Low-moisture-absorption high-chemical-stability ultraviolet-resistant PA612 multifilament fiber as well as preparation method and application thereof
By optimizing the PA612 spinning process, the problem of performance degradation of nylon fibers under ultraviolet light was solved, and low moisture absorption, high chemical stability and UV resistance PA612 multifilament fibers were prepared, which improved the strength and dimensional stability of the fibers and expanded their application range.
Patent Information
- Application Number
- CN202511751834.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-02-10
AI Technical Summary
Existing nylon fibers suffer from decreased strength, yellowing, and shortened lifespan under ultraviolet radiation. Furthermore, existing spinning processes cannot effectively utilize the low water absorption and high dimensional stability of PA612, resulting in poor fiber performance.
A spinning process specifically designed for PA612 is employed, including adjusting the spinning temperature, draw ratio, and cooling conditions, combined with side-blowing cooling, to form PA612 multifilament fibers with low moisture absorption, high chemical stability, and UV resistance.
It significantly improves the fiber's UV resistance and chemical stability, reduces water absorption, and enhances the fiber's strength and dimensional stability, making it suitable for a variety of applications.
Smart Images
Figure CN121496596A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polymer spinning technology, and relates to a low moisture absorption, high chemical stability, and UV resistant PA612 multifilament fiber, its preparation method, and its application. Background Technology
[0002] Nylon fiber (also known as polyamide fiber) is an important synthetic fiber widely used in textiles and engineering. While Nylon 6 (PA6) and Nylon 66 (PA66) are the mainstream in the market, they suffer from poor UV resistance. Long-term UV exposure causes the molecular chains of these materials to break, leading to decreased strength, yellowing, and shortened lifespan. Existing technologies, such as adding UV stabilizers, can partially improve this problem, but this often comes with increased costs and reduced spinnability. Currently, the closest solution is multifilament fiber prepared from ordinary nylon materials (such as PA6 or PA66) using conventional melt spinning processes. However, these fibers have significant shortcomings in UV stability; their strength retention rate after UV aging is typically below 70%, severely limiting their application in high UV environments such as outdoor settings.
[0003] Nylon 612 (PA612), as a long-chain polyamide, has a relatively low density of amide groups and a relatively long methylene chain in its molecular structure. This unique molecular structure naturally gives it lower water absorption, better dimensional stability, and inherent resistance to chemicals and ultraviolet radiation. Although PA66 and PA612 belong to the same polyamide family, it is not feasible to directly apply the spinning parameters of PA66 or PA6 to PA612, due to the fundamental differences between the two in molecular structure, thermal properties, and crystallization behavior. The most critical difference lies in their thermal properties: PA66 has a higher melting point, approximately 260℃, and its typical spinning box temperature needs to be set at around 300℃ to ensure good melt flowability; while PA612 has a significantly lower melting point. Applying the same spinning temperature as PA66 to PA612 would cause its polymer molecular chains to undergo thermal degradation due to overheating, producing bubbles and gels, resulting in problems such as yarn breakage and filament drift, severely affecting fiber quality. Therefore, the spinning temperature of PA612 must be significantly lowered according to its own melting point. Secondly, the two have different molecular structures. PA66 is formed by the condensation polymerization of hexamethylenediamine and adipic acid, with symmetrical and regular molecular chains, high amide bond density, and strong intermolecular hydrogen bonding, resulting in very high crystallization ability and crystallization rate. PA612 is formed by the condensation polymerization of hexamethylenediamine and dodecanoic acid. Its molecular chain has a longer methylene sequence, a relatively lower amide bond density, and a more flexible molecular chain. This results in significantly different crystallization behavior and kinetics compared to PA66. This difference directly affects the core process of "spinning-stretching-orientation-crystallization" in the spinning process. Directly applying the draw ratio and cooling conditions of PA66 may not guide the PA612 molecular chain to form an ideal and stable orientation and crystal structure, leading to poor mechanical properties (such as strength and dimensional stability) in the final fiber. PA612's superiority lies in its extremely low water absorption and better dimensional stability; inappropriate draw and heat setting processes cannot fully express these characteristics through the fiber structure. Similarly, due to the differences in molecular structure and physical properties between PA6 and PA612, the spinning parameters of PA6 (such as spinning temperature and draw ratio) are not suitable for PA612: PA6 has a melting point of approximately 215-225℃, while PA612 has a slightly lower melting point of approximately 210-220℃. Using the higher spinning temperature of PA6 directly may cause PA612 to overheat, resulting in a lower melt viscosity and affecting fiber quality. The more crucial difference lies in the fact that PA612, due to its higher proportion of methylene groups and lower amide bond density in its molecular chain, has extremely low water absorption. This leads to significant differences in its water absorption behavior, crystallization kinetics, and final fiber dimensional stability during spinning compared to PA6. Therefore, the processes used for PA6 or PA66 cannot be simply applied. Improper process control may not only fail to fully realize the potential of PA612 but could even result in poor fiber performance.
[0004] Therefore, there is an urgent need to develop a special spinning technology for PA612 material to systematically balance its low water absorption, high dimensional stability, chemical resistance and UV resistance, so as to overcome the limitations of existing technology. Summary of the Invention
[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a PA612 multifilament fiber with low water absorption, high dimensional stability, chemical resistance and UV resistance, as well as its preparation method and application, to solve the technical problem of insufficient UV stability and chemical stability of existing nylon fibers.
[0006] To achieve the above and other related objectives, the technical solution of the present invention is as follows: The present invention discloses a method for preparing a low-moisture-absorbing, high-chemical-stability, and UV-resistant PA612 multifilament fiber, the preparation method comprising the following steps: Step 1, Raw material preparation: Select PA612 granules with a melt index of 2-10 g / 10min, and dry them at 70-105℃ until the moisture content is 200-400 ppm to obtain dried PA612; Step 2, Melt spinning: The dried PA612 is fed into a screw extruder. After melt extrusion, the melt stream formed by homogenization in the spinning box is then sent into the spinning assembly by a metering pump, and finally ejected from the spinneret to form a melt stream. The screw temperature is 225-255℃, the spinning box temperature is 220-260℃, and the spinneret temperature is 232-256℃. Step 3, Cooling and Shaping: The molten stream is cooled by side blowing to form filaments; the side blowing temperature is controlled at 14-20℃, the wind speed is 0.3-0.5m / s, and the relative humidity is 60-70%; Step 4, Stretching and Heat Setting: After stretching, heat setting and winding the filament bundle, PA612 multifilament fiber is obtained; wherein, the total draw ratio is 3-5.5; the heat setting temperature is 160-190℃; and the winding speed is 1300-3600 m / min.
[0007] Preferably, in step 1, the melt index of PA612 particles is 3.5-8.5 g / 10min.
[0008] Preferably, in step 1, the drying is carried out by vacuum drying or hot air drying; wherein, the conditions for vacuum drying are: drying temperature of 70~100℃ and vacuum degree of 0.05-0.3Kpa; the conditions for hot air drying are: drying hot air temperature controlled at 80-105℃ and hot air dew point below -30℃.
[0009] Preferably, in step 2, the temperature of the spinning box is 240-258℃.
[0010] Preferably, in step 3, the side-blowing air temperature is controlled at 14-17℃ and the wind speed is 0.3-0.48m / s.
[0011] Preferably, in step 4, the total stretch ratio is 4.5-5.4; the heat setting temperature is 180-190℃; and the winding speed is 2200-3200 m / min.
[0012] Preferably, the spinning box temperature is 245℃; the total draw ratio is 4.9; the heat setting temperature is 185℃; and the winding speed is 2550 m / min.
[0013] This invention provides a low-moisture-absorbing, high-chemical-stability, UV-resistant PA612 multifilament fiber, which is prepared by the aforementioned preparation method.
[0014] Preferably, the fineness of the PA612 multifilament fiber is 50-500 dtex.
[0015] Preferably, the strength of the PA612 multifilament fiber is ≥6.0 cN / dtex.
[0016] Preferably, the breaking elongation of the PA612 multifilament fiber is ≥20%.
[0017] Preferably, the PA612 multifilament fiber has a dry heat shrinkage rate of ≤8% when tested under dry heat conditions at 180°C.
[0018] This invention provides an application of the low moisture absorption, high chemical stability, and UV resistant PA612 multifilament fiber in the preparation of cord, industrial fabric, cable, conveyor belt, tent, or fishing net.
[0019] Preferably, in the aforementioned applications, the PA612 multifilament fiber may also contain various inorganic and organic additives, such as matting agents, flame retardants, antioxidants, ultraviolet absorbers, infrared absorbers, nucleating agents, fluorescent whitening agents, antistatic agents, hygroscopic agents (such as polyvinylpyrrolidone), and antibacterial agents (such as silver zeolite and zinc oxide). The content of these additives accounts for 0.001% to 10% of the mass of the PA612 multifilament fiber, and the specific proportion is adjusted according to the application scenario.
[0020] The present invention has the following beneficial effects: (1) Significantly reduced water absorption and excellent dimensional stability: Based on the inherent characteristics of PA612 molecular structure, which has a high proportion of long carbon chain methylene groups and low amide bond density, combined with optimized heat setting process, the dimensional change of PA612 multifilament fiber is significantly suppressed in humid environment. The heat shrinkage rate tested under dry heat conditions of 180℃ is ≤8%, which is about 5% lower than the heat shrinkage rate of PA6 (about 12.5%). This characteristic can effectively avoid the mechanical property decay caused by environmental humidity fluctuations, and is particularly suitable for high-precision application scenarios such as precision instrument parts and outdoor equipment.
[0021] (2) Inherent high alkali resistance: The fiber has good resistance to acids, alkalis, most inorganic salt aqueous solutions, haloalkanes, hydrocarbons, esters, ketones, etc., and is suitable for industrial environments that may come into contact with chemical media. In particular, PA612 multifilament fiber has excellent resistance to alkalis, and the strength retention rate is >90% after soaking in 10% NaOH for 24 hours.
[0022] (3) Good UV resistance: The molecular structure of PA612 is relatively stable to ultraviolet light. After UV accelerated aging test, the fiber strength retention rate is high (≥85%), which is at least 21.4% higher than that of ordinary fibers, enabling it to maintain high mechanical properties in harsh environments and effectively extend its outdoor service life.
[0023] (4) Balanced comprehensive performance: The new process of this application can cover fine denier to coarse denier specifications, with a variety of linear deniers. Combined with outstanding flexibility, abrasion resistance and processing performance, it can be widely used in various scenarios and high-strength fiber fields. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the spinning process (1-metering pump; 2-rear heating shroud; 3-oil nozzle; 4-network nozzle; 5-filament bundle).
[0025] Figure 2 A schematic diagram of the PA612 multifilament fiber prepared in Example 1 of the present invention after UV aging (a is the initial sample; b is the sample after UV treatment for 72 hours). Detailed Implementation
[0026] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.
[0027] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.
[0028] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.
[0029] Example 1
[0030] This embodiment provides a method for preparing PA612 multifilament fibers with low moisture absorption, high chemical stability, and UV resistance. The preparation method includes the following steps: Step 1, Raw material preparation: Select PA612 particles with a melt index of 5.0 g / 10min (230°C, 2.16kg) and vacuum dry them at 85°C and 0.1 kPa until the moisture content is about 280 ppm to obtain dried PA612; this step aims to ensure that the raw material is not easily hydrolyzed during the melting process and to reduce molecular chain degradation. Step 2, Melt Spinning: The dried PA612 is fed into a screw extruder. After melt extrusion, the melt stream formed by homogenization in the spinning box is fed into the spinning assembly and finally ejected from the spinneret to form a melt stream. The temperatures of each zone of the screw extruder are: Zone 1 235℃, Zone 2 245℃, Zone 3 245℃, Spinning box temperature 245℃, and Spinneret temperature 245℃. The spinneret temperature needs to be slightly higher than the melting point of PA612 to ensure good melt flowability and stability, while avoiding thermal degradation caused by excessive temperature. Step 3, Cooling and Shaping: The molten fine stream is cooled by side blowing using an enhanced side blowing cooling system, and oil is applied to form filament bundles; the side blowing temperature is controlled at 15℃, the wind speed is 0.4m / s, and the relative humidity is 65%; the strong cooling conditions help the fibers to form quickly and form a uniform microstructure, which is beneficial to improving the strength and dimensional stability of the fibers. Step 4, Drawing and Heat Setting: After drawing, heat setting, and winding of the filament bundle, PA612 multifilament fiber is obtained; the total draw ratio is 4.9; the drawing roller temperatures are set as follows: 30℃ for the first pair, 60℃ for the second pair, and 165℃ for the third pair; the heat setting temperature is 185℃; and the winding speed is 2550 m / min. This combination of process parameters aims to effectively guide the molecular chain orientation and crystallization, thereby optimizing the mechanical properties and thermal stability of the fiber.
[0031] The performance indicators and spinning conditions of the PA612 multifilament fiber prepared in this embodiment were tested. The test standards are shown in Table 1, the test parameters are shown in Table 2, and the test results are shown in Table 3.
[0032] Table 1 Performance test standards for each indicator
[0033] Example 2
[0034] This embodiment provides a method for preparing PA612 multifilament fibers with low moisture absorption, high chemical stability, and UV resistance. The preparation method includes the following steps: Step 1, Raw material preparation: Select PA612 granules with a melt index of 3.5 g / 10min (230°C, 2.16kg), dry them with hot air at 95°C with a dew point below -30°C, so that the moisture content is about 250ppm, to obtain dried PA612; this step aims to ensure that the raw material is not easily hydrolyzed during the melting process and to reduce molecular chain degradation. Step 2, Melt Spinning: The dried PA612 is fed into a screw extruder. After melt extrusion, the melt stream formed by homogenization in the spinning box is fed into the spinning assembly and finally ejected from the spinneret to form a melt stream. The temperatures of each zone of the screw extruder are: Zone 1 240℃, Zone 2 255℃, Zone 3 255℃, spinning box temperature 255℃, and spinneret temperature 252℃. The spinneret temperature needs to be slightly higher than the melting point of PA612 to ensure good melt flowability and stability, while avoiding thermal degradation caused by excessive temperature. Step 3, Cooling and Shaping: The molten fine stream is cooled by side blowing using an enhanced side-blowing cooling system, and oil is applied to form filaments; the side-blowing temperature is controlled at 18℃, the wind speed at 0.45m / s, and the relative humidity at 65%; Step 4, Stretching and Heat Setting: After stretching, heat setting, and winding the filament bundle, PA612 multifilament fiber is obtained; the total draw ratio is 5.2; the stretching roller temperatures are set as follows: 30℃ for the first pair, 60℃ for the second pair, and 165℃ for the third pair; the heat setting temperature is 188℃ to further improve the strength and modulus of the fiber; the winding speed is 2800 m / min.
[0035] Example 3
[0036] This embodiment provides a method for preparing PA612 multifilament fibers with low moisture absorption, high chemical stability, and UV resistance. The preparation method includes the following steps: Step 1, Raw material preparation: Select PA612 granules with a melt index of 7.0 g / 10min (230°C, 2.16kg), and vacuum dry them at 80°C and 0.08 KPa to reduce the moisture content to about 250ppm, thus obtaining dried PA612. This step aims to ensure that the raw material is not easily hydrolyzed during the melting process and to reduce molecular chain degradation. Step 2, Melt Spinning: The dried PA612 is fed into a screw extruder. After melt extrusion, the melt stream formed by homogenization in the spinning box is fed into the spinning assembly and finally ejected from the spinneret to form a melt stream. The temperatures of each zone of the screw extruder are: Zone 1 230℃, Zone 2 240℃, Zone 3 240℃, spinning box temperature 240℃, and spinneret temperature 238℃. The spinneret temperature needs to be slightly higher than the melting point of PA612 to ensure good melt flowability and stability, while avoiding thermal degradation caused by excessive temperature. Step 3, Cooling and Shaping: The molten fine stream is cooled by side blowing using an enhanced side blowing cooling system, and oil is applied to form filament bundles; the side blowing temperature is controlled at 17℃, the wind speed is 0.35m / s, and the relative humidity is 65% to prevent breakage caused by excessive cooling; Step 4, Stretching and Heat Setting: After stretching, heat setting, and winding the filament bundle, PA612 multifilament fiber is obtained; the total draw ratio is 4.5; the stretching roller temperatures are set as follows: 30℃ for the first pair, 60℃ for the second pair, and 160℃ for the third pair; the heat setting temperature is 182℃ to obtain a lower shrinkage rate; and the winding speed is 3000 m / min.
[0037] Example 4
[0038] This embodiment provides a method for preparing PA612 multifilament fibers with low moisture absorption, high chemical stability, and UV resistance. The preparation method includes the following steps: Step 1, Raw material preparation: Select PA612 granules with a melt index of 4.0 g / 10min (230°C, 2.16kg), and vacuum dry them at 90°C and 0.12 kPa to reduce the moisture content to about 250 ppm, thus obtaining dried PA612. This step aims to ensure that the raw material is not easily hydrolyzed during the melting process and to reduce molecular chain degradation. Step 2, Melt Spinning: The dried PA612 is fed into a screw extruder. After melt extrusion, the melt stream formed by homogenization in the spinning box is fed into the spinning assembly and finally ejected from the spinneret to form a melt stream. To ensure uniform distribution and extrusion of the porous melt, the temperatures of the spinning box and spinneret are appropriately increased. The temperatures of each zone of the screw extruder are: Zone 1 245℃, Zone 2 255℃, Zone 3 255℃, spinning box temperature 258℃, and spinneret temperature 256℃. The spinneret temperature needs to be slightly higher than the melting point of PA612 to ensure good melt flowability and stability, while avoiding thermal degradation caused by excessive temperature. Step 3, Cooling and Shaping: The molten fine stream is cooled by side blowing using an enhanced side blowing cooling system, and oil is applied to form filament bundles; the side blowing temperature is controlled at 16℃, the wind speed is 0.5m / s, and the relative humidity is 65% to prevent breakage caused by excessive cooling; Step 4, Stretching and Heat Setting: After stretching, heat setting, and winding the filament bundle, PA612 multifilament fiber is obtained; the total draw ratio is 5.0; the stretching roller temperatures are set as follows: 30℃ for the first pair, 60℃ for the second pair, and 170℃ for the third pair; the heat setting temperature is 182℃ to obtain a lower shrinkage rate; and the winding speed is 2200 m / min.
[0039] Example 5
[0040] This embodiment provides a method for preparing PA612 multifilament fibers with low moisture absorption, high chemical stability, and UV resistance. The preparation method includes the following steps: Step 1, Raw material preparation: Select PA612 granules with a melt index of 8.5 g / 10min (230°C, 2.16kg), and vacuum dry them at 75°C and 0.05KPa to reduce the moisture content to about 200ppm, thus obtaining dried PA612. This step aims to ensure that the raw material is not easily hydrolyzed during the melting process and to reduce molecular chain degradation. Step 2, Melt Spinning: The dried PA612 is fed into a screw extruder. After melt extrusion, the melt stream formed by homogenization in the spinning box is fed into the spinning assembly and finally ejected from the spinneret to form a melt stream. A relatively low spinning temperature is used to reduce degradation: the temperatures of each zone of the screw extruder are: Zone 1 225℃, Zone 2 235℃, Zone 3 235℃, spinning box temperature 235℃, and spinneret temperature 232℃. The spinneret temperature needs to be slightly higher than the melting point of PA612 to ensure good melt flowability and stability, while avoiding thermal degradation due to excessive temperature. Step 3, Cooling and Shaping: The molten fine stream is cooled by side blowing using an enhanced side blowing cooling system, and oil is applied to form filament bundles; the side blowing temperature is controlled at 15℃, the wind speed is 0.3m / s, and the relative humidity is 65% to prevent breakage caused by excessive cooling; Step 4, Stretching and Heat Setting: After stretching, heat setting, and winding the filament bundle, PA612 multifilament fiber is obtained; the total draw ratio is 4.8; the stretching roller temperatures are set as follows: 30℃ for the first pair, 60℃ for the second pair, and 160℃ for the third pair; the heat setting temperature is 180℃ to obtain a lower shrinkage rate; and the winding speed is 3200 m / min.
[0041] Example 6
[0042] This embodiment provides a method for preparing PA612 multifilament fibers with low moisture absorption, high chemical stability, and UV resistance. The preparation method includes the following steps: Step 1, Raw material preparation: Select PA612 granules with a melt index of 3.0 g / 10min (230°C, 2.16kg), and vacuum dry them at 100°C and 0.15KPa to reduce the moisture content to about 200ppm, thus obtaining dried PA612. This step aims to ensure that the raw material is not easily hydrolyzed during the melting process and to reduce molecular chain degradation. Step 2, Melt Spinning: The dried PA612 is fed into a screw extruder. After melt extrusion, the melt stream formed by homogenization in the spinning box is fed into the spinning assembly and finally ejected from the spinneret to form a melt stream. A relatively low spinning temperature is used to reduce degradation: the temperatures of each zone of the screw extruder are: Zone 1 242℃, Zone 2 252℃, Zone 3 252℃, spinning box temperature 254℃, and spinneret temperature 252℃. The spinneret temperature needs to be slightly higher than the melting point of PA612 to ensure good melt flowability and stability, while avoiding thermal degradation caused by excessive temperature. Step 3, Cooling and Shaping: The molten fine stream is cooled by side blowing using an enhanced side blowing cooling system, and oil is applied to form a filament bundle; the side blowing temperature is controlled at 14℃, the wind speed is 0.48m / s, and the relative humidity is 65% to prevent breakage caused by excessive cooling; Step 4, Stretching and Heat Setting: After stretching, heat setting, and winding the filament bundle, PA612 multifilament fiber is obtained; the total draw ratio is 5.4; the stretching roller temperatures are set as follows: 30℃ for the first pair, 60℃ for the second pair, and 170℃ for the third pair; the heat setting temperature is 188℃ to obtain a lower shrinkage rate; and the winding speed is 2500 m / min.
[0043] The methods for demonstrating the PA612 multifilament fibers obtained in Examples 2-6 are similar to those in Example 1, and will not be repeated here.
[0044] Table 2 Specific Process Parameters
[0045] Comparative Example 1 This comparative example uses the PA66 spinning process to spin PA612, and the specific method is as follows: (1) Raw material preparation: PA612 granules (melt index of 5.0 g / 10min) were selected as in the example. Following the typical PA66 spinning pretreatment process, the granules were dried in a circulating air oven at 120°C for 4 hours, and the moisture content after drying was approximately 200 ppm.
[0046] (2) Melt spinning: Add the dried PA612 to the melt spinning equipment. According to the PA66 spinning process, set the temperature of each zone of the screw as follows: Zone 1 275℃, Zone 2 285℃, Zone 3 285℃, spinning box temperature 300℃, and spinneret temperature 300℃.
[0047] Results: The melt turned yellow rapidly after extrusion, and a large number of bubbles and gels appeared at the spinneret outlet, accompanied by the volatilization of irritating gases. The melt stream was unstable, with frequent breakage and filament drift, making continuous spinning impossible. Analysis of the small amount of nascent fibers collected revealed a significant decrease in intrinsic viscosity, indicating severe thermal degradation of the PA612 polymer molecular chains.
[0048] Comparative Example 2 This comparative example uses the PA6 spinning process to spin PA612, and the specific method is as follows: (2) Raw material preparation: The raw materials are the same as in the example. Referring to the hygroscopic properties of PA6, it is dried in hot air at 100°C for 12 hours. After drying, the moisture content is controlled at about 200 ppm.
[0049] (2) Melt spinning: Add the dried PA612 to the melt spinning equipment. According to the typical spinning process of PA6, set the temperature of each zone of the screw as follows: Zone 1 250℃, Zone 2 260℃, Zone 3 260℃, box temperature 260℃, and spinneret temperature 260℃.
[0050] (3) Cooling and molding: Side blowing air cooling is adopted, with an air temperature of 18℃ and an air speed of 0.5 m / s.
[0051] (4) Stretching and heat setting: The total stretch ratio was set to 4.0. The heat setting temperature was set to 170℃. Results and performance: The spinning process was relatively continuous, but the surface of the nascent fibers was rough, and a small amount of fuzz was visible. Product indicators are shown in Table 3.
[0052] Table 3 Product Indicators
[0053] As can be seen from the data in Table 3, Comparative Example 1, referring to the typical PA66 spinning pretreatment process, could not produce qualified products using PA612 as raw material. The reason is that although PA612 and PA66 / PA6 are both polyamides, directly applying their spinning parameters cannot produce qualified products. The fundamental reason lies in the significant differences in molecular structure, thermal properties, and crystallization behavior: PA66 has a melting point of approximately 260℃, requiring 300℃ for spinning to ensure melt flowability, while PA612 has an even lower melting point. Using the same temperature as PA66 would lead to thermal degradation of the molecular chains, the formation of bubbles and gels, causing breakage and filament drift; therefore, the temperature needs to be significantly lowered. Furthermore, PA66 has a symmetrical and regular molecular chain, a high density of amide bonds, and strong crystallization ability, while... PA612 has a longer methylene sequence, lower amide bond density, and more flexible molecular chains, resulting in different crystallization kinetics. Directly applying the draw ratio and cooling conditions of PA66 cannot guide PA612 to form an ideal oriented crystalline structure, affecting the fiber's mechanical properties. Due to its high methylene ratio and low amide bond density, PA612 has extremely low water absorption and superior dimensional stability, but a matching draw and heat setting process is required to fully realize its potential. PA6 has a slightly higher melting point than PA612, and its spinning temperature will still reduce the melt viscosity of PA612. Moreover, the water absorption behavior and crystallization kinetics of the two are significantly different, so the processes of PA6 or PA66 cannot be simply applied. Therefore, directly applying the PA66 pre-spinning treatment process will not produce qualified products.
[0054] The linear densities of Examples 1-6 range from 85-398 dtex, encompassing fine to coarse denier specifications, fully demonstrating the diversity of linear densities. The breaking strength is ≥5.9 cN / dtex, with Example 6 achieving a breaking strength of 7.0 cN / dtex, significantly higher than Comparative Example 2's 5.0 cN / dtex, representing an improvement of 18%-40%. This indicates that the Examples exhibit superior mechanical properties compared to traditional materials. The dry heat shrinkage rate of the Example group is 6.8%-7.9%, while Comparative Example 2 is 12.5%. The shrinkage rate of the Example group is significantly lower, by approximately 37%-45%, indicating better dimensional stability under high-temperature conditions. The equilibrium water absorption rate of Example 1 is ≈2.45%, while Comparative Example 2 is ≈4.0-4.5%. The lower water absorption rate of the Example indicates stronger water resistance, making it suitable for humid environments. The strength retention rate after UV aging of Example 1 is ≥85%, while that of Comparative Example 2 is <70%. The Example exhibits significantly better UV aging resistance and a longer service life than the Comparative Example. Example 1 exhibits an alkali resistance rate >90%, while Comparative Example 2 shows "severe damage and low retention rate," indicating that the Example 1 demonstrates stronger tolerance to alkaline environments and a wider range of applications. The Example 1 product significantly outperforms the Comparative Example in key indicators such as mechanical properties (18%-40% increase in breaking strength), dimensional stability (29%-45% reduction in elongation at break and 37%-45% reduction in dry heat shrinkage), water resistance (35%-46% reduction in equilibrium water absorption), UV aging resistance (≥21% increase in strength retention), and alkali resistance (>90%), demonstrating superior overall performance. The product prepared in Example 1 offers balanced overall performance and is suitable for applications with conventional requirements for strength, UV stability, and dimensional stability. The product prepared in Example 2 achieves an elongation at break of 6.8%, making it suitable for scenarios requiring good durability. The product prepared in Example 3 has the lowest linear density at 85 dtex, representing a fine denier filament that emphasizes fiber softness and low shrinkage, making it suitable for applications with high requirements for tactile feel and dimensional accuracy. Example 4 prepared a high-density, high-porosity PA612 multifilament fiber, suitable for industrial fabrics requiring high toughness and fatigue resistance. Example 5 prepared an ultra-fine denier PA612 multifilament fiber suitable for precision applications requiring high uniformity of fineness and strength. Example 6 prepared a high-strength PA612 multifilament fiber, suitable for fields with stringent requirements for tensile strength and modulus, ranging from civilian textiles to military and aerospace applications (such as drone weight reduction and bulletproof vests), covering both high-end and specialized needs, demonstrating significant technological innovation and practicality. Upgraded properties such as low water absorption, UV resistance, and alkali resistance expand the product's application boundaries under complex working conditions, resulting in superior overall competitiveness compared to conventional materials in the comparative examples. Figure 2 The diagram shows a sample made of PA612 multifilament fiber prepared in Example 1 after UV treatment (a is the initial sample; b is the sample after 72 hours of UV treatment). The sample was rated as having a yellowing resistance of level 5, indicating that its UV stability was greatly improved.
[0055] This application innovatively proposes a spinning process using PA612 as raw material. By optimizing the PA612 spinning process (such as lowering the spinning temperature, adjusting the draw ratio, and cooling conditions), problems such as molecular chain thermal degradation and bubble gelation can be effectively avoided, significantly improving the mechanical properties (strength and dimensional stability) of the fiber and fully leveraging the advantages of PA612's low water absorption and high dimensional stability. This innovative process solves the problems of fiber breakage, filament drift, and crystalline structure defects caused by directly applying PA66 / PA6 parameters, providing a reliable technical path for the efficient preparation of PA612 fibers. It also highlights its application potential in the field of high-performance fibers. PA612 multifilament fibers prepared using this process have a wide range of linear denier (covering fine denier to coarse denier specifications), and their low water absorption, UV resistance, and alkali resistance properties are significantly upgraded. The prepared PA612 multifilament has both high strength and high UV stability, and can be widely used in traditional fields such as tire cord, industrial fabric, cable, and conveyor belt. It also shows unique application value in high-performance fiber fields such as high-end protective equipment and marine engineering ropes, providing a reliable technical path for the industrial application of PA612 fiber.
[0056] The above embodiments are for illustrating the implementation schemes disclosed in this invention and should not be construed as limiting the invention. Furthermore, various modifications listed herein, as well as variations in the methods and compositions of the invention, will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been specifically described in conjunction with various specific preferred embodiments, it should be understood that the invention should not be limited to these specific embodiments. In fact, various modifications as described above that are obvious to those skilled in the art to obtain the invention should be included within the scope of this invention.
Claims
1. A method for preparing PA612 multifilament fiber with low moisture absorption, high chemical stability, and UV resistance, characterized in that, The preparation method includes the following steps: Step 1, Raw material preparation: Select PA612 granules with a melt index of 2-10 g / 10min, and dry them at 70-105℃ until the moisture content is 200-400 ppm to obtain dried PA612; Step 2, Melt spinning: The dried PA612 is fed into a screw extruder. After melt extrusion, the melt stream formed by homogenization in the spinning box is fed into the spinning assembly and finally ejected from the spinneret to form a melt stream. The screw temperature is 225-255℃, the spinning box temperature is 220-260℃, and the spinneret temperature is 232-256℃. Step 3, Cooling and Molding, and Oiling: The molten stream is cooled by side blowing and oiled to form filaments; the side blowing temperature is controlled at 14-20℃, the wind speed is 0.3-0.5m / s, and the relative humidity is 60-70%. Step 4, Stretching and Heat Setting: After stretching, heat setting and winding the filament bundle, PA612 multifilament fiber is obtained; wherein, the total draw ratio is 3-5.5; the heat setting temperature is 160-190℃; and the winding speed is 1300-3600 m / min.
2. The method for preparing low moisture absorption, high chemical stability, and UV resistant PA612 multifilament fiber according to claim 1, characterized in that, In step 1, the melt index of PA612 particles is 3.5-8.5 g / 10min.
3. The method for preparing low moisture absorption, high chemical stability, and UV resistant PA612 multifilament fiber according to claim 1, characterized in that, In step 1, drying is carried out using vacuum drying or hot air drying. The conditions for vacuum drying are: drying temperature of 70~100℃ and vacuum degree of 0.05-0.3Kpa. The conditions for hot air drying are: drying hot air temperature controlled at 80-105℃ and hot air dew point below -30℃.
4. The method for preparing low moisture absorption, high chemical stability, and UV resistant PA612 multifilament fiber according to claim 1, characterized in that, In step 2, the temperature of the spinning box is 240-258℃.
5. The method for preparing low moisture absorption, high chemical stability, and UV-resistant PA612 multifilament fiber according to claim 1, characterized in that, In step 3, the side-blowing air temperature is controlled at 14-17℃ and the wind speed is 0.3-0.48m / s.
6. The method for preparing low moisture absorption, high chemical stability, and UV-resistant PA612 multifilament fiber according to claim 1, characterized in that, In step 4, the total stretch ratio is 4.5-5.4; the heat setting temperature is 180-190℃; and the winding speed is 2200-3200 m / min.
7. The method for preparing low moisture absorption, high chemical stability, and UV-resistant PA612 multifilament fiber according to claim 1, characterized in that, The spinning box temperature is 245℃; the total draw ratio is 4.9; the heat setting temperature is 185℃; and the winding speed is 2550 m / min.
8. A PA612 multifilament fiber with low moisture absorption, high chemical stability, and UV resistance, characterized in that, Prepared by the preparation method according to any one of claims 1-7.
9. The low moisture absorption, high chemical stability, and UV resistant PA612 multifilament fiber according to claim 8, characterized in that, PA612 multifilament fiber has a fineness of 50-500 dtex, a strength of ≥6.0 cN / dtex, a breaking elongation of ≥20%, and a dry heat shrinkage rate of ≤8% when tested under dry heat conditions at 180℃.
10. The application of the low moisture absorption, high chemical stability, and UV resistant PA612 multifilament fiber as described in claim 8 in the preparation of cord, industrial fabric, cable, conveyor belt, tent, shoe upper or fishing net.