Superfine denier profiled polyester staple fiber and preparation method thereof

Abstract

The invention provides a superfine denier profiled polyester staple fiber and a preparation method thereof.The preparation method includes the steps of raw material pretreatment, melt spinning, nascent filament treatment, heat setting and curling, oiling and cutting off and the like, polyester chips have high intrinsic viscosity and melting point, and under the action of six-zone temperature control, a high-hole-density spinneret plate and a high draft multiple, the polyester chips are subjected to melt spinning, so that the polyester chips are prepared into the superfine denier profiled polyester staple fiber. The superfine, special-shaped and hollow polyester staple fibers are prepared. The obtained polyester staple fiber has good breaking strength, rebound resilience and a low-defect structure, the bulkiness, flexibility and structural consistency of the fiber are remarkably improved, the environment and process limitation of a traditional sea-island fiber alkali stripping method is broken through, and the polyester staple fiber is suitable for the fields of high-end filling, plush imitation, non-woven materials and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of functional fibers, in particular to an ultra-fine denier special-shaped polyester staple fiber and a preparation method thereof. Background Art

[0002] Today, polyester staple fibers are widely used in clothing, home textile filling, and industrial applications due to their excellent strength, toughness, and abrasion resistance. The research and development and production of functional, differentiated polyester staple fibers are also becoming increasingly mature. Ultrafine denier fibers, a typical representative of differentiated polyester staple fibers, typically have a linear density of less than 0.5 denier and a diameter of only 5-8 microns, equivalent to 1 / 20th the thickness of a human hair. This extremely fine diameter imparts the soft touch and luster of natural silk. The dense arrangement of fibers creates a microporous structure that significantly enhances warmth and breathability, making them suitable for filling lightweight, warm clothing and high-end home textiles. Furthermore, the morphology of ultrafine denier staple fibers makes them easy to disperse and blend. In nonwoven processes, they form a uniform mesh structure, enhancing bulk and resilience. They are widely used in imitation fur, toy filling, and medical and sanitary products.

[0003] In terms of cross-sectional morphology, ultrafine denier polyester staple fibers can be fabricated into multi-petal, hollow, or special-shaped structures through composite spinning technology. For example, a four-leaf clover cross-section can achieve rapid sweat conduction by increasing the specific surface area and enhancing the capillary effect, while the hollow structure further reduces fiber density, creating a fluffy and lightweight feel. By constructing nanoscale grooves and micropores on the fiber surface, a soft silky luster is achieved through the principle of diffuse reflection, while the cohesion and anti-pilling properties of the fibers are enhanced. Chinese invention patent application publication number CN117535820A discloses a hygroscopic ultrafine polyester fiber. By adding abundant reduced graphene and polyether structural fragments to the modifier molecular structure, the antistatic and moisture absorption and breathability properties of the polyester fiber can be significantly improved. A Chinese invention patent application with publication number CN115961366A discloses a method for preparing non-fluorescent ultrafine polyester staple fibers. The fiber length index can reach 9.5~12.5mm and the fineness can reach 0.5~0.7D. By adding an antistatic smoothing agent to the oil sprayed on the spun silk, the smoothness and cohesion of the ultrafine polyester staple fibers are increased.

[0004] However, due to the limitations of production equipment and process conditions, the production of traditional ultra-fine denier polyester staple fibers can only be carried out through the sea-island composite spinning process. In the process of removing the sea components, alkali treatment is usually required, which brings certain environmental pressures. If melt spinning is used directly, traditional spinnerets are difficult to meet the requirements of fiber fineness, and it brings great challenges to the process settings in the production process. Temperature, ring blowing, winding speed, etc. may cause the fiber defect content to be too high and the fluffiness to be poor, thereby affecting the subsequent application. Therefore, how to produce ultra-fine denier polyester fibers with stable product quality in an environmentally friendly way under existing process conditions and give them functionality on this basis has become one of the important research directions in the production of ultra-fine denier fibers. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide an ultra-fine denier special-shaped polyester staple fiber and a preparation method thereof.

[0006] A method for preparing ultrafine denier special-shaped polyester staple fibers comprises the following steps: S1 Raw material pretreatment: Drying the polyester chips; S2 melt spinning: The dried polyester chips are melted in zones 1 to 6 in a screw extruder in sequence, with the temperature range of zones 1 to 6 being 280-305°C, and melt-spinned through a spinneret; the spinning box temperature is 285-295°C, the pump supply is 700-840 g / min, the pressure difference between the annular air inlet and return air is 580-730 Pa, and the winding speed is 1050-1150 m / min to obtain ultra-fine denier special-shaped polyester spun yarn; S3 spun yarn processing: The ultra-fine denier special-shaped polyester spun yarn is subjected to bundling, primary oil bath drawing, and secondary drawing in sequence; the primary oil bath drawing temperature is controlled at 65-70°C, and the secondary drawing temperature is 100-120°C; S4 heat setting and curling: the stretched fibers are subjected to tension heat setting treatment and curling treatment in sequence; S5 oiling and cutting: oil is applied to the surface of the curled fiber, and the fiber is then relaxed, heat-set, dried and cut to obtain ultra-fine denier special-shaped polyester staple fibers.

[0007] The present invention systematically optimizes the entire polyester fiber process, from raw material drying to staple fiber formation, through clearly defined staged control (S1 to S5). In particular, it integrates coordinated control of multiple key parameters in the melt spinning and post-processing stages, significantly improving fiber forming stability and shape retention. By setting segmented temperature control (280-305°C) for screw zones one to six and the spinning box temperature (285-295°C), multi-stage thermal-fluid coupling control of the polyester melt from initial melting, homogenization, steady flow to the outlet is achieved, effectively preventing local overheating degradation or uneven crystallinity, and ensuring rheological stability and die-forming consistency during the spinning process. The present invention stabilizes the fiber contraction trajectory during melt solidification by combining a ring-blowing air pressure difference (580-730 Pa) with a high-precision winding speed (1050-1150 m / min), thereby reducing yarn deviation, adhesion, and cross-sectional deformation. The present invention also uses primary (65-70°C) and secondary (100-120°C) stretching to fully stretch and directionally crystallize the polymer chain segments, thereby improving the breaking strength and resilience of the fiber and preventing the cross-section from shrinking and becoming rounded.

[0008] Compared with the traditional method of preparing ultrafine fibers through the island method or chemical stripping, the present invention is the first to achieve stable and continuous production through physical processes without relying on stripping or alkali treatment, significantly reducing the environmental burden and improving the versatility of the production line.

[0009] Furthermore, in the S1 raw material pretreatment step, the polyester chips are high-viscosity polyester chips with an intrinsic viscosity of 0.68 to 0.75 dL / g and a melting point of 257 to 268°C.

[0010] A high intrinsic viscosity (0.68-0.75 dL / g) indicates that the polyester has a longer molecular chain and a higher molecular weight. This molecular structure provides enhanced rheological stability and degradation resistance during high-temperature screw extrusion (zones 1 through 6 are set at 280-305°C). This ensures that the melt maintains a consistent, well-formed state when passing through precision spinnerets (e.g., hollow 4400 holes, cross 4000 holes) to form fine-denier, shaped fibers, avoiding fiber breakage, uneven thickness, or cross-sectional distortion often associated with low-viscosity melts.

[0011] Secondly, under the dynamic balance of spinning pump feed (700-840 g / min), high winding speed (1050-1150 m / min), and annular air pressure difference (580-730 Pa), the segmental strength and thermal stability of high-viscosity polyester enable it to withstand the stress caused by high draw ratios (3.38-3.91 times) without breaking or necking, thereby significantly improving the final fiber's breaking strength and crimp recovery. This characteristic is fundamental to the practical application of ultra-fine denier fibers—achieving a synergistic combination of "fineness" and "strength," rather than sacrificing strength in exchange for a lower denier.

[0012] The ample thermal safety window between the high melting point range (257-268°C) and the set heat setting temperature range (165-175°C) allows the fiber to maintain its melt structure and directionally solidify during the setting process, rather than undergoing excessive softening or shrinkage. This has significant advantages for maintaining the stability of the cross-sectional morphology of complex special-shaped cross-sections (such as trilobes and hollow cross structures), significantly improving the ratio of special-shaped degree and hollow ratio that retains morphology after curling and cutting.

[0013] Furthermore, in the S2 melt spinning step, the temperature of zone one of the screw extruder is 280°C to 290°C, the temperature of zone two is 285°C to 295°C, the temperature of zone three is 290°C to 300°C, the temperature of zone four is 295°C to 305°C, the temperature of zone five is 290°C to 300°C, the temperature of zone six is ​​285°C to 295°C, and the temperature of the spinning box is 285 to 295°C.

[0014] Using high-viscosity polyester chips as raw materials, the step-by-step temperature setting of each zone (such as 280-290°C in zone one and a maximum of 305°C in zone four) can effectively promote the dissolution of polyester crystals, chain segment stretching and thermal flow field balance, ensuring that the melt has a stable viscoelastic window from initial melting, plasticization, steady flow to extrusion stage. This overcomes the problems of melt degradation, bubble entrainment or dead zone in the traditional integrated heating or large temperature difference design, and significantly improves spinning consistency.

[0015] Secondly, spinnerets for fine-denier shaped fibers typically have complex geometric structures (such as trilobal, cross, or hollow structures), placing extremely high demands on the melt's shear stability and pressure distribution uniformity. The aforementioned six-stage zoned temperature control strategy creates a continuous and progressive melt viscosity gradient and shear rate field along the barrel. This, in synergy with the spinneret flow field design, significantly improves the ability to maintain the cross-sectional morphology of shaped fibers and reduces the incidence of melt deviation and localized distortion.

[0016] Furthermore, during the melt spinning process, the chamber temperature is controlled between 285–295°C, facilitating controlled heat exchange between the melt at the spinning outlet and the annular air cooling system. Combined with the pump flow rate (700–840 g / min) and the annular air pressure differential (580–730 Pa), this temperature range ensures that the fiber maintains ideal elongation and tension stability before cooling and setting. This prevents initial defects such as fuzz and misalignment, improves fiber winding uniformity, and provides a high-quality precursor for the subsequent drawing and crimping processes.

[0017] Furthermore, in the S2 melt spinning step, the spinneret is selected from one of 4000 holes, 4800 holes, hollow 4400 holes and cross 4000 holes.

[0018] By selecting spinnerets with specialized structures (such as hollow 4400 holes and cross 4000 holes), the fiber cross-section can be designed and controlled, effectively forming a variety of special-shaped cross-sections (such as trilobal, cross, and hollow elliptical). Compared to conventional round-hole spinnerets, this solution significantly improves the fiber's profile (≥85%) and hollow ratio (≥16%), thereby improving the fiber's fluffiness, moisture absorption, and gloss, creatively balancing structural function with processing efficiency.

[0019] Furthermore, in the S3 spun silk processing step, the drafting ratio is controlled at 3.38 to 3.91 times.

[0020] After cooling, polyester melt forms an amorphous state. To obtain high-strength, high-resilience fibers, axial tension must be applied to the molecular chains during the drafting process to achieve segmental rearrangement and partial crystallization. Too low a draft ratio prevents sufficient stretching of the segments, resulting in poor fiber mechanical properties. Too high a draft ratio can easily lead to breakage or necking, affecting yield.

[0021] The selected draft ratio range of 3.38 to 3.91 for this invention falls within the stable processing window for polyester materials between 65°C and 120°C (corresponding to the primary and secondary oil bath drafting temperatures), where maximum molecular chain orientation without chain breakage occurs. This effectively improves fiber breaking strength and elongation at break without sacrificing fine denier. Furthermore, ultrafine denier fibers, due to their low linear density and small fiber diameter, typically suffer from high breakage rates and low tensile strength. By fully drafting within this range, the fibers, even in their fine denier state, maintain sufficient segmental structure and strength support, ensuring stress tolerance during subsequent crimping, heat setting, oiling, and cutting processes, significantly reducing breakage rates and uneven curling.

[0022] In addition, the stretching ratio, the first-level oil bath temperature (65-70°C), and the second-level stretching temperature (100-7120°C) form a "temperature-stress" dual synergistic system, which not only promotes segment tension-induced crystallization, but also provides a structural preset basis for morphology fixation during the tensile heat setting process. It is a pre-support mechanism for constructing special-shaped hollow + curled structures.

[0023] Furthermore, in the S4 heat setting and curling step, the curling main pressure is controlled at 0.36-0.42 MPa, the back pressure is controlled at 0.18-0.22 MPa, and the line speed of the curling process is 190-210 m / min.

[0024] The main and back pressures of the crimp are precisely controlled within an optimal range, coupled with a line speed of 190-210 m / min, to ensure a consistent and resilient crimp structure. This configuration avoids the problems of uneven crimping in traditional processes, which can lead to poor fiber loft and stagnation, significantly improving the elastic recovery and down-like feel of the finished product.

[0025] Furthermore, in the S4 heat setting and curling step, the heat setting temperature is controlled at 165-175°C.

[0026] Controlling the heat setting temperature in the range of 165-175°C, which is just above the glass transition temperature of polyester but below the melting temperature, is conducive to locking the fiber curling state and eliminating residual stress in drafting, effectively improving curl stability and dimensional retention, and providing guarantee for the uniformity of staple fibers in the non-woven laying or spinning process.

[0027] Furthermore, in the oiling and cutting step S5, the silicone oil component in the applied oil accounts for 7% to 8% of the total mass of the oil.

[0028] By controlling the silicone oil concentration between 7% and 8%, the fiber maintains excellent surface lubricity and antistatic properties, reduces fiber breakage and entanglement rates, and effectively improves fiber transport and opening efficiency. Compared to traditional lubricant formulations with low silicone oil content, this method improves process continuity and post-processing adaptability while maintaining environmental friendliness.

[0029] A superfine denier shaped polyester staple fiber prepared by the above-mentioned preparation method of superfine denier shaped polyester staple fiber, wherein the superfine denier shaped polyester staple fiber has a shape degree ≥85%, a hollow fiber hollow rate ≥16%, a fiber linear density of 0.33-0.77 dtex, and a compression elasticity ≥70%.

[0030] Furthermore, the fiber breaking strength is 4.0-5.2 cN / dtex, the breaking elongation is 30%-45%, the fiber length is 12mm-52mm, the extra-long fiber content is 0-5mg / 100g, the defect content is 2-30mg / 100g, the number of crimps is 9-14 / 25mm, and the crimp rate is 9%-17%.

[0031] The finished fiber has a profile of ≥85%, a hollowness of ≥16%, a linear density of 0.33-0.77 dtex, and a compressive modulus of ≥70%. These structural indicators demonstrate that the present invention achieves a multi-faceted fusion structure of "ultrafine + profile + hollow," enhancing touch and lightweighting while ensuring the coordinated optimization of functional properties such as bulk, moisture absorption, and heat retention, significantly different from traditional single round or coarse denier polyester staple fibers. The fiber has a breaking strength of 5.2 cN / dtex and an elongation of 45%. The ultra-long fiber content is controlled at 0-5 mg / 100g, the defect content is controlled at 2-30 mg / 100g, and the crimp number and crimp ratio remain within an excellent range. These data comprehensively reflect the fiber's finished product quality control capabilities and excellent mechanical processing adaptability, fully demonstrating the technical maturity and advancement of the preparation system in high-consistency, high-precision mass production.

[0032] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects: (1) The polyester staple fibers obtained by the present invention have a profile of ≥85% and a hollow ratio of ≥16%, while maintaining a linear density within the ultra-fine denier range (0.33-0.77 dtex), breaking through the density limitation of traditional circular fiber structures. The fibers also have lightweight, flexible, and functional cross-sectional characteristics, giving the material better bulk, moisture absorption, and thermal conductivity.

[0033] (2) The present invention precisely controls the viscoelasticity and homogenization degree of the polyester melt at each stage by setting up six independent temperature control zones (280-305°C) + a spinning box temperature zone (285-295°C); matches the special-shaped plate structure with 4000-4800 spinneret holes and a high winding speed (1050-1150 m / min) to achieve continuous and highly consistent spinning and significantly reduce defects caused by deflected yarns, hairy yarns and unstable melt shearing.

[0034] (3) The present invention uses a high draft ratio of 3.38 to 3.91 times in combination with a first-level oil bath (65 to 70°C) and a second-level drafting temperature zone (100 to 120°C) to form a stress-temperature synergistic orientation mechanism, which allows the molecular chains to be arranged in an orderly manner, and the breaking strength is increased to 5.2 cN / dtex, and the elongation at break is 45%. The fiber maintains good tensile and resilience properties during subsequent curling and laying.

[0035] (4) The present invention controls the main pressure (0.36-0.42 MPa), back pressure (0.18-0.22 MPa) and curling line speed (190-210 m / min) by matching and controlling the curling shape with the setting temperature (165-175°C). The fiber compression elasticity is generally higher than 70%, and has a stable curling structure of 9-14 per 25 mm. It is suitable for imitation wool and down substitute products with high fluffiness requirements.

[0036] (5) Compared with the traditional sea-island composite spinning + alkali treatment stripping method that ultrafine denier fibers rely on, the present invention is completely based on the melt spinning-physical curling-heat setting process, which does not require alkali washing, stripping, and recycling. The process is more green and environmentally friendly, avoids the discharge of alkaline wastewater, and improves industrial adaptability and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 An optical microscope photograph of the cross section of an ultrafine denier special-shaped polyester staple fiber prepared in Example 1.

[0038] Figure 2 An optical microscope photograph of the cross section of an ultrafine denier special-shaped polyester staple fiber prepared in Example 2.

[0039] Figure 3 An optical microscope photograph of the cross section of an ultrafine denier special-shaped polyester staple fiber prepared in Example 3. DETAILED DESCRIPTION

[0040] The present invention is described in detail below with reference to the embodiments.

[0041] Example 1 An ultra-fine denier special-shaped polyester staple fiber and a preparation method thereof, the specific steps are as follows: S1 Raw material pretreatment: The polyester chips were first dried at 80°C for 2 hours and then vacuum dried at 120°C for 10 hours to complete the raw material pretreatment.

[0042] Polyester chips: The manufacturer is Zhejiang Hengyi Petrochemical Co., Ltd. The intrinsic viscosity of polyester chips is 0.72 dL / g and the melting point is 265°C.

[0043] S2 melt spinning: The dried polyester chips are fed into a screw extruder for melting. The temperature settings of each section of the extruder are as follows: The temperature of zone 1 is 285℃, the temperature of zone 2 is 290℃, the temperature of zone 3 is 295℃, the temperature of zone 4 is 300℃, the temperature of zone 5 is 295℃, and the temperature of zone 6 is 290℃; The spinning box temperature was set at 290°C; The spinneret used was a circular structure with 4000 holes; The pump supply is 783 g / min; The pressure difference between the inlet and return air of the annular airflow is 700 Pa; Winding speed is 1100 m / min; Through this step, ultra-fine denier special-shaped polyester spun yarn is obtained.

[0044] S3 spun yarn treatment: The ultra-fine denier special-shaped polyester spun yarn is subjected to bundling, primary oil bath drawing, and secondary drawing in sequence; the primary oil bath temperature is set at 68°C, the secondary drawing temperature is 110°C, and the drawing ratio is 3.61 times.

[0045] S4 heat setting and curling: The stretched fiber is subjected to tension heat setting treatment and curling treatment in sequence; the heat setting temperature is 170°C, the curling main pressure is 0.36 MPa, the back pressure is 0.18 MPa, and the curling treatment line speed is 200 m / min.

[0046] S5 Oiling and Cutting: The curled fibers are lubricated and treated with an oil containing 7 wt.% silicone oil for antistatic treatment, followed by relaxation, heat setting, drying, and cutting to obtain ultrafine denier shaped polyester staple fibers with a length of 12 mm.

[0047] The difference between Examples 2-12 and Example 1 is that the process parameters in each process step are set differently, as shown in Tables 1 to 4 below.

[0048] Table 1 Table 2 Table 3 Table 4 Comparative Example 1 According to a preparation method of non-fluorescent ultrafine polyester staple fiber with publication number CN115961366A, the staple fiber was prepared as follows: Step 1: Drying The polyester raw material was placed in a vacuum drying oven and dried at a drying temperature of 160°C, a vacuum degree of 0.08 MPa, and a drying time of 5 hours. The moisture content after drying was 145 ppm.

[0049] Step 2: Melt Spinning The dried polyester chips were fed into a screw extruder and melted at 288°C. The metering pump was set at 3900 g / min and the spinning speed was set at 3000 m / min. The polyester chips were 0.6 dL / g and had a melting point of 260°C.

[0050] Step 3: Cooling and forming The air blowing cooling technology is adopted, with the air temperature of 20℃, the side blowing speed of 0.45 m / s and the relative humidity of 60%.

[0051] Step 4: Winding into the barrel The compressed air is used to pull the yarn bundle, which is then wound and concentrated and then sent into the yarn drum.

[0052] Step 5: Drafting The drawing speed is 600 m / min, the drawing ratio is 1.55, and the heating box temperature is 160°C.

[0053] Step 6: Curl The crimping machine speed was 4.0 m / s, the crimping wheel main pressure was 0.35 MPa, and the back pressure was 0.08 MPa.

[0054] Step 7: Oiling The oil spraying treatment was carried out using an oil sprayer with an oiling rate of 0.5%. The composition of the oil applied was: 10 wt% silicone oil, 8 wt% emulsifier, 1 wt% penetrant, and the rest deionized water.

[0055] Step 8: Heat setting The heat setting temperature is 171°C and the time is 13 minutes.

[0056] Step 9: Cut and pack.

[0057] Comparative Example 2 The difference from Example 1 is that the spinneret is circular with 1800 holes, and other process parameters are appropriately adjusted according to the fiber production situation.

[0058] Comparative Examples 3 to 6 The differences between Comparative Examples 3 to 6 and Example 1 are shown in Table 5 below.

[0059] Table 5 Detection method The fibers obtained in Examples 1, 2, and 3 were photographed using an optical microscope. Figure 1 、 2 , cross-sectional view of 3.

[0060] The following tests were performed on the ultrafine denier shaped polyester staple fibers prepared in Examples 1-12 and Comparative Examples 1-2: 1. Linear density: measured in accordance with GB / T 14335-2008.

[0061] 2. Cut length and extra-long fiber content: measured in accordance with GB / T 14336-2008.

[0062] 3. Breaking strength and elongation at break: measured in accordance with GB / T 14337-2022, with a tensile speed of 30 mm / min.

[0063] 4. Defect content: Determined in accordance with GB / T 14339-2008.

[0064] 5. Number of curls and curl rate: measured in accordance with GB / T 14338-2022.

[0065] 6. Degree of irregularity: measured in accordance with FZ / T 50002-2013 standard.

[0066] 7. Fluffiness: measured in accordance with FZ / T 50009.4-2019 standard.

[0067] The test results are shown in Table 6 below.

[0068] Table 6 The present invention incorporates a synergistic parameter control mechanism across key processes, including fiber raw materials, melt spinning temperature control, spinneret structure, drafting process, crimping, and heat setting, significantly improving fiber forming stability, fine denier structure control, and cross-sectional profile retention. Test results confirm that the present invention's approach effectively creates a structural system that synergizes fine denier, profile, and crimp elasticity, significantly improving the fiber's mechanical properties, dimensional uniformity, and fluffiness.

[0069] Compared with the comparative samples using traditional single-zone temperature control, low-hole number spinnerets or unoptimized heat setting and curling parameters, the fibers produced by the present invention have obvious advantages in appearance uniformity, structural integrity and adaptability, which fully confirms the significant effect of the technical solution described in the present invention in improving the comprehensive performance of the product and achieving industrial stability.

[0070] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine denier special-shaped polyester staple fibers, characterized in that: The steps include: S1 Raw material pretreatment: Drying the polyester chips; S2 melt spinning: The dried polyester chips are melted in zones 1 to 6 in a screw extruder in sequence, with the temperature range of zones 1 to 6 being 280-305°C, and melt-spinned through a spinneret; the spinning box temperature is 285-295°C, the pump supply is 700-840 g / min, the pressure difference between the annular air inlet and return air is 580-730 Pa, and the winding speed is 1050-1150 m / min to obtain ultra-fine denier special-shaped polyester spun yarn; S3 spun yarn processing: The ultra-fine denier special-shaped polyester spun yarn is subjected to bundling, primary oil bath drawing, and secondary drawing in sequence; the primary oil bath drawing temperature is controlled at 65-70°C, and the secondary drawing temperature is 100-120°C; S4 heat setting and curling: the stretched fibers are subjected to tension heat setting treatment and curling treatment in sequence; S5 oiling and cutting: oil is applied to the surface of the curled fiber, and the fiber is then relaxed, heat-set, dried and cut to obtain ultra-fine denier special-shaped polyester staple fibers.

2. The method for preparing ultrafine denier special-shaped polyester staple fibers according to claim 1, wherein: In the raw material pretreatment step S1, the polyester chips are high-viscosity polyester chips with an intrinsic viscosity of 0.68 to 0.75 dL / g and a melting point of 257 to 268°C.

3. The method for preparing ultrafine denier special-shaped polyester staple fibers according to claim 1, wherein: In the S2 melt spinning step, the temperature of zone 1 of the screw extruder is 280°C to 290°C, the temperature of zone 2 is 285°C to 295°C, the temperature of zone 3 is 290°C to 300°C, the temperature of zone 4 is 295°C to 305°C, the temperature of zone 5 is 290°C to 300°C, and the temperature of zone 6 is 285°C to 295°C.

4. The method for preparing ultrafine denier special-shaped polyester staple fibers according to claim 1, wherein: In the S2 melt spinning step, the spinneret is selected from one of 4000 holes, 4800 holes, hollow 4400 holes and cross 4000 holes.

5. The method for preparing ultrafine denier special-shaped polyester staple fibers according to claim 1, wherein: In the S3 spun yarn processing step, the total drafting ratio of the primary oil bath drafting and the secondary drafting is controlled at 3.38 to 3.91 times.

6. The method for preparing ultrafine denier special-shaped polyester staple fibers according to claim 1, wherein: In the S4 heat setting and curling step, the curling main pressure is controlled at 0.36-0.42 MPa, the back pressure is controlled at 0.18-0.22 MPa, and the linear speed of the curling process is 190-210 m / min.

7. The method for preparing ultrafine denier special-shaped polyester staple fibers according to claim 1, wherein: In the S4 heat setting and curling step, the heat setting temperature is controlled at 165-175°C.

8. The method for preparing ultrafine denier special-shaped polyester staple fibers according to claim 1, wherein: In the oiling and cutting step S5, the silicone oil component in the applied oil accounts for 7% to 8% of the total mass of the oil.

9. An ultra-fine denier shaped polyester staple fiber produced by the method for producing an ultra-fine denier shaped polyester staple fiber according to any one of claims 1 to 8, characterized in that: The ultra-fine denier special-shaped polyester staple fibers have a special-shaped degree of ≥85%, a hollow fiber hollow rate of ≥16%, a fiber linear density of 0.33-0.77 dtex, and a compression elasticity of ≥70%.

10. The ultra-fine denier special-shaped polyester staple fiber according to claim 9, characterized in that: The fiber has a breaking strength of 4.0 to 5.2 cN / dtex, an elongation at break of 30% to 45%, a fiber length of 12 mm to 52 mm, an extra-long fiber content of 0 to 5 mg / 100 g, a defect content of 2 to 30 mg / 100 g, a crimp number of 9 to 14 per 25 mm, and a crimp rate of 9% to 17%.

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