is 2800m / min. The temperature of the second hot roller is 120-125℃ and the speed is 3200m / min. Step 7: Winding and shaping. The drawn fibers are wound at a speed of 3300 m / min and the tension is controlled at 8-10 cN. The residence time of the melt blending step shall not exceed 15 minutes, the melt temperature fluctuation shall be controlled within ±2℃, and the winding tension deviation shall not exceed 5%, so as to reduce the melting point to below 160℃, increase the fiber strength to greater than 3.5 cN / dtex, reduce the breakage rate by 20%, and reduce energy consumption by 15%. Preferably, the raw material preparation in step one includes drying the polyester chips and low molecular weight polyester copolymer at a temperature of 80°C for 4 hours to ensure that the moisture content of the raw materials is below 0.01% and to prevent fluctuations in melt viscosity.

[0008] Preferably, in step one, the mixing mass ratio of polyester chips to low molecular weight polyester copolymer is 95:5 to 92:8, preferably 95:5. The low molecular weight polyester copolymer is a copolyester of terephthalic acid and adipic acid and similar low molecular weight polyesters, which lowers the melting point by reducing the regularity of the molecular chain.

[0009] Preferably, in step two, the melt blending is carried out in a screw extruder, with the temperature of each zone of the extruder set to 250-260℃, the temperature deviation of each zone not exceeding ±2℃, and the residence time controlled to 10-15 minutes, in order to suppress the widening of the molecular weight distribution and avoid abnormal fluctuations in melt viscosity.

[0010] Preferably, the spinning process in step three includes a spinneret extrusion process, with the spinneret pressure set at 12MPa±0.5MPa, the extrusion speed controlled at 300-400m / min, and the melt precisely delivered by a metering pump with a delivery accuracy deviation of less than 1% to reduce the risk of fiber breakage.

[0011] Preferably, in step four, the gradient cooling adopts a side-blowing system with a wind speed of 0.4m / s ± 0.05m / s, a wind temperature decrease gradient of 1℃ / min, an initial wind temperature of 25℃, a final wind temperature of 20℃, and a relative humidity of 65% ± 5%, so as to uniformly cool the fiber surface and inhibit abnormal growth of crystallinity.

[0012] Preferably, in step five, the oiling agent used is a water-soluble oiling agent with a concentration range of 12% ± 0.5% and an oiling rate controlled at 0.8% ± 0.1%. The oiling methods are spraying and roller coating to ensure the lubricity of the fiber surface and reduce frictional damage during the stretching process.

[0013] Preferably, the stretching process in step six further includes a three-stage hot roller step-stretching as an alternative, wherein the temperature of the first-stage hot roller is 70-75℃ and the speed is 2500-2800m / min; the temperature of the second-stage hot roller is 100-110℃ and the speed is 3000-3200m / min; and the temperature of the third-stage hot roller is 120-125℃ and the speed is 3200-3300m / min. Through low-temperature high-speed stretching and synergistic copolymerization, the fiber structure is optimized.

[0014] Preferably, step seven, winding and forming, includes real-time monitoring by a tension sensor, tension control of 8-10 cN ± 0.5 cN, winding speed of 3300 m / min ± 50 m / min, and package density of 0.9-1.0 g / cm³. 3 The winding angle is controlled at 5°-7° to ensure uniform fiber winding and reduce defects in subsequent processing.

[0015] Preferably, it also includes precise control of melt temperature, using a PID controller to adjust the temperature of the screw extruder and spinning box in real time, controlling temperature fluctuations within ±2℃, a melt pressure monitoring range of 10-15MPa, an abnormal fluctuation alarm threshold set at ±5%, and linkage with winding tension. When the tension deviation exceeds 5%, the drawing speed is automatically adjusted to maintain process stability, achieving a melting point of less than 160℃, fiber strength greater than 3.5cN / dtex, reduced breakage rate, and reduced energy consumption.

[0016] The present invention has the following beneficial effects: 1. In this invention, by setting a component control end, the synergistic mechanism of the polyester matrix and the low-melting-point copolymer is precisely matched during the preparation of low-melting-point polyester FDY, ensuring the uniformity of melt components and avoiding abnormal melt rheological behavior caused by differences in molecular chain compatibility during melt blending. At the same time, the copolymer structure design is directed to regulate the regularity of molecular chains, suppressing the thermal stability fluctuations during the spinning process in real time, ensuring that the fiber maintains continuous forming capability under high-speed spinning conditions, further reducing the risk of fiber breakage and improving the stability of the production line.

[0017] 2. In this invention, by setting a gradient cooling end, the response relationship between wind temperature and fiber crystallization kinetics is dynamically matched during the fiber cooling and forming stage. The crystallization rate shift induced by copolymerization modification is compensated in real time, enabling the system to eliminate the structural differences between the fiber surface and core layers, avoid core-sheath delamination defects caused by cooling stress concentration, and correct the cooling trajectory shift in real time through the adaptive adjustment mechanism of wind field parameters when the fiber structure is about to change, ensuring the uniformity of fiber cross-sectional shape and orientation consistency, and reducing the fiber breakage rate in post-processing.

[0018] 3. In this invention, by setting a stretching linkage end, the synergistic enhancement effect of low temperature environment and high speed stretching is coupled during the fiber orientation strengthening process. The dynamic contradiction between molecular chain relaxation and orientation freezing is balanced in real time, so that the process can adaptively match the softening characteristics of low melting point components, avoid the imbalance of fiber strength and toughness caused by heat history transfer in the stretching zone. At the same time, in the winding and forming stage, the spatial distribution deviation of the package density is corrected in real time through the tension fluctuation transmission suppression mechanism, ensuring the structural integrity of the fiber from spinning to bundling, and improving the interfacial bonding strength and uniformity of the finished fiber in thermal bonding applications. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: A process for preparing low-melting-point polyester FDY, comprising the following steps: Step 1: Raw material preparation: Polyester chips: Polyethylene terephthalate chips, intrinsic viscosity 0.85 dL / g, end carboxyl group content less than 25 mol / t; Low molecular weight polyester copolymer: terpolymer of terephthalic acid, adipic acid, and ethylene glycol, with intrinsic viscosity of 0.45 dL / g, acid value less than 1.5 mg KOH / g, and number-average molecular weight of 8,000 ± 500. Mixing ratio: PET chips: copolymer = 95:5, copolymer addition amount 5wt%; Drying treatment: Vacuum drying at 80℃ for 4 hours, moisture content less than 0.01%; Polyester chips and low molecular weight polyester copolymers were selected and mixed in a certain proportion. The amount of low molecular weight polyester copolymer added was 5 wt%, and the intrinsic viscosity of the mixture was 0.65 dL / g. Step 2: Melt blending. Place the mixed raw materials in a screw extruder and melt blend at 250°C. Step 3: Spinning process. The melt after molten blending is transported to the spinning box, and the temperature of the box is controlled at 265℃. The nascent fibers are extruded through the spinneret. Step 4: Gradient cooling. The extruded nascent fibers are cooled by gradient side blowing, with the air temperature decreasing from 25℃ to 20℃, the air velocity being 0.4m / s, and the relative humidity being 65%. Step 5: Oiling. The cooled fibers are oiled with an oil concentration of 12% and an oiling rate of 0.8%. Step 6: Drafting treatment. The oiled fibers are fed into the drafting zone, which includes a first hot roller and a second hot roller. The temperature of the first hot roller is 70℃ and the speed is 2800m / min. The temperature of the second hot roller is 120℃ and the speed is 3200m / min. Step 7: Winding and shaping. The drawn fibers are wound at a speed of 3300 m / min and the tension is controlled at 8 cN. The residence time in the melt blending step shall not exceed 15 minutes, the melt temperature fluctuation shall be controlled within ±2℃, and the winding tension deviation shall not exceed 5%, in order to lower the melting point to below 160℃, increase the fiber strength to greater than 3.5 cN / dtex, reduce the breakage rate by 20%, and reduce energy consumption by 15%.

[0021] Step 1 involves preparing the raw materials by drying the polyester chips and low molecular weight polyester copolymer at a temperature of 80°C for 4 hours to ensure that the moisture content of the raw materials is below 0.01% and to prevent fluctuations in melt viscosity.

[0022] In step one, the mixing mass ratio of polyester chips to low molecular weight polyester copolymer is 95:5 to 92:8, preferably 95:5. The low molecular weight polyester copolymer is a copolyester of terephthalic acid and adipic acid and similar low molecular weight polyesters, which reduces the melting point by lowering the molecular chain regularity.

[0023] In step two, melt blending is carried out in a screw extruder. The temperature of each zone of the extruder is set to 250℃, and the temperature deviation of each zone does not exceed ±2℃. The residence time is controlled at 10 minutes to suppress the widening of the molecular weight distribution and avoid abnormal fluctuations in melt viscosity.

[0024] Step 3, the spinning process includes the spinneret extrusion process. The spinneret pressure is set to 12MPa±0.5MPa, the extrusion speed is controlled at 300m / min, and the melt is accurately delivered by a metering pump with a delivery accuracy deviation of less than 1% to reduce the risk of fiber breakage.

[0025] In step four, gradient cooling is achieved using a side-blowing system with a wind speed of 0.4 m / s ± 0.05 m / s, a wind temperature decrease gradient of 1℃ / min, an initial wind temperature of 25℃, a final wind temperature of 20℃, and a relative humidity of 65% ± 5%, in order to uniformly cool the fiber surface and inhibit abnormal growth in crystallinity.

[0026] In step five, a water-soluble oil is used for oiling, with an oil concentration range of 12% ± 0.5% and an oiling rate controlled at 0.8% ± 0.1%. The oiling methods are spraying and roller coating to ensure the lubricity of the fiber surface and reduce frictional damage during the stretching process.

[0027] Step six of the drawing process also includes using a three-stage hot roller step drawing as an alternative, wherein the temperature of the first stage hot roller is 70℃ and the speed is 2500m / min; the temperature of the second stage hot roller is 100℃ and the speed is 3000m / min; and the temperature of the third stage hot roller is 120℃ and the speed is 3200m / min. Through low-temperature high-speed drawing and synergistic copolymerization, the fiber structure is optimized.

[0028] Step seven, winding and forming, includes real-time monitoring by a tension sensor, with tension controlled at 8 cN ± 0.5 cN, a winding speed of 3300 m / min ± 50 m / min, and a winding density of 0.9 g / cm³. 3 The winding angle is controlled at 5° to ensure uniform fiber winding and reduce defects in subsequent processing.

[0029] It also includes precise melt temperature control, using a PID controller to adjust the screw extruder and spinning box temperature in real time, with temperature fluctuations controlled within ±2℃, melt pressure monitoring range of 10MPa, abnormal fluctuation alarm threshold set at ±5%, and linkage with winding tension. When the tension deviation exceeds 5%, the drawing speed is automatically adjusted to maintain process stability, achieving a melting point of less than 160℃, fiber strength greater than 3.5cN / dtex, reduced breakage rate, and reduced energy consumption.

[0030] Example 2: A process for preparing low-melting-point polyester FDY, comprising the following steps: Step 1: Raw material preparation: Polyester chips: Polyethylene terephthalate chips, intrinsic viscosity 0.84 dL / g; Low molecular weight polyester copolymer: terephthalic acid-sebacic acid-butanediol copolyester, intrinsic viscosity: 0.48 dL / g, melting point: 135℃, AA monomer molar content: 18%; Mixing ratio: PET chips: copolymer = 93:7, copolymer addition amount 7wt%; Drying process: Same as in Example 1; Polyester chips and low molecular weight polyester copolymers were selected and mixed in a certain proportion. The amount of low molecular weight polyester copolymer added was 7 wt%, and the intrinsic viscosity of the mixture was 0.68 dL / g. Step 2: Melt blending. Place the mixed raw materials in a screw extruder and melt blend at 255°C. Step 3: Spinning process. The melt after molten blending is transported to the spinning box, and the temperature of the box is controlled at 265℃. The nascent fibers are extruded through the spinneret. Step 4: Gradient cooling. The extruded nascent fibers are cooled by gradient side blowing, with the air temperature decreasing from 25℃ to 20℃, the air velocity being 0.4m / s, and the relative humidity being 65%. Step 5: Oiling. The cooled fibers are oiled with an oil concentration of 12% and an oiling rate of 0.8%. Step 6: Drafting treatment. The oiled fibers are fed into the drafting zone, which includes a first hot roller and a second hot roller. The temperature of the first hot roller is 73℃ and the speed is 2800m / min. The temperature of the second hot roller is 122℃ and the speed is 3200m / min. Step 7: Winding and shaping. The drawn fibers are wound at a speed of 3300 m / min and the tension is controlled at 9 cN. The residence time in the melt blending step shall not exceed 15 minutes, the melt temperature fluctuation shall be controlled within ±2℃, and the winding tension deviation shall not exceed 5%, in order to lower the melting point to below 160℃, increase the fiber strength to greater than 3.5 cN / dtex, reduce the breakage rate by 20%, and reduce energy consumption by 15%.

[0031] Step 1 involves preparing the raw materials by drying the polyester chips and low molecular weight polyester copolymer at a temperature of 80°C for 4 hours to ensure that the moisture content of the raw materials is below 0.01% and to prevent fluctuations in melt viscosity.

[0032] In step one, the mixing mass ratio of polyester chips to low molecular weight polyester copolymer is 95:5 to 92:8, preferably 95:5. The low molecular weight polyester copolymer is a copolyester of terephthalic acid and adipic acid and similar low molecular weight polyesters, which reduces the melting point by lowering the molecular chain regularity.

[0033] In step two, melt blending is carried out in a screw extruder. The temperature of each zone of the extruder is set to 255℃, and the temperature deviation of each zone does not exceed ±2℃. The residence time is controlled at 13 minutes to suppress the widening of the molecular weight distribution and avoid abnormal fluctuations in melt viscosity.

[0034] Step 3, the spinning process includes the spinneret extrusion process. The spinneret pressure is set to 12MPa±0.5MPa, the extrusion speed is controlled at 350m / min, and the melt is accurately delivered by a metering pump with a delivery accuracy deviation of less than 1% to reduce the risk of fiber breakage.

[0035] In step four, gradient cooling is achieved using a side-blowing system with a wind speed of 0.4 m / s ± 0.05 m / s, a wind temperature decrease gradient of 1℃ / min, an initial wind temperature of 25℃, a final wind temperature of 20℃, and a relative humidity of 65% ± 5%, in order to uniformly cool the fiber surface and inhibit abnormal growth in crystallinity.

[0036] In step five, a water-soluble oil is used for oiling, with an oil concentration range of 12% ± 0.5% and an oiling rate controlled at 0.8% ± 0.1%. The oiling methods are spraying and roller coating to ensure the lubricity of the fiber surface and reduce frictional damage during the stretching process.

[0037] Step six of the drawing process also includes using a three-stage hot roller step drawing as an alternative, wherein the temperature of the first stage hot roller is 73℃ and the speed is 2600m / min; the temperature of the second stage hot roller is 105℃ and the speed is 3100m / min; and the temperature of the third stage hot roller is 123℃ and the speed is 3250m / min. Through low-temperature high-speed drawing and synergistic copolymerization, the fiber structure is optimized.

[0038] Step seven, winding and forming, includes real-time monitoring by a tension sensor, with tension controlled at 9cN ± 0.5cN, a winding speed of 3300m / min ± 50m / min, and a winding density of 0.95g / cm³. 3 The winding angle is controlled at 6° to ensure uniform fiber winding and reduce defects in subsequent processing.

[0039] It also includes precise melt temperature control, using a PID controller to adjust the screw extruder and spinning box temperature in real time, with temperature fluctuations controlled within ±2℃, melt pressure monitoring range of 12MPa, abnormal fluctuation alarm threshold set at ±5%, and linkage with winding tension. When the tension deviation exceeds 5%, the drawing speed is automatically adjusted to maintain process stability, achieving a melting point of less than 160℃, fiber strength greater than 3.5cN / dtex, reduced breakage rate, and reduced energy consumption.

[0040] Example 3: A process for preparing low-melting-point polyester FDY, comprising the following steps: Step 1: Raw material preparation: Polyester chips: Polyethylene terephthalate chips, intrinsic viscosity 0.86 dL / g; Low molecular weight polyester copolymer: terephthalic acid, adipic acid, and ethylene glycol copolyester, intrinsic viscosity 0.50 dL / g, AA monomer content 20 mol%. Mixing ratio: PET chips: copolymer = 92:8, copolymer addition amount 8wt%; Drying process: Same as in Example 1; Polyester chips and low molecular weight polyester copolymers were selected and mixed in a certain proportion. The amount of low molecular weight polyester copolymer added was 8 wt%, and the intrinsic viscosity of the mixture was 0.70 dL / g. Step 2: Melt blending. Place the mixed raw materials in a screw extruder and melt blend at 260°C. Step 3: Spinning process. The melt after molten blending is transported to the spinning box, and the temperature of the box is controlled at 265℃. The nascent fibers are extruded through the spinneret. Step 4: Gradient cooling. The extruded nascent fibers are cooled by gradient side blowing, with the air temperature decreasing from 25℃ to 20℃, the air velocity being 0.4m / s, and the relative humidity being 65%. Step 5: Oiling. The cooled fibers are oiled with an oil concentration of 12% and an oiling rate of 0.8%. Step 6: Drafting treatment. The oiled fibers are fed into the drafting zone, which includes a first hot roller and a second hot roller. The temperature of the first hot roller is 75℃ and the speed is 2800m / min. The temperature of the second hot roller is 125℃ and the speed is 3200m / min. Step 7: Winding and shaping. The drawn fibers are wound at a speed of 3300 m / min and the tension is controlled at 10 cN. The residence time in the melt blending step shall not exceed 15 minutes, the melt temperature fluctuation shall be controlled within ±2℃, and the winding tension deviation shall not exceed 5%, in order to lower the melting point to below 160℃, increase the fiber strength to greater than 3.5 cN / dtex, reduce the breakage rate by 20%, and reduce energy consumption by 15%.

[0041] Step 1 involves preparing the raw materials by drying the polyester chips and low molecular weight polyester copolymer at a temperature of 80°C for 4 hours to ensure that the moisture content of the raw materials is below 0.01% and to prevent fluctuations in melt viscosity.

[0042] In step one, the mixing mass ratio of polyester chips to low molecular weight polyester copolymer is 95:5 to 92:8, preferably 95:5. The low molecular weight polyester copolymer is a copolyester of terephthalic acid and adipic acid and similar low molecular weight polyesters, which reduces the melting point by lowering the molecular chain regularity.

[0043] In step two, melt blending is carried out in a screw extruder. The temperature of each zone of the extruder is set to 260℃, and the temperature deviation of each zone does not exceed ±2℃. The residence time is controlled at 15 minutes to suppress the widening of the molecular weight distribution and avoid abnormal fluctuations in melt viscosity.

[0044] Step 3, the spinning process includes the spinneret extrusion process. The spinneret pressure is set to 12MPa±0.5MPa, the extrusion speed is controlled at 400m / min, and the melt is accurately delivered by a metering pump with a delivery accuracy deviation of less than 1% to reduce the risk of fiber breakage.

[0045] In step four, gradient cooling is achieved using a side-blowing system with a wind speed of 0.4 m / s ± 0.05 m / s, a wind temperature decrease gradient of 1℃ / min, an initial wind temperature of 25℃, a final wind temperature of 20℃, and a relative humidity of 65% ± 5%, in order to uniformly cool the fiber surface and inhibit abnormal growth in crystallinity.

[0046] In step five, a water-soluble oil is used for oiling, with an oil concentration range of 12% ± 0.5% and an oiling rate controlled at 0.8% ± 0.1%. The oiling methods are spraying and roller coating to ensure the lubricity of the fiber surface and reduce frictional damage during the stretching process.

[0047] Step six of the drawing process also includes a three-stage hot roller step drawing as an alternative, wherein the temperature of the first stage hot roller is 75℃ and the speed is 2800m / min; the temperature of the second stage hot roller is 110℃ and the speed is 3200m / min; and the temperature of the third stage hot roller is 125℃ and the speed is 3300m / min. Through low-temperature high-speed drawing and synergistic copolymerization, the fiber structure is optimized.

[0048] Step seven, winding and forming, includes real-time monitoring by a tension sensor, with tension controlled at 10cN ± 0.5cN, a winding speed of 3300m / min ± 50m / min, and a winding density of 1.0g / cm³. 3 The winding angle is controlled at 7° to ensure uniform fiber winding and reduce defects in subsequent processing.

[0049] It also includes precise melt temperature control, using a PID controller to adjust the screw extruder and spinning box temperature in real time, with temperature fluctuations controlled within ±2℃, melt pressure monitoring range of 15MPa, abnormal fluctuation alarm threshold set at ±5%, and linkage with winding tension. When the tension deviation exceeds 5%, the drawing speed is automatically adjusted to maintain process stability, achieving a melting point of less than 160℃, fiber strength greater than 3.5cN / dtex, reduced breakage rate, and reduced energy consumption.

[0050] Comparative Example 1: The difference between this comparative example and Example 1 is that no low molecular weight polyester copolymer was added in the melt blending step of this comparative example.

[0051] Comparative Example 2 differs from Example 2 in that the spinning box temperature is set to 280°C in the spinning process, which exceeds the temperature control range of this invention.

[0052] Comparative Example 3 differs from Example 3 in that it uses constant temperature side blowing in the gradient cooling step and does not implement gradient cooling.

[0053] Comparative Example 4 differs from Example 3 in that the tension linkage control mechanism is turned off in the winding forming step, and the tension fluctuation range is expanded to ±15%.

[0054] The performance of the low-melting-point polyester FDY prepared in Examples 1-3 and Comparative Examples 1-4 was tested. The test items and test methods are as follows: Melting point was tested using a differential scanning calorimeter at a heating rate of 10℃ / min under nitrogen protection, and the melting endothermic peak temperature was recorded. The test standard was GB / T19466.3-2004. The tensile strength test was conducted using an electronic tensile tester with a clamping distance of 20 mm and a tensile rate of 100 mm / min. The maximum load at which the fiber broke was recorded. Breakage rate test: On a continuous spinning production line, the number of fiber breaks within a 100km fiber length is counted and converted into the number of breaks per 10,000 meters. Energy consumption testing involves recording the power consumption per unit of output through an online power monitoring system, eliminating the impact of auxiliary equipment power consumption.

[0055] The test data of the low melting point polyester FDY prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the table below: Test group Melting point (°C) Fracture strength (cN / dtex) Decapitation rate (times / meter) Energy consumption (kWh / ton) Example 1 158 3.58 10 1180 Example 2 156 3.62 8 1150 Example 3 159 3.55 11 1190 Comparative Example 1 248 2.75 28 1350 Comparative Example 2 162 3.05 19 1280 Comparative Example 3 161 3.20 25 1220 Comparative Example 4 160 3.42 16 1320 By comparing and analyzing the data in the table, it can be seen that the low-melting-point polyester FDY prepared by the process in Examples 1-3 has optimized fiber performance compared with the fiber prepared by the process in Comparative Examples 1-4. The melting point reduction mechanism is as follows: the low molecular weight polyester copolymer destroys the regularity of molecular chains through its copolymerization structure, reduces the perfection of crystal regions, and at the same time forms molecular-level dispersion with the polyester matrix in melt blending, amplifying the melt entropy increase effect, and synergistically acting on the directional control of melting point. The strength and breakage rate improvement mechanism is as follows: gradient cooling inhibits premature crystallization of the fiber surface by decreasing the air temperature, allowing the core-sheath structure to develop synchronously and reducing internal stress concentration. At the same time, the precise temperature control of the spinning box avoids the deterioration of melt rheological properties and ensures the uniformity of the nascent fiber structure. On this basis, low temperature and high speed drawing promotes the molecular chains to achieve high-magnification orientation below the softening point, forming a stable structure with high density and small crystals. The energy consumption control mechanism is as follows: the tension linkage system compensates for the dynamic deviation of winding in real time, avoiding repeated adjustments of the drawing speed due to sudden tension changes. At the same time, the low temperature process directly reduces the heating energy consumption of the hot roller, and together with the copolymerization modification, it realizes the feasibility of low temperature processing.

[0056] By comparing and analyzing the relevant data in the table, it can be seen that the low-melting-point polyester FDY prepared by the molding process of the present invention has excellent melting characteristics, mechanical properties and processing stability. This indicates that the low-melting-point polyester FDY preparation process provided by the present invention has a broader prospect for industrial application and is more suitable for large-scale promotion.

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled 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 invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing low-melting-point polyester FDY, characterized in that, Includes the following steps: Step 1: Raw material preparation. Select polyester chips and low molecular weight polyester copolymer, and mix them in a certain proportion. The amount of low molecular weight polyester copolymer added is 5-8 wt%, and the intrinsic viscosity of the mixture is 0.65-0.70 dL / g. Step 2: Melt blending. Place the mixed raw materials in a screw extruder and melt blend at 250-260℃. Step 3: Spinning process. The melt after molten blending is transported to the spinning box, and the temperature of the box is controlled at 265℃. The nascent fibers are extruded through the spinneret. Step 4: Gradient cooling. The extruded nascent fibers are cooled by gradient side-blowing air, with the air temperature decreasing from 25℃ to 20℃, the air velocity being 0.4m / s, and the relative humidity being 65%. Step 5: Oiling. Apply oil to the cooled fibers. The oil concentration is 12%, and the oiling rate is 0.8%. Step 6: Drafting treatment. The oiled fibers are fed into the drafting zone, which includes a first hot roller and a second hot roller. The temperature of the first hot roller is 70-75℃ and the speed is 2800m / min. The temperature of the second hot roller is 120-125℃ and the speed is 3200m / min. Step 7: Winding and shaping. The stretched fibers are wound at a speed of 3300 m / min and the tension is controlled at 8-10 cN. The residence time of the melt blending step shall not exceed 15 minutes, the melt temperature fluctuation shall be controlled within ±2℃, and the winding tension deviation shall not exceed 5%, so as to reduce the melting point to below 160℃, increase the fiber strength to greater than 3.5cN / dtex, reduce the breakage rate by 20%, and reduce energy consumption by 15%.

2. The process for preparing low-melting-point polyester FDY according to claim 1, characterized in that, The raw material preparation in step one includes drying the polyester chips and low molecular weight polyester copolymer at a temperature of 80°C for 4 hours to ensure that the moisture content of the raw materials is below 0.01% and to prevent fluctuations in melt viscosity.

3. The process for preparing low-melting-point polyester FDY according to claim 1, characterized in that, In step one, the mixing mass ratio of polyester chips to low molecular weight polyester copolymer is 95:5 to 92:8, preferably 95:

5. The low molecular weight polyester copolymer is a copolyester of terephthalic acid and adipic acid and similar low molecular weight polyesters, which reduces the melting point by decreasing the regularity of the molecular chain.

4. The process for preparing low-melting-point polyester FDY according to claim 3, characterized in that, In step two, melt blending is carried out in a screw extruder. The temperature of each zone of the extruder is set to 250-260℃, and the temperature deviation of each zone does not exceed ±2℃. The residence time is controlled to 10-15 minutes to suppress the widening of the molecular weight distribution and avoid abnormal fluctuations in melt viscosity.

5. The process for preparing low-melting-point polyester FDY according to claim 4, characterized in that, The spinning process in step three includes a spinneret extrusion process. The spinneret pressure is set to 12MPa±0.5MPa, the extrusion speed is controlled at 300-400m / min, and the melt is accurately delivered by a metering pump with a delivery accuracy deviation of less than 1% to reduce the risk of fiber breakage.

6. The process for preparing low-melting-point polyester FDY according to claim 1, characterized in that, In step four, gradient cooling employs a side-blowing system with a wind speed of 0.4 m / s ± 0.05 m / s, a wind temperature decrease gradient of 1℃ / min, an initial wind temperature of 25℃, a final wind temperature of 20℃, and a relative humidity of 65% ± 5%, in order to uniformly cool the fiber surface and inhibit abnormal growth in crystallinity.

7. The process for preparing low-melting-point polyester FDY according to claim 1, characterized in that, In step five, a water-soluble oil is used for oiling, with an oil concentration range of 12% ± 0.5% and an oiling rate controlled at 0.8% ± 0.1%. The oiling methods are spraying and roller coating to ensure the lubricity of the fiber surface and reduce frictional damage during the stretching process.

8. The process for preparing low-melting-point polyester FDY according to claim 1, characterized in that, The stretching process in step six also includes using a three-stage hot roller step-stretching as an alternative. The temperature of the first-stage hot roller is 70-75℃ and the speed is 2500-2800m / min; the temperature of the second-stage hot roller is 100-110℃ and the speed is 3000-3200m / min; and the temperature of the third-stage hot roller is 120-125℃ and the speed is 3200-3300m / min. The fiber structure is optimized through low-temperature high-speed stretching and synergistic copolymerization.

9. The process for preparing low-melting-point polyester FDY according to claim 1, characterized in that, Step seven, winding and forming, includes real-time monitoring by a tension sensor, tension control of 8-10cN±0.5cN, winding speed of 3300m / min±50m / min, package density of 0.9-1.0g / cm³, and winding angle control of 5°-7° to ensure fiber winding uniformity and reduce subsequent processing defects.

10. The process for preparing low-melting-point polyester FDY according to claim 1, characterized in that, It also includes precise melt temperature control, using a PID controller to adjust the screw extruder and spinning box temperature in real time, with temperature fluctuations controlled within ±2℃, melt pressure monitoring range of 10-15MPa, abnormal fluctuation alarm threshold set at ±5%, and linkage with winding tension. When the tension deviation exceeds 5%, the drawing speed is automatically adjusted to maintain process stability, achieving a melting point of less than 160℃, fiber strength greater than 3.5cN / dtex, reduced breakage rate, and reduced energy consumption.