A method for regulating the elasticity of polyester composite fibers by cooling air blowing

Abstract

This invention discloses a method for controlling the elasticity of polyester composite fibers through cooling air blowing. Two sets of polyester component melts are separately metered and fed into a composite spinning assembly, where they are extruded through a spinneret to form fine composite melt streams. Subsequently, elastic directional cooling is performed, including a slow cooling zone, a main cooling air blowing zone, and an optional secondary temperature-controlled cooling zone. By adjusting the length and temperature of the slow cooling zone, the air temperature, speed, direction, and volume distribution and cooling length of the main cooling air blowing zone, as well as the temperature and length of the secondary temperature-controlled cooling zone, nascent fibers with controllable internal orientation, crystallization, and thermal shrinkage differences are formed, which are then transformed into different degrees of crimp elasticity during subsequent processing. This method is applicable to various composite fiber systems, transforming the cooling air blowing method from a conventional forming process into a means of actively controlling the curing path of the two components. This achieves controllable design of shrinkage differences and crimp structures, enabling the stable preparation of low, medium, and high elasticity polyester composite fibers without relying on raw material selection.

Description

Technical Field

[0001] This invention relates to a method for controlling the elasticity of polyester composite fibers, and more particularly to a method for controlling the elasticity of polyester composite fibers by cooling air blowing, belonging to the field of polyester composite fiber preparation technology. Background Technology

[0002] Polyester composite fibers are typically produced by a composite spinning process using two or more polyester components. Due to differences in glass transition temperature, crystallization rate, melt viscosity, orientation ability, and heat shrinkage properties among the different components, differential shrinkage occurs between the components during subsequent drawing, heat setting, and relaxation processes. This results in a crimped structure, giving the fiber a certain degree of elasticity. Typical polyester composite fibers include PET / PTT composite fibers, PET / PBT composite fibers, polyester elastomer / PET composite fibers, and low-melting-point polyester / conventional polyester composite fibers. In existing technologies, the control of elasticity in polyester composite fibers typically focuses on the raw material composition, the mass ratio of the two components, the intrinsic viscosity of the polymer, and the cross-sectional structure of the fiber. Differential shrinkage can be generated by selecting polyester elastomer as one component and PET as the other, or by using asymmetrical cross-sectional structures such as side-by-side or eccentric core-sheath types, thus obtaining composite fibers with crimped elasticity. For example, Chinese patent CN201010257439.4 discloses a modified polyester composite fiber, which uses modified polyester and thermoplastic resins such as PBT, PTT, or PA6 in parallel or eccentric core-sheath cross-sectional structures to impart self-crimping elasticity to the fiber by utilizing the difference in thermal shrinkage between the two components. However, this type of method still relies on the adjustment of raw material formulation and the design of cross-sectional structure. Once the formulation and spinneret are determined, the elasticity level is fixed, making it difficult to switch between multiple elasticity levels within the same system. In addition, unlike the composite fibers mentioned above that focus on elasticity regulation, existing technologies for low-melting-point polyester composite fibers pay more attention to their low-melting-point thermal bonding properties, melt spinnability, and stability in continuous production to meet the needs of specific application scenarios.

[0003] However, in actual spinning processes, the composite melt streams ejected from the spinneret need to be cooled and solidified. Traditionally, cooling air is considered a routine process condition to ensure fiber formation and evenness, primarily focusing on issues such as fiber breakage, yarn twisting, insufficient cooling, and unevenness, while rarely being utilized as an independent means of elasticity control. Especially in polyester composite fibers, different components exhibit significant differences in their response to cooling rates, airflow direction, airflow speed, and temperature gradients. Therefore, the cooling and solidification stage directly affects the orientation freezing, crystallization development, interfacial stress formation, and subsequent thermal shrinkage differences of each component. Consequently, adjusting fiber elasticity solely by modifying the raw material formulation or cross-sectional structure has limitations such as a narrow applicability, a small process window, and the difficulty in obtaining multiple grades of elasticity products from the same formulation.

[0004] For the same or similar composite spinning systems, if controllable differences in curing and thermal shrinkage can be created by changing the cooling air blowing method, then flexible switching between low-elasticity, medium-elasticity, and high-elasticity products can be achieved without significantly altering the raw material system. Based on this, it is necessary to propose a method for controlling the elasticity of polyester composite fibers with the cooling air blowing method as the core control variable. This transforms the cooling process from a mere conventional forming step into a crucial element for actively controlling the crimp elasticity and elasticity level of the composite fibers. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems and provide a method for adjusting the elasticity of polyester composite fibers by cooling air blowing.

[0006] The technical solution of this invention is: a method for regulating the elasticity of polyester composite fibers by cooling air blowing, comprising the following steps:

[0007] Step (I) Selects the first polyester component melt and the second polyester component melt as raw materials for preparing polyester composite fibers. Both the first and second polyester component melts are provided by a continuous polymerization melt direct spinning system and / or by melt extrusion of polyester chips via a screw extruder. This method is applicable to various spinning routes, such as: 1) Continuous polymerization melt direct spinning route: The first and / or second polyester component melts are directly provided by a continuous polymerization system and transported to the composite spinning assembly via melt pipelines. This route is suitable for the continuous production of low-melting-point polyester composite fibers, modified polyester composite fibers, and conventional polyester composite fibers; 2) Chip melt composite spinning route: The first and second polyester component melt chips are pre-crystallized, dried, and melted by screw extrusion before entering the composite spinning assembly. This route is suitable for composite elastic fibers such as polyester elastomer / PET, PET / PTT, PET / PBT, and PET / modified polyester; 3) Combined route: One component is directly provided by a continuous polymerization melt, while the other component is provided by melt extrusion of chips via a screw extruder. This approach is suitable for industrial scenarios where one component is not suitable for chip drying or is more suitable for continuous polymerization, while the other component is suitable for chip spinning.

[0008] Step (II) involves separately metering the first and second polyester component melts, then feeding them together into a composite spinning assembly. The metered first and second polyester component melts are ejected through a spinneret, forming a composite melt stream. After being ejected from the spinneret, the first and second polyester component melts cool and solidify together within the same filament. Due to differences in glass transition temperature, crystallinity, thermal diffusivity, melt viscosity, and interfacial adhesion between the two components, the cooling conditions affect the order of solidification and the degree of orientation freezing. When using a strong, low-temperature, high-speed, and symmetrical cooling method, the composite melt stream solidifies rapidly, the chain segment relaxation time of the two components is short, the orientation and crystallization differences are limited, the subsequent thermal shrinkage difference is small, and the fiber crimping driving force is weak, making it suitable for preparing low-elasticity or dimensionally stable products. When using a moderately slow cooling method with medium wind speed and slight asymmetric cooling, one polyester component melt can maintain a high orientation, while the other polyester component melt obtains a certain chain segment relaxation and crystallization adjustment time, and the two components form a moderate differential shrinkage, making it suitable for preparing medium-elasticity products with a relatively balanced elasticity and strength. When using a long, slow cooling method with higher wind temperature, lower wind speed, and asymmetric cooling, a significant temperature gradient and crystallization gradient are formed within the cross-section of the composite fiber, and the two polyester component melts produce a large differential shrinkage during subsequent stretching, heat setting, and relaxation processes, thereby forming a stronger two-dimensional or three-dimensional crimped structure, making it suitable for preparing high-elasticity, fluffy, or soft products.

[0009] Step (III) involves elastically directional cooling of the composite melt stream from Step (II). During this elastic directional cooling process, in which cooling air is applied to the spun filament to create differential shrinkage between the two components, the tension of the filament before entering the first drafting roller or the guide roller is controlled to be 0.02–0.30 cN / dtex. This tension range prevents the filament from being excessively stretched beyond 0.30 cN / dtex in the cooling zone, thereby reducing the offsetting effect of excessive tension on the difference in cooling rates between the two components and the crimping shrinkage potential stored by this difference. The difference in cooling rates refers to the difference in shrinkage potential formed by the different crystallization rates of the two components during cooling. The crimping shrinkage potential refers to the degree of crimping that the fiber can spontaneously form under subsequent tension-free relaxation conditions. This elastic directional cooling includes several cooling zones arranged sequentially along the melt stream's direction of travel. The domains are the slow cooling zone below the spinneret, the main cooling air blowing zone, and any one of the secondary temperature-controlled cooling zones. Simultaneously, an elastic control method is employed, adjusting the cooling parameters of at least one of these zones. These parameters include one or more of cooling air temperature, cooling air velocity, cooling air humidity, cooling time, and cooling zone length. This causes the first and second polyester component melts to form pre-defined orientation, crystallization, and thermal shrinkage differences during the cooling and solidification process. The thermal shrinkage difference directly leads to different degrees of shrinkage in the two components during subsequent heat treatment or relaxation, thereby driving the fiber to form a specific morphological crimped structure. The crimp degree, crimp elasticity, and elastic recovery performance of this crimped structure are determined by the numerical combination of the orientation, crystallization, and thermal shrinkage differences.

[0010] Step (iv) After the cooled nascent yarn is subjected to stretching, heat setting and relaxation treatment in sequence, it is wound and / or cut to obtain elastic adjustable polyester composite fiber.

[0011] Specifically, the slow cooling zone is located between the spinneret outlet and the starting point of the main cooling airflow. This slow cooling zone comprises at least one or a combination of an insulation cylinder, a slow cooling hood, a heating jacket, a hot air protection zone, and an adjustable baffle plate. The length of the slow cooling zone is 20–350 mm, and the temperature is 35–130°C. The function of the slow cooling zone includes mitigating the rapid cooling impact on the composite melt stream immediately after ejection, extending the relaxation time of molecular chain segments, reducing stress concentration at the interface between the two components, and laying the foundation for differential curing during the main cooling airflow stage. Furthermore, a shorter slow cooling zone results in faster curing and generally better fiber evenness and strength, but correspondingly weaker crimp elasticity. Appropriately extending the slow cooling zone can increase the potential crimp driving force, but an excessively long slow cooling zone may lead to problems such as filament bundling, adhesion, or unstable forming.

[0012] Specifically, the main cooling air blowing zone uses at least one of the following methods or any combination of circumferential blowing, radial blowing, and side blowing: side blowing, which includes single-sided side blowing, double-sided symmetrical side blowing, eccentric side blowing, or segmented asymmetrical side blowing. The cooling air temperature of the main cooling air blowing zone is 8–40°C, the cooling air velocity is 0.10–1.50 m / s, and the cooling length is 500–2000 mm.

[0013] Specifically, the secondary temperature-regulating cooling zone is located after the main cooling air blowing zone along the melt stream's direction of travel. It is used to perform secondary temperature-regulating cooling on the material cooled by the main cooling air blowing zone. The secondary temperature-regulating cooling zone employs at least one or any combination of natural cooling, low-speed constant-temperature air cooling, temperature and humidity controlled cooling, and low-tension slow cooling. The temperature of the secondary temperature-regulating cooling zone is 20–70℃ (preferably 20–70℃), and its length is 300–2500 mm (preferably 300–2500 mm). The functions of the secondary temperature-regulating cooling zone include: reducing the internal and external temperature difference of the nascent filament; preventing residual stress concentration due to localized rapid freezing; stabilizing the orientation structure of the nascent filament; preserving the potential curl structure under low tension; and improving curl retention after heat setting. For high-elasticity products, a longer secondary temperature-regulating cooling zone can be provided; for low-elasticity products, this zone can be shortened or eliminated.

[0014] Furthermore, in the above-mentioned method for controlling the elasticity of polyester composite fibers by cooling air blowing, the first polyester component melt and the second polyester component melt are both one or more of polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, low-melting-point copolyester, polyester elastomer and modified polyester; the first polyester component melt and the second polyester component melt differ from each other in at least one of glass transition temperature, crystallization rate, melt viscosity, orientation ability and heat shrinkage properties.

[0015] Furthermore, in the above-mentioned method for regulating the elasticity of polyester composite fibers by cooling air blowing, the main cooling air blowing zone is set into at least two sections along the fiber bundle running direction. The air temperature, air speed, air direction, air volume distribution, and cooling length of each section can be independently adjusted to form a cooling gradient that varies along the fiber bundle axis (for example, the first section uses a higher air temperature and a lower air speed to maintain chain segment relaxation; the second section uses a medium air speed to complete stable curing; and the third section uses a low-speed constant temperature air to reduce the internal and external temperature difference). The main cooling air blowing zone also forms an asymmetric cooling field in the direction of the fiber bundle cross-section. The asymmetric cooling field is achieved by at least one of the following methods: unilateral blowing, eccentric air outlet, local shading, zoned air supply, setting different air speeds or different air temperatures on both sides. When setting different air speeds on both sides, the air speed difference between the two sides is 10-80%. When setting different air temperatures on both sides, the air temperature difference between the two sides is 3-20℃.

[0016] Furthermore, in the above-mentioned method for controlling the elasticity of polyester composite fibers by cooling air blowing, the polyester composite fibers are in the form of filaments or staple fibers, wherein the filaments are at least one of fully drawn yarns, pre-oriented yarns, and drawn textured yarns; and the staple fibers are composite staple fibers composed of a single component, wherein the composite staple fibers are staple fibers made by composite spinning of at least two polymer components.

[0017] Furthermore, in the above-mentioned method of regulating the elasticity of polyester composite fibers by cooling air blowing, the cross-sectional structure of the polyester composite fibers is any one of the following: parallel type, eccentric parallel type, core-sheath type, eccentric core-sheath type, island type, multi-leaf type, or multi-component irregular cross-sectional structure. The term "parallel type" refers to the first polyester component melt and the second polyester component melt being distributed side-by-side along the fiber axis, with each component occupying a region in the fiber cross-section, separated by an interface, and the line connecting the centroids of the two regions passing through the geometric center of the fiber cross-section. The term "eccentric parallel type" refers to the first polyester component melt and the second polyester component melt being distributed side-by-side, with the line connecting the centroids of the two regions not passing through the geometric center of the fiber cross-section. The term "core-skin type" refers to the core component being located at the fiber's geometric center, with the skin component concentrically and uniformly covering the core component. The term "eccentric core-skin type" refers to the core component being offset from the fiber's geometric center, resulting in an uneven thickness distribution of the skin component at different circumferential positions. The term "island type" refers to multiple island components dispersed discretely within a continuous sea component. The term "multi-leaf type" refers to the fiber cross-section having three or more outwardly protruding lobes. The term "multi-component irregular cross-section structure" refers to a non-circular and irregularly symmetrical cross-sectional shape formed by two or more polymer components.

[0018] Preferably, when the polyester composite fiber's primary performance objective is crimp elasticity, the cross-sectional structure is selected from side-by-side, eccentric side-by-side, or eccentric core-sheath type. This utilizes the difference in crystallization rate and shrinkage rate between the two components during cooling curing and subsequent stretching to obtain enhanced crimp potential, allowing the polyester composite fiber to form a high crimp curvature (at least 0.1 μm) in a tension-free relaxed state. -1 Two-dimensional or three-dimensional curled structures with high curling frequency (at least 5 curls / cm).

[0019] When the polyester composite fiber is of low elasticity, a slow cooling zone of 20–80 mm in length is used during its preparation. In the main cooling air blowing zone, cooling air with a temperature of 8–22°C and a velocity of 0.70–1.50 m / s is used, employing a symmetrical cooling method. This symmetrical cooling method can be any one of annular blowing, radial blowing, or bilateral symmetrical side blowing. The cooling length from the beginning to the end of the main cooling air blowing zone is 1000–2000 mm. Under this scheme, the composite melt stream solidifies rapidly, and the differential shrinkage between the two components is small, resulting in a lower fiber crimp, but better evenness, strength, and dimensional stability.

[0020] When the polyester composite fiber is of medium elasticity, its preparation process employs a slow cooling zone with a length of 80–170 mm and a temperature of 45–95 °C. In the main cooling air blowing zone, cooling air with a temperature of 18–30 °C and a velocity of 0.35–0.80 m / s is used, corresponding to an asymmetric cooling method. This asymmetric cooling method can be any one of single-sided side blowing, weak asymmetric side blowing, or segmented combined blowing. The cooling length from the beginning to the end of the main cooling air blowing zone is 800–1500 mm. Single-sided side blowing means that the cooling air blows out from only one side of the fiber bundle. Weak asymmetric side blowing means that the cooling air blown from two opposite sides of the fiber bundle has a 10–30% velocity difference. Segmented combined blowing refers to setting two or more cooling sections with different temperatures or velocities sequentially along the cooling length. Under this scheme, the fiber exhibits relatively stable two-dimensional or three-dimensional crimp, with a relatively balanced elastic recovery and strength.

[0021] When the polyester composite fiber is of high elasticity, a slow cooling zone with a length of 150–350 mm and a temperature of 70–130 °C is used in its preparation process. In the main cooling air blowing zone, cooling air with a temperature of 24–40 °C and a velocity of 0.10–0.50 m / s is used, corresponding to an asymmetric cooling method. This asymmetric cooling method is single-sided side blowing (i.e., the cooling air is blown horizontally from only one side of the fiber bundle (e.g., the left or right side), while the other side is subject to natural convection). Or in a windless state. This results in uneven cooling of the filament bundle circumferentially: the windward side cools faster and has higher crystallinity, while the leeward side cools slower and has lower crystallinity. If the two components are arranged side by side or eccentrically in this asymmetrical layout, the difference in contraction will be further amplified, forming a highly elastic three-dimensional curl. Eccentric side blowing (i.e., when the air outlet center of the blowing device is not on the same axis as the center of the filament bundle, that is, the cooling air is not blown horizontally from the side towards the center of the filament bundle, but is blown obliquely or eccentrically from the side that is away from the center). This arrangement results in a more complex asymmetric state in the wind intensity and heat distribution at different parts of the fiber bundle cross-section, enabling precise control of the cooling rate difference between the two components. It is suitable for medium or high-elasticity fibers. Alternatively, segmented asymmetric side blowing (i.e., the segmented asymmetric side blowing divides the cooling zone into two or more segments along the fiber bundle's travel direction (from top to bottom), each segment employing different side blowing directions (e.g., the first segment is left-side blowing, the second segment is right-side blowing) or different combinations of wind speed and temperature. By switching between segmented asymmetric forms, opposite cooling differences can be applied alternately during fiber bundle formation, thereby controlling the final curl shape, density, and directionality, avoiding uneven curling or knotting due to excessive unilateral asymmetry) can be used. The cooling length from the beginning to the end of the main cooling blowing zone is 500–1300 mm, and a secondary temperature-regulating cooling zone is set after the main cooling blowing zone. This secondary temperature-regulating cooling zone has a temperature of 30–70°C and a length of 800–2500 mm. The fiber crimping drive is stronger under this scheme, resulting in higher crimp and elastic recovery, a softer feel, and better fluffiness.

[0022] Compared with the prior art, the technical solution of this invention has the following beneficial effects:

[0023] 1) This invention improves the cooling blowing method from conventional spinning forming conditions to a key means of controlling the elasticity of polyester composite fibers, enabling the production of different products with low elasticity, medium elasticity and high elasticity grades under the same raw material system or similar raw material system.

[0024] 2) This invention is applicable to continuous polymerization melt spinning process, chip melt spinning process and combined composite spinning process, and has a wide range of application.

[0025] 3) By setting up a slow cooling zone, a main cooling air blowing zone and a secondary temperature-regulating cooling zone that are connected in sequence, the present invention realizes a zoned and controllable design of the curing path of the two components, so as to stably adjust the orientation difference, crystallization difference and thermal shrinkage difference between the two components.

[0026] 4) The present invention employs an asymmetric blowing method and a segmented blowing method along the spinning direction to form controllable cooling gradients in the fiber cross-section direction and fiber axial direction, thereby improving the ability to form three-dimensional crimped structures and improving crimp retention.

[0027] 5) This invention does not rely on changing the formula of a single raw material to adjust fiber elasticity, thus reducing production fluctuations caused by frequent changes in raw material formulas and improving process switching efficiency and production stability. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process flow for adjusting the elasticity of polyester composite fibers by means of cooling air blowing according to the present invention.

[0029] Figure 2 This is a schematic diagram of the cooling and blowing system for the low-elasticity, medium-elasticity, and high-elasticity polyester fibers of the present invention;

[0030] Figure 3 This is a schematic diagram of the cooling gradient of the fiber cross section formed by the asymmetric side blowing of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings to make it easier to understand and master. In addition, the following embodiments do not constitute a limitation on the scope of protection of the present invention. Any non-substantial adjustments to process parameters based on the cooling air blowing control concept disclosed in this invention should fall within the scope of protection of this invention. Non-substantial adjustments include changes to any one or more parameters among cooling air temperature, cooling air velocity, cooling air direction, length of the slow cooling zone, length of the secondary temperature control zone, and the composite cross-sectional form of the polyester composite fiber.

[0032] Example 1

[0033] like Figures 1-3 As shown, a method for preparing melt-spun low-elasticity polyester composite fiber is provided, which includes the following process steps:

[0034] 1) The first polyester component melt and conventional PET melt are provided as the second polyester component melt by continuous polymerization melt direct spinning. The two melts are metered separately and then enter the eccentric core-shell type composite spinning assembly, and are ejected by the spinneret to form a composite melt stream.

[0035] 2) After spinning, a low-elasticity cooling system is adopted: the length of the slow cooling zone below the spinneret is 50mm; the main cooling air blowing zone adopts double-sided symmetrical side blowing, the cooling air temperature is 18℃, the cooling air velocity is 0.90m / s, and the cooling length is 1300mm; no independent secondary temperature-regulating cooling zone is set or only a short-distance natural cooling zone is set.

[0036] Under the cooling conditions of Example 1, the composite melt stream solidifies rapidly and uniformly, with minimal differences in orientation and crystallization between the two components. The resulting composite fiber exhibits stable yarn count, high breaking strength, and low crimp elasticity, making it suitable for thermally bonded nonwoven fabrics, ordinary hot-air cotton, and low-elasticity filler materials.

[0037] Example 2

[0038] like Figures 1-3 As shown, a method for preparing medium-elastic polyester composite fibers by chip spinning is provided, which adopts the following process steps:

[0039] 1) Polyester elastomer chips and PET chips are used as raw materials. The two types of chips are pre-crystallized, dried and screw extruded and melted, and then enter the parallel composite spinning assembly. They are then spun out by the spinneret to form parallel composite melt streams.

[0040] 2) After the spinneret is spun, a medium-spring cooling system is adopted: the slow cooling zone below the spinneret is 120mm long and the temperature of the slow cooling zone is 70℃; the main cooling air blowing zone adopts a single-sided side blowing, the cooling air temperature is 24℃, the cooling air velocity is 0.50m / s, and the cooling length is 1000mm; a secondary temperature-regulating cooling zone is set after the main cooling zone, with a temperature of 40℃ and a length of 800mm.

[0041] Under the cooling conditions of Example 2, the two components exhibit moderate differences in orientation and thermal shrinkage. The resulting composite fiber has significant three-dimensional crimp, a balanced elastic recovery performance and breaking strength, and is suitable for elastic nonwoven fabrics, garment linings, elastic wadding, and flexible thermal bonding materials.

[0042] Example 3

[0043] like Figures 1-3 As shown, a method for preparing melt-spun high-elasticity polyester composite fiber is provided, which includes the following process steps:

[0044] 1) One polyester component melt is provided by continuous polymerization melt direct spinning, and the other polyester component melt is one of PET, PBT or PTT. The two melts enter the eccentric parallel type or eccentric core type composite spinning assembly and are ejected by the spinneret to form a composite melt stream.

[0045] 2) After spinning, a high-elasticity cooling system is adopted: the slow cooling zone is 220mm long and the temperature of the slow cooling zone is 90℃; the main cooling air blowing zone adopts asymmetrical side blowing, the cooling air temperature is 30℃, the cooling air velocity is 0.28m / s, and the cooling length is 800mm; a secondary temperature-regulating cooling zone is set after the main cooling zone, with a temperature of 50℃ and a length of 1200mm.

[0046] Under the cooling conditions of Example 3, a significant temperature gradient and crystallization gradient are formed in the cross-section of the composite fiber, resulting in substantial differential shrinkage during subsequent stretching, heat setting, and relaxation processes. The resulting composite fiber exhibits high crimp, high elastic recovery, and a soft hand feel, making it suitable for high-elasticity filling materials, elastic nonwovens, and soft elastic fabrics.

[0047] Example 4

[0048] like Figures 1-3 As shown, a method for preparing high-loft polyester composite staple fiber by combined spinning is provided, which adopts the following process steps:

[0049] 1) A continuous polymerization system is used to provide the first polyester component melt, and PET chips are used to provide the second polyester component melt via screw extrusion. The two melts are metered and then fed into an eccentric core-shell type composite spinning assembly.

[0050] 2) After spinning, a slow cooling hood and a segmented asymmetrical side-blowing device are installed. The cooling regime is as follows: the slow cooling zone is 180mm long and the temperature is 80℃; the first main cooling section has an air temperature of 28℃, an air velocity of 0.30m / s, and is unilaterally side-blown; the second main cooling section has an air temperature of 24℃, an air velocity of 0.45m / s, and is weakly symmetrically supplemented with air; the secondary temperature-adjusting cooling zone has a temperature of 45℃ and a length of 1000mm. The cooled nascent yarn is then drawn, crimped, heat-set, and cut to obtain high-loft polyester composite staple fiber.

[0051] Comparative Example 1

[0052] Under the same raw materials and composite cross-sectional structure, the slow cooling zone was eliminated, and cooling was performed directly below the spinneret using a fully symmetrical forced cooling method. This forced cooling method used cooling air with a temperature below 8°C and a velocity above 1.50 m / s. Because the slow cooling zone was eliminated and a low-temperature, high-velocity forced cooling method was used, the composite melt stream solidified rapidly after being extruded from the spinneret orifice. The two components could not form sufficient differences in crystallization rate and shrinkage rate during the cooling process. The result was a significantly reduced differential shrinkage of the obtained fibers, a substantial decrease in crimp potential, and a significantly lower degree of crimp in the final fibers compared to the low-elasticity, medium-elasticity, or high-elasticity polyester composite fibers obtained using the slow cooling zone and corresponding cooling parameters in the examples.

[0053] Comparative Example 2

[0054] Under the same raw materials and composite cross-sectional structure, ordinary single-sided blowing is used as the sole cooling method, without controlling the length, temperature, and speed of the slow cooling zone or the setting of the secondary temperature control zone. Specifically: no slow cooling zone is set up, or the length of the slow cooling zone exceeds the range of 20-350mm; the cooling temperature and speed are not adjusted in segments according to the target elasticity type (low elasticity, medium elasticity, or high elasticity); and no secondary temperature control cooling zone is set up, or the temperature and length of the secondary temperature control zone are not within the range of 30-70℃ and 800-2500mm. Due to the lack of targeted graded control of cooling conditions, the temperature and velocity fields fluctuate greatly during the cooling process, resulting in inconsistent cooling uniformity between different batches of filaments, and even between different spindles within the same batch. The result is that the fiber's elasticity indicators (e.g., crimp elasticity recovery rate, crimp curvature, or crimp frequency) fluctuate greatly, the product batch-to-batch stability is poor, and the target elasticity level cannot be consistently obtained.

[0055] The performance comparison between the examples and the comparative examples is shown in Tables 1 and 2:

[0056] Table 1 Results of Curvature Test for Each Group of Samples

[0057]

[0058] Table 2 Test results of curling frequency of each group of samples

[0059]

[0060] Based on the comparative analysis of the test data in Tables 1 and 2, the embodiment demonstrates significant technical superiority over the comparative example, specifically as follows:

[0061] 1) Significantly improved curling performance: The curling curvature and curling frequency of the example samples were significantly higher than those of the comparative samples, exhibiting stronger curling ability. Regarding curling curvature: the average value of the three batches of the examples was 0.054–0.148 μm. -1 The value was significantly higher than that of the comparative example (0.031–0.080 μm). -1 Regarding the curling frequency, the average value of the three batches in the examples was 3.7–8.4 curls per centimeter. -1 It is also significantly superior to the comparative ratio of 2.2–5.1 cm⁻¹. -1 This indicates that the curling effect of the sample in the example is denser and more significant.

[0062] Significantly improved performance uniformity: The coefficient of variation (CV) of the examples was much lower than that of the comparative examples, demonstrating excellent batch-to-batch performance stability and consistency. Specifically, the CV value of the curl curvature of the examples was generally controlled between 4.3% and 6.1%, with an average of 5.19%, while the CV value of the curl curvature of the comparative examples was as high as 8.9% to 19.4%, with an average of 13.92%. In particular, the CV value of the curl curvature of batch 2 in the comparative examples was close to 20%, indicating significant batch-to-batch differences. The CV value of the curl frequency of the examples was 4.7% to 6.7%, with an average of 5.58%, far lower than the CV value of the curl frequency of the comparative examples (10.8% to 20.6%, average 15.42%). The CV value of the curl frequency of batch 2 in the comparative examples was close to 20%, indicating that the examples exhibited stronger performance consistency and more stable and controllable product quality in mass production.

[0063] Therefore, considering the data on curl curvature, curl frequency, and batch stability, the embodiment surpasses the comparative embodiment in terms of curl performance strength, density, and uniformity, effectively demonstrating its significant advantages in technical solution. Moreover, the lower CV value also indicates that the preparation process of the embodiment has better repeatability and is suitable for large-scale production applications.

[0064] In summary, by employing a zoned cooling and directional air blowing system to stabilize and control the elasticity of polyester composite fibers, the difference in crystallization rates between the two components during the cooling and solidification process can be controlled within a set range under the synergistic effect of zoned cooling and directional air blowing. This difference in crystallization rate determines the radius of curvature and curling frequency of the fiber crimp structure, thereby achieving stable control over the fiber's elastic recovery rate and its fluctuation range. By adjusting the temperature, wind speed, and length parameters of each zone in the zoned cooling system and combining this with directional air blowing, the fluctuation range of the elastic recovery rate of polyester composite fibers of the same specification can be effectively controlled.

[0065] In the technical solution of this invention, the cooling blowing method is not just a conventional forming process, but is used to actively control the curing paths of the two components in the polyester composite fiber, thereby achieving controllable design of the shrinkage difference and curling structure of the two components. This is the key technology of this case.

[0066] Thus, using the technical solution of this invention, the method focuses on the cooling and solidification process of the composite melt stream after it is ejected from the spinneret. In the cooling and solidification path, a slow cooling zone, a main cooling air blowing zone, and a secondary temperature-regulating cooling zone are sequentially set along the fiber bundle's direction of travel, and each zone is subject to zoned control. By independently adjusting the temperature, flow rate, and duration of the cooling medium in each zone, differences in molecular orientation, crystallinity, and thermal shrinkage rate are created between the first and second polyester component melts constituting the composite fiber. These differences in shrinkage potential are all controlled within a predetermined range, collectively determining the crimp morphology and crimp elasticity exhibited by the composite fiber in a subsequent tension-free relaxation state, thereby obtaining a polyester composite fiber with an adjustable elasticity level within a predetermined range.

[0067] As can be seen from the above description, compared with the prior art, the technical solution of this invention is also applicable to melt spinning and chip spinning processes, regardless of whether the first polyester component melt and the second polyester component melt constituting the composite fiber are directly supplied from a continuous polymerization system, or supplied from chips melted by a screw extruder; or, where one polyester component melt originates from a continuous polymerization system and the other polyester component melt originates from chip melt supply. When the first polyester component melt and the second polyester component melt have the potential to produce differential shrinkage during the cooling and solidification process and subsequent heat treatment, the elasticity level can be controlled using the cooling blowing regime defined in this invention.

[0068] The technical solution, working process, and implementation effects of the present invention have been described in detail above. It should be noted that the described examples are only typical examples of the present invention. In addition, the present invention may have many other specific implementation methods. All technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed by the present invention.

Claims

1. A method for controlling the elasticity of polyester composite fibers by cooling air blowing, characterized in that, Includes the following steps: Step S1: Select the first polyester component melt and the second polyester component melt as raw materials for preparing polyester composite fibers. Both the first polyester component melt and the second polyester component melt are provided by a continuous polymerization melt direct spinning system and / or polyester chips after screw extrusion and melting. Step S2: The first polyester component melt and the second polyester component melt are metered separately, and then fed together into the composite spinning assembly. The metered first polyester component melt and the second polyester component melt are ejected through the spinneret to form a composite melt stream. Step S3: Perform elastic directional cooling on the composite melt stream in step S2. This elastic directional cooling includes several cooling zones arranged sequentially along the flow direction of the melt stream, namely, a slow cooling zone below the spinneret, a main cooling air blowing zone, and any one of the secondary temperature-regulating cooling zones. At the same time, an elastic control method is adopted to adjust the cooling parameters of at least one of the following cooling zones: the slow cooling zone below the spinneret, the main cooling air blowing zone, and the secondary temperature-regulating cooling zone. The cooling parameters are one or more of the following: cooling air temperature, cooling air velocity, cooling air humidity, cooling time, and cooling zone length. Step S4: After cooling, the nascent yarn is sequentially stretched, heat-set and relaxed, and then wound and / or cut to obtain elastically adjustable polyester composite fiber. The slow cooling zone is located between the spinneret outlet and the position where the main cooling air begins to act, and the slow cooling zone is composed of at least one or a combination of a heat insulation cylinder, a slow cooling cover, a heating jacket, a hot air protection zone and an adjustable baffle plate. The length of the slow cooling zone is 20-350 mm and the temperature of the slow cooling zone is 35-130 °C. The main cooling air blowing zone uses at least one of the following methods or any combination: annular blowing, radial blowing, and side blowing. The side blowing includes single-sided side blowing, double-sided symmetrical side blowing, eccentric side blowing, or segmented asymmetrical side blowing. The cooling air temperature of the main cooling air blowing zone is 8–40°C, the cooling air velocity is 0.10–1.50 m / s, and the cooling length is 500–2000 mm. The secondary temperature-regulating cooling zone is located after the main cooling air blowing zone along the melt stream direction. It is used to perform secondary temperature-regulating cooling on the material cooled by the main cooling air blowing zone. The secondary temperature-regulating cooling zone adopts at least one or any combination of natural cooling, low-speed constant temperature air cooling, temperature and humidity controlled cooling, and low-tension slow cooling. The temperature of the secondary temperature-regulating cooling zone is 20-70℃ and the length is 300-2500mm.

2. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 1, characterized in that: The first polyester component melt and the second polyester component melt are both one of polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, low-melting-point copolyester, polyester elastomer and modified polyester, and the two are different.

3. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 2, characterized in that: The first polyester component melt and the second polyester component melt differ from each other in at least one of the following: glass transition temperature, crystallization rate, melt viscosity, orientation ability, and heat shrinkage properties.

4. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 1, characterized in that: The main cooling air blowing zone is set into at least two sections along the direction of the filament bundle. The air temperature, air speed, air direction, air volume distribution and cooling length of each section can be adjusted independently to form a cooling gradient that varies along the axial direction of the filament bundle.

5. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 4, characterized in that: The main cooling air blowing area also forms an asymmetric cooling field in the direction of the filament cross section. The asymmetric cooling field is achieved by at least one of the following methods: unilateral air blowing, eccentric air outlet, local shading, zoned air supply, setting different wind speeds or different wind temperatures on both sides. When the method of setting different wind speeds on both sides is adopted, the wind speed difference between the two sides is 10-80%. When the method of setting different wind temperatures on both sides is adopted, the wind temperature difference between the two sides is 3-20℃.

6. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 1, characterized in that: The polyester composite fiber is in the form of filament or staple fiber. The filament is at least one of fully drawn yarn, pre-oriented yarn, and drawn textured yarn. The staple fiber is a composite staple fiber composed of a single component. The composite staple fiber is a staple fiber made by composite spinning of at least two polymer components.

7. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 1, characterized in that: The cross-sectional structure of the polyester composite fiber is any one of the following: parallel type, eccentric parallel type, core-sheath type, eccentric core-sheath type, island type, multi-leaf type, or multi-component irregular cross-sectional structure.

8. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 1, characterized in that: When the polyester composite fiber is low-elasticity, a slow cooling zone with a length of 20-80 mm is used in its preparation process, and cooling air with a temperature of 8-22℃ and a speed of 0.70-1.50 m / s is used in the main cooling air blowing zone. A symmetrical cooling method is used, which can be any one of ring blowing, radial blowing or double-sided symmetrical side blowing. The cooling length from the beginning end to the end end of the main cooling air blowing zone is 1000-2000 mm.

9. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 1, characterized in that: When the polyester composite fiber is of medium elasticity, a slow cooling zone with a length of 80-170 mm and a temperature of 45-95 °C is used in its preparation process, and a cooling air with a temperature of 18-30 °C and a wind speed of 0.35-0.80 m / s is used in the main cooling air blowing zone. Correspondingly, an asymmetric cooling method is used, which can be any one of single-sided side blowing, weak asymmetric side blowing, or segmented combined blowing. The cooling length from the beginning end to the end end of the main cooling air blowing zone is 800-1500 mm.

10. The method for adjusting the elasticity of polyester composite fibers by cooling air blowing according to claim 1, characterized in that: When the polyester composite fiber is of high elasticity, a slow cooling zone with a length of 150-350 mm and a temperature of 70-130°C is used in its preparation process. In the main cooling air blowing zone, a cooling air with a temperature of 24-40°C and a wind speed of 0.10-0.50 m / s is used, corresponding to an asymmetric cooling method. This asymmetric cooling method can be any one of single-sided side blowing, eccentric side blowing, or segmented asymmetric side blowing. The cooling length from the beginning to the end of the main cooling air blowing zone is 500-1300 mm. A secondary temperature-regulating cooling zone is set after the main cooling air blowing zone. The temperature of the secondary temperature-regulating cooling zone is 30-70°C and the length is 800-2500 mm.

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