Method for dyeing para-aramid fabrics

Abstract

The application provides a dyeing method of para-aramid fabric, and belongs to the field of textile dyeing and finishing. The method comprises the following steps: pretreating the para-aramid fabric to remove surface oil and impurities, and obtaining pretreated fabric; immersing the pretreated fabric into a chlorosulfonic acid solution, and reacting for 10-60 min at-20-20 DEG C to form an activated intermediate containing a sulfonyl chloride group on the surface of the fabric; placing the obtained fabric into an organic solution containing a nucleophile, and reacting for 2-8 h at room temperature to obtain modified para-aramid fabric; and dyeing the modified para-aramid fabric in a dye bath containing reactive dyes to obtain dyed para-aramid fabric. The method combines chlorosulfonylation-nucleophilic derivatization with conventional reactive dyeing and finishing processes, introduces active sites on the surface of the para-aramid fabric which can covalently combine with reactive dyes, and makes the color depth value and soaping fastness of the modified fabric significantly higher than those of the unmodified fabric after conventional aqueous dyeing and finishing, and the modified fabric has high color depth and excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of textile dyeing and finishing technology, and specifically to a dyeing method for para-aramid fabrics. Background Technology

[0002] Para-aramid fibers possess excellent mechanical properties due to their highly oriented, rigid main chain structure. However, this structural characteristic also endows them with significant chemical inertness, making surface modification a major challenge. Traditional modification methods typically require disrupting the polymer backbone, weakening intermolecular forces, or employing extreme conditions such as irradiation or fluorination to achieve functionalization. These methods not only often damage the fiber's mechanical properties but also lack precision and controllability, making it difficult to target the introduction of specific functional groups. Therefore, how to perform precise and controllable derivatization modification on the fiber surface without compromising its mechanical properties to meet the personalized functional customization needs of different application scenarios is a key scientific problem that urgently needs to be solved.

[0003] Existing dyeing systems (such as cationic dyes and reactive dyes) are designed for traditional fibers like cotton and nylon, and their dyeing mechanisms differ significantly from the surface chemical properties of para-aramid fibers. Developing new fiber dyeing technologies typically involves the synthesis of novel dyes, modification of dyeing equipment, and restructuring of processes, which greatly increases the difficulty and cost of research and development. Therefore, achieving efficient compatibility and matching between derivatized para-aramid fibers and existing mature dyeing systems, thereby minimizing costs and process complexity, is another key challenge in the development of dyeing technologies for high-performance fibers such as para-aramid.

[0004] In view of this, it is necessary to design a dyeing method for para-aramid fabrics to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a dyeing method for para-aramid fabrics, which aims to solve the technical problems of insufficient dyeing depth and difficulty in achieving both fiber mechanical properties in existing para-aramid dyeing methods.

[0006] This application provides a dyeing method for para-aramid fabrics, comprising the following steps: S1. Pre-treat the para-aramid fabric to remove surface oil and impurities, and obtain the pre-treated fabric. S2. Immerse the pretreated fabric in chlorosulfonic acid solution and react at -20°C to 20°C for 10 to 60 minutes to form an activated intermediate containing sulfonyl chloride groups on the fabric surface; S3. Place the fabric obtained in step S2 in an organic solution containing a nucleophile and react at room temperature for 2-8 hours to obtain a modified para-aramid fabric; S4. The modified para-aramid fabric is placed in a dye bath containing reactive dyes for dyeing to obtain dyed para-aramid fabric.

[0007] As a further improvement of this application, in step S1, the pretreatment includes: placing the para-aramid fabric in an organic solvent, reflux washing at 60~90℃ for 2~6 hours, then washing with ethanol and deionized water, and drying to obtain the pretreated fabric; wherein the organic solvent is selected from at least one of ethanol, petroleum ether, and acetone.

[0008] As a further improvement of this application, in step S2, the chlorosulfonic acid solution is formed by dissolving chlorosulfonic acid in anhydrous dichloromethane, and the concentration of chlorosulfonic acid is 5~25g / L.

[0009] As a further improvement of this application, in step S3, the nucleophile is selected from at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, diethylenetriamine, triethylenetetramine, ethylene glycol, propylene glycol, ethanolamine, diethanolamine, and polyethyleneimine.

[0010] As a further improvement of this application, in step S3, the organic solution is dichloromethane, and the volume ratio of the nucleophile to the dichloromethane is 1:20 to 1:50.

[0011] As a further improvement of this application, in step S4, the dyeing process is as follows: the modified para-aramid fabric is added to an aqueous solution containing reactive dye, stirred at 55~65℃ for 10~20 min, a dyeing accelerator is added and the reaction continues for 10~20 min, then the temperature is raised to 80~100℃, a fixing agent is added and the reaction continues for 20~40 min.

[0012] As a further improvement of this application, the reactive dye is selected from monochlorotriazine type reactive dyes, dichlorotriazine type reactive dyes, vinyl sulfone type reactive dyes, or reactive dyes containing dual reactive groups.

[0013] As a further improvement of this application, the dyeing accelerator is sodium chloride, and the fixing agent is sodium carbonate.

[0014] As a further improvement to this application, the heating rate is 1~3℃ / min.

[0015] As a further improvement of this application, the dyeing bath ratio is 1:30 to 1:80, and the dye dosage is 1 to 10% owf.

[0016] The beneficial effects of this application are as follows: This application provides a dyeing method for para-aramid fabrics. The method involves pretreating the para-aramid fabric to remove surface oils and impurities, resulting in a pretreated fabric. The pretreated fabric is then immersed in a chlorosulfonic acid solution and reacted at -20°C to 20°C for 10 to 60 minutes to form an activated intermediate containing sulfonyl chloride groups on the fabric surface. The resulting fabric is then placed in an organic solution containing a nucleophilic reagent and reacted at room temperature for 2 to 8 hours to obtain a modified para-aramid fabric. Finally, the modified para-aramid fabric is dyed in a dye bath containing reactive dyes to obtain a dyed para-aramid fabric. This application employs a two-step modification process—surface-confined chlorosulfonation and nucleophilic grafting—to introduce active sites on the surface of para-aramid fibers that can covalently bind with reactive dyes without damaging the fiber's bulk structure. This results in a significant improvement in color depth and wash fastness of the modified fabric after conventional aqueous dyeing and finishing compared to the unmodified fabric, exhibiting both high color depth and excellent mechanical properties. Furthermore, this method is directly compatible with existing commercial reactive dyes and conventional dyeing and finishing equipment, enabling multi-color dyeing without the need for special equipment or synthetic dyes. This provides a low-damage, high-fastness, and easily industrialized technical solution for high-quality coloring of para-aramid fibers.

[0017] This application employs a surface-confined chlorosulfonation-nucleophilic grafting route, primarily introducing reaction sites into the accessible surface layer of the para-aramid fiber, thus avoiding significant damage to the polyamide backbone through methods such as strong acid / base hydrolysis or high-energy irradiation. Experimental results show that the modified warp tensile strength retains over 97%, and approximately 92% after dyeing, while the weft strength retains over 94%, making it suitable for protective and industrial textiles requiring high strength.

[0018] This application introduces amino / hydroxyl sites on the fiber surface that can react with reactive dyes, enabling commercial reactive dyes to form covalent fixation with modified aramid fibers. Compared to the K / S value of approximately 0.89 for direct dyeing of unmodified para-aramid, the K / S value for reactive red dyeing after ethylenediamine derivatization can reach approximately 10.93-11.23; the color fastness of the dyed samples after soaping is mostly grade 4-5 to grade 5, indicating good dye fixation stability.

[0019] The subsequent dyeing steps in this application adopt a conventional aqueous reactive dyeing and finishing process, including adsorption, salt-induced dyeing, heating, alkali-based color fixing, soaping, and washing. It does not require supercritical carbon dioxide equipment, autoclaves, plasma equipment, irradiation equipment, or specialized synthetic dyes, making it easy to integrate with existing printing and dyeing processes. This method is not only suitable for single-color red dyeing but also for yellow, blue, and tri-color blending systems, yielding a variety of mixed colors and near-neutral black. This is beneficial for the application of para-aramid fibers in high-visibility protection, camouflage identification, equipment marking, and multi-color functional textiles.

[0020] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0022] Figure 1 This is a diagram illustrating the surface derivatization process of para-aramid fibers in an embodiment of this application. Figure 2 This is a schematic diagram of the reactive dyeing process in an embodiment of this application; Figure 3 This is a comparison of the mechanical properties of the aramid fabric before and after surface modification and dyeing treatment in Example 1 of this application; Figure 4 This document compares the modification effects of different nucleophilic reagents in Examples 1-5 of this application. Figure 5 This document compares the effects of chlorosulfonic acid activation parameters on the K / S value in Examples 6-17 of this application. Figure 6 This is a comparison of the effect of ethylenediamine treatment time on the K / S value in Examples 18-20 of this application; Figure 7 This document compares the dyeing effects of different reactive dyes in Examples 1 and 21-22 of this application. Figure 8 This refers to the mixed color and black dyeing effects of the modified para-aramid fabric in Example 23 of this application. Detailed Implementation

[0023] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0024] 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 application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0025] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0026] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0027] Existing para-aramid dyeing technologies suffer from the following main problems: Due to the highly regular molecular chains, high crystallinity, and lack of surface-active groups, para-aramid exhibits extremely low color depth when directly dyed with conventional dyes. While existing coatings or pigments provide some color, they often lead to issues such as fabric stiffness, coating peeling, and insufficient wash and rubbing fastness. To improve dyeability, reported methods such as carrier methods, supercritical carbon dioxide dyeing, chemical etching, plasma treatment, high-energy irradiation, and fluorination modification either require high-temperature, high-pressure equipment and large amounts of organic media, resulting in high industrialization costs; or they may damage the fiber's aggregated structure, leading to a significant decrease in tensile strength; or they require the pre-synthesis of special functional molecules, resulting in complex synthetic routes and poor compatibility with existing industrial dyeing and finishing systems. Therefore, existing technologies struggle to simultaneously achieve high color depth dyeing, maintain the fiber's intrinsic mechanical properties, and achieve efficient compatibility with commercial dyes / conventional dyeing and finishing processes on para-aramid.

[0028] To address the technical problem of insufficient dyeing depth and difficulty in simultaneously achieving optimal fiber mechanical properties in existing para-aramid dyeing methods, this application provides a dyeing method for para-aramid fabrics. This method involves introducing sulfonyl chloride active intermediate groups through a confined chlorosulfonation reaction on the surface of the para-aramid fabric, followed by grafting amino / hydroxyl active sites that can react with reactive dyes onto the fiber surface using a nucleophilic reagent. This allows the reactive dyes to be covalently fixed to the fiber surface, thereby significantly improving the color depth and wash fastness of the dyed fabric without the need for high-temperature, high-pressure equipment or special synthetic dyes. Simultaneously, it greatly increases the retention rate of warp and weft strength after modification and dyeing, achieving a comprehensive technical effect that combines high color depth, excellent dyeing fastness, and good mechanical property retention.

[0029] This application provides a dyeing method for para-aramid fabrics, comprising the following steps: S1. Pre-treat the para-aramid fabric to remove surface oil and impurities, and obtain the pre-treated fabric. S2. Immerse the pretreated fabric in chlorosulfonic acid solution and react at -20℃ to 20℃ for 10~60min to form an activated intermediate containing sulfonyl chloride groups on the fabric surface; S3. Place the fabric obtained in step S2 in an organic solution containing a nucleophile and react at room temperature for 2-8 hours to obtain a modified para-aramid fabric; S4. The modified para-aramid fabric is placed in a dye bath containing reactive dyes for dyeing to obtain dyed para-aramid fabric.

[0030] In the technical solution of this application embodiment, the oil and impurities on the surface of the para-aramid fabric are first removed through pretreatment to ensure the uniformity of subsequent chemical reactions. Then, in an anhydrous organic medium, chlorosulfonic acid is used to undergo an electrophilic substitution reaction with the aromatic rings of the aramid, introducing highly active sulfonyl chloride groups onto the fiber surface. This active intermediate then reacts with nucleophiles such as ethylenediamine to form a stable sulfonamide or sulfonate structure, while retaining amino or hydroxyl groups that can react with reactive dyes. During dyeing, the above-mentioned active sites can react with reactive groups such as chlorotriazine and vinyl sulfone in the reactive dye molecule under alkaline fixing conditions to form covalent bonds between the dye and the fiber. This mechanism differs from the traditional physical coating and the traditional dyeing route that relies on the diffusion of dye into the interior of para-aramid, thus enabling the achievement of higher color depth and better fastness under milder aqueous dyeing and finishing conditions. Currently, research on chlorosulfonic acid-modified para-aramid mainly focuses on improving the interfacial interaction between the fiber and resin, composite material, or catalyst support, and has not yet fully utilized the reaction matching relationship between this type of surface-active intermediate group and mature commercial reactive dye systems. This application combines chlorosulfonation-nucleophilic derivatization with conventional reactive dyeing and finishing processes, enabling the surface of para-aramid fibers to obtain reactive anchoring points similar to those of fibers such as cotton and wool, thereby solving the problems of difficult dyeing, difficult color fixing, and difficult multi-color control of para-aramid fibers.

[0031] Further, in some embodiments, in step S1, the pretreatment includes: placing the para-aramid fabric in an organic solvent, reflux washing at 60~90°C for 2~6 hours, then washing with ethanol and deionized water, and drying to obtain the pretreated fabric; wherein the organic solvent is selected from at least one of ethanol, petroleum ether, and acetone.

[0032] In the technical solution of this application embodiment, a non-polar organic solvent is used to effectively dissolve and remove surface impurities such as hydrophobic oils, sizing agents, and antistatic agents remaining during the spinning and weaving process of para-aramid fibers. Subsequently, the fibers are washed with ethanol and water to thoroughly remove residual organic solvents, and then dried in an oven at 50-70°C. The organic solvent is preferably a mixed solution of ethanol and petroleum ether in a 1:1 volume ratio.

[0033] Furthermore, in some embodiments, in step S2, the chlorosulfonic acid solution is formed by dissolving chlorosulfonic acid in anhydrous dichloromethane, and the concentration of chlorosulfonic acid is 5~25 g / L.

[0034] In the technical solution of this application embodiment, chlorosulfonic acid undergoes an electrophilic substitution reaction with the para-aramid benzene ring in a non-aqueous organic medium, introducing sulfonyl chloride groups as active intermediates for further derivatization onto the fiber surface. Dichloromethane, as an inert organic solvent, effectively dissolves chlorosulfonic acid and ensures its uniform diffusion on the fabric surface. Furthermore, it avoids excessive erosion of the fiber polyamide backbone by chlorosulfonic acid in the aqueous system due to hydrolysis to generate sulfuric acid, thus achieving mild sulfonation modification within a confined surface area. If the concentration of chlorosulfonic acid is too low, the amount of active groups introduced is insufficient, resulting in a low density of subsequent nucleophilic grafting sites, affecting the final dyeing color depth. If the concentration is too high, it may cause excessive surface reaction or local unevenness, which in turn lowers the dyeing K / S value. Controlling the low-temperature, short-time reaction conditions suppresses side reactions and maximizes the preservation of the fiber's aggregated structure and mechanical properties while ensuring sufficient sulfonation. Preferably, the reaction temperature in step S2 is -10°C to 0°C, and the reaction time is 20~40 min.

[0035] Further, in some embodiments, in step S3, the nucleophile is selected from at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, diethylenetriamine, triethylenetetramine, ethylene glycol, propylene glycol, ethanolamine, diethanolamine, and polyethyleneimine. The organic solution is dichloromethane, and the volume ratio of the nucleophile to dichloromethane is 1:20 to 1:50.

[0036] In the technical solution of this application embodiment, the high reactivity of the sulfonyl chloride group is utilized to undergo a nucleophilic substitution reaction with a nucleophilic reagent, forming a stable sulfonamide bond or sulfonate bond structure, while retaining free amino or hydroxyl active functional groups on the fiber surface. Dichloromethane, as an anhydrous organic medium, can effectively swell the fiber surface and dissolve the nucleophilic reagent, while avoiding premature hydrolysis and inactivation of the sulfonyl chloride group in the system, ensuring that the grafting reaction proceeds confined to the fiber surface. If the concentration of the nucleophilic reagent is too low or the reaction time is insufficient, it will lead to a low grafting density; if the concentration of the nucleophilic reagent is too high or the reaction time is too long, it is easy to cause excessive surface modification or a decrease in uniformity.

[0037] Furthermore, in some embodiments, in step S4, the dyeing process is as follows: the modified para-aramid fabric is added to an aqueous solution containing reactive dye, stirred at 55~65℃ for 10~20 min, a dyeing accelerator is added and the reaction continues for 10~20 min, then the temperature is raised to 80~100℃, a fixing agent is added and the reaction continues for 20~40 min; the dyeing accelerator is sodium chloride, and the fixing agent is sodium carbonate; the heating rate is 1~3℃ / min.

[0038] In the technical solution of this application embodiment, the dyeing process first fully wets the modified aramid fabric in the dye bath under mild conditions, allowing dye molecules to be adsorbed and evenly distributed on the fiber surface. Then, a dyeing accelerator is added to continue the reaction, utilizing electrolytes to weaken the electrostatic repulsion between the fiber surface and dye anions, thus promoting the enrichment of more dye on the fiber surface. Next, the temperature is raised to 80-100°C, accelerating the diffusion of dye molecules to the fiber surface and increasing reactivity at high temperatures. Finally, a fixing agent is added and the temperature is maintained for 20-40 minutes. The alkaline environment activates the amino / hydroxyl groups on the fiber surface, enhancing their nucleophilic reaction ability. Simultaneously, it neutralizes byproducts such as HCl released during the formation of dye-fiber covalent bonds, promoting the forward direction of nucleophilic substitution or addition reactions, and causing irreversible covalent bonding between the dye's active groups and the amino or hydroxyl groups on the fiber surface. After dyeing, soaping and washing processes thoroughly remove floating dye adsorbed on the fiber surface but not forming covalent bonds with the fiber, ensuring high color depth and excellent color fastness of the dyed fabric. The fabric is then dried at 60°C for 10-12 hours to obtain the dyed para-aramid fabric.

[0039] Furthermore, in some embodiments, the reactive dye is selected from monochlorotriazine type reactive dyes, dichlorotriazine type reactive dyes, vinyl sulfone type reactive dyes, or reactive dyes containing dual reactive groups.

[0040] In the technical solutions of this application, various reactive dyes contain reactive leaving groups or unsaturated bonds that can covalently bond with amino or hydroxyl groups. Therefore, they can all undergo nucleophilic substitution or addition reactions with the active hydrogen sites on the surface of aramid fabrics grafted with nucleophiles such as ethylenediamine, forming a stable dye-fiber covalent bond on the fiber surface. For example, the reactive dyes can be Reactive Red 2, Reactive Yellow 4, or Reactive Blue 19. These dyes can be used alone or in combination of two or three in a specific ratio; dyes with different structures can form stable covalent bonds with the active sites on the fiber surface in the same dye bath, achieving co-fixation of multiple dyes and uniform color formation.

[0041] When using a binary compound system, changing the ratio of Reactive Red 2 to Reactive Yellow 4 can produce an orange series, changing the ratio of Reactive Yellow 4 to Reactive Blue 19 can produce a green series, and changing the ratio of Reactive Red 2 to Reactive Blue 19 can produce a purple series. When using a ternary compound system, the comprehensive color and dark color can be obtained by adjusting the ratio of the three primary colors, and the comprehensive hue and brightness can be continuously controlled.

[0042] Furthermore, in some embodiments, the dyeing bath ratio is 1:30 to 1:80, and the dye amount is 1 to 10% owf.

[0043] In the technical solution of this application embodiment, the appropriate setting of the liquor ratio and dye dosage helps to ensure that the dye concentration in the dye bath is sufficient to drive its effective diffusion to the fiber surface and capture by active sites, while avoiding resource waste and floating color problems caused by excessive dye, thus achieving the highest covalent fixation rate and the best color depth performance. If the liquor ratio is too small, the amount of dye bath is insufficient, making it difficult to ensure that the fabric is fully immersed and uniformly adsorbed in the dye bath, which easily leads to uneven dyeing; if the liquor ratio is too large, the amount of dye bath is too large, the dye concentration per unit volume of dye bath is relatively reduced, weakening the concentration gradient driving force for dye molecules to diffuse to the fiber surface, and increasing wastewater discharge and energy consumption. The amount of dye used (as a percentage of fabric weight) directly affects the final dyeing color depth. If the amount is too low, even if there are sufficient active sites on the fiber surface, the dye supply is insufficient to saturate all sites, resulting in a low K / S value. If the amount is too high, due to the limited density of amino / hydroxyl sites available for reaction on the fiber surface, the dye exceeding the saturation adsorption capacity cannot form covalent bonds with the fiber and can only exist on the fiber surface in the form of physical adsorption. It is easily removed after soaping, which not only wastes dye but also increases the burden of floating dye washing and the color of wastewater.

[0044] Figure 1 This diagram illustrates the overall construction strategy for the confined derivatization of para-aramid fabrics in this application. The left side shows a fragment of the original para-aramid molecular structure. The middle section shows the activated intermediate structure, which, after low-temperature activation with chlorosulfonic acid in anhydrous dichloromethane, introduces a sulfonyl chloride group (-SO2Cl) onto the aromatic ring. The right side shows the activated intermediate reacting further with ethylenediamine to generate a sulfonamide structure retaining a free amino group (AF-NH), or reacting with ethylene glycol to generate a sulfonate structure retaining a free hydroxyl group (AF-OH). This diagram clarifies that the key to this application lies in introducing a designable active intermediate through electrophilic substitution of the para-aramid aromatic ring, and then retaining reactive functional groups capable of reacting with reactive dyes on the fiber surface through nucleophilic grafting.

[0045] Figure 2 This diagram illustrates the reactive dyeing and fixation mechanism using ethylenediamine-derived aramid fiber (AF-NH) as an example. The left side shows the chemical state of the free amino groups (-NH2) retained on the fiber surface after ethylenediamine grafting. The middle section shows the diffusion and adsorption of reactive dye molecules (taking chlorotriazine type as an example) onto the fiber surface, where their reactive groups undergo nucleophilic substitution reactions with the amino groups on the fiber surface. The right side shows the final state of the dye fixed to the fiber surface via covalent bonds (CN bonds) after the reaction. The diagram also illustrates the deprotonation activation of amino groups and the departure of chloride ions under alkaline conditions. This diagram reveals the chemical essence of the high colorfastness dyeing achieved in this application, namely, the covalent bond between the dye and the fiber.

[0046] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0047] Example 1 This embodiment provides a dyeing method for para-aramid fabrics, including the following steps: S1. Take the para-aramid fabric and place it in a mixed solution of ethanol and petroleum ether in a volume ratio of 1:1. Reflux and wash at 80°C for 4 hours to remove surface oil, sizing agents and other extractable impurities. Then wash with ethanol and deionized water and dry in an oven at 60°C to obtain the pretreated fabric. S2. Dissolve 2g of chlorosulfonic acid in 200mL of dichloromethane to obtain a chlorosulfonic acid solution. Immerse the pretreated fabric in the chlorosulfonic acid solution and stir at -10℃ for 20min to form an activated intermediate containing sulfonyl chloride groups on the fabric surface. S3. The fabric obtained in step S2 was placed in 200 mL of dichloromethane containing 10 mL of ethylenediamine and reacted at room temperature for 4 h. After the reaction was completed, the fabric was ultrasonically washed twice with dichloromethane for 20 min each time, and then washed with ethanol and deionized water in sequence. It was then dried at 60 °C for 10 h to obtain the modified para-aramid fabric, denoted as AF-NH. S4. Cut 1g of modified para-aramid fabric and add it to 50mL of aqueous solution containing 0.1g of Reactive Red 2 (dye dosage is 10% owf, liquor ratio is 1:50). Stir at 60℃ for 15min. Add 2g of NaCl as a dyeing accelerator and continue the reaction for 15min. Then, raise the temperature to 90℃ at about 2℃ / min and add 0.5g of Na2CO3 as a fixing agent and continue the reaction for 30min to allow the active dye groups to covalently bond with the amino groups on the surface of the modified fabric. After the reaction is completed, cool to room temperature, take out the fabric, soap and wash it with water, and dry it at 60℃ for 10h to obtain dyed para-aramid fabric.

[0048] Comparative Example 1 Comparative Example 1 provides a dyeing method for para-aramid fabric. Compared with Example 1, the only difference is that the original para-aramid fabric (Origin) is dyed with reactive dyes without any modification treatment. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here. The product obtained is denoted as AF.

[0049] To further verify the effects of surface modification and subsequent dyeing on the mechanical properties of para-aramid fabrics, tensile properties were tested on the original aramid (Origin), modified aramid (AF-NH), and dyed aramid (RED) from Example 1. The results are shown in Table 1 and below. Figure 3 As shown, where, Figure 3 In the figure, (a)~(c) represent the tensile strength and elongation at break measured along the warp direction, and (d)~(f) represent the tensile strength and elongation at break measured along the weft direction.

[0050] Table 1 Mechanical properties of fabrics before and after modification and dyeing From Table 1 and Figure 3 It can be seen that after surface modification, the warp and weft tensile strength retention rates of the AF-NH fabric were 97.5% and 98.6%, respectively; after further dyeing, the RED fabric still retained 92.5% and 94.5%, respectively. Meanwhile, the changes in warp and weft breaking elongation before and after modification and dyeing were minimal. These results indicate that the chlorosulfonation-nucleophilic grafting and reactive dye fixation of this application mainly occur on the fiber surface, significantly improving dyeing performance while effectively maintaining the mechanical properties of para-aramid fabrics.

[0051] Test method: 1. Staining performance test The K / S value of the fabric was tested using a colorimeter (Color i7), and the calculation formula is as follows: K / S = (1-Rλ) 2 / (2Rλ), where Rλ is the reflectivity of the fabric at wavelength λ, which ranges from 400nm to 700nm; 2. Mechanical property testing The tensile strength and elongation at break of the fabric were tested using an electronic universal testing machine (Instron) in accordance with the GB / T 3923.1-2013 standard. 3. Colorfastness test Color fastness to soap washing was tested according to GB / T 3921-2008 standard, and color fastness to rubbing was tested according to GB / T 3920-2008 standard.

[0052] Examples 2-5 Examples 2-5 provide a dyeing method for para-aramid fabrics. Compared with Example 1, the only difference is the nucleophilic reagent in step S3, as shown in Table 2. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here. Figure 4Examples 1-5 show a comparison of the modification effects of different nucleophilic reagents. (a) is a photograph of the dyed fabric after modification with different nucleophilic reagents, and (b) is the corresponding K / S value. It can be seen that the K / S value of the dyed fabric modified with ethylenediamine is the highest, indicating that the amino group has a higher nucleophilic reactivity with reactive dyes under alkaline conditions than the hydroxyl group.

[0053] Table 2 Test Results of Examples 1-5 Table 2 shows that the K / S value of the original para-aramid was only 0.09, and even after direct dyeing of the unmodified fabric, it was only 0.89. After nucleophilic derivatization, the K / S values ​​of all samples increased to varying degrees. Among them, the K / S value of the ethylenediamine-modified sample reached 10.93, which is about 12.3 times that of the unmodified directly dyed sample and significantly higher than the 1.93 of the ethylene glycol-modified sample, indicating that amino sites are more conducive to the covalent fixation of reactive dyes than hydroxyl sites. Among diamine reagents, ethylenediamine is more effective than 1,3-propanediamine, 1,4-butanediamine, and triethylenetetramine, indicating that shorter molecular spacing is beneficial to increasing the surface amino density and reducing steric hindrance. Therefore, ethylenediamine is preferred as the nucleophile.

[0054] Examples 6-8 Examples 6-8 provide a dyeing method for para-aramid fabrics. Compared with Example 1, the only difference is the reaction temperature in step S2, as shown in Table 3. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0055] Table 3 Test Results of Examples 6-8 As shown in Table 3, when the activation temperature of chlorosulfonic acid increased from -10℃ to 0℃, the K / S value increased from 10.93 to 11.28; it remained at 10℃, but dropped significantly to 5.20 after further increasing the temperature to 20℃. This indicates that low temperature conditions are conducive to the controlled reaction of chlorosulfonic acid on the fiber surface. The highest color depth was obtained at 0℃, but the uniformity was not as good as at -10℃. Excessively high surface temperatures may lead to over-reaction or uneven modification. Considering color depth, reaction controllability, and repeatability, activation at -10℃ to 0℃ is preferred.

[0056] Examples 9-13 Examples 9-13 provide a dyeing method for para-aramid fabrics. Compared with Example 1, the only difference is the reaction time in step S2, as shown in Table 4. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here.

[0057] Table 4 Test Results of Examples 9-13 Table 4 shows that as the chlorosulfonic acid activation time increased from 10 min to 60 min, the K / S value gradually increased from 9.68 to 11.07, indicating that extending the reaction time is beneficial for increasing the number of graftable surface active sites. However, the increase slowed down significantly after 20-30 min, with only a 0.79 difference between 20 min and 60 min, while the treatment time increased threefold. Considering factors such as staining depth, treatment efficiency, and avoiding over-reaction, the optimal activation time is 20-40 min.

[0058] Examples 14-17 and Comparative Examples 2-3 Examples 14-17 and Comparative Examples 2-3 each provide a dyeing method for para-aramid fabrics. Compared with Example 1, the only difference is the concentration of chlorosulfonic acid in step S2, as shown in Table 5. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here.

[0059] Table 5 Test Results of Examples 14-17 As shown in Table 5, when the concentration of chlorosulfonic acid increased from 5 g / L to 10 g / L, the K / S value increased from 8.24 to 10.93; however, when the concentration was further increased to 15-25 g / L, the K / S value decreased to 8.53-9.99. This indicates that too low a concentration of chlorosulfonic acid results in insufficient introduction of surface active sites, while too high a concentration may cause over-sulfonation, localized surface damage, or uneven modification, all of which are detrimental to subsequent dye fixation. Therefore, 10 g / L is the optimal concentration.

[0060] Figure 5 The graph shows the influence of chlorosulfonic acid activation parameters on the color depth (K / S value) of aramid dyeing. (a) and (b) represent the effect of activation temperature, (c) and (d) represent the effect of activation time, and (e) and (f) represent the effect of chlorosulfonic acid concentration. It can be seen that the K / S value is optimal within the temperature range of -10℃ to 0℃; too low a temperature results in insufficient reaction rate, while too high a temperature leads to decreased surface uniformity. The activation time reaches its peak at around 20 minutes; excessively long activation times increase energy consumption. The optimal concentration is around 10 g / L; too low a concentration results in insufficient site introduction, while too high a concentration may cause excessive surface reaction.

[0061] Examples 18-20 and Comparative Examples 4-5 Examples 18-20 and Comparative Examples 4-5 each provide a dyeing method for para-aramid fabrics. Compared with Example 1, the only difference is the reaction time in step S3, as shown in Table 6. Other experimental parameters and conditions are basically the same as those in Example 1, and will not be repeated here. Figure 6The comparison of the effects of ethylenediamine treatment time on the K / S value shows that the K / S value increases rapidly in the range of 2-4 hours, and then plateaus and decreases slightly after 4 hours, indicating that 4 hours is sufficient for the sulfonyl chloride group to be fully grafted.

[0062] Table 6 Test Results of Examples 18-20 As shown in Table 6, extending the ethylenediamine treatment time from 2 h to 4 h significantly increased the K / S value from 8.62 to 10.93; further extending it to 6 h resulted in a smaller increase of 11.23, while extending it to 8 h reduced it to 10.12. This indicates that 4 h is sufficient for adequate ethylenediamine grafting, and further extending the reaction time does not further improve the color depth; on the contrary, it may reduce the dyeing performance due to surface cross-linking, side reactions, or decreased accessibility of active sites. Therefore, a treatment time of 4 h is preferred for ethylenediamine treatment.

[0063] Examples 21-22 Examples 21-22 provide a dyeing method for para-aramid fabrics. Compared with Example 1, the only difference is the use of different reactive dyes, as shown in Table 7. Other experimental parameters and conditions are basically the same as in Example 1, and will not be repeated here. Figure 7 A comparison of the dyeing effects of different reactive dyes shows that the K / S value of unmodified para-aramid fabrics directly dyed is relatively low. However, after modification using the method described in this application, Reactive Red 2, Reactive Yellow 4, and Reactive Blue 19 can all produce bright and saturated colors on aramid fabrics, with a significant increase in color depth. This indicates that the surface amino sites significantly enhance the dyeing and fixing abilities of reactive dyes. Furthermore, blending the three reactive dyes in specific proportions can yield mixed colors such as orange, green, and purple.

[0064] Table 7 Test results for Examples 1 and 21-22 Table 7 shows that after dyeing with Reactive Red 2, Reactive Yellow 4, and Reactive Blue 19, the dry rubbing color fastness of the fabrics was grade 3-4, and the wet rubbing color fastness was also grade 3-4, with the Reactive Blue 19-dyed fabric exhibiting relatively higher rubbing color fastness. The soaping color fastness of all three dyed fabrics reached grade 4-5 or higher, and the staining color fastness to fibers such as wool, acrylic, polyester, cotton, and acetate generally reached grade 4-5, with most reaching grade 5. The staining color fastness of the Reactive Blue 19-dyed fabric to nylon and cotton was grade 3 and 4, respectively, slightly lower than that to other fibers. These results indicate that the method of this application is applicable to the dyeing of reactive dyes with different structures. The dyes exhibit good fixation stability on the surface of modified para-aramid fabrics, and the resulting dyed fabrics have good rubbing color fastness and soaping color fastness.

[0065] Example 23 This embodiment provides a mixed-color dyeing method for para-aramid fabrics. Compared with Example 1, the only difference is that the reactive dye in step S4 is a blend of two or three reactive dyes; the remaining experimental parameters and conditions are basically the same as in Example 1. For binary blending, Reactive Red 2 and Reactive Yellow 4, and Reactive Yellow 4 and Reactive Blue 19 are blended respectively, and the proportion of each dye is adjusted within the range of 1-10% owf of the total dye usage to obtain orange, green, and purple series respectively. For ternary blending, Reactive Red 2, Reactive Yellow 4, and Reactive Blue 19 are used, and different hues and brightness levels of combined colors and dark colors are obtained by adjusting the proportions of the three dyes. Figure 8 Image (a) shows a sample of a mixed-color fabric obtained by blending the three primary reactive dyes in different proportions. Figure 8 Image (b) shows a sample of a fabric dyed with the three primary colors and a black fabric obtained by mixing the three primary colors. Figure 8 In the figure, (c) represents the K / S curves of the original para-aramid fabric, the unmodified para-aramid blended dyed fabric, and the modified para-aramid blended dyed fabric.

[0066] like Figure 8 As shown in (a), based on the three primary colors of red, yellow, and blue, various hues such as red, orange, yellow, green, blue, and purple can be obtained by changing the compounding ratio of binary or ternary reactive dyes, and further, composite colors with different brightness and hue can be obtained. The colors of the mixed-color fabrics are uniform, without obvious color spots or local color differences, indicating that different reactive dyes can achieve common fixation and uniform coloring on the surface of modified para-aramid fabrics.

[0067] Based on the three primary colors, staining was performed using Reactive Red 2 (1.5% owf), Reactive Blue 19 (3% owf), and Reactive Yellow 4 (5.5% owf) to obtain the following results: Figure 8 The uniform black fabric shown in (b) is an example. The L of this black fabric... The value is 22.35, a The value is 0.04, b A value of -6.27 indicates that the resulting fabric has low brightness and a near-neutral overall hue, effectively masking the inherent yellow undertone of para-aramid fabrics.

[0068] Figure 8(c) shows the K / S curves of the original para-aramid fabric, the unmodified para-aramid blended dyed fabric, and the modified para-aramid blended dyed fabric. It can be seen that the original and unmodified fabrics still have low K / S values ​​in most visible light wavelengths after blended dyeing; the modified fabric, after blended dyeing with three primary colors, shows a significantly improved and broader spectral absorption in the 400-700 nm range, indicating that the blended dyes form a higher overall color depth on the modified fabric. These results demonstrate that the method of this application can not only achieve monochromatic dyeing with reactive dyes, but also obtain continuously tunable mixed colors and deep black through the co-fixation and ratio adjustment of multiple reactive dyes.

[0069] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and function as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A dyeing method for para-aramid fabrics, characterized in that, Includes the following steps: S1. Pre-treat the para-aramid fabric to remove surface oil and impurities, and obtain the pre-treated fabric. S2. Immerse the pretreated fabric in chlorosulfonic acid solution and react at -20°C to 20°C for 10 to 60 minutes to form an activated intermediate containing sulfonyl chloride groups on the fabric surface; S3. Place the fabric obtained in step S2 in an organic solution containing a nucleophile and react at room temperature for 2-8 hours to obtain a modified para-aramid fabric; S4. The modified para-aramid fabric is placed in a dye bath containing reactive dyes for dyeing to obtain dyed para-aramid fabric.

2. The dyeing method for para-aramid fabrics according to claim 1, characterized in that, In step S1, the pretreatment includes: placing the para-aramid fabric in an organic solvent, reflux washing at 60~90℃ for 2~6 hours, then washing with ethanol and deionized water, and drying to obtain the pretreated fabric; wherein the organic solvent is selected from at least one of ethanol, petroleum ether, and acetone.

3. The dyeing method for para-aramid fabrics according to claim 1, characterized in that, In step S2, the chlorosulfonic acid solution is formed by dissolving chlorosulfonic acid in anhydrous dichloromethane, and the concentration of chlorosulfonic acid is 5~25 g / L.

4. The dyeing method for para-aramid fabrics according to claim 1, characterized in that, In step S3, the nucleophile is selected from at least one of ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, diethylenetriamine, triethylenetetramine, ethylene glycol, propylene glycol, ethanolamine, diethanolamine, and polyethyleneimine.

5. The dyeing method for para-aramid fabrics according to claim 1, characterized in that, In step S3, the organic solution is dichloromethane, and the volume ratio of the nucleophile to the dichloromethane is 1:20 to 1:

50.

6. The dyeing method for para-aramid fabrics according to claim 1, characterized in that, In step S4, the dyeing process is as follows: the modified para-aramid fabric is added to an aqueous solution containing reactive dye, stirred at 55~65℃ for 10~20 min, a dyeing accelerator is added and the reaction continues for 10~20 min, then the temperature is raised to 80~100℃, a fixing agent is added and the reaction continues for 20~40 min.

7. The dyeing method for para-aramid fabrics according to claim 6, characterized in that, The reactive dye is selected from monochlorotriazine type reactive dyes, dichlorotriazine type reactive dyes, vinyl sulfone type reactive dyes, or reactive dyes containing dual reactive groups.

8. The dyeing method for para-aramid fabrics according to claim 6, characterized in that, The dyeing accelerator is sodium chloride, and the fixing agent is sodium carbonate.

9. The dyeing method for para-aramid fabrics according to claim 6, characterized in that, The heating rate is 1~3℃ / min.

10. The dyeing method for para-aramid fabrics according to claim 6, characterized in that, The dyeing bath ratio is 1:30 to 1:80, and the dye dosage is 1 to 10% owf.

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