Polyimide yarn and preparation method and application thereof

Abstract

The invention discloses a polyimide yarn and a preparation method and application thereof, and the preparation method comprises the following steps: providing a polyimide endless tow, carrying out antistatic and / or softening pretreatment, preparing stretch-cut strips through a stretch-cut strip forming device, and spinning the stretch-cut strips into the yarn through drawing, roving and spinning processes. According to the method, the cutting, opening and carding procedures of traditional short fiber spinning are replaced with the traction spinning technology, the problems that polyimide fibers are large in static electricity and poor in cohesive force are solved in combination with targeted pretreatment, the breaking strength of finished yarn is larger than or equal to 3.5 cN / dtex, and the elongation at break is 6%-18%. The method is short in process, high in efficiency, low in energy consumption and small in fiber damage, the prepared yarn is suitable for the fields of high-temperature-resistant protective clothing, high-temperature filtering materials and the like, and compared with the prior art, the yarn forming quality and the production efficiency are better.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyimide fiber spinning, in particular to a polyimide yarn and a preparation method and application thereof. BACKGROUND

[0002] As a representative of high-performance fibers, polyimide fiber has excellent high-temperature resistance, flame resistance, chemical corrosion resistance and mechanical properties, and is in urgent demand in the fields of aerospace, metallurgy, fire fighting, etc. However, its special molecular structure leads to a smooth surface, a low moisture regain (usually < 2%), easy static electricity in the spinning process, and poor fiber cohesion, which are the key bottlenecks restricting its large-scale application.

[0003] The existing polyimide fiber spinning technology mainly falls into two categories: (1) Traditional short fiber spinning process (two-step method): long filament bundles are mechanically cut into 51 mm or 38 mm short fibers, which are then spun through multiple processes such as opening, carding, and drawing. This process has the problems of long process flow, low production efficiency, severe fiber damage caused by multiple mechanical actions, low yarn strength, and high energy consumption and production cost.

[0004] (2) Compact spinning process: as disclosed in the Chinese patent application CN109554790A, the process route of cleaning, carding, three-drawing, and compact spinning is adopted to try to enhance the cohesion of the fibers by agglomeration. However, this method still needs multiple mechanical treatments, and the fiber damage has not been fundamentally improved. Moreover, only by controlling the workshop humidity to alleviate static electricity, without designing a special solution for the characteristics of polyimide fiber, the effect of static electricity suppression is limited, which cannot meet the demand of high-performance applications.

[0005] Draft spinning technology, as an advanced pre-spinning process, can directly form a sliver by drafting and breaking long filament bundles online, saving the cutting, opening, and carding processes, and has been successfully applied to conventional fibers such as polyester. However, due to the special properties of polyimide fiber, it faces technical difficulties such as severe static electricity, easy fiber breakage, and poor sliver uniformity in the draft spinning process. Currently, there is no related report on the application of draft spinning technology to polyimide fiber spinning. Therefore, it is of great industrial value to develop a draft spinning process suitable for polyimide fiber and solve the defects of the existing technology. SUMMARY

[0006] In view of the problems of long spinning process flow, severe fiber damage, severe static electricity, and poor yarn quality in the existing technology, the purpose of the present application is to provide a preparation method of polyimide yarn, which realizes efficient and low-damage spinning and improves the comprehensive performance of the yarn through the synergistic optimization of draft spinning process and pretreatment and spinning process.

[0007] Another object of the present application is to provide a polyimide yarn obtained by the above preparation method and its application.

[0008] According to the object of the present application, the present application provides a preparation method of a polyimide yarn, comprising the following steps: (1) providing a polyimide filament bundle; (2) pretreating the polyimide filament bundle, the pretreatment comprising antistatic treatment and / or softening treatment; (3) drawing and breaking the pretreated filament bundle into slivers by a draw-breaking slivering device to obtain polyimide draw-breaking slivers; (4) spinning the polyimide draw-breaking slivers into polyimide yarns through a spinning process, the spinning process comprising a drawing, a roving and a spinning process.

[0009] The preparation method of the present application can realize efficient and low-damage spinning and improve the comprehensive performance of the yarn through the synergistic optimization of the draw-breaking spinning process and the pretreatment and spinning process.

[0010] In the above preparation method, regarding step (1) providing a polyimide filament bundle: the polyimide filament bundle comprises polyimide homopolymer fibers, copolymer polyimide fibers and modified polyimide fibers, which can be obtained by self-making or purchasing.

[0011] Preferably, when self-made, dry spinning, wet spinning or dry-wet spinning combined with thermal imidization and multi-stage heat stretching process is adopted, the total draw ratio of multi-stage heat stretching is 2-10 times, and the stretching temperature is 120-600℃ with gradient rising, which can adapt to the forming needs of different types of polyimide fibers and ensure the stability of the basic mechanical properties of the filament bundle.

[0012] Regarding step (2) pretreatment: the pretreatment comprises antistatic treatment and / or softening treatment, and the purpose is to eliminate static electricity and improve the fiber cohesion.

[0013] Preferably, the treatment method is selected from one or more of immersion, spraying, roller coating or atomization treatment, the functional additives used include at least one of antistatic agents and softening agents, a hygroscopic agent can be optionally added, the total concentration of the functional additives is 0.3-5.0wt%, the treatment temperature is 10-70℃, and the treatment time is 1-60 seconds, which can flexibly adapt to the equipment conditions of different production scenes.

[0014] In the preferred embodiment, the pretreatment liquid contains 0.5-2.0wt% antistatic agent (cationic or nonionic) and 0.3-1.5wt% softener (polysiloxane or fatty acid ester), the treatment temperature is 40-60℃, the treatment time is 2-5 seconds, and the fiber belt liquid rate is controlled at 8-12%. The technical effect of this preferred scheme is more optimal: the immersion treatment allows the fiber to fully contact the additives, and the additives form a uniform adsorption film on the surface of the fiber, resulting in more durable antistatic effect (electrostatic half-life ≤2 seconds, more than 60% shorter than spray treatment); the matching of specific concentration and temperature and time can avoid the hardening of yarn hand caused by excessive residue of additives, while ensuring that the softener can effectively reduce the fiber friction coefficient (to below 0.2), increase the cohesion between fibers by 40-50%, and significantly reduce the winding and flying phenomenon during spinning.

[0015] Regarding step (3) drawing and slivering: the pretreated filament bundle is sent to a drawing and slivering device to form polyimide drawn sliver through drawing and breaking, preferably, the fiber length of the drawn sliver is 50-120mm, and the length dispersion coefficient CV is ≤15%, ensuring the uniformity of slivering.

[0016] In the preferred embodiment, the drawing and slivering device in step (3) includes a preheating zone, a main drawing zone and a stabilization zone arranged in sequence, wherein: the preheating zone temperature is 80-120℃, the roller linear speed ratio is 1:1.05-1.15; the main drawing zone temperature is 150-220℃, the roller linear speed ratio is 1:3.5-7.5; the stabilization zone temperature is 100-150℃, the roller linear speed ratio is 1:1.1-1.3; the roller linear speed of the three zones increases in sequence, and the total speed ratio (stabilization zone output speed / preheating zone input speed) is 5-10 times, ensuring that the filament bundle is effectively broken.

[0017] Regarding step (4) spinning process: the polyimide drawn sliver is processed through drawing, roving and spinning to obtain yarn.

[0018] In the preferred embodiment, the 2-10 drawn slivers are combined and processed using the siro-spinning process, the distance between the two rovings in the siro-spinning process is 4-8mm, the twist is 300-1000, and the spinning speed is 8000-12000rpm; the production environment temperature is 20-30℃, and the relative humidity is 60-75%; the fine yarn mechanical draft ratio is 30-40 times, and the roller gauge is 22-28mm x 30-45mm. The technical effect of this preferred scheme is more optimal: the siro-spinning double roving combination and twisting method makes the yarn structure more compact, and the yarn breaking strength is further improved by 10-15%; the synergistic optimization of various process parameters can adapt to the production needs of different denier yarns, ensuring high spinning speed (8000-12000rpm) while controlling the fine yarn breakage rate at 1 root per thousand spindles For processes under 24 hours, production efficiency is increased by 25-30% compared to compact spinning; precise control of ambient temperature and humidity can help suppress static electricity regeneration and further ensure the stability of the spinning process.

[0019] According to another objective of the present invention, the present invention provides a polyimide yarn prepared by the above method, comprising polyimide short fibers (length 50-120 mm, length dispersion coefficient CV ≤ 15%) formed by stretching and breaking, having a yarn breaking strength ≥ 3.5 cN / dtex, a breaking elongation of 6-18%, and a yarn count of 20-40, possessing both excellent mechanical properties and surface quality. The yarn prepared using the preferred technical solution of the present invention exhibits even better performance: a breaking strength of 4.0-4.6 cN / dtex, a yarn unevenness ≤ 13%, and a breaking strength retention rate ≥ 90% after 1000 hours of use at a high temperature (250°C), representing an improvement of more than 20% compared to yarn prepared by conventional processes.

[0020] This invention also provides applications of the aforementioned polyimide yarn, which can be used to prepare high-temperature protective clothing (such as metallurgical and fire-fighting protective clothing), high-temperature filter materials (such as boiler flue gas filter bags), and special industrial fabrics or textiles (such as high-temperature resistant fabrics for the aerospace field). Among these, the yarn prepared using the preferred embodiment of this invention exhibits superior mechanical properties and stronger stability, making it particularly advantageous in high-end protective equipment and long-life high-temperature filter materials. It can increase the number of wear cycles of protective clothing by more than 50% and extend the service life of filter materials by 1-2 times.

[0021] The present invention can achieve the following beneficial effects: (1) Simplified process and improved efficiency: The draw-cut spinning process eliminates the cutting, opening and carding processes of the traditional process, shortens the production process by more than 40%, reduces the overall energy consumption by 30-50%, and significantly improves production efficiency; (2) Complete solution to static electricity problem: By combining antistatic and softening pretreatment with environmental humidity control, the static electricity problem of polyimide fibers is specifically solved, the fiber cohesion is improved, and the stability of the spinning process is significantly improved. (3) Less fiber damage and better yarn quality: Controllable stretching and breaking replaces mechanical cutting, the fiber ends are naturally stretched, resulting in less damage and yarn strength is 15-25% higher than traditional processes; the uniformity of the spun yarn is good, and combined with Siro spinning process, the yarn surface is smooth. (4) Wide range of applications: Polyimide filament bundles cover a variety of modification types, and the pretreatment and process parameters can be flexibly adjusted to adapt to spinning processes with different performance requirements. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0023] In this invention, the short fiber refers to a crimped fiber of 51mm or 38mm; the filament bundle refers to a bundle of long filaments; the draw-cut spinning refers to a process of directly producing short fiber strips from a long filament bundle through drawing and breaking; and the Sirospinning refers to a process of spinning two rovings together, which can improve the yarn structure and performance.

[0024] The present invention will be described in detail below through examples and comparative examples. Unless otherwise specified, all reagents and materials used in the following examples are commercially available. The polyimide filament bundles were provided by Jiangsu Xiannuo New Material Technology Co., Ltd.

[0025] The fiber performance testing methods in the following examples and comparative examples are as follows: (1) Performance testing methods: Breaking strength and elongation at break: tested according to GB / T14337-2008 "Test Method for Tensile Properties of Chemical Fibers (Short Fibers)"; Length dispersion coefficient CV: Tested and calculated according to GB / T14335 "Test method for linear density of short chemical fibers"; Evenness: Tested according to GB / T3292.1-2018 "Determination of linear density of yarns - Part 1: skein method".

[0026] (2) Raw material specifications: Polyimide filament bundle: monofilament fineness 3.5 dtex, breaking strength 5.2 cN / dtex, breaking elongation 12%, moisture regain 1.5% (used in Examples 1-5 and Comparative Examples 2 and 4); Antistatic agent: Quaternary ammonium salt cationic antistatic agent (ASA-10); Softener: Polysiloxane-based softener (SR-301).

[0027] Example 1 (1) Provide polyimide filament bundles: dry spinning combined with online thermal imidization and multi-stage hot stretching process, with a total stretching ratio of 5.5 times and a stretching temperature of 160℃→220℃→280℃→350℃; (2) Pretreatment: Impregnation treatment, antistatic agent concentration 1.2wt%, softener concentration 0.8wt%, treatment temperature 50℃, treatment time 3 seconds; (3) Slicing: The slicing device includes a preheating zone, a main slicing zone, and a stabilizing zone. The preheating zone is 100℃ with a speed ratio of 1:1.08; the main slicing zone is 180℃ with a speed ratio of 1:4.2; the stabilizing zone is 120℃ with a speed ratio of 1:1.05; the total speed ratio is 1.08×4.2×1.05≈5.0, the average fiber length of the slicing strip is 85mm, and the coefficient of variation CV is 7.9%; the subsequent crimping process is carried out with a crimping box temperature of 75℃ and a crimping number of 12 / 25mm. (4) Spinning: Siro spinning process, after the two draft slivers are combined, they first go through the drawing process: 4 slivers are combined, mechanical drafting is 5.0 times, roller spacing is 22mm×28mm; then go through the roving process: roving spacing is 6mm, roving twist coefficient is 75, drafting ratio is 6 times, spindle speed is 800rpm; finally go through the spinning process: spinning twist is 700, spinning speed is 10000rpm; ambient temperature is 24℃, relative humidity is 65%.

[0028] Test results: Yarn count 32, breaking strength 4.2 cN / dtex, breaking elongation 11.3%, yarn evenness 12.6%.

[0029] Example 2 (1) Provide polyimide filament bundles: dry spinning combined with online thermal imidization and multi-stage hot stretching process, with a total stretch ratio of 7.2 times and a stretching temperature of 180℃→250℃→320℃→380℃; the filament bundle has a single filament fineness of 4.5dtex, a breaking strength of 5.6cN / dtex, and a breaking elongation of 12%; (2) Pretreatment: Impregnation treatment, antistatic agent concentration 1.5wt%, softener concentration 1.0wt%, treatment temperature 55℃, treatment time 4 seconds; (3) Slitting into strips: The slitting into strips device includes a preheating zone, a main slitting zone, and a stabilizing zone. The preheating zone is 110℃ with a speed ratio of 1:1.12; the main slitting zone is 200℃ with a speed ratio of 1:4.5; the stabilizing zone is 130℃ with a speed ratio of 1:1.08; the total speed ratio is 1.12×4.5×1.08≈5.4, the average length of the slitting strip fiber is 90mm, and the dispersion coefficient CV=7.2%; the subsequent crimping process is carried out with a crimping box temperature of 80℃ and a crimping number of 14 / 25mm. (4) Spinning: Siro spinning process, after the two draft slivers are combined, they first go through the drawing process: 5 slivers are combined, mechanical drafting is 5.5 times, roller spacing is 24mm×30mm; then go through the roving process: roving spacing is 6mm, roving twist coefficient is 75, drafting ratio is 7 times, spindle speed is 800rpm; finally go through the spinning process: spinning twist is 700, spinning speed is 11000rpm; ambient temperature is 25℃, relative humidity is 68%.

[0030] Test results: Yarn count 30, breaking strength 4.4 cN / dtex, breaking elongation 10.6%, yarn evenness 11.9%.

[0031] Example 3 (1) Provide polyimide filament bundles: Purchase copolyimide filament bundles with a single filament fineness of 3.0 dtex and a breaking strength of 5.0 cN / dtex; (2) Pretreatment: Spraying treatment, antistatic agent concentration 0.3wt%, softener concentration 0.3wt%, treatment temperature 30℃, treatment time 1 second; (3) Slitting into strips: The slitting into strips device includes a preheating zone, a main slitting zone, and a stabilizing zone. The preheating zone is 80°C with a speed ratio of 1:1.05; the main slitting zone is 150°C with a speed ratio of 1:4.3; the stabilizing zone is 100°C with a speed ratio of 1:1.1; the total speed ratio is 1.05×4.3×1.1≈5.0; the fiber length of the slitting strip is 50mm; the dispersion coefficient CV is 14.5%; there is no crimping step. (4) Spinning: Ordinary ring spinning, the sliver first goes through the drawing process: 3 slivers are drawn together, mechanical drafting is 4.5 times, roller spacing is 20mm×26mm; then it goes through the spinning process: spinning twist is 750, spinning speed is 8000rpm; ambient temperature is 22℃, relative humidity is 60%.

[0032] Test results: Yarn count 40, breaking strength 3.6 cN / dtex, breaking elongation 17.0%, yarn evenness 13.7%.

[0033] Example 4 (1) Provide polyimide filament bundles: wet spinning combined with thermal imidization and multi-stage hot stretching process, with a total stretching ratio of 10 times and a stretching temperature of 120℃→200℃→280℃→350℃→400℃. (2) Pretreatment: Roller coating, antistatic agent concentration 2.0wt%, softener concentration 1.5wt%, add 0.5wt% desiccant, treatment temperature 70℃, treatment time 10 seconds; (3) Slitting into strips: The slitting into strips device includes a preheating zone, a main slitting zone, and a stabilizing zone. The preheating zone is 120℃ with a speed ratio of 1:1.15; the main slitting zone is 220℃ with a speed ratio of 1:4.8; the stabilizing zone is 150℃ with a speed ratio of 1:1.1; the total speed ratio is 1.15×4.8×1.1≈6.1; the fiber length of the slitting strip is 120mm; the dispersion coefficient CV is 6.1%; the crimping process is carried out with a crimping box temperature of 90℃ and a crimping number of 15 / 25mm. (4) Spinning: Siro spinning process, after the two draft slivers are combined, they first go through the drawing process: 6 slivers are combined, mechanical drafting is 6.0 times, roller spacing is 26mm×32mm; then go through the roving process: roving spacing is 6mm, roving twist coefficient is 80, drafting ratio is 8 times, spindle speed is 850rpm; finally go through the spinning process: spinning twist is 560, spinning speed is 12000rpm; ambient temperature is 26℃, relative humidity is 75%.

[0034] Test results: Yarn count 20, breaking strength 4.7 cN / dtex, breaking elongation 8.4%, yarn evenness 11.3%.

[0035] Example 5 (1) Provide polyimide filament bundles: dry spinning combined with online thermal imidization process, total stretch ratio 4 times, stretching temperature 160℃→250℃→320℃; (2) Pretreatment: atomization treatment, antistatic agent concentration 0.8wt%, no softener, treatment temperature 45℃, treatment time 3 seconds; (3) Slitting into strips: The slitting into strips device includes a preheating zone, a main slitting zone, and a stabilizing zone. The preheating zone is 90℃ with a speed ratio of 1:1.10; the main slitting zone is 160℃ with a speed ratio of 1:3.8; the stabilizing zone is 110℃ with a speed ratio of 1:1.06; the total speed ratio is 1.10×3.8×1.06≈4.4; the fiber length of the slitting strip is 70mm; the coefficient of variation (CV) is 9.0%; the crimping process is carried out with a crimping box temperature of 60℃ and a crimping number of 8 per 25mm. (4) Spinning: Siro spinning process, after the two draft slivers are combined, they first go through the drawing process: 4 slivers are combined, mechanical drafting is 5.2 times, roller spacing is 23mm×29mm; then go through the roving process: roving spacing is 6mm, roving twist coefficient is 75, drafting ratio is 6.5 times, spindle speed is 800rpm; finally go through the spinning process: spinning twist is 600, spinning speed is 9500rpm; ambient temperature is 24℃, relative humidity is 65%.

[0036] Test results: Yarn count 25, breaking strength 3.9 cN / dtex, breaking elongation 13.3%, yarn evenness 12.3%.

[0037] Comparative Example 1 (Traditional Two-Step Process) (1) Preparation of short fibers: The polyimide filament bundle used in Example 1 was mechanically cut into 51mm short fibers; (2) Opening and carding: Short fibers are opened by an opening machine (beater speed 750r / min) and carded into sliver by a carding machine (cylinder speed 320r / min); (3) Sliver drawing: Two-stage drawing, the first drawing combines 6 slivers and the mechanical drawing ratio is 3.5 times; the second drawing combines 8 slivers and the mechanical drawing ratio is 6 times. (4) Spinning: Ordinary ring spinning, with the same parameters as in Example 1.

[0038] Test results: Yarn count 32, breaking strength 3.0 cN / dtex, breaking elongation 9.8%, yarn evenness 16.8%.

[0039] Comparative Example 2 (Draw-spinning process without pretreatment) The steps are the same as in Example 1, except that the pretreatment process in step (2) is omitted.

[0040] Test results: Severe static electricity in the fibers during spinning, frequent entanglement of the rollers, yarn breaking strength of 3.2 cN / dtex, breaking elongation of 9.5%, and yarn unevenness of 15.6%.

[0041] Comparative Example 3 (Compact spinning process of CN109554790A) Prepared according to the method disclosed in CN109554790A: (1) Cleaning and combing process: The polyimide filament bundle used in Example 1 is cut into 51mm short fibers, opened by an opening machine (beater speed 700r / min), and spun into sliver by a carding machine (dry weight 20.68g / 5m). (2) Combined strips: Two strips are combined, with parameters the same as CN109554790A; (3) Spinning: compact spinning, roving twist 3.7 twists / 10cm, fine yarn mechanical draft ratio 34.1 times, twist coefficient 96; (4) Winding: Electronic yarn clearer removes yarn defects.

[0042] Test results: Yarn count 32, breaking strength 3.4 cN / dtex, breaking elongation 11.2%, yarn evenness 14.7%.

[0043] This invention successfully solves the core challenges of polyimide fiber spinning by synergistically optimizing the draft spinning process with pretreatment and spinning processes. Test results in Examples 1-5 show that the yarn prepared by the method of this invention has a breaking strength ≥3.5 cN / dtex, and its overall performance is superior to the traditional two-step method (Comparative Example 1), the no-pretreatment process (Comparative Example 2), and the compact spinning process of CN109554790A (Comparative Example 3). Furthermore, through the synergistic application of optimized technical solutions, this invention further improves yarn strength by 10-15% and production efficiency by more than 25%, significantly enhancing the market competitiveness of the product.

[0044] The scope of protection of this invention is defined by the claims. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention shall be included within the scope of protection of this invention.

Claims

1. A method for preparing polyimide yarn, characterized in that, Includes the following steps: (1) Provide polyimide filament bundles; (2) The polyimide filament bundle is pretreated, the pretreatment including antistatic treatment and / or softening treatment; (3) The pretreated filament bundle is drawn and broken into strips by a drawing and cutting device to obtain polyimide drawn strips; (4) The polyimide sliver is spun into polyimide yarn through a spinning process, wherein the spinning process includes drawing, roving and spinning processes.

2. The preparation method according to claim 1, characterized in that, The pretreatment method described in step (2) is selected from one or more of immersion, spraying, roller coating or atomization treatment. The functional additives used include at least one of antistatic agents and softeners. A hygroscopic agent may be added optionally. The total concentration of the functional additives is 0.3-5.0 wt%. The treatment temperature is 10-70℃ and the treatment time is 1-60 seconds.

3. The preparation method according to claim 1 or 2, characterized in that, After being drawn into strips as described in step (3), the fiber length of the polyimide drawn strip is 50-120 mm, and the length dispersion coefficient CV ≤ 15%.

4. The preparation method according to claim 1 or 2, characterized in that, The pretreatment described in step (2) is an immersion treatment. The pretreatment solution contains 0.5-2.0 wt% antistatic agent and 0.3-1.5 wt% softener. The treatment temperature is 40-60℃ and the treatment time is 2-5 seconds.

5. The preparation method according to claim 1, characterized in that, The polyimide filament bundles described in step (1) are prepared by dry spinning, wet spinning, or a combination of dry and wet spinning with thermal imidization and multi-stage thermal stretching. The total multiple of the multi-stage thermal stretching is 2-10 times, and the stretching temperature increases in a gradient from 120 to 600℃.

6. The preparation method according to claim 1, characterized in that, The strip-cutting device described in step (3) includes a preheating zone, a main cutting zone, and a stabilizing zone arranged sequentially, wherein: the temperature of the preheating zone is 80-120℃ and the roller linear speed ratio is 1:1.05-1.15; the temperature of the main cutting zone is 150-220℃ and the roller linear speed ratio is 1:3.5-7.5; the temperature of the stabilizing zone is 100-150℃ and the roller linear speed ratio is 1:1.1-1.3; the roller linear speeds of the three zones increase sequentially, and the total speed ratio is 5-10 times, wherein the total speed ratio is the output speed of the stabilizing zone / the input speed of the preheating zone.

7. The preparation method according to claim 1, characterized in that, The spinning process described in step (4) is Siro spinning, in which 2-10 polyimide slivers are combined and then processed into yarn through drawing, roving and spinning processes.

8. The preparation method according to claim 7, characterized in that, In the Siro spinning process, the distance between the two rovings is 4-8mm, the twist is 300-1000, and the spinning speed is 8000-12000rpm; the production environment temperature is 20-30℃ and the relative humidity is 60-75%.

9. A polyimide yarn, characterized in that, Prepared by any one of the methods described in claims 1-8, or comprising polyimide short fibers formed by stretching and breaking, wherein the short fibers have a length of 50-120 mm, a length dispersion coefficient CV ≤ 15%, a yarn breaking strength ≥ 3.5 cN / dtex, and a breaking elongation of 6-18%.

10. The application of the polyimide yarn according to claim 9, characterized in that, The yarn is used to prepare high-temperature resistant protective clothing, high-temperature filter materials, or special industrial fabrics or textiles.