Polyacrylonitrile pre-oxidized fiber yarn, its preparation method and application

Abstract

This invention relates to the field of textile technology, and more particularly to a pre-oxidized polyacrylonitrile fiber yarn, its preparation method, and its application. The invention provides a method for preparing pre-oxidized polyacrylonitrile fiber yarn, comprising the following steps: sequentially subjecting pre-oxidized polyacrylonitrile fibers to opening and cleaning, carding, three-stage drawing, and vortex spinning to obtain the pre-oxidized polyacrylonitrile fiber yarn; the three-stage drawing is suitable for processing single-specification pre-oxidized polyacrylonitrile fibers, and also for blending multi-specification pre-oxidized polyacrylonitrile fibers. The preparation method provided by this invention involves scientifically sound and highly operable optimization of air-jet vortex spinning process parameters, which can improve the structural stability of the pre-oxidized polyacrylonitrile fiber yarn and significantly enhance the anti-pilling and anti-fuzzing properties of the fabric; it avoids additional processing steps and has a lower cost.

Description

Technical Field

[0001] This invention relates to the field of textile technology, and in particular to a pre-oxidized polyacrylonitrile fiber yarn, its preparation method, and its application. Background Technology

[0002] As a precursor material for carbon fiber, pre-oxidized polyacrylonitrile fiber can transform the linear molecular chains of polyacrylonitrile precursor fibers into a heat-resistant trapezoidal structure through gradient heating and oxidation treatment. This results in excellent properties such as high temperature resistance, flame retardancy, and corrosion resistance, making it a promising candidate for applications in aerospace, construction engineering, battery manufacturing, and protective equipment. However, pre-oxidized polyacrylonitrile fiber is brittle, has a smooth surface, and poor cohesion, leading to increased fuzzing during spinning. This results in woven fabrics being highly susceptible to pilling and fuzzing during use, severely impacting the product's appearance, lifespan, and suitability for high-end applications. Current solutions for improving anti-pilling properties of fibers primarily focus on pretreatment, blending, or finishing processes. These methods not only increase production steps and processing costs but may also damage the intrinsic properties of the fiber. Furthermore, they only offer passive optimization at the process level and cannot actively control the fiber cohesion at the yarn structure design level. Therefore, it is necessary to explore a technical path that integrates process parameter optimization with structural design to address these technical challenges at their source. Compared to traditional spinning technologies such as ring spinning and rotor spinning, air-jet vortex spinning, as a novel and highly efficient spinning technology, utilizes a high-speed rotating airflow to rapidly twist fibers into yarn. It boasts advantages such as high production efficiency, less yarn hairiness, and uniform yarn evenness. Furthermore, its airflow field can drive radial directional transfer of fibers, providing a feasible path for optimizing the spinning process and self-assembly of gradient structures in polyacrylonitrile pre-oxidized fibers. Currently, research and industrial applications of air-jet vortex spinning are mostly focused on cotton, viscose, or polyester fibers, with insufficient research on polyacrylonitrile pre-oxidized fibers. In particular, there is a lack of systematic optimization schemes for key process parameters of air-jet vortex spinning, and no reports on related technologies that combine fiber characteristics with the airflow field of vortex spinning to achieve gradient structure design and self-assembly of yarns. Existing technologies can only achieve simple spinning of single-specification polyacrylonitrile pre-oxidized fibers, making it difficult to enhance the yarn's anti-pilling and mechanical properties through structural design, resulting in a significant bottleneck in improving yarn performance.

[0003] In summary, there is an urgent need for a synergistic technology that integrates the inherent properties of pre-oxidized polyacrylonitrile fibers with the optimization of jet vortex spinning process parameters and the precise design of yarn structure, in order to achieve stable yarn structure and efficient fiber cohesion, thereby improving the anti-pilling performance of fabrics from the source. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a pre-oxidized polyacrylonitrile fiber yarn, its preparation method and application, with the aim of improving the anti-pilling and anti-fuzzing properties of pure spun polyacrylonitrile pre-oxidized fiber yarn and fabric.

[0005] This invention provides a method for preparing pre-oxidized polyacrylonitrile fiber yarn, comprising the following steps:

[0006] Polyacrylonitrile pre-oxidized fiber is subjected to opening and cleaning, carding, three-stage drawing and vortex spinning in sequence to obtain polyacrylonitrile pre-oxidized fiber yarn.

[0007] The three-layer drawing process is suitable for processing single-specification polyacrylonitrile pre-oxidized fibers, and also suitable for blending multi-specification polyacrylonitrile pre-oxidized fibers.

[0008] Preferably, the vortex spinning treatment employs an air-jet vortex spinning process with the following process parameters:

[0009] The spinning speed is 320~370 m / min, the nozzle air pressure is 0.48~0.55 MPa, the feed ratio is 0.96~1.00, the distance from the front roller to the spindle is 18~20 mm, the feed sliver weight is 16~18 g / 5m, the front drafting zone distance of the drafting device is 38~44 mm, the rear drafting zone distance is 43~48 mm, the total draft ratio is 120~230 times, the main draft ratio is 30~32 times, the rear draft ratio is 3.0~3.2 times, and the take-up ratio is 1.0~1.02.

[0010] The performance indicators of the pre-oxidized polyacrylonitrile fiber yarn are: hairiness index H value ≤ 1.2, breaking strength ≥ 5.8 cN / tex, and breaking elongation ≥ 8.5%.

[0011] Preferably, the polyacrylonitrile pre-oxidized fiber is a single-specification pure spun polyacrylonitrile pre-oxidized fiber, and the resulting polyacrylonitrile pre-oxidized fiber yarn is a pure spun polyacrylonitrile pre-oxidized fiber yarn with no gradient structure.

[0012] The fineness of the single-specification polyacrylonitrile pre-oxidized fiber is 1.1~2.0 dtex, and the length is 38~51 mm;

[0013] The performance indicators of the single-specification polyacrylonitrile pre-oxidized fiber are: breaking strength ≥6.0cN / tex, breaking elongation ≥9.0%, and impurity content ≤0.5%.

[0014] Preferably, the polyacrylonitrile pre-oxidized fiber is a pure spun polyacrylonitrile pre-oxidized fiber with three specifications of gradient design, and the resulting polyacrylonitrile pre-oxidized fiber yarn is a pure spun polyacrylonitrile pre-oxidized fiber yarn with a three-layer gradient wrapping structure, which consists of an inner core layer, an intermediate wrapping layer, and an outer layer from the inside out.

[0015] In the three-layer gradient wrapping structure pure spun polyacrylonitrile pre-oxidized fiber yarn, the inner core layer accounts for 30%~50% of the mass, the middle wrapping layer accounts for 25%~35% of the mass, and the outer layer accounts for 20%~40% of the mass.

[0016] The fineness of the inner core fiber is 1.5~2.0 dtex, the length is 38~42 mm, the initial modulus is ≥90 cN / dtex, and the breaking strength is ≥6.2 cN / tex;

[0017] The intermediate entanglement layer fiber has a fineness of 1.2~1.4 dtex, a length of 44~48 mm, an initial modulus of 75~85 cN / dtex, and a breaking strength ≥6.0 cN / tex;

[0018] The outer layer fibers have a fineness of 1.1~1.2 dtex, a length of 50~51 mm, an initial modulus of 60~70 cN / dtex, and a breaking strength ≥5.8 cN / tex.

[0019] Preferably, the cotton opening and cleaning process is as follows:

[0020] The pre-oxidized polyacrylonitrile fibers were sequentially processed through an FA002 cotton grabber, an FA029 cotton blender, an FA106 cotton opener, and an FA171 cotton box. During the processing, the relative humidity was controlled above 65%, and an antistatic agent with a mass concentration of 2.5% to 3% was sprayed by atomization. The beater speed of the FA002 cotton grabber was 700 to 720 r / min. The FA106 cotton opener used a carding needle beater with a beater speed of 420 to 480 r / min.

[0021] The cotton drop spacing is configured as follows: from the inlet to the outlet, it is 11~12 mm, 9~10 mm, and 7~8 mm respectively.

[0022] The spacing between the comb needles and dust bars is: 16~20 mm at the inlet and 20~24 mm at the outlet.

[0023] Preferably, the carding process is as follows:

[0024] The pre-oxidized polyacrylonitrile fibers after opening and cleaning are combed by a carding machine to obtain slivers.

[0025] The carding machine has a working angle of 75~80°, a feed plate height of 10~15 mm, a licker-in speed of 700~750 rpm, a cylinder speed of 250~280 rpm, a doffer speed of 18~22 rpm, and a flat plate speed of 50~80 mm / min.

[0026] The carding machine is equipped with a front fixed cover and a rear fixed cover;

[0027] The spacing between the front fixed cover plate and the cylinder is 8-10 filaments, 7-9 filaments, and 6-8 filaments respectively along the fiber travel direction;

[0028] The spacing between the rear fixed cover and the cylinder is 10-12 filaments, 11-13 filaments, and 12-14 filaments respectively along the fiber travel direction.

[0029] Preferably, the three-pass rolling process is as follows:

[0030] The first drawing process uses a TMFD81S type drawing frame with a drawing speed of 150~200 m / min, combining 6 slivers, a total draft ratio of 6~8 times, a rear draft ratio of 1.7~2.0 times, and a front draft interval of 12~15 mm and a rear draft interval of 20~25 mm for the drawing frame drafting device.

[0031] The second drawing process uses a TMFD81S type drawing frame with a drawing speed of 150~200 m / min, combining 6~8 slivers, a total draft ratio of 6~9 times, a rear draft ratio of 1.4~1.6 times, and a front draft interval of 12~15 mm and a rear draft interval of 20~25 mm for the drawing frame drafting device.

[0032] The third drawing frame uses a TMFD81L type drawing frame with a self-adjusting leveling device. The output speed is 150~200 m / min, 6~8 slivers are combined, the total draft ratio is 6~9 times, the rear draft ratio is 1.1~1.2 times, the front drafting interval of the drawing frame drafting device is 12~15 mm, and the rear drafting interval is 20~25 mm.

[0033] The present invention also provides a pre-oxidized polyacrylonitrile fiber yarn prepared by the preparation method described above.

[0034] This invention also provides a method for preparing polyacrylonitrile pre-oxidized fiber fabric, comprising the following steps:

[0035] The polyacrylonitrile pre-oxidized fiber yarn of claim 8 is woven to obtain a polyacrylonitrile pre-oxidized fiber fabric.

[0036] Preferably, the weaving process is performed using an air-jet loom, and the process parameters are as follows:

[0037] The warp tension is 2.30~2.50 kN, the weft insertion tension is 5~8 cN, the shedding time is 280°~290°, the weft insertion time is 85°~240° for the main jet and 90°~260° for the auxiliary jet, the heddle leveling time is 300°~310°, the machine speed is 500~550 r / min, and the relative humidity is controlled at 64%~70%.

[0038] The present invention also provides a polyacrylonitrile pre-oxidized fiber fabric prepared by the preparation method described above.

[0039] The preparation method provided by this invention involves the optimization of air jet vortex spinning process parameters in a scientific, reasonable and highly operable manner, which can improve the structural stability of polyacrylonitrile pre-oxidized fiber yarn and significantly enhance the anti-pilling and anti-fuzzing properties of the fabric; it avoids additional processing steps and has a lower cost.

[0040] The core of this invention lies in the synergistic innovation of optimizing the process parameters of air-jet vortex spinning and precisely designing the yarn gradient structure, aiming to improve the anti-pilling performance of pure spun polyacrylonitrile pre-oxidized fiber yarns and fabrics. This invention addresses the inherent characteristics of polyacrylonitrile pre-oxidized fibers, such as high brittleness and weak cohesion, by synergistically controlling key process parameters of air-jet vortex spinning, including spinning speed, nozzle air pressure, feed ratio, distance from the front roller to the spindle, and drafting distance. Simultaneously, it designs a self-assembled three-layer gradient wrapping structure adapted to the vortex spinning airflow field. By adapting the process to fiber characteristics and strengthening yarn cohesion through structural enhancement, it addresses the technical pain points of excessive fiber hairiness and easy pilling in fabrics from the source. After optimization, the hairiness index H value of the polyacrylonitrile pre-oxidized fiber yarn is ≤1.2, and the anti-pilling performance of the fabric is ≥4 levels, while maintaining the high-efficiency production advantages of air-jet vortex spinning without adding extra processes. It is suitable for fields such as fire emergency response, special protection, and new energy vehicles. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] This invention provides a method for preparing pre-oxidized polyacrylonitrile fiber yarn, comprising the following steps:

[0043] Polyacrylonitrile pre-oxidized fiber is subjected to opening and cleaning, carding, three-stage drawing and vortex spinning processes in sequence to obtain polyacrylonitrile pre-oxidized fiber yarn.

[0044] The three-layer drawing process is suitable for processing single-specification polyacrylonitrile pre-oxidized fibers, and also suitable for blending multi-specification polyacrylonitrile pre-oxidized fibers.

[0045] In some embodiments of the present invention, the polyacrylonitrile pre-oxidized fiber is a single-specification pure spun polyacrylonitrile pre-oxidized fiber, and the resulting polyacrylonitrile pre-oxidized fiber yarn is a non-gradient structure pure spun polyacrylonitrile pre-oxidized fiber yarn. The fineness of the single-specification polyacrylonitrile pre-oxidized fiber is 1.1~2.0 dtex, for example 1.2 dtex; the length is 38~51 mm, for example 44 mm. The performance indicators of the single-specification polyacrylonitrile pre-oxidized fiber are: breaking strength ≥6.0 cN / tex, breaking elongation ≥9.0%, and impurity content ≤0.5%.

[0046] In some embodiments of the present invention, the polyacrylonitrile pre-oxidized fiber is a pure spun polyacrylonitrile pre-oxidized fiber of different specifications, specifically a gradient-designed pure spun polyacrylonitrile pre-oxidized fiber of three specifications. The resulting polyacrylonitrile pre-oxidized fiber yarn is a pure spun polyacrylonitrile pre-oxidized fiber yarn with a three-layer gradient wrapping structure, consisting of an inner core layer, an intermediate wrapping layer, and an outer surface layer from the inside out.

[0047] In a three-layer gradient-wound yarn structure, the inner core layer, the middle wrapping layer, and the outer layer are designed in a gradient manner according to their modulus, length, and linear density. Specifically:

[0048] The inner core fiber has a fineness of 1.5~2.0 dtex, e.g., 1.8 dtex; a length of 38~42 mm, e.g., 38 mm; an initial modulus ≥90 cN / dtex, e.g., 92 cN / dtex; and a tensile strength ≥6.2 cN / tex. The intermediate wrapping layer fiber has a fineness of 1.2~1.4 dtex, e.g., 1.4 dtex; a length of 44~48 mm, e.g., 44 mm; an initial modulus of 75~85 cN / dtex, e.g., 80 cN / dtex; and a tensile strength ≥6.0 cN / tex. The outer layer fiber has a fineness of 1.1~1.2 dtex, e.g., 1.1 dtex; a length of 50~51 mm, e.g., 51 mm; an initial modulus of 60~70 cN / dtex, e.g., 65 cN / dtex; and a tensile strength ≥5.8 cN / tex.

[0049] In a three-layer gradient wrapping structure pure spun polyacrylonitrile pre-oxidized fiber yarn, the inner core layer accounts for 30% to 50% of the mass, for example, 40%; the middle wrapping layer accounts for 25% to 35% of the mass, for example, 30%; and the outer layer accounts for 20% to 40% of the mass, for example, 30%.

[0050] Due to the brittleness of polyacrylonitrile pre-oxidized fiber materials, the fiber length needs to be appropriately increased to increase the contact area and cohesion between fibers and reduce the proportion of slipped fibers; selecting low-fineness fibers can improve the strength of air-jet vortex spun yarns; the gradient structure, through the differentiated design of fiber modulus, length, and linear density, adapts to the radial transfer law of fibers in the air-jet vortex spinning air field, and realizes fiber self-assembly and forming.

[0051] In some embodiments of the present invention, the cotton opening and cleaning process is as follows:

[0052] The pre-oxidized polyacrylonitrile fibers are sequentially processed through an FA002 cotton grabber, an FA029 cotton blender, an FA106 cotton opener, and an FA171 cotton box. During processing, the relative humidity is controlled above 65%, for example, 66%. Atomized spraying of an antistatic agent at a concentration of 2.5% to 3% (e.g., 2.6%) reduces static electricity caused by the poor hygroscopicity of the pre-oxidized polyacrylonitrile fibers. The antistatic agent can be TN303. The beater speed of the FA002 cotton grabber is 700 to 720 r / min, for example, 720 r / min. Controlling the beater speed reduces fiber damage. The FA106 cotton opener uses a carding beater with a beater speed of 420 to 480 r / min, for example, 480 r / min. Reducing the beater speed decreases fiber damage and improves yarn strength.

[0053] The cotton drop spacing should meet the following requirements: inlet spacing > middle spacing > outlet spacing, with the spacing gradually decreasing to ensure more reasonable impact, stable airflow, and improved opening effect. Specifically, the cotton drop spacing configuration is as follows: from inlet to outlet, it is 11~12mm, 9~10mm, and 7~8mm respectively; specifically, it is 12mm, 9mm, and 7mm respectively.

[0054] The spacing between the comb needles and dust bars is such that the outlet spacing is not less than the inlet spacing, which can better supplement the airflow.

[0055] The spacing between the comb bar and the dust bar is as follows: inlet spacing is 16~20 mm, and outlet spacing is 20~24 mm. Specifically, the spacing configuration of the comb bar is as follows: along the fiber flow direction, the inlet spacing is 18 mm, and the outlet spacing is 22 mm.

[0056] In the cotton opening and cleaning process, adopting the principle of gentle beating and minimal shedding can reduce damage to the fibers.

[0057] In some embodiments of the present invention, the carding process is as follows:

[0058] The pre-oxidized polyacrylonitrile fibers, after opening and cleaning, are carded by a carding machine to obtain sliver. The working angle of the carding machine is 75~80°, for example, 76°; the feed plate is raised by 10~15 mm, for example, 11 mm (raising the feed plate height can reduce the impact on the fibers and reduce fiber damage); the licker-in speed is 700~750 rpm, for example, 710 rpm; the cylinder speed is 250~280 rpm, for example, 255 rpm; the doffer speed is 18~22 rpm, for example, 19 rpm; and the flats speed is 50~80 mm / min, for example, 60 mm / min.

[0059] The carding process employs a low-speed, large-spaced, and gentle carding principle, reducing the speed of the licker-in, cylinder, and flats, and increasing the carding space to reduce damage to the fibers. The reduced speed of the licker-in, cylinder, and flats also reduces the impact on the fibers, thus minimizing fiber damage. The operation utilizes a variable frequency servo motor, which allows for more precise control of the speed of each optional component.

[0060] Increase the spacing between the combing sections to reduce the combing of fibers and minimize fiber damage.

[0061] In a carding machine, the spacing between multiple working covers and the cylinder is distributed in a 10-9-9-9-10 filament pattern from the inlet to the outlet (i.e., the spacing between multiple working covers and the cylinder is 10 filaments, 9 filaments, 9 filaments, 9 filaments and 10 filaments respectively from the fiber flow inlet to the outlet direction). This can improve the fiber carding effect and effectively remove impurities and short fibers from the fibers.

[0062] The carding machine is equipped with a front fixed cover and a rear fixed cover. The distance between the front fixed cover and the cylinder gradually decreases along the fiber travel direction; the distance between the rear fixed cover and the cylinder gradually increases along the fiber travel direction. Specifically, the distance between the front fixed cover and the cylinder is successively 8-10 filaments, 7-9 filaments, and 6-8 filaments along the fiber travel direction, for example, successively 10 filaments, 9 filaments, and 8 filaments. This configuration forms a gradually tightening carding channel, which is conducive to progressive and strong carding of fibers and effectively removes neps. The distance between the rear fixed cover and the cylinder is successively 10-12 filaments, 11-13 filaments, and 12-14 filaments along the fiber travel direction, for example, successively 10 filaments, 11 filaments, and 12 filaments. This configuration forms a gradually widening channel, which is conducive to the smooth transfer of fibers to the doffer and reduces fiber damage. A lower tension drafting ratio is used, such as 1 to 1.05. The purpose of tension drafting is to protect the excellent structure already achieved during the critical stage of forming the cotton web into a sliver.

[0063] Because the fibers have relatively poor cohesion, lower tensile stretching can reduce accidental stretching of the sliver and improve the uniformity of the sliver. Therefore, the quality control indicators for the raw sliver are: impurity content (mass content) ≤1%, for example 0.85% or 0.12%; sliver CV% value ≤2.5%, for example 2.3% or 2.5%; sliver weight unevenness ≤1.5%, for example 1.3% or 1.5%; sliver short fiber content ≤3.0%, for example 2.8% or 3%.

[0064] In some embodiments of the present invention, in the three-stage drawing process, when preparing single-specification yarn (i.e., the non-gradient structure pure spun polyacrylonitrile pre-oxidized fiber yarn mentioned above), it is a single fiber with multiple uniform drafting stages; when preparing gradient structure yarn (i.e., the three-layer gradient wrapping structure pure spun polyacrylonitrile pre-oxidized fiber yarn mentioned above), the inner core layer, the middle wrapping layer, and the outer surface layer sliver are mixed according to the mass ratio of the three layers of fibers and then drawn to achieve uniform blending of fibers of different specifications.

[0065] Specifically, the three-stage rolling process is as follows:

[0066] The first drawing process uses a TMFD81S type drawing frame with an output speed of 150~200 m / min (e.g., 170 m / min). Six slivers are combined, with a total draft ratio of 6~8 times (e.g., 7 times) and a rear draft ratio of 1.7~2.0 times (e.g., 1.8 times). The rear drafting is concentrated to eliminate the front hook. The rear drafting interval of the drawing frame's drafting device is greater than the front drafting interval. Specifically, the front drafting interval of the drawing frame's drafting device is 12~15 mm (e.g., 13 mm), and the rear drafting interval is 20~25 mm (e.g., 22 mm).

[0067] The second drawing process uses a TMFD81S type drawing frame with an output speed of 150~200 m / min (e.g., 170 m / min), combining 6~8 slivers (e.g., 7 slivers), a total draft ratio of 6~9 times (e.g., 8 times), and a rear draft ratio of 1.4~1.6 times (e.g., 1.5 times). The rear drafting interval of the drawing frame's drafting device is greater than the front drafting interval. Specifically, the front drafting interval of the drawing frame's drafting device is 12~15 mm (e.g., 13 mm), and the rear drafting interval is 20~25 mm (e.g., 22 mm).

[0068] The third drawing process uses a TMFD81L type drawing frame, equipped with a self-adjusting leveling device to improve the uniformity of the finished sliver quality. The output speed is 150~200 m / min (e.g., 170 m / min), 6~8 slivers (e.g., 7 slivers) are combined, the total draft ratio is 6~9 times (e.g., 8 times), and the back zone draft ratio is 1.1~1.2 times (e.g., 1.15 times). The third draw uses a smaller back zone draft ratio to reduce the unevenness of the drawn sliver. The back zone drafting distance of the drawing frame's drafting device is larger than the front zone drafting distance. Specifically, the front zone drafting distance of the drawing frame's drafting device is 12~15 mm (e.g., 13 mm), and the back zone drafting distance is 20~25 mm (e.g., 22 mm).

[0069] In the case of preparing three-layer gradient wrapped yarn, the three layers of raw sliver are mixed by the three-stage drawing process.

[0070] After three rolling processes, the cooked strip is obtained.

[0071] In some embodiments of the present invention, the vortex spinning treatment employs an air-jet vortex spinning process with optimized parameters. The spinning speed is reduced based on the characteristics of the fiber to improve yarn strength. An oil spraying device is used to reduce weak twist and improve yarn strength. A small sliver weight is used to reduce accidental drafting and improve yarn evenness. Small-sized nozzles are used to improve yarn strength.

[0072] The sliver is processed using an air-jet vortex spinning machine. Addressing the core characteristics of pre-oxidized polyacrylonitrile fibers—high brittleness and weak cohesion—the spinning speed, nozzle air pressure, feed ratio, front roller to spindle distance, sliver feed weight, drafting zone parameter configuration, and take-up ratio are synergistically optimized to achieve efficient twisting of the fibers into yarn. This optimized parameter setting is applied to both single-gauge yarns and gradient structure yarns. Specific preferred parameters are as follows:

[0073] The spinning speed is 320~370 m / min, such as 350 m / min, 370 m / min, 330 m / min; the nozzle air pressure is 0.48~0.55 MPa, such as 0.48 MPa, 0.53 MPa, 0.51 MPa. The spinning speed of jet vortex spinning directly determines the residence time of fibers in the vortex field of the twisting zone. Within the speed range described in this invention, the fiber wrapping time is longer, the fiber transfer is sufficient, and the wrapping is tight. This not only improves the brittle characteristics of polyacrylonitrile pre-oxidized fibers and avoids the strength reduction caused by the reduction of fibers wrapped in yarn at excessively high speeds, but also maintains the high-efficiency production advantages of jet vortex spinning. For gradient structure yarns, this speed can drive fibers of different specifications to achieve precise radial transfer according to differences in modulus and length, ensuring the straight arrangement of the inner core layer and the effective wrapping of the outer layer. The nozzle air pressure can affect the tangential and axial velocity of the airflow in the nozzle. Within the air pressure range described in this invention, the airflow tangential velocity is relatively large, which can effectively increase the fiber bundle twist and yarn strength, while avoiding irregular wrapping and pull-out of free-end fibers caused by excessive atmospheric pressure, which would lead to a decrease in yarn strength. This air pressure can provide a stable rotating airflow for gradient structure fibers, achieving tight cohesion of the three-layer structure.

[0074] The feed ratio is 0.96~1.00, for example, 0.98 or 0.97. The feed ratio is the ratio of the linear speed of the output roller to that of the front roller. When the feed ratio is appropriately reduced, the tension in the spinning section decreases, the number of wrapped fibers increases, and the yarn cohesion effect can be optimized to some extent; however, if the feed ratio is too low, it is not conducive to yarn output and may even increase the risk of yarn breakage during the spinning process, deteriorating the yarn quality. The feed ratio described in this invention can ensure that the fibers receive a stable and sufficient supply in the twisting zone, avoiding loose yarn structure caused by feeding imbalance.

[0075] The distance from the front roller to the spindle is 18-20 mm, such as 18.5 mm or 19 mm. This distance range improves the cohesion between fibers. If the distance is too small, the ends of the fibers are easily bound, making it difficult to achieve a free end state, resulting in a lower proportion of wrapped fibers and ultimately insufficient yarn twist strength. If the distance is too large, the number of free-end fibers increases, the wrapping effect is enhanced, and the twist strength is simultaneously improved, making the yarn performance closer to true twist yarn; however, in this state, the fibers are difficult to effectively constrain, easily leading to loose and deteriorated yarn structure and a significant increase in fiber shedding.

[0076] The feed weight is 16-18 g / 5m, for example, 18 g / 5m. This invention uses a lighter feed weight, which can reduce spinning draft stress and improve yarn quality.

[0077] The parameters for the draw zone are configured as follows:

[0078] The rear drafting zone distance of the drafting device is greater than the front drafting zone distance (specifically, the front drafting zone distance of the drafting device is 38~44 mm, for example 41 mm; the rear drafting zone distance is 43~48 mm, for example 45 mm), the total drafting ratio is 120~230 times, for example 180 times, 183 times, 186 times; the main drafting ratio is 30~32 times, for example 30 times, 31 times, 32 times; and the rear drafting ratio is 3.0~3.2 times, for example 3 times, 3.1 times.

[0079] The take-up ratio is 1.0 to 1.02, such as 1.005 or 1.01. The take-up ratio range described in this invention can ensure the tightness and uniformity of yarn take-up, and improve the yarn forming quality and subsequent weaving adaptability.

[0080] This invention also provides a pre-oxidized polyacrylonitrile fiber yarn prepared by the method described above. Specifically, it can be a pure spun pre-oxidized polyacrylonitrile fiber yarn.

[0081] In some embodiments of the present invention, the polyacrylonitrile pre-oxidized fiber yarn is a single-gauge pure spun polyacrylonitrile pre-oxidized fiber yarn with no gradient structure (i.e., the yarn with no gradient structure mentioned above) or a pure spun polyacrylonitrile pre-oxidized fiber yarn with a three-layer gradient wrapping structure (i.e., the yarn with a three-layer gradient wrapping structure mentioned above); the performance indicators are: hairiness index H value ≤ 1.2, breaking strength ≥ 5.8 cN / tex, and breaking elongation ≥ 8.5%.

[0082] This invention also provides a method for preparing polyacrylonitrile pre-oxidized fiber fabric, comprising the following steps:

[0083] The polyacrylonitrile pre-oxidized fiber yarn described above is woven to obtain polyacrylonitrile pre-oxidized fiber fabric.

[0084] The weaving process employs an air-jet loom with the following specific parameters: warp tension of 2.30~2.50 kN (e.g., 2.40 kN); weft insertion tension of 5~8 cN (e.g., 6 cN); shedding time of 280°~290° (e.g., 285°); weft insertion time: main jet 85°~240° (e.g., 162.5°), auxiliary jet 90°~260° (e.g., 175°); heddle leveling time: 300°~310° (e.g., 305°); loom speed of 500~550 r / min (e.g., 520 r / min); and relative humidity controlled at 64%~70% (e.g., 67%). These measures ensure fabric quality and prevent pilling and fuzzing due to tension fluctuations or environmental factors.

[0085] In some embodiments of the present invention, the weaving process uses the polyacrylonitrile pre-oxidized fiber yarns described above as warp and weft yarns. The fabric structure of the polyacrylonitrile pre-oxidized fiber fabric is plain weave, with a warp density of 260-340 yarns / 10 cm, for example, 320 yarns / 10 cm; and a weft density of 220-320 yarns / 10 cm, for example, 280 yarns / 10 cm.

[0086] The present invention also provides a polyacrylonitrile pre-oxidized fiber fabric prepared by the preparation method described above.

[0087] According to GB / T 4802.1-2008 standard, the performance indicators of the polyacrylonitrile pre-oxidized fiber fabric are as follows: anti-pilling grade ≥4, warp breaking strength ≥280 N, weft breaking strength ≥250 N, warp breaking elongation ≥7.0%, and weft breaking elongation ≥6.5%.

[0088] Beneficial effects:

[0089] 1. This invention specifically addresses the core pain points of polyacrylonitrile pre-oxidized fibers, such as high brittleness, weak cohesion, and excessive yarn hairiness. It achieves synergistic optimization of process parameters throughout the entire process, including opening and cleaning, carding, drawing, and vortex spinning, with a particular focus on precise control of key parameters in air-jet vortex spinning. Simultaneously, it incorporates a self-assembled three-layer gradient wrapping structure designed based on fiber characteristics, eliminating the need for additional pretreatment or finishing processes. This improves the anti-pilling and anti-fuzzing properties of yarn and fabric from the source of spinning, balancing production efficiency and cost control.

[0090] 2. This invention overcomes the problem of fuzziness caused by the high brittleness and weak cohesion of polyacrylonitrile pre-oxidized fibers by optimizing the parameters of jet vortex spinning. The subsequent weaving process is adapted to the yarn characteristics to ensure the quality of fabric formation. The fabric retains the inherent advantages of polyacrylonitrile pre-oxidized fibers, such as high temperature resistance and flame retardancy, while also having excellent anti-pilling and mechanical properties.

[0091] 3. The gradient structure design of this invention is highly compatible with the parameters of the jet vortex spinning process. It relies on the vortex field to naturally achieve radial self-assembly of fibers. The high-modulus short fibers in the inner core layer form a stable mechanical skeleton, the middle wrapping layer achieves tight interlayer connection, and the low-modulus long fibers in the outer layer form high-density wrapping, further strengthening the fiber cohesion. Compared with single-specification yarn, the gradient structure yarn has better structural stability and anti-pilling performance.

[0092] The present invention does not impose any special restrictions on the source of the raw materials used above, and they can be commercially available.

[0093] To further illustrate the present invention, the following detailed description of a pre-oxidized polyacrylonitrile fiber yarn, its preparation method, and its application, in conjunction with embodiments, is provided by the present invention, but should not be construed as limiting the scope of protection of the present invention.

[0094] Experimental materials:

[0095] The non-gradient structure yarn uses single-gauge pure spun polyacrylonitrile pre-oxidized fiber (Examples 1-3, Comparative Examples 1-2), with a fineness of 1.2 dtex and a length of 44 mm. The fiber performance indicators are: breaking strength ≥6.0 cN / tex, breaking elongation ≥9.0%, and impurity content ≤0.5%.

[0096] The three-layer gradient-wrapped yarn (Example 4) uses three specifications of pure spun polyacrylonitrile pre-oxidized fibers with a gradient design, consisting of an inner core layer, an intermediate wrapping layer, and an outer layer from the inside out; the inner core layer accounts for 40% of the weight, the intermediate wrapping layer accounts for 30%, and the outer layer accounts for 30%. Specific specifications are as follows:

[0097] The inner core fiber has a fineness of 1.8 dtex, a length of 38 mm, an initial modulus of 92 cN / dtex, and a tensile strength ≥6.2 cN / tex;

[0098] The fineness of the intermediate entanglement layer fiber is 1.4 dtex, the length is 44 mm, the initial modulus is 80 cN / dtex, and the tensile strength is ≥6.0 cN / tex;

[0099] The outer layer fibers have a fineness of 1.1 dtex, a length of 51 mm, an initial modulus of 65 cN / dtex, and a breaking strength ≥5.8 cN / tex.

[0100] Example 1

[0101] The pure spun polyacrylonitrile pre-oxidized fiber of a single specification is sequentially subjected to opening and cleaning, carding, three-stage drawing and vortex spinning to obtain pure spun polyacrylonitrile pre-oxidized fiber yarn.

[0102] The cotton opening and cleaning process is as follows:

[0103] The single-specification pure spun polyacrylonitrile pre-oxidized fiber is sequentially processed by FA002 cotton grabber, FA029 cotton blender, FA106 cotton opener and FA171 cotton box.

[0104] During the treatment process, the relative humidity of the environment is controlled at 66%; TN303 antistatic agent with a mass concentration of 2.6% is sprayed by atomization; the beater speed of the FA002 cotton grabber is 720 r / min; the FA106 cotton opener uses a combing needle beater with a beater speed of 480 r / min.

[0105] The cotton drop spacing is configured as follows, from the inlet to the outlet, as 12 mm, 9 mm, and 7 mm respectively.

[0106] The spacing of the comb bar is configured as follows: along the fiber flow direction, the inlet spacing is 18 mm and the outlet spacing is 22 mm.

[0107] The carding process is as follows:

[0108] The pre-oxidized polyacrylonitrile fibers after opening and cleaning are carded by a carding machine to obtain slivers. The working angle of the carding machine is 76°, the feed plate is raised by 11 mm, the licker-in speed is 710 rpm, the cylinder speed is 255 rpm, the doffer speed is 19 rpm, and the flats speed is 60 mm / min.

[0109] In a carding machine, the spacing between multiple working covers and the cylinder is as follows: from the fiber flow inlet to the outlet direction, the spacing between the 1st to the 5th working covers and the cylinder is 10 filaments, 9 filaments, 9 filaments, 9 filaments and 10 filaments respectively.

[0110] The carding machine is equipped with a front fixed cover and a rear fixed cover. The spacing between the front fixed cover and the cylinder is 10 filaments, 9 filaments, and 8 filaments respectively along the fiber travel direction. The spacing between the rear fixed cover and the cylinder is 10 filaments, 11 filaments, and 12 filaments respectively along the fiber travel direction. A low tension draft of 1.05 times is used.

[0111] The quality control indicators for raw slivers are: impurity content (mass content) of 0.85%, CV% of sliver size of 2.3%, weight unevenness of raw slivers of 1.3%, and short fiber content of raw slivers of 2.8%.

[0112] The three-layer rolling process is as follows:

[0113] The first drawing process uses a TMFD81S type drawing frame with a drawing speed of 170 m / min, combining 6 slivers, a total draft ratio of 7, a rear draft ratio of 1.8, concentrated rear drafting, eliminating front hooks, and the front drafting interval of the drawing frame drafting device is 13 mm and the rear drafting interval is 22 mm.

[0114] The second drawing process uses a TMFD81S drawing frame with a drawing speed of 170 m / min, combining 7 slivers, a total draft ratio of 8, a rear draft ratio of 1.5, and a front draft interval of 13 mm and a rear draft interval of 22 mm.

[0115] The third drawing frame uses a TMFD81L type drawing frame with a self-adjusting leveling device. The output speed is 170 m / min, 7 frames are combined, the total draft ratio is 8, the rear draft ratio is 1.15, the front draft interval of the drawing frame drafting device is 13 mm, and the rear draft interval is 22 mm.

[0116] After three rolling processes, the cooked strip is obtained.

[0117] The eddy spinning process is as follows:

[0118] The process employs air-jet vortex spinning, where the sliver is processed using an air-jet vortex spinning machine; specific parameters are as follows:

[0119] The spinning speed is 350 m / min, the nozzle air pressure is 0.48 MPa, the feed ratio is 0.98, the distance from the front roller to the spindle is 18.5 mm, the feed sliver weight is 18 g / 5m, the front drafting zone distance of the drafting device is 41 mm, the back drafting zone distance is 45 mm, the total draft ratio is 180 times, the main draft ratio is 30 times, the back draft ratio is 3 times, and the take-up ratio is 1.005.

[0120] Finally, 20s (29.5 tex) pure spun polyacrylonitrile pre-oxidized fiber yarn was obtained.

[0121] Example 2

[0122] The difference from Example 1 is as follows:

[0123] The eddy spinning process is as follows:

[0124] The process employs air-jet vortex spinning, where the sliver is processed using an air-jet vortex spinning machine; specific parameters are as follows:

[0125] The spinning speed is 370 m / min, the nozzle air pressure is 0.53 MPa, the feed ratio is 0.98, the distance from the front roller to the spindle is 19 mm, the feed sliver weight is 18 g / 5m, the front drafting zone distance of the drafting device is 41 mm, the rear drafting zone distance is 45 mm, the total draft ratio is 183 times, the main draft ratio is 31 times, the rear draft ratio is 3.1 times, and the take-up ratio is 1.01.

[0126] Finally, 25s (23.6 tex) pure spun polyacrylonitrile pre-oxidized fiber yarn was obtained.

[0127] Example 3

[0128] The difference from Example 1 is as follows:

[0129] The eddy spinning process is as follows:

[0130] The process employs air-jet vortex spinning, where the sliver is processed using an air-jet vortex spinning machine; specific parameters are as follows:

[0131] The spinning speed is 330 m / min, the nozzle air pressure is 0.51 MPa, the feed ratio is 0.97, the distance from the front roller to the spindle is 18.5 mm, the feed sliver weight is 18 g / 5m, the front drafting zone distance of the drafting device is 41 mm, the rear drafting zone distance is 45 mm, the total draft ratio is 186 times, the main draft ratio is 32 times, the rear draft ratio is 3 times, and the take-up ratio is 1.005.

[0132] Finally, 30s (19.6 tex) pure spun polyacrylonitrile pre-oxidized fiber yarn was obtained.

[0133] Example 4

[0134] Three types of pure spun polyacrylonitrile pre-oxidized fibers with gradient design were sequentially subjected to opening and cleaning, carding, three-stage drawing and vortex spinning to produce pure spun polyacrylonitrile pre-oxidized fiber yarn with a three-layer gradient wrapping structure.

[0135] The cotton opening and cleaning process is as follows:

[0136] The three specifications of pure spun polyacrylonitrile pre-oxidized fibers with gradient design are sequentially processed by FA002 cotton grabber, FA029 cotton blender, FA106 cotton opener and FA171 cotton box.

[0137] During the treatment process, the relative humidity of the environment is controlled at 66%; TN303 antistatic agent with a mass concentration of 2.6% is sprayed by atomization; the beater speed of the FA002 cotton grabber is 720 r / min; the FA106 cotton opener uses a combing needle beater with a beater speed of 480 r / min.

[0138] The cotton drop spacing is configured as follows, from the inlet to the outlet, as 12 mm, 9 mm, and 7 mm respectively.

[0139] The spacing of the comb bar is configured as follows: along the fiber flow direction, the inlet spacing is 18 mm and the outlet spacing is 22 mm.

[0140] The carding process is as follows:

[0141] The pre-oxidized polyacrylonitrile fibers after opening and cleaning are carded by a carding machine to obtain slivers. The working angle of the carding machine is 76°, the feed plate is raised by 11 mm, the licker-in speed is 710 rpm, the cylinder speed is 255 rpm, the doffer speed is 19 rpm, and the flats speed is 60 mm / min.

[0142] In a carding machine, the spacing between multiple working covers and the cylinder is as follows: from the fiber flow inlet to the outlet direction, the spacing between the 1st to the 5th working covers and the cylinder is 10 filaments, 9 filaments, 9 filaments, 9 filaments and 10 filaments respectively.

[0143] The carding machine is equipped with a front fixed cover and a rear fixed cover. The spacing between the front fixed cover and the cylinder is 10 filaments, 9 filaments, and 8 filaments respectively along the fiber travel direction. The spacing between the rear fixed cover and the cylinder is 10 filaments, 11 filaments, and 12 filaments respectively along the fiber travel direction. A low tension draft of 1.05 times is used.

[0144] The quality control indicators for raw slivers are: impurity content (mass content) of 0.12%, CV% of sliver size of 2.5%, weight unevenness of raw slivers of 1.5%, and short fiber content of raw slivers of 3%.

[0145] The three-layer rolling process is as follows:

[0146] The first drawing process uses a TMFD81S type drawing frame with a drawing speed of 170 m / min, combining 6 slivers, a total draft ratio of 7, a rear draft ratio of 1.8, concentrated rear drafting, eliminating front hooks, and the front drafting interval of the drawing frame drafting device is 13 mm and the rear drafting interval is 22 mm.

[0147] The second drawing process uses a TMFD81S drawing frame with a drawing speed of 170 m / min, combining 7 slivers, a total draft ratio of 8, a rear draft ratio of 1.5, and a front draft interval of 13 mm and a rear draft interval of 22 mm.

[0148] The third drawing frame uses a TMFD81L type drawing frame with a self-adjusting leveling device. The output speed is 170 m / min, 7 frames are combined, the total draft ratio is 8, the rear draft ratio is 1.15, the front draft interval of the drawing frame drafting device is 13 mm, and the rear draft interval is 22 mm.

[0149] After three drawing processes, the finished strip is obtained. In the three drawing processes, three layers of green strip are mixed together.

[0150] The eddy spinning process is as follows:

[0151] The process employs air-jet vortex spinning, where the sliver is processed using an air-jet vortex spinning machine; specific parameters are as follows:

[0152] The spinning speed is 350 m / min, the nozzle air pressure is 0.48 MPa, the feed ratio is 0.98, the distance from the front roller to the spindle is 18.5 mm, the feed sliver weight is 18 g / 5m, the front drafting zone distance of the drafting device is 41 mm, the back drafting zone distance is 45 mm, the total draft ratio is 180 times, the main draft ratio is 30 times, the back draft ratio is 3 times, and the take-up ratio is 1.005.

[0153] Finally, a 20s (29.5 tex) three-layer gradient wrapped structure pure spun polyacrylonitrile pre-oxidized fiber yarn was obtained.

[0154] Comparative Example 1

[0155] Preparation of ring-spun 20s pure spun polyacrylonitrile pre-oxidized fiber yarn:

[0156] The difference from Example 1 lies in the spinning process, namely:

[0157] The sliver after three draws is processed using a BHFA498 roving frame, a ZP516 spinning frame, and a 21C winding machine; specific parameters are as follows:

[0158] Spinning speed: 180 m / min; twist: 850 twists / 10cm; front roller speed: 200 r / min; back roller speed: 35 r / min; back zone draft ratio: 2.8; front draft zone spacing: 40 mm; back draft zone spacing: 45 mm; feed weight: 18 g / 5m; ring type: PG1-42; traveler type: OSS-4 / 0; winding density: 0.45 g / cm³. 3 .

[0159] Finally, ring-spun 20s (29.5 tex) pure spun polyacrylonitrile pre-oxidized fiber yarn was obtained.

[0160] Comparative Example 2

[0161] Preparation of vortex-spun 20s pure spun polyacrylonitrile pre-oxidized fiber yarn:

[0162] The difference from Example 1 is that the eddy spinning process parameters are different, namely:

[0163] Conventional chemical fiber spinning parameters were used, without optimizing the parameters to address the brittleness and cohesion characteristics of polyacrylonitrile pre-oxidized fibers. The specific parameters are as follows:

[0164] Spinning speed 380 m / min, nozzle air pressure 0.6 MPa, feed ratio 0.95, distance from front roller to spindle 21 mm, feed weight 18 g / 5m; drafting zone parameters: front drafting zone spacing 41 mm, rear drafting zone spacing 45 mm, total draft ratio 180 times, main draft ratio 20 times, rear draft ratio 3.6 times, take-up ratio 1.03.

[0165] Finally, vortex-spun 20s (29.5 tex) pure spun polyacrylonitrile pre-oxidized fiber yarn was obtained.

[0166] Comparative Example 3

[0167] The difference from Example 3 is as follows:

[0168] The three-stage drawing process parameters were modified, adopting a smaller spacing design typical for chemical fibers. The front drafting spacing of the first drawing frame drafting device was 10 mm, and the rear drafting spacing was 18 mm; the front drafting spacing of the second and third drawing frames drafting devices was 8 mm, and the rear drafting spacing was 18 mm. Other parameter settings were consistent with Example 3, ultimately producing 30s (19.6 tex) pure spun polyacrylonitrile pre-oxidized fiber yarn.

[0169] Application examples

[0170] Using the yarns obtained in Examples 1-4 and Comparative Examples 1-3 as warp and weft yarns, a pure spun polyacrylonitrile pre-oxidized fiber fabric (plain weave, warp density of 320 yarns / 10 cm, weft density of 280 yarns / 10 cm) was produced through a weaving process. Specific weaving process parameters are as follows:

[0171] It is woven on an air-jet loom with a warp tension of 2.40 kN, a weft insertion tension of 6 cN, a shedding time of 285°, a weft insertion time of 162.5° for the main jet and 175° for the auxiliary jet, a heddle leveling time of 305°, a machine speed of 520 r / min, and a relative humidity of 67%.

[0172] The yarns and corresponding fabrics obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to core performance tests. All performance tests were performed according to the corresponding national standards: yarn hairiness index was tested according to GB / T 14344-2008; yarn breaking strength and elongation were tested according to GB / T 3916-2013; fabric pilling resistance was tested according to GB / T 4802.1-2008 (circular trajectory method); and fabric breaking strength and elongation were tested according to GB / T 3923.1-2013. The test results are shown in Table 1.

[0173] Table 1. Test results of core performance of yarns and corresponding fabrics in Examples 1-4 and Comparative Examples 1-3.

[0174]

[0175] Table 1 (Continued from Table 1)

[0176]

[0177] As shown in Table 1, the yarns and fabrics prepared using the optimized air-jet vortex spinning process of Examples 1-3 of this invention are significantly superior to those of Comparative Example 1 (using conventional ring spinning), Comparative Example 2 (using conventional vortex spinning), and Comparative Example 3 (using conventional three-pass drawing parameters) in terms of core performance indicators. Furthermore, Example 4, which combines the optimized process with a gradient structure design, achieves even greater performance improvement.

[0178] 1. Yarn Hairiness Performance: In Examples 1-3, the number of hairs larger than 3mm per meter was ≤1, and the hairiness H-value was ≤0.76, which is significantly lower than that of Comparative Example 1 (164.4 hairs / meter, H-value 3.42), Comparative Example 2 (3 hairs / meter, H-value 1.5), and Comparative Example 3 (660 hairs / meter, H-value 6.7). This demonstrates that the process of the present invention can effectively suppress hairiness generation during the spinning process of polyacrylonitrile pre-oxidized fibers, solving the hairiness problem at its source. Example 4, combined with a gradient structure design, relies on the high-density spiral locking and wrapping of low-modulus long fibers in the outer layer to maximize the sealing of fiber ends, reducing 2mm hairiness to 2.1 hairs / meter and 3mm hairiness to only 0.3 hairs / meter, with a hairiness H-value as low as 0.42. This fully demonstrates that the gradient structure design can further enhance the hairiness control effect of yarn based on process optimization.

[0179] 2. Yarn Mechanical Properties: The breaking strength of the yarns in Examples 1-3 is ≥8.28 cN / tex, and the breaking elongation is ≥6.11%, meeting the requirements of actual weaving and use. Among them, the breaking strength of Example 1 reaches 9.65 cN / tex, which is better than Comparative Example 2 (9.1 cN / tex) and Comparative Example 3 (7.04 cN / tex), and close to Comparative Example 1 (9.62 cN / tex). This shows that the process of the present invention reduces hairiness without sacrificing the mechanical properties of the yarn. On the contrary, it improves the fiber cohesion effect through parameter optimization, thus ensuring the yarn strength. Example 4, through gradient structure design, forms a straight mechanical skeleton with high-modulus short fibers in the inner core layer, and the intermediate wrapping layer achieves tight interlayer connection, which greatly improves the cohesion between fibers and the stability of the yarn structure. The breaking strength is further increased to 10.12 cN / tex, which is 4.9% higher than that of Example 1, and the breaking elongation increases to 9.35%. The yarn uniformity and mechanical properties are optimized simultaneously, demonstrating the synergistic effect of process optimization and structural design.

[0180] 3. Fabric Performance: The fabrics in Examples 1-3 all achieved a pilling resistance level of 4, meeting the requirements for appearance stability in high-end applications. In contrast, the fabrics in Comparative Examples 1-3 only achieved a pilling resistance level of 3. In Example 4, relying on the excellent hair control and structural characteristics of the gradient structure yarn, the pilling resistance level of the fabric was further improved to 4-5. At the same time, the warp and weft breaking strength and elongation of the fabrics in Examples 4 were better than those in Comparative Examples 2 and 3, and close to or better than those in Comparative Example 1. This indicates that the yarn prepared by the process and structure of this invention is adapted to weaving requirements, and the fabric retains the intrinsic characteristics of the fiber while possessing excellent pilling resistance and mechanical properties.

[0181] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing pre-oxidized polyacrylonitrile fiber yarn, characterized in that, Includes the following steps: Polyacrylonitrile pre-oxidized fiber is subjected to opening and cleaning, carding, three-stage drawing and vortex spinning in sequence to obtain polyacrylonitrile pre-oxidized fiber yarn. The three-layer drawing process is suitable for processing single-specification polyacrylonitrile pre-oxidized fibers, and also suitable for blending multi-specification polyacrylonitrile pre-oxidized fibers. The vortex spinning process employs an air-jet vortex spinning technique with the following process parameters: The spinning speed is 320~370 m / min, the nozzle air pressure is 0.48~0.55 MPa, the feed ratio is 0.96~1.00, the distance from the front roller to the spindle is 18~20 mm, the feed sliver weight is 16~18 g / 5m, the front drafting zone distance of the drafting device is 38~44 mm, the rear drafting zone distance is 43~48 mm, the total draft ratio is 120~230 times, the main draft ratio is 30~32 times, the rear draft ratio is 3.0~3.2 times, and the take-up ratio is 1.0~1.

02. The performance indicators of the pre-oxidized polyacrylonitrile fiber yarn are: hairiness index H value ≤ 1.2, breaking strength ≥ 5.8 cN / tex, and breaking elongation ≥ 8.5%.

2. The preparation method according to claim 1, characterized in that, The polyacrylonitrile pre-oxidized fiber is a single-specification pure spun polyacrylonitrile pre-oxidized fiber, and the resulting polyacrylonitrile pre-oxidized fiber yarn is a pure spun polyacrylonitrile pre-oxidized fiber yarn with no gradient structure. The fineness of the single-specification polyacrylonitrile pre-oxidized fiber is 1.1~2.0 dtex, and the length is 38~51 mm; The performance indicators of the single-specification polyacrylonitrile pre-oxidized fiber are: breaking strength ≥6.0cN / tex, breaking elongation ≥9.0%, and impurity content ≤0.5%.

3. The preparation method according to claim 1, characterized in that, The polyacrylonitrile pre-oxidized fiber is a pure spun polyacrylonitrile pre-oxidized fiber with three specifications designed in a gradient. The resulting polyacrylonitrile pre-oxidized fiber yarn is a pure spun polyacrylonitrile pre-oxidized fiber yarn with a three-layer gradient wrapping structure, consisting of an inner core layer, an intermediate wrapping layer, and an outer layer from the inside out. In the three-layer gradient wrapping structure pure spun polyacrylonitrile pre-oxidized fiber yarn, the inner core layer accounts for 30%~50% of the mass, the middle wrapping layer accounts for 25%~35% of the mass, and the outer layer accounts for 20%~40% of the mass. The fineness of the inner core fiber is 1.5~2.0 dtex, the length is 38~42 mm, the initial modulus is ≥90 cN / dtex, and the breaking strength is ≥6.2 cN / tex; The intermediate entanglement layer fiber has a fineness of 1.2~1.4 dtex, a length of 44~48 mm, an initial modulus of 75~85 cN / dtex, and a breaking strength ≥6.0 cN / tex; The outer layer fibers have a fineness of 1.1~1.2 dtex, a length of 50~51 mm, an initial modulus of 60~70 cN / dtex, and a breaking strength ≥5.8 cN / tex.

4. The preparation method according to claim 1, characterized in that, The cotton opening and cleaning process is as follows: The pre-oxidized polyacrylonitrile fibers were sequentially processed through an FA002 cotton grabber, an FA029 cotton blender, an FA106 cotton opener, and an FA171 cotton box. During the processing, the relative humidity was controlled above 65%, and an antistatic agent with a mass concentration of 2.5% to 3% was sprayed by atomization. The beater speed of the FA002 cotton grabber was 700 to 720 r / min. The FA106 cotton opener used a carding needle beater with a beater speed of 420 to 480 r / min. The cotton drop spacing is configured as follows: from the inlet to the outlet, it is 11~12 mm, 9~10 mm, and 7~8 mm respectively. The spacing between the comb needles and dust bars is: 16~20 mm at the inlet and 20~24 mm at the outlet.

5. The preparation method according to claim 1, characterized in that, The carding process is as follows: The pre-oxidized polyacrylonitrile fibers after opening and cleaning are combed by a carding machine to obtain slivers. The carding machine has a working angle of 75~80°, a feed plate height of 10~15 mm, a licker-in speed of 700~750 rpm, a cylinder speed of 250~280 rpm, a doffer speed of 18~22 rpm, and a flat plate speed of 50~80 mm / min. The carding machine is equipped with a front fixed cover and a rear fixed cover; The spacing between the front fixed cover and the cylinder is 8-10 filaments, 7-9 filaments, and 6-8 filaments respectively along the fiber travel direction; The spacing between the rear fixed cover and the cylinder is 10-12 filaments, 11-13 filaments, and 12-14 filaments respectively along the fiber travel direction.

6. The preparation method according to claim 1, characterized in that, The three-stage rolling process is as follows: The first drawing process uses a TMFD81S type drawing frame with a drawing speed of 150~200 m / min, combining 6 slivers, a total draft ratio of 6~8 times, a rear draft ratio of 1.7~2.0 times, and a front draft interval of 12~15 mm and a rear draft interval of 20~25 mm for the drawing frame drafting device. The second drawing process uses a TMFD81S type drawing frame with a drawing speed of 150~200 m / min, combining 6~8 slivers, a total draft ratio of 6~9 times, a rear draft ratio of 1.4~1.6 times, and a front draft interval of 12~15 mm and a rear draft interval of 20~25 mm for the drawing frame drafting device. The third drawing frame uses a TMFD81L type drawing frame with a self-adjusting leveling device. The output speed is 150~200 m / min, 6~8 slivers are combined, the total draft ratio is 6~9 times, the rear draft ratio is 1.1~1.2 times, the front drafting interval of the drawing frame drafting device is 12~15 mm, and the rear drafting interval is 20~25 mm.

7. The polyacrylonitrile pre-oxidized fiber yarn prepared by the preparation method according to any one of claims 1 to 6.

8. A method for preparing a pre-oxidized polyacrylonitrile fiber fabric, comprising the following steps: The polyacrylonitrile pre-oxidized fiber yarn of claim 7 is woven to obtain a polyacrylonitrile pre-oxidized fiber fabric.

9. The preparation method according to claim 8, characterized in that, The weaving process is performed using an air-jet loom, and the process parameters are as follows: The warp tension is 2.30~2.50 kN, the weft insertion tension is 5~8 cN, the shedding time is 280°~290°, the weft insertion time is 85°~240° for the main jet and 90°~260° for the auxiliary jet, the heddle leveling time is 300°~310°, the machine speed is 500~550 r / min, and the relative humidity is controlled at 64%~70%.

10. The polyacrylonitrile pre-oxidized fiber fabric prepared by the preparation method according to any one of claims 8 to 9.

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