Preparation method of high-strength fine denier bright nylon 66 fully drawn fiber

Abstract

The application discloses a preparation method of high-strength fine denier large-brightness nylon 66 fully-drawing fiber. Firstly, nylon 66 spinning grade chips with a relative viscosity of 2.4-2.6 are solid-phase increased in viscosity to obtain nylon 66 medium-high viscosity chips with water content of less than or equal to 300 ppm and a relative viscosity of 3.0-3.2; then the chips are sent to a screw extruder for melt extrusion; the extruded melt is sent into a spinning box and is pressed into a spinning assembly by a metering pump; the melt is sprayed from a spinneret plate of the spinning assembly to form a fiber bundle; the sprayed melt is cooled to form a nascent fiber bundle; the obtained nascent fiber bundle is oiled by an oil nozzle crude oil; the oiled fiber bundle is subjected to three-stage hot drawing and two-stage relaxation heat setting; and finally, the fiber bundle is wound to obtain the high-strength fine denier large-brightness nylon 66 fully-drawing fiber. According to the application, the high-strength fine denier fiber with more stable structure and higher orientation degree can be prepared, the physical properties of the obtained high-strength fine denier fiber are more uniform, and the breaking strength and the breaking strength retention rate are higher, so that the continuous and stable production of the high-strength fine denier nylon 66 fiber is realized.

Description

I. Technical Field:

[0001] This invention belongs to the field of nylon 66 fiber preparation technology, specifically relating to a method for preparing high-strength, fine-denier, bright nylon 66 fully drawn fiber. II. Background Technology:

[0002] Compared to high-strength fine denier nylon 6 fiber, high-strength fine denier nylon 66 fiber (linear density <100D, breaking strength ≥8g / D) boasts advantages such as abrasion resistance, cold resistance, high strength, and high-temperature aging resistance, making it widely used in high-end apparel fields such as work clothes, outdoor jackets, protective clothing, tents, sleeping bags, and parachutes. Nylon 66 fine denier fiber is typically produced using a chip melt spinning process. To achieve high fiber strength, the chips after solid-phase thickening must have high viscosity and the filament bundle must possess a high degree of orientation. Traditional processes employ high-viscosity chips and high draw ratios, forcing macromolecules to align regularly along the macromolecular chain direction to achieve high orientation. While this method achieves high fiber strength, it increases production difficulty and leads to more waste and defects throughout the production process.

[0003] There are also relevant patent documents reporting on the preparation of fine denier nylon 66 fibers. For example: 1. Invention patent CN 101871134A discloses "a spinning production process for fine denier nylon 66 fully drawn fibers". This patent uses a slicing and single-stage drawing method (a pair of hot rollers) spinning process, without heat relaxation and heat setting, producing nylon 66 fibers with a strength of 5.2 cN / dtex of 11 dtex / 7f. The nylon 66 fibers produced by this patent have low strength and cannot meet the needs of some applications with high strength requirements; in addition, the production process disclosed in this patent only uses single-stage drawing without relaxation and heat setting, which may lead to unstable fiber properties, especially after moisture absorption, its strength decreases significantly, affecting the performance of subsequent products. 2. Invention patent application CN 111441097A discloses "a fine denier high-strength nylon 66 fiber and its preparation method". This patent uses nylon 66 chips with a relative viscosity of 2.5-3.0 to solid-phase thicken them into ultra-high viscosity chips with a relative viscosity of 3.5-3.8 as spinning raw materials. It employs a drawing and setting process consisting of a set of feed rollers for natural stretching, four pairs of hot rollers, two-stage hot stretching, and a first-stage relaxation heat setting. By increasing the natural stretching ratio, the orientation degree of the filament bundle is improved in the early stage. Then, two-stage hot stretching is used to allow the macromolecules of the filament bundle to continue to orient, resulting in higher strength. This process produces nylon 66 fine denier high-strength fibers with a fineness of 10-40D, a porosity of 5-34f, and a breaking strength of over 8.5g / d. In this patented technology, high-viscosity chips are used as spinning raw materials, which imposes stringent requirements on the viscosity of the raw material chips. The chips need to be thickened to ultra-high viscosity chips, which places high demands on the solid-phase thickening process and increases energy consumption. After melting, the ultra-high viscosity chips have poor fluidity and easily form "gels" in the pipes, which can easily generate fuzz during spinning, reduce spinnability, and lead to short equipment life and increased scrap rate. At the same time, the high viscosity of the dry filament at the spinneret makes it difficult to doff the filaments and results in poor operability. In addition, the method of increasing the initial filament orientation by increasing the natural draw ratio to obtain higher strength is easily affected by external factors (spinning speed, spinneret orifice diameter, metering pump efficiency, etc.), making it difficult to continuously and stably control and resulting in poor operability. Two-stage drafting leads to a large tensile gradient on the filament bundle, and rapid stretching makes it difficult for the molecular chains to form a stable orientation structure, resulting in filament breakage or residual stress in the molecular chains, thus affecting the spinnability and physical property uniformity of high-strength filaments. III. Summary of the Invention:

[0004] The technical problem this invention aims to solve is: based on the current development status and existing problems of nylon 66 fine denier fiber preparation processes, this invention provides a method for preparing high-strength, fine denier, high-brightness nylon 66 fully drawn fibers. This invention utilizes conventional spinning-grade chips to increase viscosity into medium-to-high viscosity chips, and employs a three-stage progressive hot drawing process to increase the hot drawing time of the fiber bundle on the drawing rollers, resulting in more complete orientation of the macromolecular chains and higher orientation and crystallinity. Through a two-stage relaxation setting process, the disorientation of the macromolecular chains and the internal stress within the molecular chains are further reduced, ultimately obtaining fibers with a more stable structure and higher orientation degree. The resulting high-strength, fine denier fibers have more uniform physical properties, higher breaking strength and its retention rate, and extend the service life of the equipment, thereby achieving continuous and stable production of high-strength, fine denier nylon 66 fibers.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for preparing high-strength, fine-denier, high-brightness nylon 66 fully drawn fiber, the method comprising the following steps:

[0007] a. Solid-phase thickening: Nylon 66 spinning grade chips with a relative viscosity of 2.4 to 2.6 are subjected to solid-phase thickening to obtain Nylon 66 medium-high viscosity chips with a water content of ≤300ppm and a relative viscosity of 3.0 to 3.2;

[0008] b. Melt extrusion: The high-viscosity Nylon 66 chips obtained in step a are fed into a screw extruder for melt extrusion, with the temperature of each zone of the screw being 270-310℃.

[0009] c. High-pressure spinning: The melt extruded in step b enters the spinning box through a melt pipe at a temperature of 285-300℃, and is quantitatively injected into the spinning assembly by a metering pump, and is ejected from the spinneret of the assembly to form a filament bundle;

[0010] d. Cooling and molding: The molten stream sprayed in step c is first passed through a slow cooler with the temperature set at 220-250℃, and then cooled by side blowing air. After cooling, it forms nascent fiber bundles.

[0011] e. Bundling and oiling: The nascent fiber bundles obtained in step d are oiled with crude oil through an oil nozzle, and the amount of oil adhering is controlled to be 0.5-1.5%;

[0012] f. Stretching and shaping: The bundled and oiled filaments from step e are subjected to stretching and shaping treatment;

[0013] The drawing process involves a set of feed rollers for pre-stretching and six pairs of hot rollers for drawing and shaping. This includes three stages of hot drawing and two stages of relaxation hot shaping, with a total draw ratio of 3.8 to 4.8. (Through three stages of drawing, the draw ratio is gradually increased, and the hot drawing residence time of the filament on the hot rollers is increased, thereby improving the orientation of the filament and effectively reducing the stress gradient during the stretching process, increasing the upper limit of stretching, and further improving the breaking strength of the filament.)

[0014] g. Winding: The drawn and shaped filament bundles are wound automatically at a speed of 3000-4000 m / min to obtain high-strength, fine denier, bright nylon 66 fully drawn fibers.

[0015] According to the above-mentioned method for preparing high-strength, fine-denier, high-brightness nylon 66 fully drawn fibers, the thickening step a involves conveying nylon 66 spinning-grade chips to a drying tower for thickening; the solid-phase thickening is performed on the chips at 140–170°C using nitrogen in a counter-current circulation.

[0016] According to the above-mentioned method for preparing high-strength, fine denier, bright nylon 66 fully drawn fibers, during the side-blowing cooling in step d, the temperature is controlled at 15-19°C and the humidity at 60-70%.

[0017] According to the above-described method for preparing high-strength, fine-denier, high-brightness nylon 66 fully drawn fiber, in step f, the feed roller is not heated, and the speed ratio between the feed roller and the first set of hot rollers is 1.01–1.09; the temperature of the first set of hot rollers is 60–70℃, the temperature of the second set of hot rollers is 170–190℃, and the first stage of hot drawing is performed between the second set of hot rollers and the first set of hot rollers, with a speed ratio of 1.3–2.6; the temperature of the third set of hot rollers is 200℃–220℃, and the second stage of hot drawing is performed between the third set of hot rollers and the second set of hot rollers, with a speed ratio of 1.1–1.4; the temperature of the fourth set of hot rollers is 210℃–230℃, and the third stage of hot drawing is performed between the fourth set of hot rollers and the third set of hot rollers, with a speed ratio of 1.2–1.5 (the three-stage progressive hot drawing increases the residence time of the fiber bundle on the hot rollers, making the fiber bundle more fully drawn and more oriented). Okay, this provides more time for polymer molecular chain crystallization, thereby effectively improving the crystallinity of the filament bundle and increasing its breaking strength; the temperature of the fifth group of hot rollers is 205-220℃, and the filament bundle is relaxed and heat-set between the fifth group of hot rollers and the fourth group of hot rollers, with a speed ratio of 0.92-0.99 (the function of the fifth group of hot rollers is to relax and set the filament bundle, reduce the disorientation of the macromolecular chains, and reduce the internal stress of the filament bundle); the temperature of the sixth group of hot rollers is 200-220℃, and the filament bundle is further relaxed and heat-set between the sixth group of hot rollers and the fifth group of hot rollers, with a speed ratio of 0.90-0.95 (the function of the sixth group of hot rollers is to further relax and set the filament bundle, and by controlling the secondary relaxation ratio, control the breaking elongation of the filament bundle, further reduce the disorientation of the macromolecular chains, and obtain high-strength nylon 66 fibers with a more stable molecular structure).

[0018] According to the above-described method for preparing high-strength, fine-denier, high-brightness nylon 66 fully drawn fibers, the total draw ratio in step f is 4.0 to 4.8.

[0019] According to the above-described method for preparing high-strength, fine-denier, high-brightness nylon 66 fully drawn fibers, the winding speed in step g is 3000–3800 m / min.

[0020] The positive and beneficial effects of this invention are:

[0021] 1. This invention uses conventional spinning-grade chips to increase viscosity into medium-high viscosity chips, and employs a three-stage hot drawing process to increase the hot drawing time of the filament bundle on the drawing rollers, resulting in more complete orientation of the macromolecular chains and higher orientation and crystallinity. In addition, a two-stage relaxation setting process further reduces the disorientation of the macromolecular chains and the internal stress of the molecular chains, ultimately obtaining a fiber with a more stable structure and a higher degree of orientation. This results in more uniform physical properties of the high-strength fine denier fibers prepared from these fibers (linear density coefficient of variation ≤1.0%, breaking strength coefficient of variation ≤4.0%, breaking elongation coefficient of variation ≤6.0%), and higher breaking strength and its retention rate, thereby achieving continuous and stable production of high-strength fine denier nylon 66 fibers.

[0022] 2. The technical solution of this invention aims to achieve the same orientation effect for fiber macromolecules, reduce production difficulty and the generation of defective products. It employs a solid-phase thickening process to convert conventional spinning-grade nylon 66 chips into medium-to-high viscosity chips, a multi-stage drawing and heat-setting spinning process to increase the residence time of the fiber bundle on the hot rollers and achieve more thorough drawing and setting, and the use of oil nozzles for crude oil application to improve the uniformity of oil coating on the fiber bundle and increase fiber bundle cohesion. Compared with the conventional two-stage hot drawing and one-stage heat setting process using four pairs of hot rollers and the oiling method using oil rollers, this invention uses six pairs of hot rollers and a three-stage hot drawing and two-stage heat setting process to increase the residence time of the fiber bundle on the hot rollers, resulting in more thorough drawing and setting, thereby improving the orientation degree of macromolecules and obtaining high-strength nylon 66 fine denier fibers with more stable molecular structure and physical properties. Meanwhile, by using spinning-grade chips of conventional viscosity, conventional solid-phase thickening process, and crude oil oiling method with oil nozzles, the total draw ratio is reduced, the uniformity of oil coating on the filament bundle is improved, the fuzziness is reduced, the spinnability is good, energy saving and consumption reduction are achieved, and the operability is good, thereby realizing continuous, stable and large-scale production.

[0023] 3. This invention uses spinning-grade nylon 66 chips with a relative viscosity of 2.4-2.6 as raw material. A conventional solid-phase thickening process is employed to thicken the raw material chips to a relative viscosity of 3.0-3.2. The thickened chips are then melt-extruded using a screw extruder. A six-pair hot roller stretching and setting process, consisting of a set of feeding rollers, three-stage hot stretching, and two-stage relaxation setting, along with crude oil application via oil nozzles, is used to improve the uniformity of oil application on the filament bundle and its residence time on the hot rollers. This increases the cohesion of the filament bundle, allowing for more thorough stretching and setting, thereby improving the fiber orientation and obtaining high-strength nylon 66 fine denier fibers with a more stable molecular structure and more uniform physical properties. The total denier of the filament bundle is 40-90D, the number of pores is 10-68f, the linear density variation coefficient is ≤1.0%, the breaking strength variation coefficient is ≤4.0%, the breaking elongation variation coefficient is ≤6.0%, and the breaking strength is ≥8.7g / D. After six months of storage, the breaking strength retention rate is ≥97%.

[0024] 4. The high-strength nylon 66 fine denier fiber prepared by this invention has the strength to meet the requirements of high-end clothing fields such as windbreakers, parachutes, ropes, tents, sleeping bags and other special fields for the use of high-strength and wear-resistant nylon 66 fiber, breaking the foreign technology monopoly. IV. Detailed Implementation Methods:

[0025] The present invention will be further illustrated below with reference to the embodiments, but this does not limit the scope of protection of the technical solution of the present invention.

[0026] Example 1:

[0027] The present invention discloses a method for preparing high-strength, fine-denier 90D / 68f nylon 66 fully drawn fibers, the detailed steps of which are as follows:

[0028] a. Solid-phase thickening: High-gloss Nylon 66 chips with a relative viscosity of 2.4 (sulfuric acid method) are fed into a drying tower for thickening. The lower part of the drying tower is supplied with a flow rate of 105 Nm³ at a temperature of 156°C. 3 The nitrogen gas was used for countercurrent circulation drying at a pressure of 4.0 kPa and a viscosity-enhancing time of 28 h to obtain nylon 66 medium-high viscosity chips with a water content of 300 ppm and a relative viscosity of 3.0 (sulfuric acid method).

[0029] b. Melt extrusion: The high-viscosity Nylon 66 chips obtained in step a are fed into a screw extruder for melt extrusion. The screw heating area is divided into five heating zones: the temperature of the first zone is 303℃, the temperature of the second zone is 298℃, the temperature of the third zone is 297℃, the temperature of the fourth zone is 295℃, and the temperature of the fifth zone is 294℃.

[0030] c. High-pressure spinning: The melt extruded in step b enters the spinning box through a melt pipeline at a temperature of 293°C, and is quantitatively injected into the spinning assembly by a metering pump, and is ejected from the spinneret of the assembly to form a filament bundle; the spinning box has 1 position / box and 8 heads / position;

[0031] d. Cooling and forming: The molten stream sprayed out after spinning in step c is first passed through a slow cooler with the temperature set at 230°C, and then cooled by side blowing (side blowing temperature is 18°C ​​and humidity is 68%). After cooling, it forms a nascent fiber bundle.

[0032] e. Bundling and oiling: The nascent fiber bundles obtained in step d are oiled with crude oil through an oil nozzle, and the oil content is controlled at 1.2%.

[0033] f. Stretching and shaping: The bundled and oiled filaments from step e are subjected to stretching and shaping treatment;

[0034] The drawing process involves a set of feed rollers for pre-stretching and six pairs of hot rollers for drawing and shaping, including three-stage hot drawing and two-stage relaxation hot shaping, with a total draw ratio of 4.2 (through three-stage drawing, the draw ratio is gradually increased, the hot drawing residence time of the filament on the hot rollers is increased, thereby improving the orientation of the filament and effectively reducing the stress gradient during the stretching process, increasing the upper limit of stretching, and further improving the breaking strength of the filament).

[0035] During the stretching and shaping process, the feed roller is not heated, and the speed ratio between the feed roller and the first set of hot rollers is 1.02. The temperature of the first set of hot rollers is 60℃, the temperature of the second set of hot rollers is 175℃, and the first stage of hot stretching is performed between the second set of hot rollers and the first set of hot rollers at a speed ratio of 1.7. The temperature of the third set of hot rollers is 205℃, and the second stage of hot stretching is performed between the third set of hot rollers and the second set of hot rollers at a speed ratio of 1.2. The temperature of the fourth set of hot rollers is 218℃, and the third stage of hot stretching is performed between the fourth set of hot rollers and the third set of hot rollers at a speed ratio of 1.3. (This three-stage progressive hot stretching increases the residence time of the filament on the hot rollers, resulting in more complete hot stretching and better orientation of the filament, providing more time for polymer molecular chain crystallization.) The fifth group of hot rollers, with a temperature of 215℃, performs relaxation heat setting on the filament bundle between the fifth and fourth groups at a speed ratio of 0.98 (the fifth group of hot rollers relaxes and sets the filament bundle, reducing the disorientation of macromolecular chains and reducing internal stress in the filament bundle); the sixth group of hot rollers, with a temperature of 210℃, further relaxes and sets the filament bundle between the sixth and fifth groups at a speed ratio of 0.93 (the sixth group of hot rollers further relaxes and sets the filament bundle, controlling the breaking elongation of the filament bundle by controlling the secondary relaxation ratio, further reducing the disorientation of macromolecular chains, and obtaining high-strength nylon 66 fiber with a more stable molecular structure).

[0036] g. Winding: The drawn and shaped filament bundles are wound automatically at a speed of 3150m / min. After winding, high-strength, fine denier 90D / 68f nylon 66 fully drawn fibers with a bright appearance are obtained.

[0037] According to the test results, the high-strength fine denier bright 90D / 68f nylon 66 fully drawn fiber prepared in this embodiment has a breaking strength of 9.2 g / D, a linear density coefficient of variation of 0.97%, a breaking strength coefficient of variation of 3.9%, and a breaking elongation coefficient of variation of 5.5%; after being stored for half a year, its breaking strength retention rate is 97.3%.

[0038] Example 2:

[0039] The present invention discloses a method for preparing high-strength, fine-denier 75D / 34f nylon 66 fully drawn fibers, the detailed steps of which are as follows:

[0040] a. Solid-phase thickening: High-gloss Nylon 66 chips with a relative viscosity of 2.45 (sulfuric acid method) are fed into a drying tower for thickening. The lower part of the drying tower is supplied with a flow rate of 110 Nm³ at a temperature of 158°C. 3 The nitrogen gas was used for countercurrent circulation drying at a pressure of 4.5 kPa and a viscosity-enhancing time of 26 h to obtain nylon 66 medium-high viscosity chips with a water content of 250 ppm and a relative viscosity of 3.1 (sulfuric acid method).

[0041] b. Melt extrusion: The high-viscosity Nylon 66 chips obtained in step a are fed into a screw extruder for melt extrusion. The screw heating area is divided into five heating zones: the temperature of the first zone is 300℃, the temperature of the second zone is 295℃, the temperature of the third zone is 293℃, the temperature of the fourth zone is 292℃, and the temperature of the fifth zone is 291℃.

[0042] c. High-pressure spinning: The melt extruded in step b enters the spinning box through a melt pipeline at a temperature of 290°C, and is quantitatively injected into the spinning assembly by a metering pump, and is ejected from the spinneret of the assembly to form a filament bundle; the spinning box has 1 position / box and 8 heads / position;

[0043] d. Cooling and shaping: The molten stream sprayed out after spinning in step c is first passed through a slow cooler with the temperature set at 225°C, and then cooled by side blowing (side blowing temperature is 17°C and humidity is 66%). After cooling, it forms nascent fiber bundles.

[0044] e. Bundling and oiling: The nascent fiber bundles obtained in step d are oiled with crude oil through an oil nozzle, and the oil content is controlled to be 1.0%.

[0045] f. Stretching and shaping: The bundled and oiled filaments from step e are subjected to stretching and shaping treatment;

[0046] The drawing process involves a set of feed rollers for pre-stretching and six pairs of hot rollers for drawing and shaping, including three-stage hot drawing and two-stage relaxation hot shaping, with a total draw ratio of 4.3 (through three-stage drawing, the draw ratio is gradually increased, the hot drawing residence time of the filament on the hot rollers is increased, thereby improving the orientation of the filament and effectively reducing the stress gradient during the stretching process, increasing the upper limit of stretching, and further improving the breaking strength of the filament).

[0047] During the stretching and shaping process, the feed roller is not heated, and the speed ratio between the feed roller and the first set of hot rollers is 1.03. The temperature of the first set of hot rollers is 60℃, the temperature of the second set of hot rollers is 170℃, and the first stage of hot stretching is performed between the second set of hot rollers and the first set of hot rollers at a speed ratio of 1.8. The temperature of the third set of hot rollers is 200℃, and the second stage of hot stretching is performed between the third set of hot rollers and the second set of hot rollers at a speed ratio of 1.1. The temperature of the fourth set of hot rollers is 210℃, and the third stage of hot stretching is performed between the fourth set of hot rollers and the third set of hot rollers at a speed ratio of 1.2. (This three-stage progressive hot stretching increases the residence time of the filament on the hot rollers, resulting in more complete hot stretching and better orientation of the filament, providing more time for polymer molecular chain crystallization.) The fifth group of hot rollers, at a temperature of 205℃, further relaxes and heat-sets the filament bundle between itself and the fourth group, with a speed ratio of 0.96 (the fifth group of hot rollers relaxes and sets the filament bundle, reducing the disorientation of macromolecular chains and reducing internal stress). The sixth group of hot rollers, also at 205℃, further relaxes and heat-sets the filament bundle between itself and the fifth group, with a speed ratio of 0.92 (the sixth group of hot rollers further relaxes and sets the filament bundle; by controlling the secondary relaxation ratio, the breaking elongation of the filament bundle is controlled, further reducing the disorientation of macromolecular chains and obtaining high-strength nylon 66 fiber with a more stable molecular structure).

[0048] g. Winding: The drawn and shaped filament bundles are wound automatically at a speed of 3350m / min. After winding, high-strength, high-denier 75D / 34f nylon 66 fully drawn fibers are obtained.

[0049] According to the test results, the high-strength fine denier 75D / 34f nylon 66 fully drawn fiber prepared in this embodiment has a breaking strength of 9.0 g / D, a linear density coefficient of variation of 0.94%, a breaking strength coefficient of variation of 3.6%, and a breaking elongation coefficient of variation of 5.1%; after being stored for half a year, its breaking strength retention rate is 97.8%.

[0050] Example 3:

[0051] The present invention discloses a method for preparing high-strength, fine-denier 40D / 10f nylon 66 fully drawn fibers, the detailed steps of which are as follows:

[0052] a. Solid-phase thickening: High-gloss Nylon 66 chips with a relative viscosity of 2.6 (sulfuric acid method) are fed into a drying tower for thickening. The lower part of the drying tower is supplied with a flow rate of 115 Nm³ at a temperature of 160℃. 3 The nitrogen gas was used for countercurrent circulation drying at a pressure of 5.0 kPa and a viscosity-enhancing time of 24 h to obtain nylon 66 medium-high viscosity chips with a water content of 230 ppm and a relative viscosity of 3.2 (sulfuric acid method).

[0053] b. Melt extrusion: The high-viscosity Nylon 66 chips obtained in step a are fed into a screw extruder for melt extrusion. The screw heating area is divided into five heating zones: the temperature of the first zone is 302℃, the temperature of the second zone is 298℃, the temperature of the third zone is 296℃, the temperature of the fourth zone is 293℃, and the temperature of the fifth zone is 291℃.

[0054] c. High-pressure spinning: The melt extruded in step b enters the spinning box through a melt pipeline at a temperature of 290°C, and is quantitatively injected into the spinning assembly by a metering pump, and is ejected from the spinneret of the assembly to form a filament bundle; the spinning box has 1 position / box and 8 heads / position;

[0055] d. Cooling and shaping: The molten stream sprayed out after spinning in step c is first passed through a slow cooler with the temperature set at 221°C, and then cooled by side blowing (side blowing temperature is 15°C and humidity is 64%). After cooling, it forms nascent fiber bundles.

[0056] e. Bundling and oiling: The nascent fiber bundles obtained in step d are oiled with crude oil through an oil nozzle, and the oil content is controlled at 0.8%;

[0057] f. Stretching and shaping: The bundled and oiled filaments from step e are subjected to stretching and shaping treatment;

[0058] The drawing process involves a set of feed rollers for pre-stretching and six pairs of hot rollers for drawing and shaping, including three-stage hot drawing and two-stage relaxation hot shaping, with a total draw ratio of 4.6 (through three-stage drawing, the draw ratio is gradually increased, the hot drawing residence time of the filament on the hot rollers is increased, thereby improving the orientation of the filament and effectively reducing the stress gradient during the stretching process, increasing the upper limit of stretching, and further improving the breaking strength of the filament).

[0059] During the stretching and shaping process, the feed roller is not heated, and the speed ratio between the feed roller and the first set of hot rollers is 1.04. The temperature of the first set of hot rollers is 65℃, the temperature of the second set of hot rollers is 173℃, and the first stage of hot stretching is performed between the second set of hot rollers and the first set of hot rollers, with a speed ratio of 1.92. The temperature of the third set of hot rollers is 212℃, and the second stage of hot stretching is performed between the third set of hot rollers and the second set of hot rollers, with a speed ratio of 1.23. The temperature of the fourth set of hot rollers is 213℃, and the third stage of hot stretching is performed between the fourth set of hot rollers and the third set of hot rollers, with a speed ratio of 1.35. (This three-stage progressive hot stretching increases the residence time of the filament on the hot rollers, resulting in more complete hot stretching and better orientation of the filament, providing more space for polymer molecular chain crystallization.) The process involves several steps: First, the temperature of the fifth group of hot rollers is 212℃. The fifth group of hot rollers, along with the fourth group, performs relaxation heat setting on the filaments at a speed ratio of 0.95. (The fifth group of hot rollers relaxes and sets the filaments, reducing the disorientation of macromolecular chains and decreasing internal stress.) Second, the temperature of the sixth group of hot rollers is 207℃. The sixth group of hot rollers, along with the fifth group, further relaxes and sets the filaments at a speed ratio of 0.91. (The sixth group of hot rollers further relaxes and sets the filaments, controlling the breaking elongation by controlling the secondary relaxation ratio, further reducing the disorientation of macromolecular chains, and obtaining high-strength nylon 66 fibers with a more stable molecular structure.)

[0060] g. Winding: The drawn and shaped filament bundles are wound automatically at a speed of 3600m / min. After winding, high-strength, fine denier 40D / 10f nylon 66 fully drawn fibers with a bright appearance are obtained.

[0061] According to the test results, the high-strength fine denier 40D / 10f nylon 66 fully drawn fiber prepared in this embodiment has a breaking strength of 8.8 g / D, a linear density coefficient of variation of 0.90%, a breaking strength coefficient of variation of 3.3%, and a breaking elongation coefficient of variation of 4.8%; after being placed for half a year, its breaking strength retention rate is 98.1%.

Claims

1. A method for preparing high-strength, fine-denier, high-brightness nylon 66 fully drawn fiber, characterized in that, The preparation method includes the following steps: a. Solid-phase viscosity enhancement: Nylon 66 spinning grade chips with a relative viscosity of 2.4 to 2.6 are transported to a drying tower and solid-phase viscosity enhancement is performed on the chips using nitrogen countercurrent circulation at 140 to 170°C to obtain medium-high viscosity Nylon 66 chips with a water content of ≤300ppm and a relative viscosity of 3.0 to 3.

2. b. Melt extrusion: The high-viscosity Nylon 66 chips obtained in step a are fed into a screw extruder for melt extrusion, with the temperature of each zone of the screw being 270-310℃. c. High-pressure spinning: The melt extruded in step b enters the spinning box through a melt pipe at a temperature of 285-300℃, and is quantitatively injected into the spinning assembly by a metering pump, and is ejected from the spinneret of the assembly to form a filament bundle; d. Cooling and molding: The molten stream sprayed in step c is first passed through a slow cooler with the temperature set at 220-250°C, and then cooled by side blowing air, with the temperature controlled at 15-19°C and the humidity at 60-70%. After cooling, nascent fiber bundles are formed. e. Bundling and oiling: The nascent fiber bundles obtained in step d are oiled with crude oil through an oil nozzle, and the oil content is controlled at 0.5-1.5%; f. Stretching and shaping: The bundled and oiled filaments from step e are subjected to stretching and shaping treatment; The drawing process involves a set of feed rollers for pre-stretching and six pairs of hot rollers for drawing and shaping, including three-stage hot drawing and two-stage relaxation hot shaping, with a total drawing ratio of 3.8 to 4.

8. The feed roll is not heated, and the speed ratio between the feed roll and the first set of hot rolls is 1.01–1.09; the temperature of the first set of hot rolls is 60–70℃, the temperature of the second set of hot rolls is 170–190℃, and the second set of hot rolls and the first set of hot rolls perform the first stage of hot drawing with a speed ratio of 1.3–2.6; the temperature of the third set of hot rolls is 200℃–220℃, and the third set of hot rolls and the second set of hot rolls perform the second stage of hot drawing with a speed ratio of 1.1–1.4; the temperature of the fourth set of hot rolls… The temperature is 210℃~230℃. The third stage of hot drawing is performed between the fourth and third groups of hot rollers, with a speed ratio of 1.2~1.

5. The temperature of the fifth group of hot rollers is 205~220℃. The fifth group of hot rollers and the fourth group of hot rollers perform relaxation heat setting on the filament bundle, with a speed ratio of 0.92~0.

99. The temperature of the sixth group of hot rollers is 200~220℃. The sixth group of hot rollers and the fifth group of hot rollers further relax and heat set the filament bundle, with a speed ratio of 0.90~0.

95. g. Winding: The drawn and shaped filament bundles are wound automatically at a speed of 3000-3800 m / min. After winding, high-strength fine denier bright nylon 66 fully drawn fibers with a total denier of 40-90D, a hole number of 10-68f, and a breaking strength ≥8.7g / D are obtained.

2. The method for preparing high-strength, fine-denier, high-brightness nylon 66 fully drawn fiber according to claim 1, characterized in that: In step a, the system pressure inside the drying tower is 4.0–5.0 kPa, and the viscosity-enhancing time is 24–28 h.

3. The method for preparing high-strength, fine-denier, high-brightness nylon 66 fully drawn fiber according to claim 1, characterized in that: The linear density variation coefficient of the high-strength fine denier bright nylon 66 fully drawn fiber described in step g is ≤1.0%, the breaking strength variation coefficient is ≤4.0%, the breaking elongation variation coefficient is ≤6.0%, and the breaking strength retention rate is ≥97% after being placed for half a year.