Lightweight polyamide fiber and preparation method thereof

Abstract

The invention relates to the technical field of polyamide, in particular to a lightweight polyamide fiber and a preparation method thereof.According to the method, a skin-core structure mode is adopted, polyamide and polypropylene composite spinning is achieved, the lightweight polyamide fiber is produced, and the fiber has the wear resistance of polyamide and meanwhile has the advantages of being lightweight, high in strength, small in specific gravity and the like of polypropylene; the problems of poor moisture absorption performance, uneven dyeing and the like are solved. According to the method, the density of the polyamide fiber is reduced by 15-20%, the weight is remarkably reduced, the tensile strength and the wear resistance of the polyamide fiber can be effectively improved, and the requirements of the high-end application field are met. Through the method provided by the invention, the preparation process of the lightweight polyamide fiber is more efficient and environment-friendly, the performance of the fiber is remarkably improved, and the method has a wide market application prospect. The lightweight polyamide fiber has the advantages that the density of the fiber is reduced, and meanwhile, the ultra-fast moisture absorption and quick drying performance is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of polyamides, and specifically relates to a lightweight polyamide fiber and a preparation method thereof. Background Art

[0002] Polyamide fiber (PA) is one of the representative products of synthetic fibers, with characteristics such as high strength, wear resistance, chemical corrosion resistance, and easy processing. It is widely used in fields such as clothing, industrial materials (such as tire cord, ropes), automotive parts, aerospace, and sports equipment. However, with the increasing requirements for material performance in modern industry, the weight problem of traditional polyamide fibers has gradually become a bottleneck restricting their application.

[0003] Lightweight polyamide fiber is a polyamide fiber treated by a special process. This treatment method reduces the fiber density, thereby achieving weight reduction. Due to the excellent hygroscopicity, high strength, and wear resistance of polyamide fiber itself, lightweight polyamide fiber not only inherits these original excellent properties of polyamide fiber but also further reduces its own weight, expanding the application fields of the product. Such as: diving suits, car seats, sportswear, etc.

[0004] The lightweight process involves adjusting the physical or chemical structure of substances. Its core lies not only in reducing the mass of substances but also in optimizing the microstructure, such as adjusting the arrangement of internal molecules of materials, to achieve lightweight while maintaining material performance. In the aerospace field, lightweight technology can significantly improve the performance of aircraft, reduce fuel consumption, and thus improve the overall operating efficiency. In the manufacturing field, the application of lightweight technology plays a crucial role in enhancing the market competitiveness of products. With the progress of technology, consumers have put forward higher requirements for the portability and energy conservation of products. Therefore, manufacturers introduce advanced processing technologies and materials to achieve the lightweight of products and meet market demands. This process not only helps to reduce product costs but also significantly enhances the market competitiveness of products.

[0005] In the initial development stage of materials science, lightweighting technology mainly focused on the development of new materials or the application of materials with inherent lightweight characteristics. In the 1970s, the commercial production of polyacrylonitrile (PAN)-based carbon fibers not only initiated a new era of high-performance lightweight fibers but also provided revolutionary materials for the aerospace and military fields. At the beginning of the 21st century, with the rise of nanotechnology, the preparation technology of lightweight fibers entered a new development stage. The emergence of nanofibers greatly enhanced the mechanical properties and functionality of materials, bringing new application prospects to fields such as healthcare, filtration, and energy storage. In addition, the development of bio-based lightweight fibers, such as cellulose fibers based on natural polymers, not only reduced the dependence on fossil resources but also promoted the concept of sustainable development. However, it has not been widely applied in the field of polyamide fiber materials.

[0006] With the continuous progress and innovation of technology, the successful application of lightweighting technology for polyamide fibers will greatly improve wearing comfort and activity convenience. Its application in the outer shell, interior, and structural components of aerospace vehicles can not only reduce the self-weight but also enhance the impact resistance and high-temperature resistance of materials, ensuring flight safety. In the textile and clothing field, lightweight polyamide fibers, due to their unique fiber structure, have good moisture absorption and diffusion properties, increasing the fiber's absorption and drainage effects. They can be widely applied in multiple fields such as sportswear, outdoor equipment, and protective clothing. Their excellent breathability and quick-drying properties enable the wearer to stay dry and comfortable even during long-term high-intensity exercise. In addition, lightweight polyamide fibers also have significant application potential in medical supplies such as surgical gowns. With the continuous optimization and improvement of lightweighting technology, it is expected that lightweight polyamide fibers will demonstrate their unique advantages in more fields. The preparation process of lightweight polyamide usually involves special spinning techniques and post-treatment processes to ensure that the fibers can maintain their structural stability and functionality while reducing weight.

[0007] Currently, lightweight polyamide fibers are still in the conceptual stage and have not been applied on a large scale. However, due to their unique properties, potential market prospects, and wide application fields, they have attracted the attention of many research institutions and enterprises. According to market research, the most commonly used method is to change the fiber structure. For example, manufacturing hollow-structured polyamide fibers and using the internal cavity to reduce the apparent density of the hollow fibers to achieve lightweighting effects. However, this method has poor lightweighting and shape retention, and the effect is not ideal. There are also means of modifying polyamide melts by adding lightweight nanomaterials to improve performance while reducing density. This technology has high process difficulty and short performance retention time. The lightweight polyamide fiber preparation technology provided by the present invention adopts a bicomponent skin-core composite technology, which has a simple process, long-lasting effects, and ultra-fast moisture absorption and quick-drying properties. Summary of the Invention

[0008] The object of the present invention is to solve the problem of lightweight of polyamide fibers at present, thereby providing a preparation method of a new type of lightweight polyamide fiber, and using this method to prepare a new type of lightweight polyamide fiber.

[0009] The preparation method of the present invention adopts a skin-core structure mode to realize the composite spinning of polyamide and polypropylene, and produces lightweight polyamide fibers, so that such lightweight fibers have the wear resistance of polyamide and at the same time have the characteristics of lightweight, high strength and small specific gravity of polypropylene, thereby solving problems such as poor moisture absorption performance and uneven dyeing.

[0010] The successful preparation of this technology can realize the replacement of polypropylene to make lightweight structural materials and applications that require high strength, thereby further improving the mechanical properties and functionality of the fibers. This method not only reduces the density of polyamide fibers by 15-20%, significantly reducing the weight, but also effectively improves its tensile strength and wear resistance, meeting the requirements of high-end application fields. Through the method provided by the present invention, the preparation process of lightweight polyamide fibers is more efficient, environmentally friendly, and the fiber properties are significantly improved, with broad market application prospects. While achieving a reduction in fiber density, the lightweight polyamide fibers also have ultra-fast moisture absorption and quick-drying properties.

[0011] Specifically, the present invention adopts the following technical solutions: A preparation method of a lightweight polyamide fiber, the preparation method is prepared by the composite spinning process of polyamide and polypropylene, and the specific steps are as follows: Step 1: Raw material preparation, using polyamide, polypropylene and maleic anhydride. The polyamide selects polyamide chips with a melting point of 210-220°C and a viscosity of 2.42±0.03, and the polypropylene selects polypropylene chips with a melting point of 160-170°C and a viscosity of 0.4±0.2 dL / g; Step 2: Melt composite spinning, polyamide and polypropylene are respectively melted by a twin-screw extruder, and with polyamide as the skin layer and polypropylene as the core layer, a composite fiber with a skin-core structure is prepared by the composite spinning process, which is a nascent fiber; maleic anhydride grafted polypropylene is added to the core layer melt; by weight percentage, polyamide is 20-40%, polypropylene is 57-76%, and maleic anhydride grafted polypropylene is 3-4%; the spinneret holes are arranged in concentric circles or diamonds; Step 3: Post-treatment, after the nascent fiber is cooled by side blowing and oiled by an oil nozzle, the filament bundle passes through a pre-networker, a first godet roller GR1, a second godet roller GR2 for heat treatment, a network nozzle of a main networker, and a third godet roller GR3 in sequence, and finally is wound into a lightweight polyamide fiber with a skin-core structure.

[0012] Preferably, the polyamide chips and polypropylene chips are melted by a twin-screw extruder respectively, and the twin-screw melting temperatures are set at 240°C - 270°C and 260°C - 285°C respectively. Then, the melts of the two components are co-extruded into a bicomponent double-guide spinning assembly.

[0013] Preferably, in the bicomponent double-guide spinning assembly, the pressure of the skin component is set at 15 - 25 MPa, and the pressure of the core component is set at 10 - 20 MPa.

[0014] Preferably, the diameter of the round holes of the spinneret orifices is controlled within 0.15 - 0.2 mm, and the number of orifices is controlled within 36 - 48, and they are circularly distributed.

[0015] Preferably, the fineness of the composite fiber is 50D - 70D.

[0016] Preferably, the cooling air blowing direction of the side air blowing cooling is perpendicular to the filament bundle direction, the air speed is 0.40 - 0.98 m / s, the air temperature is 15 - 19°C, and the air humidity is 90 ± 10%.

[0017] Preferably, the oiling rate of the oil nozzle is controlled within 1.6 - 1.8%.

[0018] Preferably, the network pressure of the main networker is controlled within 0.07 - 0.08 Mpa.

[0019] Preferably, the speed of the first godet roller GR1 is 2925 - 3250 m / min; the speed of the second godet roller GR2 is 4000 - 4300 m / min, and the temperature is 145 - 165°C; the speed of the third godet roller GR3 is 4000 - 4250 m / min, and the total draw ratio is controlled between 1.12 - 1.26.

[0020] Preferably, the polyamide melt and polypropylene melt of the two components are respectively extruded into the first-layer distribution plate. The first-layer distribution plate distributes the polyamide melt to the outer guide channels of the second-layer distribution plate and the polypropylene melt to the inner guide channels of the second-layer distribution plate; the inner and outer guide channels of the second layer respectively guide the two components into the third-layer guide plate to form an annular distribution; the third-layer guide plate extrudes the bicomponent melt into the guide channels formed by the skin-core holes arranged in a staggered manner in the fourth-layer guide plate, thereby constructing a preliminary skin-core structure; the guide channels of the fourth-layer guide plate input the core component to the center position of the spinneret orifices, and as it flows out of the spinneret, the core component is formed; by means of extrusion, the skin component is extruded along the periphery of the spinneret orifice diameter into the spinneret holes, and the core component is wrapped therein to form the skin component.

[0021] Compared with the prior art, the beneficial effects of the present invention are: Through the interface bonding technology and by optimizing the spinning temperature, the prepared lightweight polyamide has a density reaching the theoretical extreme value of 0.949 g / cm3 。Close to the density of polypropylene at 0.91 g / cm³, it can replace polypropylene fiber and become a new material. The density of this new composite material is reduced by 17% compared with the conventional polyamide material, achieving a leapfrog breakthrough in the lightweight technical indicators. Using the polypropylene core layer to provide rigid support and the polyamide skin layer to endow surface toughness, the fiber breaking strength is ≥3.50 cN / dtex; the high hygroscopicity of the outer polyamide compensates for the almost zero moisture absorption of the core polypropylene, realizing the unidirectional moisture conduction function; the introduction of PP-g-MAH expands the tolerance of the melting temperature difference between the skin layer / core layer, reducing the spinning breakage rate; increasing the skin material coating rate reduces the easy skin breakage phenomenon when the addition amount increases. Replacing more than 50% of polyamide with low-cost polypropylene reduces the raw material cost by 20%-30%, and can be compatible with existing spinning equipment.

[0022] The fiber can further utilize the masterbatch multi-point addition technology to blend antibacterial, anti-ultraviolet and other functional masterbatches in the skin layer to achieve multi-functional modification, and is suitable for expanding the application fields of products in high-value-added fields. It is suitable for fabrics such as sportswear, socks, underwear, mountaineering clothing, and protective clothing in the medical field. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of the distribution plate of the present invention.

[0024] Figure 2 It is a schematic structural diagram of the spinneret plate of the present invention.

[0025] Figure 3 It is a cross-sectional view of the fiber prepared by the present invention.

[0026] Figure 4 It is a density comparison diagram of the fiber fabric prepared by the present invention and the conventional fiber fabric. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] Now, the representative embodiments shown in the drawings will be further refined. It should be understood that the following description is not intended to limit the embodiments to a preferred embodiment. On the contrary, it is intended to cover alternative forms, modifications, and equivalent forms that may be included in the essence and scope of the described embodiments defined by the appended claims.

[0028] A method for preparing lightweight polyamide fiber, the steps are as follows: Step 1: Raw material preparation, using polyamide, polypropylene and maleic anhydride. The polyamide selects polyamide chips with a melting point of 210-220 °C and a viscosity of 2.42 ± 0.03, and the polypropylene selects polypropylene chips with a melting point of 160-170 °C and a viscosity of 0.4 ± 0.2 dL / g; Step 2: Melt compound spinning. Polyamide and polypropylene are melted by a twin-screw extruder respectively. With polyamide as the skin layer and polypropylene as the core layer, a composite fiber with a skin-core structure is prepared through a composite spinning process to obtain a nascent fiber. Maleic anhydride grafted polypropylene is added to the core layer melt. By weight percentage, polyamide is 20 - 40%, polypropylene is 57 - 76%, and maleic anhydride grafted polypropylene is 3 - 4%. The spinneret holes are arranged in concentric circles or diamonds. Polyamide chips and polypropylene chips are melted by a twin-screw extruder respectively, and the twin-screw melting temperatures are set at 240°C - 270°C and 260°C - 285°C respectively. Then the melts of the two components are co-extruded into a bicomponent double-flow spinning component. In the bicomponent double-flow spinning component, the pressure of the skin material is set at 15 - 25 MPa, and the pressure of the core material is set at 10 - 20 MPa. The diameter of the round holes of the spinneret holes of the spinneret plate is controlled at 0.15 - 0.2 mm, and the number of filament holes is controlled at 36 - 48 holes, showing a circular distribution. The fineness of the composite fiber is 50D - 70D. Step 3: Post-treatment. After the nascent fiber is cooled by side blowing and oiled by an oil nozzle, the filament bundle passes through a pre-networker, the first godet roller GR1, the second godet roller GR2 for heat treatment, the network nozzles of the main networker, and the third godet roller GR3 in sequence, and finally is wound and formed to obtain a lightweight polyamide fiber with a skin-core structure. The cooling blowing direction of the side blowing cooling is perpendicular to the filament bundle direction, the wind speed is 0.40 - 0.98 m / s, the wind temperature is 15 - 19°C, and the relative humidity is 90 ± 10%. The oiling rate of the oil nozzle is controlled at 1.6 - 1.8%. The network pressure of the main networker is controlled at 0.07 - 0.08 Mpa. The speed of the first godet roller GR1 is 2925 - 3250 m / min; the speed of the second godet roller GR2 is 4000 - 4300 m / min, and the heat treatment temperature is 145 - 165°C; the speed of the third godet roller GR3 is 4000 - 4250 m / min, and the total draw ratio is controlled between 1.12 - 1.26.

[0029] Specifically in Step 2, the polyamide melt and the polypropylene melt of the two components are respectively extruded into the first-layer distribution plate. The first-layer distribution plate distributes the polyamide melt to the outer flow channels of the second-layer distribution plate and the polypropylene melt to the inner flow channels of the second-layer distribution plate. The inner and outer flow channels of the second layer respectively guide the two components to flow into the third-layer distribution plate to form an annular distribution. The third-layer distribution plate extrudes the bicomponent melt into the flow channels formed by the skin-core holes arranged alternately in the fourth-layer distribution plate, thereby constructing a preliminary skin-core structure. The flow channels of the fourth-layer distribution plate input the core material to the center position of the spinneret holes. As it flows out of the spinneret plate, the core material is formed. By using an extrusion method, the skin material is extruded along the periphery of the spinneret hole diameter into the spinneret hole, and the core material is wrapped therein to form the skin material.

[0030] The following are specific actual cases prepared by this method.

[0031] Example 1: First, select to prepare 60D lightweight polyamide fiber, Polyamide and polypropylene raw materials are selected. The polyamide is polyamide chips with a melting point of 220°C and a viscosity of 2.42, and the polypropylene is polypropylene chips with a melting point of 170°C and a viscosity of 0.4. Polyamide accounts for 40%, polypropylene accounts for 57%, and 3% PP-g-MAH is added.

[0032] Second, the polyamide chips and polypropylene chips are respectively melted by a twin-screw extruder. The temperatures in the twin-screw melting zone are set at 242°C, 252°C, 254°C, 257°C, and 262°C respectively. The temperatures of the boxes are 269°C, 262°C, 273°C, 275°C, 282°C, and 285°C. The temperature of the box is 285°C. Then, the melts of the two components are jointly extruded into a bicomponent double-channel spinning assembly for spinning.

[0033] Third, for composite spinning, a bicomponent double-channel spinning assembly is used. Polyamide and polypropylene respectively pass through a distribution plate and a deflector plate in sequence and converge at the spinneret. The polyamide melt is extruded into the spinneret from the periphery of the spinneret to form the skin layer, and the polypropylene is extruded into the spinneret from the center of the orifice of the spinneret to form the core layer. Finally, it flows out through the spinneret to form a nascent fiber with a skin-core structure; Among them, the pressure of the skin layer is set at 18 MPa, and the pressure of the core layer is set at 18 MPa. The diameter of the round orifice of the spinneret is controlled at 0.18 mm, and the number of orifices of the filament outlet is controlled at 48 holes, which are circularly distributed.

[0034] Fourth, after the nascent fiber is cooled by side blowing and oiled by an oiling nozzle, the filament bundle passes through a pre-networker, a first godet roller GR1, a second godet roller GR2 for heat treatment, a network nozzle of the main networker, and a third godet roller GR3 in sequence, and finally is wound and formed to obtain a lightweight polyamide fiber with a skin-core structure; The cooling blowing direction of the side blowing cooling is perpendicular to the direction of the filament bundle, the wind speed is 0.52 m / s, the wind temperature is 18°C, and the relative humidity is 80%; the oiling rate of the oiling nozzle is controlled at 1.7%; the network pressure of the main networker is controlled at 0.07 - 0.08 Mpa. The speed of the first godet roller GR1 is 3200 m / min; the speed of the second godet roller GR2 is 4080 m / min, and the temperature is 165°C; the speed of the third godet roller GR3 is 4040 m / min, the total draw ratio is controlled at 1.2, and the winding speed is 4000 m / min.

[0035] The density of the lightweight polyamide fiber prepared by the above method is calculated by the reciprocal of the volume weighted by mass fraction, and the final density is 0.984 g / cm³. Compared with the density of conventional polyamide, it is reduced by 14%.

[0036] Example 2: First, select to prepare 60D lightweight polyamide fiber. Polyamide and polypropylene raw materials are selected. The polyamide is polyamide chips with a melting point of 220°C and a viscosity of 2.42, and the polypropylene is polypropylene chips with a melting point of 170°C and a viscosity of 0.4. Polyamide accounts for 20%, polypropylene accounts for 76%, and 4% PP-g-MAH is added.

[0037] Second, the polyamide chips and polypropylene chips are respectively melted by a twin-screw extruder. The temperature in the twin-screw melting zone is set at 242°C, 252°C, 254°C, 257°C, and 262°C respectively. The box temperatures are 269°C, 262°C, 273°C, 275°C, 282°C, and 285°C. Then, the melts of the two components are co-extruded into a bicomponent double-flow spinning assembly for spinning.

[0038] Third, for composite spinning, a bicomponent double-flow spinning assembly is used. Polyamide and polypropylene respectively pass through a distribution plate and a flow guide plate in sequence and converge at the spinneret. The polyamide melt is extruded into the spinneret from the periphery of the spinneret to form the skin layer, and the polypropylene is extruded into the spinneret from the center of the spinneret holes to form the core layer. Finally, it flows out through the spinneret to form a nascent fiber with a skin-core structure. Among them, the pressure of the skin layer is set at 18 MPa, and the pressure of the core layer is set at 18 MPa. The diameter of the round holes of the spinneret holes is controlled at 0.18 mm, and the number of holes of the filament outlet is controlled at 48 holes, which are circularly distributed.

[0039] Fourth, after the nascent fiber is cooled by side blowing and oiled by an oil nozzle, the filament bundle passes through a pre-networker, the first godet roller GR1, the second godet roller GR2 for heat treatment, the network nozzles of the main networker, and the third godet roller GR3 in sequence, and finally is wound into a lightweight polyamide fiber with a skin-core structure. The cooling blowing direction of the side blowing cooling is perpendicular to the filament bundle direction, the wind speed is 0.52 m / s, the wind temperature is 18°C, and the relative humidity is 80%; the oiling rate of the oil nozzle is controlled at 1.7%; the network pressure of the main networker is controlled at 0.07 - 0.08 Mpa. The speed of the first godet roller GR1 is 3200 m / min; the speed of the second godet roller GR2 is 4080 m / min, and the temperature is 165°C; the speed of the third godet roller GR3 is 4040 m / min, the total draw ratio is controlled at 1.2, and the winding speed is 4000 m / min. The density of the lightweight polyamide fiber prepared by the above method is calculated by the reciprocal of the volume weighted by mass fraction, and the final density is 0.949 g / m 3 , compared with the density of conventional polyamide, it is reduced by 17%. After adding the graft, the fiber does not show skin-core separation and splitting phenomena, and the indexes are good.

[0040] Regarding the third step, the specific process is as follows: Extrude two-component polyamide melt and polypropylene melt into the first-layer distribution plate respectively. The first-layer distribution plate distributes the polyamide melt to the outer diversion channels of the second-layer distribution plate and the polypropylene melt to the inner diversion channels of the second-layer distribution plate. The inner and outer diversion channels of the second layer guide the two components into the third-layer diversion plate respectively, forming an annular distribution. The third-layer diversion plate extrudes the two-component melt into the diversion channels formed by the core-sheath holes arranged staggeredly in the fourth-layer diversion plate, thereby constructing a preliminary core-sheath structure. The diversion channels of the fourth-layer diversion plate input the core material to the center position of the spinneret holes. As it flows out of the spinneret, the core material is formed. By using the extrusion method, the sheath material is extruded along the periphery of the spinneret hole diameter into the spinneret holes, wrapping the core material therein to form the sheath material.

[0041] Example - Example 2 was carried out according to the following parameters.

[0042] Three samples were taken from Example 1 and three samples were taken from Example 2. Performance tests were carried out, and the test results are as follows in the table: The above performance data shows that the fibers prepared by the present invention have excellent performance.

[0043] The quick-drying performance of the fabric made of the fibers prepared by the present invention was tested, as Figure 4 shown, and the water absorption test results are as follows: Sample preparation: Conventional polyamide (66 dtex / 48 f), lightweight polyamide (66 dtex / 48 f); Fabric size: 10 * 10 cm; Quantity: 5 pieces each; Test basis: GB / T 21655.1 Single-item combined test method; Test duration: 5 min.

[0044] Water absorption test results of conventional polyamide: Water absorption test results of lightweight polyamide: From the experimental data in Table 2 and Table 3, it can be seen that the water absorption rate of the technology provided by the present invention is significantly better than that of conventional polyamide fibers.

[0045] It is obvious to those skilled in the art that on the basis of the above teaching content, certain modifications, combinations and variations can also be made.

Claims

1. A preparation method of a lightweight polyamide fiber, characterized in that: The preparation method comprises the following steps: Step 1: Raw material preparation. Polyamide, polypropylene and maleic anhydride are used. The polyamide is selected as polyamide chips with a melting point of 210 - 220°C and a viscosity of 2.42 ± 0.

03. The polypropylene is selected as polypropylene chips with a melting point of 160 - 170°C and a viscosity of 0.4 ± 0.2 dL / g. Step 2: Melt compound spinning. The polyamide and polypropylene are respectively melted by a twin-screw extruder. Taking the polyamide as the skin layer and the polypropylene as the core layer, a composite fiber with a skin-core structure is prepared through a composite spinning process, which is the nascent fiber. Maleic anhydride grafted polypropylene is added to the core layer melt. By weight percentage, the polyamide is 20 - 40%, the polypropylene is 57 - 76%, and the maleic anhydride grafted polypropylene is 3 - 4%. The spinneret holes are arranged in concentric circles or diamonds. Step 3: Post-treatment. After the nascent fiber is cooled by side blowing and oiled by an oil nozzle, the filament bundle passes through a pre-networker, a first godet roller GR1, a second godet roller GR2 for heat treatment, a network nozzle of the main networker, and a third godet roller GR3 in sequence, and finally is wound into a lightweight polyamide fiber with a skin-core structure.

2. The preparation method according to claim 1, characterized in that: The polyamide chips and polypropylene chips are respectively melted by a twin-screw extruder. The melting temperatures of the twin-screw extruder are respectively set at 240°C - 270°C and 260°C - 285°C, and then the melts of the two components are jointly extruded into a bicomponent double-flow spinning assembly.

3. The preparation method according to claim 1, characterized in that: In the bicomponent double-flow spinning assembly, the pressure of the skin material is set at 15 - 25 MPa, and the pressure of the core material is set at 10 - 20 MPa.

4. The preparation method according to claim 1, wherein: The diameter of the round holes of the spinneret holes of the spinneret plate is controlled at 0.15 - 0.2 mm, the number of the filament holes is controlled at 36 - 48 holes, and they are distributed in a circular shape. The fineness of the composite fiber is 50D - 70D.

5. The preparation method according to claim 1, characterized in that: The cooling blowing direction of the side blowing cooling is perpendicular to the filament bundle direction, the wind speed is 0.40 - 0.98 m / s, the wind temperature is 15 - 19°C, and the relative humidity is 90 ± 10%.

6. The preparation method according to claim 1, characterized in that: The oiling rate of the oil nozzle is controlled at 1.6 - 1.8%.

7. The preparation method according to claim 1, characterized in that: The network pressure of the main networker is controlled at 0.07 - 0.08 Mpa.

8. The preparation method according to claim 1, characterized in that: The speed of the first godet roller GR1 is 2925 - 3250 m / min; the speed of the second godet roller GR2 is 4000 - 4300 m / min, and the heat treatment temperature is 145 - 165°C; the speed of the third godet roller GR3 is 4000 - 4250 m / min, and the draw ratio is controlled between 1.12 - 1.

26.

9. The preparation method according to claim 1, characterized in that: The melts of the two components, the polyamide melt and the polypropylene melt, are respectively extruded into the first layer of distribution plate. The first layer of distribution plate distributes the polyamide melt to the outer flow channel of the second layer of distribution plate, and distributes the polypropylene melt to the inner flow channel of the second layer of distribution plate. The internal and external diversion channels of the second layer respectively guide the two components into the third-layer diversion plate to form an annular distribution; the third-layer diversion plate constructs a preliminary skin-core structure by extruding the two-component melt into the diversion channels formed by the skin-core holes arranged in a staggered manner in the fourth-layer diversion plate; the diversion channels of the fourth-layer diversion plate input the core material to the central position of the spinneret holes, and as it flows out of the spinneret, the core material is formed; by using an extrusion method, the skin material is extruded along the periphery of the spinneret hole diameter into the spinneret holes to wrap the core material therein, forming the skin material.

10. A lightweight polyamide fiber, characterized in that: It is prepared by using the preparation method described in any one of claims 1-9 above.

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