Polyester fiber with skin-core structure

Abstract

The invention provides a polyester fiber with a skin-core structure and a preparation method thereof. The fiber is composed of a skin layer, a core layer and a functional transition layer between skin-core interfaces, wherein the functional transition layer is composed of SEBS-g-MAH and 3%-10% of functional master batch. The thickness ratio of the skin layer to the transition layer to the core layer is (3-5): 1: (4-6), a three-channel co-extrusion technology is adopted in the preparation process, the extrusion conditions of the core layer, the transition layer and the skin layer are respectively controlled, and the problems of non-uniform dispersion and thermal degradation of functional master batches are effectively solved through an annular air cooling air speed and a high-speed traction process. The fiber has the master batch dispersity of 95% or above, and the mechanical strength of the fiber can be improved by optimizing a spinneret plate matched with the fiber.

Description

Technical Field

[0001] The present invention relates to the technical field of composite fibers, and more particularly to a polyester fiber having a sheath-core structure with a transition layer disposed therebetween for uniformly dispersing functional masterbatch. The present invention also relates to a method for preparing the polyester fiber. Background Art

[0002] Polyester fibers, represented by PET (polyethylene terephthalate), have gradually developed from a single textile raw material to a core carrier of high-performance materials. The early polyester fibers were widely used in clothing and industrial fields due to their high breaking strength and corrosion resistance. At this stage, the PET fibers had a single function and relied solely on intrinsic physical and chemical properties, making it difficult to meet the needs of the high-end market and having low added value. Since the rise of copolymerization modification technology, polyester fibers have changed their molecular chain structure by introducing a third monomer other than acids and alcohols, thereby improving dyeability, hygroscopicity and other problems, and incorporating inorganic particles to improve UV resistance or flame retardancy. However, the amount of modifier added is limited, and the functional durability is poor. Today, with the advancement of melt blending technology, in order to simplify production and improve efficiency, the functional masterbatch blending method has become the mainstream. It achieves one-step functional production by pre-encapsulating the functional agent in the polyester masterbatch and directly incorporating it into the spinning melt. Although functional masterbatch technology has significantly simplified the production process, its application in polyester fibers still faces multiple technical bottlenecks. The viscosity of polyester melt at processing temperatures of 270-290°C is as high as 200-400 Pa·s. Functional masterbatch can easily agglomerate due to insufficient shear force, resulting in a decrease in fiber mechanical properties. The polarity difference between some functional agents and polyester can cause interfacial debonding. Furthermore, the thermal stability of most functional agents is lower than the polyester processing temperature (260°C).

[0003] In view of this, it is necessary to develop a new type of polyester fiber to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a polyester fiber with a sheath-core structure, which has good processing adaptability, can effectively disperse and connect functional masterbatches, and has a very high dispersion degree of functional masterbatches, so that the functionalized polyester fiber is better suitable for industrial production. To achieve the above purpose, the technical solution provided by the present invention is as follows.

[0005] A sheath-core structured polyester fiber comprising a sheath layer, a core layer, and a functional transition layer located between the sheath and core interfaces; The skin layer and the core layer are made of polyester material, and the functional transition layer is a mixture of SEBS-g-MAH and functional masterbatch, wherein the mass proportion of the functional masterbatch is 3%-10%.

[0006] Furthermore, the functional masterbatch is selected from at least one of an antimicrobial agent, a flame retardant, a conductive filler or a light stabilizer, and has a particle size of 0.1-2 μm and a particle size distribution index of ≤0.25.

[0007] Furthermore, in order to balance the extrusion pressure and melt strength of the transition layer, avoid excessive extrusion pressure or prevent peeling of the skin-core interface, the melt index of the SEBS-g-MAH is 5-20 g / 10min, and the grafting rate of SEBS-g-MAH is 2-5%.

[0008] Furthermore, the thickness ratio of the skin layer, functional transition layer, and core layer is (3-5):1:(4-6), so that the finished polyester fiber has good mechanical properties. The difference in intrinsic viscosity between the polyester materials of the skin layer and the core layer is ≤0.1 dL / g.

[0009] The viscosity difference between the skin and core layers involves the difference in flow rate between the skin and core layer melts during the coextrusion process. The three-channel coextrusion process requires that the melt pressure gradients of each layer match. If the viscosity difference is too large, the core layer melt resistance will increase abnormally, forcing the transition layer melt pressure to exceed the process requirements, causing turbulence in the spinneret orifice melt, which in turn leads to fiber diameter deviation.

[0010] Polyester materials with similar intrinsic viscosities have similar cooling crystallization dynamics, ensuring that the skin and core layers crystallize synchronously during gradient cooling, avoiding internal stress cracks caused by differences in shrinkage rates.

[0011] Furthermore, the functional transition layer also contains 0.5%-2% of a dispersing aid, which is a silane coupling agent. The functional masterbatch surface-modified with the silane coupling agent has polar groups such as hydroxyl or epoxy groups attached thereto, which can effectively improve the dispersion effect of the functional masterbatch in the SEBS-g-MAH matrix.

[0012] Furthermore, the polyester material is polyethylene terephthalate or polybutylene terephthalate.

[0013] A method for preparing the sheath-core polyester fiber according to any one of claims 1 to 6, characterized in that it comprises the following steps: S1, raw material pretreatment: drying the skin layer and core layer polyester chips; premixing the functional masterbatch with SEBS-g-MAH particles and mixing and granulating them to obtain functional transition layer particles; S2, three-channel co-extrusion: The core layer material, transition layer material, and skin layer material are transferred from the inside to the outside through independent extruders and co-extruded into a three-channel co-extruder to obtain the primary product; S3, gradient cooling: the primary product extruded from the three-channel extruder is cooled by annular air and drawn to the spinneret; S4, spinning: The primary product after gradient cooling is pulled through the spinneret by a traction mechanism and cooled to form the finished product.

[0014] Further, In S1, the mixing temperature of the functional masterbatch and SEBS-g-MAH particles is 80-100°C and the extrusion pressure is 12-18 MPa; and / or, In S2, the core layer material has a melting temperature of 270-290°C and an extrusion pressure of 12-18 MPa, the transition layer material has a melting temperature of 210-230°C and an extrusion pressure of 6-10 MPa, and the skin layer material has a melting temperature of 260-280°C and an extrusion pressure of 8-12 MPa; and / or, In S3, the cooling wind speed of the ring air cooling is 0.4-0.8 m / s; and / or, In S4, the pulling speed of the pulling machine is 2500-3500m / min, and the initial product setting temperature is 80-120℃.

[0015] Furthermore, in S2, 0.5%-2 of a compatibilizer is added based on the total weight of the transition layer material.

[0016] Furthermore, the aspect ratio of the spinneret holes is 3-5.

[0017] The advantages and beneficial effects of the present invention are as follows: by introducing a SEBS-g-MAH-based functional transition layer between the skin layer and the core layer, the polar chain segments of SEBS-g-MAH are utilized to inhibit the migration of the masterbatch and enhance the interfacial bonding strength, so that the dispersion uniformity of the functional masterbatch reaches more than 85%. The low-temperature processing characteristics of the functional transition layer effectively protect the functional masterbatch and reduce the thermal degradation problem of the functional masterbatch. In addition, the elastic modulus of SEBS-g-MAH buffers the spinning drawing stress and enhances the breaking strength of the polyester fiber.

[0018] This invention utilizes three-channel co-extrusion technology to independently control the melt flow rate and pressure of the skin, functional layer, and core layer, achieving efficient crushing and mixing of the masterbatch particle size. Circular air cooling and low-temperature shaping enhance fiber crystallinity and heat resistance. Optimizing the spinneret's aperture ratio and aspect ratio improves fiber forming precision, making the finished fiber suitable for high-precision industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the polyester fiber of the present invention; Figure 2 It is a process flow chart of the preparation of the polyester fiber shown in the present invention. DETAILED DESCRIPTION

[0020] The present invention constructs a composite fiber with a three-layer structure of a skin layer, a functional transition layer, and a core layer. The maleic anhydride polar group of SEBS-g-MAH in the transition layer provides a dipole effect with polyester, while the styrene-ethylene / butylene block structure provides elastic cushioning. The functional masterbatch is pre-mixed and granulated with SEBS-g-MAH, and the shear thinning property of SEBS is utilized to achieve its uniform dispersion. The surface activation effect of the silane coupling agent is combined to form an "anchoring effect" to achieve enhanced dispersion.

[0021] During the molding process, independent extruders are used for temperature control of each layer to prevent thermal degradation of the functional masterbatch. During extrusion, the pressure differential between layers is maintained at ≤6 MPa to prevent interfacial slip. Ultra-high-speed extrusion at 2500-3500 m / min, combined with 0.4-0.8 m / s air cooling, ensures a uniform distribution of the high-modulus β-crystal and high-toughness α-crystal polyester fibers. In the three-layer composite fiber, melt flow is controlled in the extruder to adjust the thickness ratio, ensuring that the core layer bears over 60% of the tensile load, the transition layer provides elastic stress buffering, and the skin layer provides surface wear resistance. The functional masterbatch is retained in the SEBS matrix by the low viscosity of SEBS (50-100 Pa·s), and its mobility is significantly reduced during extrusion and stretching, achieving uniform dispersion. The styrene content in the SEBS is preferably 30-40% to ensure an elastomeric phase, with a weight-average molecular weight of 70,000-100,000 g / mol.

[0022] The particle size of the functional masterbatch in the embodiment refers to the particle size of the functional additive. The method for loading the additive itself and the functional masterbatch is as follows: based on the functional masterbatch base resin (polyurethane), 0.5-0.2% of the functional additive (such as a flame retardant) and the silane coupling agent are immersed in an ethanol-water solution with an ethanol volume fraction of 70%, ultrasonically treated and then dried, and the modified additive and polyurethane resin are melt-extruded and granulated.

[0023] The intrinsic viscosity difference between the polyester material of the skin layer and the core layer is ≤0.1dL / g. The test conditions are phenol / tetrachloroethane (60 / 40w / w) solution, temperature is 25±0.1℃, and the measurement is based on ISO 1628-5 standard.

[0024] The following embodiments are further described in conjunction with the accompanying drawings and examples. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0025] Example 1 An antibacterial polyester fiber with a sheath-core structure, wherein both the sheath and core layers are made of PET with an intrinsic viscosity of 0.72 dL / g; the functional transition layer is SEBS-g-MAH with a grafting rate of 3%, mixed with nano-silver antibacterial masterbatch with a particle size of 0.5 μm and a particle size distribution of D90 / D10=1.2; the masterbatch accounts for 3% by weight, and the thickness ratio of the sheath, transition layer, and core layer is 4:1:5.

[0026] The preparation method comprises the following steps: S1, raw material pretreatment: PET slices were vacuum dried at 120°C for 4 h, and then the nanosilver masterbatch and SEBS-g-MAH were transferred to an internal mixer and granulated at 90°C and 15 MPa pressure; S2, three-channel co-extrusion: core layer PET chips, transition layer granules, and skin layer PET chips are transferred to the extruder hoppers corresponding to each layer in the three-channel co-extruder respectively, and the melt temperature of the core layer extruder is set to 285°C and the extrusion pressure is 15 MPa, the melt temperature of the transition layer extruder is set to 220°C and the extrusion pressure is 8 MPa, and the extrusion temperature of the skin layer extruder is set to 275°C and the extrusion pressure is 10 MPa. The three are extruded together to obtain the primary product; S3, gradient cooling: the primary product extruded from the three-channel extruder is passed through a ring air cooling system and drawn to the spinneret. The ring air cooling system adopts three-stage cooling along the drawing direction, with the wind speed of the front section being 0.8 m / s, the wind speed of the middle section being 0.6 m / s, and the wind speed of the rear section being 0.4 m / s. S4, spinning molding: Use a traction mechanism to pull the initial product after gradient cooling through a spinneret with a pore size of 1 mm and an aspect ratio of 3 to form the finished polyester fiber. The traction speed of the traction machine is 3000 m / min, and the finished polyester fiber is obtained at 100°C.

[0027] Example 2 A flame-retardant polyester fiber with a sheath-core structure. The sheath and core layers are both made of PBT with an intrinsic viscosity of 0.68 dL / g. The functional transition layer is composed of a mixture of SEBS-g-MAH with a grafting rate of 4.5% and a red phosphorus flame retardant masterbatch with a particle size of 1.2 μm and a particle size distribution index of D90 / D10=1.15. The flame retardant masterbatch accounts for 8% by weight. The thickness ratio of the sheath, transition layer, and core layer is 3:1:6.

[0028] The preparation method comprises the following steps: S1, raw material pretreatment: PBT chips were vacuum dried at 130°C for 6 hours, red phosphorus flame retardant masterbatch and SEBS-g-MAH pellets were transferred to an internal mixer, and granulated at 95°C and 16 MPa pressure to produce functional transition layer pellets; S2, three-channel co-extrusion: core layer PBT slices, transition layer granules, and skin layer PBT slices are transferred to the extruder hoppers corresponding to each layer in the three-channel co-extruder respectively, and the melt temperature of the core layer extruder is set to 280°C and the extrusion pressure is 14 MPa, the melt temperature of the transition layer extruder is set to 210°C and the extrusion pressure is 7 MPa, and the extrusion temperature of the skin layer extruder is set to 265°C and the extrusion pressure is 9 MPa. The three are extruded together to obtain the primary product; S3, gradient cooling: the primary product extruded from the three-channel extruder is passed through a ring air cooling system and drawn to the spinneret. The ring air cooling system adopts three-stage air cooling along the drawing direction, with the wind speed of the front section being 0.7 m / s, the wind speed of the middle section being 0.5 m / s, and the wind speed of the rear section being 0.3 m / s. S4, spinning molding: Use a traction mechanism to pull the initial product after gradient cooling through a spinneret with a pore size of 0.9 mm and an aspect ratio of 4 to form the finished polyester fiber. The traction speed of the traction machine is 2800 m / min, and the finished polyester fiber is formed at 110°C.

[0029] Example 3 A conductive polyester fiber with a sheath-core structure, wherein both the sheath and core layers are made of PET with an intrinsic viscosity of 0.70 dL / g; the functional transition layer is composed of a mixture of SEBS-g-MAH with a grafting rate of 2.2% and a carbon nanotube / graphene composite conductive masterbatch with a particle size of 0.8 μm and a particle size distribution index D90 / D10=1.1, with the conductive masterbatch accounting for 7% by weight; and the thickness ratio of the sheath, transition layer, and core layer is 5:1:4.

[0030] The preparation method comprises the following steps: S1, raw material pretreatment: PBT slices were vacuum dried at 125°C for 5 hours, the composite conductive masterbatch and SEBS-g-MAH particles were transferred to an internal mixer, and granulated at 85°C and 12 MPa pressure to obtain functional transition layer particles; S2, three-channel co-extrusion: core layer PET chips, transition layer granules, and skin layer PET chips are transferred to the extruder hoppers corresponding to each layer in the three-channel co-extruder respectively, and the melt temperature of the core layer extruder is set to 270°C and the extrusion pressure is 12 MPa, the melt temperature of the transition layer extruder is set to 200°C and the extrusion pressure is 6 MPa, and the extrusion temperature of the skin layer extruder is set to 260°C and the extrusion pressure is 11 MPa. The three are extruded together to obtain the primary product; S3, gradient cooling: the primary product extruded from the three-channel extruder is passed through a ring air cooling system and drawn to the spinneret. The ring air cooling system adopts three-stage air cooling along the drawing direction, with the wind speed of the front section being 0.6 m / s, the wind speed of the middle section being 0.5 m / s, and the wind speed of the rear section being 0.2 m / s. S4, spinning molding: Use a traction mechanism to pull the initial product after gradient cooling through a spinneret with a pore size of 1.1 mm and an aspect ratio of 3.8 to form the finished polyester fiber. The traction speed of the traction machine is 3500 m / min, and the finished polyester fiber is obtained at 90°C.

[0031] Example 4 A UV-resistant polyester fiber with a sheath-core structure, wherein the sheath and core layer materials are PET with intrinsic viscosities of 0.75 dL / g and 0.73 dL / g, respectively; the functional transition layer is SEBS-g-MAH with a grafting rate of 5%, mixed with a benzotriazole UV-absorbing masterbatch with a particle size of 0.3 μm and a particle size distribution of D90 / D10=1.05; the masterbatch accounts for 5% by weight, and the thickness ratio of the sheath, transition layer, and core layer is 3.5:1:5.5.

[0032] The preparation method comprises the following steps: S1, raw material pretreatment: PET chips were vacuum dried at 115°C for 4.5 h, and then the UV absorber masterbatch and SEBS-g-MAH were transferred to an internal mixer and granulated at 100°C and 18 MPa pressure; S2, three-channel co-extrusion: core layer PET chips, transition layer granules, and skin layer PET chips are transferred to the extruder hoppers corresponding to each layer in the three-channel co-extruder respectively, and the melt temperature of the core layer extruder is set to 290°C and the extrusion pressure is 17 MPa, the melt temperature of the transition layer extruder is set to 230°C and the extrusion pressure is 10 MPa, and the extrusion temperature of the skin layer extruder is set to 280°C and the extrusion pressure is 12 MPa. The three are extruded together to obtain the primary product; S3, gradient cooling: the primary product extruded from the three-channel extruder is passed through a ring air cooling system and drawn to the spinneret. The ring air cooling system adopts three-stage air cooling along the drawing direction, with the wind speed of the front section being 0.5 m / s, the wind speed of the middle section being 0.3 m / s, and the wind speed of the rear section being 0.2 m / s. S4, spinning molding: Use a traction mechanism to pull the initial product after gradient cooling through a spinneret with a pore size of 1.2 mm and an aspect ratio of 5 to form the finished polyester fiber. The traction speed of the traction machine is 3200 m / min, and the finished polyester fiber is obtained at 120°C.

[0033] Example 5 A highly elastic polyester fiber with a sheath-core structure, wherein the sheath and core layers are made of PBT with an intrinsic viscosity of 0.65 dL / g; the functional transition layer is SEBS-g-MAH with a grafting rate of 3.8%, mixed with an elastomer toughening masterbatch with a particle size of 1.0 μm and a particle size distribution of D90 / D10=1.1; the masterbatch accounts for 10% by weight, and the thickness ratio of the sheath, transition layer, and core layer is 4:1:5.

[0034] The preparation method comprises the following steps: S1, raw material pretreatment: PBT chips were vacuum dried at 135°C for 7 h, and then the elastomer masterbatch and SEBS-g-MAH were transferred to an internal mixer and granulated at 88°C and 14 MPa pressure; S2, three-channel co-extrusion: core layer PET chips, transition layer granules, and skin layer PET chips are transferred to the extruder hoppers corresponding to each layer in the three-channel co-extruder respectively, and the melt temperature of the core layer extruder is set to 275°C and the extrusion pressure is 16 MPa, the melt temperature of the transition layer extruder is set to 215°C and the extrusion pressure is 9 MPa, and the extrusion temperature of the skin layer extruder is set to 270°C and the extrusion pressure is 10 MPa. The three are extruded together to obtain the primary product; S3, gradient cooling: the primary product extruded from the three-channel extruder is passed through a ring air cooling system and drawn to the spinneret. The ring air cooling system adopts three-stage air cooling along the drawing direction, with the wind speed of the front section being 0.9 m / s, the wind speed of the middle section being 0.7 m / s, and the wind speed of the rear section being 0.5 m / s. S4, spinning molding: Use a traction mechanism to pull the initial product after gradient cooling through a spinneret with a pore size of 0.8 mm and an aspect ratio of 3.2 to form the finished polyester fiber. The traction speed of the traction machine is 2500 m / min, and the finished polyester fiber is formed at 85°C.

[0035] Example 6 The invention discloses an antibacterial-flame-retardant polyester fiber with a sheath-core structure. The sheath and core layers are made of PET with an intrinsic viscosity of 0.71 dL / g. The functional transition layer is made of SEBS-g-MAH with a grafting rate of 4.0%, mixed with nano-silver antibacterial masterbatch with a particle size of 0.4 μm and a weight percentage of 4%, and magnesium hydroxide flame retardant masterbatch with a particle size of 1.0 μm and a weight percentage of 5%. The particle size distribution of the two masterbatch is consistent with D90 / D10=1.2. The thickness ratio of the sheath, transition layer and core layer is 3.2:1:5.8.

[0036] The preparation method comprises the following steps: S1, raw material pretreatment: PET chips were vacuum dried at 122°C for 4.8 h, and then the two masterbatches and SEBS-g-MAH were transferred to an internal mixer and granulated at 93°C and 15 MPa pressure; S2, three-channel co-extrusion: core layer PET chips, transition layer granules, and skin layer PET chips are transferred to the extruder hoppers corresponding to each layer in the three-channel co-extruder respectively, and the melt temperature of the core layer extruder is set to 283°C and the extrusion pressure is 15 MPa, the melt temperature of the transition layer extruder is set to 225°C and the extrusion pressure is 8 MPa, and the extrusion temperature of the skin layer extruder is set to 278°C and the extrusion pressure is 12 MPa. The three are extruded together to obtain the primary product; S3, gradient cooling: the primary product extruded from the three-channel extruder is passed through a ring air cooling system and drawn to the spinneret. The ring air cooling system adopts three-stage air cooling along the drawing direction, with the wind speed of the front section being 0.7 m / s, the wind speed of the middle section being 0.5 m / s, and the wind speed of the rear section being 0.3 m / s. S4, spinning molding: Use a traction mechanism to pull the initial product after gradient cooling through a spinneret with a pore size of 1.0 mm and an aspect ratio of 4.0 to form the finished polyester fiber. The traction speed of the traction machine is 3100 m / min, and the finished polyester fiber is formed at 105°C.

[0037] Performance testing was performed on each of the above examples. Breaking strength was measured according to ASTM D3822. Fiber samples were equilibrated at standard temperature and humidity for 24 hours using a universal material testing machine set at a clamping distance of 20 mm and a tensile speed of 20 mm / min. The average value of at least 30 fibers per group was measured. Masterbatch dispersion was tested by subjecting the fiber samples to liquid nitrogen fracture fractures. After gold spraying, images of the transition layer region were taken using a scanning electron microscope (SEM). ImageJ software was used to calculate the masterbatch agglomeration area. Dispersion was calculated using the formula (1 - agglomeration area / observation area) * 100%. Thermal degradation rate was measured by heating 10 mg each of the functional masterbatch and transition layer material at a rate of 10°C / min to 300°C under a nitrogen atmosphere. The mass loss curve was recorded, and the residual carbon content of the masterbatch at the processing temperature (e.g., 270°C) was calculated. Thermal degradation rate = (initial mass - residual mass) / initial mass * 100%.

[0038] In addition, the functional characteristics of each embodiment were tested, and the results are shown in the following table. Test items Breaking strength (cN / dtex) Masterbatch dispersion (%) Thermal degradation rate (%) Features Example 1 6.2 86.5 2.3 Bacterial inhibition rate ≥98% (ISO 20743) Example 2 5.5 85.8 3.2 Limiting oxygen index ≥25% (ASTM D2863) Example 3 6.3 87.2 1.8 <![CDATA[Surface resistance ≤ 10 5 Ω·cm (ASTM D257)]]> Example 4 5.9 86.0 2.5 UV absorbance ≥90% (AATCC 183) Example 5 5.0 84.5 4.0 Elastic recovery rate ≥85% (ASTM D3107) Example 6 5.7 85.7 3.5 Bacterial inhibition rate ≥95% Limiting oxygen index ≥30% The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A sheath-core polyester fiber, characterized in that: It includes a skin layer, a core layer and a functional transition layer located between the skin and core interface; The skin layer and the core layer are made of polyester material, and the functional transition layer is a mixture of SEBS-g-MAH and functional masterbatch, wherein the mass proportion of the functional masterbatch is 3%-10%.

2. The sheath-core polyester fiber according to claim 1, characterized in that: The functional masterbatch is selected from at least one of an antibacterial agent, a flame retardant, a conductive filler or a light stabilizer, and has a particle size of 0.1-2 μm and a particle size distribution index of ≤0.

25.

3. The sheath-core structure polyester fiber according to claim 1, characterized in that: The melt index of the SEBS-g-MAH is 5-20 g / 10 min, and the grafting rate of the SEBS-g-MAH is 2-5%.

4. The sheath-core polyester fiber according to claim 1, characterized in that: The thickness ratio of the skin layer, the functional transition layer and the core layer is (3-5):1:(4-6), and the difference in characteristic viscosity between the polyester materials of the skin layer and the core layer is ≤0.1 dL / g.

5. The sheath-core polyester fiber according to claim 1, characterized in that: The functional transition layer also contains 0.5%-2% of a silane coupling agent.

6. The sheath-core polyester fiber according to claim 1, characterized in that: The polyester material is polyethylene terephthalate or polybutylene terephthalate.

7. A method for preparing the sheath-core structure polyester fiber according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, raw material pretreatment: drying the skin layer and core layer polyester chips; premixing the functional masterbatch with SEBS-g-MAH particles and mixing and granulating them to obtain functional transition layer particles; S2, three-channel co-extrusion: The core layer material, transition layer material, and skin layer material are transferred from the inside to the outside through independent extruders and co-extruded into a three-channel co-extruder to obtain the primary product; S3, gradient cooling: the primary product extruded from the three-channel extruder is cooled by annular air and drawn to the spinneret; S4, spinning: The primary product after gradient cooling is pulled through the spinneret by a traction mechanism and cooled to form the finished product.

8. The preparation method according to claim 7, characterized in that In S1, the mixing temperature of the functional masterbatch and SEBS-g-MAH particles is 80-100°C and the extrusion pressure is 12-18 MPa; and / or, In S2, the core layer material has a melting temperature of 270-290°C and an extrusion pressure of 12-18 MPa, the transition layer material has a melting temperature of 210-230°C and an extrusion pressure of 6-10 MPa, and the skin layer material has a melting temperature of 260-280°C and an extrusion pressure of 8-12 MPa; and / or, In S3, the cooling wind speed of the ring air cooling is 0.4-0.8 m / s; and / or, In S4, the pulling speed of the pulling machine is 2500-3500m / min, and the initial product setting temperature is 80-120℃.

9. The preparation method according to claim 7, characterized in that In S2, 0.5%-2 of the compatibilizer is added based on the total weight of the transition layer material.

10. The preparation method according to claim 7, characterized in that The aspect ratio of the spinneret channel is 3-5.

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