Low-chlorine para-aramid activated fiber and preparation method thereof

Abstract

The present application relates to the technical field of fiber impregnation, and particularly relates to a low-chlorine activated para-aramid fiber and a preparation method thereof, the preparation method being as follows: according to weight fractions, raw materials of an impregnating solution include 2-5 parts of low-chlorine epoxy resin, 3-6 parts of non-ionic aliphatic water-based blocked polyisocyanate, 1-3 parts of water-based low-hydroxy polyester polyol, and 85-95 parts of deionized water; the raw materials are mixed to obtain the impregnating solution; after para-aramid fiber after twisting is impregnated in the impregnating solution, heating, water removal, drying, drawing and heat treatment are performed to obtain the low-chlorine activated para-aramid fiber. The low-chlorine activated para-aramid fiber can be adapted to low-chlorine low-halogen high-end scenarios, is more environmentally friendly, can significantly improve the interfacial bonding performance of aramid, and can improve the mechanical strength, anti-peeling property and long-term bonding stability of the composite material, and meets the performance requirements of reinforcing materials.

Description

Technical Field

[0001] This invention relates to a low-chlorine para-aramid activated fiber and its preparation method, belonging to the field of fiber impregnation technology. Background Technology

[0002] Para-aramid fibers possess excellent properties such as high strength, high modulus, temperature resistance, fatigue resistance, and dimensional stability, and are widely used in rubber reinforcement, composite materials, cable reinforcement, and electronic communication materials. However, para-aramid molecules have a regular molecular chain structure, smooth surface, and few active groups, resulting in weak interfacial bonding with matrix materials such as rubber and resins. Therefore, impregnation activation treatment is necessary to introduce active groups and improve surface wettability and adhesion.

[0003] Existing para-aramid activated impregnation systems mostly employ components such as ordinary epoxy resins, chlorine-containing curing agents, halogen-containing additives, or solvent-based isocyanates, inevitably introducing halogen elements such as chlorine into the system. When these chlorine-containing activated fibers are used in applications such as electronic communications, cables, precision electronic devices, and low-smoke halogen-free flame-retardant materials, halogen elements are prone to precipitating, migrating, or releasing halides under high temperature, high humidity, and long-term service conditions. This poses risks such as corroding metal conductors, accelerating insulation aging, reducing the flame-retardant safety of materials, and contaminating electronic devices, making it difficult to meet the stringent requirements for low-chlorine, low-halogen, and environmentally friendly safety in high-end cables, electronic communications, and new energy materials.

[0004] Meanwhile, traditional impregnation systems often employ solvent-based formulations or high-chlorine components, which not only have poor environmental performance and high VOC emissions, but also easily leave high-chlorine impurities on the fiber surface, affecting activation stability and long-term reliability. Currently, there are relatively few para-aramid activation impregnation solutions specifically developed for low-chlorine and low-halogen applications. Therefore, existing aramid activation impregnation solutions often fail to meet the comprehensive requirements of efficient fiber activation, enhanced interfacial adhesion, extremely low chlorine content, and environmental friendliness, thus restricting the large-scale application of para-aramid in the field of high-end low-chlorine and low-halogen materials. Summary of the Invention

[0005] This invention addresses the shortcomings of existing para-aramid activation impregnation systems, such as high chlorine and other halogen content, inability to adapt to low-chlorine and low-halogen scenarios, easy corrosion of electronic components, poor environmental performance, and insufficient activation stability. It provides a low-chlorine para-aramid activated fiber and its preparation method. The low-chlorine para-aramid activated fiber is suitable for high-end low-chlorine and low-halogen scenarios, is more environmentally friendly, and significantly improves the interfacial bonding performance of aramid, enhancing the mechanical strength, peel resistance, and long-term bonding stability of the composite material, thus meeting the performance requirements of reinforcing materials.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing low-chlorine para-aramid activated fibers, wherein the preparation method is as follows: S1. By weight, the raw materials of the impregnation solution include: 2-5 parts of low-chlorine epoxy resin, 3-6 parts of nonionic aliphatic waterborne blocked polyisocyanate, 1-3 parts of waterborne low-hydroxyl polyester polyol, and 85-95 parts of deionized water; the impregnation solution is obtained by mixing the raw materials. S2. After the twisted para-aramid fiber is impregnated in the impregnation solution, it is heated to remove water and dried, stretched and heat-treated to obtain the low-chlorine para-aramid activated fiber.

[0007] Further, in step S1, the low-chlorine epoxy resin is at least one of EX-810P, EX-201-IM, and EX-121.

[0008] Furthermore, in step S1, the unsealing temperature of the nonionic aliphatic aqueous blocked polyisocyanate is 130-160℃.

[0009] Furthermore, in step S1, the hydroxyl value of the aqueous low-hydroxyl polyester polyol is 35-59.

[0010] Furthermore, in step S2, the immersion time is 30-80 seconds.

[0011] Furthermore, in step S2, the temperature for heating and dehydration drying is 90-120°C, and the drying time is 90-180 seconds.

[0012] Furthermore, in step S2, the temperature conditions for the heat treatment are 180-220℃, and the heat treatment time is 60-120s.

[0013] Furthermore, in step S2, the heat treatment adopts a gradient heating method, and the step heating conditions are: first, treat at 120-140℃ for 20-40s, then treat at 150-170℃ for 20-40s, and finally treat at 190-220℃ for 20-40s.

[0014] Furthermore, in step S2, the traction speed is 4-8 m / min and the traction tension is 3-6 N.

[0015] The present invention also discloses a low-chlorine para-aramid activated fiber, which is prepared by the preparation method described in the present invention.

[0016] The beneficial effects of this invention are: In the preparation method of low-chlorine para-aramid activated fiber described in this invention, the impregnation solution formulation is controlled at the source. A water-based compound system of low-chlorine epoxy resin, nonionic aliphatic waterborne blocked polyisocyanate, and waterborne low-hydroxyl polyester polyol is used. No chlorine-containing curing agents or halogen-containing additives are used. The introduction of chlorine and other halogen elements is eliminated from the source of raw materials. The chlorine and halogen content in the obtained low-chlorine para-aramid activated fiber is significantly reduced compared with traditional processes. It can be directly applied to fields with strict requirements for low chlorine and low halogen, such as electronic communication cables, precision electronic reinforcement, low-smoke halogen-free flame retardant materials, and new energy insulation components. It effectively avoids the risks of corrosion of metal conductors, accelerated aging of insulation layers, and pollution of electronic devices caused by halide precipitation.

[0017] In the impregnation solution used in this invention, a large number of hydroxyl groups carried by the aqueous low-hydroxyl polyester polyol undergo urethane addition reaction with the unsealed -NCO during heat treatment, and simultaneously undergo secondary crosslinking with the hydroxyl groups of the epoxy ring-opening product, constructing an epoxy-polyurethane interpenetrating crosslinking network and improving the overall crosslinking density. The low-chlorinated epoxy resin provides a rigid skeleton and reaction anchor points, while the low-hydroxyl polyester polyol compensates for insufficient crosslinking density and introduces flexible segments. The two form a synergistic relationship in the reaction path, which significantly improves the crosslinking density and structural stability of the activated film layer on the fiber surface. This effectively improves the amount of active group grafting and interfacial bonding strength on the fiber surface, and solves the technical defects of low-chlorinated epoxy resin, such as decreased epoxy group reactivity and incomplete crosslinking caused by deep dechlorination and purification. As a result, the adhesion performance and long-term bonding stability of the activated fiber with matrix materials such as rubber and resin are greatly improved, ensuring the long-term reliable use of the composite material under dynamic loads and harsh working conditions.

[0018] In the preparation method described in this invention, the low-hydroxyl-value polyester polyol selected has a low hydroxyl density, so when added to the aqueous compound system, the emulsion stability is not compromised due to excessive polarity differences. The unblocking temperature of the nonionic aliphatic aqueous blocked polyisocyanate and the subsequent heat treatment temperature step form a time mismatch of "dehydration-unblocking-crosslinking": during the drying stage, the blocked isocyanate remains in a blocked state and does not participate in the reaction, and the water in the system is fully removed. When the temperature rises above the unblocking temperature, the -NCO group begins to unblock. At this time, the free water in the system has been basically removed, effectively avoiding the competitive side reaction between -NCO and water (generating urea and CO2 bubbles), so that the unblocked -NCO can react efficiently with the hydroxyl groups of the low-hydroxyl polyester polyol in a directional manner. The low hydroxyl value ensures the stability of the emulsion, and the unsealing temperature ensures the reaction sequence. The two work together to ensure that the reaction proceeds precisely according to the designed path. The film layer on the fiber surface is dense and uniform, and the cross-linking reaction is complete. This ensures both the stability of the emulsion and the selectivity of the reaction, and avoids film defects and performance degradation caused by side reactions.

[0019] More specifically, in the gradient heating method, each temperature step corresponds to one of the three reaction stages: "preheating and homogenization → main cross-linking → deep curing." This works in conjunction with the desealing kinetics of isocyanate, avoiding the defects of premature surface curing and insufficient internal cross-linking caused by direct high-temperature heat treatment. It also avoids the problem of concentrated release of -NCO and exacerbated side reactions due to rapid desealing at high temperatures. The progressive treatment with three temperature steps allows the fiber and film to achieve sufficient thermal equilibrium. The desealed -NCO has ample reaction time and orderly cross-linking with hydroxyl groups at each stage, ensuring thorough curing of the activated film from the surface inwards, with a uniform cross-linking density distribution. This imparts a stable activation effect and consistent mechanical properties to the fiber.

[0020] More specifically, in the preparation method described in this invention, the twisted aramid fibers have a helical structure with close contact between the monofilaments within the fiber bundle. This invention ensures sufficient residence time for the fibers in the impregnation solution through a moderate traction speed, allowing the low-viscosity aqueous impregnation solution to fully penetrate the fiber bundle along the helical gaps, achieving uniform coating at the monofilament level. Combined with appropriate traction tension, the twisted fiber bundle unfolds moderately during operation without excessive stretching, allowing the impregnation solution to wet each monofilament and form a uniform activation film layer on its surface. This synergistic matching of speed and tension ensures that the activation film layer not only forms on the outer surface of the fiber bundle but also penetrates deep into the fiber bundle to coat each monofilament, effectively increasing the interfacial bonding area and bonding strength with the rubber matrix. Simultaneously, it avoids damage to the fiber's mechanical properties due to excessive stretching, fully preserving the fiber's high-strength characteristics and achieving a simultaneous improvement in activation effect and mechanical properties.

[0021] In summary, this invention achieves superior overall performance by synergistically combining low-chlorine epoxy resin, waterborne low-hydroxyl polyester polyol, and nonionic aliphatic waterborne blocked polyisocyanate, along with synergistic processes involving traction parameters and gradient heat treatment. This results in a significant reduction in chlorine content, a substantial increase in adhesive strength, and the retention of high fiber strength in para-aramid activated fibers. The chlorine content is effectively controlled at the source, meeting the requirements of high-end low-chlorine and low-halogen applications. The construction of the interpenetrating crosslinking network significantly enhances adhesive performance, and the mild process conditions fully preserve the fiber's intrinsic high strength characteristics. This effectively solves the long-standing technical challenge of achieving both high performance and low chlorine content in high-end applications. Furthermore, this invention utilizes a water-based system with deionized water as the medium, contains no organic solvents, has low VOC emissions, no irritating odor, and a safe and environmentally friendly production process that complies with green manufacturing and environmental regulations, making it suitable for continuous industrial production. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0024] A method for preparing low-chlorine para-aramid activated fibers, the preparation method comprising: S1. By weight, the raw materials of the impregnation solution include: 2-5 parts of low-chlorine epoxy resin, 3-6 parts of nonionic aliphatic waterborne blocked polyisocyanate, 1-3 parts of waterborne low-hydroxyl polyester polyol, and 85-95 parts of deionized water; the impregnation solution is obtained by mixing the raw materials. S2. After the twisted para-aramid fiber is impregnated in the impregnation solution, it is heated to remove water and dried, stretched and heat-treated to obtain the low-chlorine para-aramid activated fiber.

[0025] Specifically, in step S1, the low-chlorine epoxy resin is at least one of EX-810P (NAGASE Group), EX-201-IM (NAGASE Group), and EX-121 (NAGASE Group).

[0026] Specifically, in step S1, the unsealing temperature of the nonionic aliphatic waterborne blocked polyisocyanate is 130-160℃.

[0027] The unsealing temperature is significantly higher than the dehydration drying temperature (90-120℃), ensuring that the blocked isocyanate remains blocked and does not participate in the reaction during the drying stage. Free water in the system is fully removed during this stage. When the temperature continues to rise above the unsealing temperature, the -NCO groups begin to unseale and react directionally with the hydroxyl groups of the low-hydroxyl polyester polyol. At this point, the water in the system has been almost completely removed, thus effectively avoiding the competitive side reaction between -NCO and water to generate urea and CO2 bubbles. This allows the crosslinking reaction to proceed precisely along the designed path, resulting in a dense, uniform, and fully crosslinked activated film layer on the fiber surface. At the same time, this unsealing temperature is precisely matched with the gradient heating process, achieving stepwise reaction sequence control of "dehydration → unsealing → deep crosslinking," making the crosslinking reaction process orderly and controllable, and ensuring uniform and sufficient film layer curing. In addition, the non-ionic emulsion structure avoids the impact of electrolyte effects on the stability of the compound system, and the aliphatic structure endows the activated film layer with excellent resistance to yellowing and long-term stability, ensuring the performance durability of the activated fiber during long-term use.

[0028] More specifically, in step S1, the nonionic aliphatic aqueous blocked polyisocyanate is at least one of FB-10 (Sivo Chemical), FB-12 (Sivo Chemical), and FB-15 (Sivo Chemical).

[0029] Specifically, in step S1, the hydroxyl value of the water-based low-hydroxyl polyester polyol is 35-59.

[0030] More specifically, in step S1 of this embodiment of the invention, the waterborne low-hydroxyl polyester polyol is selected from at least one of Asahikawa Chemical XCP-2000N (hydroxyl value 53-59) and Asahikawa Chemical XCP-3000N (hydroxyl value 35-39).

[0031] In chlorinated epoxy resins, organochlorine can catalyze the ring-opening of the epoxy, improving the crosslinking efficiency with isocyanates. However, the NAGASE series of low-chlorinated epoxy resins (EX-810P / EX-201-IM / EX-121) undergo deep dechlorination and purification, resulting in the removal of a large amount of intramolecular catalytic chlorine impurities and a decrease in the reactivity of epoxy groups. After the impregnation solution is coated onto a smooth para-aramid surface, the epoxy and isocyanate crosslinking is incomplete, leading to a thin, loose, and easily detached film layer on the fiber surface, making it impossible to stably introduce active groups. Low-hydroxyl polyester polyols, due to their low hydroxyl value, do not compromise emulsion stability due to excessive polarity differences before and after addition, and possess a large number of hydroxyl groups. During heat treatment, they undergo a urethane addition reaction with the unsealed -NCO, simultaneously crosslinking with the hydroxyl groups of the epoxy ring-opening product, constructing an epoxy-polyurethane interpenetrating crosslinking network. This significantly increases the overall crosslinking density and compensates for the incomplete crosslinking defects caused by the absence of chlorine catalysis.

[0032] More specifically, in step S1, the impregnation solution is prepared by: first adding the low-chlorine epoxy resin to deionized water and stirring to disperse it, then adding the waterborne low-hydroxyl polyester polyol and stirring to disperse it, and finally adding the nonionic aliphatic waterborne blocked polyisocyanate and stirring to mix it evenly. The temperature conditions during the preparation process are 35-45℃ and the stirring time is 1-3h.

[0033] During the preparation of the impregnation solution, the epoxy resin first forms a stable base emulsion in water, providing a compatible medium environment for the subsequently added low-hydroxyl polyester polyol, thus avoiding the risk of hydrolysis caused by direct contact of the polyol with a large amount of aqueous phase. Isocyanate, as the most reactive component, is added last to prevent premature contact with the polyol or epoxy resin and the occurrence of localized pre-crosslinking reactions. It also avoids damage to the closed particle structure caused by high shear or prolonged stirring, effectively ensuring the storage stability, batch uniformity, and reactivity of the impregnation solution. The medium-temperature preparation conditions of 35-45℃ are conducive to the thorough softening of all components. The stirring process promotes uniform mixing of the ternary compound system at the molecular scale through dispersion and molecular chain segment movement, while preventing premature desealing of isocyanates or thickening and gelation of the system due to excessively high temperatures. This provides a precursor structure basis for the precise construction of the epoxy-polyurethane interpenetrating network in the subsequent heat treatment stage. The stirring time of 1-3 hours ensures that each component is fully diffused and penetrated to a homogeneous state, resulting in a uniform distribution of epoxy groups, blocked isocyanate groups and hydroxyl groups in the impregnation solution. This ensures that the para-aramid fibers obtain a uniform amount of active components during impregnation, ultimately endowing the activated fibers with stable and consistent film quality and adhesion performance.

[0034] Specifically, in step S2, the soaking time is 30-80 seconds.

[0035] Specifically, in step S2, the temperature for heating and dehydration is 90-120°C, and the time for heating and dehydration is 90-180 seconds.

[0036] Specifically, in step S2, the temperature conditions for the heat treatment are 180-220℃, and the heat treatment time is 60-120s.

[0037] The drying temperature (90-120℃) is significantly lower than the unblocking temperature (130-160℃) of nonionic aliphatic waterborne blocked polyisocyanates, ensuring that the blocked isocyanates remain blocked during the drying stage and do not participate in the crosslinking reaction. Free water and volatile substances in the system are fully removed at this stage, avoiding competitive side reactions between -NCO and water (generating urea and CO2 bubbles) caused by residual moisture during subsequent high-temperature heat treatment. At the same time, this temperature is sufficient to allow the fiber and film layer to reach thermal equilibrium, preparing thermodynamically for the subsequent crosslinking reaction. The subsequent heat treatment temperature window (180-220℃) is higher than the unblocking temperature of the isocyanate, ensuring that the -NCO groups are fully unblocked and undergo urethane addition with the hydroxyl groups of the low-hydroxyl polyester polyol. The reaction occurs at a temperature that also reaches the activation energy threshold required for ring-opening crosslinking of the epoxy resin, promoting ring-opening of the epoxy groups and secondary crosslinking with the residual hydroxyl groups in the system, ultimately forming a high-density epoxy-polyurethane interpenetrating crosslinked network. The stepwise combination of drying time (90-180s) and heat treatment time (60-120s) ensures that the reaction at each stage is fully carried out, while avoiding thermal damage caused by excessive fiber residence time in the high-temperature zone or film embrittlement caused by excessive crosslinking, thus fully preserving the high strength properties of the fiber. In addition, the segmented temperature design of "low-temperature dehydration-high-temperature crosslinking" allows for flexible selection of two-stage or gradient heat treatment schemes according to actual production needs, which is highly operable and conducive to temperature control and quality stability assurance in continuous industrial production.

[0038] Preferably, in step S2, the heat treatment adopts a gradient heating method, and the step heating conditions are: first, treat at 120-140℃ for 20-40s, then treat at 150-170℃ for 20-40s, and finally treat at 190-220℃ for 20-40s.

[0039] This gradient heating method precisely matches the deblocking temperature (130-160℃) of nonionic aliphatic waterborne blocked polyisocyanate. The first step temperature (120-140℃) is located near the starting point of the deblocking temperature, allowing the fiber and film layer to reach thermal equilibrium and prepare for subsequent deblocking. The second step temperature (150-170℃) triggers a large-scale deblocking of -NCO and a main crosslinking reaction with the hydroxyl groups of the low-hydroxyl polyester polyol. The third step temperature (190-220℃) promotes deep ring-opening of the epoxy resin and full crosslinking with the residual active groups in the system, forming a high-density interpenetrating network. The three temperature steps correspond to "preheating and homogenization → main crosslinking ... The three reaction stages of "body crosslinking → deep curing" are highly consistent with the desealing kinetics of isocyanate, enabling precise timing control of the crosslinking reaction process. This effectively avoids the defects of one-step direct high-temperature heat treatment, such as the concentrated explosive deheating of -NCO and the aggravation of side reactions caused by the rapid temperature rise, as well as the "inconsistency between surface and interior" problem of premature curing of the film layer and insufficient internal crosslinking. This ensures that the activated film layer is fully cured from the surface to the interior, with a uniform distribution of crosslinking density, thereby endowing the activated fiber with stable and excellent adhesive properties. At the same time, it avoids the thermal stress and film cracking caused by rapid temperature transition, ensuring that the high strength characteristics of the fiber are fully preserved, making it suitable for continuous industrial production.

[0040] Specifically, in step S2, the traction speed is 4-8 m / min and the traction tension is 3-6 N.

[0041] This traction speed ensures sufficient residence time for the para-aramid fibers in the impregnation solution, guaranteeing thorough wetting of the fiber surface and penetration into the fiber bundle. Simultaneously, it avoids over-immersion and excessive adhesion of the fibers due to excessively slow speed, which could negatively impact subsequent drying efficiency and film uniformity. Conversely, it prevents insufficient impregnation time and low adhesion of active components due to excessively fast speed, thus affecting the activation effect. This traction tension maintains the twisted para-aramid fiber bundle in a moderately spread state during operation, preventing excessive stretching. Too low a tension results in a tightly twisted fiber bundle, hindering the penetration of the impregnation solution into each filament and potentially causing a "dry core" phenomenon. Too high a tension causes excessive tensile stress on the fibers, which may... This can lead to monofilament breakage or damage to mechanical properties. Appropriate tension ensures that the gaps between monofilaments in the fiber bundle are adequately opened to allow the impregnating solution to fully penetrate and form a uniform activated film on the surface of each monofilament. It also avoids damage to the intrinsic high strength properties of the fiber caused by excessive stretching, thus maintaining a high level of tensile strength retention. Simultaneously, this traction speed and tension parameter, combined with the subsequent gradient heat treatment process, ensures that the fiber maintains a stable operating state and consistent initial tension before entering the heat treatment system. This effectively avoids problems such as inconsistent film thickness, differences in thermal shrinkage, and fiber slippage caused by speed fluctuations or uneven tension, ensuring consistency in product performance between batches and stability of the production line during long-term operation.

[0042] More specifically, the twisted para-aramid fibers used in the embodiments of the present invention have the following properties: 1000D (fineness of a single twisted fiber), 1×3 (yarn structure), S / Z (twisting direction of primary / secondary twist), and 225 / 130 (twisting degree of primary / secondary twist). However, this does not constitute a limitation of the present invention.

[0043] A low-chlorine para-aramid activated fiber, wherein the low-chlorine para-aramid activated fiber is prepared by the preparation method described in this invention.

[0044] Example 1: Preparation of low-chlorine para-aramid activated fibers.

[0045] A method for preparing low-chlorine para-aramid activated fibers is as follows: (1) Preparation of low-chlorine activated impregnation solution: By weight, 2.6 parts of EX-810P (NAGASE Group) were added to 91.2 parts of deionized water and stirred to disperse. Then, 2.0 parts of XCP-2000N were added and stirred to disperse. Finally, 4.2 parts of FB-10 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 40℃ and the stirring time was 2 hours.

[0046] (2) Preparation of low-chlorine para-aramid activated fibers: The twisted para-aramid fibers were impregnated in a low-chlorine activation impregnation solution for 60 seconds, then dried at 95 ℃ for 110 seconds, and finally drawn (drawing speed of 8 m / min and drawing tension of 3 N) to a heat treatment system for heat treatment to obtain low-chlorine activated para-aramid fibers. The heat treatment adopted a gradient heating method, with the following step heating conditions: first treated at 130℃ for 30 seconds, then treated at 150℃ for 30 seconds, and finally treated at 190℃ for 40 seconds.

[0047] Example 2: Preparation of low-chlorine para-aramid activated fibers.

[0048] A method for preparing low-chlorine para-aramid activated fibers is as follows: (1) Preparation of low-chlorine activated impregnation solution: According to the weight percentage, 3.2 parts of EX-201-IM (NAGASE Group) were added to 91.0 parts of deionized water and stirred to disperse. Then, 1.0 part of XCP-3000N was added and stirred to disperse. Finally, 4.8 parts of FB-12 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 38℃ and the stirring time was 3h.

[0049] (2) Preparation of low-chlorine para-aramid activated fibers: The twisted para-aramid fibers were impregnated in a low-chlorine activation impregnation solution for 70 seconds, then dried at 95 ℃ for 100 seconds, and finally drawn (drawing speed of 7 m / min and drawing tension of 3 N) to a heat treatment system for heat treatment to obtain low-chlorine activated para-aramid fibers. The heat treatment adopted a gradient heating method, with the following step heating conditions: first treated at 120℃ for 30 seconds, then treated at 170℃ for 40 seconds, and finally treated at 200℃ for 40 seconds.

[0050] Example 3: Preparation of low-chlorine para-aramid activated fibers.

[0051] A method for preparing low-chlorine para-aramid activated fibers is as follows: (1) Preparation of low-chlorine activated impregnation solution: By weight, 4.8 parts of EX-810P (NAGASE Group) were added to 88.6 parts of deionized water and stirred to disperse. Then, 3.0 parts of XCP-2000N were added and stirred to disperse. Finally, 3.6 parts of FB-15 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 42℃ and the stirring time was 1.5h.

[0052] (2) Preparation of low-chlorine para-aramid activated fibers: The twisted para-aramid fibers were impregnated in a low-chlorine activation impregnation solution for 80 seconds, then dried at 110℃ for 90 seconds, and finally drawn (drawing speed of 4 m / min, drawing tension of 6 N) to a heat treatment system for heat treatment to obtain low-chlorine activated para-aramid fibers. The heat treatment adopted a gradient heating method, with the following step heating conditions: first treated at 140℃ for 20 seconds, then treated at 160℃ for 30 seconds, and finally treated at 220℃ for 40 seconds.

[0053] Example 4: Preparation of low-chlorine para-aramid activated fibers.

[0054] A method for preparing low-chlorine para-aramid activated fibers is as follows: (1) Preparation of low-chlorine activated impregnation solution: According to the weight percentage, 3.2 parts of EX-121 (NAGASE Group) were added to 89.6 parts of deionized water and stirred to disperse. Then, 2.0 parts of XCP-3000N were added and stirred to disperse. Finally, 5.2 parts of FB-12 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 40℃ and the stirring time was 3 hours.

[0055] (2) Preparation of low-chlorine para-aramid activated fibers: The twisted para-aramid fibers were impregnated in a low-chlorine activation impregnation solution for 75 seconds, then dried at 92 ℃ for 105 seconds, and finally drawn (drawing speed of 5 m / min and drawing tension of 4 N) to a heat treatment system for heat treatment to obtain low-chlorine activated para-aramid fibers. The heat treatment adopted a gradient heating method, with the following step heating conditions: first treated at 130℃ for 40 seconds, then treated at 160℃ for 40 seconds, and finally treated at 195℃ for 35 seconds.

[0056] Example 5: Preparation of low-chlorine para-aramid activated fibers.

[0057] A method for preparing low-chlorine para-aramid activated fibers is as follows: (1) Preparation of low-chlorine activated impregnation solution: By weight, 2.0 parts of EX-121 (NAGASE Group) were added to 94 parts of deionized water and stirred to disperse. Then, 1.0 part of XCP-2000N was added and stirred to disperse. Finally, 3.0 parts of FB-10 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 40℃ and the stirring time was 2 hours.

[0058] (2) Preparation of low-chlorine para-aramid activated fibers: The twisted para-aramid fibers were impregnated in a low-chlorine activation impregnation solution for 80 seconds, then dried at 100℃ for 100 seconds, and finally drawn (drawing speed of 4 m / min, drawing tension of 6 N) to a heat treatment system for heat treatment to obtain low-chlorine activated para-aramid fibers. The heat treatment adopted a gradient heating method, with the following step heating conditions: first treated at 135℃ for 35 seconds, then treated at 165℃ for 40 seconds, and finally treated at 200℃ for 40 seconds.

[0059] Example 6: Preparation of low-chlorine para-aramid activated fibers.

[0060] A method for preparing low-chlorine para-aramid activated fibers is as follows: (1) Preparation of low-chlorine activated impregnation solution: By weight, 5.0 parts of EX-121 (NAGASE Group) were added to 86 parts of deionized water and stirred to disperse. Then, 3.0 parts of XCP-3000N were added and stirred to disperse. Finally, 6.0 parts of FB-15 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 45℃ and the stirring time was 3 hours.

[0061] (2) Preparation of low-chlorine para-aramid activated fibers: The twisted para-aramid fibers were impregnated in a low-chlorine activation impregnation solution for 70 seconds, then dried at 90 ℃ for 100 seconds, and finally drawn (drawing speed of 7 m / min, drawing tension of 3 N) to a heat treatment system for heat treatment to obtain low-chlorine activated para-aramid fibers. The heat treatment adopted a gradient heating method, with the following step heating conditions: first treated at 120 ℃ for 40 seconds, then treated at 150 ℃ for 20 seconds, and finally treated at 190 ℃ for 30 seconds.

[0062] Example 7: Preparation of low-chlorine para-aramid activated fibers.

[0063] A method for preparing low-chlorine para-aramid activated fibers is as follows: (1) Preparation of low-chlorine activated impregnation solution: By weight, 2.6 parts of EX-810P (NAGASE Group) were added to 91.2 parts of deionized water and stirred to disperse. Then, 2.0 parts of XCP-2000N were added and stirred to disperse. Finally, 4.2 parts of FB-10 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 40℃ and the stirring time was 2 hours.

[0064] (2) Preparation of low-chlorine para-aramid activated fibers: The twisted para-aramid fibers were impregnated in a low-chlorine activated impregnation solution for 60 seconds, then dried at 95 °C for 110 seconds, and finally drawn (drawing speed of 8 m / min and drawing tension of 3 N) to a heat treatment system and heat-treated at 190 °C for 100 seconds to obtain low-chlorine activated para-aramid fibers.

[0065] Example 8: Preparation of low-chlorine para-aramid activated fibers.

[0066] A method for preparing low-chlorine para-aramid activated fibers is as follows: (1) Preparation of low-chlorine activated impregnation solution: According to the weight percentage, 3.2 parts of EX-201-IM (NAGASE Group) were added to 91.0 parts of deionized water and stirred to disperse. Then, 1.0 part of XCP-3000N was added and stirred to disperse. Finally, 4.8 parts of FB-12 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 38℃ and the stirring time was 3h.

[0067] (2) Preparation of low-chlorine para-aramid activated fibers: The twisted para-aramid fibers were impregnated in a low-chlorine activated impregnation solution for 70 seconds, then dried at 95 °C for 100 seconds, and finally drawn (drawing speed of 7 m / min and drawing tension of 3 N) to a heat treatment system and heat-treated at 200 °C for 110 seconds to obtain low-chlorine activated para-aramid fibers.

[0068] Comparative Example 1: Preparation of para-aramid activated fibers.

[0069] A method for preparing para-aramid activated fibers is as follows: (1) Preparation of conventional activation impregnation solution: By weight, 2.6 parts of epoxy E51 were added to 97.4 parts of deionized water and stirred at 40°C for 2 hours to obtain the impregnation solution.

[0070] (2) Preparation of para-aramid activated fibers: The process method is the same as in Example 1.

[0071] Comparative Example 2: Preparation of para-aramid activated fibers.

[0072] A method for preparing para-aramid activated fibers is as follows: (1) Preparation of activation impregnation solution (the difference from Example 1 is that no aqueous low-hydroxyl polyester polyol was added in this Comparative Example 2): By weight, 2.6 parts of EX-810P (NAGASE Group) were added to 93.2 parts of deionized water and stirred to disperse. Then, 4.2 parts of FB-10 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 40℃ and the stirring time was 2 hours.

[0073] (2) Preparation of para-aramid activated fibers: The process method is the same as in Example 1.

[0074] Comparative Example 3: Preparation of para-aramid activated fibers.

[0075] A method for preparing para-aramid activated fibers is as follows: (1) Preparation of activated impregnation solution (the difference from Example 1 is that the proportion of aqueous low-hydroxyl polyester polyol added is increased in this Comparative Example 3): By weight, 2.6 parts of EX-810P (NAGASE Group) were added to 88.2 parts of deionized water and stirred to disperse. Then, 5.0 parts of XCP-2000N were added and stirred to disperse. Finally, 4.2 parts of FB-10 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 40℃ and the stirring time was 2 hours.

[0076] (2) Preparation of para-aramid activated fibers: The process method is the same as in Example 1.

[0077] Comparative Example 4: Preparation of para-aramid activated fibers.

[0078] A method for preparing para-aramid activated fibers is as follows: (1) Preparation of activated impregnation solution (the difference from Example 1 is that the polyester polyol used in Comparative Example 4 has a hydroxyl value > 59, which is higher than the hydroxyl value specified in this invention): By weight, 2.6 parts of EX-810P (NAGASE Group) were added to 91.2 parts of deionized water and stirred to disperse. Then, 2.0 parts of Asahikawa Chemical XCP-1000N (high hydroxyl value waterborne polyester polyol, hydroxyl value 106-118) were added and stirred to disperse. Finally, 4.2 parts of FB-10 (Siwo Chemical) were added and stirred to mix evenly. The temperature conditions during the preparation process were 40℃ and the stirring time was 2 hours.

[0079] (2) Preparation of para-aramid activated fibers: The process method is the same as in Example 1.

[0080] Comparative Example 5: Preparation of para-aramid activated fibers.

[0081] A method for preparing para-aramid activated fibers is as follows: (1) Preparation of activated impregnation solution (the difference from Example 1 is that the nonionic aliphatic aqueous blocked polyisocyanate used in Comparative Example 5 has an unblocking temperature of less than 120°C): By weight, 2.6 parts of EX-810P (NAGASE Group) were added to 91.2 parts of deionized water and stirred to disperse. Then, 2.0 parts of XCP-2000N were added and stirred to disperse. Finally, 4.2 parts of PT-1202G (Guangzhou Lvbao) were added and stirred to mix evenly. The temperature conditions during the preparation process were 40℃ and the stirring time was 2 hours.

[0082] (2) Preparation of para-aramid activated fibers: The process method is the same as in Example 1.

[0083] Comparative Example 6: Preparation of para-aramid activated fibers.

[0084] A method for preparing para-aramid activated fibers is as follows: (1) Preparation of activation impregnation solution: Same as Example 1.

[0085] (2) Preparation of para-aramid activated fibers (the difference from Example 7 is that the dehydration and drying and heat treatment processes in this Comparative Example 6 were not carried out separately, that is, the dehydration and drying were not carried out separately, but the heat treatment conditions were directly extended): The twisted para-aramid fibers were impregnated in a low-chlorine activation impregnation solution for 60 seconds, and then drawn (drawing speed of 8 m / min, drawing tension of 3 N) to a heat treatment system and heat-treated at 190℃ for 150 seconds to obtain activated para-aramid fibers.

[0086] The performance of the para-aramid activated fibers prepared in the above embodiments and comparative examples was tested using the following test methods.

[0087] (1) Halogen detection test instructions: The halogen content of all examples and comparative samples was tested in accordance with the standard EN 14582:2016 Characterization of waste - Determination of halogen and sulfur content - Combustion in oxygen and ion chromatography. Ion chromatography was used to analyze and detect halogen elements such as fluorine, chlorine, bromine, and iodine. The detection process was carried out in accordance with the compliance judgment rules of ILAC-G8:09 / 2019. The method detection limits for each element were 20 ppm for fluorine, 50 ppm for chlorine, 50 ppm for bromine, and 50 ppm for iodine. At least 3 parallel samples were tested for each group of samples, and the average value of the valid data was recorded as the final result.

[0088] (2) Extraction Test Description: All activated fibers in the examples and comparative examples underwent secondary treatment using RFL, followed by the preparation of adhesive samples and testing of adhesive properties using natural styrene-butadiene rubber according to the GB / T2942-2009 standard "Determination of Static Adhesion Strength between Vulcanized Rubber and Fiber Cords - Extraction Method". The extraction test of the adhesive force between para-aramid and rubber was conducted on an electronic tensile testing machine manufactured by INSTRON in the UK, according to the GB / T2942-2009 standard. The test speed was 130 mm / min, and the maximum force when the fiber was pulled out of the rubber was recorded. At least 10 samples were tested, and the average value of at least 10 valid data points was recorded.

[0089] (3) Peel test instructions: The adhesive peel test was conducted on an electronic tensile testing machine in accordance with GB / T 40725-2021 standard. The test speed was 300 mm / min. The maximum force when the fiber peeled from the rubber at 180° was recorded. At least 6 samples were tested, and the average value of at least 6 valid data was recorded. The specific test results are shown in Table 1 below.

[0090] Table 1 Performance test results of para-aramid activated fibers

[0091] As shown in Table 1, the low-chlorine para-aramid activated fibers prepared in Examples 1-6 (using the preparation method described in this invention) have certain advantages in use. On the one hand, they exhibit excellent control over chlorine content. Testing revealed that the conventional activated fibers in Comparative Example 1, prepared using traditional processes, contained as much as 1647 ppm of halogens, while the halogen content in the samples from each example of this invention was only 132-171 ppm, a reduction of over 90%. This achieves the goal of low chlorine and low halogens from the source of raw materials, effectively avoiding problems such as halide precipitation corroding devices and accelerating insulation aging. This meets the usage requirements of high-end fields such as electronic communication cables, precision electronic reinforcement, low-smoke halogen-free flame-retardant materials, and new energy insulation components. Secondly, Examples 1-6 demonstrate superior activation effects on the fibers. A uniform activated film layer is formed on the fiber surface, introducing active groups and enhancing the bonding ability with the rubber matrix. Compared to traditional products, the para-aramid activated fibers prepared by the method described in this invention exhibit superior H-pull-out force and 180° peel force, resulting in enhanced adhesion and ensuring long-term stable use of the composite material. Furthermore, the comparison results between Example 7 and Example 1, and between Example 8 and Example 1, show that using gradient heating in the heat treatment process is more conducive to obtaining para-aramid activated fibers with excellent activation and strength properties.

[0092] A comparison of the experimental results of Comparative Example 2 and Example 1 shows that: Comparative Example 2's impregnation solution did not contain any waterborne low-hydroxyl polyester polyol, but was only composed of low-chlorinated epoxy resin and nonionic aliphatic waterborne blocked polyisocyanate. The results indicate that the adhesive performance of Comparative Example 2 was significantly lower than that of Example 1, and the fiber strength retention rate also decreased. This suggests that the low-chlorinated epoxy resin, due to deep dechlorination and purification, had a large amount of intramolecular catalytic chlorine impurities removed, resulting in decreased epoxy group reactivity, incomplete crosslinking between epoxy and isocyanate, and a thin, loose, and easily detached film layer on the fiber surface, making it impossible to stably introduce active groups. In contrast, the addition of the waterborne low-hydroxyl polyester polyol, through its numerous hydroxyl groups, allows for urethane addition reactions with the unblocked -NCO during heat treatment, and simultaneously secondary crosslinking with the epoxy ring-opening product hydroxyl groups, constructing an epoxy-polyurethane interpenetrating crosslink network. This significantly increases the overall crosslinking density, thereby significantly enhancing the adhesive performance between the fiber and the rubber matrix. Simultaneously, due to the effective coating and protection of the fiber surface by the film layer, the tensile strength of the fiber is also better maintained.

[0093] A comparison of the experimental results of Comparative Example 3 and Example 1 shows that the proportion of aqueous low-hydroxyl polyester polyol added in Comparative Example 3 was increased to exceed the 1-3 parts range specified in this invention. The results indicate that the adhesive performance of Comparative Example 3 was significantly lower than that of Example 1, and the fiber strength was also significantly reduced. This demonstrates that the amount of polyol added is not necessarily better the more it is added. Excessive polyol can disrupt the emulsion stability of the aqueous compound system, leading to stratification, thickening, or even demulsification of the impregnation solution. Simultaneously, excessive hydroxyl groups can excessively consume -NCO groups, disrupting the stoichiometric balance between epoxy resin, isocyanate, and polyol, thus interfering with the orderly construction of the epoxy-polyurethane interpenetrating network and reducing the crosslinking density of the film layer. Furthermore, excessive flexible polyol segments may have a counterproductive "internal plasticizing" effect, reducing the rigidity and density of the activated film layer, thereby affecting the adhesive performance. Therefore, controlling the amount of aqueous low-hydroxyl polyester polyol within a suitable range is more conducive to balancing system stability and crosslinking density, resulting in activated fibers with excellent overall performance.

[0094] A comparison of the experimental results of Comparative Example 4 and Example 1 shows that the adhesive performance and fiber strength of Comparative Example 4 are significantly lower than those of Example 1. This is because high-hydroxyl-value polyester polyols contain a higher density of hydroxyl groups and polar groups. When added to an aqueous compounding system, the excessive polarity difference can disrupt the uniformity and stability of the emulsion, leading to thickening or flocculation during impregnation preparation. Simultaneously, the high reactivity of high-hydroxyl-value polyols may cause excessively rapid and excessive crosslinking reactions with -NCO during heat treatment, resulting in an uneven crosslinking network and localized over-crosslinking that embrittles the film layer. This is detrimental to the formation of a structurally uniform and stable activated film layer. Therefore, selecting low-hydroxyl-value polyester polyols (35-59) ensures emulsion stability while providing appropriate reactivity to construct a uniform interpenetrating network, which is beneficial for achieving excellent adhesive performance in fibers.

[0095] A comparison of the experimental results of Comparative Example 5 and Example 1 shows that the adhesive performance and fiber strength of Comparative Example 5 are significantly lower than those of Example 1. This is because when the unsealing temperature is below 120°C, the blocked isocyanate begins to partially unseale during the dehydration and drying stage at 90-120°C. At this time, the free water in the system has not been completely removed. The unsealed -NCO preferentially undergoes a competitive side reaction with water to generate urea and CO2 bubbles, resulting in: a large amount of -NCO being consumed and unable to effectively participate in the target crosslinking reaction with hydroxyl groups; the generated CO2 bubbles forming defects in the film layer, making the activated film layer non-dense and uneven; and film layer defects leading to stress concentration, reducing the interfacial bonding strength between the fiber and the rubber. Therefore, controlling the unsealing temperature of the blocked isocyanate at 130-160°C, which is significantly higher than the drying temperature (90-120°C), and ensuring the reaction sequence of "dehydration first, unsealing later," can effectively avoid side reactions and ensure the crosslinking reaction effect.

[0096] A comparison of the experimental results of Comparative Example 6 and Example 7 shows that the adhesive performance and fiber strength of Comparative Example 6 are lower than those of Example 7. This indicates that if high-temperature heat treatment is performed directly without independent dehydration and drying, a large amount of free water in the system will rapidly vaporize at high temperatures, and -NCO will rapidly de-encapsulate at high temperatures. The side reactions of both are aggravated, and the generated CO2 bubbles form a large number of defects in the film layer. In addition, the one-step high-temperature treatment makes the de-encapsulation and cross-linking reactions of -NCO too violent and concentrated, lacking the gradual process of "preheating and homogenization → main cross-linking → deep curing" in the gradient heating method, resulting in the "inconsistency between surface and interior" defect of premature curing of the film layer surface and insufficient internal cross-linking. In contrast, the present invention adopts a segmented process of dehydration and drying at 90-120℃ and heat treatment at 180-220℃, so that the moisture is fully removed in the low-temperature section before high-temperature cross-linking, which effectively avoids side reactions and film defects, ensures the density and uniformity of the activated film layer and sufficient cross-linking, thereby giving the fiber better adhesive performance and strength retention.

[0097] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0098] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing low-chlorine para-aramid activated fibers, characterized in that, The preparation method is as follows: S1. By weight, the raw materials of the impregnation solution include: 2-5 parts of low-chlorine epoxy resin, 3-6 parts of nonionic aliphatic waterborne blocked polyisocyanate, 1-3 parts of waterborne low-hydroxyl polyester polyol, and 85-95 parts of deionized water; the impregnation solution is obtained by mixing the raw materials. S2. After the twisted para-aramid fiber is impregnated in the impregnation solution, it is heated to remove water and dried, stretched and heat-treated to obtain the low-chlorine para-aramid activated fiber.

2. The method for preparing low-chlorinated para-aramid activated fiber according to claim 1, characterized in that, In step S1, the low-chlorine epoxy resin is at least one of EX-810P, EX-201-IM, and EX-121.

3. The method for preparing low-chlorinated para-aramid activated fiber according to claim 1, characterized in that, In step S1, the unsealing temperature of the nonionic aliphatic waterborne blocked polyisocyanate is 130-160℃.

4. The method for preparing low-chlorinated para-aramid activated fiber according to claim 1, characterized in that, In step S1, the hydroxyl value of the waterborne low-hydroxyl polyester polyol is 35-59.

5. The method for preparing low-chlorinated para-aramid activated fiber according to claim 1, characterized in that, In step S2, the soaking time is 30-80 seconds.

6. The method for preparing low-chlorinated para-aramid activated fiber according to claim 1, characterized in that, In step S2, the temperature for heating and dehydration is 90-120℃, and the time for heating and dehydration is 90-180s.

7. The method for preparing low-chlorinated para-aramid activated fiber according to claim 1, characterized in that, In step S2, the temperature conditions for the heat treatment are 180-220℃, and the heat treatment time is 60-120s.

8. The method for preparing low-chlorinated para-aramid activated fiber according to claim 1, characterized in that, In step S2, the heat treatment adopts a gradient heating method, and the step heating conditions are: first, treat at 120-140℃ for 20-40s, then treat at 150-170℃ for 20-40s, and finally treat at 190-220℃ for 20-40s.

9. The method for preparing low-chlorinated para-aramid activated fiber according to claim 1, characterized in that, In step S2, the traction speed is 4-8 m / min and the traction tension is 3-6 N.

10. A low-chlorine para-aramid activated fiber, characterized in that, The low-chlorine para-aramid activated fiber is prepared by the preparation method described in any one of claims 1-9.

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