Permanent, three-dimensional crimped, horsehair-like bicomponent polyester staple fibers and method of making

Abstract

This application relates to the field of textile materials and discloses a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber and its preparation method. The fiber is produced by melt-spinning a sheath component A and a core component B at a mass ratio of 40-60:60-40, exhibiting an eccentric sheath-core structure with an eccentricity of 10%-25%. Sheath A is a high-viscosity polyethylene terephthalate, and core B is a low-viscosity, high-shrinkage isophthalic acid-modified copolyester. The preparation method includes: melt extrusion with the sheath A extrusion temperature controlled 10-15°C higher than that of the core B, followed by spinning, two-stage drafting, and stepped relaxation heat setting. This invention utilizes the difference in shrinkage rates between the components to generate a transverse bending moment, giving the fiber a three-dimensional spiral crimped structure and excellent compression elastic recovery rate. Simultaneously, through reverse temperature difference extrusion and stepped setting processes, the spinning breakage rate is effectively reduced, fiber bundle clumping is avoided, and engineering processability is improved.

Description

Technical Field

[0001] This invention relates to the field of textile materials technology, specifically to a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber and its preparation method. Background Technology

[0002] Natural mohair, with its unique three-dimensional curly shape, possesses a fluffy and crisp feel and excellent compressive strength, making it widely used in textiles. Due to the limited production of natural mohair, developing imitation mohair polyester fibers with similar appearance and feel has become a research focus in the chemical fiber industry.

[0003] Currently, conventional imitation mohair polyester staple fibers are mostly produced by mechanically crimping to give the fibers a crimped structure. The crimp produced by this method often exhibits a two-dimensional planar serrated shape, and the macromolecular segments within the fiber do not form a stable crystalline solidified structure. When the fiber is subjected to tensile tension during subsequent processing, or experiences washing and external compression during daily use, its internal stress is prone to relaxation. This results in a decreased crimp recovery rate, ultimately causing the fabric to become flat and making it difficult to maintain the fluffy, supportive feel similar to natural mohair.

[0004] To address the defects of mechanical crimping, the industry has experimented with bicomponent composite spinning using two polyesters with different shrinkage properties, aiming to induce spontaneous three-dimensional crimping of the fibers through thermal shrinkage differences. However, in actual production, this bicomponent spinning process faces challenges in processing stability. When the two polyester melts with different intrinsic viscosities converge within the composite spinning assembly, the significant difference in apparent viscosity easily leads to abrupt shear stress changes at the interface, causing unstable fiber breakage and macroscopically manifesting as a high fiber breakage rate. Furthermore, during the post-treatment heat setting stage to induce crimping, the presence of high-shrinkage components causes the fiber bundles to undergo severe, disordered shrinkage when exposed to a high-temperature, dry heat environment, resulting in large-area fiber entanglement and agglomeration. This affects subsequent cutting processes, limiting overall processability. Summary of the Invention

[0005] The technical problem solved by this invention is that existing imitation mohair polyester staple fibers are mostly crimped by mechanical means to give them curl. Their macroscopic curl morphology is a two-dimensional planar sawtooth structure. When subjected to washing and external compression, the internal stress is easy to relax, which usually leads to low curl recovery rate, poor fluffiness of the final product and lack of the pressure-resistant skeleton feel of natural mohair.

[0006] Meanwhile, if conventional high and low viscosity polyesters are used for bicomponent spinning, the difference in melt viscosity can easily lead to problems such as unstable spinning flow field and high breakage rate. Furthermore, there is a risk of entanglement and clumping due to the rapid shrinkage of the filament bundle during the subsequent heat setting process, resulting in poor processability.

[0007] To address the above problems, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber, employing the following technical solution:

[0009] A permanent three-dimensional crimped mohair-like bicomponent polyester staple fiber is produced by melt composite spinning of sheath component A and core component B in a mass ratio of 40-60:60-40.

[0010] The outer layer component A is high-viscosity polyethylene terephthalate, and the core layer component B is low-viscosity, high-shrinkage isophthalic acid modified copolyester.

[0011] The cross-section of the short fiber has an eccentric core-shell structure, and the eccentricity of the cross-section center of the core component B from the cross-section center of the short fiber is 10% to 25% of the fiber cross-section radius.

[0012] By adopting the above technical solution, since isophthalic acid monomers are used in the synthesis of copolyesters, isophthalic acid introduces a 1,3-substituted benzene ring asymmetric structure into the main chain.

[0013] This nonlinear structure generates steric hindrance within the molecule, which to some extent disrupts the geometric regularity of the polyester macromolecular chains when they are arranged in space.

[0014] During the spinning and cooling process, irregular chain segments have difficulty arranging themselves into the crystal lattice for crystallization, which correspondingly increases the volume fraction of the amorphous region inside the core layer component B.

[0015] In the subsequent heat setting stage, the molecular chain segments in the amorphous region that are in a frozen orientation state gain thermal energy, undergoing disorientation and high-entropy elastic retraction, causing the core component B to exhibit high shrinkage characteristics.

[0016] Meanwhile, under a geometric setting with an eccentricity of 10% to 25%, the high-shrinkage core layer component B deviates from the center of the fiber cross section.

[0017] When the fiber is heated, the eccentrically distributed core layer component B tends to shorten longitudinally, while the highly crystalline and low-shrinkage skin layer component A resists this shrinkage behavior.

[0018] The uneven distribution of shrinkage stress along the fiber axis transforms this longitudinal shrinkage stress difference into a transverse bending moment on the fiber cross-section. This bending moment forces the entire fiber to twist and bend towards the high-shrinkage core layer, thereby establishing a helical coil shape in three-dimensional space.

[0019] The establishment of the three-dimensional spiral structure allows a single fiber to extend in multiple directions in space. The contact mode inside the fiber assembly changes from line-plane contact to point contact, creating support nodes and air-retention gaps with a certain degree of stability, thereby giving the fiber a better compression elastic recovery rate and a crisp macroscopic skeletal feel.

[0020] Preferably, the intrinsic viscosity of the skin layer component A is 0.65–0.75 dL / g, the intrinsic viscosity of the core layer component B is 0.45–0.55 dL / g, and the intrinsic viscosity difference between the skin layer component A and the core layer component B is controlled within 0.20 dL / g.

[0021] By adopting the above technical solution and controlling the apparent viscosity difference of 0.20 dL / g, it is beneficial to enable the outer shell component A, which serves as the shell, to have a relatively sufficient mechanical modulus to provide a basic support skeleton for the fiber, while enabling the core component B to have a high degree of freedom of molecular chain movement. This helps to reduce shrinkage resistance and thus promotes the occurrence of macroscopic crimping moment.

[0022] Preferably, core layer component B is polymerized from monomers comprising purified terephthalic acid, isophthalic acid and ethylene glycol, and the molar ratio of the total molar amount of purified terephthalic acid and isophthalic acid to that of ethylene glycol is 1:1.2 to 1.5.

[0023] Isophthalic acid accounts for 10% to 20% of the total molar amount of dicarboxylic acids.

[0024] By adopting the above technical solution, controlling the molar percentage of isophthalic acid in dicarboxylic acids to be between 10% and 20% can effectively regulate the crystallinity of polyester while maintaining its basic spinning and stretchability properties.

[0025] If the isophthalic acid content is below this range, the proportion of amorphous regions may be insufficient, making it difficult to induce sufficient thermodynamic shrinkage bending moment; while when the content is above this range, the softening point and glass transition temperature of the modified copolyester decrease, which often increases the risk of filament adhesion during the spinning, extrusion and cooling stages.

[0026] Preferably, the boiling water shrinkage rate of core component B is 30% to 45%;

[0027] The cut length of the short fibers is 38–51 mm.

[0028] By adopting the above technical solution, it is helpful to ensure that the core layer component B has a basic absolute shrinkage base. Combined with the specific length of cutting specifications, the finished short fiber maintains a reasonable number of peaks per unit length, thereby avoiding excessive crimping and loss of fluffiness to a certain extent.

[0029] Secondly, the present invention provides a method for preparing permanently three-dimensional crimped mohair-like bicomponent polyester staple fibers, employing the following technical solution:

[0030] A method for preparing a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber includes the following steps:

[0031] The dried skin layer component A and core layer component B are fed into two separate extruders for melting, and the extrusion temperature of skin layer component A is controlled to be 10-15°C higher than that of core layer component B.

[0032] After being metered, the two melts are fed into the composite spinning assembly, extruded through a distribution plate with an eccentric flow channel, cooled and solidified by side blowing, and then wound and collected to obtain the nascent filament bundle.

[0033] The nascent filament bundles are subjected to two stages of stretching.

[0034] The drawn fiber bundles are subjected to a step-by-step relaxation heat setting treatment to release the internal stress of the fiber bundles and spontaneously form three-dimensional wavy curls. They are then cut and packaged to obtain short fibers.

[0035] By adopting the above technical solution, since there is an apparent viscosity difference when the high-viscosity skin melt and the low-viscosity core melt meet in the composite flow channel, shear stress abrupt changes are likely to occur at the interface, which may cause unstable fracture of the melt flow.

[0036] This scheme increases the melt processing temperature of high-viscosity component A by setting a reverse thermal differential extrusion process of 10-15℃, thereby reducing the apparent viscosity of its melt and making its rheological properties when entering the composite component more consistent with those of the relatively low-viscosity component B.

[0037] Rheological matching helps balance the interfacial shear forces of the two melts within the microchannel, stabilizing the composite extrusion flow field and thus improving the problems of component pressure fluctuations and excessive spinning breakage caused by flow channel interface instability.

[0038] Preferably, the temperature of each zone of the extruder for skin component A is set to 285-295°C, and the temperature of each zone of the extruder for core component B is set to 275-280°C.

[0039] By adopting the above technical solution, within this temperature setting range, not only are the melting enthalpy requirements of each independent polyester material basically met to prevent the occurrence of unmelted crystal points, but it also helps to reduce the end-group thermal oxidation degradation caused by high temperature on low viscosity core layer component B, and maintain the stability of layered extrusion.

[0040] Preferably, the two-stage drawing process includes a first-stage drawing in a water bath at 70 to 85°C and a second-stage drawing in a steam bath at 90 to 100°C, with the total drawing ratio controlled between 2.5 and 4.0.

[0041] By employing the above technical solution, progressive water bath and steam bath thermal stretching provides activation energy for macromolecular chain segments to overcome intermolecular forces. The molecular chains then undergo directional slippage and oriented crystallization in a direction parallel to the fiber axis.

[0042] This process endows the precursor fiber with basic breaking strength and stores polymer conformational internal stress for the shrinkage bending moment in the subsequent shaping stage.

[0043] Preferably, the stepped relaxation heat setting treatment specifically includes: Pre-relaxation treatment: The yarn bundle first enters the steaming box under extremely low tension and is treated with saturated humid heat steam at 100-115°C for 3 to 5 minutes;

[0044] Dry heat setting treatment: The pre-relaxed yarn bundles are put into a tensionless conveyor belt hot air drying and setting machine and stay in dry hot air at 120-160℃ for 5-10 minutes.

[0045] By adopting the above technical solution and using a step-by-step shaping process that includes both humid and dry heat environments, it helps to improve the problem of fiber entanglement and agglomeration caused by the rapid and disordered shrinkage of polymer chain segments in the amorphous region due to instantaneous exposure to high temperature environment.

[0046] During the pre-relaxation stage, water molecules in the saturated humid heat steam penetrate into the amorphous region of the polyester, playing a plasticizing role and expanding the free volume of the molecules, allowing the fiber bundle to undergo preliminary internal stress release under a relatively mild thermal field and low tension conditions.

[0047] This stage facilitates the initial construction of the basic crimped morphology and reduces the possibility of fiber dead knots caused by local stress concentration. After pre-relaxation, the fibers entering the high-temperature environment have a basic skeleton. The heat energy of 120-160℃ causes the molecular chain segments to rearrange the crystal regions and solidify the structure under the new three-dimensional bending morphology, transforming the thermodynamic deformation into a more stable crystalline structure, giving the product good water resistance.

[0048] Preferably, the process for preparing core component B includes:

[0049] Purified terephthalic acid, isophthalic acid, ethylene glycol, and antimony trioxide catalyst added in an amount of 200 to 400 ppm of the total polymer mass are mixed and added into an esterification reactor, and the esterification reaction is carried out at 240 to 260°C and 0.1 to 0.3 MPa gauge pressure.

[0050] When the water distillation reaches 95% of the theoretical value and the temperature at the top of the column drops, the esterification product is transferred to the polycondensation reactor. The system pressure is reduced to 700-900 Pa by vacuuming within 30-50 minutes, and the temperature is raised to 260-270℃ for pre-polycondensation reaction.

[0051] Continue to evacuate to 70-90 Pa, then raise the temperature to 275-285℃ to carry out the final polycondensation reaction. When the melt reaches the target intrinsic viscosity, cool and pelletize.

[0052] By adopting the above technical solution, the esterification stage is controlled with reasonable temperature and gauge pressure, which promotes the esterification and dehydration reaction of aromatic dicarboxylic acids and ethylene glycol.

[0053] The polycondensation stage employs a process path of gradual pressure reduction and stepwise temperature increase, which removes the small molecules of ethylene glycol and oligomers generated in the reaction. This can, to some extent, reduce the deteriorating effect of small molecule residues on the final fiber mechanical properties and facilitate the uniform distribution of isophthalic acid copolymer units in the polyester macromolecular chain segments.

[0054] This invention provides a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber and its preparation method. It has the following beneficial effects:

[0055] 1. This invention employs an eccentric core-sheath structure, using isophthalic acid-modified copolyester as the core layer and high-viscosity polyethylene terephthalate as the sheath layer, utilizing the difference in shrinkage rates between the two during heat treatment to generate a transverse bending moment. This structural design allows the fibers to spontaneously form a three-dimensional spiral crimp, transforming the internal contact between the fiber assembly from line and surface to point contact, constructing spatial nodes with supporting functions, thereby endowing the polyester staple fiber with a compression elastic recovery rate and fluffiness similar to natural mohair.

[0056] 2. This invention incorporates a reverse temperature difference extrusion process during the bicomponent spinning process, controlling the extrusion temperature of the high-viscosity skin layer component to be higher than that of the low-viscosity core layer component. This process condition reduces the apparent viscosity of the high-viscosity component, narrows the viscosity difference between the two melt streams at the interface of the composite flow channel, balances the interfacial shear force, and improves the situation where the melt streams become unstable and break due to interfacial rheological mismatch. This, in turn, reduces the spinning breakage rate and improves the engineering processability for large-scale production.

[0057] 3. The post-processing steps of this invention employ a stepped relaxation heat-setting method that includes both humid and dry heat environments. The humid heat pre-relaxation stage utilizes the plasticizing effect of water molecules to allow the fiber bundle to release initial internal stress under low tension, preventing entanglement and clumping caused by the instantaneous disordered shrinkage of the fibers when directly exposed to high temperatures. The subsequent dry heat-setting stage promotes crystalline rearrangement and structural solidification of molecular chain segments in a new bending shape. This setting method ensures smooth fiber bundle processing and improves the morphological stability and washability of the three-dimensional crimped structure. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the structure of the permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber of the present invention, wherein, Figure 1 (a) is a schematic diagram of the eccentric core-sheath cross-section structure of the fiber. Figure 1 (b) is a schematic diagram of the three-dimensional curled shape of the fiber;

[0059] Figure 2 This is a schematic diagram of the differential scanning calorimetry temperature rise and fall procedure in this invention;

[0060] Figure 3 This is a schematic diagram of the single-component fiber boiling water shrinkage test method in this invention;

[0061] Figure 4 This is a schematic diagram of the continuous spinning and heat setting process evaluation method in this invention;

[0062] Figure 5 This is a schematic diagram of the fiber crimping characteristics and durability testing method in this invention;

[0063] Figure 6 This is a schematic diagram of the method for testing the bulkiness and compression recovery performance of fiber products in this invention. Detailed Implementation

[0064] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Unless otherwise specified, all reagents are commercially available analytical grade or chemically pure grade products.

[0066] High-viscosity polyethylene terephthalate chips (CAS No.: 25038-59-9), with intrinsic viscosity IV of 0.65 dL / g to 0.75 dL / g;

[0067] Purified terephthalic acid (CAS No.: 100-21-0), purity ≥99.5%;

[0068] Isophthalic acid (CAS No.: 121-91-5), purity ≥99.0%;

[0069] Ethylene glycol (CAS No.: 107-21-1), purity ≥ 99.9%;

[0070] Antimony trioxide (CAS No.: 1309-64-4), purity ≥99.5%.

[0071] Preparation Example 1:

[0072] This preparation example provides a method for preparing a low-viscosity, high-shrinkage isophthalic acid-modified copolyester, comprising the following steps:

[0073] The polymer was prepared by mixing purified terephthalic acid and isophthalic acid in a total molar ratio of 1:1.3 to ethylene glycol, wherein isophthalic acid accounted for 15% of the total molar amount of the dicarboxylic acids, and the amount of antimony trioxide catalyst added was 300 ppm of the total mass of the polymer.

[0074] Purified terephthalic acid, isophthalic acid, ethylene glycol, and antimony trioxide are added to an esterification reactor and mixed under nitrogen protection.

[0075] The esterification reaction temperature was controlled at 250℃, and the reaction pressure was 0.2 MPa gauge pressure. As the reaction proceeded, water produced during esterification was continuously distilled off. The esterification reaction ended when the amount of water distilled off reached 95% of the theoretical value and the temperature at the top of the column decreased.

[0076] The esterification product was transferred to a polycondensation reactor, and a vacuum was steadily applied over 40 minutes to reduce the system pressure to 800 Pa. At the same time, the temperature was gradually increased to 265 °C to carry out a pre-polycondensation reaction.

[0077] Then, the vacuum was continued to reduce the residual pressure of the system to 80 Pa, and the temperature was raised to 280°C to carry out the final polycondensation reaction.

[0078] The melt viscosity was monitored by the torque change of the reactor agitator. When the target intrinsic viscosity of 0.50 dL / g was reached, nitrogen was introduced to break the vacuum. The melt was extruded by pressurization, cooled with water and granulated to obtain low viscosity, high shrinkage isophthalic acid modified copolyester chips (core component B1) with a boiling water shrinkage rate of 38%.

[0079] Preparation Example 2:

[0080] This preparation example provides a method for preparing a low-viscosity, high-shrinkage isophthalic acid-modified copolyester, comprising the following steps:

[0081] The ingredients were prepared according to a total molar ratio of purified terephthalic acid and isophthalic acid to ethylene glycol of 1:1.2, wherein isophthalic acid accounted for 10% of the total molar amount of the dicarboxylic acids, and the amount of antimony trioxide catalyst added was 200 ppm of the total mass of the polymer.

[0082] Purified terephthalic acid, isophthalic acid, ethylene glycol, and antimony trioxide were added to an esterification reactor and mixed by slurrying under nitrogen protection. The esterification reaction temperature was controlled at 240℃, and the reaction pressure was 0.1 MPa gauge pressure.

[0083] As the reaction proceeds, water produced during esterification is continuously distilled off. The esterification reaction ends when the amount of water distilled off reaches 95% of the theoretical value and the temperature at the top of the column decreases.

[0084] The esterification product was transferred to a polycondensation reactor, and a vacuum was steadily drawn within 30 minutes to reduce the system pressure to 900 Pa. At the same time, the temperature was gradually increased to 260 °C to carry out a pre-polycondensation reaction.

[0085] Then, the vacuum was continued to reduce the residual pressure of the system to 90 Pa, and the temperature was raised to 275°C to carry out the final polycondensation reaction.

[0086] The melt viscosity was monitored by the torque change of the reactor agitator. When the target intrinsic viscosity of 0.45 dL / g was reached, nitrogen was introduced to break the vacuum. The melt was extruded by pressurization, cooled with water and granulated to obtain low viscosity, high shrinkage isophthalic acid modified copolyester chips (core component B2) with a boiling water shrinkage rate of 30%.

[0087] Preparation Example 3:

[0088] This preparation example provides a method for preparing a low-viscosity, high-shrinkage isophthalic acid-modified copolyester, comprising the following steps:

[0089] The raw materials were prepared according to a total molar ratio of purified terephthalic acid and isophthalic acid to ethylene glycol of 1:1.5, with isophthalic acid accounting for 20% of the total molar amount of the diacids. The catalyst, antimony trioxide, was added at 400 ppm of the total polymer mass. Purified terephthalic acid, isophthalic acid, ethylene glycol, and antimony trioxide were added to an esterification reactor and mixed by slurrying under nitrogen protection. The esterification reaction temperature was controlled at 260℃, and the reaction pressure at 0.3 MPa gauge pressure.

[0090] As the reaction proceeds, water produced during esterification is continuously distilled off. The esterification reaction ends when the amount of water distilled off reaches 95% of the theoretical value and the temperature at the top of the column decreases.

[0091] The esterification product was transferred to a polycondensation reactor, and a vacuum was steadily drawn within 50 minutes to reduce the system pressure to 700 Pa. At the same time, the temperature was gradually increased to 270 °C to carry out the pre-polycondensation reaction.

[0092] Then, the vacuum was continued to reduce the residual pressure of the system to 70 Pa, and the temperature was raised to 285°C to carry out the final polycondensation reaction.

[0093] The melt viscosity was monitored by the torque change of the reactor agitator. When the target intrinsic viscosity of 0.55 dL / g was reached, nitrogen was introduced to break the vacuum. The melt was extruded by pressurization, cooled with water and granulated to obtain low viscosity, high shrinkage isophthalic acid modified copolyester chips (core component B3) with a boiling water shrinkage rate of 45%.

[0094] Example 1:

[0095] This embodiment provides a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber and its preparation method, including the following steps:

[0096] High-viscosity polyethylene terephthalate chips with an intrinsic viscosity of 0.70 dL / g were selected as skin layer component A, and low-viscosity, high-shrinkage isophthalic acid modified copolyester chips with an intrinsic viscosity of 0.50 dL / g obtained in Preparation Example 1 were selected as core layer component B.

[0097] The intrinsic viscosity difference between the two is 0.20 dL / g.

[0098] The dried components A and B are fed into two separate single-screw extruders for melting.

[0099] The temperature of each zone of the extruder for component A is set to 290℃, and the temperature of each zone of the extruder for component B is set to 275℃, with a temperature difference of 15℃ between the two.

[0100] The two melts are metered by a metering pump and fed into the composite spinning assembly according to the mass ratio of component A to component B of 50:50.

[0101] The overall temperature of the composite spinning assembly is set to 285℃.

[0102] The melt is extruded through a distribution plate with an eccentric flow channel. The eccentricity of the cross-sectional center of core component B from the cross-sectional center of the entire fiber is 15% of the fiber cross-sectional radius. The extruded nascent fibers are cooled and solidified by side blowing air at a temperature of 20℃ and a wind speed of 0.6m / s, and the nascent filament bundles are collected at a winding speed of 1000m / min.

[0103] The nascent filament bundles were drawn in two stages: the first stage was carried out in a water bath at 75°C, and the second stage was carried out in a steam bath at 95°C, with the total drawing ratio controlled at 3.5 times.

[0104] After being drawn, the filament bundles enter a stepped relaxation heat setting stage.

[0105] The fiber bundles are first introduced into the steam chamber under extremely low tension and pre-relaxed by saturated humid heat steam at 110°C for 4 minutes.

[0106] It then enters a tensionless tracked hot air drying and setting machine, where it stays in hot dry air at 140°C for 8 minutes for heat setting, causing the fibers to spontaneously form three-dimensional wavy curls.

[0107] The cooled and shaped filament bundles are cut by a cutting machine with a cutting length set to 51mm, and then packaged to obtain finished short fibers.

[0108] Example 2:

[0109] This embodiment provides a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber and its preparation method, including the following steps:

[0110] High-viscosity polyethylene terephthalate (PET) chips with an intrinsic viscosity of 0.65 dL / g were selected as skin layer component A, and low-viscosity, high-shrinkage isophthalic acid-modified copolyester chips with an intrinsic viscosity of 0.45 dL / g obtained in Preparation Example 2 were selected as core layer component B. The intrinsic viscosity difference between the two is 0.20 dL / g.

[0111] The dried components A and B are fed into two separate single-screw extruders for melting.

[0112] The temperature of each zone of the extruder for component A is set to 285℃, and the temperature of each zone of the extruder for component B is set to 275℃, with a temperature difference of 10℃ between the two. The two melt streams are metered by a metering pump and fed into the composite spinning assembly according to a mass ratio of component A to component B of 40:60.

[0113] The overall temperature of the composite spinning assembly is set to 275℃.

[0114] The melt is extruded through a distribution plate with an eccentric flow channel. The eccentricity of the cross-sectional center of core component B from the cross-sectional center of the entire fiber is 10% of the fiber cross-sectional radius.

[0115] The extruded nascent fibers are cooled and solidified by side blowing air at a temperature of 15℃ and a speed of 0.5m / s, and the nascent fiber bundles are collected at a winding speed of 800m / min.

[0116] The nascent filament bundles are drawn in two stages: the first stage is carried out in a water bath at 70°C, and the second stage is carried out in a steam bath at 90°C, with the total drawing ratio controlled at 2.5 times.

[0117] After being drawn, the filament bundles enter a stepped relaxation heat setting stage. The filament bundles are first placed in a steam chamber under extremely low tension and pre-relaxed by being treated with saturated humid heat steam at 100°C for 3 minutes.

[0118] It then enters a tensionless tracked hot air drying and setting machine, where it stays in hot dry air at 120°C for 5 minutes for heat setting, causing the fibers to spontaneously form three-dimensional wavy curls.

[0119] After the filaments have been shaped and cooled, they are cut by a cutting machine with a cutting length set to 38mm, and then packaged to obtain finished short fibers.

[0120] Example 3:

[0121] This embodiment provides a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber and its preparation method, including the following steps:

[0122] High-viscosity polyethylene terephthalate chips with an intrinsic viscosity of 0.75 dL / g were selected as skin layer component A, and low-viscosity, high-shrinkage isophthalic acid modified copolyester chips with an intrinsic viscosity of 0.55 dL / g obtained in Preparation Example 3 were selected as core layer component B.

[0123] The intrinsic viscosity difference between the two is 0.20 dL / g.

[0124] The dried components A and B are fed into two separate single-screw extruders for melting.

[0125] The temperature of each zone of the extruder for component A is set to 295℃, and the temperature of each zone of the extruder for component B is set to 280℃, with a temperature difference of 15℃ between the two.

[0126] The two melts are metered by a metering pump and fed into the composite spinning assembly according to the mass ratio of component A to component B of 60:40.

[0127] The overall temperature of the composite spinning assembly is set to 290℃.

[0128] The melt is extruded through a distribution plate with an eccentric flow channel, and the eccentricity of the cross-sectional center of core component B is 25% of the cross-sectional radius of the entire fiber.

[0129] The extruded nascent fibers are cooled and solidified by side blowing at a temperature of 25°C and a speed of 0.8 m / s, and the nascent filament bundles are collected at a winding speed of 1500 m / min.

[0130] The nascent filament bundles were drawn in two stages: the first stage was carried out in a water bath at 85°C, and the second stage was carried out in a steam bath at 100°C, with the total drawing ratio controlled at 4.0 times.

[0131] After being drawn, the filament bundles enter a stepped relaxation heat setting stage. The filament bundles are first placed in a steam chamber under extremely low tension and pre-relaxed by being treated with saturated humid heat steam at 115°C for 5 minutes.

[0132] It then enters a tensionless tracked hot air drying and setting machine, where it stays in hot dry air at 160°C for 10 minutes for heat setting, causing the fibers to spontaneously form three-dimensional wavy curls.

[0133] The cooled and shaped filament bundles are cut by a cutting machine with a cutting length set to 51mm, and then packaged to obtain finished short fibers.

[0134] Example 4:

[0135] This embodiment provides a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber and its preparation method, including the following steps:

[0136] High-viscosity polyethylene terephthalate chips with an intrinsic viscosity of 0.70 dL / g were selected as skin layer component A, and low-viscosity, high-shrinkage isophthalic acid modified copolyester chips with an intrinsic viscosity of 0.50 dL / g obtained in Preparation Example 1 were selected as core layer component B.

[0137] The intrinsic viscosity difference between the two is 0.20 dL / g.

[0138] The dried components A and B are fed into two separate single-screw extruders for melting.

[0139] The temperature of each zone of the extruder for component A is set to 290℃, and the temperature of each zone of the extruder for component B is set to 275℃, with a temperature difference of 15℃ between the two.

[0140] The two melts are metered by a metering pump and fed into the composite spinning assembly according to the mass ratio of component A to component B of 50:50.

[0141] The overall temperature of the composite spinning assembly is set to 285℃.

[0142] The melt is extruded through a distribution plate with an eccentric flow channel. The eccentricity of the cross-sectional center of core component B from the cross-sectional center of the entire fiber is 20% of the fiber cross-sectional radius.

[0143] The extruded nascent fibers are cooled and solidified by side blowing air at a temperature of 20°C and a speed of 0.6 m / s, and the nascent filament bundles are collected at a winding speed of 1000 m / min.

[0144] The nascent filament bundles were drawn in two stages: the first stage was carried out in a water bath at 75°C, and the second stage was carried out in a steam bath at 95°C, with the total drawing ratio controlled at 3.5 times.

[0145] After being drawn, the filament bundles enter a stepped relaxation heat setting stage. The filament bundles are first placed in a steam chamber under extremely low tension and pre-relaxed by being treated with saturated humid heat steam at 110°C for 4 minutes.

[0146] It then enters a tensionless tracked hot air drying and setting machine, where it stays in hot dry air at 140°C for 8 minutes for heat setting, causing the fibers to spontaneously form three-dimensional wavy curls.

[0147] The cooled and shaped filament bundles are cut by a cutting machine with a cutting length set to 51mm, and then packaged to obtain finished short fibers.

[0148] Comparative Example 1:

[0149] The difference compared to Example 1 is as follows:

[0150] The spinning assembly is extruded using a distribution plate with concentric flow channels. The center of the cross-section of core component B coincides with the center of the cross-section of the entire fiber (i.e., the eccentricity is 0), and the rest are the same.

[0151] Comparative Example 2:

[0152] The difference compared to Example 1 is as follows:

[0153] The temperature settings for each zone of the extruder for component A and component B are the same, both at 285℃ (i.e., the gradient temperature difference compensation for extrusion temperature is cancelled), and everything else is the same.

[0154] Comparative Example 3:

[0155] The difference compared to Example 1 is as follows:

[0156] The drawn filaments are directly fed into a tensionless crawler-type hot air drying and setting machine, where they are held in hot dry air at 140°C for 12 minutes for hot dry setting (i.e., the pre-relaxation stage of 110°C saturated humid steam is eliminated), and everything else is the same.

[0157] Comparative Example 4:

[0158] The difference compared to Example 1 is as follows:

[0159] High-viscosity polyethylene terephthalate (PET) chips with an intrinsic viscosity of 0.70 dL / g were selected as skin layer component A, and similarly, high-viscosity PET chips with an intrinsic viscosity of 0.70 dL / g were selected as core layer component B (i.e., the core layer did not use low-viscosity, high-shrinkage isophthalic acid modified copolyester). After heat setting, the filament bundles did not spontaneously curl, and were subsequently subjected to forced mechanical crimping and curling treatment using a mechanical crimping machine. All other aspects were the same.

[0160] Test Example 1:

[0161] This test example provides instructions for testing the melt rheological behavior of skin component A and core component B at different set temperatures. The specific test steps are as follows:

[0162] Extract the slices of component A and component B, and process them in a vacuum drying oven with a vacuum degree of less than 100 Pa and a temperature of 110 °C for 12 hours to control the moisture content of the slices to below 30 ppm.

[0163] The test was conducted using a capillary rheometer with a length-to-diameter ratio of 40:1 and a die diameter of 1.0 mm.

[0164] The test shear rate range is set as follows: .

[0165] For the process parameters of Example 1, the test cylinder temperature was set to 290°C to test the apparent viscosity of component A, and set to 275°C to test the apparent viscosity of component B.

[0166] For the process parameters of ratio 2, the temperature of the test cylinder was uniformly set to 285℃, and the apparent viscosity of component A and component B was tested respectively.

[0167] After reaching the set temperature and maintaining it for 10 minutes, the plunger is started to extrude the melt. The instrument automatically collects the corresponding shear stress and shear rate data and calculates the apparent viscosity.

[0168] Table 1. Apparent viscosity test data of component A and component B at different temperatures.

[0169] Shear rate ( ) Apparent viscosity of component A at 290℃ Apparent viscosity of component B at 275°C Apparent viscosity of component A at 285℃ Apparent viscosity of component B at 285°C 100 621.3 589.6 753.8 412.4 500 312.5 298.1 384.2 215.8 1000 204.8 195.3 256.7 148.6 3000 115.4 108.7 142.1 82.3 6000 78.6 73.2 95.3 56.1 10000 52.1 49.5 61.8 38.4

[0170] Based on the data in Table 1 and Figure 1 The content states that polymer melts, as typical pseudoplastic fluids, exhibit a nonlinear decrease in apparent viscosity with increasing shear rate.

[0171] Under the temperature difference extrusion process set in Example 1, that is, when component A is at 290°C and component B is at 275°C, the apparent viscosity of the two components remains highly similar within the full shear rate range.

[0172] Inside the composite spinning assembly, especially in the high-shear region of the spinneret micropores, the viscosity difference between the two melts is controlled within a reasonable range.

[0173] This matching of rheological characteristics results in a smaller difference in velocity gradient between the two melt streams when they merge, and a more synchronized advance of the fluid front, thereby maintaining the structural stability of the eccentric cross-section design and avoiding interfacial slippage, composite interface instability, and melt stream disturbance during the spinning process.

[0174] During the composite spinning process, independent melt pipelines, metering pumps, and spinning box temperature control are used to maintain the melt temperatures of components A and B at approximately 290°C and 275°C respectively before they enter the composite spinning assembly, thereby ensuring that the two melts have a good apparent viscosity match before they merge.

[0175] In contrast, under the same temperature extrusion conditions as in Comparative Example 2, when both component A and component B are at 285°C, there is a significant difference in apparent viscosity due to the inherent differences in their molecular weight and properties.

[0176] At the same shear rate, the viscosity of component A is much greater than that of component B.

[0177] Fluid mechanics principles show that in a pipe flow shear field, low-viscosity fluids tend to coat the high-shear pipe wall region, while high-viscosity fluids are pushed towards the center.

[0178] This viscosity mismatch leads to uneven shear stress distribution at the composite interface, causing the original eccentric flow channel distribution to fail and triggering melt fracture. This manifests macroscopically as the knee bending phenomenon of nascent fibers and subsequent spinning breakage.

[0179] The test results verified the theoretical basis and practical effect of the gradient temperature difference setting in this invention in solving the defects of the composite spinning process of dual viscosity components.

[0180] Test Example 2:

[0181] This test example provides instructions for differential scanning calorimetry (DSC) analysis of cortical component A and different core components B. The specific test steps are as follows:

[0182] Extract the cortical component A slices and the core component B slices (denoted as B1, B2, and B3, respectively) prepared in Examples 1 to 3, and let them stand in a constant temperature and humidity environment for 24 hours.

[0183] Weigh 5.1 to 5.4 mg of each component sample, place them into standard aluminum sample crucibles and seal them with caps. At the same time, prepare an empty aluminum crucible as a reference.

[0184] The sample crucible and the reference crucible were placed in the heating test chamber of the differential scanning calorimeter, and nitrogen gas with a purity of 99.99% was introduced as a purge gas with a flow rate controlled at 50 ml / min.

[0185] Start the heating program and heat from room temperature to 300°C at a rate of 20°C / minute. Hold this temperature for 5 minutes to eliminate thermal history and mechanical stress from the slicing process.

[0186] Turn on the liquid nitrogen cooling system and rapidly cool the sample to 25°C at a cooling rate of 50°C / min. Maintain this temperature for 3 minutes to allow the system to reach thermal equilibrium.

[0187] A second temperature scan was performed, with the heating rate set at 10℃ / minute, and the change in heat flux was recorded during the process of heating from 25℃ to 300℃.

[0188] The transition inflection point and endothermic / exothermic peak area on the second heating curve were extracted using the instrument's accompanying analysis software. The glass transition temperature, melting peak temperature, and crystallinity were then calculated. Crystallinity was determined according to... , It is the enthalpy of cold crystallization. This is the theoretical enthalpy of melting for a fully crystalline polyester.

[0189] Table 2. Test data of thermodynamic parameters of cortex component A and each core component B.

[0190] Sample object Glass transition temperature (°C) Peak melting temperature (°C) Crystallinity (%) Cortical component A 78.4 256.2 41.7 Preparation Example 2 (Component B2) 74.8 243.6 26.3 Preparation Example 1 (Component B1) 72.3 231.1 18.9 Preparation Example 3 (Component B3) 68.9 221.7 12.4

[0191] Based on the data in Table 2 and the appendix Figure 2 The content shows that the cortex component A exhibits typical thermodynamic parameters of conventional polyethylene terephthalate, with high crystallinity and melting temperature.

[0192] Under the preparation conditions in this group, as the molar proportion of isophthalic acid in the dicarboxylic acid increases, and in conjunction with the adjustment of the target intrinsic viscosity and polymerization process conditions, the glass transition temperature, melting peak temperature and overall crystallinity of the core component B in the preparation example show a decreasing trend.

[0193] The introduction of isophthalic acid structural units alters the original para-symmetrical arrangement of polymer molecular chains, increases the steric hindrance of the molecular backbone, and reduces the regularity of molecular chain stacking and crystallization ability.

[0194] During the cooling and curing process, this structural asymmetry hinders the orderly stacking of polymer chain segments into the lattice, resulting in an increase in the proportion of amorphous regions in the polyester system.

[0195] The thermal shrinkage behavior of polymer materials mainly originates from the entropic elasticity of oriented chain segments in amorphous regions after heating.

[0196] The decrease in crystallinity means that there is a larger volume fraction of amorphous regions inside the core layer components, which provides structural conditions for the fiber to produce a high proportion of thermal shrinkage in the subsequent heat setting process.

[0197] The differences in crystallinity and phase transition temperature between the two components reflect the changes in the physical aggregate structure of the material, supporting the technical logic of constructing a two-component structure with shrinkage difference through copolymerization modification.

[0198] Test Example 3:

[0199] This test example provides basic test instructions for the boiling water shrinkage rate of single-spun fibers of cortex component A and core component B with different modification ratios. The specific test steps are as follows:

[0200] Cuttings of cortex component A and core component B obtained in Preparation Examples 1-3 were taken, dried under vacuum, and then melt-extruded and spun using a single-component spinning machine. The resulting nascent filament bundles of each pure component were collected after cooling.

[0201] Each nascent filament bundle was subjected to a 3.5-fold hot stretching treatment to prepare single-component fully stretched filament samples with a fineness controlled between 2.5 and 3.0 mm. Within the range.

[0202] A filament segment of approximately 500 mm in length was randomly selected from each of the single-component drawn filament samples as a test sample, and a 0.05 ohm pressure was applied to the sample. The pre-tension was applied, and its actual initial length was measured.

[0203] Remove the pre-applied tension, place the sample into a water-permeable mesh bag without tension, and immerse it completely in a boiling water bath at 100°C for 15 minutes.

[0204] Remove the mesh bag from the boiling water, allow the sample to cool naturally at room temperature, and allow it to reach constant weight.

[0205] Apply 0.05 to the processed sample again. The pre-tension was applied, and the final length after boiling water treatment was measured.

[0206] Table 3. Test data on boiling water shrinkage rate of monofilament samples of cortex component A and each core component B.

[0207] Sample object Test batch Initial length (mm) Length after boiling water treatment (mm) Boiling water shrinkage rate (%) Cortical component A 1 502.1 438.6 12.65 Cortical component A 2 498.7 434.2 12.93 Cortical component A 3 501.5 441.9 11.88 Core layer component B2 (Preparation Example 2) 1 501.3 349.5 30.28 Core layer component B2 (Preparation Example 2) 2 499.6 353.1 29.32 Core layer component B2 (Preparation Example 2) 3 503.2 348.6 30.72 Core layer component B1 (Preparation Example 1) 1 503.5 312.4 37.95 Core layer component B1 (Preparation Example 1) 2 497.8 304.7 38.79 Core layer component B1 (Preparation Example 1) 3 501.1 314.5 37.24 Core layer component B3 (Preparation Example 3) 1 500.4 272.6 45.52 Core layer component B3 (Preparation Example 3) 2 502.9 279.3 44.46 Core layer component B3 (Preparation Example 3) 3 499.8 271.8 45.62

[0208] Based on the data in Table 3 and the appendix Figure 3 The content shows that the skin component A, which is composed of conventional polyester material, exhibits a low level of heat shrinkage, with a boiling water shrinkage rate of around 12%.

[0209] The core layer components B series modified with isophthalic acid showed a significant upward trend in boiling water shrinkage as the content of the modified monomers increased, and the target intrinsic viscosity and polymerization process conditions were adjusted. The shrinkage rates of components B2, B1 and B3 reached approximately 30%, 38% and 45%, respectively.

[0210] These test results reflect the high-entropy elastic recoil characteristics of the amorphous region oriented molecular chains inside the modified copolyester under the action of a thermal field.

[0211] The difference in shrinkage between component A and component B constitutes the thermodynamic driving force for the three-dimensional crimping of the bicomponent composite fiber. Under the geometric conditions of an eccentric composite structure, this longitudinal shrinkage asymmetry of up to 17%–33% is converted into transverse bending moment within the fiber.

[0212] During the heat setting process, the release of stress drives the fibers to bend towards the core component on the high shrinkage side, thereby forming a macroscopic three-dimensional spiral curl shape.

[0213] Experimental data confirm that using this isophthalic acid-modified copolyester as the core material can provide sufficient internal structural strain basis for the fiber.

[0214] The shrinkage rate of boiling water is calculated according to the following formula: shrinkage rate of boiling water = (initial length - length after boiling water treatment) / initial length × 100%.

[0215] Test Example 4:

[0216] This test example provides a comparative test description for the smoothness of the spinning process and the settling yield. The specific test steps are as follows:

[0217] The spinning and post-processing were carried out continuously for 72 hours on a bicomponent composite spinning machine according to the process parameters set in Example 1, Comparative Example 2 and Comparative Example 3 respectively.

[0218] During the spinning and extrusion stage, melt pressure data is continuously recorded for 72 hours by a melt pressure sensor installed at the inlet of the spinning assembly. The maximum and minimum pressure values ​​within each recording period are extracted, and the peak-to-valley difference of the assembly pressure fluctuation is calculated.

[0219] The number of spinning ends that occurred in each test object during a 72-hour continuous production cycle was counted, and combined with the actual amount of raw filament chips fed, the breakage rate was calculated as per 100 tons of raw filament.

[0220] After the subsequent stepped relaxation heat setting process (or comparative single heat setting process), the finished filament bundles are randomly sampled before cutting and packaging, with each sample size controlled at around 50 kg.

[0221] The sampled filament bundles are laid flat on the inspection table, and hard knots, dead knots, and tangled clumps that cannot be untied due to abnormal shrinkage are manually picked out.

[0222] Using an electronic platform scale with an accuracy of 0.01 kg, the selected clumps of waste filaments and the normally curled qualified filament bundles were weighed separately, and the mass percentage of the clumps in the total sample weight was calculated.

[0223] Table 4. Data Records of Continuous Spinning and Heat Setting Processes in Example 1 and Comparative Examples

[0224] Test object Test batch Peak-to-valley difference in component pressure fluctuation (MPa) Spinning breakage rate (times / 100 tons) Tow agglomeration rate (%) Example 1 1 0.42 1.1 0.85 Example 1 2 0.51 0.9 0.72 Example 1 3 0.38 1.4 0.91 Comparative Example 2 1 2.84 14.6 1.84 Comparative Example 2 2 3.15 16.2 2.15 Comparative Example 2 3 2.67 13.8 1.93 Comparative Example 3 1 0.46 1.5 18.32 Comparative Example 3 2 0.39 1.2 21.45 Comparative Example 3 3 0.55 1.6 19.67

[0225] Based on the data in Table 4 and the appendix Figure 4 In the spinning and extrusion stage, Comparative Example 2, due to the lack of a temperature difference compensation process, showed a significant viscosity difference between the melts of component A and component B when they entered the spinning assembly.

[0226] When high and low viscosity fluids converge in a microchannel, the distribution of interfacial shear stress becomes unbalanced, resulting in an extremely unstable flow field. This manifests as severe fluctuations in the component inlet pressure, ranging from 2.67 to 3.15 MPa.

[0227] This rheological mismatch directly disrupts the melt flow on the spinning line, causing "knee bending" and resulting in high-frequency breakage, with a breakage rate of 13.8-16.2 times per 100 tons.

[0228] In Example 1, by adjusting the extrusion temperature difference by 15°C, the apparent viscosity of the two melts tends to be consistent, the flow field stability is improved, the component pressure fluctuation is basically maintained at a low level of about 0.5MPa, with a maximum of only 0.51MPa, and the breakage rate is reduced to no more than 1.4 times / 100 tons.

[0229] During the heat setting stage, the nascent filament bundles of Comparative Example 3 were directly introduced into a high-temperature dry heat environment of 140℃. The polyester macromolecular chain segments instantly gained high energy, resulting in violent and uncontrollable shrinkage of the amorphous region.

[0230] Before the overall tension of the fiber bundle has reached equilibrium, adjacent fibers become physically entangled due to mutual compression and irregular, rapid bending. This can result in localized adhesion, cohesion, or hard knots that are difficult to disperse, forming a large number of dead knots with a clump rate approaching 20%.

[0231] Example 1 uses a stepped relaxation heat setting method that introduces 110°C saturated humid heat steam as a pre-relaxation condition.

[0232] Water molecules enter the amorphous region of polyester and act as plasticizers, reducing the activation energy of polymer chain rearrangement, allowing the fiber to complete the initial release and pre-shrinkage of internal stress under lower temperature field and gentle tension conditions.

[0233] This process effectively avoids stress concentration and entanglement caused by instantaneous shrinkage at high temperatures. Subsequently, when the fiber skeleton is dried and heat-set at 140℃, it tends to be stable, ensuring the independent molding of three-dimensional curls, and the agglomeration rate is controlled within 1%.

[0234] Experimental results confirm the role of temperature difference extrusion and stepped setting in solving the pain points of composite spinning engineering.

[0235] Test Example 5:

[0236] This test case provides comparative test instructions for the three-dimensional crimp characteristics and permanence of fibers. The specific test steps are as follows:

[0237] The finished short fibers prepared in Example 1, Comparative Example 1 and Comparative Example 4 were used as test objects and conditioned for 24 hours under standard temperature and humidity environment (temperature 20°C, relative humidity 65%).

[0238] Five fiber bundles, each containing 20 individual fibers, were randomly selected from each test group and placed on a black velvet board. A precision crimp count tester was used to measure the crimp count at 0.05... Under extremely light tension, the number of crimp peaks per 25 mm fiber length was measured, and the average value was taken as the initial crimp number.

[0239] Apply 0.05 to the extracted individual fiber. Under slight tension, its curl length in this state is measured.

[0240] Subsequently, apply 2.0. The tension causes the fiber to be essentially straightened, and its straightened length is measured. The initial crimp rate is obtained by calculating the percentage of the difference between the straightened length and the crimped length relative to the straightened length.

[0241] The remaining finished fibers from each group were sewn into test samples measuring 20 cm × 20 cm.

[0242] According to the national standard for textile washing tests, the sample was placed in a standard washing machine and washed using a 0.5% industrial standard detergent solution at a water temperature of 40°C for 30 minutes each time. After washing, the sample was dehydrated and laid flat to air dry. This washing cycle was repeated 50 times.

[0243] After completing 50 water washing cycles, the sample was disassembled, and individual fibers were extracted again. Following the methods in steps 2 and 3, the number of curls and the curl rate were measured again.

[0244] The durability of the three-dimensional crimp morphology of the fiber, i.e., the crimp recovery rate, is evaluated by calculating the percentage of crimp rate after 50 washes relative to the initial crimp rate.

[0245] Table 5. Fiber crimp characteristics and durability test data of Example 1 and each comparative example.

[0246] Test object Initial number of curls (per 25mm) Initial curl rate (%) Number of curls after 50 washes (per 25mm) Curl rate (%) after 50 washes Curl recovery rate (%) Example 1 (Batch 1) 14.2 26.5 13.8 24.9 93.96 Example 1 (Batch 2) 15.6 28.1 15.2 26.8 95.37 Example 1 (Batch 3) 13.9 25.8 13.5 24.1 93.41 Comparative Example 1 (Batch 1) 1.2 2.5 0.8 1.1 44.00 Comparative Example 1 (Batch 2) 0.8 1.8 0.4 0.6 33.33 Comparative Example 1 (Batch 3) 1.5 2.9 1.1 1.5 51.72 Comparative Example 4 (Batch 1) 12.8 21.4 5.6 8.2 38.32 Comparative Example 4 (Batch 2) 13.5 23.2 6.2 9.5 40.95 Comparative Example 4 (Batch 3) 11.9 19.8 4.8 6.9 34.85

[0247] Based on the data in Table 5 and the appendix Figure 5 In the process of bicomponent composite spinning, the design of the geometric structure plays a decisive role in establishing the fiber crimp morphology.

[0248] Comparative Example 1 uses concentric flow channel extrusion, with the core layer component wrapped around the geometric center of the skin layer.

[0249] Although there is a thermodynamic difference in shrinkage between the two materials, the symmetrical distribution of cross-sectional mass and shrinkage stress causes the shrinkage stresses in each direction to cancel each other out along the fiber axis, preventing the generation of bending moments. Therefore, the fiber in Comparative Example 1 is macroscopically basically straight, with an initial crimp rate of less than 3%.

[0250] Example 1 uses a 15% eccentricity setting, with the high-shrinkage core layer component deviating from the center.

[0251] During the heat setting process, the shrinkage of molecular chain segments in the amorphous region is transformed into a non-uniform stress distribution along the fiber axis. The high shrinkage side has a greater tendency to shorten longitudinally, forcing the entire fiber to undergo three-dimensional helical bending towards the core layer, with its initial crimp rate stabilizing at around 26%.

[0252] From the perspective of permanent curling, Comparative Example 4 uses homogeneous high-viscosity polyester chips, which are physically curled using a mechanical crimping machine.

[0253] This mechanical curling mainly relies on plastic deformation at room temperature; the crystalline morphology and polymer network inside the fiber are not reconstructed due to curling.

[0254] After 50 washes and mechanical kneadings, the mechanical deformation caused by water molecules and external forces easily leads to stress relaxation and recovery to the original shape. The curl rate drops sharply from 21.4% to about 8.2%, and the curl recovery rate is less than 40%.

[0255] The stereo curl produced in Example 1 is based on the thermodynamics of the heterogeneous shrinkage of polymer inner chain segments, and the two components complete the solidification of the crystalline region during the heat setting stage.

[0256] This macroscopic morphology, formed by differences in the microscopic aggregate structure of polymers, exhibits high thermal stability and morphological retention.

[0257] After 50 washing cycles, its crimp recovery rate remained above 93%, proving that the eccentric bicomponent design can give the fiber excellent permanent structure retention ability and meet the morphological requirements of imitation mohair products in long-term use.

[0258] Test Example 6:

[0259] This test example provides a comprehensive evaluation of the macroscopic sensory and fluffiness indicators of the final imitation mohair product. The specific test steps are as follows:

[0260] The finished short fibers prepared in Examples 1 to 4 and Comparative Example 4 were collected and placed in a standard laboratory with an ambient temperature of 20°C and a relative humidity of 65% for 24 hours to achieve moisture regain equilibrium.

[0261] Conduct fiber specific volume (loft) tests.

[0262] After opening and combing the fibers in each group, 20.0 grams of sample were weighed and evenly filled into a transparent cylindrical measuring container with an inner diameter of 100 mm.

[0263] A 50-gram metal pressure plate, matching the inner diameter of the container, is placed above the container and allowed to fall freely onto the surface of the fiber mass. After 30 seconds of rest, the height of the fiber mass is read, and the volume occupied by a unit mass of fiber under extremely low pressure is calculated, i.e., the initial specific volume.

[0264] Perform a compression elastic recovery rate test. Replace the metal pressure plate with a heavy pressure plate weighing 2000 grams, apply a static pressure load for 5 minutes, record the height of the fiber clusters at this time, and calculate the specific volume after compression.

[0265] Remove the 2000g heavy pressure plate and allow the sample to stand and recover for 30 minutes under no-load conditions.

[0266] Then, the 50-gram metal pressure plate was placed back in, and after standing for 30 seconds, the restored height was read.

[0267] The compressive elastic recovery rate is obtained by calculating the ratio of the recovered height to the initial height.

[0268] An evaluation team of 10 textile testing engineers with more than 5 years of experience was organized to conduct a blind evaluation of the hand feel and crispness. Each group of fibers was processed into nonwoven samples weighing 150 grams per square meter.

[0269] Without knowing the source of the samples, the evaluators subjectively scored the mohair based on its unique skeletal structure and firm, smooth and supple feel by touching and kneading the samples. The maximum score was 100 points, and the highest and lowest scores were removed before the average score was taken as the final score.

[0270] Table 6. Blind evaluation data on the bulk and hand feel of the fiber products in the examples and comparative examples.

[0271] Test object Test number Initial specific volume (cm³ / g) Specific volume after compression (cm³ / g) Specific volume after recovery (cm³ / g) Compression elastic recovery rate (%) Blind rating score Example 1 1 85.6 15.2 78.2 91.4 93.5 Example 1 2 87.2 14.8 80.3 92.1 94.2 Example 1 3 84.9 15.5 77.1 90.8 92.8 Example 2 1 79.4 14.1 70.3 88.5 88.6 Example 2 2 80.1 13.9 71.4 89.2 89.4 Example 3 1 92.5 16.3 87.5 94.6 96.1 Example 3 2 91.8 16.5 86.2 93.9 95.7 Example 4 1 88.4 15.8 81.8 92.5 94.6 Example 4 2 89.1 15.4 83.0 93.1 95.0 Comparative Example 4 1 62.3 11.2 47.0 75.4 71.2 Comparative Example 4 2 64.5 11.5 49.5 76.8 72.5 Comparative Example 4 3 61.8 10.9 45.9 74.2 69.8

[0272] Based on the data in Table 6 and the appendix Figure 6 The examples prepared by eccentric composite spinning of component A and modified component B all exhibit highly optimized spatial structure characteristics in terms of macroscopic physical properties.

[0273] The core sensory characteristics of mohair products lie in the effective support between its fibers and its air content.

[0274] Comparative Example 4 uses homogeneous high-viscosity polyester chips, whose mechanical wrinkling and curling mostly present a serrated zigzag structure in a two-dimensional plane.

[0275] This two-dimensional structure is prone to parallel bonding and stacking in fiber assemblies, resulting in a low space occupancy rate and an initial specific volume of only about 62 to 65 cm³ / g.

[0276] Meanwhile, under heavy compression, the serrated physical creases are unable to provide effective normal support, and the elastic recovery rate after unloading is less than 77%, exhibiting defects such as a flat feel and lack of resilience in blind evaluation. Examples 1 to 4 constructed a three-dimensional helical coil morphology driven by polymer thermodynamic contraction.

[0277] This spiral spatial geometry allows a single fiber to extend in all directions within three-dimensional space, transforming the contact points between fibers from surface contact to point contact, thus forming a large number of stable three-dimensional network gaps.

[0278] Therefore, the initial specific volume of Example 1 was increased to approximately 85-87 cm³ / g or higher.

[0279] When the fiber assembly is subjected to external compressive force, the three-dimensional helical structure can distribute the compressive stress evenly and convert it into its own torsional strain energy, just like a micro spring.

[0280] After unloading, the elastic strain energy stored in the high-viscosity cortex skeleton is rapidly released, resulting in the compression elastic recovery rate of Examples 1, 3 and 4 reaching over 90%, and the compression elastic recovery rate of Example 2 also approaching 90%. All examples are significantly better than Comparative Example 4.

[0281] In particular, Example 3, with the synergistic effect of using high-shrinkage core layer component B3, high intrinsic viscosity skin layer component A, large eccentricity, and high stretching and setting conditions, further enhanced the fiber crimping moment and structural rigidity, with an initial specific volume of about 92 cm³ / g and a blind evaluation score of about 96 points.

[0282] Test data confirms that the embodiments of the present invention not only improve the process stability during composite spinning, but also effectively endow the fiber with a skeletal feel similar to natural mohair and good fluffy and compressive strength, thus achieving the expected product development goals.

[0283] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber, characterized in that, Made from melt-spun composite fibers containing the following components in the indicated mass percentages: Cortical component A: 40%–60%; Core layer component B: 40%–60%; The skin layer component A is high-viscosity polyethylene terephthalate, and the core layer component B is low-viscosity, high-shrinkage isophthalic acid modified copolyester. The short fiber has an eccentric core-shell structure in its cross-section, and the eccentricity of the center of the core layer component B's cross-section from the center of the short fiber's cross-section is 10% to 25% of the fiber's cross-sectional radius. Specifically, the isophthalic acid structural units in the core layer component B reduce the regularity and crystallinity of the molecular chains within the copolyester system. Under the eccentric core-sheath structure, the difference in shrinkage between the core layer component B and the sheath component A is released during the heat setting process, thereby converting it into the transverse bending moment of the fiber. This endows the short fiber with a spontaneous and permanent three-dimensional spiral crimp structure to form a fluffy and pressure-resistant skeleton similar to mohair.

2. The permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to claim 1, characterized in that, The intrinsic viscosity of the skin layer component A is 0.65–0.75 dL / g, and the intrinsic viscosity of the core layer component B is 0.45–0.55 dL / g. Preferably, the intrinsic viscosity difference between the skin layer component A and the core layer component B is 0.20 dL / g.

3. The permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to claim 1, characterized in that, The core layer component B is polymerized from monomers containing purified terephthalic acid, isophthalic acid and ethylene glycol, and the total molar amount of purified terephthalic acid and isophthalic acid to the molar ratio of ethylene glycol is 1:(1.2~1.5). The isophthalic acid accounts for 10% to 20% of the total molar amount of the dicarboxylic acid.

4. A permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to claim 1 or 3, characterized in that, The boiling water shrinkage rate of the core layer component B is 30% to 45%.

5. The permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to claim 1, characterized in that, The cut length of the short fibers is 38–51 mm.

6. A method for preparing a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber, comprising the permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to any one of claims 1-5, characterized in that, Includes the following steps: (1) The dried skin layer component A and core layer component B are respectively fed into two independent extruders for melting, wherein the set temperature of the extruder for skin layer component A is higher than the set temperature of the extruder for core layer component B. (2) The two melts are metered and then fed into the composite spinning assembly. They are extruded through a distribution plate with an eccentric flow channel, cooled and solidified by side blowing, and then wound and collected to obtain the nascent filament bundle. (3) The nascent filament bundle is subjected to two-stage stretching treatment; (4) The drawn fiber bundle is subjected to a step-by-step relaxation heat setting treatment to release the internal stress of the fiber bundle and spontaneously form a three-dimensional wavy curl. Then it is cut and packaged to obtain the short fiber.

7. The method for preparing a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to claim 6, characterized in that, In step (1), the temperature of each zone of the extruder for the skin layer component A is set to 285-295°C, and the temperature of each zone of the extruder for the core layer component B is set to 275-280°C. The extrusion temperature of the skin layer component A is maintained at a temperature difference of 10 to 15°C from the extrusion temperature of the core layer component B.

8. The method for preparing a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to claim 6, characterized in that, In step (3), the two-stage drawing process includes a first-stage drawing in a water bath at 70-85°C and a second-stage drawing in a steam bath at 90-100°C, with the total drawing ratio controlled between 2.5 and 4.0 times.

9. The method for preparing a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to claim 6, characterized in that, In step (4), the stepped relaxation heat setting process specifically includes: Pre-relaxation treatment: The fiber bundle is first introduced into the steaming box under extremely low tension and treated with saturated humid heat steam at 100-115℃ for 3-5 minutes; Dry heat setting treatment: The pre-relaxed yarn bundles are put into a tensionless conveyor belt hot air drying and setting machine and stay in dry hot air at 120-160℃ for 5-10 minutes.

10. The method for preparing a permanently three-dimensional crimped mohair-like bicomponent polyester staple fiber according to claim 6, characterized in that, The core component B is prepared prior to step (1) by the following steps: The proportions of purified terephthalic acid, isophthalic acid, ethylene glycol, and antimony trioxide catalyst are mixed by slurry and then added to an esterification reactor for esterification reaction. The esterification reaction temperature is controlled at 240-260℃ and the reaction pressure is 0.1-0.3 MPa gauge pressure. The amount of antimony trioxide catalyst added is 200-400 ppm of the total polymer mass. When the water distillation reaches 95% of the theoretical value and the temperature at the top of the column drops, the esterification product is transferred to the polycondensation reactor. The system pressure is reduced to 700-900 Pa by vacuuming within 30-50 minutes, and the temperature is raised to 260-270℃ for pre-polycondensation reaction. The vacuum was then further reduced to 70–90 Pa, and the temperature was raised to 275–285 °C for the final polycondensation reaction. When the melt reached the target intrinsic viscosity, it was extruded, cooled, and pelletized to obtain the core layer component B.

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