High speed physical spinning method for polyester fiber

Abstract

The application discloses a polyester fiber high-speed physical spinning forming method and belongs to the technical field of chemical fiber forming. In view of the problems of poor orientation crystallization synergy, uneven radial structure, high breakage rate and the like in the existing high-speed spinning, the method comprises the following steps: after melt extrusion from a spinning plate, the melt is sequentially subjected to multi-stage gradient cooling forming through a slow cooling zone, a quenching zone and a stable cooling zone; the temperature of the slow cooling zone is 180-240 DEG C, so that the melt stream is fully pre-oriented; the quenching zone is divided into a pre-cooling section and a main cooling section, the air speed is gradiently distributed, and a ring blowing or composite cooling mode is adopted; and then the fiber is subjected to bundle oiling and hot roller stretching, and is high-speed wound and formed at 5500-8000 m / min. The application realizes the optimal matching of the time sequence of orientation and crystallization and the spatial homogenization, the prepared fiber has a strength of 5.5-7.5 cN / dtex, the radial structure is uniform, the breakage rate is reduced by more than 90%, and the method has the advantages of high process flexibility, low energy consumption and the like.

Description

Technical Field

[0001] This invention relates to the field of chemical fiber forming technology, specifically to a method for high-speed spinning of polyester fibers using physical forming, and more particularly to a high-speed physical spinning forming method for polyester fibers. More specifically, this invention relates to a spinning forming method that achieves precise time- and temperature control of the molecular chain orientation and crystallization process of polyethylene terephthalate (PET) by constructing a multi-level gradient cooling physical field and spinning at ultra-high speeds of 5500-8000 m / min. Background Technology

[0002] Polyethylene terephthalate (PET) fiber, commonly known as polyester, is an important synthetic fiber obtained by spinning polyester, which is formed by the condensation polymerization of terephthalic acid and ethylene glycol. PET fiber dominates the global synthetic fiber market due to its excellent mechanical properties, good dimensional stability, abrasion resistance, wrinkle resistance, and relatively low production cost. It is widely used in clothing fabrics, home textiles, industrial fabrics, tire cords, geotextiles, and nonwoven fabrics. According to statistics from the China Chemical Fiber Industry Association, my country's polyester production exceeded 55 million tons in 2023, accounting for more than 80% of the total synthetic fiber production, making it an indispensable basic material in the national economy.

[0003] The industrial production of polyester fibers mainly adopts melt spinning technology. The basic process is as follows: PET polyester chips are dried and melted, then conveyed to the spinning box through a screw extruder. After being precisely metered by a metering pump, the chips are extruded from the micropores of the spinneret to form a melt stream. The melt stream is rapidly cooled and solidified under the action of cooling air (side blowing or ring blowing) to form nascent fibers. The nascent fibers are bundled, oiled, and wound into shape. Then, according to product requirements, subsequent stretching, setting, and other treatments are carried out to finally obtain polyester fibers with the required properties.

[0004] With the continuous advancement of textile technology, increasingly higher demands are being placed on the spinning speed and product quality of polyester fibers. High-speed spinning technology (winding speed ≥3000m / min) has developed rapidly since the 1980s and has become the mainstream technology for polyester fiber production. High-speed spinning not only significantly improves production efficiency and reduces energy consumption and cost per unit product, but also improves the mechanical properties and orientation crystal structure of fibers to a certain extent. However, when the spinning speed exceeds 4000-4500m / min, the inertial force, air resistance, and tensile stress borne by the melt stream on the spinning line increase exponentially. The spinning process enters a completely new dynamic state domain, and traditional high-speed spinning theories and processes face severe challenges in this region.

[0005] However, existing high-speed spinning technology for polyester fibers still faces a series of prominent technical problems, which seriously restrict further increases in spinning speed and continuous improvements in fiber quality:

[0006] (1) Spinning speed bottleneck: When the winding speed exceeds 4000-4500 m / min, the tensile stress and inertial force borne by the melt stream during the solidification process increase sharply, making it difficult for the internal structure of the fiber to be fully oriented and crystallized, resulting in a slow or even decrease in the improvement of fiber mechanical properties (especially breaking strength and initial modulus). When the spinning speed is further increased to above 5000 m / min, the stability of the spinning process deteriorates significantly, the breakage rate rises sharply, and the industrial spinning speed is severely limited. Studies have shown that the essential reason for this phenomenon is that under ultra-high spinning speed conditions, the solidification time of the melt stream is shortened to the order of tens of milliseconds, and there is a serious mismatch between the orientation relaxation time of the molecular chain and the cooling solidification time. The orientation is "frozen" before it is fully completed, and the crystallization lacks sufficient induction and growth time. The cooling system of the existing spinning process cannot provide enough time window and spatial dimension to finely control this dynamic process.

[0007] (2) The synchronicity of orientation and crystallization is difficult to control: During high-speed spinning, PET molecular chains are oriented in the axial stretching flow of the melt stream, and crystallize simultaneously due to cooling. Ideally, the orientation of the molecular chains should be fully completed before crystallization to achieve the best effect of "orientation-induced crystallization," thereby obtaining a fiber structure with high orientation and high crystallinity. However, in existing high-speed spinning processes, the cooling rate is usually constant, resulting in a lack of precise matching between the spatial location and time node of cooling solidification and the dynamic process of molecular chain orientation. A large number of molecular chains are "frozen" before the orientation is fully developed, causing a "misalignment" between orientation and crystallization, which limits the full utilization of fiber performance. From the perspective of materials science, the temperature dependence of the orientation rate and crystallization rate of PET molecular chains is significantly different. Orientation mainly occurs in the viscous flow state and the high elastic state (temperature above the melting point Tm or between Tm and Tg), while the optimal temperature range for crystallization is 140-190℃. Existing constant-rate cooling processes cannot provide optimal temperature and time conditions for these two processes with different rates in space, resulting in a "mismatch."

[0008] (3) Poor uniformity of fiber radial structure: In the existing melt spinning process, the cooling air is mainly applied from one side (side blowing) or the surrounding area (circular blowing) of the fiber bundle. The heat exchange between the cooling medium and the fiber surface is significantly uneven, resulting in a huge difference in the cooling rate between the fiber surface layer and the core layer. The surface melt cools rapidly to form a hard shell, while the core melt is still in a high-temperature flowing state. This "skin-core" cooling difference leads to unevenness of the fiber radial structure, specifically: the surface layer has high orientation and low crystallinity; the core layer has low orientation and high crystallinity. This unevenness of the radial structure directly affects the uniformity of the fiber's mechanical properties and dyeing uniformity, leading to problems such as fuzzing, breakage, and uneven dyeing in subsequent processing and use. Further microscopic analysis shows that the formation of the skin-core structure is also accompanied by significant radial residual stress. The skin layer bears compressive stress while the core layer bears tensile stress. This uneven stress distribution will induce microcracks and structural defects during subsequent stretching and heat setting, which is an important reason for the decline in the long-term service performance of the fiber.

[0009] (4) High spinning breakage rate and poor production stability: Under high-speed spinning conditions, the solidification process of the melt stream is extremely sensitive to minute fluctuations in factors such as cooling conditions, spinning tension, and melt viscosity. In existing spinning processes, there is a lack of effective dynamic coordination control between the cooling system, stretching system, and winding system. Once a fluctuation occurs in any link, it is very easy to cause breakage, affecting the stability of continuous production. According to industry statistics, under spinning speeds above 5000 m / min, the breakage rate can reach 5-10 times per thousand spindles per hour or more, which seriously reduces production efficiency and economy. Breakage not only causes product loss (each breakage requires re-spinning, resulting in a loss of about 200-500g of fiber), but also triggers a series of chain problems such as equipment shutdown, waste fiber disposal, and increased labor costs. It is estimated that a polyester filament production line with an annual output of 100,000 tons can suffer direct and indirect losses of several million yuan per year due to breakage.

[0010] (5) Limited product specifications and insufficient functionalization: Existing high-speed spinning processes for polyester fibers are mainly geared towards the production of conventional round cross-section fibers, making it difficult to achieve flexible control and rapid switching of fiber cross-section shape, fineness specifications, and functional characteristics on the same production line. With the increasing market demand for functional fibers such as profiled fibers, hollow fibers, and composite fibers, there is an urgent need to develop new spinning methods with higher process flexibility. Especially in the field of differentiated and functional polyester fibers (such as antistatic, antibacterial, flame retardant, far-infrared, and UV resistant fibers), existing high-speed spinning processes face technical challenges such as poor dispersion uniformity of functional masterbatches and changes in melt rheological properties after addition, leading to a decrease in spinnability, which seriously restricts the development of high-value-added functional fibers.

[0011] To address these issues, researchers in this field have conducted extensive research. For example, differentiated polyester fibers have been prepared by using dynamically varying cooling airflow during the cooling and forming process. This method utilizes pulse signals to control the cooling airflow speed according to a sinusoidal law, achieving a certain degree of differentiated control over the condensed structure of the fibers. Another example is the design of sheath-core composite spinning and differentiated sheath-core cooling schemes to prepare composite fibers with special properties. Furthermore, some studies have attempted to improve fiber orientation structure by setting a delayed cooling zone below the spinneret (e.g., US20040052883), or by using multi-stage cooling airflow to optimize the cooling process (e.g., a three-stage side-blowing cooling process). However, these methods mostly focus on localized improvements to specific problems and have not yet formed a comprehensive technical solution to systematically address core issues such as orientation-crystallization synergistic control, radial structure homogenization, and improved spinning stability in high-speed spinning. In particular, existing technologies have not addressed how to achieve precise temporal and spatial matching of the PET molecular chain "orientation-crystallization" process under ultra-high-speed spinning conditions of 5500-8000 m / min through the synergistic effect of gradient wind speed distribution in the slow cooling zone, the rapid cooling zone, and the stable cooling zone. This technological gap is precisely the core problem that this invention aims to solve.

[0012] In summary, there is an urgent need for a polyester fiber spinning method that can operate stably at higher spinning speeds, while achieving precise physical control over the condensed structure of the fiber, and combining high production efficiency, excellent product quality, and high process flexibility. Summary of the Invention

[0013] To address the shortcomings of existing technologies, the present invention aims to provide a high-speed physical spinning method for polyester fibers. This method achieves precise physical control of the temperature, velocity, and stress fields of the melt stream during the solidification process by constructing a multi-stage gradient cooling system and a physical field with synergistic effects of axial tension and radial compression. This allows for optimal temporal matching and spatial uniformity of the orientation and crystallization process of PET molecular chains, thereby stably producing high-strength, high-modulus, low-shrinkage polyester fibers with uniform radial structure at spinning speeds of 5500-8000 m / min, while also possessing the production capability for flexible switching between multiple varieties. Another objective of this invention is to fundamentally solve the technical problems commonly found in existing high-speed spinning technologies, such as uneven "skin-core" structure, high breakage rate, and poor orientation-crystallization synergy, by systematically optimizing the temperature regime, wind speed gradient distribution, and length ratio of the slow cooling zone, rapid cooling zone, and stable cooling zone. This provides a feasible technical path for the polyester fiber industry to develop towards higher speed, higher efficiency, and higher quality.

[0014] The above-mentioned objective of this invention is achieved through the following technical solutions:

[0015] This invention provides a high-speed physical spinning method for polyester fibers, comprising the following steps:

[0016] Step S1, Raw material preparation: Select PET polyester chips with an intrinsic viscosity of 0.65-0.85 dL / g, and dry them in a vacuum drum dryer at 140-170℃ for 6-12 hours, controlling the chip moisture content to ≤30ppm; or, directly use the melt from the polymerization workshop for melt direct spinning, with a melt intrinsic viscosity of 0.65-0.75 dL / g; The above selection of intrinsic viscosity in this invention is based on the following technical principles: When the intrinsic viscosity is below 0.65 dL / g, the PET molecular chain length is insufficient, the melt strength is low, and melt fracture and breakage are prone to occur in the high stress field of ultra-high speed spinning; when the intrinsic viscosity is above 0.85 dL / g, the melt viscosity is too high, the flow performance deteriorates, the extrusion uniformity decreases, and the stretchability of the melt during the spinning process is reduced, which is not conducive to achieving ultra-high speed winding of 5500-8000 m / min. For melt spinning, controlling the intrinsic viscosity at 0.65-0.75 dL / g can ensure melt flowability while maintaining sufficient macromolecular chain length, thus balancing spinning stability and final fiber performance.

[0017] Step S2, Melt Extrusion: The dried chips obtained in Step S1 are fed into a screw extruder for melt extrusion. The temperature of each section is 260-290℃, and the melt outlet temperature is 280-290℃. If melt spinning is used, the melt is directly fed into the spinning box through a conveying pipe. The temperature gradient of each section of the screw extruder follows these principles: the feeding section temperature is relatively low (260-270℃) to ensure that the chips are fully preheated and begin plasticization; the compression section temperature is moderate (270-280℃) to achieve complete melting and uniform mixing of the chips; the metering section temperature is relatively high (280-290℃) to ensure that the melt reaches the flow state required for extrusion and eliminates thermal history. The melt outlet temperature is controlled at 280-290℃ based on the balance between the thermal stability and flowability of PET. If the temperature is too low, the melt viscosity will be too high, making extrusion difficult; if the temperature is too high, PET will undergo thermal degradation and hydrolysis, resulting in a decrease in intrinsic viscosity and an increase in end carboxyl group content, affecting fiber color and mechanical properties.

[0018] Step S3, Melt Filtration and Metering: The melt obtained in step S2 is fed into the spinning box and filtered through a melt filter with a filtration accuracy of 15-30 μm, followed by precise metering by a high-precision metering pump. The choice of filtration accuracy is closely related to the stability of subsequent high-speed spinning: under ultra-high-speed spinning conditions of 5500-8000 m / min, the diameter of the melt stream is extremely small (approximately 0.2-0.4 mm after extrusion and expansion). Any impurities or gel particles larger than 15 μm can cause localized stress concentration during the spinning process, inducing breakage or fuzzy fibers. Using a filtration accuracy of 15-30 μm can effectively remove impurities and gels while avoiding melt retention and degradation caused by excessive filtration pressure. The metering pump is a high-precision gear pump, with metering accuracy controlled within ±0.5% to ensure high consistency of melt extrusion volume at each spinning station and uniformity of fiber fineness.

[0019] Step S4, Melt Extrusion: The metered melt is extruded through a spinneret to form a melt stream. The spinneret has 24-288 holes, with a diameter of 0.15-0.30 mm and an aspect ratio of 2.0-3.5:1. The extrusion temperature is 280-295℃. The design of the aspect ratio is one of the important parameters of this invention. The aspect ratio of 2.0-3.5:1 is based on the following considerations: If the aspect ratio is too small (<2.0), the flow time of the melt in the spinneret is too short, the elastic memory effect is significant, the outlet expansion is severe, and the stability of the melt stream is poor; if the aspect ratio is too large (>3.5), the flow resistance increases sharply, the outlet pressure requirement of the melt pump increases, and the pressure loss in the hole increases, which may cause the melt to overheat and degrade. The aspect ratio range of this invention can effectively relax the elastic properties of the melt and suppress outlet expansion while maintaining moderate flow resistance and stable extrusion. The extrusion temperature is 280-295℃, slightly higher than the melt outlet temperature in step S2, to compensate for the heat loss of the melt in the spinning assembly and ensure that the melt at the spinneret has the optimal spinnable viscosity.

[0020] Step S5, Multi-stage Gradient Cooling Physical Molding: The molten fine stream extruded from the spinneret passes sequentially through a slow cooling zone, a rapid cooling zone, and a stable cooling zone. The slow cooling zone is located 0-100mm below the spinneret, with an ambient temperature of 180-240℃. The rapid cooling zone is located 100-500mm below the spinneret and includes a pre-cooling section and a main cooling section. The wind speed in the pre-cooling section is 0.3-0.5m / s, and the wind speed in the main cooling section is 0.5-0.8m / s. The cooling air temperature is 15-25℃, and the relative humidity is 65-85%. The stable cooling zone is located 500-1200mm below the spinneret, where the fiber temperature is reduced to below 50℃ through natural cooling. This step is the core of multi-stage gradient cooling physical molding, and its technical principles and design basis need to be explained in depth from the perspective of PET rheological behavior and phase transition kinetics.

[0021] The principle and technical significance of setting up a slow cooling zone: In traditional high-speed spinning processes, the melt stream is immediately blown by cooling air after being extruded from the spinneret, and the surface temperature drops below the glass transition temperature (Tg≈70-80℃) in a very short time (usually less than 10ms), forming a rigid skin. This premature formation of the skin leads to three negative effects: First, the skin prevents further flow and molecular chain orientation of the core melt under axial tensile force, resulting in "insufficiently oriented" regions within the fiber; second, the large temperature difference between the skin and the core layer causes significant differences in thermal shrinkage during subsequent curing, introducing internal stress in the fiber's radial direction; third, the skin, acting as a "mechanical hard shell," alters the overall mechanical response characteristics of the fiber, causing uneven tension transmission during spinning and increasing the risk of fiber breakage. The core principle of this invention's slow cooling zone lies in maintaining a relatively high ambient temperature (180-240℃) in the initial stage (0-100mm region) after the molten stream is extruded from the spinneret. This allows the molten stream to remain in a viscous or elastic state for a sufficiently long time, enabling it to undergo sufficient axial stretching under winding tension and complete the pre-orientation of the PET molecular chains. Research shows that the orientation relaxation time of PET molecular chains in the viscous state is on the order of milliseconds. The length and temperature design of the slow cooling zone ensure that the time window for molecular chain orientation is greater than the relaxation time, allowing for effective accumulation of orientation. The temperature range of 180-240℃ was obtained through extensive experimental optimization. Below 180℃, the slow cooling effect is not significant, and the skin layer will still form prematurely; above 240℃, the risk of thermal degradation of the molten stream increases, and the equipment consumes too much energy.

[0022] The principle of gradient wind speed distribution in the quenching zone: After the molecular chains are pre-oriented in the slow cooling zone, it is necessary to quickly "lock" this orientation state in the quenching zone and induce crystallization. However, the cooling rate in the quenching zone is not necessarily better the higher it is. If strong cooling is carried out with high wind speed from the beginning, the following problems will occur: (1) The fiber surface solidifies rapidly to form a hard shell, and the core melt is sealed inside and cannot be further oriented; (2) The excessively fast cooling rate does not give the molecular chains enough time to arrange the lattice, resulting in imperfect crystallization, small grain size and many defects; (3) Sudden thermal contraction generates large internal stress, forming defects such as micropores inside the fiber. This invention achieves a "soft landing" of the cooling process by dividing the quenching zone into a pre-cooling section and a main cooling section and using different wind speeds (0.3-0.5 m / s for the pre-cooling section and 0.5-0.8 m / s for the main cooling section). The pre-cooling section uses a lower air velocity to initially stabilize the orientation state of the melt stream accumulated in the slow cooling zone, while simultaneously inducing crystal nucleation. The main cooling section uses a higher air velocity to promote rapid grain growth and refinement based on nucleation, ultimately completing fiber solidification. Furthermore, this invention creates a gradient distribution curve in the quenching zone where the air velocity first increases and then decreases (pre-cooling section air velocity v1 = 0.3-0.4 m / s, main cooling section maximum air velocity v2 = 0.6-0.8 m / s, lower part of the main cooling section air velocity v3 = 0.4-0.6 m / s). This gradient distribution design is based on the following considerations: in the middle of the quenching zone (corresponding to the region where the melt temperature drops the fastest, i.e., the temperature window of 140-190℃ where the PET crystallization rate is highest), the highest air velocity is required to achieve efficient cooling solidification and crystallization induction; while in the lower part of the quenching zone, the fiber temperature is already low, and excessively high air velocities are not only unnecessary but may also cause fiber vibration and stranding. Therefore, appropriately reducing the air velocity is more conducive to stable fiber operation.

[0023] The function of the stabilizing cooling zone: After the quenching zone, the fiber temperature has dropped to approximately 80-120℃ (close to Tg but not fully cured), requiring further cooling to ensure sufficient curing and dimensional stability before winding. The stabilizing cooling zone uses natural cooling to lower the fiber temperature to below 50℃, and its length is set to 6-8 times that of the quenching zone, ensuring a smooth transition in the cooling process and avoiding stress concentration within the fiber caused by sudden temperature changes. Another important function of this zone is to allow the fiber to complete its final crystallization and structural adjustment in a low-tension, low-wind-velocity environment, providing a stable physical state for subsequent bundling, oiling, and winding processes.

[0024] Step S6, Bundling and Oiling: The cured nascent fibers are gathered by a bundler, and a spinning oil is applied with an oiling rate of 0.3-0.8%. Specifically, the cooled and cured nascent fibers are bundled into fiber bundles by a bundler, and then a spinning oil is applied to the fiber bundles through an oiling device. After oiling, the oil content uniformity CV value of the fiber bundles is ≤5%. Controlling the oiling rate is crucial for high-speed spinning processes. If the oiling rate is too low (<0.3%), the fiber surface is not sufficiently lubricated, resulting in excessive friction during subsequent stretching and winding, which easily leads to fuzzing and breakage. If the oiling rate is too high (>0.8%), it not only wastes oil and increases costs, but also causes the oil to coke on the surface of the hot roller, contaminating the equipment and affecting heat transfer. The spinning oil used in this invention is a special oil for high-speed spinning of polyester fibers, and its main components are alkyl polyoxyethylene ether, fatty alcohol polyoxyethylene ether phosphate potassium salt, polyether silicone oil, etc., which have good lubricity, antistatic properties, and thermal stability. The preferred method for applying the oil is to apply it using an oil roller or an oil nozzle. The amount of oil applied is controlled by a precision metering pump to ensure that the deviation of the amount of oil applied at each spinning position is ≤3%.

[0025] Step S7, Hot Roller Stretching: The fiber bundle is stretched by a first hot roller and a second hot roller. The temperature of the first hot roller is 80-95℃, and the temperature of the second hot roller is 120-140℃. The stretching ratio is 1.5-2.2 times, and the stretching method is either two-stage stretching or one-stage stretching. Hot roller stretching is a key process for shaping the condensed structure of the fiber. The temperature of the first hot roller, 80-95℃, is set near the glass transition temperature of PET (Tg≈70-80℃). The purpose is to provide a uniform thermal environment at the critical temperature point where the fiber begins plastic deformation, so that the molecular chains inside the fiber have sufficient mobility to respond to the stretching force. The temperature of the second hot roller, 120-140℃, is set in the cold crystallization temperature range of PET (approximately 120-150℃). At this temperature, the fiber undergoes a refinement of its crystalline structure and a further increase in orientation under the assistance of tensile stress, forming a stable shish-kebab structure. The draw ratio of 1.5-2.2 is determined based on a combination of the target fiber properties and the spinning speed: If the draw ratio is too low (<1.5), the molecular chain orientation and crystallinity are insufficient, and the fiber's mechanical properties will not meet the requirements; if the draw ratio is too high (>2.2), the internal stress of the fiber is too large, making it prone to relaxation and shrinkage in subsequent processes and during service, resulting in decreased dimensional stability. At a winding speed of 5500-8000 m / min, the nascent fiber already has a certain degree of pre-orientation, so the draw ratio can be appropriately reduced, which helps to reduce the breakage rate during the drawing process.

[0026] Step S8, Winding and Forming: After stretching, the fibers are wound at high speed using a winding machine at a speed of 5500-8000 m / min and a winding tension of 0.15-0.30 cN / dtex. The winding speed is one of the core process parameters of this invention. The speed range of 5500-8000 m / min breaks through the upper limit of traditional high-speed spinning (usually 3000-5000 m / min), increasing the productivity per unit spinning position by 40-100%. The key to achieving this ultra-high-speed winding lies in the following: a multi-stage gradient cooling system ensures that the melt stream can still complete sufficient orientation and crystallization within an extremely short solidification time (usually less than 100ms), giving the nascent fibers sufficient mechanical strength to withstand the centrifugal force and tension of high-speed winding before they enter the winding process; the use of gradient wind speed distribution and ring blowing significantly reduces the radial structural inhomogeneity of the fibers and improves the mechanical uniformity of the fibers, making them less prone to breakage caused by local stress concentration during high-speed winding; the winding tension of 0.15-0.30cN / dtex is slightly lower than that of traditional processes (usually 0.20-0.40cN / dtex) to compensate for the additional tension caused by increased air resistance during ultra-high-speed winding and prevent overstretching of the fibers.

[0027] According to one embodiment of the present invention, in step S5, the cooling method of the quenching zone adopts an annular ring-blowing method, where cooling air is blown uniformly from all sides of the fiber bundle towards the center, forming a 360° symmetrical cooling flow field; or a combination of side-blowing and annular blowing is adopted, with side-blowing in the upper part of the quenching zone and annular blowing in the lower part. The selection of the annular blowing method is based on the following principle: In the traditional side-blowing method, the cooling air is only blown in from one side of the fiber bundle, resulting in a significant difference in the cooling rate between the windward and leeward sides. Specifically, the fibers on the windward side are in direct contact with the low-temperature cooling air, and the surface layer solidifies rapidly; while the fibers on the leeward side are blocked by the fiber bundle, and the temperature of the cooling air they receive has increased and the wind speed has decreased, resulting in a significantly delayed solidification rate. This difference manifests as an asymmetric skin-core structure on the fiber cross-section at the monofilament level, and as structural and performance differences between monofilaments at different positions at the fiber bundle level. The annular airflow method blows cooling air evenly and symmetrically from all around the fiber bundle, eliminating directional differences and ensuring that each monofilament receives an equal amount of cooling medium in all circumferential directions, fundamentally improving cooling uniformity. For certain special products (such as shaped fibers), a combination of side-blowing and annular airflow can utilize the simplicity of side-blowing equipment in the upper part of the quenching zone and the cooling uniformity of annular airflow in the lower part of the quenching zone, thus balancing the requirements for optimized equipment feasibility and cooling quality.

[0028] According to one embodiment of the present invention, in step S5, the ambient temperature of the slow cooling zone is precisely regulated by a closed-loop temperature control system with a temperature control accuracy of ±2℃, and the length of the slow cooling zone is adjustable from 20-100mm. The ±2℃ temperature control accuracy is achieved by setting multiple electric heating elements and temperature sensors in the slow cooling zone, employing a PID closed-loop control algorithm to monitor and adjust the heating power in real time. The adjustable length of the slow cooling zone gives this method high process flexibility, allowing for flexible adjustment of the slow cooling time based on factors such as the intrinsic viscosity of the polyester melt, spinning speed, and target fiber properties, thus achieving precise control over the degree of molecular chain pre-orientation.

[0029] According to one embodiment of the present invention, in step S5, the cooling air velocity distribution in the quenching zone exhibits a gradient change along the axial direction. Specifically, the air velocity is lower in the upper part (pre-cooling section), highest in the middle part (upper part of the main cooling section), and then lower in the lower part (lower part of the main cooling section), forming a gradient distribution curve where the air velocity first increases and then decreases. The specific parameters of the air velocity gradient distribution curve are: air velocity v1 = 0.3-0.4 m / s in the pre-cooling section, maximum air velocity v2 = 0.6-0.8 m / s in the main cooling section, and air velocity v3 = 0.4-0.6 m / s in the lower part of the main cooling section. The shape of this air velocity gradient distribution curve has an inherent correspondence with the shape of the PET crystallization rate-temperature curve. The crystallization rate of PET is highest in the range of 140-190℃, and the middle part of the quenching zone corresponds precisely to the spatial position where the fiber temperature passes through this range. Therefore, setting the highest wind speed in the main cooling section can provide the strongest cooling driving force in the temperature range where the crystallization rate is fastest, allowing the crystallization process to be fully completed within the optimal temperature window; using a lower wind speed in the pre-cooling section and the lower part of the main cooling section can avoid surface hardening and fiber vibration caused by over-cooling, achieving "precise matching" of the cooling process.

[0030] According to one embodiment of the present invention, in step S5, the ratio of the axial lengths of the slow cooling zone, the quenching zone, and the stable cooling zone is 1:3-5:6-8. This length ratio is the optimal range obtained through extensive experiments and numerical simulations, and its design is based on the following: The slow cooling zone has the smallest length because its function is to provide the time window required for molecular chain pre-orientation. If it is too long, the melt stream will remain at high temperature for too long, which may cause thermal degradation of PET, and the increased equipment height will lead to increased investment and energy consumption; The quenching zone has a moderate length, which needs to provide enough space for the fiber temperature to drop from about 200°C to about 80-100°C to complete the main orientation locking and crystallization process. If the length is too short, the cooling will be insufficient, and if it is too long, the cooling will be excessive and the energy consumption will increase; The stable cooling zone has the largest length because the cooling rate of the fiber naturally decreases in the temperature range close to Tg, and a longer distance is needed to complete the final cooling and crystallization. Moreover, this area is naturally cooled, and extending its length will not significantly increase energy consumption.

[0031] According to one embodiment of the present invention, in step S7, a steam-heated stretching zone is provided between the first and second hot rollers, with a stretching temperature of 100-110°C, so that the fiber completes the main stretching under humid heat conditions to improve the mobility of molecular chains and the uniformity of stretching. Humid heat stretching (steam-heated stretching) is one of the preferred features of the present invention. Compared with dry heat stretching, humid heat stretching has the following advantages: water molecules, as plasticizers, penetrate into the amorphous region of PET, reducing the van der Waals forces between molecular chains, lowering Tg by about 10-15°C, and significantly enhancing the mobility of molecular chains; the heat transfer coefficient of steam is much higher than that of air, which can make the fiber uniformly heated to the stretching temperature in a very short time, reducing the radial and axial temperature gradients of the fiber; the tensile stress under humid heat conditions is lower, which can effectively reduce the stretching breakage rate, and is particularly suitable for the stretching treatment of nascent fibers under ultra-high-speed spinning conditions of 5500-8000 m / min.

[0032] According to one embodiment of the present invention, in step S2, if a chip melting method is used, the PET polyester chips are semi-dull chips (TiO2 content 0.3-0.5%), fully dull chips (TiO2 content 2.0-2.5%), or highly glossy chips (TiO2 content ≤0.1%); if a melt spinning method is used, the melt comes from a continuous polymerization production line of PTA and EG. Different matte grades of PET chips have different effects on the luster, hand feel, dyeing properties, and performance of the fibers. Semi-dull chips are the most widely used type, suitable for conventional clothing and home textile fabrics; fibers prepared from fully dull chips have a soft matte appearance and soft hand feel, suitable for high-end imitation silk fabrics; fibers prepared from highly glossy chips have a bright luster and vibrant colors, suitable for decorative fabrics and industrial yarns. The method of the present invention has good adaptability to chips of different matte grades, and stable production can be achieved without major adjustments to the parameters of the multi-stage gradient cooling system.

[0033] According to one embodiment of the present invention, in step S1, functional masterbatch may be added to the PET polyester chips. The functional masterbatch is selected from one or more of antistatic masterbatch, antibacterial masterbatch, flame retardant masterbatch, far-infrared masterbatch, and anti-ultraviolet masterbatch. The amount of functional masterbatch added is 1-10% of the mass of the polyester chips. The addition of functional masterbatch is an important way to achieve product functionalization and differentiation in this method. The addition range of 1-10% is an optimized balance between ensuring functional effect and maintaining spinnability. When the addition amount is less than 1%, the concentration of functional components is insufficient to exert a significant functional effect; when the addition amount is higher than 10%, the rheological properties of the melt change significantly (such as decreased viscosity and increased elasticity), spinnability deteriorates, and quality problems such as breakage and fuzz are prone to occur. The multi-stage gradient cooling system of the present invention has good tolerance to changes in the rheological properties of the melt. Even when the amount of functional masterbatch added is high, good spinning stability can still be maintained by appropriately adjusting parameters such as the temperature of the slow cooling zone and the wind speed of the quenching zone.

[0034] According to one embodiment of the present invention, in step S4, the cross-sectional shape of the spinneret is selected from one or more of the following: circular, trilobal, cross-shaped, hollow, flat, triangular, or polygonal. Different spinneret cross-sectional shapes can produce polyester fibers with different cross-sectional morphologies, thereby endowing the fibers with different properties such as luster, hand feel, moisture absorption and wicking, and warmth retention. For example, trilobal cross-sectional fibers have a triangular cross-section similar to natural silk, with an elegant luster and soft hand feel; hollow cross-sectional fibers have continuous axial hollow channels, making them lightweight, warm, moisture-wicking, and breathable; flat cross-sectional fibers have a large specific surface area, making them suitable for preparing high-coverage fabrics. The multi-stage gradient cooling system combined with the ring blowing method of the present invention can ensure the stability of the cross-sectional shape of the irregularly shaped cross-section melt stream during the solidification process (irregularity ≥ 85%), solving the technical problem of poor shape retention of irregularly shaped fiber cross-sections in existing high-speed spinning processes.

[0035] According to one embodiment of the present invention, in step S7, the stretched fiber bundle can also undergo relaxation heat setting treatment at a temperature of 150-180°C and a relaxation rate of 3-8% to eliminate internal stress in the fiber and improve dimensional stability. Relaxation heat setting treatment is an important means to further improve fiber dimensional stability. During the stretching process, the molecular chains are forced to orient and stretched, resulting in a thermodynamic non-equilibrium state and a tendency to spontaneously revert to a coiled conformation, manifested as boiling water shrinkage and dry heat shrinkage. Relaxation heat setting, by heat-treating the fiber at 150-180°C (higher than the upper limit of the crystallization temperature range of PET) and under low tension, causes the molecular chains in some oriented amorphous regions to relax and rearrange, and some imperfect crystalline regions to melt and recrystallize, thereby releasing internal stress, improving the crystalline structure, and significantly reducing the fiber's post-shrinkage rate. The relaxation rate of 3-8% is an adjustable parameter determined according to the target fiber performance requirements: a higher relaxation rate is used when a low shrinkage rate is required, and a lower relaxation rate is used when a high modulus is required.

[0036] According to one embodiment of the present invention, the method further includes step S9: the wound fiber bobbin is subjected to balancing treatment at a temperature of 20-28°C and a relative humidity of 60-70% for 12-24 hours to eliminate internal stress generated during the winding process. Balancing treatment is a "final" step in polyester fiber production; seemingly simple, it has a significant impact on the fiber's subsequent processing and performance. During ultra-high-speed winding at 5500-8000 m / min, the fiber bundle is tightly wound onto the bobbin under winding tension, resulting in radial compressive stress between the fiber layers. If subsequent processing (such as texturing or weaving) is performed immediately after winding, these residual stresses can cause dimensional changes and fluctuations in mechanical properties during unwinding, affecting processing stability and product quality. Balancing treatment for 12-24 hours under constant temperature and humidity conditions allows the PET molecular chains to undergo slow conformational adjustment and stress relaxation under the plasticizing effect of water molecules and driven by thermal motion, enabling the fiber to reach a stable physical state. The balanced fiber bobbins can be directly sold or enter downstream processing stages.

[0037] This invention also provides a polyester fiber prepared using the above method. The polyester fiber has the following characteristics: a breaking strength of 5.5-7.5 cN / dtex, an elongation at break of 15-25%, an initial modulus of 80-120 cN / dtex, a boiling water shrinkage of 3.0-5.5%, a radial birefringence difference ΔΔn ≤ 0.005, and a radial crystallinity difference ≤ 2%. These performance indicators comprehensively reflect the technical advantages of the method of this invention: high strength and high modulus stem from sufficient orientation-induced crystallization and the formation of a shish-kebab structure; low shrinkage stems from a perfect crystalline structure and relaxation heat setting treatment; and excellent radial uniformity (ΔΔn ≤ 0.005) stems from the synergistic effect of ring blowing and gradient cooling.

[0038] Furthermore, this invention also provides the application of the above method in the preparation of functional polyester fibers. This includes: adding antistatic masterbatch to PET polyester chips in step S1 to prepare antistatic polyester fibers, adding antibacterial masterbatch to prepare antibacterial polyester fibers, adding flame-retardant masterbatch to prepare flame-retardant polyester fibers, adding far-infrared masterbatch to prepare far-infrared polyester fibers, and adding UV-resistant masterbatch to prepare UV-resistant polyester fibers. This application fully utilizes the tolerance of the method to changes in melt rheological properties and the ability to flexibly switch between multiple varieties, enabling stable production of different functional fibers on the same production line by simply adjusting process parameters.

[0039] The core innovative principles of this invention are summarized as follows:

[0040] Time window theory: By setting a slow cooling zone of 180-240℃ below the spinneret, a sufficient time window is provided for the orientation of PET molecular chains in the viscous / elastic state, so that the molecular chain orientation can fully develop before curing, thus solving the fundamental contradiction of "freezing before orientation is completed" in traditional processes.

[0041] Precision matching theory: By using a gradient wind speed distribution that "increases first and then decreases" in the quench zone, the cooling rate and the PET crystallization rate-temperature curve are precisely matched in space. The strongest cooling driving force is provided in the temperature range with the highest crystallization rate (140-190℃), and the cooling intensity is appropriately reduced in the temperature range with the lower crystallization rate, thereby achieving the best synergy between orientation locking and crystallization induction.

[0042] Radial homogenization theory: By constructing a 360° symmetrical cooling flow field through ring blowing, the asymmetry of the skin-core structure and the structural differences between monofilaments within the fiber bundle caused by the directional differences of traditional side blowing are eliminated, thus ensuring the structural uniformity of the fiber radial and fiber bundle layers from the source.

[0043] System synergy: The three-stage gradient cooling system—slow cooling zone, rapid cooling zone (pre-cooling section + main cooling section), and stable cooling zone—along with the gradient wind speed distribution and annular air blowing method, forms a functional mutual support and a multiplier effect. The slow cooling zone provides a fully oriented state "to be locked" for the gradient cooling of the rapid cooling zone. The gradient wind speed distribution in the rapid cooling zone ensures that this orientation state is "precisely locked." The annular air blowing method ensures that the locking process is highly uniform in radial space. The stable cooling zone provides a gentle subsequent cooling for the solidified fibers. This systematic synergy enables the present invention to achieve comprehensive effects that cannot be achieved by a single technical feature, simultaneously achieving high strength (up to 7.5 cN / dtex), high radial uniformity (ΔΔn≤0.005), low breakage rate (reduced by more than 90%), and low energy consumption (reduced by 20-30%) at ultra-high-speed spinning of 5500-8000 m / min.

[0044] In summary, compared with the prior art, the present invention has at least one of the following beneficial technical effects:

[0045] This invention significantly improves spinning speed and fiber properties. By constructing a multi-stage gradient cooling system, the melt stream fully completes the axial stretching flow-induced molecular chain orientation in the slow cooling zone, and in the rapid cooling zone, the gradient cooling air velocity "locks" the molecular chain orientation state and induces crystallization, achieving optimal matching of orientation and crystallization in the time series and high uniformity in spatial position. Experimental data show that, using the method of this invention, at spinning speeds of 5500-8000 m / min, the polyester fibers prepared can achieve a breaking strength of 5.5-7.5 cN / dtex, a breaking elongation of 15-25%, and an initial modulus of 80-120 cN / dtex, significantly superior to existing high-speed spinning technologies (typically with a breaking strength of 4.5-5.5 cN / dtex). Taking a spinning speed of 6500 m / min as an example, the fiber prepared by this invention achieves a breaking strength of 6.8 cN / dtex, which is approximately 30-40% higher than existing technologies. This strength improvement is particularly valuable in the field of ultra-high-speed spinning, because PET spinning usually experiences a strength plateau or even a decline after the spinning speed exceeds 5000m / min, and this invention has successfully broken through this technical bottleneck.

[0046] This invention effectively improves the uniformity of the radial structure of fibers. By employing annular ring-blowing or a combination of side-blowing and ring-blowing, the cooling medium is applied uniformly and symmetrically from all sides of the fiber bundle, significantly reducing the radial temperature gradient and cooling rate differences. Simultaneously, the inclusion of a slow-cooling zone effectively prevents premature solidification of the fiber surface, ensuring more synchronized solidification processes between the fiber surface and core. Characterization results show that fibers prepared using this method have a radial birefringence difference ΔΔn ≤ 0.005 and a radial crystallinity difference ≤ 2%, far superior to the corresponding indicators of existing technologies (ΔΔn is typically 0.010-0.015, and the radial crystallinity difference is 4-6%), effectively solving the problem of uneven "skin-core" structure. The improvement in radial structural uniformity directly translates into improved dyeing uniformity (dyeing uniformity reaching grade 4.5 or higher) and optimized subsequent processing performance (reduced fuzz and lower breakage rate), demonstrating significant economic value.

[0047] This invention significantly reduces the spinning breakage rate and improves production stability. By optimizing the length of the slow cooling zone, the wind speed gradient distribution of the quenching zone, and the length ratio of each cooling zone, the solidification curve of the melt stream becomes smoother and more controllable, effectively reducing stress concentration and tension fluctuations during the spinning process. Simultaneously, the temperature and wind speed parameters of the multi-stage gradient cooling system are independently controllable, achieving fully digital closed-loop control of the spinning process. Pilot production data shows that, using the method of this invention, operating continuously for 72 hours at a spinning speed of 6000 m / min, the breakage rate is only 0.2-0.5 times / thousand spindles / hour, while the breakage rate of existing technologies at the same spinning speed is typically as high as 5-10 times / thousand spindles / hour, representing a breakage rate reduction of over 90%. This significant reduction in breakage rate means: a waste yarn reduction of over 90%; an increase in equipment utilization rate (OEE) of approximately 15-20%; a reduction in labor costs of approximately 30%; and a decrease in the overall cost per unit product of approximately 5-8%. For a polyester filament plant with an annual production capacity of 100,000 tons, this can generate direct economic benefits of tens of millions of yuan annually.

[0048] This invention improves the dimensional stability and dyeing uniformity of fibers. By precisely controlling the synergistic process of orientation and crystallization, the fiber achieves higher and more uniform crystallinity and orientation, thereby significantly improving the fiber's dimensional stability. Fibers prepared using this method exhibit a boiling water shrinkage rate controlled at 3.0-5.5%, a dry heat shrinkage rate (180℃, 30min) controlled at 4.0-6.5%, and a dyeing uniformity of 4.5 or higher (grey card rating), fully meeting the quality requirements of high-end textiles. The low shrinkage characteristic makes the fibers of this invention particularly suitable for blending or interweaving with low-shrinkage fibers (such as polyester-cotton blends, elastic fabrics, etc.), avoiding quality problems such as uneven fabric surface and wrinkled seams caused by shrinkage differences.

[0049] This invention enhances process flexibility and product diversity. The method of this invention offers excellent process flexibility. By adjusting process conditions such as the spinneret cross-sectional shape, the addition of functional masterbatch, the stretching ratio, and heat setting parameters, polyester fiber products with different cross-sectional shapes (round, irregular, hollow, etc.), different functional characteristics (antistatic, antibacterial, flame retardant, etc.), and different mechanical properties can be flexibly produced on the same production line. This achieves a "one-line-for-multiple-uses" production mode, significantly reducing equipment investment and switching costs for multi-variety production. Taking irregularly shaped fibers as an example, traditional processes require significant adjustments to the cooling system (including replacing the air mesh and adjusting the air box position) when switching from round fibers to irregularly shaped fibers, taking approximately 8-12 hours per cycle. With the method of this invention, only the spinneret assembly needs to be replaced and the wind speed parameters in the quenching zone fine-tuned, reducing the switching time to 2-3 hours per cycle and increasing product switching efficiency by 3-4 times.

[0050] This invention demonstrates significant energy-saving and emission-reduction effects. The spinning speed of this method is far higher than that of traditional spinning processes. Under the same production capacity conditions, the number of spinning stations and equipment required is significantly reduced, thereby significantly lowering fixed asset investment, factory floor space, utility consumption (electricity, water, gas, etc.), and labor costs per unit product. Preliminary calculations show that compared with traditional spinning processes, the overall energy consumption for producing one ton of polyester fiber using this method can be reduced by 20-30%, and carbon dioxide emissions can be reduced by more than 20%, demonstrating good economic and environmental friendliness. Specifically, taking a production line with an annual output of 100,000 tons as an example: the number of spinning positions is reduced from approximately 480 in the traditional process to approximately 320 (estimated based on an increase in spinning speed from 3500m / min to 6500m / min), resulting in a reduction of equipment investment of approximately 25%; the electricity consumption per unit product is reduced from approximately 800kWh / t to approximately 600kWh / t, saving approximately 20 million kWh of electricity annually; and the compressed air consumption per unit product is reduced from approximately 1200 Nm³ / t to approximately 900 Nm³ / t, saving approximately 30 million Nm³ of air annually. These energy-saving and emission-reduction effects not only reduce production costs but also meet the requirements of the national "dual carbon" target.

[0051] This invention broadens the application areas of polyester fibers. The high-performance polyester fibers prepared using this method, with their high strength, high modulus, excellent dimensional stability, and uniform dyeing properties, can be widely used in high-end apparel fabrics (especially imitation silk and wool fabrics), high-performance industrial textiles (such as tire cord, conveyor belts, safety belts, geotextiles, etc.), high-end home textiles, and various functional textiles, effectively expanding the application scope and market space of polyester fibers. Particularly in the field of industrial textiles, the high strength (≥7.0 cN / dtex) and low shrinkage (≤4.0%) characteristics of the fibers of this invention make them promising replacements for some nylon 66 and aramid fibers in the mid-to-high-end industrial yarn market, opening up new market opportunities. Attached Figure Description

[0052] Figure 1 This is a process flow diagram of the high-speed physical spinning method for polyester fibers according to the present invention. Detailed Implementation

[0053] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0054] In the description of this application, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0055] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0056] In the following embodiments, the mechanical properties of polyester fibers were tested according to GB / T 14344-2022 "Test Method for Tensile Properties of Chemical Fiber Filaments"; the boiling water shrinkage rate was tested according to GB / T 6505-2017 "Test Method for Heat Shrinkage Rate of Chemical Fiber Filaments"; the radial birefringence difference (ΔΔn) was measured using a polarizing microscope with a Berrick compensator; the radial crystallinity difference was measured using wide-angle X-ray diffraction (WAXD) combined with the layer-by-layer peeling method; and the dyeing uniformity was determined using the grey card rating method (GB / T 250-2008).

[0057] Example 1

[0058] Reference Figure 1 This embodiment provides a method for preparing ordinary polyester fibers using circular spinnerets, the specific steps of which are as follows:

[0059] Step S1: Raw Material Preparation: Semi-dull PET polyester chips with an intrinsic viscosity of 0.68 dL / g and a TiO2 content of 0.35% were selected. The chips were placed in a vacuum drum dryer for drying at 160℃ for 8 hours, resulting in a moisture content of 25 ppm. Controlling the moisture content of the chips is crucial for spinning stability. PET is highly susceptible to hydrolysis at melting temperatures; each mole of water molecule can lead to the breakage of one mole of ester bond, causing a decrease in molecular weight. A moisture content ≤30 ppm ensures that the intrinsic viscosity drop during melt extrusion is ≤0.02 dL / g, maintaining the stability of the fiber's mechanical properties.

[0060] Step S2, Melt Extrusion: The dried PET chips are fed into a single-screw extruder for melt extrusion. The feed section temperature of the screw extruder is 265℃, the compression section temperature is 280℃, the metering section temperature is 285℃, and the melt outlet temperature is controlled at 286℃. The screw extruder uses a BM-type split screw with a length-to-diameter ratio of 30:1 and a compression ratio of 3.5:1 to ensure sufficient plasticization, uniform mixing, and stable extrusion of the chips.

[0061] Step S3, Melt Filtration and Metering: After the melt enters the spinning box, it is first filtered through a melt filter with a filtration accuracy of 20μm, and then metered by a high-precision metering pump. The metering pump speed is set according to the target fineness of 167dtex / 48f. The filter is a disc melt filter with a filtration area ≥0.5m² / position to ensure filtration accuracy and dirt holding capacity.

[0062] Step S4, Melt Extrusion: The metered melt is extruded through a spinneret assembly. The spinneret has 48 holes, each with a diameter of 0.25 mm and an aspect ratio of 3.0:1. The spinneret cross-section is circular. The melt extrusion temperature is 288℃.

[0063] Step S5, Multi-stage gradient cooling physical forming: The molten stream extruded from the spinneret passes through the slow cooling zone, the rapid cooling zone and the stable cooling zone in sequence.

[0064] The slow cooling zone is located 30mm below the spinneret. An electric heating device surrounding the zone maintains the ambient temperature at 200℃, with a temperature control accuracy of ±2℃. The melt stream maintains a relatively high temperature in this zone, undergoing sufficient axial stretching under winding tension to pre-orient the PET molecular chains. According to online fiber temperature monitoring data during the spinning process, after passing through the slow cooling zone, the surface temperature of the melt stream remains at approximately 190-195℃, and the core temperature is approximately 210-215℃. The fiber remains in a highly elastic state, and the molecular chains possess sufficient mobility.

[0065] The quenching zone is located 30-400mm below the spinneret, employing a ring-shaped airflow system where cooling air is evenly blown from the periphery of the fiber bundle towards the center. The cooling air temperature is 20℃, and the relative humidity is 75%. The quenching zone is further divided into a pre-cooling section and a main cooling section: the pre-cooling section is located in the upper part of the quenching zone (30-150mm) with an air velocity of 0.35m / s; the main cooling section is located in the lower part of the quenching zone (150-400mm) with an air velocity of 0.65m / s. In this region, the molten fine stream rapidly cools and solidifies, "locking" the orientation structure of the pre-oriented molecular chains and inducing PET crystallization. The ring-blowing system uses a porous sintered metal cylinder as the airflow distribution element, with an opening ratio of approximately 40%, ensuring that the velocity distribution deviation of the cooling air in the circumferential direction of the fiber bundle is ≤5%.

[0066] The stable cooling zone is located 400-1000 mm below the spinneret, where the fibers are further cooled to below 45°C under natural ambient cooling. The length of the stable cooling zone is 600 mm, approximately 1.62 times the length of the quenching zone (370 mm) and 20 times the length of the slow cooling zone (30 mm). The actual length ratio (1:12.3:20) is within the preferred range of this invention.

[0067] Step S6, Bundling and Oiling: The cured nascent fibers are bundled into filament bundles by a bundler, and spinning oil is applied by an oiling device. The oiling rate is 0.5%, and the oiling uniformity CV value is 3.2%.

[0068] Step S7, Hot Roller Stretching: The fiber bundle is stretched sequentially through a first hot roller and a second hot roller. The temperature of the first hot roller is 85℃, and the temperature of the second hot roller is 130℃, with a stretching ratio of 1.8 times. A steam-heated stretching zone is set between the first and second hot rollers, with a stretching temperature of 105℃ to improve stretching uniformity. The steam-heated stretching zone uses a saturated steam injection device with a steam pressure of 0.2MPa. The steam injection direction is perpendicular to the fiber running direction to ensure that the fibers are uniformly heated in a humid and hot environment.

[0069] Step S8, Winding and Forming: After the stretched fibers are networked, they are fed into a winding machine for high-speed winding at a speed of 6500 m / min and a winding tension of 0.22 cN / dtex, forming a cylinder. The networking process uses an air networker with a network pressure of 0.3 MPa and a network density of 20-25 fibers / m.

[0070] Step S9, Balancing Treatment: The wound fiber tubes are balanced for 24 hours at a temperature of 25°C and a relative humidity of 65% to eliminate internal stress and obtain the finished product.

[0071] Performance Testing: The 167dtex / 48f polyester fiber prepared in this embodiment exhibits the following performance indicators: breaking strength 6.8 cN / dtex, breaking elongation 18.5%, initial modulus 95 cN / dtex, boiling water shrinkage 4.2%, dry heat shrinkage (180℃, 30 min) 5.0%, dyeing uniformity grade 4.5, fiber evenness CV value 1.2%, radial birefringence difference ΔΔn = 0.004, and breakage rate 0.3 times / 1000 spindles per hour (continuous operation for 72 hours at a spinning speed of 6000 m / min). Compared with Comparative Example 1 (traditional high-speed spinning process), the breaking strength is increased by 30.8%, the initial modulus by 35.7%, the boiling water shrinkage is reduced by 35.4%, the radial ΔΔn is reduced by 66.7%, and the breakage rate is reduced by 96.5%. The comprehensive and significant improvement in various performance indicators fully demonstrates the remarkable technical effect of the multi-stage gradient cooling system of this invention under ultra-high-speed spinning conditions of 6500 m / min.

[0072] Example 2

[0073] The difference between this embodiment and Embodiment 1 is that in step S5, the quenching zone uses a combination of side-blowing and annular-blowing airflow. Side-blowing airflow is used in the upper part (30-200mm) of the quenching zone, with a wind speed of 0.4m / s; annular-blowing airflow is used in the lower part (200-400mm) of the quenching zone, with a wind speed of 0.6m / s. In step S8, the winding speed is 7500m / min. Other steps and process parameters are the same as in Embodiment 1.

[0074] The technical basis for using a combination of side-blowing and ring-blowing in this embodiment is as follows: In the upper part of the quenching zone (the area closer to the spinneret), the melt stream has a higher temperature and lower viscosity. Side-blowing facilitates equipment layout and operation and maintenance, and the wind speed is relatively low (0.4 m / s) at this stage, so the directional difference of the side-blowing has a relatively small impact. In the lower part of the quenching zone, the fiber has been initially solidified, and ring-blowing ensures the symmetry of cooling and the uniformity of the radial structure. Increasing the winding speed to 7500 m / min is the upper limit of the speed range of this invention, aiming to verify the feasibility of this method and the fiber performance under extreme high-speed conditions.

[0075] Performance Testing: The 167 dtex / 48f polyester fiber prepared in this embodiment exhibits the following performance indicators: breaking strength 7.2 cN / dtex, breaking elongation 16.5%, initial modulus 105 cN / dtex, boiling water shrinkage 3.8%, dry heat shrinkage (180℃, 30 min) 4.5%, dyeing uniformity grade 4.5, radial birefringence difference ΔΔn = 0.005, and breakage rate 0.4 times / thousand spindle hours (continuous operation for 72 hours at a spinning speed of 7500 m / min). The results of this embodiment demonstrate that even at the limiting spinning speed of 7500 m / min, the method of this invention can still stably prepare high-performance fibers with a breaking strength of 7.2 cN / dtex and a breakage rate of only 0.4 times / thousand spindle hours. This verifies that the multi-stage gradient cooling system has good adaptability to ultra-high-speed spinning conditions. By combining side blowing and ring blowing, the uniformity of the radial structure (ΔΔn = 0.005) is maintained while ensuring cooling efficiency.

[0076] Example 3

[0077] The difference between this embodiment and Embodiment 1 is as follows: In step S4, the spinneret cross-sectional shape is trilobal, the number of spinneret holes is 36, and the target fineness is 83 dtex / 36f; in step S5, the length of the slow cooling zone is 40 mm, and the temperature is 210℃; the upper wind speed in the quenching zone is 0.30 m / s, and the lower wind speed is 0.70 m / s; in step S7, the stretching ratio is 1.6 times; in step S8, the winding speed is 6000 m / min. Other steps and process parameters are the same as in Embodiment 1.

[0078] This embodiment verifies the applicability of the method of the present invention to irregularly shaped cross-section fibers. The specific surface area of ​​the trilobal melt stream is larger than that of circular fibers, resulting in a faster heat dissipation rate. Therefore, the temperature of the slow cooling zone is appropriately increased to 210°C and its length extended to 40 mm to compensate for the faster heat dissipation rate and ensure sufficient pre-orientation of the molecular chains. The wind speed gradient in the quenching zone is appropriately adjusted (lower at the top and higher at the bottom) to adapt to the spatial distribution characteristics of the cooling rate of the irregular cross-section.

[0079] Performance Testing: The performance indicators of the 83dtex / 36f trilobal shaped polyester fiber prepared in this embodiment are as follows: breaking strength 6.2cN / dtex, breaking elongation 20.5%, initial modulus 82cN / dtex, shapedness ≥85%, boiling water shrinkage 4.5%, dyeing uniformity grade 4.5, and breakage rate 0.25 times / thousand spindle hours. A shapedness ≥85% indicates that the method of this invention, combined with ring-blowing cooling, can effectively maintain the shape stability of the shaped cross-section during the curing process, solving the problem of poor shape retention of shaped fiber cross-sections in traditional high-speed spinning processes. A breakage rate of 0.25 times / thousand spindle hours, even lower than the 0.3 times / thousand spindle hours in Example 1, indicates that by specifically adjusting process parameters (increasing the temperature of the slow cooling zone and reducing the upper wind speed of the quenching zone), the spinning stability of the shaped fiber can be further improved.

[0080] Example 4

[0081] The difference between this embodiment and Embodiment 1 is as follows: In step S1, antibacterial masterbatch is added to the PET polyester chips. The amount of antibacterial masterbatch added is 3% of the mass of the polyester chips, and the antibacterial agent in the antibacterial masterbatch is a silver-based inorganic antibacterial agent. In step S5, the wind speed distribution in the quenching zone adopts a gradient distribution: the wind speed in the pre-cooling section is 0.3 m / s, the maximum wind speed in the main cooling section is 0.7 m / s, and the wind speed at the bottom of the main cooling section is 0.5 m / s, forming a gradient distribution curve in which the wind speed first increases and then decreases. Other steps and process parameters are the same as in Embodiment 1.

[0082] This embodiment verifies the applicability of the method of the present invention to functional polyester fibers, and demonstrates the technical effect of the "first increase, then decrease" gradient wind speed distribution in the quenching zone. The addition of antibacterial masterbatch causes changes in the melt rheological properties, and the presence of silver-based inorganic antibacterial agent particles slightly increases the melt viscosity and slightly decreases the elasticity. The method of the present invention achieves flexible adaptation to different melt rheological properties by adjusting the wind speed in the quenching zone to a gradient distribution (v1=0.3m / s→v2=0.7m / s→v3=0.5m / s): the low wind speed in the pre-cooling section avoids the thin flow fluctuations that easily occur after the melt elasticity decreases; the high wind speed in the main cooling section ensures sufficient cooling and crystallization induction; and the medium wind speed in the lower part of the main cooling section avoids fiber vibration and yarn twisting.

[0083] Performance Testing: The 167dtex / 48f antibacterial polyester fiber prepared in this embodiment has the following performance indicators: breaking strength 6.5cN / dtex, breaking elongation 19.0%, initial modulus 90cN / dtex, boiling water shrinkage 4.3%, antibacterial rate against Staphylococcus aureus ≥99%, antibacterial rate against Escherichia coli ≥99%, antibacterial rate still ≥95% after 50 washes, and breakage rate 0.35 times / 1000 spindles / hour. The antibacterial performance test was conducted according to GB / T 20944.3-2008 "Evaluation of Antibacterial Properties of Textiles Part 3: Vibration Method". The antibacterial rate still ≥95% after 50 washes indicates that the antibacterial agent has good dispersion uniformity and binding strength in the PET matrix, which is closely related to the stable curing conditions provided by the multi-stage gradient cooling system.

[0084] Example 5

[0085] The difference between this embodiment and Embodiment 1 is as follows: In step S1, melt from the polymerization workshop is directly used for melt spinning, with a melt intrinsic viscosity of 0.70 dL / g. The melt is directly fed into the spinning box after passing through a melt conveying pipeline, a booster pump, and a melt cooler. In steps S2-S3, the chip drying and melt extrusion steps are omitted. In step S5, the slow cooling zone is 50 mm long and the temperature is 190°C; the upper air velocity in the quenching zone is 0.38 m / s, and the lower air velocity is 0.58 m / s. In step S7, a relaxation heat setting treatment is added after stretching, with a relaxation heat setting temperature of 165°C and a relaxation rate of 5%. In step S8, the winding speed is 7000 m / min. Other steps and process parameters are the same as in Embodiment 1.

[0086] This embodiment demonstrates the synergistic effect of melt spinning and relaxation heat setting. Melt spinning eliminates the drying and remelting steps of the chips, shortening the process flow and avoiding the inevitable thermal degradation of molecular chains during chip remelting, thus helping to maintain higher molecular weight and fiber mechanical properties. Relaxation heat setting (165°C, 5% relaxation rate) further optimizes the dimensional stability of the fiber, reducing boiling water shrinkage to 3.5%.

[0087] Performance Testing: The 167dtex / 48f polyester fiber prepared in this embodiment exhibits the following performance indicators: breaking strength 7.0 cN / dtex, breaking elongation 17.5%, initial modulus 98 cN / dtex, boiling water shrinkage 3.5%, dry heat shrinkage (180℃, 30 min) 4.0%, dyeing uniformity grade 4.5, and breakage rate 0.28 times / thousand spindles per hour. Compared with chip spinning, melt spinning eliminates the chip drying and remelting steps, shortening the process by more than 30 hours and reducing the overall energy consumption per unit product by about 25%. The breaking strength of this embodiment (7.0 cN / dtex) is slightly higher than that of Example 1 (6.8 cN / dtex), while the boiling water shrinkage (3.5%) is significantly lower than that of Example 1 (4.2%). This verifies the advantages of the melt spinning route in maintaining high molecular weight and the significant effect of relaxation heat setting in improving dimensional stability.

[0088] Example 6

[0089] The difference between this embodiment and Embodiment 1 is as follows: In step S4, the spinneret cross-sectional shape is hollow (C-shaped), the spinneret has 24 holes, and the target fineness is 55 dtex / 24f. In step S5, the upper air velocity in the quenching zone is 0.32 m / s, and the lower air velocity is 0.55 m / s. In step S7, the draw ratio is 1.5 times. In step S8, the winding speed is 5500 m / min. Other steps and process parameters are the same as in Embodiment 1.

[0090] This embodiment verifies the applicability of the method of the present invention to hollow fibers. During the cooling and solidification process of the molten stream extruded from the hollow (C-shaped) spinneret, the hollow structure is particularly sensitive to cooling conditions; excessively rapid cooling can cause the hollow channels to collapse, while excessively slow cooling can lead to instability in the hollow structure. This embodiment ensures that the hollow structure is fully shaped during the solidification process by appropriately reducing the air velocity in the quenching zone (0.32 m / s at the top and 0.55 m / s at the bottom) and the winding speed (5500 m / min).

[0091] Performance Testing: The 55dtex / 24f hollow polyester fiber prepared in this embodiment has the following performance indicators: breaking strength 5.8cN / dtex, breaking elongation 22.0%, initial modulus 75cN / dtex, hollowness ≥20%, boiling water shrinkage 5.0%, and breakage rate 0.45 times / thousand spindle hours. A hollowness of ≥20% indicates that this method can effectively maintain the cross-sectional structure of the hollow fiber. The formation of the hollow structure reduces the fiber density by approximately 20-25%, resulting in superior warmth retention and coverage at the same weight, making it particularly suitable for thermal insulation applications such as winter clothing, sleeping bags, and bedding fillings.

[0092] Example 7

[0093] The difference between this embodiment and Embodiment 1 is as follows: In step S1, flame-retardant masterbatch is added to the PET polyester chips, with the amount of flame-retardant masterbatch added being 8% of the mass of the polyester chips, and the flame retardant is a phosphorus-based environmentally friendly flame retardant. In step S7, the stretch ratio is 1.9 times. In step S8, the winding speed is 5800 m / min. Other steps and process parameters are the same as in Embodiment 1.

[0094] This embodiment verifies the applicability of the method of the present invention to flame-retardant functional polyester fibers. The addition of phosphorus-based flame retardants has a significant impact on the melt rheological properties, with flame retardant particles increasing melt viscosity and flow activation energy. To adapt to this change, the draw ratio was appropriately increased to 1.9 times in this embodiment to enhance molecular chain orientation and crystallization, compensating for the potential loss of mechanical properties due to the addition of flame retardants. The winding speed was reduced to 5800 m / min to increase the curing time of the melt stream, ensuring uniform dispersion and good coating of flame retardant particles in the fiber matrix.

[0095] Performance Testing: The 167dtex / 48f flame-retardant polyester fiber prepared in this embodiment exhibits the following performance indicators: breaking strength 6.3cN / dtex, breaking elongation 20.0%, initial modulus 85cN / dtex, limiting oxygen index (LOI) ≥32%, vertical burning performance meeting GB / T 17591-2006 B1 grade, and breakage rate 0.38 times / thousand spindle hours. LOI ≥32% indicates that the fiber has good self-extinguishing properties and can quickly self-extinguish after being removed from the flame; the B1 grade vertical burning performance indicates a damage length ≤150mm, afterflame time ≤5s, and smoldering time ≤5s, meeting the fabric requirements for flame-retardant protective clothing. The fiber still maintains a breaking strength of 6.3cN / dtex, indicating that the addition of phosphorus-based flame retardants and the multi-stage gradient cooling system of this invention have good compatibility.

[0096] Comparative Example 1 (Traditional High-Speed ​​Spinning Process)

[0097] This comparative example uses a traditional high-speed spinning process to prepare polyester fibers. The specific steps are as follows: Semi-dull PET chips, the same as in Example 1, were selected, dried, and then melt-extruded in a screw extruder. The melt was metered and extruded through a circular spinneret (48 holes) at an extrusion temperature of 285°C. Side-blowing air was applied directly below the spinneret for cooling; the cooling air temperature was 20°C, the air velocity was 0.5 m / s, and the cooling zone length was 800 mm. After bundling and oiling (oiling rate 0.5%), the fibers were stretched by hot rollers (first hot roller 85°C, second hot roller 130°C, stretching ratio 1.8 times), and finally wound into a tube at a speed of 5000 m / min.

[0098] This comparative example represents a typical high-speed spinning process (POY process) in the current industry. Compared with Example 1 of the present invention, the core differences are: (1) there is no slow cooling zone, and the melt stream directly enters the cooling air field after extrusion; (2) a constant wind speed side blowing is used, and there is no wind speed gradient distribution; (3) the cooling method is single side blowing; (4) the winding speed is only 5000m / min (which is the upper limit of stable operation of this process).

[0099] Performance testing: The performance indicators of the 167dtex / 48f polyester fiber prepared in this comparative example are as follows: breaking strength 5.2cN / dtex, breaking elongation 24.0%, initial modulus 70cN / dtex, boiling water shrinkage 6.5%, radial birefringence difference ΔΔn=0.012, dyeing uniformity grade 3.5, and breakage rate 8.5 times / thousand spindles per hour (continuous operation for 72 hours at a spinning speed of 5000m / min).

[0100] Comparative Example 2 (only a slow cooling zone is set up, without gradient wind speed distribution)

[0101] The difference between this comparative example and Example 1 is that the quenching zone uses a constant wind speed of 0.5 m / s, does not distinguish between the pre-cooling section and the main cooling section, and has no wind speed gradient distribution. Other steps and process parameters are the same as in Example 1.

[0102] This comparative example aims to verify the independent technical effect of gradient wind speed distribution in the quenching zone. By comparing with Example 1, the improvement in fiber performance and spinning stability caused by changing from a constant wind speed to a gradient distribution can be quantitatively evaluated.

[0103] Performance Testing: The 167 dtex / 48f polyester fiber prepared in this comparative example exhibits the following performance indicators: breaking strength 6.0 cN / dtex, breaking elongation 21.5%, initial modulus 80 cN / dtex, boiling water shrinkage 5.2%, radial birefringence difference ΔΔn = 0.008, and breakage rate 2.5 times / 1000 spindles / hour. Compared with Example 1, the breaking strength decreased by approximately 11.8%, the initial modulus decreased by approximately 15.8%, the boiling water shrinkage increased by approximately 23.8%, the radial birefringence difference ΔΔn increased by 100%, and the breakage rate increased by approximately 7.3 times. These data fully demonstrate the significant contribution of the gradient wind speed distribution in the quenching zone to the improvement of fiber performance and spinning stability.

[0104] Comparative Example 3 (without slow cooling zone)

[0105] The difference between this comparative example and Example 1 is that a slow cooling zone is not set up; the melt stream is directly cooled in the quenching zone after being extruded from the spinneret. Other steps and process parameters are the same as in Example 1.

[0106] This comparative example aims to verify the independent technical effect of the slow cooling zone setting. By comparing with Example 1, the influence of the slow cooling zone on fiber radial uniformity, mechanical properties, and spinning stability can be quantitatively evaluated.

[0107] Performance Testing: The 167dtex / 48f polyester fiber prepared in this comparative example exhibits the following performance indicators: breaking strength 5.5 cN / dtex, breaking elongation 23.0%, initial modulus 72 cN / dtex, boiling water shrinkage 5.8%, radial birefringence difference ΔΔn = 0.010, and breakage rate 5.0 times / 1000 spindles / hour. Compared with Example 1, the breaking strength decreased by approximately 19.1%, the initial modulus decreased by approximately 24.2%, the radial birefringence difference ΔΔn increased by 150%, and the breakage rate increased by approximately 15.7 times. This result profoundly reveals the crucial role of the slow cooling zone in ultra-high-speed spinning. Without a slow cooling zone, even with ring blowing and gradient airflow distribution, fiber performance still significantly decreased, and the breakage rate increased sharply. This indicates that the molecular chains did not obtain a sufficient orientation time window before solidification, resulting in the subsequent gradient cooling losing the "to-lock" highly oriented state.

[0108] Comparative Example 4 (using side blowing air instead of ring blowing air)

[0109] The difference between this comparative example and Example 1 is that the quenching zone uses side blowing instead of ring blowing, while the other steps and process parameters are the same as in Example 1.

[0110] This comparative example aims to verify the independent technical effect of the ring blowing method on the radial structural uniformity of fibers.

[0111] Performance Testing: The 167dtex / 48f polyester fiber prepared in this comparative example exhibits the following performance indicators: breaking strength 6.3 cN / dtex, radial birefringence difference ΔΔn = 0.009, and dyeing uniformity grade 3.5. Compared to Example 1, the breaking strength decreased by approximately 7.4%, the radial ΔΔn increased by 125%, and the dyeing uniformity decreased from grade 4.5 to grade 3.5. These data demonstrate the crucial role of the ring-blowing method in improving the radial structural uniformity of the fiber, and the direct impact of radial uniformity on dyeing performance. The cooling difference between the windward and leeward sides caused by side-blowing (ΔΔn = 0.009) manifests as significant dyeing unevenness in subsequent dyeing processes.

[0112] Comprehensive comparative analysis of the examples and comparative examples

[0113] The performance indicators of Examples 1-7 and Comparative Examples 1-4 were summarized and compared, and the results are shown in Table 1.

[0114] Table 1 Performance comparison of each embodiment and comparative example

[0115] index Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Fracture strength (cN / dtex) 6.8 7.2 6.2 6.5 7.0 5.8 6.3 5.2 6.0 5.5 6.3 Elongation at break (%) 18.5 16.5 20.5 19.0 17.5 22.0 20.0 24.0 21.5 23.0 — Initial modulus (cN / dtex) 95 105 82 90 98 75 85 70 80 72 — Boiling water shrinkage rate (%) 4.2 3.8 4.5 4.3 3.5 5.0 — 6.5 5.2 5.8 — Radial ΔΔn 0.004 0.005 — 0.004 0.003 — — 0.012 0.008 0.010 0.009 Breakage rate (times / thousand spindles per hour) 0.3 0.4 0.25 0.35 0.28 0.45 0.38 8.5 2.5 5.0 — Spinning speed (m / min) 6500 7500 6000 6500 7000 5500 5800 5000 6500 6500 6500 Dyeing uniformity (grade) 4.5 4.5 4.5 — 4.5 — — 3.5 — — 3.5

[0116] As can be seen from the data in Table 1:

[0117] (1) Significantly improved mechanical properties: The breaking strength and initial modulus of Examples 1-7 were significantly higher than those of Comparative Examples 1-4. Among them, Example 2 achieved a breaking strength of 7.2 cN / dtex and an initial modulus of 105 cN / dtex at an ultra-high speed of 7500 m / min, which were 38.5% and 50.0% higher than those of Comparative Example 1, respectively. This shows that the multi-level gradient cooling system and orientation-crystallization synergistic control strategy of the present invention can effectively maintain and improve the mechanical properties of fibers under ultra-high speed spinning conditions. It is particularly noteworthy that the fiber strength (7.2 cN / dtex) prepared in Example 2 at 7500 m / min was higher than that of Example 1 at 6500 m / min (6.8 cN / dtex), which is completely contrary to the traditional understanding that "the higher the spinning speed, the lower the strength," and is an unexpected technical effect produced by the present invention.

[0118] (2) Significantly improved radial structural uniformity: The radial birefringence difference ΔΔn in Examples 1-5 is ≤0.005, which is much smaller than 0.012 in Comparative Example 1 and 0.010 in Comparative Example 3. This indicates that the present invention significantly reduces the radial temperature gradient and cooling rate difference of the fiber by setting up a slow cooling zone and adopting annular air blowing / composite cooling method, effectively improving the problem of uneven "skin-core" structure. The improvement in radial uniformity directly translates into an improvement in dyeing uniformity. The dyeing uniformity of Example 1 reaches grade 4.5, while that of Comparative Example 1 and Comparative Example 4 is only grade 3.5.

[0119] (3) Enhanced dimensional stability: The boiling water shrinkage rates of Examples 1-6 were all controlled within the range of 3.5-5.0%, significantly lower than the 6.5% of Comparative Example 1, indicating that the fibers prepared by the method of the present invention have higher crystallinity and a more complete crystal structure, thus exhibiting superior dimensional stability. Example 5 adopted melt direct spinning + relaxation heat setting, with a boiling water shrinkage rate as low as 3.5%, which was 46.2% lower than that of Comparative Example 1, demonstrating the synergistic effect of multiple preferred features.

[0120] (4) Significantly improved production stability: The breakage rate of Examples 1-7 was between 0.25-0.45 times / thousand spindle hours, while Comparative Example 1 was as high as 8.5 times / thousand spindle hours, Comparative Example 2 was 2.5 times / thousand spindle hours, and Comparative Example 3 was 5.0 times / thousand spindle hours. The breakage rate of the examples was only 3-5% of that of the traditional process, which fully demonstrates that the multi-stage gradient cooling system of the present invention can effectively improve the stability of the spinning process and significantly reduce the breakage rate.

[0121] (5) Importance of the slow cooling zone: Comparing the data of Example 1 and Comparative Example 3 (without the slow cooling zone), the fracture strength decreased from 6.8 cN / dtex to 5.5 cN / dtex without the slow cooling zone, the breakage rate increased dramatically from 0.3 times / thousand spindle hours to 5.0 times / thousand spindle hours, and the radial ΔΔn increased from 0.004 to 0.010. This shows that the slow cooling zone is crucial for the sufficient orientation of the melt stream before solidification and for preventing premature surface solidification, which is one of the core innovations of this invention.

[0122] (6) Contribution of gradient wind speed distribution: Comparing the data of Example 1 and Comparative Example 2 (without gradient wind speed distribution), the fracture strength decreased from 6.8 cN / dtex to 6.0 cN / dtex when there was no gradient wind speed distribution, while the breakage rate increased from 0.3 times / thousand spindle hours to 2.5 times / thousand spindle hours. This indicates that the gradient wind speed distribution in the quenching zone (low wind speed in the pre-cooling section and high wind speed in the main cooling section) can better match the different cooling rate requirements of the melt stream at different stages of solidification, and is a key means to optimize the orientation-crystallization synergistic process.

[0123] (7) Contribution of the ring-blowing method: Comparing the data of Example 1 and Comparative Example 4 (using side-blowing), when using side-blowing, the breaking strength decreased from 6.8 cN / dtex to 6.3 cN / dtex, the radial ΔΔn increased from 0.004 to 0.009, and the dyeing uniformity decreased from grade 4.5 to grade 3.5. This demonstrates the important role of the ring-blowing method in improving radial uniformity and dyeing performance.

[0124] (8) Comprehensive analysis of synergistic effect: By comparing the data of Example 1 with Comparative Examples 2, 3 and 4, the synergistic relationship between various technical features can be further revealed: Only a slow cooling zone is set but no gradient wind speed distribution (Comparative Example 2): the intensity is increased by about 15.4% (compared to the absence of a slow cooling zone in Comparative Example 3); Only a gradient wind speed distribution is set but no slow cooling zone (Comparative Example 3): the intensity is 5.5 cN / dtex; Only annular air blowing is used but no slow cooling zone + no gradient wind speed distribution (Comparative Example 4): the intensity is 6.3 cN / dtex, but the radial uniformity is poor; Simultaneously setting a slow cooling zone + gradient wind speed distribution + annular air blowing (Example 1): the intensity reaches 6.8 cN / dtex, radial ΔΔn=0.004, and the breakage rate is 0.3 times / thousand spindle hours.

[0125] The above data demonstrates a significant synergistic effect among the three technical features: slow cooling zone, gradient air velocity distribution, and annular blowing. The combined technical effect (strength 6.8 cN / dtex, ΔΔn=0.004, breakage rate 0.3 times / thousand spindles per hour) when all three are used simultaneously is far greater than the sum of the effects of each individual feature. Specifically: the slow cooling zone provides a sufficient time window for pre-orientation (solving the question of "when to orient"), the gradient air velocity distribution provides a cooling regime that matches crystallization kinetics (solving the question of "how to lock"), and the annular blowing provides a radially symmetrical cooling flow field (solving the question of "where to solidify" and ensuring spatial uniformity). All three are indispensable and together constitute a complete and systematic technical solution.

[0126] The core innovation of this invention lies in constructing a multi-stage gradient cooling system consisting of a "slow cooling zone → rapid cooling zone (pre-cooling section + main cooling section) → stable cooling zone," thereby achieving precise physical control of the temperature, velocity, and stress fields of the melt stream throughout the solidification process. This results in optimal matching of PET molecular chain orientation and crystallization in both temporal and spatial dimensions. The principles and mechanisms of each technical feature are analyzed in detail below.

[0127] In traditional high-speed spinning processes, the molten filament is immediately blown by cooling air after being extruded from the spinneret, causing the surface temperature to drop rapidly below the glass transition temperature (Tg), forming a rigid skin. This premature formation of the skin not only prevents further orientation and alignment of the molecular chains under axial tensile force but also generates significant skin-core shrinkage differences during subsequent cooling, leading to uneven internal stress and structure.

[0128] The core principle of this invention's slow cooling zone lies in maintaining a relatively high ambient temperature (180-240℃) in the initial stage (0-100mm region) after the molten stream is extruded from the spinneret. This allows the molten stream to remain in a viscous or elastic state for a sufficiently long time, enabling it to undergo sufficient axial stretching under winding tension and complete the pre-orientation of the PET molecular chains. Research shows that the orientation relaxation time of PET molecular chains in the viscous state is on the order of milliseconds. The length and temperature design of the slow cooling zone ensure that the time window for molecular chain orientation is greater than the relaxation time, allowing for effective accumulation of orientation. Taking a winding speed of 6500m / min as an example, the time for the molten stream to pass through the 30mm slow cooling zone is approximately 2.8ms. This time window is greater than the orientation relaxation time of PET at 200℃ (approximately 1.5-2.0ms), thus allowing for effective accumulation of molecular chain orientation without being negated by the relaxation process.

[0129] Another important function of the slow cooling zone is to prevent premature solidification of the molten flow surface. PET has a Tg of approximately 70-80℃, and a hard shell forms when the surface temperature drops below Tg. The slow cooling zone controls the ambient temperature at 180-240℃, which is much higher than Tg, effectively delaying the surface curing time. This allows the fiber surface and core layer to complete the curing process more synchronously, significantly improving the uniformity of the radial structure.

[0130] The comparison results between Example 1 and Comparative Example 3 fully verify the key role of the slow cooling zone: without the slow cooling zone, the fiber breaking strength decreases by about 20%, the breakage rate increases by about 15 times, and the radial ΔΔn increases by 1.5 times.

[0131] After the molecular chains are pre-oriented in the slow cooling zone, this orientation state needs to be "locked" quickly in the quenching zone to induce crystallization. However, the cooling rate in the quenching zone is not necessarily better the higher it is. If strong cooling is carried out at a high wind speed from the beginning, the following problems will occur: (1) The fiber surface solidifies rapidly to form a hard shell, and the core melt is sealed inside and cannot be further oriented; (2) The excessively fast cooling rate does not give the molecular chains enough time to arrange the lattice, resulting in incomplete crystallization, small grain size and many defects; (3) Sudden thermal contraction generates large internal stress.

[0132] This invention achieves a "soft landing" in the cooling process by dividing the quenching zone into a pre-cooling section and a main cooling section, and employing different air velocities (0.3-0.5 m / s in the pre-cooling section and 0.5-0.8 m / s in the main cooling section). The pre-cooling section uses a lower air velocity to initially stabilize the orientation state accumulated in the slow cooling zone of the melt stream, while simultaneously inducing crystal nucleation. The main cooling section uses a higher air velocity to promote rapid grain growth and refinement based on nucleation, ultimately completing the fiber solidification.

[0133] Furthermore, this invention proposes a gradient distribution curve in the quenching zone where the wind speed first increases and then decreases (wind speed v1 = 0.3-0.4 m / s in the pre-cooling section, maximum wind speed v2 = 0.6-0.8 m / s in the main cooling section, and wind speed v3 = 0.4-0.6 m / s in the lower part of the main cooling section). This gradient distribution design is based on the following considerations: in the middle of the quenching zone (corresponding to the area where the melt temperature drops the fastest), the highest wind speed is required to achieve efficient cooling and solidification; while in the lower part of the quenching zone, the fiber temperature is already low, and excessively high wind speeds are not only unnecessary but may also cause fiber vibration and yarn twisting. Therefore, appropriately reducing the wind speed is more conducive to the stable operation of the fiber.

[0134] The comparison results between Example 1 and Comparative Example 2 verify the superiority of gradient wind speed distribution: with gradient distribution, the fracture strength is increased by about 13% and the breakage rate is reduced by about 88%.

[0135] In the traditional side-blowing method, the cooling air is blown in from only one side of the fiber bundle, resulting in a significant difference in the cooling rate between the windward and leeward sides, which is one of the main reasons for the uneven radial structure of the fiber.

[0136] This invention employs a ring-shaped airflow method, where cooling air is blown evenly and symmetrically from all sides of the fiber bundle towards its center, forming a 360° symmetrical cooling flow field. This ensures that each monofilament receives an equal amount of cooling medium in all circumferential directions, making the cooling process completely symmetrical in the circumferential direction. For certain special products (such as irregularly shaped fibers), this invention also proposes a combined side-blowing and ring-blowing method. Side-blowing is used in the upper part of the quenching zone (for ease of operation and equipment layout), while ring-blowing is used in the lower part of the quenching zone (to ensure cooling uniformity), thus balancing the dual requirements of equipment feasibility and cooling uniformity. Another advantage of the ring-blowing method is that, because the cooling air converges from all sides towards the center, a certain positive pressure is formed in the central area of ​​the fiber bundle, effectively preventing the entrainment of ambient air and avoiding the impact of ambient temperature and humidity fluctuations on the stability of the cooling process.

[0137] In this invention, the preferred ratio of the axial lengths of the slow cooling zone, the quenching zone, and the stable cooling zone is 1:3-5:6-8. This length ratio is the optimal range obtained through extensive experimental optimization. If the slow cooling zone is too short, the molecular chain pre-orientation will be insufficient; if the slow cooling zone is too long, it will affect production efficiency, and the excessive residence time of the melt stream at high temperature may lead to thermal degradation. If the quenching zone is too short, the cooling will be insufficient, and the fiber will not solidify completely; if the quenching zone is too long, it will increase the equipment height and energy consumption. The function of the stable cooling zone is to ensure that the fiber is sufficiently cooled before winding. If it is too short, the fiber temperature will be too high during winding, affecting the winding quality; if it is too long, it will increase the equipment height and floor space. Taking Example 1 as an example, the actual length ratio of the slow cooling zone:quenching zone:stable cooling zone is 1:12.3:20. Although it slightly exceeds the upper limit of the quenching zone ratio in the preferred range (1:3-5:6-8), it is still within an acceptable range, and it is compensated for by adjusting the wind speed gradient distribution in the quenching zone. In actual industrial production, the length ratio of each zone can be flexibly adjusted within the above-mentioned preferred range according to equipment conditions and product requirements.

[0138] Under ultra-high-speed spinning conditions of 5500-8000 m / min, the inertial force and air resistance experienced by the melt stream are much greater than those under traditional spinning conditions, and the stress on the spinning line can reach as high as 0.1-1.0 MPa. Under this high stress, the orientation behavior of PET molecular chains changes from the traditional "stretch flow-induced orientation" to "stress-induced orientation," with both the orientation speed and the degree of orientation significantly improved.

[0139] This invention provides a sufficient time window for stress-induced orientation by setting up a slow cooling zone, allowing the molecular chains to achieve a highly oriented alignment in a high-stress field. Subsequently, under the gradient cooling effect of the quenching zone, the oriented molecular chains rapidly crystallize during the cooling process, forming a highly oriented crystal structure (shish-kebab structure), which endows the fiber with excellent mechanical properties. The realization of this orientation-crystallization synergistic mechanism is the fundamental reason why this invention can prepare high-performance fibers under ultra-high-speed spinning conditions.

[0140] The formation mechanism of the shish-kebab structure is as follows: In the high-stress field of the slow-cooling zone, some PET molecular chains are highly extended and oriented along the fiber axis, forming shish (the "string" of crystals), which are extended chain nuclei arranged along the fiber axis. After entering the quenching zone, the temperature drops to the crystallization temperature window (140-190℃), and the remaining molecular chains use the shish as a template for epigenetic crystallization, forming kebabs (the "crystals" of crystals), which are folded chain crystalline wafers perpendicular to the fiber axis. This shish-kebab structure combines the high orientation of the shish portion with the high crystallinity of the kebab portion, which is the essential source of the fiber's high strength and high modulus. This invention maximizes the formation efficiency of the shish-kebab structure through a combination of slow-cooling zone (creating high-stress orientation conditions) and quenching zone gradient cooling (providing the optimal temperature window for epigenetic crystallization), thereby achieving a breakthrough improvement in the fiber's mechanical properties.

[0141] The implementation principle of this invention is as follows: This invention discloses a high-speed physical spinning method for polyester fibers, belonging to the field of chemical fiber forming technology. Addressing the problems of poor orientation and crystallization synergy, uneven radial structure, and high breakage rate in existing high-speed spinning methods, this invention's method includes: the melt is extruded from the spinneret and sequentially undergoes multi-stage gradient cooling and forming through a slow cooling zone, a rapid cooling zone, and a stable cooling zone; the slow cooling zone temperature of 180~240℃ ensures sufficient pre-orientation of the melt stream; the rapid cooling zone is divided into a pre-cooling section and a main cooling section with a gradient air velocity distribution, employing a ring-blowing or composite cooling method; then, the fibers are bundled, oiled, and stretched with hot rollers, and wound at high speed at 5500~8000 m / min. This invention achieves optimal timing matching and spatial homogenization of orientation and crystallization, producing fibers with a strength of 5.5~7.5 cN / dtex, uniform radial structure, and a breakage rate reduced by more than 90%, while also possessing advantages such as high process flexibility and low energy consumption.

[0142] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-speed physical spinning method for polyester fibers, characterized in that, Includes the following steps: Step S1, Raw material preparation: Select PET polyester chips with an intrinsic viscosity of 0.65-0.85 dL / g and dry them in a vacuum drum dryer at 140-170℃ for 6-12 hours, controlling the moisture content of the chips to ≤30ppm; or, directly use the melt from the polymerization workshop for melt direct spinning, with a melt intrinsic viscosity of 0.65-0.75 dL / g; Step S2, Melt Extrusion: The dried chips obtained in step S1 are fed into a screw extruder for melt extrusion. The temperature of each section is 260-290℃, and the melt outlet temperature is 280-290℃. If melt direct spinning is used, the melt is directly fed into the spinning box through the conveying pipe. Step S3, Melt Filtration and Metering: The melt obtained in step S2 is fed into the spinning box, filtered by a melt filter with a filtration accuracy of 15-30μm, and then accurately metered by a high-precision metering pump. Step S4, Melt Extrusion: The metered melt is extruded through a spinneret to form a fine melt stream. The spinneret has 24-288 holes, the diameter of the spinneret holes is 0.15-0.30 mm, the length-to-diameter ratio of the spinneret holes is 2.0-3.5:1, and the extrusion temperature is 280-295℃. Step S5, Multi-stage gradient cooling physical forming: The molten fine stream extruded from the spinneret passes sequentially through a slow cooling zone, a rapid cooling zone, and a stable cooling zone; the slow cooling zone is located 0-100mm below the spinneret, with an ambient temperature of 180-240℃; the rapid cooling zone is located 100-500mm below the spinneret, including a pre-cooling section and a main cooling section, with a wind speed of 0.3-0.5m / s in the pre-cooling section and 0.5-0.8m / s in the main cooling section, a cooling air temperature of 15-25℃, and a relative humidity of 65-85%; the stable cooling zone is located 500-1200mm below the spinneret, where natural cooling reduces the fiber temperature to below 50℃; Step S6, Bundling and Oiling: The cured nascent fibers are bundled by a bundler and a spinning oil is applied, with an oiling rate of 0.3-0.8%; Step S7, Hot Roller Stretching: The fiber bundle is stretched by the first hot roller and the second hot roller. The temperature of the first hot roller is 80-95℃, the temperature of the second hot roller is 120-140℃, and the stretching ratio is 1.5-2.2 times. Step S8, winding and forming: After stretching, the fiber is wound at high speed by a winding machine at a speed of 5500-8000m / min and a winding tension of 0.15-0.30cN / dtex.

2. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, In step S5, the cooling method of the quenching zone is a ring-shaped air blowing method, in which the cooling air is blown evenly from all sides of the fiber bundle to the center to form a 360° symmetrical cooling flow field; or a combination of side blowing and ring blowing is used, with side blowing in the upper part of the quenching zone and ring blowing in the lower part.

3. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, In step S5, the cooling air velocity distribution in the quench zone varies along the axial direction in a gradient manner, forming a gradient distribution curve in which the air velocity first increases and then decreases: the air velocity in the pre-cooling section is v1=0.3-0.4m / s, the maximum air velocity in the main cooling section is v2=0.6-0.8m / s, and the air velocity in the lower part of the main cooling section is v3=0.4-0.6m / s.

4. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, In step S5, the ratio of the axial lengths of the slow cooling zone, the rapid cooling zone, and the stable cooling zone is 1:3-5:6-8.

5. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, In step S7, a steam-heated stretching zone is provided between the first hot roller and the second hot roller, with a stretching temperature of 100-110℃, so that the fiber completes the main stretching under humid and hot conditions.

6. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, In step S2, if the chip melting method is used, the PET polyester chips are semi-dull chips, full-dull chips, or highly glossy chips; if the melt spinning method is used, the melt comes from the continuous polymerization production line of PTA and EG.

7. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, In step S1, functional masterbatch may be added to the PET polyester chips. The functional masterbatch is selected from one or more of antistatic masterbatch, antibacterial masterbatch, flame retardant masterbatch, far-infrared masterbatch, and anti-ultraviolet masterbatch. The amount of functional masterbatch added is 1-10% of the mass of the polyester chips.

8. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, In step S4, the cross-sectional shape of the spinneret is selected from one or more of the following: circular, trilobal, cross-shaped, hollow, flat, triangular, or polygonal.

9. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, In step S7, the stretched fiber bundles can also undergo relaxation heat setting treatment. The relaxation heat setting temperature is 150-180℃, and the relaxation rate is 3-8%.

10. The high-speed physical spinning method for polyester fibers according to claim 1, characterized in that, The method further includes step S9: the wound fiber tube is subjected to equilibration treatment at a temperature of 20-28℃ and a relative humidity of 60-70% for 12-24 hours.

Images