Ultrafine polyethylene / polyester composite fiber and method for producing the same

Abstract

This invention discloses an ultrafine polyethylene / polyester composite fiber and its preparation method, belonging to the field of composite fiber technology. It solves the problems of poor compatibility between the core and sheath layers, excessive fineness of PE / PET fibers, and difficulties in achieving ultrafine fiber production in existing technologies. The method involves preparing ultrafine polyethylene / polyester composite fibers using a core-sheath composite spinning process. The single filament fineness of the ultrafine polyethylene / polyester composite fiber is 0.6~0.8 dtex. The ultrafine polyethylene / polyester composite fiber has a core-sheath structure, with the sheath material being polyethylene and the core material being a blend of modified polyester and a compatibilizer. The modified polyester molecular chain consists of terephthalic acid segments, ethylene glycol segments, and isophthalic acid segments. The compatibilizer is a graft copolymer of polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate. The preparation method of this invention is simple and easy to implement, with excellent core-sheath compatibility, which is beneficial for achieving ultrafine fiber production. The composite fiber exhibits excellent performance and can meet the demands of the high-end market.

Description

Technical Field

[0001] This invention belongs to the field of composite fiber technology and relates to an ultrafine polyethylene / polyester composite fiber and its preparation method. Background Technology

[0002] Bicomponent spunbond nonwovens are gaining increasing attention due to their high strength, elongation, and soft hand feel. Different combinations of raw materials and formulations can create a variety of bicomponent spunbond nonwoven fabrics, resulting in diverse products with distinct characteristics and properties. Polyethylene / polyester (PE / PET) bicomponent spunbond nonwovens are formed by extruding PE and PET chips separately using independent screw extruders, followed by melt spinning and reinforcement into a web. PE / PET core-sheath composite fibers exhibit high strength, good bulkiness, and high elastic recovery. The nonwoven fabric produced after hot rolling of its web is characterized by a soft hand feel and good elasticity, and is currently widely used in hygiene products such as surgical masks and bandages.

[0003] With economic development, people's quality of life has improved year by year. At the same time, consumer demand is also changing, with increasing demands for multifunctional and high-quality products such as sanitary napkins and diapers, including dryness, breathability, softness, and non-irritation. This places higher demands on the performance and quality of raw materials. PE / PET fibers, with their enhanced functionality and adaptability, are ideal materials for manufacturing high-end sanitary napkins and diapers, aligning with the trend of high-end consumption and possessing excellent development prospects. Currently, 80% of domestic PE / PET fiber products are mid-to-low-end, while high-value-added, high-end products are basically monopolized by foreign manufacturers. The main reason is the relatively high fineness of domestic PE / PET fibers and their susceptibility to core-sheath separation and slippage, affecting subsequent processing and the comfort of the fabric layer in finished sanitary products. Currently, the main domestic products only achieve a single filament fineness of around 2.0 dtex, severely limiting their application.

[0004] When the fineness of a single filament is reduced to a certain level, fabrics woven from these ultrafine fibers exhibit many unique characteristics, such as softness, high flexibility, and high water absorption. Therefore, improving the quality of PE / PET fibers and researching and developing ultrafine PE / PET fibers to meet the demands of the high-end market is of great significance. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems existing in the prior art and to provide an ultrafine polyethylene / polyester composite fiber and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An ultrafine polyethylene / polyester composite fiber, wherein the single filament fineness of the ultrafine polyethylene / polyester composite fiber is 0.6~0.8 dtex;

[0008] The ultrafine polyethylene / polyester composite fiber has a core-sheath structure, with the sheath material being polyethylene (PE) and the core material being a blend of modified polyester and a compatibilizer.

[0009] The molecular chain of the modified polyester is composed of terephthalic acid segments, ethylene glycol segments, and isophthalic acid segments;

[0010] The compatibilizer is a graft copolymer of polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate.

[0011] As a preferred technical solution:

[0012] The ultrafine polyethylene / polyester composite fiber described above has a breaking strength of 3.3~3.7 cN / dtex, a breaking elongation of 50.0±10.0%, a crimp number of 13~16 / 25mm, a crimp degree of 14~18%, and a fiber length of 35~40mm.

[0013] The ultrafine polyethylene / polyester composite fiber described above has a core-sheath weight ratio of 40~50:50~60.

[0014] The ultrafine polyethylene / polyester composite fiber described above has a melt index of 20±2 g / 10 min measured at 190°C and 0.3 MPa, and the modified polyester has an intrinsic viscosity of 0.64~0.66 dL / g.

[0015] The preparation process of the modified polyester in the above-described ultrafine polyethylene / polyester composite fiber is as follows:

[0016] (1) After preparing terephthalic acid, isophthalic acid and ethylene glycol into a slurry, an esterification reaction is carried out. The reaction is carried out under pressure in a nitrogen atmosphere, with a pressure of atmospheric pressure to 0.3 MPa and a reaction temperature of 230 to 250 °C. The esterification reaction ends when the amount of water distilled out in the esterification reaction reaches more than 95% of the theoretical value, and the esterification product is obtained.

[0017] (2) After the esterification reaction in step (1) is completed, under the action of catalyst and stabilizer, the low vacuum stage polycondensation reaction is started under negative pressure. In this stage, the pressure is steadily reduced from atmospheric pressure to below 500 Pa absolute pressure, the temperature is controlled at 260~270℃, and the reaction time is 30~50 minutes. Then, the vacuum is continued to reduce the reaction pressure to less than 70 Pa absolute pressure, and the high vacuum stage polycondensation reaction is carried out. The reaction temperature is controlled at 275~280℃, and the reaction time is 50~90 minutes. After the polycondensation is completed, the material is discharged and granulated to obtain the modified polyester.

[0018] In the ultrafine polyethylene / polyester composite fiber described above, in step (1), the molar ratio of terephthalic acid, isophthalic acid, and ethylene glycol is 1:0.3~0.5:1.7~2.3;

[0019] In step (2), the catalyst is antimony trioxide, antimony glycolate, or antimony acetate, and the stabilizer is triphenyl phosphate, trimethyl phosphate, or trimethyl phosphite; the amount of catalyst added is 0.01% to 0.05% of the total weight of terephthalic acid and isophthalic acid, and the amount of stabilizer added is 0.01% to 0.05% of the total weight of terephthalic acid and isophthalic acid.

[0020] The compatibilizer for the ultrafine polyethylene / polyester composite fiber described above is prepared as follows:

[0021] (1) The initiator 4,4'-azo (4-cyanopentanoic acid), monomer methyl methacrylate and chain transfer agent mercaptoacetic acid were added to the reaction vessel in sequence, and then tetrahydrofuran was added to dissolve them. The reaction was carried out in a nitrogen atmosphere at 60~65℃ for 4~5 hours. After the reaction was completed, the product was purified and dried to obtain carboxyl-containing polymethyl methacrylate (PMMA-COOH).

[0022] (2) After drying poly(ethylene-co-glycidyl methacrylate) (EGMA) and carboxyl-containing polymethyl methacrylate, they are added together with the initiator benzoyl peroxide into a mixer and granulated by mixing to obtain poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate (EGMA-g-PMMA); wherein the temperature of the mixer is 180~190℃, the speed is 50~60rpm, and the mixing time is 8~10min;

[0023] (3) After the polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate are dried, they are added to a mixer and granulated by mixing to obtain the compatibilizer; wherein the temperature of the mixer is 180~190℃, the speed is 50~60rpm, and the mixing time is 10~15min.

[0024] In the ultrafine polyethylene / polyester composite fiber described above, the molar ratio of methyl methacrylate, mercaptoacetic acid and 4,4'-azo (4-cyanopentanoic acid) in step (1) is 100:5~6:1~1.5, and the mass ratio of methyl methacrylate to tetrahydrofuran is 1:1~1.5.

[0025] In step (2), the mass ratio of poly(ethylene-co-glycidyl methacrylate) to carboxyl-containing polymethyl methacrylate is 100:5~8, and the amount of benzoyl peroxide used is 0.2%~0.3% of the total mass of poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing polymethyl methacrylate.

[0026] In step (3), the mass ratio of polyethylene to poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate is 100:3~5.

[0027] The present invention also provides a method for preparing ultrafine polyethylene / polyester composite fiber as described in any of the preceding claims, wherein the ultrafine polyethylene / polyester composite fiber is prepared by a core-sheath composite spinning process, specifically including the following steps:

[0028] (1) The dried polyethylene is melted by the screw, and the metered polyethylene melt enters the spinning box A;

[0029] (2) The dried modified polyester and compatibilizer are mixed at a mass ratio of 100:2.5~3.5 and then successively melted by screw and vented. The metered mixed melt enters the spinning box B.

[0030] (3) The melt in spinning box A and spinning box B is ejected through the composite spinneret to form a core-sheath structure filament, which is then successively spun, cooled, bundled, stretched, crimped, cut and dried to obtain ultrafine polyethylene / polyester composite fiber.

[0031] As a preferred technical solution:

[0032] In the preparation method of the ultrafine polyethylene / polyester composite fiber as described above, the screw melting temperature in step (1) is 220~250℃ and the polyethylene melt conveying temperature is 260~265℃.

[0033] In step (2), the screw melting temperature is 260~270℃, and the mixed melt conveying temperature is 275~280℃;

[0034] In step (3), the spinning temperature is 275~280℃ and the spinning speed is 1000~1200m / min; the cooling is done by ring blowing, the ring blowing temperature is 14~18℃ and the ring blowing speed is 1.0~1.2m / s; the first stretching temperature is 70~75℃, the second stretching temperature is 100℃, and the total stretching ratio is 3.4~3.6 times; the drying temperature is 100~110℃.

[0035] Invention Mechanism:

[0036] Due to their small diameter, microfibers have very low bending stiffness and an exceptionally soft feel. Their large specific surface area significantly improves the coverage, bulkiness, and warmth of microfiber fabrics, while also providing waterproof and breathable properties. The main factors limiting the microfiber production of PE / PET fibers are: firstly, the poor compatibility between the PE sheath and the PET core in PE / PET core-sheath fibers causes them to easily detach during stretching, resulting in fuzz and increasing the difficulty of achieving microfiber production; secondly, the polyester core crystallizes during stretching, and the low melting point of polyethylene leads to a lower stretching temperature for PE / PET fibers, resulting in a lower stretch ratio.

[0037] This invention incorporates a PE graft copolymer as a compatibilizer into the PET core layer of PE / PET fibers. This compatibilizer is formed by copolymerizing and grafting polyethylene with ethylene-glycidyl methacrylate (GMA)-methyl methacrylate (MMA). The glycidyl methacrylate molecule in the compatibilizer contains two hydroxyl groups, which can form ether bonds with the terminal hydroxyl groups of PET and react with the terminal carboxyl groups to form an ester.

[0038] Because of the viscosity difference between PET and the compatibilizer, the low-viscosity component of the compatibilizer migrates from the central low-shear rate region to the outer high-shear rate region and accumulates on the outside of the core polyester fiber. On the one hand, the compatibilizer enhances the compatibility with polar polyester by introducing polar groups, thereby increasing the interaction force between the compatibilizer and the polyester. On the other hand, because the compatibilizer aggregates outside the core polyester fiber and is preferentially distributed at the interface between the two phases, the ethylene-co-glycidyl methacrylate in the compatibilizer copolymer reduces the interfacial tension between PET and PE, which can appropriately increase the interfacial adhesion between PET and PE, reduce the interfacial energy between the two phases, and increase the compatibility between PET and PE. At the same time, due to the increased specific surface area of ​​the sheath fiber and the core fiber in the microfiber, higher requirements are placed on the interfacial adhesion between the sheath fiber and the core fiber. Methyl methacrylate (MMA) in the compatibilizer can not only increase the compatibility of PET, but also improve the mechanical properties of the material. The ester bond of PMMA is easy to form intermolecular hydrogen bond with PET at the phase interface, which makes the molecular chains of PE and PET easy to entangle, further enhancing the interaction between the two components, which is conducive to increasing the elongation of PE / PET fiber and provides conditions for the preparation of microfiber. The polyolefin portion of the compatibilizer is similarly compatible with the polyethylene in the skin layer. The compatibilizer increases the bonding tightness between the core layer PET and the skin layer PE, connecting the PET and PE macromolecular chains and improving the compatibility of the two materials. This improves the interaction force between the skin layer and the core layer, strengthens the bonding force between the skin and the core layer, and improves the incompatibility of components such as the slippage of the skin and core fibers. It solves the problems of skin-core layer separation and poor strength caused by poor compatibility.

[0039] In the nascent stage of PE / PET fibers, the polyester is amorphous, and its stretching process takes place above the glass transition temperature of the polyester. The water bath temperature for the primary stretching of PE / PET fibers is 70-75℃. After primary stretching, the fibers have a certain degree of orientation, and the crystallinity of the polyester has also increased. Therefore, a higher steam stretching temperature of 100℃ must be used for secondary steam stretching. However, the stretching temperature of PE / PET fibers is only suitable for polyethylene stretching and is too low for polyester. The conventional stretching temperature for polyester is 80-85℃ for primary stretching and 125-130℃ for secondary stretching. Due to the low melting point of polyethylene, if the temperature is too high, it will increase the sliding of macromolecular chains, thereby reducing fiber strength and even causing the fiber sheath to soften, stick, or melt. How to increase the stretching ratio under the existing stretching temperature of PE / PET fibers is the key to solving the problem.

[0040] This invention introduces isophthalic acid into polyester. The introduction of isophthalic acid segments disrupts the molecular structure of polyester, transforming it from a highly ordered, regular structure into a disordered, chaotic one. The addition of isophthalic acid segments alters the proportions and sizes of different submacroscopic crystalline morphologies of the polyester, making crystallization difficult and tending towards an amorphous state. This amorphous modified polyester achieves higher elongation at lower temperatures, thereby increasing the overall elongation of PE / PET composite fibers and facilitating fiber microfiber refinement. Simultaneously, by controlling the isophthalic acid content, the melting point of the modified polyester is maintained at around 200℃, ensuring dimensional stability during fabric processing and providing structural support.

[0041] Therefore, the combined effect of compatibilizer polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate graft copolymer with modified polyester overcomes the main influencing factors restricting the ultrafineness of PE / PET fibers, making it possible to prepare ultrafine polyethylene / polyester composite fibers.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] (1) The present invention provides an ultrafine polyethylene / polyester composite fiber, wherein the core layer is mixed with a specific compatibilizer. The compatibilizer contains two hydroxyl groups in the glycidyl methacrylate molecule. These two hydroxyl groups can form ether bonds with the terminal hydroxyl groups of PET and react with the terminal carboxyl groups to form esters. The compatibilizer grafted with PMMA can increase the compatibility of PET and improve the mechanical properties of the material. The compatibilizer increases the tightness of the core layer PET and the skin layer PE, so that the macromolecular chains of PET and PE are connected, thereby improving the compatibility of the two materials and thus improving the interaction force between the skin layer and the core layer, solving the problems of poor compatibility causing the skin and core layers to separate and facilitating the ultrafineness of the fiber.

[0044] (2) In the present invention, an ultrafine polyethylene / polyester composite fiber is made by adding isophthalic acid segments to polyester to destroy the molecular structure, making it difficult for polyester to crystallize and tending to exist in an amorphous manner; the amorphous modified polyester can obtain a higher elongation at a lower temperature, thereby increasing the total elongation of PE / PET composite fiber, which is beneficial to the ultrafineness of the fiber. Detailed Implementation

[0045] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0046] In the embodiments of the present invention, the melt index of polyethylene measured at 190°C and 0.3MPa is 20g / 10min, and the intrinsic viscosity of polyester is 0.67dL / g.

[0047] Example 1

[0048] A method for preparing ultrafine polyethylene / polyester composite fibers, the specific steps of which are as follows:

[0049] (1) Preparation of modified polyester;

[0050] S1. Terephthalic acid, isophthalic acid and ethylene glycol in a molar ratio of 1:0.3:1.7 were mixed to form a slurry, and then an esterification reaction was carried out. The reaction was carried out under pressure in a nitrogen atmosphere at atmospheric pressure and a reaction temperature of 230°C. The esterification reaction ended when the amount of water distilled out in the esterification reaction reached 95% of the theoretical value, and the esterification product was obtained.

[0051] After the esterification reaction in step S1 is completed, a low-vacuum polycondensation reaction begins under negative pressure conditions, with the catalyst antimony trioxide (added at 0.01% of the total weight of terephthalic acid and isophthalic acid) and the stabilizer triphenyl phosphate (added at 0.01% of the total weight of terephthalic acid and isophthalic acid). In this stage, the pressure is steadily increased from atmospheric pressure to an absolute pressure of 500 Pa, the temperature is controlled at 260 °C, and the reaction time is 50 minutes. Then, the vacuum is continued to reduce the reaction pressure to an absolute pressure of 68 Pa, and a high-vacuum polycondensation reaction is carried out, with the reaction temperature controlled at 275 °C and the reaction time being 90 minutes. After the polycondensation is completed, the material is discharged and granulated to obtain the modified polyester.

[0052] (2) Preparation of compatibilizer;

[0053] S1 4,4'-azo (4-cyanopentanoic acid), methyl methacrylate and mercaptoacetic acid were added sequentially to a reaction vessel, and then tetrahydrofuran was added to dissolve them. The reaction was carried out at 60°C under a nitrogen atmosphere for 5 hours. After the reaction was completed, the product was purified and dried to obtain carboxyl-containing polymethyl methacrylate. The molar ratio of methyl methacrylate, mercaptoacetic acid and 4,4'-azo (4-cyanopentanoic acid) was 100:5:1, and the mass ratio of methyl methacrylate to tetrahydrofuran was 1:1.

[0054] S2: Poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing polymethyl methacrylate (PMMA) in a mass ratio of 100:5 were dried separately and then added together with benzoyl peroxide (0.2% of the total mass of poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing PMMA) into an internal mixer. After mixing and granulation, poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained. The temperature of the internal mixer was 180℃, the speed was 50 rpm, and the mixing time was 10 min.

[0055] S3 Polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate in a mass ratio of 100:3 were dried separately and then added to an internal mixer. After mixing and granulation, a graft copolymer of polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained, which is the compatibilizer. The temperature of the internal mixer was 180℃, the speed was 50 rpm, and the mixing time was 10 min.

[0056] (3) Spinning;

[0057] S1 The dried polyethylene is melted by a screw, and the metered polyethylene melt enters the spinning box A; wherein, the screw melting temperature is 220℃, and the polyethylene melt conveying temperature is 260℃;

[0058] S2 The dried modified polyester and compatibilizer are mixed at a mass ratio of 100:2.5 and then sequentially melted by a screw and vented. The metered mixed melt enters the spinning box B. The screw melting temperature is 260℃ and the mixed melt conveying temperature is 275℃.

[0059] The melt in spinning boxes A and B (S3) is extruded through a composite spinneret at a weight ratio of 40:60 to form a core-sheath structure filament. This filament then undergoes a series of processes including spinning, cooling, bundling, stretching, crimping, cutting, and drying to obtain ultrafine polyethylene / polyester composite fibers. The spinning temperature is 275℃, and the spinning speed is 1000 m / min. Cooling is achieved using an annular airflow system with a temperature of 14℃ and a velocity of 1.0 m / s. The first stretching temperature is 70℃, the second stretching temperature is 100℃, and the total stretching ratio is 3.4 times. The drying temperature is 100℃.

[0060] The final ultrafine polyethylene / polyester composite fiber has a single filament fineness of 0.6 dtex, a breaking strength of 3.30 cN / dtex, a breaking elongation of 60%, a crimp number of 13 / 25 mm, a crimp degree of 14%, and a fiber length of 35 mm.

[0061] Example 2

[0062] A method for preparing ultrafine polyethylene / polyester composite fibers, the specific steps of which are as follows:

[0063] (1) Preparation of modified polyester;

[0064] S1. Terephthalic acid, isophthalic acid and ethylene glycol in a molar ratio of 1:0.3:1.9 are mixed to form a slurry, which is then subjected to an esterification reaction. The reaction is carried out under pressure in a nitrogen atmosphere at atmospheric pressure and a reaction temperature of 230°C. The esterification reaction ends when the amount of water distilled out in the esterification reaction reaches 96% of the theoretical value, and the esterified product is obtained.

[0065] After the esterification reaction in step S1 is completed, a low-vacuum polycondensation reaction begins under negative pressure conditions, with the catalyst antimony trioxide (added at 0.02% of the total weight of terephthalic acid and isophthalic acid) and the stabilizer triphenyl phosphate (added at 0.02% of the total weight of terephthalic acid and isophthalic acid). In this stage, the pressure is steadily increased from atmospheric pressure to an absolute pressure of 480 Pa, the temperature is controlled at 262 °C, and the reaction time is 35 minutes. Then, the vacuum is continued to reduce the reaction pressure to an absolute pressure of 68 Pa, and a high-vacuum polycondensation reaction is carried out, with the reaction temperature controlled at 277 °C and the reaction time being 85 minutes. After the polycondensation is completed, the material is discharged and granulated to obtain the modified polyester.

[0066] (2) Preparation of compatibilizer;

[0067] S1 4,4'-azo (4-cyanopentanoic acid), methyl methacrylate and mercaptoacetic acid were added sequentially to a reaction vessel, followed by the addition of tetrahydrofuran for dissolution. The reaction was carried out at 62°C under a nitrogen atmosphere for 5 hours. After the reaction was completed, the product was purified and dried to obtain carboxyl-containing polymethyl methacrylate. The molar ratio of methyl methacrylate, mercaptoacetic acid and 4,4'-azo (4-cyanopentanoic acid) was 100:5:1.5, and the mass ratio of methyl methacrylate to tetrahydrofuran was 1:1.2.

[0068] S2: Poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing polymethyl methacrylate (PMMA) in a mass ratio of 100:6 were dried separately and then added together with benzoyl peroxide (0.25% of the total mass of poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing PMMA) into an internal mixer. After mixing and granulation, poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained. The temperature of the internal mixer was 180℃, the speed was 55 rpm, and the mixing time was 10 min.

[0069] S3 Polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate in a mass ratio of 100:3 were dried separately and then added to an internal mixer. After mixing and granulation, a graft copolymer of polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained, which is the compatibilizer. The temperature of the internal mixer was 185℃, the speed was 55 rpm, and the mixing time was 12 min.

[0070] (3) Spinning;

[0071] S1 The dried polyethylene is melted by a screw, and the metered polyethylene melt enters the spinning box A; wherein, the screw melting temperature is 225℃, and the polyethylene melt conveying temperature is 261℃;

[0072] S2 The dried modified polyester and compatibilizer are mixed at a mass ratio of 100:3 and then sequentially melted by a screw and vented. The metered mixed melt enters the spinning box B. The screw melting temperature is 262℃ and the mixed melt conveying temperature is 277℃.

[0073] The melt in spinning boxes A and B (S3) is extruded through a composite spinneret at a weight ratio of 50:50 to form a core-sheath structure filament. This filament then undergoes a series of processes including spinning, cooling, bundling, stretching, crimping, cutting, and drying to obtain ultrafine polyethylene / polyester composite fibers. The spinning temperature is 277℃, and the spinning speed is 1150 m / min. Cooling is achieved using an annular airflow system with a temperature of 15℃ and a velocity of 1.1 m / s. The first stretching temperature is 70℃, the second stretching temperature is 100℃, and the total stretching ratio is 3.4 times. The drying temperature is 100℃.

[0074] The final ultrafine polyethylene / polyester composite fiber has a single filament fineness of 0.75 dtex, a breaking strength of 3.46 cN / dtex, a breaking elongation of 55%, a crimp number of 16 / 25 mm, a crimp degree of 18%, and a fiber length of 38 mm.

[0075] Example 3

[0076] A method for preparing ultrafine polyethylene / polyester composite fibers, the specific steps of which are as follows:

[0077] (1) Preparation of modified polyester;

[0078] S1. Terephthalic acid, isophthalic acid and ethylene glycol in a molar ratio of 1:0.4:2.3 were mixed to form a slurry, which was then subjected to an esterification reaction. The reaction was carried out under pressure in a nitrogen atmosphere at a pressure of 0.15 MPa and a reaction temperature of 235 °C. The esterification reaction ended when the amount of water distilled out during the esterification reaction reached 98.5% of the theoretical value, and the esterified product was obtained.

[0079] After the esterification reaction in step S1 is completed, a low-vacuum polycondensation reaction begins under negative pressure conditions, with the catalyst antimony glycolate (added at 0.02% of the total weight of terephthalic acid and isophthalic acid) and the stabilizer trimethyl phosphate (added at 0.02% of the total weight of terephthalic acid and isophthalic acid). In this stage, the pressure is steadily increased from atmospheric pressure to an absolute pressure of 490 Pa, the temperature is controlled at 265 °C, and the reaction time is 40 minutes. Then, the vacuum is continued to reduce the reaction pressure to an absolute pressure of 65 Pa, and a high-vacuum polycondensation reaction is carried out, with the reaction temperature controlled at 278 °C and the reaction time being 70 minutes. After the polycondensation is completed, the material is discharged and granulated to obtain the modified polyester.

[0080] (2) Preparation of compatibilizer;

[0081] S1 4,4'-azo (4-cyanopentanoic acid), methyl methacrylate and mercaptoacetic acid were sequentially added to a reaction vessel, followed by the addition of tetrahydrofuran for dissolution. The reaction was carried out at 65°C under a nitrogen atmosphere for 4.5 hours. After the reaction was completed, the product was purified and dried to obtain carboxyl-containing polymethyl methacrylate. The molar ratio of methyl methacrylate, mercaptoacetic acid and 4,4'-azo (4-cyanopentanoic acid) was 100:4.5:1, and the mass ratio of methyl methacrylate to tetrahydrofuran was 1:1.2.

[0082] Poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing polymethyl methacrylate (PMMA) with a mass ratio of 100:6.5 were dried separately and then added together with benzoyl peroxide (0.3% of the total mass of poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing PMMA) into an internal mixer. After mixing and granulation, poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained. The temperature of the internal mixer was 185℃, the speed was 55 rpm, and the mixing time was 9 min.

[0083] S3: Polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate (PMMA) in a mass ratio of 100:3.5 are dried separately and then added to an internal mixer. After mixing and granulation, a graft copolymer of polyethylene and PMMA is obtained, which is the compatibilizer. The temperature of the internal mixer is 187℃, the speed is 55 rpm, and the mixing time is 12 min.

[0084] (3) Spinning;

[0085] S1 The dried polyethylene is melted by a screw, and the metered polyethylene melt enters the spinning box A; wherein, the screw melting temperature is 230℃, and the polyethylene melt conveying temperature is 265℃;

[0086] S2 The dried modified polyester and compatibilizer are mixed at a mass ratio of 100:3.5 and then sequentially melted by a screw and vented. The metered mixed melt enters the spinning box B. The screw melting temperature is 265℃ and the mixed melt conveying temperature is 276℃.

[0087] The melt in spinning boxes A and B (S3) is extruded through a composite spinneret at a weight ratio of 50:50 to form a core-sheath structure filament. This filament then undergoes a series of processes including spinning, cooling, bundling, stretching, crimping, cutting, and drying to obtain ultrafine polyethylene / polyester composite fibers. The spinning temperature is 278℃, and the spinning speed is 1200 m / min. Cooling is achieved using a ring-blown air system with a temperature of 15℃ and a velocity of 1.1 m / s. The first stretching temperature is 72℃, the second stretching temperature is 100℃, and the total stretching ratio is 3.45. The drying temperature is 105℃.

[0088] The final ultrafine polyethylene / polyester composite fiber has a single filament fineness of 0.8 dtex, a breaking strength of 3.55 cN / dtex, a breaking elongation of 50%, a crimp number of 14 / 25 mm, a crimp degree of 15%, and a fiber length of 38 mm.

[0089] Example 4

[0090] A method for preparing ultrafine polyethylene / polyester composite fibers, the specific steps of which are as follows:

[0091] (1) Preparation of modified polyester:

[0092] S1. Terephthalic acid, isophthalic acid and ethylene glycol in a molar ratio of 1:0.5:2.3 were mixed to form a slurry, which was then subjected to an esterification reaction. The reaction was carried out under pressure in a nitrogen atmosphere at a pressure of 0.2 MPa and a reaction temperature of 240°C. The esterification reaction ended when the amount of water distilled out in the esterification reaction reached 98% of the theoretical value, and the esterified product was obtained.

[0093] After the esterification reaction in step S1 is completed, a low-vacuum polycondensation reaction begins under negative pressure conditions, with the catalyst antimony glycolate (added at 0.05% of the total weight of terephthalic acid and isophthalic acid) and the stabilizer trimethyl phosphite (added at 0.05% of the total weight of terephthalic acid and isophthalic acid). In this stage, the pressure is steadily reduced from atmospheric pressure to an absolute pressure of 485 Pa, the temperature is controlled at 270 °C, and the reaction time is 40 minutes. Then, the vacuum is continued to reduce the reaction pressure to an absolute pressure of 63 Pa, and a high-vacuum polycondensation reaction is carried out, with the reaction temperature controlled at 280 °C and the reaction time being 60 minutes. After the polycondensation is completed, the material is discharged and granulated to obtain the modified polyester.

[0094] (2) Preparation of compatibilizer;

[0095] S1 4,4'-azo (4-cyanopentanoic acid), methyl methacrylate and mercaptoacetic acid were sequentially added to a reaction vessel, and then tetrahydrofuran was added to dissolve them. The reaction was carried out at 60°C under a nitrogen atmosphere for 4 hours. After the reaction was completed, the product was purified and dried to obtain carboxyl-containing polymethyl methacrylate. The molar ratio of methyl methacrylate, mercaptoacetic acid and 4,4'-azo (4-cyanopentanoic acid) was 100:6:1.2, and the mass ratio of methyl methacrylate to tetrahydrofuran was 1:1.5.

[0096] S2: Poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing polymethyl methacrylate (PMMA) in a mass ratio of 100:7 were dried separately and then added together with benzoyl peroxide (0.3% of the total mass of poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing PMMA) into an internal mixer. After mixing and granulation, poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained. The temperature of the internal mixer was 190℃, the speed was 55 rpm, and the mixing time was 8 min.

[0097] S3 Polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate in a mass ratio of 100:5 were dried separately and then added to an internal mixer. After mixing and granulation, a graft copolymer of polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained, which is the compatibilizer. The temperature of the internal mixer was 190℃, the speed was 60 rpm, and the mixing time was 15 min.

[0098] (3) Spinning;

[0099] S1 The dried polyethylene is melted by a screw, and the metered polyethylene melt enters the spinning box A; wherein, the screw melting temperature is 240℃, and the polyethylene melt conveying temperature is 264℃;

[0100] S2 The dried modified polyester and compatibilizer are mixed at a mass ratio of 100:2.5 and then sequentially melted by a screw and vented. The metered mixed melt enters the spinning box B. The screw melting temperature is 270℃ and the mixed melt conveying temperature is 280℃.

[0101] The melt in spinning boxes A and B (S3) is extruded through a composite spinneret at a weight ratio of 50:50 to form a core-sheath structure filament. This filament then undergoes a series of processes including spinning, cooling, bundling, stretching, crimping, cutting, and drying to obtain ultrafine polyethylene / polyester composite fibers. The spinning temperature is 280℃, and the spinning speed is 1200 m / min. Cooling is achieved using a ring-blown air system with a temperature of 18℃ and a speed of 1.2 m / s. The first stretching temperature is 74℃, the second stretching temperature is 100℃, and the total stretching ratio is 3.5 times. The drying temperature is 110℃.

[0102] The final ultrafine polyethylene / polyester composite fiber has a single filament fineness of 0.7 dtex, a breaking strength of 3.63 cN / dtex, a breaking elongation of 45%, a crimp number of 15 / 25 mm, a crimp degree of 16%, and a fiber length of 40 mm.

[0103] Example 5

[0104] A method for preparing ultrafine polyethylene / polyester composite fibers, the specific steps of which are as follows:

[0105] (1) Preparation of modified polyester;

[0106] S1. Terephthalic acid, isophthalic acid and ethylene glycol in a molar ratio of 1:0.3:2.1 were mixed to form a slurry, which was then subjected to an esterification reaction. The reaction was carried out under pressure in a nitrogen atmosphere at a pressure of 0.3 MPa and a reaction temperature of 250°C. The esterification reaction ended when the amount of water distilled out in the esterification reaction reached 99% of the theoretical value, and the esterified product was obtained.

[0107] After the esterification reaction in step S1 is completed, a low-vacuum polycondensation reaction begins under negative pressure conditions with the catalyst antimony acetate (added at 0.05% of the total weight of terephthalic acid and isophthalic acid) and the stabilizer trimethyl phosphite (added at 0.05% of the total weight of terephthalic acid and isophthalic acid). In this stage, the pressure is steadily reduced from atmospheric pressure to an absolute pressure of 480 Pa, the temperature is controlled at 270 °C, and the reaction time is 30 minutes. Then, the vacuum is continued to reduce the reaction pressure to an absolute pressure of 65 Pa, and a high-vacuum polycondensation reaction is carried out. The reaction temperature is controlled at 280 °C, and the reaction time is 50 minutes. After the polycondensation is completed, the material is discharged and granulated to obtain the modified polyester.

[0108] (2) Preparation of compatibilizer;

[0109] S1 4,4'-azo (4-cyanopentanoic acid), methyl methacrylate and mercaptoacetic acid were added sequentially to a reaction vessel, followed by the addition of tetrahydrofuran for dissolution. The reaction was carried out at 62°C under a nitrogen atmosphere for 4.2 hours. After the reaction was completed, the product was purified and dried to obtain carboxyl-containing polymethyl methacrylate. The molar ratio of methyl methacrylate, mercaptoacetic acid and 4,4'-azo (4-cyanopentanoic acid) was 100:5:1.5, and the mass ratio of methyl methacrylate to tetrahydrofuran was 1:1.5.

[0110] S2: Poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing polymethyl methacrylate (PMMA) with a mass ratio of 100:8 were dried separately and then added together with benzoyl peroxide (0.3% of the total mass of poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing PMMA) into an internal mixer. After mixing and granulation, poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained. The temperature of the internal mixer was 190℃, the speed was 60 rpm, and the mixing time was 8 min.

[0111] S3 Polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate in a mass ratio of 100:5 were dried separately and then added to an internal mixer. After mixing and granulation, a graft copolymer of polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate was obtained, which is the compatibilizer. The temperature of the internal mixer was 190℃, the speed was 60 rpm, and the mixing time was 15 min.

[0112] (3) Spinning;

[0113] S1 The dried polyethylene is melted by a screw, and the metered polyethylene melt enters the spinning box A; wherein, the screw melting temperature is 250℃, and the polyethylene melt conveying temperature is 265℃;

[0114] S2 The dried modified polyester and compatibilizer are mixed at a mass ratio of 100:2.8 and then sequentially melted by a screw and vented. The metered mixed melt enters the spinning box B. The screw melting temperature is 270℃ and the mixed melt conveying temperature is 280℃.

[0115] The melt in spinning boxes A and B (S3) is extruded through a composite spinneret at a weight ratio of 60:40 to form a core-sheath structure filament. This filament then undergoes a series of processes including spinning, cooling, bundling, stretching, crimping, cutting, and drying to obtain ultrafine polyethylene / polyester composite fibers. The spinning temperature is 280℃, and the spinning speed is 1200 m / min. Cooling is achieved using a ring-blown air system with a temperature of 18℃ and a velocity of 1.2 m / s. The first stretching temperature is 75℃, the second stretching temperature is 100℃, and the total stretch ratio is 3.6 times. The drying temperature is 110℃.

[0116] The final ultrafine polyethylene / polyester composite fiber has a single filament fineness of 0.65 dtex, a breaking strength of 3.70 cN / dtex, a breaking elongation of 40%, a crimp number of 16 / 25 mm, a crimp degree of 18%, and a fiber length of 38 mm.

Claims

1. A type of ultrafine polyethylene / polyester composite fiber, characterized in that: The single filament fineness of the ultrafine polyethylene / polyester composite fiber is 0.6~0.8 dtex; The ultrafine polyethylene / polyester composite fiber has a core-sheath structure, with the sheath material being polyethylene and the core material being a blend of modified polyester and a compatibilizer. The molecular chain of the modified polyester is composed of terephthalic acid segments, ethylene glycol segments, and isophthalic acid segments; The compatibilizer is a graft copolymer of polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate. The weight ratio of the core to the skin in the core-skin structure is 40~50:50~60; The preparation process of the modified polyester is as follows: (1) After preparing terephthalic acid, isophthalic acid and ethylene glycol into a slurry, an esterification reaction is carried out. The reaction is carried out under pressure in a nitrogen atmosphere, with a pressure of atmospheric pressure to 0.3 MPa and a reaction temperature of 230 to 250 °C. The esterification reaction ends when the amount of water distilled out in the esterification reaction reaches more than 95% of the theoretical value, and the esterification product is obtained. (2) After the esterification reaction in step (1) is completed, under the action of catalyst and stabilizer, the low vacuum stage polycondensation reaction begins under negative pressure. In this stage, the pressure is reduced from atmospheric pressure to below 500 Pa absolute pressure, the temperature is controlled at 260~270℃, and the reaction time is 30~50 minutes. Then, the vacuum is continued to reduce the reaction pressure to less than 70 Pa absolute pressure, and the high vacuum stage polycondensation reaction is carried out. The reaction temperature is controlled at 275~280℃, and the reaction time is 50~90 minutes. After the polycondensation is completed, the material is discharged and granulated to obtain the modified polyester. In step (1), the molar ratio of terephthalic acid, isophthalic acid, and ethylene glycol is 1:0.3~0.5:1.7~2.3; In step (2), the catalyst is antimony trioxide, antimony glycolate, or antimony acetate, and the stabilizer is triphenyl phosphate, trimethyl phosphate, or trimethyl phosphite; the amount of catalyst added is 0.01% to 0.05% of the total weight of terephthalic acid and isophthalic acid, and the amount of stabilizer added is 0.01% to 0.05% of the total weight of terephthalic acid and isophthalic acid.

2. The ultrafine polyethylene / polyester composite fiber according to claim 1, characterized in that, The ultrafine polyethylene / polyester composite fiber has a breaking strength of 3.3~3.7 cN / dtex, a breaking elongation of 50.0±10.0%, a crimp number of 13~16 / 25mm, and a crimp degree of 14~18%.

3. The ultrafine polyethylene / polyester composite fiber according to claim 1, characterized in that, The polyethylene has a melt index of 20±2 g / 10 min measured at 190°C and 0.3 MPa, and the modified polyester has an intrinsic viscosity of 0.64~0.66 dL / g.

4. The ultrafine polyethylene / polyester composite fiber according to claim 1, characterized in that, The preparation process of the compatibilizer is as follows: (1) 4,4'-azo (4-cyanopentanoic acid), methyl methacrylate and mercaptoacetic acid were added to the reaction vessel in sequence, and then tetrahydrofuran was added to dissolve them. The reaction was carried out in a nitrogen atmosphere at 60~65℃ for 4~5 hours. After the reaction was completed, the product was purified and dried to obtain carboxyl-containing polymethyl methacrylate. (2) After drying poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing polymethyl methacrylate, they are added together with benzoyl peroxide into a mixer and granulated by mixing to obtain poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate; wherein the temperature of the mixer is 180~190℃, the speed is 50~60rpm, and the mixing time is 8~10min; (3) After the polyethylene and poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate are dried, they are added to a mixer and granulated by mixing to obtain the compatibilizer; wherein the temperature of the mixer is 180~190℃, the speed is 50~60rpm, and the mixing time is 10~15min.

5. The ultrafine polyethylene / polyester composite fiber according to claim 4, characterized in that, In step (1), the molar ratio of methyl methacrylate, mercaptoacetic acid and 4,4'-azo (4-cyanopentanoic acid) is 100:5~6:1~1.5, and the mass ratio of methyl methacrylate to tetrahydrofuran is 1:1~1.

5. In step (2), the mass ratio of poly(ethylene-co-glycidyl methacrylate) to carboxyl-containing polymethyl methacrylate is 100:5~8, and the amount of benzoyl peroxide used is 0.2%~0.3% of the total mass of poly(ethylene-co-glycidyl methacrylate) and carboxyl-containing polymethyl methacrylate. In step (3), the mass ratio of polyethylene to poly(ethylene-co-glycidyl methacrylate)-g-polymethyl methacrylate is 100:3~5.

6. A method for preparing ultrafine polyethylene / polyester composite fiber as described in any one of claims 1 to 5, characterized in that: The ultrafine polyethylene / polyester composite fiber is prepared by a core-sheath composite spinning process, specifically including the following steps: (1) The dried polyethylene is melted by the screw, and the metered polyethylene melt enters the spinning box A; (2) The dried modified polyester and compatibilizer are mixed at a mass ratio of 100:2.5~3.5 and then successively melted by screw and vented. The metered mixed melt enters the spinning box B. (3) The melt in spinning box A and spinning box B is ejected through the composite spinneret to form a core-sheath structure filament, which is then successively spun, cooled, bundled, stretched, crimped, cut and dried to obtain ultrafine polyethylene / polyester composite fiber.

7. The method for preparing ultrafine polyethylene / polyester composite fiber according to claim 6, characterized in that, In step (1), the screw melting temperature is 220~250℃, and the polyethylene melt conveying temperature is 260~265℃; In step (2), the screw melting temperature is 260~270℃, and the mixed melt conveying temperature is 275~280℃; In step (3), the spinning temperature is 275~280℃ and the spinning speed is 1000~1200m / min; the cooling is done by ring blowing, the ring blowing temperature is 14~18℃ and the ring blowing speed is 1.0~1.2m / s; the first stretching temperature is 70~75℃, the second stretching temperature is 100℃, and the total stretching ratio is 3.4~3.6 times; the drying temperature is 100~110℃.